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Biomedical subjects

S Allen

Publications and source records attributed to S Allen.

At least 73 records · Page 4Linked to original sources
PubMed2000

Ascorbate levels in red blood cells and urine in patients with sickle cell anemia.

UNLABELLED: Ascorbic acid can be important in sickle cell anemia (SCA) because significant oxidative stress occurs in the disease. Ascorbate could contribute to reduction of the increased oxygen free radicals generated in sickle red blood cells (SRBC) and to the recycling of vitamin E in the cells, while renal loss could contribute to the low plasma levels. Evaluation of red blood cell (RBC) and urine ascorbate in SCA has not been reported. Results showed (1) ascorbate levels in SRBC were similar to those in normals; (2) urine ascorbate excretion was increased in 36% of patients; (3) plasma levels of ascorbate were decreased. CONCLUSIONS: (1) Ascorbate is present in SRBC, most likely due to ascorbate recycling, despite increased free-radical generation. (2) The increase in renal excretion may contribute to the low plasma levels of ascorbate. (3) The presence of ample ascorbate in SRBC and decreased plasma ascorbate suggests that ascorbate movement across the SRBC membrane may differ from normal RBC.

Adult↗
PubMed2000

Knowledge of human papillomavirus infection among young adult men and women: implications for health education and research.

Human papillomavirus (HPV) infection of the genital tract is one of the most common sexually transmitted diseases (STDs), and a subset of genital tract HPVs are etiologically associated with cervical cancer. The prevalence of HPV infection is highest among adolescents and young adults. This study was undertaken to explore first year college students' knowledge about HPVs and to determine whether there were gender differences in this knowledge. An anonymous survey was distributed to all first year students at a private university. The results were analyzed by gender. We found that 96.2% of males and 95.4% of females had heard of genital warts, although only 4.2% of males and 11.6% of females knew that HPV caused genital warts. Although there was a greater awareness of genital warts than HPV in this population, students were uncertain about modes of transmission of both genital warts and HPVs, and unclear about the importance of HPV infection relative to other STDs. For both men and women (87% and 87.4%, respectively), health education classes were the major source of information about STDs. We conclude that health education should be reconceptualized to incorporate a better understanding of STDs, including HPV infection, by engaging adolescents and young adults in exploring the biological and social context of STDs, their public health importance, strategies for prevention, and the uncertainty of our scientific knowledge.

Adult↗
PubMed2000

Involvement of luminal bacteria, heat shock protein 60, macrophages and gammadelta T cells in dextran sulfate sodium-induced colitis in rats.

The in vivo immunological events in dextran sulfate sodium (DSS) -induced colitis were evaluated. Rats were fed water (control) or 5% DSS. Colonic sections were assessed by light microscopy, Gram stain, immunohistochemistry, and electron microscopy. A progressive decline in number and increase in fragmentation of bacteria in the colonic lumen was observed over time. Luminal bacteria were the first to show heat shock protein 60 (HSP60) staining (day 3). Macrophages in close proximity to these bacteria were next to show such staining (day 6), and finally the damaged epithelial cells when colitis became severe (day 15). Ultrastructural assessment showed cell-cell contact interactions between macrophages and dendritic gammadelta T cells. An increase in the number of gammadelta T cells and ED1-positive macrophages in the affected colonic tissue over time was documented. These results suggest colonic bacteria, host macrophages, and gammadelta T cells play specific roles in the immunological reactions in DSS-induced colitis, possibly via an HSP60-mediated mechanism.

Animals↗
PubMed2000

Increased defibrillation threshold with right-sided active pectoral can.

