Serelaxin reduces oxidative stress and asymmetric dimethylarginine in angiotensin II-induced hypertension.

Recent findings suggest the therapeutic action of relaxin during hypertension is dependent on nitric oxide synthase (NOS) activation; however, the mechanisms underlying the beneficial effects of relaxin on the NOS system have not been fully elucidated. We hypothesized that the protective effects of relaxin include reducing both oxidative stress and the endogenous NOS inhibitor asymmetric dimethylarginine (ADMA). We examined the effect of Serelaxin [human recombinant relaxin-2 (RLX)] in male Sprague-Dawley rats given high-dose angiotensin (ANG) II (400 ng·kg(-1)·min(-1) sc) for 6 wk or shams. RLX was administered (4 µg/h sc) to half of the rats in each group after 2 wk of ANG II for the remaining 4 wk. ANG II induced hypertension and proteinuria, reduced NO oxidation products (NOx), and increased oxidative stress (NADPH oxidase activity, thiobarbituric acid-reactive substances, and 8-isoprostane excretion) and plasma ADMA. While RLX had no effect on sham rats, RLX attenuated the ANG II-dependent hypertension (165 ± 5 vs. 135 ± 13 mmHg, P < 0.05) and proteinuria at 6 wk (62 ± 6 vs. 41 ± 4 mg·day(-1)·100 g(-1), P < 0.05) and normalized oxidative stress and circulating ADMA, in association with restored NOx excretion and kidney cortex NOx. We found that RLX had no impact on the ADMA-regulatory enzymes protein arginine methyltransferase and dimethylarginine-dimethylaminohydrolase (DDAH). Furthermore, RLX treatment did not increase DDAH activity in kidney cortex or liver. These data suggest that benefits of RLX treatment include reduced ADMA levels and increased NO bioavailability, possibly due to its antioxidant effects.

Nitric oxide synthase derangements and hypertension in kidney disease.

PURPOSE OF REVIEW: Nitric oxide deficiency occurs by multiple mechanisms and contributes to the pathogenesis of progression of chronic kidney disease (CKD) and its cardiovascular complications. This article concentrates on recent developments on the regulation of the endogenous nitric oxide synthase (NOS) inhibitor asymmetric dimethylarginine (ADMA) in CKD and on the importance of the nitric oxide synthases in kidney disease progression, particularly in diabetic nephropathy. RECENT FINDINGS: The increased plasma ADMA seen in renal disease is generally predictive of severity of CKD progression and cardiovascular risk. However, some assumptions about the control of ADMA have been challenged: the primacy of the kidney as a metabolic organ for plasma ADMA regulation has come under scrutiny and the relative importance of the two isoforms of the ADMA-metabolizing enzymes dimethylarginine dimethylaminohydrolases (DDAHs) is being re-evaluated. Alterations in NOS also contribute to CKD progression with the endothelial isoform playing a major role in diabetic nephropathy. SUMMARY: Improving our understanding of ADMA regulation is important since pharmacologic targeting of DDAH is underway. The major role of endothelial NOS-derived nitric oxide in diabetic nephropathy should lead to novel therapies. The beneficial actions of dietary nitrate supplementation on blood pressure and kidney disease are of considerable clinical relevance.

Arginine and asymmetric dimethylarginine in puromycin aminonucleoside-induced chronic kidney disease in the rat.

BACKGROUND/AIMS: Reduced renal L-arginine (L-Arg) synthesis/transport, induction of arginases and increased endogenous NOS inhibitor, asymmetric dimethylarginine (ADMA) will inhibit NO production. This study investigated pathways of L-Arg synthesis/uptake/utilization, ADMA degradation and oxidant/antioxidants in puromycin aminonucleoside (PAN) chronic kidney disease (CKD). METHODS: Rats were given low- (LD) or high-dose (HD) PAN and followed for 11 weeks for proteinuria. BP was measured and blood and tissues were harvested and analyzed for abundance of argininosuccinate synthase (ASS) and lyase (ASL), arginase, cationic amino acid transporter (CAT1) and dimethylargininedimethylaminohydrolase (DDAH) in kidney, cortex, aorta and liver. Arginase and DDAH activity, plasma L-Arg and ADMA, renal pathology and creatinine clearances were also measured. RESULTS: PAN caused dose-dependent kidney damage and hypertension and creatinine clearance fell in HD-PAN. Renal ASS fell in HD-PAN, renal cortex and aortic ASL and membrane CAT1 fell in both PAN groups. There was no activation of renal arginase, but aortic arginase increased in LD-PAN. Renal DDAH activity fell moderately in LD-PAN and markedly in HD-PAN where hepatic DDAH activity also fell. Plasma L-Arg was unchanged while ADMA rose moderately and dose-dependently with PAN. There were several indices of oxidative stress which was most prominent in HD-PAN. CONCLUSION: Reduction in renal ASS/ASL and loss of renal cortex CAT1 compromises renal L-Arg synthesis and release. Loss of aortic CAT1 impairs L-Arg uptake. Increased plasma ADMA was associated with progressive loss of renal DDAH activity. However, loss of renal clearance and falls in hepatic DDAH activity in HD-PAN did not have additive effects on plasma ADMA.

Hyperbaric oxygen therapy mediates increased nitric oxide production associated with wound healing: a preliminary study.

