Original Research
22 February 2024
DOI 10.3389/fmars.2024.1303025
TYPE
PUBLISHED
OPEN ACCESS
EDITED BY
Jelena Vladic,
NOVA University of Lisbon, Portugal
REVIEWED BY
Ljiljana Popovic,
University of Novi Sad, Serbia
Fiaz Ahmad,
Northwestern Polytechnical University, China
*CORRESPONDENCE
Sirasit Srinuanpan
sirasit.s@cmu.ac.th
Chayakorn Pumas
chayakorn.pumas@gmail.com
27 September 2023
01 February 2024
PUBLISHED 22 February 2024
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CITATION
Htoo NYM, Kraseasintra O, Buncharoen W,
Kaewkod T, Pekkoh J, Tragoolpua Y, Khoo KS,
Chaipoot S, Srinuanpan S and Pumas C
(2024) In vitro immunomodulation activity of
protein hydrolysate from spirulina (Arthrospira
platensis): the ingredient of future foods.
Front. Mar. Sci. 11:1303025.
doi: 10.3389/fmars.2024.1303025
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© 2024 Htoo, Kraseasintra, Buncharoen,
Kaewkod, Pekkoh, Tragoolpua, Khoo, Chaipoot,
Srinuanpan and Pumas. This is an open-access
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Creative Commons Attribution License (CC BY).
The use, distribution or reproduction in other
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which does not comply with these terms.
In vitro immunomodulation
activity of protein hydrolysate
from spirulina (Arthrospira
platensis): the ingredient of
future foods
Nang Yee Mon Htoo 1,2, Oranit Kraseasintra 1,
Wararut Buncharoen 1, Thida Kaewkod 1, Jeeraporn Pekkoh 1,
Yingmanee Tragoolpua 1, Kuan Shiong Khoo 3,
Supakit Chaipoot 4, Sirasit Srinuanpan 1,5,6*
and Chayakorn Pumas 1,6*
1
Department of Biology, Faculty of Science, Chiang Mai University, Chiang Mai, Thailand, 2 Master of
Science Program in Applied Microbiology (International Program), Department of Biology, Faculty of
Science, Chaing Mai University, Chiang Mai, Thailand, 3 Department of Chemical Engineering and
Materials Science, Yuan Ze University, Taoyuan, Taiwan, 4 Multidisciplinary Research Institute, Chiang
Mai University, Chiang Mai, Thailand, 5 Center of Excellence in Microbial Diversity and Sustainable
Utilization, Faculty of Science, Chiang Mai University, Chiang Mai, Thailand, 6 Environmental Science
Research Center, Faculty of Science, Chiang Mai University, Chiang Mai, Thailand
Microalgae, especially spirulina, have been globally used as a food supplement
due to their rich protein content, safety for human consumption, and provision of
enhanced immunomodulatory capabilities. There are, however, few reports that
have investigated the immunomodulatory properties of spirulina protein
hydrolysate. Consequently, this study aims to optimize the best extraction
techniques for spirulina protein hydrolysate and characterize its antioxidant
activities and immunomodulation properties in vitro. The results indicated that
protein hydrolysate with Flavourzyme and alkaline extraction after
ultrasonication and pre-enzymatic assistant with cellulase exhibited superior
antioxidant properties compared to other methods. Additionally, all the protein
extracts demonstrated a dose-dependent inhibition of nitric oxide production
without significantly impacting cell viability. Furthermore, in vitro
immunomodulatory properties were evaluated using Candida albicans (DMST
5815) as the test pathogen, with phagocytic activity and index measurements
conducted. Notably, the results correlated with the previous assessments,
wherein the protein hydrolysate with Flavourzyme displayed the highest
phagocytic percentage, measuring 52.3% at a concentration of 10 mg/mL.
These findings suggest that enzymatically derived protein hydrolysates from
spirulina could serve as a potential source for enhancing immunostimulant
activity. Thus, they hold promise as natural bioactive ingredients for
therapeutic purposes and the development of functional foods.
KEYWORDS
anti-inflammation, hydrolysate, immunomodulation, protein, microalgae, spirulina
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1 Introduction
species, the specific pretreatments have to be optimized to achieve
high protein yields (O’Connor et al., 2022). Once the protein is
extracted, enzymatic hydrolysis synthesizes bioactive peptides from
microalgal proteins, which are used for clinical applications since it
depletes the harmful substances to give a good yield (Sathya et al.,
2021). Moreover, different protease enzymes have different
preferred cleavage sites, resulting in different bioactive properties.
For example, immune peptides are responsible for modulating both
lymphocyte proliferation and increasing the phagocytic activity of
macrophages in humans (Ahn et al., 2008), and previous studies of
macroalgae called Porphyra columbina exhibited that enzymatic
hydrolysis using Alcalase and trypsin had immunosuppressive
effects on rat splenocytes as they enhanced IL-10 production
while the production of TNF-a and IFN-g was inhibited (Cian
et al., 2012b).
Despite previous studies that have reported on anti-inflammatory
activities of aqueous spirulina extracts under full-range solar
spectrum or controlled light conditions (Tzachor et al., 2021), to
our knowledge, no investigation into the immune activities of both
crude extracts and protein hydrolysate from A. platensis has been
documented previously. This highlights the novelty and significance
of exploring the immunomodulatory properties of spirulina-derived
extracts, providing a new avenue for potential health applications.
Therefore, in this study, we meticulously optimized the methods of
cell disruption to enhance the production of protein hydrolysate from
spirulina (Arthrospira platensis). Subsequently, we conducted a
comprehensive characterization of the spirulina protein to assess its
immunomodulatory properties in an in vitro study.
Proteins play a crucial role in every stage of life, from infancy to
old age. Insufficient protein consumption can lead to various
consequences, including growth failure and a higher rate of
infection (Jayawardena et al., 2020). According to the Centers for
Disease Control and Prevention, individuals with compromised
immune systems are more susceptible to illnesses and infections.
Moreover, protein deficiency has become evident in many parts of
the world due to food insecurity. Consequently, numerous
researchers have sought alternative protein sources to reduce
dependency on existing agricultural and food production systems,
which may struggle to meet the growing food demand from the
increasing global population (Rösch et al., 2019; Bé né et al., 2015).
Microalgae might be a good source due to less competition for
space and resources during production. Moreover, they contain all
essential amino acids and are rich in other compounds such as
lipids and carbohydrates, making them suitable as food
supplements (Mathur, 2018). In the past, microalgae powder was
encapsulated into edible tablets for therapeutic purposes; however,
the inclusion of all compounds in these tablets could compromise
the properties of some individual components. Consequently, many
researchers have focused on extracting specific components, with
protein extract garnering considerable attention due to the
aforementioned reasons. While several microalgae species boast
high protein content in their dry weight, such as Chlorella vulgaris,
with 51%–58% protein content (Liu and Hu, 2013), Haematococcus
pluvialis with 26% protein content, and Dunaliella salina with 26%–
29% protein content (Ba et al., 2016), spirulina stands out as one of
the most promising potential protein sources with 70% protein
content (El-Kassas et al., 2015).
Spirulina, also known as the biomass of cyanobacterium
Arthrospira platensis, has been globally used as a food supplement
for many years, owing to its high nutritional values and safety for
human consumption. Notably, its protein content in dry weight
surpasses that of soybean by 20 times, corn by 40 times, and beef by
a staggering 400 times. Additionally, the proteins derived from
spirulina have been intensively documented for their numerous
health benefits, including enhancement of antioxidant properties,
anti-inflammatory effects, and immunomodulatory capabilities
(Sedighi et al., 2019). Furthermore, it is important to consider
that various protein extraction techniques may influence the
bioactive metabolite content of spirulina. For instance,
hydrolyzation yields and bioactive peptides from spirulina have
been reported to exhibit anticancer properties and effectiveness
against immunodeficiency diseases caused by HIV and other viral
infections (Sathasivam et al., 2019).
