Tokihito Yukimura

Sex differences in ischemia/reperfusion-induced acute kidney injury are dependent on the renal sympathetic nervous system

Resistance to ischemic acute kidney injury has been shown to be higher in female rats than in male rats. We found that renal venous norepinephrine overflow after reperfusion played important roles in the development of ischemic acute kidney injury. In the present study, we investigated whether sex differences in the pathogenesis of ischemic acute kidney injury were derived from the renal sympathetic nervous system using male and female Sprague-Dawley rats. Ischemia/reperfusion-induced acute kidney injury was achieved by clamping the left renal artery and vein for 45 min followed by reperfusion, 2 weeks after contralateral nephrectomy. Renal function was impaired after reperfusion in both male and female rats; however, renal dysfunction and histological damage were more severe in male rats than in female rats. Renal venous plasma norepinephrine levels after reperfusion were markedly elevated in male rats, but were not in female rats. These sex differences were eliminated by ovariectomy or treatment with tamoxifen, an estrogen receptor antagonist, in female rats. Furthermore, an intravenous injection of hexamethonium (25mg/kg), a ganglionic blocker, 5 min before ischemia suppressed the elevation in renal venous plasma norepinephrine levels after reperfusion, and attenuated renal dysfunction and histological damage in male rats, and ovariectomized and tamoxifen-treated female rats, but not in intact females. Thus, the present findings confirmed sex differences in the pathogenesis of ischemic acute kidney injury, and showed that the attenuation of ischemia/reperfusion-induced acute kidney injury observed in intact female rats may be dependent on depressing the renal sympathetic nervous system with endogenous estrogen.

Moxonidine prevents ischemia/reperfusion-induced renal injury in rats.

Enhancement of renal sympathetic nerve activity during renal ischemia and its consequent effect on norepinephrine overflow from nerve endings after reperfusion play important roles in the development of ischemic acute kidney injury. In the present study, we evaluated whether moxonidine, an alpha(2)-adrenaline/I(1)-imidazoline receptor agonist which is known to elicit sympathoinhibitory action, would prevent the post-ischemic renal injury. Ischemic acute kidney injury was induced by clamping the left renal artery and vein for 45 min followed by reperfusion, 2 weeks after contralateral nephrectomy. Intravenous (i.v.) injection of moxonidine at a dose of 360 nmol/kg to ischemic acute kidney injury rats suppressed the enhanced renal sympathetic nerve activity during the ischemic period, to a degree similar to findings with intracerebroventricular (i.c.v.) injection of moxonidine at a dose of 36 nmol/kg. On the other hand, suppressive effects of the i.v. treatment on renal venous norepinephrine overflow, renal dysfunction and tissue injury in the post-ischemic kidney were significantly greater than those elicited by the i.c.v. treatment. These results suggest that renoprotective effects of moxonidine on ischemic acute kidney injury probably result from its suppressive action on the ischemia-enhanced renal sympathetic nerve activity followed by norepinephrine spillover from the nerve endings of the post-ischemic kidney.

Protective effect of 17β-estradiol on ischemic acute kidney injury through the renal sympathetic nervous system.

Enhanced renal sympathetic nerve activity during an ischemic period and renal venous norepinephrine overflow after reperfusion play important roles in the development of ischemic acute kidney injury. In this study, we examined the effect of 17β-estradiol on the renal sympathetic nervous system and kidney function in ischemia/reperfusion-induced acute kidney injury in anesthetized rats. Ischemic acute kidney injury was induced by clamping the left renal artery and vein for 45 min followed by reperfusion, 2 weeks after a contralateral nephrectomy. Intravenous injection of 17β-estradiol (100 μg/kg) 15 min before reperfusion suppressed enhanced renal sympathetic nerve activity during renal ischemia, also suppressed renal venous norepinephrine overflow after reperfusion, and attenuated ischemia/reperfusion-induced renal dysfunction with histological damage. The above renoprotective effects of 17β-estradiol were reversed by pretreatment with tamoxifen (5 mg/kg), an estrogen receptor antagonist, or N(G)-nitro-L-arginine methyl ester (0.3 mg/kg), a non-selective nitric oxide synthase inhibitor. These results indicate that 17β-estradiol can suppress enhanced renal sympathetic nerve activity during renal ischemia, and its consequent effect on norepinephrine overflow from nerve endings, by nitric oxide production via estrogen receptors. These effects appear to contribute to renoprotection against ischemia/reperfusion-induced renal injury.

