Abstract Ticlopidine, a thienopyridine that prevents the
progression of diabetic retinopathy in humans, was
re-cently shown to increase nitric oxide (NO) production in
human neutrophils. The thienopyridine clopidogrel has
been found to be clinically useful in the secondary
pre-vention of thrombotic events. The aim of the present
study was to evaluate the effect of clopidogrel on
isch-emic retinopathy in streptozotocdiabetic rats and its
in-fluence on prostanoids and NO production. We compared
nondiabetic rats and rats after 3 months of diabetes that
were given three doses (1, 10 or 20 mg/kg per day p.o.) of
ticlopidine or clopidogrel from the first day of diabetes.
The variables recorded after 3 months of diabetes were
platelet aggregation, thromboxane B
2(TxB
2) production,
6-keto-prostaglandin F
1α(stable metabolite of
prostacy-clin), aortic NO, plasma nitrites/nitrates, and the
percent-age of the retinal surface occupied by horseradish
peroxi-dase (HRP)-permeable vessels. In diabetic rats, platelet
ag-gregation and thromboxane concentration were increased,
and prostacyclin, NO and area occupied by
HRP-perme-able vessels were decreased.
Ticlopidine and clopidogrel reduced the maximum
ex-tent of platelet aggregation in a dose-dependent manner:
maximal inhibition with respect to untreated diabetic rats
was 48.6% with ticlopidine and 66.6% with clopidogrel.
Ticlopidine reduced thromboxane B
2only at a dose of
20 mg/kg per day p.o. (47.4% inhibition) and clopidogrel at
doses of 10 mg/kg per day (51% inhibition) or 20 mg/kg
per day (51.7% inhibition). Aortic prostacyclin
produc-tion did not change after treatment with either
thienopyri-dine. Treatment with ticlopidine reduced the inhibition of
NO production in untreated rats (89.6% inhibition) to
0.9%, and clopidogrel reduced inhibition to 30%.
Treat-ment with ticlopidine or clopidogrel reduced the retinal
nonperfused area from 86.8% inhibition in untreated rats
to 45.6% and 25.3%, respectively.
In conclusion, the early administration of
thienopyr-idines in streptozotocin-diabetic rats partly prevented the
appearance of diabetic retinal ischemia.
Keywords Ticlopidine · Clopidogrel · Diabetic
retinopathy · Nitric oxide · Prostacyclin
Introduction
Two of the mechanisms involved in the genesis and
pro-gression of microangiopathic complications in patients
with diabetes mellitus and in experimental diabetic
ani-mals are increased platelet activation (Boeri et al. 2001;
Dallinger et al. 1987; De La Cruz et al. 1997; Ishii et al.
1992) and increased thromboxane synthesis (De La Cruz
et al. 1997; Hendra and Betteridge 1989; Moreno et al.
1995). A decrease in platelet sensitivity to endogenous
platelet substances such as prostacyclin or nitric oxide
(NO), and a decrease in the synthesis of these mediators,
have also been described (De La Cruz et al. 2002b, 2002c;
Hendra and Betteridge 1989). In diabetic retinopathy,
these alterations are closely related with endothelial
dys-function, one of the earliest alterations to appear
(Chakrabarti et al. 2000).
Some antiplatelet drugs such as aspirin (De La Cruz et
al. 1990, 1997, 2002b), dipyridamole, mopidamol (De La
Cruz et al. 1996), ditazol (Moreno et al. 1995),
camona-grel and other antagonists of thromboxane synthase (De
La Cruz et al. 1998, 2000b) have shown a prophylactic
ef-fect on the development and progression of these retinal
vascular lesions in streptozotocin-diabetic rats. From
these studies we concluded that these drugs exerted two
effects that correlated with the prevention of ischemic
di-J. P. De La Cruz · M. M. Arrebola
·
J. A. González-Correa · E. Martinez-Cerdán
·
A. Moreno · F. Sánchez de la Cuesta
Effects of clopidogrel and ticlopidine
on experimental diabetic ischemic retinopathy in rats
DOI 10.1007/s00210-002-0657-4Received: 19 July 2002 / Accepted: 11 October 2002 / Published online: 9 January 2003
O R I G I N A L A RT I C L E
J.P. De La Cruz (✉) · M.M. Arrebola · J.A. González-Correa · F.S. de la Cuesta
Department of Pharmacology and Therapeutics, School of Medicine, University of Málaga, Campus de Teatinos s/n, 29071 Málaga, Spain e-mail: [email protected],
Tel.: +34-952-131567, Fax: +34-952-131568
E. Martinez-Cerdán · A. Moreno
Department of Ophthalmology, School of Medicine, University of Málaga,
Campus de Teatinos s/n, 29071 Málaga, Spain © Springer-Verlag 2003
abetic retinopathy: inhibition of platelet thromboxane, and
increased vascular production of prostacyclin and NO.
