Aims/hypothesis
Mitochondrial dysfunction and increased intramyocellular lipid (IMCL) content have both been implicated in the development
of insulin resistance and type 2 diabetes mellitus, but the relative contributions of these two factors in the aetiology of
diabetes are unknown. As obesity is an independent determinant of IMCL content, we examined mitochondrial function and IMCL
content in overweight type 2 diabetes patients and BMI-matched normoglycaemic controls.
Methods
In 12 overweight type 2 diabetes patients and nine controls with similar BMI (29.4 ± 1 and 29.3 ± 0.9 kg/m2 respectively) in vivo mitochondrial function was determined by measuring phosphocreatine recovery half-time (PCr half-time)
immediately after exercise, using phosphorus-31 magnetic resonance spectroscopy. IMCL content was determined by proton magnetic
resonance spectroscopic imaging and insulin sensitivity was measured with a hyperinsulinaemic–euglycaemic clamp.
Results
The PCr half-time was 45% longer in diabetic patients compared with controls (27.3 ± 3.5 vs 18.7 ± 0.9 s, p < 0.05), whereas IMCL content was similar (1.37 ± 0.30 vs 1.25 ± 0.22% of the water resonance), and insulin sensitivity was
reduced in type 2 diabetes patients (26.0 ± 2.2 vs 18.9 ± 2.3 μmol min−1 kg−1, p < 0.05 [all mean ± SEM]). PCr half-time correlated positively with fasting plasma glucose (r
2 = 0.42, p < 0.01) and HbA1c (r
2 = 0.48, p < 0.05) in diabetic patients.
Conclusions/interpretation
The finding that in vivo mitochondrial function is decreased in type 2 diabetes patients compared with controls whereas IMCL
content is similar suggests that low mitochondrial function is more strongly associated with insulin resistance and type 2
diabetes than a high IMCL content per se. Whether low mitochondrial function is a cause or consequence of the disease remains
to be investigated.
Keywords Diabetes - IMCL - Insulin resistance - Lipid metabolism - Skeletal muscle - Mitochondrial function - Oxidative capacity