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Biomedical subjects

A Kumar

Publications and source records attributed to A Kumar.

At least 55 records · Page 3Linked to original sources
PubMed1992

Differential effect of ultraviolet-B radiation on certain metabolic processes in a chromatically adapting Nostoc.

The impact of UV-B radiation on growth, pigmentation and certain physiological processes has been studied in a N2-fixing chromatically adapting cyanobacterium, Nostoc spongiaeforme. A brownish form (phycoerythrin rich) was found to be more tolerant to UV-B than the blue-green (phycocyanin rich) form of N. spongiaeforme. Continuous exposure to UV-B (5.5 W m-2) for 90 min caused complete killing of the blue-green strain whereas the brown strain showed complete loss of survival after 180 min. Pigment content was more strongly inhibited in the blue-green strain than in the brown. Nitrogenase activity was completely abolished in both strains within 35 min of UV-B treatment. Restoration of nitrogenase occurred upon transfer to fluorescent or incandescent light after a lag of 5-6 h, suggesting fresh synthesis of nitrogenase. Unlike the above processes, in vivo nitrate reductase activity was stimulated by UV-B treatment, the degree of enhancement being significantly higher in the blue-green strain. Like the effect of UV-B on nitrogenase, 14CO2 uptake was also completely abolished by UV-B treatment in both strains. Our findings suggest that UV-B may produce a deleterious effect on several metabolic activities of cyanobacteria, especially in cells lacking phycoerythrin. Strains containing phycoerythrin appear to be more tolerant to UV-B, probably because of their inherent property of adapting to a variety of light qualities.

Adaptation, Physiological↗
PubMed1992

Bilateral branch vein occlusion.

Bilateral branch retinal vein occlusion is a relatively rare occurrence. We report 4 patients who presented with bilateral branch retinal vein occlusion and in each of these cases the fellow eyes were involved within 6 months of the initial episode. The patients were relatively young and all of them had associated essential hypertension. The patients maintained a relatively good visual acuity through a 6-months to 1-year follow-up. This report highlights this rare entity, the associated risk factors and visual prognosis.

Adult↗
PubMed1992

Aspergillus antigen-induced eosinophil differentiation in a murine model.

Eosinophilia is a prominent feature of the cellular response in allergic and parasitic diseases. Allergic bronchopulmonary aspergillosis due to colonization of the lungs of some asthmatics with Aspergillus fumigatus is characterized by high levels of serum immunoglobulin E and peripheral blood (PB) and lung eosinophilia. This study investigates the role of eosinophils in the pathogenesis of allergic bronchopulmonary aspergillosis by using a mouse model. BALB/c mice were immunized intranasally and intraperitoneally with A. fumigatus antigens (Ag), and the eosinophils in PB and bone marrow (BM) were enumerated. Eosinophilopoiesis in BM cultures was studied in the presence of murine recombinant interleukin-5 (mrIL-5) and supernatants from pokeweed mitogen-stimulated spleen cells as the source of eosinophil differentiation factors. Eosinophils were quantitated by direct counting and by estimating eosinophil peroxidase activity. The results indicate that the percentage of eosinophils in the PB (5.77 +/- 1.17) and the BM (11.19 +/- 4.31) of mice exposed to A. fumigatus Ag was higher than in controls (PB, 2.42 +/- 0.76; BM, 5.12 +/- 2.79; P less than 0.01 for both). Similarly, a significant increase in eosinophils was observed in the BM population from mice exposed to A. fumigatus Ag compared with that in controls when cultured with murine recombinant interleukin-5 (23.13 +/- 7.14 versus 13.77 +/- 5.79, P less than 0.01), indicating that the mice exposed to A. fumigatus Ag had significantly greater numbers of eosinophil precursors in their BM. This study demonstrates that A. fumigatus Ag may be involved in the in vivo commitment of stem cells in the eosinophil differentiation pathway.

Animals↗
PubMed1992

Binding of a host cell nuclear protein to the stem region of human immunodeficiency virus type 1 trans-activation-responsive RNA.

Human immunodeficiency virus type 1 (HIV-1) transcription is regulated by both viral and host cell factors. Although the viral trans-activator protein, Tat, and its cis-responsive element, trans-activation-responsive (TAR) RNA, have been identified and characterized, the mechanism of HIV-1 transcriptional regulation has not been satisfactorily described. Whereas Tat is necessary to activate transcription, additional factors, derived from the host cell, are important in regulating HIV-1 transcription. To identify such host cell-specific factors, we used an RNase protection mobility shift assay and UV cross-linking to detect a 140-kDa HeLa cell nuclear protein that binds specifically to TAR RNA. By extensive mutational analysis, we determined that the binding of this protein is dependent on both the sequence and the structure of the TAR RNA stem region. Other groups have shown that the production of prematurely terminated transcripts from the HIV-1 promoter is also dependent on the sequence and structure of the TAR RNA stem. This correlation with our results suggests that the TAR RNA stem-binding protein is involved in the production of prematurely terminated transcripts from the HIV-1 promoter and in the regulation of HIV-1 gene expression.

