Arginase induction and activation during ischemia and reperfusion and functional consequences for the heart

Protein kinase C (PKC) has been a tantalizing target for drug discovery ever since it was first identified as the receptor for the tumour promoter phorbol ester in 1982. Although initial therapeutic efforts focused on cancer, additional indications--including diabetic complications, heart failure, myocardial infarction, pain and bipolar disorder--were targeted as researchers developed a better understanding of the roles of eight conventional and novel PKC isozymes in health and disease. Unfortunately, both academic and pharmaceutical efforts have yet to result in the approval of a single new drug that specifically targets PKC. Why does PKC remain an elusive drug target? This Review provides a short account of some of the efforts, challenges and opportunities in developing PKC modulators to address unmet clinical needs.

The amino acid L-arginine is a substrate for nitric oxide synthase and is increasingly used as a health supplement. Prior studies suggest that L-arginine has the potential to reduce vascular stiffness. To determine whether the addition of L-arginine to standard postinfarction therapy reduces vascular stiffness and improves ejection fraction over 6-month follow-up in patients following acute ST-segment elevation myocardial infarction. Single-center, randomized, double-blind, placebo-controlled trial with enrollment from February 2002 to June 2004. A total of 153 patients following a first ST-segment elevation myocardial infarction were enrolled; 77 patients were 60 years or older. Patients were randomly assigned to receive L-arginine (goal dose of 3 g 3 times a day) or matching placebo for 6 months. Change in gated blood pool-derived ejection fraction over 6 months in patients 60 years or older randomized to receive L-arginine compared with those assigned to receive placebo. Secondary outcomes included change in ejection fraction in all patients enrolled, change in noninvasive measures of vascular stiffness, and clinical events. Baseline characteristics, vascular stiffness measurements, and left ventricular function were similar between participants randomized to receive placebo or L-arginine. The mean (SD) age was 60 (13.6) years; of the participants, 104 (68%) were men. There was no significant change from baseline to 6 months in the vascular stiffness measurements or left ventricular ejection fraction in either of the 2 groups, including those 60 years or older and the entire study group. However, 6 participants (8.6%) in the L-arginine group died during the 6-month study period vs none in the placebo group (P = .01). Because of the safety concerns, the data and safety monitoring committee closed enrollment. L-arginine, when added to standard postinfarction therapies, does not improve vascular stiffness measurements or ejection fraction and may be associated with higher postinfarction mortality. L-arginine should not be recommended following acute myocardial infarction. Clinical Trial Registration ClinicalTrials.gov, NCT00051376.

Oxidized low-density lipoproteins increase arginase activity and reciprocally decrease endothelial NO in human aortic endothelial cells. Here, we demonstrate that vascular endothelial arginase activity is increased in atherogenic-prone apolipoprotein E-null (ApoE(-/-)) and wild-type mice fed a high cholesterol diet. In ApoE(-/-) mice, selective arginase II inhibition or deletion of the arginase II gene (Arg II(-/-) mice) prevents high-cholesterol diet-dependent decreases in vascular NO production, decreases endothelial reactive oxygen species production, restores endothelial function, and prevents oxidized low-density lipoprotein-dependent increases in vascular stiffness. Furthermore, arginase inhibition significantly decreases plaque burden. These data indicate that arginase II plays a critical role in the pathophysiology of cholesterol-mediated endothelial dysfunction and represents a novel target for therapy in atherosclerosis.