Search PubMed⌕ Search

Biomedical subjects

R Kumar

Publications and source records attributed to R Kumar.

At least 19 recordsLinked to original sources
PubMed1992

The expression of milligram amounts of functional human 1,25-dihydroxyvitamin D3 receptor in a bacterial expression system.

We expressed milligram amounts of functional human 1,25-dihydroxyvitamin D3 receptor in a bacterial expression system in which the cloned cDNA for the hVDR was expressed under the control of bacterial T7 polymerase. The hVDR protein comprised approximately 60% of total bacterial protein. It migrated on polyacrylamide-sodium dodecyl sulfate gels with an M(r) of 48,000. It had the predicted amino acid composition and amino acid sequence analysis. The expressed protein was bound by 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) with a Kd in the nanomolar range. It sedimented on sucrose density gradients at 3.5S. Furthermore, the expressed protein bound to the osteocalcin vitamin D response element (VDRE) as assessed by a gel mobility shift assay. The expression of large amounts of hVDR protein should allow for the use of this protein in structure-function and x-ray crystallography studies.

Amino Acid Sequence↗
PubMed1992

Equal inhibition of HIV replication by stereoisomers of phosphatidyl-azidothymidine. Lack of stereospecificity of lysosomal phospholipase A1.

Glycerol-1-P and glycerol-3-P stereoisomers of dipalmitoylphosphatidylazidothymidine were synthesized and found to have equal antiretroviral activity in HIV-infected HT4-6C cells. It was anticipated that the glycerol-1-P isomer would be less active because of slow metabolic conversion by cellular phospholipases A and C, but the antiretroviral results suggested that the human cell line (HT4-6C) may have phospholipases capable of hydrolyzing 2,3-dipalmitoyl-sn-glycerol-1-phospho-5'-azidothymidine (AZT). To evaluate this possibility, we purified lysosomal phospholipase A1, an enzyme known to play a major role in cellular phospholipid catabolism. This enzyme rapidly hydrolyzed both the sn-1 and sn-3 isomers of dipalmitoylphosphatidyl-AZT. We synthesized sn-2,3-dipalmitoyl-glycero-1-phosphocholine and found that it is also hydrolyzed readily by lysosomal phospholipase A1 although the Vmax, 59 mumol mg-1 h-1, is slightly lower than that of the sn-1,2-dipalmitoyl-glycero-3-phosphocholine, 89 mumol mg-1 h-1. In conclusion, our studies show that sn-2,3-dipalmitoyl-glycerol-1-phospho-AZT is equal in antiviral activity to sn-1,2-dipalmitoyl-glycero-3-phospho-AZT in HIV-infected HT4-6C cells. This surprising result is due in part to the lack of stereospecificity of lysosomal phospholipase A1.

Animals↗
PubMed1992

Effect of dietary nitrate on endogenous nitrosation of piperazine in humans.

The effect of dietary nitrate on endogenous nitrosation of a therapeutic dose of piperazine has been described in five human volunteers who acted as their own controls. The urinary excretion of endogenously formed N-nitro-somonopiperazine (MNPz) ranged between 9.2 and 80.1 micrograms/24 h on a normal uncontrolled diet which increased from 25.7 to 163.7 micrograms/24 h when the diet was supplemented with 250 mg nitrate. The corresponding urinary nitrate was 63.0-122.7 mg/24 h and 119.2-322.0 mg/24 h, respectively. The dinitroso derivative of piperazine was detected only in trace amounts and no detectable increase in its excretion was observed during high nitrate exposure. The unchanged piperazine (range 294-784 mg/24 h) in urine showed a decrease under high nitrate regimen (range 185-399 mg/24 h).

Carcinogens↗
PubMed1992

Interferon alpha induces the expression of retinoblastoma gene product in human Burkitt lymphoma Daudi cells: role in growth regulation.

