Neonatal sympathectomy reduces NADPH oxidase activity and vascular resistance in spontaneously hypertensive rat kidneys

[The functions of arterial sympathetic innervation: from development to pathology]

Arterial sympathetic innervation (ASI) is a complex biological process requiring a fine axonal guidance by arteries. Its physiological impact has remained unknown for decades but recently started to be better understood and recognized. ASI is a key element of the adaptive response of the cardiovascular system to challenging situations (exposure to cold, exercise…) as ASI controls the diameter of resistance arteries, thus blood supply to organs and systemic arterial blood pressure via arterial tone modulation. Defaults in ASI can lead to diseases, acting as a main cause or as an aggravating factor. Its impact is actively studied in cardiovascular diseases representing major public health issues, like hypertension, but ASI could also play a role in aging and many more pathological processes including cancer.

A synthetic peptide from transforming growth factor-β₁ type III receptor inhibits NADPH oxidase and prevents oxidative stress in the kidney of spontaneously hypertensive rats

AIMS

The NADPH oxidases constitute a major source of superoxide anion (·O2(-)) in hypertension. Several studies suggest an important role of NADPH oxidases in different effects mediated by transforming growth factor-β₁ (TGF-β₁). We investigated whether a chronic treatment with P144, a peptide synthesized from type III TGF-β₁ receptor, inhibited NADPH oxidases in the renal cortex of spontaneously hypertensive rats (SHR).

RESULTS

Here, we show that chronic administration of P144 significantly reduced the NADPH oxidase expression and activity as well as the oxidative stress observed in control vehicle-treated SHR (V-SHR). In addition, P144 was also able to reduce the significant increase in the renal fibrosis and in mRNA expression of different components of collagen metabolism, as well as in the levels of connective tissue growth factor observed in V-SHR. Finally, TGF-β₁-stimulated NRK52E exhibited a significant increase in NADPH oxidase expression and activity as well as a TGF-β₁-dependent intracellular pathway that were inhibited in the presence of P144.

INNOVATION

Our experimental evidence suggests that reversing oxidative stress may be therapeutically useful in preventing fibrosis-associated renal damage. We show here that (i) the TGF-β₁-NADPH oxidases axis is crucial in the development of fibrosis in an experimental hypertensive renal disease animal model, and (ii) the use of P144 reverses TGF-β₁-dependent NADPH oxidase activity; thus, P144 may be considered a novel therapeutic tool in kidney disease associated with hypertension.

CONCLUSION

We demonstrate that P144 inhibits NADPH oxidases and prevents oxidative stress in kidneys from hypertensive rats. Our data also suggest that these effects are associated with the renal antifibrotic effect of P144.

Role of H(2)O(2) in hypertension, renin-angiotensin system activation and renal medullary disfunction caused by angiotensin II

BACKGROUND AND PURPOSE

Activation of the intrarenal renin-angiotensin system (RAS) and increased renal medullary hydrogen peroxide (H(2) O(2) ) contribute to hypertension. We examined whether H(2) O(2) mediated hypertension and intrarenal RAS activation induced by angiotensin II (Ang II).

EXPERIMENTAL APPROACH

Ang II (200 ng·kg(-1) ·min(-1) ) or saline were infused in Sprague Dawley rats from day 0 to day 14. Polyethylene glycol (PEG)-catalase (10 000 U·kg(-1) ·day(-1) ) was given to Ang II-treated rats, from day 7 to day 14. Systolic blood pressure was measured throughout the study. H(2) O(2) , angiotensin AT(1) receptor and Nox4 expression and nuclear factor-κB (NF-κB) activation were evaluated in the kidney. Plasma and urinary H(2) O(2) and angiotensinogen were also measured.

