Prostaglandins, Leukotrienes and Essential Fatty Acids 91 (2014) 221–225
Contents lists available at ScienceDirect
Prostaglandins, Leukotrienes and Essential
Fatty Acids
journal homepage: www.elsevier.com/locate/plefa
PPARα-L162V polymorphism is not associated with schizophrenia risk
in a Croatian population
S. Nadalin a, J. Giacometti b, A. Buretić-Tomljanović a,n
a
b
Department of Biology and Medical Genetics, School of Medicine, University of Rijeka, Braće Branchetta 20, 51000 Rijeka, Croatia
Department of Biotechnology, University of Rijeka, Slavka Krautzeka bb, 51000 Rijeka, Croatia
art ic l e i nf o
a b s t r a c t
Article history:
Received 28 February 2014
Received in revised form
18 June 2014
Accepted 4 July 2014
Disturbances of lipid and glucose metabolism have been repeatedly reported in schizophrenia.
A functional L162V polymorphism in peroxisome proliferator-activated receptor alpha (PPARα) gene
has been extensively investigated in etiology of abnormal lipid and glucose metabolism, yet not
in schizophrenia. We determined whether the schizophrenia risk was associated with L162V polymorphism and we examined the impact of L162V variant on age of onset, and data of psychopathology
scores. We also hypothesized that plasma glucose and lipid concentrations in patients may be influenced
by L162V polymorphism. Genotype and allele frequencies between 203 patients and 191 controls did not
differ significantly. Females heterozygous for the PPARα genotype (L162V) manifested significantly lower
negative symptom scores, tended toward an earlier onset, and had significantly greater triglyceride
levels. The PPARα-L162V polymorphism is not associated with schizophrenia risk in Croatian population,
but it impacts clinical expression of the illness and plasma lipid concentrations in female patients.
& 2014 Elsevier Ltd. All rights reserved.
Keywords:
L162V polymorphism
Peroxisome proliferator-activated receptor
alpha
Positive and Negative Symptom Scale
Schizophrenia
1. Introduction
Peroxisome proliferator-activated receptor alpha (PPARα) is a
ligand-activated transcription factor that belongs to the nuclear
steroid receptor superfamily [1,2]. Activated by its ligand, PPARα
heterodimerizes with retinoid X receptor, and binds to peroxisome
proliferator response elements in the promoter region of genes to
modulate their expression [2,3]. Due to its role in regulation of the
expression of genes involved in fatty acid uptake, transport, β- and
ω-oxidation, and ketogenesis, PPARα represents an important
mediator of lipid and glucose metabolism [2,3]. Dietary fatty acids,
particularly long chain polyunsaturated fatty acids (LC-PUFAs),
such as arachidonic acid (20:4n 6, ARA), eicosapentaenoic acid
(20:5n 3, EPA) and docosahexaenoic acid (22:6n 3, DHA) are
known to be potent natural ligands of PPARα [3,4]. Several
experiments in animal models suggest that PPARα may act as an
important sensor of LC-PUFA status in organism [5,6]. It has been
established that under conditions of essential fatty acid deficiency
PPARα can enhance LC-PUFA synthesis from precursor PUFAs, such
as linolenic acid (18:2n 6, LA) and alpha linolenic acid (18:3n 3,
ALA), by increasing activity of Δ6- and Δ5-desaturases and
elongases [6,7].
n
Corresponding author. Tel.: þ 385 51 651 182; fax: þ385 51 678 896.
E-mail address: alenabt@medri.uniri.hr (A. Buretić-Tomljanović).
http://dx.doi.org/10.1016/j.plefa.2014.07.003
0952-3278/& 2014 Elsevier Ltd. All rights reserved.
Patients with schizophrenia have significantly increased risk of
developing diabetes, dyslipidemia and obesity, while mortality
from coronary artery disease is two to three times greater than in
the general population [8,9]. Treatment with antipsychotic medications particularly increases abnormalities in glucose and lipid
metabolism in schizophrenia [8,10]. Furthermore, PUFA deficits
both in red blood cell (RBC) membranes and postmortem brain
tissues have been extensively reported in schizophrenia [11–14].
Decreased RBC membrane PUFA levels in patients with schizophrenia, mainly attributed to lower contents of LA, EPA and DHA,
have been previously reported in our study as well [15].