Ticlopidine is a thienopyridine that prevents the
evolu-tion of diabetic retinopathy in humans (TIMAD Study
Group 1990), and it has recently been shown to increase
NO production in human neutrophils (De La Cruz et al.
2002a). Another thienopyridine, clopidogrel, is used in
the secondary prevention of thrombotic events (CAPRIE
Steering Committee 1996). Ticlopidine and clopidogrel
act as antagonists of platelet ADP receptors (Foster et al.
2001).
The aim of the present study was to evaluate the
possi-ble effect of clopidogrel on ischemic retinopathy in
strep-tozotocin-diabetic rats, and its influence on prostanoids
and NO production.
Materials and methods
Materials
All reagents were from Sigma Chemical (St. Louis, Mo., USA), unless otherwise noted. Isophane (NPH) insulin was obtained from Novo Nordisk (Bagsvaerd, Denmark), and collagen was obtained from Menarini (Barcelona, Spain). Ticlopidine and clopidogrel were obtained from Sanofi-Synthelabo (Barcelona, Spain).
Experimental groups
We used 80 male Wistar rats with a mean body weight of 200 g at the start of the experiment. The study was carried out in accor-dance with the Guide for the Care and Use of Laboratory Animals, and the research was approved by the University of Málaga Ani-mal Use Committee.
The rats were distributed randomly into eight groups of ten an-imals each: (1) a control group of nondiabetic anan-imals studied for 3 months, (2) an untreated group of animals with diabetes followed for 3 months, (3) animals with diabetes treated with 1 mg ticlopi-dine/kg per day p.o. for 3 months, (4) rats with diabetes treated with 10 mg ticlopidine/kg per day p.o. for 3 months, (5) animals with diabetes treated with 20 mg ticlopidine/kg per day p.o. for 3 months, (6) animals with diabetes treated with 1 mg clopido-grel/kg per day p.o. for 3 months, (7) rats with diabetes treated with 10 mg clopidogrel/kg per day p.o. for 3 months, (8) animals with diabetes treated with 20 mg clopidogrel/kg per day p.o. for 3 months.
Induction of diabetes
Experimental diabetes was induced with a single intravenous in-jection of 50 mg/kg streptozotocin. Blood glucose concentration was measured by placing a Glucocard Memory II glucosimeter (Menarini, Barcelona, Spain) in contact with blood from a small incision in the tail. Animals were considered to have diabetes if blood glucose was >200 mg/dl for 2 consecutive days. Rats in the nondiabetic control groups received a single intravenous injection of isotonic saline solution, and blood glucose was measured in the same way as in animals that were made diabetic.
Observation and treatment
During the observation period, diabetic animals were treated with 4 IU/day s.c. of NPH insulin to reduce mortality due to the high levels of blood glucose. Control animals received the same volume of isotonic saline solution s.c.
Drugs were given starting on the first day of diabetes as a sin-gle oral daily dose via a flexible catheter. Nondiabetic control ani-mals received an equivalent volume of isotonic saline solution.
Sample processing
At the end of the third month all animals from each group were anesthetized with pentobarbital sodium (40 mg/kg i.p.). A medial laparotomy was made to withdraw 2 ml of blood from the vena cava; 3% sodium citrate at a proportion of 1:9 was used as the an-ticoagulant. Then a segment of the abdominal aorta 0.5 cm anterior to the bifurcation of the femoral arteries was clamped.
Sigma Type II horseradish peroxidase (HRP; 1 ml, 180 mg/kg) was injected via the carotid artery. Five minutes later both eyeballs were removed and placed in a solution of 1.2% glutaraldehyde and 1% paraformaldehyde in 0.2 M phosphate-buffered saline (pH 7.2) for 45 min. The lens and vitreous humor were removed, and the retina was separated from the sclera with a narrow surgical spatula and immersed in fixative for 48 h.
Analytical techniques
All techniques were run in a single-blind manner, i.e., the persons who did the assays were unaware of the origin and nature of the samples.