Basically, proteins contain two to 20 amino acids breaking
down during gastrointestinal digestion, food processing, or
fermentation into peptides (Cian et al., 2012b; Sathya et al., 2021;
Qian et al., 2008). Since microalgae have complex structures of
carbohydrate-rich cell walls, pretreatment, either mechanically or
nonmechanically, is required to support the disruption of the
microalgae cell wall (Geada et al., 2021). Depending on the algal
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2 Materials and methods
2.1 Spirulina biomass
Dried spirulina (Arthrospira platensis) powder provided by the
Algal and Cyanobacterial Research Laboratory, Faculty of Science,
Chiang Mai University, Thailand, was used for the extraction
of proteins.
2.2 Protein extraction from spirulina
2.2.1 Cell-free lysate by ultrasonic-assisted
cell disruption
This method is achieved by means of ultrasonication (Vibra-cell
VC505, Sonics & Materials Inc., USA), which disrupts the cell wall
completely or partially, and then a mixture of cellular components is
released from the spirulina cells into the surrounding medium
phosphate buffer (1:20 (w/v) ratio, pH 7). This mechanism could be
denoted as cell-free lysate (CFL). After that, centrifugation at 2,000×g
for 45 min by Hettich (REF 1206, SN 0027600-03) was done to
separate the biomass from the supernatant. The supernatant was taken
and lyophilized until it was dried, and this method was regarded as a
cell-free lysate by ultrasonic-assisted cell disruption (CFL).
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2.2.2 Cell-free lysate by ultrasonic and cellulasepretreated cells
0027600-03). After that, the obtained supernatant was solubilized
at alkaline pH using 1 M of NaOH (pH 10). Subsequently, another
centrifugation was conducted at 2,000×g for 45 min with the
intention of isolating the proteins from the supernatant. It was
achieved by treating with 1 M of HCL (pH 3), leading to protein
precipitation, and only the pellet was collected for further analysis
(Parimi et al., 2015). The entire process is identified as alkaline/acid
extraction of ultrasonicated and cellulase-pretreated cells (AAE).
All of the protein samples extracted from various methods were
stored at −20°C until use. The cell disruption flow chart is illustrated
in Figure 1.
This method is achieved by means of ultrasonication (Vibra-cell
VC505, Sonics & Materials Inc., USA), which disrupts the cell wall
completely or partially, and then a mixture of cellular components
is released from the spirulina cells into the surrounding medium
phosphate buffer (1:20 (w/v) ratio, pH 7). After that, the cellulase
purchased from iKnowZyme was added at a concentration of 50 U/
mL and incubated at 50°C for 90 min (Le Nguyen Doan et al., 2022).
Subsequently, centrifugation at 2,000×g for 45 min by Hettich (REF
1206, SN 0027600-03) was done to separate the biomass from the
supernatant. The supernatant was then subjected to lyophilization
until it reached a completely dried state, and this method was
named as a cell-free lysate by ultrasonic and cellulase-pretreated
cells (CFL+C).
2.3 Preparation of protein hydrolysates
The lyophilized protein obtained from the methods (CFL, CFL
+C, and AAE) was dissolved in phosphate buffer (pH 7) to achieve a
final concentration of 3.89 mg/mL. Enzymatic hydrolysis employed
two different proteases, Alcalase (70 U/mL) and Flavourzyme (≥
20,000 U/mg), purchased from Novo Nordisk (Bagsverd,
Denmark). Hydrolysis was conducted at pH 6.5, a temperature of
63°C, and for a duration of 1 h and 12 min, with an enzyme-tosubstrate ratio of 1% (v/v). To ensure enzyme inactivation, the
2.2.3 Cell-free lysate by alkaline/acid extraction
of ultrasonic and cellulase-pretreated cells
The last pretreatment technique was referred to as cell-free
lysate by alkaline/acid extraction of ultrasonic and cellulasepretreated cells (AAE). Following the incubation of the cell
suspension with ultrasonication and cellulase, centrifugation was
performed at 2,000×g for 45 min by Hettich (REF 1206, SN
FIGURE 1
The flowchart depicts the procedural details of the methodology applied in obtaining nine treatments. As regards the first, three treatments called
CFL, CFL+C, and AAE were obtained through cell disruption. Subsequently, these three treatments were hydrolyzed using two proteases—
Flavourzyme and Alcalase. As a consequence, six additional treatments named CFL+F, CFL+C+F, and AAE+F were obtained using Flavourzyme,
whereas CFL+A, CFL+C+A, and AAE+A were derived using Alcalase.
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20 μL of nine extracts from spirulina were mixed with 100 μL of a
10% Folin–Ciocalteu solution and incubated at room temperature
for 5 min. Thereafter, 80 μL of a 5% sodium carbonate solution was
added and incubated for another 1 h (Khan Yusufzai et al., 2018;
Aryal et al., 2019). The absorbance was then measured at 765 nm,
and the total phenolic content was calculated using Equation 1.
hydrolyzed samples were exposed to a temperature of 90°C for 20
min. Subsequently, centrifugation at 6,000×g at 4°C for 20 min
separated the supernatant from other components. The resulting
supernatant was stored at −20°C until further experimentation
(Pekkoh et al., 2021).
mg of gallicacid
GAE
g of extract
2.4 Analytical methods
=
Absorbance at 1 of gallic acid
(1)
Absorbance at 1 of extract
2.4.1 Total protein content analysis
The hydrosoluble protein content was determined using the
Lowry protein assay with minor modifications. The principle of the
Lowry protein assay depends on the complexity of copper with
tryptophan and tyrosine residues. Bovine serum albumin (BSA) was
set as a standard curve, and nine protein extracts were dissolved in
distilled water (1 mg/mL), and the absorbance was measured at 610
nm. The protein concentration was then calculated using the
standard curve obtained from the BSA calibration (Lowry
et al., 1951).
2.5 Analysis of the degree of hydrolysis
The degree of hydrolysis (DH) is highly dependent on the
number of peptide bonds after hydrolysis and is related to substrate
availability and the specific enzymatic sites of protease that are
determined by a specific amino acid composition and sequence. In
this study, DH was assessed based on the ratio of amino nitrogen
before and after the hydrolysis of protein based on the reaction of
primary amino nitrogen with o-phthaldialdehyde (OPA). Briefly,
the OPA solution was freshly prepared by dissolving 0.160 g of ophthaldialdehyde (C8H6O2) in 4 mL of ethanol. Another solution
was prepared by dissolving 7.62 g of sodium tetraborate
decahydrate (NaC12H25SO4) and 0.2 g of sodium dodecyl sulfate
(NaCl2H25SO4) into 150 mL of DI water. Ultimately, 0.176 g of
dithiothreitol (C4H10O2S2) was dissolved in 5 mL of DI as the third
solution. These solutions were mixed in a volumetric flask and
adjusted to the final volume by adding 200 mL of DI, 150 μL of an
OPA reagent, and 50 μL of the sample, control blank, and sample
blank to the 96-well plates and incubated exactly for 2 min (Pekkoh
et al., 2021; Bahari et al., 2020). The absorbance was measured at
340 nm, and the DH was calculated based on Equation 2.
2.4.2 Total nonprotein component analysis
2.4.2.1 Total sugar content assay
The amount of sugar in each extract was determined by using
phenol-sulfuric acid, with two main chemicals—96% sulfuric acid
and 5% phenol (DuBois et al., 1956). In the presence of phenol and
concentrated sulfuric acid, the sugars, their methyl derivatives,
oligosaccharides, and polysaccharides could be determined. The
glucose solution was set on a standard curve with various
concentrations (0.01–0.25 mg/mL). Briefly, 0.5 mL glucose or
protein extracts from spirulina, 0.5 mL of 5% phenol, and 2.5 mL
of 96% sulfuric acid were added and incubated at room temperature
for 10 min. Blank is performed by using distilled water, and the
absorbance was measured at 490 nm.
DH=
2.4.2.2 Reducing sugar assay
The presence of reducing sugars in the extracts can be
determined by using 3,5-dinitrosalicylic acid (DNS), which
detects the presence of a carboxyl group. In brief, the aldehyde
group is oxidized into a carboxyl group, and simultaneously, 3,5dinitrosalicylic acid (DNS) is reduced to 3-amino,5-nitrosalicylic
acid under alkaline conditions. The glucose solution was set as a
standard curve with various concentrations (0.02–1 mg/mL).
