Search PubMed⌕ Search

Biomedical subjects

F Martin

Publications and source records attributed to F Martin.

At least 181 records · Page 10Linked to original sources
PubMed1997

Evidence for selection of a population of multi-reactive B cells into the splenic marginal zone.

Antibody reactivity to self-antigens is a normal component of the immune system. To study the mechanism by which self-reactive B cells are generated and maintained, we analyzed B cell development in transgenic mice that express a rearranged VH81X heavy chain from the pre-immune repertoire. In these mice, > 95% of B cells express the transgene in association with a variety of kappa light chains but V kappa 1 C being the dominant light chain. These transgenic B cells with identical V kappa 1C-J kappa 5 joins do not normally secrete IgM in vivo, but antibodies derived from these B cells, through LPS activation in vitro or after hybridoma immortalization, are self-reactive and recognize an ubiquitous epitope(s) on intracytoplasmic proteins from different tissues. They have the phenotype and localization pattern of long-lived marginal zone B cells and their development in vivo is blocked by injection of soluble VH81X-V kappa 1CJ kappa 5 IgM antibody. The observations in this transgenic mouse provide evidence for positive selection of a population of self-reactive B cells. These B cells enter the peripheral pool of B cells where they localize in the marginal zone of the spleen and, in contrast to other transgene-expressing B cells, do not secrete IgM antibody.

Animals↗
PubMed1997

Development of VH81X transgene-bearing B cells in fetus and adult: sites for expansion and deletion in conventional and CD5/B1 cells.

The most D-proximal functional VH gene, VH81X, is preferentially expressed in the mouse fetal B cell repertoire; however, it is expressed in few B cells in the adult. To determine when VH81X gene expression affects size and phenotype of particular stages in B cell differentiation, transgenic mice have been developed expressing a germline fetal liver-derived VH81X-mu rearrangement. Comparative analysis of B lymphopoiesis reveals similarities and differences between fetal liver and adult bone marrow which pinpoint developmental stages in mice during which VH81X-expressing B cell progenitors expand or deplete compartment sizes. These include a similar reduction in c-kitR+ and establishment of a predominant CD43low/HSAhigh phenotype within the B220+ CD43+ compartment which is dependent on the association of the transgene with lambda 5. In contrast, the CD43- pre-B and immature B cell compartments are expanded in the fetus but not in the adult. In addition, there are other factors that later disfavor the survival of VH81X-expressing B1 and B2 cells. Thus the failure to detect VH81X-bearing B cells in the adult is the result of a multistep selection process occurring at all stages during B repertoire expansion.

Aging↗
PubMed1997

Dimerization of granulocyte-colony stimulating factor receptor: the Ig plus CRH construct of granulocyte-colony stimulating factor receptor forms a 2:2 complex with a ligand.

We have previously shown that the extracellular domain of granulocyte-colony stimulating factor receptor (soluble G-CSFR), prepared from CHO cell conditioned media, dimerizes upon binding its ligand, G-CSF. The most stable ligand-receptor complex occurs at a 2:2 stoichiometry, unlike the growth hormone and erythropoietin systems. In the latter cases, each ligand uses two sites to bring two receptors together. In this study, we have generated a truncated G-CSF receptor, known to be sufficient for high affinity ligand binding, which consists of an Ig-like domain and a cytokine receptor homology module. With an affinity purified receptor, sedimentation equilibrium experiments clearly demonstrated that this truncated form of the receptor behaves very similarly to the entire extracellular domain. The sedimentation equilibrium data are consistent with the model that the truncated receptor has a weak tendency to self-associate into a dimer in the absence of a ligand, this receptor-receptor interaction is enhanced by ligand binding, and the most stable complex occurs at a 2:2 stoichiometry. These results are very different from those described by others for various murine G-CSF receptor constructs from either Escherichia coli or insect expression systems.

Animals↗
PubMed1997

Affinity selection of a camelized V(H) domain antibody inhibitor of hepatitis C virus NS3 protease.

