BACKGROUND AND PURPOSE Renal ischaemia/reperfusion (RI/R) injury is a major cause of acute kidney injury (AKI) and an important determinant of long‐term kidney dysfunction. AMP‐kinase and histone deacetylase sirtuin 1 (SIRT1) regulate cellular metabolism and are activated during hypoxia. We investigated whether AMP‐kinase activator AICAR (5‐amino‐4‐imidazolecarboxamide riboside‐1‐β‐D‐ribofuranoside) ameliorates RI/R injury and whether SIRT1 is involved in the pathogenesis.EXPERIMENTAL APPROACH Eight‐week‐old Sprague Dawley rats were divided into five groups: (i) sham‐operated group; (ii) I/R group (40 min bilateral ischaemia followed by 24 h of reperfusion; (iii) I/R group + AICAR 50 mg·kg⁻¹ i.v. given 60 min before operation; (iv). I/R group + AICAR 160 mg·kg⁻¹ i.v; (v) I/R group + AICAR 500 mg·kg⁻¹ i.v. Serum creatinine and urea levels were measured. Acute tubular necrosis (ATN), monocyte/macrophage infiltration and nitrotyrosine expression were scored. Kidney AMP‐activated protein kinase (AMPK) and SIRT1 expressions were measured.KEY RESULTS Highest dose of AICAR decreased serum creatinine and urea levels, attenuated I/R injury‐induced nitrosative stress and monocyte/macrophage infiltration, and ameliorated the development of ATN. Kidney I/R injury was associated with decreased AMPK phosphorylation and a fivefold increase in kidney SIRT1 expression. AICAR increased pAMPK/AMPK ratio and prevented the I/R‐induced increase in renal SIRT1 expression.CONCLUSIONS AND IMPLICATIONS AICAR protects against the development of ATN after kidney I/R injury. Activators of kidney AMP kinase may thus represent a novel therapeutic approach to patients susceptible to AKI and to those undergoing kidney transplantation. The present study also suggests a role for SIRT1 in the pathogenesis of RI/R injury.

Endothelial dysfunction is associated with hypertension, hypercholesterolemia, and heart failure. We tested the hypothesis that spontaneously diabetic Goto-Kakizaki (GK) rats, a model for type 2 diabetes, exhibit endothelial dysfunction. Rats also received a high-sodium diet (6% NaCl [wt/wt]) and chronic angiotensin type 1 (AT ₁ ) receptor blockade (10 mg/kg PO valsartan for 8 weeks). Compared with age-matched nondiabetic Wistar control rats, GK rats had higher blood glucose levels (9.3±0.5 versus 6.9±0.2 mmol/L for control rats), 2.7-fold higher serum insulin levels, and impaired glucose tolerance (all P <0.05). Telemetry-measured mean blood pressure was 15 mm Hg higher in GK rats ( P <0.01) compared with control rats, whereas heart rates were not different. Heart weight– and kidney weight–to–body weight ratios were higher in GK rats ( P <0.05), and 24-hour albuminuria was increased 50%. Endothelium-mediated relaxation of noradrenaline-precontracted mesenteric arterial rings by acetylcholine was impaired compared with the control condition ( P <0.05), whereas the sodium nitroprusside–induced relaxation was similar. Preincubation of the arterial rings with the NO synthase inhibitor N ^G -nitro- l -arginine methyl ester and the cyclooxygenase inhibitor diclofenac inhibited relaxations to acetylcholine almost completely in GK rats but not in Wistar rats, suggesting that endothelial dysfunction can be in part attributed to reduced relaxation via arterial K ⁺ channels. Perivascular monocyte/macrophage infiltration and intercellular adhesion molecule-1 overexpression were observed in GK rat kidneys. A high-sodium diet increased blood pressure by 24 mm Hg and 24-hour albuminuria by 350%, induced cardiac hypertrophy, impaired endothelium-dependent relaxation further, and aggravated inflammation (all P <0.05). The serum level of 8-isoprostaglandin F _2α , a vasoconstrictor and antinatriuretic arachidonic acid metabolite produced by oxidative stress, was increased 400% in GK rats on a high-sodium diet. Valsartan decreased blood pressure in rats fed a low-sodium diet and prevented the inflammatory response. In rats fed a high-sodium diet, valsartan did not decrease blood pressure or improve endothelial dysfunction but protected against albuminuria, inflammation, and oxidative stress. As measured by quantitative autoradiography, AT ₁ receptor expression in the medulla was decreased in GK compared with Wistar rats, whereas cortical AT ₁ receptor expression, medullary and cortical angiotensin type 2 (AT ₂ ) receptor expressions, and adrenal ACE and neutral endopeptidase expressions were unchanged. A high-sodium diet did not influence renal AT ₁ , AT ₂ , ACE, or neutral endopeptidase expressions. In valsartan-treated GK rats, the cortical and medullary AT ₁ receptor expressions were decreased in the presence and absence of a high-sodium diet. A high-sodium diet increased plasma brain natriuretic peptide concentrations in presence and absence of valsartan treatment. We conclude that hypertension in GK rats is salt sensitive and associated with endothelial dysfunction and perivascular inflammation. AT ₁ receptor blockade ameliorates inflammation during a low-sodium diet and partially protects against salt-induced vascular damage by blood pressure–independent mechanisms.

