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Biomedical subjects

S Singh

Publications and source records attributed to S Singh.

At least 19 recordsLinked to original sources
PubMed1992

Non-transferrin-bound iron species in the serum of hypotransferrinaemic mice.

Serum from homozygous hypotransferrinaemic mice (a mixed group of males and females, aged 6-8 wk) was found to contain low levels of iron (mean 0.9 +/- 0.5 microM (SEM, n = 4), as assayed by conventional serum iron assays. Similarly, low levels of non-transferrin-bound iron were determined with a nitrilotriacetate chelation assay (1.3 +/- 0.4 microM, n = 4) (Singh, S., Hider, R.C. and Porter, J.B. (1990) Analytical Biochemistry 186, 320-323). Mononuclear Fe (citrate) was undectable by electron paramagnetic resonance spectroscopy (EPR). Significantly larger quantities of iron (16 +/- 5 microM, n = 8) were detected by the bleomycin assay (Gutteridge, J.M.C., Rowley, D.A. and Halliwell, B. (1981) Biochemical Journal 199, 263-265), while non-haem iron assay or atomic absorption spectrophotometry revealed up to 96 microM iron. Haemoglobin iron was detectable at approximately 10 microM by spectrophotometry. Ferri-haem was undetectable by EPR spectroscopy. Serum ferritin levels of 641 +/- 128 micrograms/l (n = 14) in hypotransferrinaemic mice (wild-types 44 +/- 6 micrograms/l, n = 14) were observed and these cannot account for the non-transferrin-bound iron. Hypotransferrinaemic mouse serum therefore contains large quantities of non-transferrin-bound iron which is unreactive in some assays used to detect such iron in human iron overload. Fractionation by Sephadex G200 chromatography revealed three distinct species with apparent molecular weights of > or = 150 kDa, 40-80 kDa and 1-5 kDa. The iron may be distinguished from known extracellular iron proteins and haem-proteins by its availability to hot acid extractions.

Animals↗
PubMed1992

The contribution of gastroesophageal reflux to chest pain in patients with coronary artery disease.

OBJECTIVE: To describe the effectiveness of investigating and treating the cause of refractory chest pain in patients with coronary artery disease who are receiving optimal antianginal therapy. DESIGN: Cohort study. SETTING: Tertiary referral center. PATIENTS: Between January 1988 and December 1989, 34 patients were identified as having angiographically proven coronary artery disease and atypical chest pain symptoms despite their having received aggressive medical or surgical antianginal therapy, or both. INTERVENTION: Patients with confirmed acid-related symptoms were treated with high-dose histamine-2 (H2) blockers or omeprazole for 8 weeks in an open-label study. MEASUREMENTS: Esophageal manometry and simultaneous 24-hour pH and Holter studies; global improvement in or disappearance of chest pain. RESULTS: Of the 34 patients, 30 (88%) experienced their identical chest pain symptoms during the study. A total of 164 pain episodes was recorded: 38 (23.2%) correlated with acid reflux; 6 (3.7%) were related to cardiac ischemia; and the remaining 120 (73.2%) had no identifiable cause. Of these 30 patients, 20 (67%) had some of their episodes of chest pain (range, 14% to 100%) secondary to acid reflux. After 8 weeks of vigorous acid suppression, 13 of these 20 patients had marked improvement or resolution of chest pain. Four other patients had ischemia-related episodes of chest pain that responded to more aggressive antianginal therapy. No episodes of acid reflux were clearly followed by ischemic chest pain. One patient had both acid- and ischemic-related episodes of chest pain that were indistinguishable. Overall, 24 of 34 (71%) patients had a definite cause of chest pain identified by combined pH and Holter monitoring. CONCLUSIONS: Gastroesophageal reflux disease is a common, treatable cause of chest pain in patients with coronary artery disease who have atypical symptoms and remain symptomatic despite aggressive antianginal therapy. Combined Holter and 24-hour esophageal pH studies are complementary investigations for elucidating the cause of chest pain in these patients.

Adult↗
PubMed1992

Metabolism of 5-hydroxytryptamine by brain synaptosomes and microsomes in the presence of cysteine and glutathione.

Incubation of 5-hydroxytryptamine (1) with L-cysteine and pig or bovine brain microsomes and an NADPH-generating system or with synaptosomes results in the rapid formation of the (2R,4R)- and (2S,4R)-epimers of 2-[(5-hydroxy-1H-indol-3-yl)methyl]thiazolidine. Incubation of 1 and glutathione under the same experimental conditions yields the (2R,4R)- and (2S,4R)-epimers of alpha-amino-4-[[(carboxymethyl)amino]carbonyl]-2-[(5-hydroxy-1H- indol-3-yl)methyl]-delta-oxo-3-thiazolidinepentanoic acid. These various thiazolidine derivatives are formed by nucleophilic addition of the thiol residues of cysteine or glutathione to the aldehyde group of 5-hydroxyindole-3-acetaldehyde (2), the primary product of the monoamine oxidase-mediated oxidative deamination of 1. The facile reaction of cysteine and glutathione with 2 might represent a mechanism designed to scavenge the biogenic aldehyde and therefore to prevent its alkylation of key intraneuronal protein nucleophiles.

