Aims: Apelin and its receptor have emerged as promising targets for the treatment of insulin resistance. Indeed, peripheral administration of apelin stimulates glucose utilization and insulin sensitivity via a nitric oxide (NO) pathway. In addition to being expressed on peripheral metabolically active adipose tissues, apelin is also found in the brain. However, no data are available on the role of central effects of apelin on metabolic control. We studied glucose metabolism in response to acute and chronic intracerebroventricular (i.c.v.) injection of apelin performed in normal and obese/diabetic mice.
Results: We demonstrate that i.c.v. injection of apelin into fed mice improves glucose control via NO-dependent mechanisms. These results have been strengthened by transgenic (eNOS-KO mice), pharmacological (L-NMMA i.c.v. treated mice), and real-time measurement of NO release with amperometric probes detection. High-fat diet-fed mice displayed a severely blunted response to i.c.v. apelin associated with a lack of NO response by the hypothalamus. Moreover, central administration of high dose apelin in fasted normal mice provoked hyperinsulinemia, hyperglycemia, glucose intolerance, and insulin resistance.
Conclusion: These data provide compelling evidence that central apelin participates in the regulation of glucose homeostasis and suggest a novel pathophysiological mechanism involved in the transition from normal to diabetic state.