KEY RESULTS

Ang II increased H(2) O(2) , AT(1) receptor and Nox4 expression and NF-κB activation in the renal medulla, but not in the cortex. Ang II raised plasma and urinary H(2) O(2) levels, increased urinary angiotensinogen but reduced plasma angiotensinogen. PEG-catalase had a short-term antihypertensive effect and transiently suppressed urinary angiotensinogen. PEG-catalase decreased renal medullary expression of AT(1) receptors and Nox4 in Ang II-infused rats. Renal medullary NF-κB activation was correlated with local H(2) O(2) levels and urinary angiotensinogen excretion. Loss of antihypertensive efficacy was associated with an eightfold increase of plasma angiotensinogen.

CONCLUSIONS AND IMPLICATIONS

The renal medulla is a major target for Ang II-induced redox dysfunction. H(2) O(2) appears to be the key mediator enhancing intrarenal RAS activation and decreasing systemic RAS activity. The specific control of renal medullary H(2) O(2) levels may provide future grounds for the treatment of hypertension.

Intrarenal artery superoxide is mainly NADPH oxidase-derived and modulates endothelium-dependent dilation in elderly patients

AIMS

The present study was performed to investigate the contribution of NADPH oxidases (Nox) to superoxide formation in human renal proximal resistance arteries and to test whether superoxide formation contributes to acute vasoconstrictor responses and endothelium-dependent vasodilation in these vessels.

METHODS AND RESULTS

Arcuate and proximal interlobular artery segments were from patients who underwent nephrectomy because of a renal tumour. Vessels were dissected from tumour-free parts of the kidneys. Additional intrarenal arteries were obtained from rats. Superoxide formation was measured by lucigenin-enhanced chemiluminescence, expression of Nox isoforms was analysed by RT-PCR, and functional studies were performed by small vessel wire myography. Sixty per cent of superoxide formation in human arcuate and proximal interlobular arteries was due to Nox activity. mRNA expression analyses revealed the presence of Nox2 and Nox4 but not Nox1. Phenylephrine and endothelin-1 induced powerful concentration-dependent vasoconstrictions that were unaffected by superoxide scavengers. Vasopressin elicited small and variable vasoconstrictions with signs of tachyphylaxis. Endothelium-dependent vasodilation was blunted by tiron and Nomega-nitro-L-arginine methyl ester but not by superoxide dismutase or catalase. Exogenous hydrogen peroxide elicited vasoconstriction.

CONCLUSION

Nox activity is the major source of superoxide formation in renal proximal resistance arteries from elderly patients. Acute vasoconstrictor responses to alpha1-adrenoreceptor activation and to endothelin-1 do not depend on superoxide formation, while endothelium-dependent vasodilation in intrarenal arteries is reactive oxygen species-dependent.

Dietary sodium modulates the interaction between efferent renal sympathetic nerve activity and afferent renal nerve activity: role of endothelin

Increasing efferent renal sympathetic nerve activity (ERSNA) increases afferent renal nerve activity (ARNA), which in turn decreases ERSNA via activation of the renorenal reflexes in the overall goal of maintaining low ERSNA. We now examined whether the ERSNA-induced increases in ARNA are modulated by dietary sodium and the role of endothelin (ET). The ARNA response to reflex increases in ERSNA was enhanced in high (HNa)- vs. low-sodium (LNa) diet rats, 7,560 +/- 1,470 vs. 900 +/- 390%.s. The norepinephrine (NE) concentration required to increase PGE(2) and substance P release from isolated renal pelvises was 10 pM in HNa and 6,250 pM in LNa diet rats. In HNa diet pelvises 10 pM NE increased PGE(2) release from 67 +/- 6 to 150 +/- 13 pg/min and substance P release from 6.7 +/- 0.8 to 12.3 +/- 1.8 pg/min. In LNa diet pelvises 6,250 pM NE increased PGE(2) release from 64 +/- 5 to 129 +/- 22 pg/min and substance P release from 4.5 +/- 0.4 to 6.6 +/- 0.7 pg/min. In the renal pelvic wall, ETB-R are present on unmyelinated Schwann cells close to the afferent nerves and ETA-R on smooth muscle cells. ETA-receptor (R) protein expression in the renal pelvic wall is increased in LNa diet. In HNa diet, renal pelvic administration of the ETB-R antagonist BQ788 reduced ERSNA-induced increases in ARNA and NE-induced release of PGE(2) and substance P. In LNa diet, the ETA-R antagonist BQ123 enhanced ERSNA-induced increases in ARNA and NE-induced release of substance P without altering PGE(2) release. In conclusion, activation of ETB-R and ETA-R contributes to the enhanced and suppressed interaction between ERSNA and ARNA in conditions of HNa and LNa diet, respectively, suggesting a role for ET in the renal control of ERSNA that is dependent on dietary sodium.

