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M Lecomte

Publications and source records attributed to M Lecomte.

35 records · Page 2Linked to original sources
PubMed1996

Immunohistochemical study of 100 pancreatic tumors in 28 patients with multiple endocrine neoplasia, type I.

One hundred pancreatic tumors ranging in size from 0.3 to 7 cm were studied in 28 patients (17 male and 11 female patients; mean age 35 years) with multiple endocrine neoplasia, type I. An immunohistochemical study was performed on deparaffinized sections using the following antibodies: neuron-specific enolase, chromogranin A or synaptophysin, insulin, glucagon, somatostatin, pancreatic polypeptide (PP), vasoactive intestinal peptide (VIP), gastrin, adrenocorticotropic hormone, alpha-subunit of human chorionic gonadotropin, gonadotropin-releasing factor, serotonin, and calcitonin. Among the 100 tumors (all multiple), seven were unclassified, 10 were plurihormonal, and 83 produced a predominant hormonal secretion (with 50-90% of the same cell type), including 37 "A-cell tumors" (glucagon), 27 "B-cell tumors" (insulin), 11 PP-cell tumors, one G-cell tumor (gastrin) and one vasoactive intestinal peptide (VIP)-cell tumor. These multiple tumors had a different predominant hormonal secretion in the same patient in 23 of the 28 cases. There was a preferential association of A-cell tumor and B-cell tumor. Hyperplasia of the islets of Langerhans was not detected in adjacent pancreas. Nesidioblastosis was observed in 30% of cases.

Adolescent↗
PubMed1995

Selective inhibition of prostaglandin endoperoxide synthase-1 (cyclooxygenase-1) by valerylsalicylic acid.

Aspirin causes a time-dependent inhibition of prostaglandin endoperoxide H synthases (PGHS)-1 and -2 by acetylating active site serines present in both isozymes. In the case of PGHS-1, aspirin acetylation blocks cyclooxygenase activity, apparently by preventing arachidonate binding to the cyclooxygenase active site. With PGHS-2, acetylation does not block substrate binding but rather alters the enzyme in such a way that the acetylated form of PGHS-2 produces 15R-hydroxyeicosatetraenoic acid (15R-HETE) instead of the usual prostaglandin endoperoxide product. Based on these differences between PGHS-1 and PGHS-2, we reasoned that a salicylate ester containing an acyl group somewhat larger than the acetyl group of aspirin might be a selective inhibitor of PGHS-2. Accordingly, we prepared and tested eight different acyl salicylates as inhibitors of human (h) PGHS-1 and -2 expressed transiently in cos-1 cells. Valeryl(pentanoyl)salicylate (VSA) was the only compound in this series which showed isozyme selectivity, and, surprisingly, VSA inhibited hPGHS-1 much more effectively than hPGHS-2. Inhibition of hPGHS-1 by VSA was time-dependent. VSA also inhibited ovine PGHS-1 but did not inhibit the S530A mutant of ovine PGHS-1. This latter mutant, which lacks the active site serine hydroxyl group, is also refractory to inhibition by acetylsalicylate. Thus, we conclude that VSA acylates the active site serine of PGHS-1. VSA inhibited prostanoid synthesis by serum-starved murine NIH 3T3 cells which express only PGHS-1; in contrast, VSA caused only partial inhibition of prostanoid synthesis by serum-stimulated 3T3 cells which express both PGHS isozymes. Our results establish that VSA can be used as a reasonably selective inhibitor of PGHS-1.

3T3 Cells↗
PubMed1994

Acetylation of human prostaglandin endoperoxide synthase-2 (cyclooxygenase-2) by aspirin.

