Possible mechanisms underlying statin-induced skeletal muscle toxicity in L6 fibroblasts and in rats.

3-Hydroxy-3-methylglutaryl CoA reductase inhibitors (statins) are safe and well-tolerated therapeutic drugs. However, they occasionally induce myotoxicity such as myopathy and rhabdomyolysis. Here, we investigated the mechanism of statin-induced myotoxicity in L6 fibroblasts and in rats in vivo. L6 fibroblasts were differentiated and then treated with pravastatin, simvastatin, or fluvastatin for 72 h. Hydrophobic simvastatin and fluvastatin decreased cell viability in a dose-dependent manner via apoptosis characterized by typical nuclear fragmentation and condensation and caspase-3 activation. Both hydrophobic statins transferred RhoA localization from the cell membrane to the cytosol. These changes induced by both hydrophobic statins were completely abolished by the co-application of geranylgeranylpyrophosphate (GGPP). Y27632, a Rho-kinase inhibitor, mimicked the hydrophobic statin-induced apoptosis. Hydrophilic pravastatin did not affect the viability of the cells. Fluvastatin was continuously infused (2.08 mg/kg at an infusion rate of 0.5 mL/h) into the right internal jugular vein of the rats in vivo for 72 h. Fluvastatin infusion significantly elevated the plasma CPK level and transferred RhoA localization in the skeletal muscle from the cell membrane to the cytosol. In conclusion, RhoA dysfunction due to loss of lipid modification with GGPP is involved in the mechanisms of statin-induced skeletal muscle toxicity.

[Effect of the brand and generic medicine of pravastatin on dyslipidemia in rabbits fed a high cholesterol diet].

Mevalotin containing pravastatin, a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor, is the brand medicine and well known to be effective for patients with dyslipidemia. Now, more than 20 generic pravastatins are available for clinical therapy. We compared pharmaceutical property of Mevan,a generic pravastatin, with that of Mevalotin.According to the definition of the Japanese Pharmacopoeia, Mevalotin 10 mg tablets were uniform in pravastatin content, whereas 5 mg tablets were rather variable. Variation in pravastatin content of Mevan 5 mg tablets was the same as Mevalotin 5 mg, whereas that of 10 mg tablets was very variable. The plasma concentration of pravastatin in the normal rabbits continuously increased until 180 min after oral administration of 30 mg Mevan, whereas it increased in a biphasic pattern after 30 mg Mevalotin.All rabbits were fed 0.2% cholesterol diet throughout the experiment. After 8 weeks, oral administration of either Mevalotin or Mevan was started at the dose of 30 mg pravastatin/day for 16 weeks. After a transient increase for a few weeks, the plasma levels of total- and LDL-cholesterol gradually decreased in Mevalotingroup, whereas these levels did not significantly changed in Mevan group within 16 weeks. The level of HDL-cholesterol in Mevan group tended to increase but not in Mevalotin group. The triglyceride level in Mevan group changed as well as that in Mevalotin group until 10 weeks after administration, and then gradually increased. The present results suggest that pharmaceutical properties of Mevan are not always identical with those of Mevalotin.

Improvement of stunned myocardium in dogs with olmesartan, an angiotensin II type 1 receptor antagonist, is independent of type 2 receptors.

Olmesartan is a selective angiotensin II type 1 receptor (AT1) antagonist. In pentobarbital-anesthetized open-chest dogs, ischemia/reperfusion was induced by ligating the left anterior descending coronary artery for 20 min and releasing it for 60 min, respectively. The myocardial contraction in the ischemic area decreased and returned towards its pre-ischemic level during reperfusion but incompletely. Olmesartan improved the recovery of myocardial contraction during reperfusion associated with restoration of myocardial ATP. Angiotensin II repelled by AT1 receptors occupied by olmesartan can reach and stimulate the angiotensin II type 2 (AT2) receptors, resulting in some beneficial effects on the ischemic myocardium. In fact, AT2 receptor mRNA was found in the adult dog myocardium. In addition, the plasma level of angiotensin II was significantly increased by olmesartan. PD123319, a selective AT2 receptor antagonist, however, did not modify the effect of olmesartan on the cardiac contraction. The hypertensive response to exogenous angiotensin II was completely inhibited by olmesartan, whereas PD123319 did not abolish the effect of olmesartan. In conclusion, olmesartan protects the ischemic/reperfused heart against ischemic injury through inhibition of AT1 receptors but not indirect activation of AT2 receptors.

All hydrophobic HMG-CoA reductase inhibitors induce apoptotic death in rat pulmonary vein endothelial cells.

