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Biomedical subjects

D Smith

Publications and source records attributed to D Smith.

At least 343 records · Page 19Linked to original sources
PubMed1999

Mouse models of madness.

Psychiatric disorders have important genetic contributions, but it has been very difficult to identify the responsible genes using human populations. Recent developments in mouse genomics hold considerable promise of providing important insights into the genetics of these diseases.

Animals↗
PubMed1999

Young Investigator's Award: induction of apoptosis following traumatic head injury in humans.

Apoptosis or programmed cell death plays an important role in many developmental and pathological processes of the central nervous system. In head injury, apoptosis has been recently implicated in many studies on animal brain samples the phenomenon of apoptotic gene expression (bax and bcl-2). Twenty specimens of contused brain tissue (temporal and frontal lobe) from 20 patients who underwent emergency craniotomy and removal of mass lesions were obtained from May to October 1997. The samples collected were immediately snap frozen in liquid nitrogen and stored at -80 degrees C. Immunohistochemical analysis was performed to detect the expression of bcl-2, bax and p53 using standard avidin-biotin complex second antibody conjugate methodology utilising commercially available primary and secondary antibodies. The average age of cohort was 46.24 +/- 22.17 years, the average Glasgow Coma Scale on admission was 9.19 +/- 4.72, and the average duration from injury to collection of the sample was 20.62 +/- 40.57 hours. There was documented hypoxia and hypotension seen in 5 of the 20 patients (25%). Significant levels of bax protein expression were noted in all samples, and p53 expression in 30% of samples. No bcl-2 expression was observed. Our study showed that for the first time the strong expression of the pro-apoptotic gene (bax) and low levels of the anti-apoptotic gene (bcl-2), thus implicating the mechanism of apoptosis in brain injury following trauma. The use of agents to inhibit apoptosis may be beneficial in head injury patients.

Apoptosis↗
PubMed1999

Chronic infections and coronary heart disease.

The rapidly changing patterns of coronary heart disease (CHD) prevalence and presentation fail to be explained by conventional cardiovascular risk factors alone. An infectious basis to atherosclerosis may, at least in part, be contributing to the variable rates of prevalence of CHD in different parts of the world. The evidence for such an association appears to be strongest for Chlamydia pneumoniae. Results of recent anti-chlamydia antibiotic intervention pilot studies have renewed interest in the role of C. pneumoniae, and corroborated the evidence from sero-epidemiological, pathological and animal-model studies. The results of larger, on-going, purpose-designed intervention studies should help to increase our understanding of the role of infection in atherogenesis and potentially lead to a novel and effective treatment strategy for patients with CHD--broad spectrum antibiotics.

Anti-Bacterial Agents↗
PubMed1998

The effect of long-term dietary supplementation with antioxidants.

The impact of diet and specific food groups on aging and age-associated degenerative diseases has been widely recognized in recent years. The modern concept of the free radical theory of aging takes as its basis a shift in the antioxidant/prooxidant balance that leads to increased oxidative stress, dysregulation of cellular function, and aging. In the context of this theory, antioxidants can influence the primary "intrinsic" aging process as well as several secondary age-associated pathological processes. For the latter, several epidemiological and clinical studies have revealed potential roles for dietary antioxidants in the age-associated decline of immune function and the reduction of risk of morbidity and mortality from cancer and heart disease. We reported that long-term supplementation with vitamin E enhances immune function in aged animals and elderly subjects. We have also found that the beneficial effect of vitamin E in the reduction of risk of atherosclerosis is, in part, associated with molecular modulation of the interaction of immune and endothelial cells. Even though the effects of dietary antioxidants on aging have been mostly observed in relation to age-associated diseases, the effects cannot be totally separated from those related to the intrinsic aging process. For modulation of the aging process by antioxidants, earlier reports have indicated that antioxidant feeding increased the median life span of mice to some extent. To further delineate the effect of dietary antioxidants on aging and longevity, middle-aged (18 mo) C57BL/6NIA male mice were fed ad libitum semisynthetic AIN-76 diets supplemented with different antioxidants (vitamin E, glutathione, melatonin, and strawberry extract). We found that dietary antioxidants had no effect on the pathological outcome or on mean and maximum life span of the mice, which was observed despite the reduced level of lipid peroxidation products, 4-hydroxynonenol, in the liver of animals supplemented with vitamin E and strawberry extract (1.34 +/- 0.4 and 1.6 +/- 0.5 nmol/g, respectively) compared to animals fed the control diet (2.35 +/- 1.4 nmol/g). However, vitamin E-supplemented mice had significantly lower lung viral levels following influenza infection, a viral challenge associated with oxidative stress. These and other observations indicate that, at present, the effects of dietary antioxidants are mainly demonstrated in connection with age-associated diseases in which oxidative stress appears to be intimately involved. Further studies are needed to determine the effect of antioxidant supplementation on longevity in the context of moderate caloric restriction.

