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Biomedical subjects

A Chauhan

Publications and source records attributed to A Chauhan.

At least 37 records · Page 2Linked to original sources
PubMed2001

The role of fenestrations and channels on the transverse motion of a soft contact lens.

PURPOSE: Ineffectual removal of potentially harmful species from the postlens tear film (POLTF) may lead to adverse responses among extended wearers of soft contact lenses. It is apparently important to remove bacteria, cell debris, and metabolic products from the postlens tear film to the outer tear lake; the flushing or dispersion rate of these species is enhanced by increasing fluid movement in the tear film driven by periodic lens motion. The contact lens moves laterally (up-down) and transversally (in-out) due to the action of the eyelid forces during blinking. Viscous drag in the POLTF resists lens motion. Consequently, any design change in the lens that reduces viscous drag increases motion and improves flushing of unwanted species from the POLTF. We investigate quantitatively the effect of channels cut on the back surface of the lens and fenestrations (holes) drilled through the lens on transverse lens motion. METHODS: We model the lens as a curved solid body with a periodic arrangement of channels/holes. The cornea is treated as a flat surface, and the hydrodynamic equations of motion are solved for Newtonian fluid transport in the POLTF assuming lubrication and creeping flow. POLTF pressure profiles, obtained by solving these equations, are integrated to determine the lens settling velocity in the transverse direction for a given amount of applied lid force. Lens settling velocity is then compared with the same velocity in the absence of channels/fenestrations. Further, we calculate the total transverse motion in a blink for lenses with and without channels/fenestrations to estimate the possible enhancement in transverse motion due to the channels/fenestrations. RESULTS: Variables that affect the fluid mixing in the POLTF are the postlens tear film thickness, lens thickness, channel length, depth and spacing, and the hole diameter, location, and spacing. We study the effect of each of these variables on the enhancement of transverse motion for channels and holes of diameters varying from 0.1 to 2 mm with spacing varying from 1 to 5 mm. CONCLUSIONS: We demonstrate that incorporation of channels and holes reduces viscous resistance and increases transverse lens motion, and thus increases fluid mixing and dispersive flushing from the POLTF. The increase in transverse motion depends strongly on the postlens tear film thickness. Enhancement of the transverse motion varies from a factor of about 2 to 20 depending on the particular lens design and the postlens tear film thickness. Because fluid mixing increases up to the square of the transverse motion, channels/holes are expected to render flushing of the POLTF considerably more effective. We find that channels and/or fenestrations, when appropriately designed, can provide significant improvement in flushing from the POLTF. This work provides a new quantitative tool for the efficient design of channels/holes in soft contact lenses.

Biomechanical Phenomena↗
PubMed2000

Chemotaxis and biodegradation of 3-methyl- 4-nitrophenol by Ralstonia sp. SJ98.

3-Methyl-4-nitrophenol is one of the major breakdown products of fenitrothion [O,O-dimethyl O-(3-methyl-4-nitrophenyl) thiophosphate], a recalcitrant organophosphate insecticide used in agriculture. Being the non-polar methylated aromatic compound, 3-methyl-4-nitrophenol is highly toxic and, therefore, a complete degradation of this compound is important for environmental decontamination/bioremediation purposes. A gram negative, motile Ralstonia sp. SJ98 was isolated by selective screening from a soil sample contaminated with pesticides. The microorganism was capable of utilizing 3-methyl-4-nitrophenol as the sole source of carbon and energy. Thin layer chromatography (TLC), gas chromatography (GC), gas chromatography-mass spectrometry (GC-MS), and high performance liquid chromatography (HPLC) were performed to determine the possible intermediates in the degradative pathway of this compound. Taken together, catechol was found to be one of the major intermediate of the pathway. Furthermore, the chemotactic behavior of Ralstonia sp. SJ98 towards 3-methyl-4-nitrophenol was tested using three different methods i.e., drop assay, swarm plate assay and capillary assay, which were found to be positive towards this compound. This is the first report clearly indicating the involvement of a microorganism in the chemotaxis and biodegradation of methyl-4-nitrophenol and formation of catechol as an intermediate in the degradative pathway.

Amiloride↗
PubMed2000

Kinetics of biodegradation of p-nitrophenol by different bacteria.

