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Biomedical subjects

R J O'Brien

Publications and source records attributed to R J O'Brien.

At least 37 records · Page 2Linked to original sources
PubMed1998

The use of restriction fragment length polymorphism (RFLP) analysis for epidemiological studies of tuberculosis in developing countries.

DNA fingerprinting, of which restriction fragment length polymorphism (RFLP) typing is the most common method used, has permitted novel investigations of the epidemiology and pathogenesis of tuberculosis. The use of IS6110, an insertion sequence which is present in Mycobacterium tuberculosis, is generally considered to be the standard RFLP method, but other molecular typing techniques may be used as adjuncts in selected circumstances. A number of epidemiologic studies using RFLP typing have been done in both industrialized and developing countries. The major findings include the confirmation or identification of chains of transmission (of both drug-sensitive and drug-resistant strains of tuberculosis), distribution of strain clusters within populations, differentiation of relapse from exogenous reinfection, better understanding of the pathogenesis of tuberculosis, identification of laboratory cross-contamination, and insight into the molecular evolution of the species. For developing countries, where the burden of tuberculosis is greatest, three major areas of investigation for the use of RFLP analysis in epidemiologic studies of tuberculosis have been identified: 1) community transmission, 2) nosocomial transmission, and 3) human immunodeficiency virus (HIV)-related tuberculosis. Elements of protocols are suggested which can be used by investigators to perform well-designed epidemiologic studies which will be relevant to developing countries and which are likely to have an impact on control programmes in these settings.

AIDS-Related Opportunistic Infections↗
PubMed1997

The development of excitatory synapses in cultured spinal neurons.

Immunohistochemical studies of synapses in the CNS have demonstrated that glutamate receptors (GluRs) are concentrated at postsynaptic sites in vivo and in vitro (Baude et al., 1995). The mechanisms leading to receptor clustering at excitatory synapses are far less understood than those governing acetylcholine receptor accumulation at the neuromuscular junction () or glycine receptor aggregation at central inhibitory synapses (). Using cultured rat spinal cord neurons, we demonstrate that clustering of the AMPA receptor subunit GluR1 is among the earliest events in excitatory synapse formation in vitro, coincident with the onset of miniature EPSCs and in many cases preceding presynaptic vesicle accumulation. Postsynaptic receptor clustering is induced in a highly specific and reiterative pattern, independent of receptor activation, by contact with a subset of axons capable of inducing receptor clusters. The subunit composition of AMPA receptor clusters varied significantly between neurons but was invariant within a given neuron. The presence of either GluR2 or GluR3 was common to all receptor clusters. Neither high-affinity glutamate transporters nor NMDA receptors appeared to be concentrated with AMPA receptor subunits at these excitatory synapses.

ATP-Binding Cassette Transporters↗
PubMed1997

Redistribution and stabilization of cell surface glutamate receptors during synapse formation.

Although the regulation of neurotransmitter receptors during synaptogenesis has been studied extensively at the neuromuscular junction, little is known about the control of excitatory neurotransmitter receptors during synapse formation in central neurons. Using antibodies against extracellular N-terminal (N-GluR1) and intracellular C-terminal (C-GluR1) domains of the AMPA receptor subunit GluR1, combined with surface biotinylation and metabolic labeling studies, we have characterized the redistribution and metabolic stabilization of the AMPA receptor subunit GluR1 during synapse formation in culture. Before synapse formation, GluR1 is distributed widely, both on the surface and within the dendritic cytoplasm of these neurons. The diffuse cell surface pool of receptor appears to be mobile within the membrane and can be induced to cluster by the addition of N-GluR1 to live neurons. As cultures mature and synapses form, there is a redistribution of surface GluR1 into clusters at excitatory synapses where it appears to be immobilized. The change in the distribution of GluR1 is accompanied by an increase in both the half-life of the receptor and the percentage of the total pool of GluR1 that is present on the cell surface. Blockade of postsynaptic AMPA and NMDA receptors had no effect on the redistribution of GluR1. These results begin to characterize the events regulating the distribution of AMPA receptors and demonstrate similarities between synapse formation at the neuromuscular junction and at excitatory synapses in cultured neurons.

Animals↗
PubMed1997

GRIP: a synaptic PDZ domain-containing protein that interacts with AMPA receptors.