Protective effect of ischemic preconditioning on ischemia/reperfusion-induced acute kidney injury through sympathetic nervous system in rats

We have found that a series of brief renal ischemia and reperfusion (preconditioning), before the time of ischemia significantly attenuated the ischemia/reperfusion-induced acute kidney injury through endothelial nitric oxide synthase. In this study, we examined the effects of ischemic preconditioning on renal sympathetic nervous system and kidney function in ischemia/reperfusion-induced acute kidney injury with or without nitric oxide synthase inhibitor. Ischemia/reperfusion-induced acute kidney injury was made by clamping the left renal artery and vein for 45-min followed by reperfusion, 2 weeks after the contralateral nephrectomy. Ischemic preconditioning, consisting of three cycles of 2-min ischemia followed by 5-min reperfusion, was performed before the 45-min ischemia. Ischemic preconditioning suppressed the enhanced renal sympathetic nerve activity during ischemia and the elevated renal venous plasma norepinephrine level after reperfusion, and attenuated renal dysfunction and histological damage. The renoprotective effect of ischemic preconditioning was diminished by N(G)-nitro-L-arginine methyl ester (0.3 mg/kg, i.v.), a nonselective nitric oxide synthase inhibitor, 5 min before the start of ischemic preconditioning. Thus, ischemic preconditioning decreased renal sympathetic nerve activity and norepinephrine release probably through activating nitric oxide production, thereby improving ischemia/reperfusion-induced acute kidney injury.

Protective effect of moxonidine on ischemia/reperfusion-induced acute kidney injury through α2/imidazoline I1 receptor

Enhancement of renal sympathetic nerve activity during renal ischemia and norepinephrine overflow from the kidney after reperfusion play important roles in the development of ischemic acute kidney injury. Recently, we have found that moxonidine, an α2/imidazoline Ι1-receptor agonist, has preventive effects on ischemic acute kidney injury by suppressing the excitation of renal sympathetic nervous system after reperfusion. In the present study, to clarify the renoprotective mechanisms of moxonidine (360 nmol/kg, i.v.) against ischemic acute kidney injury, we investigated the effect of intravenous (i.v.) and intracerebroventricular (i.c.v.) injection of efaroxan, an α2/Ι1 receptor antagonist, on the moxonidine-exhibited actions. Ischemic acute kidney injury was induced by clamping the left renal artery and vein for 45 min followed by reperfusion, 2 weeks after contralateral nephrectomy. The suppressive effect of moxonidine on enhanced renal sympathetic nerve activity during renal ischemia was not observed in the rat treated with either i.v. (360 nmol/kg) or i.c.v. (36 nmol/kg) of efaroxan. Furthermore, i.v. injection of efaroxan eliminated the preventive effect of moxonidine on ischemia/reperfusion-induced kidney injury and norepinephrine overflow, and i.c.v. injection of efaroxan did not completely inhibit the moxonidines effects. These results indicate that moxonidine prevents the ischemic kidney injury by sympathoinhibitory effect probably via α2/Ι1 receptors in central nervous system and by suppressing the norepinephrine overflow through α2/Ι1 receptors on sympathetic nerve endings.

Renoprotective effect of yohimbine on ischaemia/reperfusion-induced acute kidney injury through α2C-adrenoceptors in rats

Excitation of renal sympathetic nervous activity and the resulting increased levels of renal venous norepinephrine play important roles in renal ischaemia/reperfusion injury in rats. This study examined the effects of yohimbine, a non-selective α2-adrenoceptor antagonist, on renal venous norepinephrine levels and kidney function in acute kidney injury. Acute ischaemia/reperfusion-induced kidney injury was induced in rats by clamping the left renal artery and vein for 45min, followed by reperfusion, 2 weeks after a contralateral nephrectomy. Intravenous injection of yohimbine (0.1mg/kg) 5min prior to ischaemia significantly attenuated kidney injury and decreased the renal venous norepinephrine levels, as compared with vehicle-treated rats. To investigate the involvement of α2-adrenoceptor subtypes, we pre-treated with JP-1302, a selective α2C-adrenoceptor antagonist (1mg/kg). This suppressed renal venous norepinephrine levels and tumour necrosis factor-α and monocyte chemoattractant protein-1 mRNA levels after reperfusion and improved kidney function. Pre-treatment with BRL44408, a selective α2A-adrenoceptor antagonist (1mg/kg), or imiloxan, a selective α2B-adrenoceptor antagonist (1mg/kg) had no effect on renal function or tissue injury. These results suggest that yohimbine prevented ischaemia/reperfusion-induced kidney injury by inhibiting α2C-adrenoceptors and suppressing pro-inflammatory cytokine expression.

Effect of monoamine oxidase inhibitors on ischaemia/reperfusion-induced acute kidney injury in rats

Abstract Increases in renal sympathetic nerve activity during ischaemia and renal venous norepinephrine levels after reperfusion play important roles in the development of ischaemia/reperfusion‐induced acute kidney injury. In the present study, we examined the effect of isatin, an endogenous monoamine oxidase inhibitor, on renal venous norepinephrine levels, superoxide production after reperfusion, and ischaemia/reperfusion‐induced acute kidney injury. Ischaemia/reperfusion‐induced acute kidney injury was accomplished by clamping the left renal artery and vein for 45 min, followed by reperfusion, 2 weeks after contralateral nephrectomy. Renal superoxide production and norepinephrine overflow were elevated and significant renal tissue damage was observed following ischaemia/reperfusion injury. Intravenous injection of isatin (10 mg/kg) at 5 min before ischaemia increased the renal venous plasma norepinephrine level after reperfusion and aggravated ischaemia/reperfusion‐induced renal dysfunction and histological damage. The excessive superoxide production after reperfusion was significantly suppressed by isatin administration, indicating that the inhibition of oxidative deamination effectively suppressed superoxide production. These data suggest that the exacerbation effect of isatin is associated, at least in part, with increased norepinephrine levels but not with superoxide production. To the best of our knowledge, this is the first report of isatin involvement in the pathogenesis and/or development of acute kidney injury.