Briefly, 0.5 mL of glucose or protein extracts from spirulina and
0.5 mL of DNS were added and incubated at 98°C for 15 min. After
that, they were diluted with 5 mL of distilled water. Blank is
performed by using distilled water, and the absorbance was
measured at 540 nm (DuBois et al., 1956).
(2)
Where, A is the absorbance of the sample after hydrolysis, B is
the absorbance of the sample blank after hydrolysis, C is the
absorbance of control blank, D is the absorbance of the sample
before hydrolysis, and E is the absorbance of a sample blank
before hydrolysis.
2.6 Analyzing the biological activities
2.6.1 Potassium ferricyanide-reducing
antioxidant power
Reducing the ferricyanide complex (Fe3+) to its ferrous form
plays a crucial role in food antioxidants.
Phosphate buffer at 0.2 M (pH 6.6) was prepared, and 30 mL of
buffer was added in 1% (w/v) potassium ferricyanide solution.
Subsequently, 10% (w/v) trichloroacetic acid (TCA) solution and
0.1% (w/v) ferric chloride FeCl3 were dissolved in 30 mL of DI, 3 g
and 0.03 g, respectively. The gallic acid was set as a standard curve
(Benzie and Strain, 1999). The experimental procedure involved
using 96-well plates, where 145 μL of 0.2 M phosphate buffer and
1% K3Fe(CN)6 were mixed with 60 μL of samples, and the mixture
2.4.2.3 Total phenolic content assay
The total phenolic content was measured using Folin–
Ciocalteu. The Folin–Ciocalteu is an electron transfer-based assay
that has a reduced capacity and is expressed as phenolic content. By
using a 96-well plate, the phenolic compounds present in different
extracts from spirulina were detected. The calibration curve was
performed with gallic acid from 0.02mg/mL to 0.2 mg/mL. In brief,
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(D−E−C)
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Chiang Mai University, Chiang Mai, Thailand, were cultured in
Dulbecco’s modified Eagle’s medium (DMEM) Gibco (Grand
Island, NY, USA) supplemented with 10% fetal bovine serum
(FBS), penicillin (100 U/mL), and streptomycin (100 μg/mL). The
cell culture was incubated at 37°C in a humidified atmosphere in a
5% CO2 incubator for 48 h. After this, the cells were seeded in a
96-well plate (2 × 105 cells/well) and kept at 37°C in a humidified
atmosphere with a 5% CO2 incubator for 24 h to ensure cell
adherence and readiness for further experiments (Flores
Hernandez et al., 2017). All reagents and chemicals used were of
analytical grade.
was incubated at 50°C for 20 min. After that, 145 μL of 10% TCA
solution was added. The resulting mixture was centrifuged at
3,000×g for 10 min. Following this, 500 μL of DI and 100 μL of
0.1% FeCl3 were added to the supernatant. However, sample control
was prepared in the same volume with only 290 μL of buffer, 745 μL
of DI, and 60 μL of samples. The absorbance was measured at 700
nm, and increased adsorption of the reaction mixture indicates an
increase in reducing power. The activity was calculated using
Equation 3.
GAE
mg of gallicacid
Absorbance at 1 of gallic acid
=
g of extract
Absorbance at 1 of extract
(3)
2.7.2 Inhibitory effects on nitric oxide production
2.6.2 Antioxidant activity determined by
radical cations
After being incubated for 24 h, the cells were stimulated with 1
μg/mL LPS (50 μL) for 10 min. The cells were then treated with
various concentrations of five different extracts derived from
spirulina that showed the highest antioxidant activities during
the screening process (0.03–5 mg/mL). The extracts were diluted
with DMEM without phenol red (Grand Island, NY, USA) and
supplemented with 10% FBS. The untreated cells were set as a
control. The cells were then incubated for 24 h at 37°C in a
humidified atmosphere with 5% CO 2 . After incubation, the
supernatant from the cells was taken, and nitric oxide
production was estimated using the Griess reaction. In brief,
the supernatant was mixed with Griess reagent and incubated at
room temperature for 15 min. After that, the absorbance of
each well was measured at 540 nm by a microplate reader,
and the inhibitory effects of the various extracts on nitric oxide
(NO) production were measured using Equation 6 (Maruyama
et al., 2010).
The ABTS assay was conducted according to the reference
method (Lomakool et al., 2023). In brief, 0.0192 ABTS was
dissolved in 5 mL of distilled water. Subsequently, 0.3784 g of
potassium persulfate was also dissolved in 10 mL of distilled water.
The two solutions were mixed into a 1:1 ratio and kept in the dark
for 16 h before use. Next, the mixture was diluted with distilled
water, and the absorbance was measured at 734 nm to a value of
0.70 ± 0.02. Trolox was used to establish a standard curve. Using 96well plates, the ABTS assay was conducted as follows: 10 μL of the
sample was mixed with 190 μL of radical cation (ABTS+·) solution
and left at room temperature for exactly 6 min. After the incubation,
the absorbance was measured at 734 nm. The ABTS+· radical
inhibition capacity of the extract was then compared with the
Trolox standard to determine its Trolox Equivalent Antioxidant
Capacity (TEAC) using Equation 4.
mg
IC50 of Trolox ( mL
)
mg of Trolox
TEAC
=
g
g of extract
IC50 of extract ( mL
)
(4)
Percentage of inhibition (%)=
The metal chelating activity was determined following the
procedure outlined in reference (Gulcin and Alwasel, 2022). In
brief, 2 mM of iron (II) chloride tetrahydrate was dissolved in
distilled water to detect this activity. After that 5 mM of ferrozine
was also dissolved in distilled water. The EDTA was employed as a
standard curve. Using 96-well plates, 400 μL of sample was mixed
with 50 μL of FeCl2 and 200 μL of ferrozine. As soon as this step was
done, they were incubated at room temperature for 10 min, and the
absorbance was measured at 562 nm. The activity was calculated
using Equation 5.
mg
IC50 of EDTA ( mL
)
mg of EDTA
=
g
)
g of extract
IC50 of extract ( mL
(A0−A1)
100
A0
2.7.3 Cytotoxicity assay on RAW264.7 cells
Cell viability was measured by 93-(4,5-dimethylthiazol-1-yl)2,5-diphenyl tetrazolium bromide) MTT assay from Bio Basic
(Amherst, NY, USA). The metabolically active cells possess a
mitochondrial enzyme called succinate dehydrogenase, which
reduces MTT into insoluble purple formazan crystals. The cell
viability was measured by using a spectrophotometer. In brief, 30 μL
of 2 mg/mL MTT solution was added to each well after the
supernatant was removed and incubated for 3 h. Subsequently,
200 μL of dimethyl sulfoxide (DMSO) was added to each well and
incubated for another 10 min. The absorbance was measured at
540 nm with a reference wavelength of 630 nm by a microplate
reader (Maruyama et al., 2010), and cell viability was measured
using Equation 7.
(5)
2.7 Anti-inflammation activity
Percentage of cell viability ( % ) = ½
2.7.1 Cell culture
(A0 − A1)
100
A0
(7)
Where, A0 is the absorbance of the control and A1, the
absorbance of the extract/standard.
RAW264.7 cells obtained from 2711, the Division of
Microbiology, Department of Biology, Faculty of Science,
Frontiers in Marine Science
(6)
Where, A0 is the absorbance of the control and A1 is the
absorbance of the extract/standard.
2.6.3 Metal chelating activity
EDTA
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2.8 Characterization of immunomodulatory
properties in vitro
at 95°C for 3 min to cleave noncovalent bonds and centrifuged at
6,000×g for 4 min. The Precision Plus Protein™ Dual Color
Standards markers ranging from 2 kDa to 250 kDa (Bio-Rad,
Hercules, CA, USA) were applied as a reference for the molecular
weight of protein bands in the samples. Electrophoresis conditions
were set at a constant current setting of 120 V for 120 min (Pekkoh
et al., 2021; Meinlschmidt et al., 2016a).
