José Iglesias

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.

Inhibition of chick brain cholesterogenic enzymes by phenyl and phenolic derivatives of phenylalanine

Phenylalanine and its phenyl metabolites produced a clear inhibition of chick brain mevalonate 5-pyrophosphate decarboxylase, while mevalonate kinase and mevalonate 5-phosphate kinase were not significantly affected. Phenolic derivatives produced a similar or higher inhibition than that found in the presence of phenyl metabolites. The inhibition was progressive with increasing concentrations of inhibitors (1.25-5.00 mM). Phenylpyruvate and p-hydroxyphenyl-lactate were the most potent inhibitors of decarboxylase activity. Simultaneous supplementation of each metabolite at 0.25 mM concentration produced a considerable inhibition of brain decarboxylase and 3-hydroxy-3-methylglutaryl-CoA reductase. At our knowledge this is the first report on the in vitro inhibition of both brain regulatory enzymes of cholesterogenesis in phenylketonuric-like conditions.

In vivo utilization of [3-14C]acetoacetate for lipid and amino acid synthesis in the 15-day-old chick

1. The utilization of different concentrations of acetoacetate for the in vivo synthesis of lipids and amino acids has been studied in brain, spinal cord, liver, small intestine and kidney of 15-day-old chicks. Both lipid and amino acid synthesis increased in an almost linear fashion with precursor concentration in the five tissues mentioned. 2. Lipid synthesis was very high in spinal cord, followed in decreasing order by brain, small intestine, liver and kidney. At the highest concentration assayed (48 mM) the main lipids synthesized were triglycerides in liver (75%) and kidney (52%) and cholesterol in brain (47%), spinal cord (47%) and small intestine (42%). 3. Amino acid synthesis from acetoacetate did not vary markedly among the five organs, although brain and spinal cord showed higher rates at the maximal concentrations of precursor. Glutamate was always the main amino acid formed.

Mevalonate 5-pyrophosphate decarboxylase in isolated villus and crypt cells of chick intestine.

Mevalonate 5-pyrophosphate decarboxylase was studied in isolated enterocytes obtained from duodenal, jejunal and ileal villi and crypts. In our assay conditions, decarboxylase activity was linear for 60 min and up to 0.3 mg of protein. The subcellular location of decarboxylase in chick enterocytes was investigated. About 94% of the total activity was recovered in the cytosol. The distribution of enzyme activity in epithelial cells also was studied. Maximal specific activity was found in cell fractions from jejunum followed by ileum and duodenum. About 80% of total activity was recovered in the villus cells, indicating an active role of these cells in cholesterogenesis. Ileal cells showed the highest cholesterol content. In all the intestinal epithelial cells assayed, free cholesterol represented about 95% of the total cholesterol.

Regulation of Mevalonate 5-pyrophosphate Decarboxylase in HeLa Cells. Inhibition of Enzymatic Protein Synthesis by Serum Lipoproteins

Mevalonate 5-pyrophosphate decarboxylase (EC 4.1.1.33) has been considered as a secondary site of regulation of cholesterogenesis. Because of this, we have studied the regulation of decarboxylase in HeLa cells by serum lipoproteins in the cell culture medium. A first group of experiments was performed with cells grown in Eagles medium with 10% foetal calf serum. The specific activity of decarboxylase was increased when whole foetal calf serum was replaced with lipoprotein-poor serum. This increase was clearly reduced in the presence of cycloheximide. Addition of serum lipoproteins to a medium containing lipoprotein-poor serum led to a clear decrease in the decarboxylase activity. An identical decrease was observed after the addition of lipoproteins alone or in combination with cycloheximide. These results suggest for the first time that the effect of serum lipoproteins on decarboxylase activity should be a decrease in the rate of enzymatic protein synthesis, and corroborate the important role of reactions other than those catalysed by 3-hydroxy-3-methylglutaryl-CoA reductase in the regulation of cholesterogenesis.

Effect of phenylpyruvate on mevalonate-activating enzymes from chick brain and liver

Mevalonate-activating enzymes from chick brain and liver were stable when 105,000 x g supernatants were stored at -4 degrees C for 168 h. Mevalonate kinase and mevalonate 5-phosphate kinase retained their activities for 72 h at 4 degrees C while mevalonate 5-pyrophosphate decarboxylase activity significantly decreased after 24-48 h of storage at 4 degrees C. Direct addition of 2.5 mM phenylpyruvate to the reaction mixture produced a significant inhibition of decarboxylase activity in brain and liver. When enzyme preparations were preincubated with 2.5 mM phenylpyruvate for 20 min before the addition of substrate, an increased inhibition was observed. Mevalonate kinase and mevalonate 5-phosphate kinase from both tissues were not affected in the same conditions. The inhibition of brain and liver decarboxylase was progressive with increasing concentrations (2.5-10.0 mM) of phenylpyruvate. No significant difference was observed in the inhibition of decarboxylase after 10 or 20 min of preincubation.

In vivo utilization ofd(−)-3-hydroxybutyrate by chick brain and spinal cord

The in vivo utilization ofd-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 as14CO2 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.

Cholesterol synthesis and esterification in isolated enterocytes: Regulation by cholesterol and cholestyramine feeding

The purpose of the present study was to investigate the physiological control of the main regulatory enzymes of cholesterol metabolism in isolated enterocytes obtained from chick duodenum, jejunum and ileum. Cholesterol feeding resulted in an inhibition of 3-hydroxy-3-methylglutaryl-CoA reductase and mevalonate 5-pyrophosphate decarboxylase, while cholestyramine feeding increased reductase activity in all the regions studied and decarboxylase activity only in duodenum. Cholesterol feeding markedly increased acyl-CoA:cholesterol acyltransferase, but the effects of cholestyramine were less clear. The effects on transferase activity cannot be due to differences in the availability of acyl-CoA as exogenous substrate as no significant differences were found in acyl-CoA hydrolase activity after any of the dietary treatments. The effects of cholesterol feeding were related to changes in the cholesterol content of epithelial cells, whereas in the case of cholestyramine this relationship was less apparent.

Oleoyl-CoA incorporation into triglycerides and phospholipids by chick enterocytes. Effect of cholesterol and cholestyramine feeding

Abstract Incorporation of 1[1- 14 Cloleoyl-CoA] into triglycerides was similar in villus and crypt cells from chick duodenum and lower than than in the upper and mid villus cells from jejunum. Cholesterol feeding produced a significant decrease of triglyceride synthesis in duodenum, while this specific activity increased in jejunum. Cholestyramine feeding did not affect triglyceride synthesis in duodenum and decreased that found in upper and mid villus cells from jejunum. Levels of oleoyl-CoA incorporation into phospholipids were higher than those observed in the incorporation into triglycerides. Cholesterol and cholestyramine feeding did not affect this activity. Incorporation of oleoyl-CoA into both triglycerides and phospholipids in enterocytes isolated from ileum was lower than that found in duodenum and jejunum, and did not change significantly by cholesterol or cholestyramine feeding.