Lipid derivative higher in muscles of athletes than non-athletes
MedWire News: Levels of the lipid intermediate diacylglycerol (DAG) are significantly higher in the skeletal muscle of highly trained athletes than in the same muscle of obese or normal-weight sedentary individuals, show study findings.
The study, published in the journal Diabetes, "provides novel evidence supporting a role for specific skeletal-muscle proteins involved in intramyocellular lipids, mitochondrial oxidative capacity, and insulin resistance," remark the authors.
The findings arise from the analysis of the muscle biopsies of 42 participants with a mean age of 66 years. Of these, 14 were endurance-trained athletes with normal weight (NWA), seven were normal-weight sedentary (NWS) individuals, and 21 were obese sedentary (OBS) individuals.
Levels of intramyocellular triglycerides (IMTGs), ceramides, and DAGs were measured in the biopsy samples.
Bret Goodpaster (University of Pittsburgh, Pennsylvania, USA) and team found that overall DAG levels were twice as high among NWA as OBS participants, and 50% higher among NWA than NWS individuals.
Furthermore, DAG levels correlated positively with insulin sensitivity, which was assessed in the study participants before muscle biopsies were taken.
"Our data suggest that higher DAG content in chronically exercised, insulin sensitive muscle represents another athlete's paradox - that is that total cellular DAG content is associated with better insulin sensitivity," explain Goodpaster and team.
When the researchers investigated the levels of DAG subtypes in muscle tissue, they found that the myocellular levels of specific DAG species did not follow the aforementioned trend. For example, DAG subtypes with two unsaturated fatty acids were higher among OBS than in NWA or NWS individuals.
This observation, say the authors, indicates that "particular DAG species may differentially affect insulin action."
In contrast to the observed relationship between total DAG content and endurance training, total ceramide levels were two-fold higher among the OBS group than in any other participant group.
Levels of IMTGs were significantly higher among NWA than among NWS and OBS individuals. In light of these findings, Goodpaster and team say that further study is required to determine exactly how IMTGs affect insulin action within muscle tissue.
The expression of mitochodrially produced proteins was also assessed in the study. Higher expression levels of these proteins were observed in the NWA group than in the NWS and OBS groups.
This, conclude Goodpaster and team, indicates a high mitochondrial content and insulin sensitivity level in endurance-trained muscle tissue.
By Lauretta Ihonor