2.8.1 Preparation of test pathogen
Candida albicans (DMST 5815), obtained from SCB 2711, the
Department of Biology, Faculty of Science, Chiang Mai University,
Thailand, was used as a test pathogen for the phagocytosis assay.
Sabouraud agar was used as a growth medium for this strain,which was
incubated at 37°C for 24–48 h. They are transferred to the same
medium without agar to prepare them for the in vitro assay. After that,
it was mixed with 1x phosphate buffer (pH 7.4), and the cells were
counted and adjusted to 1 × 106 cells/mL by hematocytometer,
ensuring a standardized number of cells for the
phagocytosis assessment.
2.10 Statistical analysis
Means of three replicates of determination ± standard deviation
(SD) was used. One-way ANOVA using Duncan’s multiple range
test (p< 0.05) was used to assess differences in significance values
between treatments. Statistical analyses were conducted using SPSS
for Windows software (Version 10, Chicago, IL, USA) to determine
the significant differences. For the phagocytosis assay, an Analysis
of Variance (ANOVA) test was performed in R studio to assess the
statistical significance of differences among the means of
multiple groups.
2.8.2 Phagocytosis assay in vitro
The phagocytosis assay, as described by the reference, was
performed as an in vitro assay (Gabhe et al., 2006). First of all, the
blood was collected by the puncture of the caudal vein. As soon as the
blood was obtained, it was mixed with ethylenediaminetetraacetic
acid (EDTA), an anticoagulant. Next, the blood is diluted with 1×
phosphate buffer in a 1:1 ratio (pH 7.4). The white blood cell layer
was then collected and separated polymorphonuclear leucocyte
(PMN) by Ficoll–Hypaque media with the same ratio (PMN:
Ficoll–Hypaque media) and centrifuged at 800×g for 20 min by
SANTRIFUJ (Bench-Top Centrifuge) NF800. After that, only PMN
was selected and mixed with 1× phosphate buffer in a 1:1 ratio (pH
7.4) three times and centrifuged at 600×g for 7 min in each round.
After that, only PMN was mixed with Candida albicans (DMST
5815). After mixing, various concentrations of four different
extracts from spirulina that exhibited the highest antioxidant
activities during screening (1–10 mg/mL) were added and
incubated at room temperature for 90 min. The control was set
without the extract from spirulina. After incubation, cytosmears
were prepared, fixed, and stained with Wright–Giemsa stain. The
phagocytic cells were visualized under an optical microscope under
×100 using immersion oil, and the phagocytic number and
phagocytic index were calculated using Equations 8, 9.
Phagocytic number=
total number of phagocytic yeasts
total number of phagocytes
Percentage of phagocytic index=
number of phagocytes
100
number of neutrophils
3 Results
3.1 Total protein concentration, phenolic
content, and sugar assay
In this section, an assessment is undertaken to quantify the
presence of potential interferents that could impact biological
activities. This is motivated by the findings of a preceding study
indicating that proteins are commonly co-extracted alongside other
interferents, such as sugar or phenolic compounds (Peter et al.,
2021). Consequently, the detection of phenolic and sugar assays is
deemed essential to ascertaining whether the observed activities can
be attributed to proteins or interfering substances. Table 1 presents
data on total protein concentration, phenolic content, total sugar
assay, and reducing sugar assay. The results reveal elevated protein
concentrations in the protein hydrolysate compared to other
interferents. Consequently, it can be inferred that the bioactive
properties, to be discussed subsequently, are primarily derived from
proteins, despite potential disruptions from phenolic and
sugar content.
(8)
(9)
3.2 Effect of degree of hydrolysis
In this study, DH was assessed based on the ratio of amino
nitrogen before and after the hydrolysis of protein based on the
reaction of primary amino nitrogen with o-phthaldialdehyde
(OPA). According to the experimental results exhibited in
Figure 2, after hydrolysis, the DH increases significantly from
0.018 to 10 with Flavourzyme and Alcalase in the case of CFL.
Similarly, CFL+C also demonstrated a sharp increase from 0.025
before and 2.3 with Flavourzyme and Alcalase. There was also a
substantial increase from 0.023 to around 7 with Flavourzyme and
almost 12 with Alcalase.
2.9 Sodium dodecyl sulfate-polyacrylamide
gel electrophoresis analysis
The molecular mass distributions of all treatments were
estimated by sodium dodecyl sulfate-polyacrylamide gel
electrophoresis (SDS-PAGE) using the TGX Stain-Free ™
FastCast™ Acrylamide Kit from Bio-Rad (Hercules, CA, USA).
To begin, the samples were suspended in phosphate buffer (pH 7)
and mixed with 6% SDS dye. After that, the mixture was incubated
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TABLE 1 Total protein concentration, phenolic content, and sugar assay.
Type
of
extraction
Name
of extracts
Protein
concentration
(mg/g dw)
Total phenolic content GAE (mg
gallic acid/g extract)
Total sugar
assay (mg/mL)
Reducing sugar
assay (mg/mL)
Cell disruption
CFL
4.36
11.2
1.45 ± 0.15 a
0.09 ± 0.003 b
CFL+C
21.73
11.3
1.05 ± 0.1 b
0.139 ± 0.01 a
AAE
25.11
21.7
0.64 ± 0.06 d
0.006 ± 0.002 d
CFL+F
40.16
3.4
0.88 ± 0.05 b
0.009 ± 0.001 d
CFL+C+F
8.93
5.9
0.76 ± 0.04 c
ND
AAE+F
35.85
1.2
0.83 ± 0.06 c
ND
CFL+A
30.83
4.3
0.29 ± 0.05 e
0.027 ± 0.0005 c
CFL+C+A
32.45
3.7
0.55 ± 0.01 d
0.007 ± 0.0005 d
AAE+A
49.39
5.9
0.92 ± 0.04 b
0.015 ± 0.002 d
Protein
hydrolysate
Means followed by a different lowercase letter (a–e) are significantly different in relation to Duncan’s multiple range test; values are expressed as means ± SD (p< 0.05) on these assays.
ND, the activity was not detected; CFL, cell-free lysate by ultrasonic-assisted cell disruption; CFL+C, cell-free lysate by ultrasonic and cellulase-pretreated cells; AAE, cell-free lysate by alkaline/
acid extraction of ultrasonic and cellulase-pretreated cells; CFL+F, cell-free lysate by ultrasonic-assisted cell disruption and Flavourzyme; CFL+C+F, cell-free lysate by ultrasonic and cellulasepretreated cells with Flavourzyme; AAE+F, cell-free lysate by alkaline extraction of ultrasonic and cellulase-pretreated cells with Flavourzyme; CFL+A, cell-free lysate by ultrasonic-assisted cell
disruption and Alcalase; CFL+C+A, cell-free lysate by ultrasonic and cellulase-pretreated cells with Alcalase; AAE+A, cell-free lysate by alkaline extraction of ultrasonic and cellulase-pretreated
cells with Alcalase.
3.3 Effects on antioxidant activities
3.4 Effects of anti-inflammation
3.3.1 Potassium ferricyanide-reducing
antioxidant power
3.4.1 Inhibitory effects of spirulina extracts on
nitric oxide production
The result of the antioxidant activity that was determined by
means of potassium ferricyanide-reducing antioxidant power
(PFRAP) in relation to a standard curve revealed that the extracts
that encountered hydrolysis showed higher antioxidant activities
than just a protein extraction. An equal gallic acid equivalent
antioxidant capacity was found in AAE and CFL+C+F, with 1.2
in each, followed by CFL+F, which contributed to 0.8. The rest of
the six treatments were not more than 0.5, as illustrated
in Figure 3A.
The five extracts on NO production were estimated using the
Griess reagent on RAW246.7 cells at various concentrations from
0.039 mg/mL to 0.16 mg/mL. After being induced by LPS for 24 h,
the nitrite content of the supernatants was calculated. The result
illustrated that CFL+F contributed the highest percentage of
inhibition. It was apparent that the lowest percentage of
inhibition came from CFL, not more than 15%.