Investigation of the role of the amino acid residue at position 230 for catalysis in monomeric carbonyl reductase 3.

Monomeric carbonyl reductase 3 (CBR3) is a member of the short-chain dehydrogenase/reductase family. CBR3 exhibits much lower activity than monomeric carbonyl reductase 1 (CBR1) in humans and Chinese hamsters although they are highly homologous to each other in amino acid sequence levels. In the present study, we first cloned the CBR3 gene of rat origin (rCBR3), and characterized its enzymatic activity. rCBR3 also exhibited a limited catalytic efficiency similarly to the other CBR3 orthologues of humans and Chinese hamsters. Among the CBR3 orthologues, the human enzyme showed considerably lower activity. Compared with the amino acid sequences of CBR1 and CBR3 among humans, rats, Chinese hamsters, and mice, the tryptophan residue at position 230 is highly conserved while human CBR3 possesses rigid amino acid, proline, at that position instead. Thus, the Trp-230 was expected to be one of the important residues for catalysis since it locates in the hinge region at the substrate-binding loop. The substitution of tryptophan for proline in hCBR3 failed to affect the enzymatic characteristics. Similarly, the substitution of proline for tryptophan in either Chinese hamster CBR3 (CHCR3) or rCBR3 showed no significant change in the catalytic properties. These results suggest that limited catalytic efficiency of carbonyl reductase activity of CBR3 is a common property among animal species, and the substitution of the amino acid residue at position 230 alone has no apparent impact on their enzymatic activities.

Inhibition of α2C-adrenoceptors ameliorates cisplatin-induced acute renal failure in rats

Abstract Nephrotoxicity is a major adverse reaction of the anticancer drug, cisplatin. We investigated the renoprotective effects of the &agr;2‐adrenoceptor antagonist, yohimbine and selective &agr;2C‐adrenoceptor antagonist, JP‐1302, in cisplatin‐treated Sprague Dawley rats. Rats were given a single intravenous dose of 7.5 mg/kg cisplatin and then yohimbine or JP‐1302 was administered intraperitoneally at 0.1 or 3 mg/kg/day, respectively, for four days. Renal functional parameters, such as blood urea nitrogen, plasma creatinine, creatinine clearance and renal venous norepinephrine concentrations were measured. Kidney tissue damage and tumour necrosis factor‐&agr; (TNF‐&agr;) and monocyte chemoattractant protein‐1 (MCP‐1) mRNA levels were assessed after the animals were euthanized. Cisplatin treatment aggravated the kidney functional parameters of blood urea nitrogen, plasma creatinine and creatinine clearance. Renal venous norepinephrine concentrations were also elevated after cisplatin administration. Treatment with yohimbine or JP‐1302 clearly ameliorated kidney function and cell apoptosis. These treatments suppressed elevated renal plasma norepinephrine, TNF‐&agr;, MCP‐1 and cleaved caspase 3 expressions which occurred after administration of cisplatin. These results suggest that yohimbine can prevent cisplatin‐induced renal toxicity associated with acute kidney injury by suppressing cytokine expression through &agr;2C‐adrenoceptors.

Sex differences in ischaemia/reperfusion-induced acute kidney injury depends on the degradation of noradrenaline by monoamine oxidase

Ischaemic acute kidney injury (AKI) is a leading killer of both sexes; however, resistance to this injury is higher among women than men. We found that renal venous noradrenaline (NAd) overflow after reperfusion played important roles in the development of ischaemic AKI, and that the attenuation of AKI observed in female rats may be dependent on depressing the renal sympathetic nervous system with endogenous oestrogen. In the present study, we used male and female Sprague‐Dawley rats to investigate whether sex differences in the pathogenesis of ischaemic AKI are related to the degradation of NAd by monoamine oxidase (MAO) in the kidney. Ischaemic AKI was achieved by clamping the left renal artery and vein for 45 minutes followed by reperfusion 2 weeks after contralateral nephrectomy. Renal injury was more severe in male rats than in female rats and renal venous plasma NAd levels after reperfusion were markedly elevated in males, but not in females. These sex differences were eliminated by a treatment with isatin, a non‐selective MAO inhibitor, and moclobemide, a selective MAOA inhibitor, but not by selegiline, a selective MAOB inhibitor. Ischaemia decreased the mRNA expression levels of both MAOs in the kidney 1 day after reperfusion; however, MAOA mRNA expression levels were higher in female rats than in male rats. These results suggest that the degradation of NAd by MAOA in the kidney contributes to sex differences in the pathogenesis of ischaemia/reperfusion‐induced AKI.