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Biomedical subjects

D Brown

Publications and source records attributed to D Brown.

At least 739 records · Page 41Linked to original sources
PubMed1990

Prevalence of hepatitis C in South Africa: detection of anti-HCV in recent and stored serum.

The prevalence of anti-HCV was studied in a cohort of 2,072 South Africans. The results were compared in selected recently collected sera and in stored sera. The serum ALT and anti-HBc were also studied as surrogate markers in this population. The following groups were tested: (a) 498 urban, black blood donors (b) 500 white blood donors (c) 500 Asian blood donors (d) 216 rural hospitalized patients (e) 358 rural mineworkers. Sera found positive by the original ELISA were retested, and reproducibly positive tests in rural black men (group d) were confirmed both by recombinant immunoblot assay and by a second ELISA. An anti-HCV prevalence of 1.2%, 0.8%, and 0.6% in urban blacks, Asians, and whites was found. Antibodies to hepatitis B core antigen were found in 42.9%, 3.4%, and 1.2% of black, Asian, and white donors, respectively; 76% of donors positive for anti-HCV were anti-HBc negative. In rural African men, 17% of stored serum samples and 9.2% of recently collected serum samples were positive for anti-HCV. In this cohort 3.84% were positive by all three assays. These results suggest that the prevalence of anti-HCV in low and high-risk South African urban blood donors is comparable to high and low prevalence areas in Europe, the United States, and Japan, but indicates a relatively high degree of exposure to hepatitis C in rural African men. The reactivity of stored, frozen sera in this population requires further investigation. In South African urban blood donors, surrogate marker testing will not expedite HCV screening.

Adult↗
PubMed1990

Bond strengths of three chemical adhesive cements adhered to a nickel-chromium alloy for direct bonded retainers.

Sandblasted surfaces of a beryllium-free, nickel-chromium alloy were bonded with one of three chemical adhesives. After either immersion in water for up to 6 months or thermal cycling between 5 degrees and 60 degrees C for 500 cycles, the bonded specimens were tested for both shear and tensile strength. The highest values of tensile and shear bond strengths were found with Panavia Ex material, and these values showed no significant changes after thermal cycling. For ABC cement and for Super-Bond C & B material, the strength of the bond was significantly improved with thermal cycling. However, immersion in water for 6 months caused a significant decrease in the strength of the bond of specimens adhered with ABC cement.

Acrylates↗
PubMed1990

Ovine haemopoiesis: the development of bone marrow-derived colony-forming cells in vitro in the presence of factors derived from lymphoid cells and helper T-cells.

Techniques for the development of ovine bone marrow-derived haemopoietic progenitor cells and in situ identification of colony morphology are described. Both mitogen stimulated lymphoid cells and antigen stimulated helper T-cells generated potent colony-stimulating activity in conditioned medium. Monocyte/macrophage, neutrophil, eosinophil, basophil/mast cell, neutrophil/monocyte and mixed phenotype colonies developed in stimulated bone marrow cultures in a conditioned medium dose-dependent manner. Neutrophil, monocyte/macrophage and eosinophil colonies were detected in greater numbers than the other types, with mixed colonies representing only around 1% of the total. Eosinophil colonies were particularly abundant when compared to published reports of the numbers obtained with similar cultures of 'normal' mouse or human bone marrow cells. This culture technique will allow a detailed analysis of both ovine colony-stimulating factors and of the distribution of haemopoietic progenitor cells in vivo.

Animals↗
PubMed1990

Phenotypic analysis of ovine bone marrow cells using monoclonal antibodies and lectins.

Three major subpopulations of ovine bone marrow cells were identified by flow cytometry on the basis of differences in forward (FSC) versus right angle (SSC) light scattering properties and binding of monoclonal antibodies. Region 1 (low FSC, low SSC) contained erythroid series cells and some small lymphocytes. Region 2 (high FSC, low SSC) contained monocytes, myeloid blast cells, medium-large lymphocytes and virtually all of the progenitor/stem cells capable of forming colonies in soft agar cultures. Region 3 (high SSC) contained granulocytes at various stages of development, predominantly (greater than 90%) neutrophils and eosinophils. Using this technique it was possible to identify several cell-surface antigens on bone marrow cells of different lineages using specific monoclonal antibodies and lectins. Amongst the haemopoietic stem/progenitor cell population, immature colony-forming cells were leucocyte common antigen (LCA) negative while more mature colony-forming cells expressed LCA. A proportion of progenitor cells were MHC class I positive. This analysis is an important first step in characterising ovine haemopoietic cells for future studies on: the development of inflammatory cells, the migration of stem/progenitor cells in vivo and the tropism of pathogens.

