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Biomedical subjects

G Ponsin

Publications and source records attributed to G Ponsin.

At least 19 recordsLinked to original sources
PubMed1998

Association between plasma HDL-cholesterol concentration and Taq1B CETP gene polymorphism in non-insulin-dependent diabetes mellitus.

The effects of CETP gene Taq1B polymorphism on plasma lipoproteins were investigated in 176 patients with non-insulin-dependent diabetes mellitus. The distribution of CETP genotypes was similar to that previously described in the general population. A significant association was found between CETP genotype and both CETP and HDL cholesterol (HDL-c) concentrations. B1B1 had the highest CETP and the lowest HDL-c whereas B2B2 had the lowest CETP and the highest HDL-c. However, HDL-c was not correlated with CETP concentration, even when genetic groups were separately considered. By multivariate analysis, the determinants of HDL were body mass index, triglycerides concentration, net mass CE transfer, and CETP genotype. No association was found between CETP genetic groups and HDL or LDL size distribution. In contrast, net mass CET was positively and HDL and LDL sizes were negatively correlated with plasma triglyceride concentration. Overall, our work demonstrates that, in a population of diabetic patients where lipoprotein-related parameters vary over a large range, the association of CETP gene polymorphism with HDL-c is independent of plasma CETP concentration.

Adult↗
PubMed1997

Characterization of a new case of autoimmune type I hyperlipidemia: long-term remission under immunosuppressive therapy.

Only a few cases of type I hyperlipidemia occurring in patients with autoimmune disease have been reported. We describe the case of a 35-yr-old woman suffering from severe type I hyperchylomicronemia. A combination of various hypolipidemic treatments, including strict hypolipidemic dietary therapy and administration of fibrates or n-3 fatty acids, was inefficient. Because of a history of familial autoimmunity, we introduced an immunosuppressive therapy that resulted in consistent long term and stable remission. Two attempts to reduce the immunosuppressor dose resulted in major relapses. To explain the defect of chylomicron hydrolysis, we investigated the postheparin plasma lipase activities. Hepatic triglyceride lipase activity was normal, whereas that of lipoprotein lipase (LPL) was reduced to about 30% of normal. Immunosuppressive therapy resulted in a complete and durable normalization of LPL activity. Using Western blot analysis, we found in the plasma of the patient a circulating IgG specifically directed against LPL, which became undetectable during immunosuppressive therapy. Western blot analysis revealed that the whole circulating anti-LPL autoantibody was bound to chylomicrons. Proteins extracted from patient's chylomicrons were able to induce a dose-related inhibition of LPL activity in vitro, whereas that of hepatic triglyceride lipase remained unchanged. These data constitute the first description of autoimmune hyperchylomicronemia due to an exclusive defect of LPL activity, and they show that a complete remission has been obtained after immunosuppressive therapy. Finally, our finding that the anti-LPL autoantibody is bound to chylomicrons emphasizes their previously unrecognized ability to transport LPL, already described for other lipoprotein fractions.

Adult↗
PubMed1996

Alterations in composition and concentration of lipoproteins and elevated cholesteryl ester transfer in non-insulin-dependent diabetes mellitus (NIDDM).

Cholesteryl esters (CE) exchange between lipoproteins through the action of cholesteryl ester transfer protein (CETP). Situations at high risk for atherosclerosis are often accompanied by an accelerated net mass CE transfer (CET) from high density lipoproteins (HDL) to very low (VLDL) and low density lipoproteins (LDL). However, the question as to whether the net mass CET is increased or decreased in non-insulin-dependent diabetes mellitus (NIDDM) has led to controversial data. To clarify this point, we have undertaken a detailed study of CET in 105 NIDDM patients by comparison with 17 control subjects. Net mass CET was approximately doubled in NIDDM. Plasma CETP activity and unidirectional CET from HDL to VLDL + LDL (CETHDL-->VLDL + LDL) or from VLDL + LDL to HDL (CETVLDL + LDL-->HDL) were measured under controlled lipoprotein concentrations using radioisotopic assays. No difference was observed in plasma CETP activity between NIDDM and controls. In NIDDM, CETHDL-->VLDL + LDL and CETVLDL + LDL-->HDL were decreased by 25% and 20%, respectively, as a consequence of alterations in lipoprotein compositions. Net mass CET was highly correlated with plasma triglyceride (TG) concentration (r = 0.66, P < 0.001) but not with that of LDL-cholesterol (r = 0.06, P > 0.6). When TG levels were decreased following dietetic recommendations or insulinotherapy, the net mass CET was lowered accordingly. We conclude that net mass CET is accelerated in NIDDM in spite of a decreased unidirectional CETHDL-->VLDL + LDL. This results from a lowered CETVLDL + LDL-->HDL and from elevated TG concentration, and the latter probably reflects a concentration effect of VLDL.