3.3.2 Antioxidant activity determined by
radical cations
The cytotoxicity effects of five spirulina extracts on Raw264.7
cell macrophages were evaluated by MTT assay. Various
concentrations of samples (0.039–0.156 mg/mL) were tested, and
results indicated that all the extracts did not significantly affect cell
viability. Consequently, all of the extracts were used for the
subsequent experiments since they are considered to be highly
safe and noncytotoxic to RAW264.7 cells.
3.4.2 Cytotoxicity of spirulina extracts on
RAW264.7 cells
The ABTS radical scavenging activity (Figure 3B) is used to
evaluate the ABTS+ stable radical cation, whose intensity decreases
in the presence of antioxidants. Similar to the PFRAP method, the
Trolox equivalent antioxidant capacity revealed that the maximum
antioxidant activity was obtained from AAE, AAE+F, and CFL+C
+A, with 0.13, 0.19, and 0.06, respectively.
3.5 Effects of spirulina extracts on
phagocytic activity
3.3.3 Metal chelating activity
Metal chelating activity can be considered the most putative and
common way to detect antioxidant activity. In the biological system,
an excess of free ions could perform induction and form free
radicals. The result of the antioxidant activity that was
determined by means of metal chelating activity in relation to a
standard curve was in accordance with the previous methods where
AAE, CFL+C+A, and C had strong chelating activity, amounting to
0.04, 0.02, and 0.03 as depicted in Figure 3C.
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Four extracts (CFL+C+F, CFL+F, AAE, and CFL+A) that
exhibited the highest antioxidant and anti-inflammatory
properties were further evaluated for phagocytic activity at
concentrations of 1 mg/mL, 2 mg/mL, 4 mg/mL, 6 mg/mL, and
10 mg/mL and compared to the control group. When there is an
invading pathogen, neutrophils serve as part of the innate immune
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75 kDa, 50 kDa, 37 kDa, 25 kDa, 20 kDa, and 15 kDa. Notably, the
most intense bands were detected within the 15–25-kDa range.
However, the electrophoretic profiles of proteins hydrolyzed using
Flavourzyme and Alcalase enzymes displayed distinct
characteristics that exhibited around 15 kDa in Flavourzymetreated samples and a single weak band at Mw< 10 kDa in
Alcalase-treated samples.
3.7 Comparison with previous studies on
the anti-inflammatory and
immunomodulatory assays (in vitro)
Table 2 shows a comparative analysis of our study’s findings on
two different bioactive properties, namely anti-inflammatory
activity and immunomodulatory activity, with previous findings.
Similar to the bioactive properties obtained from protein
hydrolysate of plant- and animal-based sources regarding antiinflammatory and immunomodulatory properties, protein
hydrolysate from spirulina could also provide those properties,
indicating that algae-based products hold the potential to serve as
a valuable protein source with beneficial properties.
FIGURE 2
4 Discussion
Degree of hydrolysis. Means followed by a different letter (a–c) are
significantly different in relation to Duncan’s multiple range test;
values are expressed mean ± SD (p > 0.05) before hydrolysis, (p<
0.05) on post-Flavourzyme hydrolysis and post-Alcalase hydrolysis.
CFL, cell-free lysate by ultrasonic-assisted cell disruption; CFL+C,
cell-free lysate by ultrasonic and cellulase-pretreated cells; AAE,
cell-free lysate by alkaline/acid extraction of ultrasonic and
cellulase-pretreated cells; CFL+F, cell-free lysate by ultrasonicassisted cell disruption and Flavourzyme, CFL+C+F, cell-free lysate
by ultrasonic and cellulase-pretreated cells with Flavourzyme; AAE
+F, cell-free lysate by alkaline extraction of ultrasonic and cellulasepretreated cells with Flavourzyme; CFL+A, cell-free lysate by
ultrasonic-assisted cell disruption and Alcalase; CFL+C+A, cell-free
lysate by ultrasonic and cellulase-pretreated cells with Alcalase; AAE
+A, cell-free lysate by alkaline extraction of ultrasonic and cellulasepretreated cells with Alcalase.
The percentage of protein content in spirulina is relatively
higher than that of lipids, carbohydrates, and ash, standing
notably at 70% (Parimi et al., 2015). Additionally, the proteins
derived from spirulina have been intensively documented for their
numerous health benefits, including enhanced antioxidant
properties, anti-inflammatory effects, and immunomodulatory
capabilities (Sedighi et al., 2019). Consequently, there has been a
remarkable increase in the investigation of protein properties. As
depicted in Figure 1, protein extraction was performed by means of
ultrasonication as the first treatment, with the aim of disrupting cell
wall polysaccharides. The resulting suspension underwent a
secondary treatment with cellulase, which has been characterized
as a food-degrade approach to breaking down the cell wall. Alkaline
extraction was followed as the third treatment. After the cell
suspension was subjected to ultrasonication and cellulase, the
solution was subjected to NaOH, which is usually used to extract
proteins and is used in various food matrices (Naseri et al., 2020).
Both the values of the second and third treatments exceeded the
protein content achieved through ultrasonication, which was 4.4
mg/g. These findings could deduce that cell disruption by
ultrasonication assisted in protein extraction only partially. More
protein content was obtained from ultrasonic-assisted cellulasepretreated cells (21.73 mg/g), which could break down into shortchain cellulose, promoting the release of more intracellular
biomolecules after ultrasonication since the cell wall of spirulina
is mainly composed of cellulose (Le Nguyen Doan et al., 2022). The
protein content showed the best when all the parameters were
simultaneously involved as the third treatment, or AAE, with 25
mg/g, where some of the protein might have alkaline-soluble
properties when treated with NaOH. It is logical that a higher
response and respond at a fast rate. Therefore, the stimulation of
neutrophils could result in an increase in the immediate cellular
immune response. The result showed that there was a significant
increase in the phagocytic activity in CFL+F and CFL+C+F. The
former showed the highest activity at concentrations of 6 mg/mL
(36.61%) and 10 mg/mL (52.33%), while the latter exhibited the
highest activity at the same concentrations, with 39.98% and
42.12%, respectively. However, the other two extracts, AAE and
CFL+A, did not show any significant increase in the percentage of
phagocytosis versus the control group (Figures 4, 5).
3.6 SDS-PAGE analysis
The molecular weight distribution of all nine samples was
estimated through gel electrophoresis. As shown in Figure 6, the
electrophoretic pattern of the CFL, C, and AAE samples exhibited
prominent bands with high intensity at molecular weights (Mw) of
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A
B
C
FIGURE 3
Effects of antioxidant properties. (A) Potassium ferricyanide-reducing antioxidant power (PFRAP), p< 0.05 of GAE (mg gallic acid/g extract), (B) ABTS
radical scavenging activity, p< 0.05 of TEAC (mg Trolox/g extract), (C) metal chelating activity, p< 0.05 of EDTA (mg EDTA/g of extract). Means
followed by a different letter (a–c) are significantly different in relation to Duncan’s multiple range test. Value are expressed mean ± SD. CFL, cellfree lysate by ultrasonic-assisted cell disruption; CFL+C, cell-free lysate by ultrasonic and cellulase-pretreated cells; AAE, cell-free lysate by alkaline/
acid extraction of ultrasonic and cellulase-pretreated cells; CFL+F, cell-free lysate by ultrasonic-assisted cell disruption and Flavourzyme; CFL+C+F,
cell-free lysate by ultrasonic and cellulase-pretreated cells with Flavourzyme; AAE+F, cell-free lysate by alkaline extraction of ultrasonic and
cellulase-pretreated cells with flavozyme; CFL+A, cell-free lysate by ultrasonic-assisted cell disruption and Alcalase; CFL+C+A, cell-free lysate by
ultrasonic and cellulase-pretreated cells with Alcalase; AAE+A, cell-free lysate by alkaline extraction of ultrasonic and cellulase-pretreated cells
with Alcalase.
To elucidate this mechanism, a hypothesis may be proposed
that, in the case of the sample of CFL+C, two types of cell disruption
were encountered. Ultrasonication partially disrupts the cell wall of
the spirulina; subsequently, cellulase enzyme is added in order to
hydrolyze the cellulose into short-chain cellulose, promoting the
release of intracellular biomolecules, leading to an increased
amount of protein in the extract (Le Nguyen Doan et al., 2022).
