It has been suggested that the cytokine vascular endothelial growth factor (VEGF) has an important role in the pathogenesis of diabetic retinopathy, but its role in nephropathy has not been clearly demonstrated. Assessment of VEGF, 125I-VEGF binding, and vascular endothelial growth factor receptor-2 (VEGFR-2) in the kidney was performed after 3 and 32 weeks of streptozotocin-induced diabetes. Gene expression of both VEGF and VEGFR-2 was assessed by Northern blot analysis and the localization of the ligand and receptor was examined by in situ hybridization. VEGF and VEGFR-2 protein were also evaluated by immunohistochemistry. Binding of the radioligand 125I-VEGF was evaluated by in vitro and in vivo autoradiography. Diabetes was associated with increased renal VEGF gene expression. VEGF mRNA and protein were localized to the visceral epithelial cells of the glomerulus and to distal tubules and collecting ducts in both diabetic and nondiabetic rats. Renal VEGFR-2 mRNA was increased after 3 weeks of diabetes but not in long-term diabetes. In situ hybridization and immunohistochemical studies revealed that glomerular endothelial cells were the major site of VEGFR-2 expression. In addition, VEGFR-2 gene expression was detected in cortical and renomedullary interstitial cells and on endothelial cells of peritubular capillaries. There was an increase in 125I-VEGF binding sites after 3 but not 32 weeks of diabetes. The major VEGF binding sites were in the glomeruli. 125I-VEGF binding was also observed in medullary rays and in the renal papillae. These studies indicate an early and persistent increase in renal VEGF gene expression in association with experimental diabetes. In addition, an early and transient increase in renal VEGF receptors was also observed in diabetic rats. These findings are consistent with a role for VEGF in mediating some of the changes observed in the diabetic kidney.

It has been postulated that the accumulation of advanced glycation end products (AGEs) in the kidney is important in the pathogenesis of diabetic nephropathy. Previously, aminoguanidine has been shown to inhibit the accumulation of renal AGEs and to retard the development of experimental diabetic nephropathy. The present study serially assessed the accumulation of AGEs in the aorta and kidney, as well as renal functional and structural parameters over 32 weeks of experimental diabetes in the absence and presence of aminoguanidine. In addition, it was determined if aminoguanidine was more effective if administered earlier or later in the evolution of diabetic nephropathy by treating diabetic rats with aminoguanidine in the first or second half of the 32-week study period. In the serial studies, glomerular and renal tubular fluorescence increased over the 32 week period and this increase was attenuated by aminoguanidine treatment. Concomitant with the effects of aminoguanidine on fluorescence, there was a retardation in the rise in urinary albumin excretion and prevention of mesangial expansion. Early or late administration of aminoguanidine in diabetic rats reduced tissue fluorescence in glomeruli and renal tubules. At 32 weeks, renal AGEs were increased in diabetic rats as assessed by tissue fluorescence. Using a specific RIA, renal AGEs were increased in diabetic rats and decreased by aminoguanidine treatment, administered over the entire 32 weeks or in the first or latter half of the 32-week study period. Aminoguanidine therapy for the entire 32-week study period retarded the rise in albuminuria in the diabetic rats and was more effective than 16 weeks of treatment either in the first or second half of the study. Early and late aminoguanidine administration were similar in their capacity to retard the development of albuminuria in diabetic rats. Similar effects were observed on mesangial expansion. The increased glomerular basement thickness in diabetic rats was not affected by aminoguanidine, irrespective of duration or timing of therapy. This study confirms that in vivo generation of AGEs in the kidney is time dependent and closely linked to the development of experimental diabetic nephropathy. The renoprotective effects of aminoguanidine in diabetes appear to be related to the duration but not to the timing of treatment.

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Angiotensin-converting enzyme (ACE) activity and vascular mass are both increased in the mesenteric arteries of diabetic rats. As vascular hypertrophy may result from smooth muscle growth following increased formation of angiotensin II, we have examined the histological nature of the increase in mesenteric arterial mass and the role of elevated ACE activity in diabetic vascular hypertrophy by administration of an ACE inhibitor (perindopril). Cross-sectional area of the media was measured in perfusion-fixed mesenteric vessels of diabetic rats 3 weeks after streptozotocin injection. The media was significantly larger (63%) in mesenteric vessels of diabetic rats compared to age-matched control animals. Medial hypertrophy in these vessels was not associated with increased blood pressure or plasma renin activity but there was evidence for increased hemodynamic load due to hyperphagia and intestinal enlargement. Increased mesenteric ACE activity was involved in this process as there was significant inhibition of medial hypertrophy by perindopril. Other markers of cardiovascular hypertrophy such as left ventricular weight and aortic medial area were less affected, but increased in the diabetic group when corrected for significant body weight effects, consistent with a systemic influence of diabetes on cardiovascular mass. These data provide new insights into the mechanisms of vascular complications of diabetes and may have implications for the use of ACE inhibitors in preventing or arresting diabetes-associated vascular pathology.

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1. The effects of a high cholesterol diet on urinary albumin excretion were examined in spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats over 36 weeks. 2. Cholesterol feeding resulted in an increase in total-cholesterol and a decrease in HDL-cholesterol without influencing triglyceride levels in both strains. 3. Urinary albumin excretion was significantly elevated in cholesterol-fed SHR and WKY rats. 4. These results suggest that hyperlipidaemia may be important in acceleration of experimental nephropathy.

Experimental studies have indicated that angiotensin converting enzyme (ACE) inhibitors have multiple actions on the kidney and blood vessels which include both haemodynamic and antitrophic effects. Inhibition of angiotensin II and potentiation of bradykinin have both been postulated to be major mechanisms in mediating the effects of ACE inhibitors. Clinical studies have indicated that these agents postpone end-stage renal failure in macroproteinuric patients with insulin-dependent diabetes mellitus (IDDM). Indeed, these drugs are useful in both hypertensive and normotensive diabetic patients with macroproteinuria. In IDDM patients with microalbuminuria, ACE inhibitors have been shown to decrease albuminuria and to retard the development of overt renal disease. The role of these agents in patients with non-insulin-dependent diabetes mellitus (NIDDM) and early or overt renal disease remains to be clearly delineated. However, preliminary studies suggest a similar beneficial renoprotective effect of ACE inhibitors in NIDDM. It should be appreciated that the presence of micro- or macroproteinuria in NIDDM is a predictor of cardiovascular rather than renal morbidity and mortality. The possibility of cardiovascular protection, in addition to renal protection, being conferred by these drugs needs to be considered in both IDDM and NIDDM, although this issue has not been evaluated in detail.