3-Hydroxy-3-methyl-glutaryl-CoA (HMG-CoA) reductase inhibitors (statins) are effective in patients with hypercholesterolemia to reduce risk of cardiovascular diseases, because of not only their lowering cholesterol effects but also their pleiotropic effects, such as improvement of endothelial cell dysfunction. On the other hand, statins prevent cell proliferation of various cells, including endothelial cells. We examined effects of all statins available at present on the viability of cultured rat pulmonary vein endothelial cells. Lovastatin, simvastatin, atorvastatin, fluvastatin and cerivastatin, which are hydrophobic statins, markedly reduced cell viability associated with DNA fragmentation, DNA laddering and activation of caspase-3, suggesting apoptotic cell death. Pravastatin, which is a hydrophilic statin, however, did not induce cell apoptosis. Apoptosis induced by hydrophobic statins was associated with activation of apoptosis-related intracellular signal transduction systems; attenuation of localization of RhoA to the membrane, induction of Rac1, and increase in phosphorylation of c-Jun N-terminal kinase and c-Jun. Endothelial cell apoptosis is underlying the improvement of the endothelial dysfunction with hydrophobic statins.

Effects of nebivolol on ischemia-induced metabolic changes in dog hearts.

dl-Nebivolol has a beta(1)-adrenergic blocking property and l-nebivolol has an endothelial-dependent vasodilating property, sp that a racemic mixture, deltal-nebivolol, shows both properties. This study examined the effect of dl-nebivolol on ischemic myocardium in anesthetized open chest dogs. Ischemia was induced for 3 min by ligating the left anterior descending coronary artery 10 min after IV injection of vehicle, dl-nebivolol (0.03, 0.1, and 0.3 mg/kg), or d- or l-nebivolol (0.15 mg/kg). Ischemia significantly decreased the levels of ATP, creatine phosphate, and fructose-1,6-diphosphate and increased those of ADP, AMP, hexose monophosphates, and ratio of [lactate]/[pyruvate]. dl-Nebivolol at higher doses significantly attenuated some metabolic changes caused by ischemia. Although neither enantiomers significantly affected these ischemia-induced metabolic changes, d-nebivolol appeared to attenuate adenine nucleotide reduction due to ischemia. Pretreatment with Nw-nitro-l-arginine methyl ester did not abolish the restoration of ischemia-induced myocardial metabolic changes by dl-nebivolol. In conclusion, dl-nebivolol lessens ischemic derangement of myocardial metabolism, and the effects may be due mainly to its beta-adrenergic blocking property but not to endothelium-dependent vasorelaxing property.

Effects of minoxidil on ischemia-induced mechanical and metabolic dysfunction in dog myocardium.

Effects of minoxidil on ischemia-induced myocardial mechanical and metabolic dysfunction were examined in anesthetized open-chest dogs. A regional portion of the left ventricle was made ischemic for 20 min by ligating the left anterior descending coronary artery, and then reperfused for 120 min. Dimethylsulfoxide or minoxidil (0.3, or 1.0 mg/kg) was injected intravenously 10 min before ligation. Ischemia decreased regional myocardial contraction, and reperfusion recovered it but incompletely. Myocardial metabolic derangement was observed during ischemia, such as decreases in the myocardial levels of ATP and creatine phosphate. These metabolic changes caused by ischemia were restored by reperfusion. Minoxidil injection at 0.3 and 1.0 mg/kg significantly decreased blood pressures but increased coronary flow. Pretreatment with minoxidil significantly enhanced the recovery of myocardial contraction during reperfusion after ischemia. The levels of ATP and creatine phosphate in the ischemic myocardium were significantly preserved by minoxidil at 0.3 mg/kg. No significant effect of minoxidil on the metabolism was observed in the 120 min reperfused myocardium. In conclusion, minoxidil improved the mechanical dysfunction in the reperfused heart and the drug at low dose preserved high-energy phosphates during ischemia.

Effects of radical scavengers, TA248 and TA276, on stunned myocardium in dogs: involvement of K ATP channels.

TA248 (7-(beta-D-glucopyranosyloxy)-4-hydroxy-3-octyloxy-2H-1-benzopyran-2-one) and TA276 (sodium 7-hydroxy-3-octyloxy-2H-1-benzopyran-2-one-4-oxide) were newly developed as radical scavengers. In vitro, TA276 scavenged both superoxide anions (. O(2)(-)) and hydroxyl radicals (. OH). TA248 also trapped. O(2)(-), but had less activity on. OH. In vivo, left ventricular contractile functions were determined in pentobarbital-anesthetized open-chest dogs. A regional portion of the left ventricular wall was made ischemic for 20 min by ligating the left anterior descending coronary artery and then reperfused for 60 min. TA248 (3 mg/kg) and TA276 (3 mg/kg) injected i.v. 10 min before occlusion significantly improved myocardial stunning that is contractile dysfunction observed after reperfusion following brief ischemia. Glibenclamide (1 mg/kg) injected i.v. 20 min before occlusion significantly worsened the myocardial stunning. Pretreatment with glibenclamide completely abolished the beneficial effect of TA276 on myocardial stunning, whereas it only partially attenuated that of TA248, showing some improvement even in the presence of glibenclamide. Because of the incomplete scavenging activity of TA248, residual. OH may play some roles in improvement of myocardial stunning with TA248 in the presence of glibenclamide. We speculate that the. OH may eject glibenclamide from its binding site on K(ATP) channels, leading to opening of the channels.