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Biomedical subjects

R Parmar

Publications and source records attributed to R Parmar.

14 recordsLinked to original sources
PubMed1997

Analysis of the mismatch and insertion/deletion binding properties of Thermus thermophilus, HB8, MutS.

The methyl-directed long patch repair pathway in Escherichia coli is involved in increasing the fidelity of replication specific repair of DNA polymerase incorporation errors. This pathway is mediated by three gene products, MutS, MutL, and MutH, which are conserved in higher eukaryotes. Mutations in human homologues of these proteins have been shown to be implicated in hereditary non-polyposis colorectal cancer (HNPCC). A MutS homologue has recently been identified in the extremely thermophilic bacterium, Thermus thermophilus. Here we describe analysis of the binding properties of this protein, which has indicated it can identify all specific base mismatches as well as one, two and three base pair insertion/deletion mutations. We therefore believe this protein may be generally useful for applications involving mismatch detection.

Adenosine Triphosphatases↗
PubMed1996

Mutational analysis of the nucleotide binding domain of the mismatch repair enzyme hMSH-2.

The genes involved in postreplicative DNA mismatch repair are a highly conserved family of proteins. In humans, germline mutations in these genes (hMSH-2, hMLH-1, hPMS-1, and hPMS-2) have been implicated in hereditary nonpolyposis colorectal cancer (HNPCC). We have previously shown that a region of high homology between the members of this class of proteins in different species contains a type A nucleotide binding site consensus sequence which has ATPase activity and is sufficient to bind DNA containing specific mismatched residues (1). To identify residues which are necessary for this activity, we have created a range of mutants containing amino acid substitutions within the nucleotide binding domain of hMSH-2. These mutants have been expressed and assessed for ATPase activity and their ability to identify mismatch-containing DNA. Here we demonstrate that a variant protein which has the conserved residue Lys 675 within the nucleotide binding consensus sequence altered to an alanine has severely impaired ATPase activity and is unable to bind DNA containing specific mismatched residues.

Adenosine Triphosphatases↗
PubMed1996

Autism and multiple pituitary deficiency.

We describe a 9-year-old boy who presented with abnormal development in language and social interaction. He also showed evidence of stereotyped behaviour, thus fulfilling all the criteria for an ICD-10 diagnosis of autism. This was associated with multiple pituitary deficiency. No case of autism associated with hypopituitarism has hitherto been reported. The authors discuss the evidence for linking the two conditions as opposed to accepting them as coincidental. In some studies of autism, anatomical and imaging studies have provided evidence of pathology in the limbic lobe. This lobe plays an essential role in the modification and expression of emotional reactions. Together with other areas, the limbic system sends outputs from the hypothalamus and from there to the pituitary. Our case illustrates a possible link between emotional expression and hypopituitarism.

Autistic Disorder↗
PubMed1996

Butyrate enema therapy stimulates mucosal repair in experimental colitis in the rat.

BACKGROUND: The short chain fatty acid (SCFA) butyrate provides energy for colonocytes, stimulates colonic fluid and electrolyte absorption and is recognised as an effective treatment for multiple types of colitis. AIM: To examine the impact of butyrate enema therapy on the clinical course, severity of inflammation, and SCFA stimulated Na+ absorption in a chronic experimental colitis. METHODS: Distal colitis was induced in rats with a trinitrobenzenesulphonic acid (TNBS) enema. Five days after induction, rats were divided into groups to receive: no treatment, saline enemas, or 100 mM Na-butyrate enemas daily. On day 24, colonic damage score and tissue myeloperoxidase (MPO) activity were evaluated. Colon was mounted in Ussing chambers and Na+ transport and electrical activities were measured during a basal period and after stimulation with 25 mM butyrate. RESULTS: In the untreated and the saline enema treated TNBS groups, diarrhoea and extensive colonic damage were seen, associated with increased tissue MPO activities and absent butyrate stimulated Na+ absorption. In contrast, in the butyrate enema treated TNBS group, diarrhoea ceased, colonic damage score improved, and tissue MPO activity as well as butyrate stimulated Na+ absorption recovered to control values. CONCLUSION: Butyrate enema therapy stimulated colonic repair, as evidenced by clinical recovery, decreased inflammation, and restoration of SCFA stimulated electrolyte absorption.

