EFFECT OF THIOL DRUGS ON THE OXIDATIVE HEMOLYSIS IN HUMAN ERYTHROCYTES
M A Ł G O R Z A T A IC IE K , M A R T A P O L A K an d L ID IA W Ł O D E K
In stitu te o f M ed ical B io ch em istry , Ja g ie llo n ia n U niversity C o lleg iu m M edicum 7 M . K o p ern ik a Str., 3 1 -0 3 4 C raco w , P oland
A b s t r a c t . T h e e ffe c t o f d iffe re n t th io l d ru g s an d 2 - m e th y l- th ia z o ] id in e - 2 ,4 - d ic a r b o x y ! ic ac id on th e o x id a tiv e stre s s , in d u c e d b y h y d ro g e n p e ro x id e , w a s ex a m in e d in h u m a n e ry th ro c y te s . T h e re su lts in d ic a te d th a t c a p to p ril (C A ), m e th im a z o le , N - a c e ty lc y s te in e (N A C ), p e n ic illa m in e a n d p re c u rs o r o f L - c y s te in e 2 - m e th y l- th ia z o lid i- n e - 2 ,4 - d ic a r b o x y lic a c id (C P ) m ig h t p ro te c t th e e ry th ro c y te m e m b ra n e a g a in s t lip id p e ro x id a tio n in th e ex p e rim e n ta l c o n d itio n s. C a p to p ril, m e th im a z o le an d p e n ic illa m in e h a d th e stro n g e s t a n tio x id a tiv e p ro p e rtie s at th e c o n c e n tra tio n le v el o f 0 .5 m M . T h e p ro te c tiv e e ffe c ts g ra d u a lly d e c re a s e d a t h ig h e r an d lo w er c o n c e n tra tio n s o f th e se d ru g s. C o n tra ry , th e a n tio x id a tiv e p ro p e rtie s o f N - a c e ty lc y s te in e in c re a s e d w ith its le v e ls g ro w in g in th e re a c tio n m ix tu re, a n d o n ly N - a c e ty lp e n ic illa m in e d id n o t p ro te c t e ry th ro c y te s ag a in st o x id a tiv e d a m a g e s . T h e e ffe c t o f 2 - m e th y l- th ia z o lid in e - 2 ,4 —d ic a rb o x y lic a c id sh o w e d in th e se in vitro ex p e rim e n ta l co n d itio n s th a t it c o u ld a c t as an a n tio x id a n t a t th e c o n c e n tra tio n as h ig h as 5 m M a n d h ig h e r.
K e y w o r d s : ca p to p ril / m e th im a z o le / N - a c e ty lc y s te in e / p e n ic illa m in e / N - a c e ty lp e n ic illa m in e / 2 - m e - th y l- th ia z o lid in e - 2 ,4 - d ic a r b o x y lic a c id / o x id a tiv e h e m o ly sis
S tu d ies in vitro dem o n strate th at thiols can have both a n ti- and p ro o x id ativ e effect d ep en d in g on th e ir co n cen tratio n , the p resen ce o f transitory m etal ions, th e pK value o f the su lp h y d ry l group, and ev en on th e p o larity o f the en v iro n m en t (1).
