Possible Bio-Marker for Type 2 Diabetes Identified

Researchers have found that retinol-binding protein 4 (RBP4), a molecule that transports vitamin A in the blood, might be an effective marker for predicting the likelihood of developing non-insulin-dependent diabetes (type 2) diabetes.

Type 2 diabetes, also called adult-onset diabetes, results from the inability of the cells in the body to respond to insulin. About 90% of diabetics have this form, which is more prevalent in non-whites and usually occurs after age 40. Although the cause is not completely understood, there is a genetic factor and 90% of those affected are obese.

Investigators at Harvard Medical School (Boston, MA, USA) exploited previous findings that RBP4, a protein secreted from adipose tissue, was linked to insulin resistance in mice. In the current study they measured serum RBP4 levels, insulin resistance, and components of the metabolic syndrome in three groups of subjects (from the United States, Sweden, and Germany). Individuals in one set of subjects were obese, demonstrated impaired glucose tolerance, or were ill with type 2 diabetes. Individuals in a second group had normal body weight and normal blood glucose, but had a strong family history of type 2 diabetes.

Results published in the June 15, 2006, issue of The New England Journal of Medicine, revealed that serum RBP4 levels correlated with the magnitude of insulin resistance in subjects with obesity, impaired glucose tolerance, or type 2 diabetes and in non-obese, non-diabetic subjects with a strong family history of type 2 diabetes. Elevated serum RBP4 was associated with components of the metabolic syndrome, including increased body-mass index, waist-to-hip ratio, serum triglyceride levels, systolic blood pressure, and decreased high-density lipoprotein cholesterol levels.

Some patients were assigned an exercise regimen to lower their weight and degree of insulin resistance. Only those showing an improvement in insulin resistance experienced a reduction in serum RBP4 levels.

"Collectively, these findings tell us that RBP4 is a useful marker for therapeutic improvement and that this protein could play a causal role in insulin resistance in humans, just as our lab previously showed in mice,” said senior author Dr. Barbara Kahn, professor of endocrinology at Harvard Medical School. "Furthermore, because RBP4 levels consistently corresponded with insulin resistance--even among lean subjects whose genetic risk for the development of diabetes might otherwise be overlooked--this protein could be an important marker for type 2 diabetes among the general population. Being able to determine diabetes risk well before the onset of symptoms could provide an important opportunity for patients to take preventive measures.”



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