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Biomedical subjects

M Charbonneau

Publications and source records attributed to M Charbonneau.

At least 55 records · Page 3Linked to original sources
PubMed1991

Obstructive sleep apnea during pregnancy. Therapy and implications for fetal health.

A 32 yr-old woman in her last trimester of pregnancy was found to have severe obstructive sleep apnea (OSA). The overnight polysomnogram demonstrated an apnea plus hypopnea index of 159 events per hour. Apneas were associated with severe oxygen desaturation to 40% during rapid eye movement sleep, maternal bradycardia, and second degree heart block. External cardiotocography showed normal fetal heart rate reactivity to fetal movements, even during the apneas and episodes of oxygen desaturation. Nasal continuous positive airway pressure at a level of 15 cm H2O effectively treated the apneas and desaturation and had no effect on the fetal heart rate. The patient was induced electively during the 39th wk of pregnancy and gave birth to a newborn with growth retardation. Early recognition and treatment of OSA in pregnancy might prevent problems with fetal development.

Adult↗
PubMed1991

Intracellular pH and intracellular free calcium responses to protein kinase C activators and inhibitors in Xenopus eggs.

Cell activation during fertilization of the egg of Xenopus laevis is accompanied by various metabolic changes, including a permanent increase in intracellular pH (pHi) and a transient increase in intracellular free calcium activity ([Ca2+]i). Recently, it has been proposed that protein kinase C (PKC) is an integral component of the Xenopus fertilization pathway (Bement and Capco, J. Cell Biol. 108, 885-892, 1989). Indeed, activators of PKC trigger cortical granule exocytosis and cortical contraction, two events of egg activation, without, however, releasing the cell cycle arrest (blocked in second metaphase of meiosis). In the egg of Xenopus, exocytosis as well as cell cycle reinitiation are supposed to be triggered by the intracellular Ca2+ transient. We report here that PKC activators do not induce the intracellular Ca2+ transient, or the activation-associated increase in pHi. These results suggest that the ionic responses to egg activation in Xenopus do not appear to depend on the activation of PKC. In addition, in eggs already pretreated with phorbol esters, those artificial activators that act by releasing Ca2+ intracellularly, triggered a diminished increase in pHi. Finally, sphingosine and staurosporine, two potent inhibitors of PKC, were found to trigger egg activation, suggesting that a decrease in PKC activity might be an essential event in the release of the metaphase block, in agreement with recent findings on the release of the prophase block in Xenopus oocytes (Varnold and Smith, Development 109, 597-604, 1990).

Alkaloids↗
PubMed1990

Patterns of protein synthesis during Xenopus oocyte maturation differ according to the type of stimulation.

We examined the qualitative patterns of protein synthesis in fully grown prophase-blocked oocytes of Xenopus laevis and after meiosis reinitiation accompanying maturation of the oocytes. Newly synthesized proteins labelled with [35S]methionine were run on isoelectric focusing gels and further separated in the second dimension on SDS-polyacrylamide slab gels. Three types of maturation inducer were compared: progesterone, considered as the natural inducer of Xenopus oocyte maturation, hCG (human chorionic gonadotropin) and insulin. Three polypeptides with apparent molecular masses of 37 kDa (pI 4.7-4.8), 78 kDa (pI 4.7) and 138 kDa (pI 4.6-4.7) were found to be always synthesized in all three types of stimulation, while the synthesis of a fourth one (molecular mass 116 kDa, pI 4.7) was arrested during oocyte maturation. Moreover, when the follicular cells surrounding the oocytes were part of the stimulating pathway, which is the case during hCG-induced maturation, an additional polypeptide was synthesized by the oocytes (molecular mass 106 kDa, pI 6.0-6.2). This polypeptide was not synthesized during progesterone- or insulin-induced oocyte maturation, two types of stimulation which do not require the presence of the follicular cells. The biological significance of the hCG-induced polypeptide, not necessary for oocyte maturation, is discussed. On the other hand, the four other modifications in protein synthesis taking place during all three types of maturation-inducing stimulation appear to be necessary for oocyte maturation, since oocytes which failed to mature in response to stimulation always missed one or several of these four polypeptides.

Animals↗
PubMed1990

The organization of the cortical endoplasmic reticulum in Xenopus eggs depends on intracellular pH: artefact of fixation or not?

