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Biomedical subjects

M Allen

Publications and source records attributed to M Allen.

At least 127 records · Page 7Linked to original sources
PubMed1995

Toxicity of particulate silicon carbide for macrophages, fibroblasts and osteoblast-like cells in vitro.

There is widespread interest in the use of interfacial layers in the preparation of diamond and diamond-like carbon (DLC) coatings. These DLC coatings deposited onto metal substrates with a silicon carbide (SiC) interfacial layer exhibit improved adhesion and show promise as wear-retardant coatings for biomedical implants. Although the DLC coatings show excellent biocompatibility in vitro, they may be susceptible to damage within the biological environment, leading to exposure of the interfacial silicon carbide. We have investigated the effects of two forms of silicon carbide (alpha-SiC and beta-SiC) on macrophages, fibroblasts and bone cells in vitro. Both alpha- and beta-SiC are well-tolerated by cells at concentrations of up to 0.1 mg/ml but cause severe cytotoxicity at a concentration of 1 mg/ml. If SiC is to be used as an interfacial layer on biomedical implants, the quality of the DLC coating must be optimised to minimise the risk of film breakdown.

Adhesiveness↗
PubMed1994

A photochemical model of the martian atmosphere.

The factors governing the amounts of CO, O2, and O3 in the martian atmosphere are investigated using a minimally constrained, one-dimensional photochemical model. We find that the incorporation of temperature-dependent CO2 absorption cross sections leads to an enhancement in the water photolysis rate, increasing the abundance of OH radicals to the point where the model CO abundance is smaller than observed. Good agreement between models and observations of CO, O2, O3, and the escape flux of atomic hydrogen can be achieved, using only gas-phase chemistry, by varying the recommended rate constants for the reactions CO + OH and OH + HO2 within their specified uncertainties. Similar revisions have been suggested to resolve discrepancies between models and observations of the terrestrial mesosphere. The oxygen escape flux plays a key role in the oxygen budget on Mars; as inferred from the observed atomic hydrogen escape, it is much larger than recent calculations of the exospheric escape rate for oxygen. Weathering of the surface may account for the imbalance. Quantification of the escape rates of oxygen and hydrogen from Mars is a worthwhile objective for an upcoming martian upper atmospheric mission. We also consider the possibility that HOx radicals may be catalytically destroyed on dust grains suspended in the atmosphere. Good agreement with the observed CO mixing ratio can be achieved via this mechanism, but the resulting ozone column is much higher than the observed quantity. We feel that there is no need at this time to invoke heterogeneous processes to reconcile models and observations.

Atmosphere↗
PubMed1994

Biphasic effects of intraaccumbens mu-opioid peptide agonist DAMGO on locomotor activities.

The effects of bilateral microinjections of mu-opioid receptor agonist DAMGO (0.00, 0.01, 0.1, or 1.0 microgram/side) were tested in rats for 120 min in activity monitors. The horizontal movement, rearing, and stereotypy times in seconds were measured during 12 consecutive 10-min time blocks. DAMGO (0.01, 0.1, and 1.0 microgram) resulted in biphasic effects, inhibition followed by activation for each of the three measures. These data replicate the behavioral effects of ICV DAMGO except that the duration of the behavioral effects were longer with Acb injections.

Amino Acid Sequence↗
PubMed1994

A comprehensive polymerase chain reaction-oligonucleotide typing system for the HLA class I A locus.

A comprehensive system for genetic typing of the HLA class I A locus is described, based on PCR amplification and typing with nonradioactively labeled SSO probes. Exons 1-3 of the A locus are amplified and typing is performed with a set of 30 nonradioactively labeled oligonucleotide probes. This system resolves 34 of 39 known alleles and 561 (94%) of 595 possible genotypes. Among a sample of 354 individuals from Sweden and China, 97.5% of the genotypes were resolved. Probes were directed preferentially at replacement substitutions in foreign antigen-binding sites, in order to detect not only the known alleles but also new combinations of polymorphic motifs, indicative of previously unrecognized alleles. Three individuals were found with a new combination of polymorphic motifs, suggesting the presence of at least one previously undescribed allele in the populations sampled. This typing system is useful for disease association studies, tissue typing, and in forensic medicine.