Aspirin (acetylsalicylate) treatment of human (h) prostaglandin endoperoxide H synthase (PGHS)-1 expressed in cos-1 cells caused a time-dependent inactivation of oxygenase activity. Aspirin treatment of hPGHS-2 produced an enzyme which retained oxygenase activity but formed exclusively 15-hydroxy-5,8,11,13-eicosatetraenoic acid (15-HETE) instead of PGH2. The 15-HETE was exclusively of the 15R configuration. The Km values for arachidonate of native and aspirin-treated hPGHS-2 were about the same suggesting that arachidonate binds to both aspirin-treated and native hPGHS-2 in a similar manner. If, as expected, the formation of 15R-HETE proceeds through abstraction of the 13proS hydrogen from arachidonate, O2 insertion must occur from the same side as the hydrogen abstraction; with all other lipoxygenases and cyclooxygenases, O2 addition is antarafacial. When microsomal hPGHS-2 was incubated with [acetyl-14C]aspirin, the enzyme was acetylated. An S516A mutant of hPGHS-2, which retains enzyme activity, was not acetylated. This indicates that Ser-516 is the site of aspirin acetylation of hPGHS-2; this residue is homologous to the "active site" serine of PGHS-1. An S516N mutant of hPGHS-2 was catalytically active; in contrast, an S516Q mutant lacked cyclooxygenase but retained peroxidase activity. Because in the case of PGHS-1 a smaller asparagine substitution is sufficient to eliminate cyclooxygenase activity, we conclude that the active site of PGHS-2 is slightly larger than that of PGHS-1. An S516M mutant of hPGHS-2 was obtained which resembled aspirin-acetylated hPGHS-2 in that this mutant made 15R-HETE as its major product; however, unlike the aspirin-acetylated hPGHS-2, the Km value of the S516M mutant for arachidonate was 100 times that of native hPGHS-2.

Acetylation↗
PubMed1994

Role of the cyclic adenosine 3',5'-monophosphate and the phosphatidylinositol-Ca2+ cascades in mediating the effects of thyrotropin and iodide on hormone synthesis and secretion in human thyroid slices.

There are two major known regulatory pathways in human thyrocytes: the phosphatidylinositol-Ca2+ cascade (PiP2 cascade) and the cAMP cascade. We study here the regulation of the PiP2 cascade by TSH, ATP, NaF, and bradykinin. Our data show that protein iodination and, thus, the synthesis of thyroid hormones in human thyroid is under the control of both the PiP2 cascade and the cAMP cascade. Activation of the PiP2 cascade by TSH (10 mU/mL), NaF, bradykinin, ionomycin, and 12-O-tetradecanoylphorbol-13-acetate stimulates iodide organification. Conversely, activation of the cAMP cascade by forskolin, TSH (0.3 mU/mL), and dibutyryl cAMP inhibits iodide organification. These metabolic effects are correlated to activations and inhibitions of the H2O2-generating system, showing that H2O2 is a limiting factor for protein iodination in these cells. The cascades also regulate in parallel the activity of the pentose phosphate pathway. The effects of various concentrations of TSH on H2O2 generation and [1-14C]glucose oxidation were tested, showing a dual effect with an inhibition of these metabolisms for low concentrations of TSH (that stimulate the cAMP cascade) and an activation for high concentrations of TSH (that stimulate the PiP2 cascade). The control of thyroid secretion differs from that of protein iodination, in that the cAMP cascade greatly enhances secretion, whereas the PiP2 cascade has no effect on basal secretion and even an inhibitory effect on TSH-stimulated secretion (1 mU/mL). We also demonstrate here the presence of an inhibitory effect of iodide on its own organification in human thyroid (Wolff-Chaikoff effect). This effect is probably mediated through an inhibition of the inositol trisphosphate response to TSH and of the H2O2 response to Ca2+.

Adenosine Triphosphate↗
PubMed1991

Treatment of diversion colitis by short-chain fatty acids. Prospective and double-blind study.

