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V Kumar

Publications and source records attributed to V Kumar.

At least 379 records · Page 21Linked to original sources
PubMed1994

Identification, synthesis, and characterization of a unique class of N-methyl-D-aspartate antagonists. The 6,11-ethanobenzo[b]quinolizinium cation.

A series of novel N-methyl-D-aspartate antagonists acting at the phencyclidine site has been identified. Compound 2 has a Ki = 8 +/- 1 nM (vs [3H]thienylcyclidine, [3H]TCP) as a mixture of enantiomers. Resolution and further testing indicate that (-)-2, Ki = 4 +/- 0.7 nM, is a potent and selective TCP site ligand with neuroprotective activity in cultured neurons in the presence of excitotoxic concentrations of NMDA (IC50 = 26 nM). Compound (-)-2 is > 1000-fold selective for the TCP site vs a panel of receptor types including opiate, adrenergic, serotonergic, dopamine, adenosine, dihydropyridine, and benzodiazepine and displays increased selectivity for the activated (open) NMDA receptor-ion channel complex vs PCP and MK801 as measured by patch recordings in cultured, voltage-clamped neurons. Highly enhanced "open-channel" selectivity leads to tentative classification of these ligands as uncompetitive vs NMDA. Ligands with these characteristics may enable deconvolution of the pharmacologic effects associated with typical noncompetitive NMDA antagonists. We report here on the identification, synthesis, and activity of compounds of this structural class.

Animals↗
PubMed1994

Expression of CD43 on murine and human pluripotent hematopoietic stem cells.

To understand regulation of hemopoiesis, it would be helpful to identify physiologically relevant function-associated molecules on stem cells. Here, we report the detailed examination of CD43 expression on murine and human pluripotent hemopoietic stem cells. Mouse stem cells were found within the Ly6+Lin-CD43high subpopulation of bone marrow. These cells, upon transfer into SCID mice, caused rapid repopulation of thymus, spleen, and bone marrow. Retransfer of bone marrow cells from primary SCID recipients of Ly6+Lin-CD43high cells into secondary recipients resulted in repopulation of lymphohemopoietic cells. All Ly6+Lin-CD43high cells were found to express high levels of c-kit. In contrast, Ly6+Lin-CD43-/low cells caused limited and variable thymic and splenic repopulation. These cells failed to repopulate the marrow cavity and did not contain retransplantable stem cells. These data indicate that murine pluripotent stem cells express high levels of CD43. Examination of human fetal bone marrow cells revealed a population of CD34+CD38-CD43+ cells. When single sorted cells with this phenotype were cultured in vitro, they were able to produce colonies with a dispersed growth pattern. Cells with this growth pattern have previously been shown to have myeloid and lymphoid growth potentials and extensive self-renewal capacity. Furthermore, CD34+CD38-HLA-DR+ cells, recently shown to be highly enriched in stem cell activity, expressed relatively high levels of CD43. Because CD43 has recently been shown to bind to intercellular adhesion molecule-1, these data suggest a possible role for CD43 in the regulation of hemopoiesis.

ADP-ribosyl Cyclase↗
PubMed1994

Androgen receptor affinity of 5'-acyl furanosteroids.

Syntheses of 5'-acyl furanosteroids are described from the corresponding unsubstituted [3,2-b]furanosteroids using acid anhydrides and acid chlorides in the presence or absence of Lewis acids. New methods have been developed to prepare 5'-acetyl derivatives: reduction of a 5'-trichloroacetyl intermediate either by sodium formaldehyde sulfoxylate or with 10% Pd/C. Most of these 5'-acyl derivatives bind to the rat ventral prostate androgen receptor. However the antiandrogenic activity was diminished when compared with 4,5'-methylsulfonyl furanosteroid. Biological studies revealed that 5'-acyl furanosteroids were either androgens or modest antiandrogens. The electrostatic potential maps of the substructures of 3, 4, and 5'-acetyl syn- and anti-furanosteroids showed striking differences which may explain, to some extent, the lack of significant antiandrogenic activity of 5'-acyl furanosteroids.

Androgen Antagonists↗
PubMed1994

Differences in anionic inhibition of human carbonic anhydrase I revealed from the structures of iodide and gold cyanide inhibitor complexes.

