Increased susceptibility to oxidative damage in post-diabetic human myotubes

Abstract

Aims/hypothesis Obesity is an important risk factor for the development of type 2 diabetes, but not all obese individuals develop this complication. The clinical signs of type 2 diabetes can often be reversed with weight loss; however, it is unknown whether the skeletal muscle oxidative stress associated with type 2 diabetes remains after weight loss. We hypothesised that chronic exposure to high glucose and insulin would re-elicit impaired metabolism in primary myotubes from patients with a history of type 2 diabetes. Methods Obese participants with or without type 2 diabetes completed a standardised weight loss protocol, following which all participants were euglycaemic and had similar indices of insulin sensitivity. Satellite cells were isolated from muscle biopsies and differentiated under low or high glucose and insulin conditions (HGI).

Galactose Enhances Oxidative Metabolism and Reveals Mitochondrial Dysfunction in Human Primary Muscle Cells

“…However, the GAL medium was able to identify decreased OCR in post-diabetic myotubes, revealing the utility of this approach to detect mitochondrial dysfunction in vitro . Our results also confirm that post-diabetic myotubes display an abnormal metabolic flexibility when challenged with different substrates (here with galactose) as previously published by others who studied myotubes derived from (post-)diabetic, insulin resistant or obese patients when challenged with high fat levels [9], [11], [41] or high glucose levels [40]. In the present study, the lack of an increase in OCR in post-diabetic myotubes appears to be related to unaltered COX expression or activity levels or AMPK phosphorylation.…”

“…Myotubes derived from post-diabetic subjects are also known to have a decreased oxidative capacity when challenged with a high glucose medium (decreased mitochondrial content, decreased citrate synthase and COX activities) compared to myotubes derived from matched obese non-diabetic individuals [40]. Despite this decrease oxidative capacity [5], [9], [40], no difference in OCR was found in the present study between obese non-diabetic and post-diabetic myotubes differentiated in either HG or LG. This is presumably due to the fact that under these conditions, myotubes were highly glycolytic rendering it more difficult to detect a decrease in OCR in post-diabetic compared to obese non-diabetic myotubes.…”

“…Other studies have described a decrease in oxidative metabolic capacity in myotubes derived from diabetic patients as indicated by a decrease in citrate synthase activity [7] and a decrease in lipid oxidation capacity [5], [9]. Myotubes derived from post-diabetic subjects are also known to have a decreased oxidative capacity when challenged with a high glucose medium (decreased mitochondrial content, decreased citrate synthase and COX activities) compared to myotubes derived from matched obese non-diabetic individuals [40]. Despite this decrease oxidative capacity [5], [9], [40], no difference in OCR was found in the present study between obese non-diabetic and post-diabetic myotubes differentiated in either HG or LG.…”

“…Biopsies of vastus lateralis were obtained from 7 lean and healthy participants (male/female: 6/1, age: 41 years ±6.7, BMI (Body Mass Index): 20.8 kg/m 2 ±0.5) and from 5 obese non-diabetic persons (male/female: 4/1, age: 55 years ±2.1, BMI: 39.2 kg/m 2 ±1.3) and 5 obese post-diabetic patients (male/female: 4/1, age: 54 years ±2.3, BMI: 36.6 kg/m 2 ±1.3) after local anesthesia, using a 5 mm Bergstrom needle (Opitek, Glostrup, Denmark) as described previously by Costford et al [40]. The post-diabetic patients had a documented history of obesity-associated T2DM prior to a 26-week standard clinical weight loss program at the Ottawa Hospital Weight Management Clinic and were no longer diabetic after the weight loss program (blood glucose <6.1 mmol/l and HbA1c <5.7%).…”

“…The post-diabetic patients had a documented history of obesity-associated T2DM prior to a 26-week standard clinical weight loss program at the Ottawa Hospital Weight Management Clinic and were no longer diabetic after the weight loss program (blood glucose <6.1 mmol/l and HbA1c <5.7%). Characterization of primary muscle cells from the obese non-diabetic and the obese post-diabetic participants was previously published by our lab [40].…”