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L Leclerc

Publications and source records attributed to L Leclerc.

At least 19 recordsLinked to original sources
PubMed1992

Decreased G3PDH binding to erythrocyte membranes in sickle cell disease.

Several membrane abnormalities have been described in red cells from patients with sickle cell disease, responsible for chronic hemolytic anemia. We describe here a 35-50% inhibition of the binding of glyceraldehyde-3-phosphate dehydrogenase (G3PDH) to the membrane of sickle red cells. Varying the phosphorylation state of the membrane proteins did not change their affinity for the enzyme. Protein band 3 and the cytoplasmic domain of this protein isolated from sickle red cells showed normal interaction with the enzyme. The inhibition observed with intact membranes is not due to short term oxidation of membrane proteins, as various procedures inducing acute oxidative stress in normal membranes did not reproduce the inhibition of G3PDH binding. We conclude that the alteration of the binding of G3PDH to the membrane of sickle erythrocytes is probably related to long term processes involving cycles of HbS polymer formation.

Adult↗
PubMed1991

Inhibition of the erythrocyte (Ca2+ + Mg2+)-ATPase by nonheme iron.

The erythrocyte calmodulin-stimulated (Ca2+ + Mg2+)-ATPase (CaM-ATPase), an integral membrane protein, is inhibited in different types of congenital hemolytic anemias for which oxidative processes appear as a common feature. The oxidation of hemoglobin and its degradation lead to the accumulation of ferric heme (hemin) and nonheme iron in the red cell. We have shown previously that hemin inhibits the activity of the enzyme of normal erythrocyte (Leclerc et al. (1988) Biochim. Biophys. Acta, 946, 49-56) involving an oxidation of thiol groups. The present study demonstrates that nonheme iron also inhibits the CaM-ATPase activity. In contrast with hemin, the inhibition of the enzyme induced by the nonheme treatment is prevented by butylated hydroxytoluene, a protecting agent of unsaturated phospholipid peroxidations, while dithiothreitol, a reducing agent of protein disulfide bridges, does not restore the activity of the enzyme. We conclude that nonheme iron inhibits the enzyme at least in part, through the peroxidation of phospholipids of the membrane bilayer.

Butylated Hydroxytoluene↗
PubMed1991

Hypothyroidism following combined treatment for hypopharyngeal and laryngeal carcinoma.

The development of hypothyroidism following combined treatment for pharyngeal and laryngeal cancer has received little attention in the literature. We prospectively studied 32 patients over 4 years to determine the incidence of such hypothyroidism and to examine the effect of hemithyroidectomy associated with a combined treatment modality. All patients were men with pharyngeal or laryngeal squamous cell carcinomas and no prior history of thyroid disease. Treatment consisted of radical surgery (30 of 32 patients), followed by postoperative radiotherapy (31 patients). The results of thyroid function tests (free triiodothyronine, free thyroxine, and thyroid-stimulating hormone [TSH]) were all normal preoperatively; tests were repeated every 3 months after treatment. Elevation of TSH values in two successive blood samples was required to make a diagnosis of hypothyroidism. Of 12 patients who underwent hemithyroidectomy as part of total pharyngolaryngectomy and postoperative radiotherapy, 7 became hypothyroid a mean of 6 months after treatment. Twenty patients had similar combined treatment but without thyroid resection. Hypothyroidism developed a mean of 10 months after treatment in only four patients in this group (p less than 0.05). We conclude that hypothyroidism frequently develops following combined treatment for pharyngeal and laryngeal cancer even when thyroid resection has not been performed. Patients should be evaluated postoperatively and carefully monitored by means of serial thyroid function tests.

Carcinoma, Squamous Cell↗
PubMed1990

Heme-CO as a probe of the conformational state of calmodulin.

The interaction of heme-CO with calmodulin, in the presence of calcium, leads to a complex of four heme-CO molecules per protein. No interaction was observed in the absence of calcium. The binding of heme-CO to calmodulin was monitored by the shift in the Soret absorption band from 407 to 420 nm (bound form); the four sites are not spectrally identical. The ligand CO can be photodissociated from the calmodulin-heme-CO complex and the biomolecular recombination kinetics also indicate a heterogeneous mixture. The complex does not bind oxygen reversibly. As calmodulin has only one histidine, the hemes are apparently not bound by the iron atom as in hemoglobin, but are probably loosely associated (Kd = 0.5 microM) in hydrophobic pockets which apparently open when the protein is activated by calcium.