Animals↗
PubMed1993

Prenatal diazepam induced persisting downregulation of peripheral (omega 3) benzodiazepine receptors on rat splenic macrophages.

Prenatal treatment with a low dose of diazepam (1.25 mg/kg/d, gestational day 14-20) has previously been found to cause longterm impairment of cellular immune responses in rat offspring. A possible site of action of diazepam, i.e., the peripheral-type (omega 3) benzodiazepine receptor, was characterized on splenic macrophages as well as on a rat splenic cell preparation containing mainly lymphocytes. In membranes of both preparations, [3H]PK 11195 bound to a single site which in competition experiments exhibited characteristics of the (omega 3) site. Prenatal exposure to diazepam was followed, at 8 weeks of life, by a marked decrease in maximal binding capacity (Bmax) of spleen macrophage membranes in offspring of both sexes, while membranes of the splenic cell preparation exhibited an increase of the dissociation constant of [3H]PK 11195 at 2 and 8 weeks of life. Both types of delayed effects may reduce the metabolic capacity of these immune cells, in which we have also observed deficits of cytokine release.

Animals↗
PubMed1992

Mechanisms of cytotoxicity caused by antitumour drugs.

Although the nature of the interaction between a drug or toxin and its target is of critical importance in determining the fate of a cell, we have argued here that the biological outcome of that interaction will also be determined by the nature of cellular events "downstream" of the initial interactions. We suggest that some type of coupling must take place between the formation of a drug-target interaction (the stimulus?) and the response of the cell. That response will depend upon the phenotypically determined repertoire of response open to the cell as well as upon the quantitative and qualitative measures of the events that the drug induces (DNA or protein damage, inhibition of growth etc.). For example we have described how the HL-60 cell appears to respond to low levels of toxins by engaging a programme of terminal differentiation whilst at greater concentrations apoptosis becomes engaged. Consideration of the cellular response to a toxic insult may provide valuable insights into the selective toxicity of agents as well as providing avenues for the discovery of toxins which might be useful in the treatment of cancer.

Animals↗
PubMed1992

Nervous and immune systems as targets for developmental effects of benzodiazepines. A review of recent studies.

Prenatal exposure to benzodiazepines (BDZ) can cause behavioral dysfunctions both in humans and in experimental animals. In addition, prolonged impairment of cellular immune functions is found in rats after low dose BDZ exposure (e.g., diazepam 1.25 mg/kg/day) during part of fetal life [gestational days (GD) 14-20]. Analysis of diazepam and its metabolites in maternal and fetal tissues revealed that in this rat model the drug is no longer present at birth, which excludes direct effects of diazepam during the postnatal period. The main target of BDZ in brain, the GABAA receptor complex, is structurally and functionally heterogeneous. Besides alpha- and beta-subunits, gamma 2- or gamma 3-subunit should be coexpressed for a fully functional BDZ response. Signals of mRNAs encoding for alpha 1, beta 2 and gamma 2 are detected in fetal rat spinal cord and lower brainstem by GD 14 and reach telencephalic regions in later fetal life, reminiscent of BDZ receptor ontogeny. Regional subunit distribution differs from the adult brain, one interesting feature being a preponderance of gamma 2 mRNA throughout fetal life. Since subunit composition influences the sensitivity to BDZ, these data suggest that prenatal effects of BDZ depend upon regional subunit compositions present at different developmental stages. The delayed depression of cellular immune responses in prenatally BDZ-exposed rat offspring during the first 2 postnatal months is accompanied by various changes in immune cell biology. Binding characteristics of the peripheral (omega 3) type BDZ receptor are altered until adulthood (8 weeks). Membranes of spleen cell preparations containing mainly lymphocytes exhibit a decrease of affinity for the peripheral ligand [3H]PK11195, splenic macrophage preparations a decrease of maximal binding capacity. Various defects in cytokine production by macrophages and T lymphocytes were observed: Mitogen-stimulated release of macrophage-derived tumor necrosis factor-alpha (TNF-alpha) and of the T cell-derived interleukin-2 (IL-2) was drastically reduced at 2 and 4 weeks of life and recovered in young adulthood, exhibiting the same time course of depression as lymphocyte proliferation in response to immune stimuli. Interleukin-6 (IL-6) release remained diminished until adulthood. In female offspring, additional alterations were found in splenic noradrenaline turnover after immune stimulation. The mechanisms underlying the breakdown of the cytokine network in prenatally diazepam-exposed offspring, and the long-term consequences are as yet unknown.

