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Biomedical subjects

S Martin

Publications and source records attributed to S Martin.

At least 325 records · Page 18Linked to original sources
PubMed1996

Acid sphingomyelinase-deficient human lymphoblasts and mice are defective in radiation-induced apoptosis.

Stress is believed to activate sphingomyelinase to generate ceramide, which serves as a second messenger in initiating the apoptotic response. Conclusive evidence for this paradigm, however, is lacking. In the present study, we used a genetic approach to address this issue directly. We show that lymphoblasts from Niemann-Pick patients, which have an inherited deficiency of acid sphingomyelinase activity, fail to respond to ionizing radiation with ceramide generation and apoptosis. These abnormalities are reversible up on restoration of acid sphingomyelinase activity by retroviral transfer of human acid sphingomyelinase cDNA. Acid sphingomyelinase knockout mice also expressed defects in radiation-induced ceramide generation and apoptosis in vivo. Comparison with p53 knockout mice revealed that acid sphingomyelinase-mediated apoptosis and p53-mediated apoptosis are likely distinct and independent. These genetic models provide definitive evidence for the involvement of acid sphingomyelinase in one form of stress-induced apoptosis.

Animals↗
PubMed1996

Dose response characteristics of methylphenidate on different indices of rats' locomotor activity at the beginning of the dark cycle.

Using a computerized infrared activity analysis system, the dose-response relationship, timing, and duration for stimulation of motor activity after a single dose of methylphenidate was studied in Sprague-Dawley rats. After 5 days of acclimation and 2 days of monitored baseline activity, rats received a single subcutaneous injection of vehicle or of 0.6, 2.5, 10 or 40 mg/kg methylphenidate 1 h into the dark cycle. Recording was then resumed for an additional 36 h. Five locomotor indices were analyzed. Each locomotor parameter monitored different aspects of motor activity. The doses of 2.5, 10 and 40 mg/kg significantly increased (P < 0.01) locomotor activity. The time to maximal effect (20, 50, and 90 min) and duration of effect (70, 210, and 280 min) increased with dose respectively. Ten mg/kg had the maximum effect on locomotor activity, while the largest dose, 40 mg/kg, elicited a more focused stereotyped activity that limited the amount of forward ambulation. Single injections of methylphenidate did not alter motor activity the next day. Pharmacological parameters and specific locomotor parameters describing the effects of methylphenidate at the beginning of the dark cycle can later be used in chronopharmacologic studies. They will also provide the basis for investigation of adaptive mechanisms during repeated or chronic administration of methylphenidate.

Analysis of Variance↗
PubMed1996

Evaluation of the flow cytometric crossmatch. Preliminary results of a multicenter study.

The flow cytometric crossmatch is a technique that is increasingly being used by clinical transplant laboratories. In this multicenter study by the British Society for Histocompatibility and Immunogenetics Flow Cytometry Group, a series of crossmatches were carried out to determine whether different centers obtained same results when performing the same crossmatch. There was greater than 80% agreement among participating laboratories on the results of 35/54 tests. There was no clear agreement in the remaining 20 cases. Quantitative analysis, estimating the number of cell-bound fluorescein molecules, demonstrated that differences in the criteria used by each center to define a positive crossmatch were responsible for some discordant results. When applied, definition of positivity based on the molecules of fluorescein increased concordance from 57.5% to 81.4%.l. These results suggest that a criterion for the interpretation of results based on quantitative analysis of bound antibody may be more reliable than methods in current routine use.

Flow Cytometry↗
PubMed1996

Importance of minimizing HLA-DR mismatch and cold preservation time in cadaveric renal transplantation.