T he p ro tectiv e effect o f thiols is asso ciate d w ith th eir ability to react w ith reactiv e oxy g en species, w hile th e ir p ro o x id ativ e effect is related to th eir sp o n tan eo u s ox id atio n to su lp h id es, as w ell as to the fo rm atio n o f thiyl rad icals (2,3). N um ero u s d rugs ch aracterized by a d ifferen t p h arm aco lo g ical pro file co n tain su lphydryl g ro u p s the presen ce o f w hich m ay trig g er both a p r o - an d an tio x id ativ e effect. In o th e r w ords, th e ir sid e effect m ay be both, beneficial a n d d isad v an tag eo u s fo r the cells. T he in v e s tig a tio n s in th is p a p e r in c lu d e d d ru g s c o n ta in in g th e - S H g ro u p a n d h a v in g d iv e r s if ie d p h a rm a c o lo g ic a l p ro p e r tie s , su c h as c a p to p ril, m e th im a z o le , N - a c e ty lc y s te in e a n d p e n ic illa m i
ne, as w ell a s c o m p o u n d s w h ic h h a v e no m e d ical a p p lic a tio n , 2 - m e th y l - th i a z o li d in e - 2 ,4 - d ic a r b o - x y lic a c id a n d N - a c e ty lp e n ic illa m in e . C a p to p ril re d u c e s b lo o d p re s s u re as a s p e c ific c o m p e titiv e in h ib ito r o f a n g io te n s in e c o n v e rta s e . It is k n o w n to m a n ife s t a n tio x id a tiv e p ro p e r tie s (4 ,5 ,6 ). M e th im a z o le , a n o th e r d ru g u n d e r o u r in v e s tig a tio n , is e m p lo y e d in h y p e rth y ro id is m . T o d a te , it is little k n o w n a b o u t its a n t i - o r p ro o x id a tiv e e ffe c t b u t it w as fo u n d to a c t as an a n tio x id a n t re d u c in g th e n e p h ro to x ic a c tiv ity o f g e n ta m y c in (7 ). N - a - c e ty lc y s te in e (N A C ) is a c o m m o n ly u se d m u c o
ly tic an d h e p a to p r o te c tiv e a g e n t w h ic h sh o w s a n tio x id a tiv e p ro p e r tie s (8). 2 - M e th y l- th i a z o li - d in e - 2 ,4 - d ic a r b o x y lic a c id (C P ) is a p ro d u c t o f n o n - e n z y m a tic c o n c e n tra tio n o f p y ru v a te an d c y s te in e a n d sh o w s h e p a to p r o te c tiv e p ro p e rtie s (8 ,9 ,1 0 ).
T he effect o f the a b o v e m en tio n ed thiols on o x id ativ e pro cesses w as stu d ied in hum an ery th ro cy tes w here o x id atio n w as in d u ced by h ydrogen p ero x id e in the presen ce o f n atriu m azide, a catala- se inhibitor. T he effect o f the a b o v e th io ls w as stu d ied w ithin a given co n cen tratio n ran g es 0.1 m M - 2.0 m M fo r C A , m eth im azo le, N A C , p en icil
lam ine, N -a c e ty lp e n ic illa m in e , an d 0.1 m M - 25 m M fo r C P. T h e lev els o f m alo n y ld iald eh y d e (M D A ), reactiv e o x ygen species (R O S ) and h e m o glo b in released w ere e v a lu a te d as the m easure o f red cell p ero x id ativ e hem olysis.
EXPERIMENTAL
Chemicals
2 -T h io b a rb itu ric acid, N -a c e ty lc y ste in e , 2 ’, 7 ’-d ic h lo ro flu o rescein w ere o b ta in e d from S ig m a C h em ical C o (G erm any) w h ereas m eth im azo le and N -a c e ty l-D L - p e n ic illa m in e fro m S ig m a C hem ical C o (St. L o u is U S A ). T rich lo ro acetic acid w as p u rch ased from U b ich em pic S ig m a C h em ical Co, cap to p ril from F lu k a C h em ie A G C H -9 4 7 0 B uchs.
D - L - p en icillam in e and 2 ’,7 ’-d ic h lo ro flu o re sc e in diace tate w ere p u rch ased from S erv a F ein b io ch e-
449
450 MAŁGORZATA ICIEK et al.
m ica (H eidelberg) and M o le c u la r P robes E ugene O R (U SA ), resp ectiv ely . 2 -M e th y l- th ia z o lid in e -2 , 4 -d ic a rb o x y lic acid w as sy n th esized in the L ab o ra
tory o f C h em ical S y n th esis o f the Jag iello n ian U niversity.
Isolation of erythrocytes
H um an b lo o d w as o b tain ed from healthy vo
lunteers and w as sam p led into natrium citrate co n tain in g tubes. T he cells w ere sep arated by ce n trifu g atio n at 2500 g fo r 10 m in. T he e ry th rocytes w ere w ashed th ree tim es w ith the sam e v olum e o f p h y sio lo g ical saline.