To date, only one study, performed in the Japanese population,
has been investigated association between PPARα gene polymorphic variations and etiology of schizophrenia [16]. However,
no association between investigated Val227Ala polymorphism of
the PPARα gene and risk for schizophrenia has been reported in
their study [16]. Furthermore, there are no reports of Val227Ala
polymorphism in the European population [17]. The leucine 162
valine (L162V) polymorphism, caused by a C to G transversion
in exon 5, is the most studied variant of the PPARα gene [4,18].
While the influence of PPAR-L162V polymorphism has been intensively studied in dyslipidemia, some measures of adiposity, risk for
coronary ischemic events, and age of onset in patients with
diabetes [3,18–20], the relevance of L162V polymorphic variation
on lipid and glucose metabolism in patients with schizophrenia
has not been investigated so far. The less common V allele, the
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S. Nadalin et al. / Prostaglandins, Leukotrienes and Essential Fatty Acids 91 (2014) 221–225
frequency of which varies from from 2–4%, however, was found
exclusively in the European population [21]. To date, several
studies have reported gender specific differences in L162V genotype effect on lipid metabolism [3,22,23].
Because PPARα gene is a key regulator of glucose and lipid
homeostasis, variations of this gene could possibly contribute to
the etiology of schizophrenia, or may influence its clinical expression. We aimed to determine whether the risk for schizophrenia
was associated with L162V polymorphism of the PPARα gene in
the Croatian population, and to examine the possible impact of the
L162V polymorphism on mean age of onset, and baseline psychopathology data, measured via Positive and Negative Symptom
Scale (PANSS) scores, in the patient group. We further hypothesized that PPARα-L162V polymorphism may influence plasma
glucose and lipid concentrations in patients with schizophrenia.
2. Patients and methods
2.1. Study participants
Our study group was comprised of 203 chronically ill schizophrenia patients (111 males and 92 females), recruited from the
Department of Psychiatry, Clinical Medical Centre in Rijeka, Croatia
(n¼110), and Psychiatric Hospital in Rab, Croatia (n¼93), between
2007 and 2010, and 191 non-psychiatric control subjects (87 males
and 104 females). Rijeka and the island of Rab belong to the same
geographic area. Patients' clinical data are presented in Table 1.
Diagnoses were assessed according to the Diagnostic and Statistical
Manual of Mental Disorders (DSM-IV) criteria using the structured
clinical interview. Age of onset was obtained from medical records
and determined as the patient's age at the time at their first hospital
admission due to a psychotic episode at which the diagnosis of
schizophrenia was used. Evaluation of PANSS psychopathology was
performed at the time of last admission, during an acute state of the
illness requiring hospitalization. The investigation was carried out in
accordance with the latest version of the Declaration of Helsinki.
After the study's purpose and methods had been described, all
participants provided written informed consent to participate in
the study, which had been approved by the Ethics Committee of the
School of Medicine, University of Rijeka, Croatia.
The control individuals were blood donors who underwent no
specific examination for psychiatric status, but declared no
psychiatric records. The practice with blood donation in Croatia
includes providing a written statement about health status at
every session. Therefore, blood donors are representatives of
healthy general population, free of chronic diseases or regular
medication.
2.2. Methods
2.2.1. Genotyping
Genomic DNA was extracted from whole blood using a FlexiGene DNA kit 250 (QIAGEN GmbH, Hilden, Germany) according to
the manufacturer's instructions. Genotyping was performed in the
Laboratory for Molecular Genetics (Department of Biology and
Medical Genetics, School of Medicine, Rijeka) by polymerase chain
reaction/restriction fragment length polymorphism analysis using
protocol previously described [24].
2.2.2. Biochemical measurements
Venous blood samples were collected from fasting patients.
Plasma was separated by centrifugation at 1100g for 10 min from
blood cells and used immediately for the determinations of
glucose, total cholesterol and triglycerides. The analyses were
carried out in the Department of Clinical Laboratory Diagnostics
of the Clinical Medical Centre Rijeka. Fasting plasma glucose
levels Z7.0 mmol/l, total cholesterol levels45.0 mmol/l and
triglyceride levels4 2.0 mmol/l were considered elevated for the
Croatian population [25].
2.2.3. Statistical analysis
Descriptive statistics was used to calculate the mean ages and
mean PANSS scores in the patient group. Genotype and allele
distributions between patients and controls, as well as observed
and expected genotype proportions under Hardy–Weinberg equilibrium, were compared by the χ2-test. The t-test was applied to
compare the means of investigated clinical and biochemical
measurements in patients with schizophrenia according to PPARα
genotypes.