Proteins obtained from this stage are considered intact proteins; as a
consequence, the amount of proteins in this sample is 21.73. mg/g
dw when detecting with Lowry assay.
On the other hand, when this sample of CFL+C was hydrolyzed
with Flavourzyme to obtain CFL+C+F, the Flavourzyme hydrolyzed
the intact proteins, which could bind to the active site of the
protease Flavourzyme to obtain peptides (Sun et al., 2019).
Moreover, Flavourzyme contains a mixture of aminopeptidase,
carboxypeptidase, and endoprotease, exhibiting complex cleavage
specificity (Xu et al., 2022). The aminopeptidase and
carboxypeptidase cleavage peptide bonds in the N-terminus or Cterminus, while the endoprotease breaks the protein molecules,
providing more –NH 2 and –COOH sites for the action of
aminopeptidase and carboxypeptidase (Zhou et al., 2021; Zhang
et al., 2023).
Additionally, the electrophoretic pattern of the CFL+C was
detected within the 25–25-kDa range, corresponding to the
subunits of C-phycocyanin (C-PC), whereas electrophoretic
profiles of proteins hydrolyzed using Flavourzyme displayed
distinct characteristics where low molecular weight was less
visible in Flavourzyme (Figure 6). This might be due to the ability
of Flavourzyme, which favors the formation of single amino acids
rather than longer polypeptides, which may not be visible on the gel
or may be obscured by the dye front (Aiello et al., 2019). Thus, it
seems that a complex type of mechanism was established where
detecting at wavelength 660 nm by means of a Lowry assay was not
accomplished, and further work is required to elucidate it and to
protein content is obtained with AAE because they can only be
extracted in an alkaline environment, unlike the previous two
treatments at pH 7, where the solubility of proteins is not high,
and therefore the extraction is weaker. Additionally, other
compounds are present (simple sugars and phenols). As depicted
in Table 1, all of these three parameters did not encounter
enzymatic hydrolysis and were denoted as without proteases.
After protein extractions were performed by the three different
methods mentioned above, all of the treatments mentioned above
encountered enzymatic hydrolysis by using two proteases named
Flavourzyme and Alcalase and obtained six further treatments.
Enzymatic hydrolysis is more specific to the desired peptides,
results in higher peptide yield, and becomes biologically active.
Since the DH is highly dependent on the number of peptide bonds
after hydrolysis and is related to substrate availability and the
specific enzymatic sites of protease that are determined by a
specific amino acid composition and sequence, this method was
applied in our study. As depicted in Figure 2, the degree of
hydrolysis of the spirulina was increased when compared to
unhydrolyzed samples at enzyme/substrate ratio (1%) and
hydrolysis time (1 h and 12 min). Previous reports by Pekkoh
et al. (2021) mentioned that a lower enzyme/substrate ratio with
increasing hydrolyzing time will support an increase in the number
of peptides cleaved by protease enzymes (Pekkoh et al., 2021). This
result was in alignment with the previous report using two different
proteases: pepsin, which exhibited a higher degree of hydrolysis
(16%), whereas protein hydrolysate with pancreatin showed an
11% degree of hydrolysis in spirulina (Arthrospira platensis)
(Mohammadi et al., 2022a). Furthermore, Cian et al. (2012a)
showed that protein hydrolysate with Flavourzyme increased the
degree of hydrolysis in 7 h to 14% in Porphyra columbina (red
seaweed). Similarly, values of the index in the hydrolysates of
spirulina (Arthrospira platensis) with Alcalase were revealed
(42.4%) (Akbarbaglu et al., 2022).
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A
B
C
D
E
F
G
H
FIGURE 4
In vitro phagocytosis test: (A, C, E, G) Phagocytic number of different extracts (p< 0.05); (B, D, F, H) The percentage of the phagocytic index of
different extracts (p< 0.05). Means followed by a different letter (a–c) are significantly different in relation to Tukey’s HSD, n = 100 cells in each
sample. AAE, cell-free lysate by alkaline/acid extraction of ultrasonic and cellulase-pretreated cells; CFL+F, cell-free lysate by ultrasonic-assisted cell
disruption and Flavourzyme; CFL+C+F, cell-free lysate by ultrasonic and cellulase-pretreated cells with Flavourzyme; CFL+A, cell-free lysate by
ultrasonic-assisted cell disruption and Alcalase.
confirmed that the amount of proteins is relatively higher than
that of other interferents (sugars and phenolic compounds).
All of the treatments were lyophilized and screened for
antioxidant properties as superior activity. Antioxidants play a
crucial role in maintaining human health and preventing and
treating diseases because of their ability to reduce oxidative stress,
which occurs when there is an imbalance between pro-oxidants and
antioxidants (Munteanu and Apetrei, 2021). Among the treatments
without proteases, AAE had the highest antioxidant activities,
which could conclude that protein extraction by conventional
understand the possible contributions of protein content in
these samples.
Proteins are generally co-extracted with other interferents, such
as sugar or phenolic compounds (Peter et al., 2021), so it is often
suggested to purify by means of ultrafiltration, ionic-exchange
chromatography, and dialysis. However, our study did not
conduct purification, and as a consequence, it is important to
ensure the target bioactive properties mainly come from the
proteins. Table 1 shows the analysis of protein yields together
with sugar assay and phenolic compounds, and the result
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FIGURE 5
Wright–Giemsa-stained white blood cells (×1,000) show phagocytosis activity at different concentrations: (A) 1 mg/mL, (B) 2 mg/mL, (C) 4 mg/mL,
(D) 6 mg/mL, and (E) 10 mg/mL; scale bar (-) = 3µm; arrowhead = phagocytic cells engulfed the yeasts. AAE, cell-free lysate by alkaline/acid
extraction of ultrasonic and cellulase-pretreated cells; CFL+F, cell-free lysate by ultrasonic-assisted cell disruption and Flavourzyme; CFL+C+F, cellfree lysate by ultrasonic and cellulase-pretreated cells with Flavourzyme; CFL+A, cell-free lysate by ultrasonic-assisted cell disruption and Alcalase.
fragments required for antioxidant activities. In addition, it is very
crucial to note that the complexity of protein hydrolysates,
including various peptide fragments and amino acids, could result
in elaborate interactions between different functional groups.
Consequently, the specific arrangement of these groups within the
peptide sequences results in lower antioxidant properties compared
to those without proteases (Rao et al., 2016).
Antioxidants play a crucial role in maintaining human health
and preventing and treating diseases because of their ability to
reduce oxidative stress, which occurs when there is an imbalance
between pro-oxidants and antioxidants (Munteanu and Apetrei,
2021). In this study, three different antioxidant properties were
screened as superior properties: PFRAP, ABTS radical scavenging
activity, and metal chelating activity. Firstly, PFRAP detects the
ability of an antioxidant to transfer an electron to reduce metallic
ions, carbonyl groups, and free radicals, so this mechanism is
known as a single electron transfer reaction, or SET.
Additionally, it is based primarily on the deprotonation and
ionization potential of the reactive functional group. Therefore, SET
reactions are pH-dependent, and PFRAP was done under acidic
conditions. However, it is suggested to test with other methods to
distinguish the dominant mechanisms for different antioxidants since
this method has a low relation with the process of radical extinction
(HAT mechanism). Unlike PFRAP, the ABTS radical scavenging
activity can be screened over a wide pH range, and this test offers the
determination of a large variety of antioxidant substances. For
example, ABTS+· radical reacts rapidly with both synthetic and
natural antioxidant substances (i.e., phenols, amino acids, peptides,
vitamin E, and vitamin C) in food components. Moreover, it is
interesting to screen metal chelating properties that link existing ions
methods with slight modifications had the ability against the
harmful ABTS+ free radicals through the oxidation reaction
(Pekkoh et al., 2022; Conde et al., 2021), PFRAP, which occurs
via the action of electron-donating antioxidants as reductants by
breaking the free radical chains by donating a hydrogen atom
(Giannoglou et al., 2022; Harnedy and FitzGerald, 2013), and
metal chelating activity, where molecules in extracts chelate iron
ions with biologically active –OH and –OCH3 groups (Ak and
Gülçin, 2008a). Spirulina contains various antioxidant compounds,
where the subunits of C-phycocyanin (C-PC) the predominant
protein in spirulina (20% of the dry biomass), are more soluble in
alkaline solutions. Notably, the SDS-polyacrylamide gel
electrophoretogram of AAE showed intense bands within the 15–
25-kDa range, corresponding to the subunits of C-PC (Aiello et al.,
2019), suggesting these compounds could relate with higher
antioxidant properties.