Multidrug resistance-related protein 2 genotype of the donor affects kidney graft function

OBJECTIVES

We tested the effect of kidney-specific multidrug resistance-related protein (MRP2, ABCC2) deficiency on renal organic solute disposition as well as on renal protein and gene expression. Furthermore, we investigated whether a particular kidney donor ABCC2 genotype is associated with delayed graft function in patients.

METHODS

A new MRP2-deficient rat strain was established. Renal cross-transplantations were performed between congenic MRP2-deficient and wild-type rats. Renal disposition of MRP2 substrates was investigated in native and transplanted rats. Proteomic analyses and transcriptional profiling were performed in rat kidney graft cortices. Ninety-eight human kidney donor-recipient pairs were genotyped for five ABCC2 polymorphisms. The relationship between delayed graft function and ABCC2 genetic variants in donors and recipients was analyzed by backward stepwise logistic regression.

RESULTS

In rats, the absence of renal MRP2 reduced renal bilirubin glucuronide excretion at pathologic plasma concentrations, modified renal p-aminohippurate excretion and did not affect renal morphine-6-glucuronide excretion. Renal MRP2 deficiency led to renal cortical protein or mRNA upregulation of glutathione transferase isoenzymes, glutaredoxin 2, and heme oxygenase-1. In patients, a particular donor ABCC2 genotype was associated with an increased incidence of delayed graft function.

CONCLUSION

Kidney graft-specific MRP2 deficiency has mild effects on the renal excretion of some organic solutes under experimental conditions and induces a protein and gene expression pattern indicative of activated antioxidant defense mechanisms. This suggests that MRP2 is a determinant of the redox status in tubular epithelial cells and thus of the susceptibility to renal damage under conditions of treatment with multiple drugs and increased oxygen radical formation.

Renin-angiotensin-aldosterone system-mediated redox effects in chronic kidney disease

The renin-angiotensin-aldosterone system (RAAS) is central to the pathogenesis of hypertension, cardiovascular disease, and kidney disease. Evidence supports various pathways through which a local renal RAAS can affect kidney function, hypertension, and cardiovascular disease. A prominent mechanism seems to be the loss of reduction-oxidation (redox) homeostasis and the formation of excessive free radicals. Free radicals such as reactive oxygen species (ROS) are necessary in normal physiologic processes, which include the development of nephrons, erythropoeisis, and tubular sodium transport. However, the loss of redox homeostasis contributes to proinflammatory and profibrotic pathways in the kidney that in turn lead to decreased vascular compliance, podocyte pathology, and proteinuria. Both the blockade of the RAAS and the oxidative stress produce salutary effects on hypertension and glomerular filtration barrier injury. Thus, the focus of current research is on understanding the pathophysiology of chronic kidney disease in the context of an increased RAAS and unbalanced redox mechanisms.

Redox control of renal function and hypertension

Loss of redox homeostasis and formation of excessive free radicals play an important role in the pathogenesis of kidney disease and hypertension. Free radicals such as reactive oxygen species (ROS) are necessary in physiologic processes. However, loss of redox homeostasis contributes to proinflammatory and profibrotic pathways in the kidney, which in turn lead to reduced vascular compliance and proteinuria. The kidney is susceptible to the influence of various extracellular and intracellular cues, including the renin-angiotensin-aldosterone system (RAAS), hyperglycemia, lipid peroxidation, inflammatory cytokines, and growth factors. Redox control of kidney function is a dynamic process with reversible pro- and anti-free radical processes. The imbalance of redox homeostasis within the kidney is integral in hypertension and the progression of kidney disease. An emerging paradigm exists for renal redox contribution to hypertension.

