title: Investigating Mitochondrial Dysfunction as a Mechanism of Drug-Induced Muscle Toxicity
Creators: name: Bin Dayel, Faten
Publisher: name: University of Liverpool Repository
Year: 2028

description: Drug-induced skeletal muscle toxicity is described using various terminology including muscle spasms, myalgia, myopathy, myositis, and rhabdomyolysis. This side effect plays role in the compliance of patients with medications prescribed by health care providers and in many cases, the patients who cannot tolerate these side effects discontinue the medication. In the most severe cases, they are admitted to the hospital often with rhabdomyolysis, which can result in detrimental impacts on patients' life if not treated immediately. The U.S Food and Drug Administration Adverse Event Reporting System (FAERS) logged 27,140 rhabdomyolysis cases from 2004 to March 31, 2020. Analysis of these cases identified 14 drugs that have been frequently reported in 6,583 rhabdomyolysis cases. These drugs represent ≥ 1.8% of cases in which the drug suspected to induce rhabdomyolysis was reported as a monotherapy. The harmful effects of a few of those drugs upon mitochondrial function have been implicated as one of several proposed mechanisms by which muscle toxicity could be potentiated in some patients. Therefore, this study aimed first to identify drugs that can cause rhabdomyolysis using FAERS public database before investigating whether these suspect drugs induce skeletal muscle toxicity due to adversely affecting mitochondrial function in skeletal muscle cells. In this study, murine L6 cells were utilized as a convenient and reproducible in vitro skeletal muscle model to screen these selected drugs for mitochondrial toxicity. Specifically, to investigate direct mitochondrial dysfunction as a mechanism of drug-induced skeletal muscle toxicity. The acute metabolic switch assay was employed, where differentiated L6 myotubes undergo a metabolic modification (galactose media) over a 2 h period immediately before suspect drug addition, to force the muscle cells to rely upon oxidative phosphorylation (OXPHOS) rather than glycolysis (glucose media). Drugs were administered over an acute period (2 h), which is sufficient to identify the drugs that induce mitochondrial toxicity by measuring the change in cellular ATP content. Any drugs that were identified by the screen underwent further investigation, using real-time respirometry (Seahorse) to confirm this designation and to provide more detail on the mechanism of mitochondrial toxicity induced. To confirm the human relevance of findings in such a murine screen, selected drugs that had been labelled as mitotoxic were next evaluated in primary human skeletal muscle-derived cells (HSKMDC). Overall, these studies demonstrate that from the fourteen suspect drugs analysed, five drugs FBT, RIS, PRE, PROP, and SVL are mitochondrial toxicants in the L6 muscle model. These findings were supported in HSKMDC for fenofibrate and risperidone, although toxic effects to the mitochondria were more pronounced in HSKMDC in the absence of cell death. Finally, real-life clinical data from the UK-based prospective Pharmacogenetics of Acute Coronary Syndrome (PhACS) was used to investigate the hypothesis that concomitant use of any of the 10 drugs (excluding statins) most frequently reported within FAERS could influence statin-associated muscle toxicity by comparing patients with statin use only to patients on a statin and any of the suspect drugs. Within this study, 1376 patients were discharged on statin therapy (atorvastatin, rosuvastatin, or simvastatin daily). From these cases, only 5 suspect drugs (EZE, OLZ, QTP, FBT, and PRE) were reported in 35 patients who were discharged on a statin with a concomitant suspect drug. Overall, no association was observed between concomitant use of statins with any of these suspect drugs and changes in statin prescribing patterns or the occurrence of self-reported myopathic symptoms. However, larger sample sizes are needed to investigate this hypothesis further. To conclude, the novelty of this thesis was achieved by establishing the L6 model as a reference model of skeletal muscle, which can be used as a first and fast screen to investigate drug-induced skeletal muscle toxicities via a direct effect on mitochondrial functions, with the ultimate goal of enhancing the preclinical investigation of susceptibility factors for myopathic symptoms and reducing the mortality and morbidity rate associated with rhabdomyolysis. Importantly, drug-induced mitochondrial dysfunction may be a common mechanism shared by drugs that induce myotoxicity.