Base Sequence↗
PubMed1992

Human immunodeficiency virus type 1 Tat-mediated trans activation correlates with the phosphorylation state of a cellular TAR RNA stem-binding factor.

Protein kinase C (PKC) is involved in the mitogenic stimulation of cell proliferation and has recently been reported to be essential for Tat-mediated trans activation. We have determined that RNA binding of a cellular factor which specifically interacts with the trans-activation response region (TAR) is blocked in cells depleted of PKC activity by chronic phorbol myristate acetate stimulation. We also show that nuclear extracts can be depleted of the cellular TAR-binding factor by in vitro treatment with purified protein phosphatase 2A. Furthermore, TAR RNA-binding activity can be partially restored to depleted nuclear extracts in vitro by addition of PKC. Chimeric constructs in which the Tat protein is artificially tethered to viral RNA show PKC independence for Tat-mediated trans activation. Specific mutations in the TAR RNA stem region which cause reduced binding of host cell factor in vitro also cause reduced Tat-mediated trans activation in vivo. Together, these results suggest that phosphorylation-dependent binding of a cellular cofactor to TAR RNA is an essential step in Tat-mediated trans activation. Deciphering the regulation of Tat-mediated trans activation by phosphorylation will be critical in fully understanding the regulation of human immunodeficiency virus type 1 activation.

Base Sequence↗
PubMed1992

A single transcription factor binds to two divergent sequence elements with a common function in cardiac myosin light chain-2 promoter.

The cardiac myosin light chain-2 (MLC-2) gene promoter contains several positive and negative cis-acting sequences that are involved in the regulation of its expression. We describe here the properties of two activator sequences, elements A and P, and their DNA-binding factors (ABFs). Element A (CCAAAAGTGG), located at -61, has homology with the evolutionarily conserved sequence CC(A/T)6GG, present in the genes of many contractile proteins. Element P (TAACCTTGAAAGC), located 114 bp upstream of element A, is conserved in both chicken and rat cardiac MLC-2 gene promoters. Deletion mutagenesis demonstrated that these two elements are involved in the positive regulation of MLC-2 gene transcription. At least two sequence-specific element A-binding proteins, ABF-1 and ABF-2, were identified by gel shift analysis of the fractionated cardiac nuclear proteins. ABF-1 binds to element A with strict dependence on the internal element A sequence AAAAGT. In contrast, ABF-2 exhibits a relaxed sequence requirement, as it recognizes the consensus CArG and CCAAT box sequences as well. ABF-2 also recognizes the distal element P despite the fact that the sequences of elements A and P are divergent. DNase I footprinting, methylation interference, and gel shift analyses demonstrated unequivocally that the element A-DNA affinity-purified protein ABF-2 binds to element P with sequence specificity. Since both elements A and P play a positive regulatory role in MLC-2 gene transcription and bind to a single protein (ABF-2), it would appear that ABF-2 is a key transcription factor with the ability to recognize divergent sequence elements involved in a common regulatory pathway during myogenesis.

Animals↗
PubMed1992

Antibacterial properties of investigational, new, and commonly used antibiotics against isolates of Pseudomonas cepacia in Michigan.

Microdilution antimicrobial susceptibility testing was performed with 73 isolates of Pseudomonas cepacia collected from the sputum of patients throughout Michigan with cystic fibrosis. Susceptibility testing was done using new and investigational antibiotics (loracarbef, cefixime, cefpirome, desacetyl-cefotaxime, cefpodoxime, cefmetazole, cefepime, cefprozil, and fleroxacin) and commonly used antibiotics (ceftazidime, mezlocillin, piperacillin, ciprofloxacin, tobramycin, and amikacin). Ceftazidime was the most active antibiotic, and 91.8% of isolates were susceptible to it with MIC50 and MIC90 values of < or = 4 and 16 micrograms/ml, respectively. For mezlocillin, piperacillin, and ciprofloxacin 84.9, 89 and 39.7% of the isolates, respectively, were mostly moderately susceptible. Loracarbef, cefixime, cefprozil, cefmetazole, cefepime, fleroxacin, cefpodoxime, tobramycin, and amikacin did not show activity against P. cepacia. For cefpirome and desacetylcefotaxime 24.7 and 60.3% of the isolates, respectively, were moderately susceptible. Both MIC50 and MIC90 were > 32 micrograms/ml for cefpirome and 32 and > 64 micrograms/ml for desacetylcefotaxime.

