On The Mechanism of Saponin Hemolysis-I: Ruth Sectal. Puah Shatkovsky Ilana Milo-Goldzwhg
On The Mechanism of Saponin Hemolysis-I: Ruth Sectal. Puah Shatkovsky Ilana Milo-Goldzwhg
On The Mechanism of Saponin Hemolysis-I: Ruth Sectal. Puah Shatkovsky Ilana Milo-Goldzwhg
THE HEMOLYT’ICactivity of plant saponins has been known for a long time. However,
only after it had been proved that there exists no causal relationship between this
characteristic and their capability to reduce surface activity’ 3 research on the fac-
tors endowing the saponins with hemolytic capability was started.
Some progress was achieved when it was shown that the hemolytic effect must be
ascribed to the aglyconic part of the molecule. namely, the sapogenin.3 This conclu-
sion was drawn from the facts that all sapogenins by themselves are strongly hemoly-
tic. and that minor modifications in the composition of the aglyconic part of the
saponin may have enormous effects on the hemolytic potencies of both saponins
and their corresponding sapogenins. Thus, elimination of the ester functions in
aescin’.” and styrax saponin A3-both very potent hemolysins-yield completely
inactive glycosides, and the corresponding active estcrsapogenins lose all their activity
on basic hydrolysis.
It was further suggested that a common mechanism must underlie the hemolytic
activity of saponins and sapogenins. 6 This was inferred from the observation that
both saponins and sapogenins are rapidly and irreversibly absorbed by the red cell
membrane, long before hemolysis commences,
Testing the hemolytic activity of a great variety of sapogenins and sapogenin deri-
vatives, made it possible to deduce an accurate structure activity relationship for
these compoundsP9 However, in spite of the great similarity between saponin and
sapogenin induced hemolysis, no such relationship could be found for the saponins.
Although all hemolytically active saponins yield active sapogenins, no quantitative
correlation could be found between hemolytic potency and the presence of the sugar
moiety in the molecule. 3,10 In some cases it enhances the hemolytic capability of the
sapogenin, while in others it inhibits or even annuls it. The highly active P-amyrin
is converted to an inactive j-glucoside,” but in the case of digitonin the glycosidic
bond enhances hemolysis a hundredfold.3 Moreover, different glycosides of identical
sapogenins may differ markedly in their hemolytic potencies. For instance T-hederin
973
A plausible Cxplanation for the diversifying cft‘ects of the gljcositlic parI must
account for the fact that sapogcnin induced hemolysis is always ;\dvaxI! atl2ctcrl
by additional polar groups.‘.’ ’ Therefore the problem arises hoM saponins hearing
such strong polar functions as the glycosidic parts can be hemotytic al all.
To testl~~potlwscs.
this membtxncs obtained from hcmolysed blood \scrc
cstractcd. the adsorbed
and hcmolyxing factor idcntilicd 1~1 chlolnatograpli! t
mechanism for saponin mduced hcmol>,sis based on the raults obtninccl in thcsc L’x-
perimcnts is discussed.
Blood. Citrated rat blood was used. The erythrocytes were separated 111centrifuge-
tion and washed with saline until the supernatant was colourlcss. The erythrocklcs
were then diluted with buffer to give a suspension of the desired concentration.
Sol14rior~s c~f’.s~rpor7i77s: All saponins were dissolved in buffer solution.
Solutions of sapogenins. The sapogcnins were dissolved in dimethyl sull;>side
(DMSO). (C’arc was taken that no precipitation occurred on dilution with watcr.~
Before use the DMSO solutions were diluted with distilied water in the proportion
of DMSO solution: water 5 : 1. This avoids s~~ont~n~oLts hemolysis.
Dcrt~7~777irrctrio77 of riw ~?~~~Jz~~~~~~~ rrc’lit’if~~. The test solLftions consisted t>L‘I4 ml ttl
erythrocyfe suspension. varying volumes of hemot);sin solution and bull& (in c;tsc
of saponins). or DMSO water mixture 5: I (in case of sapogcnins) making up a total
volume of 2 ml. The components were added in the following order: first the crythro-
cyte suspension. then the buffer or the DMSO water mixture and last the hemolysing
agent. The mixtures were incubated for 2 hr at 37’. then centrifuged at 1.500 rev.‘min
for IO min and the optical densit) of the supernatant determined at 540 nm. The per-
centage of hemolysis was determined by comparison with a sample in which IOO”,,
hemolysis was clfccted by treatment with digitonin.
I.so/trtior~ c$~g/~o.stc~l1.s.Ghost cells from hemolysed blood were obtained by ccntri-
fugation in a Beckman model L2-50 ultraccntrifuge rotor R-30. 13.000 rev;min
(20.000 g) at 4 for 20 min. The precipitated ghosts were twice washed with aqueous
NaCl solution (0.05 M).