The crystal structures of two anionic inhibitor complexes of human carbonic anhydrase I (HCAI), namely, HCAI-iodide and HCAI-Au(CN)(2)(-), have been refined by the restrained least-squares method at 2.2 and 2 A nominal resolution, respectively, with good stereochemistry for the final models. The R values have improved from 30.3 to 16.6% for HCAI-iodide and from 28.8 to 17.1% for HCAI-Au(CN)(2)(-). The sites of inhibitor binding as elucidated are totally different in the two structures. The iodide anion replaces the zinc-bound H(2)O/OH(-) ligand and renders the enzyme inactive. This result confirms that the zinc-bound H(2)O/OH(-) is the activity-linked group in carbonic anhydrase enzymes. Au(CN)(2)(-) binds at a different and new site near the zinc ion, without liganding to the metal. The N atom of Au(CN)(2)(-) is within hydrogen-bonding distance of the zinc-bound H(2)O/OH(-) group which shifts by about 0.4 A away from the zinc ion in relation to its position in the native HCAI. It is proposed that the presence of the inhibitor Au(CN)(2)(-) results in a conformational reorientation of the activity-linked group, due to hydrogen-bond formation with the inhibitor, which in turn sterically hinders the binding of the substrate CO(2) molecule in the active site, leading to the inhibition of HCAI enzyme.

Journal Article↗
PubMed1994

Antigen-specific early primary humoral responses modulate immunodominance of B cell epitopes.

Accumulation of primary Abs against two distinct epitopes on a designed polypeptide, MEP-1, was examined. The early primary response was predominantly against a C-terminal epitope (MEP 77-100), although subsequent maturation established an epitope within the N-terminal half (MEP 17-31) as the immunodominant one. Inversion of immunodominance correlated with the inability of anti-MEP 77-100 B cells to interact productively with T cells, which consequently received reduced help. Interaction between epitope-specific B and T cells was found to be attenuated in the presence of early primary anti-MEP-1 antiserum, and the extent of inhibition was directly proportional to the level and affinity of epitope-specific Igs. Therefore, it seems that early primary Abs to a multideterminant Ag selectively down-regulate maturation of epitope-specific primary humoral responses.

Amino Acid Sequence↗
PubMed1994

Enzyme-substrate interactions. Structure of human carbonic anhydrase I complexed with bicarbonate.

The structure of HCAI-HCO3- complex has been refined with 10-1.6A X-ray diffraction data to an R-value of 17.7%. The structure reveals monodentate binding of the HCO3- anion at an apical tetrahedral position to the zinc ion. The binding mode and interactions of HCO3- in HCAI differ from that in HCAII. The activity linked H2O/OH- group in the free HCAI is replaced by the hydroxyl group of the bicarbonate anion. This result rules out the rearrangement of the bound HCO3- advocated earlier to explain the microscopic reversibility of the catalysed reaction. From the geometry of the H-bonds between Glu106-Thr199 pair and Glu117-His119 couple, the glutamic acids are expected to be ionized and accept H-bonds from their partners. The product-inhibiton by HCO3- anion is explained on the basis of proton localization on His119 in the Glu117-His119 couple. These results are consistent with the hypothesis that Glu117-His119 tunes the ionicity of the Zn2+ and the binding strength of HCO3- anion. A pi hydrogen bond is observed between a water and phenyl ring of the Tyr114 residue.

Bicarbonates↗
PubMed1994

Purification and characterization of avian oligosaccharyltransferase. Complete amino acid sequence of the 50-kDa subunit.

We have purified oligosaccharyltransferase from hen oviduct microsomes some 850-fold. Oligosaccharyltransferase activity copurified with a 200-kDa complex consisting of two 65-kDa polypeptides and a 50-kDa polypeptide. N-terminal sequence analysis indicated that the 50-kDa subunit was the avian form of OST48, a canine pancreatic microsomal protein associated with oligosaccharyltransferase. As the first step toward reconstitution of the oligosaccharyltransferase complex, the 50-kDa subunit was purified to homogeneity under nondenaturing conditions. The complete amino acid sequence of the 50-kDa subunit was determined by sequence analysis of peptides isolated by a combination of gel filtration and high performance liquid chromatography from chemical and enzymatic digests. The protein consists of 412 residues in a single polypeptide chain. The amino acid sequence of the 50-kDa subunit of avian oligosaccharyltransferase is 92% identical to the sequence of canine OST48 protein and about 25% identical to WBP1 protein from the yeast Saccharomyces cerevisiae. The yeast WBP1 protein has been shown in vitro, as well as in vivo, to be essential for the oligosaccharyltransferase activity.

Amino Acid Sequence↗
PubMed1994

Holes in the T cell repertoire to myelin basic protein owing to the absence of the D beta 2-J beta 2 gene cluster: implications for T cell receptor recognition and autoimmunity.