Adult↗
PubMed1996

Multiple abnormalities in the transfer of phospholipids from VLDL and LDL to HDL in non-insulin-dependent diabetes.

Transfers or exchanges of cholesterol esters and triglycerides between lipoproteins are mediated by a specialized protein referred to as cholesteryl ester transfer protein (CETP), whereas those of phospholipids (PLs) are facilitated by both CETP and a specific phospholipid transfer protein (PLTP). In the present study, the authors compared phospholipid transfer (PLT) in normal subjects and in patients with non-insulin-dependent diabetes (NIDD), which is associated with an increased risk of atherosclerosis. PLT was measured in different recombination experiments using an isotopic assay in which the transfer of labelled PLs from very low-density lipoprotein (VLDLs) and low-density lipoproteins (LDLs) to high-density lipoproteins (HDLs) was determined. This allowed discrimination between the roles of VLDLs + LDLs, HDLs, and plasma PLT activity (PLTA). VLDL + LDL-dependent PLT, HDL-dependent PLT and PLTA were decreased in NIDD. VLDL + LDL-dependent PLT was found to be negatively correlated with the PL/apolipoprotein B ratio, whereas HDL-dependent PLT was positively correlated with the HDL2/HDL3 and PL/apolipoprotein A-I ratios and negatively correlated with the flow activation energy at the HDL surface. The HDL2/HDL3 ratio was positively correlated with PLTA but not with CETP, which confirms previous reports suggesting that PLTP might act as an HDL conversion factor. These data show that several abnormalities in PLT occur in NIDD and raise the question as to whether a lowered PLT might be a new characteristic of dis factors associated with an increased risk of atherosclerosis.

Adult↗
PubMed1995

Plasma factors affecting the in vitro conversion of high-density lipoproteins labeled with a non-transferable marker.

We studied the in vitro conversion of HDL3 labeled with a radioiodinated diacyl lipid associating peptide (diLAP). DiLAP was previously shown to be nontransferable, which permitted its' use as a reliable marker of HDL particles. DiLAP-labeled HDL3 was incubated for 23 h at 37 degrees C in human or rat plasma or in reconstituted media containing delipidated plasma and/or lipoproteins and/or partially purified CETP. At the end of the incubations, the samples were adjusted to a density of 1.125 g/ml and ultracentrifuged. The two resulting fractions containing HDL2 and HDL3, respectively, were analyzed by gradient gel electrophoresis. Depending upon experimental conditions, diLAP-labeled HDL3 was converted into HDL2b- and/or small HDL3c-like particles. LCAT inhibition and to a lesser extent CETP promoted the formation of small HDL3c. Reactivation of LCAT led to the disappearance of small HDL3c. No HDL3c formed from HDL2 even in the absence of LCAT activity. When the incubations were performed in the presence of 100 mM thimerosal, which inhibited PLTP but not CETP activity, the conversion of diLAP-labeled HDL3 into HDL2 was almost completely blocked. Collective consideration of these data indicates that the formation of small HDL is moderately facilitated by CETP; that small HDL are converted to larger HDL species by LCAT and that the transformation of HDL3 into HDL2 is a process which largely depends upon PLTP activity.

Animals↗
PubMed1995

Cholesterol ester transfer and high-density lipoprotein conversion in normolipidemic, hypercholesterolemic, and hypertriglyceridemic non-insulin-dependent diabetics.

Non-insulin-dependent diabetes (NIDD) is a situation at elevated risk for atherosclerosis. The plasma concentration of high-density lipoprotein (HDL) is often lowered. This may be accompanied by an abnormal composition and profile of HDL subfractions. These abnormalities might result in part from a defect in the net cholesterol ester transfer (CET) from HDL to apo B-containing lipoproteins. In the present work, we have studied the net CET and HDL conversion in normolipidemic, hypercholesterolemic, and hypertriglyceridemic NIDD, by comparison with control subjects. HDL conversion was determined by gradient gel electrophoresis after 23 h incubation in plasma with HDL3 labeled with a nontransferable synthetic marker. The net CET in normolipidemic NIDD was similar to that of controls, while it was approximately doubled in hypercholesterolemic or hypertriglyceridemic NIDD. In all groups, HDL conversion was comparable, with the exception of hypertriglyceridemic NIDD. In the latter group, the labeled HDL2/HDL3 ratio was increased, indicating a more complete conversion that was correlated with the triglyceride/cholesterol ester ratio in HDL. In addition, when lecithin:cholesterol acyl transferase was inhibited, a distinct peak of small HDL particles appeared in the density range of HDL2 in contrast with the other groups where only small HDL3 was formed. Recombination experiments showed that these abnormalities were attributable to the plasma in which labeled HDL3 was incubated rather than to the origin (control or hypertriglyceridemic NIDD) of labeled HDL3. These data suggest that in NIDD, hypertriglyceridemia may result in abnormalities of HDL conversion due to alterations in HDL composition.(ABSTRACT TRUNCATED AT 250 WORDS)