The association between several clinical features (mean age at
first hospital admission, and positive, negative, general and total
PANSS scores) and PPARα genotypes, as possible predictors, was
tested using multiple stepwise regression analysis, adjusted for
age at PANSS assessment, and sex, in patients with schizophrenia.
Table 1
Clinical and biochemical features according to PPARα genotypes.
Patients (n¼ 203)
Age (years)
Age at first hospital admission
PANSS positive symptoms score
PANSS negative symptoms score
PANSS general psychopathology score
PANSS total score
Body mass index (kg/m2)
Glucose (mmol/L)
Total cholesterol (mmol/L)
Triglycerides (mmol/L)
Males
Females
Males
Females
Males
Females
Males
Females
Males
Females
Males
Females
Males
Females
Males
Females
Males
Females
Males
Females
L162L
L162V
42.8 712.3
44.6 711.7
26.1 77.7
29.0 79.1
26.8 75.5
26.1 75.1
29.3 75.9
30.0 75.8
52.1 76.8
52.9 76.9
108.2 713.3
109.0 713.1
26.8 73.8
26.9 74.5
5.7 71.2
5.7 71.0
5.4 71.5
5.8 71.0
2.1 71.2
1.5 70.7
40.17 8.8
39.17 8.8
26.5 7 5.6
22.4 7 5.0
26.2 7 4.5
28.8 7 5.7
31.7 7 6.7
24.0 7 7.6
52.8 7 8.3
53.7 7 3.6
110.7 7 18.0
106.57 9.8
25.6 7 4.8
29.2 7 5.1
5.4 7 1.1
5.8 7 0.7
4.4 7 1.4
5.4 7 1.3
1.7 7 1.2
2.4 7 1.0
t
p
1.20
0.60
0.18
1.88
0.28
1.22
0.93
2.34
0.25
0.31
0.42
0.46
0.44
0.99
0.65
0.24
1.02
0.53
0.53
2.09
n. s.
n. s.
n. s.
n. s.
n. s.
n. s.
n. s.
o 0.05
n. s.
n. s.
n. s.
n. s.
n. s.
n. s.
n. s.
n. s.
n. s.
n. s.
n. s.
o 0.05
S. Nadalin et al. / Prostaglandins, Leukotrienes and Essential Fatty Acids 91 (2014) 221–225
We considered p o0.05 statistically significant. All statistical
analyses were conducted using Statistica for Windows, version 9
(StatSoft, Inc., Tulsa, OK, USA).
223
patients. Female carriers of the V162 allele had higher triglyceride
concentrations (t-test: t¼2.09, po0.05) (Table 1).
4. Discussion and conclusions
3. Results
3.1. PPARα genotypes and alleles distribution
The genotype frequencies of L162V polymorphism in both
patients and control individuals were consistent with Hardy–
Weinberg equilibrium (Table 2). Allele frequencies were 0.956
(L162¼388) and 0.044 (V162 ¼18) in the patient group, and 0.953
(L162¼364) and 0.047 (V162¼ 18) in the control group. There
were no significant differences in the frequencies of genotype and
allele distributions between patients and controls (Table 2). Genotype and allele frequencies between males and females also did
not show significant difference (data not shown). Based on the
number of total subjects involved (203 patients and 191 controls),
the statistical power of our study was 80% in detecting a 2.1-fold
increase in PPARα-V162 allele frequency.
3.2. Clinical expression and biochemical measurements in relation
to PPARα genotype
Evidence suggests that variability in the clinical presentation of
schizophrenia favors females, since women affected by the illness
tend to have better premorbid functioning, a later age of onset,
lower prevalence of negative symptoms and better course of
illness [26–28]. However, age at first hospital admission between
males and females did not reach statistical significance in our
sample (data not shown). We did not find statistically significant
association between mean age at first hospital admission, and
investigated PPARα genotypes, although heterozygous females
(L162V) tended toward an earlier onset of illness when compared
to those homozygous (L162L) (22.4 75.0 vs. 29.0 79.1, respectively) (Table 1).
Since severity of negative symptoms is known to increase
with patient's age [29], we included mean age of our patients into
predictor variables to control for the age effect in regression
analysis. Multiple regression analysis detected significant correlation between PPARα genotype and negative symptoms severity
in female patients (βPPARα ¼
0.25, F¼ 4.09, p o0.05). Females
heterozygous for the PPARα genotype (L162V), manifested significantly lower negative symptom scores when compared to
those homozygous (L162L) (t-test: t¼ 2.34, p o0.05) (Table 1).
