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Biomedical subjects

M I Johnston

Publications and source records attributed to M I Johnston.

At least 19 recordsLinked to original sources
PubMed2002

HIV vaccine development.

Optimism prevails that a safe and at least partially effective HIV vaccine will be identified within this decade. Public, philanthropic and private sector efforts to expand the development pipeline and to indude candidates based on diverse HIV subtypes have proved successful. Yet both scientific and logistical obstacles remain. No vaccine candidate yet induces broadly neutralizing antibodies. The type, level, location and durability of immune responses necessary for protection remain unknown. For those vaccines that may not prevent HIV infection but control replication and prevent disease, the issue of transmissibility must be addressed. Other challenges indude improving infrastructure and research capabilities and establishing or strengthening regulatory agencies in developing countries. Another key issue is ensuring access to successful vaccines, which will require large-scale manufacturing and development of policies and processes to distribute vaccine to those most in need.

AIDS Vaccines↗
PubMed2001

Season of birth in females with anorexia nervosa in Northeast Scotland.

OBJECTIVE: To determine whether patients with anorexia nervosa exhibit an abnormal pattern in their season of birth. METHOD: Case records of female patients presenting to secondary services in Northeast Scotland from 1965 to 1997 who received a clinical diagnosis of anorexia nervosa were examined. The months of birth of the 446 anorexic patients with a confirmed diagnosis were compared with 5,766 female control subjects born locally in 1951, 1961, 1971, and 1981. RESULTS: Patients with anorexia nervosa had an excess of births in the first 6 months of the year (p =.013). The greatest excess was from March to June. DISCUSSION: This provides further evidence that birth dates of anorexics peak in the late spring and early summer. There are parallels with the epidemiology of schizophrenia. The evidence suggests that a seasonally fluctuating factor, most plausibly an intrauterine effect of common infectious agents during the winter months, is of etiological significance.

Adult↗
PubMed2001

Progress in HIV vaccine development.

Recent advances in HIV vaccine development include initiation of the first efficacy trials and substantial expansion of the preclinical pipeline. Several preclinical candidate vaccines have induced strong cellular immune responses and provided impressive protection against AIDS in non-human primate models; however, candidates that induce broadly neutralizing antibodies remain elusive.

AIDS Vaccines↗
PubMed2001

Optimism is growing as researchers move toward an AIDS vaccine.

Slow to start, the race for an effective AIDS vaccine now has more than 20 contenders, including some novel approaches that incorporate genetic engineering and the use of vectors, such as a canarypox that doesn't cause disease in humans. Researchers and public health officials say they are more optimistic than ever about the possibility of bringing an AIDS vaccine to market.

AIDS Vaccines↗
PubMed2000

The role of nonhuman primate models in AIDS vaccine development.

Although animal models have been useful in guiding vaccine development, HIV/AIDS models have not yielded a clear correlate of immunity nor given consistent results on the potential efficacy of various vaccine approaches. Further development and improved uniformity in the use of animal models would maximize their potential to meet the urgent worldwide need for a safe and effective HIV vaccine.

AIDS Vaccines↗
PubMed2000

Immunization. Update: search for an AIDS vaccine.

Identifying a successful HIV preventive vaccine is among the highest research priorities of the US NIH. While therapies for HIV have brought hope to those who are already HIV-infected, stopping the worldwide epidemic will require safe, effective HIV vaccines. Here, we describe scientific and other obstacles to attaining that goal and provide a brief synopsis of clinical trial results, recent preclinical results, and future priorities.

AIDS Vaccines↗
PubMed1999

Changes in the presenting features of females with anorexia nervosa in northeast Scotland, 1965-1991.

OBJECTIVE: Rates of anorexia nervosa among females presenting to specialist services in northeast Scotland had increased significantly between 1965 and 1991. We sought to elucidate possible causes of this change. METHOD: Hospital and primary care records were searched. Age, weight, and body mass index (BMI) were determined for 196 patients and duration of symptoms from onset to presentation was established in 190 cases. Changes in these parameters were investigated over the 27-year period of the study. RESULTS: There was no significant change in duration of illness or in age at presentation. BMIs increased significantly, but this arose because patients decreased in height, not because they increased in weight. There was no increase in seriously underweight patients with BMIs of < or =15. DISCUSSION: Anorexic females were not referred at an earlier stage of their illness, but primary care teams may be identifying and referring milder cases. Alternatively, the findings may reflect an increasing incidence of eating disorders coupled with changes in their presenting symptomatology.

