Changes in chemical composition and physico-chemical properties of chick low- and high-density lipoproteins induced by supplementation of coconut oil to the diet

Linoleate supplementation in steers modifies lipid composition of plasma lipoproteins but does not alter their fluidity

The health value for man of lipids in bovine muscles can be improved by the addition of PUFA to the animals' diets, but such treatments can modify fluidity of plasma lipoproteins and therefore their metabolic functions. The aim of the present study was to analyse whether changes in chemical composition of lipoproteins in steers fed sunflower oil-rich diets altered lipoprotein fluidity, measured by fluorescence polarization and electron spin resonance. LDL, light HDL and heavy HDL fractions were isolated by ultracentrifugation from plasma of eighteen crossbred Charolais×Salers steers. For a period of 70d, animals were given a control diet (C,n6) consisting of hay (540g/kg) and concentrate mixture (460g/kg) or the same basal diet supplemented with sunflower oil rich inn-6 PUFA (40g/kg diet DM), given either as crushed seeds (S,n6) or as a free oil infused directly into the duodenum (O,n6), thus avoiding ruminal hydrogenation of PUFA. We have shown that in bovine animals: (1) fluidity measurements by fluorescence polarization must be made at the bovine physiological temperature (38·5°C); (2) heavy HDL always appear as the less fluid lipoparticles; (3) electron spin resonance, which does not depend on lipoparticle size, is more appropriate to compare the fluidity of LDL with that of light HDL. The values for lipoprotein fluidity measured by both methods indicated that linoleate-rich diets did not have any effect when compared with diet C; however, chemical variables support a fluidification of lipoparticles, since in steers given the diet O,n-6 PUFA concentrations increased in polar (×1·8) and neutral (×1·6) lipids in lipoparticles (P=0·0001). The phospholipid:protein ratio increased in light (+20%,P=0·019) and heavy (+23%,P=0·06) HDL and especially in LDL (+46%,P=0·0001); the total cholesterol:phospholipid ratio decreased in the three lipoprotein classes (−15 to −30%, NS). Diet S led to similar but less pronounced effects. We concluded that linoleate-rich diets modified the chemical composition of plasma lipoproteins in steers, but did not alter their fluidity; this probably occurred as a result of ‘homeoviscous adaptation’, which ensured their functional capacity.

Influence of fasting status on the effects of coconut oil on chick plasma and lipoprotein composition

For a better understanding of the hyperlipidemic function of saturated fat, we have studied the effects of diet supplementation with 10-20% coconut oil on the chick plasma and lipoprotein composition under postprandial and starvation conditions. A significant hypercholesterolemia was found in chicks fed the standard diet after 12 h of food deprivation. In these conditions, LDL-cholesterol also increased, whereas triglyceride levels were reduced in HDL, VLDL and chylomicron fractions. Coconut oil induced a significant hypercholesterolemia under both conditions, also increasing the plasma triglyceride content under postprandial conditions, but not after starvation. Coconut oil feeding increased all the chemical components of HDL, especially under postprandial conditions, but did not affect the HDL-triglycerides under food-deprivation conditions. Total cholesterol and triglyceride levels in LDL increased after coconut oil supplementation to the diet. Differences were more pronounced under postprandial conditions. Changes in VLDL and chylomicron composition were less evident.

Dipyridamole reduces cholesterol and triglyceride levels in plasma and lipoproteins from young chicks fed a saturated fat-enriched diet

We have studied the value of dipyridamole for the prevention of hypercholesterolemia caused by saturated fat. This study shows that supplementation of 10-20% coconut oil to the diet induced a significant hypercholesterolemia under postprandial conditions. Simultaneous administration of dipyridamole and 10% coconut oil for 2 weeks maintained plasma cholesterol and triglycerides at levels similar to control, counteracting the increase induced by coconut oil. Dipyridamole significantly reduced cholesterol levels in all the chick plasma lipoproteins that were increased by coconut oil administration. However, it should be emphasized that cholesterol and other chemical components were more drastically reduced by dipyridamole in intermediate- and very-low-density lipoproteins than in other lipoprotein fractions.

