Selective antagonism of the ETA receptor, but not the ETB receptor, is protective against ischemic acute renal failure in rats

Endothelin receptor antagonists in chronic kidney disease

Endothelin-1 is a potent vasoconstrictor that has diverse physiological functions in the kidney, including in the regulation of blood flow and glomerular filtration, electrolyte homeostasis and endothelial function. Overexpression of endothelin-1 contributes to the pathophysiology of both diabetic and non-diabetic chronic kidney disease (CKD). Selective endothelin receptor antagonists (ERAs) that target the endothelin A (ETA) receptor have demonstrated benefits in animal models of kidney disease and in clinical trials. In patients with type 2 diabetes and CKD, the selective ETA ERA, atrasentan, reduced albuminuria and kidney function decline. Concerns about the increased risks of fluid retention and heart failure with ERA use have led to the design of further trials to optimize dosing and patient selection. More recent studies have shown that the dual ETA receptor and angiotensin receptor blocker, sparsentan, preserved kidney function with minimal fluid retention in patients with IgA nephropathy. Moreover, combined administration of a low dose of the ETA-selective ERA, zibotentan, with the sodium-glucose cotransporter 2 (SGLT2) inhibitor, dapagliflozin, enhanced albuminuria reduction and mitigated fluid retention in patients with CKD. Notably, sparsentan and aprocitentan have received FDA approval for the treatment of IgA nephropathy and treatment-resistant hypertension, respectively. This Review describes our current understanding of the use of ERAs in patients with CKD to guide their optimal safe and effective use in clinical practice.

Modulation by antenatal therapies of cardiovascular and renal programming in male and female offspring of preeclamptic rats

Morbidity and mortality risks are enhanced in preeclamptic (PE) mothers and their offspring. Here, we asked if sexual dimorphism exists in (i) cardiovascular and renal damage evolved in offspring of PE mothers, and (ii) offspring responsiveness to antenatal therapies. PE was induced by administering N^G-nitro-L-arginine methyl ester (L-NAME, 50 mg/kg/day, oral gavage) to pregnant rats for 7 days starting from gestational day 14. Three therapies were co-administered orally with L-NAME, atrasentan (endothelin ETA receptor antagonist), terutroban (thromboxane A2 receptor antagonist, TXA2), or α-methyldopa (α-MD, central sympatholytic drug). Cardiovascular and renal profiles were assessed in 3-month-old offspring. Compared with offspring of non-PE rats, PE offspring exhibited elevated systolic blood pressure and proteinuria and reduced heart rate and creatinine clearance (CrCl). Apart from a greater bradycardia in male offspring, similar PE effects were noted in male and female offspring. While terutroban, atrasentan, or α-MD partially and similarly blunted the PE-evoked changes in CrCl and proteinuria, terutroban was the only drug that virtually abolished PE hypertension. Rises in cardiorenal inflammatory (tumor necrosis factor alpha, TNFα) and oxidative (isoprostane) markers were mostly and equally eliminated by all therapies in the two sexes, except for a greater dampening action of atrasentan, compared with α-MD, on tissue TNFα in female offspring only. Histopathologically, antenatal terutroban or atrasentan was more effective than α-MD in rectifying cardiac structural damage, myofiber separation, and cytoplasmic alterations, in PE offspring. The repair by antenatal terutroban or atrasentan of cardiovascular and renal anomalies in PE offspring is mostly sex-independent and surpasses the protection offered by α-MD, the conventional PE therapy.

Lack of an apparent role for endothelin-1 in the prolonged reduction in renal perfusion following severe unilateral ischemia-reperfusion injury in the mouse

Therapeutic approaches to block the progression from acute kidney injury to chronic kidney disease are currently lacking. Endothelin‐1 (ET‐1) is a powerful vasoconstrictor, induced by hypoxia, and previously implicated in renal ischemia‐reperfusion (IR) injury. This study tested the hypothesis that blunting the vascular influence of ET‐1, either through endothelin ET_A receptor blockade (ABT‐627) or vascular endothelial cell deletion of ET‐1 (VEET KO), would improve recovery of renal perfusion and repair of injury following a severe ischemic insult in mice (45 min unilateral renal ischemia). Male C57Bl/6 mice receiving vehicle or ABT‐627 commencing 2 days prior to surgery, and VEET KO mice and wild‐type littermates (WT) underwent 45 min unilateral renal IR surgery followed by 28 days recovery. Renal blood velocity was measured by pulsed‐wave Doppler ultrasound before and after surgery. Renal blood velocity was not significantly different between pairs of groups before surgery. Unilateral IR induced a marked reduction in renal blood velocity of the IR kidney at 24 h postsurgery in all groups, which partially recovered but remained below baseline at 28 days post‐IR. Despite the lack of effect on renal blood velocity, ET_A receptor blockade significantly attenuated the atrophy of the post‐IR kidney, whereas this was not significantly affected by lack of endothelial ET‐1 expression. These data suggest that although blockade of the ET_A receptor is mildly beneficial in preserving renal mass following a severe ischemic insult, this protective effect does not appear to involve improved recovery of renal perfusion.