Platelet aggregometry. Platelet aggregation capacity in whole
blood was tested at 37°C with the electrical impedance method (Cardinal and Flower 1980). Collagen (10 µg/ml) was used as the inducing agent, and maximum aggregation intensity was deter-mined as the maximum resistance between the two poles of the electrode obtained 10 min after collagen was added.
Platelet thromboxane B2. After aggregation was complete the
blood sample was centrifuged at 10,000 g for 5 min, and the su-pernatant was frozen at –80°C until thromboxane B2production
was quantified with an enzyme immunoassay (Oxford Biomedical Research, Oxford, Mich., USA).
Vascular 6-keto-prostaglandin F1α. The aortic segment was cut
into two parts and incubated at 37°C in buffer containing (mM): 100 NaCl, 4 KCl, 25 NaHCO3, 2.1 Na2SO4, 20 sodium citrate, 2.7
glucose and 50 Tris (pH 8.3). One segment was placed in 500 µl of fresh buffer, and 10 µl calcium ionophore A23187 (final concen-tration 1 µM) was added. Five minutes later the sample was dried and weighed, and the supernatant was frozen at –80°C until the as-say. The production of 6-keto-prostaglandin F1α (6-keto-PGF1α; stable metabolite of prostacyclin) was quantified with an enzyme immunoassay (Oxford Biomedical Research).
Vascular nitric oxide production. The other part of the aortic
seg-ment was incubated in fresh buffer, and 100 µM L-arginine was
added. Nitric oxide production was quantified by an electrochemi-cal method (Shibuki 1990), with an ISO-NOP 200 electrode for NO detection (World Precision Instruments, Stevenage, UK). Pro-duction was induced with 1 µM calcium ionophore A23187 to stimulate constitutive NO-synthase.
Plasma nitrite/nitrate levels. As an indirect indicator of overall NO
production in each animal, we determined plasma nitrite/nitrate levels. One milliliter of blood (with anticoagulant) was centrifuged at 10,000 g for 10 min, and the supernatant was filtered through Ultrafree MC microcentrifuge filters (Gif-sur-Yvette, France) to eliminate hemoglobin released by cell lysis. The nitrite/nitrate level was measured with a commercial kit (Cayman Chemical, Ann Arbor, Mich., USA), based on the Griess reaction, after the nitrates were converted to nitrites with nitrate reductase. Levels of nitrite/nitrate were determined spectrophotometrically at 540 nm and compared with a standard curve obtained with sodium nitrite.
Retinal vasculature. The fixed retinas were prepared histologically
with the method of Mesulam (1982). They were incubated with a solution of tetramethylbenzidine and sodium nitroferrocyanide as the chromogenic substrate, then dehydrated in an alcohol gradient, incubated in xylene, and mounted in sections for microphotography. Retinal vessels permeable to HRP were photographed at ×40, and microscopic images were processed in an IBAS Kontron 2000 image analyzer (Kontron Bidanalyse, Munich, Germany). The per-centage of the retinal surface occupied by peroxidase-permeable vessels was calculated by the system as a standard parameter. Horseradish peroxidase is a high-molecular-weight substance that mainly stains red blood cells; thus in occluded vessels HRP does not stain the vasculature.
Statistical analysis
All values in the text and figures are the means ± standard error of the mean (SEM) of the data for all animals in each group. The data were analyzed with the Statistical Package for Social Sciences (SPSS, Chicago, Ill., USA). Groups were compared with analysis of variance followed by the test of minimum significant differ-ences when the difference between groups was significant. A P-value of <0.05 was taken as the minimum level of significance.
Results
Mean body weight and blood cell counts are shown in
Table 1. There were no differences in the body weight
in-crements from day 0 to day 90 in any of the diabetic
groups, although the differences between untreated
dia-betic rats and nondiadia-betic rats were statistically
signifi-cant. There were no statistical differences in blood cell
counts between groups. All other variables measured in
rats are shown in Table 2.
Platelet parameters
In diabetic rats, platelet aggregation induced with
colla-gen in whole blood was higher than in nondiabetic rats.
