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R Kapur

Publications and source records attributed to R Kapur.

At least 37 records · Page 2Linked to original sources
PubMed1998

Cellular and cytoskeleton morphology and strength of adhesion of cells on self-assembled monolayers of organosilanes.

The objective of this study was to explore the potential use of self-assembled monolayers (SAMs) of alkylamine and arylalkyamine as well-defined, homogeneous, tailored in vitro model surfaces for exploring the effect of hydrodynamic flow on morphology and strength of adhesion of human umbilical vein endothelial cells. The cell surface area, shape, f-actin distribution, and adhesion strength of human umbilical vein endothelial cells cultured on self-assembled monolayers of organosilanes were found to be dependent on the chemical composition of the organosilane film and the magnitude of wall shear stress. The direct effects of the differences in chemistry between the two silanes, in modulating cellular response, are probably only secondary to the modulation of cellular functions mediated by differential protein adsorption and conformation on the two silanes. For short seeding times (30 min), prior to application of flow, both substrate chemistry and shear stress modulated the cellular morphology and cytoskeletal organization. For longer seeding times (24 h), prior to application of flow, the chemistry of the underlying surface was the dominant variable in modulating cellular morphology, while the hydrodynamic shear stress modulated the cytoskeleton organization. Cells on N-(2-aminoethyl)-3-aminopropyl trimethoxysilane (EDA) were pleomorphic, while cells on ((((aminoethyl)amino)methyl)phenylethyl)trimethoxysilane (PEDA) expressed a rounded morphology. Application of an incrementally loaded flow regime (0.07-1.25 ml/s) resulted in a time- and shear stress-dependent (10-180 dyn/cm2) detachment of cells, with the cells on EDA depicting higher resistance to wall shear stress. Cellular morphology correlated with the strength of adhesion; cells with rounded morphology on a hydrophobic silane, PEDA, were less tightly bound to the silane, while spread cells on a hydrophilic silane, EDA, were more tightly bound. The higher surface free energy of EDA is speculated to influence the increased cell spreading and strength of adhesion observed in these studies. The presence of the phenyl group in PEDA reduces the surface free energy and may account for the reduced spreading and lower strength of adhesion. The use of well-defined systems, such as monolayer organosilanes, with tunable surface physicochemical properties may serve to deconstruct the complex interaction of cells with extracellular matrix components: surface charge, surface hydrophobicity, and other short- and long-range forces can be individually controlled and correlated with cellular functions. The organosilane monolayers could serve as the building blocks for sequential addition of proteins or cell adhesive/cell repulsive cues to stepwise engineering and construction of more complex systems resembling ECM matrices.

Biocompatible Materials↗
PubMed1998

Signaling through the interaction of membrane-restricted stem cell factor and c-kit receptor tyrosine kinase: genetic evidence for a differential role in erythropoiesis.

Mutations of the receptor tyrosine kinase c-kit or its ligand stem cell factor (SCF), which is encoded as a soluble and membrane-associated protein by the Steel gene in mice, lead to deficiencies of germ cells, melanocytes, and hematopoiesis, including the erythroid lineage. In the present study, we have used genetic methods to study the role of membrane or soluble presentation of SCF in hematopoiesis. Bone marrow-derived stromal cells expressing only a membrane-restricted (MR) isoform of SCF induced an elevated and sustained tyrosine phosphorylation of both c-kit and erythropoietin receptor (EPO-R) and significantly greater proliferation of an erythrocytic progenitor cell line compared with stromal cells expressing soluble SCF. Transgene expression of MR-SCF in Steel-dickie (Sld) mutants resulted in a significant improvement in the production of red blood cells, bone marrow hypoplasia, and runting. In contrast, overexpression of the full-length soluble form of SCF transgene had no effect on either red blood cell production or runting but corrected the myeloid progenitor cell deficiency seen in these mutants. These data provide the first evidence of differential functions of SCF isoforms in vivo and suggest an abnormal signaling mechanism as the cause of the severe anemia seen in mutants of the Sl gene.

Animals↗
PubMed1997

Overexpression of human stem cell factor impairs melanocyte, mast cell, and thymocyte development: a role for receptor tyrosine kinase-mediated mitogen activated protein kinase activation in cell differentiation.

