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Biomedical subjects

S Mitra

Publications and source records attributed to S Mitra.

At least 109 records · Page 6Linked to original sources
PubMed2000

Staging of cervical cancer with soft computing.

This paper describes a way of designing a hybrid decision support system in soft computing paradigm for detecting the different stages of cervical cancer. Hybridization includes the evolution of knowledge-based subnetwork modules with genetic algorithms (GA's) using rough set theory and the Interactive Dichotomizer 3 (ID3) algorithm. Crude subnetworks obtained via rough set theory and the ID3 algorithm are evolved using GA's. The evolution uses a restricted mutation operator which utilizes the knowledge of the modular structure, already generated, for faster convergence. The GA tunes the network weights and structure simultaneously. The aforesaid integration enhances the performance in terms of classification score, network size and training time, as compared to the conventional multilayer perceptron. This methodology also helps in imposing a structure on the weights, which results in a network more suitable for extraction of logical rules and human interpretation of the inferencing procedure.

Algorithms↗
PubMed2000

Silent alpha(2C)-adrenergic receptors enable cold-induced vasoconstriction in cutaneous arteries.

Cold constricts cutaneous blood vessels by increasing the reactivity of smooth muscle alpha(2)-adrenergic receptors (alpha(2)-ARs). Experiments were performed to determine the role of alpha(2)-AR subtypes (alpha(2A)-, alpha(2B)-, alpha(2C)-ARs) in this response. Stimulation of alpha(1)-ARs by phenylephrine or alpha(2)-ARs by UK-14,304 caused constriction of isolated mouse tail arteries mounted in a pressurized myograph system. Compared with proximal arteries, distal arteries were more responsive to alpha(2)-AR activation but less responsive to activation of alpha(1)-ARs. Cold augmented constriction to alpha(2)-AR activation in distal arteries but did not affect the response to alpha(1)-AR stimulation or the level of myogenic tone. Western blot analysis demonstrated expression of alpha(2A)- and alpha(2C)-ARs in tail arteries: expression of alpha(2C)-ARs decreased in distal compared with proximal arteries, whereas expression of the glycosylated form of the alpha(2A)-AR increased in distal arteries. At 37 degrees C, alpha(2)-AR-induced vasoconstriction in distal arteries was inhibited by selective blockade of alpha(2A)-ARs (BRL-44408) but not by selective inhibition of alpha(2B)-ARs (ARC-239) or alpha(2C)-ARs (MK-912). In contrast, during cold exposure (28 degrees C), the augmented response to UK-14,304 was inhibited by the alpha(2C)-AR antagonist MK-912, which selectively abolished cold-induced amplification of the response. These experiments indicate that cold-induced amplification of alpha(2)-ARs is mediated by alpha(2C)-ARs that are normally silent in these cutaneous arteries. Blockade of alpha(2C)-ARs may prove an effective treatment for Raynaud's Phenomenon.

Adrenergic alpha-Agonists↗
PubMed2000

Requirement for human AP endonuclease 1 for repair of 3'-blocking damage at DNA single-strand breaks induced by reactive oxygen species.

The major mammalian apurinic/apyrimidinic (AP) endonuclease (APE1) plays a central role in the DNA base excision repair pathway (BER) in two distinct ways. As an AP endonuclease, it initiates repair of AP sites in DNA produced either spontaneously or after removal of uracil and alkylated bases in DNA by monofunctional DNA glycosylases. Alternatively, by acting as a 3'-phosphoesterase, it initiates repair of DNA strand breaks with 3'-blocking damage, which are produced either directly by reactive oxygen species (ROS) or indirectly through the AP lyase reaction of damage-specific DNA glycosylases. The endonuclease activity of APE1, however, is much more efficient than its DNA 3'-phosphoesterase activity. Using whole extracts from human HeLa and lymphoblastoid TK6 cells, we have investigated whether these two activities differentially affect BER efficiency. The repair of ROS-induced DNA strand breaks was significantly stimulated by supplementing the reaction with purified APE1. This enhancement was linearly dependent on the amount of APE1 added, while addition of other BER enzymes, such as DNA ligase I and FEN1, had no effect. Moreover, depletion of endogenous APE1 from the extract significantly reduced the repair activity, suggesting that APE1 is essential for repairing such DNA damage and is limiting in extracts of human cells. In contrast, when uracil-containing DNA was used as the substrate, the efficiency of repair was not affected by exogenous APE1, presumably because the AP endonuclease activity was not limiting. These results indicate that the cellular level of APE1 may differentially affect repair efficiency for DNA strand breaks but not for uracil and AP sites in DNA.