Sulfenic Acid Modification of Endothelin B Receptor is Responsible for the Benefit of a Nonsteroidal Mineralocorticoid Receptor Antagonist in Renal Ischemia

AKI is associated with high mortality rates and the development of CKD. Ischemia/reperfusion (IR) is an important cause of AKI. Unfortunately, there is no available pharmacologic approach to prevent or limit renal IR injury in common clinical practice. Renal IR is characterized by diminished nitric oxide bioavailability and reduced renal blood flow; however, the mechanisms leading to these alterations are poorly understood. In a rat model of renal IR, we investigated whether the administration of the novel nonsteroidal mineralocorticoid receptor (MR) antagonist BR-4628 can prevent or treat the renal dysfunction and tubular injury induced by IR. Renal injury induced by ischemia was associated with increased oxidant damage, which led to a cysteine sulfenic acid modification in endothelin B receptor and consequently decreased endothelial nitric oxide synthase activation. These modifications were efficiently prevented by nonsteroidal MR antagonism. Furthermore, we demonstrated that the protective effect of BR-4628 against IR was lost when a selective endothelin B receptor antagonist was coadministered. These data describe a new mechanism for reduced endothelial nitric oxide synthase activation during renal IR that can be blocked by MR antagonism with BR-4628.

Reduced NO production rapidly aggravates renal function through the NF-κB/ET-1/ETA receptor pathway in DOCA-salt-induced hypertensive rats

AIMS

It has been reported that endothelin-1 (ET-1) overproduction and reduced nitric oxide (NO) production are closely related to the progression of renal diseases. In the present study, we examined the interrelation between ET-1 and NO system using rats treated with the combination of deoxycorticosterone acetate (DOCA)-salt and a non selective NO synthase inhibitor N(ω)-nitro-L-arginine (NOARG).

MAIN METHODS

Rats were treated with DOCA-salt (15 mg/kg, plus drinking water containing 1% NaCl) for two weeks, and then additional treatment of NOARG (0.6 mg/ml in the drinking water) was performed for three days.

KEY FINDINGS

Combined treatment of DOCA-salt and NOARG drastically developed the severe renal dysfunction and tissue injury. This treatment additionally enhanced renal ET-1 production compared to the rats treated with DOCA-salt alone, whereas a selective ET(A) receptor antagonist ABT-627 completely prevented renal dysfunction and tissue injury. On the other hand, combined treatment of DOCA-salt and NOARG induced the phosphorylation of inhibitory protein kappa B (IκB), followed by the activation of nuclear factor-kappa B (NF-κB) in the kidney. In addition, pyrrolidine-dithiocarbamate completely suppressed not only NF-κB activation but also renal dysfunction and ET-1 overproduction.

SIGNIFICANCE

These results suggest that NF-κB/ET-1/ET(A) receptor-mediated actions are responsible for the increased susceptibility to DOCA-salt induced renal injuries in the case of reduced NO production.

Expression of endothelin-1 and its receptors in Cisplatin-induced acute renal failure in mice

Endothelin-1 (ET-1) is unequivocally elevated in the kidney with ischemic acute renal failure (ARF), whereas ET receptors (ET(A)R and ET(B)R) are variably expressed. Although renal functional and structural changes are similar between ischemic and nephrotoxic ARF, there are few reports on the alteration in the ET system in nephrotoxic ARF. This study was, therefore, undertaken to investigate changes in renal expression of ET-1 and its receptors in nephrotoxic ARF induced by cisplatin. Mice were intraperitoneally injected with 16 mg of cisplatin/kg at a single dose, and the expression of mRNA and protein was then quantified by real-time RT-PCR and Western blot, respectively. Immunohistochemistry was conducted for localization. Three days after treatment, ET-1 transcript in cisplatin-treated mice was thirteen times higher than that in controls, whereas ET-1 peptide was increased by 1.5-fold. Cisplatin caused a 2-fold increase in the levels of ET(A)R mRNA and protein. Most of the increased immunoreactive ET-1 and ET(A)R were localized in damaged tubules. Neither the expression of ET(B)R mRNA nor the abundance and immunoreactive level of ET(B)R protein were changed. The findings suggest that the individual components of the renal ET system are differentially regulated in cisplatin-induced nephrotoxic ARF.

Ozone oxidative preconditioning protects the rat kidney from reperfusion injury: the role of nitric oxide

BACKGROUND

Ischemia/reperfusion (I/R) injury, which is commonly seen in the field of renal surgery or transplantation, is a major cause of acute renal failure. Previous studies have shown that ozone oxidative preconditioning (OzoneOP) attenuated renal I/R injury. The objective of this study was to examine the hypothesis that protective effects of OzoneOP in renal I/R injury were associated with endogenous NO.

MATERIALS AND METHODS

In a right-nephrectomized rat mode, anesthetized rats underwent 45 min of renal ischemia. OzoneOP (1 mg/kg) was administered before I/R injury. Rats were killed at 24, 48, and 72 h after I/R injury and blood samples and renal tissues were obtained.

RESULTS

OzoneOP prevented the renal dysfunction induced by I/R and increased nitric oxide (NO) release and renal NO synthase (endothelial, eNOS, and inducible, iNOS) expression. In contrast, enhancement of endothelin-1 in the kidney after the reperfusion was markedly suppressed by OzoneOP.

CONCLUSIONS

Our findings indicated that the protective effect of OzoneOP was closely related to the NO production following the increase in eNOS and iNOS expression. Ozone treatment may have important clinical implications, particularly in view of the minimizing renal damage before transplantation.

Influence of heme oxygenase-1 on microcirculation after kidney transplantation

BACKGROUND

Cytoprotective proteins, such as heme oxygenase-1 (HO-1), play a decisive role in ischemia-reperfusion injury during kidney transplantation. The aim of this study was to investigate the impact of heme oxygenase-1 on microcirculation and on ischemia-reperfusion injury in an isogenic kidney transplantation rat model.