Univariate and multivariate analyses have been performed on donor an d recipient variables to determine possible effects on the outcome of 516 primary cadaveric renal transplants performed in our single center from 1989 until 1993. The overall actuarial patient survival at 1 year and 5 years was 94.4% and 87.4%, respectively; the 1 year and 5 year graft survival rates were 88.3% and 77.8%, respectively. A total of 95 grafts were lost; death with function (35%) and chronic rejection (22%) were the major causes. Three variables (HLA-DR mismatch, delayed graft function, and prolonged cold ischemia time) had a significant detrimental effect on both short- and long-term graft survival. Zero HLA-DR mismatched grafts showed significantly enhanced survival over those with 1 HLA-DR mismatch both at 1 year (92.8% vs. 84.5%) and at 5 years (88.3% vs. 73.9%) only if cold ischemia time was less than 26 hours (P=0.0009). Occurrence of delayed graft function significantly lowered graft survival at both 1 year and 5 years (P=0.002), and the incidence was significantly associated with prolonged cold ischemia time (P<0.0001). HLA-A or HLA-B matching, percentage panel reactive antibodies (PRA), and anastomosis time showed no independent effect on long-term survival. The small number of 2 HLA-DR mismatched grafts (n=6) precluded separate analysis of this group. Acute rejection accounted for 12% of losses but had no statistically significant effect on graft survival, even though an increased frequency of rejection episodes was significantly associated with HLA-DR mismatch (P<0.0001). These results would suggest that significant survival benefits may be achieved by prospective HLA matching if cold ischemia times are limited. The efficiency of organ sharing must he improved to make optimal use of a limited resource.

Adolescent↗
PubMed1996

T cell immune responses to haptens. Structural models for allergic and autoimmune reactions.

Protein-reactive chemicals, metal salts and drugs, commonly classified as immunological haptens, are major environmental noxes targeted at the immune system of vertebrates. They may not only interfere with this defense system by toxicity alone, but more often by evoking hapten-specific immune responses resulting in allergic and eventually autoimmune responses. Here, we review recent developments in the analysis of the structural basis of hapten recognition, particularly by T lymphocytes, which represent central elements in cell-mediated, as well as in IgE dependent, allergies. A break-through in this field was the finding that T cells detect haptens as structural entities, attached covalently or by complexation to self-peptides anchored in binding grooves of major histocompatibility antigens (MHC-proteins). Synthetic hapten-peptide conjugates were shown to induce hapten-specific contact sensitivity in mice, opening new routes for studying hapten-induced immune disorders.

Amino Acid Sequence↗
PubMed1996

Analysis of major histocompatibility complex class I-restricted hapten recognition by mutation of the V-J joining of T cell receptor alpha chains.

Hapten-specific T cell responses are responsible for chemically induced immune disorders. However, the molecular details of hapten interactions with T cell receptors (TCR) are poorly understood. Recent studies of trinitrophenyl (TNP)-specific responses revealed major histocompatibility complex-associated TNP-peptides as dominant epitopes for CD8+ and CD4+ T cells. The present study is based on the observation that two H-2Kb/TNP-specific CTL clones (II/7 and III/1), differing exclusively in two amino acids of their TCR alpha chains, also differed in their carrier specificities for various TNP-peptides. The genes of the two alpha chains and the common beta chain were cloned into expression vectors. Transfection of the TCR alpha chain of clone III/1 into a hybridoma of clone II/7 also transferred the fine specificity of clone III/1, indicating that the small alpha chain variations were indeed responsible for the different carrier specificities. Point mutations bridging the difference between the alpha chains of clones II/7 and III/1 and functional studies of the respective TCR alpha beta transfectants into a TCR-negative hybridoma revealed an unexpected result: the two receptors did not represent examples of structural complementarity for different sets of hapten-peptide conjugates; rather, they resembled two structures of principally similar specificity but of significantly different overall affinity. This was demonstrated more directly by comparing the fine specificities of III/1 transfectants expressing or not expressing the co-receptor CD8: the CD8-negative III/1 transfectant assumed a specificity pattern indistinguishable from that of a CD8-expressing, II/7-derived transfectant. Hence, comparable alterations of antigen recognition may be induced either by subtle TCR alterations or by removal of CD8, i.e. by the presence or absence of a non-polymorphic adhesion molecule.

Amino Acid Sequence↗
PubMed1996

HLA-associated inverse correlation between T cell and antibody responsiveness to islet autoantigen in recent-onset insulin-dependent diabetes mellitus.