Analysis of Variance↗
PubMed1990

Developmental expression of a Theileria annulata merozoite surface antigen.

Culture of a lymphoblastoid cell line infected with the macroschizont stage of the protozoan parasite Theileria annulata at 41 degrees C induces differentiation to the next stage, the merozoite. We have demonstrated that this development results in the loss of monoclonal antibody epitopes associated with the macroschizont stage, and the appearance of epitopes associated with the piroplasm (the intra-erythrocytic stages). One of the monoclonals (5E1) was shown by immunoelectron microscopy to bind to the surface of heat-induced culture forms which had size and structural characteristics of the merozoite. The monoclonal was found to detect two polypeptides of 30 kDa and 25 kDa in extracts of piroplasms. The 30-kDa polypeptide was also detected in a merozoite extract, but was not detected in an extract derived from macroschizont-infected lymphoblastoid cells. We conclude that the heat-induced differentiation of T. annulata in vitro results in the expression of a 30-kDa molecule which is located at the surface of the merozoite, and discuss the potential of this molecule as a component in a subunit vaccine.

Animals↗
PubMed1990

Retroviral expressed hemagglutinin-neuraminidase protein protects chickens from Newcastle disease virus induced disease.

The hemagglutinin-neuraminidase (HN) gene and the phosphoprotein (P) gene of Newcastle disease virus (NDV) were inserted into a replication competent avian leukosis virus vector. The expression of the HN gene from this vector in chick embryo cells has been previously reported. The P gene is also expressed from this vector in chick embryo cells. The retroviruses were used to immunize 4-week-old chickens. Birds receiving the virus containing the HN gene developed low levels of serum HI titers and NDV neutralization titers. Upon challenge, all birds vaccinated with the HN gene containing virus were protected from disease but not viral infection and replication. In contrast, birds immunized with the P gene containing retrovirus developed more severe clinical signs of disease earlier than birds receiving no immunization or retrovirus alone. The results obtained with the HN gene may have potential application to reducing disease due to NDV genetically engineered vaccines.

Animals↗
PubMed1990

Differential effect of restraint stress on MHC class II expression by murine peritoneal macrophages.

The effect of restraint stress on the expression of MHC class II glycoproteins by peritoneal macrophages was evaluated. Restraint suppressed the expression of I-A by macrophages from mice that are susceptible to Mycobacterial infection. In contrast, restraint did not affect I-A expression by macrophages from resistant mice. The suppression of MHC class II expression required at least 8 h of restraint and recovered within 4 h after stress. The amount of restraint necessary to suppress I-A expression also resulted in higher levels of plasma corticosterone. Changes in I-A expression were under circadian rhythm control. The differences in the effect of restraint stress on expression of I-A by peritoneal macrophages from resistant and susceptible mice may, in part, be due to differences in the effect of corticosterone in MHC class II expression.

Animals↗
PubMed1990

Spontaneous induction of an homologous robertsonian translocation, Rb(11.11) in a murine embryonic stem cell line.

Karyotype analysis of a series of established mouse embryonic stem cell (MESC) lines showed that the majority were aneuploid by the 7th and 9th passage and that all lines contained a single Robertsonian (Rb) translocation chromosome with a symmetrical, homologous, arm composition Rb(11.11). Although the chromosomal imbalance makes these MESC lines unsuitable for genetic manipulation in vitro and hence for subsequent production of transgenic animals, the spontaneous occurrence and stable retention of the homologous Rb(11.11) as the only metacentric chromosome in an otherwise all acrocentric karyotype, provides potentially useful cell lines for gene assignment and recombinant DNA studies.