Animals↗
PubMed1989

Flash photolysis of the serum albumin-heme-CO complex.

Protoheme-CO in aqueous solution does not exhibit a geminate ligand recombination reaction. Addition of a protein, either globin or serum albumin, to which heme binds strongly, leads to an observable geminate reaction in aqueous solution. The bimolecular kinetic data for the albumin-heme-CO complex show two stable components, one heme-like in rate and difference spectrum, and one hemoglobin-like. The geminate reaction correlates spectrally with the hemoglobin-like component.

Binding Sites↗
PubMed1989

Muscarinic cholinergic induced secretin subsensitivity in rat isolated pancreatic acini. Effects on amylase release, cyclic adenosine monophosphate and inositol phosphate formation.

In this study, dispersed rat pancreatic acini exhibited secretin subsensitivity in their capacity to release amylase after preexposure to increasing concentrations of the muscarinic cholinergic agonist carbamylcholine. The present study also explores the potential mechanisms involved in this cellular desensitization phenomenon. Secretin subsensitivity of pancreatic acini pre-exposed to 10(-4) M carbamylcholine was observed only at secretin concentrations above 10(-8) M. The desensitized cells had not recovered 3 h after the cholinergic agonist exposure. In these acini, the adenylate cyclase pathway remained unaltered because cholera toxin, forskolin, and 8-Br-cAMP still induced weak, but normal, amylase release when compared with control acini. In vivo administration of pertussis toxin failed to protect the dispersed pancreatic acini against carbamylcholine-induced secretin subsensitivity. Moreover, cAMP production by these acini in response to secretin, cholera toxin, and forskolin was similar to that observed in control acini. Secretin stimulation of inositol phosphate (InsP1, InsP2, InsP3) production after carbamylcholine pre-exposure remained equivalent to that observed in acini that had never been exposed to the cholinergic agonist. Thus, after muscarinic cholinergic agonist exposure, pancreatic acini showed secretin subsensitivity in their capacity to release enzyme. This phenomenon appears to result from modifications at post-second messenger loci.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1988

Inhibition of membrane erythrocyte (Ca2+ + Mg2+)-ATPase by hemin.

Red blood cell lysis is a common symptom following severe or prolonged oxidative stress. Oxidative processes occur commonly in sickle cells, probably mediated through denatured hemoglobin and the accumulation of ferric hemes in the membranes. Calmodulin-stimulated (Ca2+ + Mg2+)-ATPase from sickle red cell membranes is partially inactivated (Leclerc et al. (1987) Biochim. Biophys. Acta 897, 33-40). In this study (Ca2+ + Mg2+)-ATPase activity from normal adult erythrocyte membranes was measured in the presence of hemin. We report a time- and concentration-dependent inhibition of the activity of the enzyme by hemin due to a decrease in the maximum velocity. Only a mild inhibitory effect was observed in the presence of iron-free protoporphyrin IX, indicating the catalytic influence of the iron. Experiments carried out with hemin (ferric iron) liganded with imidazole or with reduced protoheme (ferrous iron) liganded with carbon monoxide, demonstrated that the inhibition requires that hemin be capable of binding additional ligands. The inhibition was not influenced by the absence of oxygen but was prevented by addition of bovine serum albumin. Addition of butylated hydroxytoluene, a protective agent of lipid peroxidation, failed to prevent the inhibition of calmodulin-stimulated (Ca2+ + Mg2+)-ATPase. As dithiothreitol partially restores the enzyme activity, we postulated that hemin interacts with the thiol groups of the enzyme.

Ca(2+) Mg(2+)-ATPase↗
PubMed1988

[Hyperreninemic hypoaldosteronism syndrome induced by plasma exchange].