Insulin-dependent diabetes mellitus (IDDM) is a T cell-dependent immune-mediated disease. Recently, a novel islet cell antigen (ICA69) recognized by autoantibodies was described. We tested T cell responsiveness to ICA69 in peripheral blood of patients with recent onset IDDM (n = 46), patients with long-standing IDDM (n = 44), non-diabetic age-matched, islet cell autoantibody- and glutamic acid decarboxylase (GAD)65 antibody-negative first-degree relatives of IDDM patients (n = 15) and rheumatoid arthritis patients (n = 22). T cell responsiveness was significantly higher in recent onset IDDM patients, compared to IDDM patients post-disease onset, non-diabetic first degree relatives and rheumatoid arthritis patients (p < 0.001). In responding IDDM patients a significant inverse correlation between T cell and autoantibody responsiveness to ICA69 was observed (p < 0.0005). Immunogenetic evaluation revealed an association of HLA-DR3 with T cell responsiveness to ICA69 (p < 0.02) and absence of ICA69-reactive autoantibodies (p < 0.04). The increased T cell reactivity to ICA69 in the absence of antibody reactivity at onset of IDMM is associated with an HLA class II immune response gene, and therefore suggestive of a genetically controlled selective activation of T helper subsets to a specific autoantigen in humans.

Antibody Formation↗
PubMed1996

Differential expression of ICAM-1 and LFA-1 versus L-selectin and VCAM-1 in autoimmune insulitis of NOD mice and association with both Th1- and Th2-type infiltrates.

The infiltration of pancreatic islets by mononuclear cells is the hallmark of the development of insulin dependent diabetes mellitus (IDDM) in the NOD mouse, an animal model for human IDDM. The aim, of this study was to correlate adhesion molecule expression with the degree of islet infiltration and to compare Th1- and Th2-driven islet inflammation. Cryostat sections of NOD mouse pancreata before and after diabetes development were analysed by semiquantitative immunohistochemistry. NOD mouse islets did not show the expression of ICAM-1, LFA-1, L-selectin and VCAM-1 prior to infiltration by mononuclear cells. Furthermore, islets with early stage insulitis (grade 1, periinsular location of small infiltrates) still were devoid of adhesion molecule expression. ICAM-1 and LFA-1 were first demonstrable in islets with strong periinsular infiltrates (insulitis grade 2) while L-selectin and VCAM-1 were only seen in islets with mild or strong intraislet infiltration (grade 3-4). Adhesion molecules were demonstrable in areas of macrophage and T-lymphocyte infiltrates but not in adjacent endocrine islet tissue. Islets of all infiltration stages contained Th2 lymphocytes (positive for IL-4). Substantial numbers of Th1 cells (positive for IFN-gamma, TNF-alpha, IL-2 and/or IL-2 receptor) were observed only after acceleration of diabetes development by a single injection of cyclophosphamide (250 mg/kg i.p.). Interestingly, the adhesion molecule expression pattern in islets with "Th1' versus "Th2 insulitis' was not different. In conclusion, the expression of adhesion molecules in islets during the development of autoimmune diabetes does not precede mononuclear infiltration but probably occurs in response to the activation of initial small infiltrates. ICAM-1 and LFA-1 expression is seen prior to L-selectin and VCAM-1. However, adhesion molecule expression during Th1 versus Th2 cell infiltration is very similar, suggesting similar adhesion molecule requirements of the two Th subsets.

Animals↗
PubMed1996

Acute Myocardial Infarction in Canada: New Epidemiologic Insights on Incidence, Therapy, and Risk.