Interferon alpha (IFN-alpha) is a regulatory secretory protein with distinctive biological effects such as antiproliferative actions against many tumor cell lines, including human Burkitt lymphoma Daudi cells. The mechanism underlying growth inhibition by IFN-alpha is not well established. The growth of many mammalian cell types is also regulated by tumor suppressor retinoblastoma (RB) gene product, the RB protein. In the studies presented here, we explored the possible involvement of RB protein in the growth inhibitory action of IFN-alpha in the Daudi cell model system. We observed that IFN-alpha induces a 3- to 10-fold increased expression of RB protein in growth-sensitive Daudi cells but not in the growth-resistant variant of Daudi cells. IFN-alpha-mediated induction of RB protein was an early event that preceded the period of growth inhibition of Daudi cells. IFN-alpha-induced RB protein predominantly exists as the underphosphorylated form. Addition of antibody against IFN-alpha to Daudi cells resulted in the inhibition of constitutive expression of RB protein and stimulation of [3H]thymidine incorporation. These results demonstrate that the induction of RB protein expression in IFN-alpha-treated Daudi cells could constitute an important mechanism of IFN-alpha-mediated growth regulation.

Burkitt Lymphoma↗
PubMed1992

Growth regulation of human renal carcinoma cells: role of transforming growth factor alpha.

Findings of increased numbers of epidermal growth factor receptors (EGF-R) and increased expression of transforming growth factor alpha (TGF-alpha) in surgical specimens of human renal cell carcinoma have led to the proposal that growth of these tumors may be regulated by TGF-alpha in an autocrine manner. In the studies presented here, we have examined this hypothesis using two human renal carcinoma cell lines, SKRC-4 and SKRC-29. We demonstrated that both SKRC-4 and SKRC-29 cells were growth stimulated by greater than 35% when cultured in the presence of TGF-alpha or EGF and were inhibited by 29% to 46% if cultured in the presence of anti-EGF-R monoclonal antibody 225. Treatment of cells with TGF-alpha enhanced the levels of expression of EGF-R mRNA and TGF-alpha mRNA. In addition, incubation of cells with monoclonal antibody 225 significantly elevated the levels of excreted TGF-alpha species in the culture medium. Our findings suggest that proliferation of human renal carcinoma cells may be regulated by endogenously produced TGF-alpha and that this regulatory pathway can be interrupted using antibody to its receptor, EGF-R.

Carcinoma, Renal Cell↗
PubMed1992

A vasopressin analog that binds but does not activate V1 or V2 vasopressin receptors is not internalized into cells that express V1 or V2 receptors.

To assess whether receptor binding is sufficient to initiate vasopressin receptor endocytosis in cells expressing the vasopressin V1 or V2 receptors, we synthesized a novel fluorescent-labeled vasopressin analog, [1-(beta-mercapto-beta, beta-cyclopentamethylene propionic acid), 2-(O-ethyl)-D-tyrosine, 4-valine, 8-lysine-N6-carboxytetramethylrhodamine] vasopressin (R-CLVP), that binds to vasopressin receptors but does not activate intracellular events such as the mobilization of intracellular calcium or the activation of adenylate cyclase. We compared the manner in which this analog was endocytosed in cells expressing V1 (A-10, rat smooth muscle cells) or V2 (LLC-PK1, porcine kidney cells) receptors with that of a full agonist, [1-(beta-mercaptopropionic acid), 8-lysine-N6-carboxytetramethylrhodamine] vasopressin (R-MLVP) [Lutz et al. (1990) J. Biol. Chem. 265, 4657-4663; Lutz et al. (1990) Proc. Natl. Acad. Sci. U.S.A. 87,6507-6511]. We showed that R-CLVP bound to both types of receptors with good affinity. It failed to increase cyclic AMP concentrations in LLC-PK1 cells and did not increase the mobilization of intracellular calcium in A-10 cells. It bound to the surface of both these cell types in a diffuse manner and it did not undergo receptor endocytosis in either cell type. In contrast, R-MLVP, an agonist that bound to both receptor subtypes and elicited changes in intracellular cyclic AMP and calcium, bound to the surface of these cells in a diffuse manner at early times after exposure, and rapidly underwent endocytosis. We conclude that binding of vasopressin to its receptors alone is insufficient to cause receptor endocytosis, and other events distal to the receptor are required to initiate endocytosis. R-CLVP should be a useful analog in determining the factors responsible for initiating receptor endocytosis.

Amino Acid Sequence↗
PubMed1992

Prosopis cineraria leaf tannins: their inhibitory effect upon ruminal cellulase and the recovery of inhibition by polyethylene glycol-4000.