The cortical endoplasmic reticulum (CER), which develops and becomes organized during oocyte maturation in Xenopus laevis (anuran amphibians), has been thought to be essential for the propagation of the activating signal at the time of fertilization, possibly by regulating intracellular Ca2+ (Ca2+i) (Charbonneau and Grey, Dev. Biol. 102, 90-97, 1984). The present paper demonstrates that changing intracellular pH (pHi) has an influence on the structure and organization of the CER in unactivated Xenopus eggs. Acidifying the egg cytoplasm from its normal value, pH 7.5, to about 6.8, with CO2, produced a dramatic increase in the proportion of the CER being in the form of a continuous and well-developed network. On the other hand, alkalinizing the egg cytoplasm from 7.5 to about 8.2, with NH4Cl, induced a general disruption and vesicularization of the CER. These effects of pHi on a Cai2(+)-regulating system are discussed, taking into account possible artefacts generated during fixation.

Animals↗
PubMed1990

Cycling of intracellular pH during cell division of Xenopus embryos is a cytoplasmic activity depending on protein synthesis and phosphorylation.

In Xenopus embryos, the successive and rapid cell divisions that follow fertilization are accompanied by periodic oscillations of intracellular pH (pHi). Cycling of pHi occurs in phase with several other oscillatory activities, namely nuclear divisions, M phase-promoting factor (MPF) activity, and surface contraction waves (SCWs). We report that treatments that abolish cycling of MPF activity and the SCWs also suppress the pHi oscillations, whereas those that block cell division without affecting neither MPF activity nor the SCWs do not suppress the pHi oscillations. Experiments on enucleated oocytes, matured in vitro and activated, demonstrated that the activity governing the rhythmicity of the pHi oscillations resided in the cytoplasm of the oocyte. In this respect, the activity responsible for the pHi oscillations was different from that which drives the SCWs, which necessitated the presence of the oocyte germinal vesicle (Ohsumi et al., 1986), but more closely resembled MPF activity that did not require the presence of the oocyte germinal vesicle (Dabauvalle et al., 1988). In mature eggs enucleated at the time of egg activation, the pHi oscillations were similar to those in control nucleated eggs, whereas the period between two peaks of SCWs was 35-60 min vs. 20-35 min in nucleated control eggs. Previous studies had shown that the periodicity of SCWs was larger in anucleate egg fragments than in their nucleate counterparts (Sakai and Kubota, 1981), the difference being on the order of 6-15 min (Shinagawa, 1983). However, in these previous studies, enucleation was performed 30-50 min after fertilization. Our results clearly demonstrate that the periodicity of the SCWs is lengthened when the interval between egg activation and enucleation is shortened, thereby providing an easier way to assess the nuclear dependency of the SCWs. Finally, the various possibilities concerning the role of pHi cycling during cell division are discussed.

Adenine↗
PubMed1990

Replacement of Leu227 by Pro in thyroxine-binding globulin (TBG) is associated with complete TBG deficiency in three of eight families with this inherited defect.

The T4-binding globulin (TBG) gene is a single copy located on the X-chromosome. Previous studies have failed to elucidate the molecular defect in individuals with complete TBG deficiency (TBG-CD). Indeed, no major deletions, insertions, or other rearrangements were observed in the TBG gene of six unrelated males with this defect. To clarify the molecular basis of TBG-CD, we have cloned and sequenced the TBG gene of an affected male (CD5) of French Canadian origin. The sequence of the exons encoding the mature protein, adjacent introns, and the promoter region revealed two nucleotide substitutions: CTA(Leu)----CCA(Pro) at codon 227 and TTG(Leu)----TTT(Phe) at codon 283. The Leu----Phe substitution, a relatively conservative replacement, is a TBG polymorphism present in 16% (3 of 19) of French Canadian males. It has no effect on the serum concentration or properties of the common type TBG (TBG-C). The new Leu----Pro substitution, which is predicted to alter the higher order of TBG structure, is probably responsible for the TBG-CD phenotype of the individual studied and two other families with TBG-CD. It possibly impairs TBG biosynthesis or secretion or perhaps alters TBG structure to such a degree that the molecule is not recognized by antibodies against native or denatured TBG and does not bind T4.

Adult↗
PubMed1989

Involvement of reversible binding to alpha 2u-globulin in 1,4-dichlorobenzene-induced nephrotoxicity.