Gl7ost cc~//.s,fiw77 strpor7ir7 hcv77o/~wt/ hlootl: The mixtures described in Table I were
incubated for 2 hr at 37 The saponin concentrations were made up so that about
70”,, hemolbsis was obtained after 2 hr incubation. With glycyrrhizin only 30”,, hemo-
lysis could be obtained at maximal saponin concentration. After 2 hr incubation the
non-hemolysed erythrocytes were separated by centrifugation at 1500 revimin for IO
min. Ghost cells wcrc obtained from the hemolytic supernatants as described.
Nanre of sapngfilin
Idrnti’cation qf’ adsorbed hrmolysin yfiu curious imhation periods. Ghost cells
were collected from the supernatants. and the remaining whole erythrocytes from the
preceding experiment. Extractions and t.1.c. analysis were performed as described.
Name of conlp0Llnd
Styrax saponin-A
Styrax sapogenin-A
Styrax sapomn-B
Glycqrrhirin
G!yyyrrhetinic acid
Dlgltonin
Digitogenin
Solanin
Solanidin
Tomatin
Tomatldin
Only in one case, that of styrax saponin-A, the presence of the sugar part does
not effect hemolysis. and the activity of the saponin equals that of the aglycone. In
all other saponins it has either an enhancing or an inhibiting effect. Thus digitonin
and tomatin are more potent than their corresponding aglycones. while glycyrrhe-
tinic acid and solanin are less active.
We started by trying to clarify whether the constitution of the saponin undergoes
any changes after being adsorbed to the membrane. Three possibilities were consi-
dered-the glycosidic bond undergoes hydrolysis; the aglyconic part undergoes
some chemical change; the saponin remains unchanged.
Ghost cells were collected from the hemolysed portion of blood which had been
incubated for 2 hr with a saponin concentration giving 707, hemolysis. Partially
hemolysed blood (70 per cent) was chosen to avoid an excess of saponin which might
be adsorbed to the membranes by some secondary process. We extracted the ghost
cells with 70% ethanol to remove glycosides and with chloroform to remove agly-
cones.
Table 4 summarizes the results obtained from testing the extracts by t.1.c. In all
cases no saponin whatsoever remained adsorbed to the membrane, and only the cor-
responding aglycones could be detected.
Since the ghosts were collected only from the hemolysed part of the blood (approx
70 per cent), it seemed interesting to test whether sapogenins could also be extracted
from the residual 30 per cent namely the non-hemolysed erythrocytes. The unhemo-
lysed cells were disrupted by distilled water and the ghosts collected and extracted
with chloroform and with ethanolic water. The results which are summarized in
columns 4 and 5 of Table 4 show that sapogenins are present on the non-hemolysed
erythroq Its but that they arc still accompanied b! the intact saponins. The fact that
in the hcniol~sed part of tho blood onI\’ aglyx~nes could lx founci on the mcmhr;~n~s.
c‘Gvt‘s rise to the assumption that li~drnl>sis of the gl\cosidic bond is ;t prcrcqitisitc
for obtaining hcmol\sis. To test thih assumption iv; incutxttcd erythroqtcs \vith
sapotiins for wrious periods. thus ohtaitiin g ;I \ariet\ of hcmol) tic utcnts. The
ghost!, V’CK collected ftmlll all satnplCs. chtrac~cti anti &ed Ibr the pt-cs”llcc of hoth
sapo~~it~s and sapogcnins. The results. which arc‘ ~utntn:tri/cd in Table 5. clcarl~ S~OM
th:tl c\cii after OCR> short iticuhalioti pcriodh rlro.5~~ m~nib~-;~ii~s \vhich \\crc collcc~ed
from the heniol!,scd part of the blood. had ottl! upofcnins adsorbed to thcit
metnbt-ancs. \vliilc to the non-lictnolysed tn~mhtxnes ho~li sapotiitis and sapogcnins
wcrc adsorbed.
The fact that the not1 l~ctnol~scti cl-> lhroq tch ha\c saponins adsot-bed to theit
n~ant~rnnes. and in the cast of ~rIwxrrhi/in.
c _ _ if Iho iticub:ttion periods wt’rt’ short
cnoiigh. onl! saponins. shows that the lirst phase in the hcniolytic process is that
of the adsorption of the saponins to the cl-1 throq tcs. The hydrolysis which preccdcs
Ihe rupture of the the metnbranc. is probably the wxnd ph~rsc.
