Effects of angiotensin type 1 receptor blockade on arginine and ADMA synthesis and metabolic pathways in fawn-hooded hypertensive rats

Overexpression of dimethylarginine dimethylaminohydrolase 1 protects from angiotensin II-induced cardiac hypertrophy and vascular remodeling

Cardiovascular complications are the leading cause of death, and elevated levels of asymmetric dimethyarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, are implicated in their pathophysiology. We investigated the role of dimethylarginine dimethylaminohydrolase 1 (DDAH1), an enzyme hydrolyzing ADMA, in prevention of cardiovascular remodeling during hypertension. We hypothesized that the animals overexpressing DDAH1 will be protected from angiotensin II (ANG II)-induced end organ damage. Angiotensin II (ANG II) was infused in two doses: 0.75 and 1.5 mg/kg/day in DDAH1 transgenic mice (DDAH1 TG) and wild-type (WT) littermates for 2 or 4 wk. Echocardiography was performed in the first and fourth weeks of the infusion, systolic blood pressure (SBP) was measured weekly, and cardiac hypertrophy and vascular remodeling was assessed by histology. Increase in SBP after 1 wk of ANG II infusion was not different between the groups, whereas TG mice had lower SBP at later time points. TG mice were protected from cardiovascular remodeling after 2 wk of ANG II infusion in the high dose and after 4 wk in the moderate dose. TG mice had higher left ventricular lumen-to-wall ratio, lower cardiomyocyte cross-sectional area, and less interstitial fibrosis compared with WT controls. In aorta, TG mice had less adventitial fibrosis, lower medial thickness with preserved elastin content, lower counts of inflammatory cells, lower levels of active matrix metalloproteinase-2, and showed better endothelium-dependent relaxation. We demonstrated that overexpression of DDAH1 protects from ANG II-induced cardiovascular remodeling and progression of hypertension by preserving endothelial function and limiting inflammation.NEW & NOTEWORTHY We showed that overexpression of dimethylarginine dimethylaminohydrolase 1 (DDAH1) protects from angiotensin II-induced cardiovascular damage, progression of hypertension, and adverse vascular remodeling in vivo. This protective effect is associated with decreased levels of asymmetric dimethylarginine, preservation of endothelial function, inhibition of cardiovascular inflammation, and lower activity of matrix metalloproteinase-2. Our findings are highly clinically relevant, because they suggest that upregulation of DDAH1 might be a promising therapeutic approach against angiotensin II-induced end organ damage.

Renoprotective effects of melatonin in young spontaneously hypertensive rats with L-NAME

BACKGROUND

Nitric oxide (NO) deficiency occurs in humans and animals with hypertension and chronic kidney disease (CKD). An inhibitor of NO synthase, N(G)-nitro-l-arginine methyl ester (L-NAME) exacerbates kidney damage in the adult spontaneously hypertensive rat (SHR). We examined whether L-NAME exacerbated hypertensive nephrosclerosis in young SHRs and whether melatonin protects SHRs against kidney damage by restoration of the asymmetric dimethylarginine (ADMA)-NO pathway.

METHODS

Rats aged 4 weeks were randomly assigned into three groups (n = 10 for each group): Group 1 (control), SHRs without treatment; Group 2 (L-NAME), SHRs received L-NAME (80 mg/L) in drinking water; and Group 3 (L-NAME + melatonin), SHRs received L-NAME (80 mg/L) and 0.01% melatonin in drinking water. All rats were sacrificed at 10 weeks of age.

RESULTS

L-NAME exacerbates the elevation of blood pressure, renal dysfunction, and glomerular sclerosis in young SHRs. L-NAME induced an increase of ADMA and a decrease of arginine-to-ADMA ratio in the SHR kidney. Melatonin therapy prevented L-NAME-exacerbated hypertension and nephrosclerosis in young SHRs. In addition, melatonin restored L-NAME-induced reduction of dimethylarginine dimethylaminohydrolase (DDAH; ADMA-metabolizing enzymes) activity in the SHR kidney. Next, melatonin decreased renal ADMA concentrations, increased renal arginine-to-ADMA ratio, and restored NO production in L-NAME-treated young SHRs. Moreover, melatonin reduced the degree of oxidative damaged DNA product, 8-hydroxydeoxyguanosine immunostaining in L-NAME-treated SHR kidney.

CONCLUSION

Our results indicated that L-NAME/SHR is a useful model for hypertensive nephrosclerosis in young rats. The blood pressure-lowering and renoprotective effects of melatonin is due to increases of DDAH activity, decreases of ADMA, and reduction of oxidative stress in L-NAME-treated SHR kidney. Specific therapy targeting the DDAH-ADMA pathway may be a promising approach to slowing chronic kidney disease progression in children.

