Postnatal development of the sterol and nonsterol mevalonate metabolism in chick liver and kidneys. Effect of cholesterol feeding

Dipyridamole prevents the coconut oil-induced hypercholesterolemia. A study on lipid plasma and lipoprotein composition

For a better understanding of the hypolipidemic function of dipyridamole, we have studied the comparative effects of diet supplementation with 10% coconut oil with and without dipyridamole on the lipid plasma and lipoprotein composition in chicks. This study was performed under postprandial and food-deprivation (12h) conditions. Coconut oil induced a clear hypercholesterolemia under both feeding conditions. Simultaneous administration of dipyridamole maintained total and esterified cholesterol at levels similar to those observed in control animals sacrificed under postprandial conditions. Under these conditions, our results also show that dipyridamole significantly reduced cholesterol levels in all the chick plasma lipoproteins that were increased by coconut oil administration. Nevertheless, it should be emphasised that the levels of total cholesterol found in intermediate- and very-low-density lipoproteins were lower than in control. All chemical components of these fractions were significantly decreased by dipyridamole. The effects were not significant in chicks deprived of food. In conclusion, our results show that the hypercholesterolemia induced by coconut oil was prevented by dipyridamole. To our knowledge, this is one of the first reports on the antihypercholesterolemic effects of dipyridamole.

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.

Differential effects of dietary fat on chick plasma and liver composition and HMG-CoA reductase activity

The comparative effects of diet supplementation with 10% saturated fat rich in 12:0 and 14:0 fatty acids (coconut oil), without and with 1% added cholesterol, and with 10% unsaturated fat rich in n-3 polyunsaturated fatty acids (menhaden oil) on cholesterol metabolism in neonatal chicks were examined to clarify the different mechanisms of their hyper- and hypolipidemic action. Supplementation of coconut oil produced a significant hypercholesterolemia after 7 days of treatment, with a similar increase in the amount of both free and esterified cholesterol. Supplementation of coconut oil plus cholesterol produced a higher increase of plasma cholesterol levels (approximately two to three times higher than those found with standard diet). However, supplementation of menhaden oil induced a significant decrease in total cholesterol after only 2 weeks of treatment. Levels of plasma triglycerides did not change by coconut oil addition to the diet, but a significant increase was observed after coconut oil plus cholesterol feeding. Menhaden oil produced a transient decrease in plasma triglycerides. Hepatic 3-hydroxy-3-methylglutaryl-CoA reductase activity did not change with coconut oil treatment. However, both coconut oil plus cholesterol and menhaden oil supplemented diets drastically decreased reductase activity after 1 week of dietary manipulation. These results show that different nutrients with the same inhibitory effect on reductase activity produced opposite effects on plasma cholesterol content, suggesting the existence of important differences in the regulatory mechanisms implied in cholesterol biosynthesis and its accumulation in plasma.

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.

Effect of dietary coconut oil on lipoprotein composition of young chick (Gallus domesticus)

1. The composition of HDL, the major lipoprotein fraction from chick serum, drastically changed after 2 weeks of coconut oil feeding. Total cholesterol and triacylglycerols significantly increased following dietary 10 or 20% coconut oil supplementation. 2. Changes in LDL composition were less profound, cholesterol being the only component that increased by coconut oil supplementation (10 or 20%). 3. IDL proteins were the only components that increased following the same dietary treatment (20%). 4. VLDL cholesterol and proteins also increased after 1-2 weeks of 20% coconut oil supplementation to the diet. 5. Of total lipoproteins, the cholesterol content strongly increased after dietary treatment, while triacylglycerols did not change significantly.

Diurnal rhythm of the in vivo acetate metabolism to CO2 and nonsaponifiable lipids by neonatal chick

The in vivo incorporation of acetate into nonsaponifiable lipids was studied in different tissues from 14-day-old chick. Total nonsaponifiable lipids (nmol/30 min/g tissue) were mainly synthesized in testicles and liver. The in vivo CO2 production from acetate by 1-day-old chick did not exhibit diurnal variations. However, in 14-day-old chick, a maximal value was observed in the middle of the light period, while a minimal value was found 9 h after the start of the dark period. No significant diurnal differences were detected in the in vivo acetate incorporation into nonsaponifiable lipids by liver and duodenal mucosa from 1-day-old chick. Nevertheless, a clear diurnal rhythm was found in liver and duodenal mucosa from 14-day-old chick, but not in brain and kidney from animals of the same age. Distribution of radioactivity from (1-14C)acetate among the different constituents of the nonsaponifiable fraction has been also studied at 3-h intervals. Cholesterol was the major sterol formed from acetate by chick liver at any time of day. In duodenal mucosa and kidney, maximal values in the percentage of cholesterol synthesized were observed during the light period.