The HCV genome encodes, within the NS3 gene, a serine protease whose activity specifically cleaves the viral polyprotein precursor. Proteolytic processing of HCV polyprotein precursor by the viral NS3 proteinase is essential for virion maturation and designing specific inhibitors of this protease as possible anti-viral agents is a desirable and practical objective. With a view to studying both the function of HCV NS3 protease and to designing inhibitors of this enzyme, we directed our interest towards engineering macromolecular inhibitors of the viral protease catalytic activity. We describe here the affinity-selection and biochemical characterization of one inhibitor, cV(H)E2, a 'camelized' variable domain antibody fragment, isolated from a phage displayed synthetic repertoire, which is a potent and selective inhibitor of proteolysis by the NS3 enzyme. In addition to being useful as a biological probe to study the function of HCV protease, this inhibitor can serve as a potential pharmacophore model to design antivirals. Moreover, the results suggest a way of engineering improved human-derived small recognition units tailored for enzyme inhibition.

Animals↗
PubMed1997

Injury from dairy cattle activities.

Animals have been implicated as an important source of injury for farm household members. Little is known, however, about the specific activities associated with the animal/livestock operations that place a person at increased or decreased risk for injuries. The primary aim of this case-control study was to identify which dairy cattle operation activities (that is, milking, feeding, cleaning barns, trimming and treating feet, dehorning, assisting with difficult calvings, and doing treatments) were associated with an increased or decreased risk of injury. We found milking to have the greatest increase in risk for injury. The ratios for increasing hours per week spent at milking (0, 1-10, 11-20, 21-30, 31-63) were 1.0, 2.3, 5.5, 10.9, and 20.6, respectively. We also found an increased rate ratio associated with trimming or treating hooves (rate ratio = 4.2).

Adolescent↗
PubMed1997

Effects of chair-restraint on gastrointestinal transit time and colonic fermentation in male rhesus monkey (Macaca mulatta).

The incidence of an 18 day chair-restraint on the digestive physiology of male rhesus monkey was investigated for space research purposes, comparing four trained restraint subjects with two vivarium controls. Chair-restraint induced a 2.5-fold acceleration of the gastrointestinal transit time, which persisted throughout the 7 day postrestraint period, and an increase of the fecal dry matter content, which mean value rose from 40.7% to 69.6%. Fecal pH remained unaltered throughout the experiment. Modifications of fermentative metabolites produced by the colonic microflora and excreted through the breath (hydrogen and methane) or in the feces (short chain fatty acids and ammonia) could not be reliably related to chair-restraint and probably involved side-stress factors. On the whole, alterations due to chair-restraint are shown to be different from those reported in the literature, following a modification of the dietary composition. These data may help to predict the alterations of digestive physiology likely to occur in immobilized human patients.

Ammonia↗
PubMed1997

Ribosomal DNA internal transcribed spacers to estimate the proportion of Pisolithus tinctorius and Eucalyptus RNAs in ectomycorrhiza.

Ectomycorrhiza is a complex association of several types of plant and fungal cells. Differentiation of symbiotic structures is correlated with large changes in mRNA synthesis, leading to novel protein patterns. Quantification of up- and down-regulated specific transcripts is complicated by the intermingling of root and hyphal components. Determination of steady-state levels of symbiosis-regulated mRNA requires a normalization to the housekeeping RNA content of each partner. In this study, the usefulness of the internal transcribed spacer (ITS)-5.8S ribosomal DNAs (rDNAs) as molecular markers of the root colonization by fungal mycelium was assayed. The rDNA ITSs of Pisolithus tinctorius and Eucalyptus globulus were cloned by PCR amplification, and their sequences were determined. They contained the 5.8S rDNAs, and these two probes did not cross-hybridize. Steady-state levels of the ITS-5.8S rRNAs in the vegetative mycelium, in the noninfected root, and in ectomycorrhizas of E. globulus-P. tinctorius 441 were estimated at different stages of development. Colonization of roots by the mycelium provoked a large decrease in the proportion of root rRNAs. At the end of mycorrhiza formation, about 80% of the ectomycorrhizal RNA belonged to the mycobiont. The ITS-5.8S can be used as a specific probe for the estimation of fungal or plant rRNA in the symbiotic tissues and to determine whether an mRNA is down- or up-regulated in ectomycorrhiza.