OBJECTIVE: The objective of this preliminary study was to document general somatic and wound nitric oxide (NO) levels during and after hyperbaric oxygen therapy (HBOT). DESIGN: The study evaluated 6 chronic wound patients that responded favorably to HBOT treatment (20 treatments; 2.0 atmosphere absolute [ATA] x 90 minutes). Successful HBOT was associated with increased wound granulation tissue formation and significantly improved wound closure. Wound fluid and fasting plasma samples were obtained for measurement of nitrate and nitrite (NOx), the stable oxidation products of NO; plasma L-arginine (L-Arg); and asymmetric dimethylarginine (ADMA). NOx measurements were obtained before treatment (baseline), after 10 and 20 treatments, and at 1 and 4 weeks after therapy. RESULTS: Wound fluid NOx levels tended to increase during treatments, were significantly elevated at 1 and 4 weeks after therapy, and correlated with reductions in wound area. Plasma L-Arg and ADMA were unchanged during and after HBOT. CONCLUSION: This preliminary study documents a significant increase in local wound NO levels (by NOx measurements) after successful HBOT and suggests that this mechanism may be an important factor in promoting enhanced wound healing and wound closure associated with this therapy.

Intravenous bilirubin provides incomplete protection against renal ischemia-reperfusion injury in vivo.

Exogenous bilirubin (BR) substitutes for the protective effects of heme oxygenase (HO) in several organ systems. Our objective was to investigate the effects of exogenous BR in an in vivo model of ischemia-reperfusion injury (IRI) in the rat kidney. Four groups of male Sprague-Dawley rats were anesthetized using isoflurane in oxygen and treated with 1) 5 mg/kg intravenous (iv) BR, 1 h before ischemia and 6-h reperfusion; 2) vehicle 1 h before ischemia and 6-h reperfusion; 3) 20 mg/kg iv BR, 1 h before and during ischemia; and 4) vehicle 1 h before and during ischemia. Bilateral renal clamping (30 min) was followed by 6-h reperfusion. Infusion of 5 mg/kg iv BR achieved target levels in the serum at 6 h postischemia (31 +/- 9 micromol/l). Infusion of 20 mg/kg BR reached 50 +/- 22 micromol/l at the end of ischemia, and a significant improvement was seen in serum creatinine at 6 h (1.07 +/- 28 vs. 1.38 +/- 0.18 mg/dl, P = 0.043). Glomerular filtration rate, estimated renal plasma flow, fractional excretion of electrolytes, and renal vascular resistance were not significantly improved in BR-treated groups. Histological grading demonstrated a trend toward preservation of cortical proximal tubules in rats receiving 20 mg/kg iv BR compared with control; however, neither BR dose provided protection against injury to the renal medulla. At the doses administered, iv BR did not provide complete protection against IRI in vivo. Combined supplementation of both BR and carbon monoxide may be required to preserve renal blood flow and adequately substitute for the protective effects of HO in vivo.

Arginine, arginine analogs and nitric oxide production in chronic kidney disease.

Nitric oxide (NO) production is reduced in renal disease, partially due to decreased endothelial NO production. Evidence indicates that NO deficiency contributes to cardiovascular events and progression of kidney damage. Two possible causes of NO deficiency are substrate (L-arginine) limitation and increased levels of circulating endogenous inhibitors of NO synthase (particularly asymmetric dimethylarginine [ADMA]). Decreased L-arginine availability in chronic kidney disease (CKD) is due to perturbed renal biosynthesis of this amino acid. In addition, inhibition of transport of L-arginine into endothelial cells and shunting of L-arginine into other metabolic pathways (e.g. those involving arginase) might also decrease availability. Elevated plasma and tissue levels of ADMA in CKD are functions of both reduced renal excretion and reduced catabolism by dimethylarginine dimethylaminohydrolase (DDAH). The latter might be associated with loss-of-function polymorphisms of a DDAH gene, functional inhibition of the enzyme by oxidative stress in CKD and end-stage renal disease, or both. These findings provide the rationale for novel therapies, including supplementation of dietary L-arginine or its precursor L-citrulline, inhibition of non-NO-producing pathways of L-arginine utilization, or both. Because an increase in ADMA has emerged as a major independent risk factor in end-stage renal disease (and probably also in CKD), lowering ADMA concentration is a major therapeutic goal; interventions that enhance the activity of the ADMA-hydrolyzing enzyme DDAH are under investigation.

Resistance to renal damage by chronic nitric oxide synthase inhibition in the Wistar-Furth rat.

Chronic nitric oxide synthase inhibition (NOSI) causes chronic kidney disease (CKD) in the Sprague Dawley (SD) rat. We previously showed that the Wistar-Furth (WF) rats are resistant to several models of CKD and maintain renal nitric oxide (NO) production compared with SD rats, whereas low-dose NOSI caused progression of CKD in WF rats. Here, we evaluate the impact of high-dose chronic NOSI in WF and SD rats, as well as intrarenal responses to an acute pressor dose of NOSI in the normal WF. Rats were given N(G)-nitro-l-arginine methyl ester (l-NAME) (150 and 300 mg/l for 6-10 wk) in the drinking water after an initial bolus tail vein injection. Both strains showed significant reductions in total NO production with chronic l-NAME. SD given 150 mg/l l-NAME for 6 wk developed proteinuria and renal injury, whereas WF rats receiving 150 mg/l l-NAME for 6-10 wk or 300 mg/l for 6 wk developed no proteinuria and minimal renal injury. Blood pressure was significantly elevated with chronic NOSI in both strains but was higher in the SD rat. There was little impact on renal nitric oxide synthase expression with l-NAME, except that cortical endothelial nitric oxide synthase abundance increased in WF after 6 wk (150 mg/l). Micropuncture experiments with acute pressor NOSI resulted in similar increases in systemic blood pressure in SD and WF rats, whereas WF rats showed a much smaller increment in glomerular blood pressure compared with SD rats. In conclusion, WF rats do not develop renal injury after chronic NOSI at, or above, a dose that causes significant injury in the SD rat. This protection may be associated with protection from glomerular hypertension.