Anti-Bacterial Agents↗
PubMed1992

Functional bladder neck obstruction in males: a progressive disorder?

Functional bladder neck obstruction is often an elusive cause of outlet obstruction in males. If the entity escapes timely diagnosis and treatment, it may progress to acute or chronic retention, terminating in renal failure. The diagnosis can be accurately made by a synchronous pressure flow electromyograph (EMG) study. This is a report on 16 men under 45 years of age encountered during the past 2.5 years. A high sustained detrusor pressure (mean 157 cm H2O) during voiding with poor flow (mean 9.89 ml/s) was observed in all patients. External sphincteric activity during EMG and video study was found to be completely quiescent at the time of voiding. All these patients had inadequate funneling and bladder neck opening. Some of these patients had intermittent bladder neck opening. Three patients presented with renal failure. Following therapy, renal function could be reversed back to normal in 2 patients. Clean intermittent catheterisation, pharmacotherapy using alpha-blockers and endoscopic bladder neck incision were the modalities used to treat this group of patients.

Adolescent↗
PubMed1992

Pathways of fibrin turnover of human pleural mesothelial cells in vitro.

The mesothelium contains both procoagulant and fibrinolytic activities. An imbalance between these activities could account for the abnormal fibrin turnover and pleural fibrin deposition that is characteristic of pleural inflammation. Procoagulant activity of human pleural mesothelial cells (HPMC) is in part due to tissue factor, and the prothrombinase complex can also assemble at the HPMC surface. HPMC express tissue plasminogen activator (tPA) but no detectable fibrinolytic activity in a fibrin plate assay. Inhibition of HPMC fibrinolytic activity is due, in part, to elaboration of plasminogen activator inhibitors-1 and -2 (PAI-1 and PAI-2) as well as antiplasmins. Synthesis of PAI-1 and PAI-2 is inhibited by actinomycin D and cyclohexamide. HPMC PAI-1 is increased by transforming growth factor-beta (TGF-beta) and tumor necrosis factor-alpha (TNF-alpha), as is tPA release, while PAI-1 mRNA is unchanged and tPA mRNA is increased. PAI-2 release is induced by TNF-alpha and TGF-beta. Because they are a rich source of PAI-1 and PAI-2, HPMC may contribute to the high levels of these inhibitors in pleural exudates. Stimulation of HPMC by TNF-alpha or TGF-beta in vitro did not alter HPMC procoagulant activity nor the balance of elevated PAI and antiplasmins relative to PA, changes that collectively favor formation and persistence of pericellular fibrin.

Base Sequence↗
PubMed1992

Antibodies to T- and L-isoforms of the cytoskeletal protein, fimbrin, in patients with systemic lupus erythematosus.

The cytoskeleton is a complex network of proteins that maintain cell shape, mobility, and organelle function. Its components can be divided into three distinct classes: microfilaments, microtubules, and intermediate filaments. Fimbrins are microfilament proteins, a family of cytoplasmic phosphoproteins. Expression of the L-fimbrin isoform is restricted to replicating blood cells and expression of the T-fimbrin isoform to replicating cells of solid tissues. Sera from normals and from patients with systemic lupus erythematosus (SLE), juvenile arthritis, rheumatoid arthritis, Sjögren's syndrome, osteoarthritis, vasculitis, scleroderma, and mixed connective tissue disease were tested for the presence of antibodies to T- and L-fimbrin by ELISA, using purified recombinant fimbrin. The mean OD of sera from SLE patients was significantly higher than in normals (T-fimbrin, P less than 0.0001; L-fimbrin, P less than 0.001). 48 of 98 SLE sera had antibodies to T-fimbrin; 32 had antibodies to L-fimbrin; 20 had antibodies to both; 28 had only anti-T, and 12 had only anti-L-fimbrin. The mean OD for sera of the other rheumatic diseases was not significantly different from normals. The presence of either L- or T-fimbrin antibody was associated with pleuropericarditis (P = 0.015), photosensitivity (P = 0.011), and anti-Sm antibody (P = 0.010). Central nervous system SLE was associated with the presence of the L-fimbrin antibody alone (P = 0.016). There was a strong association between DR7 (but not other MHC alleles) and anti-L-fimbrin antibodies in SLE patients (chi square = 18; P less than 0.00002). No MHC association was observed with anti-T-fimbrin antibodies.

Autoantibodies↗
PubMed1992

Modification of radiosensitivity by the so-called tissue recovery stimulator. I. Radiosensitizing effects of solcoseryl.