Base Sequence↗
PubMed1997

Characterization of a thermosensitive Escherichia coli aspartyl-tRNA synthetase mutant.

The Escherichia coli tls-1 strain carrying a mutated aspS gene (coding for aspartyl-tRNA synthetase), which causes a temperature-sensitive growth phenotype, was cloned by PCR, sequenced, and shown to contain a single mutation resulting in substitution by serine of the highly conserved proline 555, which is located in motif 3. When an aspS fragment spanning the codon for proline 555 was transformed into the tls-1 strain, it was shown to restore the wild-type phenotype via homologous recombination with the chromosomal tls-1 allele. The mutated AspRS purified from an overproducing strain displayed marked temperature sensitivity, with half-life values of 22 and 68 min (at 42 degrees C), respectively, for tRNA aminoacylation and ATP/PPi exchange activities. Km values for aspartic acid, ATP, and tRNA(Asp) did not significantly differ from those of the native enzyme; thus, mutation Pro555Ser lowers the stability of the functional configuration of both the acylation and the amino acid activation sites but has no significant effect on substrate binding. This decrease in stability appears to be related to a conformational change, as shown by gel filtration analysis. Structural data strongly suggest that the Pro555Ser mutation lowers the stability of the Lys556 and Thr557 positions, since these two residues, as shown by the crystallographic structure of the enzyme, are involved in the active site and in contacts with the tRNA acceptor arm, respectively.

Aspartate-tRNA Ligase↗
PubMed1997

Characterization of engineered hepatitis C virus NS3 protease inhibitors affinity selected from human pancreatic secretory trypsin inhibitor and minibody repertoires.

Given the extent of hepatitis C virus (HCV) infection as a worldwide health problem and the lack of effective treatment, the development of anti-HCV drugs is an important and pressing objective. Previous studies have indicated that proteolytic events mediated by the NS3 protease of HCV are fundamental to the generation of an active viral replication apparatus, as unequivocably demonstrated for flaviviruses. As a result, the NS3 protease has become a major target for discovering anti-HCV drugs. To gain further insight into the biochemical and biophysical properties of the NS3 enzyme binding pocket(s) and to generate biological tools for developing antiviral strategies, we decided to engineer macromolecular ligands of the NS3 protease domain. Phage-displayed repertoires of minibodies ("minimized" antibody-like proteins) and human pancreatic secretory trypsin inhibitor were sampled by using the recombinant NS3 protease domain as a ligate molecule. Two protease inhibitors were identified and characterized biochemically. These inhibitors show marked specificity for the viral protease and potency in the micromolar range but display different mechanisms of inhibition. The implications for prospective development of low-molecular-weight inhibitors of this enzyme are discussed.

Amino Acid Sequence↗
PubMed1997

Expression of nonmuscle myosin heavy chain-B isoform in the vessel wall of porcine coronary arteries after balloon angioplasty.

Nonmuscle myosin heavy chain-B isoform (NMMHC-B) is expressed by proliferating vascular smooth muscle cells (SMCs), and its expression in primary lesions has been proposed to be predictive of restenosis after atherectomy. The present study was designed to study the time-course expression of NMMHC-B after angioplasty of porcine coronary arteries by in situ hybridization and immunohistochemistry. Domestic juvenile swine underwent percutaneous transluminal coronary angioplasty (PTCA) of the left anterior descending and circumflex coronary arteries with standard clinical angioplasty catheters. To identify proliferating cells, 5'-bromo-2'-deoxyuridine (BrdU) was administered and detected by immunohistochemistry on serial sections. Vessels were examined at 3, 7, and 14 days after balloon angioplasty, and uninjured coronary vessels were used as controls. Normal arteries showed hybridization to 35S-labeled NMMHC-B riboprobes localized mainly in the medial layer. NMMHC-B expression in the adventitia was markedly increased 3 days after balloon angioplasty. Seven and 14 days after injury, NMMHC-B mRNA-containing cells were localized in the adventitia and neointima at the arterial injury site. Cell proliferation, as indicated by BrdU staining, colocalized with NMMHC-B mRNA expression 3 and 7 days after angioplasty. These data indicate that cells proliferating in the adventitia and neointima express NMMHC-B; however, its expression is not limited to the proliferative state, since NMMHC-B mRNA was also found in quiescent SMCs of normal coronary arteries and in nonproliferating adventitial and neointimal cells 14 days after angioplasty.

