Biomedical subjects

G Boivin

Publications and source records attributed to G Boivin.

At least 73 records · Page 4Linked to original sources

PubMed1996

Adenine phosphoribosyltransferase-deficient mice develop 2,8-dihydroxyadenine nephrolithiasis.

Adenine phosphoribosyltransferase (APRT) deficiency in humans is an autosomal recessive syndrome characterized by the urinary excretion of adenine and the highly insoluble compound 2,8-dihydroxyadenine (DHA) that can produce kidney stones or renal failure. Targeted homologous recombination in embryonic stem cells was used to produce mice that lack APRT. Mice homozygous for a null Aprt allele excrete adenine and DHA crystals in the urine. Renal histopathology showed extensive tubular dilation, inflammation, necrosis, and fibrosis that varied in severity between different mouse backgrounds. Thus, biochemical and histological changes in these mice mimic the human disease and provide a suitable model of human hereditary nephrolithiasis.

Adenine↗

PubMed1996

APRT: a versatile in vivo resident reporter of local mutation and loss of heterozygosity.

We describe an in vivo mutagenesis model that utilizes reverse mutation and forward mutation at the endogenous Aprt locus. Reverse mutation provides an in situ method for detecting environments or agents that cause point mutations. Forward mutation detects large chromosomal events, including mitotic recombination, chromosome loss, and large multilocus deletion, all of which can lead to loss of heterozygosity. Detection of reverse mutation in vivo is based on the differential capacity of Aprt and Aprt cells to sequester radiolabeled adenine by catalyzing its conversion to adenosine monophosphate with subsequent incorporation into nucleic acids. Cells lacking APRT activity cannot accumulate exogenously administered, tagged adenine, whereas Aprt+ cells can and will thereby become marked. Thus, genetically modified mice with mutant but revertible Aprt alleles should be a useful vehicle for in situ detection of mutagenic activity in the whole animal. the feasibility of this model has been illustrated, first, by showing that APRT-deficient mice are viable and, second, by demonstrating that the minority of Aprt+ cells within a chimeric tumor growing in an Aprt+ mouse can be selectively labeled following IP injection of [14C]-adenine and can be identified by autoradiography. Forward mutation, detected by growth in selective medium of primary cells derived from Aprt+/- heterozygous mice, provides on independent estimate of in vivo mutation frequency. The frequency with which Aprt colonies arise provides a measure of the frequency of Aprt(-)-negative cells in the tissue at that point in time. Culture of skin fibroblasts in 2,6-diaminopurine (DAP) produced Aprt+ colonies with a frequency of about 10(-4). This frequency is similar to that found for human T lymphocytes from individuals heterozygous at the Aprt locus. In both cases, the majority of mutagenic events involved allele loss. Polymerase chain reaction with linked polymorphic microsatellites on mouse chromosome 8 demonstrated that allele loss was mediated mostly by mitotic recombination, as was the case for human T lymphocytes. The high frequency of mitotic recombination and allele loss at a neutral locus has significant implications for the process of tumorigenesis and argues that spontaneous or induced mitotic recombination may play a causal role in the progression to cancer.

Adenine↗

PubMed1996

Strontium distribution and interactions with bone mineral in monkey iliac bone after strontium salt (S 12911) administration.

