The arginase enzyme developed in early life forms and was maintained during evolution. As the last step in the urea cycle, arginase cleaves l-arginine to form urea and l-ornithine. The urea cycle provides protection against excess ammonia, while l-ornithine is needed for cell proliferation, collagen formation, and other physiological functions. In mammals, increases in arginase activity have been linked to dysfunction and pathologies of the cardiovascular system, kidney, and central nervous system and also to dysfunction of the immune system and cancer. Two important aspects of the excessive activity of arginase may be involved in diseases. First, overly active arginase can reduce the supply of l-arginine needed for the production of nitric oxide (NO) by NO synthase. Second, too much l-ornithine can lead to structural problems in the vasculature, neuronal toxicity, and abnormal growth of tumor cells. Seminal studies have demonstrated that increased formation of reactive oxygen species and key inflammatory mediators promote this pathological elevation of arginase activity. Here, we review the involvement of arginase in diseases affecting the cardiovascular, renal, and central nervous system and cancer and discuss the value of therapies targeting the elevated activity of arginase.

BACKGROUND AND PURPOSENO produced by endothelial NOS is needed for normal vascular function. During diabetes, aging and hypertension, elevated levels of arginase can compete with NOS for available L-arginine, reducing NO and increasing superoxide (O2 .-) production via NOS uncoupling. Elevated O2 .-combines with NO to form peroxynitrite (ONOO -), further reducing NO. Oxidative species increase arginase activity, but the mechanism(s) involved are not known. Our study determined the mechanism involved in peroxynitrite and hydrogen peroxide-induced enhancement in endothelial arginase activity. We hypothesized that oxidative species increase arginase activity through PKC-activated RhoA/Rho kinase (ROCK) pathway. EXPERIMENTAL APPROACHArginase activity/expression was analysed in bovine aortic endothelial cells (BAEC) treated with an ONOO -generator (SIN-1) or H2O2. Pretreatment with inhibitors of Rho kinase (Y-27632) or PKC (Gö6976) was used to investigate the mechanism involved in arginase activation. KEY RESULTSExposure to SIN-1 (25 mM, 24 h) or H2O2 (25 mM, 8 h) increased arginase I expression and arginase activity (35% and 50%, respectively), which was prevented by ROCK inhibitor, Y-27632, PKC inhibitor, Gö6976 or siRNA to p115-Rho GEF. There was an early activation of p115-Rho GEF (SIN-1, 2 h; H2O2, 1 h) and Rho A (SIN-1, 4 h; H2O2, 1 h) that was prevented by using the PKC inhibitor. Exposure to SIN-1 and H2O2 also reduced NOS activity, which was blocked by pretreatment with p115-RhoGEF siRNA. CONCLUSIONS AND IMPLICATIONSOur data indicate that the oxidative species ONOO -and H2O2 increase arginase activity/expression through PKC-mediated activation of RhoA/Rho kinase pathway.

Gold nanorods have promising applications in drug delivery and cancer treatment and are generally administered via direct injection into circulation. Thus it is necessary to evaluation their potential adverse effects on blood vessels. Herein we use gold nanorods with various surface modifications to evaluate the toxicity and cellular uptake of gold nanorods into vascular endothelial and smooth muscle cells of isolated rat aortic rings. Surfactant-capped gold nanorods (GNRs) were synthesized and either: 1) coated with polyelectrolytes (PE) in order to prepare PE-GNRs; or 2) modified with thiolated polyethylene glycol (PEG) in order to prepare PEG-GNRs. Using toxicity assays, small vessel myography, fluorescence microscopy and electron microscopy, we show that therapeutic concentrations of PE-GNRs but not PEG-GNRs are toxic to the vascular endothelium, which leads to impaired relaxation function of aortic rings. However, no toxicity to smooth muscles was observed. Moreover, electron microscopy analysis confirmed the cellular uptake of PE-GNRs but not PEG-GNRs into the endothelium of exposed aortic rings. The difference in toxicity and cellular uptake for PE-GNRs versus PEG-GNRs is explained and linked to free surfactant molecules and protein adsorption, respectively. Our results indicate that toxicity and cellular uptake in vascular endothelium in blood vessels are potential adverse effects of systemically administered gold nanorod solutions, which can be prevented by appropriate surface functionalization.