Abstract
Free fatty acids released during triglyceride lipolysis play an important role in obesity-associated insulin resistance of glucose disposal. Individual sensitivity of lipolysis to the suppressive effect of insulin varies greatly among healthy subjects. It is possible that genetic factors contribute to this variation. Among the many proteins involved in the regulation of lipolysis, hormone-sensitive lipase (HSL) represents a prime candidate for genetic variants contributing to the biological variation of insulin sensitivity of lipolysis. We determined the insulin sensitivity of lipolysis (suppression of isotopically [primed-continuous infusion of d5 glycerol] measured glycerol rate of appearance) and of glucose disposal, using a three-step (n = 20) or standard (n = 53) hyperinsulinemic euglycemic clamp in 73 healthy, unrelated subjects. To assess the possible role of genetic polymorphisms, we directly sequenced the coding region of the HSL gene and the noncoding exon B from these subjects. We identified two silent mutations and three amino acid polymorphisms: Arg262Met (prevalence, 5%), Glu620Asp (prevalence, 31%) and Ser681Ile (prevalence, 22%). The latter two are located in the regulatory domain of HSL but neither had a significant impact on insulin sensitivity of lipolysis or glucose disposal (with and without adjustment for obesity and age as covariates; all P values > 0.20). We conclude that a number of genetic polymorphisms in HSL exist, some of which are highly prevalent. Neither of the polymorphisms we identified in the coding region, however, contributed measurably to the biological variation of insulin sensitivity in our lean, healthy population.—Stumvoll, M., H. G. Wahl, S. Jacob, A. Rettig, F. Machicao, and H. Häring. Two novel prevalent polymorphisms in the hormone-sensitive lipase gene have no effect on insulin sensitivity of lipolysis and glucose disposal.
Highlights
Represents a prime candidate for genetic variants contributing to the biological variation of insulin sensitivity of lipolysis
Neither of the polymorphisms we identified in the coding region, contribt uted measurably to the biological variation of insulin sensitivity in our lean, healthy population.—Stumvoll, M., H
It is possible that insulin resistance of glucose disposal, which favors the development of type 2 diabetes, is a result of insulin resistance of lipolysis
Summary
Blood glucose was determined with a bedside glucose ana lyzer (glucose oxidase method; Yellow Springs Instruments, Yellow Springs, CO). Genomic DNA was isolated from whole blood with a commercial DNA isolation kit All subjects underwent the standard t preparatory procedures and investigations of the protocol of the Tübingen Family Study (medical history, physical examination, c routine blood test, oral glucose tolerance test). PCR was per formed with intronic primers for amplification of the coding HSL exons and the noncoding exon located 1.5 kb upstream of the first coding exon. The nine exons and the noncoding regions were amplified by PCR and specific primers (Table 1). PCR products were sequenced bidirectionally, using arm was cannulated retrogradely and placed under a heating an ABI Prism dye terminator cycle sequencing ready reaction kit device to permit sampling of arterial blood. 8:00 am one of the following clamp protocols was started
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