The analysis of the interaction of strontium (Sr) with bone mineral is of interest because a new agent containing Sr (S 12911) has shown positive effects on bone mass in various animal models of osteoporosis and is currently being developed for preventive and curative treatment of postmenopausal osteoporosis. Iliac bone samples were obtained from 20 male monkeys: 4 untreated control animals, 12 animals sacrificed at the end of a 13-week treatment with high dose levels of S 12911 (750, 275, or 100 mg/kg/day orally), and 4 animals sacrificed 6 weeks after the end of a 13-week treatment with S 12911 (750 or 100 mg/kg/day orally). The distribution of Sr was determined and quantified by X-ray microanalysis. Changes at the crystal level were evaluated by X-ray diffraction and Raman microspectrometry. In the control animals, traces of Sr were found to be homogeneously distributed throughout the bone tissue. In the treated monkeys, Sr could only be detected in calcified matrix. In monkeys sacrificed at the end of the treatment, Sr was found to be dose-dependently incorporated into the mineral substance of the compact and cancellous bone. Sr was heterogeneously distributed with three to four times more Sr in new than in old compact bone, and approximately two and a half times more Sr in new than in old cancellous bone. The bone Sr content dramatically decreased in the animals sacrificed 6 weeks after the end of the treatment. Diffraction showed no significant changes in the characteristics of the crystal lattice. Sr appeared to be easily exchangeable from bone mineral and was slightly linked to mature crystals through ionic substitutions. Even at the highest dose level tested, less than 1 calcium ion out of 10 was substituted by 1 Sr ion in each crystal. In conclusion, taken up by bone, Sr was heterogeneously distributed with a higher concentration in new than in old bone but induced no major modifications of the bone mineral (crystallinity, crystal structure) at the crystal level. As a result, a treatment with S 12911 Sr salt should not induce any alteration of bone mineral.

Administration, Oral↗

PubMed1996

Chemical and X-ray analysis of fluoride, phosphorus, and calcium in human foetal blood and hard tissues.

To evaluate the beneficial effect of prenatal fluoride supplementation, the presence of fluoride in hard tissues in two populations of human foetuses coming from fluoridated (> or = 0.7 parts/10(6) F in drinking water) and non-fluoridated areas (< or = 0.1 parts/10(6) F in drinking water) were compared by chemical analysis and X-ray microanalysis. The fluoride concentrations measured in maternal and venous cord blood confirmed that placental transfer of fluoride was passive when fluoride intake was low. Total fluoride contents of tooth germs and mandibular bone appeared to increase with fluoride level in drinking water. However, these concentrations were too low to be detected by X-ray microanalysis. Phosphorus and calcium total contents were identical in mandibular and femoral bone of both populations. In incisor germs, phosphorus and calcium concentrations in enamel and dentine close to the amelodentinal junction did not differ significantly between the two populations. It is suggested that the low fluoride concentrations in enamel and dentine formed in utero would not have a significant effect on acid solubility.

Abortion, Induced↗

PubMed1996

HPRT-APRT-deficient mice are not a model for lesch-nyhan syndrome.

Complete hypoxanthine-guanine phosphoribosyl-transferase (HPRT) deficiency in humans results in the Lesch-Nyhan syndrome which is characterized, among other features, by compulsive self-injurious behavior. HPRT-deficient mice generated using mouse embryonic stem cells exhibit none of the behavioral symptoms associated with the Lesch-Nyhan syndrome. Administration of drugs that inhibit adenine phosphoribosyltransferase (APRT) in HPRT-deficient mice has produced the suggestion that deficiency of APRT in combination with HPRT-deficiency in mice may lead to self-mutilation behavior [C.L. Wu and D.W. Melton (1993) Nature Genet. 3, 235-240]. To test this proposition, we bred HPRT-APRT-deficient mice. Although the doubly-deficient mice excrete adenine and its highly insoluble derivative, 2,8-dihydroxyadenine, which are also associated with human APRT deficiency, additional abnormalities or any self-injurious behavior were not detected. Thus, APRT-HPRT-deficient mice, which are devoid of any purine salvage pathways, show no novel phenotype and are not a model for the behavioral abnormalities associated with the Lesch-Nyhan syndrome as previously suggested.

Adenine Phosphoribosyltransferase↗

PubMed1996

Detection of ganciclovir resistance mutations quantitation of cytomegalovirus (CMV) DNA in leukocytes of patients with fatal disseminated CMV disease.