Adult↗
PubMed1997

HIV vaccines: problems and prospects.

Several lines of evidence now argue strongly that a successful HIV vaccine does not need to block infection completely. It has to mimic what already occurs in a minority of unvaccinated individuals--namely, rapid clearance of infection or reduction of viral load to a level that does not produce symptoms or permit transmission to others. The various vaccine candidates are reviewed.

AIDS Vaccines↗
PubMed1995

Progress in AIDS vaccine development.

Because of a unique combination of challenges facing human immunodeficiency virus vaccine developers, a number of traditional and novel vaccine designs are being evaluated essentially in parallel. Monomeric proteins, poxvirus vectors, peptides, and particle-based candidate vaccines have entered or will soon enter human trials. Other designs are at earlier stages of development. All candidates evaluated to date in phase I/II human trials have proven safe and immunogenic. One or more of the most promising designs will soon progress to 'test of concept' clinical trials to determine efficacy.

AIDS Vaccines↗
PubMed1995

Increasing incidence of anorexia nervosa in the female population of northeast Scotland.

OBJECTIVE: The aim of the study was to determine whether there has been an increase in the incidence of anorexia nervosa in the female population in the northeast of Scotland since the 1960s. METHOD: Standardized diagnostic criteria were applied to the case records of female subjects who had been diagnosed as suffering from anorexia nervosa and had presented for the first time to psychiatric services between 1965 and 1991 or had been admitted for the first time to a general hospital between 1970 and 1991. Age-standardized annual incidence rates were calculated from 1965 through 1991. As a broad measure of severity, the weights of patients in 3 early years of the study, 1970-1972, were compared with those of patients in the last 3 years, 1989-1991. RESULTS: Over the 27-year period studied, 287 patients received confirmed diagnoses of anorexia nervosa, and the mean annual increase in incidence was 5.3%. The rate of increase was highly statistically significant. Comparison of weights at presentation showed a trend for patients presenting in 1970-1972 to be lighter than those presenting in 1989-1991. CONCLUSIONS: Rates of referral for female subjects with anorexia nervosa have greatly increased since the 1960s. These rates likely reflect a genuine increase in incidence, but the data suggest that less severely ill patients are now being referred.

Adolescent↗
PubMed1994

Recent advances in AIDS vaccine research and development.

There is an urgent need for a prophylactic vaccine to protect individuals from AIDS and to help abate the growing epidemic. In October 1993, the Conference on Advances in AIDS Vaccine Development reviewed the state-of-the-art in vaccine research and confirmed both the progress that has been made and the challenges that remain. Approximately 12 candidate vaccines are now in phase I/II clinical trials. To date, these products appear to be safe and capable of eliciting immune responses in vaccinees. Other vaccine strategies in development include the use of new formulations and the design of vaccine products capable of inducing a mucosal immune response. Progress has also been made in the establishment of domestic and international sites at which efficacy trials can be conducted when appropriate vaccine candidates are identified, and preparatory activities at these sites are ongoing. The possibility that one or more candidates may enter efficacy trials within the next 2 years underscores numerous issues that must be considered in preparation for these trials. These include the importance of ease of vaccine administration and cost, and an array of social, legal, and ethical issues of concern to those individuals who will be asked to participate in efficacy trials. The purpose of this article is to highlight recent advances in vaccine research and development and to define the complex factors that will impact the NIAID's position on advancing candidates into phase III trials.

AIDS Vaccines↗
PubMed1993

Present status and future prospects for HIV therapies.

Since the discovery of human immunodeficiency virus (HIV) in 1983, significant progress has been made toward the discovery, development, and licensing of anti-HIV drugs. In vitro screens against whole virus are now being complemented by screens against specific viral targets, resulting in the development of clinical candidates acting at several critical stages of the viral life cycle. Despite these advances, clinical therapy remains largely palliative. In addition, it has recently been recognized that HIV resistance to most drugs may pose even greater obstacles. Moreover, emerging data on immunopathogenesis raise the possibility that even if virus was eliminated from an infected individual, the patient's immune system might not be capable of restoration to normal function. In the face of such obstacles, deeper insights into the pathogenic mechanisms of disease, aggressive exploitation of those mechanisms for therapeutic gain, and continued commitment of both public and private sectors to support and collaborate in this research are needed.