The effect of solcoseryl on the growth, radiosensitization and ability of V79 cells to recover from X-ray-induced damage has been observed. Solcoseryl at 0.8 mg/ml was the optimal concentration for the stimulation of cell growth. Increased sensitivity to X-irradiation was found in the shoulder region of V79 cells treated before and after irradiation with solcoseryl (0.8 mg/ml). The Dq and extrapolation number (n) decreased. Solcoseryl treatment apparently does not reduce split dose recovery or inhibit the repair of potentially lethal damage. Flow cytofluorometry studies of the cell cycle distribution and mitotic index show that solcoseryl inhibits the expression of radiation-induced cell arrest in the G2 phase of the cell cycle. Although this action increases radiation sensitization, additional mechanisms probably exist.

Actihaemyl↗
PubMed1992

Binocular infrared oculography.

A new system of infrared oculography has been developed which provides binocular recordings and allows simultaneous measurement of horizontal and vertical eye movements. The sensitivity of the system is 1 minute of arc, and it has a horizontal range of +/- 30 degrees and a vertical range of +/- 20 degrees. Using this system for routine clinical evaluations, it was possible to record divergent spontaneous nystagmus and divergent thermally induced nystagmus. Rotatory nystagmus can also be recorded. The binocular infrared oculographic system (BIRO) satisfies nearly all the requirements of an ideal recording system.

Brain Ischemia↗
PubMed1992

A simple radioassay for detection of antithyroglobulin autoantibodies.

Radioassay technique for detection of anti-thyroglobulin autoantibodies (ATA) in serum samples using protein-A rich Staphylococcus aureus as an immune complex separating agent was comparable (r = 0.99; n = 42; P < 0.001) to that evaluated with anti-human gammaglobulin (AHGG). The inter- and intra-assay coefficient of variations were lower (7.4 and 2.2% respectively) using Staph. aureus as compared to that observed with AHGG (10.4 and 4.7% respectively). A highly significant correlation was observed (r = 0.53; n = 71; P < 0.001) between per cent bound radiolabel thyroglobulin in radioassay and log reciprocal titre of ATA by haemagglutination method. Radioassay scored more number of positive sera as compared to haemagglutination method for normal controls (6 vs 1; n = 46) and patients of thyroid diseases (151 vs 70; n = 238). Due to the relatively poor stability of tracer on storage larger inter-assay coefficient of variations were observed with the radiolabelled preparations older than 10-12 days. The radioassay method evaluated is sensitive, reproducible and useful in detecting presence of anti-thyroglobulin autoantibodies.

Autoantibodies↗
PubMed1992

An immunoradiometric assay for measurement of serum thyroglobulin.

A two-site immunoradiometric assay (IRMA) for estimation of serum thyroglobulin (tg) is optimized using partially purified rabbit anti-tg antibodies (ammonium sulphate precipitated) as a solid phase antibody and affinity purified 125I labeled anti-tg antibodies as a tracer. The IRMA correlated well (r = 0.93, n = 200, P < 0.001) with conventional radioimmunoassay (RIA). The inter- and intra-assay coefficient of variation were comparable for both methods. The IRMA method gave a superior sensitivity and working range (2 ng/ml, 3-1000 ng/ml) as compared to that of RIA method (6 ng/ml, 9-500 ng/ml). Using IRMA the total incubation time was curtailed to 4 h as compared to 90 h required for conventional RIA. The shelf-life of tracer antibody used in IRMA was much longer (3 months) as compared to tracer tg (3-4 wk) used in RIA. The optimized IRMA for quantitation of serum tg has superior assay characteristics as compared to RIA.

Humans↗
PubMed1992

An assessment of preoxygenation techniques using the pulse oximeter.

The effect of preoxygenation with varying inspired oxygen concentration on the arterial oxygen saturation during induction of anaesthesia and intubation was studied using the pulse oximeter. Sixty-five healthy, young adults, (American Society of Anaesthesiologists Class I) undergoing elective surgery were randomly divided into three groups. Group I patients were not preoxygenated. Groups II and III patients were preoxygenated with 50% oxygen and nitrous oxide and 100% oxygen respectively for one minute. All were then induced with thiopentone, paralysed with suxamethonium and orally intubated. During intubation, severe arterial desaturation occurred in those patients who were not preoxygenated (lowest saturation was 81.7 +/- 7.8% occurring 87 +/- 24.5 seconds after suxamethonium injection). This was significantly lower than the other two groups (p < 0.001). No patient had clinical signs of hypoxaemia. Patients who were preoxygenated with either 50% oxygen and nitrous oxide or 100% oxygen showed similar and clinically insignificant desaturation during this period. One minute after intubation and manual ventilation with 100% oxygen, the saturations of all patients returned to preinduction levels.

Adolescent↗