Cytomegalovirus (CMV) UL97 mutations associated with ganciclovir resistance at codons 460, 594, and 595 were detected by polymerase chain reaction (PCR) followed by restriction enzyme analysis in CMV blood isolates and directly in polymorphonuclear leukocyte (PMNL) DNA extracts of 4 subjects who died of progressive disseminated CMV disease due to ganciclovir-resistant CMV strains. The CMV DNA load was also serially determined in leukocyte fractions of these patients using a quantitative-competitive PCR assay. There was excellent concordance between specific UL97 mutations in blood culture isolates and those detected in PMNL fractions for all patients. Emergence of such UL97 mutations during ganciclovir therapy was associated with an increasing CMV DNA burden in leukocytes of the 2 patients with AIDS but not in the 2 subjects with chronic lymphocytic leukemia. Rapid molecular strategies, including detection of common CMV UL97 mutations and CMV DNA quantitation, can be used directly in leukocytes of immunocompromised subjects with CMV disease to monitor antiviral therapy.

AIDS-Related Opportunistic Infections↗

PubMed1996

Quantitation of cytomegalovirus DNA and characterization of viral gene expression in bronchoalveolar cells of infected patients with and without pneumonitis.

Cytomegalovirus (CMV) is often present in bronchoalveolar lavage (BAL) fluid of immunosuppressed patients without CMV pneumonitis. The amount of viral DNA within BAL cells of patients with definite CMV pneumonitis and of viral shedders was quantitated by polymerase chain reaction (PCR) and the extent of CMV gene expression within BAL cells was defined by reverse transcription - PCR. No viral DNA was detected in 6 viral shedders, and 12 had low copy numbers (mean, 72 copies/10(5) BAL cells; median, 20) compared with numbers in pneumonitis patients (267,580 and 57,000, respectively). When CMV intranuclear inclusions were absent within BAL cells of patients with pneumonitis, copy numbers (mean, 9362; median, 7110) were still significantly higher than among shedders. Expression of viral glycoprotein H mRNA was detected in BAL cells of all 11 pneumonitis patients tested but in 0 of 18 viral shedders. Thus, high-grade infection and viral replication within BAL cells are integral features of CMV pneumonitis but not viral shedding.

Base Sequence↗

PubMed1996

Effect of foscarnet on quantities of cytomegalovirus and human immunodeficiency virus in blood of persons with AIDS.

Four intravenous dosages of foscarnet given for 10 days were compared with no therapy in persons with AIDS who had asymptomatic cytomegalovirus (CMV) viremia. CMV viremia was quantitated by endpoint cell dilution microcultures, pp65 antigenemia assay, and measurement of CMV DNA in peripheral blood leukocytes by a quantitative-competitive PCR. Human immunodeficiency virus type 1 (HIV-1) viremia was quantitated by endpoint cell dilution microculture, serum p24 antigen assay, and PCR for HIV-1 RNA in plasma. Twenty-seven subjects who had received a median of 22 months of nucleoside antiretroviral therapy were enrolled. Twenty-two subjects received foscarnet, which was well tolerated and decreased the CMV burden, as reflected by all three indicator assays. During the 10 days of dosing, the level of CMV viremia, as measured by 50 percent tissue culture infective doses, decreased from 117.5 to 12.7 (P = 0.001), the amount of CMV DNA decreased from 20,328 copies to 622 copies per 150,000 leukocytes (P = 0.02), and the level of CMV pp65 antigenemia decreased from 14.9 to 1.6 positive peripheral blood mononuclear cells per 50,000 leukocytes (P = 0.008). A significant pharmacodynamic relationship was found between the peak foscarnet concentration and a decrease in the level of CMV antigenemia (P < 0.05). Foscarnet had no effect on quantitative HIV-1 microcultures during the 10 days of treatment, but the HIV-1 p24 antigen level in serum decreased significantly, from 454 to 305 pg/ml (P = 0.01). Also, a significant pharmacodynamic relationship was seen between plasma HIV-1 RNA concentrations and both peak foscarnet concentration (P < 0.01) and the area under the foscarnet time-concentration curve (P < 0.05). Reductions in the levels of CMV and HIV-1 viremia correlated quantitatively with systemic exposure to foscarnet, whereas control subjects actually experienced an increase in CMV and HIV-1 burdens. The dual antiviral activity of foscarnet shown in this trial encourages investigation of its use in combination with other antiretroviral therapies for persons with AIDS.