Arteriosclerosis↗
PubMed1995

Decreased capacity to inhibit platelet hyperactivity and to stabilize prostacyclin of high-density lipoproteins in experimental diabetes.

Twenty-eight male Sprague Dawley rats were divided into two groups: a control group (C) of 15 animals and a streptozotocin-induced diabetes group mildly balanced by insulin (D) of 13 animals. After 15 weeks, plasma and high-density lipoprotein (HDL) lipids were determined in each group. Apoprotein A-I concentration was evaluated in HDL fractions. The capacity of the HDL fraction to inhibit thrombin and ADP-induced aggregation of normal platelets was determined for each rat, and in an additional experiment the relation dose-effect of HDL was established. The effect of HDL of the two groups on the stabilization of prostacyclin was compared by aggregation bioassay. After 15 weeks, HDL cholesterol (free + esterified). After 15 weeks, HDL cholesterol (free + esterified) tended to increase in group D compared with group C (P < 0.08). By contrast, apoprotein A-I was very significantly decreased in HDL-D compared with HDL-C (P < 0.001). These alterations were accompanied by a significantly decreased capacity of HDL (60 micrograms/ml platelet suspension) to inhibit ADP-induced aggregation (P< 0.0001) in group D compared with group C. Furthermore, HDL-D incubated 45 or 90 min with prostacyclin showed a significantly decreased capacity to stabilize prostacyclin compared with HDL-C (P<0.04; P <0.03, respectively). These alterations in HDL could be involved in thrombosis and atheromatous complications associated with this disease.

Adenosine Diphosphate↗
PubMed1994

The transformation of nascent disc shaped high density lipoproteins into mature spherical high density lipoproteins: conformational analysis of apolipoprotein A-I in model intermediate particles.

The conformation of apolipoprotein A-I (apo A-I) was studied in reassembled lipoprotein particles containing various proportions of apo A-I, phospholipids and cholesteryl esters or triglycerides, using both theoretical and experimental approaches. The proportions of the components were chosen to permit the formation of swollen discs mimicking the intermediate particles that must result from the lecithin:cholesterol acyl transferase (LCAT)-mediated transformation of nascent discoidal high-density lipoprotein (HDL) into mature spherical HDL. Three groups of particles were defined by the number of helices per apo A-I molecule that could fit the edge of the swollen discs. Groups I, II and III had six, seven and eight helices per apo A-I, respectively. The conformation of apo A-I was studied by quenching of tryptophan fluorescence in the presence of KI. In all groups the tryptophan (Trp) residues belonging to the helices located on the edge of the particles were very sparingly hydrated. In contrast, the degree of hydration of Trp residues in external position was different in each group. The structural organization of phospholipids was assessed by measurements of the fluorescence anisotropy of 1-(4-trimethylammonium phenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH) probe. In group I, which contained the less swollen particles, a segment of apo A-I of about 46 amino acids contributed to the area of the faces of the particles, resulting in a highly condensed and ordered phospholipid matrix. In groups II and III, the external segment of apo A-I did not interact with phospholipids.

Apolipoprotein A-I↗
PubMed1994

Mechanism of the gemfibrozil-induced decrease in the transfer of cholesterol esters from high density lipoproteins to very low and low density lipoproteins.

