Pravastatin improves renal ischemia-reperfusion injury by inhibiting the mevalonate pathway.

Statins are known to lessen the severity of renal ischemia-reperfusion injury. The present study was undertaken to define the mechanism of renoprotective actions of statins using a mouse kidney injury model. Treatment of mice with pravastatin, a widely used statin, improved renal function after renal ischemia-reperfusion without lowering the plasma cholesterol level. Administration of pravastatin with mevalonate, a product of HMG-CoA reductase, eliminated renal protection suggesting an effect of pravastatin on mevalonate or its metabolism. In hypercholestrolemic apolipoprotein E knockout mice with reduced HMG-CoA reductase activity; the degree of injury was less severe than in control mice, however, there was no protective action of pravastatin on renal injury in the knockout mice. Treatment with a farnesyltransferase inhibitor (L-744832) mimicked pravastatin's protective effect but co-administration with the statin provided no additional protection. Both pravastatin and L-744832 inhibited the injury-induced increase in plasma IL-6 concentration to a similar extent. Our results suggest the protective effect of pravastatin on renal ischemia-reperfusion injury is mediated by inhibition of the mevalonate-isoprenoid pathway independent of its lipid lowering action.

Resistance to the skeletal muscle injury expressed by repeated treatment with compound A that has HMG-CoA reductase inhibitory activity.

It has been noted that chemical-induced initial insult is sometimes no longer detected in examinations after additional consecutive treatments, suggesting that the target organs acquire resistance to the chemical toxicity. In this study, whether acquired resistance to the skeletal muscle toxicity is observed during repeated treatment of a toxic dose of Compound A that has a 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitory activity was examined. F344 male rats (7-weeks old) were given a mixed diet with 0.12% Compound A (corresponding to approximately 100 mg/kg/day) for up to 56 days. Blood samples were obtained from the tail vein periodically during the dosing period, and utilized for the measurement of creatine kinase (CK) as a marker of skeletal muscle injury. In the necropsies on Days 4, 8, 11, 28, 42 and 56, the skeletal muscles from the rectus femoris were removed for histopathology or gene expression analysis. A satellite group was provided to measure the plasma concentrations of Compound A and M1, the active metabolite of Compound A. CK levels increased from Day 9 and reached approximately 30 times those of the controls on Day 12. Histopathology of the skeletal muscle on Day 11 revealed severe necrosis of the muscle fibers. However, in spite of continuous treatments to the damaged rats, the CK levels decreased after that and returned to normal levels on Day 18. No skeletal muscle injury was observed on Days 42 and 56. There were no marked differences in the exposure levels of Compound A and M1 between Days 8 (prior to CK elevation) and 28 (post CK elevation). As for the most significant changes in the gene expression analysis for the skeletal muscle on Days 42 and 56, the probe for IkappaBa, which is known as an inhibitor for nuclear factor-kappaB (NF-kappaB), increased 2-fold compared to the control. Furthermore, an increased probe for CCAAT/enhancer-binding protein (C/EBP) delta, a transcriptional factor, and a decreased probe for cAMP-response element-binding protein (CBP)/p300, a transcriptional coactivator, were also noted significantly on Day 56. These changes in the gene expression analysis suggested suppressed NF-kappaB-mediated transactivation, which was responsible for the protective effects on the muscle injury. Based on the present findings, the resistance to skeletal muscle injury observed in this study may be attributable to the suppressed NF-kappaB-mediated transactivation, but not to the decreased exposure to toxicants.

Renal effects of 26-week administration of olmesartan medoxomil/hydrochlorothiazide in rats.

The combination of an angiotensin II type 1 receptor blocker (ARB) and a diuretic is effective clinically in treatment of hypertension. As a non-clinical safety evaluation of a combination of the ARB olmesartan medoxomil (OM) and the diuretic hydrochlorothiazide (HCTZ), male and female normotensive rats were administered OM/HCTZ (fixed ratio of 8 : 5) orally by gavage for 26 weeks at dose levels of 0, 4.88, 16.25, 48.75, 162.5, 487.5, or 1625 mg/kg/day. Additional groups were given 1000 mg/ kg/day OM or 625 mg/kg/day HCTZ. Statistically significant and marked decreases in urinary protein excretion were observed in males and females given doses of 16.25 mg/kg/day or higher compared to vehicle-control groups. Increases in blood urinary nitrogen (BUN) were observed in males and females given doses of 16.25 and 162.5 mg/kg/day or higher, respectively. Increased incidence of chronic progressive nephropathy (CPN), a rat-specific spontaneous renal lesion, was observed in males and females given doses of 48.75 mg/kg/day or higher. An additional mechanistic study, consisting of male and female rats given 0, or 162.5 mg/kg/day OM/HCTZ, was conducted to clarify the toxicological significance of the increases in BUN and the increased incidence of CPN described above. This additional study clearly demonstrated that saline-supplementation through free access to saline in the drinking water ameliorated the elevation in BUN and also ameliorated the incidence of CPN. Consequently, the effects on BUN and CPN observed in the first study can be explained by the hemodynamic disturbances caused by the large doses and an exaggerated pharmacological action in volume-depleted normotensive animals. Importantly, the marked decreases in urinary protein were not affected by the saline-supplementation, and indicated that OM/HCTZ elicited a renoprotective effect, probably by an effect on the glomeruli. An additional toxicokinetic study revealed no drug interactions between OM and HCTZ. In conclusion, OM/HCTZ induced a renoprotective effect as well as changes probably attributed to the exaggerated pharmacological action of the ARB with diuretic in normotensive rats. These results suggest that OM/HCTZ may have renoprotective effects in clinical treatment of hypertensive patients.

Amelioration of renal ischemia-reperfusion injury by inhibition of IL-6 production in the poloxamer 407-induced mouse model of hyperlipidemia.

It is largely unknown whether hyperlipidemia is involved in the pathobiology of renal ischemia-reperfusion (I/R) injury that is an important cause of acute kidney injury. Here we studied the effect of experimental dyslipidemia on renal I/R injury. Renal I/R injury was less severe in hyperlipidemic mice treated with poloxamer 407 than in the control mice. Cytokine analyses revealed decreased levels of renal and serum IL-6 in the hyperlipidemic mice after renal I/R. Protection from renal I/R injury in the hyperlipidemic mice was diminished by administration of recombinant IL-6. Concanavalin A-induced IL-6 release from cultured splenocytes derived from the hyperlipidemic mice was lower than that from splenocytes of normal mice. In hypercholesterolemic apolipoprotein E-knockout mice, in which renal I/R injury is less severe than in control mice, renal I/R-induced IL-6 production was also less than that in controls. In angiopoietin-like 3-deficient mice, which were hypolipidemic, renal dysfunction and renal IL-6 level after I/R were similar to those of control mice. Our data indicate that the presence of experimental hyperlipidemia may be associated with a decreased risk of renal I/R injury, possibly mediated by reduced renal IL-6 production after the insult and extend the notion that an anti-IL6 agent would be useful for the treatment of acute kidney injury.