AMPA glutamate receptors mediate the majority of rapid excitatory synaptic transmission in the central nervous system and play a role in the synaptic plasticity underlying learning and memory. AMPA receptors are heteromeric complexes of four homologous subunits (GluR1-4) that differentially combine to form a variety of AMPA receptor subtypes. These subunits are thought to have a large extracellular amino-terminal domain, three transmembrane domains and an intracellular carboxy-terminal domain. AMPA receptors are localized at excitatory synapses and are not found on adjacent inhibitory synapses enriched in GABA(A) receptors. The targeting of neurotransmitter receptors, such as AMPA receptors, and ion channels to synapses is essential for efficient transmission. A protein motif called a PDZ domain is important in the targeting of a variety of membrane proteins to cell-cell junctions including synapses. Here we identify a synaptic PDZ domain-containing protein GRIP (glutamate receptor interacting protein) that specifically interacts with the C termini of AMPA receptors. GRIP is a new member of the PDZ domain-containing protein family which has seven PDZ domains and no catalytic domain. GRIP appears to serve as an adapter protein that links AMPA receptors to other proteins and may be critical for the clustering of AMPA receptors at excitatory synapses in the brain.

Amino Acid Sequence↗
PubMed1997

Association between leprosy and HIV infection in Tanzania.

SETTING: An epidemiological study of the interaction of leprosy and HIV infection in Tanzania. OBJECTIVE: To establish the prevalence of HIV infection among leprosy patients, and to measure the association of HIV and leprosy by comparing the HIV prevalence in leprosy patients and blood donors. DESIGN: Testing for HIV infection in consecutively diagnosed leprosy patients (new and relapsed after MDT) in all regions in Tanzania successively for a period of 3 to 6 months during 1991, 1992 and 1993. RESULTS: Out of the total estimated eligible leprosy patients, 697 patients (69%) entered the final analysis. The HIV prevalence among these leprosy patients was 12% (83/697) as compared to 6% (8960/ 158,971) in blood donors examined in Tanzania during the same period. There were no significant differences in HIV seroprevalence by age, sex, residence or type of disease. However, the adjusted odds ratio (OR) of the presence of a BCG scar was 1.9 [95% confidence interval (CI) 1.1-3.3] among HIV-positive leprosy cases compared to HIV-negative leprosy cases. Comparing leprosy cases with blood donors as controls, the logistic regression model, controlling for sex, age group and residence, showed the OR for HIV seropositivity among leprosy patients to be 2.5 (95% CI 2.0-3.2). This association existed in all strata, but was strongest in the 15-34-year age group. No difference of HIV status between multibacillary and paucibacillary leprosy could be shown to exist. The point estimate of the population attributable risk of HIV infection for leprosy was 7%. CONCLUSION: HIV infection is associated with leprosy and might reverse the epidemiological trend of the slow decline in case notification in Tanzania if HIV infection is increasing greatly. Previous BCG vaccination loses its protection against leprosy in the presence of HIV infection. A repeated study is recommended in order to validate these findings, whereby recording of the disability grading of the cases is necessary to adjust for delay in diagnosis.

Adolescent↗
PubMed1996

Characterization of multiple phosphorylation sites on the AMPA receptor GluR1 subunit.

We have characterized the phosphorylation of the glutamate receptor subunit GluR1, using biochemical and electrophysiological techniques. GluR1 is phosphorylated on multiple sites that are all located on the C-terminus of the protein. Cyclic AMP-dependent protein kinase specifically phosphorylates SER-845 of GluR1 in transfected HEK cells and in neurons in culture. Phosphorylation of this residue results in a 40% potentiation of the peak current through GluR1 homomeric channels. In addition, protein kinase C specifically phosphorylates Ser-831 of GluR1 in HEK-293 cells and in cultured neurons. These results are consistent with the recently proposed transmembrane topology models of glutamate receptors, in which the C-terminus is intracellular. In addition, the modulation of GluR1 by PKA phosphorylation of Ser-845 suggests that phosphorylation of this residue may underlie the PKA-induced potentiation of AMPA receptors in neurons.

Amino Acid Sequence↗
PubMed1996

An epidemiological study of tuberculosis and HIV infection in Tanzania, 1991-1993.

