INTERLEUKIN-6 IN RESPONSE TO HIGH INTENSITY AND MODERATE INTENSITY EXERCISE TRAINING IN AFRICAN AMERICAN INDIVIDUALS
Skeletal muscle has been identified as an endocrine organ that releases myokines with contraction. These myokines have been defined as cytokines and peptides that are produced, expressed, and released by muscle fibers that can have either an autocrine, paracrine, or endocrine action¹. Interleukin-6 (IL-6) has been identified as a prototypic exercise myokine and can be measured in plasma after a single, acute bout of exercise². IL-6, however, has implications in both the development and prevention of metabolic disease. The effect of exercise duration on IL-6 has been outlined in the literature³⁻⁵, but the effect of exercise intensity has yet to receive the same attention. In addition, racial disparities in the development of metabolic disease have been shown with African Americans having a significantly greater prevalence of CVD and type 2 diabetes than Caucasians in the United States⁶. PURPOSE: The purpose of the present study was to determine the effects of moderate and high intensity aerobic exercise training on basal, plasma IL-6 in overweight and obese African American individuals. METHODS: A randomized controlled trial was performed on overweight and obese (body mass index of 25-45 kg/m2), sedentary African American individuals (35-65 years) (n=24). Participants were randomly assigned to either a non-exercise control group or a moderate or high intensity aerobic exercise training group for 24 weeks. Supervised exercise was performed at a heart rate associated with 45-55% of VO2 max for the moderate intensity group or 70-80% of VO2 max for the high intensity group for a total exercise dose of 600 metabolic equivalents of task (MET- ) minutes per week. Pre- and post-exercise intervention 12-hour fasted intravenous glucose tolerance tests (IVGTT) were performed. IVGTT samples were analyzed for insulin, glucose, lactate, and IL-6 using the Beckman Coulter clinical analyzer system. Bergman's Minimal Model⁷ was used to assess insulin and glucose kinetics of the IVGTT. Additional bloodsamples were also drawn and sent to a clinical laboratory (LabCorp Inc., Burlington, NC) to beanalyzed for a complete lipid and metabolic profile. RESULTS: In the control group, there were 11 participants, 6 participants in the moderate intensity exercise group, and 7 participants in the high intensity exercise group. Nosignificant differences were found between the randomization groups for age, gender, weight, BMI, waist circumference, body fat percentage, glucose, insulin, and IL-6. Baseline BMI was significantly associated with baseline HOMA-IR (r=786, p[less-than]0.01) and baseline insulin (r=0.784, p[less-than]0.01). \ There was no significant change in IL-6 with the moderate or high intensity exercise group compared to the control group (p=0.8364). In addition, there was no significant change in SI (p=0.233), DI (p=0.422), or HOMA-IR (p=0.653). There was no significant correlation between relative fold change of IL-6 and SI (p=0.772), DI (p=0.545), or HOMA-IR (p=0.165). CONCLUSION: The present study did not find that moderate intensity aerobic exercise training nor high intensity aerobic exercise training decreased basal, plasma IL-6 in sedentary, obese and overweight African Americans. Insulin sensitivity was not improved in either exercise group when compared to the non-exercise control group. A broader scope on IL-6 is suggested for future studies and should include not only plasma but adipocyte IL-6 production as well as mRNA for IL-6. In addition, allowing enrollment of Caucasian individuals will allow for a direct comparison with African American individuals to further understand racial differences in the exercise response.
East Carolina University