Antibodies target HMG-CoA protein, triggering autoimmune myopathy in statin-treated patients
Baltimore, IL - New research suggests that statins appear to upregulate the expression of 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMG-CoA), the major target of autoantibodies in patients who develop statin-associated autoimmune necrotizing myopathy. The results, according to investigators, provide a mechanistic link between an environmental trigger, statin therapy, and the development of a sustained autoimmune disorder that persists even after the drugs have been stopped.
âIn the vast majority of cases, in patients who develop muscle symptoms while taking statins, the symptoms resolve once you have the patient stop taking the statin, without any needed form of treatment,â lead investigator Dr Andrew Mammen (Johns Hopkins Medical Institute, Baltimore, MD) told heartwire. âBut there is a rare group of patients who develop a sustained autoimmune process that actually requires immunosuppressive therapy to treat. Otherwise, they continue to get worse and worse, with many of our patients coming into the clinic in wheelchairs, even after having been off the statin for months.â
Their findings are published in the December 2010 issue of Arthritis & Rheumatism.
Mammen explained that some of their initial research involved evaluating patients who had developed myopathy, with elevated creatinine kinase (CK) levels and muscle weakness, who appeared to have autoimmune muscle disease but without any inflammation, an unusual feature, in the muscle biopsy specimens. As a result, they wanted to determine whether these patients had any novel autoantibodies, which are often found in patients who have autoimmune muscle disease.
The researchers identified unique autoantibodies in 16 of 26 individuals currently treated at the Johns Hopkins Myositis Center for necrotizing myopathy. When they analyzed the patients, they discovered that 12 of the 16 patients 50 years of age and older had been treated with a statin prior to developing the muscle disease.
âWhen you talked to the patients, a very typical story was that they got put on a statin medication,â said Mammen. âIt was recognized that it was causing some muscle problems, it was stopped, maybe switched to another one, and then finally the medication was discontinued. But instead of getting better, which is what usually happens with statin myopathy, it just continued to progress and get worse. It didnât get better until they were put on immunosuppressive medications.â
Rare, but serious side effect
With that background, the group then wanted to determine what the antibodies were recognizing. In this latest study, they learned the antibodies recognize HMG-CoA reductase, the target of statin therapy. After 750 patients with muscle symptoms at the clinic were screened, 45 patients, or 6%, were identified as having the HMG-CoA-reductase antibodies. Among patients 50 years of age and older, 92% of patients were exposed to statin therapy.
Mammen said that normal muscle has very low levels of HMG-CoA reductase, but regenerating muscle, muscle that has been previously damaged, has very high levels. As a result, that damaged muscle continues to serve as a rich source of the HMG-CoA-reductase protein even after the statin is discontinued, which helps explain why an autoimmune muscle disease process started with the statin continues after the drugs have been stopped.
Approximately 5% of individuals prescribed statins develop some sort of muscle side effects, such as cramping or muscle pain, that can lead to switching to another drug or stopping the medication altogether. Mammen stressed that the response resulting in necrotizing myopathy is extremely rare, doing a back-of-envelope calculation suggesting that one or two individuals per million per year develop the autoimmune disorder.
âThis is not a reason not to take statins,â he told heartwire. âItâs a very rare side effect, but itâs one to know about because nobody really knows whatâs going on with these patients after the medication is stopped. Itâs important to recognize it as a rare but serious side effect of statin use.â
One of the potential benefits of the new research is the possible development of tests that identify antibodies targeting HMG-CoA reductase, allowing clinicians to know which patients are developing an autoimmune myopathy following statin therapy that needs to be treated with immunosuppressive therapy, said Mammen.