AIDS-Related Opportunistic Infections↗

PubMed1995

Distribution of thrombospondin and integrin alpha V in DCIS, invasive ductal and lobular human breast carcinomas. Analysis by electron microscopy.

The ultrastructural distribution of thrombospondin (TSP) and its cell surface receptor, integrin alpha V, was studied in two cases of human breast carcinoma: one of ductal carcinoma in situ (DCIS) with an invasive component, and one of invasive lobular carcinoma. In DCIS, moderate immunolabelling for TSP and integrin alpha V was observed in the rough endoplasmic reticulum and at the plasma membrane of intraductal carcinoma cells. TSP was also associated with extracellular matrix collagen fibrils surrounding in situ carcinoma cells. In the invasive part of this ductal carcinoma, most of the malignant cells were negative for TSP, while integrin alpha V was moderately expressed in these cells. In sharp contrast, typical strands of invasive lobular carcinoma cells in "Indian file" showed moderate TSP immunostaining in the rough endoplasmic reticulum and strong immunoreactivity for TSP at the plasma membrane and in the extracellular matrix. Moderate to strong immunoreactivity for integrin alpha V was also observed in invasive lobular carcinoma cells. Because of the role of TSP during cancer cell invasion, the different expression patterns of TSP in invasive ductal versus lobular carcinoma may well reflect biological differences between these two types of breast carcinoma and could account for the peculiar diffuse invasive behaviour of breast lobular carcinoma cells.

Antigens, CD↗

PubMed1995

Quantitation of human cytomegalovirus glycoprotein H gene in cells using competitive PCR and a rapid fluorescence-based detection system.

A technique is described for quantitation of the human cytomegalovirus (HCMV) glycoprotein H (gH) gene in cells using a quantitative-competitive polymerase chain reaction (QC-PCR). Two recombinant DNA molecules, differing in size due to a 92-bp deletion within the HCMV gH sequence, were used in co-amplification studies to construct a standard curve from which the copy number of the gH gene present in clinical samples could be interpolated. The use of primers labeled with a fluorescent dye allowed direct detection of the amplified products by measuring the amount of fluorescence emitted by each specific PCR fragment with an automated DNA sequencer coupled to a software program. This system was validated subsequently using bronchoalveolar lavage cells obtained from immunocompromised patients and found to be highly sensitive and reproducible over a range of 5-50,000 HCMV gH copies. This rapid procedure could easily be applied to study the pathogenesis of HCMV infection, identify the patients at high risk of developing HCMV disease, and monitor the effects of antiviral therapy at the molecular level.

Base Sequence↗

PubMed1994

Ultrastructural localization of endogenous hormones and receptors in bone tissue: an immunocytological approach in frozen samples.

In addition to their well-known mechanical role, bones are essential for the regulation of calcium phosphate metabolism. Most of the peptide and steroid hormones acting on bone tissue exert their cellular effects directly on bone cells after binding to cell receptors. A combined method using immunocytology on ultrathin frozen sections has been applied to bone tissue and made possible the ultrastructural localization of endogenous hormones and hormone receptors. There is immunocytological evidence, at the osteoblast level, for: (1) the presence of calcitonin, parathyroid hormone, growth hormone, 1,25 dihydroxyvitamin D3, aldosterone, corticosterone and progesterone; (2) the existence of 1,25 dihydroxyvitamin D3 and progesterone receptors; (3) the absence of estradiol and receptors, testosterone and gonadoliberin. Ultimate goals of future studies are to extend the ultrastructural localization of hormones at the osteoclast level, to assess the distribution of adhesive proteins and of their receptors in bone cells and matrix, and to use well-calcified human bone samples in order to evaluate better the role of therapeutic agents.

