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Biomedical subjects

H Lafont

Publications and source records attributed to H Lafont.

At least 19 recordsLinked to original sources
PubMed1992

Eicosapentaenoic and docosahexaenoic acids in cultured rat ventricular myocytes and hypoxia-induced alterations of phospholipase-A activity.

Hypoxia was reported to induce a decrease in phosphatidylcholine-hydrolyzing phospholipase activity (PC-PLA) in cultured rat cardiomyocytes. This work was intended to compare the influence of the presence of either eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA) in the phospholipids on the PC-PLA activity in normoxic and hypoxic conditions. The enrichment of the medium with EPA or DHA resulted in cell phospholipids containing about 2% or 22% DHA, respectively. These cells were then submitted for 3.5 h to either normoxia or hypoxia and the PC-PLA activities were assayed using [1-14C] dioleoyl-PC (pH 8.4 for PC-PLA2 and 4.9 for PC-PLA1). The results show that both enzymic activities are significantly higher in DHA-rich cardiomyocytes. Hypoxia induced a significant decrease in PC-PLA2 (about 25%) which was not statistically different between the two groups of cells. The hypoxia-induced decrease in PC-PLA1 was not found significant. In conclusion, the nature of the long chain n-3 polyunsaturated fatty acids in the phospholipids appears to contribute to the regulation of PC-PLA activity but not to influence its decrease during hypoxia.

Animals↗
PubMed1992

Heart and liver membrane phospholipid homeostasis during acute administration of various antitumoral drugs to the rat.

The purpose of this study was to investigate in the rat heart and liver the effects of an acute administration of three anthracyclines, doxorubicin, epirubicin and pirarubicin, and an anthracenedione, mitoxantrone, on the membrane peroxidative status, which was estimated by the composition of polyunsaturated fatty acids (PUFA), and on the activities of the enzymes involved in membrane repair processes and lipid hydroperoxide detoxification. Rats were injected for four consecutive days with the drugs or saline (control) and killed 24 hr after the last injection. All the drugs induced an increase in plasma thiobarbituric reactive substances and alpha-tocopherol concentrations, both expressed per milligram of plasma lipids. Plasma vitamin A was decreased by about a factor of two by all the drugs. The fatty acid profile in the heart lipids showed that the polyunsaturated species (20:4 n-6, 22:6 n-3) remained at the same or even higher levels after anthracycline treatment. This can be explained by the fact that the activities of the enzymes involved in either the recycling of membrane phospholipids, such as phospholipases A1 and A2 (EC 3.1.1.4 and EC 3.1.1.32), lysophospholipases (EC 3.1.1.5) and acylCoA:lysophosphatidylcholine acyltransferases (EC 2.3.1.23), or hydroperoxide detoxification, such as selenium-dependent glutathione peroxidase (GSH-PX, EC 1.11.1.9) and glutathione S-transferases (GSH-T, EC 2.1.5.18), were maintained at the same level of activity after the antitumoral treatment. In liver, membrane phospholipid levels of PUFA were maintained as well as the activities of phospholipid-metabolizing enzymes. GSH-PX activity was not affected whereas that of GSH-T was slightly lowered by the drugs. These results suggest that during acute antitumoral-induced lipid peroxidation of membranes, the multi-enzymatic complex of the immediate processes of repair and detoxification is fully operational, allowing the membrane to rapidly recover its functional status. The results are discussed in the context of the equivocal relationships between antitumoral-induced lipid peroxidation and cardiac disturbances.

1-Acylglycerophosphocholine O-Acyltransferase↗
PubMed1992

Structural and functional importance of dietary polyunsaturated fatty acids in the nervous system.

The nervous system is the organ with the second greatest concentration of lipids. These lipids participate directly in membrane functioning. Brain development is genetically programmed. It is therefore necessary to ensure that nerve cells receive an adequate supply of nutrients, especially of lipids, during their differentiation and multiplication, and throughout their lives. The effects of polyunsaturated fatty acid deficiency have been extensively studied; prolonged deficiency leads to death in animals. Linoleic acid is now universally recognized to be an essential nutrient. Until recently, however, alpha-linolenic acid was considered non-essential. Feeding animals with oils that have a low alpha-linolenic content results in all brain cells and organelles and various organs having reduced amounts of 22:6n-3, which is compensated for by an increase in 22:5n-6. The speed of recuperation from these anomalies is extremely slow for brain cells, organelles, and microvessels, in contrast to other organs. A decrease in alpha-linolenic series acids in the membranes results in a 40% reduction in the Na(+)-K(+)-ATPase of nerve terminals and a 20% reduction in 5'-nucleotidase. Some other enzymatic activities are not affected, although membrane fluidity is altered. A diet low in alpha-linolenic acid induces alterations in the electroretinogram which disappear with age; motor function and activity are little affected, but learning behavior is markedly altered. The presence of alpha-linolenic acid in the diet confers a greater resistance to certain neurotoxic agents (triethyl-lead). During the period of cerebral development, there is a linear relationship between brain content of n-3 acids and the n-3 content of the diet up to the point where alpha-linolenic levels reach 200 mg for 100 g of food intake. Beyond that level there is a plateau. For other organs, such as the liver, the relationship is also linear up to 200 mg/100 g, but then there is merely an abrupt change in slope and not a plateau. When dietary 18:2n-6 content was varied, it was noted that 20:4n-6 optimum values were obtained at 150 mg/100 g for all nerve structures, 300 mg for testicle and muscle, 800 mg for kidney, and 1200 mg for liver, lung and heart. A deficiency in alpha-linolenic acid and an excess of linoleic acid have the same main effect: an increase in 22:5n-6 levels.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1992

Thawed human hepatocytes in primary culture.

