Dietary ω3 fatty acids & metabolic syndrome in the rat : consequences on sensitivity and retinal functionality.

Abstract

Purpose: High fructose diets have been widely used to trigger metabolic syndrome (MetS) in rodents. Insulin resistance is a major risk factor for the development of type 2 diabetes leading in 30 to 40% of the cases to the development of diabetic retinopathy in humans. In the other hand, ω3 fatty acids have been associated with the prevention of MetS. Few studies have been interested in the early changes occurring in the retina after induction of MetS and to potential of ω3 fatty acids to reverse those effects.

Methods: 96 male Brown Norway rats (6 weeks of age) were fed for 3 and 8 days with either of the four following diets (n=8 in each group): a regular chow diet (S) , a 60% fructose enriched diet (F), a regular chow diet enriched with ω3 fatty acids (Sω3) or a 60% fructose + ω3 fatty acids-enriched diet (Fω3). Flicker (8Hz) and scotopic single flash electroretinograms were recorded from both eyes to study respectively the sensitivity of the photoreceptors and the functionality of the retina. At the time of euthanasia, blood was collected to measure glycaemia and plasma circulating insulin and leptin levels. The fatty acid profile of the retina was analyzed by gas chromatography.

Results: We reported a significant loss of cone sensitivity (Δ=1.5 log) after 8 days of fructose feeding which was not counterbalanced by ω3 supplementation. However, ω3 supplementations reduced the latency time of the a- and b-waves at high light intensities after 8 days of feeding (b-wave: S/Sω3 -7ms F/Fω3 -9ms ; a-wave : S/Sω3 -6ms F/Fω3 -3ms ). The amplitude of the a-and b-waves was not affected by the different diets. Plasma analyses showed a significant increase of insulin and leptin levels after 8 days of fructose feeding (respectively +64%, +173%). Fω3 diet significantly increased plasma insulin but restored leptin levels. ω3 fatty acids were expectedly incorporated in the retina and in the brain of rats supplemented with ω3 FA (+0.65% DHA ). The levels were surprisingly increased to higher levels in Fω3 fed rats.

Conclusions: Our findings in rats fed with fructose suggested that the early steps of MetS were characterized by hyperinsulinemia and hyperleptinemia, and were associated to the loss of cone sensitivity. ω3 FA, that have been associated with the prevention of MetS, showed beneficial although marginal effects on photoreceptors and inner retinal cells.

Keywords: 688 retina • 583 lipids • 498 diabetes