Diminished production of short-chain fatty acids (SCFA) by altered flora has been suggested in the pathogenesis of diversion colitis (DC). We evaluated prospectively the effectiveness of SCFA irrigation in 13 patients with excluded colon (eight males, five females; mean age, 48 years). The causes of diversion were inflammatory bowel disease (n = 4), colonic cancer (n = 2), sigmoid diverticulitis with perforation (n = 3), ischiorectal abscess (n = 2), and miscellaneous (n = 2). Patients were given, twice a day for 14 days in a double-blind manner, a 60-ml enema containing either SCFA (acetate: 60 mmol/liter; propionate: 30 mmol/liter; and N-butyrate: 40 mmol/liter) (Group 1; n = 7) or isotonic NaCl (Group 2; n = 6). Endoscopy with biopsies was performed before starting the trial (D1) and 14 days later (D14). On D1 all patients had endoscopic and histologic findings suggestive of DC. No endoscopic or histologic changes were observed on D14 in either group. We conclude that endoscopic and histologic lesions of DC were not improved by SCFA irrigation during the 14 days.

Adult↗
PubMed1990

Covalent binding of arachidonic acid metabolites to human platelet proteins. Identification of prostaglandin H synthase as one of the modified substrates.

The covalent modification of proteins by metabolites of arachidonic acid (AA) was investigated in human platelets. Following incubation of washed human platelets with radiolabeled AA, ethanol precipitation of the proteins, and lipid extraction by organic solvents, a small fraction of the radioactivity added (0.3%) was tightly bound to the protein pellet. A dozen labeled protein bands were resolved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Exhaustive hydrolysis of platelet proteins by proteases released an amphipathic radiolabeled material which had a chromatographic behavior similar to that of a known peptidolipid, leukotriene C4. These findings suggest a covalent nature for the observed binding. This binding was specific for AA since palmitate, myristate, or linoleate did not bind to a significant extent. It involved products of both cyclooxygenase and lipoxygenase pathways: it was indeed inhibited to a greater extent by eicosatetraynoic acid than by indomethacin. The protein-associated radioactivity was increased by the thromboxane synthase inhibitor dazoxiben. Indomethacin completely abolished this increase in binding, which could not be reproduced by exogenous prostaglandin (PG) E2, F2 alpha, or D2, and might thus involve PGG2 and/or PGH2. Diamide, an agent known to inhibit the reduction of 12-hydroperoxyeicosatetraenoic acid in platelets, produced an increase of the covalent binding, which was abolished by eicosatetraynoic acid but not by indomethacin: this suggests that the lipoxygenase product bound was 12-hydroperoxyeicosatetraenoic acid or a by-product. Dazoxiben and diamide produced distinct patterns of protein labeling after sodium dodecyl sulfate-polyacrylamide gel electrophoresis. One labeled band had a Mr of 70,000 as the PGH synthase monomer. Addition of AA at 17 microM enhanced the labeling of this band, while 100 microM was inhibitory. Labeling of this band was also induced by thrombin in prelabeled platelets. Two monoclonal antibodies against PGH synthase caused immune precipitation of a 70-kDa labeled protein in homogenates of [3H]AA-labeled platelets. PGH synthase, purified from ram seminal vesicles, was covalently modified after incubation with [3H]AA: this labeling was almost completely abolished by indomethacin. As much as 40% of platelet PGH synthase was covalently modified after incubation with 17 microM AA. It can be concluded that in intact platelets PGH synthase is covalently modified by an eicosanoid following incubation with exogenous AA or after AA mobilization from phospholipids by thrombin.

Animals↗
PubMed1990

Amiloride analogs induce the phosphorylation of elongation factor-2 in vascular endothelial cells.