AIDS Vaccines↗
PubMed1992

A model for the role of multiple cysteine residues involved in ribonucleotide reduction: amazing and still confusing.

Ribonucleotide reductase from Escherichia coli catalyzes the conversion of nucleotides to deoxynucleotides. Multiple cysteins have been postulated to play a key role in this process. To test the role of various cysteines in nucleotide reduction, a variety of single and double mutants of the R1 subunit were prepared: C754S, C759S, C754-759S, C462S, C462A, C230S, and C292S. Due to the expression system, each mutant contains small amounts of contaminating wt-R1 (estimated to be 1.5-3% based on activity). An epitope tagging method in conjunction with anion exchange chromatography was used to partially resolve the mutant R1 from the wt-R1. The interaction of these mutants with the normal substrate was studied, which allowed a model to be proposed in which five cysteines of the R1 subunit of RDPR play a role in catalysis. C754S and C759S R1s catalyze CDP formation at rates similar to wt-R1 when DTT is used as a reductant. However, when thioredoxin (TR)/thioredoxin reductase (TRR)/NADPH is used as reductant, the rates of dNDP production are similar to those expected for contaminating wt-R1 present as a heterodimer with the mutant. The impaired nature of these mutants with respect to reduction by TR suggests that their function is to transfer reducing equivalents from TR to the active site disulfide of R1 produced during NDP reduction. Single-turnover experiments, designed to avoid the problem of contaminating wt-R1, also support this role for C754 and C759. The double serine mutant of 754 and 759 has catalytic activity with DTT that is one-third the rate of wt-R1 with thioredoxin. C225 and C462 are thought to be the active site cysteines oxidized concomitantly with NDP reduction. Conversion of these cysteines to serines results in R1 mutants which convert the normal substrate into a mechanism-based inhibitor. C462SR1 upon incubation with R2 and [3'-3H,U-14C]UDP results in uracil release, 3H2O production, 3H,14C-labeled protein which has an absorbance change at 320 nm, and slow loss of the tyrosyl radical on R2. The isotope effect (kH/k3H) on 3' carbon-hydrogen bond cleavage is 1.7. This sequence of events is independent of the reductant, consistent with the postulate that C462 is an active site thiol. The C462AR1 has properties similar to C462SR1. Several additional mutant R1s, C230SR1, and C292SR1 were shown to have activities similar to wt-R1 with both TR/TRR/NADPH and DTT.

Base Sequence↗
PubMed1992

Interaction of C225SR1 mutant subunit of ribonucleotide reductase with R2 and nucleoside diphosphates: tales of a suicidal enzyme.

Ribonucleotide reductase (RDPR) from Escherichia coli is composed of two subunits, R1 and R2, both of which are required to catalyze the conversion of nucleotides to deoxynucleotides. This reduction process is accompanied by oxidation of two cysteines within the active site to a disulfide. One of these putative active site cysteines, C225, has been mutated to a serine, and the properties of this mutant (C225SR1) have been investigated in detail. Incubation of C225SR1 and R2 with [3'-3H,U-14C]UDP results in time-dependent inactivation of the enzyme! This inactivation is accompanied by production of 2.4 uracils, 3H2O, and 3H,14C-labeled protein with an absorbance change at 320 nm. There is an isotope effect (kH/k3H) on uracil production of 3.2. In addition, the tyrosyl radical on R2 is reduced. The observation of 3H2O, indicative of 3' carbon-hydrogen bond cleavage and loss of the tyrosyl radical, provides a direct test of our mechanistic hypothesis that cleavage of this bond occurs concomitantly with tyrosyl radical reduction. Incubation of [3'-2H]UDP with C225SR1 and R2 resulted in a V and V/K isotope effect on loss of the radical of 2.0 and 2.0, respectively. These studies provide the first direct evidence for protein radical involvement in catalysis. Reduction of the tyrosyl radical on R2 is accompanied by a stoichiometric cleavage of the R1 polypeptide into two new polypeptides of 26 and 61 kDa. The 26-kDa polypeptide is the N-terminus of R1, and hence cleavage of the polypeptide is occurring in the region of the mutation. The N-terminus of the 61-kDa polypeptide is blocked.(ABSTRACT TRUNCATED AT 250 WORDS)

Catalysis↗
PubMed1992

Computer-assisted structure-activity correlations of halodideoxynucleoside analogs as potential anti-HIV drugs.