Reaction mixtures
E ach reactio n m ixture in a final v olum e o f 2 ml co n tain ed 0.2 ml o f p ack ed red cells. T he final co n cen tratio n o f natrium azid e w as 2 m M , o f hy d ro g en p ero x id e 10 m M , and o f th e thiol c o m p o u n d s 0.1, 0.5, 1.0, an d 2 .0 m M . S im u ltan eo u sly , control sam p les w ith o u t th io ls w ere p repared. T he sam p les w ere ad ju sted to a final volu m e w ith p h o sp h a te -b u ffe re d salin e (0.9% N aC l, 5 m M so
d iu m /p o tassiu m p h o sp h ate, pH 7.4) an d then w ere incu b ated fo r 30 m in at 37°C.
Lipid peroxidation assay
L ip id p e ro x id atio n w as m easu red in reaction w ith th io b arb itu ric acid (T B A ) in acid m ed iu m (11) an d w as ex p ressed as m icro m o les o f m alonyldial- deh y d e p er g o f h em o g lo b in in reactio n m ixture.
A fter incu b atio n , 0.25 ml o f reactio n m ix tu re w as d ep ro tein ized w ith 2 ml o f 28% trich lo ro acetic acid and then c en trifu g ed at 2 5 0 0 g fo r 10 m in. N ext 2 ml o f th e su p ern atan t w as m ixed w ith 0.5 ml o f 0.9% T B A an d h eated at 100°C fo r 10 m in. T he a b so rb an ce o f th e co lo u red p ro d u ct w as m easu red at 535 nm .
Reactive oxygen species (ROS) assay
R eactiv e oxy g en species w ere assay ed fluoro- m etrically acco rd in g to th e m ethod o f B o ndy (12).
0.01 ml o f ery th ro cy tes su sp en sio n w as incu b ated w ith 0.01 m l o f 2 ’,7 ’-d ic h lo ro flu o re sc e in diacetate in a final v olum e o f 1 ml p h o sp h ate b u ffer pH 7.4 at 37°C fo r 30 m in. T h en sam p les w ere c en trifu g ed at
T a b le 1. E ffec t o f v a rio u s ca p to p ril c o n c e n tra tio n s o n lip id p e ro x id a tio n (M D A ), re a c tiv e o x y g e n s p e c ie s (R O S ) a n d tre e h e m o g lo b in levels.
C o n tro l C a p to p ril
0,1 mM 0,5 mM 1 mM 2 mM
M D A gm ol/g Hb
0.304 ± 0,022 0 ,2 11* * ± 0,017 0,179** ± 0,006 0,183** ± 0,005 0,262* + 0,025
R O S pm ol/g Hb
4,236 ± 0,373 3,125* + 0,141 2,789* + 0,119 3,119* + 0,155 3,535* ± 0,266
H b g/cm 3
0,120 ± 0,004 0,083* ± 0 ,0 1 2 0,071* ± 0,004 0,076* ± 0,003 0,101* ± 0,006
* p < 0 ,0 5 ; **p< 0,001
T a b le 2. E ffe c t o f v a rio u s m e th im a z o le c o n c e n tra tio n s o n lip id p ero x id a tio n (M D A ), re a c tiv e o x y g e n s p ec ie s (R O S ) a n d free h e m o g lo b in le v els.
C o n tro l M e th im azo le
0,1 mM 0,5 mM 1 mM 2 mM
M D A lim ol/g Hb
0,295 + 0,020 0,229* ± 0,012 0,201* ± 0,018 0,229* ± 0,020 0,262 ± 0,022
R O S pm ol/g Hb
4,216 ± 0,199 3,515 * ± 0,129 3,150** ± 0,077 3,353** ± 0,065 3,403 ± 0,411
H b g/cm 3
0,120 ± 0,004 0,106* ± 0,006 0,084* ± 0,004 0,088* ± 0,005 0,107 ± 0,006
*p<0,05; **p<0,001
T a b le 3 .E ffe c t o f v a rio u s p e n ic illa m in e c o n c e n tra tio n s o n lip id p ero x id a tio n (M D A ), re a c tiv e o x y g e n s p e c ie s (R O S ) an d free h em o g lo b in lev els.
