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Biomedical subjects

H Lafont

Publications and source records attributed to H Lafont.

At least 73 records · Page 4Linked to original sources
PubMed1992

Long-term wheat germ intake beneficially affects plasma lipids and lipoproteins in hypercholesterolemic human subjects.

In previous short-term studies in rats and humans, the ingestion of raw wheat germ lowered plasma triglycerides and cholesterol. Thus, the present study was designed to investigate the possible long-term effects of wheat germ intake. Diet supplementation with raw wheat germ or partially defatted wheat germ was tested in two separate groups of 10 and 9 free-living human subjects, respectively. They all exhibited hypercholesterolemia (6.14-9.67 mmol/L cholesterol) and 11 had hypertriglyceridemia. None was diabetic. Fasting blood samples were taken at the beginning of the study, after 4 wk of 20 g/d wheat germ intake, after 14 additional weeks of 30 g/d wheat germ intake and after 12 wk without any supplementation. Dietary records were kept for seven and three consecutive days, before and during the wheat germ intake periods, respectively. Raw wheat germ intake significantly decreased plasma cholesterol (-8.7%) and tended to reduce VLDL cholesterol (-19.6%) after 4 wk. After 14 additional weeks, plasma cholesterol (-7.2%) and LDL cholesterol (-15.4%) remained lower and plasma triglycerides (-11.3%) tended to be lower. The apo B:apo A1 ratio significantly decreased after both periods. Partially defatted wheat germ transiently decreased plasma triglycerides and cholesterol after a 4-wk intake. The present data indicate that wheat germ reduces cholesterolemia in the long term and could play a beneficial role in the dietary management of type IIa and IIb hyperlipidemia.

Adult↗
PubMed1992

Effects of cyclosporine and corticosteroids on bile secretion in the rat.

In order to study their effects on the bile secretion, cyclosporine and methylprednisolone were injected intravenously into rats at a dose of 10 mg/kg b.w. for 30 min. Methylprednisolone had no effect on bile secretion. Cyclosporine led to transient intrahepatic cholestasis characterized by decreased bile flow as well as a decrease of bile salts and cholesterol in bile. Phospholipid levels were not affected. Liver biopsy showed no particular anomaly. These findings suggest that the observed cholestatic reaction may be due to impairment of the metabolism of cholesterol into bile salts or of the conjugation of bile salts rather than to disturbances in bile secretion. After liver transplantation in humans, cholestasis associated with acute rejection or nonspecific cholestasis cannot be attributed directly to the effect of cyclosporine. Cholestasis can be offset by administering taurocholate at a dose of 10 mumol/min/kg b.w. in order to maintain bile salt and phospholipid levels high enough to ensure proper "vectorization" of cholesterol to bile.

Animals↗
PubMed1992

Influence of dehydrocholic and cholic acids on the biliary secretion of anionic polypeptide fraction, the major apoprotein of the biliary lipoprotein complex.

This work was undertaken to study the effect of intravenously infused dehydrocholate (DHCA) and cholate (CA) on lipid and anionic polypeptide fraction (APF) secretion in bile. APF is a small acidic amphipathic apoprotein closely associated with biliary lipids and bilirubin and involved in the control of bile-destined cholesterol. Rats were infused with increasing doses of DHCA (2 and 3 mumols/min/100 g b.w.) and then CA (1, 2, and 3 mumols/min/100 g b.w.). Each dose was infused for 30 min. As expected, intravenous DHCA inhibited biliary phospholipid (PL) and cholesterol secretion, and CA restored it. When DHCA was infused, the level of APF increased fourfold compared with controls. The APF/PL ratio also increased, but biliary albumin remained stable. When bile secretion was stimulated by infusion of CA, biliary APF returned to normal. These data indicate that biliary secretion of APF depends on the nature and the amount of bile salts returning to the liver, and consequently, APF can be considered a marker of bile secretion disorders.

Animals↗
PubMed1992

Epitope mapping of the human biliary amphipathic, anionic polypeptide: similarity with a calcium-binding protein isolated from gallstones and bile, and immunologic cross-reactivity with apolipoprotein A-I.

