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Biomedical subjects

S Mitra

Publications and source records attributed to S Mitra.

At least 127 records · Page 7Linked to original sources
PubMed1999

What is hypertension in chronic haemodialysis? The role of interdialytic blood pressure monitoring.

BACKGROUND: Hypertension in chronic haemodialysis patients contributes significantly to morbidity and mortality. Treatment decisions are usually based on predialysis readings, which may not accurately reflect control during the interdialytic period. METHODS: We studied 40 randomly selected subjects on haemodialysis and compared readings by different methods at set times during the dialysis session with the 48-h interdialytic ambulatory readings. Conventional sphygmomanometer, automated Dinamap and Tm 2421(A&D) ambulatory monitor were used for BP measurements. RESULTS: Conventional sphygmomanometry and self measured automatic readings (Dinamap) were highly correlated (systolic r=0.93, P<0.001; diastolic r=0.90, P<0.001). Mean blood pressure on arrival ((PreC(0)) 158 mmHg systolic, 80 mmHg diastolic and 106 mmHg mean) significantly overestimated the mean ambulatory reading during the 6 h prior to attendance ((preAm(6h)) systolic 147 (P<0.01), diastolic 75 (P<0.01), mean 99 (P<0.01)). Fifteen patients (41%) demonstrated a marked difference (>20/10 mmHg) between the PreC(0) and preAm(6h) (white-coat effect) persisting in seven patients (19%) after a period of rest 10 min predialysis (preC(10)) and present even in self-recorded Dinamap readings. There was a significant negative relationship between the systolic rise and the number of months on dialysis (P<0.05). Mean ambulatory BP on interdialytic day 2 was significantly greater than on day 1 whereas the awake-sleep differences were less on day 2 than day 1, both perhaps reflecting differences in volume status. The 20 min post-dialysis measurement (PoC(20)) for systolic, diastolic, and mean, unlike predialysis (PreC(0) and preC(10)), onset (onC) and end of dialysis readings (enC) did not differ significantly from 48 h interdialytic means. CONCLUSIONS: The best representation of interdialytic pressure was the 20-min post-dialysis reading. Walk-in predialysis pressures overestimate mean interdialytic pressures due to a high incidence of white-coat effect, which shows some habituation with time on dialysis. Ambulatory monitoring has a role in evaluating persistent poor blood pressure control in haemodialysis patients.

Adult↗
PubMed1999

Evolving experience with direct puncture therapeutic embolization for adjunctive and palliative management of head and neck hypervascular neoplasms.

OBJECTIVES: The use of percutaneous, direct puncture therapeutic embolization (DPTE) of hypervascular head and neck neoplasms is a relatively new modality that may be used to supplement or supplant conventional endovascular transarterial embolization. Although the preliminary clinical experience reported by a single group has been favorable, extensive case series experience is lacking. This prompted us to review our recent clinical experience with these techniques to determine safety, efficacy, and emerging role in the overall neurointerventional therapeutic armamentarium. STUDY DESIGN: A retrospective analysis of the previous 34 consecutive cases of hypervascular tumors undergoing DPTE referred to our service for therapeutic devascularization was performed. METHODS: Complete case record review was undertaken. Twenty-six of 34 cases involved DPTE of head and neck neoplasms. Conventional diagnostic angiography was performed for therapeutic planning and to assist in precise localization. When performed, standard microcatheter transarterial embolization techniques were used either before or after attempted DPTE. Cyanoacrylate embolic mixtures (n-butyl cyanoacrylate [NBCA], lipiodol, powdered tungsten) were used in 21 of 24 cases, and absolute ethanol in 3 of 24. Direct puncture angiography of the targeted tumor neovasculature was always performed before DPTE. RESULTS: Twenty-four of 26 cases had technically successful DPTE. Combined transarterial embolization with DPTE was used in 16 of 24 cases, although for the last 12 cases, 9 were treated predominantly or exclusively by DPTE. There were no major or minor clinical complications, and there was one asymptomatic technical complication. Total or near-total devascularization was achieved in all cases. All preoperative cases had excellent hemostasis within the resected tumor bed. CONCLUSIONS: Our results lend further support to the safety and efficacy of DPTE in the management of hypervascular neoplasms of the head and neck. With our increasing experience, this technique is evolving into a primary therapeutic modality for optimal tumor devascularization.