Induction in Gallus domesticus of experimental hypercholesterolemia by saturated fat. Effects on cholesterogenic enzyme activity

The effect of coconut oil supplementation to the diet (10 or 20%) on lipid levels in plasma and liver as well as on the cholesterogenic enzyme activity were studied in 14-day-old chicks. Treatments for 1 or 2 weeks did not interfere in the growth rate of animals nor in the liver weight. The 10% coconut oil group showed a significant increase of plasma cholesterol after 2 weeks of treatment, while after 1 week the increase was not statistically significant. The 20% coconut oil group increased plasma cholesterol from the first week. Triacylglycerol content increased after each coconut oil supplementation to the diet during the first week. Hepatic cholesterol did not change significantly after any treatment assayed. No significant difference was observed in the cholesterogenic activity, measured as hepatic 3-hydroxy-3-methylglutaryl-CoA reductase, so that this study provides a perfect model of hypercholesterolemic animals without changes in their cholesterogenic ability.

Characterization of chick serum lipoproteins isolated by density gradient ultracentrifugation

Serum lipoproteins from 12h fasted male chicks (15-day-old) were separated into 20 fractions by isopycnic density gradient ultracentrifugation. A new procedure was described by collecting the different fractions from the bottom of tube instead of by aspiration from the meniscus of each tube. Analyses of chemical composition of serum lipoproteins have permitted to reevaluate the density limits of major classes: VHDL, d greater than 1.132 g/ml; HDL, d 1.132-1.084 g/ml; LDL, d 1.084-1.038; IDL, d 1.038-1.022; and VLDL d less than 1.022. HDL fractions clearly predominated (approx. 77% of total lipoproteins) while IDL and VLDL were present at low percentage. LDL was the fraction richest in cholesterol; triacylglycerol content clearly increased from HDL to VLDL, while protein content decreased. All the chemical components of chick serum lipoproteins were accumulated in HDL, although triacylglycerol was relatively distributed in all the lipoprotein classes.

In vivo utilization of D(-)-3-hydroxybutyrate by chick brain and spinal cord

The in vivo utilization of D-3-hydroxy[3-14C]butyrate for oxidation in the whole animal and for lipid and amino acid synthesis in brain and spinal cord of overnight-fasted 15-day-old chicks has been measured. Appreciable amounts of injected 3-hydroxy[3-14C]butyrate were expired as 14CO2 one hour after injection, the total amount of which increased with increasing dosages. Lipid synthesis was high in both brain and spinal cord. Free cholesterol and phospholipids were the main lipids labeled in both tissues, increasing with time after injection up to 120 min. The incorporation of radioactivity into triglycerides, esterified cholesterol and free fatty acids was not time-dependent. Increased concentrations of 3-hydroxybutyrate gave rise to higher synthetic rates both in brain and spinal cord. The rate of amino acid synthesis was slightly higher in brain than in spinal cord. Glutamate was always the major amino acid formed.

Age-related changes in the mevalonate metabolism in vivo in chick kidneys

The mevalonate incorporation in vivo into total nonsaponifiable lipids by chick kidneys drastically increased after hatching, reaching similar levels to those previously observed in liver. Cholesterol was the major sterol formed from mevalonate from 11 days onward, while a fraction of polar nonsaponifiable lipid(s) was observed as the major compound(s) synthesized at 5-8 days. Relative percentages of squalene, squalene oxide(s) and lanosterol synthesized from mevalonate also increased between 11-18 days after hatching. Results in this paper demonstrate for the first time the accumulation of a fraction of nonsaponifiable lipid(s) identified as lanosterol derivatives and cholesterol precursors formed by kidneys from [5-14C]mevalonate in experiments carried out in vivo, as well as their evolution during postnatal period.

