IL-6 gene expression in human adipose tissue in response to exercise--effect of carbohydrate ingestion

Interleukin-6 (IL-6) is a cytokine involved in a number of immunological processes, but it is also linked to exercise and possibly energy status. During exercise, muscle IL-6 mRNA levels and plasma IL-6 levels are increased and further augmented when intramuscular glycogen levels are low. In contrast, the increase in plasma IL-6 is blunted if carbohydrate is administered, indicating a substrate-regulated induction of IL-6 in human skeletal muscle. Recent studies have demonstrated that IL-6 is also released from adipose tissue in response to an exercise bout. Furthermore, IL-6 has been demonstrated to have a lipolytic effect, thus possibly playing a role in mobilisation of energy as free fatty acids (FFA) in response to exercise. The purpose of the present study was to investigate the gene expression pattern of IL-6 in adipose tissue in response to exercise, and to determine whether gene expression was affected by the ingestion of carbohydrate. Eight male subjects performed 3 h of bicycling with ingestion of a carbohydrate drink or placebo. Fat biopsy samples and blood samples were obtained before, during and in the recovery phase of exercise. Both plasma IL-6 and adipose IL-6 mRNA levels increased in response to exercise. IL-6 gene expression was lower (P<0.05) in the CHO trial (1.98-fold increase, confidence interval (CI) 1.16-3.83) compared with the control (6.49-fold increase, CI 3.57-13.91) at end of exercise. Furthermore, CHO ingestion blunted the increase in plasma IL-6 levels (P<0.05) at end of exercise (26.0+/-3.7 pg ml(-1) in the control vs. 15.6+/-2.4 pg ml(-1) in the CHO trial). In conclusion, exercise results in an increase in IL-6 gene expression in adipose tissue in response to exercise, an effect that is significantly blunted by ingestion of carbohydrate.