Effect of a high dose of simvastatin on muscle mitochondrial metabolism and calcium signaling in healthy volunteers.

Statin use may be limited by muscle side effects. Although incompletely understood to date, their pathophysiology may involve oxidative stress and impairments of mitochondrial function and of muscle Ca(2+) homeostasis. In order to simultaneously assess these mechanisms, 24 male healthy volunteers were randomized to receive either simvastatin for 80 mg daily or placebo for 8 weeks. Blood and urine samples and a stress test were performed at baseline and at follow-up, and mitochondrial respiration and Ca(2+) spark properties were evaluated on a muscle biopsy 4 days before the second stress test. Simvastatin-treated subjects were separated according to their median creatine kinase (CK) increase. Simvastatin treatment induced a significant elevation of aspartate amino transferase (3.38±5.68 vs -1.15±4.32 UI/L, P<0.001) and CK (-24.3±99.1±189.3 vs 48.3 UI/L, P=0.01) and a trend to an elevation of isoprostanes (193±408 vs 12±53 pmol/mmol creatinine, P=0.09) with no global change in mitochondrial respiration, lactate/pyruvate ratio or Ca(2+) sparks. However, among statin-treated subjects, those with the highest CK increase displayed a significantly lower Vmax rotenone succinate and an increase in Ca(2+) spark amplitude vs both subjects with the lowest CK increase and placebo-treated subjects. Moreover, Ca(2+) spark amplitude was positively correlated with treatment-induced CK increase in the whole group (r=0.71, P=0.0045). In conclusion, this study further supports that statin induced muscular toxicity may be related to alterations in mitochondrial respiration and muscle calcium homeostasis independently of underlying disease or concomitant medication.

Muscle mitochondrial metabolism and calcium signaling impairment in patients treated with statins.

The most common and problematic side effect of statins is myopathy. To date, the patho-physiological mechanisms of statin myotoxicity are still not clearly understood. In previous studies, we showed that acute application in vitro of simvastatin caused impairment of mitochondrial function and dysfunction of calcium homeostasis in human and rat healthy muscle samples. We thus evaluated in the present study, mitochondrial function and calcium signaling in muscles of patients treated with statins, who present or not muscle symptoms, by oxygraphy and recording of calcium sparks, respectively. Patients treated with statins showed impairment of mitochondrial respiration that involved mainly the complex I of the respiratory chain and altered frequency and amplitude of calcium sparks. The muscle problems observed in statin-treated patients appear thus to be related to impairment of mitochondrial function and muscle calcium homeostasis, confirming the results we previously reported in vitro.

Intramyocellular lipid accumulation is associated with permanent relocation ex vivo and in vitro of fatty acid translocase (FAT)/CD36 in obese patients.

AIMS/HYPOTHESIS: Intramyocellular lipids (IMCL) accumulation is a classical feature of metabolic diseases. We hypothesised that IMCL accumulate mainly as a consequence of increased adiposity and independently of type 2 diabetes. To test this, we examined IMCL accumulation in two different models and four different populations of participants: muscle biopsies and primary human muscle cells derived from non-obese and obese participants with or without type 2 diabetes. The mechanism regulating IMCL accumulation was also studied. METHODS: Muscle biopsies were obtained from ten non-obese and seven obese participants without type 2 diabetes, and from eight non-obese and eight obese type 2 diabetic patients. Mitochondrial respiration, citrate synthase activity and both AMP-activated protein kinase and acetyl-CoA carboxylase phosphorylation were measured in muscle tissue. Lipid accumulation in muscle and primary myotubes was estimated by Oil Red O staining and fatty acid translocase (FAT)/CD36 localisation by immunofluorescence. RESULTS: Obesity and type 2 diabetes are independently characterised by skeletal muscle IMCL accumulation and permanent FAT/CD36 relocation. Mitochondrial function is not reduced in type 2 diabetes. IMCL accumulation was independent of type 2 diabetes in cultured myotubes and was correlated with obesity markers of the donor. In obese participants, membrane relocation of FAT/CD36 is a determinant of IMCL accumulation. CONCLUSIONS/INTERPRETATION: In skeletal muscle, mitochondrial function is normal in type 2 diabetes, while IMCL accumulation is dependent upon obesity or type 2 diabetes and is related to sarcolemmal FAT/CD36 relocation. In cultured myotubes, IMCL content and FAT/CD36 relocation are independent of type 2 diabetes, suggesting that distinct factors in obesity and type 2 diabetes contribute to permanent FAT/CD36 relocation ex vivo.

Limited predictive value of the IDF definition of metabolic syndrome for the diagnosis of insulin resistance measured with the oral minimal model.

AIM: To assess the agreement of the NCEP ATP-III and the IDF definitions of metabolic syndrome and to determine their predictive values for the diagnosis of insulin resistance. METHODS: For this purpose, we recruited 150 subjects (94 women and 56 men) and determined the presence of metabolic syndrome using the NCEP-ATP III and IDF definitions. We evaluated their insulin sensitivity S(I) using Caumo's oral minimal model after a standardized hyperglucidic breakfast test. Subjects whose S(I) was in the lowest quartile were considered as insulin resistant. We then calculated sensitivity, specificity, positive and negative predictive values of both definitions for the diagnosis of insulin resistance. RESULTS: The prevalence of metabolic syndrome was 37.4% (NCEP-ATP III) and 40% (IDF). Agreement between the two definitions was 96%. Using NCEP-ATP III and IDF criteria for the identification of insulin resistant subjects, sensitivity was 55.3% and 63%, specificity was 68.8% and 67.8%, positive predictive value was 37.5% and 40%, negative predictive value was 81.9% and 84.5%, respectively. Positive predictive value increased with the number of criteria for both definitions. CONCLUSION: Whatever the definition, the scoring of metabolic syndrome is not a reliable tool for the individual diagnosis of insulin resistance, and is more useful for excluding this diagnosis.