Ticlopidine and clopidogrel reduced the maximum
inten-sity of platelet aggregation in a dose-dependent manner:
22.2%, 37.5% and 48.6% inhibition with respect to
un-Table 1 Mean values for body weight and blood cell counts in nondiabetic rats (NDR), untreated diabetic rats (DR) and DR treated orally for 3 months with ticlopidine (TCP) or clopidogrel (CLOP). Each value represents the mean ± SEM of ten rats per group
Body weight Body weight Platelet count Hematocrit Red blood cells Leukocytes
(day 0) (day 90) (×109/l) (l/l) (×1012/l) (×109/l)
NDR 275±18 365±25 705±31 45.2±0.6 4.2±0.1 6.4±0.2
DR 268±15 321±19* 694±71 45.3±2.2 4.5±0.4 6.4±0.4
DR + TCP
1 mg/kg per day 263±17 319±18 700±58 44.1±0.9 4.8±0.4 6.1±0.3
10 mg/kg per day 265±19 316±19 682±68 44.7±0.9 4.5±0.5 6.1±0.7
20 mg/kg per day 277± 6.2 324±12 689±58 44.9±0.9 4.5±0.6 6.3±0.4
DR + CLOP
1 mg/kg per day 273±10 322±25 688±85 44.4±1.3 4.5±0.6 6.1±0.5
10 mg/kg per day 270±23 319±15 693±60 44.1±1.1 4.6±0.3 6.2±0.4
20 mg/kg per day 264±11 321±12 686±48 44.5±0.8 4.6±0.5 6.1±0.7
*P<0.001 with respect to NDR
Table 2 Mean values for variables measured in nondiabetic rats (NDR), untreated diabetic rats (DR) and DR treated orally for 3 months with ticlopidine (TCP) or clopidogrel (CLOP). Each value represents the means ± SEM of ten rats per group
Maximum TxB2 6-keto-PGF1α NO–2/NO–3 Calcium- % retinal surface
intensity (nmol/109 (nmol/mg (µM) induced NO covered with
of aggregation platelets) tissue) (nmol/mg HRP-permeable
(ohms) tissue) vessels
NDR 5.60±0.63 23.63±1.86 95.41±7.55 12.53±1.10 1.16±0.09 15.37±1.60
DR 14.28±1.26* 40.82±3.27* 32.16±2.58* 2.25±0.16* 0.12±0.01* 2.03±0.13*
DR + TCP
1 mg/kg per day 11.10±0.95** 42.49±6.92 35.46±4.16 2.38±0.18 0.68±0.04*** 6.11±0.56*** 10 mg/kg per day 8.92±0.76*** 33.41±8.66 43.05±5.13** 3.51±0.22** 0.85±0.08*** 7.88±0.54*** 20 mg/kg per day 7.34±0.51*** 21.46±1.51** 45.58±5.21** 10.14±1.38*** 1.19±0.07*** 8.35±0.49***
DR + CLOP
1 mg/kg per day 11.42±0.96** 41.10±4.25 52.13±7.44*** 2.51±0.18 0.26±0.05*** 7.13±0.30*** 10 mg/kg per day 7.14±0.53*** 20.03±3.73*** 69.00±8.17*** 4.63±0.31** 0.46±0.07*** 8.82±0.42*** 20 mg/kg per day 4.76±0.23*** 19.69±0.43*** 85.76±9.08*** 12.62±1.44*** 1.51±0.07*** 12.47±0.61***
*P<0.001 with respect to NDR
treated diabetic rats with 1, 10 and 20 mg/kg per day of
ticlopidine, and 19.5%, 50% and 66.6% inhibition with 1,
10 and 20 mg/kg per day of clopidogrel, respectively.
Platelet thromboxane B
2production increased 72.7%
in untreated diabetic rats with respect to nondiabetic rats.
The reduction in synthesis with ticlopidine reached
statis-tical significance only after 3 months of treatment with
20 mg/kg per day p.o. (47.4% inhibition with respect to
untreated diabetic rats). Clopidogrel inhibited platelet
pro-duction of thromboxane B
2after chronic treatment with
10 mg/kg per day (51% inhibition) or 20 mg/kg per day
(51.7% inhibition); the differences in comparison to
non-diabetic rats were not statistically significant.
Endothelial parameters
Aortic production of prostacyclin, measured as
6-keto-PGF
1α, was significantly lower in diabetic rats (66.3%)
than in nondiabetic animals. Treatment with 1, 10 or 20
mg/kg per day of ticlopidine for 3 months reduced the
dif-ferences between untreated diabetic rats and nondiabetic
rats to 63%, 54% and 42%, respectively. Treatment with
1, 10 or 20 mg/kg per day of clopidogrel for 3 months
re-duced the differences between untreated diabetic rats and
nondiabetic rats to 45%, 27% and 10.5%, respectively.