Animals↗
PubMed1990

1,2,4-Triazolo[4,3-a]pyrazine derivatives with human renin inhibitory activity. 1. Synthesis and biological properties of alkyl alcohol and statine derivatives.

A series of 1,2,4-triazolo[4,3-a]pyrazine derivatives with human renin inhibitory activity, which incorporate (1S,2S)-2-amino-1,3-dicyclohexyl-1-hydroxypropane, statine (Sta), and (3S,4S)-4-amino-5-cyclohexyl-3-hydroxy-pentanoic acid (ACHPA) transition-state mimetics, have been prepared. Structure-activity relationships for renin inhibitory activity in the series are consistent with the 2-[8-isobutyl-6-phenyl-1,2,4-triazolo[4,3-a]pyrazin-3-yl]-3-(3 pyridyl)propionic acid moiety 10b acting as a non-peptidic replacement for the P4-P2 (Pro-Phe-His) residues of the natural substrate angiotensinogen. Compounds 12m, 12o and 12q were potent inhibitors of partially purified human renin (IC50 values 1.7, 6.8, and 3.7 nM, respectively), and also effectively lowered blood pressure in anesthetized, sodium depleted marmosets following intravenous administration. On oral administration however, no blood pressure lowering activity could be detected, and absorption studies in bile duct cannulated rats indicate that this may be due primarily to poor oral absorption, rather than rapid biliary excretion. The reason for the observed poor oral activity is not clear, but it seems unlikely that poor aqueous solubility or metabolic instability to gut enzymes are rate-determining, and other factors such as high molecular weight may also be very important.

Administration, Oral↗
PubMed1990

Pretransfer tissue expansion of a scalp free flap for burn alopecia reconstruction in a child: a case report.

A nine-year-old boy who sustained severe grease-fire burns over his right scalp, face, neck, and trunk 14 months previously, presented with extensive alopecia over the right frontotemporoparietal scalp. Near complete coverage of the scalp defect was obtained with pretransfer expansion of the left temporoparietal scalp, followed by free-flap transfer of the expanded tissue to the defect. Pretransfer tissue expansion has the advantages of increasing flap surface area and minimizing donor site deformity. This case illustrates the applicability of pretransfer tissue expansion of free flaps, and demonstrates the excellent results achievable with free-flap scalp transfers.

Alopecia↗
PubMed1990

Localization of membrane-associated carbonic anhydrase type IV in kidney epithelial cells.

Rat carbonic anhydrase (CA) IV was purified by affinity chromatography and used to produce a specific antiserum in rabbits for immunolocalization studies in rat kidney. CA IV was localized in apical plasma membranes of the proximal convoluted tubule and the thick ascending limb of Henle. Both of these segments are involved in bicarbonate reabsorption in the rat. Immunofluorescent staining of the brush border was faint in the S1 segment, greatest in the S2 segment, and absent from the S3 segment of the proximal tubule. CA IV was also detected in the basolateral plasma membrane of proximal-tubule and thick-ascending-limb epithelial cells by immunofluorescence and immunoelectron microscopy. In the proximal tubule, an extracellular membrane CA had been previously suggested on the basis of electrophysiological studies. CA IV was not detected in intercalated cells of the collecting ducts. These cells contain, in contrast, abundant cytosolic CA II. Thus, the distribution of CA IV is quite distinct from that of CA II; it corresponds with the localization of an isoenzyme(s) that did not stain with antibodies against CA II but that was revealed by histochemical-staining procedures. We conclude that the apical CA IV is the luminal CA responsible for bicarbonate reabsorption in the proximal tubule and the thick ascending limb in the rat kidney. These studies also suggest that CA IV plays a role in bicarbonate transport across the basolateral plasma membrane in these two segments of the rat nephron.

Animals↗
PubMed1990

Endocytic vesicles from renal papilla which retrieve the vasopressin-sensitive water channel do not contain a functional H+ ATPase.