Objective: To define the changing incidence, risk, and therapy of acute myocardial infarction (A311). Data sources: Review of contemporary AMI data from the University of Alberta Hospitals, six other sites of the Clinical Quality Improvement Network (CQIN), and other Canadian and international centers. Data synthesis: Ischemic heart disease is age-related and the Canadian population is rapidly aging. At the University of Alberta Hospitals, the incidence of Q wave AMI (per 100,000 population) in 1985 was 113 and has remained unchanged (NS) since that time (129 in 1994). In contrast, the combined incidence of non.Q-wave AMI and unstable angina has increased markedly, from 74 in 1985 to 226 in 1994 (p < 0.05). The use of proven efficacious therapies for AMI has greatly increased in recent years, with thrombolytic drugs being given to approximately 35;percnt; of all patients by 1993; and beta-blockers and aspirin to 75;percnt; and 98;percnt; of patients, respectively. However, females and patients older than 70 years' despite their greater risk, received significantly less efficacious medication than males and younger AMI patients. The use of calcium antagonists decreased from a peak utilization rate of 60;percnt; for all AMI patients in 1989 to less than 10;percnt; by 1993. In-hospital AMI mortality risk has also decreased in the last several years, particularly among higher risk older patients (35;percnt;, 1987 vs. 19;percnt;,1993). In a population of 3896 consecutive AMI patients, recruited largely in 1992 and 1993 from seven CQIN sites, logistic regression analyses revealed aspirin was associated with the greatest relative risk reduction (61%); beta-blocker and thrombolytic therapy were related to risk reductions of 55;percnt; and 16;percnt;, respectively. Incremental age was the most important factor associated with increased relative risk in AMI, overall and in both sexes; sex was not an independent risk predictor. Qualitatively very similar AMI incidence, risk, and treatment data have also been recently observed in other centers in Canada, the United States, and elsewhere. Conclusions: Although widespread primary or secondary prevention is possibly contributory, the recent static incidence of Q-wave AMI and the marked increase in unstable angina and non-Q-wave AMI are more likely due to enhanced health awareness and diagnosis-seeking behavior in the population at risk. The decline in AMI mortality, at least for high-risk acute care patients, is compatible with a clinically relevant secondary prevention effect. There are still, however, windows of opportunity to further improve AMI outcomes by increasing the utilization of proven efficacious therapy, especially among women and older patients. Another particularly attractive epidemiologic benefit in the immediate future would accrue from the further development and effective use of efficacious therapies directed against unstable angina and n-Q-wave AMI.

Journal Article↗
PubMed1996

Pentoxifylline, a phosphodiesterase inhibitor, induces immune deviation in patients with multiple sclerosis.

The outcome of immune responses can be predicted by the lymphokine production pattern of the participating cells. Cytokines of the T helper type 1 (Th1) cells mediate inflammatory responses and delayed-type hypersensitivity (DTH), whereas Th2-like T cells predominantly produce cytokines, which stimulate antibody production by B cells. Immunoregulatory therapy of autoimmune diseases with unknown antigens may be achieved by inhibiting the production of inflammatory cytokines and induction of protective cytokines of Th2-like T cells. To determine the immunoregulatory capacity of the phosphodiesterase inhibitor pentoxifylline (PTX), which is known to suppress the production of tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma), this drug was used in mitogen and antigen-stimulated lymphocyte cultures as well as in patients with multiple sclerosis. PTX significantly decreased TNF-alpha and interleukin-12 (IL-12), whereas it increased IL-4 and IL-10 production. In addition, PTX inhibited cell proliferation, which was associated with a marked reduction in CD25 (IL-2 receptor alpha-chain) and CD54 (intercellular adhesion molecule-1; ICAM-1) expression. Increasing doses of PTX significantly reduced TNF-alpha and IL-12 mRNA expression of blood mononuclear cells, but increased IL-4 and IL-10 expression in eight patients with relapsing-remitting multiple sclerosis. These results indicate that PTX modulates immune reactions favouring a Th2-like response and may therefore be useful for the treatment of autoimmune diseases with a dominant Th1-like T cell response.

Autoimmune Diseases↗
PubMed1996

Explaining variations in inpatient length of stay in the National Health Service.

This paper seeks to explain variations in acute inpatient length of stay in the National Health Service in England. A model is proposed in which the length of stay is allowed to vary according to patient characteristics, the local supply of NHS care. the local pressure on NHS resources, other non-NHS health care supply factors, and local policy effects. Length of stay data are obtained from the 1991/1992 Hospital Episode Statistics. They are standardized for age, sex and broad specialty group, and are aggregated to the level of small areas with populations of about 10,000. Explanatory variables include socio-economic data from the 1991 Census of Population, health status data, waiting time data, measures of access to inpatient and GP services, and measures of local private health care provision. The paper finds that variability in length of stay is greatest in the over-65 age group. The most important determinants of variations in length of stay are access to NHS hospitals, access to private hospitals, waiting times for elective surgery, indicators of poverty, and indicators of the availability of informal care.

Analysis of Variance↗
PubMed1996

Does warming local anesthetic reduce the pain of subcutaneous injection?