Animals↗
PubMed1992

Purification and characterization of a DNA-binding protein activated by ionizing radiation.

Exposure of mammalian cells to a variety of agents leads to the activation of pre-existing proteins and the induction of specific genes. We have recently described the appearance of a specific DNA-binding protein in nuclei from cells exposed to ionizing radiation (Singh, S. P., and Lavin, M. F. (1990) Mol. Cell. Biol. 10, 5279-5285). This protein is present in the cytoplasm of unperturbed cells and is apparently translocated to the nucleus in response to radiation damage. We describe here the purification and characterization of this specific DNA-binding protein. Purification involved the use of affinity chromatography employing a multimeric form of the DNA-binding motif conjugated to cyanogen bromide-activated Sepharose. Three DNA-binding species were recognized by UV-cross-linking and South-Western analysis. The major species or that with the highest affinity was approximately 70 kDa in size. DNase-1 footprint analysis revealed a single binding site in the kappa immunoglobulin gene enhancer and in a putative control sequence upstream from the c-myc gene. At salt concentrations as high as 1 M, up to 40% of the DNA-binding activity was maintained and the Kd was calculated to be 1.205 x 10(-6) M-1. Binding activity was found to be modulated by phosphorylation. Removal of phosphate groups from the protein resulted in a major loss of binding activity. It is not clear at this stage whether the factor(s) described here plays a role in transcription control or a more general DNA-processing role in response to radiation damage.

Alkaline Phosphatase↗
PubMed1992

Quantification of desferrioxamine and its iron chelating metabolites by high-performance liquid chromatography and simultaneous ultraviolet-visible/radioactive detection.

An HPLC-based method for quantification of desferrioxamine (DFO) and its iron chelating metabolites in plasma has been developed. This assay overcomes stability problems associated with DFO by the addition of radioactive iron to convert unbound drug and metabolites to radio-iron-bound species. A dual detection system utilizing uv-vis absorption and radioactive (beta-particle) detector was used to quantify total and radio-iron-bound species. The use of octadecyl silanol solid phase extraction cartridges permits concentration of samples and allows accurate quantification of drug and metabolites down to 0.1 nmol/ml.

Chromatography, High Pressure Liquid↗
PubMed1992

High-performance liquid chromatographic determination of 1,2-diethyl-3-hydroxypyridin-4-one and its 2-(1-hydroxyethyl) metabolite in rat blood.

A sensitive and selective high-performance liquid chromatographic (HPLC) method for the analysis of 1,2-diethyl-3-hydroxypyridin-4-one (CP94, I) and its 2-(1-hydroxyethyl) metabolite (II) in rat blood is described. I, II and the internal standard, 1-propyl-2-ethyl-3-hydroxypyridin-4-one (CP95, III) were extracted into dichloromethane (3 x 5 ml, with the addition of 1 g of sodium chloride) from blood (0.25 ml plus 0.75 ml of pH 7.0 morpholinopropanesulphonic acid buffer). Extractability approached 100% for I and III, and approximately 65% for II under these conditions. Chromatographic analysis was carried out using a Hypercarb porous graphitised carbon HPLC column (10 cm x 0.46 cm). The mobile phase was 14:86 (v/v) acetonitrile-NaH2PO4 buffer (10 mM, containing 2 mM EDTA, pH adjusted to 3 with phosphoric acid) and detection was by ultraviolet at 280 nm. Calibration curves were linear (correlation coefficient greater than 0.99) and reproducible over the concentration range 0-80 micrograms/ml and the coefficient of variation was less than 16% even at low (1 microgram/ml) concentrations. The minimum quantifiable level was 0.5 microgram/ml for both I and II.

Animals↗
PubMed1992

Stroma is critical for preventing or permitting immunological destruction of antigenic cancer cells.