The result of antioxidant properties in enzymatic hydrolysis
with two proteases—Flavourzyme and Alcalase—exhibited different
variations in different methods. For example, CFL+F and CFL+C+F
showed the highest antioxidant activities by means of PFRAP
whereas AAE+F and CFL+C+A showed the best in ABTS+·
hazardous molecules, and all of the treatments did not show
significant antioxidant properties in metal chelating activity.
The outcomes are illustrated in Figure 6. The electrophoretic
pattern of hydrolyzed proteins is 10–15 kDa, where proteins are
cleaved into specific peptide bonds with desired functional
properties, and the protein content is relatively higher than that
without proteases. However, the processing conditions employed
during hydrolysis, such as enzymatic or chemical treatment, pH,
and reaction time, influence the availability and reactivity of active
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FIGURE 6
SDS-PAGE analysis. Lane 1 displays Precision Plus Protein™ Dual Color Standards markers ranging from 2 kDa to 250 kDa. Lanes 2–10 are ordered
as follows based on their labels: cell-free lysate by ultrasonic-assisted cell disruption (CFL), cell-free lysate by ultrasonic and cellulase-pretreated
cells (CFL+C), cell-free lysate by alkaline/acid extraction of ultrasonic and cellulase-pretreated cells (AAE), cell-free lysate by ultrasonic-assisted cell
disruption and Flavourzyme (CFL+F), cell-free lysate by ultrasonic and cellulase-pretreated cells with Flavourzyme (CFL+C+F), cell-free lysate by
alkaline extraction of ultrasonic and cellulase-pretreated cells with Flavourzyme (AAE+F), cell-free lysate by ultrasonic-assisted cell disruption and
Alcalase (CFL+A), cell-free lysate by ultrasonic and cellulase-pretreated cells with Alcalase (CFL+C+A), and cell-free lysate by alkaline extraction of
ultrasonic and cellulase-pretreated cells with Alcalase (AAE+A).
of pro-inflammatory cytokines and inflammatory cytokines like IL1ß, IL-6, NO, iNOS, COX-2, and TNF during inflammation in
response to LPS.
Moreover, the bioactive compounds from macroalgae and
microalgae have been potential candidates for exhibiting iNOS
inhibitory activity (Figure 7), which can prevent inflammationrelated diseases due to the overproduction of NO. Our result also
indicated that all the extracts were able to inhibit NO production in
a dose-dependent manner (0.039–0.16 mg/mL), where CFL+F and
CFL+C+F indicated the highest percentage from 25% to 40%.
Similar to current results, two previous reports studied a marine
bivalve mollusk (Cyclina Sinensis), and egg yolk also demonstrated
the production of NO. The former case exhibited the production of
NO (μM/L) in a dose-dependent manner when hydrolyzed with
pepsin. Additionally, the latter produced a NO of around 25 μM
when hydrolyzed with pancreatin and neutrase (Li et al., 2019; Lee
et al., 2022). Furthermore, Flores Hernandez et al. (2017) reported
that the NO inhibition from banana Musa paradisiaca ranged from
19% to 52% based on the extracts (Rao et al., 2016) (Table 2).
Moreover, the cytotoxic effect of the five extracts on RAW264.7 cells
was determined by an MTT assay, as shown in Figure 7B. The result
demonstrated that our five extracts did not significantly affect the
or molecules of a ligand to a central metal atom or ion through an
acyclic or ring-like coordination bond. For instance, in this study,
molecules in different treatments chelate iron ions with biological
compounds containing two or more –OH, –COOH, –SH, –OCH3, –
C=O, –PO3H2, –NR2, –O, and –S functional groups in a suitable
function structure. Consequently, it can be concluded that the
extracts that revealed the best antioxidant properties in all methods
are potentially more effective in protecting biological systems from
oxidative stress and related damage. By neutralizing free radicals and
reducing oxidative stress, other undesirable consequences, such as the
activation of proinflammatory transcription factors and reducing the
production of inflammatory mediators such as cytokines, might
be prohibited.
After the superior antioxidant properties screening, the top five
extracts that exhibited the highest antioxidant properties were
further screened for the production of nitric oxide on Raw264.7
cells. In murine macrophage RAW 264.7 cells, stimulation with LPS
only has been indicated to induce iNOS transcription and its
protein synthesis, which could raise NO production (Flores
Hernandez et al., 2017). Macrophages, as important components
of the immune system, play an essential role in controlling various
immunopathological phenomena, for example, the overproduction
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example, the overproduction of proinflammatory cytokines and
inflammatory cytokines like IL-1ß, IL-6, NO, iNOS, COX-2, and
TNF (Chen et al., 2016), a phagocytosis assay was detected in vitro
using the peripheral blood. The function of macrophages involved
in the innate immune system is to respond at a fast rate whenever
there is a pathogen. After mixing white blood cells with Candida
albicans (DMST 5815), the top four extracts that exhibited the
highest anti-inflammatory properties were used, and the percentage
of phagocytic activity and phagocytic index were evaluated
according to Gabhe et al. (2006) (Gabhe et al., 2006). As shown
cell viability. Our result was in accordance with previous reports
extracting phycocyanin (PC) from Spirulina platensis, where the
percentage of cell viability is around 90%, which did not
significantly affect the cell viability (Kraseasintra et al., 2022).
Similarly, the water and ethanolic (70%) extracts from Spirulina
platensis also showed similar results on the cytotoxicity assay
(Flores Hernandez et al., 2017).
In order to understand the role of macrophages, which are
important components of the immune system and play an essential
role in controlling various immunopathological phenomena, for
TABLE 2 Comparison with previous studies on anti-inflammatory and immunomodulatory activities.
Source
of protein
Enzyme
Type of
protein/
extraction
Anti-inflammatory activity
Percentage
of inhibition
Percentage
of
cell viability
Immunomodulatory
assay
References
Spirulina platensis
NA
Phycocyanin (PC)
NA
>90%
NA
(Kraseasintra
et al., 2022)
Spirulina platensis
NA
Water extract
of spirulina
NA
14.17%–106%
NA
(Flores
Hernandez
et al., 2017)
Ethanolic (70%)
of
spirulina extract
Porphyra tenera
Protamex
14%–64.72%
Protein
hydrolysate
Dosedependent
manner
≥ 90%
NA
(Senevirathne
et al., 2010)
Neutrase
Flavourzyme
Alcalase
Cyclina sinensis (a
marine
bivalve mollusk)
Pepsin
Protein
hydrolysate
≥ 90%
≥ 70% (50 μg/mL)
Phagocytic indices: 1–2.20
(Li et al., 2019)
Musa paradisiac
a (banana)
NA
Flesh
52.21 (250
μg/mL)
68% (250 μg/mL)
NA
(Rao
et al., 2016)
Ficus benghalensis
NA
Methanol extract
NA
NA
Phagocytosis number: 53 ± 2.51
(0.5 mg/mL)
(Gabhe
et al., 2006)
Phagocytosis index: 1.90 ± 0.08
Labeo rohita egg
Pepsin,
trypsin, Alcalase
Protein
hydrolysate
NA
NA
Phagocytic capacity (%) ≥ 50%
(Chalamaiah
et al., 2014)
Milk
Mixture of papain
and trypsin
Protein
NA
NA
Phagocytic capacity (%):
26%–36%
(Pan
et al., 2013)
Phagocytic index: 0.29–0.39
Egg yolk
Two-step hydrolysis
—pancreatic
and neutrase
Protein
hydrolysate
> 20 μM (nitrite)
≥ 80%
Phagocytosis activity (%): 130%–
150% (100% for control)
(Lee
et al., 2022)
Alaska pollock
Trypsin
Protein
NA
NA
Phagocytosis activity: −20%–35%
(Hou
et al., 2016)
Phagocytosis index: −0.4–0.6
Spirulina
(Arthrospira
plantensis)
Flavourzyme
Alcalase
Protein
hydrolysate
35%–40%
≥ 80%
15%–30%
Phagocytosis activity: −20%–52%
(Flavourzyme); −4%–
11% (Alcalase)
This study
Phagocytosis index: −0.55–0.95
(Flavourzyme); −0.36–
0.74 (Alcalase)
NA, not available.