The condensed tannins from the Prosopis cineraria leaves were purified and fractionated in two groups (Kav 0.018 and 0.74) on a column of Sephadex LH-20 (2.5 x 27 cm) using 70 percent aqueous acetone as the eluent. The Kav for catechin was 0.946. Upon acid hydrolysis, both the condensed tannin fractions yielded three pigments including cyanidin-chloride, which was separated by column chromatography using polyvinylpyrrolidone absorbent and was identified by paper chromatography (Rf Forestal 0.476) and absorption maxima (lambda max 535 nm) in 1 percent HCl in methanol. The condensed tannin fraction Kav 0.74 at 0.01 percent and 0.02 percent in incubations with butanol-acetone powder of rumen liquor, inhibited cellulase activity by 65.9 +/- 2.1 and 78.99 +/- 4.5 percent, respectively. Inclusion of 0.5 percent of polyethylene glycol -4000 in the incubation mixture, reduced the inhibition to 41 and 46 percent, respectively.

Animals↗
PubMed1992

Human nutrition in cold and high terrestrial altitudes.

The calorie and nutritional requirements for a man working in an alien hostile environment of cold regions and high altitude are described and compared to those of normal requirements. Carbohydrates, fats and vitamins fulfilling the caloric and nutritional requirements are generally available in adequate amounts except under conditions of appetite loss. However, the proteins and amino acids should be provided in such a way as to meet the altered behavioral and metabolic requirements. Work in extreme cold requires fulfilling enhanced calorie needs. In high mountainous regions, cold combined with hypoxia produced loss of appetite and necessitated designing of special foods.

Altitude↗
PubMed1992

Intracardiac echocardiography during simulated aortic and mitral balloon valvuloplasty: in vivo experimental studies.

The feasibility of intracardiac echocardiography with a low-frequency transducer to assess catheter position and detect complications during experimental aortic and mitral balloon valvuloplasty was studied in 10 dogs. Intracardiac echocardiography was performed with a transesophageal echocardiographic probe placed in the right atrium. In all instances high-quality images of cardiac structures were obtained. The guide wire and balloon catheter were clearly seen as they crossed the valves. With inflation the balloon was seen as a hyperechoic structure. Doppler echocardiography documented aortic regurgitation after inflations. Acute pericardial effusion was instantly detected. It is concluded that intracardiac echocardiography is a potentially useful technique for cardiac imaging, assessing wire and balloon catheter position, evaluating valvular regurgitation, and instantly detecting acute pericardial effusion. Further research in humans with low-frequency, catheter-based transducers needs to be performed.

Animals↗
PubMed1992

Vitamin D and mineral deficiencies increase the plasma membrane calcium pump of chicken intestine.

The basolateral membrane of the enterocyte was previously shown to contain an adenosine triphosphate-dependent calcium pump. Using immunological procedures, the localization of the Ca2+ pump in chick intestine, and the effect of dietary variables on the concentration of the pump, were studied. A monoclonal antibody produced against the human erythrocyte calcium pump was shown to cross-react with a chick intestinal Ca2+ pump epitope. The most intense staining of intestinal tissue, as determined immunohistochemically, occurred at the basolateral membrane of the duodenum, jejunum, ileum, and colon, with minor staining elsewhere. By the Western blotting procedure, vitamin D repletion of vitamin D-deficient chicks was shown to significantly increase the concentration of the Ca2+ pump epitope of duodenal, jejunal, and ileal mucosa by a factor of 2-3. Chicks were also fed diets deficient in calcium or phosphorus, a situation known to result in the stimulation of the synthesis of calbindin-D28k and an enhancement of the efficiency of Ca2+ absorption. Adaptation of the chicks to these deficient diets was verified by an increase in intestinal levels of calbindin-D28k, and is now shown to increase the Ca2+ pump epitope. From these immunological studies, it seems apparent that dietary variables that enhance intestinal Ca2+ absorption also increase the amount of the intestinal basolateral Ca2+ pump.

Animals↗
PubMed1992

Contribution of psychological and social factors to psychotic and non-psychotic relapse after childbirth in women with previous histories of affective disorder.