Base Sequence↗
PubMed1994

Association of susceptibility to multiple sclerosis in Sweden with HLA class II DRB1 and DQB1 alleles.

The association of MS with HLA class II alleles was studied by PCR-based typing of the DQA1, DQB1, DRB1, and DPB1 loci in 94 Swedish patients with relapses and remissions of the disease. The haplotype DRB1*1501-DQA1*0102-DQB1*0602 was found to be positively associated and three haplotypes were found to be negatively associated with MS. Linkage disequilibrium makes it difficult to assess whether DRB1 or DQB1 plays the primary role in the disease association, while the association with DPB1 and DQA1 appears to be secondary to that of DQB1 and DRB1. Two of the three haplotypes negatively associated with MS carry the DQB1*0301 allele. Also, the negatively associated DRB1*0401-DQA1*0301-DQB1*0301 haplotype differs from those with nonassociated DRB1*0401-DQA1*0301-DQB1*0302 haplotype only at DQB1. These results suggest that DQB1 alleles, as well as some DRB1 alleles, are involved in susceptibility and protection to MS. In searching for sequence motifs in the DR beta chain associated with MS susceptibility, all DRB1 alleles on haplotypes positively associated with MS, including the DRB1*1501, were found to encode a Val at position 86 of the DR beta chain. Also, DRB1 alleles that are negatively associated with MS all encode a Gly at position 86, suggesting that the residue at position 86 may be critical in conferring susceptibility and protection to MS. Finally, when the effect of the DRB1*1501 haplotype was removed there was no support for the hypothesis that MS is associated with a putative DQ-alpha beta heterodimer, encoded for by certain DQA1 and DQB1 alleles.

Alleles↗
PubMed1994

The effects of diamond-like carbon coatings on macrophages, fibroblasts and osteoblast-like cells in vitro.

The elaboration of metallic and polymeric particles from the wear of joint replacement components is widely implicated in the pathogensis of aseptic loosening of these implants. Diamond-like carbon (DLC) coatings show great potential as wear-retardant coatings and may offer a possible solution to this problem. We have studied the effects of DLC coatings on cells derived from the tissues that surround a total joint replacement (macrophages, fibroblasts and osteoblast-like cells). There was no evidence that DLC coatings, deposited on a variety of different substrates, caused cytotoxicity in vitro. Cells grown on the coated substrates exhibited normal cellular growth and morphology. DLC coatings are biocompatible in vitro and should now be tested in animal models to determine their behaviour in vivo.

Animals↗
PubMed1994

Lactate dehydrogenase activity as a rapid and sensitive test for the quantification of cell numbers in vitro.

Lactate dehydrogenase (LDH) has been used extensively as a marker for cell death both in vitro and in vivo. The release of LDH into tissue culture medium accurately reflects cell viability in vitro. We have investigated the relationship between cell concentration and total LDH activity in samples of cell lysate. Although there are differences in the amount of LDH present in different cell types, the total enzyme activity in a sample of cell lysate is directly proportional to the concentration of cells in the sample. The measurement of LDH activity in vitro provides a sensitive, accurate and cost-effective alternative to the use of either radioisotopic or dye-based assays for the determination of cell numbers.

Animals↗
PubMed1994

Correlation of perinatal transmission of human immunodeficiency virus type 1 with maternal viremia and lymphocyte phenotypes.

OBJECTIVE: To determine whether maternal transmission of human immunodeficiency virus (HIV) is correlated with increased quantities of HIV, decreased frequencies of CD4+ T cells, or increased levels of CD8+ T cells in the transmitting mother. METHODS: Peripheral blood obtained from HIV-infected women at different times during pregnancy was used to measure quantitative cell-associated HIV-1 and CD3+CD4+ and CD3+CD8+ proportions; the plasma was used to perform measurements of quantitative viremia by culture and subsequently to measure quantitative HIV-1 ribonucleic acid levels. These measurements were analyzed with respect to their association with HIV transmission to the baby, which occurred in one fourth of the cases. The children were also studied to determine whether HIV-1 was detected near birth or not until 1 to 8 weeks of life. RESULTS: Increased clonal frequencies of HIV-1-infected peripheral blood mononuclear cells were found in mothers of infected children; fivefold fewer cells were required for a positive culture result (median cell numbers of 10(4.5) vs 10(5.2); p = 0.008). Higher frequencies of infected cells were seen in mothers of babies with evidence of infection at birth than in mothers of infected babies without evidence of infection at birth (p < 0.05). Plasma viremia was measured in 10% of cultures without regard to whether the mothers transmitted virus to their babies. Increased levels of ribonucleic acid as detected by the branched-chain DNA method were measurable more often (45% vs 17%) in the mothers of infected children than in mothers of uninfected children. Proportions of CD4+ and CD8+ T cells were indistinguishable in these two groups of women. CONCLUSIONS: Increased viremia was present in mothers who transmitted HIV to their offspring. This variable could be used to select women at highest risk of transmitting HIV to their offspring for treatment to decrease the HIV burden five-fold.

