Comparison of postprandial inflammation induced by various dietary fats according to circadian rhythm in rats

Postprandial phase peaks 3 to 6 hours after food intake and lasts 9 hours . It is generally accepted that each meal causes an inflammatory response with low intensity and short duration. Chylomicrons and chylomicron remnants have been thought to be the major lipoproteins which are increased in the postprandial plasma. Postprandial lipemia has been proposed to be one of the common risk factor of cardiovascular diseases independent of the total cholesterol, LDL as well as HDL cholesterol levels. Endothelial dysfunction is characterised by proinflamatory alterations in the endothelium and results in leucocyte adhesion and transmigration which are early steps in atherogenesis. There are some recent evidence indicating that triacylglycerol rich lipoproteins occuring in postprandial plasma influence vascular inflamation. Endothelial actions of dietary lipoproteins derived from the diet depends mostly upon their fatty acid compositions. Studies have demonstrated a strong association between the type of fatty acids ingested and the incidence of cardiovascular diseases. The percentage of saturated fatty acids and the ratio of n-3 to n-6 polyunsaturated fatty acids in a meal appears to determine the magnitute of postprandial inflammatory response. The circadian clock controls and coordinates multiple behavioral and physiological processes during daily light/dark cycle including activity, sleeping, feeding and metabolism. The biological rhythms profoundly effect absorption of dietary lipids, expression of microsomal transfer proteins and apo B-48 which are known to be important in chylomicron assembly, plasma levels of postprandial remnant lipoproteins and triacylglycerol. The circadian rhythm regulates lipid metabolism and vice versa. However, how reciprocal interaction of different dietary fats and light/dark cycle of the day affects postprandial inflamation is currently unknown. Moreover, whether or not time-of day-dependent dietary fat consumption can influence postprandial inflammatory markers are waiting to be established. To this end, effects of various dietary fats given in light or dark cycle of the day on postprandial inflamation, vascular and systemic, were compared. Cytokines taking part inflammatory response including IL-1ß, TNF-?, IL-6 and soluble adhesion molecules (sVEGF, sE-Selectin) were analysed in blood samples by ELISA. Monocyte, granulocyte, lympocyte levels and the levels of VCAM-1, ICAM-1, L-Selectin on these cells detected by flow-cytometric analysis. Olive oil and sunflower oil administrations lowered serum VEGF and TNF-? levels of rats in both dark and light cycle of the day while decreasing sE-selectin levels in light cycle . On the contrary to our expectations, serum VEGF levels were considerably increased by fish oil in both cycles whereas TNF-? levels were enhanced in dark period only. On the other hand administrations of butter or fish oil resulted in inducements of much more CD receptor types compared to olive oil or sunflower oil administrations. Induction of adhesive CD receptors were more prominent in dark cycle of rats given butter whereas that were more noticeable in light cycle of rats given fish oil. It appears that postprandial inflamation induced by sunflower oil or olive oil is much less prominent compared to butter or fish oil. In addition, inflammatory effects of dietary fat or oil consumption might be time-of day-dependent. However long term studies are required . Variations in post prandial inflammation according to the timing and type of the fat ingestion will provide additional information in the prevention of coronary heart disease and other disorders influenced by low grade inflammation.