Tissue-Specific Splicing and Dietary Interaction of a Mutant As160 Allele Determine Muscle Metabolic Fitness in Rodents

<a>Ethnic groups are physiologically and genetically adapted to their diets. Inuit bear a frequent AS160^R684X mutation that causes type 2 diabetes. Whether this</a> mutation evolutionarily confers adaptation in Inuit and how it causes metabolic disorders upon dietary changes are unknown due to limitations in human studies. Here, we develop a genetically-modified rat model bearing an orthologous AS160^R693X mutation, which mimics human patients exhibiting postprandial hyperglycemia and hyperinsulinemia. Importantly, a sugar-rich diet aggravates metabolic abnormalities in AS160^R693X rats. The AS160^R693X mutation diminishes a dominant long-variant AS160 without affecting a minor short-variant AS160 in skeletal muscle, which suppresses muscle glucose utilisation but induces fatty acid oxidation. This fuel switch suggests a possible adaptation in Inuit who traditionally had lipid-rich hypoglycemic diets. Finally, induction of the short-variant AS160 restores glucose utilisation in rat myocytes and a mouse model. Our findings have implications for development of precision treatments for patients bearing the AS160^R684X mutation.

Tissue-Specific Splicing and Dietary Interaction of a Mutant As160 Allele Determine Muscle Metabolic Fitness in Rodents

<a>Ethnic groups are physiologically and genetically adapted to their diets. Inuit bear a frequent AS160^R684X mutation that causes type 2 diabetes. Whether this</a> mutation evolutionarily confers adaptation in Inuit and how it causes metabolic disorders upon dietary changes are unknown due to limitations in human studies. Here, we develop a genetically-modified rat model bearing an orthologous AS160^R693X mutation, which mimics human patients exhibiting postprandial hyperglycemia and hyperinsulinemia. Importantly, a sugar-rich diet aggravates metabolic abnormalities in AS160^R693X rats. The AS160^R693X mutation diminishes a dominant long-variant AS160 without affecting a minor short-variant AS160 in skeletal muscle, which suppresses muscle glucose utilisation but induces fatty acid oxidation. This fuel switch suggests a possible adaptation in Inuit who traditionally had lipid-rich hypoglycemic diets. Finally, induction of the short-variant AS160 restores glucose utilisation in rat myocytes and a mouse model. Our findings have implications for development of precision treatments for patients bearing the AS160^R684X mutation.

Dynamic modulation of glucose utilisation by glucocorticoid rhythms in health and disease

A systems level coordination of physiological rhythms is essential to sustain healthy states, especially in the face of stimuli that may disrupt such rhythms. The timing of meals, medication and chronic stress can profoundly influence metabolism, which depends on the dynamic interactions between glucose, insulin and cortisol. Although the metabolic and stress endocrine axes are simultaneously disrupted in many diseases, a theoretical framework to understand how chronodisruption leads to disease is lacking. By developing a mathematical model of glucose utilisation that accounts for the antagonism between insulin and cortisol, we investigate the dynamic effects of glucose boluses under normal and disrupted cortisol rhythms, including the effects of cortisol agonists and antagonists. We also predict how cortisol rhythms modulate circadian responses to oral glucose diagnostic tests, and analyse the disruptions caused by hypercortisolism. Finally, we predict the mechanisms leading to type 2 diabetes in patients with normal and excess cortisol.

Iso-Mukaadial Acetate from Warburgia salutaris Enhances Glucose Uptake in the L6 Rat Myoblast Cell Line

Diabetes mellitus (DM) is a chronic metabolic disorder which has become a major risk to the health of humankind, as its global prevalence is increasing rapidly. Currently available treatment options in modern medicine have several adverse effects. Thus, there is an urgent need to develop alternative cost-effective, safe, and active treatments for diabetes. In this regard, medicinal plants provide the best option for new therapeutic remedies desired to be effective and safe. Recently, we focused our attention on drimane sesquiterpenes as potential sources of antimalarial and antidiabetic agents. In this study, iso-mukaadial acetate (Iso) (1), a drimane-type sesquiterpenoid from the ground stem bark of Warburgia salutaris, was investigated for glucose uptake enhancement in the L6 rat myoblast cell line. In vitro assays with L6 skeletal muscle cells were used to test for cytotoxicity, glucose utilisation, and western blot analysis. Additionally, the inhibition of carbohydrate digestive enzymes and 1,1-diphenyl-2- picrylhydrazyl (DPPH) scavenging activity were analysed in vitro. The cell viability effect of iso-mukaadial acetate was the highest at 3 µg/mL with a percentage of 98.4. Iso-mukaadial acetate also significantly and dose-dependently increased glucose utilisation up to 215.18% (12.5 µg/mL). The increase in glucose utilisation was accompanied by enhanced 5’ adenosine monophosphate-activated protein kinase (AMPK)and protein kinase B (AKT) in dose-dependent manner. Furthermore, iso-mukaadial acetate dose-dependently inhibited the enzymes α-amylase and α-glucosidase. Scavenging activity against DPPH was displayed by iso-mukaadial acetate in a concentration-dependent manner. The findings indicate the apparent therapeutic efficacy of iso-mukaadial acetate isolated from W. salutaris as a potential new antidiabetic agent.

Use of FDG PET scanning to evaluate 5-FU myocardial toxicity as a global metabolic effect rather than vascular spasm.

792 Background: This is the first ever case series which presents a series of PET images that conclusively demonstrate reversible abnormal myocardial glucose utilisation in 7 patients with normal coronary arteries occurring during 5-FU infusions. Fluoropyrimidine induced myocardial toxicity is estimated to occur in 9% of cases, with some instances proving fatal. Traditionally some hypothesised coronary artery spasm as the mechanism of action behind such events and an animal study suggesting dysfunction of the Krebs cycle, with depletion of high-energy phosphate compounds, was largely ignored. Having observed abnormal myocardial FDG uptake in a patient with chest pain undergoing FDG PET scanning, we prospectively evaluated a further 6 patients presenting with cardiac symptoms whilst receiving infusional 5-FU. Methods: Over an eighteen-month period, 7 patients experienced cardiac like chest pain during 5FU infusion. All were investigated for cardiac ischaemia as per institutional protocol (serial troponin, ECGs and coronary artery imaging), as well as FDG PET scanning to assess FDG uptake in the myocardium. Results: All 7 cases showed reduced FDG uptake throughout the myocardium, with the ventricular blood pool demonstrating a higher affinity for FDG than the myocardium itself. All 7 cases showed normal physiological uptake of FDG in the myocardium on previous and subsequent PET imaging. Imaging of the myocardium and coronary arteries in all cases showed no structural vascular disease. Conclusions: All cases demonstrated a global pattern of reduced FDG myocardial uptake that could not be isolated to a single coronary territory. Angiography or myocardial perfusion scanning demonstrated no significant coronary artery disease, and there were no features consistent with coronary artery spasm found on ECG. This supports the hypothesis that 5FU inhibits physiological myocardial glucose utilisation, thus acting as a direct myocardial toxin. We believe our findings warrant further investigation into the metabolic effects of 5FU on myocardial tissue.