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Biomedical subjects

J Clements

Publications and source records attributed to J Clements.

At least 73 records · Page 4Linked to original sources
PubMed1992

The genotoxicity of the anti-cancer drug mitoxantrone in somatic and germ cells of Drosophila melanogaster.

The novel antineoplastic drug mitoxantrone was studied for its genotoxic effects in Drosophila melanogaster. In male germ cells, the clinical preparation Novantrone, the dihydrochloride salt of mitoxantrone, did not induce sex-linked recessive lethal mutations in feeding and injection experiments with adult flies, although statistically the results were inconclusive rather than truly negative. However, the free base mitoxantrone was weakly, but significantly genotoxic in this test (0.14% lethals/mM exposure concentration); this is most probably the result of prolonged exposure. On the other hand, both forms of mitoxantrone assayed were clearly genotoxic in the somatic mutation and recombination test of the wing. This test assays the cells of the proliferating imaginal wing discs of larvae. Depending on the feeding method used, the overall clone induction frequency was in the range of about 2-6 x 10(-5) per cell and cell generation and per mM exposure dose. Correction of these frequencies according to mean clone size led to slightly higher estimates (by about 5-25% higher). Although the majority of the clone induction events are due to mitotic recombination, a significant proportion can be attributed to mutational events (gene and chromosome mutations). The genotoxicity of mitoxantrone seems to depend mainly on impaired DNA synthesis in cycling cells owing to the compound's ability to inhibit topoisomerase II by intercalation into DNA.

Animals↗
PubMed1992

Mutations defining functional regions of the superantigen staphylococcal enterotoxin B.

Staphylococcal enterotoxin B (SEB) is both a superantigen and toxin. As a superantigen, SEB can bind to major histocompatibility complex (MHC) class II molecules to form a ligand for alpha/beta T cell receptors bearing particular V beta elements. As a toxin, SEB causes rapid weight loss in mice sometimes leading to death. We show here that both of these functions map to the NH2-terminal portion of the toxin. Three regions were identified: one important in MHC class II binding, one in T cell recognition, and one in both functions. These results support the conclusion that the toxicity of SEB is related to massive T cell stimulation and release of cytokine mediators and show that the residues interacting with MHC and the T cell receptor are intertwined.

Amino Acid Sequence↗
PubMed1992

A re-evaluation of the tissue-specific pattern of expression of the rat kallikrein gene family.

We have used reverse transcriptase-polymerase chain reaction (RT-PCR) analysis and insitu hybridization to further define the tissue and cell-specific pattern of expression of the rat kallikrein gene family. rKlk1 gene expression has been unequivocally demonstrated in the rat heart, ovary and testis. Similarly, rKlk3, 4 and 9 gene expression has been demonstrated in the testis/ovary, heart and testis respectively. Insitu hybridization has identified the expression of kallikrein gene family members to specific cell-types in the rat ovary (granulosa cell) and testis (germ cell).

Animals↗
PubMed1992

Prolonged transgene expression in rodent lung cells.

We tested the efficiency of several different cationic liposome formulations, complexed to one of two different chloramphenicol acetyltransferase (CAT) reporter plasmids, in transfecting freshly isolated, highly purified rat lung alveolar type II cells, alveolar macrophages, and three different human lung carcinoma cell lines, as well as NIH 3T3 cells, a rapidly dividing, transformed mouse fibroblast line. Our results demonstrated that several different cationic liposome formulations can mediate high-level CAT gene expression in all the cell types tested. Electron microscopic analysis confirmed that cationic liposome-DNA complexes are avidly bound and internalized by lung cells. The time course of expression of transfected genes in nontransformed cell types with low mitotic indices, such as type II cells, is poorly characterized. NIH 3T3 cells expressed maximal CAT activity by day 4 following transfection, with virtual disappearance of activity by day 11. Conversely, type II cells expressed maximal CAT activity between days 5 and 11, and CAT activity was still clearly present 35 days after transfection. Southern blot analysis of DNA isolated from transfected type II cells revealed that the CAT gene was largely present in an extrachromosomal form, rather than integrated into genomic DNA. These observations indicate that following cationic liposome-mediated transfection, rat alveolar type II cells (the majority of which do not divide in culture) can express transfected genes for prolonged periods, apparently mediated by expression of the transgene in an episomal form.

3T3 Cells↗
PubMed1990

Thyroid dysfunction in a prospectively followed series of patients with progressive systemic sclerosis.