Stem cell factor (SCF) is synthesized as both soluble (S) and membrane-associated (MA) proteins. Indirect insight into the function of MA and S isoforms of SCF has come from studies performed in Steel (Sl) mutant mice. However, the physiologic role(s) of these two isoforms remain unknown. In an attempt to better understand the in vivo role of c-kit/SCF interactions on various cell lineages, transgenic mice were generated that overexpress MA isoform of human SCF (hSCF). In murine cells, hSCF behaves as an antagonist to normal SCF function, due to interference with the interaction between endogenous murine SCF and its receptor, c-kit, encoded by the dominant white spotting (W) gene. Mice expressing the hSCF transgene display a variety of phenotypic abnormalities, which are accentuated when combined with W alleles. Here we show that mice homozygous for the hSCF transgene demonstrate a coat color deficiency seen in some mice homozygous for mild W alleles. Specifically, homozygous hSCF transgenic mice (hSCF220) display a pronounced forehead blaze, with additional white spots over the cervical region, as well as a very large belly spot. Doubly heterozygous animals that carry both a mutated W allele and the hSCF transgene also display an unusual pigment defect and a dramatic reduction in the number of dermal mast cells. Furthermore, overexpression of MA hSCF in the thymus results in abnormal thymocyte differentiation and proliferation, which is associated with reduced mitogen activated protein (MAP) kinase activation. Thus, MAP kinase activation by a receptor tyrosine kinase, such as c-kit, may be critical for the differentiation of thymocytes in vivo.

Animals↗
PubMed1997

Reversal of 1,3-bis(2-chloroethyl)-1-nitrosourea-induced severe immunodeficiency by transduction of murine long-lived hemopoietic progenitor cells using O6-methylguanine DNA methyltransferase complementary DNA.

Bone marrow toxicity is a dose-limiting side effect of chloroethylnitrosourea (CNU) chemotherapeutic alkylating agents. A major determinant of CNU cytotoxicity is the methylation of guanine at the O6-position and the subsequent formation of interstrand DNA cross-links. O6-Methylguanine DNA methyltransferase (MGMT) removes alkyl groups from the O6 position of guanine and has been shown to repair CNU-induced DNA damage. We have previously demonstrated that transplantation of murine bone marrow cells transduced with a recombinant retroviral vector expressing MGMT via the human phosphoglycerate kinase promoter (PGK-MGMT) protects animals in vivo from acute myelotoxicity associated with CNU treatment. In the present study, we examined the effects of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), a commonly used CNU, on long term recovery of the lymphoid compartment, including thymus reconstitution, peripheral T and B cell populations, and lymphocyte mitogen responses in mice reconstituted with PGK-MGMT-transduced hemopoietic cells. Mice transplanted with either mock-infected control or PGK-MGMT-transduced stem cells were treated with five weekly doses of BCNU. Analysis of the lymphoid compartment demonstrated significant damage 3 mo after the last BCNU dose in control animals. In contrast, the profound deficiency in CD4+CD8+ double-positive thymocytes and mature lymphocytes observed in control mice surviving BCNU treatment was completely reversed in mice transplanted with PGK-MGMT-transduced bone marrow and was associated with molecular evidence of in vivo selection of transduced cells in the lymphoid compartment. Thus, long term immunodeficiency following CNU therapy may be prevented by genetic modification of murine hemopoietic stem cells with MGMT, leading to significant improvement in post-transplant immune function.

Animals↗
PubMed1996

Follow-up of a familial translocation t(10;16) with an unusual segregation pattern.

Bofinger et al. [Am J Med Genet 38:1-8, 1991] reported on a four-generation family with an unusual segregation pattern involving a translocation t(10;16)(q26.3;p13.1). All relatives either had a balanced or unbalanced translocation. We report on five additional relatives, none of whom have a normal karyotype. This unusual segregation pattern may be due to chance or be the result of meiotic drive.

Abnormalities, Multiple↗
PubMed1996

Xenogeneic expression of human stem cell factor in transgenic mice mimics codominant c-kit mutations.

Mutations of c-kit, which encodes a transmembrane receptor tyrosine kinase, have been identified in mice by abnormal coat color, anemia, and germ cell defects. Mice heterozygous for mutations of c-kit have a white forehead blaze and a white ventral spot, leading these mutants to be termed dominant White spotting (W). We have previously demonstrated that the membrane-associated isoform of human stem cell factor (hSCF220, the ligand for c-kit) is inefficiently processed in murine stromal cell transfectants. Thus, in murine cell lines analyzed in vitro, hSCF220 transfectants present SCF as a membrane restricted protein in contrast to the murine SCF220 cDNA protein product, which is slowly cleaved and secreted. We show here that transgenic mice expressing the human SCF220 isoform in vivo display a phenotype indistinguishable from some alleles of W. Specifically, hSCF220-expressing transgenic mice display a prominent forehead blaze and a white ventral spot. Generations of doubly heterozygous animals that carry both a mutated c-kit allele and the hSCF220 transgene display a more severe coat color abnormality. This phenotype appears to be due to occupancy of murine c-kit by human SCF and diminished cell surface expression of endogenous murine SCF. Normal signaling events that lead to cell survival or proliferation appear to be disrupted in vivo in these transgenic mice.