C o n tro l P en icillam in e
0,1 mM 0,5 mM I mM 2 mM
M D A pm ol/g Hb
0,292 ± 0,008 0,234* ± 0 ,0 1 2 0,221* ± 0 ,0 1 1 0,233* ± 0 ,0 1 0 0,253* ± 0 ,0 1 0
R O S pm ol/g Hb
4,048 ± 0,262 3,465** ± 0,221 3,262** ± 0,145 3,432* ± 0 ,1 1 5 3,635* ± 0,122
H b g/cm 3
0,120 ± 0,004 0,107* ± 0,004 0,103* ± 0,003 0,108* ± 0,004 0,115* ± 0,006
*p<(X05; **p<0,001
T a b le 4 . E ffec t o f v a rio u s D ,L -a c e ty lp e n ie illa m in e c o n c e n tra tio n s o n lip id p e ro x id a tio n (M D A ), re a c tiv e o x y g e n sp e c ie s (R O S ) an d free h e m o g lo b in lev els.
C o n tro l D ,L -a c ety lp e n icilla m in e
0,1 mM 0,5 mM 1 mM 2 mM
M D A pm ol/g Hb
0,290 ± 0 ,0 1 6 0,268 ± 0 ,0 1 2 0,272 ± 0 ,0 1 4 0,272 ± 0 ,0 1 9 0,276 ± 0 ,0 1 0
R O S pm ol/g Hb
4,145 ± 0,150 4,156 ± 0,112 4,162 ± 0,095 4,151 ± 0,162 3,940 ± 0 ,1 5 6
H b g /cm ’
0,120 ± 0,004 0,121 ± 0,005 0,121 ± 0,020 0,120 ± 0,004 0,120 ± 0,004
T a b le 5 . E ffe c t o f v a rio u s N -a c e ty lc y s te in e c o n c e n tra tio n s o n lip id p ero x id a tio n (M D A ), re a c tiv e o x y g e n s p e c ie s (R O S ) a n d free h e m o g lo b in lev els.
C o n tro l N -acety lcy stein e
0,1 mM 0,5 mM 1 mM 2 mM
M D A pm ol/g Hb
0,280 ± 0 ,0 1 1 0,243* ± 0 ,0 1 0 0,225* ± 0,015 0,214* ± 0,017 0,203* ± 0 ,0 1 2
R O S pm ol/g Hb
4,145 ± 0,220 3,594* ± 0 ,1 5 0 3,430* ± 0,165 3,289* ± 0 ,1 6 7 3,084* ± 0,226
H b g/cm 3
0,120 ± 0,006 0,107* ± 0,005 0,101* ± 0,009 0,095* ± 0 ,0 1 0 0,086* ± 0,008
* p < 0 .0 5
12000 g fo r 8 m in at 4°C. T h e ex citatio n w a v e length w as 4 88 nm and the em issio n w avelength 525 nm . T h e level o f R O S w as ex p ressed as m icro m o les o f 2 ’,7 ’-d ic h lo ro flu o re sc e in e p er g o f h em o g lo b in in reactio n m ixture.
Hemoglobin released assay
T he am ount o f hem oglobin released w as deter
m ined according to the m ethod o f D rabkin (13). The
reaction m ixture after incubation w as centrifuged at 2500 g for 10 m in, then the am ount o f hem oglobin in the supernatant w as determ ined. T o 5 ml o f D rabkin reagent 0.2 ml o f supernatant w as added and after 20 m in extinction w as m easured at 540 nm.