Vascular NO production induced via the
calcium-de-pendent pathway was significantly lower (89.6%) in
dia-Fig. 1 Representative images(×20) of the retinal vascular pattern from A a nondiabetic rat, B an untreated diabetic rat after 3 months, and C a dia-betic rat treated with ticlopi-dine (10 mg/kg per day p.o.) or D clopidogrel (1 mg/kg per day p.o.)
betic rats than in nondiabetic controls after 3 months.
Treatment with 1, 10 or 20 mg/kg per day of ticlopidine
for 3 months reduced the differences between untreated
diabetic rats and nondiabetic rats to 41.4% lower, 0.9%
lower and 2.6% higher, respectively. Treatment with 1, 10
or 20 mg/kg per day of clopidogrel for 3 months reduced
the differences between untreated diabetic rats and
nondi-abetic rats to 77% lower, 60% lower and 30% higher,
re-spectively.
Plasma levels of nitrites/nitrates were lower (82%) in
diabetic rats than in control animals. Treatment with 1, 10
or 20 mg/kg per day ticlopidine for 3 months reduced the
differences between untreated diabetic rats and
nondia-betic rats to 81%, 72% and 19%, respectively. Treatment
with 1, 10 or 20 mg/kg per day of clopidogrel for 3 months
reduced the differences between untreated diabetic rats
and nondiabetic rats to 80% lower, 63% lower and 0.8%
higher, respectively.
Vascular retinal pattern
Diabetes induced with streptozotocin in rats reduced
(86.8%) the retinal surface occupied by HRP-permeable
vessels. Treatment with 1, 10 or 20 mg/kg per day of
ticlopidine for 3 months reduced the differences between
untreated diabetic rats and nondiabetic rats to 60.2%,
48.6% and 45.6%, respectively. Treatment with 1, 10 or
20 mg/kg per day of clopidogrel for 3 months reduced the
differences between untreated diabetic rats and
nondia-betic rats to 53.6%, 42.6% and 25.3%, respectively.
Figure 1 shows representative images of retinal
vascu-lar patterns from a nondiabetic rat and diabetic rats with
and without treatment.
Discussion
The results of the present study show that in the model of
experimental diabetes we used, the imbalance between the
synthesis of vasoconstrictors and platelet aggregant
fac-tors such as thromboxane A
2and vasodilators and platelet
antiaggregants such as prostacyclin and NO can be
regu-lated by early treatment with the thienopyridines
clopido-grel or ticlopidine. This effect may be involved in the
abil-ity of these antiplatelet drugs to reduce the degree of
reti-nal ischemia in streptozotocin-diabetic rats. We found that
the effect of clopidogrel is slightly stronger than that of
ticlopidine.
Enhanced platelet aggregation in diabetes has been
widely reported in both animal models and humans. As
earlier studies have shown (Glassman 1993; Schrör
1997), this increase in platelet aggregation capacity is
ac-companied by an evident imbalance in prostanoid
synthe-sis, i.e., an increase in platelet thromboxane A
2production
and a decrease in vascular prostacyclin synthesis.
With respect to NO production, sustained high blood
glucose levels in diabetes mellitus are assumed to
stimu-late oxidative stress mechanisms, which may be one of
the causes of the inhibition of endothelial prostacylin
syn-thetase and the reaction of free radicals with NO to
pro-duce peroxynitrites (Giugliano et al. 1996; Tesfamariam
and Cohen 1992). Both effects are manifested as the
en-dothelial dysfunction reported in diabetes. Both
prostacy-clin and NO are vasodilators and platelet antiaggregants,
and a deficit in these substances has been linked to early
vascular alterations in diabetic retinopathy (Chakrabarti et
al. 2000). In our experimental model, vascular NO
syn-thase activity (measured indirectly as NO production after
stimulation with a calcium ionophore) was clearly
re-duced in diabetic animals, as was the plasma nitrite/nitrate
level, used here as an indirect indicator of global NO
pro-duction.
The alterations summarized above may contribute to
the reduction we found in retinal surface area occupied by
HRP-permeable vessels. However, these are not the only
mechanisms that can condition retinal ischemia in
dia-betes. It is now accepted that the appearance of ischemia
may reflect the sum of these and other factors such as
in-creased endothelin synthesis, anomalies in protein kinase
C, and increased activity of the polyol pathway
(Chakra-barti et al. 2000; De Vriese et al. 2000). However, the
syn-thesis of both prostacyclin and NO is altered as a result of
the endothelial dysfunction in diabetes.
