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Biomedical subjects

A S Kumar

Publications and source records attributed to A S Kumar.

At least 19 recordsLinked to original sources
PubMed2001

Enantiospecificity of cholesterol function in vivo.

The importance of the absolute configuration of cholesterol for its function in vivo is unknown. To directly test this question in vivo, we synthesized the enantiomer of cholesterol (ent-cholesterol) and tested its ability to substitute for natural cholesterol (nat-cholesterol) in the growth, viability, and behavior of Caenorhabditis elegans, a cholesterol auxotroph. First-generation animals grown on ent-cholesterol were viable with only mild behavioral defects. However, ent-cholesterol produced 100% lethality/arrest of their second generation progeny. Isotopically labeled ent-cholesterol incorporated into animals, indicating that its lethality was not secondary to cholesterol starvation. When mixed with nat-cholesterol, ent-cholesterol was not inert; rather, it antagonized the activity of nat-cholesterol. These results demonstrate for the first time that the absolute configuration of cholesterol, not just its physical properties, is essential for its functions in vivo.

Animals↗
PubMed2001

Inoue balloon mitral valvotomy in patients with atrial septal aneurysm.

Atrial septal aneurysms (ASA) are not uncommonly detected in patients with rheumatic mitral stenosis and pose problems during transeptal puncture in patients undergoing balloon mitral valvotomy. From a period of August 1995 to May 1998, we performed a total of 680 Inoue Balloon Mitral Valvotomy (IBMV) procedures with ASA noted in 30 patients, 13 of diffuse and 17 localized type. Transesophageal echocardiography (TOE) was used in all patients with suspected aneurysm on transthoracic echo (TTE) for exact three-dimensional delineation of the location and extent of the aneurysm. The localized type of aneurysms were further subcategorized into five types viz. antero-superior and leftwards (6), postero-superior and rightwards (2), antero-inferior and leftwards (2), postero-inferior and rightwards (5), and central (2), depending on their location in the atrial septum. The site for transeptal puncture was decided after this localization and the remainder of the IBMV procedure was as usual. In the set of thirteen patients with diffuse type of atrial septal aneurysms all but one case had a successful transeptal puncture using standard technique except for a somewhat inferior puncture site so as to be perpendicular to the plane of atrial septum and a successful mitral valve dilatation was possible at first attempt. In the set of 17 patients with localized type of aneurysms, all had a successful transeptal puncture except one. In patients with aneurysms localized antero-superiorly and leftwards the septal puncture was done in a slightly inferior location with transeptal needle pointing some what more posterior, i.e. 5 or 6 o'clock position and in patients with aneurysms localized postero-inferiorly the puncture was done more cephalic with needle directed somewhat anterior, i.e. 3-2 o'clock position. In the two patients with Atrial septal aneurysms located postero-superiorly and to the right the puncture was done slightly inferior but with transeptal needle pointing to about 3 or 2 o'clock position and in the single patient with antero-inferior location the puncture was done in slightly higher but with a more posterior directed needle, i.e. 5-6 o'clock position. The two patients with centrally located localized type of aneurysms had successful transeptal puncture with standard needle direction (4 o'clock) but at a slightly inferior location. We conclude that a good localization of atrial septal aneurysms using transesophageal echocardiography and our technique of transeptal puncture leads to a successful outcome in majority of cases undergoing Inoue balloon mitral valvotomy with associated atrial septal aneurysms.

Adult↗
PubMed2001

A mimicking enzyme analogue for chemical sensors.

An artificial enzyme analogue of Nafion/lead-ruthenium oxide pyrochlore (Py) chemically modified electrode (NPyCME) is synthesized by in situ precipitation through blocking of Nafion's hydrophilic zones. The catalytically active Py sites covered with a hydrophobic core of Nafion resemble an enzymatic structure. Moreover, the NPyCME obeys the Michaelis-Menten mechanism for the oxidation of many organic and biological molecules. This Account highlights aspects of the preparation, characterization, and application of the NPyCME.