The study was designed to measure sequential changes in plasma renin activity, aldosterone, angiotensin-converting enzyme activity and ionograms, prior to, and after therapeutic plasma exchange. Each measurement was repeated before and after stimulation of renin activity induced by furosemide. The results showed that plasma exchange induces a syndrome of hyperreninemic hypoaldosteronism associated with a depletion in angiotensin-converting enzyme activity which might account for the dissociation between plasma renin activity and aldosterone.

Adolescent↗
PubMed1988

Decrease of angiotensin-converting enzyme activity after plasma exchange.

We measured sequential changes in serum angiotensin-converting enzyme (ACE) in 12 ICU patients undergoing plasma exchange (PE) with plasma substitutes (albumin-Polygelin). A dramatic decrease in serum ACE activity was observed after each of the 51 PE procedures. Repeated PE procedures resulted in almost a total depletion of serum ACE, which returned to normal ranges in 4 to 10 days. No ACE change was observed during hemodialysis or hemofiltration. ACE activity increased after PE with fresh frozen plasma replacement. ACE changes were compared with IgG, antithrombin III, and fibronectin changes. Extraction ratio comparisons were consistent, with a loss in removed plasma accounting for 50% to 70% of the observed ACE decrease. Plasma zinc levels were not modified after PE. Mixing experiments with increasing volumes of plasma substitutes showed ACE inhibition by Polygelin. In vivo infusion of Polygelin had the same effect. The renin-induced aldosterone response studied in six exchanged patients was consistent with a relative hyperreninemic hypoaldosteronism after repeated PE. These findings may be of clinical relevance during acute hypovolemia and dehydration after PE or Polygelin infusion and in patients with impaired lung endothelial function.

Adult↗
PubMed1987

The calmodulin-stimulated (Ca2+ + Mg2+)-ATPase in hemoglobin S erythrocyte membranes: effects of sickling and oxidative agents.

A decrease in the reactivity of erythrocyte membrane (Ca2+ + Mg2+)-ATPase to calmodulin stimulation has been observed in aging red cells and in various types of hemolytic anemias, particularly in sickle red cell membranes. Unlike the aging process, the defect in the (Ca2+ + Mg2+)-ATPase from SS red blood cells is not secondary to a decrease in calmodulin activity and is already present in the least dense SS red blood cells separated on a discontinuous density gradient. Deoxygenated AS red cells were forced to sickle by lowering the pH, raising the osmolarity of the buffer (sickling pulse). Under these conditions an inhibition of the calmodulin-stimulated enzyme was observed only if several cycles of oxygenation/deoxygenation were applied. No alteration of the enzyme could be detected after submitting AS red blood cells to other conditions or in AA red blood cells submitted to the same treatments. This suggests that oxidative processes are involved in the alterations of the (Ca2+ + Mg2+)-ATPase activity. Treatment of membranes from AA erythrocytes by thiol group reagents and malondialdehyde, a by-product of auto-oxidation of membrane unsaturated lipids and a cross-linking agent of cytoskeletal proteins, led to a partial inhibition of the calmodulin-stimulated (Ca2+ + Mg2+)-ATPase. We postulate that the hyperproduction of free radicals described in the SS red blood cells and involved in the destabilization of the membrane may be also responsible for the (Ca2+ + Mg2+)-ATPase failure.

Anemia, Sickle Cell↗
PubMed1987

Activity of cyclic GMP-dependent protein kinase in aortae from spontaneously hypertensive rats.

It has been suggested that various agents induce relaxation of vascular smooth muscles through guanosine 3',5'-cyclic monophosphate (cGMP) and cGMP-dependent protein kinase (cGMP-PK). In this work, the activity of cGMP-PK was studied in the 30,000 g supernatant from aortae of 4, 6, 8 and 12-week-old spontaneously hypertensive (SHR) and age-matched normotensive Wistar-Kyoto (WKY) rats and also of 4 and 12-week-old normotensive Wistar (W) and Sprague Dawley (SD) rats. At 4 weeks of age, both basal and cGMP-stimulated activity were not different in SHR and WKY rats. Nevertheless, a greater basal activity was measured in W (+50%) and SD (+20%) rats than in SHR, while no difference was observed between stimulated activities. In contrast with observations in the three normotensive rat strains, cGMP-PK activity did not decrease in the aortae supernatant of SHR rats aged 4-12 weeks. This resulted in mean increases of 45 and 30% in the basal and the cGMP-stimulated activity, respectively, in the 12-week-old SHR rats. The abnormal evolution of cGMP-PK activity in the hypertensive strain was already detectable at 4-6 weeks of age. In apparent agreement with observations on protein kinase activity, cGMP binding activity attributable to cGMP-PK was 25% greater in 12-week-old hypertensive rats compared with age-matched WKY rats. These results indicate that in aortae of SHR rats, control of cGMP-PK activity is abnormal early in life.