Adult↗
PubMed1999

Acute and chronic stress-induced oxidative gastrointestinal mucosal injury in rats and protection by bismuth subsalicylate.

Reactive oxygen species (ROS) are implicated in the pathogenesis of stress-induced gastrointestinal mucosal injury. In the present study, we have investigated the effects of acute and chronic stress on the enhanced production of ROS including superoxide anion [SA; as determined by cytochrome c reduction (CCR)] and hydroxyl radicals (OH), and correlated the enhanced production of these free radicals with increased lipid peroxidation, membrane microviscosity and DNA fragmentation, indices of oxidative tissue damage, in the gastric and intestinal mucosa of female Sprague-Dawley rats. Furthermore, the protective ability of bismuth subsalicylate (BSS) against the gastrointestinal mucosal injury induced by acute and chronic stress was determined. Acute stress was induced for a period of 90 min, while chronic stress was induced for 15 min/day for 15 consecutive days. Half of the animals exposed to acute stress were pretreated orally with 15 mg BSS/kg 30 min prior to the exposure to acute stress. Similarly, half of the animals exposed to water-immersion restraint chronic stress were pretreated orally with 7.5 mg BSS/kg/day for 15 consecutive days 30 min prior to the exposure to chronic stress. Acute stress produced greater injury to both gastric and intestinal mucosa as compared to chronic stress. Acute stress increased CCR and OH production by 10.0- and 14.3-fold, respectively, in the gastric mucosa, and 10.4- and 17.0-fold, respectively, in the intestinal mucosa. Pretreatment with BSS prevented the acute stress-induced increase in CCR and OH production. Acute stress increased lipid peroxidation, DNA fragmentation and membrane microviscosity by 3.6-, 4.0- and 11.6-fold, respectively, in gastric mucosa, and 4.1-, 5.0- and 16.2-fold, respectively, in intestinal mucosa. BSS decreased acute stress-induced lipid peroxidation, DNA fragmentation and membrane microviscosity by approximately 26, 35 and 30%, respectively, in gastric mucosa, and by 20, 36 and 30%, respectively, in the intestinal mucosa. Chronic stress increased CCR and OH production by 4.8- and 6.3-fold, respectively, in gastric mucosa, and 4.6- and 6.9-fold, respectively, in intestinal mucosa. Chronic stress increased lipid peroxidation and DNA fragmentation by 2.9- and 3.3-fold, respectively, in gastric mucosa, and 3.3- and 4.2-fold, respectively, in intestinal mucosa. BSS decreased chronic stress-induced lipid peroxidation, DNA fragmentation and membrane microviscosity by approximately 41, 44 and 45%, respectively, in gastric mucosa, and by 39, 52 and 51%, respectively, in the intestinal mucosa. Daily administration of BSS provided greater protection against chronic stress-induced oxidative gastrointestinal injury as compared to the acute stress. These results demonstrate that both acute and chronic stress can induce gastrointestinal mucosal injury through enhanced production of ROS, and that BSS can significantly protect against gastrointestinal mucosal injury.

Animals↗
PubMed1999

Investigation of an epidemic of Reye's syndrome in northern region of India.