Twenty-six women with a history of bipolar or schizoaffective disorder, 17 women with histories of major depressive disorder and 45 control women without any previous psychiatric history were assessed in the 9th month of pregnancy on selected psychosocial measures. No subject was a 'case' as defined by the Research Diagnostic Criteria (RDC) from this time until the delivery. Within 6 months postpartum, 22 (51%) of the women with histories of mental illness were categorised as having relapsed (RDC case). Twelve women developed a psychosis (mania, hypomania or schizomania) and these illnesses occurred only in women with histories of affective or schizoaffective psychosis whereas 10 other women who became depressed after delivery came equally from the women with histories of psychosis (N = 5) as from those with histories of major depression (N = 5). Three (7%) control women also developed postpartum non-psychotic depressive disorders. Multivariate analyses suggest that different psychosocial factors contribute to the recurrence of affective and schizoaffective psychosis after delivery as opposed to non-psychotic postpartum affective disorders. A non-psychotic illness was predicted by antenatal neuroticism and a severe life event before illness onset. A recurrence of psychosis postpartum was predicted by a history of mania, hypomania or schizomania, a more recent psychiatric admission and reported marital difficulties. In this sample of women, life stress led to postpartum depression irrespective of the subject's past history and the high rates of recurrence of affective or schizoaffective psychosis (47%) probably mainly reflected a pre-existing physiological or psychological vulnerability which may have been exacerbated by, or contributed to, marital difficulties.

Bipolar Disorder↗
PubMed1992

Pernicious anaemia as a risk factor for osteoporosis.

1. If gastric acid is necessary for the absorption of dietary calcium, the total absence of gastric acid secretion that occurs in pernicious anaemia could result in bone loss. To investigate this, we measured calcium absorption and bone density in 21 postmenopausal women (ages 51-76 years) with pernicious anaemia and in 24 normal postmenopausal women (ages 51-79 years). 2. Relative to the normal women, in the women with pernicious anaemia the bone mineral density of the lumbar spine was decreased by 16% (P less than 0.001). 3. After adjustment for age and body weight, lumbar spine bone mineral density correlated with the serum concentration of group 1 pepsinogens (a group of proteins produced by the gastric fundus) (r = 0.61, P less than 0.01). 4. Despite achlorhydria, the women with pernicious anaemia had normal true fractional calcium absorption and normal serum levels of parathyroid hormone and 1,25-dihydroxyvitamin D. 5. We conclude that gastric acid is not required for the absorption of dietary calcium. Thus, the loss of cancellous bone must be caused by some mechanism yet to be identified.

Achlorhydria↗
PubMed1992

Use of the computed tomographic scan in Japanese encephalitis.

Fourteen children with laboratory-confirmed Japanese encephalitis were given cranial computed tomographic (CT) scans six to 30 days after the onset of illness. The findings were variable; there was a generalized decrease in attenuation values, three patients showed features of cerebral atrophy, and four others had normal scans. The findings appeared to relate to both the severity and the stage of the illness at the time the scans were made. CT would appear to be of little use in making a specific diagnosis of Japanese encephalitis.

Brain↗
PubMed1992

Caffeine-derived N-nitroso compounds--I: Nitrosatable precursors from caffeine and their potential relevance in the etiology of oesophageal and gastric cancers in Kashmir, India.

Salted tea prepared in Kashmir by adding sodium bicarbonate shows high methylating activity (equivalent to 3 p.p.m. N-methylnitrosourea) upon in vitro nitrosation. Pure caffeine treated under conditions of the tea preparation formed caffeidine and caffeidine acid. We report here the formation of two new compounds, mononitrosocaffeidine, an asymmetric nitrosamine, and dinitrosocaffeidine, a N-nitrosamide, on in vitro nitrosation of caffeidine. Mononitrosocaffeidine is also found after nitrosation of the typical Kashmir tea. The nitrosation of caffeidine acid produced N,N'-dimethyl-parabanic acid, mononitrosocaffeidine and N,N'-dimethyl-N-nitrosourea. In view of the well-known structure-activity relationships of these N-nitroso compounds, their possible endogenous formation due to high consumption of salted tea may be a critical risk factor for the high occurrence of oesophageal and gastric cancers in Kashmir.

Bicarbonates↗
PubMed1992

Increased exposure to dietary amines and nitrate in a population at high risk of oesophageal and gastric cancer in Kashmir (India).