Aging↗
PubMed1986

The influence of nitroheterocyclic radiosensitizers on the membrane of red blood cells.

Nitroimidazole compounds are effective radiosensitizers, but neurotoxic side effects prevent their clinical use. Studying the effect of misonidazole, metronidazole and two of its derivatives, 4.5-NO2-METRO and 4-NO2-METRO, on red blood cell, it was recently demonstrated that these compounds inhibit the red cell membrane (Na+-K+) ATPase and decrease the fluidity of the membrane bilayer. In order to extend these observations and to achieve a more complete interpretation, four additional investigations were selected: the (Ca++-Mg++)ATPase activity, the anion channel (band 3 protein) kinetics, the susceptibility of the phospholipids to peroxidation, and their influence on the concentration of reduced glutathione (GSH). The activity of the (Ca++-Mg++)ATPase and its stimulation by calmodulin were decreased by all four drugs, but the anion transport kinetics were unaltered. No lipid peroxidation could be detected, as estimated by the production of malonyldialdehyde. The red cell GSH was depleted by 4.5-NO2-METRO, probably due to the formation of a complex between GSH and the drugs [Varghese 1983]. The mechanism of the inhibition of the ATPases is not yet clearly apparent; it is presently sought in a direct interaction of the drugs with some thiol reactive groups of the ATPases.

Anions↗
PubMed1985

A new case of hemoglobin Providence (alpha 2 beta 2 82 (EF6) Lys----Asn or Asp) discovered in a French Caucasian family. Structural and functional studies.

A new case of Hb Providence was discovered in a French caucasian family presenting a mild polycythemia. Structural and functional studies of the two abnormal fractions (Hb Providence Asn and Asp) have been performed. These confirm the abnormal characteristics of Hb Providence described previously. Red cells containing Hb Providence were fractionated with a Percoll Albumin density gradient. The respective amounts of the two components were determined in the youngest and oldest cells. We observed a slight increase of Hb Providence Asp from 34 to 37% during the life span of the erythrocytes which confirms that the deamidation of Hb Providence Asn to Hb Providence Asp is a fast process, already present and close to its maximum, in the reticulocytes. Both abnormal components are stable in the presence of isopropanol.

Adolescent↗
PubMed1985

[You and digoxin].

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Arrhythmias, Cardiac↗
PubMed1979

[Effects of alanine on the metabolism of lactate and glucose in the isolated perfused rat heart (author's transl)].

Perfused non working isolated rat heart preparations have been used to study whether alanine (0,89 gl-1) could represent an energy source for the myocardium. Its influence on glucose and lactate metabolism in the heart was also studied. The use of 14C labelled compounds permitted the estimation of the oxidation rate of these three metabolites. The results show that: 1) Alanine was not utilized by the heart. 2) Alanine did not alter myocardial glucose metabolism or lactate oxidation. 3) Alanine lowered lactate uptake by the myocardium which may indicate that alanine influences lactate transport through the cell membranes. One may speculate that in vivo, alanine will not interfere with glucose or lactate metabolism by the heart as, even in acute physiological conditions (exercice, hypoxie, fasting) lactate is always present in blood at higher concentration than alanine.

Alanine↗
PubMed1979

Lactate kinetics estimated by single injection and continuous infusion of [14C-(U)]-lactate in rats.

1 Identical values of the rate of lactate turnover determined with [14C-(U)]-lactate were found with single injection or continuous infusion techniques in anaesthetized and mechanically ventilated rats. 2 The mean transit time and total minimal body mass of lactate determined graphically (Katz et al., 1974 a, b) were higher with single injection than with continuous infusion of the tracer.

Animals↗