Actins↗
PubMed1997

Organotin compounds in trimethyltin-treated rats and in human brain in Alzheimer's disease.

As blood tin concentrations are elevated in Alzheimer's disease and as some low molecular weight organotin compounds are neurotoxic, we have attempted to detect organotins in brain in Alzheimer's Disease. First we measured the concentration of trimethyltin (TMT) in the brains of rats which had been exposed to memory-impairing concentrations of TMT and, as the method of linking hydride generation, cryogenic trapping, gas chromotographic separation and atomic absorption spectrophotometric detection permitted the measurements of organotin compounds when the total tin was greater than 0.2 nanograms, we applied these techniques to human brain tissue, some of which showed neuropathological evidence of Alzheimer's Disease. No low molecular weight organotin compounds were detected in the human brain tissue, but it is possible that tin may be complexed with large organic molecules, the hydrides of which would not be volatile, but which could be identified by liquid chromatography.

Aged↗
PubMed1997

Side-effects of intravenous cyclophosphamide pulse therapy.

We reviewed the side-effects of intravenous (i.v.) cyclophosphamide (CPM) pulse therapy in a group of 75 patients suffering from various autoimmune disorders (mostly systemic lupus erythematosus and vasculitis) who received a total of 451 i.v. CPM pulses, given on a monthly basis (mean +/- s.d. CPM dose per pulse: 764 +/- 217 mg; mean +/- s.d. follow-up period: 26.7 +/- 22.1 mon). Infection was the most common side-effect (30 episodes in 21 patients; 28% of the patients) but rarely required in-patient treatment (8 episodes in 7 patients; 9% of the patients). No relationship could be found between the occurrence of infection and the dose of CPM or of glucocorticoids. Other side-effects were rare. Only one patient suffered from neutropenia. Haemorrhagic cystitis was never observed nor did premature ovarian failure in the 25 female patients at risk. Four patients developed neoplasia and three died suddenly a few days after receiving a CPM pulse but the causal relationship between CPM therapy and these poor outcomes is speculative. Taken together, our data confirm in a large group of patients that i.v. CPM pulse therapy is relatively safe. In particular, the rate of severe infection requiring in-patient treatment is rare (1.8% of 451 pulses.).

Adult↗
PubMed1997

Depression and Burnout in Hospital Health Care Professionals.

A cross-sectional study was conducted on a random sample of 1,200 health care professionals in Marseille, France, in order to assess the prevalences of depression and burnout, and to compare these two entities. Depression was assessed by the Center for Epidemiologic Studies-Depression scale (CES-D), and burnout by the Maslach Burnout Inventory (MBI). Burnout is a syndrome of emotional exhaustion, depersonalization towards patients, and reduced sense of personal accomplishment. Some psychiatrists consider burnout to be a clinical form of depression. The prevalences of depression and burnout were very close: 17.1% and 15.7% among the women, 19.4% and 22% among the men, but 6.5% of the women and 9.4% of the men were both depressive and burned-out. A correlation was found between the CES-D and the subscales Emotional Exhaustion and Depersonalization of the MBI. Multivariate analysis and logistic regression models showed that many demographic and subjective variables influenced depression and burnout in different ways.

Journal Article↗
PubMed1997

Polyethylene glycol-coated (pegylated) liposomal doxorubicin. Rationale for use in solid tumours.