Thirty-nine patients with progressive systemic sclerosis (PSS) in stable clinical conditions were extensively evaluated for the presence of thyroid disease. Two patients had previously undetected hypothyroidism while 7 additional patients had normal serum thyroid hormone levels but an exaggerated TSH response to thyrotropin-releasing hormone (TRH) administration, consistent with subclinical hypothyroidism. Four of the 9 subjects with abnormal TRH responses had positive antithyroid antibodies and of the remaining 5, 4 had been on chlorambucil or prednisone. Basal TSH and TSH response to TRH were significantly higher in PSS patients as a group when compared to a control group and increased with increasing duration of PSS. Serum antithyroid antibodies (antithyroglobulin and/or antimicrosomal antibodies) were positive in 18% and thyroid scans were abnormal in 18% of the patients. The euthyroid sick syndrome was not seen. Our findings indicate an increased frequency of, sometimes previously unsuspected, clinical and subclinical hypothyroidism in stable PSS patients which appears to be autoimmune in nature and becomes more prevalent with increased PSS duration. Careful and regular monitoring of the thyroid function in PSS patients is advisable.

Adult↗
PubMed1990

The effects of a range of anti-cancer drugs in the white-ivory somatic mutation test in Drosophila.

The white-ivory test is based upon the reversion of the X-linked, recessive eye-colour mutation white-ivory to wild-type. Somatic reversion of white-ivory results in clones of red facets in the white-ivory eyes of eclosing adult flies. 4 anti-cancer drugs, bleomycin, adriamycin, mitoxantrone and cyclophosphamide were found to significantly increase the white-ivory reversion frequency whereas cytosine arabinoside, methotrexate and vincristine did not give positive results.

Animals↗
PubMed1990

The white-ivory somatic mutation test in Drosophila. The effects of larval age, increasing the number of copies of wi and the response to some reference mutagens.

The white-ivory somatic mutation test is based on reversion of the X-linked, recessive eye-colour mutation white-ivory to wild-type. Somatic reversion of white-ivory leads to clones of red facets in the white-ivory eyes of eclosing adult flies. The alkylating agents MMS, EMS and ENU and the mutagen DEB all induce high levels of white-ivory reversion. The response of different larval instars has been investigated and dose-response data for MMS and EMS is reported. Strains with additional copies of the white-ivory mutation are more sensitive to reversion but the increase in reversion is not as high as might be expected given the number of white-ivory mutations present. Females, having twice the number of white-ivory copies, tend to show higher levels of reversion than males of the same strain.

Animals↗
PubMed1990

Social cognition and impaired social interaction in people with severe learning difficulties.

Social skills training has focused on 'performance' or overt behaviour, rather than on the other components of successful social functioning: motivation and goals, analysis of social information, and performance feedback, Some basic aspects of this 'analysis' or 'social cognition' component were compared in a preliminary study of 25 teenagers and young adults with severe learning difficulties, whose social interaction was categorized as either 'impaired' or 'appropriate'. As predicted from the literature on autistic children, there were no differences between the groups on tasks involving recognition of the visual aspects of the concept of self or perceptual role-taking. It is suggested that social impairments do not reflect social cognitive abilities which are 'lower level' (i.e. can be solved on the basis of information available to the senses). Contrary to expectations, on the four individual tasks of affective role-taking, which is 'higher level', since it requires inferences to be made about the inner emotional state of another person, the differences between the groups were not significant. However, the results were in the predicted direction, and when scores on the tasks were combined, the overall performance of the socially impaired group was significantly poorer (P less than 0.05). It is suggested that the results from this aspect of social cognition might be attributed either to methodological difficulties or to differences between autistic children and the present sample. The clinical implications of the findings of the study are discussed.

Adolescent↗
PubMed1990

A kinetic analysis of the modulation of N-methyl-D-aspartic acid receptors by glycine in mouse cultured hippocampal neurones.

1. Responses to N-methyl-D-aspartic acid (NMDA) were recorded from mouse embryonic hippocampal neurones in dissociated culture, using whole-cell patch-clamp recording. A fast perfusion system, with an exchange time constant of less than 10 ms, was used to study modulation of NMDA receptor desensitization by glycine. 2. The onset of NMDA receptor desensitization was well fitted by a single-exponential function; with 30 nM-glycine the time constant was 250 ms, corresponding to a rate of 4 s-1. The rate of onset of desensitization became faster with increasing glycine concentration, with a slope of 0.87 x 10(7) M-1 s-1. Recovery from desensitization, studied with a twin-pulse technique, was also well fitted by a single-exponential function; with 30 nM-glycine the time constant of recovery was 1.95 s-1. The rate of recovery from desensitization became faster with increasing glycine concentration, with a slope of 0.76 x 10(7) M-1 s-1. These results are consistent with a model in which the effect of glycine occurs via an increase in the rate constant for recovery from desensitization, with little effect on the rate constant for onset of desensitization. Over the range 30-300 nM-glycine, the ratio of the rate constants calculated for recovery and onset of desensitization was a good predictor of the degree of desensitization recorded at equilibrium. 3. Concentration jump experiments with glycine were performed with 100 microM-NMDA present continuously, and for a single binding site model gave estimates of the association (1.1 x 10(7) M-1 s-1) and dissociation (3.1 s-1) rate constants for interaction of glycine with the NMDA receptor. In the presence of NMDA, concentration jumps from 3 microM-glycine to lower concentrations gave relaxations which became slower with decreasing glycine concentration over the range 1 microM-30 nM. A similar slowing of desensitization occurred when the glycine concentration was altered over the same range. 4. Glycine analogues of lower affinity produced desensitization with faster kinetics. D-Alanine, 150 nM, produced desensitization with a time constant of 175 ms, faster than recorded with an equipotent concentration of glycine (50 nM, time constant 259 ms). Responses of similar peak amplitude, recorded with 60 microM-L-alanine, and 500 microM-D,L-homoserine, did not produce strong desensitization, consistent with desensitization too rapid to resolve in our experiments.(ABSTRACT TRUNCATED AT 400 WORDS)