Apocynin-induced vasodilation involves Rho kinase inhibition but not NADPH oxidase inhibition

AIMS

The present study was designed to test the hypothesis that NADPH oxidase inhibition with apocynin would lower blood pressure and improve endothelial function in spontaneously hypertensive rats (SHRs). Although apocyin effectively dilated arterial segments in vitro, it failed to lower blood pressure or improve endothelial function. Further experiments were performed in normotensive rats and in NADPH oxidase subunit knock-out mice to test if apocynin-induced vasodilation depends on NADPH oxidase inhibition at all.

METHODS AND RESULTS

SHRs were treated with apocynin orally or i.v. Arterial pressure was recorded directly. Rat and mouse arterial function was investigated in vitro by small vessel wire myography. NADPH oxidase activity was measured in human granulocytes and in rat vascular preparations. Rho kinase activity was determined by Western blot analysis. Apocynin did not reduce arterial pressure acutely in SHR when given at 50, 100, or 150 mg kg(-1) day(-1) orally over 1-week intervals or when given i.v. Apocynin potently inhibited granulocyte NADPH oxidase but not vascular NADPH-oxidase-dependent oxygen radical formation unless exogenous peroxidase was added to vascular preparations. Apocynin dilated rat intrarenal and coronary arteries independently of pharmacological interventions that reduce vascular superoxide radical abundance and actions. Aortic rings from p47phox(-/-) mice were more sensitive to apocynin-induced dilation than wild-type aortic rings. Rho kinase inhibition reduced or prevented the inhibitory effect of apocynin on agonist-induced vasoconstriction and apocynin inhibited the phosphorylation of Rho kinase substrates.

CONCLUSION

Apocynin per se does not inhibit vascular NADPH-oxidase-dependent superoxide formation. Its in vitro vasodilator actions are not due to NADPH oxidase inhibition but may be explained at least in part by inhibition of Rho kinase activity. The discrepancy between apocynin-induced vasodilation in vitro and the failure of apocynin to lower arterial pressure in SHR suggests opposing effects on arterial pressure-regulating systems in vivo. Its use as a pharmacological tool to investigate vascular NADPH oxidase should be discontinued.

Impaired coronary function in Wistar Ottawa Karlsburg W rats—a new model of the metabolic syndrome

The metabolic syndrome is associated with an increased risk for coronary heart disease. The underlying mechanisms are not well understood. The present study was designed to investigate coronary function in Wistar Ottawa Karlsburg W (WOKW) rats, a new animal model of the metabolic syndrome. The responses of coronary artery segments from WOKW and Dark Agouti (DA) control rats of different ages to several physiological vasoconstrictors and vasodilators were measured in a small vessel wire myograph, and potential mechanisms involved in the differential responses between the two strains were investigated. WOKW showed increased alpha(1)-adrenoceptor-mediated coronary constriction at 3 and 10 months of age, as well as seriously blunted beta-adrenoceptor-mediated coronary relaxation at 16 months of age. Responses to non-adrenergic agonists were not altered in WOKW compared to DA. The alpha(1)-adrenoceptor-mediated coronary constriction in WOKW was completely blocked by rho-kinase inhibition. Induced hyperinsulinemia did not cause increased alpha(1)-adrenoceptor-mediated coronary constriction or impaired beta-adrenoceptor-mediated coronary relaxation in DA. The association between blunted coronary beta-adrenoceptor responsiveness and the metabolic syndrome was confirmed in Zucker diabetic fatty rats. We conclude that the metabolic syndrome in WOKW rats is associated with impaired coronary function due to altered adrenoceptor sensitivity. The latter may contribute to inappropriately elevated coronary tone in insulin-resistant subjects, especially when sympathetic activity to the heart is increased.