OBJECTIVE: To determine the extent, epidemiological and clinical features of an epidemic of non-inflammatory encephalopathy in northern region of India. DESIGN: Surveillance of referred cases having unconsciousness after a short bout of fever during October and November 1997. Case control study in 7 most affected villages. METHODS: Active case finding was done to assess the extent and severity of the epidemic by interviewing health professionals and by reviewing mortality records in 10 districts of Haryana, Punjab and Chandigarh. A house to house survey was conducted in seven most affected villages. A case was defined as any child of less than 15 years of age, who had prodromal fever followed by vomiting and unconsciousness with subsequent recovery or death. Two age and sex matched controls who had fever without unconsciousness were taken for each case, one from nearby house and another staying furthest from the affected house. These groups were compared for various epidemiologic factors, clinical features and treatment pattern. Residual medicines used by affected patients were tested for presence of salicylate. Local village practitioners were interviewed for their knowledge and attitude towards use of aspirin in a febrile child. RESULTS: Information regarding 129 affected children (M: F=1 : 1) could be obtained. Age ranged between 1 to 12 years (mean 5.8 years). Most were from rural or semi-suburban areas. Attack rate was 5.4/1000 and case fatality rate was 72%. Multiple sibs were affected in 9.3%. History of fever was reported by 83%, vomiting preceding unconsciousness by 83% and abnormal behavior by 65%. Abnormal posturing was reported in 55%. Seventeen (61%) of 28 samples had IgM antibodies in serum/CSF against measles. Twelve (36%) of 33 serum samples tested positive for Varicella zoster virus. None gave history of aspirin intake and 10 samples of residual drugs did not contain salicylate. However, 6 out of 19 blood samples taken from affected patients contained salicylate. Environmental factors were in favor of Japanese encephalitis (JE) but brain biopsy and serology disproved it. Based on earlier report of JE from this area, the cases in present epidemic were being reported as JE before this study was undertaken. Intensive fogging with malathion was being undertaken as antimosquito measure, specially around the affected houses. Local village practitioners (n = 37) were unaware of contraindications of aspirin in a febrile child. CONCLUSION: Measles and varicella zoster emerged as the probable etiologies for the viral prodrome precipitating these cases of Reye's syndrome. Aspirin might have a contributory role. Malathion is another putative cofactor.

Case-Control Studies↗
PubMed1999

Acute nonspecific carditis in adolescents presenting with Stokes-Adams attacks.

Three patients, aged between 12 and 17 years presented with Stokes-Adams attacks as a result of atrioventricular block, atrioventricular silence and ventricular arrhythmias, complicating acute myocarditis. All the patients required temporary pacing for a few days. One patient required hemodialysis for anuria. All the patients made complete recovery.

Adams-Stokes Syndrome↗
PubMed1999

Pigmented villonodular synovitis of the temporomandibular joint: diagnostic imaging and endovascular therapeutic embolization of a rare head and neck tumor.

We report a case of pigmented villonodular synovitis involving the temporomandibular joint that presented as a rapidly growing tumor with extension through the skull base into the middle cranial fossa. The case is of interest not only because of the unusual extensive infiltration of this tumor but also because of the role modern diagnostic imaging and endovascular therapeutic techniques played in its diagnosis and management.

Adult↗
PubMed1998

APE/Ref-1 responses to ischemia in rat brain.

Cerebral ischemia and the aftermath of reperfusion form a hypoxic/hyperoxic sequence of events that can trigger oxidative stress response cascades in neurons of the central nervous system. After transient ischemia there is an increase in intracellular Ca2+ release, extracellular glutamate, reactive oxygen species (ROS) and nitric oxide, genotoxic events that stimulate DNA repair. Increased oxidative stress and interrupted blood flow in ischemia, like DNA repair, also deplete cellular ATP and commit neurons to apoptosis. We report that levels of the DNA repair enzyme apurinic/apyrimidinic endonuclease (APE/Ref-1) decreased significantly in the hippocampus but not other brain areas after 6 h of reperfusion following an induced ischemic insult. This specific inhibition of APE/Ref-1 expression may affect the extent of apoptosis after ischemia.

Animals↗
PubMed1998

APE/Ref-1 responses to oxidative stress in aged rats.