5-(N-Ethyl-N-isopropyl)amiloride (EIPA), a potent inhibitor of Na+/H+ antiport, reduced [35S]methionine incorporation in proteins and induced the phosphorylation of a Mr 95,000 protein in bovine aortic endothelial cells. This protein was previously shown to become phosphorylated in response to ATP, bradykinin, and A23187 (1) and was identified as elongation factor-2 (2). The action of EIPA was independent of changes in cytosolic pH, because it was neither mimicked by sodium acetate nor inhibited by ammonium chloride, and it was reproduced by 2',4'-dimethylbenzamil, an analog of amiloride that is inactive on the Na+/H+ antiport. Furthermore, EIPA enhanced the Ca2(+)-dependent phosphorylation of a similar Mr 95,000 protein in a cell-free system, rabbit reticulocyte lysate, where an inhibitory effect of amiloride on protein synthesis has already been described (3). Because phosphorylation decreases the activity of elongation factor-2, our observation might explain why amiloride analogs inhibit protein synthesis.

Amiloride↗
PubMed1988

Pattern of protein phosphorylation in aortic endothelial cells. Modulation by adenine nucleotides and bradykinin.

In bovine aortic endothelial cells, ATP (10-100 microM) and bradykinin (0.1-1.0 microM) enhanced the phosphorylation of two major protein substrates with apparent molecular masses of 95 and 28 kDa. The action of ATP involved P2y purinoceptors. The kinetics were distinct for the two phosphopeptides. The phosphorylation of the 95-kDa protein was rapid (within 30 s) but transient (maintained for only 2 min). This time course agrees with that observed for the increase of the cytosolic Ca2+ level induced by ATP in these cells. Ionophore A23187 (greater than or equal to 100 nM) induced this phosphorylation for a longer period (5-10 min), whereas phorbol 12-myristate 13-acetate (PMA) was completely inactive. The enhancement of the 28-kDa protein phosphorylation was detectable after a 5-min lag and was maintained for at least 20 min. PMA (50 nM) stimulated weakly the phosphorylation of the 28-kDa protein, whereas A23187 (100-300 nM) was even more effective than ATP and bradykinin. The 95-kDa phosphoprotein seems to be related to a 100-kDa substrate of calmodulin-dependent protein kinase III recently identified as elongation factor-2. The 28-kDa protein, which was resolved as three variants in bidimensional gel electrophoresis, appears very similar to a slightly heavier phosphoprotein from thrombin-stimulated human platelets. In addition, bidimensional electrophoresis allowed the detection of at least 10 substrates (from 18 to 46 kDa) whose phosphorylation was enhanced equally well by ATP, bradykinin, and A23187 and only partially by PMA. In conclusion, protein phosphorylation induced by ATP and bradykinin in aortic endothelial cells seems to be catalyzed mostly by Ca2+-dependent kinases, distinct from protein kinase C.

Adenosine Triphosphate↗
PubMed1986

Covalent binding of eicosanoids to platelet proteins.

Following an incubation of washed human platelets with 14C-arachidonic acid, a small fraction of the radioactivity became tightly bound to the protein pellet. Three criteria suggested that it was actually a covalent binding: it was not removed by exhaustive extractions with solvents of various polarities, it was not dialysable against SDS-buffer and it corresponded to the labeling of several protein bands after SDS-polyacrylamide gel electrophoresis. The use of several pharmacological agents (indomethacin, eicosatetraynoic acid, dazoxiben, diamide) has allowed us to divide this binding into three components: the first one, independent from both cyclooxygenase and lipoxygenase, the second one dependent on cyclooxygenase products and finally the third one, dependent on lipoxygenase products.

Arachidonic Acid↗
PubMed1986

[Induced prematurity].

Voluntary induction of a premature delivery, which goes against our constant battle to reduce prematurity, represents, at this time, a paradoxical situation which is not exceptional in vasculorenal syndromes and premature rupture of the membranes. Advances in ressuscitation and the care of premature newborn babies, on the one hand, and techniques of artificial induction of labor, on the other hand, account for this obvious paradox. Even advances in artificial induction of labor explain also the decrease in the cesarean sections indications, under such circumstances.

Female↗
PubMed1985

Prevention of preterm births: a perinatal study in Haguenau, France.

