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Biomedical subjects

G Karthikeyan

Publications and source records attributed to G Karthikeyan.

At least 19 recordsLinked to original sources
PubMed2006

Comparison of treatment potential of electrocoagulation of distillery effluent with and without activated Areca catechu nut carbon.

Physico-chemical characteristics of distillery effluent samples have been determined. The water quality parameters (WQPs) measured are colour, pH, electrical conductivity, turbidity, total dissolved solids (TDS), chloride, total hardness (THA), calcium, iron, bio-chemical oxygen demand (BOD) and chemical oxygen demand (COD). Almost all the values of WQPs of the distillery effluents have been found to be very high and well above the permissible limit suggested by Bureau of Indian Standards (BIS). Electrocoagulation (EC) technique is employed to treat the distillery effluents. Removal efficiency of WQPs is compared by adopting EC technique with and without the addition of indigenously prepared activated areca nut [botanical name: Areca catechu; kotta pakku, in (vernacular)] carbon (AAC). About 99% of turbidity has been removed in both the cases. The experimental results also revealed that the WQPs like EC, TDS, etc. of the effluents could be reduced. Loss of weight of sacrificial electrode (anode) is also ascertained. EC with AAC is found to be more effective than EC without AAC.

Aluminum↗
PubMed2006

Managing patients undergoing non-cardiac surgery: need to shift emphasis from risk stratification to risk modification.

Many patients undergo non-invasive testing for the detection of coronary artery disease before non-cardiac surgery. This is despite the low predictive value of positive tests in this population and the lack of any evidence of benefit of coronary revascularisation before non-cardiac surgical procedures. Further, this strategy often triggers a clinical cascade exposing the patient to progressively riskier testing and intervention and results in increased costs and unnecessary delays. On the other hand, administration of beta blockers, and more recently statins, has been shown to reduce the occurrence of perioperative ischaemic events. Therefore, there is a need for a shift in emphasis from risk stratification by non-invasive testing to risk modification by the application of interventions, which prevent perioperative ischaemia--principally, perioperative beta adrenergic blockade and perhaps treatment with statins. Clinical risk stratification tools reliably identify patients at high risk of perioperative ischaemic events and can guide in the appropriate use of perioperative medical treatment.

Adrenergic beta-Antagonists↗
PubMed2005

Use of a restriction endonuclease cytotoxicity assay to identify inducible GAL1 promoter variants with reduced basal activity.

Inducible promoter fusions are commonly employed to study the biological functions of genes as well as to investigate mechanisms of transcription regulation. A concern for many studies of heterologous gene expression is that steady state transcription may be too high under non-inducing conditions, producing undesired phenotypes prior to induction. Fusions containing the galactose-inducible GAL1 promoter joined to PvuII, a bacterial DNA endonuclease gene, are toxic to yeast cells even under non-inducing conditions, i.e., in glucose media. This toxicity was utilized in conjunction with PCR-based mutagenesis of the GAL1 regulatory region to isolate mutant promoters that retained high inducibility but exhibited reduced basal level expression. The Mig1 repressor binding and putative TATA box regions were unchanged among four mutant promoters examined in detail. However, each promoter contained one or more mutations within previously identified binding sites for the Gal4 activator protein. Genetic assays developed to monitor GAL1p::I-SceI endonuclease-induced recombination demonstrated that basal expression from two of the new promoters (designated GAL1-V4 and GAL1-V10) was strongly reduced. These experiments and additional quantitative luciferase reporter gene assays demonstrate the utility of the approach for identifying promoters that permit more tightly controlled gene expression.

Base Sequence↗
PubMed2005

Reduction of nucleosome assembly during new DNA synthesis impairs both major pathways of double-strand break repair.

Assembly of new chromatin during S phase requires the histone chaperone complexes CAF-1 (Cac2p, Msi1p and Rlf2p) and RCAF (Asf1p plus acetylated histones H3 and H4). Cells lacking CAF-1 and RCAF are hypersensitive to DNA-damaging agents, such as methyl methanesulfonate and camptothecin, suggesting a possible defect in double-strand break (DSB) repair. Assays developed to quantitate repair of defined, cohesive-ended break structures revealed that DSB-induced plasmid:chromosome recombination was reduced approximately 10-fold in RCAF/CAF-1 double mutants. Recombination defects were similar with both chromosomal and plasmid targets in vivo, suggesting that inhibitory chromatin structures were not involved. Consistent with these observations, ionizing radiation-induced loss of heterozygosity was abolished in the mutants. Nonhomologous end-joining (NHEJ) repair proficiency and accuracy were intermediate between wild-type levels and those of NHEJ-deficient yku70 and rad50 mutants. The defects in NHEJ, but not homologous recombination, could be rescued by deletion of HMR-a1, a component of the a1/alpha2 transcriptional repressor complex. The findings are consistent with the observation that silent mating loci are partially derepressed. These results demonstrate that defective assembly of nucleosomes during new DNA synthesis compromises each of the known pathways of DSB repair and that the effects can be indirect consequences of changes in silenced chromatin structure.