UNLABELLED: The aim of this study was to identify the optimal position on the chest wall to place an implant able cardioverter defibrillator in a two-electrode system, consisting of a right ventricular electrode and active can. METHODS AND RESULTS: Defibrillation thresholds (DFT) were measured in 10 anaesthetised pigs (weight 33-45 kg). An Angeflextrade mark lead was introduced transvenously to the right ventricular apex. The test-can (43 cc) was implanted submuscularly in each of four locations: left pectoral (LP), right pectoral (RP), left lateral (LL) and apex (A). The sequence in which the four locations were tested was randomized. Ventricular fibrillation (VF) was induced using 60 Hz alternating current. Rectangular biphasic shocks were delivered 10 seconds after VF induction. The DFT was measured using a modified four-reversal binary search. The results of the four configurations were: LP, 14.6+/- 4.0 J; RP, 18.8+/- 4.2 J; LL, 14.7+/- 4.1 J; A, 14.9+/- 3.1 J. Repeated measures analysis of variance showed that the DFT of RP was significantly higher than LP, LL and A (p < 0.05). CONCLUSIONS: Implanting an active can in the RP position increases the DFT by 29% compared to LP, LL and A sites. The can position on the left thorax does not appear to have a significant influence on DFT.

Animals↗
PubMed2000

A kinetic microassay for glutathione in cells plated on 96-well microtiter plates.

We describe a modified enzymatic, kinetic, glutathione microassay based on the original macroassay described by Tietze and modified by Anderson. It is coupled with the Triton X-100 lysis and an acid extraction that can be performed in 96-well microtiter plates. The microassay can be read in a microplate reader equipped with a standard 405 nm filter. Intracellular glutathione levels are not significantly different when comparing the proposed Triton X-100 lysis and acid extraction method from those found with the cellular homogenization and acid extraction method typically employed. By combining a rapid sample extraction method, which can be done on the microtiter plate, with an assay based on the technology of a microplate reader, we have devised a rapid, reproducible, inexpensive and easy to use GSH microassay that can process several hundred samples daily and will be useful in studies where many replicate samples are required. We have successfully used this method to monitor glutathione status in a human cell line exposed to organochlorine pesticides and cells exposed to naturally occurring mixtures of metals extracted from aquatic sediments.

Carcinoma, Hepatocellular↗
PubMed2000

Probing protein-peptide-protein molecular architecture by atomic force microscopy and surface plasmon resonance.

We demonstrate the creation of a protein multilayer which utilises the high affinity interaction between streptavidin and biotin and incorporates a peptidic spacer. Surface plasmon resonance measurements enabled us to monitor the construction of the multilayer in real time. Atomic force microscopy was utilised to determine surface functionality at each stage of the multilayer construction, allowing us to investigate the associated mechanical properties. In this context we observed an increase in biomolecular stretching on the formation of the multilayer. We demonstrate, utilising circular dichroism, that variations in the solvent can affect the secondary structure of the peptide linker and hence its mechanical properties. Trifluoroethanol titrations on the assembled system indicate that the multilayer properties are also stimuli responsive with regard to solvent conditions. These results indicate that the multilayer stretch before cleavage is increased in the presence of trifluoroethanol. This was not expected from the study of the individual linker alone, indicating the need to study the system as a whole as opposed to the isolated components.

Biosensing Techniques↗
PubMed2000

Reduction in defibrillation threshold using an auxiliary shock delivered in the middle cardiac vein.