The administration of thienopyridines modifies these
effects of the disease. Platelet aggregation induced by
col-lagen is inhibited by the oral administration of ticlopidine
or clopidogrel, as is platelet thromboxane production. The
antiaggregant effect of thienopyridines is more potent
when aggregation is induced with ADP than with collagen
(De La Cruz et al. 2002a; Geiger et al. 1998). However, in
our study we chose collagen to induce platelet
aggrega-tion because this inducer most frequently stimulates
platelets in the early phases of activation, as in the
suben-dothelial stimulation by collagen in blood vessels with
le-sions to the vascular wall (Badimón and Badimón 1996).
A possible explanation for the inhibition of platelet
thromboxane B
2can be found in the observations of Chap
et al. (1981) and Lagarde et al. (1979). They showed that
ticlopidine increases arachidonic acid release from
phos-pholipids and the synthesis of prostaglandin E
2from
cyclic endoperoxides, thus reducing substrate (cyclic
en-doperoxides) for thromboxane A
2synthesis. The
thieno-pyridine derivative clopidogrel may act in a manner
simi-lar to ticlopidine. Another hypothesis is the possible
inhi-bition of cyclooxygenase activity, but in this case
prosta-cyclin synthesis would be reduced, and this was not
ob-served in our experimental model (Table 2).
The vascular production of prostacyclin, which is
re-duced in diabetic rats, was stimulated by thienopyridines,
particularly clopidogrel. This effect is important because
it means that these drugs may inhibit prothrombotic
fac-tors such as thromboxane, while sparing endogenous
anti-aggregant substances such as prostacyclin. Moreover,
ac-cording to the results of previous studies in this
experi-mental model, using antiplatelet drugs, there was a
pro-portional relation between the ability to increase (or at
least not to modify) prostacyclin production and the
de-gree of prevention of ischemic retinal vascular alterations
(De La Cruz et al. 1990, 1996, 1997, 1998, 2000b, 2000c,
2002b).
Treatment with thienopyridines stimulated the capacity
of arteries in our diabetic animals to produce NO via a
calcium-dependent pathway. In fact, this effect was strong
enough to restore normal levels of NO production in
dia-betic rats. We also found that ticlopidine stimulates
cal-cium-dependent NO production in human neutrophils in
vitro, which is inhibited after incubation with
L-NAME
(an inhibitor of NO synthase; De La Cruz et al. 2002a).
Moreover, an earlier study by De Logeril et al. (1998)
showed that ticlopidine did not modify prostacyclin
pro-duction but did increase systemic NO propro-duction in heart
transplant recipients. Our results confirm this finding in
streptozotocin-diabetic rats.
The consequence of treatment with other antiplatelet
drugs that inhibit platelet activation, and that increase (or
do not affect) prostacyclin or NO production, is to partly
prevent the appearance of retinal ischemia in
strepto-zotocin-diabetic rat alterations (De La Cruz et al. 1990,
1996, 1997, 1998, 2000b, 2000c, 2002b; Moreno et al.
1995). The results obtained with the thienopyridines in
this study further support these observations. Despite the
interspecies differences, a dose of ticlopidine of 10 mg/kg
per day, equivalent to the dose of 500 mg/day used in
clin-ical practice, reduced ischemic retinal damage from
86.8% (percentage with respect to nondiabetic rats) in
un-treated rats to 48.6%. Clopidogrel at a dose of 1 mg/kg per
day, equivalent to a dose of 75 mg/day in humans,
re-duced ischemic retinal damage to 53.6%.
In conclusion, the early administration of
thienopyr-idines to streptozotocin-diabetic rats partly prevented the
appearance of diabetic retinal ischemia; the intensity of
the effect was similar with both drugs. The CAPRIE trial
(CAPRIE Steering Committee 1996) reported a lower
in-cidence of side effects (mainly diarrhea and neutropenia)
in comparison to ticlopidine (Fitchett et al. 2001; Hass et
al. 1989). We therefore suggest that clopidogrel may be an
alternative to ticlopidine in the prevention of diabetic
retinopathy.
Acknowledgements We thank A. Pino for his excellent technical assistance and K. Shashok for checking the use of English. Partial support for this study was provided by Sanofi-Synthelabo in Barcelona, Spain.
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