In drug metabolism studies, isolated and cultured human hepatocytes provide a useful model for overcoming the difficulty of extrapolating from animal data. In vitro studies with human hepatocytes are scarce because of the lack of livers and suitable methods of storage. After developing a new method for cryopreservation of human hepatocytes, we evaluated the effects of deep freezing storage on their viability, morphology, and functional and toxicological capabilities in classical culture conditions. Freshly isolated human hepatocytes were cryopreserved in medium containing 10% Me2SO and 20% fetal calf serum, using a Nicool ST20 programmable freezer (-1.9 degrees C/min for 18 min and -30 degrees C/min for 4 min). Cells were stored in liquid nitrogen. Viability of thawed human hepatocytes was 50-65% as assessed by erythrosin exclusion test prior to purification on a Percoll density gradient. Morphological criteria showed that thawed human hepatocytes require an adaptation period to the medium after seeding. Functional assessments showed that human hepatocytes which survive freezing and thawing preserve their protein synthesis capabilities and are able to secrete a specific protein, anionic peptidic fraction, which is involved in the hepatic uptake of bile-destined cholesterol. We then studied Midazolam biotransformation to test metabolic functions, and erythromycin toxicity by Neutral Red test (cell viability) and 3-(4,5-dimethylthiazol-2-yl)-diphenyl tetrazolium bromide test (cell metabolism). All of these experiments indicated that thawed human hepatocytes should be used 38 h after seeding for optimum recovery of their functions: membrane integrity, protein synthesis, and stabilization of drug metabolism enzymes.

Biotransformation↗
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

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↗
PubMed1979

The apoprotein fraction of the bile lipoprotein complex: isolation, partial characterization and phospholipid binding properties.

A bile apoprotein fraction (Apo BLC) was isolated by preparative isoelectric focusing (I.E.F.) from the detergent-free form of the bile lipoprotein complex (BLC). Analytical I.E.F. of Apo BLC yields a characteristic and reproducible pattern of two narrow acidic bands (pI 4,8-5,0). This apoprotein presents a strong tendency to undergo self-aggregation in aqueous buffer. A low molecular weight constituent of Apo BLC has been isolated after gel filtration, its mean Mw is estimated by SDS-PAGE at 7,500 daltons. The binding capacity of Apo BLC for phospholipids was investigated on dimyristoylphosphatidylcholine liposomes by gel filtration and zone electrophoresis. The resulting structures, larger than the original single-shelled vesicles, acquire and anodic electrophoretic mobility. Apo BLC has a weaker affinity for lysophosphatidylcholines: these phospholipids decrease the degree of aggregation of the apoprotein. These studies contribute additional data concerning the high affinity of Apo BLC for phosphatidylcholines, which are the major phospholipid constituents of bile. The discussion deals with the fact that association of Apo BLC with bile phosphatidylcholines may present some implications in the pathogeny of LpX and in the process of intestinal fat absorption.

Apolipoproteins↗
PubMed1979

[Dynamic study of the coronary vascular bed by selective coronary scanning using hyperaemia].

Advantage may be taken of the hyperaemic response to the iodine contained in the contrast medium injected during coronary angiography to assess the functional value of the coronary tree using radioactive microspheres. This series comprises 73 selective coronary scans performed in the resting state (113 m In marked microspheres) and during the hyperaemic phase (99 m TC marked microspheres) in 70 patients. A positive hyperaemic response distal to severe truncular stenosis indicates a good distal arteriolar bed and collateral circulation for aorto-coronary bypass grafting. After aorto-coronary bypass (23 cases), the hyperaemic response gives an indication of the functional value of the revascularised myocardium. In 71% cases, the results correlate well with the measurement of the peroperative blood flow through the graft. It is usually positive when the bypass graft is implanted with good distal arterial run off.

Adult↗
PubMed1978

Possible roles of bile lipids and colipase in lipase adsorption.

The adsorption isotherms of bile salts, phospholipids, and cholesterol were determined with siliconized glass beads. It was observed that the molar fractions of cholesterol, phospholipid, and bile polypeptide fractions increased simultaneously and considerably on the surface of the beads in comparison to the corresponding fractions found in bile. The composition of the adsorbed film is approximately 1 cholesterol: 2 phospholipid: 3 bile salt molecules. The performed complex of lipase, colipase, and bile lipids behaves as an entity which determines lipase adsorption. The modification of the interface quality of a lipid substrate by a detergent is not perse the reason for the lack of lipase adsorption. A model is proposed according to which lipolysis under physiological conditions would occur in two steps requiring two cofactors. Colipase would be necessary for the formation of the lipase-bile lipoprotein complex, and bile lipids would be required to direct the adsorption of this lipolytic entity toward the emulsified substrate.

Adsorption↗
PubMed1978

Inhibition of lipase adsorption at interfaces. Role of bile salt micelles and colipase.

The effects of bile salts and colipase on the adsorption of lipase at an interface were studied by hydrophobic affinity chromatography on phenyl- and octyl-Sepharose. In the absence of bile salts, lipase or colipase binds separately to the gel. This is unchanged in the presence of adsorbed bile salts, when one bile salt molecule is associated per hydrophobic ligand. The same data are obtained in the presence of monomeric bile salt solutions. In contrast, lipase adsorption is totally prevented in a micellar bile salt solution. These results favor the idea that the formation of a lipase-bile salt complex in solution is responsible for the lack of interfacial lipase adsorption.

Adsorption↗