Models of T cell recognition suggest that amino acid residues in the CDR3 region of the T cell receptor (TCR) alpha or beta chain directly contact the major histocompatibility complex-bound peptide, and thus are crucial for providing peptide specificity. T cells derived from B10.PL or PL/J mice of H-2u haplotype, use only D beta 2 and J beta 2 gene segments in the recognition of the dominant determinant, Ac1-9/Au, of myelin basic protein (MBP). New Zealand White (NZW) mice, with identical class II H-2u genes (I-A and I-E), carry an 8.8-kb deletion in their TCR beta chain locus encompassing D beta 2 and J beta 2 gene segments. How does this deletion of the crucial D beta 2-J beta 2 region in NZW mice influence specific responses to Ac1-9/Au as well as to other known Au or Eu determinants of MBP? We found that these mice respond very poorly to the dominant Ac1-9/Au and to the subdominant 31-50/Eu determinant in in vitro proliferation assays as well as in their in vivo capacity to induce experimental autoimmune encephalomyelitis. This loss of response is apparently owing to the absence of high avidity TCRs with essential CDR3 residues contributed by D beta 2 or J beta 2 gene segments. These data reveal constraints in the recognition of certain antigenic structures, and further support a TCR-recognition model in which CDR3 residues of the TCR alpha and beta chains constitute the antigenic peptide-binding sites on the TCR molecule. Implications for autoimmune manifestations contributed by NZW genes in (NZB x NZW)F1 disease are also discussed.

Animals↗
PubMed1994

T cell determinant structure of myelin basic protein in B10.PL, SJL/J, and their F1S.

Recent experiments have shown that during the course of chronic experimental allergic encephalomyelitis, there is a shift in the determinant hierarchy away from the dominant to other subdominant and cryptic self determinants. It was therefore of interest to define the pattern of dominance for mouse myelin basic protein in the three commonly used experimental allergic encephalomyelitis model strains of mice, i.e., B10.PL, SJL/J, and (SJL x B10.PL)F1. Our studies indicate that many cryptic determinants are demonstrable, which only activate T cells on injection as individual peptides and not with the native protein. The core amino acid residues of the various determinants are defined and range in size between 5 and 10 amino acids. Interestingly, there is a bias toward H-2u-restricted response vis-a-vis the H-2s-restricted response in the (SJL x B10.PL)F1 strain. The TCR V beta 8.2 gene segment was not predominantly used for responses to other determinants, although some B10.PL and (SJL x B10.PL)F1 cell lines expressed V beta 8.2 more than others. This study represents the most comprehensive analysis so far of the pattern of dominant and cryptic proliferative T cell determinants and their core sequences for mouse myelin basic protein.

Amino Acid Sequence↗
PubMed1994

Novel cAMP PDE III inhibitors: imidazo[4,5-b]pyridin-2(3H)-ones and thiazolo[4,5-b]pyridin-2(3H)-ones and their analogs.

The transformation of milrinone to 1,3-dihydro-5-methyl-6-(4-pyridinyl)-2H-imidazo[4,5-b]pyridin-2-one (13a), 5-methyl-6-(4-pyridinyl)thiazolo[4,5-b]pyridin-2(3H)-one (51), and 7-methyl-6-(4-pyridinyl)-1,8-naphthyridin-2(1H)-one (22) resulted in very potent cAMP PDE III inhibitors with in vitro activity in the nanomolar range. 1,3-Dihydro-2H-imidazo[4,5-b]pyridin-2-ones 13 were prepared from 2-aminopyridine-3-carboxylic acids (7, 10) via Curtius rearrangement. 1,8-Naphthyridin-2(1H)-one 22 and the corresponding 3,4-dihydro derivative 28 were prepared from 5-bromo-2-methyl[3,4'-bipyridin]-6-amine (21) and 5-bromo-2-methyl[3,4-bipyridin]-6(1H)-one (24), respectively, via Heck reaction. Thiazolo[4,5-b]pyridin-2(3H)-ones 35 were prepared from 6-bromo[3,4'-bipyridin]-6-amines 30 and 32 via a four-step sequence. Treatment of 6-amino-2-methyl[3,4'-bipyridine]-5-thiol (59) with ethyl bromoacetate and ethyl bromodifluoroacetate gave pyridothiazinones 60 and 61, respectively.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1994

Microassay for oligosaccharyltransferase: separation of reaction components by partitioning in detergent solution followed by ultrafiltration.