Defibrillation in the middle cardiac vein (MCV) has been shown to reduce ventricular defibrillation thresholds (DFTs). Low amplitude auxiliary shock (AS) from an electrode sutured to the left ventricle at thoracotomy have also been shown to reduce DFT if delivered immediately prior to a biphasic shock (between the ventricular RV and superior vena caval (SVC) electrodes). This study investigates the impact on DFT of an AS shock from a transvenously placed MCV lead system. A standard defibrillation electrode was positioned in the RV in eight anesthetized pigs (35-43 kg). A 50 x 1.8-mm electrode was inserted in the MCV through an 8 Fr angioplasty guide catheter. A 150-V (leading edge) monophasic AS was delivered (95 microF capacitor) from the MCV-->Can with three different pulse widths (3, 5, 7 ms). A primary biphasic shock (PS) (95 microF capacitor, phase 1: 44% tilt, 1.6-ms extension and phase 2: 2.5-ms fixed duration) was delivered from the RV-->Can +/- AS. The four configurations were randomized and DFTs (PS + AS) assessed using a modified binary search. Ventricular fibrillation (VF) was induced with 60 Hz AC followed 10 seconds later by the test shock. The DFTs were compared using repeated measures analysis of variance (ANOVA). All configurations incorporating AS produced significant (P < 0.05) reduction in the DFT compared to no AS (13.8 +/- 7.4 J). There was no difference in the efficacy of differing pulse widths (P > 0.05); 3 ms (11.0 +/- 5.4 J), 5 ms (11.5 +/- 6.0), and 7 ms (10.6 +/- 5.3 J). In conclusion, delivering an AS from a transvenous lead system deployed in the MCV reduces the DFT by 23% compared to a conventional RV-->Can shock alone.

Analysis of Variance↗
PubMed2000

Rapid voluntary testing and counseling for HIV. Acceptability and feasibility in Zambian antenatal care clinics.

Voluntary testing and counseling (VTC) for HIV/AIDS is now widely accepted as an effective HIV prevention and control strategy among heterosexual couples in sub-Saharan Africa. The most appropriate format and venue for VTC remains a topic of debate among clinicians and public health professionals. Our research done in Lusaka, Zambia, took a tripartite approach to exploring the most acceptable format and venue for VTC: a community survey of attitudes towards VTC, a pre- and postcounseling knowledge survey, and a pilot study of same-day VTC in urban antenatal care clinics. A community survey of 181 individuals was conducted in July-August 1996 based on a structured questionnaire. A pre- and post-VTC intervention knowledge survey was conducted during the same period among 82 couples attending the Zambia-UAB HIV Research Project (ZUHRP) HIV VTC center in Lusaka. Finally, same-day HIV VTC was pilot tested in six antenatal clinic locations during February-May 1997 and June-August 1998. The community survey revealed that 98% of participants support promotion of HIV VTC in the community and 83.8% prefer the same-day testing format. The knowledge survey revealed misconceptions about discordance within a couple and perinatal transmission of HIV. Pilot testing in antenatal clinics was well received, with 84% of pregnant women requesting testing and 25% having positive HIV serologies. Women with primary school or less education, those seeking antenatal care in local clinics, and those seen before the third trimester of pregnancy were more likely to request HIV testing. Testing and counseling for HIV were shown to be feasible and effective in the antenatal clinic setting. Implementation of same-day HIV VTC in antenatal clinics is an effective strategy to prevent vertical transmission and should be expanded to include couples to leverage a decrease in heterosexual transmission as well.

Acquired Immunodeficiency Syndrome↗
PubMed2000

A multifilamented electrode in the middle cardiac vein reduces energy requirements for defibrillation in the pig.

OBJECTIVE: To compare the defibrillation efficacy of a novel lead system placed in the middle cardiac vein with a conventional non-thoracotomy lead system. METHODS: In eight pigs (weighing 35-71 kg), an electrode was advanced transvenously to the right ventricular apex (RV), with the proximal electrode in the superior caval vein (SCV). Middle cardiac vein (MCV) angiography was used to delineate the anatomy before a three electrode system (length 2 x 25 mm + 1 x 50 mm) was positioned in the vein. An active housing (AH) electrode was implanted in the left pectoral region. Ventricular fibrillation was induced and biphasic shocks were delivered by an external defibrillator. The defibrillation threshold was measured and the electrode configurations randomised to: RV-->AH, RV+MCV-->AH, MCV-->AH, and RV-->SCV+AH. RESULTS: For these configurations, mean (SD) defibrillation thresholds were 27.3 (9.6) J, 11.9 (2.9) J, 15.2 (4.3) J, and 21.8 (9.3) J, respectively. Both electrode configurations incorporating the MCV had defibrillation thresholds that were significantly less than those observed with the RV-->AH (p < 0.001) and RV-->SCV+AH (p < 0.05) configurations. Necropsy dissection showed that the MCV drained into the coronary sinus at a location close to its orifice (mean distance = 2.7 (2.2) mm). The MCV bifurcated into two main branches that drained the right and left ventricles, the left branch being the dominant vessel in the majority (6/7) of cases. CONCLUSIONS: Placement of specialised defibrillation electrodes within the middle cardiac vein provides more effective defibrillation than a conventional tight ventricular lead.