Carbon-Oxygen Lyases↗
PubMed2000

Methemoglobinemia in aluminium phosphide poisoning in rats.

Aluminium phosphide (AlP) a grain fumigant is the leading cause of intentional poisoning in North India. The mechanisms involved in toxicity are not known and there is no antidote till date. The present study was carried out to investigate the oxygen free radical generation, methemoglobinemia and effect of methylene blue treatment on survival time in rat model of AlP poisoning. AlP (50 mg/kg, intragastric) was administered in one group and the other group received AlP + Methylene Blue (MB) (0.1%, 1 mg/kg/5 min, i.v.). Malonyldialdehyde (MDA) and methemoglobin (MeHb) levels were measured at 10 and 30 min intervals. Blood MDA levels increased at 10 and 30 min after AlP exposure with simultaneous rise in MeHb levels suggesting methemoglobinemia could be due to increased oxygen free radical generation. Methylene blue caused a significant fall in both the parameters with prolongation of survival time. It is concluded that AlP causes methemoglobinemia responding to methylene blue treatment.

Aluminum Compounds↗
PubMed1999

An unexpected link between the secretory path and the organization of the nucleus.

Yeast sec mutations define the machinery of vesicular traffic. Surprisingly, many of these mutations also inhibit ribosome biogenesis by reducing transcription of rRNA and genes encoding ribosomal proteins. We observe that these mutants reversibly inhibit protein import into the nucleus, with import cargo accumulating at the nucleoplasmic face of nuclear pore complexes, as when Ran-GTP cannot bind importins. They also rapidly and reversibly relocate multiple nucleolar and nucleoplasmic proteins to the cytoplasm. The import block and relocation are antagonized by overexpression of yeast Ran, Hog1p kinase, or Ssa/Hsp70 proteins or by inhibition of protein synthesis. These nucleocytoplasmic signaling events document an extraordinary plasticity of nuclear organization.

Biological Transport↗
PubMed1999

Characterization of a chlorambucil-resistant human ovarian carcinoma cell line overexpressing glutathione S-transferase mu.

Ovarian carcinoma cells 10-fold resistant to the alkylating agent chlorambucil (CBL) were isolated after repeated exposure of the parent cells to gradually escalating concentrations of the drug. The resistant variant, A2780(100), was highly cross-resistant (9-fold) to melphalan and showed lower-level resistance to other cross-linking agents. The resistant A2780(100) cells had almost 5-fold higher glutathione S-transferase (GST) activity than the parental A2780 cells with 1-chloro-2,4-dinitrobenzene (CDNB) as substrate. The pi-class GST(s) was the major isoform(s) in both cell lines. However, the resistant A2780(100) cells had at least 11-fold higher GST mu as compared with the parental cells, in which this isoform was barely detectable. A significant induction of GST mu was observed in A2780 cells, but not in the resistant cells, 18 hr after a single exposure to 100 microM CBL. The induction of GST mu by CBL was both time- and concentration-dependent. Assays of the conjugation of CBL with GSH showed that the human mu-class GST had 3.6- and 5.2-fold higher catalytic efficiency relative to the pi- and alpha-class GSTs, respectively. This difference was reflected in the relatively higher (about 6-fold) efficiency of CBL conjugation in A2780(100) cells as compared with the parental cells. These results have demonstrated for the first time a near-linear correlation between CBL resistance and overexpression of mu-class GSTs and suggest that this overexpression maybe responsible, at least in part, for the acquired resistance of ovarian carcinoma cells to CBL, and possibly the other bifunctional alkylating agents. Consistent with this hypothesis, we found evidence for decreased formation of DNA lesions in A2780(100) compared with the drug-sensitive A2780 cells after exposure to CBL.