MATERIALS AND METHODS

Seventy male Lewis rats were distributed into three groups. In Group 1(control), the kidneys were only mobilized. In Groups 2 and 3, bilateral nephrectomy was performed, and a kidney from another Lewis rat was orthotopically transplanted on the left side. The donor animals in Group 3 received preconditioning with the HO-1 inductor hemin. 24 h after reperfusion graft function and morphology were examined. Microcirculation was investigated by in vivo microscopy of the renal surface 1 h after reperfusion.

RESULTS

HO-1 preconditioning led to significantly lower serum creatinine and serum urea, as well as less histological damage and inducible nitric oxide synthase expression. Microcirculation was improved by a significant enlargement of the vascular diameter and an increase of the capillary flow.

CONCLUSIONS

Treatment with hemin improves microcirculation by induction of HO-1 and reduces ischemia-reperfusion injury after kidney transplantation. HO-1 induction was shown to be a promising approach in the preconditioning of donor kidneys.

[Endothelin-1 production and its involvement in cardiovascular diseases]

Endothelin (ET) has been implicated in the pathogenesis of several cardiovascular disorders because of its powerful vasoconstrictor and growth-promoting properties. The ET family consists of three isoforms, ET-1, ET-2 and ET-3. ET-1 appears to be the predominant member of the family generated by vascular endothelial cells. In view of the multiple cardiovascular actions of ET-1, there has been much interest in its contribution to the pathophysiology of hypertension and arteriosclerosis. We have been investigating the roles of ET(A) and ET(B) receptors in ET-1-related cardiovascular diseases using subtype-selective ET receptor antagonists and ET(B) receptor-deficient animals. Our studies have demonstrated that ET-1 overproduction and ET(A)-mediated ET-1 actions seem to play a crucial role in the development of several types of hypertensive and post-ischemic diseases. On the other hand, ET-1 biosynthesis and release are regulated at the transcriptional level, and various endogenous substances are known to stimulate ET-1 gene expression by DNA binding of transcription factors. We and others have recently demonstrated that nuclear factor-kappaB (NF-kappaB), a transcription factor with a pivotal role in inducing genes involved in immune, inflammatory and stress responses, is responsible for endothelial ET-1 production. In in vivo studies, agents that can inhibit the NF-kappaB activation improved the development of ET-1-related cardiovascular diseases. Thus, NF-kappaB inhibition may be a pertinent treatment for ET-1 related diseases.

Role of Na+/H+ exchanger in the pathogenesis of ischemic acute renal failure in mice

We evaluated the effects of 5-(N-ethyl-N-isopropyl) amiloride (EIPA), a Na+/H+ exchanger (NHE) inhibitor, on ischemia/reperfusion (I/R)-induced acute renal failure (ARF) in mice. Ischemic ARF was induced by clamping the left renal artery and vein for 40 minutes followed by reperfusion 2 weeks after the contralateral nephrectomy. Preischemic treatment with EIPA attenuated the I/R-induced renal dysfunction. Histopathological examination of the kidney of ARF mice revealed severe renal damage such as tubular necrosis and proteinaceous casts in the tubuli. Histologically evident damage was also improved by preischemic treatment with EIPA. In addition, the I/R-induced increase in renal endothelin-1 (ET-1) content was suppressed by preischemic treatment with EIPA, reflecting the difference in immunohistochemical ET-1 localization in necrotic tubular epithelium. However, the postischemic treatment with EIPA failed to improve the I/R-induced renal dysfunction and ET-1 overproduction. These findings suggest that NHE activation, followed by renal ET-1 overproduction, plays an important role in the pathogenesis of I/R-induced renal injury. The inhibition of NHE by EIPA may be considered as a therapeutic approach to protect the postischemic ARF.

Perinecrotic hypoxia contributes to ischemia/reperfusion-accelerated outgrowth of colorectal micrometastases

Ischemia/reperfusion (I/R) is often inevitable during hepatic surgery and may stimulate the outgrowth of colorectal micrometastases. Postischemic microcirculatory disturbances contribute to I/R damage and may induce prolonged tissue hypoxia and consequent stabilization of hypoxia-inducible factor (HIF)-1alpha. The aim of this study was to evaluate the contribution of postischemic microcirculatory disturbances, hypoxia, and HIF-1alpha to I/R-accelerated tumor growth. Partial hepatic I/R attributable to temporary clamping of the left liver lobe induced microcirculatory failure for up to 5 days. This was accompanied by profound and prolonged perinecrotic tissue hypoxia, stabilization of HIF-1alpha, and massive perinecrotic outgrowth of pre-established micrometastases. Restoration of the microcirculation by treatment with Atrasentan and L-arginine minimized hypoxia and HIF-1alpha stabilization and reduced the accelerated outgrowth of micrometastases by 50%. Destabilization of HIF-1alpha by the HSP90 inhibitor 17-DMAG caused an increase in tissue necrosis but reduced I/R-stimulated tumor growth by more than 70%. In conclusion, prevention of postischemic microcirculatory disturbances and perinecrotic hypoxia reduces the accelerated outgrowth of colorectal liver metastases after I/R. This may, at least in part, be attributed to the prevention of HIF-1alpha stabilization. Prevention of tissue hypoxia or inhibition of HIF-1alpha may represent attractive approaches to limiting recurrent tumor growth after hepatic surgery.

