Mechanisms underlying statin-induced modulation of ryanodine receptors

Thesis

Statins, a class of HMG-CoA reductase inhibitors, are amongst the most widely prescribed drugs for the treatment of elevated cholesterol. Despite their success, their use is associated with debilitating muscle side effects such a myopathy, myalgia and in the most serious cases, rhabdomyolysis. These effects have limited the ability of many patients to tolerate statin treatment. There is mounting evidence suggesting that statins cause a dysfunction of cellular Ca2+-release in skeletal muscle, which results in muscle damage and myopathy.

In this thesis, I have investigated, using single-channel techniques, how statins interact with the skeletal ryanodine receptor (RyR1), the channel which acts as the pathway for Ca2+-release in skeletal muscle. I have shown that statins as a class, activate RyR1 in a concentration-dependent, reversible manner. These effects were seen at nanomolar levels, which correspond to concentrations found in the skeletal muscle during statin treatment. In contrast, statin effects on the cardiac isoform (RyR2) were more complex, causing inhibition at low concentrations, and activation at higher concentrations, a finding that may be clinically important given the reports that statins reduce instances of arrhythmia.

To investigate if the ability of statins to bind to RyR1 can be reduced without affecting their binding HMG-CoA reductase, the statin minimal pharmacophore was synthesised. It was found not to activate RyR1, indicating that the activation could be separated from the effect on their intended target. Subsequently, single-channel experiments indicated that the RyR1 ATP-site is a plausible location for statin binding, and a molecular modelling study ultilising Autodock software revealed the key structural features required for binding to this site. This facilitated the identification of statin analogues with no effect on RyR1, but potent HMG-CoA reductase inhibition.

In summary, my experiments have revealed that statins can potently alter the activity of cardiac and skeletal RyR channels by distinct gating mechanisms. I suggest that these interactions of statins with RyR channels may contribute to the statin-induced changes in muscle Ca2+-release that are reported in the literature and hence may be the main underlying cause of statin-induced myopathy. In view of this hypothesis, I have screened a number of atorvastatin analogues and identified new statin compounds devoid of the ability to activate RyR1. This work will provide a firm foundation for future work investigating the usefulness of these compounds as lipid lowering agents with reduced side effects.

Authors: Lindsay, C

• DOI: 10.5287/ora-5z9jk9qq4
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: ryanodine receptors; pharmacophore; statins; ion channels; HMG-CoA reductase
• Subjects: Electrophysiology; Medicinal Chemistry; Pharmacology