Polyethylene glycol (PEG)-coated (pegylated; Stealth) liposomes are stable, long-circulating drug carriers useful for delivering doxorubicin to the sites of solid tumours. Compared with conventional liposomes, pegylated liposomes are less extensively taken up by cells of the reticuloendothelial system (RES) and have a reduced tendency to leak drug while in circulation. The pharmacokinetics of PEG-liposome encapsulated doxorubicin are characterised by an extremely long circulating half-life, slow plasma clearance and a reduced volume of distribution compared with conventional liposomal doxorubicin or free doxorubicin. The long circulation and ability of pegylated liposomes to extravasate through 'leaky' tumour vasculature results in localisation of doxorubicin in tumour tissue. In a number of animal and human tumours, including breast, prostate, pancreatic and ovarian xenografts, pegylated liposomal doxorubicin produced higher intratumoural drug concentrations and better therapeutic responses than equivalent doses of conventional (nonpegylated)-liposome encapsulated doxorubicin or free doxorubicin. Low peak plasma concentrations of free doxorubicin after administration of pegylated liposomal doxorubicin and the reduced tendency of the liposomal drug to accumulate in myocardium suggest that a reduction in cardiac toxicity compared with free doxorubicin may be observed. Thus, the rationale for the use of pegylated liposomal doxorubicin in solid tumours may be summarised as follows: change in the toxicity profile with a decrease in acute adverse effects (such as nausea and vomiting) and reduced incidence of alopecia, greater activity in highly angiogenic tumours (such as Kaposi's sarcoma) and effective treatment of tumours moderately sensitive to doxorubicin (such as breast and ovarian carcinomas), with the possibility of increased tumour response because of enhanced drug accumulation. In addition, although no comparative study yet exists, there is a suggestion from early human studies with pegylated liposomal doxorubicin that cardiotoxicity may be reduced compared with the free drug.

Animals↗
PubMed1997

B cell development in mice.

The development and establishment of the B Cell Repertoire is the net result of both genetic and environmental forces. The primary event at the genetic level is Ig gene rearrangement resulting in numerous possible combination of genes which can be further modified by somatic events such as N segment addition and somatic mutation. Environmental forces in the form of self and exogenous Ags also shape the repertoire by positively or negatively selecting B cells according to the specificity of their Ig receptors. These are dynamic processes beginning with the earliest expression of immunoglobulins in fetal life and continuing throughout life. In this review we discuss the genetic and selective mechanisms responsible for differences in the early immune system compared to that of the adult.

Animals↗
PubMed1997

ARMEDA: accessing remote medical databases over the World Wide Web.

We have created a computer system to access medical information located at remote databases over the World Wide Web, for epidemiological ad health services research. We made a preliminary prototype where a specific database model could be searched and information be retrieved. We are currently working on a new component-based architecture, where different databases scheme from various sites can be used to create a unified model, giving users a "virtual" vision of a single, local database. Different software engineering and artificial intelligence methods are used to access, integrate, filter and deliver information to users.

Computer Communication Networks↗
PubMed1997

Human immunodeficiency virus risk awareness. Evaluation of a CME program for family physicians.

OBJECTIVE: To determine whether a continuing medical education (CME) program on AIDS risk awareness would enhance physicians' knowledge of HIV and AIDS, their "intent-to-change" practice behaviour, and their ability to integrate their knowledge into hypothetical clinical scenarios; and to identify participant characteristics that affect their knowledge of risks and how they intend to behave regarding HIV testing. DESIGN: Before-and-after study using a questionnaire. SETTING: The city of Winnipeg and 16 rural communities in Manitoba. PARTICIPANTS: Convenience sample of physicians who attended the AIDS Risk Awareness Program and completed a questionnaire before the presentation (96 of 142 eligible physicians). MAIN OUTCOME MEASURE: A two-point or greater change on a Likert scale in the desired direction for each questionnaire item. RESULTS: Physicians were classified as sensitized or less sensitized depending on previous experience with HIV-positive and AIDS patients. Less sensitized physicians significantly improved their scores in all three areas. Sensitized physicians and women physicians significantly improved their knowledge and reported more intent to ask patients routinely about HIV risk behaviours. Physicians' sex, age, religion, and years in practice had an effect on these improvements. CONCLUSIONS: The AIDS Risk Awareness Program was successful in improving physicians' knowledge, attitude to intent-to-change behaviour and ability to integrate knowledge into practice scenarios. Physicians with true learning needs benefited the most from the CME program.

Adult↗