[Conservative treatment of upper urinary tract tumours]

The conservative management of kidney cancer is widely accepted as a therapeutic option for tumours measuring less than 4 cm or in case of underlying renal disease and solitary kidney. The functional and carcinologic success of this conservative treatment results from a radical resection of the tumour and a careful repair of the collecting system and selective ligature of the vessels. Kidney artery clamping is a key to reach these objectives. The cooling of the kidney preserves from warm ischemia and reperfusion lesions. In this review, we explain the physiological basis of warm ischemia induced kidney lesions due to the kidney artery clamping and the advantage of hypothermia. The surgical technique as described by Novick is detailed. This well standardized technique has the advantage of being reproducible and adaptable to all situations.

Endothelin-1-mediated inflammation in acute renal failure

Acute renal failure presents a serious and life-threatening problem in hospitalized patients. Current therapies address the systemic alterations in renal failure. Cellular changes also occur. These changes affect the glomerular filtration rate and the integrity of the glomerular membrane. ET-1, the most potent vasoconstrictor known, has a negative effect on both the rate of filtration and the integrity of the filtering membrane in renal failure. Using ET-1 antagonists along with the current therapies may prove useful in patients.

Retraction：Effects of Pre- and Post-ischemic Treatments with FK409, a Nitric Oxide Donor, on Ischemia/Reperfusion-Induced Renal Injury and Endothelin-1 Production in Rats

We have demonstrated that ischemic acute renal failure (ARF) is attenuated by pre-ischemic treatment with a spontaneous nitric oxide (NO) donor, (+/-)-(E)-4-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexenamide (FK409). In the present study, we evaluated the effect of post-ischemic treatment with FK409 on ARF, compared with the pre-ischemic treatment effect. Ischemic ARF was induced by occlusion of the left renal artery and vein for 45 min followed by reperfusion, 2 weeks after contralateral nephrectomy. At 24 h after reperfusion, renal function in untreated ARF rats markedly decreased. In addition, increases in renal contents of endothelin-1 (ET-1), a deleterious mediator in the pathogenesis of ischemic ARF, were evident in untreated ARF rats at 24 h after reperfusion. Pre-ischemic treatment with FK409 (1 or 3 mg/kg, i.v.) at 5 min before ischemia attenuated ischemia/reperfusion-induced renal dysfunction and increased ET-1 contents after reperfusion. In contrast, post-ischemic treatment with FK409 (3 or 10 mg/kg, i.v.) at 6 h after reperfusion aggravated the renal injury, but did not affect the increased ET-1 content after reperfusion. These results suggest that pre-ischemic treatment with FK409 exerts renoprotective effects on ischemic ARF, probably through the suppression of renal ET-1 overproduction, whereas post-ischemic treatment with the NO donor worsens the ischemia/reperfusion-induced renal injury, through mechanisms unrelated to the ET-1 production after reperfusion.

Protective effect of nitric oxide on ischemia/reperfusion-induced renal injury and endothelin-1 overproduction

To elucidate the role of nitric oxide (NO) in the pathogenesis of ischemic acute renal failure, we examined the effects of (+/-)-(E)-4-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexenamide (FK409) and N(G)-nitro-L-arginine methyl ester (L-NAME) as a NO donor and a non-selective NO synthase inhibitor on ischemia/reperfusion-induced renal injury and renal endothelin-1 content. Ischemic acute renal failure was induced by occlusion of the left renal artery and vein for 45 min followed by reperfusion, 2 weeks after contralateral nephrectomy. At 24 h after reperfusion, renal function in untreated acute renal failure rats markedly decreased and histological examination revealed severe renal damage. In addition, increases in renal endothelin-1 contents were evident in the acute renal failure rats at 2, 6, and 24 h after reperfusion, respectively. Pretreatment with FK409 (1 or 3 mg/kg, i.v.) attenuated ischemia/reperfusion-induced renal dysfunction, histological damage, and endothelin-1 overproduction after reperfusion. In contrast, pretreatment with L-NAME (1 or 10 mg/kg, i.v.) aggravated renal injuries of acute renal failure rats at 24 h after reperfusion, and the effect is accompanied by further increases in the renal endothelin-1 content at 2 and 6 h, but not at 24 h, after reperfusion. These results suggest that suppressive effects of NO on the renal endothelin-1 overproduction induced by ischemia/reperfusion in an early phase are probably responsible for the protective effect of NO against ischemic acute renal failure.

Endothelin-1 overexpression leads to further water accumulation and brain edema after middle cerebral artery occlusion via aquaporin 4 expression in astrocytic end-feet

Stroke patients have increased levels of endothelin-1 (ET-1), a strong vasoconstrictor, in their plasma or cerebrospinal fluid. Previously, we showed high level of ET-1 mRNA expression in astrocytes after hypoxia/ischemia. It is unclear whether the contribution of ET-1 induction in astrocytes is protective or destructive in cerebral ischemia. Here, we generated a transgenic mouse model that overexpress ET-1 in astrocytes (GET-1) using the glial fibrillary acidic protein promoter to examine the role of astrocytic ET-1 in ischemic stroke by challenging these mice with transient middle cerebral artery occlusion (MCAO). Under normal condition, GET-1 mice showed no abnormality in brain morphology, cerebrovasculature, absolute cerebral blood flow, blood-brain barrier (BBB) integrity, and mean arterial blood pressure. Yet, GET-1 mice subjected to transient MCAO showed more severe neurologic deficits and increased infarct, which were partially normalized by administration of ABT-627 (ET(A) antagonist) 5 mins after MCAO. In addition, GET-1 brains exhibited more Evans blue extravasation and showed decreased endothelial occludin expression after MCAO, correlating with higher brain water content and increased cerebral edema. Aquaporin 4 expression was also more pronounced in astrocytic end-feet on blood vessels in GET-1 ipsilateral brains. Our current data suggest that astrocytic ET-1 has deleterious effects on water homeostasis, cerebral edema and BBB integrity, which contribute to more severe ischemic brain injury.