Biosensing Techniques↗
PubMed2001

Electrocatalytic cyclization of dithiothreitol on a chemically modified electrode by analogy with protein action.

Electrocatalytic oxidative cyclization of dithiothreitol (DTT(SH)2) to a disulfide product was demonstrated on a Nafion/lead-ruthenium oxide pyrochlore chemically modified electrode (NPyCME). The process at the NPyCME with DTT(SH)2 is similar to the behaviour of protein in a disulfide linkage, which can be demonstrated by product analysis using HPLC coupled with UV spectroscopy. A possible electrocatalytic mechanism for DTT(SH)2 oxidation to dihydroxydithiane [i.e. cyclized DTT(S-S)] on the NPyCME was proposed in terms of Py-Ru(IV)/Py-Ru(VI) redox active sites. This physical aspect was further utilized for high precision analytical assays using flow injection analysis (FIA), with a linearity up to 50 microM and a detection limit (S/N = 3) of 28 nM (8.64 pg) in a 20 microL sample loop. This is the most sensitive method ever reported for DTT(SH)2 detection assays. The interference from dissolved oxygen, disulfide and glucose is almost negligible. The present method offers an easy route for extension to redox-related protein studies.

Journal Article↗
PubMed2001

Fate of mild aortic valve disease after mitral valve intervention.

OBJECTIVE: This study was performed to assess the long-term outcome of untreated mild aortic valve disease present at the time of initial mitral valve intervention. METHODS: A total of 284 patients with rheumatic heart disease aged 7 to 62 years (mean, 23.5 +/- 12.2 years) who underwent mitral valve intervention and had mild aortic valve disease initially were followed up for 2 to 18 years (mean, 10.8 +/- 3.7 years). At initial intervention, 232 patients had pure mild aortic regurgitation, and 52 patients had mild aortic stenosis with or without aortic regurgitation. RESULTS: Among patients with mild aortic regurgitation initially, 11 (5%) patients progressed to moderate (n = 6) or severe (n = 5) regurgitation over an interval of 9 to 17 years (mean, 12.1 +/- 2.8 years), and 1 patient had moderate aortic stenosis and severe aortic regurgitation after 10 years. Freedom from development of moderate-severe aortic valve disease in patients who initially had mild aortic regurgitation was 100%, 97.0% +/- 1.7%, and 87.4% +/- 4.6% at 5, 10, and 15 years, respectively. Seventeen (35%) patients with initial mild aortic stenosis (with or without regurgitation) had moderate or severe stenosis (with or without moderate-severe regurgitation) after an interval of 4.9 +/- 3.8 years. Freedom from development of moderate-severe aortic valve disease in patients who initially had mild aortic stenosis was 75.6% +/- 6.2%, 61.5% +/- 8.5%, and 46.1% +/- 11.2% at 5, 10, and 15 years, respectively. Ten patients required aortic valve replacement for aortic valve dysfunction. CONCLUSIONS: Mild aortic regurgitation present at the time of mitral valve intervention progresses very slowly and less frequently requires reintervention. However, mild aortic stenosis diagnosed initially progresses more often and more rapidly and thus needs closer follow-up.

Adolescent↗
PubMed2001

The nonfeminizing enantiomer of 17beta-estradiol exerts protective effects in neuronal cultures and a rat model of cerebral ischemia.