Alanine↗
PubMed1989

Regulation of NMDA receptor desensitization in mouse hippocampal neurons by glycine.

Responses to the excitatory amino acid N-methyl-D-aspartate (NMDA) are markedly potentiated by nanomolar concentrations of glycine. This is due to the action of glycine at a novel strychnine-resistant binding site with an anatomical distribution identical to that for NMDA receptors, suggesting that the NMDA receptor channel complex contains at least two classes of amino-acid recognition site. Antagonists at the glycine-binding site associated with NMDA receptors act as potent non-competitive antagonists, but do not alter the mean open time or conductance, as estimated by fluctuation analysis. The mechanisms by which glycine acts on NMDA receptors are unknown, but single-channel recording experiments show an increase in opening frequency with no change in mean open time or conductance, suggesting that glycine could regulate transitions to states that are intermediate between binding of NMDA receptor agonists and ion-channel gating. It has been suggested that glycine acts as a co-agonist at the NMDA receptor, and that responses to NMDA cannot be obtained in the complete absence of glycine, but in these experiments the response to NMDA was measured at equilibrium, and it is unlikely that sufficient temporal resolution was achieved to detect rapid alterations in receptor gating. Using a fast perfusion system we find that glycine regulates desensitization at NMDA receptors; this has a major effect on the response to NMDA measured at equilibrium, as would occur with slower applications of agonist. Reduction of NMDA receptor desensitization by glycine provides an example of a novel mechanism for regulation of ion-channel activity.

Animals↗
PubMed1989

Immuno- and bioactive inhibin and inhibin alpha-subunit expression in rat Leydig cell cultures.

The rise in serum immunoactive inhibin levels in male rats following hCG stimulation raised the possibility that Leydig cells may produce inhibin. This study therefore evaluated whether Percoll-purified Leydig cells from adult male rats synthesized and secreted inhibin in vitro as measured by Northern blot analysis, radioimmunoassay and in vitro bioassay. Northern blot analysis demonstrated the presence of alpha-inhibin subunit mRNA in the Leydig cell and inhibin bioactivity was detected in Leydig cell culture media. Levels of immunoactive inhibin increased in culture over 20 h and were directly dependent on the number of Leydig cells in culture. rLH (NIADDK-rLH-I-6) and not rFSH (NIADDK-rFSH-I-6) stimulated immunoactive inhibin levels in a dose-dependent manner. This study demonstrates that Leydig cells express mRNA for the alpha-subunit of inhibin and produce inhibin which is biologically and immunologically active prompting a re-evaluation of our concepts of testicular inhibin production.

Animals↗
PubMed1989

Assessing the understanding of emotional states in a population of adolescents and young adults with mental handicaps.

This study investigated emotional awareness, the recognition and understanding of different emotional states, among a non-clinical population of adolescents and young adults with mental handicaps. While emotional awareness showed a high positive correlation with language comprehension, the results suggest that many of these individuals have specific emotional awareness deficits which are not in line with their language comprehension abilities. This finding suggests that the assessment of emotional awareness would be an important step in the choice of a self-report measure to assess an individual's emotional state.

Adolescent↗
PubMed1988

The Drosophila wing test: a comparison of the sensitivity of different strains.

A range of 5 chemical mutagens were tested in the Drosophila wing test using 2 different strains and carrying out the experiments in parallel under standardised conditions. The mutagens chosen for the study were the 2 alkylating agents MMS and ENU and the anti-cancer drugs methotrexate, cytosine-arabinoside and adriamycin. As a result of the different genetic backgrounds there was a marked variation in the response of the 2 strains to the mutagens.

Alkylating Agents↗