The L162V polymorphism accounted for approximately 6% of
negative symptoms variability (Multiple R2 change ¼0.06; not
shown).
According to the biochemical reference values for the Croatian
population, plasma cholesterol and triglyceride levels were slightly
elevated [25]. Furthermore, the PPARα genotype significantly contributed to the variations of plasma triglyceride levels in female
Table 2
The frequency of PPARα genotypes.
Genotype frequency
a
b
c
a,b,c
patients (n¼ 203)
controls (n¼ 191)
L162L
L162V
χ2
p
185(91.1)
173(90.6)
18(8.9)
18(9.4)
0.04
n. s.
Hardy–Weinberg: patients χ2 ¼ 0.44, p¼ 0.51; controls χ2 ¼0.47, p ¼0.49.
Percentages are given in parenthesis.
No significant difference between males and females in both groups.
PPARα has emerged as master transcription regulator of glucose and lipid metabolism [3,10]. It is known to regulate the
expression of genes involved in PUFA synthesis, fatty acid uptake,
transport, oxidation, and ketogenesis [2,30]. Disturbances of lipid
metabolism and PUFA deficits have been repeatedly reported in
patients with schizophrenia [10,31]. Although a functional L162V
polymorphism of the PPARα gene has been extensively investigated in etiology of abnormal lipid and glucose metabolism
[18,22,30], to the best of our knowledge, this is the first study
performed in schizophrenia subjects. Moreover, our current study
was also the first to determine the association between schizophrenia and L162V polymorphism, as a possible risk factor for the
illness.
The results of our study showed no evidence of the statistically
significant association between L162V polymorphism of the
PPARα gene and elevated risk for developing schizophrenia in a
Croatian population. We did not detect any differences in the
L162V polymorphism allele and genotype frequencies between
patients and control individuals. Distribution of the V162 allele
was less frequent in both patient and control groups, when
compared to L162 allele (4.4% and 4.7%, respectively), and its
frequency was similar to previously reported distribution in other
European populations. Unfortunately, since the L162V polymorphism has been detected only in the European population, further
studies are limited [21].
However, our results argue in favor of the L162V polymorphism
having modulator role in the expression of the illness in female
patients. Females heterozygous for the PPARα genotype (L162V)
tended an interesting trend to develop the illness at slightly
younger age, and they also manifested significantly less severe
negative symptoms than those homozygous (L162L). Therefore,
according to our results, L162V polymorphic variant of the PPARα
gene could have a possible protective effect toward negative
symptoms severity in female patients with schizophrenia.
It is plausible that in the PUFA deficient diet, as occurs in
schizophrenia, by acting as a sensor of PUFA deprivation, PPARα
induces activity of Δ6- and Δ5-desaturases and elongases to
increase PUFA biosynthesis from their dietary precursors, such as
LA and ALA. Moreover, functional studies have demonstrated that
V162 allele has higher transcriptional activity in vitro, than L162
allele [18,22,32]. Thus, the L162V polymorphic variant could
possibly modulate more efficiently the ability of PPARα to induce
the activity of enzymes that act in PUFA biosynthesis. Several
novel findings indicate the possible influence of PPARα genotype
in response to antipsychotic medications [33,34]. In fact, the
induction of PUFA biosynthesis enzymes has been attributed to
the action of antipsychotic drugs as well [34,35]. One in vitro study
detected that treatment with several typical and atypical antipsychotic medications up-regulate Δ6- and Δ5-desaturase mRNA
expression in human cell lines [34]. Increased Δ6-desaturase
mRNA expression, after chronic exposure to atypical antipsychotic
medications, has also been demonstrated in recent in vivo study,
performed in rats [35]. Furthermore, chronic treatment with both
typical and atypical antipsychotic drugs in rats was found to
significantly increase PUFA levels, in RBC membranes, as well as
in brain tissue [33,35]. The observed inconsistencies regarding
effects of antipsychotic treatment on membrane PUFA profile may
be linked to several confounding effects of disease-related factors,
such as state of illness, its duration, type of antipsychotic medication, etc. [31,36]. Recent study in Tunisian population examined
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S. Nadalin et al. / Prostaglandins, Leukotrienes and Essential Fatty Acids 91 (2014) 221–225
RBC membranes PUFA profile in patients with schizophrenia
before and after antipsychotic treatment and tested their association with psychopathology [36]. At enrollment, decreased levels of
ARA and DHA were associated with higher severity of several
negative symptoms, while treatment with typical antipsychotic
medications over a period of 3 months, normalized PUFA levels, in
parallel with improvement of psychopathology. Partial normalization of membrane PUFA levels following antipsychotic therapy
(atypical 4typical) in post-mortem brain of patients with schizophrenia has also been reported by McNamara et al. [11]. However,
recent meta-analysis confirmed RBC membranes PUFA deficits, in
particular DHA, in patients with schizophrenia, irrespective of the
type of antipsychotic medication intake [31].
