Statins have a known side effect as myopathy, and this could be aggravated by simultaneous use of some other drugs, especially those which inhibit CYP3A4 as the cytoplasmic enzyme responsible for metabolization of statins like simvastatin, lovastatin and atorvastatin (10). A similar effect is seen also when statins are co-prescribed with fibrates (16). Fibrates have been associated with muscle toxicity; an effect that is more pronounced in patients also treated with a statin. The mechanism is not agreed upon. Glucuronidation, which is an important pathway for renal excretion of lipophilic statins, appears to be significantly inhibited by gemfibrozil (17).
The incidence of myopathy with the simultaneous administration of some statins and gemfibrozil is estimated 1 to 5 percent (18, 19), including rhabdomyolysis as the most severe form (4). Muscle toxicity can be reduced by changing the type of fibrate (e.g., fenofibrate is found to bring the lowest risk) and by using statins at relatively low doses because the adverse effect is dose-dependent (20, 21). Since the concomitant use of statins and fibrates in a common practice, and many patients have hypertriglyceridemia accompanied by hypercholesterolemia, this subject was a trigger for the current study.
Physical exertion has already been found to aggravate SAMS (22) leading to increase in plasma CK levels, understandably more in untrained people. So, the risk of myopathy would be lower if a gradual program of increasing exercise is followed in these individuals, letting time for metabolic clearance of drugs and adaptation. However, the muscle injury from exercise even without such adaptation is usually mild and subclinical (22).
In our project, we exposed the rats to a sudden challenge of forced maximal exercise to see the highest possible myopathy. Hence, the serum levels of CK, aldolase and LDH were significantly more in those rats which had forced physical activity vs. the rats without any enforced physical exercise. The rats receiving combined ATV and GMF showed further increase in the plasma enzyme levels. Swimming tolerance time was strikingly decreased (P value < 0.001) in rats consuming ATV and GMF (figure 2), supporting the synergistic effect of exertion and drug.
To compare our work with other studies in this field a few are available. In a study by Osaki et al., a model for statin-induced myopathy was created using skeletal muscle-specific HMGCAR knockout mice. They showed postnatal myopathy with high serum CK levels and myonecrosis, which underlines the role of HMGCAR in metabolization of statins (23). In another work, Nakahara et al induced myopathy by HMGCAR Inhibitors in rabbits, followed by histopathological examination of skeletal muscle and measurement of CK. The findings included light microscopic muscle fiber necrosis and degeneration, altered acid phosphatase activity in cells, and electron microscopic alterations including autophagic vacuoles, swelling of mitochondria, disruption and hypercontraction of myofibrils (24).
In the current research, the most dramatic effect of ascorbic acid was reducing elevated CK (as a main biomarker of skeletal muscle damage) levels in ATV/GMF plus swim group (figure 3). It increased swimming tolerance time in the drug-induced myopathy group, too (figure 2). Ascorbic acid could not alter elevated LDH and aldolase levels in the drug-induced myopathy group, though (figures 4, 5). Perhaps the molecular mechanism is that ascorbic acid provides electrons needed for reducing oxygen, the antioxidant capabilities also shared by a number of other compounds, including vitamin E and folic acid. It is also a cofactor for reduction of folate to dihydro- and tetrahydrofolate (14).
Ascorbic acid is involved in the following biologic processes: 1. Fatty acid transport: The transport of long-chain fatty acids across the mitochondrial membrane is a carnitine-dependent process, and carnitine synthesis requires ascorbic acid as an electron donor (25). 2. Collagen synthesis: Formation of collagen requires enzymatic hydroxylation of two amino acids, proline and lysine; ascorbic acid is an electron donor in reactions catalyzed by the enzymes; prolyl hydroxylase and lysyl hydroxylase, which form hydroxyproline and hydroxylysine, respectively. Failure of this step in collagen synthesis results in impaired wound healing, defective tooth formation, and deficient osteoblast and fibroblast function. 3. Synthesis of neurotransmitter norepinephrine, which involves hydroxylation of dopamine by the enzyme dopamine-beta-mono-oxygenase, where ascorbic acid is a required cofactor 4. Metabolism of prostaglandin and prostacyclin: It may be capable of attenuating the inflammatory response or even sepsis syndrome (24). 5. Nitric oxide synthesis: Ascorbic acid may promote synthesis of nitric oxide, a potent vasodilator (26, 27). 6. Mitochondrial health: Regarding the extreme dependence of muscle activity to mitochondria for ATP, it is worth mentioning that mitochondrial injuries in general result in oxidative stress, i.e., higher levels of reactive oxygen species (28, 29) leading to cell membrane damage through lipid peroxidation.