Inhibition of brain and liver 3-hydroxy-3-methylglutaryl-CoA reductase and mevalonate-5-pyrophosphate decarboxylase in experimental hyperphenylalaninemia

Experimental hyperphenylalaninemia has been induced in 5-day-old chicks by dietary treatments with phenylalanine and alpha-methylphenylalanine. An increase of nearly 8-fold in plasma Phe/Tyr ratio was found after 4 days of supplementation the standard diet with 5% phenylalanine plus 0.4% alpha-methylphenylalanine. The increase in this ratio was about 13-fold after 9 days of the same treatment. Similar results were observed in brain and liver, although the increases were smaller than those found in plasma. Total body, brain and liver weight decreased after 9 days of treatment. Phenylalanine plus alpha-methylphenylalanine administration to 5-day-old chicks produced a significant decrease in the 3-hydroxy-3-methylglutaryl-CoA reductase and mevalonate-5-pyrophosphate decarboxylase specific activities from both brain and liver. These results demonstrated for the first time that experimental hyperphenylalaninemia inhibited different enzyme activities directly implicated in the regulation of cholesterogenesis. Therefore, a reduced cholesterol synthesis in brain may evidenciate the theory of an impaired myelination leading to mental retardation in phenylketonuria patients.

Regulation of hepatic cholesterogenesis by polar steroids accumulated after cholesterol feeding

The incorporation of mevalonate into nonsaponifiable lipids by chick liver in vivo strongly increased between 1-18 days after hatching. Cholesterol feeding (2%) inhibited this. Synthesis of cholesterol was strongly inhibited, whereas the intermediates isolated by TLC accumulated. Most of the polar nonsaponifiable lipids that accumulated in liver 90 minutes after mevalonate administration to 18-day-old cholesterol-fed chicks were identified as lanosterol derivatives. 3-Hydroxy-3-methylglutaryl-CoA reductase activity, as well as acetate and mevalonate incorporation into nonsaponifiable lipids, was inhibited by the presence of these compounds. To our knowledge, this is the first report of such inhibition; this confirms the physiological function of polar steroids in the regulation of cholesterogenesis in vivo.

Quantitative role of different embryonic tissues in mevalonate metabolism by sterol and nonsterol pathways. Relationship with enzyme activities of cholesterogenesis

3-Hydroxy-3-methylglutaryl-CoA reductase, mevalonate kinase, mevalonate-5-phosphate kinase and mevalonate-5-pyrophosphate decarboxylase activities have been determined in brain, liver, intestine and kidneys from 19-day-old chick embryo. Levels of brain reductase and decarboxylase were clearly higher than those found in the other tissues assayed. However, only small differences were observed in the activity of both kinases among the different tissues. Mevalonate metabolism by sterol and nonsterol pathways has been investigated in chick embryo at the same developmental stage. Mevalonate incorporation into total nonsaponifiable lipids was maximal in liver, followed by intestine, brain and kidneys. The shunt pathway of mevalonate not leading to sterols was negligible in both brain and liver, while a clear CO2 production was observed in intestine and kidneys. Sterols running in TLC as lanosterol and cholesterol were the major sterols formed from mevalonate by brain and kidney slices, while squalene and squalene oxide(s) were found to be mainly synthesized by liver slices. Minor differences in the percentage of different sterols were observed in chick embryo intestine. The importance of free and esterified cholesterol accumulation in the different tissues on the inhibition of cholesterogenic activity is discussed.

Embryonic development of mevalonate metabolism by sterol and nonsterol pathways in chick brain and liver

The embryonic development of the sterol and nonsterol mevalonate metabolism has been investigated in chick brain and liver. The shunt pathway of mevalonate was negligible in both tissues throughout 10-21 days of embryo development. Mevalonate incorporation into nonsaponifiable lipids was higher in liver than in brain. A pronounced peak was found in liver at 12 days of incubation, while only small differences were observed in brain. Lanosterol and cholesterol were the major sterols synthesized in brain, followed by desmosterol and squalene. Their relative percentages did not change significantly during 10-16 days and slightly decreased thereafter. In liver, cholesterol and squalene were the major sterols observed during the first days of incubation with a developmental pattern similar to that found in the mevalonate incorporation into nonsaponifiable lipids, while relative percentage of squalene oxides sharply increased between 12 and 16 days of embryonic development. The importance of cholesterol esters accumulation in the inhibition of cholesterogenic activity is discussed.

Development of lipidic composition of neonatal chick liver and intestine microsomes: changes induced by cholesterol feeding

Changes in cholesterol and phospholipid content of chick liver and intestine microsomes were studied throughout the two first weeks of life. Differences observed throughout postnatal development were mainly due to the free cholesterol. Cholesterol feeding resulted in a clear increase of the amounts of both free and esterified cholesterol. Phospholipid content of chick liver and intestine microsomes did not change significantly after hatching. Phosphatidylcholine and phosphatidylethanolamine were found to be the major phospholipids. Although the amount of each phospholipid could be affected by cholesterol feeding, its relative percentage did not change by this treatment.