A reduction in preterm births has been observed in Haguenau (Eastern France) during a 12-year intervention study with a program for prevention of preterm deliveries. The Perinatal Study of Haguenau was an observation tool used in a stable population, and it allowed measurement of the way women have progressively responded to the new proposals in prenatal care. It also allowed measurement of the results of the interventions: low birth weight (less than 2,500 g) and preterm birth rates (less than 37 weeks of gestation) among single live births. The total duration of the study was divided into three periods of four years (1971 through 1974, 1975 through 1978, and 1979 through 1982), for which the numbers of single live births are 5,763, 4,957, and 5,919, respectively. For the same periods, the low-birth-weight rates, 4.6%, 4.0%, and 3.8%, respectively, showed a significant decrease (P less than .001). Following a similar pattern, the rates of preterm birth were 5.4%, 4.1%, and 3.7% (a significant reduction with P less than .001). These improvements in pregnancy outcome do not disappear after standardization of mother's age, high blood pressure, or social class distribution. These findings, which concur with the results of others, enhance the hypothesis of a direct relationship between a prevention program and a reduction in preterm birth rates.

Birth Weight↗
PubMed1981

Protein-bound and free plasma phenytoin during pregnancy.

In a clinical study using low doses of phenytoin as an ovulation inducer, the plasma levels and the binding percentages of this drug and the plasma level of its main metabolite, p-hydroxyphenytoin, were monitored. The results show that during pregnancy, plasma levels of both remain stabile and low as compared with those observed in epilepsy treatment. This could be one explanation for the absence of teratogenic effects observed in this and other studies using phenytoin for the same therapeutic aim.

Blood Proteins↗
PubMed1980

Binding of digitoxin, digoxin and gitoxin to human serum albumin.

The binding of three digitalis glycosides, digitoxin, digoxin and gitoxin, to human serum albumin was studied in vitro by equilibrium dialysis. The results obtained showed that binding is a non saturable process and that probably the same binding mechanism is involved for each of the three drugs. Their binding sites seem to be different from of those of acidic and basic drugs. However, the three drugs were found to be partially displaced by large amounts of fatty acids.

Digitalis Glycosides↗
PubMed1979

Phenytoin binding to human albumin.

Binding of phenytoin to human plasma proteins and to human serum albumin is studied using equilibrium dialysis method at pH 7.4 and 37 degrees C. Phenytoin is mainly bound to albumin, the percentage of bound drug being constant over a wide range of total drug concentrations. Calculation of the drug binding parameters show a low affinity, k = 745 M-1, and a high number of binding sites, n = 8. Palmitic acid and some acidic drugs, warfarin and phenylbutazone added to human serum albumin, decreased phenytoin binding in a non competitive way. Basic and non-ionizable drugs, on the other hand, did not modify phenytoin binding.

Anilino Naphthalenesulfonates↗
PubMedDate not supplied

Levamisole adds granulocyte toxicity to 5FU-based chemotherapies in adjuvant treatment of Dukes B-C colorectal cancer. A preliminary report.

41 patients (pilot study-I) and 50 patients (multicenter study II) were randomized to receive as systemic chemotherapy for 6 courses with 5 FU alone (A) [440 (I)-450 (II) mg/m2 IV bolus, 5/21 days] or folinic acid followed by 5 FU (B) (respectively 200 and 370 mg/m2 IV bolus, 5/21 days). In the multicenter trial, oral levamisole at the dose of 150 mg/day (3/14 days) was added to chemotherapy for one year. Ten patients in study I and 19 patients in study II also received a post-operative course of intra-portal chemotherapy. Toxicity was evaluated respectively on 232 (I) and 276 (II) courses. Clinical limiting toxicities were stomatitis and diarrhea. In protocol II, a significant enhancement of grades 3-4 granulocyte toxicity was seen (17.3% of courses in II vs only 3.4% in I; p < 0.001). This was especially recorded in the group treated with 5-FU alone (26% of courses in A vs 11% in B; p < 0.001). Levamisole was therefore stopped in 12 cases (10 cases in A; 2 cases in B).

Aged↗