Inoculated immunogenic cancer cells after initial growth are potentially rejected by specific host immunity; however, the outcome of the interaction between host and inoculated cancer cells is a function of multiple factors including the route of inoculation, the number of cells, the density of antigens on the injected cancer cells, and the state of the immune system of the host. In the present study, we have examined a different kind of variable: the stroma that inoculated tumor cells initially reside in. The impetus to examine this factor arises from observations that cancer cells from several lines inoculated as fragments of solid tumors often grow progressively, whereas the same number or more than 10-fold larger numbers of identical type cells injected as a suspension are rejected, even though fragments or suspended cells are both tumorigenic at the same doses in nude mice. In the present studies, we found that: (a) indeed, cancer cells inoculated as fragments were more tumorigenic than cancer cells in suspension; (b) the tumorigenicity of suspended cancer cells was increased by injection of the cells into polyurethane sponge implants; (c) cancer cells were more tumorigenic embedded in syngeneic stroma than in transgenic antigenic stroma expressing the K216 major histocompatibility complex class I antigen; and (d) antigenic, bone marrow-derived, stromal components (presumably passenger leukocytes) were sufficient to cause rejection of immunogenic but antigenically unrelated cancer.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Left ventricular perforation during percutaneous balloon mitral valvuloplasty.

Percutaneous balloon mitral valvuloplasty has been reported to be complicated by left ventricular perforation with fatal results. We report two cases of left ventricular perforation following balloon mitral valvuloplasty. In one patient left ventricular perforation occurred silently without any hemodynamic sequelae and was only detected at left ventricular angiography after valvuloplasty. In the second patient left ventricular perforation was caused by the mitral dilating balloon catheter. The subsequent tamponade was relieved by immediate aspiration with hemodynamic stabilization thereafter. Neither patient required surgery. Both patients are well 6 mon after the procedure. We discuss the mechanism of this serious complication in these two patients.

Balloon Occlusion↗
PubMed1992

Simultaneously occurring alopecia areata and Hodgkin's lymphoma: complete remission of both diseases with MOPP/ABV chemotherapy.

A 43-year-old man presented with simultaneously occurring alopecia areata and stage IIIB nodular sclerosing Hodgkin's disease. Systemic symptoms of Hodgkin's disease were present for 6 months, and rapidly developing patchy hair loss of the scalp was present for 2 weeks prior to presentation. The patient was treated with eight cycles of MOPP-ABV chemotherapy that resulted in complete remission of Hodgkin's-disease. Four months after the completion of chemotherapy, the patient had normal hair regrowth with no evidence of alopecia areata. Alopecia areata may be an autoimmune disease and may respond to chemotherapy.

Adult↗
PubMed1992

Comparison of a cloned ANF-sensitive guanylate cyclase (GC-A) with particulate guanylate cyclase from adrenal cortex.

Recently, an ANF-sensitive guanylate cyclase (GC-A) has been cloned from a rat brain cDNA library. Here we studied the stimulation of cyclic GMP accumulation in response to atrial natriuretic factor (ANF), urodilatin and atriopeptin I (AP-1) in a rat glioma C6 cell line permanently transfected with GC-A as well as GC-A activity in membranes from these C6 cells and in membranes from COS-7 cells that were transiently transfected with GC-A. We also measured binding affinities for these natriuretic peptides in the membrane preparations. These characteristics of GC-A were compared to those of membrane preparations from adrenal cortex of bovine and human origin. The order of potency of stimulation of cyclic GMP accumulation in permanently transfected glioma cells was ANF greater than urodilatin greater than AP I; AP I stimulated cyclic GMP accumulation. A similar order of potency was obtained for stimulation of guanylate cyclase activity in membranes from permanently transfected glioma cells as well as from transiently transfected COS-7 cells. In contrast, AP-1 was uneffective to stimulate guanylate cyclase in membrane preparations from adrenal cortex from bovine as well as from human origin. Furthermore, urodilatin was equipotent to ANF in these preparations. Binding affinities were comparable for ANF and urodilatin in membranes from cells transfected with GC-A and in membranes from adrenal cortex of both sources, whereas AP-1 had a weaker affinity in all preparations studied.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Cortex↗
PubMed1992

Mosaicism in 45,X Turner syndrome: does survival in early pregnancy depend on the presence of two sex chromosomes?

Cytogenetic and molecular genetic findings in 91 patients with Turner syndrome are reported. In 87 patients, chromosome studies were carried out both in lymphocyte and fibroblast cultures. Mosaicism was demonstrated in 58 of these patients (66.7%), whereas only 18 (20.7%) were apparent non-mosaic 45,X, and 11 patients (12.6%) showed non-mosaic structural aberrations of the X chromosome. Among the mosaic cases 16 (18.4% of all patients) displayed a second cell line containing small marker chromosomes. The association of Y-specific chromosomal material with the presence of marker chromosomes was demonstrated in 6 out of 7 mixoploid fibroblast cell lines by polymerase chain reaction amplification and by Southern-blot analysis. The observation of ring formation and morphological variability in vivo and in vitro, and the continuous reduction in the percentage of cells containing marker chromosomes in longterm cultivation experiments indicated an increased instability of marker chromosomes. The findings suggest that in vivo selection of structurally altered sex chromosomes exists. Thus, the observation of apparent non-mosaic 45,X chromosomal complements in liveborn individuals with Turner syndrome does not contradict the hypothesis that some degree of mosaicism is necessary for survival in early pregnancy.