Antineoplastic Agents, Alkylating↗
PubMed1999

Intragenic suppression of an active site mutation in the human apurinic/apyrimidinic endonuclease.

The apurinic/apyrimidinic endonucleases (APE) contain several highly conserved sequence motifs. The glutamic acid residue in a consensus motif, LQE96TK98 in human APE (hAPE-1), is crucial because of its role in coordinating Mg2+, an essential cofactor. Random mutagenesis of the inactive E96A mutant cDNA, followed by phenotypic screening in Escherichia coli, led to isolation of an intragenic suppressor with a second site mutation, K98R. Although the Km of the suppressor mutant was about sixfold higher than that of the wild-type enzyme, their kcat values were similar for AP endonuclease activity. These results suggest that the E96A mutation affects only the DNA-binding step, but not the catalytic step of the enzyme. The 3' DNA phosphoesterase activities of the wild-type and the suppressor mutant were also comparable. No global change of the protein conformation is induced by the single or double mutations, but a local perturbation in the structural environment of tryptophan residues may be induced by the K98R mutation. The wild-type and suppressor mutant proteins have similar Mg2+ requirement for activity. These results suggest a minor perturbation in conformation of the suppressor mutant enabling an unidentified Asp or Glu residue to substitute for Glu96 in positioning Mg2+ during catalysis. The possibility that Asp70 is such a residue, based on its observed proximity to the metal-binding site in the wild-type protein, was excluded by site-specific mutation studies. It thus appears that another acidic residue coordinates with Mg2+ in the mutant protein. These results suggest a rather flexible conformation of the region surrounding the metal binding site in hAPE-1 which is not obvious from the X-ray crystallographic structure.

Carbon-Oxygen Lyases↗
PubMed1999

Activation of human O6-methylguanine-DNA methyltransferase gene by glucocorticoid hormone.

O6-methylguanine-DNA methyltransferase (MGMT), a ubiquitous DNA repair protein, removes the mutagenic DNA adduct O6-alkylguanine, which is synthesized both endogenously and after exposure to alkylnitrosamines and alkylating antitumor drugs such as 2-chloroethyl-N-nitrosourea (CNU). The MGMT gene is highly regulated in mammalian cells and its overexpression, observed in many types of tumor cells, is often associated with cellular resistance to CNU. Dexamethasone, a synthetic glucocorticoid hormone, was found to increase MGMT expression in HeLa S3 cells, concomitant with their increased resistance to CNU. Two putative glucocorticoid responsive elements (GREs) were identified in the human MGMT (hMGMT) promoter. Transient expression of the luciferase reporter gene driven by an hMGMT promoter fragment containing these GREs was activated by dexamethasone. DNase I footprinting assays demonstrated the binding of glucocorticoid receptor to these sequences. In vitro transcription experiment showed that these DNA sequences are functional in glucocorticoid receptor signal-mediated activation of transcription. These results suggest glucocorticoid-mediated induction of the MGMT gene contributes to high level expression of MGMT.

DNA Footprinting↗
PubMed1999

Experimental autoimmune cystitis: further characterization and serum autoantibodies.

Previously, we described an animal model for interstitial cystitis (IC), experimental autoimmune cystitis (EAC) [Luber-Narod et al. Urol Res 24:367]. Further characterization of animals with EAC indicates that peak and mean urinary frequency are elevated compared with sham-injected controls and that the disease progresses with at least two cycles of exacerbations and remissions. We had shown evidence suggesting EAC to be autoimmune in nature. In this paper, we identify serum autoantibodies from 9/10 EAC animals which bind to a protein specific to rat bladder with a relative molecular weight of 12-kDa. Such autoantibodies are absent in 12/13 normal and sham-injected animals as well as animals which fail to develop EAC despite disease induction. These findings suggest that EAC is a reproducible model of cyclical increases of urinary frequency, and that a 12-kDa antigen is the target of autoantibodies which correlate with those elevations. Identification of this target antigen may explain the pathogenesis of increased urinary frequency in these animals and potentially in IC as well.