Influence of the AT(2) receptor on the L-arginine-nitric oxide pathway and effects of (-)-epicatechin on HUVECs from women with preeclampsia

Pregnancy is a state of vasodilation mediated by nitric oxide (NO). This vasodilation is impaired in women with preeclampsia, and an alteration in the L-arginine-NO pathway may be a causal factor. The production of NO and arginase activity were investigated in plasma and human umbilical vein endothelial cells (HUVECs) from women with preeclampsia, which were associated with arginase II, eNOS, caveolin, angiotensin 1 and 2 receptor expression (AT1R and AT2R, respectively). The effect of (-)-epicatechin on arginase activity and production of anion superoxide in HUVEC also were investigated. Healthy volunteer non-pregnant (HV), normal pregnant (NP) and preeclamptic (PE) women were recruited for this study. Higher values of nitrite/nitrate (NO(2)/NO(3)) were detected in the plasma from PE women as opposed to HV and NP. Lower arginase activity in PE versus HV or NP women was observed. HUVECs from PE women showed lower values of NO(2)/NO(3), higher activity of arginase and higher expression of AT(1)R and AT(2)R than HUVECS from NP women. Interestingly, arginase activity was associated with AT(2)R stimulation; indeed this activity and the high NADPH (nicotinamide adenine dinucleotide phosphate) oxidase activity in HUVECs from PE women can uncouple the production or inactivation of NO. However, we demonstrated that (-)-epicatechin could lead to a decrease in the activity of both enzymes.

Aliskiren prevents hypertension and reduces asymmetric dimethylarginine in young spontaneously hypertensive rats

Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of NOS, decreases NO synthesis. Plasma ADMA concentrations increase markedly in hypertension. We tested whether the development of hypertension and the increases in ADMA in spontaneously hypertensive rats (SHR) are prevented by aliskiren, a renin inhibitor. Male SHRs and normotensive Wistar Kyoto (WKY) control rats, aged 4 weeks (pre-hypertensive stage), were assigned to 4 groups: untreated SHRs and WKY rats, and SHRs that received oral aliskiren 10 and 30 mg/kg/day for 6 weeks. All rats were sacrificed at age 10 weeks. Blood pressure decreased at age 6, 8, and 10 weeks in SHRs that received high-dose aliskiren. Aliskiren mitigated the increases in plasma ADMA in SHRs. Renal ADMA levels were lower in SHRs that received high-dose aliskiren versus SHRs. SHRs experienced decreased plasma and kidney l-Arg-to-ADMA ratios versus control rats, which were reverted by 30 mg/kg aliskiren. Renal cortical neuronal NOS-α and -β levels increased in SHRs fed with high-dose aliskiren. Early aliskiren treatment mitigates increases in ADMA, restores l-Arg-to-ADMA ratios, enhances neuronal NOS-α, prevents decreased nNOS-β levels in the kidney-which might restore NO bioavailability and contribute to the decrease of blood pressure in young SHRs. Our findings suggest that aliskiren is a therapeutic agent for prehypertension that regulates the ADMA/NO pathway.

Angiotensin II-induced vascular endothelial dysfunction through RhoA/Rho kinase/p38 mitogen-activated protein kinase/arginase pathway

Enhanced vascular arginase activity impairs endothelium-dependent vasorelaxation by decreasing l-arginine availability to endothelial nitric oxide (NO) synthase, thereby reducing NO production. Elevated angiotensin II (ANG II) is a key component of endothelial dysfunction in many cardiovascular diseases and has been linked to elevated arginase activity. We determined signaling mechanisms by which ANG II increases endothelial arginase function. Results show that ANG II (0.1 μM, 24 h) elevates arginase activity and arginase I expression in bovine aortic endothelial cells (BAECs) and decreases NO production. These effects are prevented by the arginase inhibitor BEC (100 μM). Blockade of ANG II AT(1) receptors or transfection with small interfering RNA (siRNA) for Gα12 and Gα13 also prevents ANG II-induced elevation of arginase activity, but siRNA for Gαq does not. ANG II also elevates active RhoA levels and induces phosphorylation of p38 MAPK. Inhibitors of RhoA activation (simvastatin, 0.1 μM) or Rho kinase (ROCK) (Y-27632, 10 μM; H1152, 0.5 μM) block both ANG II-induced elevation of arginase activity and phosphorylation of p38 MAPK. Furthermore, pretreatment of BAECs with p38 inhibitor SB-202190 (2 μM) or transfection with p38 MAPK siRNA prevents ANG II-induced increased arginase activity/expression and maintains NO production. Additionally, inhibitors of p38 MAPK (SB-203580, 5 μg·kg(-1)·day(-1)) or arginase (ABH, 8 mg·kg(-1)·day(-1)) or arginase gene knockout in mice prevents ANG II-induced vascular endothelial dysfunction and associated enhancement of arginase. These results indicate that ANG II increases endothelial arginase activity/expression through Gα12/13 G proteins coupled to AT(1) receptors and subsequent activation of RhoA/ROCK/p38 MAPK pathways leading to endothelial dysfunction.