Statistical methods
S tu d e n t’s t - t e s t w as u se d fo r s ta tis tic a l a n a ly sis a n d a p v a lu e o f < 0 .0 5 w as c o n s id e re d
452 MAŁGORZATA ICIEK et al.
mM -*■ MDA
-a- ROS
* Hb
F ig u re 1. E ffe c t o f v a rio u s 2 - m e ty lth ia z o lid in e - 2 ,4 —d ic a rb o x ilic a c id c o n c e n tra tio n s on lip id p ero x id a tio n (M D A ), re a c tiv e o x y g e n s p e c ie s (R O S ) a n d free h em o g lo b in le v els.
sig n ific a n t. V a lu e s a re e x p re s s e d as m e a n s
± S E M . RESULTS
T he control sam p les co n tain in g none o f the studied co m p o u n d s w ere ch aracterized by a high level o f M D A , R O S and h e m o g lo b in released.
A ll th e in v estig ated co n cen tratio n v alu es o f captopril w ere fo u n d to sig n ifican tly d ecrease o x i
dative hem o ly sis (T ab le 1). T h e g reatest d rop in the level o f M D A , R O S an d released h e m o g lo b in w as n oted at 0.5 m M , w hen the level o f M D A d ecreased to 58% , R O S d im in ish ed to 65% an d hem o g lo b in to 59% o f the control sam ples. A t h ig h er co n c e n t
ratio n values, the an tio x id ativ e effect o f cap to p ril w as w eaker.
S im ilarly as in the case o f cap to p ril, all the stu d ied m eth im azo le co n cen tratio n values resu lted in a sig n ifican t d ecrease o f the M D A , R O S and h e m o g lo b in lev els (T ab le 2). A ll th ese p aram eters reach ed th eir lo w est v alu es at the m eth im azo le co n cen tratio n o f 0.5 m M . A t th is level th e value o f M D A d ro p p ed to 68% , R O S to 7 4% and free h e m o g lo b in to 70% o f the co n tro l values. T h e se levels g rad u ally in creased at h ig h er and low er m eth im azo le co n cen tratio n s.
P en icillam in e w as p ro v ed to e x ert a b eneficial e ffect on a d rop o f all th e in v estig ated param eters (T able 3). A lso in th is case th e lo w est level o f M D A , R O S and free h e m o g lo b in w as n o ted at 0.5
m M . T h e level o f M D A reach ed 7 5% o f the co n tro ls w h ile fo r R O S , the value w as 80% , fo r free h em o g lo b in 90% . T h ese values also in creased at h ig h er an d lo w er p en icillam in e levels.
S tudies on N -a c e ty lp e n ic illa m in e d em o n stra
ted th at the co m p o u n d ex erted no p ro tectiv e effect ag ain st o x id ativ e d am ag e o f th e cells. N o n e o f the in v estig ated D ,L -a c e ty lp e n ic illa m in e c o n cen tra
tion levels resu lted in the d ecrease o f M D A , R O S an d free h em o g lo b in v alu es, o r th ese values w ere d im in ish ed on ly neg lig ib ly (T ab le 4).
Investigations carried out on N A C (Table 5) confirm ed its antioxidative properties. It is show ed that the level o f M D A , R O S, hem olysis and free hem oglobin decreased with the increase in N AC concentration. F or the m ost beneficial and at the sam e tim e the highest N A C concentration level (2.0 m M ), the value o f M D A dropped to 72% , R O S to 74% and free hem oglobin to 71% o f the control levels.
F ig u re 1 illu strates the effect o f vario u s C P co n cen tratio n values on the level o f M D A , R O S and free hem o g lo b in . T h e asso ciatio n w as studied fo r the co n cen tratio n range o f 0 .0 1 -2 5 .0 m M . T he resu lts in d icated th a t in th e ex p erim en tal co n d itio n s in vitro, th e p ro tectiv e effect o f C P c o u ld be o b serv ed only at 5 .0 -2 5 .0 m M . A t the highest co n cen tratio n (2 5 .0 m M ), th e level o f M D A d ec
reased to 6 8 % , R O S to 61% , an d free h em o g lo b in to 59% o f the control values.