Three bacterial species, i.e., Ralstonia sp. SJ98, Arthrobacter protophormiae RKJ100, and Burkholderia cepacia RKJ200, have been examined for their efficiency and kinetics behavior toward PNP degradation. All the three bacteria utilized PNP as the sole source of carbon, nitrogen, and energy. The rates of radiolabeled [U-(14)C]PNP degradation by all the bacteria were higher in the nitrogen-free medium compared to the medium with nitrogen. The apparent K(m) values of PNP degradation by SJ98, RKJ100, and RKJ200 were 0.32, 0.28, and 0.23 mM, respectively, as determined from the Michaelis-Menten curves. The maximum rates of PNP degradation (V(max)) according to Lineweaver-Burk's plots were 11.76, 7.81, and 3.84 micromol PNP degraded/min/mg dry biomass, respectively. The interpretation drawn from the Lineweaver-Burk's plots showed that the PNP degradation by SJ98 was stimulated by 4-nitrocatechol and 1, 2,4-benzenetriol. Benzoquinone and hydroquinone inhibited PNP degradation by RKJ100 noncompetitively and competitively, respectively, whereas in the case of RKJ200, benzoquinone and hydroquinone inhibited PNP degradation in an uncompetitive manner. beta-Ketoadipate did not affect the rate of PNP degradation in any case.

Arthrobacter↗
PubMed2000

Plasmid-encoded degradation of p-nitrophenol and 4-nitrocatechol by Arthrobacter protophormiae.

Arthrobacter protophormiae strain RKJ100 is capable of utilizing p-nitrophenol (PNP) as well as 4-nitrocatechol (NC) as the sole source of carbon, nitrogen and energy. The degradation of PNP and NC by this microorganism takes place through an oxidative route, as stoichiometry of nitrite molecules was observed when the strain was grown on PNP or NC as sole carbon and energy sources. The degradative pathways of PNP and NC were elucidated on the basis of enzyme assays and chemical characterization of the intermediates by TLC, GC, (1)H NMR, GC-MS, UV spectroscopy, and HPLC analyses. Our studies clearly indicate that the degradation of PNP proceeds with the formation of p-benzoquinone (BQ) and hydroquinone (HQ) and is further degraded via the beta-ketoadipate pathway. Degradation of NC involved initial oxidation to generate 1,2,4-benzenetriol (BT) and 2-hydroxy-1,4-benzoquinone; the latter intermediate is then reductively dehydroxylated, forming BQ and HQ, and is further cleaved via beta-ketoadipate to TCA intermediates. It is likely, therefore, that the same set of genes encode the further metabolism of HQ in PNP and NC degradation. A plasmid of approximately 65 kb was found to be responsible for harboring genes for PNP and NC degradation in this strain. This was based on the fact that PNP(-) NC(-) derivatives were devoid of the plasmid and had simultaneously lost their capability to grow at the expense of these nitroaromatic compounds.

Arthrobacter↗
PubMed2000

Chemotaxis of a Ralstonia sp. SJ98 toward different nitroaromatic compounds and their degradation.

A Ralstonia sp. SJ98, isolated by a chemotactic enrichment technique, was capable of utilizing different nitroaromatic compounds (NACs). It utilized p-nitrophenol, 4-nitrocatechol, o-nitrobenzoic acid, and p-nitrobenzoic acid as the sole source of carbon and energy. It was observed that Ralstonia sp. SJ98 was chemotactic to the above-mentioned NACs as tested by the drop assay, swarm plate assay, and capillary assay. However, it failed to show chemotactic behavior toward those compounds which were not degraded by the microorganism. This is the first report which shows the chemotaxis of a microorganism toward different NACs and their subsequent degradation. Some of the intermediates of the NACs' degradative pathways have been identified using TLC, GC, and GC-MS studies. The results presented here indicate a correlation between chemotaxis and biodegradation of NACs.

Betaproteobacteria↗
PubMed2000

A Sorption-Kinetic Model for Surfactant-Driven Spreading of Aqueous Drops on Insoluble Liquid Substrates.