Tempol Protects against Ischemic Acute Renal Failure by Inhibiting Renal Noradrenaline Overflow and Endothelin-1 Overproduction

The effects of tempol, a superoxide dismutase mimetic, on ischemia/reperfusion-induced acute renal failure (ARF), noradrenaline (NA) overflow and endothelin-1 (ET-1) overproduction in rats were examined. Ischemic ARF was induced by occlusion of the left renal artery and vein for 45 min followed by reperfusion, 2 weeks after contralateral nephrectomy. Renal functional parameters such as blood urea nitrogen, plasma creatinine concentration, and fractional excretion of sodium, NA concentrations in renal venous plasma, and renal ET-1 contents were determined. Renal function in ARF rats markedly decreased at 1 d after reperfusion. Pre-ischemic treatment with tempol (10, 100 mg/kg, i.v.) dose-dependently attenuated the ischemia/reperfusion-induced renal dysfunction. Histopathological examination of the kidney of ARF rats revealed severe renal damages, such as tubular necrosis, proteinaceous casts in tubuli and medullary congestion, which were also significantly suppressed by the tempol treatment. There was a significant increase in NA concentrations in renal venous plasma after the ischemia/reperfusion, and this increase was markedly suppressed by the treatment with tempol. In addition, tempol treatment significantly attenuated the increment of ET-1 content in the kidney exposed to the ischemia/reperfusion. These findings suggest that tempol improves the post-ischemic renal injury by inhibiting the neural activity of renal sympathetic nerve and ET-1 overproduction.

Pathogenesis of renal ischemia/reperfusion injury: lessons from knockout mice

Ischemia/reperfusion-induced acute renal failure is a common clinical problem associated with a high morbidity and mortality. Upon hypoxic injury, the depletion of ATP causes mitochondrial dysfunction, and accumulation of intracellular sodium, calcium and reactive oxygen species. Subsequently, multiple enzyme systems including proteases, nitric oxide synthases, phospholipases and endonuclease are activated and responsible for cytoskeleton disruption, membrane damage, and DNA degradation, and eventually cell death. Ischemia/reperfusion injury also activates complement, cytokines, and chemokines, which are cytotoxic themselves, but also attract leukocytes into the ischemic area to cause further damage. The vascular endothelial cell injury and dysfunction prolong ischemia and induce vascular congestion, edema, and further infiltration of inflammatory cells. Many players in renal ischemia/reperfusion injury and their mechanisms have been investigated using genetically manipulated mouse models. In this review, we focus on the information gathered from these studies. Deficiency of the Na/Ca exchanger, inducible nitric oxide synthase, Caspase-1, A3 adenosine receptor, C3, C5, C6, Factor B, or midkine protects the kidney against I/R injury. Conversely, deficiency of the interleukin-1 receptor, osteopontin, C4, or recombination activation gene-1 is not protective, while the absence of adrenomedullin or endothelin receptor B delays the recovery of ischemia/reperfusion injury. The knowledge obtained from these studies provides new direction for designing potential therapeutic agents for treating ischemia/reperfusion injury.

A novel and selective Na+/Ca2+ exchange inhibitor, SEA0400, improves ischemia/reperfusion-induced renal injury

We evaluated the effects of SEA0400 (2-[4-[(2,5-difluorophenyl)methoxy]phenoxy]-5-ethoxyaniline), a novel and selective Na+/Ca2+ exchange inhibitor, on ischemic acute renal failure. Ischemic acute renal failure in rats was induced by clamping the left renal artery and vein for 45 min followed by reperfusion, 2 weeks after the contralateral nephrectomy. SEA0400 administration (0.3, 1 and 3 mg/kg, i.v.) before ischemia dose-dependently attenuated the ischemia/reperfusion-induced renal dysfunction and histological damage such as tubular necrosis. SEA0400 pretreatment at the higher dose suppressed the increment of renal endothelin-1 content after reperfusion. The ischemia/reperfusion-induced renal dysfunction was also overcome by post-ischemia treatment with SEA0400 at 3 mg/kg, i.v. In in vitro study, SEA0400 (0.2 and 1 microM) protected cultured porcine tubular cells (LLC-PK1) from hypoxia/reoxygenation-induced cell injury. These findings support the view that Ca2+ overload via the reverse mode of Na+/Ca2+ exchange, followed by endothelin-1 overproduction, plays an important role in the pathogenesis of ischemia/reperfusion-induced renal injury. The possibility exists that a selective Na+/Ca2+ exchange inhibitor such as SEA0400 is useful as effective therapeutic agent against ischemic acute renal failure in humans.

Role of nitric oxide in the renal protective effects of ischemic preconditioning

Possible involvement of nitric oxide (NO) in the protective effect of ischemic preconditioning against the ischemia/reperfusion-induced acute renal failure was investigated. Ischemic preconditioning, which consists of three cycles of 2-minute ischemia followed by 5-minute reperfusion, was performed prior to 45-minute ischemia. Ischemic preconditioning significantly improved the renal dysfunction induced by 45-minute ischemia followed by 24-hour reperfusion. Histopathological examination of the kidney of ischemia/reperfusion rats revealed severe renal damage, and suppression of the damage was seen with the ischemic preconditioning treatment. NO metabolites (NOx) production in the kidney after 45-minute ischemia and reperfusion was markedly increased in ischemia/reperfusion rats with ischemic preconditioning, compared with animals not subjected to ischemic preconditioning, and these increases correlated with changes in endothelial NO synthase (eNOS) protein expression in renal tissues. The improvement of renal dysfunction in ischemic preconditioning rats was abolished by the pretreatment with NG-nitro-L-arginine, a nonselective NOS inhibitor, but not with aminoguanidine, an inducible NOS inhibitor. In addition, increment of endothelin-1 (ET-1) content in the kidney after the reperfusion was markedly suppressed by ischemic preconditioning treatment. These findings suggest that the protective effect of ischemic preconditioning on ischemia/reperfusion -induced acute renal failure is closely related to the renal nitric oxide production following the increase in eNOS expression after the reperfusion and that the suppressive effect of ischemic preconditioning on the ischemia/reperfusion -induced renal ET-1 overproduction may be partly involved in the ameliorating effect of ischemic preconditioning.