The most frequent complaint noted with the use of lidocaine (or other amide local anesthetic) is stinging or burning pain associated with subcutaneous infiltration. The purpose of this study was to evaluate the efficacy of warming buffered lidocaine for reducing the pain of infiltration. Forty adult volunteers were entered into a randomized, crossover study conducted at a community teaching hospital. Blinded subjects underwent 1-mL subcutaneous injections of the study agent through 27-gauge needles over 30 seconds. Following a crossover protocol, "room temperature" buffered lidocaine (20 degrees C) was injected into one midvolar forearm and "body temperature" buffered lidocaine (37 degrees C) into the opposite arm. The order and the handedness of the two injections were randomized; an independent observer prepared the anesthetic solutions. Pain was assessed using a 100-mm visual analog pain scale and subjects' comparison of pain on injection. Twenty subjects (50%) reported that 20 degrees C buffered lidocaine was more painful and 17 (42.5%) reported that the 37 degrees C solution was more painful (sign test, P = .74). Similarly, a median pain score difference of 5.0 mm favoring 37 degrees C lidocaine was not statistically significant (sign rank test, P = .42). The order or the initial side of the injection did not influence the pain scores. The study had a power of 80% to detect a 10-mm difference between the two solutions at alpha = .05. These results suggest that warming buffered lidocaine to body temperature (37 degrees C) does not reduce the pain of subcutaneous infiltration.

Adult↗
PubMed1996

T and B cell crossmatching using three-colour flow cytometry.

We have developed a highly sensitive method for the simultaneous crossmatching of T and B cells using three-colour flow cytometry. This method identifies T and B cell populations in a lymphocyte sample and analyses each for the presence of bound patient IgG alloantibodies. A fluorescein isothiocyanate conjugated rabbit anti-human IgG antibody was used to detect bound IgG following incubation of donor lymphocytes with patient serum. R-phycoerythrin conjugated anti-human CD19, and Quantum Red conjugated anti-human CD3 monoclonal antibodies were used to detect T and B cell populations, respectively. A comparison of results between conventional and three-colour flow cytometry crossmatches showed that there was no difference in detection of bound IgG between the two methods for ten test sera, doubling dilutions of a positive control serum and 72 donor-recipient pairs. Three-colour flow cytometry has proved particularly helpful in determining whether an antibody is directed against donor T and/or B cells and was shown to be more sensitive than complement-dependent cytotoxicity assay in eight out of 72 crossmatches.

B-Lymphocytes↗
PubMed1996

The glucose transporter (GLUT-4) and vesicle-associated membrane protein-2 (VAMP-2) are segregated from recycling endosomes in insulin-sensitive cells.

Insulin stimulates glucose transport in adipocytes by translocation of the glucose transporter (GLUT-4) from an intracellular site to the cell surface. We have characterized different synaptobrevin/vesicle-associated membrane protein (VAMP) homologues in adipocytes and studied their intracellular distribution with respect to GLUT-4. VAMP-1, VAMP-2, and cellubrevin cDNAs were isolated from a 3T3-L1 adipocyte expression library. VAMP-2 and cellubrevin were: (a) the most abundant isoforms in adipocytes, (b) detectable in all insulin responsive tissues, (c) translocated to the cell surface in response to insulin, and (d) found in immunoadsorbed GLUT-4 vesicles. To further define their intracellular distribution, 3T3-L1 adipocytes were incubated with a transferrin/HRP conjugate (Tf/HRP) and endosomes ablated following addition of DAB and H2O2. While this resulted in ablation of > 90% of the transferrin receptor (TfR) and cellubrevin found in intracellular membranes, 60% of GLUT-4 and 90% of VAMP-2 was not ablated. Immuno-EM on intracellular vesicles from adipocytes revealed that VAMP-2 was colocalized with GLUT-4, whereas only partial colocalization was observed between GLUT-4 and cellubrevin. These studies show that two different v-SNAREs, cellubrevin and VAMP-2, are partially segregated in different intracellular compartments in adipocytes, implying that they may define separate classes of secretory vesicles in these cells. We conclude that a proportion of GLUT-4 is found in recycling endosomes in nonstimulated adipocytes together with cellubrevin and the transferrin receptor. In addition, GLUT-4 and VAMP-2 are selectively enriched in a postendocytic compartment. Further study is required to elucidate the function of this latter compartment in insulin-responsive cells.

3T3 Cells↗