CD4-CD8 Ratio↗
PubMed1994

Breast augmentation surgery: a women's health issue.

Surgery to increase breast size is a common procedure. In this paper we examine the reasons why women choose to undergo the procedure, the history of breast enhancement, current surgical approaches, possible complications and their treatment. Driving forces behind the choice to have augmentation surgery appear to be related to feelings of low self-esteem and self-confidence. Although there is a large literature related to breast augmentation, little of it is research-based. The research that there is focuses on complications and their treatment, with an emphasis on capsular contracture. Few of the studies are long-term, although complications have been noted as long as 25 years after initial implantation. There is a need for research into the experience of women undergoing augmentation mammaplasty but, perhaps more importantly, there is also a need to examine ways in which women can be helped to accept themselves as they are.

Breast Implants↗
PubMed1994

Immunohistochemical detection of a novel 22- to 25-kilodalton glycoprotein of Paracoccidioides brasiliensis in biopsy material and partial characterization by using species-specific monoclonal antibodies.

Two murine monoclonal antibodies (MAbs) specific to Paracoccidioides brasiliensis (as determined by enzyme-linked immunosorbent assay [ELISA] and Western blot [immunoblot]) were produced by using a modification of standard hybridization protocols, with cyclophosphamide included as an immunomodulator to abolish responses to highly cross-reactive immunodominant epitopes. MAbs PS14 and PS15 are two different clones which exhibit similar characteristics by ELISA and Western blot. They are directed against a 22- to 25-kDa antigen which is present in P. brasiliensis and which could not be identified in other dimorphic fungi by ELISA or Western blot. Partial purification of the antigen was accomplished by isoelectric focusing, and deglycosylation studies suggested that the 22- to 25-kDa antigen is a glycoprotein with a pI of between 4.5 and 5 and that O-linked sugars may be part of the recognized epitope. The MAbs stained the cytoplasm of P. brasiliensis yeast and hyphal cells in cryostat sections of fresh cultures of the fungus. In addition, the MAbs stained the wall of paracoccidioidomycotic granulomas, as well as the cytoplasm of the fungus, as determined by the use of immunofluorescence, immunoperoxidase, and immuno-alkaline phosphatase staining techniques in paraffin-embedded sections of human biopsy material, and they failed to stain granulomas resulting from other clinical conditions. These findings suggest that these MAbs have potential use in the immunohistochemical identification of P. brasiliensis.

Adrenal Glands↗
PubMed1994

PCR-based DNA typing of saliva on stamps and envelopes.

In forensic cases involving mail bombs, extortion, kidnapping or threatening letters, biological evidence such as the saliva used to attach the stamp and seal the envelope could be used for genetic analysis. We have developed a highly sensitive semi-nested PCR method for the HLA-DRB1 locus; suitable for the analyses of very limited amounts of DNA. When applied to a set of stamps and envelopes with saliva from control individuals, typing results were consistent with those obtained using hairs drawn from the same individuals. No interference was found due to DNA from the fingerprints of people handling the letters. The system was applied to three forensic cases with threatening letters. The first case resulted in an exclusion of the suspect. In the second case, the suspect could not be excluded (probability of identical genotype by chance > 0.01). These results demonstrate that biological evidence in cases with threatening letters is amenable to genetic typing.

Base Sequence↗
PubMed1994

Prolonged endurance exercise and sleep disruption.