Mechanisms underlying the contractile response to endothelin-1 in the rat renal artery

We assessed the functional response and the mechanisms following receptor stimulation of endothelin-1 (ET-1) in the rat renal artery. In this study, isometric tension was recorded in renal artery rings without endothelium. Cumulative application of ET-1 from 0.1 to 100 nmol/l induced a sustained concentration-dependent contraction in the renal artery. Submaximal contraction induced by 10 nmol/l ET-1 in 2.5 mmol/l Ca(2+) and in the absence of inhibitors was used as control response (100%). The relative contribution of different sources of Ca(2+) in ET-1-induced contraction was evaluated. The contractile response to 10 nmol/l ET-1 in 2.5 mmol/l Ca(2+ )(1.2 +/- 0.2 g) was significantly inhibited either in Ca(2+)-free solution containing 100 micromol/l ethylene glycol bis-(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (0.6 +/- 0.1 g) or after depletion of intracellular Ca(2+) stores (0.62 +/- 0.05 g). The contribution of phospholipase C and protein kinase C was evaluated by using their inhibitors 2-nitro-4-carboxyphenyl N,N-diphenylcarbamate (NCDC) and [1-(5-isoquinolinesulfonyl)-2-methylpiperazine] (H-7), respectively. The contractile response to 10 nmol/l ET-1 was inhibited by 10 micromol/l NCDC (to 80 +/- 6%) and 30 micromol/l H-7 (to 76.6 +/- 6.5%). We found that 1 micromol/l nifedipine inhibited the ET-1-induced contraction (to 48.7 +/- 6.9%), indicating the contribution of Ca(2+) influx through voltage-gated L-type Ca(2+) channels to this response. Further, the inhibitory effect of nifedipine was to a greater extent as compared with NCDC or H-7. Additive inhibition of ET-1-induced contraction was not observed in the presence of both nifedipine and NCDC. We also evaluated the role of the ionic transport system in the ET-1-induced response by using 20 nmol/l 5-(N-ethyl-N-isopropyl)-amiloride (EIPA), an inhibitor of Na(+)-H(+) exchange, or 100 micromol/l ouabain, an inhibitor of Na(+)-K(+)-ATPase. The response to ET-1 was decreased by both EIPA (to 61.6 +/- 8.4%) and ouabain (to 62.1 +/- 8.6%). The contribution of Na(+)-Ca(2+) exchange to ouabain action was tested using the inhibitor dimethyl amiloride HCl (10 micromol/l). The decrease in ET-1-induced contraction by the combination of ouabain and dimethyl amiloride HCl was similar to that observed with ouabain alone. In view of these observations, both extra- and intracellular sources of Ca(2+) contribute to the contractile response induced by ET-1 in the renal artery. Our findings also revealed the importance of Ca(2+) influx through voltage-gated L-type Ca(2+) channels in mediating contraction to ET-1 in the renal artery, whereas a minor role of phospholipase C and protein kinase C was observed. Na(+)-H(+) exchange and Na(+)-K(+)-ATPase also play a role in the ET-1-induced contraction in renal artery. Moreover, the contribution of Na(+)-K(+)-ATPase in ET-1 contraction is not an Na(+)-Ca(2+) exchange-related process.

Endothelin-receptor blockade mitigates the adverse effect of preretrieval warm ischemia on posttransplantation renal function in rats

BACKGROUND

Ischemia-reperfusion injury has been established as a nonimmunologic risk factor for the development of chronic graft nephropathy after renal transplantation. This objective of this study was to determine if oral administration of an endothelin-1 receptor (ET-R) antagonist over a 2-month period after renal transplantation would mitigate long-term dysfunction associated with 30 min of preretrieval warm ischemia (pre-WI).

METHODS

The left kidney was retrieved from 250-g Lewis rats. Recipients underwent left nephrectomy and isografting using standard techniques. Animals were divided into three groups: nonischemic controls (no pre-WI, n=8); ischemic controls (pre-WI only, n=6); and pre-WI kidneys in which recipients received the ET(A/B) receptor antagonist, A182086, daily (30 mg/kg/day) (pre-WI/ET-R antagonist, n=6). Isograft glomerular filtration rate (GFR) was measured at 2 months.

RESULTS

Measurement of GFR (mL/min) were as follows: no pre-WI, 2.1+/-0.26; pre-WI only, 1.24+/-0.14 (P<0.05 vs. no pre-WI); and pre-WI/ET-R antagonist, 2.3+/-0.45 (P<0.05 vs. pre-WI only and P=NS vs. no pre-WI).

CONCLUSIONS

Chronic administration of a nonselective ET-R antagonist given after the ischemic insult, mitigated the decline in GFR at 2 months. These observations provide an experimental rationale for further investigation of the potential long-term protective effect of nonselective ET-R blockade versus ischemia-reperfusion injury in the clinical setting.