Chronic oxidative stress has been hypothesized to be a major contributor to the aging process. The continued exposure to reactive oxygen species (ROS) generated by oxidative metabolism or environmental sources can damage critical cellular structures and be responsible for some age-related pathology. The exposure of rodents to 100% oxygen, isobaric hyperoxia, increases ambient ROS levels and significantly increases apoptosis in brain. The deleterious effects of ROS also include increased lipid peroxidation, protein oxidation, and DNA damage. Although differences in the relative amounts of oxidative stress in young and old brains have been observed, the mechanisms responsible for impaired aging-associated DNA repair processes have not been characterized. We measured DNA levels of the DNA repair enzyme apurinic/apyrimidinic endonuclease (APE/Ref-1) protein by Western blot analysis in the brains of young (3-month) and old (30-month) male rats exposed to isobaric hyperoxia. Given that APE/Ref-1 is the rate-limiting enzyme in the repair pathway of apurinic/apyrimidinic sites generated in DNA by oxidative damage, we assumed that APE/Ref-1 protein levels were a good reflection of ongoing DNA base excision repair. Isobaric hyperoxia stimulated APE/Ref-1 expression in the hippocampus and basal forebrain of young rats experiencing 100% oxygen for 6 hr, while aged rats showed no significant changes in APE/Ref-1 protein levels in all brain areas at any time tested (0-48 hr) after hyperoxia. Differences in the stress-induced levels of expression of DNA repair enzymes may contribute to apoptotic increases and pathology associated with the aging process.

Aging↗
PubMed1998

The presence of two distinct 8-oxoguanine repair enzymes in human cells: their potential complementary roles in preventing mutation.

8-Oxoguanine (8-oxoG), induced by reactive oxygen species (ROS) and ionizing radiation, is arguably the most important mutagenic lesion in DNA. This oxidized base, because of its mispairing with A, induces GC-->TA transversion mutations often observed spontaneously in tumor cells. The human cDNA encoding the repair enzyme 8-oxoG-DNA glycosylase (OGG-1) has recently been cloned, however, its activity was never detected in cells. Here we show that the apparent lack of this activity could be due to the presence of an 8-oxoG-specific DNA binding protein. Moreover, we demonstrate the presence of two antigenically distinct OGG activities with an identical reaction mechanism in human cell (HeLa) extracts. The 38 kDa OGG-1, identical to the cloned enzyme, cleaves 8-oxoG when paired with cytosine, thymine and guanine but not adenine in DNA. In contrast, the newly discovered 36 kDa OGG-2 prefers 8-oxoG paired with G and A. We propose that OGG-1 and OGG-2 have distinct antimutagenic functions in vivo . OGG-1 prevents mutation by removing 8-oxoG formed in DNA in situ and paired with C, while OGG-2 removes 8-oxoG that is incorporated opposite A in DNA from ROS-induced 8-oxodGTP. We predict that OGG-2 specifically removes such 8-oxoG residues only from the nascent strand, possibly by utilizing the same mechanism as the DNA mismatch repair pathway.

Carbon-Oxygen Lyases↗
PubMed1998

The role of distal histidine in peroxidase activity of myoglobin--transient-kinetics study of the reaction of H2O2 with wild-type and distal-histidine-mutanted recombinant human myoglobin.