Analysis of Variance↗
PubMed2000

Characteristics of HLA class I and class II polymorphisms in Rwandan women.

OBJECTIVE: To define HLA class I and class II polymorphisms in Rwandans. METHODS: PCR-based HLA genotyping techniques were used to resolve variants of HLA-A, B, and C to their 2- or 4-digit allelic specificities, and those of DRB1 and DQB1 to their 4- or 5-digit alleles. RESULTS: Frequencies of 14 A, 8 C, and 14 B specificities and of 13 DRB1 and 8 DQB1 alleles were >/=0.02 in a group of 280 Rwandan women. These major HLA factors produced 6 haplotypes extending across the class I and class II regions: A*01-Cw*04-B* 4501-DRB1*1503-DQB1*0602 (A1-Cw4-B12- DR15 - DQ6), A * 01 - Cw * 04 - B * 4901 -DRB1 * 1302-DQB1*0604 (A1-Cw4-B21-DR13-DQ6), A*30 - Cw*04 - B*15 - DRB1*1101 - DQB1*0301 (A19-Cw4-B15-DR11-DQ7), A*68-Cw*07-B* 4901-DRB1*1302-DQB1*0604(A28-Cw7-B21- DR13 - DQ6), A*30 - Cw*07 - B*5703 - DRB1* 1303-DQB1*0301(A19 - Cw7 - B17 - DR13 - DQ7), and A*74-Cw*07-B*4901-DRB1*1302-DQB1* 0604 (A19-Cw7-B21-DR13-DQ6), respectively. Collectively, these extended haplotypes accounted for about 19% of the total. Other apparent class I-class II haplotypes (e.g., Cw*17-B*42-DRB1*0302-DQB1*0402, Cw*06- B*58-DRB1*1102-DQB1*0301, and Cw*03- B*15-DRB1*03011-DQB1*0201) did not extend to the telomeric HLA-A locus, and other 3-locus class I haplotypes (e.g., A*68-Cw*04-B*15, A*74-Cw*04-B*15, and A*23-Cw*07-B*4901) completely or partially failed to link with any specific class II alleles. DISCUSSION: Frequent recombinations appeared to occur between the three evolutionarily conserved HLA blocks carrying the class I and class II loci. The HLA class I profile seen in Rwandans was not directly comparable with those known in the literature, although the class II profile appeared to resemble those in several African populations. These data provide additional evidence for the extensive genetic diversity in Africans.

Alleles↗
PubMed2000

Treatment of spit tobacco users with transdermal nicotine system and mint snuff.

The purpose of this study was to examine the effects of nicotine patch and mint snuff (a nonnicotine product) on craving, withdrawal symptoms, and treatment outcome. This study involved a 2 x 2 factorial design, with Active Nicotine Versus Placebo Patch as one of the factors and Mint Snuff Versus No Mint Snuff as the other factor. Spit tobacco users (N = 402, n = 100-101 in each condition) were randomly assigned to 1 of the 4 treatment conditions for a period of 10 weeks. Treatment outcome was measured up to 62 weeks. The results showed that the nicotine patch was effective in increasing short-term abstinence over the placebo patch and in reducing craving and withdrawal signs and symptoms from spit tobacco. Although mint snuff was not effective in enhancing treatment outcome, it reduced craving and withdrawal symptoms. No interaction effects were observed. At this time, the use of the nicotine patch and mint snuff should be primarily considered for the reduction of craving and withdrawal symptoms.