[New expansion of endothelin research: perspectives for clinical application of endothelin-receptor antagonists]

Three isopeptides of endothelin (ET-1, -2, and -3) exert various actions through stimulation of two sub-types of receptor (ETA and ETB). Vascular endothelial cells produce only ET-1. In addition to its powerful vasoconstrictor action, ET-1 has direct mitogenic actions on cardiovascular tissues, as well as comitogennic actions with a wide variety of growth factors and vasoactive substances. ET-1 also promotes the synthesis and secretion of growth factors and various substances, including extracellular constituents. These effects of endogenous ET-1 would naturally be thought to be concerned with the development and/or aggravation of chronic cardiovascular diseases; e.g., hypertension, pulmonary hypertension, vascular remodeling (stenosis, atherosclerosis), renal failure, and heart failure. A large number of peptide and orally active non-peptide endothelin receptor antagonists have been developed, and utilized to analyze physiological and pathophysiological roles of endogenous ET-1. These antagonists have been shown to exert excellent therapeutic effects in animal models of various kinds of diseases by either acute or chronic treatment. Therapeutic treatment of patients suffering from the above-mentioned cardiovascular diseases with ET-receptor antagonists have also been taking place, and bosentan (ETA/ETB antagonist) was recently approved by the FDA as a formal therapeutic drug for pulmonary hypertension. In this review, perspectives for therapeutic applicability of ET-receptor antagonists will be explored.

Attenuation of ischemia/reperfusion-induced renal injury in mice deficient in Na+/Ca2+ exchanger

Using Na+/Ca2+ exchanger (NCX1)-deficient mice, the pathophysiological role of Ca2+ overload via the reverse mode of NCX1 in ischemia/reperfusion-induced renal injury was investigated. Because NCX1(-/-) homozygous mice die of heart failure before birth, we used NCX1(+/-) heterozygous mice. NCX1 protein in the kidney of heterozygous mice decreased to about half of that of wild-type mice. Expression of NCX1 protein in the tubular epithelial cells and Ca2+ influx via NCX1 in renal tubules were markedly attenuated in the heterozygous mice. Ischemia/reperfusion-induced renal dysfunction in heterozygous mice was significantly attenuated compared with cases in wild-type mice. Histological renal damage such as tubular necrosis and proteinaceous casts in tubuli in heterozygous mice were much less than that in wild-type mice. Ca2+ deposition in necrotic tubular epithelium was observed more markedly in wild-type than in heterozygous mice. Increases in renal endothelin-1 content were greater in wild-type than in heterozygous mice, and this reflected the difference in immunohistochemical endothelin-1 localization in necrotic tubular epithelium. When the preischemic treatment with KB-R7943 was performed, the renal functional parameters of both NCX1(+/+) and NCX1(+/-) acute renal failure mice were improved to the same level. These findings strongly support the view that Ca2+ overload via the reverse mode of Na+/Ca2+ exchange, followed by renal endothelin-1 overproduction, plays an important role in the pathogenesis of ischemia/reperfusion-induced renal injury.

Role of endothelin B receptor in the pathogenesis of ischemic acute renal failure

This study evaluated the role of endothelin B (ET ) receptor-mediated action in the development and maintenance of ischemic acute renal failure (ARF), using the spotting-lethal ( ) rat that carries a naturally occurring deletion in the ET receptor gene. Because homozygous ( ) rats die shortly after birth due to congenital distal intestinal aganglionosis, genetic rescue of rats from the developmental defect using a dopamine-beta-hydroxylase (DbetaH)-ET transgene was performed to produce ET -deficient adult rats. Rescued homozygous (DbetaH-ET ) and wild-type (DbetaH-ET +/+) rats were subjected to ischemic ARF by clamping the renal pedicle for 45 min followed by reperfusion. At 24 h after the reperfusion, renal glomerular dysfunction and histologic damage, such as proteinaceous casts in tubuli, were markedly and observed equally in homozygous and wild-type groups, and these renal injuries gradually recovered. However, when the ischemia/reperfusion-induced renal injury was examined 7 days after the reperfusion, the recovery in homozygous ARF rats was obviously delayed compared with the wild-type animals. Two of the eight homozygous ARF rats died within 3 days after the reperfusion. Increment of renal endothelin-1 content after the ischemia/reperfusion was more marked in homozygous than in wild-type rats. Thus, ET receptor-mediated actions do not play an important role in the development of ischemic ARF but may be involved in the recovery process from ischemia/reperfusion-induced renal injury.

Basic and therapeutic relevance of endothelin-mediated regulation

Three endothelin family peptides (endothelin-1, -2 and -3) exert an extremely potent and long-lasting vasoconstrictor action as well as other various actions through stimulating two subtypes of receptor (ETA and ETB). Vascular endothelial cells produce only endothelin-1. Although the pharmacological actions of exogenous endothelin-1 have been extensively analyzed, the physiological roles of endogenous endothelin-1 have long been obscure. Using potent and selective receptor antagonists, endothelin-1 has been demonstrated to contribute slightly to the maintenance of regional vascular tone. In gene-targeted mice, endothelin family peptides and their receptors have been shown to play an important role in the embryonic development of neural crest-derived tissues. In addition to its potent vasoconstrictor action, endothelin-1 has direct mitogenic actions on cardiovascular tissues, as well as co-mitogenic actions with a wide variety of growth factors and vasoactive substances. Endothelin-1 also promotes the synthesis and secretion of various substances including extracellular constituents. These effects of endogenous endothelin-1 would appear to be naturally concerned with the development and/or aggravation of chronic cardiovascular diseases, e.g. hypertension, pulmonary hypertension, vascular remodeling (restenosis, atherosclerosis), renal failure, and heart failure. A great many non-peptide and orally active endothelin receptor antagonists have been developed, and shown to exert excellent therapeutic effects in animal models as well as human patients with these diseases.