Cell Cycle Proteins↗
PubMed2003

Mapping of fluoride endemic areas and correlation studies of fluoride with other quality parameters of drinking water of Veppanapalli block of Dharmapuri district in Tamil Nadu.

193 drinking water samples from water sources of 27 panchayats of Veppanapalli block of Dharmapuri district of Tamil Nadu were analysed for chemical quality parameters. Based on the fluoride content of the water sources, fluoride maps differentiating regions with high / low fluoride levels were prepared using Isopleth mapping technique. The interdependence among the important chemical quality parameters were assessed using correlation studies. The experimental results of the application of linear and multiple regression equations on the influence of hardness, alkalinity, total dissolved solids and pH on fluoride are discussed.

Child↗
PubMed2002

Conventional ventilation in neonates: experience from Saudi Arabia.

OBJECTIVE: To study the clinical profile and immediate outcome of inborn neonates receiving intermittent positive pressure ventilation (IPPV) at the neonatal intensive care unit of Civil Hospital, Khamis Mushayt, Saudi Arabia, a level II nursery. METHODS: 78 liveborn neonates who had received IPPV over a 20 months period from January 1999 to August 2000 were reviewed from their charts and nursery registers. The indications for IPPV and the immediate outcome including complications were studied with respect to various weight groups (1 kg or less, > 1-1.25 kg, > 1.25-1.5, > 1.5-2 kg and > 2 kg) and gestation groups (28 weeks or less, 29-32 weeks, 33-36 weeks and full term). RESULT: Hyaline Membrane disease (n = 31, 39.7%) and perinatal asphyxia (n = 29, 37.2%) were the major indications for IPPV. 67.9% (53 of the 78) ventilated neonates survived. The chances for survival showed a statistically significant increase with increasing birthweight (P = 0.0006) and with increasing gestational age (P = 0.002). (80%) (44 of 55) of neonates weighing more than 1.25 kg survived vs 39.1% (9 of 23) of those 1.25 kg or less, P = 0.0011. Similarly, 79.3% (46 of 58) of neonates of 29 or more weeks of gestation survived vs 35% (7 of 20) of those 28 weeks or less, P = 0.0007. The complications seen in the study group included blood culture positive sepsis (n = 7), pulmonary hemorrhage (n = 6), air leak syndromes (n = 4), endotracheal tube related problems (n = 5), chronic lung disease (n = 3) and retinopathy of prematurity (n = 2). CONCLUSION: Gestational age of less than 28 weeks and birth weight less than 1.25 kg can be recommended as the cut off weight and gestation criteria for in utero transfer in this centre and upgradation of existing facilities are urgently called for to improve the survival rates further.

Birth Weight↗
PubMed2002

Differential suppression of DNA repair deficiencies of Yeast rad50, mre11 and xrs2 mutants by EXO1 and TLC1 (the RNA component of telomerase).

Rad50, Mre11, and Xrs2 form a nuclease complex that functions in both nonhomologous end-joining (NHEJ) and recombinational repair of DNA double-strand breaks (DSBs). A search for highly expressed cDNAs that suppress the DNA repair deficiency of rad50 mutants yielded multiple isolates of two genes: EXO1 and TLC1. Overexpression of EXO1 or TLC1 increased the resistance of rad50, mre11, and xrs2 mutants to ionizing radiation and MMS, but did not increase resistance in strains defective in recombination (rad51, rad52, rad54, rad59) or NHEJ only (yku70, sir4). Increased Exo1 or TLC1 RNA did not alter checkpoint responses or restore NHEJ proficiency, but DNA repair defects of yku70 and rad27 (fen) mutants were differentially suppressed by the two genes. Overexpression of Exo1, but not mutant proteins containing substitutions in the conserved nuclease domain, increased recombination and suppressed HO and EcoRI endonuclease-induced killing of rad50 strains. exo1 rad50 mutants lacking both nuclease activities exhibited a high proportion of enlarged, G2-arrested cells and displayed a synergistic decrease in DSB-induced plasmid:chromosome recombination. These results support a model in which the nuclease activity of the Rad50/Mre11/Xrs2 complex is required for recombinational repair, but not NHEJ. We suggest that the 5'-3' exo activity of Exo1 is able to substitute for Rad50/Mre11/Xrs2 in rescission of specific classes of DSB end structures. Gene-specific suppression by TLC1, which encodes the RNA subunit of the yeast telomerase complex, demonstrates that components of telomerase can also impact on DSB repair pathways.