Analysis of the structure-anti-HIV activity correlations of halo dideoxynucleosides (ddN's) in the public domain was accomplished through computer substructure searching, retrieval and sorting of in vitro anti-HIV data. In the survey, selectivity index (ratio of cytotoxicity to the potency in inhibiting HIV replication in vitro) was used to rank compounds in congeneric groups. Factors contributing to the anti-HIV activity, e.g. the nature and location of the halogen on the sugar or the base and its stereochemical configuration, could not be generalized for all the halogenated ddN's. Conclusions were drawn for specific classes within the pyrimidine and purine series, with compounds further divided into halo substitutions at the sugar 2',3',4'-positions or in the pyrimidine or purine ring systems. At the 3'-position, only a fluoro substitution enhanced the activity of the dideoxypyrimidine nucleosides. A 2'-ara fluoro substituent increased the activity of purine ddN's but decreased activity of pyrimidine ddN's. Halogenation of the side chain in acyclic adenine and 2,6-diaminopurine nucleosides improved their anti-HIV activity. Halo substitution at the 6- or 2'-ara position of selected purine ddN's resulted in compounds with increased lipophilicity, chemical stability and retention of anti-HIV activity. The number of halodideoxynucleosides tested as anti-HIV reagents suggested that this class of compounds is well studied.

Antiviral Agents↗
PubMed1990

Expression and biochemical characterization of human immunodeficiency virus type 1 nef gene product.

nef genes from human immunodeficiency virus type 1 isolates BH10 and LAV1 (lymphadenopathy-associated virus type 1) were expressed in Escherichia coli under the deo operon promoter. The two proteins found in the soluble compartment of the bacterial lysate were purified by ion-exchange column chromatography to apparent homogeneity. Determination of the amino-terminal sequence revealed glycine as the first amino acid in the Nef protein, indicating removal of the initiator methionine during expression in E. coli. Under native conditions, the recombinant Nef protein is a monomer of 23 kilodaltons. In denaturing polyacrylamide gels, however, BH10 and LAV1 Nef proteins migrate as 28 and 26 kilodaltons, respectively. GTP binding and GTPase activity were monitored during Nef protein purification. These activities did not copurify with the recombinant Nef protein from either the BH10 or the LAV1 isolate. Purified recombinant BH10 Nef protein was used as an immunogen to elicit mouse monoclonal antibodies. A series of monoclonal antibodies were obtained which reacted with sequences at either the amino or carboxy terminus of Nef. In addition, a conformational epitope reacting with native BH10, but not LAV1, Nef was isolated.

Amino Acid Sequence↗
PubMed1990

Effects of zidovudine on Friend virus complex infection in Rfv-3r/s genotype-containing mice used as a model for HIV infection.

Infection with the Friend virus complex (FV) in (B10.A x A/WySn)F1 mice containing the Rfv-3r/s genotype results in several disease manifestations analogous to those seen in patients with acquired immune deficiency syndrome, predominantly high levels of specific antibody and low levels of infectious virus with eventual retroviral disease-induced death of the host. Other immunologic manifestations of FV infection in this murine host included inhibition of percent total T, T-helper, and T-suppressor/cytotoxic cells of total splenic lymphocytes and phytohemagglutinin-induced response of spleen cells. Interleukin-1 production was not affected but the numbers of splenic B cells were increased by the infection. 3'-Azido-3'-deoxythymidine (zidovudine, AZT) administered (a) intraperitoneally three times daily for 24 days beginning 4 h after virus inoculation in doses of 60 to 480 mg/kg/day, (b) in drinking water for 22 days beginning 4 h after virus inoculation in doses of 22 to 216 mg/kg/day, or (c) in drinking water for 29 days beginning 6 days after virus inoculation in doses of 22 to 216 mg/kg/day markedly inhibited FV-induced disease. In the mice receiving early-initiated AZT therapy, FV-induced splenomegaly and hematocrit values were inhibited and infectious centers in the spleen and FV titers in the plasma were reduced to below detectable levels at the higher AZT dosage levels. The percent of total T cells in splenic lymphocytes was increased in the infected, AZT-treated mice. In the intraperitoneal experiment, FV disease-induced death was prevented by treatment with all doses of AZT. Neutralizing antibody to FV was significantly reduced in all AZT-treated groups. Toxicologic manifestations of these AZT treatments included splenic enlargement and reduced hematocrit, although all treated, uninfected mice survived the treatments, gained weight, and displayed no significant effects on enumeration of T and B cells.

Animals↗