Analytical data on aliphatic amines and nitrate from the most commonly used fresh and sun-dried vegetables, red chillies and a widely consumed beverage, salted tea, are presented from a high risk area for oesophageal and gastric cancer in Kashmir. Exposure estimates for the adult population show that high consumption of boiled Brassica vegetables leads to a high nitrate intake of 237 mg/day. The frequent consumption of hot salted tea is shown to result in exceptionally high exposure to methylamine (1200 micrograms/day), ethylamine (14,320 micrograms/day), dimethylamine (150 micrograms/day) and diethylamine (400 micrograms/day). The indiscriminate use of red chillies in the area leads to exposure to dimethylamine (280 micrograms/day), pyrrolidine (517 micrograms/day) and methylbenzylamine (40 micrograms/day). This is to our knowledge the first report where a chronic exposure to methylbenzylamine has been shown in a population at high risk of oesophageal cancer.

Adult↗
PubMed1992

Cloning and expression of the murine gene and chromosomal location of the human gene encoding N-acetylglucosaminyltransferase I.

A mouse cDNA clone previously isolated from an F9 teratocarcinoma cell library and shown to confer N-acetylglucosaminyltransferase I (GlcNAc-TI) activity on Lec1 Chinese hamster ovary (CHO) cell transfectants [Kumar, R., Yang,J., Larsen,R.D. and Stanley,P. (1990) Proc. Natl. Acad Sci. USA, 87, 9948-9952] has been sequenced. The nucleotide and deduced amino acid sequences are highly homologous to previously described human and rabbit GlcNAc-TI cDNAs. A 1250 bp portion of the mouse cDNA encoding all but the first 34 amino acids of the deduced protein sequence was inducibly expressed in Escherichia coli and gave rise to a prominent fusion protein of mol. wt approximately 45 kDa whose presence correlated with high levels of GlcNAc-TI activity in cell lysates. Probes generated from the cDNA were used to show that the GlcNAc-TI gene is present in a single copy in mammals and that a homologous gene was not detectable (under low-stringency hybridization conditions) in DNA from yeast, sea urchin, Drosophila or Chaenorhaditis elegans. Genomic DNA clones that hybridized to probes generated from the GlcNAc-TI cDNA were isolated from a mouse liver library. Restriction analyses, Southern hybridization and DNA sequence analyses of subcloned genomic DNA fragments and a polymerase chain reaction (PCR) product provided evidence that the coding and 3' untranslated regions of the cDNA reside in a single exon. However, the mouse GlcNAc-TI gene (Mgat-1) includes at least one additional exon 5' of the coding region. Southern analyses of DNA from mouse-human somatic cell hybrids and in situ hybridization were used to locate the human GlcNAc-TI gene (MGAT-1) between positions q31.2 and q31.3 on chromosome 5, a region of chromosome 5 that is syntenic with a region of mouse chromosome 11. Northern analyses of adult mouse tissues revealed two GlcNAc-TI gene transcripts that are differentially expressed in different tissues.

Amino Acid Sequence↗
PubMed1992

Intestinal calcium transport and calcium extrusion processes at the basolateral membrane.

The intestinal absorption of calcium has been proposed to occur by the transcellular transfer of Ca2+ through the enterocyte proper and between the cells of the intestinal epithelium, i.e., the paracellular path. Attention in this report is given to the transcellular models of Ca2+ absorption and, more specifically, the Ca2+ extrusion events occurring at the basolateral membrane. These extrusion processes include the operation of an ATP-dependent Ca2+ pump and a Na+/Ca2+ exchanger, as well as exocytosis as the terminal event in a proposed vesicular transport mechanism. Evidence for the presence of an ATP-dependent Ca2+ pump at the basolateral membrane is documented and illustrated with biochemical and immunological data from studies on the avian intestinal basolateral membrane. As shown immunohistochemically, the Ca2+ pump was primarily localized on the enterocyte basolateral membrane. The ATP-dependency and vitamin D enhancement of Ca2+ uptake by isolated basolateral membrane vesicles are shown. Western blot analysis of intestinal mucosa, by using a monoclonal antibody produced against the erythrocyte Ca2+ pump, indicated that the number of pump units is increased by 1,25-dihydroxycholecalciferol. The possible involvement of calbindin-D28K as a direct stimulator of the Ca2+ pump is discussed, and the quantitative relationship between Ca2+ transport rates and Ca2+ pumping activity has been estimated. Information related to the basolateral membrane Na+/Ca2+ exchanger and the vesicular transport model of Ca2+ absorption is also briefly reviewed.

Animals↗