Animals↗
PubMed1991

Autoreactivity in women with endometriosis.

Serum samples from 71 patients with laparoscopically staged endometriosis and from 109 age-matched non-pregnant control women were tested for antibodies to nuclear, phospholipid, smooth muscle and sperm antigens. Immunoglobulin G, M and A and complement components C3 and C4 were measured. Prevalence of the following autoantibodies was statistically significantly greater in women with endometriosis than in the control group: antinuclear antibodies, antibodies to ribonucleoproteins, smooth muscle antibodies, lupus anticoagulant and anticardiolipin antibody. Forty-one women with endometriosis (58%) had some type of autoantibody compared with 13 controls (12%). More women in the endometriosis group had IgG and IgM levels above the normal range. This was statistically significant for IgG in women with grade 3 and for IgM in those with grade 4 endometriosis, IgG levels were significantly higher in antibody-positive women with endometriosis than in the control group. Immunoglobulin and complement component levels tended to have a positive correlation with stage of disease.

Adolescent↗
PubMed1990

Prenatal benzodiazepine immunosuppression: possible involvement of peripheral benzodiazepine site.

Treatment of pregnant Long Evans rats with a low dose of diazepam (1.25 mg/kg from gestational day 14-20) produced offspring suffering from suppression of cellular immune responses. Analogous effects were produced by clonazepam, a benzodiazepine (BDZ) with high affinity for the central-type, and Ro 5-4864, a BDZ with selective affinity for the peripheral-type BDZ receptor. Peripheral-type BDZ receptors are found to develop early in fetal life in peripheral organs including primary (thymus) and secondary (spleen) lymphoid organs, in the central nervous system and on immune cells (lymphocytes). In prenatally diazepam-exposed offspring the affinity constant is significantly changed. BDZ and PK 11195 also inhibit mitogen and alloantigen-induced T and B cell proliferation in vitro in adult murine lymphocytes. Diazepam, Ro 5-4864 and PK 11195 were found to be the most active compounds.

Animals↗
PubMedDate not supplied

Laminar distribution of GABAA receptor alpha 1, beta 2, and gamma 2 subunit mRNAs in the granular and agranular frontal cortex of the rat during pre- and postnatal development.

The expression of mRNAs encoding the three GABAA receptor subunits that are associated with the most abundant benzodiazepine-sensitive GABAA receptor in adult cortex, that is, the alpha 1, beta 2, and gamma 2 subunits, was studied in rat cortex during pre- and postnatal development by means of in situ hybridization, gamma 2 and beta 2 mRNAs become detectable in neocortex at gestational day 16 (GD16), alpha 1 at GD18. gamma 2 mRNA exhibits the highest level of expression at early ages, while alpha 1 mRNA levels are low. beta 2 mRNA rises steeply during the last days of gestation. Around birth, it shows the highest expression of the three subunits studied in cortex, and increases further until postnatal day 15 (PD15). The expression of alpha 1 subunit mRNA also increases markedly shortly before birth and accelerates between PD8 and PD15, when it reaches higher levels than the other two subunits. Following the initial high expression, gamma 2 mRNA increases gradually and slowly until PD25. During prenatal development, highest expression of all three subunit mRNAs is found in the upper layers of cortex, that is, cortical plate and marginal zone. The subplate layer does not start to express GABAA receptor subunit mRNAs until GD18. At birth, all developing layers of the cortex express mRNAs for the three subunits, except the marginal zone. Highest levels are found in the upper part of the cortical plate. At the end of the first postnatal week (PD8), the laminar distribution of mRNA expression in neocortex becomes more differentiated. For all three subunit mRNAs, highest expression is then observed in neuron-like cells in layer IV in the granular areas, and over layers III and upper V in agranular areas. Subsequently, between PD8 and PD25, increasing levels of expression are observed over the pyramidal cell layer V. This regionally differentiated, developmental pattern suggests a close relationship between development of GABAA receptor subunits, ingrowth of thalamocortical projections, and maturation of neocortical circuitry.

Animals↗