Mechanisms, Significance and Treatment of Vascular Dysfunction in Type 2 Diabetes Mellitus

Effect of simvastatin on high glucose- and angiotensin II-induced activation of the JAK/STAT pathway in mesangial cells

In the current study, we investigated the effect of simvastatin on the ability of high glucose (HG) and ANG II to activate the JAK2-STAT signaling cascade and induce glomerular mesangial cell (GMC) growth. We found that pretreatment with simvastatin significantly inhibited HG- and ANG II-induced collagen IV production, JAK2 activation, and phosphorylation of STAT1 and STAT3 in GMC. We also found that the activation of JAK2 by HG and ANG II was dependent on the Rho family of GTPases. Consistent with these in vitro results, both albumin protein excretion and phosphorylation of JAK2, STAT1, and STAT3 were attenuated in renal glomeruli by administration of simvastatin in a streptozotocin-induced rat model of HG diabetes. This study demonstrates that simvastatin blocks ANG II-induced activation of the JAK/STAT pathway in the diabetic environment, in vitro and in vivo, and, thereby, provides new insights into the molecular mechanisms underlying early diabetic nephropathy.

A novel complex of arginine-silicate improves micro- and macrovascular function and inhibits glomerular sclerosis in insulin-resistant JCR:LA-cp rats

AIMS/HYPOTHESIS

The metabolic syndrome, with associated vasculopathy, is a major cause of cardiovascular disease and nephropathy. Impaired nitric oxide (NO) metabolism and endothelial function is an important component of the disease process. Increasing the availability of arginine, the precursor of NO, might enhance vascular function and protect against end-stage disease.

MATERIALS AND METHODS

Insulin-resistant JCR:LA-cp rats were treated with arginine-silicate-inositol complex or arginine-HCl at 1.0 g kg(-1) day(-1) (expressed as arginine-HCl) from 8 to 13 weeks of age. The contractile/relaxant function of thoracic aortae and coronary arteries was assessed in vitro. Kidneys were assessed for severity of glomerular sclerosis.

RESULTS

Arginine-silicate complex, but not arginine-HCl, normalised the hypercontractile response of the aorta to phenylephrine via an NO-dependent pathway. Coronary artery function, as indicated by reactive hyperaemia to warm ischaemia, was enhanced by both arginine compounds. In addition, the arginine-silicate complex increased coronary vasodilatation in response to bradykinin. Glomerular sclerosis was significantly reduced in rats treated with the arginine-silicate complex.

CONCLUSIONS/INTERPRETATION

Treatment with exogenous arginine, in an efficiently absorbed form, improves vascular function and reduces nephropathy in an animal model of insulin resistance and cardiovascular disease, via mechanism(s) independent of insulin concentration. Enhancement of NO metabolism through increased availability of the precursor arginine appears to offer protection against micro- and macrovascular disease associated with the metabolic syndrome and insulin resistance.

Osteoporosis and atherosclerosis: biological linkages and the emergence of dual-purpose therapies

Osteoporosis and atherosclerosis are both widely prevalent in an ageing population, and induce serious morbidities and death. There is growing evidence that in addition to their relationship to ageing, osteoporosis and atherosclerosis are also linked by biological associations. This article reviews their clinical interrelations, discusses the basic biology of bone and the arterial wall, and presents five examples that illustrate their biological linkages. Current therapeutic approaches emerging from these linkages, including statins, bisphosphonates, and the thiazolidinediones, have dual effects on bone and the vasculature. Additional therapies derived from experimental studies that enhance bone density and reduce atherogenesis hold further promise to diminish the morbidity and mortality of osteoporosis and atherosclerosis, with attendant benefits to society.