Biliary amphipathic anionic polypeptide (APF) the major protein of the pigment-lipoprotein complex in bile, and calcium-binding protein (CBP) from gallstones are both small (less than 10 kDa), highly acidic, amphipathic proteins present in bile and closely associated also with pigmented areas in human gallstones. Polyclonal antibodies against APF have shown cross-reactivity with plasma high density lipoproteins (HDL). This study examines the hypothesis that APF and CBP might be closely related or even identical, and might also share common epitopes with the larger apoA-I (23 kDa). To assess this, immunoreactivity of the three delipidated, highly purified proteins was determined against a panel of 12 monoclonal antibodies (MAbs) prepared against APF and a panel of 4 MAbs against apoA-I. APF was isolated from bile by zonal ultracentrifugation. CBP was isolated from proteins precipitated from bile by CaCl2, as well as from the calcium bilirubinate shells of cholesterol gallstones, by extraction successively with methyl-t-butyl ether, methanol, and Na2EDTA, followed by Sephadex G-25 chromatography and two-stage preparative SDS-PAGE. ApoA-I was prepared by two types of chromatography: Sephacryl S200 chromatography and heparin-chromatographic immunoaffinity. Specific polyclonal antibodies to APF and apoA-I were prepared from immunized rabbits. MAbs to APF and apoA-I were prepared by immunization of mice, using standard hybridoma technique. Western blotting of APF and CBP in 15% SDS-PAGE yielded one band with an apparent molecular weight of 6.5 kDa, which, along with apoA-I, was immunostained by polyclonal antibodies to APF and apoA-I. Using 12 MAbs against APF with three types of ELISA (direct antigen binding, competitive antigen displacement, and epitope competition between antibodies), it was shown that APF and delipidated apoA-I shared six epitopes, three of which were detected also on the surface of intact HDL particles. Six other epitopes were present in APF but not apoA-I, four of which were exposed on the surface of HDL. Four MAbs against apoA-I reacted with APF and CBP. Amino acid analyses of APF and CBP were similar with 20-23% acidic and 7-11% basic amino acids and low contents of cysteine, methionine, and tyrosine; both differed from apoA-I in containing isoleucine and cysteine. Using ELISA and one MAb (no. 32) against APF, this polypeptide was detected in human plasma HDL, the pigment-lipoprotein complex in the bile of humans, dogs, and rats, and in both pigment and cholesterol gallstones.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1992

Effects of dietary n-6/n-3 ratios on lipid and prostaglandin E2 metabolism in rat gastric mucosa.

The effects of increased dietary n-3 polyunsaturated fatty acids on gastric mucosal lipid metabolism were studied in rats fed for 8 weeks with different combinations of fish and corn oils. Lipid composition, ex vivo prostaglandin E2 (PGE2) production and enzymatic activities involved in phospholipid metabolism and peroxisomal oxidative catabolism of fatty acids and PGE2 were examined. With dietary n-6/n-3 compositional ratios ranging between 75 and 3.3 it was observed that: (i) the arachidonic acid-to-eicosapentaenoic acid ratio (AA/EPA) fell from infinity to 3.1 and 5.1 in phosphatidylcholines (PC) and phosphatidylethanolamines (PE), respectively; (ii) ex vivo production of PGE2 was lowered by a factor of about 2; and (iii) gastric phospholipase A2 activity was enhanced by 32%. With dietary n-6/n-3 ratio lower than 3.3, stimulation of PGE2-CoA oxidase activity was observed whilst the PGE2 level remained constant. These data suggest that the fish oil-induced decrease in ex vivo PGE2 production is more closely related to a decrease in the membrane AA level than to an enhanced oxidative catabolism of PGE2.

1-Acylglycerophosphocholine O-Acyltransferase↗
PubMed1991

Subcellular localization of rat gastric phospholipase A2.

In the present study, we have performed experiments to gain some insight into the subcellular localization and biochemical properties of gastric mucosal phospholipase A2. After classical subcellular fractionation of whole glandular stomach mucosa, we found that gastric phospholipase A2 was essentially enriched in the 105,000 x g pellet that contains microsomes and plasma membranes. Except for the cytosol, all the subcellular fractions exhibited similar phospholipase A2 activity (i.e., optimum of pH, calcium dependence, apparent Km and positional specificity). The high-speed pellet was further characterized by ultracentrifugation on a sucrose gradient. Data showed that the sedimentation profile of phospholipase A2 was quite similar to those of plasma membrane markers and more specifically to an apical membrane marker. These results, taken together, showed that a gastric phospholipase A2 is distributed among the various subcellular fractions (as a result of cross-contamination) together with the membrane fraction on which it is associated. It is proposed that this fraction is the apical plasma membrane which would be the main site of phospholipase A2 action for arachidonic acid release. Lysophospholipase showed the same sedimentation profile as phospholipase A2, whereas acyl CoA-lysophosphatidylcholine: acyltransferase mainly sedimented with heavy microsomes. The substrate specificity of the enzyme was assessed by endogenous hydrolysis of gastric mucosal phospholipids. We were able to show that the enzyme acts at nearly the same rate on two major gastric membrane phospholipids, namely phosphatidylcholine and phosphatidylethanolamine.