Spreading of aqueous drops on hydrocarbon liquids occurs only when particular surfactants are added to the droplets above a critical concentration. For surfactant solutions of didodecyl ammonium bromide (DDAB) in water spreading over mineral oil, rates of droplet expansion are much slower than those corresponding to pure liquids spreading over immiscible liquid substrates with the same initial spreading coefficients. We present a sorption-kinetic model to explain quantitatively the spreading histories for aqueous DDAB droplets on mineral oil. Due to surfactant transport limitations, spreading occurs only when enough surfactant arrives at the dilating lens surfaces to establish a slightly positive, but near-zero spreading coefficient. We solve the convective diffusion equation for a cylindrical disk-like lens under the integral constraint of a constant surfactant adsorption density corresponding to a near-zero spreading coefficient. All observed spreading behavior is correctly portrayed by the proposed sorption-kinetic model including final equilibrium lens formation and spreading rates that are sensibly independent of drop volume, but are strongly dependent on drop surfactant concentration. Quantitative agreement is found with the experimental spreading data for a surfactant diffusion coefficient of 6x10(-12) m(2)/s and an effective adsorption rate constant of 6.5x10(-7) m/s. Both values prove physically reasonable. The sorption-kinetic model provides a new mechanism for understanding slow surfactant-driven spreading. Copyright 2000 Academic Press.

Journal Article↗
PubMed2000

Gelsolin inhibits the fibrillization of amyloid beta-protein, and also defibrillizes its preformed fibrils.

Amyloid beta-protein (Abeta) is present in soluble form in the plasma and cerebrospinal fluid (CSF) of normal people and patients with Alzheimer's disease (AD). However, in AD patients, Abeta gets fibrillized as the main constituent of amyloid plaques in the brain. Soluble synthetic Abeta also forms amyloid-like fibrils when it is allowed to age. The mechanism that prevents soluble Abeta from fibrillization in biological fluids is not clear. We recently reported that gelsolin, a secretory protein, binds to Abeta, and that gelsolin/Abeta complex is present in the plasma [V.P.S. Chauhan, I. Ray, A. Chauhan, H.M. Wisniewski, Biochem. Biophys. Res. Commun. 258 (1999) 241-246.]. We now studied the effect of gelsolin on Abeta fibrillization. Congo red staining and electron microscopic examination in negative staining of aged samples of Abeta alone and Abeta incubated with gelsolin showed that gelsolin inhibits the fibrillization of synthetic Abeta 1-40 and Abeta 1-42 at gelsolin to Abeta molar ratio of 1:40. In addition, gelsolin also defibrillized the preformed fibrils of Abeta 1-40 and Abeta 1-42 in a time-dependent manner. These results suggest that gelsolin functions as an anti-amyloidogenic protein in the plasma and CSF, where it prevents Abeta from fibrillization, and helps to maintain it in the soluble form.

Amyloid beta-Peptides↗
PubMed2000

Degradation of o-nitrobenzoate via anthranilic acid (o-aminobenzoate) by Arthrobacter protophormiae: a plasmid-encoded new pathway.

An Arthrobacter protophormiae strain RKJ100, isolated by selective enrichment, was capable of utilizing o-nitrobenzoate (ONB(+)) as the sole carbon, nitrogen, and energy source. The degradation of ONB proceeds through an oxygen insensitive reductive route as shown by the release of ammonia in the culture medium aerobically rather than nitrite ions. Thin-layer chromatography, gas chromatography, and gas chromatography-mass spectrometry of the intermediates have shown that ONB is degraded by a two-electron reduction of the nitro moiety, yielding o-hydroxylaminobenzoate and anthranilic acid. Quantitation of the intermediates, inhibition studies, and simultaneous induction studies have shown that anthranilic acid is produced as the terminal aromatic intermediate of a catabolic energy-yielding pathway and not as a side reaction taking place concurrently which is the first such report. A plasmid of approximately 65 kb was found to be responsible for harboring genes for ONB degradation in this strain. The same plasmid also encoded resistance to cobalt ions.

Aerobiosis↗
PubMed2000

Occlusive systolic bridging of circumflex artery.

Intramural course of coronary arteries is a well known phenomenon on autopsy. On angiography, however, it is usually seen in relation to the left anterior descending artery. Clinically this entity may be associated with myocardial ischemia, infarction or sudden cardiac death. In this case we report an unusual angiographic finding of circumflex coronary bridging.

Adult↗
PubMed2000

Failed thrombolysis in myocardial infarction.

Prompt treatment with thrombolytic therapy in acute myocardial infarction has been proven to reduce infarct size and mortality. However, reperfusion fails to occur in 30-50% of patients, either due to impaired epicardial artery flow or microvascular occlusion, with these patients experiencing a higher morbidity and mortality. We review the diagnosis and management of failed thrombolysis in acute myocardial infarction.