The water permeability of the kidney collecting duct epithelium is regulated by vasopressin (VP)-induced recycling of water channels between an intracellular vesicular compartment and the plasma membrane of principal cells. To test whether the water channels pass through an acidic endosomal compartment during the endocytic portion of this pathway, we measured ATP-dependent acidification of FITC-dextran-labeled endosomes in isolated microsomal fractions from different regions of Brattleboro rat kidneys. Both VP-deficient controls and rat treated with exogenous VP were examined. ATP-dependent acidification was not detectable in endosomes containing water channels from distal papilla (osmotic water permeability Pf = 0.038 +/- 0.004 cm/s). In contrast, the addition of ATP resulted in a strong acidification of renal cortical endosomes (pHmin = 5.8, initial rate = 0.18-0.25 pH U/s). Acidification of cortical endosomes was reversed with nigericin and strongly inhibited by N-ethyl-maleimide. Passive proton permeability was similar and low in both cortical and papillary endosomes from rats treated or not treated with VP. The fraction of labeled endosomes present in microsomal preparations was determined by fluorescence imaging microscopy of microsomes nonspecifically bound to poly-l-lysine-coated coverslips and was 25% in cortical preparations compared to 14% (+VP) and 9% (-VP) in papillary preparations. The fraction of cortical endosomes was enriched 1.5-fold by immunoabsorption to coverslips coated with mAbs against the bovine vacuolar proton pump. In contrast, the fraction of papillary endosomes was depleted more than twofold by immunoabsorption to identical coverslips. Finally, sections of distal papilla stained with antibodies against the lysosomal glycoprotein LGP120 showed that most of the entrapped FITC-dextran did not colocalize with this lysosomal protein. These results demonstrate that vesicles which internalize water channels in kidney collecting duct principal cells lack functional proton pumps, and do not deliver the bulk of their FITC-dextran content to lysosomes. The data suggest that the principal cell contains a specialized nonacidic apical endocytic compartment which functions primarily to recycle membrane components, including water channels, to the plasma membrane.

Adenosine Triphosphate↗
PubMed1990

Water, proton, and urea transport in toad bladder endosomes that contain the vasopressin-sensitive water channel.

Vasopressin (VP) increases the water permeability of the toad urinary bladder epithelium by inducing the cycling of vesicles containing water channels to and from the apical membrane of granular cells. In this study, we have measured several functional characteristics of the endosomal vesicles that participate in this biological response to hormonal stimulation. The water, proton, and urea permeabilities of endosomes labeled in the intact bladder with fluorescent fluid-phase markers were measured. The diameter of isolated endosomes labeled with horse-radish peroxidase was 90-120 nm. Osmotic water permeability (Pf) was measured by a stopped-flow fluorescence quenching assay (Shi, L.-B., and A. S. Verkman. 1989. J. Gen. Physiol. 94:1101-1115). The number of endosomes formed when bladders were labeled in the absence of a transepithelial osmotic gradient increased with serosal [VP] (0-50 mU/ml), and endosome Pf was very high and constant (0.08-0.10 cm/s, 18 degrees C). When bladders were labeled in the presence of serosal-to-mucosal osmotic gradient, the number of functional water channels per endosome decreased (at [VP] = 0.5 mU/ml, Pf = 0.09 cm/s, 0 osmotic gradient; Pf = 0.02 cm/s, 180 mosmol gradient). Passive proton permeability was measured from the rate of pH decrease in voltage-clamped endosomes in response to a 1 pH unit gradient (pHin = 7.5, pHout = 6.5). The proton permeability coefficient (PH) was 0.051 cm/s at 18 degrees C in endosomes containing the VP-sensitive water channel; PH was not different from that measured in vesicles not containing water channels. Measurement of urea transport by the fluorescence quenching assay gave a urea reflection coefficient of 0.97 and a permeability coefficient of less than 10(-6) cm/s. These results demonstrate: (a) VP-induced endosomes from toad urinary bladder have extremely high Pf. (b) In states of submaximal bladder Pf, the density of functional water channels in endosomes in constant in the absence of an osmotic gradient, but decreases in the presence of a serosal-to-mucosal gradient, suggesting that the gradient has a direct effect on the efficiency of packaging of water channels into endosomes. (c) The VP-sensitive water channel does not have a high proton permeability. (d) Endosomes that cycle the water channel do not contain urea transporters. These results establish a labeling procedure in which greater than 85% of labeled vesicles from toad urinary bladder are endosomes that contain the VP-sensitive water channel in a functional form.

Animals↗