Alleles↗
PubMed1996

Human monocyte morphology is affected by local substrate charge heterogeneity.

Cells are sensitive to topological, chemical, and electrical properties of substrates on which they are grown. However, most studies of cell-surface interactions have neglected electrical effects or confounded them with other substrate properties. The use of nanofabrication technology has made it possible to fabricate optically transparent surfaces with controlled chemistry and topology, and with active, controllable surface charge density in domains as small as 1-4 microns. Human monocytes incubated on polystyrene with 3.3 microns-wide strip domains, alternately charged so as to maintain overall charge neutrality, show significant charge density and time-dependent increases (greater than twofold) in cell area and cell perimeter after challenge with a phagocytic trigger (human IgG opsonized zymosan particles). Additional utlrastructural studies on silicon dioxide substrates show charge-density-dependent qualitative morphological differences. These studies clearly demonstrate that human monocytes respond in vitro to local surface-charge heterogeneity in the absence of substrate topology and compositional variation.

Biocompatible Materials↗
PubMed1996

Fabrication and selective surface modification of 3-dimensionally textured biomedical polymers from etched silicon substrates.

A new method is described for producing biomedically relevant polymers with precisely defined micron scale surface texture in the x, y, and z planes. Patterned Si templates were fabricated using photolithography to create a relief pattern in photoresist with lateral dimensions as small as 1 micron. Electroless Ni was selectively deposited in the trenches of the patterned substrate. The Ni served as a resilient mask for transferring the patterns onto the Si substrate to depths of up to 8.5 microns by anisotropic reactive ion etching with a fluorine-based plasma. The 3-dimensional (3-D) textured silicon substrates were used as robust, reusable molds for pattern transfer onto poly (dimethyl siloxane), low density poly (ethylene), poly (L-lactide), and poly (glycolide) by either casting or injection molding. The fidelity of the pattern transfer from the silicon substrates to the polymers was 90 to 95% in all three planes for all polymers for more than 60 transfers from a single wafer, as determined by scanning electron microscopy and atomic force microscopy. Further, the 3-D textured polymers were selectively modified to coat proteins either in the trenches or on the mesas by capillary modification or selective coating techniques. These selectively patterned 3-D polymer substrates may be useful for a variety of biomaterial applications.

Biocompatible Materials↗
PubMed1996

Postprandial elevation of activated factor VII in young adults.

The Northwick Park Heart Study found that factor VII (FVII) activity was a risk factor for ischemic heart disease, and other studies based on indirect assays of activated factor VII (FVIIa) found an elevation of FVIIa postprandially. We hypothesized that postprandial elevation of FVIIa would produce intermittent activation of factor X to Xa and, subsequently, prothrombin to thrombin. We chose to study postprandial activation of coagulation with a new assay specific for FVIIa that uses soluble tissue factor and with a prothrombin fragment 1 + 2 (F1 + 2) assay to detect the activation of prothrombin by factor Xa. We fed a high-fat breakfast (30 g/m2) to 30 healthy volunteer subjects (30.8 +/- 9.8 years; range, 20 to 49 years) on no medication. Fasting blood samples were collected for FVIIa, FVII antigen (FVIIag). and F1 + 2 as well as triglycerides and total and HDL cholesterol. A significant difference was found between fasting (2.82 +/- 1.49 ng/mL. mean +/- SD) and 6-hour postprandial (3.45 +/- 2.08 ng/mL) FVIIa levels (P < .004); FVIIag did not change significantly (mean, 0.89 U/mL fasting and 0.90 U/mL at 6 hours). In contrast, F1 + 2 levels were slightly lower 6 hours postprandially than fasting (median, 0.39 versus 0.44 nmol/L, P < .02). Four-hour postprandial triglyceride levels correlated significantly (p = 0.51, P < .02) with 6-hour postprandial FVIIag but not with 6-hour postprandial FVIIa. Postprandial F1 + 2 levels (at 6 hours) correlated significantly (p = 0.39, P < .04) with fasting FVIIag levels but not with 6-hour postprandial FVIIa levels. Thus, the basal FVIIag level, in the fasting state, may be involved in control of the generation of F1 + 2. We found a postprandial increase in FVIIa levels after a dietary fat load but did not find a concomitant postprandial burst of activation of factor X and prothrombin as measured by F1 + 2. Further studies are to test whether postprandial FVIIa generation leads to enhanced activation of coagulation.