To better understand the effects of lipid-lowering drugs on the transfer of esterified cholesterol (EC) between lipoproteins, we investigated the changes induced by gemfibrozil administration on the unidirectional transfer of radiolabeled EC from high density lipoproteins (HDL) to very low (VLDL) and low density lipoproteins (LDL) in 10 normolipidemic subjects. HDL, VLDL/LDL, and the d > 1.21 g/ml fraction containing cholesterol ester transfer protein (CETP) were isolated from plasma before and after 8 weeks of gemfibrozil administration. The same fractionation procedure was applied to aliquots of a control plasma pool to permit different recombination experiments. When the CETP fractions of the subjects studied were incubated in the presence of control HDL and VLDL/LDL, no effect of gemfibrozil was observed on the rate of EC transfer, indicating that the drug did not induce any change in the plasma transfer activity. When HDL of the subjects studied were recombined with the CETP fraction and VLDL/LDL isolated from the control plasma pool, the rate of EC transfer was decreased by 43% after gemfibrozil administration. Thus, the drug induced a decrease in the HDL-dependent transfer of EC. This effect was accompanied by a decrease of the triglyceride (TG)/EC ratio in HDL, a decrease of the Stokes radius of large HDL determined after gradient gel electrophoresis, and an increase of the HDL viscosity. Since both HDL size and viscosity are in part dependent upon their TG/EC ratio, further investigations will be necessary to answer the question as to whether one of these structural criteria is predominant for the regulation of the HDL-dependent transfer of EC.

Adult↗
PubMed1993

High density lipoprotein interconversions in rat and man as assessed with a novel nontransferable apolipopeptide.

A nontransferable peptide analog of a plasma apolipoprotein diacyl lipid-associating peptide (diLAP) incorporates into model reassembled high density lipoproteins (R-HDL). In whole plasma in vitro, diLAP irreversibly transfers to native rat HDL2 and human HDL3, but not to rat HDL1 or human HDL2. The rate of transfer is dependent on the physical state of the lipid in the R-HDL. Exogenous cholesterol promotes the formation of larger HDL. When diLAP-labeled R-HDL were injected into rats, the diLAP that initially associated with HDL2 transferred to HDL1 over a period of 48 h. The rate of clearance of diLAP-labeled HDL was slower than that of apoA-I. The liver was the preferred site for diLAP-labeled HDL1 uptake. In contrast, diLAP-labeled HDL2 were associated with liver, ovaries, and adrenal glands, with the adrenal grands exhibiting the highest specific association. DiLAP was not found in the kidneys. These data show that 1) rat HDL is cleared more slowly than rat apoA-I; 2) HDL is removed from the plasma compartment as a particle; 3) there are tissue-specific differences in the removal of rat HDL1 and HDL2; 4) HDL2 is a precursor to HDL1; and 5) cholesterol and the activity of lecithin:cholesterol acyltransferase are essential to HDL remodeling.

Amino Acid Sequence↗
PubMed1993

Simvastatin-induced decrease in the transfer of cholesterol esters from high density lipoproteins to very low and low density lipoproteins in normolipidemic subjects.

Hyperlipidemic patients often have an accelerated esterified cholesterol transfer (ECT) from high density lipoproteins (HDL) to very low (VLDL) and low density lipoproteins (LDL). We investigated the effect of simvastatin on ECT in twelve normolipidemic subjects. After 6 weeks of simvastatin administration, ECT was decreased by 23%. To determine the mechanism of action of simvastatin, we measured ECT in different recombination experiments, using an isotopic assay in which the transfer of labelled EC from HDL to VLDL/LDL was determined. When HDL of the treated subjects were incubated with VLDL/LDL and CETP fractions isolated from control plasma, no effect of simvastatin was observed, indicating that the drug did not alter the HDL-dependent ECT. This might be expected since simvastatin induced only minor modifications of HDL structure. When HDL and VLDL/LDL of control plasma were incubated with CETP fractions of the treated subjects, a clear reduction of ECT occurred after simvastatin administration. The decrease of plasma transfer activity was correlated to that of CETP concentration and accounted for the simvastatin-induced lowering of ECT. The diminution of plasma CETP was correlated to that of the apo B-containing lipoproteins concentration. This finding confirms previous reports suggesting a relationship between LDL level and CETP activity. In conclusion, our work shows that simvastatin administration results in a decrease of ECT and that this effect occurs through a lowering of plasma CETP activity.

Adult↗
PubMed1993

Effects of a fenugreek seed extract on feeding behaviour in the rat: metabolic-endocrine correlates.

Fenugreek seeds (Trigonella foenum graecum L.) are assumed to have restorative and nutritive properties. The present work was designed to investigate the effects of a fenugreek seed extract on feeding behaviour. Experiments were performed to determine food consumption and motivation to eat as well as metabolic-endocrine changes in chronically treated animals. Male Wistar rats were given the seed extract orally (10 and 100 mg/day per 300 g body weight), mixed together with food, and control animals were monitored in parallel. The results show that chronic oral administration of the fenugreek extract significantly increases food intake and the motivation to eat. The treatment, however, does not prevent the anorexia nor the decreased motivation to eat induced by d-fenfluramine (2 mg/kg, IP). An increase in plasma insulin and a decrease in total cholesterol and very low-density lipoprotein (VLDL)-low-density lipoprotein (LDL) total cholesterol were also observed. In conclusion, chronic administration of a fenugreek seed extract enhances food consumption and motivation to eat in rats and also induces hyperinsulinemia as well as hypocholesterolemia.