Abciximab↗
PubMed2000

Interaction of amyloid beta-protein with anionic phospholipids: possible involvement of Lys28 and C-terminus aliphatic amino acids.

Fibrillar amyloid beta-protein (Abeta) is the major protein of amyloid plaques in the brains of patients with Alzheimer's disease (AD). The mechanism by which normally produced soluble Abeta gets fibrillized in AD is not clear. We studied the effect of neutral, zwitterionic, and anionic lipids on the fibrillization of Abeta 1-40. We report here that acidic phospholipids such as phosphatidic acid, phosphatidylserine, phosphatidylinositol (PI), PI 4-phosphate, PI 4,5-P2 and cardiolipin can increase the fibrillization of Abeta, while the neutral lipids (diacylglycerol, cholesterol, cerebrosides), zwitterionic lipids (phosphatidylcholine, phosphatidylethanolamine, sphingomyelin) and anionic lipids lacking phosphate groups (sulfatides, gangliosides) do not affect Abeta fibrillization. Abeta was found to increase the fluorescence of 1-acyl-2-[12-[(7-nitro-2-1, 3-benzoxadiazol-4-yl) amino] dodecanoyl]-sn-glycero-3-phosphate (NBD-PA) in a concentration-dependent manner, while no change was observed with 1-acyl-2- [12-[(7-nitro-2-1, 3-benzoxadiazol-4-yl) amino] dodecanoyl]-sn-glycero-3-phosphoethanolamine (NBD-PE). Under similar conditions, other proteins such as apolipoprotein E, gelsolin and polyglutamic acid did not interact with NBD-PA. The order of interaction of amyloid beta-peptides with NBD-PA was Abeta 1-43 = Abeta 1-42 = Abeta 17-42 > Abeta 1-40 = Abeta 17-40. Other Abeta peptides such as Abeta 1-11, Abeta 1-16, Abeta 1-28, Abeta 1-38, Abeta 12-28, Abeta 22-35, Abeta 25-35, and Abeta 31-35 did not increase the NBD-PA fluorescence. These results suggest that phosphate groups, fatty acids, and aliphatic amino acids at the C-terminus end of Abeta 1-40/Abeta 1-42 are essential for the interaction of Abeta with anionic phospholipids, while hydrophilic Abeta segment from 1-16 amino acids does not participate in this interaction. Since positively charged amino acids in Abeta are necessary for the interaction with negatively charged phosphate groups of phospholipids, it is suggested that Lys28 of Abeta may provide anchor for the phosphate groups of lipids, while aliphatic amino acids (Val-Val-Ile-Ala) at the C-terminus of Abeta interact with fatty acids of phospholipids.

Amino Acid Sequence↗
PubMed2000

Degradation of 4-nitrocatechol by Burkholderia cepacia: a plasmid-encoded novel pathway.

Pseudomonas cepacia RKJ200 (now described as Burkholderia cepacia) has been shown to utilize p-nitrophenol (PNP) as sole carbon and energy source. The present work demonstrates that RKJ200 utilizes 4-nitrocatechol (NC) as the sole source of carbon, nitrogen and energy, and is degraded with concomitant release of nitrite ions. Several lines of evidence, including thin layer chromatography, gas chromatography, 1H-nuclear magnetic resonance, gas chromatography-mass spectrometry, spectral analyses and quantification of intermediates by high performance liquid chromatography, have shown that NC is degraded via 1,2, 4-benzenetriol (BT) and hydroquinone (HQ) formation. Studies carried out on a PNP- derivative and a PNP+ transconjugant also demonstrate that the genes for the NC degradative pathway reside on the plasmid present in RKJ200; the same plasmid had earlier been shown to encode genes for PNP degradation, which is also degraded via HQ formation. It is likely, therefore, that the same sets of genes encode the further metabolism of HQ in NC and PNP degradation.

Burkholderia cepacia↗
PubMed2000

Multicenter evaluation of the phosphorylcholine-coated biodivYsio stent in short de novo coronary lesions: The SOPHOS study.

