Insulin administered intranasally may lower food intake in men, improve memory in women

Insulin administered intranasally, acutely decreases food intake in men but not women and in contrast, the compound improves memory function in women but not men according to a new study accepted for publication in the Journal of Clinical Endocrinology & Metabolism (JCEM).

“Our findings indicate that gender is a critical factor in brain insulin signaling that affects both food intake and cognitive functions,” said Dr. Christian Benedict of the University of Lubeck in Germany. “They further suggest that intranasal insulin may be helpful in the treatment of cognitive and metabolic disorders like Alzheimer's disease and obesity that are assumed to derive at least in part from malfunctions of central nervous insulin signaling.”

Previous studies have shown that insulin plays a pivotal role in the regulation of central nervous functions such as energy metabolism and memory processing. This study set out to assess the effects of a single dose of intranasal insulin on these functions and to determine any gender differences.

For this study, 14 men and 18 women were administered regular human insulin intranasally before performing a battery of cognitive tests. Subsequently, study subjects took part in a breakfast buffet and their food intake was measured.

The nasal spray device used in this study atomizes the insulin solution before inhalation so that it penetrates the nasal cavities more effectively.

The pancreatic hormone insulin plays a pivotal role in the regulation of central nervous functions such as the neuroendocrine control of energy metabolism and memory processing. Insulin reaches the brain via a saturable transport system, and binds to receptors primarily located in cerebral cortex, olfactory bulb, hippocampus, cerebellum, and hypothalamus.

“Our findings show that men are more sensitive to the central anorexigenic actions of insulin whereas women benefit to a greater extent from its acute cognitive effects,” said Benedict. “Gender differences will have to be considered in the possible future development of intranasal insulin therapeutics.”

Other researchers working on the study include Werner Kern, Jan Born, and Manfred Hallschmid of the University of Lubeck in Germany; and Bernd Schultes of the Interdisciplinary Obesity Center East-Switzerland, Kantonsspital St. Gallen in Switzerland.

A rapid release version of this paper has been published on-line and will appear in the April 2008 issue of JCEM, a publication of The Endocrine Society.