Blotting, Southern↗
PubMed1992

Distribution of ADH2 and ALDH2 genotypes in different populations.

The distribution of the human liver alcohol dehydrogenase, ADH2, and aldehyde dehydrogenase, ALDH2, genotypes in 21 different populations comprising Mongoloids, Caucasoids, and Negroids was determined by hybridization of the amplified genomic DNA with allele-specific oligonucleotide probes. Whereas the frequency of the ADH1(2) allele was found to be relatively high in the Caucasoids, Mexican Mestizos, Brazilian Indios, Swedish Lapps, Papua New Guineans and Negroids, the frequency of the ADH2(2) gene was considerably higher in the Mongoloids and Australian Aborigines. The atypical ALDH2 gene (ALDH2(2)) was found to be extremely rare in Caucasoids, Negroids, Papua New Guineans, Australian Aborigines and Aurocanians (South Chile). In contrast, this mutant gene was found to be widely prevalent among the Mongoloids. Individuals possessing the abnormal ALDH2 gene show alcohol-related sensitivity responses (e.g. facial flushing), have the tendency not to be habitual drinkers, and apparently suffer less from alcoholism and alcohol-related liver disease.

Alcohol Dehydrogenase↗
PubMed1992

Photoperiodic response of pineal-thyroid axis of the female Indian palm squirrel, Funambulus pennanti.

Effect of short (SP: 10 L: 14 D: Light: Dark) and long (LP: 14 L: 10 D) photoperiod was tested on pineal-thyroid axis in a tropical seasonally breeding rodent F. pennanti during sexually regressive phase of reproduction. SP reduced thyroid weight and plasma thyroxine (T4) as well as increased melatonin (aMT) while pinealectomy (Px) prevented such an effect of SP. LP and Px plus LP had no significant effect on thyroid activity when compared with their respective controls. These results suggest that SP stimulated pineal activity which increased the concentration of aMT, hence inhibited thyroid gland activity. However, the plasma aMT concentration under LP regime had no significant difference from controls, as the ambient photoperiodic length (13.6 hr) was almost similar to the experimental one (14.0 hr). It is suggested that being innervated from the same ganglion (SCG) which conveys photic stimuli to the pineal gland, the thyroid gland like the pineal is also under the influence of photoperiodic responses. Further pineal/melatonin also influences thyroid function indirectly.

Animals↗
PubMed1992

Effects of a pH electrode across the lower esophageal sphincter.

Recent studies have suggested that combined monitoring of the esophagus and stomach for prolonged periods may be the best method for investigating patients with upper gastrointestinal complaints. However, the effects of an electrode across the LES on esophageal reflux parameters have not been extensively studied. We studied 10 healthy volunteers and 10 patients with GERD twice with 24-hr pH monitoring. In phase 1, two glass electrodes were placed 1 cm below the UES and 5 cm above the LES. One week later in phase 2, patients were restudied with one electrode 5 cm above and one 5 cm below the LES. Although total acid exposure remained the same in healthy volunteers, three volunteers who spontaneously refluxed at night had abnormal prolongation of their supine acid exposure during phase 2 of the study. In patients with GERD, the electrode across the LES resulted in significant (P = 0.01) increase in supine acid exposure and showed a strong tendency for the number of reflux episodes greater than 5 min supine (P = 0.02) and longest reflux episode supine (P = 0.06) to increase without a change in the number of reflux episodes. In conclusion, a small glass electrode across the LES results in prolongation of supine acid exposure in both healthy volunteers spontaneously refluxing at night and the majority of patients with GERD. This results from the electrode interfering with clearance of refluxed acid in the supine position. Thus, combined esophageal and gastric pH monitoring may have important limitations in investigating gastroesophageal symptoms.

Circadian Rhythm↗
PubMed1992

Antioxidant defenses in the bile duct-ligated rat.

Changes in pro-oxidant and antioxidant balance in the serum and liver were studied in an experimental model of obstructive jaundice in the rat. The results showed a decrease in plasma vitamin E concentration (P < 0.01) and a threefold reduction in liver vitamin E concentration (P < 0.001). There was also a threefold reduction in levels of the liver enzymes glutathione peroxidase (P < 0.01) and glutathione transferase (P < 0.001), together with a six-fold reduction in catalase activity (P < 0.001). The serum selenium level decreased by 35% in the jaundiced rats (P < 0.05). The total liver glutathione level decreased to half the control value (P < 0.01). The malonyldialdehyde level, the measure of lipid peroxidation used in this study, doubled (P < 0.01). The results suggest a shift in the pro-oxidant/antioxidant balance in favor of lipid peroxidation. The possible etiology of this change and its relationship to human cholestasis are discussed.

Animals↗