OBJECTIVE: In Tanzania during the past 6 years reported tuberculosis (TB) cases have nearly doubled, with proportionately much greater increases in smear-negative and extrapulmonary cases compared with smear-positive cases. At the same time, HIV infection has become widespread throughout the country. This survey was undertaken in order to study the association of TB and HIV and to determine the impact of HIV on present and future TB cases in Tanzania. METHODS: The survey design provided for HIV testing of a representative country-wide sample of approximately one-sixth of all new and relapse cases registered between January 1991 and December 1993, with linkage to demographic, clinical and bacteriological data for these cases. HIV surveillance data were used for comparison purposes. RESULTS: A total of 6928 TB cases from all of the country's 20 mainland regions were tested. The overall HIV seroprevalence was 32%. Both crude and adjusted odds ratios (OR) for HIV infection were higher in women, those aged 25-44 years, urban residents, cases of smear-negative and extrapulmonary disease, and persons with a bacille Calmette-Guérin (BCG) vaccination scar. The age-and sex-adjusted relative risk for HIV infection in TB patients compared to blood donors in the same regions was 7.1 (95% confidence interval, 6.6-7.5), and was significantly higher among those aged 25-34 years. Of 3360 patients with bacteriological culture results 46% were culture-positive for Mycobacterium tuberculosis. Drug susceptibility tests were performed on 1164 isolates with the overall rate of drug resistance of 6.2%. Rates of initial resistance were low in both HIV-positive (4%) and HIV-negative (5.8%) patients. Rates of acquired resistance were higher (19% overall) and did not vary significantly by HIV serostatus. Initial combined resistance to both isoniazid and rifampicin was uncommon (0.4%) as was monoresistance to rifampicin (0.3%). CONCLUSIONS: The higher OR for women and young adults reflect the higher rates of HIV infection in those populations. The finding that smear-positive relapse cases were no more likely to have HIV infection than new smear-positive cases suggests that the treatment regimen for new cases is effective in HIV-associated TB. The low rates of both initial and acquired drug resistance in HIV-positive patients is further evidence of adequacy of treatment. The higher relative risk for HIV infection among patients aged 25-34 years suggests increased HIV-related TB transmission. Finally, it is estimated that approximately two-thirds of the increase in the rate of smear-positive tuberculosis in the country can be directly attributed to HIV infection.

Adult↗
PubMed1994

Preventive therapy of tuberculosis with rifapentine in immunocompetent and nude mice.

The effectiveness of intermittent administration of rifapentine (RPT), with or without isoniazid (INH), for preventive therapy of tuberculosis was evaluated in immunocompetent (normal) and nude mice. After infection with a small inoculum of Mycobacterium tuberculosis H37Rv, normal mice developed a chronic and nonfatal infection, and the bacterial population became relatively stable after an initial period of limited multiplication. On the other hand, nude mice developed an acute and fatal infection, and all untreated mice died within 5 wk, with very high colony-forming-unit (CFU) counts in their organs. Various degrees of bactericidal activity were shown in normal mice after daily treatment with rifampin (RMP) plus pyrazinamide (PZA) for 13 wk, INH daily for 26 wk, or RPT once weekly for 13 or 26 wk or once fortnightly for 26 wk. The activity of RPT was significantly enhanced when INH was added at the same dosing frequency. In nude mice the response of M. tuberculosis infection to certain regimens was less favorable than that in normal mice, suggesting that preventive therapy may be less effective in severely immunodeficient hosts even during treatment. After chemotherapy was stopped, virtually all nude mice relapsed within 12 wk regardless of the regimen administered, whereas no or very few relapses were observed in normal mice that had been treated with RMP+PZA daily for 13 wk, or RPT alone or RPT+INH once weekly for 26 wk. The latter three regimens and RPT+INH once weekly for 13 wk may be applied for fixed-duration preventive therapy in human immunodeficiency virus (HIV)-negative subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

[Compliance and tolerance of new antitubercular short-term chemopreventive regimens in childhood--a pilot project].

Efficacy of preventive chemotherapy in tuberculosis-infected children depends to a great extend on medical compliance and drug tolerability. Two new short-course chemoprevention-regimes of tuberculosis--four months Rifampin (A) and two months Rifampin plus Pyrazinamide (B)--were compared with the well established regimen of six months Isoniacid (C). 150 children (mean age 3.6 years with Tb conversion) were randomly allocated to these three regimens. 13 patients were non-compliant, in terms of interview, urinary INH-test strips, urine colour and prescription frequency: 7 in group C and 3 in group A and B, respectively. Adverse effects were observed in 5 patients: 3 in group C and 1 in group A and B. 1 child (group B) developed tuberculosis two years after stopping short course chemoprevention. Good compliance (94%) as well as neglectable risks of adverse effects (2%) justify further controlled studies to evaluate the efficacy of short course chemoprevention in childhood.

Adolescent↗
PubMed1994

Drug-resistant tuberculosis: etiology, management and prevention.