To determine whether exercise duration effects the recovery sleep following exercise, eight fit male endurance athletes, ages 23-42 yr, had their sleep electrophysiologically studied. This was done on four separate occasions: after a day on which no specific exercise was performed; after a day of a 15-km run; after a 42.2-km run day; after a day in which the athletes participated in a strenuous ultra-triathlon. Sleep patterns following the no exercise day and the 15-km and the 42.2-km run days were similar. The sleep pattern of the ultra-triathlon day when compared with the other three days showed significantly increased wakefulness and delayed and decreased rapid eye movement (REM) sleep. The duration of slow wave sleep (SWS) in the first 6 h after lights out, however, was no different. The increased wakefulness and decreased REM clearly indicate increased stress after the ultra-triathlon. REM sleep appears to be a more sensitive index of exercise induced stress than SWS.

Adult↗
PubMed1994

A simple inpatient psychiatric clinical information system designed and developed by clinicians.

OBJECTIVE: The growth of computer technology allows clinicians to develop a separate information system to replace inefficient paper-based approaches to documenting clinical care. METHODS: A clinician team developed a system to replace standard paper forms using computer software running on 486 PC computer. Clinicians, directing the project at every step, refined handwritten forms to create a complete word processor application merging information from an individual database. RESULTS: A system developed outside the traditional hospital information system simplifies the generation of a variety of required inpatient documents (treatment plans, progress notes, patient lists, and treatment summaries). A wide variety of clinicians converted from a traditional paper-based approach to the computer system. CONCLUSIONS: Computer technology allows the local development of an information system oriented toward clinical needs. Hospital clinical information systems will benefit from the input of clinicians with experience designing a computerized solution.

Clinical Medicine↗
PubMed1994

A study of the pharmacologic treatment of medication-compliant schizophrenics who relapse.

BACKGROUND: Maintenance antipsychotic medications greatly diminish the risk of relapse in schizophrenic patients. A significant number, however, will relapse despite ongoing drug treatment. This is a report of a pilot study of a group of schizophrenic patients who relapsed despite having been compliant with treatment. METHOD: The authors studied 32 schizophrenic patients who had been compliant with pharmacologic treatment but who had suffered a relapse and were admitted to the hospital. Maintained on their usual pharmacologic treatment, they also received in a double-blind fashion either fluphenazine or placebo. Clinical assessments were done on Day 1 and Day 10. RESULTS: The authors found no effect of additional neuroleptic treatment on outcome. Two-thirds of the subjects showed at least moderate improvement during the study. Subjects who were experiencing greater severity of depression on admission were more likely to improve. There was no association between baseline ratings of psychosis and outcome. CONCLUSION: This study offers preliminary evidence that increasing the dose of neuroleptic does not improve outcome in schizophrenics who have relapsed while taking antipsychotic medications. Most of these patients will improve during the course of a brief hospitalization.

Adult↗
PubMed1993

Structure-based design of inhibitors of purine nucleoside phosphorylase. 3. 9-Arylmethyl derivatives of 9-deazaguanine substituted on the methylene group.

X-ray crystallography and computer-assisted molecular modeling (CAMM) studies aided in the design of a potent series of mammalian purine nucleoside phosphorylase (PNP) inhibitors. Enhanced potency was achieved by designing substituted 9-(arylmethyl)-9-deazaguanine analogs that interact favorably with all three of the binding subsites of the PNP active site, namely the purine binding site, the hydrophobic pocket, and the phosphate binding site. The most potent PNP inhibitor prepared during our investigation, (S)-9-[1-(3-chlorophenyl)-2-carboxyethyl]-9-deazaguanine (18b), was shown to have an IC50 of 6 nM, whereas the corresponding (R)-isomer was 30-fold less potent.

Binding Sites↗
PubMed1993

Minisatellite variant repeat mapping: application to DNA typing and mutation analysis.

Most DNA typing systems assay allele length variation at tandemly repeated loci such as minisatellites and microsatellites. Allele length measurements are approximate, which impedes the use of such loci in forensic analysis and in studies of allelic variability at hypervariable loci. We now review progress in the development of alternative DNA typing systems based on allelic variation in the interspersion patterns of variant repeat units along minisatellite alleles. Minisatellite variant repeat mapping by PCR (MVR-PCR) not only provides a powerful new digital approach to DNA typing, but also for the first time allows investigation of the true level of allelic variability at minisatellite loci and of the mutational mechanisms that generate ultravariability.

Alleles↗