Aging↗
PubMed1998

Specific suppression of human CD4+ Th cell responses to pig MHC antigens by CD8+CD28- regulatory T cells.

Evidence that T cells can down-regulate the immune response by producing or consuming certain cytokines or by lysing APCs or Th cells has been provided in various systems. However, the generation and characterization of suppressor T cell lines have met with limited success. Here we show that xenospecific suppressor T cells can be generated by in vitro stimulation of human T cells with pig APCs. Similar to allospecific suppressors, these xenospecific suppressor T cells carry the CD8+CD28- phenotype and react to MHC class I Ags expressed by the APCs used for priming. TCR spectratyping of T suppressor cells showed oligoclonal usage of TCR-Vbeta families, indicating that xenostimulation of CD8+CD28- T cells results in Ag-driven selection of a limited Vbeta repertoire. Xenospecific T suppressor cells prevent the up-regulation of CD154 molecules on the membrane of Th cells, inhibiting their ability to react against the immunizing MHC class II xenoantigens. The mechanism of this suppression, therefore, appears to be blockade of CD154/CD40 interaction required for efficient costimulation of activated T cells.

Animals↗
PubMed1998

HLA antibodies present in the sera of sensitized patients awaiting renal transplant are also reactive to swine leukocyte antigens.

BACKGROUND: To determine whether preformed HLA alloantibodies present in the sera of patients awaiting kidney transplantation will be detrimental to a potential porcine xenograft, we tested their cross-reactivity to swine leukocyte antigens (SLA). METHODS: Sera obtained from patients with varying levels of HLA sensitization (high panel-reactive antibodies > 70%, n= 7; moderate panel-reactive antibodies 30-40%, n=2) were analyzed. Pooled normal human AB sera and sera from nonsensitized patients (n=3) served as negative control. IgG was purified by protein-G chromatography, and xenoreactive natural antibodies (XNA) were depleted by passing the IgG through a series of melibiose and thyroglobulin-agarose columns. The elimination of XNA from HLA IgG preparations was confirmed by GS-IB4 lectin blocking assay and by an ELISA. RESULTS: IgG isolated from normal AB serum and three nonsensitized patients, which was depleted of XNA (HLA-IgG), did not react to human or porcine lymphocytes (peripheral blood mononuclear cells; PBMC) either by flow cytometry or by complement-dependent microcytotoxicity assays. However, HLA-IgG isolated from nine sensitized patients were reactive to a panel of porcine peripheral blood lymphocytes (n=6) by flow cytometry (>50 mean channel shift) and in complement-dependent microcytotoxicity assays in addition to their reactivity to human PBMC. The binding of HLA-IgG to porcine PBMC was significantly reduced by preabsorption with pooled human platelet concentrate. Further, the HLA IgG showed recognition of 45-kDa affinity-purified SLA class I on Western blots. CONCLUSIONS: This study demonstrates that HLA antibodies present in the sera of sensitized individuals can cross-react with SLA. Thus, xenotransplantation of porcine organs into HLA-sensitized patients has the potential to be rejected by humoral mechanisms. Testing to avoid such cross-reactive antibodies should be considered.

Animals↗
PubMed1998

Crystal structure of polygalacturonase from Erwinia carotovora ssp. carotovora.

