Statin therapy induces ultrastructural damage in skeletal muscle in patients without myalgia

Human skeletal muscle drug transporters determine local exposure and toxicity of statins

RATIONALE

The 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, or statins, are important drugs used in the treatment and prevention of cardiovascular disease. Although statins are well tolerated, many patients develop myopathy manifesting as muscle aches and pain. Rhabdomyolysis is a rare but severe toxicity of statins. Interindividual differences in the activities of hepatic membrane drug transporters and metabolic enzymes are known to influence statin plasma pharmacokinetics and risk for myopathy. Interestingly, little is known regarding the molecular determinants of statin distribution into skeletal muscle and its relevance to toxicity.

OBJECTIVE

We sought to identify statin transporters in human skeletal muscle and determine their impact on statin toxicity in vitro.

METHODS AND RESULTS

We demonstrate that the uptake transporter OATP2B1 (human organic anion transporting polypeptide 2B1) and the efflux transporters, multidrug resistance-associated protein (MRP)1, MRP4, and MRP5 are expressed on the sarcolemmal membrane of human skeletal muscle fibers and that atorvastatin and rosuvastatin are substrates of these transporters when assessed using a heterologous expression system. In an in vitro model of differentiated, primary human skeletal muscle myoblast cells, we demonstrate basal membrane expression and drug efflux activity of MRP1, which contributes to reducing intracellular statin accumulation. Furthermore, we show that expression of human OATP2B1 in human skeletal muscle myoblast cells by adenoviral vectors increases intracellular accumulation and toxicity of statins and such effects were abrogated when cells overexpressed MRP1.

CONCLUSIONS

These results identify key membrane transporters as modulators of skeletal muscle statin exposure and toxicity.

Hyaline inclusion myopathy: unmasked by statin therapy

We report a case of a patient with history of alcohol abuse, treatment for hepatitis C and repeated strenuous physical activity who developed severe muscle pain and weakness during statin therapy. The symptoms persisted after discontinuation of the drug. The diagnosis of myopathy was made clinically and by electromyography. As his symptoms persisted a muscle biopsy was performed which showed inclusions consistent with hyaline inclusions. Hyaline inclusion myopathy is discussed in the context of this case with review of the literature.

Association between statin-associated myopathy and skeletal muscle damage

BACKGROUND

Many patients taking statins often complain of muscle pain and weakness. The extent to which muscle pain reflects muscle injury is unknown.

METHODS

We obtained biopsy samples from the vastus lateralis muscle of 83 patients. Of the 44 patients with clinically diagnosed statin-associated myopathy, 29 were currently taking a statin, and 15 had discontinued statin therapy before the biopsy (minimal duration of discontinuation 3 weeks). We also included 19 patients who were taking statins and had no myopathy, and 20 patients who had never taken statins and had no myopathy. We classified the muscles as injured if 2% or more of the muscle fibres in a biopsy sample showed damage. Using reverse transcriptase polymerase chain reaction, we evaluated the expression levels of candidate genes potentially related to myocyte injury.

RESULTS

Muscle injury was observed in 25 (of 44) patients with myopathy and in 1 patient without myopathy. Only 1 patient with structural injury had a circulating level of creatine phosphokinase that was elevated more than 1950 U/L (10x the upper limit of normal). Expression of ryanodine receptor 3 was significantly upregulated in patients with biopsy evidence of structural damage (1.7, standard error of the mean 0.3).

INTERPRETATION

Persistent myopathy in patients taking statins reflects structural muscle damage. A lack of elevated levels of circulating creatine phosphokinase does not rule out structural muscle injury. Upregulation of the expression of ryanodine receptor 3 is suggestive of an intracellular calcium leak.

Use of an electronic medical record to characterize cases of intermediate statin-induced muscle toxicity

Statin use can be accompanied by a variety of musculoskeletal complaints. The authors describe the clinical characteristics of case patients who experienced adverse statin-induced musculoskeletal symptoms within a large population-based cohort in Central Wisconsin. Case status was determined based on elevated serum creatine kinase (CK) levels and the presence of at least 1 physician note reflecting an increased index of suspicion for statin intolerance. From the medical records of nearly 2 million unique patients, the authors identified more than 20,000 potential study patients ( approximately 1%) having CK data and at least 1 exposure to a statin drug. Manual screening was completed on 2227 patients with CK levels in the upper 10th percentile. Of those screened, 267 met inclusion criteria (12.0% eligibility) and 218 agreed to participate in a retrospective study characterizing the risk determinants of statin-induced muscle toxicity. Three categoric pain variables were graded retrospectively (distribution, location, and severity of pain). The presenting complaints of the case patients were extremely heterogeneous. The number of patients with a compelling pain syndrome (diffuse, proximal muscle pain of high intensity) increased at higher serum CK levels; the number of patients with indeterminate pain variables decreased at higher serum CK levels. The lines reflecting these relationships cross at a CK level of approximately 1175 U/L, approximately half the threshold level needed to make a clinical diagnosis of "myopathy" (ie, CK >10-fold the upper limit of normal).