Oligosaccharyltransferase catalyzes the transfer of oligosaccharide from a lipid dolichol to asparagine acceptor sites on nascent polypeptides. We have developed an assay for this enzyme which is based on the specific distribution of the substrate and product of the reaction in detergent solution. GlcNAc-[3H]GlcNAc-PP-Dol was synthesized for use as a carbohydrate donor. Benzoyl-Asn-Leu-Thr-amide, a commercially available peptide, was used as the oligosaccharyltransferase glycan acceptor substrate. In the presence of Triton X-100, GlcNAc-[3H]GlcNAc-PP-Dol partitions into detergent micelles while glycosylated acceptor peptide partitions into the intermicellar aqueous compartment. Separation of GlcNAc-[3H]GlcNAc-PP-Dol and glycopeptide was achieved by ultrafiltration. With this method oligosaccharyltransferase activity in microsomal preparations could be measured with as little as 1 microgram of protein.

Amino Acid Sequence↗
PubMed1994

Immunological characteristics of a recombinant hepatitis B virus-derived multiple-epitope polypeptide: a study in polyvalent vaccine design.

Immunological properties of a model polyepitope immunogen (MEP-1) consisting of selected determinants from envelope proteins of hepatitis B virus (HBV) were examined. Immunization with MEP-1 induced high-titre antibodies in a variety of murine strains and in rabbits although an overall hierarchy of B-cell immunodominance was observed as pre-S1-derived > S-derived > pre-S2-derived segments. Anti MEP-1 antibody responses in all hosts were found to be exclusive for HBV-derived sequences in the absence of any fraction directed against the various interepitope junctions. With panels of overlapping peptides it was observed that the anti-pre-S1 and anti-pre-S2 components of anti-MEP-1 antibodies were, in all animals tested, of the desired specificity from the standpoint of potential virus-neutralizing ability. The MEP-1 segment representing residues 124-127 of the major protein of hepatitis B surface antigen (HBsAg) was found to elicit a conformation-specific antibody response. Furthermore, this subpopulation was either predominantly or exclusively against the Met133-Lys141-dependent group-specific epitope. Finally, the HBV sequences in MEP-1 were shown to retain their Th-cell activities. These studies suggest that MEP-1 provides a useful tool in the study of polyvalent vaccine design.

Amino Acid Sequence↗
PubMed1994

Seasonal prevalence of gastrointestinal nematodes in communal land goats from the highveld of Zimbabwe.

On six occasions during a 1 year period, goats run on communal pastures by small-scale farmers, were purchased, housed indoors for 3 weeks and autopsied for examination of their gastrointestinal nematode burden. All of the 32 goats examined were infected. The four dominant species, Haemonchus contortus, Trichostrongylus axei, Trichostrongylus colubriformis and Oesophagostomum columbianum, were present in 88-97% of the animals. Three other nematodes, Strongyloides papillosus, Bunostomum spp. and Trichuris spp. occurred respectively in 9%, 3% and 21% of the goats. The total nematode burden was least at the end of the dry season in November and increased gradually through the rainy season to reach a peak at the end of the rains in April. The population of H. contortus followed the same trend as that of the total worm burden. Trichostrongylus colubriformis showed a peak in April and T. axei in June. The fourth stage larvae (L4) of H. contortus accounted for 0-6.8% of the total H. contortus population during most of the year except in August, when they comprised 46.1% of the burden. It can be concluded that there is a direct relationship between rainfall and intensity of infection with gastrointestinal nematodes.

Animals↗
PubMed1994

Evaluation of the activity of Ambrosia maritima L. against Schistosoma mansoni infection in mice.

Two groups of mice, showing a patent infection of Schistosoma mansoni, were orally treated with an alcoholic extract of Ambrosia maritima leaves. One group received a single dose, equivalent to 15 g leaves/kg body weight, whereas the other received 5 consecutive doses. The schistosomicidal activity of the plant extract was evaluated 1 week after treatment using 4 parameters: worm load, motility of the worms, oogram and the number of eggs in the liver and intestinal wall. In comparison to the control group no effect at all was observed in the mice who received one single dose of A. maritima. In the group receiving 5 consecutive daily doses, however, the percentage of immature eggs in the intestinal wall had slightly decreased as compared to the controls, but this was compensated by an increase in the number of eggs in the liver. Given the high doses of plant extract used, it is concluded that oral administration of A. maritima has a negligible effect on S. mansoni in mice.

Administration, Oral↗
PubMed1994

Evaluation of the demented patient.

Approaching the patient with Alzheimer's disease often requires the participation of a team of collaborating physicians and psychologists as well as others both for diagnosis and for management. This article describes the approach to the disease by a neurologist, geriatrician, psychiatrist, and psychologist. Each describes a specific diagnostic approach, and the reader can appreciate the incremental value to assessment and care that emerges from the aggregate.

Age Factors↗