Blunted β-adrenoceptor–mediated fat oxidation in overweight subjects: a role for the hormone-sensitive lipase gene

Abstract

Obesity is associated with blunted β-adrenoceptor–mediated lipolysis and fat oxidation, which persist after weight reduction. We investigated whether dinucleotide (CA) n repeat polymorphisms in intron 6 (i6) or 7 (i7) and a C-60G promoter substitution of the hormone-sensitive lipase (HSL) gene are associated with a blunted in vivo β-adrenoceptor–mediated increase in circulating fatty acids and glycerol (estimation of lipolytic response) and fat oxidation in overweight-obese subjects. A total of 103 overweight (25 kg/m 2 ≤ body mass index < 30 kg/m 2) and obese (body mass index ≥30 kg/m 2) subjects (62 men, 41 women) were included. Energy expenditure, respiratory quotient (RQ), and circulating fatty acid and glycerol were determined after stepwise infusion of increasing doses of the nonselective β-agonist isoprenaline. The i6, i7 (CA) n repeat polymorphisms were determined by size-resolved capillary electrophoresis; and a C-60G promoter substitution was determined by restriction enzyme digestion assay. Female noncarriers of allele 184 i7 (n = 18) and female carriers of allele 240 i6 (n = 12) showed an overall reduced fat oxidation (as indicated by changes in RQ) after β-adrenoceptor–mediated stimulation, explaining, respectively, 6.9% and 20.8% of the variance in RQ. These effects were not seen in male subjects. In conclusion, our results suggest that variation in i7 and i6 of the HSL gene might be associated with a physiological effect on in vivo β-adrenoceptor–mediated fat oxidation, at least in overweight-obese female subjects.