DISCUSSION
T he p resen t in v estig atio n s d em o n strated that w hen hum an ery th ro cy tes w ere ex p o sed to h y d ro gen p ero x id e in th e presen ce o f natrium azide, the levels o f M D A , R O S and h em o ly sis ro se rap id ly in co m p ariso n to sam ples co n tain in g hyd ro g en p e ro xide itse lf o r n atriu m azid e only. T h is su p p o rts our h y p o th esis th a t hem o ly sis resu lts from p ero x id ativ e d am ag e s o f b iological m em b ran es an d o th e r c e l
lu lar stru ctu res in flicted by h y d ro g en p ero x id e. T he studies sh o w ed th at ery th ro cy tes w ere c h a ra c te ri
zed by hig h resistan ce to hyd ro g en p ero x id e and, thus, in o u r e x p erim en t it w as n ecessary to em ploy hig h c o n cen tratio n s o f the co m p o u n d (1 0 m M ) in the p resen ce o f natrium azide, a cata lase inhibitor.
O n ly in such co n d itio n s the ery th ro cy te a n tio x id a ti
ve sy stem s b reak dow n, w hich u ltim ately lead s to hem olysis.
T he in v estig atio n s in clu d ed th e g ro u p o f thiols w hich, as it is w ell know n, d u e to th e ir su lphydryl gro u p c o u ld m an ifest ch an g eab le an d co n trary ef
fects in p r o - and an tio x id ativ e p ro cesses (4, 5, 14,15). T he resu lts dem o n strate th at in the e x perim ental co n d itio n s at 0.5 m M co n cen tratio n ,
cap to p ril, m eth im azo le an d p en icillam in e e x ert the stro n g est p ro tectiv e effect on ery th ro cy tes. In this group, th e m ost p ro n o u n ced an tio x id ativ e activity is characteristic o f captopril.
N -a c e ty lc y ste in e beh av es d ifferen tly , b ecau se its an tio x id ativ e p ro p ertie s in crease w ith increasing N A C co n cen tratio n in reactio n m ixture. It seem s to confirm its generally accep ted low toxicity. M ost likely, in o rd er to v isualize a d rop in its p ro tectiv e effect, in v estig atio n s sh ould be carried out on the c o m p o u n d w ith h ig h er co n cen tratio n values. C o n t
rary to pen icillam in e (T able 3), N -a c e ty lp e n ic il- lam ine (T able 4) has no effect on o x id ativ e p ro ces
ses in ery th ro cy tes an d it show s th at acety latio n by nitrogen resu lts in a total loss o f p ro tectiv e p ro p er
ties o f this com p o u n d .
In this w ork, 2 -m e th y l-th ia z o lid in e -2 ,4 -d ic a r- b o x y lic ac id (C P ), a p ro d u c t o f n o n -e n z y m a tic c o n d e n sa tio n o f c y ste in e a n d p y ru v a te re le a se d in a re v e rse re a c tio n s im u lta n e o u sly tw o a n tio x i
d ants: c y ste in e n e c e ssa ry fo r the G S H b io s y n t
h esis an d p y ru v a te . T h e la tte r k e to a c id p ro v e d to e x e rt the a n tio x id a tiv e p ro p e rtie s (8, 16). In the p re v io u s stu d ie s in v iv o a n d in vitro, C P w as p ro v e d to h a v e an e ffe c tiv e a n d lo n g - la s tin g (up to 12 ho u rs) h e p a to p ro te c tiv e e ffe c t in eth y l a l
cohol (17) a n d p a ra c e ta m o l in to x ic a tio n (1 8 ). T h is is w hy th e 3 0 -m in u te in c u b a tio n o f 2 - m e t- h y l- th ia z o lid in e - 2 ,4 - d ic a r b o x y lic a c id w ith e ry t
h ro c y te su s p e n sio n w as m o st lik ely to o sh o rt to allo w an y p ro te c tiv e e ffe c t o f lo w e r C P c o n c e n t
ra tio n s to be n o ted .