Administration, Cutaneous↗
PubMed1999

The influence of epitope availability on atomic-force microscope studies of antigen-antibody interactions.

The ability of the atomic-force microscope (AFM) to detect interaction forces between individual biological molecules has recently been demonstrated. In this study, force measurements have been obtained between AFM probes functionalized with the beta-subunit of human chorionic gonadotrophin (betahCG) and surfaces functionalized with anti-betahCG antibody. A comparison of the obtained results with previous anti-ferritin antibody-binding data identifies differences when the antigen molecule expresses only a single epitope (betahCG), rather than multiple epitopes (ferritin), for the monoclonal antibodies employed. Specifically, the probability of observing probe-sample adhesion is found to be higher when the antigen expresses multiple epitopes. However, the periodic force observed in the adhesive-force distribution, due to the rupture of single antigen-antibody interactions, is found to be larger and more clearly observed for the mono-epitopic system. Hence, these findings indicate the potential of the AFM to distinguish between multivalent and monovalent antibody-antigen interactions, and demonstrate the influence of the number of expressed epitopes upon such binding studies.

Adhesiveness↗
PubMed1999

Typing of Leishmania lipophosphoglycans by electrospray mass spectrometry.

A method has been developed to identify the repeating phosphosaccharide units of Leishmania lipophosphoglycans using electrospray mass-spectrometry (ES-MS). Cone voltage-induced fragmentation of intact lipophosphoglycan was found to be as effective as analysis of mild acid hydrolysates in identifying the degree of modification of the repeating units of lipophosphoglycans derived from Leishmania mexicana and Leishmania major. This finding was exploited in a 'rapid-analysis' method in which a crude organic extract of approximately 2 x 10(9) L. major promastigote cells was loaded onto a reverse-phase cartridge for immediate elution into the mass-spectrometer. Using this approach, it was possible to identify the repeating units by total ion scanning and scanning for parents of the m/z 79 (PO3-) fragment ion. This approach is suitable for quick-typing of lipophosphoglycan repeats and was shown to detect alterations in repeat side chains caused by: (1) culturing L. major promastigotes in the presence of L-fucose; and (2) in vitro metacyclogenesis of L. major promastigotes. It is anticipated that the method will be applicable to small samples of cultured field isolates or genetically-manipulated strains.

Animals↗
PubMed1999

HLA class I homozygosity accelerates disease progression in human immunodeficiency virus type 1 infection.

Polymorphic products of HLA class I genes restrict cytotoxic T lymphocyte responses to the constantly evolving spectrum of HIV-1 antigens. Accordingly, homozygosity at class I loci can reduce the repertoire for such HLA-dependent interactions, leading to accelerated disease progression. To test this hypothesis we studied subjects from two distinct HIV/AIDS cohorts: 140 Dutch homosexual men and 202 Rwandan heterosexual women followed up to 13 years from HIV-1 seroconversion. We performed intermediate- and selective high-resolution molecular typing at HLA class I (A, B, and C) and high-resolution typing at HLA class II DRB1 and DQB1. Homozygosity at the HLA-A or -B locus or both was found at increasingly high frequency among individuals with successively more rapid progression to late-stage HIV-1-related conditions. In the combined cohorts (n = 342) the odds ratio (OR) due to HLA-A or -B antigen homozygosity in rapid versus slow progressors was 3.8 (p = 0.003); for Dutch men alone the OR was 3.5 (p = 0.102), and for Rwandan women the OR was 4.1 (p = 0.009). In contrast, homozygous genotypes at either HLA-C, DRB1, or DQB1 alone, or DRB1-DQB1 haplotypes, did not exert any deleterious effect on HIV-1 disease progression. These findings suggest strongly that diversity in addition to sequence specificity at HLA-A and -B loci can influence the rate of disease progression following HIV-1 infection.

Cohort Studies↗