The distal histidine has been proposed to play a crucial role in the reaction of peroxidases with hydroperoxide. Myoglobin (Mb), due to its close similarity with peroxidases, also reacts with various peroxides. The effect of mutation of the distal histidine on the peroxidase activity of Mb has been investigated by stopped-flow kinetics of the reaction of hydrogen peroxide with wild-type Mb and [Gly64]Mb. The results indicate kinetic and mechanistic differences in the formation of peroxide compounds from these two forms of Mb. The rate of reaction of H2O2 with the wild-type Mb decreased 8-9-fold on mutation of the distal histidine to glycine ([Gly64]Mb). A second slow phase was observed for the reaction of H2O2 with [Gly64]Mb, but was not observed in the corresponding reaction with wild-type Mb. It is suggested that the decrease in the rate of the reaction on mutation is due to the absence of a general acid-base catalyst. The effect of pH on the rate of reaction of H2O2 with wild-type Mb and [Gly64]Mb is contrasting. While the rate of the Mb [corrected] reaction decreased for wild-type Mb at higher pH, probably due to the acid-alkaline transition of Mb at higher pH, the rate of reaction was found to increase at higher pH for mutant Mb. The increase in the rate of the reaction is suggested to be due to an increase in the ionization of H2O2 at higher pH, the rate-determining step being the formation of the intermediate Fe-O-O-H complex and not the subsequent step of oxo-ferryl complex formation. The thermodynamic parameters calculated from the temperature-dependent study showed that the enthalpy of binding of H2O2 with Mb is positive, indicating that the process is endothermic. The apparent energy of activation of the reaction of H2O2 with Mb was found to be higher than that of peroxidases, suggesting that this may be oue of the reasons for the slower rate of the reaction of H2O2 with Mb compared with peroxidases.

Amino Acid Sequence↗
PubMed1998

Identification of APN2, the Saccharomyces cerevisiae homolog of the major human AP endonuclease HAP1, and its role in the repair of abasic sites.

Abasic (AP) sites arise in DNA through spontaneous base loss and enzymatic removal of damaged bases. APN1 encodes the major AP-endonuclease of Saccharomyces cerevisiae. Human HAP1 (REF1) encodes the major AP endonuclease which, in addition to its role in DNA repair, functions as a redox regulatory protein. We identify APN2, the yeast homolog of HAP1 and provide evidence that Apn1 and Apn2 represent alternate pathways for repairing AP sites. The apn1Delta apn2Delta strain displays a highly elevated level of MMS-induced mutagenesis, which is dependent on the REV3, REV7, and REV1 genes. Our findings indicate that AP sites are highly cytotoxic and mutagenic in eukaryotes, and that the REV3, REV7-encoded DNA polymerase zeta mediates the mutagenic bypass of AP sites.

Amino Acid Sequence↗
PubMed1998

Regulation of expression of the DNA repair gene O6-methylguanine-DNA methyltransferase via protein kinase C-mediated signaling.

O6-Alkylguanine is the major mutagenic and cytotoxic DNA lesion induced by alkylating agents, including 2-chloroethyl-N-nitrosourea-based antitumor drugs. This lesion is repaired by O6-methylguanine-DNA methyltransferase (MGMT), the expression of which is highly variable in both normal tissues and in tumor cells. The promoter of the human MGMT gene was found to contain two putative activator protein (AP)-1 sites. Here, we show that the level of MGMT mRNA in HeLa S3 cells was increased 3-5-fold by phorbol-12-myristate-13-acetate (TPA) and 1,2-diacyl-sn-glycerol (DAG), which are activators of protein kinase C (PKC), as well as by okadaic acid, an inhibitor of protein phosphatases. The PKC inhibitor 1-(5-isoquinoline sulfonyl)-2-methylpiperazine-HCl eliminated MGMT activation by TPA and DAG but not by OA. Prior down-regulation of PKC abolished subsequent effects of TPA or DAG. The results indicate AP-1 to be involved in regulation of MGMT expression. This hypothesis was supported by showing AP-1 binding to two target sequences of the MGMT promoter and transactivation of the MGMT promoter upon cotransfection with c-fos and c-jun in F9 cells. That TPA-mediated induction of MGMT caused increased cellular resistance to 2-chloroethyl-N-nitrosourea suggests a therapeutic significance for PKC-mediated MGMT modulation.

Alkylating Agents↗
PubMed1998

Purification and characterization of human NTH1, a homolog of Escherichia coli endonuclease III. Direct identification of Lys-212 as the active nucleophilic residue.