Animals↗
PubMed1999

Mechanism of gastroprotection by bismuth subsalicylate against chemically induced oxidative stress in cultured human gastric mucosal cells.

Reactive oxygen species (ROS) are implicated in the pathogenesis of chemically induced gastric mucosal injury. We have investigated the effects of ethanol, hydrochloric acid (HCl), and sodium hydroxide (NaOH) on: (1) enhanced production of ROS including superoxide anion and hydroxyl radicals, (2) modulation of intracellular oxidized states by laser scanning confocal microscopy, and (3) DNA fragmentation, indices of oxidative tissue, and DNA damage in a primary culture of normal human gastric mucosal cells (GC), which were isolated and cultured from Helicobacter pylori-negative endoscopic biopsies from human subjects. The induction of ROS and DNA damage in these cells following exposure to ethanol (15%), HCl (150 mM) and NaOH (150 mM) were assessed by cytochrome c reduction (superoxide anion production), HPLC detection for enhanced production of hydroxyl radicals, changes in intracellular oxidized states by laser scanning confocal microscopy, and DNA damage by quantitating DNA fragmentation. Furthermore, the protective ability of bismuth subsalicylate (BSS) was assessed at concentrations of 25, 50, and 100 mg/liter. Incubation of GC with ethanol, HCI, and NaOH increased superoxide anion production by approximately 8.0-, 6.1-and 7.1-fold and increased hydroxyl radical production by 13.3-, 9.6-, and 8.9-fold, respectively, compared to the untreated gastric cells. Incubation of GC with ethanol, HCl, and NaOH increased DNA fragmentation by approximately 6.7-, 4.3-, and 4.8-fold, respectively. Approximately 20.3-, 17.5-, and 13.1-fold increases in fluorescence intensities were observed following incubation of gastric cells with ethanol, HCl, and NaOH, respectively, demonstrating dramatic changes in the intracellular oxidized states of GC following exposure to these necrotizing agents. Preincubation of GC with 25, 50, and 100 mg/liter of BSS decreased ethanol-induced increases in intracellular oxidized states in these cells by 36%, 56%, and 66%, respectively, demonstrating a concentration-dependent protective ability by BSS. Similar results were observed with respect to BSS in terms of superoxide anion and hydroxyl radical production, and DNA damage. The present study demonstrates that ethanol, HCl, and NaOH induce oxidative stress and DNA damage in GC and that BSS can significantly attenuate gastric injury by scavenging these ROS.

Bismuth↗
PubMed1999

Is the measurement of serum testosterone routinely indicated in men with erectile dysfunction?

OBJECTIVE: To investigate the usefulness of serum testosterone levels as a relevant or useful indicator of sexual potency in men attending an erectile dysfunction clinic. PATIENTS AND METHODS: Ninety consecutive men attending the erectile dysfunction clinic completed a sexual-activity questionnaire, and underwent a focused physical examination and questioning about their medical history. The serum testosterone level was measured in all patients and the results analysed in relation to the patient's age. Patients with low serum testosterone levels commenced replacement therapy comprising three intramuscular injections of testosterone (Sustanontrade mark, Organon, The Netherlands) 250 mg every third week. Potency status and serum testosterone were reassessed after 3 months' treatment. RESULTS: Of the 90 men, 28 (31%) were aged < 50 years whilst 62 (69%) were >/=50 years old. Nineteen (21%) patients overall had low testosterone levels; four of these were < 50 and 15 were >/=50 years old. Five of 90 patients had a decreased libido; two of these also had low testosterone levels and all were < 50 years old. Testosterone levels returned to normal in all patients who received replacement therapy but potency returned in only two (10%); both were in the older group. CONCLUSION: Measuring testosterone was not helpful in assessing potency or libido and low serum levels were not related to age. Correcting low testosterone did not improve either impotence or libido.

Adult↗