Estrogens are potent neuroprotective compounds in a variety of animal and cell culture models, and data indicate that estrogen receptor (ER)-mediated gene transcription is not required for some of these effects. To further address the requirement for an ER in estrogen enhancement of neuronal survival, we assessed the enantiomer of 17beta-estradiol (ENT-E(2)), which has identical chemical properties but interacts only weakly with known ERs, for neuroprotective efficacy. ENT-E(2) was both as potent and efficacious as 17beta-estradiol in attenuating oxidative stress-induced death in HT-22 cells, a murine hippocampal cell line. Further, ENT-E(2) completely attenuated H(2)O(2) toxicity in human SK-N-SH neuroblastoma cells at a 10 nM concentration. In a rodent model of focal ischemia, 17beta-estradiol (100 microgram/kg) or ENT-E(2) (100 microgram/kg), injected 2 h before middle cerebral artery occlusion, resulted in a 60 and 61% reduction in lesion volume, respectively. ENT-E(2), at the doses effective in this study, did not stimulate uterine growth or vaginal opening in juvenile female rats when administered daily for 3 days. These data indicate that the neuroprotective effects of estrogens, both in vitro and in vivo, can be disassociated from the peripheral estrogenic actions.

Animals↗
PubMed2001

Mitral valve replacement with chordal preservation in a rheumatic population.

BACKGROUND AND AIM OF THE STUDY: Mitral valve replacement (MVR) with preservation of the subvalvular apparatus may maintain postoperative left ventricular (LV) function better than conventional MVR. A prospective study was undertaken to assess the advantages of chordal preservation in rheumatic patients undergoing isolated MVR. METHODS: Between January 1996 and January 1999, 240 patients with rheumatic etiology and normal LV ejection fraction (>50%) underwent isolated MVR using a St. Jude Medical prosthesis. Patients were allocated to two groups: in group I (n = 168), both the anterior and posterior chordae were preserved; in group II (n = 72), the entire native mitral valve apparatus was excised. Patients from both groups were evaluated postoperatively (mean 12.5 months) by echocardiography and treadmill testing. RESULTS: Demographic and clinical profiles were comparable in both groups. There were three early deaths in group I, and one in group II. There were no late deaths. One patient in group I required reoperation for a stuck mitral prosthesis. LV function (ejection fraction >50%) was better in group I (94%) than in group II (82%) (p <0.05). No patient in either group had LV outflow tract obstruction on echocardiography. Patients in group I showed better exercise performance on treadmill (Bruce protocol): 92% of group I patients versus 88% of group II patients (p >0.05) completed stage I; 16% of group I patients, but no group II patients, were able to complete stage IV (p <0.05). CONCLUSION: Mitral valve replacement with preservation of the subvalvular apparatus maintains LV function, and does not cause LV outflow tract obstruction.

Adult↗
PubMed2001

Mitral valve repair in a predominantly rheumatic population. Long-term results.

Valve repair in rheumatic patients poses special problems due to valve deformity and mixed lesions. We present our experience from January 1988 through June 1999, in this retrospective study of 818 patients (377 males). The mean age was 22.8 +/- 11.3 years (range, 2 to 70 years). The cause of mitral regurgitation was rheumatic in 718 (88%) patients, congenital in 51, myxomatous in 34, infective in 7, and ischemic in 8. Most patients (64%) were in New York Heart Association functional class III or IV. Congestive heart failure was present in 116 patients (14%). Reparative procedures included posterior collar annuloplasty (n=710), commissurotomy (n=482), cusp-level chordal shortening (n=237), cusp thinning (n=222), cleft suture (n= 166), and cusp excision/plication (n=42). Operative mortality was 4% (32 patients). Preoperative left ventricular dysfunction, presence of congestive heart failure, and advanced functional class were associated with greater mortality. Follow-up ranged from 1 to 144 months (mean, 44.9 +/- 33.2 months) and was 96% complete. Most survivors (70%) had no or trivial mitral regurgitation. Forty patients required reoperation for valve dysfunction. There were 23 (2.8%) late deaths. Actuarial, reoperation-free, and event-free survival at 11 years were 92.6% +/- 1.0%, 65.0% +/- 10%, and 38% +/- 6.0%, respectively Among the survivors, 85% were in New York Heart Association functional class I. We conclude that mitral valve repair in rheumatic patients, using current techniques, can effectively correct hemodynamic and functional abnormalities with satisfactory results.

Adolescent↗
PubMed2000

Effects of cholesterol and enantiomeric cholesterol on P-glycoprotein localization and function in low-density membrane domains.