Animals↗
PubMed1991

Plasma lipid lowering effects of wheat germ in hypercholesterolemic subjects.

The present study was performed to investigate the possible effects of wheat germ supplementation on lipid metabolism in humans. Ten free-living adult subjects participated in the study. None was obese or diabetic. They all presented an hypercholesterolemia (from 6.58 to 9.50 mM), associated in 6 over 10 cases to an hypertriglyceridemia (from 1.70 to 5.00 mM). The subjects were studied in three consecutive periods, during which they first were on their usual diet (first week), they then ingested a daily supplement of 30 g wheat germ (4 weeks) and then they returned to their usual basal diet (4 weeks follow-up). Dietary records were obtained for 7 and 3 consecutive days before and during wheat germ supplementation, respectively. Fasting blood samples were taken at the end of each period. After 4 weeks of wheat germ intake, glycemia did not change while total plasma cholesterol significantly decreased (paired Student's t test, p less than or equal to 0.05) from 7.80 to 7.15 mM. LDL and HDL cholesterol values did not show marked changes, but VLDL cholesterol significantly dropped by 40.6%. Thus, the plasma/HDL total cholesterol ratio was significantly lower. Apoprotein B and A1 decreased. In the hypertriglyceridemic subjects, this was accompanied by a significant reduction of plasma triglycerides (1.64 vs. 2.68 mM) and a marked drop of VLDL triglycerides (-51%). Taken as a whole, the present results obtained in humans are very close to those previously obtained in the rat and point out that wheat germ may play a beneficial role in the dietary management of hyperlipidemia.

Adult↗
PubMed1991

Gastric lipase: evidence of an adaptive response to dietary fat in the rabbit.

In the rabbit, the stomach is the only source of preduodenal lipase, and in humans, it is quantitatively the most important. Thus, the adaptive response of gastric and pancreatic lipases to dietary fat was studied in the adult rabbit. Effect of duration was studied by feeding rabbits 12% dietary fat for 1, 2, or 4 weeks or 2.7% for 2 weeks (control). To study the effects of the amount of fat, rabbits were fed the control diet (2.7% fat) or 6% and 12% dietary fat for 2 weeks. The influence of sunflower oil and butter was compared by feeding rabbits 12% dietary fat for 2 weeks. Approximately doubling (6% vs. 2.7%) the usual amount of dietary fat was sufficient to induce a maximum increase in gastric lipase activity in the fundus [+ 66.3% (units per gram tissue) or + 85.2% (units per milligram protein)] and the total stomach mucosa [+ 84.5% (units per mucosa)], whereas pancreatic lipase activity only significantly increased when rabbits were fed 12% dietary fat. A full adaptive response was observed for both gastric and pancreatic lipases after 2 weeks of diet. Triglyceride composition did not noticeably change the adaptive response of both lipolytic enzymes. The present results agree closely with those concerning lingual lipase in the rat and evidence that gastric lipase shows an adaptive response to moderate fat intake. The implications of these findings concerning humans are discussed.

Adaptation, Physiological↗
PubMed1991

Modulation of lipid chylomicron-synthesizing enzymes in rats by the dietary (n-6):(n-3) fatty acid ratio.

The effect of diets with various (n-6):(n-3) polyunsaturated fatty acid (PUFA) ratios and a constant polyunsaturated: saturated fatty acid ratio on the basal activity of chylomicron lipid synthesizing enzymes was investigated in rat intestinal microsomes. Enzymes studied were: acyl-CoA:cholesterol acyltransferase (ACAT); acyl-CoA:lysophosphatidylcholine acyltransferase (MGAT) and acyl-CoA:1,2-diacylglycerol acyltransferase (DGAT). Results showed that after a 4-wk feeding period, ACAT, ACLAT and DGAT basal activities were significantly enhanced by the dietary fatty acids of the (n-3) series, whereas MGAT activity was not affected. When the highest (n-6):(n-3) ratio (51.0) was compared with the lowest (0.8), the increase attained was about 58, 76 and 73% for ACAT, ACLAT and DGAT, respectively. Fatty acid composition of microsomal lipids was drastically altered by the diets because (n-3) PUFA replaced the (n-6) series as the dietary (n-6):(n-3) ratio was lowered. These compositional changes could explain the observed modification in the membrane-bound enzyme activities. We suggest that (n-3) PUFA ingestion leads to an enhanced velocity of chylomicron synthesis in rats.