Since the hydrolytic prwxs wxrs alter adsorption to Ihe metiibranc. wc must
;ISSLI~C the prcscnce ofa proper membrane glywidasc catal~sinp this reaction. Gil-
cosidasex at-c kno\vn to bc of high specificit! both (0 Ihe sugar cotnponcnt and to
the nature of the glycosidic bond. but the constitution of the aglyxnic part INS onI>
intlucncc on the rate of hydrol> sis. ’ -’
In it previous comtnitnicatic~~i we dcmonstratcd that the process of the suponin
adsorption is irtuusible and completed within \vr! \IIOI.C incubation periods. long
bcfot-c hciiiol~si~ ~omnicnccs. ” ‘l‘his phaw can lhcrclOi-c h;t\c 110 itillucncc L\ ha1-
xwvcr on the rate of hemolqsis. ~‘onsequentl!. if the proposed conception of the
heiii~~l!tic mechanism is valid. and if Ihc Iasl s1cp Lhc rup1ttrc of Ihe ccl1 mcm-
brunt ih not I-ate dctcrmining. the tratc of hcmol~sis should var\ markedly from one
saponin to the other. Figure I sl~ows the time dependcncc of hemol~sis for four difkr-
ent saponins. i.e. digitonin, lomatin. st\rax saponin-A :rnd gl!c>rrhi/in. The great
varintions in the hcmol! tic rates arc obvious. in digitonin and loniatiti hotI pm-
In glyc!t-rhirin howc\w the hcniol:\ tic process is w slou Ihat it ~!\lcnds over ;I period
of at Icas;t 12 III-. ;I period aficr \vhtch spontaneous hciiic~l! si’i i4 too pronounced for
the experiment to be continued. Since glycyrrhizin is readily absorbed by the erythro-
cytes (Table 5), the reason for the low hemolytic activity of this saponin~~~~especiall!,
when compared with that of the corresponding sapogenin (Table 3) can be due
either to a low activity, or to a IOLVconcentration of the proper glycosidase ({Gglucuro-
nidasc).‘”
Our experiments also furnish an explanation for the the total lack of hcmolytic
potency in Styrax saponin B (Table 3). This saponin is for some as yet uncxplicablc
reason not adsorbed to the erythrocytes (Table 4). and therefore the first stage obliga-
tory for the hcmol!,tic process does not occur.
It was mentioned above that some alterations in the aglyconic moiety of the
saponins might occur during the hcmolytic process. The most probable reactions to
be considcrcd arc oxidations of h!drolcyl groups or h>,drolysis of cstcr bonds. !‘cl
t.1.c. examination of the mcnibrane extracts alw:ays showed the prescncc of the corrc-
sponding sapogenin onI>. This holds true also for st!ra\ saponin-A N hich i\ cstcri-
fied in the aglyconic part of the molecule. This observation ~vas strengthened bq.
examining various sapogenins. including sapogcnin esters, after hemolysis. Since
in these tests dimethyl sulfoxide was used for achieving dissolution of the
hemolysins, no ghosts were collected. but chloroform extractions were done on
the hemolysed part of the blood. The sapogenins tested ivere: styrax sapogenin-A.
smilagenin, smilagenin acetate. oleanolic acid acetate and oleanolic acid methyl ester.
In all these compounds-sapogenins or sapogenin esters-only the original hemolysin
used could be extracted, showing that no chemical change had occurred during
hemolysis.
The results of our present investigations confirm our previous deductions” that
the aglyconic part of the saponin molecule is responsible for its hemolytic activity.
Two conditions must be fulfilled in order to bestow on a saponin hemolysing acti-
vity. It must be adsorbed to the erythrocyte membrane and the glycosidic bond must
be hydrolysed. This is based on the assumption that all aglycones produced on the
membrane are active in accordance with our observation that all steroids and triter-
penes are hemolytic provided they can be dissolved.h,7 It seems therefore reasonable
to assume that the cause for the inactivity of some saponins must be looked for either
in their non adsorbability to the erythrocqte membrane. or the lack of a proper mem-
brane enzyme capable of hydrolysing the glycosidic bond.
The mechanism 01‘uponin hcmolqsis I 981
Furthermore. we can now explain the fact that saponins. although they are charac-
terized by the presence of the highly polar glycosidic function which generally inhi-
bits hemolysis, are hemolytically active. As a matter of fact this function is no longer
existent in the active hemolysin since hydrolysis precedes hemolysis. An explanation
is also provided for the fact that some sapogenins are more potent than the saponins
from which they are derived. as was exemplified by the case of glycyrrhizin. The results
do not however furnish a plausible explanation for the observation that in certain
cases the saponins are more active than their corresponding aglycones. Possibly two
parallel hemolytic mechanisms operate in these cases. the one described above and
a second by way of reducing the surface activity which has formerly been considered
as the main factor causing hemolysis.