Multidrug resistance P-glycoprotein (Pgp) has been reported to localize in low-density, cholesterol-enriched membranes. However, effects of low-density membrane domains on function of Pgp remain unexplored in whole cell systems. In cells that express modest levels of the protein endogenously or through drug selection, Pgp predominantly localized to low-density membranes following separation on a sucrose gradient. When highly overexpressed in NIH 3T3 cells, a prominent amount of Pgp also was detected in high-density membranes. Removing cholesterol from cells with beta-methylcyclodextrin (CD), a sterol acceptor molecule, shifted fractions that contained Pgp from low toward high density, and this effect was reversed to a similar extent by restoring sterols with either cholesterol or enantiomeric cholesterol. However, function of human MDR1 Pgp as probed with Tc-Sestamibi, a transport substrate for Pgp, was not dependent on localization of Pgp in cholesterol-enriched membranes. Specific inhibition of MDR1 Pgp with GF120918 or LY335979 also was independent of cholesterol. Cell-type-specific effects of cholesterol content on function of human Pgp were detected by use of daunomycin, another substrate for Pgp, although efficacy of inhibitors remained independent of cholesterol. Conversely, both function and inhibition of hamster Pgp as measured with Tc-Sestamibi and daunomycin were in part dependent on normal cell content of cholesterol. These data show that Pgp preferentially localizes to low-density, cholesterol-enriched membrane domains, but acute depletion of cholesterol impacts Pgp-mediated drug transport in a substrate- and cell-type-specific manner.

3T3 Cells↗
PubMed2000

Transforming growth factor-beta(1) regulation of surfactant protein B gene expression is mediated by protein kinase-dependent intracellular translocation of thyroid transcription factor-1 and hepatocyte nuclear factor 3.

The transforming growth factor-beta (TGF beta) polypeptides control a variety of cellular processes including organogenesis and cellular proliferation and differentiation. In the developing lung, TGF beta(1) treatment inhibits airway branching and expression of the genes for surfactant proteins (SP). Many effects of TGF beta are mediated at the level of gene transcription but there is limited information regarding signaling pathways and target transcription factors. In this study with human pulmonary adenocarcinoma H441 cells, we investigated TGF beta(1) effects on SP-B, a protein which is essential for normal function of pulmonary surfactant. TGF beta(1) (10 ng/ml) reduced SP-B mRNA content in a time-dependent fashion, and transient transfection studies localized responsiveness to the region of the SP-B promoter (-112/-72 bp) containing binding sites for thyroid transcription factor-1 (TTF-1) and hepatocyte nuclear factor 3 (HNF3), transcription factors that are important enhancers of SP gene expression. Using electrophoretic mobility shift assay and immunofluorescence, we demonstrated rapid accumulation of these transcription factors in the cytoplasm and subsequent loss from the nucleus on TGF beta(1) treatment of both adenocarcinoma cells and cultured human fetal lung. TGF beta(1) treatment caused intracellular translocation of protein kinase C and effects of TGF beta(1) were mostly abrogated in the presence of the protein kinase inhibitor calphostin C. We conclude that TGF beta(1), acting via protein phosphorylation, blocks nuclear translocation of TTF-1 and HNF3 which results in down-regulation of the SP-B gene and presumably other pulmonary genes which are transactivated by these factors.

5' Untranslated Regions↗
PubMed2000

A dual electrochemical sensor for nitrite and nitric oxide.

Nafion/lead-ruthenate pyrochlore chemically modified electrode (NPyCME) showed a remarkable dual sensing activity toward NO2- oxidation and NO reduction as demonstrated by cyclic voltammetry (CV), ac-impedance spectroscopy and flow injection analysis (FIA). The mechanistic parameters of current function, charge transfer resistance and exchange current for the NPyCME, GCE and Nafion-coated GCE were evaluated and compared. The disproportionation reaction of NIIIO2- into NIVO3- + NIIO in acidic solution was used as a model system for testing the dual sensing ability of the NPyCME. The obtained crossover peak response for NO2- oxidation and NO reduction in pH 1.65 buffer solution gave the direct proof for the applicability of the NPyCME in the dual electrocatalytic action. By flow injection analysis, under optimized conditions, the calibration curve was linear in the range of 100 nM-100 microM and 800 nM-63.3 microM and the detection limit (S/N = 3) was 4.8 nM and 15.6 nM for NO2- and NO, respectively.

