Effects on protein kinase C-β inhibition on glomerular vascular endothelial growth factor expression and endothelial cells in advanced experimental diabetic nephropathy

Abstract

Ruboxistaurin is an inhibitor of the beta isoform of protein kinase C (PKC-beta) that reduces the actions of vascular endothelial growth factor (VEGF) and attenuates the progression of diabetic retinopathy. In the glomerulus VEGF is constitutively expressed where it likely has a role in maintaining endothelial cell integrity, particularly in disease states. Given its potential use in diabetic nephropathy, we sought to determine the effects of PKC-beta inhibition on VEGF and glomerular endothelial cells in experimental diabetic nephropathy. Studies were conducted in (mRen-2)27 rat, a transgenic rodent with hypertension and an enhanced renin-angiotensin system that following induction of diabetes with streptozotocin develops many of the features of diabetic nephropathy. Moreover, to mimic the clinical context, the effects of PKC-beta inhibition were examined both with and without concomitant angiotensin-converting enzyme (ACE) inhibitor therapy. Diabetic Ren-2 rats were randomized to receive either vehicle, the ACE inhibitor, perindopril (0.2 mg/l in drinking water), ruboxistaurin (10 mg.kg(-1).day(-1), admixed in chow), or their combination and studied for 12 wk. Diabetic Ren-2 rats displayed glomerular endothelial cell loss in association with overexpression of VEGF mRNA. Both cell loss and VEGF overexpression were attenuated by the administration of either perindopril or ruboxistaurin, as single agent treatments with their combination providing additional, incremental improvements, reducing these manifestations of injury down to levels seen in nondiabetic, normotensive, nontransgenic animals. Combination therapy was also associated with additional improvements in albuminuria and glomerulosclerosis.

PKC-β1 Mediates Glucose-Induced Akt Activation and TGF-β1 Upregulation in Mesangial Cells

“…A group of diabetic rats was treated with the PKC-␤ inhibitor ruboxistaurin (LY333531) as described previously. 28 This model, in which overexpression of the mouse renin gene leads to hypertension, has been shown to develop renal lesions similar to those observed in human diabetic nephropathy as early as 12 wk after STZ injection. 29 Ruboxistaurin prevents ATP binding to the active site of PKC-␤, thereby inhibiting its ability to phosphorylate substrates and functioning as a specific PKC-␤ inhibitor.…”

“…Diabetic rats had an average plasma glucose level Ͼ25 mmol/L, unaffected by treatment with ruboxistaurin (control 5.78 Ϯ 0.51 mmol/L, STZ 25.7 Ϯ 1.94 mmol/L, STZϩRub 28.5 Ϯ 0.84 mmol/L; P Ͻ 0.01 for STZϩRub versus Con). 28 Figure 9A shows that pAktS473 was increased in the cortex of diabetic rats and that this was inhibited by ruboxistaurin. Data are quantified in Figure 9B.…”

“…28 Briefly, diabetes was induced in female homozygous (mRen-2)27 rats with 55 mg/kg STZ (Sigma) by tail-vein injection. Control rats received 0.1 M citrate buffer (pH 4.5).…”

The protective effect of the RAS inhibitor on diabetic patients with nephropathy in the context of VEGF suppression

“…In rats with streptozotocin-induced diabetes, treatment with RAS inhibitor decreased renal VEGF mRNA and simultaneously reduced albuminuria [9,10] . However, in this study, the mechanism of uVEGF decrease was unclear.…”

“…Recently, it was reported that VEGF overexpression in diabetic rats [9,10] and in cultured human proximal tubule cells [11] could be attenuated by the administration of renin angiotensin system (RAS) inhibitor. The use of RAS inhibitor led to a decreased incidence of albuminuria in the diabetic rats.…”