Amelioration of post-ischaemic renal injury by contralateral uninephrectomy: a role of endothelin-1

BACKGROUND

Previous studies showed that unilateral renal damage is attenuated by prior contralateral uninephrectomy (Nx) in ischaemia-induced acute renal failure (ARF). Since renal ischaemia increases endothelin-1 (ET-1) production in the kidney, we examined whether the alteration of renal ET-1 content may contribute to the nephrectomy-induced attenuation of renal injury.

METHODS

Ischaemic renal injury was provoked by 60-min left renal artery occlusion (RAO). Removal of the right kidney was performed just before RAO in the Nx group. Forty-eight hours after release of the clamp, renal ET-1 content was measured in both non-nephrectomized and unilaterally nephrectomized rats. We also examined the effects of a selective ET(A) receptor (FR139317) and monoclonal ET antibody (AwETN40) on the RAO-induced changes in renal haemodynamics at 2 and 48 h after RAO respectively.

RESULTS

The plasma concentration of ET-1 did not change in the two groups of ARF rats, but the cortical content of ET-1 increased to a lesser extent in Nx animals after ischaemia. Prior removal of the right kidney significantly facilitated the percentage recovery of left renal blood flow (RBF) during the first 2 h after release of the clamp. The percentage recovery of inulin clearance (Cin) by the kidney was also significantly better in Nx than sham-Nx rats at 48 h after RAO. Continuous administration of FR139317 (50 mg/kg/day) using osmotic minipumps for 3 days significantly attenuated exogenous ET-1-induced decrease in Cin and RBF. Infusion of FR139317 restored the decrease in RBF to control values during first 2 h in sham-Nx rats. However, FR139317 and AwETN40 did not ameliorate the RAO-induced decline of Cin in sham-Nx or Nx rats at 2 and 48 h after ischaemia respectively.

CONCLUSIONS

Contralateral uninephrectomy prior to ischaemia-induced ARF attenuated the increase in cortical ET-1 content and subsequent renal response to ischaemic injury. This beneficial effect of unilateral nephrectomy, however, was not mediated through well-preserved RBF due to reduced intrarenal ET-1 action.

KB-R7943, a selective Na+/Ca2+ exchange inhibitor, protects against ischemic acute renal failure in mice by inhibiting renal endothelin-1 overproduction

We investigated whether the preischemic or postischemic treatment with KB-R7943, a novel and selective Na+/Ca2+ exchange inhibitor, has renal protective effects in mice with ischemic acute renal failure (ARF). Ischemic ARF was induced by clamping the left renal pedicle for 45 min followed by reperfusion, 2 weeks after contralateral nephrectomy. Renal function was markedly diminished 24 h after reperfusion. Preischemic treatment with KB-R7943 attenuated the ARF-induced renal dysfunction. The ischemia/reperfusion-induced renal dysfunction was also overcome by postischemic treatment with KB-R7943. Histopathologic examination of the kidneys of ARF mice revealed severe renal damage such as tubular necrosis, proteinaceous casts in tubuli, and medullary congestion. Histologically evident damage and Ca2+ deposition in necrotic tubular epithelium were improved by preischemic treatment with KB-R7943. In addition, preischemic treatment with KB-R7943 significantly suppressed the increment of endothelin-1 (ET-1) content in the kidney at 2, 6, and 24 h after reperfusion. These findings suggest that Ca2+ overload via the reverse mode of Na+/Ca2+ exchange, followed by renal ET-1 overproduction, plays an important role in the pathogenesis of the ischemia/reperfusion-induced ARF. KB-R7943 may prove to be an effective therapeutic agent for cases of ischemic ARF in humans.

Protective effect of SM-19712, a novel and potent endothelin converting enzyme inhibitor, on ischemic acute renal failure in rats

Effects of SM-19712 (4-chloro-N-[[(4-cyano-3-methyl- 1-1-phenyl- 1H-pyrazol-5-yl)amino]carbonyl] benzenesulfonamide, monosodium salt), a novel endothelin converting enzyme (ECE) inhibitor, on ischemic acute renal failure (ARF) in rats were examined in comparison with those of phosphoramidon, a conventional ECE inhibitor. ARF was induced by occlusion of the left renal artery and vein for 45 min followed by reperfusion, 2 weeks after contralateral nephrectomy. Renal function in ARF rats markedly decreased at 24 h after reperfusion. Intravenous bolus injection of SM-19712 (3, 10, 30 mg/kg) prior to the occlusion attenuated dose-dependently the ischemia/reperfusion-induced renal dysfunction. Histopathological examination of the kidney of ARF rats revealed severe renal damages such as tubular necrosis, proteinaceous casts in tubuli and medullary congestion, all of which were dose-dependently attenuated by SM-19712. Protective effects of phosphoramidon (10 mg/kg) on ARF-induced functional and tissue damages were less potent than that of the same dose of SM-19712. Endothelin-1 (ET-1) content in the kidney after the ischemia/reperfusion was significantly increased, being the maximum level at 6 h after reperfusion, and this elevation was completely suppressed by the higher dose of SM-19712. Our findings support the view that renal ET-1 plays an important role in the development of ischemia/reperfusion-induced renal injury. SM-19712 may be useful in the treatment of ischemic ARF.