In accordance with previous studies [4,20,30], the PPARα
genotype affected plasma lipid concentrations in our sample as
well, although significant impact has been detected only for
plasma triglyceride levels in female patients (Table 1). Additionally, Tai et al. [37] reported an interesting PPARα genotype-diet
interaction that may also contribute to variations in plasma lipid
concentrations, possibly by modulating activity of the PPARα. In
their study the presence of 162V allele in PPARα genotype was
associated with greater triglycerides and apolipoprotein C-III
concentrations in subjects consuming low PUFA diet, while higher
PUFA intake, in 162V carriers, surprisingly, reduced their concentrations. In contrast, among subjects that were homozygotes for
the 162L allele, the amount of PUFA intake, however, did not affect
either triglycerides or apolipoprotein C-III concentrations. These
findings suggest that 162V carriers that suffer from dyslipidemia,
and especially patients with schizophrenia to whom have been
prescribed atypical antipsychotics, could possibly benefit from use
of dietary treatment with higher PUFA intake, or additional PUFA
supplementation. Furthermore, since in our current study significantly greater plasma triglyceride levels have been detected in
female carriers of the 162V allele (Table 1), it would be particularly
useful to genotype females receiving antipsychotic therapy for the
PPARα-L162V polymorphism and, regarding genotype, to modify
diet habits/regimen for each individual.
To date, a whole series of studies have reported gender specific
differences in PPARα genotype effect on lipid plasma levels, response
to statin treatment, and risk for developing hypertension and obesity
[3,22,23], indicating a possible role of sex hormones on expression
and/or PPARα activity. Furthermore, there is also evidence, based on
studies performed in animal models, that PPARα expression and/or
activity might be regulated by estrogen signaling pathways [2].
Estrogen binding to its membrane receptors activates extracellular
receptor kinase–mitogen activated protein kinase (ERK–MAPK) and
protein kinase A and they further phosphorylate and increase the
activity of the PPARα. In addition, estrogen activation of ERK-MAPK
pathways, increases intracellular concentration of PUFA and eicosanoids, strong natural PPARα ligands, via elevated phospholipase A2
(PLA2) and cyclooxygenase-2 (COX-2) enzyme activities.
The current study has got several limitations. Relatively small
sample size as well as low frequency of PPARα-V allele carriers
leaves the possibility that some real effects were not detected.
Furthermore, correlation analyses regarding plasma glucose and
lipid concentrations were limited only to schizophrenia group.
Further studies in other European populations, in whom PPARαL162V variant is present, controlling for the contribution of dietary
habits and antipsychotic medications could be helpful in elucidating the relationship between PPARα-L162V polymorphism and
schizophrenia. Moreover, clarifying the underlying molecular
mechanisms which may associate L162V polymorphism with
schizophrenia requires further experimentation as well.
In conclusion, although L162V polymorphism of the PPARα
gene could not be associated with an elevated risk for developing
schizophrenia in our study, the investigated polymorphic variant,
according to its possible protective effect toward negative symptoms severity in females with schizophrenia, might have a
modifier role in clinical expression of the illness. However, since
the impact of L162V polymorphism on clinical expression was
relatively weak (it accounted for only 6% of the symptoms'
variability), other endogenous factors (genetic, hormonal) as well
as environmental factors (i.e. nutrition, medication treatment), by
affecting PUFA and lipid homeostasis, contribute to variable
clinical expression in schizophrenia.
Acknowledgments
This research was supported by grant no. 839-10-1339 from the
University of Rijeka, Croatia. The University of Rijeka had no
further role in the study design; in the collection, analysis, or
interpretation of data; or in the decision to submit this paper for
publication.
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