Arginase promotes endothelial dysfunction and hypertension in obese rats

Abstract

Objective: This study investigated whether arginase contributes to endothelial dysfunction and hypertension in obese rats.

Methods: Endothelial function and arginase expression were examined in skeletal muscle arterioles from lean and obese Zucker rats (ZRs). Arginase activity, arginine bioavailability, and blood pressure were measured in lean and obese animals.

Results: Arginase activity and expression was increased while global arginine bioavailability decreased in obese ZRs. Acetylcholine or luminal flow caused dilation of isolated skeletal muscle arterioles, but this was reduced or absent in vessels from obese ZRs. Treatment of arterioles with a nitric oxide synthase inhibitor blocked dilation in lean arterioles and eliminated differences among lean and obese vessels. In contrast, arginase inhibitors or l-arginine enhanced vasodilation in obese ZRs and abolished differences between lean and obese animals, while d-arginine had no effect. Finally, mean arterial blood pressure was significantly increased in obese ZRs. However, administration of l-arginine or arginase inhibitors lowered blood pressure in obese but not lean animals, and this was associated with an improvement in systemic arginine bioavailability.

Conclusions: Arginase promotes endothelial dysfunction and hypertension in obesity by reducing arginine bioavailability. Therapeutic approaches targeting arginase represent a promising approach in treating obesity-related vascular disease.

Figure 1

Obesity stimulates vascular arginase activity and expression, and plasma arginase activity. Obesity increases arginase activity in the aorta (A), arginase (Arg) I and II, but not endothelial nitric oxide synthase (eNOS), mRNA expression in gracilis muscle arterioles (B), and arginase activity in the plasma (C). Results are means ± SEM (n=4–5). ^*Statistically significant effect of obesity.

Figure 2

Obesity-induced impairment in acetylcholine (Ach)-mediated vasodilation is corrected by arginase inhibition or L-arginine administration. Ach-mediated increases in luminal diameter of gracilis muscle arterioles are reduced in obese relative to lean Zucker rats (ZR) and this is reversed by S-(2-Boronoethyl)-L-cysteine (BEC; 100μM) or N^ω-hydroxy-nor-L-arginine (OHNA; 100μM) (A). N^ω-nitro-L-arginine methyl ester (L-NAME; 1 mM) attenuates Ach-mediated vasodilation (B). L-Arginine (1 mM) (C), but not D-arginine (1 mM) (D) restores Ach-mediated vasodilation in obese ZR. Results are means ± SEM (n=4–6). ^*Statistically significant effect of obesity.

Figure 3

Obesity-induced impairment in flow-mediated vasodilation is corrected by arginase inhibition or L-arginine administration. Flow-mediated increases in luminal diameter of gracilis muscle arterioles are reduced in obese relative to lean Zucker rats (ZR) and this is reversed by S-(2-boronoethyl)-L-cysteine (BEC;100μM) or N^ω-hydroxy-nor-L-arginine (OHNA;100μM) (A). N^ω-nitro-L-arginine methyl ester (L-NAME; 1 mM) blocks flow-mediated vasodilation (B). L-arginine (1 mM) (C), but not D-arginine (1 mM) (D) restores flow-mediated vasodilation in obese ZR. Results are means ± SEM (n=4–6). ^*Statistically significant effect of obesity.

Figure 4

Obesity inhibits plasma arginine concentration and global arginine bioavailability. Plasma amino acid concentrations in lean and obese Zukcer rats (ZR) (A). Global arginine bioavailability is improved by dietary L-arginine supplementation (L-Arg; 1% in drinking water for 6 days) or arginase inhibition (intraperitoneal administration of S-(2-boronoethyl)-L-cysteine (BEC; 55.6μg/h for 6 days) (B). Results ± SEM (n=5–8). ^*Statistically significant effect of obesity. ^†Statistically significant effect of L-arginine or BEC. Arg, arginine; Orn, ornithine; Cit, citrulline; Leu, leucine, Ile, isoleucine; Val, valine; Phe, phenylalanine; Tyr, tyrosine; His, histidine; Lys, lysine; Met, methionine; Thr, threonine.

Figure 5

Obesity-induced hypertension is reversed by arginase inhibition or L-arginine administration. Mean arterial blood pressure (BP) is reduced in obese, but not lean, Zucker rats (ZR) by dietary L-arginine supplementation (L-Arg; 1% in drinking water for 6 days) (A and B) or arginase inhibition (intraperitoneal administration of S-(2-boronoethyl)-L-cysteine (BEC;55.6μg/h for 6 days) (C and D). N^ω-hydroxy-nor-L-arginine (OHNA;50 mg/kg, ip, daily for 6 days) reduces mean arterial BP in obese, but not lean, ZR (E). Results are means ± SEM (n=5–6). ^*Statistically significant effect of obesity.