Insulin Resistance and Impaired Mitochondrial Function in Obese Adolescent Girls

Background: Mitochondrial dysfunction plays a role in the development of muscle insulin resistance (IR) and the accumulation of intramyocellular lipid (IMCL) in skeletal muscle that can, in turn, interfere with insulin signaling. The purpose of this study was to assess mitochondrial function (MF) and IMCL in obese adolescent girls with and without IR to determine whether: (1) Girls with IR have impaired MF, and (2) impaired MF in girls with IR is related to higher IMCL. Methods: We examined 22 obese girls aged 13-21 years old for IR [defined as a homeostasis model assessment of insulin resistance (HOMA-IR) value >4. Phosphorus magnetic resonance spectroscopy (31P-MRS) and proton magnetic resonance spectroscopy (1H-MRS), respectively, were used to determine MF and IMCL of the soleus muscle along with magnetic resonance imaging (MRI) measures of visceral, subcutaneous, and total adipose tissue (VAT, SAT, and TAT) in girls with HOMA-IR >4 (insulin-resistant group) versus HOMA-IR 4 (insulin-sensitive group). Serum lipids and waist-to-hip ratio (W/H) were also measured. Results: Girls with IR (n=8) did not differ from the insulin-sensitive group (n=14) for age, bone age, weight, VAT, SAT, TAT, or IMCL. However, the insulin-resistant group had higher W/H. Additionally the insulin-resistance group had a lower log rate of postexercise phosphocreatine (PCr) recovery (ViPCr) and a higher log PCr recovery constant (tau), indicative of impaired MF. Conclusions: Obese girls with increased IR have impaired mitochondrial function. This association is not mediated by alterations in IMCL or adipose tissue. Further studies are necessary to determine whether there is a causal relation between impaired mitochondrial function and IR in obesity and mediators of such a relationship.