Similarly to unleaded gasoline, 1,4-dichlorobenzene (1,4-DCB) administered for 2 years caused a dose-related increase in the incidence of renal tumors in male but not in female rats or in either sex of mice. Unleaded gasoline and 2,2,4-trimethylpentane (TMP), a component of unleaded gasoline, increased protein droplet formation and cell proliferation in male but not in female rat kidneys. These protein droplets contained, alpha 2u-globulin, a male rat-specific low-molecular-weight protein and 2,4,4-trimethyl-2-pentanol, a metabolite of TMP that was reversibly bound to this protein. Studies were undertaken to determine if 1,4-DCB produced similar effects; 1,2-DCB was used for comparison since it did not produce renal carcinogenesis in male rats. Gel filtration chromatography of a 116,000g supernatant prepared from kidneys of 1,4-[14C]DCB-treated rats showed that radiolabel coeluted with alpha 2u-globulin as one sharp peak as opposed to a multipeak pattern observed for 1,2-[14C]DCB; the maximal quantity of radiolabel for 1,4-DCB was twice that for 1,2-DCB. Equilibrium dialysis of kidney cytosol in the presence or absence of sodium dodecyl sulfate demonstrated that the radiolabel was reversibly bound to alpha 2u-globulin; the amount for 1,4-[14C]DCB-treated rats was almost twice as much as that for 1,2-[14C]DCB-treated rats. 1,2-DCB was also shown to be covalently bound to renal alpha 2u-globulin, and covalently bound to liver and plasma high-molecular-weight proteins. 1,4-DCB and, to a minor extent, 2,5-dichlorophenol, the major metabolite of 1,4-DCB, were reversibly bound to renal alpha 2u-globulin from 1,4-DCB-treated rats. 1,4-DCB increased protein droplet formation in male but not in female rat kidneys, whereas equimolar doses of 1,2-DCB showed no effect in either sex. Renal cell proliferation, measured by [3H]thymidine incorporation into renal DNA, was increased after 1,4-DCB but not after 1,2-DCB treatment. Nephrotoxicity and biochemical alterations induced by 1,4-DCB resemble those of unleaded gasoline and suggest that a similar mechanism is involved in the induction of alpha 2u-globulin nephropathy in male rats.

Alpha-Globulins↗
PubMed1989

A requirement for protein phosphorylation in regulating the meiotic and mitotic cell cycles in echinoderms.

Populations of hormone-stimulated starfish oocytes and fertilized sea urchin eggs undergo synchronous meiotic and mitotic divisions. We have studied the requirement for protein phosphorylation during these events by testing the effects of 6-dimethylaminopurine (6-DMAP) upon the incorporation of [32P]orthophosphate. It was found that 6-DMAP blocked meiosis reinitiation and early cleavage and simultaneously inhibited protein phosphorylation, without changing the rate of [35S]methionine incorporation or pattern of protein synthesis. The protein, cyclin (54 kDa in starfish and 57 kDa in sea urchin), continues to be synthesized in the presence of 6-DMAP. This protein is destroyed at first and second cell cycles when 6-DMAP is added 30 min following fertilization but not when this drug is present before fertilization. Thus, cyclin breakdown does not depend on the completion of the nuclear events of M-phase, and its time of breakdown is set at an early step between fertilization and first cleavage. Using tubulin immunostaining, we found that 6-DMAP did not affect the cortical microtubules and resting female centrioles of prophase-arrested starfish oocytes, whereas it induced a precocious disappearance of spindle fibers when applied to hormone-stimulated oocytes. While an early addition of 6-DMAP precluded nuclear breakdown and spindle formation in both systems, a late treatment always allowed chromosome separation and centriole separation. Under these conditions pericentriolar tubulin persisted and could organize new spindles after the inhibitor was removed. It is suggested that (1) the assembly of cortical and centriolar-associated microtubules is not controlled by the same factors as spindle-associated tubulin; (2) specific proteins which are required for the cell to enter the following M-phase can become operative only via a process depending upon protein phosphorylation; (3) microtubule-associated kinases may play an important role in MPF function and spindle dynamics.

Adenine↗
PubMed1989

An increase in the intracellular pH of fertilized eggs of Xenopus laevis is associated with inhibition of protein and DNA syntheses and followed by an arrest of embryonic development.

In many systems, events participating in cell division are controlled by intracellular pH (pHi). In Xenopus eggs, fertilization is accompanied by an increase in pHi which occurs concomitantly with an increase in protein synthesis and a reinitiation of DNA synthesis, leading the embryo to cell division. In this paper, we have shown that increasing pHi of fertilized eggs from 7.8 to 8.2 by using weak bases produced an arrest in embryonic development. Such a change in pHi was accompanied by a severe inhibition of both protein and DNA syntheses. In order to discriminate between a direct effect of pHi and a pH-independent effect of weak bases on these biosyntheses, the situation was studied in vitro. For this purpose, cytoplasmic extracts were used in which weak base addition did not produce any change in pH. Under these conditions, protein synthesis was not inhibited, suggesting that pH is probably one of the events implicated in the regulation of protein synthesis. On the other hand, DNA synthesis was inhibited by weak bases in vitro, without any change in pH intervening.