Flow Injection Analysis↗
PubMed2000

Pulmonary homograft: should it be used in the aortic position?

OBJECTIVE: Retrospective analysis was performed to determine the suitability of pulmonary homograft as an aortic valve substitute. METHODS: From January 1994 through June 1999, 147 patients (mean age, 32.2 +/- 17.3 years) underwent aortic valve replacement with either an aortic homograft (group 1: n = 103, 25 fresh antibiotic preserved and 78 cryopreserved) or a pulmonary homograft (group 2: n = 44, 11 antibiotic preserved and 33 cryopreserved). In group 1 a scalloped subcoronary technique was used in 64 patients, and a root replacement technique was used in 39 patients. In group 2 the scalloped subcoronary technique was used in 34 patients, and the root replacement technique was used in 10 patients. RESULTS: There were 131 operative survivors (group 1 = 91; group 2 = 40). Follow-up ranged from 2 to 62 months. In group 1 none of the patients had significant aortic regurgitation during the hospital stay. Three patients (all having undergone the scalloped subcoronary technique) had moderate aortic regurgitation after 6 to 32 months. In group 2, 10 patients (9 having undergone the scalloped subcoronary technique and 1 having undergone the root replacement technique) developed significant regurgitation: 2 intraoperatively, 5 in the early postoperative period before discharge from the hospital, and 3 during late follow-up 6 to 12 months postoperatively. Among the various risk factors analyzed for overall homograft failure, use of a pulmonary homograft was the single independent predictor of valve failure (odds ratio, 8.6; 95% confidence interval, 1.9-39; P =.006). CONCLUSION: Pulmonary homograft, when inserted by means of a scalloped subcoronary technique, is not a suitable aortic valve substitute.

Adolescent↗
PubMed2000

Homograft mitral valve replacement: five years' results.

OBJECTIVE: Results of mitral valve replacement with a mitral homograft were evaluated at 5 years to assess the suitability of the procedure. METHODS: Thirty-seven patients (25 male subjects) aged 10 to 49 years (mean, 32 +/- 10 years) with rheumatic mitral valve disease underwent total (n = 35) or partial (n = 2) mitral valve replacement with a fresh antibiotic-preserved (n = 23) or cryopreserved (n = 14) mitral homograft. The predominant lesion was mitral stenosis (n = 30). RESULTS: There were 5 early deaths. Operative survivors were followed up for 1 to 60 months (mean, 26.6 +/- 12 months). Among these, 21 patients had severe mitral regurgitation during the follow-up period; 3 died and 8 underwent reoperation. The homograft failure rate was not affected by preoperative physiologic lesion (stenosis vs regurgitation, P =.4), type of homograft (antibiotic-preserved vs cryopreserved homograft, P =.9), papillary muscle pretreatment (yes vs no, P =.9), or addition of posterior collar annuloplasty (yes vs no, P =.2). Among the remaining patients, 5 had moderate mitral regurgitation, 4 had either trivial or mild mitral regurgitation, and 2 were lost to follow-up. Study of the explanted mitral homografts (n = 8) revealed that disruption of one of the donor papillary muscles was responsible for early failures (n = 2), whereas cuspal and chordal degeneration was responsible for late failures (n = 6). Microscopically, the explanted valve lacked any viable cellular elements, and there was no evidence of immunologic injury to the homografts. CONCLUSION: The mitral homograft did not fulfill our expectations as a suitable substitute for the diseased mitral valve.

Adolescent↗