We examined whether xanthine oxidoreductase (XOR), a hypoxia-inducible enzyme capable of generating reactive oxygen species, is involved in the onset of angiotensin (Ang) II–induced vascular dysfunction in double-transgenic rats (dTGR) harboring human renin and human angiotensinogen genes. In 7-week-old hypertensive dTGR, the endothelium-mediated relaxation of noradrenaline (NA)-precontracted renal arterial rings to acetylcholine (ACh) in vitro was markedly impaired compared with Sprague Dawley rats. Preincubation with superoxide dismutase (SOD) improved the endothelium-dependent vascular relaxation, indicating that in dTGR, endothelial dysfunction is associated with increased superoxide formation. Preincubation with the XOR inhibitor oxypurinol also improved endothelium-dependent vascular relaxation. The endothelium-independent relaxation to sodium nitroprusside was similar in both strains. In dTGR, serum 8-isoprostaglandin F _2α , a vasoconstrictor and antinatriuretic arachidonic acid metabolite produced by oxidative stress, was increased by 100%, and the activity of XOR in the kidney was increased by 40%. Urinary nitrate plus nitrite (NO _x ) excretion, a marker of total body NO generation, was decreased by 85%. Contractile responses of renal arteries to Ang II, endothelin-1 (ET-1), and NA were decreased in dTGR, suggesting hypertension-associated generalized changes in the vascular function rather than a receptor-specific desensitization. Valsartan (30 mg/kg PO for 3 weeks) normalized blood pressure, endothelial dysfunction, and the contractile responses to ET-1 and NA. Valsartan also normalized serum 8-isoprostaglandin F _2α levels, renal XOR activity, and, to a degree, NO _x excretion. Thus, overproduction of Ang II in dTGR induces pronounced endothelial dysfunction, whereas the sensitivity of vascular smooth muscle cells to nitric oxide is unaltered. Ang II–induced endothelial dysfunction is associated with increased oxidative stress and vascular xanthine oxidase activity.

Kidney ischemia‐reperfusion (I/R) injury is a common cause of acute kidney injury. We tested whether dexmedetomidine (Dex), an alpha2 adrenoceptor (α2‐AR) agonist, protects against kidney I/R injury. Sprague–Dawley rats were divided into four groups: (1) Sham‐operated group; (2) I/R group (40 min ischemia followed by 24 h reperfusion); (3) I/R group + Dex (1 μg/kg i.v. 60 min before the surgery), (4) I/R group + Dex (10 μg/kg). The effects of Dex postconditiong (Dex 1 or 10 μg/kg i.v. after reperfusion) as well as the effects of peripheralα2‐AR agonism with fadolmidine were also examined. Hemodynamic effects were monitored, renal function measured, and acute tubular damage along with monocyte/macrophage infiltration scored. Kidney protein kinase B, toll like receptor 4, light chain 3B, p38 mitogen‐activated protein kinase (p38 MAPK), sirtuin 1, adenosine monophosphate kinase (AMPK), and endothelial nitric oxide synthase (eNOS) expressions were measured, and kidney transciptome profiles analyzed. Dex preconditioning, but not postconditioning, attenuated I/R injury‐induced renal dysfunction, acute tubular necrosis and inflammatory response. Neither pre‐ nor postconditioning with fadolmidine protected kidneys. Dex decreased blood pressure more than fadolmidine, ameliorated I/R‐induced impairment of autophagy and increased renal p38 and eNOS expressions. Dex downregulated 245 and upregulated 61 genes representing 17 enriched Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, in particular, integrin pathway and CD44. Ingenuity analysis revealed inhibition of Rac and nuclear factor (erythroid‐derived 2)‐like 2 pathways, whereas aryl hydrocarbon receptor (AHR) pathway was activated. Dex preconditioning ameliorates kidney I/R injury and inflammatory response, at least in part, through p38‐CD44‐pathway and possibly also through ischemic preconditioning.