AIMS: The BiodivYsio trade mark stent (Biocompatibles Ltd, Farnham, UK) is coated with a phosphorylcholine (PC)-containing copolymer to confer biocompatibility. The SOPHOS (Study Of PHosphorylcholine coating On Stents) study was designed to assess the safety and efficacy of this novel coronary stent and by indirect comparison to indicate equivalence with other formal stent studies. METHODS AND RESULTS: Patients with angina and a single short (#x2A7F;12 mm) de novo lesion in a native coronary artery of >/=2.75 mm diameter were included. A total of 425 patients were allocated in 24 centers. Clinical data were collected at one-, six- and nine-month follow-up. Angiography was performed before and after the stent implantation. In addition, in the first 200 patients (SOPHOS A) angiography was routinely performed at six months. The following 225 patients (SOPHOS B) were merely followed up clinically. The primary end-point of the study, the six-month MACE-rate (MACE = Major Adverse Cardiac Events) was 13.4% (two cardiac death; five Q-wave/nine non-Q-wave myocardial infarctions (MI); nine CABG and 32 target lesion revascularization (TLR), which is similar to the calculated 15% MACE-rate in comparable reference studies. Secondary end-points included among others restenosis at six months in the SOPHOS A population. The target vessel diameter was 2.98 +/- 0.48 mm. Minimal lumen diameter pre/post procedure and at follow-up was 1.00 +/- 0.32, 2.69 +/- 0.37, 1.91 +/- 0.71 mm, respectively. The binary restenosis rate (>/=50% diameter stenosis at follow-up) was 17.7%. CONCLUSION: The coronary BiodivYsio stent is safe and effective as a primary device for the treatment of native coronary artery lesions in patients with stable or unstable angina pectoris. Clinical and angiographic results are in the statistical range of equivalence with comparable studies with other current stents.

Journal Article↗
PubMed2000

Antiplatelet use in interventional cardiology.

Thrombosis within the target vessel is one of the most feared complications associated with coronary intervention, as it is often associated with severe adverse clinical sequelae. This thrombosis is mediated via the activation and aggregation of platelets and therefore considerable effort has been directed at ways of inhibiting platelet function. It is now mandatory to consider the use of two and often three different antiplatelet agents, particularly when intracoronary stents are inserted. Using these regimes, many of the adverse clinical outcomes associated with platelet activation can be reduced.

Cardiovascular Surgical Procedures↗
PubMed2000

Role of respiratory function in exercise limitation in chronic heart failure.

OBJECTIVE: To test the hypothesis that respiratory function contributes to limit maximal exercise performance in patients with chronic heart failure by using the technique of dead space loading during exercise. DESIGN: Blinded subjects underwent two maximal incremental exercise tests in random order on an upright bicycle ergometer: one with and one without added dead space. SETTING: : Tertiary-care university teaching hospital. SUBJECTS: Seven patients with stable chronic heart failure (mean +/- SEM left ventricular ejection fraction, 27 +/- 3%). RESULTS: Subjects were able to significantly increase their peak minute ventilation during exercise with added dead space when compared with control exercise (57.4 +/- 5.9 vs 50.0 +/- 5.6 L/min; p < 0.05). Peak oxygen uptake, workload, heart rate, and exercise duration were not significantly different between the added dead space and control tests. Breathing pattern was significantly deeper and slower at matched levels of ventilation during exercise with added dead space. CONCLUSION: Because patients with chronic heart failure had significant ventilatory reserve at the end of exercise and were able to further increase their maximal minute ventilation, we conclude that respiratory function does not contribute to limitation of exercise in patients with chronic heart failure.

Adult↗
PubMed2000

Influence of methionine and zinc on liver collagen in molybdenotic rats: relationship with lipid peroxidation.

Protective effects of methionine and zinc on collagenesis in the liver of molybdenotic rats have been studied during present investigations. Further, the relationship between two important pathobiological phenomena (viz. lipid peroxidation and collagenesis) has also been examined. Biological observations suggest that cotreatment with methionine only improves the growth of molybdenotic rats; however, the hepatosomatic index improved in rats supplemented with both methionine and zinc. Administration of methionine and zinc to molybdenum-fed rats decreased liver collagen. Results on urinary hydroxyproline support these observations. Lipid peroxidation was also inhibited in the liver of protected rats. We suggest that collagenesis can be controlled by inhibiting the generation of reactive oxygen species. An improvement in liver function in rats protected with methionine and zinc has also been suggested.

Animals↗