News & Research

By: Felicia Breedy

Deborah Muoio, PhD, the recipient of a Career Development Award from the American Diabetes Association, recently published study results in the August 21, 2009 issue of the Journal of Biological Chemistry. She found that providing obese rats with carnitine supplements helps them to clear the extra sugar they have trouble removing from their blood. Dr. Muoio, who is also the past recipient of a Junior Faculty Award, is conducting her research at the Duke University Medical Center. Dr. Muoio’s current Association project is entitled, "Mitochondrial Stress and Insulin resistance in skeletal muscle."

Carnitine is derived from an amino acid and is made in the liver. Playing a role in the energy process, carnitine transports long-chain fatty acids across the cell membrane to enter the mitochondria where they are "burned" for energy. Excess byproducts of this process are also transported by carnitine from the cells and distributed via blood to needier organs or to the kidneys for removal from the body.

Observing the skeletal muscle of obese rats, the Duke University research team found that high amounts of carnitine conjugated molecules, called acylcarnitines, were produced and this requires free carnitine.  As the acylcarnitine molecules accumulated, the amount of free carnitine decreased. The carnitine decrease was linked to an impairment of the burning of both fat and glucose. It appeared as though the fall in levels of free carnitine prevented this nutrient from performing its job.

So, an experiment was designed to add extra carnitine to the rats' diet. Dr. Muoio’s research design involved middle aged obese rats that had been fed a high fat diet for a year, which led to problems with muscle metabolism of glucose and fat. After eight weeks of supplementation with carnitine, normal energy metabolism was restored. An added outcome was the improvement in the glucose tolerance and a lower risk of diabetes.

The results offer a new hope for those with glucose intolerance and type 2 diabetes. In a related study, Dr. Muoio’s team showed that carnitine works similarly in human muscle cells. Taken together, her findings suggest that carnitine supplementation might help older people with metabolic disorders such as pre-diabetes and diabetes. Dr. Muoio's next research focus is to begin a small clinical trial of carnitine supplementation in people with glucose intolerance.

(Noland RC, Koves TR, Seiler SE, Lum H, Lust RM, Ilkayeva O, Stevens RD, Hegardt FG, Muoio DM. Carnitine insufficiency caused by aging and overnutrition compromises mitochondrial performance and metabolic control. Journal of Biological Chemistry. 2009 Aug 21;284(34):22840-52. Epub 2009 Jun 24.)