Antigens, Nuclear↗
PubMed2001

Neonatal sepsis: Staphylococcus aureus as the predominant pathogen.

96 consecutive inborn neonates with blood culture proven bacterial sepsis during the period January to June 1997 were studied. Lethargy with refusal of feeds (28%), fever (28%) and respiratory distress (31.3%) were the major presenting features. Half of them (n = 48) were of early onset (< 48 hours) and the remaining half were of late onset (> 48 hours). Staphylococcus aureus (n = 59, 61.5%) was the predominant pathogen and 66% of them were methicillin resistant followed by Klebsiella pneumoniae (n = 24, 21.9), Escherichia coli (n = 13, 13.5%) and streptococci (n = 3, 3.1%). Antibiotic resistance was common, with the sensitivity to various antibiotics being ampicillin 19%, gentamicin 21.6%, cefotaxime 32.8%, amikacin 50%, chloromycetin 59.6% and ciprofloxacin 90.3%.

Bacteremia↗
PubMed2001

Genes required for ionizing radiation resistance in yeast.

The ability of Saccharomyces cerevisiae to tolerate ionizing radiation damage requires many DNA-repair and checkpoint genes, most having human orthologs. A genome-wide screen of diploid mutants homozygous with respect to deletions of 3,670 nonessential genes revealed 107 new loci that influence gamma-ray sensitivity. Many affect replication, recombination and checkpoint functions. Nearly 90% were sensitive to other agents, and most new genes could be assigned to the following functional groups: chromatin remodeling, chromosome segregation, nuclear pore formation, transcription, Golgi/vacuolar activities, ubiquitin-mediated protein degradation, cytokinesis, mitochondrial activity and cell wall maintenance. Over 50% share homology with human genes, including 17 implicated in cancer, indicating that a large set of newly identified human genes may have related roles in the toleration of radiation damage.

Base Sequence↗
PubMed2000

RecA realigns suboptimally paired frames of DNA repeats through a process that requires ATP hydrolysis.

Microsatellite repeats such as mono-, di-, and trinucleotides are highly abundant and viable targets for homologous recombination in the genome. However, if recombination ensues in such repetitive regions, they are intrinsically prone to frame misalignments during pairing and might eventually give rise to genetic instabilities. Suboptimally paired frames lead to an abrogation of branch migration at the junctions of mixed sequences and repeats, due to a heterologous register. If so, can recombination machinery rectify such misalignments in order to avoid subsequent arrest in branch migration? We analyzed Escherichia coli RecA, the universal prototype of a recombinase, for its pairing abilities across repeats. We used a complementary pairing assay to test whether RecA can mediate realignments of stochastically paired suboptimal frames to a maximally aligned register. Here, we demonstrate that RecA-single stranded DNA filament indeed facilitates such a realignment, probably by sliding the paired strands across mono- and di- as well as trinucleotide repeats. These realignments apparently have no net directional bias. Such a putative "motor" function of RecA seems to be ATP hydrolysis-dependent.

Adenosine Triphosphate↗
PubMed2000

Spectrum of respiratory distress in very low birthweight neonates.

The incidence, etiology and the outcome of respiratory distress in 243 consecutive liveborn very low birth weight neonates (VLBW) were analysed. One hundred and forty six (60%) VLBW neonates developed respiratory distress. Hyaline membrane disease, congenital pneumonia and transient tachypnea of the newborn were the major underlying causes (35.6%, 28.1%, and 27.4% respectively). The mortality rate was significantly higher in neonates with respiratory distress (72 of 146, 49.3%) than in those without distress (28 of 97, 28.8%) (p < 0.05). This difference was more sharply reflected in the 1000-1249 birth weight group and in the 29-32 weeks gestation group. Respiratory distress is a significant determinant of VLBW mortality.

Female↗
PubMed1999

Fold-back structures at the distal end influence DNA slippage at the proximal end during mononucleotide repeat expansions.

Polymerase slippage during DNA synthesis by the Klenow fragment of DNA polymerase across A, C, G and T repeats (30 bases) has been studied. Within minutes, duplexes that contain only repeats (30 bp) expand dramatically to several hundred base pairs long. Rate comparisons in a repeat duplex when one strand was expanded as against that when both strands were expanded suggest a model of migrating hairpin loops which in the latter case coalesce into a duplex. Moreover, slippage (at the proximal or 3'-end) is subject to positive and negative effects from the 5'-end (distal) of the same strand. Growing T and G strands generate T.A:T and G-G:C motif fold-back structures at the distal end that hamper slippage at the proximal end. On the other hand, growing tails at the distal end upon annealing with excess complementary template accentuates proximal slippage several-fold.

DNA↗