Acyltransferases↗
PubMed1990

Studies on the origin of biliary phospholipid. Effect of dehydrocholic acid and cholic acid infusions on hepatic and biliary phospholipids.

The correlation between the secretion of biliary phospholipid (PL) and bile acid suggests a regulatory effect of bile acid on PL secretion. Bile acids may influence PL synthesis and/or the mobilization of a preformed PL pool. The objective of this study was to determine the contribution of these two sources to biliary PL, by using an experimental protocol in which dehydrocholic acid (DHCA) and cholic acid (CA) were infused to manipulate biliary PL secretion. In control rats, there was a steady state in bile flow. PL secretion and the biliary secretion of newly synthesized phosphatidylcholine (PC). The specific radioactivity of PC in bile was significantly higher than in plasma, microsomes and canalicular membranes. DHCA infusion decreased biliary PC secretion rate by 80%, and secretion returned to normal values at the transport maximum of CA. The specific radioactivity of biliary PC was decreased by 30% by DHCA infusion and reached normal values during CA infusion. There were no significant changes in the specific radioactivity of PC in plasma or cellular organelles during infusion of bile acids. These data indicate that: (1) newly synthesized PC contributes a small percentage to biliary PC; thus a preformed pool (microsomal and extrahepatic) is a major source of biliary PL; (2) the contribution of the extrahepatic pool to the biliary PL may be more important than the microsomal pool.

Animals↗
PubMed1990

Effects of salmon oil and corn oil on plasma lipid level and hepato-biliary cholesterol metabolism in rats.

The aim of this work was to compare the effects of n-3 and n-6 fatty acids on plasma lipid level and hepato-biliary cholesterol metabolism by studying rats fed semi-synthetic diets enriched with either 10% salmon oil, 10% corn oil, or a blend of 6% corn oil and 4% salmon oil. After 4 weeks of feeding, a drop in plasma lipid level was noted in the salmon oil group in comparison to the control group, whereas no change was observed in the corn oil group. An increase in production of cholesterol ester by the liver was recorded in the salmon oil group with a marked enhancement in acyl-CoA:cholesterol acyltransferase (ACAT: EC 2.3.1.26) activity and hepatic cholesterol concentration. Corn oil did not affect either ACAT activity or hepatic cholesterol storage. All bile parameters (flow, bile salts, phospholipids, cholesterol) increased in the salmon oil group, but the molar ratio of cholesterol participation in the bile secretion decreased. These changes in bile composition, as well as in hepatic metabolism of cholesterol, may help to explain the hypolipidemia following the intake of fish oil.

Animals↗
PubMed1990

Evidence for the synthesis and secretion of APF--a bile lipid associated protein--by isolated rat hepatocytes.

Bile lipids are thought to be secreted in a lipoprotein complex in which they are associated with cholesterol and a protein called the anionic polypeptidic fraction (APF). APF is present in both bile and serum HDL. The association of APF with both bile and lipoprotein strongly suggests that hepatocytes may be responsible for the synthesis and secretion of this protein. In the present work we attempted to verify this by studying the incorporation of [14C]leucine into APF in isolated rat hepatocytes and by immunolocalization in cell cultures. Results obtained showed that synthesis of APF by cells follows the same kinetic pattern as albumin and that it was the third most abundant protein in the bile secretion. Immunolocalization confirmed that APF is synthesized in the endoplasmic reticulum of hepatocytes. This protein which appears to be rapidly secreted could be of great value for the specific detection of the lipids destined for bile secretion.

Albumins↗
PubMed1990

Effect of increasing amounts of dietary fish oil on brain and liver fatty composition.

