Metabolic Myopathy in Endocrinopathy

Overview

Endocrine diseases including Cushing's syndrome and phaeochromocytoma/paraganglioma (PPGL) but not Conn's syndrome are associated with muscle wasting and weakness. The study's aim is to identify epigenetic determinants of muscle homeostasis in these conditions following medical treatment and adrenalectomy. This is an observational pilot study that will recruit 66 patients from 3 diagnostic groups: Cushing's syndrome (16), PPGL (20) and Conn's syndrome (30). Indices of muscle bulk and strength will be assessed at diagnosis and at outpatient follow-up 6-9 weeks after adrenalectomy. At these times blood and urine will be collected and a muscle biopsy taken from the operation site at the time of surgery. Pathway analysis in these samples will identify potentially novel signalling pathways contributing to muscle wasting via prolonged exposure to high levels of corticosteroid and catecholamines. This will highlight commonalities and differences in pathogenesis of muscle wasting from a variety of different causes. Finally, it will inform identification of novel therapies for muscle atrophy.

Muscle wasting and weakness is important because it accounts for a large proportion of the disability associated with disease and normal aging. The annual economic cost in the USA alone has been estimated at $1.8 billion. The investigators have studied muscle wasting associated with chronic and acute illness, finding a marked dissociation between wasting and disease severity. This indicated that epigenetic and genetic factors may contribute to individual susceptibility to wasting. To analyse factors controlling muscle mass, the investigators have developed a novel clinical model of muscle loss. Hence, in patients undergoing aortic surgery, a large insult is imposed on patients with a background of a disease that leads to muscle wasting (reduced cardiac function). As the timing of the insult is known, the investigators can follow muscle wasting longitudinally. Our recent work using this model has characterised novel muscle signalling pathways that mediate muscle breakdown. Specifically, the investigators found that 50% of patients undergoing cardiac surgery lose significant muscle mass (\>10% in the "wasters" group) in the 7 days after uncomplicated surgery, which correlated with loss of strength 7-9 Expression of microRNAs (miRNAs) from imprinted loci (C19MC miRNAs and miR-675) in muscle biopsy samples was strongly associated with subsequent muscle wasting and weakness. Furthermore, expression of these miRNA in myoblasts and animal models confirms their effects on muscle and suggests modes of action through transforming growth factor signalling pathways, ribosome assembly and mitochondrial function. Finally, metabolomic analysis of plasma samples from these patients suggested that exposure to higher levels of active intrinsic corticosteroid, a known cause of sarcopenia, was correlated with muscle loss. Acute muscle wasting (ICU acquired weakness) is associated with high levels of corticosteroids, owing to a defect in deactivation, and shock which is countered with high doses of catecholamines. The investigators will measure miR expression, and longitudinal muscle bulk and strength in patients undergoing adrenalectomy at SBH. Group 1: Cushing's syndrome caused by very elevated levels of corticosteroids, associated with severe wasting. Group 2: Phaeochromocytoma and paraganglioma (PPGL) caused by very elevated levels of catecholamines, associated with moderate wasting. Group 3: Conn's syndrome caused by elevated mineralocorticoid, not associated with muscle wasting (Control group) All patients will be assessed at diagnosis, after medical treatment and after completed reversal of the defect after surgery. Various measures of focal and global strength and function will be recorded alongside measures of muscle bulk. A muscle biopsy from the wound site will be taken at surgery. One of the key epigenetic determinants of muscle wasting in acute and chronic conditions is micro-RNA (miR-) 424, which targets ribosome synthesis and function as well as insulin sensitivity. The promotor for its' large non-coding RNA precursor contains a steroid responsive region. Therefore overall, the investigators expect miR-424 expression to be correlated with muscle wasting across the 3 patient groups. Mi-RNA profiles will be generated in patient blood and muscle samples: our previous studies have shown that muscle expression of selected mi-RNA is a strong predictor of the response to injury and in patients with chronic respiratory failure (COPD) corresponding circulating levels can be measured in contemporaneous blood samples. A predictive biomarker (miR expression in blood) would allow a personalised approach to clinical trials for anti-muscle atrophy therapies. The miRNA profiles in blood associated with muscle wasting are likely to be useful predictive biomarkers for several conditions associated with sarcopenia, as evidenced by previous miRNA sets associating with muscle phenotype in COPD and in patients undergoing cardiac surgery. Pathway analysis will identify potentially novel signalling pathways contributing to muscle wasting via prolonged exposure to high levels of corticosteroid or increased inflammatory sensitivity. This will highlight commonalities and differences in pathogenesis of muscle wasting from a variety of different causes. Finally, it will inform identification of novel therapies for muscle atrophy. Insensitivity to insulin is a hallmark of many acute and chronic diseases, and a feature of metabolic syndrome. The investigators will be able to determine the potential role of high circulating levels of miR-424, which could constitute a novel therapeutic approach to type 2 diabetes. Similarly, owing to the multi-system insult of cardiac surgery our patient cohorts suffered acute kidney injury and systemic inflammation requiring vasopressors. These data have been collected and could be mined in the future to identify epigenetic determinants and pathways associated with these outcomes.