The crystal structure of the 40-kDa endo-polygalacturonase from Erwinia carotovora ssp. carotovora was solved by multiple isomorphous replacement and refined at 1.9 A to a conventional crystallographic R-factor of 0.198 and Rfree of 0.239. This is the first structure of a polygalacturonase and comprises a 10 turn right-handed parallel beta-helix domain with two loop regions forming a "tunnel like" substrate-binding cleft. Sequence conservation indicates that the active site of polygalacturonase is between these two loop regions, and comparison of the structure of polygalacturonase with that of rhamnogalacturonase A from Aspergillus aculeatus enables two conserved aspartates, presumed to be catalytic residues, to be identified. An adjacent histidine, in accord with biochemical results, is also seen. A similarity in overall electrostatic properties of the substrate-binding clefts of polygalacturonase and pectate lyase, which bind and cleave the same substrate, polygalacturonic acid, is also revealed.

Amino Acid Sequence↗
PubMed1998

Distinct mechanism for antidepressant activity by blockade of central substance P receptors.

The localization of substance P in brain regions that coordinate stress responses and receive convergent monoaminergic innervation suggested that substance P antagonists might have psychotherapeutic properties. Like clinically used antidepressant and anxiolytic drugs, substance P antagonists suppressed isolation-induced vocalizations in guinea pigs. In a placebo-controlled trial in patients with moderate to severe major depression, robust antidepressant effects of the substance P antagonist MK-869 were consistently observed. In preclinical studies, substance P antagonists did not interact with monoamine systems in the manner seen with established antidepressant drugs. These findings suggest that substance P may play an important role in psychiatric disorders.

Adolescent↗
PubMed1998

Retrohoming of a bacterial group II intron: mobility via complete reverse splicing, independent of homologous DNA recombination.

The mobile group II intron of Lactococcus lactis, Ll.LtrB, provides the opportunity to analyze the homing pathway in genetically tractable bacterial systems. Here, we show that Ll.LtrB mobility occurs by an RNA-based retrohoming mechanism in both Escherichia coli and L. lactis. Surprisingly, retrohoming occurs efficiently in the absence of RecA function, with a relaxed requirement for flanking exon homology and without coconversion of exon markers. These results lead to a model for bacterial retrohoming in which the intron integrates into recipient DNA by complete reverse splicing and serves as the template for cDNA synthesis. The retrohoming reaction is completed in unprecedented fashion by a DNA repair event that is independent of homologous recombination between the alleles. Thus, Ll.LtrB has many features of retrotransposons, with practical and evolutionary implications.

Bacterial Proteins↗
PubMed1998

Elevated interleukin-12 in progressive multiple sclerosis correlates with disease activity and is normalized by pulse cyclophosphamide therapy.

Multiple sclerosis is postulated to be a Th1-type cell-mediated autoimmune disease. We investigated cytokine profiles in patients with progressive multiple sclerosis by using intracytoplasmic staining. We found increased IL-12 production by monocytes and increased IFN-gamma production by T cells in untreated patients as compared with controls. In patients treated with methotrexate, methylprednisolone, or cyclophosphamide/methylprednisolone (CY/MP), only CY/MP treatment normalized the elevated IL-12 production. Furthermore, CY/MP-treated patients had decreased IFN-gamma and increased IL-4, IL-5, and TGF-beta expression. Patients followed prospectively before and after starting CY/MP treatment showed a gradual decrease in IL-12 and IFN-gamma production and an increase in IL-4 and IL-5. In vitro, addition of 4-hydroperoxycyclophosphamide, a metabolite of cyclophosphamide decreased IL-12 production in mononuclear cell cultures. When patients were classified as having active or stable disease, IL-12 production correlated with disease activity. In summary, our results demonstrate a Th1-type cytokine bias in peripheral blood mononuclear cells of untreated progressive MS patients that is reversed by CY/MP treatment and is associated with Th2 and TGF-beta (Th3) type responses. These findings provide a basis for immune monitoring of patients with MS and suggest that treatments that downregulate IL-12 may prove to be beneficial in progressive MS.

Cyclophosphamide↗