Drug-resistant Mycobacterium tuberculosis inevitably arises from inadequate or inappropriate drug taking or drug prescribing, effectively resulting in monotherapy. This may occur in the patient being treated (acquired resistance) or in a patient who has been infected by another patient with drug resistant tuberculosis (primary resistance). There is some evidence that multidrug-resistant tuberculosis, ie, resistance to both isoniazid and rifampin, is increasing in the United States and in other countries where unsupervised treatment with rifampin has been common. Human immunodeficiency virus (HIV) infection and acquired immune deficiency syndrome (AIDS), although not causing drug-resistant tuberculosis, have certainly magnified the problem, especially in New York City. Treatment of drug-resistant tuberculosis must be based on results of drug susceptibility studies. Patients with isolated isoniazid-resistant tuberculosis respond well to modified short-course therapy with rifampin, ethambutol, and pyrazinamide. Multidrug-resistant disease is more difficult to treat, although most patients will respond to regimens of second-line drugs if the infecting organisms are susceptible to these agents. Drug-resistant tuberculosis can be prevented by accurate identification of patients with newly diagnosed tuberculosis who may be at increased risk of primary drug resistance, the administration of an appropriate treatment regimen to all newly diagnosed patients, the application of fully supervised therapy during at least the initial phase of treatment, the use of combination preparations of drugs, and the proper management of failure and relapse cases.

AIDS-Related Opportunistic Infections↗
PubMed1993

Effectiveness of rifampin, rifabutin, and rifapentine for preventive therapy of tuberculosis in mice.

To identify alternative regimens for preventive therapy of tuberculosis, the pharmacokinetics and antimicrobial activities of rifampin (RMP), rifabutin (RBT), and rifapentine (RPT) were compared in BCG-vaccinated and M. tuberculosis-infected immunocompetent mice. RPT showed the highest serum peak level (Cmax) and the longest half-life (t1/2), whereas RBT displayed the lowest Cmax and the shortest t1/2. On weight-to-weight basis, both RPT and RBT were more bactericidal than RMP. The activity of RMP was significantly reduced when the frequency of administration was reduced from six to three times weekly, whereas significant bactericidal activity was still observed in mice treated with RPT, 10 mg/kg up to once fortnightly, or RBT, 10 mg/kg twice weekly. Because the bactericidal activity of RBT, 10 mg/kg six times/wk for 6 wk, or RPT, 10 mg/kg two times/wk for 12 wk, was comparable to that of RMP, 10 mg/kg six times/wk for 12 wk in mice, the two regimens are appropriate for clinical trials of preventive therapy of tuberculosis.

Animals↗
PubMed1992

Usefulness of skin testing with mycobacterial antigens in children with cervical lymphadenopathy.

One hundred twenty-three children with chronic cervical lymphadenopathy were skin-tested with purified protein derivative (PPD)-B (Mycobacterium intracellulare), PPD-Y (Mycobacterium kansasii), PPD-G (Mycobacterium scrofulaceum) (nontuberculous mycobacterial antigens (NTMags)) and PPD-T (Mycobacterium tuberculosis). Children with culture-confirmed mycobacterial disease had significantly larger reactions to NTMags and were 6 times more likely to have PPD-B responses of greater than or equal to 10 mm than those with negative microscopy/culture results. Children with acid-fast bacilli present in clinical specimens but with negative culture results were 3 times more likely to have greater than or equal to 10 mm induration to PPD-B than those with negative microscopy/culture results. In all groups except those with culture-confirmed M. tuberculosis, responses to PPD-T were significantly smaller than those to the NTMags. We conclude that NTMags, particularly PPD-B, may be useful in diagnosing childhood mycobacterial cervical adenopathy; however, their usefulness in distinguishing disease caused by M. tuberculosis from that resulting from other mycobacteria is unknown.

Adolescent↗
PubMed1992

Evaluation of the clinical usefulness of mycobacterial skin test antigens in adults with pulmonary mycobacterioses.

A double-blind, multicenter study was conducted to evaluate the usefulness of mycobacterial skin test antigens for the specific diagnosis of adult pulmonary mycobacterial disease. The skin test antigens used were PPD-T (M. bovis) and PPD-B (M. intracellulare), made bioequivalent to 5 TU PPD-S through bioassay in human subjects. Of the 192 adults (18 yr of age or older), those with disease caused by M. tuberculosis (MTB) had significantly larger reactions to PPD-T than did those with disease caused by nontuberculous mycobacteria (NTM) or those with negative culture results (NEG)(13.41 mm versus 4.87 and 4.96 mm, respectively, p less than 0.001). The mean induration to PPD-B in NTM was not different from that in MTB or NEG. Defining a "positive" to be greater than or equal to 10 mm induration and a size difference of greater than or equal to 3 mm between PPD-T and PPD-B, the sensitivity, specificity, and positive predictive value (PPV) for PPD-T in diagnosing MTB versus NTM was 29, 90, and 75%. Corresponding values for PPD-B and NTM disease were 70, 61, and 64%. Dual testing was less useful in distinguishing disease caused by any of the mycobacteria from NEG. Although the sensitivity of PPD-B, made bioequivalent to PPD-S, was high, the specificity and PPV were low. We conclude that this preparation of PPD-B is no more useful in distinguishing adult pulmonary disease caused by NTM than is PPD-T alone.

Double-Blind Method↗