Animals↗
PubMed1993

Decreased ability of high density lipoproteins to transfer cholesterol esters in non-insulin-dependent diabetes mellitus.

Esterified cholesterol transfer (ECT) from high density lipoproteins (HDL) to very low (VLDL) and low density lipoproteins (LDL) may be abnormal in situations at high risk for atherosclerosis. It has been shown to increase in insulin-dependent diabetes and to decrease in non-insulin-dependent diabetes (NIDD). Since the net transfer of esterified cholesterol (EC) results from a bidirectional exchange between HDL and VLDL/LDL, we developed a transfer assay specifically designed to measure the unidirectional transfer of EC from HDL to lipid emulsions according to first-order kinetics. Our results show that in NIDD the rate constant of HDL-dependent ECT is decreased by 30% by comparison with control subjects. Analysis of HDL composition revealed that, in both groups, HDL-dependent ECT was positively correlated with the free cholesterol/phospholipid ratio (r = 0.94; P < 0.001) and negatively correlated with the triglyceride/EC ratio (r = -0.85; P < 0.001). It is concluded that, besides the known defect of acceptor lipoproteins, the abnormality of ECT in NIDD is also caused by a decreased ability of HDL to act as an EC donor, presumably because of a change in composition. In addition, our work shows that the amount of EC lost by HDL during the reaction transfer is counterbalanced by a reciprocal equimolar transfer of triglycerides.

Cholesterol Esters↗
PubMed1991

Cholesterol-induced alteration of apolipoprotein A-I conformation in reassembled high density lipoprotein.

Recent reports have shown that apolipoprotein A-I (apo A-I), the major protein of high density lipoprotein (HDL) may exist in different conformational states. We studied the effects of apolipoprotein A-II and/or cholesterol on the conformation of apo A-I in reassembled HDL. Analysis of tryptophan fluorescence quenching in the presence of iodine suggested that cholesterol increased the number of apo A-I tryptophan residues accessible to the aqueous phase, but decreased their mean degree of hydration. These observations cannot be totally explained on the basis of the effect of cholesterol on phospholipid viscosity as determined by fluorescence anisotropy of diphenyl hexatriene. We did not observe any effect of apo A-II on the conformation of apo A-I.

Apolipoprotein A-I↗
PubMed1991

Hepatic lipase activity during oral and parenteral 17 beta-estradiol replacement therapy: high-density lipoprotein increase may not be antiatherogenic.

OBJECTIVE: Hepatic lipase activity is involved in the removal of cholesterol and phospholipid from plasma high-density lipoprotein (HDL) to the liver. Changes in hepatic lipase are responsible for some lipoprotein modifications observed during estrogen administration (i.e., increased HDL levels). The aim of this study was to compare the effects of alternative routes of administration of estrogen on hepatic lipase activity and lipoprotein metabolism. DESIGN, PATIENTS: The effects of oral and parenteral estradiol (E2) replacement therapy on post-heparin hepatic lipase were studied in the short-term (6 weeks) in postmenopausal women. INTERVENTIONS: Ten patients received 2 mg/d or oral micronized E2 and 10 patients 3 mg/d of percutaneous E2. RESULTS: Both treatments significantly increased plasma E2 levels. Hepatic lipase decreased (-33%) significantly (P less than 0.05), and the phospholipids and free cholesterol content of HDL and HDL3 increased significantly (P less than 0.05) during oral but not during parenteral treatment. CONCLUSIONS: The short-term pharmacological effect of E2 on hepatic lipase depends on the route of administration. The inhibition of this enzyme may reduce the removal of HDL-cholesterol by the liver. The expected vascular benefits of such a pharmacological increase in HDL are questionable.

Administration, Cutaneous↗
PubMed1990

[Modifications, due to nutrition, of methyl and methylene 1H NMR signals in human plasma and normal serum samples].

The line width test has been realised on twelve normal healthy persons (seven men and five women). Blood was collected at different time during one day. The results obtained when blood samples was taking after eating, showed an appreciable decrease in the average methylene and methyl line width. The same test realised on clear serum samples added up with increasing quantities of triglycerids rich lipoproteins leads to the same result.

Blood Chemical Analysis↗