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A
B
FIGURE 7
Effect of anti-inflammation properties. (A) Inhibitory effects of extracts on NO production in various concentrations (p< 0.05) on NO production.
(B) Percentage of cell viability (p > 0.05) on cell viability. Values are expressed mean ± SD. CFL, cell-free lysate by ultrasonic-assisted cell disruption;
AAE, cell-free lysate by alkaline/acid extraction of ultrasonic and cellulase-pretreated cells; CFL+F, cell-free lysate by ultrasonic-assisted cell
disruption and Flavourzyme; CFL+C+F, cell-free lysate by ultrasonic and cellulase-pretreated cells with Flavourzyme; CFL+A, cell-free lysate by
ultrasonic-assisted cell disruption and Alcalase.
However, to the best of our knowledge, no previous studies have
reported the hydrolysis of spirulina protein with Flavourzyme.
Consequently, the DH values were compared from different
proteases and macroalgae. The previous report used two different
proteases: pepsin, which exhibited a higher degree of hydrolysis
(16%), whereas protein hydrolysate with pancreatin showed an 11%
degree of hydrolysis in spirulina (Arthrospira platensis)
(Mohammadi et al., 2022a). Furthermore, Cian et al. (2012)
showed that protein hydrolysate with Flavourzyme increased the
degree of hydrolysis in 7 h to 14% in Porphyra columbina (red
seaweed) (Cian et al., 2012b). Moreover, values of the index in the
hydrolysates of spirulina (Arthrospira platensis) with Alcalase were
revealed (42.4%) (Akbarbaglu et al., 2022). In vivo study is necessary
to investigate the efficiency, safety, and potential toxicity of these
two extracts, CFL+F and CFL+C+F, by investigating the different
blood parameters and validating the immune-enhancing effects in
animal experiments and clinical trials. Furthermore, the active
fragments are also required to be confirmed by amino acid
profiling to elucidate the bioactive properties of each peptide
involved in enzymatic hydrolysis.
in Figure 4, compared to negative control containing only
pathogens and white blood cells, all four extracts showed
phagocytic activity in a dose-dependent manner, with CFL+F and
CFL+C+F showing the best phagocytosis activity. Although AAE
exhibited the highest percentage of antioxidant properties, this was
surpassed by the two extracts called CFL+F and CFL+C+F in terms
of anti-inflammatory and immunomodulatory activity in vitro.
Further identification of active fragments, for example, through
purification or molecular weight cut-off filtration, is needed for a
better understanding of the ability of generated bioactive peptides.
Although our study did not conduct purification,
electrophoretic mobility and the measurement of the degree of
hydrolysis for monitoring the progress of before and after
hydrolysis were measured. The electrophoretic pattern of the
CFL, C, and AAE samples exhibited prominent bands with high
intensity at molecular weights (Mw) of 75 kDa, 50 kDa, 37 kDa, 25
kDa, 20 kDa, and 15 kDa. This observation parallels previous
research on isolated spirulina proteins Mohammadi et al. (2022),
which indicated that unhydrolyzed proteins displayed multiple
bands ranging from 85 kDa to 25 kDa (Mohammadi et al.,
2022a). Notably, the most intense bands were detected within the
25–25-kDa range, corresponding to the subunits of C-PC, the
predominant protein in spirulina, accounting for 20% of the dry
biomass (Aiello et al., 2019). However, the electrophoretic profiles
of proteins hydrolyzed using Flavourzyme and Alcalase enzymes
displayed distinct characteristics where low molecular weight was
less visible in Flavourzyme compared to Alcalase (Figure 6). This
might be due to the ability of Flavourzyme, which favors the
formation of single amino acids rather than longer polypeptides,
which may not be visible on the gel or may be obscured by the dye
front. Additionally, the endo-peptidase enzyme, Alcalase, could
dominate the quaternary and tertiary conformations of proteins
by cleaving peptide bonds within individual or aggregated proteins
to produce smaller peptides (Meinlschmidt et al., 2016a).
Frontiers in Marine Science
5 Conclusion
In this study, protein extraction was performed prior to protein
hydrolysate, with the aim of achieving a higher concentration of
active bioactive compounds. The antioxidant property was first
investigated in all extracts in response to oxidative stress. Antiinflammation was then followed by selecting the optimal extracts
that displayed superior antioxidant properties. As the last stage, an
in vitro assay of immunomodulatory properties was carried out, and
the phagocytic activity and index were quantified. As expected, the
protein hydrolysate generated using proteases revealed the highest
phagocytic activity compared to other extracts. Although there
14
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Htoo et al.
10.3389/fmars.2024.1303025
Funding
could have been some interferents, such as sugar and phenolic
compounds, during protein extraction, the analysis showed lower
levels of sugar content and phenolic compounds, suggesting that
most of the bioactive properties come from proteins. In addition,
the two extracts, CFL with Flavourzyme and CFL with cellulase and
Flavourzyme, showed the highest phagocytic percentage; further
study through in vivo by animal model is necessary to investigate
the efficiency, safety, and potential toxicity of these extracts with
more precision and accuracy.
The author(s) declare financial support was received for the
research, authorship, and/or publication of this article. This
research was funded by the National Research Council of
Thailand (NRCT), the CMU Presidential Scholarship Academic
Year 2022, and the Graduate School of Chiang Mai University. This
research work was partially supported by Chiang Mai University.
Additionally, the first and seventh authors were supported by the
NSTC International Internship Pilot Program (IIPP).
Data availability statement
Acknowledgments
The original contributions presented in the study are included
in the article/supplementary material. Further inquiries can be
directed to the corresponding authors.
I would like to express my sincere gratitude for having a chance
to study the Master’s Degree Program in Applied Microbiology,
Faculty of Science, Chiang Mai University, under the CMU
Presidential Scholarship. My special thanks go to Mr. Nitiphong
Kaewman, Mrs. Kritsana Duangjan, Ms. Kittiya Phinyo, and Ms.
Srithip Sensupa for their assistance with technical support.
Additionally, thank you very much to Ms. Panumat Piosinsak
and Ms. Phornphan Phrompanya for their assistance with the
phagocytosis assay.
Ethics statement
The animal study was approved by approved by the
Institutional Animal Care and Use Committee of the Biology
Department, Faculty of Science, Chiang Mai University (Re: 001/
23). The study was conducted in accordance with the local
legislation and institutional requirements.
Conflict of interest
Author contributions
The authors declare that the research was conducted in the
absence of any commercial or financial relationships that could be
construed as a potential conflict of interest.
NH: Conceptualization, Formal analysis, Investigation,
Methodology, Project administration, Resources, Writing –
original draft. OK: Methodology, Writing – review & editing.
WB: Methodology, Resources, Writing – review & editing. TK:
Methodology, Resources, Writing – review & editing. JP: Funding
acquisition, Methodology, Resources, Writing – review & editing.
YT: Methodology, Resources, Writing – review & editing.
KK: Writing – review & editing. SC: Resources, Writing – review
& editing. SS: Conceptualization, Funding acquisition, Resources,
Supervision, Writing – review & editing. CP: Conceptualization,
Funding acquisition, Project administration, Resources,
Supervision, Writing – review & editing.
Publisher’s note
All claims expressed in this article are solely those of the authors
and do not necessarily represent those of their affiliated
organizations, or those of the publisher, the editors and the
reviewers. Any product that may be evaluated in this article, or
claim that may be made by its manufacturer, is not guaranteed or
endorsed by the publisher.
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