Adult↗
PubMed1995

Azygous continuation of the interrupted inferior vena cava: a clue to prenatal diagnosis of the cardiosplenic syndromes.

We reviewed the prenatal sonographic findings in 11 consecutive fetuses diagnosed as having abdominal situs inversus (stomach on the right) at a single institution. Interruption of the inferior vena cava with azygous continuation was diagnosed by the "double vessel" sign. This sign was considered to be present in nine cases, including all eight fetuses who proved to have the polysplenia syndrome. The only false positive diagnosis of IVC interruption with azygous continuation was made prospectively in one fetus with asplenia. At autopsy, this fetus showed a large left-sided superior vena cava. We conclude that, in combination with cardiac anomalies or situs abnormalities, interruption of the IVC with azygous continuation should suggest a specific diagnosis of a cardiosplenic syndrome, especially polysplenia. This information should be helpful in patient counseling and management.

Adolescent↗
PubMed1994

Evolutionary conservation of a human function-associated molecule on murine natural killer cells: expression and function.

Using a novel anti-natural killer (NK) cell monoclonal antibody (MoAb), we have recently identified an evolutionary conserved function-associated molecule (FAM) present on fish, rat and human NK cells. This molecule is involved in NK cell function as anti-FAM MoAbs inhibit cytotoxicity, stimulate lymphokine secretion and inhibit conjugate formation between effector cells and target cells. We now have examined murine NK cells for the presence of this structure. It was observed by two-colour flow cytometric analysis that the anti-FAM MoAb 5C6 specifically bound to a subpopulation of nylon wool non-adherent splenic lymphocytes (19-20%). The expression of the FAM molecule was restricted to NK cells that expressed the NK1.1 antigen. Neither T cells, B cells, nor macrophages reacted with the anti-FAM MoAb. Analysis of FAM expression in various lymphoid tissues revealed that splenocytes expressed the greatest numbers of MoAb(+) cells. Generation of lymphokine-activated killer (LAK) cells and adherent lymphokine-activated killer (ALAK) cells resulted in higher levels of FAM expression. The anti-FAM MoAb 5C6 also detected the presence of FAM on fresh SCID NK cells. It was demonstrated that the anti-FAM MoAb 5C6 inhibited the lysis of target cells by endogenous NK cells, activated NK cells, 5d LAK cells, ALAK cells and SCID NK cells. Moreover, conjugate assays demonstrated involvement of this molecule in recognition between NK cells and target cells.

Animals↗
PubMed1993

Prenatal diagnosis of tetraploidy: a case report.

We report on the second trimester prenatal diagnosis of an apparently nonmosaic tetraploid fetus, 92,XXYY. Indications for cytogenetic studies of the fetus included abnormal ultrasound findings and abnormal maternal serum levels of alpha-fetoprotein (AFP)/estriol. Chromosome analysis of amniocytes documented tetraploidy, a finding confirmed by flow cytometry of several fetal tissues. Autopsy findings in the fetus are compared with those of other cases of tetraploidy. To our knowledge this is the first reported prenatal diagnosis of a tetraploid fetus. Additionally, it illustrates the value of flow cytometric analysis of products of conception in which polyploidy is suspected.

Abnormalities, Multiple↗
PubMed1993

Field-dependent fibroblast orientation on charged surfaces is independent of polarity and adsorbed serum proteins.

Electrets were used to induce a dipolar charge on fluorinated ethylene propylene (FEP) and bacteriological grade polystyrene (PS) films. The serum protein surface concentration adsorbed on FEP and PS from cell-free media was dependent on both the magnitude and the polarity of the surface charge density. Chick embryo fibroblasts were cultured on charged and uncharged FEP surfaces, and cellular orientation and biosynthetic activity (protein synthesis) were determined. The orientation of fibroblasts was found to be significantly dependent on the magnitude of the surface charge but independent of its polarity. The biosynthetic activity of fibroblasts was observed to be dependent on both magnitude and polarity of the surface charge density.

Adsorption↗
PubMed1993

Prenatal sonographic findings of trisomy 18: review of 47 cases.