Increasing dietary fish oil in rat had the following effect on brain lipids: Arachidonic acid regularly decreased; eicosapentanenoic acid, normally nearly undetectable, was present; 22:5(n - 3), dramatically increased but remained below 1% of total fatty acids; cervonic acid was increased by 30% at high fish oil concentration. Saturated and monounsaturated fatty acids were not affected regardless of chain-length. In contrast, in the liver, nearly all fatty acids (saturated, monounsaturated and polyunsaturated) were affected by high dietary content of fish oil, but liver function was normal: serum vitamin A and E, glutathione peroxidase, alkaline phosphatase, transaminases were not affected. Serum total cholesterol, unesterified cholesterol and phosphatidylcholine were slightly affected. In contrast, triacylglycerols were dramatically reduced in proportion to the fish oil content of the diet.

Animals↗
PubMed1990

In vitro study of docosahexaenoic acid incorporation into phosphatidylcholine by enzymes of rat heart.

Several studies have shown that in animals fed fish oils, docosahexaenoic acid (DHA) is incorporated into cardiac phosphatidylcholines (PC) mainly at the expense of arachidonic acid. In this study we were interested in examining if the enzymatic system involved in the remodeling of membrane PC presented any selectivity for DHA in rat heart. The enzymes that were studied from sequential incubations carried out in parallel, were acyl-CoA synthetase (EC 6.2.1.3) and acyl-CoA:lysophosphatidylcholine acyltransferase (EC 2.3.1.23) (ACLAT). The heart preparations examined were homogenates of whole heart and of purified cultured rat ventricular myocytes. Results showed that ACLAT tended to preferentially incorporate into PC the polyunsaturated fatty acids of the n-6 series (+30%) rather than those of the n-3 series. DHA, however, inhibited the incorporation of arachidonic acid (AA) into PC by 50% at a molar ratio (DHA/AA) of 1.5. This phenomenon seems to be related to the competitive inhibition exerted by DHA on the thio-esterification of AA, a reaction catalyzed by acyl-CoA synthetase. This inhibitory effect appears to be dependent on the kinetic properties of the acyl-CoA synthetase toward DHA which, among the fatty acids examined, exhibited the lowest apparent Km and Vmax. It is suggested that the intracellular pool of DHA-CoA is the determinant species in altering the DHA composition of cardiac PC in animals given fish oils.

Animals↗
PubMed1990

Phospholipase A activity of cultured rat ventricular myocyte is affected by the nature of cellular polyunsaturated fatty acids.

Fatty acid composition of membrane phospholipids of cultured cardiomyocytes can be modified by the type of polyunsaturated fatty acids (n-3 or n-6 PUFA) constituting the culture medium. In this study, we investigated the effect of fatty acid modification on the activities of the key enzymes involved in the deacylation-reacylation cycle of membrane phospholipids. Results showed that cardiomyocytes grown in the presence of n-6 PUFA exhibited a higher specific alkaline phospholipase A (mainly A2) activity (+34%) and a moderately lower lysophospholipase activity (-17%) than when incubated with n-3 PUFA. AcylCoA:lysophosphatidylcholine acyltransferase, acid lysosomal phospholipase A1 and acylCoA synthetase activities were not significantly altered by changes in cellular PUFA composition. It was demonstrated that the differences between phospholipase A activities of the two types of cultured cells were linked neither to a differential leakage of enzyme nor to oxidative injury to the enzyme through blockage of essential sulfhydryl groups. One likely explanation is that the PUFA-induced changes in membrane composition alter membrane physical properties which, in turn, affect membrane-bound phospholipase A activity. Possible beneficial effects of the n-3 PUFA-induced changes on membrane stability are discussed.

Animals↗
PubMed1990

Lipid diet and enterocyte microsomal membrane fluidity in rats.

Rats were fed on diets more or less enriched with n-3 and n-6 unsaturated fatty acids, before removal of the small intestine. The global protein, cholesterol and phospholipid contents of enterocyte microsomes were measured. Fatty acids of the total lipid extracts were determined. Acyl coenzyme A: cholesterol acyl transferase (ACAT) was chosen as the enzyme whose activity reflects metabolic changes induced by lipid diets. Fluorescence measurements using diphenylhexatriene as the membrane probe were performed. As dietary fat may change the fatty acid composition of membranes, the order parameter S calculated from fluorescence measurements was studied with regard to dietary fatty acid composition. The S values, distributed over a large range, were not different between rat groups. They were positively correlated with the ratios of cholesterol and proteins to phospholipids and the molar percentage of saturated fatty acids. ACAT activity was negatively correlated with S. Variations in S values among rats, whatever the diet, could in part be attributed to individual factors.

Animals↗