T h e p ro o x id ativ e activity o f th io ls d e m o n st
rated w ith use o f free cy stein e as an exam ple, show ing th at both, its deficit and its e x cess can in d u ce h em o ly sis (8). A sim ilar c o n c e n tra tio n -d e p en d en t effect on h em o ly sis is ex erted by p e n ic il
lam ine (19). In th e p resen t in v estig atio n s, the c o n c en tratio n o f p en icillam in e at w hich its m axim um p ro tectiv e effect ag ain st h y d ro g en p ero x id e is no
ted is identical w ith the v alu e o b serv ed by L o v stad (19) at w hich he also noted th e lo w est level o f h em o ly sis. A d ecrease in p ro tectiv e p ro p ertie s ob
serv ed at h ig h er co n cen tratio n levels o f the stu d ied th io ls is m o st likely related to the o x id atio n o f their su lp h y d ry l g ro u p s to co rresp o n d in g d isu lp h id es and the p o ssib le fo rm atio n o f d isu lp h id e a n d thiyl radicals. N o such co n cen tratio n o f N A C w as id en tified in the p resen t studies at w hich its p ro tectiv e effect on ery th ro cy tes w o u ld be d ecreased , as it co u ld be o b serv ed in th e case o f the o th er thiol d rugs. In th e in vivo ex p e rim e n t co n d u ced by S p ra n g e t al. (20), lo w er doses o f N A C w ere found to d ecrease the b lo o d hy d ro g en p ero x id e level and to d im in ish the m o rtality rate in rats w hile high
d oses o f N A C resu lted in the decrease o f p u l
m onary G S H and in crease o f m ortality .
T he an tio x id ativ e effect o f c a p to p ril w as first d em o n strated by A ndreoli (4). T he o b serv atio n th at in vitro, in an ac e llu la r system cap to p ril is a stro n g er a n tio x id an t than cy stein e appears very in teres
ting. F ern an d es (21) fo u n d th at cap to p ril w as a m o re effectiv e an tio x id an t th an en alap ril o r lisinopril - o th er a n g io ten sin e c o n v ertase in h ib ito rs w h ich do not co n tain the thiol group. It su g g ests th at the p ro tectiv e p ro p ertie s o f C A are asso ciate d w ith the free - S H group. T he in v estig atio n s o f G o lik (5) and A ltu n tas (6) d em o n strated th a t b lo o d co n cen tratio n lev els o f M D A in p atien ts su b jected to lo n g -te rm cap to p ril therapy sig n ifican tly d ecreased w hich co n firm s th e an tio x id ativ e p ro p ertie s o f th e drug.
O th er studies by L ap p en a p ro v ed th a t in th e p resen ce o f iron o r c o p p er ions cap to p ril e x h ib ited p ro o x id ativ e effects and, thus, it c o u ld n o t be treated as a sim ple an tio x id ativ e agent. A specific b in d in g o f c o p p er by c a p to p ril in d u ces its p ro o x id ativ e activity. S im u ltan eo u sly , p en icillam in e has an an
tio x id ativ e effect in the presen ce o f co p p er, and a p ro o x id ativ e effect in th e p resen ce o f iron (22).
T h e p ro o x id ativ e ab ility o f cap to p ril an d p e n ic il
lam ine w hich is re g u lated by th e presen ce o f transitory m etals m ust, then, be tak en into c o n sid eratio n in ex p erim en tal stu d ies an d clin ical tra
ils. T h ese reports are c o n firm e d by B arto sz w ho states th a t d eo x y rib o se d eg rad atio n in d u ced by iron o r c o p p er ions is in ten sified u n d er the in flu en ce o f cap to p ril (15).
S u m m in g up, the in v estig atio n s, o f m eth im a
zole, cap to p ril, N A C an d p en icillam in e irresp ec
tiv ely o f th eir m ain p h arm aco lo g ical u sage can be said to ex h ib it in vitro c o n c e n tra tio n -d e p e n d e n t an tio x id ativ e activ ities w h ich in th is c ase can be reg ard ed as a b en eficial side effect. O n e should b ear in m in d th at thiol drugs, as w ell as all the co m p o u n d s co n tain in g the - S H g roups, m ay also d em o n strate ad v erse p ro o x id ativ e p ro p ertie s w ithin at certain co n cen tratio n ran g es an d in th e presen ce o f tran sito ry m etals.
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Received: 22.03.2000