Identifying genetic risk factors for serious adverse drug reactions: current progress and challenges

Serious adverse drug reactions (SADRs) are a major cause of morbidity and mortality worldwide. Some SADRs may be predictable, based upon a drug's pharmacodynamic and pharmacokinetic properties. Many, however, appear to be idiosyncratic. Genetic factors may underlie susceptibility to SADRs and the identification of predisposing genotypes may improve patient management through the prospective selection of appropriate candidates. Here we discuss three specific SADRs with an emphasis on genetic risk factors. These SADRs, selected based on wide-sweeping clinical interest, are drug-induced liver injury, statin-induced myotoxicity and drug-induced long QT and torsades de pointes. Key challenges for the discovery of predictive risk alleles for these SADRs are also considered.

Distribution of creatine kinase in the general population: implications for statin therapy

BACKGROUND

Eligible subjects with mildly elevated serum creatine kinase (CK) activity are often excluded before randomization in statin trials, but patients may potentially be misclassified as having hyperCKemia when inappropriate reference limits are used. Little information is usually given regarding how reference limit data were established, although evidence suggests that the variation of CK activity in the general population is wider than reflected in reference intervals in current use.

METHODS

We determined reference intervals for serum CK according to National Committee on Clinical Laboratory Standards/Nordic Reference Interval Project guidelines, in a stratified random sample of the population, including 1444 individuals, aged 34 to 60 years, after 3 days of rest. Participants were mainly of white European (n = 503), South Asian (n = 292), or African descent (n = 580).

RESULTS

The calculated upper reference limits (97.5th percentile) for nonblack and black women and men were 2 to 5 times higher than recommended by the assay manufacturer. Respectively 13% of the white Europeans, 23% of South Asians, and 49% of the black people had serum CK activities above the manufacturer-provided limits.

CONCLUSION

The variation in CK activity within the population is wider than previously suggested in smaller, nonrandom samples, and relatively high values occur frequently in all subgroups studied after rest. Therefore, we infer that upward adjustment of the upper reference limit is necessary for all population subgroups studied. The use of appropriately established reference intervals may improve the use of statins and particularly benefit the control of dyslipidemia in those with relatively high baseline CK activity.

Chemopreventive and bioenergetic signaling effects of PDK1/Akt pathway inhibition in a transgenic mouse model of prostate cancer

The phosphoinositide-dependent kinase 1 (PDK1)/Akt pathway is an important regulator of multiple biological processes including cell growth, survival, and glucose metabolism. In light of the mechanistic link between Akt signaling and prostate tumorigenesis, we evaluated the chemopreventive relevance of inhibiting this pathway in the transgenic adenocarcinoma of the model prostate (TRAMP) mouse with OSU03012, a celecoxib-derived, but COX-2-inactive, PDK1 inhibitor. Beginning at ten weeks of age when prostatic intraepithelial neoplasia (PIN) lesions are well developed, TRAMP mice received OSU03012 via daily oral gavage for 8 weeks. The drug treatment significantly decreased the weight of all 4 prostate lobes as well as the grade of epithelial proliferation in the dorsal and lateral lobes compared to vehicle-treated control mice. The incidences of carcinoma and metastasis were decreased, although not to statistically significant levels. Treated mice lost body fat and failed to gain weight independent of food intake. This change and periportal hepatocellular atrophy can be linked to sustained PDK1 inhibition through downstream inactivation of glycogen synthase. Centrilobular hepatocellular hypertrophy and necrosis of Type II skeletal myofibers were also compound-related effects. We conclude that targeting of the PDK1/Akt pathway has chemopreventive relevance in prostate cancer and causes other in vivo effects mediated in part by an alteration of bioenergetic signaling.

Should women be offered cholesterol lowering drugs to prevent cardiovascular disease? No

Women in western countries are more likely to die from heart disease than from cancer. Scott M Grundy argues that the risks make preventive treatment essential, but Malcolm Kendrick believes the evidence of benefit is not strong enough

Fluvastatin and atorvastatin affect calcium homeostasis of rat skeletal muscle fibers in vivo and in vitro by impairing the sarcoplasmic reticulum/mitochondria Ca2+-release system

The mechanism by which the 3-hydroxy-3-methyl-glutaryl-CoA reductase inhibitors (statins) induce skeletal muscle injury is still under debate. By using fura-2 cytofluorimetry on intact extensor digitorum longus muscle fibers, here we provided the first evidence that 2 months in vivo chronic treatment of rats with fluvastatin (5 and 20 mg kg-1) and atorvastatin (5 and 10 mg kg-1) caused an alteration of calcium homeostasis. All treated animals showed a significant increase of resting cytosolic calcium [Ca2+]i, up to 60% with the higher fluvastatin dose and up to 20% with the other treatments. The [Ca2+]i rise induced by statin administration was not due to an increase of sarcolemmal permeability to calcium. Furthermore, the treatments reduced caffeine responsiveness. In vitro application of fluvastatin caused changes of [Ca2+]i, resembling the effect obtained after the in vivo administration. Indeed, fluvastatin produced a shift of mechanical threshold for contraction toward negative potentials and an increase of resting [Ca2+]i. By using ruthenium red and cyclosporine A, we determined the sequence of the statin-induced Ca2+ release mechanism. Mitochondria appeared as the cellular structure responsible for the earlier event leading to a subsequent large sarcoplasmic reticulum Ca2+ release. In conclusion, we suggest that calcium homeostasis alteration may be a crucial event for myotoxicity induced by this widely used class of hypolipidemic drugs.