Animals↗
PubMed1989

The comparative pathobiology of alpha 2u-globulin nephropathy.

alpha 2u-Globulin nephropathy is an important toxicologic syndrome that occurs in male rats following exposure to a number of important industrial and environmental chemicals. A low, but significant incidence of renal neoplasia develops in male rats as a chronic sequela to the disease. Studies on the pathogenesis of alpha 2u-globulin nephropathy have demonstrated that this protein is produced in large amounts in the male rat, that reversible binding occurs between chemicals and/or their metabolites and alpha 2u-globulin, and that this complex is resistant to proteolytic hydrolysis, leading to accumulation in renal lysosomes and subsequent cytotoxicity and cell death. This results in marked exposure-related increases in cell proliferation that persist for at least one year, providing exposure continues. This sustained increase in renal cell proliferation can promote initiated cells to form preneoplastic foci and renal neoplasia in male rats. Since this syndrome is highly species and sex specific, it is important to determine the relevance of these data for human risk assessment. The scientific considerations involved in high to low dose and species to species extrapolation are discussed.

Alpha-Globulins↗
PubMed1989

Weak bases mimic the fertilization-associated chloride conductance increase and induce morphological changes in the cortex of Xenopus laevis eggs.

Ammonia and other weak bases (methylamine, trimethylamine) including certain local anesthetics (benzocaine, procaine, lidocaine) depolarized the plasma membrane of unactivated Xenopus eggs. Exposure to different [Cl-]o or to the other halides (F-, Br-, I-) revealed a similar anion dependency of the weak base-induced conductance change to that found for the normal fertilization potential. Although transient, the induced depolarization was slower and of longer duration than the fertilization potential. Furthermore, [NH4+] greater than 40 mM elicited depolarizations of greater amplitude than the latter. In fertilized eggs, the amplitude of the induced depolarization decreased as the interval between fertilization potential and time of application of the NH4+ solution was increased. Treatment of unactivated eggs with NH4+ or procaine produced dramatic changes in the configuration of surface microvilli and thickening of the peripheral layer of cytoplasm. These effects were obtained only if the pH of the bathing solution was close to the pKa of the amine. This implicates intracellular pH, which would be expected to rise due to entry of the uncharged amine.

Ammonia↗
PubMed1989

Null mutation of copper/zinc superoxide dismutase in Drosophila confers hypersensitivity to paraquat and reduced longevity.

The role of copper/zinc-containing superoxide dismutase (cSOD; superoxide:superoxide oxidoreductase, EC 1.15.1.1) in metabolic defense against O2 toxicity in Drosophila is examined through the properties of a mutant strain carrying a cSOD-null mutation, cSODn108. Homozygotes are viable as larvae, which indicates that cSOD is not essential for cell viability per se. cSODn108 confers recessive sensitivity to the superoxide anion (O2-)-generator paraquat and to the transition metal compound CuSO4, which indicates that the cSOD-null condition in fact leads to impaired O2- metabolism. The primary biological consequences of the reduced O2- dismutation capacity of cSODn108 Drosophila are realized in the adult as infertility and reduction in life-span. We conclude that the infertility and reduced life-span of cSODn108 adults arise as a consequence of the reduced capacity of embryos, larvae, and pupae to adequately protect developing preimaginal cells from O2- -initiated cytotoxic damage.

Animals↗
PubMed1989

Intracellular pH and the increase in protein synthesis accompanying activation of Xenopus eggs.

Metabolic activation following egg fertilization corresponds to an increase in protein synthesis and the initiation of DNA synthesis, which lead to cell division and development of the embryo. Since in several biological systems protein synthesis is regulated by intracellular pH (pHi), we have decided to investigate the situation during Xenopus egg activation. We confirmed that egg activation is accompanied by a pHi rise of 0.3 pH unit. Measurements of the rates of protein synthesis is unactivated and activated eggs, after microinjection of 3H-leucine, demonstrated that activation was followed by a 2.5-fold increase. Treatment of unactivated eggs with weak bases also increased pHi, but did not result in an increase in the rate of protein synthesis. Moreover, in vitro translation in cytoplasmic extracts was found to be pH-independent, at least between 6.8 and 8.2.

