Obesity is a growing public health crisis, bringing with it many serious risk factors, including cardiovascular disease and type 2 diabetes. As the number of people who are either overweight or obese now outnumbers those with a healthy body weight by a ratio of two to one, researchers face an urgent need to better understand how the body burns fuel.Several years ago, Andrew Butler, professor of pharmacology and physiology discovered the peptide hormone adropin. Research by Butler’s lab suggested that adropin regulates whether the body burns glucose or fat.
They also found that young men with high adropin levels had lower body mass index (BMI) levels. Moreover, some studies indicated low adropin is associated with biomarkers of insulin resistance.
In the current study, Butler and his colleagues have conducted studies at California National Primate Research Center in order to explore adropin’s role in metabolic health.
They examined the plasma of 59 adult male rhesus macaques that were fed a high sugar diet.
Overall, consumption of the fructose diet produced a 10 per cent gain in body weight and increases of fasting levels of insulin, indicating insulin resistance, which reduces glucose use and elevated fasting triglycerides which in humans increases the risk of cardiovascular disease.
Animals with low plasma adropin concentrations developed a more severe metabolic syndrome. Interestingly, development of type 2 diabetes was only observed in animals with low plasma adropin concentrations. These animals also showed more pronounced dysregulation of glucose and lipid metabolism.Fasting hyperglycemia was also limited to animals with low circulating adropin, indicating glucose intolerance.
“Monkeys with low adropin may therefore not be oxidizing glucose as well, explaining their higher fat content as the glucose is converted to lipids instead of being used as a metabolic fuel,” Butler said.
“Last year we reported that adropin appeared to be an output of the biological clock using mouse models and cultured human cells. What we show in this paper is that expression of the ENHO gene is higher in daytime and lower at night in most primate tissues,” Butler said.
This is consistent with the idea that adropin expression is controlled via “clock-related” mechanisms.
The current finding suggests that adropin may link the biological clock to rhythms in the way the body uses sugar and fats as metabolic fuel.
“At night time, the body relies on energy reserves stored as lipids in fat cells and in the daytime relies more on the carbohydrates coming in from the diet,” Butler said.
In this way, stimulation of adropin expression by our internal clocks may contribute to increasing the use of glucose as a metabolic fuel during the daytime.