Retinal capillary closure induced by hyperglycemia is the principal pathophysiologic abnormality underlying diabetic retinopathy, but the mechaniss by which this induction occurs are not clear. Treatment of diabetic rats for 26 weeks with aminouanidine, an inhibitor of advanced glycosylation product formation, prevented a 2.6-fold accumulation of these products at branching sites of precapillary arterioles where abnormal periodic acid/Schiff reagentpositive deposits also occurred. A dine treatment completely prevented abnormal endothelial cell proliferation and signiflcantiy diminshed pericyte dropout. After 75 weeks, untreated diabetic animals developed an 18.6-fold increase in the number of acellular capillaries and formed capillary microaneurysms, characteristic pathologic features of background diabetic retinopathy. In contrast, aminoguanidinetreated diabetic animals had only a 3.6-fold increase in acellular capillaries and no microaneurysms. These findings indicate that advanced glycosylation product accumulation contributes to the development of diabetic retinopathy and suggest that a anqidine may have future therapeutic use in this disorder.Pathologic retinal changes are found in virtually 100%o of patients having type I diabetes for 15 yr or longer (1). Underlying the complex clinical manifestations of diabetic retinopathy are two fundamental abnormalities: increased retinal vascular permeability and progressive retinal vessel closure (2, 3). Digested retinal vasculature preparations from diabetic patients and animals characteristically show early pericyte loss which is followed by acellular capillary development and microaneurysm formation (4,5). The severity of these changes is associated with the degree of chronic hyperglycemia to which the diabetic retina has been exposed, but the mechanisms by which elevated glucose levels cause retinal damage are currently not known (6, 7). Potentially important mechanisms include increased polyol pathway activity, activation of protein kinase C by de novo diacylglycerol synthesis, and altered cell/matrix functions induced by accumulated advanced glycosylation end products (8-11).Recently the nucleophilic hydrazine compound aminoguanidine has been shown to inhibit the formation of advanced glycosylation products on collagen and basement membrane both in vitro and in vivo (12,13 pepsin/0.2% HCL. After 10 min in a water bath at room temperature, the retina was subjected to digestion by 3% trypsin/0.2 M Tris for 3.5 hr at 370C to remove the inner limiting membrane. The sample was then placed on a glass slide, and further digestion with trypsin was monitored under a dissecting microscope. The intact isolated retinal vessel preparation was washed with distilled H20 and air-dried. Retinal vessel preparations were stained with periodic acid/ Schiff reagent/hematoxylin (15) and photographed using a

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Sulfonylureas have, in the past, been reported to have adverse cardiovascular effects. Glimepiride is a new sulfonylurea. In spite of stimulating less insulin secretion, it has, depending on the species, equal or higher blood glucose decreasing activity and according to preliminary studies less cardiovascular activity than glibenclamide. Further studies were performed to confirm the lower cardiovascular activity of glimepiride. The IC50 for inhibition of rilmakalim-activated KATP channel currents in isolated ventricular myocytes was 31.6 nM for glimepiride and 6.8 nM for glibenclamide. In endotoxin shock-rats at a dose of 1 x 2 mg/kg i.v., glibenclamide induced a significantly higher blood pressure increase than glimepiride. At two i.v. doses of 20 mg/kg 4 min apart, in normal rats, glibenclamide produced signs of ischemia in the ECG in nearly all animals, glimepiride almost none, in diabetic rats, glibenclamide produced in all animals a lethal cardiogenic shock preceeded by serious ECG changes, glimepiride only in one fifth of the animals. In open-chest dogs, on intracoronary infusion of equieffective blood glucose-lowering doses, glibenclamide, gliclazide and glimepiride all reduced coronary blood flow, increased coronary resistance, depressed the mechanical activity of the heart, enhanced myocardial O2-extraction, reduced the serum potassium level and induced a moderate endocardial ST-segment elevation, but glimepiride to a significantly less extent than glibenclamide and gliclazide. The presented data confirm that glimepiride at equivalent blood glucose decreasing doses has less cardiovascular activity than conventional sulfonylureas.

Glimepiride was compared with glibenclamide for its insulin secretion stimulating and beta-cell membrane depolarizing activity as well as for its binding kinetics to beta-cell membranes and for its beta-cell membrane binding proteins. Steady state, kinetic and competitive binding studies revealed a 3- to 4-fold lower binding affinity of glimepiride to isolated beta-cell membranes and intact beta-cells compared to glibenclamide. Direct photoaffinity labeling of beta-cell membrane proteins with the radiolabeled sulfonylureas identified a 65-kDa binding protein for glimepiride and a 140-kDa binding protein for glibenclamide which may be the basis for the different binding characteristics of the two sulfonylureas. The inhibition of binding and photoaffinity labeling of glimepiride and glibenclamide to the 65- and 140-kDa protein, respectively, by glibenclamide and glimepiride can be explained with allosteric interactions between two distinct sulfonylurea binding proteins, subunits of a KATP protein complex, each regulating the open/closed-state of a common separate pore-forming subunit by allosteric interactions. Whole-cell patch clamp experiments with RINm5F cells demonstrated a 3- to 4-fold lower depolarization activity of glimepiride compared to glibenclamide which correlates well with the lower binding affinity of glimepiride. The lower binding affinity and depolarization activity of glimepiride were not reflected in vitro in perifused islets and the isolated perfused pancreas of the rat. This discrepancy remains to be elucidated. The binding, depolarisation and insulin releasing characteristics of glimepiride and glibenclamide suggest that different sulfonylureas can interact with different components of KATP.

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