Prenatal sonographic findings were reviewed in 47 consecutive fetuses with trisomy 18. One or more abnormalities, excluding choroid plexus cysts, were found in 39 fetuses (83%), including 21 of 29 (72%) fetuses examined between 14 and 24 weeks and all 18 (100%) fetuses examined after 24 weeks. Abnormalities most frequently detected before 24 weeks included cystic hygromas, nuchal thickening, and meningomyelocele. Intrauterine growth retardation, cardiac defects, and an enlarged cisterna magna were detected more frequently after 24 weeks than before 24 weeks (P < 0.05). Intrauterine growth retardation was the single most common abnormality, detected in 51% of all fetuses and 89% of fetuses examined after 24 weeks. Choroid plexus cysts were identified in 25% (12 of 47) of fetuses, including 11 of 29 (38%) fetuses seen before 24 weeks. Additional abnormalities were identified in 10 of 12 (83%) fetuses with choroid plexus cysts; one of the two remaining fetuses showed clenched hands and a cardiac anomaly at autopsy, and the other showed unusually large, multiple choroid plexus cysts. Awareness of the type of anomalies and the usual menstrual age of diagnosis in fetuses with trisomy 18 should improve patient counseling and prenatal detection of fetuses considered at risk for this disorder.

Abnormalities, Multiple↗
PubMed1991

Single umbilical artery. Prenatal detection of concurrent anomalies.

Prenatal sonographic findings were reviewed in 30 fetuses with a single umbilical artery (SUA) to determine the reliability of ultrasound for detecting concurrent anomalies. Additional anomalies were identified in 15 fetuses, including 3 fetuses with minor anomalies and 12 fetuses with major or multiple concurrent anomalies. Minor anomalies observed in 3 fetuses included 1 case each of pelvic kidney, unilateral absent kidney, and mild cerebral ventricular dilatation. Major abnormalities detected in 12 fetuses involved a variety of organ systems and included cardiac defects, holoprosencephaly, skeletal dysplasia, hydrocephalus, omphalocele, hydrothorax, enlarged cisterna magna, and diaphragmatic hernia. Clinical and pathologic correlation showed that all fetuses were correctly categorized regarding the presence of other anomalies; none of the 15 fetuses in whom an SUA was considered an isolated finding had a significant anomaly at birth. Chromosome abnormalities were found in 6 of 12 fetuses with major abnormalities but in none of the 18 remaining fetuses. We conclude that prenatal ultrasound can reliably identify major concurrent anomalies in fetuses with SUA. In the absence of additional anomalies, prenatal detection of SUA should not alter obstetric management.

Abnormalities, Multiple↗
PubMed1991

Enlarged cisterna magna and the Dandy-Walker malformation: factors associated with chromosome abnormalities.

Thirty-three fetuses with an enlarged cisterna magna (10 mm or more) were evaluated to determine factors that might be associated with an underlying chromosome abnormality. Eighteen fetuses (55%) proved to have a chromosome abnormality, including trisomy 18 or trisomy 18 variant (12), trisomy 13 (three), Turner syndrome (one), or other rearrangements (two). Among various risk factors analyzed, the absence of ventricular dilatation correlated most strongly with a chromosome abnormality. Chromosome abnormalities were found in 17 of 22 fetuses (77%) lacking ventricular dilatation, compared with only one of 11 fetuses (9%) with ventricular dilatation (P less than .001). Other factors statistically associated (P less than .01) with an underlying chromosome abnormality included mild enlargement of the cisterna magna (10-14 mm), concurrent anomalies detected sonographically, and fetal growth retardation. However, stepwise logistic regression showed that only the absence of ventricular dilatation and the presence of concurrent anomalies were significant when multiple factors were evaluated. These observations support the utility of evaluating the cisterna magna as part of a routine anatomical survey.

Cerebral Ventricles↗
PubMed1989

Isolation and Partial Characterization of a Subtilisin Inhibitor from the Mung Bean (Vigna radiata).

The subtilisin inhibitor (MBSI-A) from the mung bean (Vigna radiata (L.) Wilczek) seed has been purified to homogeneity. MBSI-A consists of a single polypeptide chain of 119 residues, with a high content of glutamic acid/glutamine, aspartic acid/asparagine, valine, threonine, and proline (19, 12, 10, 9, and 8 residue percent, respectively). MBSI-A is a potent inhibitor of subtilisin Carlsberg, but is inactive toward bovine trypsin and alpha-chymotrypsin and the plant cysteinyl proteinase papain. The MBSI is located exclusively in the cytosol of the seed cotyledon cell, unlike the mung bean trypsin inhibitor (MBTI), which is located primarily in the protein bodies. Both MBSI and MBTI accumulate in the seed during the most active period of reserve protein accumulation, 12 to 18 days after flowering. During germination MBSI, like MBTI, is broken down beginning 2 to 3 days after seed imbibition. The disappearance of MBSI-A is accompanied by the transient appearance of a new inhibitor species, MBSI-D. The amino acid composition of MBSI-D suggests that it may be produced by the loss of approximately 20 amino acid residues from MBSI-A.

Journal Article↗