Animals↗
PubMed1988

Assessment of the minimal effective dose of acetone for potentiation of the hepatotoxicity induced by trichloroethylene-carbon tetrachloride mixtures.

Administration of acetone to rats in amounts larger than or equal to a minimal effective dosage (MED) is known to potentiate the severity of the liver damage produced by CCl4 alone. It has been reported that CCl4-induced hepatotoxicity is also enhanced by the previous administration of trichloroethylene (TCE). In addition, TCE-CCl4 mixture-induced liver injury is potentiated by acetone. The present study was undertaken to determine if the acetone MED is decreased when the haloalkane challenge is a mixture of TCE-CCl4 instead of CCl4 alone. The effect of varying mixture compositions was also evaluated. In a first series of experiments, male Sprague-Dawley rats received corn oil or acetone (0.05-0.25 ml/kg, po); 18 hr later, they received an ip injection of either CCl4 (0.1 ml/kg) or [TCE (0.25 ml/kg)-CCl4 (0.1 ml/kg)]. In a second series, rats received corn oil or acetone (0.75 ml/kg), and were challenged with TCE (1.5 ml/kg), CCl4 (0.25 ml/kg), or a mixture of TCE-CCl4, where TCE and CCl4 dosages were equal to 25-75%, 50-50%, and 75-25%, respectively, of those used for the administration of the solvents alone. In both series, rats were killed 24 hr after the haloalkane challenge. Liver injury was assessed biochemically (plasma ALT activities and bilirubin concentrations) and morphologically. When TCE was added to a solution of CCl4, smaller doses of CCl4 were required to produce equally severe liver injury.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetone↗
PubMed1988

Detection of the thyroxine-binding globulin (TBG) gene in six unrelated families with complete TBG deficiency.

T4-binding globulin (TBG) is a glycoprotein of hepatic origin which transports thyroid hormone in serum. Inherited TBG defects in man are X-chromosome linked and are expressed in hemizygotes as complete deficiency, partial deficiency, or excess. Since TBG is not necessary for thyroid hormone action, affected subjects are healthy. Using DNA probes for human TBG, we searched for restriction fragment length polymorphisms in six affected males belonging to 6 unrelated families with inherited complete TBG deficiency and an equal number of normal males. TBG could not be detected in the serum of any of the TBG-deficient males by a specific and sensitive RIA capable of detecting as little as 5 micrograms TBG/L or 0.031% of the average normal serum TBG concentration. DNA isolated from white blood cells was digested with 11 restriction endonucleases, and the digests were submitted to DNA blot analysis using two cloned TBG-DNA probes which together covered the entire protein coding and the 5'-flanking sequences of the TBG gene. A total of 26 different bands were detected on DNA blots, identifying 18 restriction sites located within the 4.2-kilobase TBG gene, which includes intronic, exonic, and 5'-flanking sequences. This analysis, which sampled 2.3% of the total TBG genome, failed to reveal differences in fragment size among the 6 TBG-deficient and 6 normal males examined. One restriction endonuclease (NcoI) identified normal sequences at the putative promoter region of the gene, and four other endonucleases (TaqI, SstII, MspI, and HpaII) recognized the cytosine-guanine dinucleotide phosphate sequences representing potential mutation hot spots. Although C was methylated at these sites, no C to T (thymidine) transitions were found. These data suggest that large deletions, insertions, or rearrangements of the TBG gene, or mutations at sites of methylated cytosine-guanine dinucleotide phosphate dimers are not common mechanisms for inherited complete TBG deficiency in man.

Cloning, Molecular↗
PubMed1988

A study on the inheritance of thyroxine-binding globulin (TBG) deficiency from data obtained in 13 families detected by a neonatal screening program.

Thirteen families with thyroxine-binding globulin deficiency, detected through probands screened by the Quebec Network of Genetic Medicine, were investigated. These families were divided into two groups, depending on whether hemizygous males had low or undetectable serum thyroxine-binding globulin levels. Five families belonged to the low (hypo-TBGnemic) type while the remaining 8 families belonged to the absent (a-TBGnemic) type. On pedigree analysis, 10 families satisfied the requirements for an X-linked co-dominant mode of transmission. Three families, 2 a-TBGnemic and 1 hypo-TBGnemic, did not satisfy these requirements and three hypotheses had to be put forward to explain these situations: an autosomal recessive mode of transmission, a spontaneous mutation, or an extreme lyonisation of the defective X. Since the thyroxine-binding globulin gene has been localized to the X-chromosome, the two latter explanations appear to be the most plausible.

Female↗