Animals↗

PubMed1994

Phenotypic and genotypic characterization of acyclovir-resistant varicella-zoster viruses isolated from persons with AIDS.

Phenotypic and genotypic analyses were done on 17 varicella-zoster virus (VZV) isolates recovered from 10 persons with AIDS (mean CD4 cell count, 16.4/mm3) who had chronic VZV lesions. Eleven acyclovir-resistant isolates were recovered from 10 patients after a mean of 20.1 weeks of therapy. Six susceptible isolates were recovered before acyclovir treatment (n = 1), early during therapy (n = 4; mean time, 4.2 weeks), or after discontinuation of acyclovir (n = 1). Acyclovir-resistant VZV isolates were deficient in thymidine kinase (TK) or induced a TK with altered substrate specificity; all isolates were susceptible to foscarnet. Ten of 11 acyclovir-resistant mutants contained tk gene mutations, including single nucleotide substitutions in highly conserved binding sites (n = 2) as well as nucleotide deletions (n = 4) and insertions (n = 4). These findings suggest that multiple, nonuniform mutations within the tk gene are associated with acyclovir-resistant VZV phenotypes.

AIDS-Related Opportunistic Infections↗

PubMed1994

An analysis of the communication of adult residents of a long-term care hospital as perceived by their caregivers.

Different groups of caregivers (nurses, orderlies, professionals, student orderlies and volunteers) who were in frequent interaction with residents from a long-term care hospital were interviewed with a nominal group process. They were asked to identify concrete situations of communication in which residents with no trouble communicating, residents with aphasia and residents with dementia need to express and/or comprehend a message. A total of 196 statements were recorded and coded using a qualitative approach into different categories of communication acts specific to daily life situations and several categories of generic communication acts, which are unrelated to the daily routine of care and treatment. The results show that communication in daily life situations varies little in relation to the different residents. However, residents with language disorders are perceived to be less involved in generic communication acts than residents with no communication disorder. They also demonstrate that the perceptions of communication of the different caregivers vary. The results are discussed in relationship to the conception of an evaluation instrument for language-impaired long-term care residents, which will help in determining intervention as well as the objective evaluation of its effects.

Activities of Daily Living↗

PubMed1994

Osseointegration of titanium implants in the tibia. Electron microscopy of biopsies from 4 patients.

We studied the ultrastructure of bone tissue around implants of pure titanium inserted into the tibia in 4 patients with arthrosis or rheumatoid arthritis. Three main appearances of the interface were noted. First, a close contact between titanium and calcified bone with living osteocytes inside the newly-formed bone was observed in all samples. Secondly, a close contact was also seen between the implant and osteoid, the newly formed collagenous matrix being either uncalcified or calcifying. Thirdly, a loose extracellular matrix with fibrillar and nonfibrillar materials was sometimes observed between bone mineral and implant. There was no inflammatory reaction at the interface. We concluded that the titanium implants were osseointegrated, but the calcification of the bone tissue was not complete even after 20 months. However, mineralization of osteoid and living bone cells revealed the presence of an active tissue.

Arthritis, Rheumatoid↗

PubMed1994

[Harvesting thin and semi-thin skin from the scalp: risks and their prevention].

The complications of raising scalp grafts are dominated by the risks of haemorrhage and alopecia, which can be prevented by careful preparation of the donor site, perfect intraoperative coordination and close surveillance of epithelialisation. The authors report their experience in the Freyming-Merlebach burns unit, with particular emphasis on the value of this technique in children.

Adolescent↗

PubMed1993

In vitro exposure to sodium fluoride does not modify activity or proliferation of human osteoblastic cells in primary cultures.

