Corticosteroid myopathy is a major clinical problem in patients undergoing chronic corticosteroid treatment and shows insidious and progressive muscle atrophy in proximal limbs. Although several mechanisms underlying the pathophysiology of muscle injury have been postulated, precise pathogenesis is still not clear. We evaluated the mitochondrial functions in patients receiving corticosteroids compared with those in healthy controls or patients not receiving corticosteroids. The serum levels and total production of lactate were investigated by an aerobic exercise test using a bicycle ergometer. Mitochondrial respiratory activities and oxidative damage in biopsied skeletal muscles were also studied. The results of aerobic exercise tests revealed a significant overproduction of lactate in patients treated with corticosteroids ( p < 0.005), which was positively correlated with total corticosteroid doses administered ( p < 0.0001). In these patients, mitochondrial enzyme activity in complex I was significantly decreased ( p < 0.05) and oxidative damage of biopsied skeletal muscle was remarkable both in mitochondrial and nuclear DNAs ( p < 0.001). The results suggest that chronic corticosteroid administration induces mitochondrial dysfunction and oxidative damage in skeletal muscles, which may be the pathogenesis, at least in part, of corticosteroid-induced myopathy.
1 Cilostazol (OPC-13013) undergoes extensive hepatic metabolism. The hydroxylation of the quinone moiety of cilostazol to OPC-13326 was the predominant route in all the liver preparations studies. The hydroxylation of the hexane moiety to OPC-13217 was the second most predominant route in vitro. 2 Ketoconazole (1 mM)wasthemostpotentinhibitorof both quinone and hexane hydroxylation. Both the CYP2D6 inhibitor quinidine (0.1 mM) and the CYP2C19 inhibitor omeprazole (10 mM) failed to consistently inhibit metabolism of cilostazol via either of these two predominant routes. 3 Data obtained from a bank of pre-characterized human liver microsomes demonstrated a stronger correlation (r2=0.68, P50.01) between metabolism of cilostazol to OPC-13326 and metabolism of felodipine, a CYP3A probe, that with probes for any other isoform. Cimetidine demonstrated concentration-dependent competitive inhibition of the metabolism of cilostazol by both routes. 4 Kinetic data demonstrated a Km value of 101 mM for cilostazol, suggesting a relatively low affinity of cilostazol for CYP3A. While recombinant CYP1A2, CYP2D6 and CYP2C19 were also able to catalyze formation of specific cilostazol metabolites, they did not appear to contribute significantly to cilostazol metabolism in whole human liver microsomes.
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