The human endonuclease III (hNTH1), a homolog of the Escherichia coli enzyme (Nth), is a DNA glycosylase with abasic (apurinic/apyrimidinic (AP)) lyase activity and specifically cleaves oxidatively damaged pyrimidines in DNA. Its cDNA was cloned, and the full-length enzyme (304 amino acid residues) was expressed as a glutathione S-transferase fusion polypeptide in E. coli. Purified wild-type protein with two additional amino acid residues and a truncated protein with deletion of 22 residues at the NH2 terminus were equally active and had absorbance maxima at 280 and 410 nm, the latter due to the presence of a [4Fe-4S]cluster, as in E. coli Nth. The enzyme cleaved thymine glycol-containing form I plasmid DNA and a dihydrouracil (DHU)-containing oligonucleotide duplex. The protein had a molar extinction coefficient of 5.0 x 10(4) and a pI of 10. With the DHU-containing oligonucleotide duplex as substrate, the Km was 47 nM, and kcat was approximately 0.6/min, independent of whether DHU paired with G or A. The enzyme carries out beta-elimination and forms a Schiff base between the active site residue and the deoxyribose generated after base removal. The prediction of Lys-212 being the active site was confirmed by sequence analysis of the peptide-oligonucleotide adduct. Furthermore, replacing Lys-212 with Gln inactivated the enzyme. However, replacement with Arg-212 yielded an active enzyme with about 85-fold lower catalytic specificity than the wild-type protein. DNase I footprinting with hNTH1 showed protection of 10 nucleotides centered around the base lesion in the damaged strand and a stretch of 15 nucleotides (with the G opposite the lesion at the 5'-boundary) in the complementary strand. Immunological studies showed that HeLa cells contain a single hNTH species of the predicted size, localized in both the nucleus and the cytoplasm.

Base Sequence↗
PubMed1998

Characterization of a partially unfolded structure of cytochrome c induced by sodium dodecyl sulphate and the kinetics of its refolding.

The mechanism of unfolding of ferricytochrome c induced by the surfactant sodium dodecyl sulfate has been studied by heme absorption, tryptophan fluorescence, circular dichroism, resonance Raman scattering, stopped-flow and time-resolved resonance energy transfer to obtain a comprehensive view of the whole process. Unfolding occurred at an almost specific molecular ratio of SDS/cytochrome c in the concentration range (20-50 microM) studied here. However there appears to be a point at approximately 0.6 mM SDS where unfolding begins to occur for lower cytochrome c concentrations. The kinetics of unfolding revealed only a single transition with a rate constant of 33 s(-1) (at 298 K, [SDS] = 8.7 mM) and activation energy barrier of approximately 16 kJ/mol, indicating that other associated steps, if any, are too fast to be significantly populated. The free energy change (deltaG(o)) involved with the unfolding transition was estimated to be about 16.8 kJ/mol. The CD spectrum at 220 nm of SDS-unfolded cytochrome c shows only a partial decrease (25%), indicating that a significant amount of helical structure remains folded in contrast to a complete loss of helical structure in GdnHCl-denatured cytochrome c. The heme structure in SDS-unfolded cytochrome c, as deduced from heme absorption and resonance Raman spectra, shows a major population (approximately 95%) of mis-ligated histidine to the heme which acts as a kinetic trap in the folding process. The structural changes associated with cytochrome c unfolding were also monitored by time-resolved resonance energy transfer which shows a drastic increase in tryptophan fluorescence lifetime from 12 ps in the native protein to 0.63 ns in the unfolded one, associated with a movement of Trp59 by 10 A away from heme. The maximum entropy method analysis of fluorescence decay indicated the growth of various conformational substates in SDS-unfolded cytochrome c in contrast to narrowly distributed conformations in the native protein. The refolding was comprised of three kinetic steps; the first was significantly fast (approximately 8 ms) and was assigned to the dissociation of His26 that paves the protein towards correct folding pathway. The other two slower steps probably arise from chain misorganization and prolyl isomerization. The absence of a burst-phase amplitude supports the idea that the burst phase observed in the folding from completely unfolded cytochrome c corresponds to a molecular collapse that produces significant secondary structure. The partially unfolded state represents a unique intermediate state in the folding pathway.

Animals↗