Fish oil reduces cholesterol and arachidonic acid levels in plasma and lipoproteins from hypercholesterolemic chicks

The value of fish oil for prevention and/or treatment of human atherosclerosis has not been fully established. This study shows that replacement of saturated fat in young chick diet with menhaden oil produced a significant reversion of the hypercholesterolemia previously induced by coconut oil feeding. Fish oil also produced a clear decrease of plasma triacylglycerol levels. Coconut oil increased the percentages of 12:0 and 14:0 fatty acids, while menhaden oil increased those of 20:5 n-3 and 22:6 n-3. Percentages of 20:4 n-6, 18:2 n-6 and 18:1 n-9 significantly decreased by fish oil addition to the diet. Total cholesterol, phospholipid and protein contents of high and low density lipoproteins increased by coconut oil feeding. When coconut oil was replaced by menhaden oil, total cholesterol was significantly reduced in high, low and very low density lipoproteins. All chemical components of VLDL were decreased by menhaden oil feeding. Our results show a strong hypocholesterolemic effect of menhaden oil when this fat was supplemented to hypercholesterolemic chicks. The clear decrease found in arachidonic acid content of chick plasma and lipoproteins may contribute to the beneficial effects of fish oil consumption by lowering the production of its derived eicosanoids.

Dietary fish oil reduces cholesterol and arachidonic acid levels in chick plasma and very low density lipoprotein

The mechanisms involved in the hypolipidemic effects of fish oil have not been clearly established. This study shows that supplementation of 10% menhaden oil to the chick diet for 7 days produced a significant hypocholesterolemia and hypotriglyceridemia. Fatty acid composition of chick plasma drastically changed by the same dietary manipulation. Percentages of 20:5 and 22:6 n-3 fatty acids strongly increased, while percentages of 20:4 n-6, 18:2 n-6, and 18:1 n-9 significantly decreased. Changes observed in the relative percentages were parallel to those obtained in the amount of each fatty acid. Ratio of n-3/n-6 clearly decreased in plasma by fish oil feeding. Total cholesterol and triacylglycerol contents decreased in high density lipoprotein (HDL) but did not change in low density lipoprotein (LDL). All chemical constituents of very low density lipoprotein (VLDL) significantly decreased after the first week of menhaden oil supplementation to the diet. Similar modifications in fatty acid composition of the three lipoprotein fractions were also found. Our results suggest that the hypocholesterolemic effects of fish oil may be mediated by the depletion in VLDL synthesis and secretion into the chick plasma. On the other hand, the strong decrease found in the arachidonic acid (AA) content of chick plasma and lipoproteins may contribute to the beneficial effects of fish oil consumption by lowering the production of its derived eicosanoids.

Coconut oil induces short-term changes in lipid composition and enzyme activity of chick hepatic mitochondria

We studied the short-term effects of a 20% coconut oil supplementation to the chick diet on lipid composition of liver and hepatic mitochondria, and changes that occurred in mitochondrial-associated enzymes as a result of this diet. No significant differences were observed in the lipid contents of liver when young chicks were fed the experimental diet, whereas hepatic mitochondria rapidly changed in response to this diet. Total cholesterol significantly increased in mitochondria at 24 hours of coconut oil diet feeding and decreased when dietary treatment was prolonged for 5 to 14 days. Changes in total mitochondrial phospholipids showed an inverse profile. A significant decrease in phosphatidylethanolamine and an increase in sphingomyelin were found at 24 hours. The cholesterol/phospholipid molar ratio significantly and rapidly (24 hours) increased in mitochondria from treated animals. Cytochrome oxidase activity drastically increased after 24 hours of experimental diet feeding and lowered to the control values when dietary manipulation was prolonged for 5 to 14 days. ATPase activity showed an inverse profile. Changes in cytochrome oxidase activity were parallel to changes in the cholesterol/phospholipid molar ratio, whereas changes in ATPase activity showed an inverse correlation with changes in this molar ratio. To our knowledge, this is one of the first reports on the very rapid response (24 hours) of mitochondrial lipid composition and function to saturated fat feeding.

Synergism between the effects of dietary cholesterol and coconut oil on plasma, liver and lipoprotein composition of neonatal chick

The nature of the synergism between dietary factors and the development of atherosclerosis has not been fully defined. Our studies showed that simultaneous supplementation of 10% saturated fat rich in 12:0 and 14:0 fatty acids (coconut oil) plus 1% cholesterol to the diet produced a sharp increase of plasma cholesterol, indicating a synergic influence of both dietary constituents. This increase was especially patent in the VLDL fraction, modifying the distribution of other lipid components between the core and the surface of these particles. These changes are consistent with the atherogenic function of VLDL and its responsiveness to dietary manipulation.