The anabolic effects of sodium fluoride (NaF) on trabecular bone mass in osteoporosis is now well established. In vivo histologic studies performed in humans and other animals have shown that fluoride induces an increase in osteoblast number at the tissue level. To determine the mechanisms of action of fluoride on osteoblasts, we studied the effects of NaF on short- and long-term cultures of human osteoblastic cells derived from bone explants obtained from 21 donors. In short-term experiments, bone-derived cells were exposed to NaF for 4 days. At doses ranging from 10(-11) to 10(-5) M, NaF did not modify the alkaline phosphatase (AP) activity or osteocalcin secretion. In long-term experiments, half the bone samples from 15 donors were cultured for 4 months in the presence of 10(-5) M NaF and the other half were maintained in NaF-free medium. Observations by light and electron microscopy disclosed no morphologic modification in bone explants after 4 months of exposure to NaF, despite an increase in the bone fluoride content. After the first month of culture, slight but not significant increases were noted in 6 of 10 cases for AP activity, 4 of 10 for osteocalcin secretion, and 5 of 7 for [3H]thymidine incorporation. After 4 months of culture in the presence of NaF, no change in AP activity or cell proliferation was noted. In contrast, the osteocalcin secretion significantly decreased (p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1993

A mathematical model for fluoride uptake by the skeleton.

A mathematical model was developed that predicts fluoride accumulation and clearance from the skeleton based upon fluoride bioavailability, bone remodeling rate, and the fluoride binding characteristics of bone. It was assumed that fluoride binds to bone in a nonlinear fashion such that a smaller percentage of fluoride is bound to bone if fluoride intake is increased to high levels. Bone resorption rate was assumed to be proportional to the solubility of hydroxyfluoroapatite which is inversely related to bone fluoride content. The predictions made by the model compared favorably with experimental results from fluoride uptake and clearance studies. Parametric studies done using the model showed the following: (1) fluoride can be cleared from the skeleton by bone remodeling, but fluoride clearance takes over four times longer than does fluoride uptake; and (2) fluoride uptake by the skeleton was positively associated with bone remodeling rate. However, the concentration of fluoride in newly formed bone does not decrease with reduced remodeling rates and surpasses 10,000 ppm for intakes of fluoride greater than 9 mg/day. For osteoporosis, daily dose and duration of fluoride treatment should be selected to avoid reaching a toxic cumulative bone fluoride content.

Apatites↗

PubMed1993

Evidence for a direct effect of growth hormone on osteoblasts.

In order to determine whether growth hormone (GH) exerts a direct effect on osteoblasts, in vitro and in vivo immunocytological studies were carried out on newborn rat calvaria and a clonal osteoblast-like cell line (MC3T3-E1) isolated from newborn mouse calvaria. After exposure to human growth hormone (hGH) or 1,25 dihydroxyvitamin D3 (1,25(OH)2D3), a significant increase in alkaline phosphatase activity was observed in MC3T3-E1 cells. Simultaneous exposure of MC3T3-E1 cells to hGH and 10 nM 1,25(OH)2D3 showed a synergistic effect of the two hormones on this activity. The optimal dose of hGH was 0.1 nM. An immunocytological procedure was performed on ultrathin frozen sections from 7-day-old rat calvaria and MC3T3-E1 cells cultured with hGH. GH-like immunoreactivity was observed in both cases. In calvaria, endogenous GH-like immunoreactivity was localized at the same ultrastructural level (plasma membrane, cytoplasmic and nuclear matrices) as exogenous GH-like immunoreactivity in MC3T3-E1 cells. Following the initial step of binding to the plasma membrane, GH may be internalized in the cytoplasmic matrix and nucleus. In situ hybridization revealed the presence of mRNA coding for GH receptor in calvaria cells. The density of these receptors seemed to be lower in osteoblasts than in hepatocytes. In MC3T3-E1 cells, hGH induced a dose-dependent secretion of insulin-like growth factor 1. In conclusion, these results indicate that GH may act directly on osteoblasts.

Alkaline Phosphatase↗