Three of the major biochemical pathways implicated in the pathogenesis of hyperglycemia induced vascular damage (the hexosamine pathway, the advanced glycation end product (AGE) formation pathway and the diacylglycerol (DAG)-protein kinase C (PKC) pathway) are activated by increased availability of the glycolytic metabolites glyceraldehyde-3-phosphate and fructose-6-phosphate. We have discovered that the lipid-soluble thiamine derivative benfotiamine can inhibit these three pathways, as well as hyperglycemia-associated NF-kappaB activation, by activating the pentose phosphate pathway enzyme transketolase, which converts glyceraldehyde-3-phosphate and fructose-6-phosphate into pentose-5-phosphates and other sugars. In retinas of diabetic animals, benfotiamine treatment inhibited these three pathways and NF-kappaB activation by activating transketolase, and also prevented experimental diabetic retinopathy. The ability of benfotiamine to inhibit three major pathways simultaneously might be clinically useful in preventing the development and progression of diabetic complications.

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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