Biomedical subjects

S Maiti

Publications and source records attributed to S Maiti.

At least 19 recordsLinked to original sources

PubMed2006

Selective destabilization of soluble amyloid beta oligomers by divalent metal ions.

Aggregation of the amyloid beta (Abeta) peptide yields both fibrillar precipitates and soluble oligomers, and is associated with Alzheimer's disease (AD). In vitro, Cu(2+) and Zn(2+) strongly bind Abeta and promote its precipitation. However, less is known about their interactions with the soluble oligomers, which are thought to be the major toxic species responsible for AD. Using fluorescence correlation spectroscopy to resolve the various soluble species of Abeta, we show that low concentrations of Cu(2+) (1 microM) and Zn(2+) (4 microM) selectively eliminate the oligomeric population (within approximately 2h), while Mg(2+) displays a similar effect at a higher concentration (60 microM). This uncovers a new aspect of Abeta-metal ion interactions, as precipitation is not substantially altered at these low metal ion concentrations. Our results suggest that physiological concentrations of Cu(2+) and Zn(2+) can critically alter the stability of the toxic Abeta oligomers and can potentially control the course of neurodegeneration.

Amyloid beta-Peptides↗

PubMed2005

Physical and thermochemical characterization of rice husk char as a potential biomass energy source.

The fixed bed pyrolysis of rice husk was studied under conventional conditions with the aim of determining the characteristics of the charcoal formed for its applicability as a solid fuel. Thermoanalytic methods were used to determine the kinetic parameters of its combustion. Palletisation using different binders and techniques to improve the time of sustained combustion of the char pallets were investigated. The optimum temperature for carbonization to obtain a char having moderately high heating value was found as 400 degrees C. For the active char combustion zone, the order of reaction was nearly 1, the activation energy 73.403 kJ/mol and the pre-exponential factor 4.97 x 10(4)min(-1). Addition of starch as a binder and 10% ferrous sulphate heptahydrate or sodium hypophosphite as an additive enhanced the ignitibility of the char pallets.

Bioelectric Energy Sources↗

PubMed2005

Quantitative measurement of serotonin synthesis and sequestration in individual live neuronal cells.

Synthesis and subsequent sequestration into vesicles are essential steps that precede neurotransmitter exocytosis, but neither the total neurotransmitter content nor the fraction sequestered into vesicles have been measured in individual live neurons. We use multiphoton microscopy to directly observe intracellular and intravesicular serotonin in the serotonergic neuronal cell line RN46A. We focus on how the relationship between synthesis and sequestration changes as synthesis is up-regulated by differentiation or down-regulated by chemical inhibition. Temperature-induced differentiation causes an increase of about 60% in the total serotonin content of individual cells, which goes up to about 10 fmol. However, the number of vesicles per cell increases by a factor of four and the proportion of serotonin sequestered inside the vesicles increases by a factor of five. When serotonin synthesis is inhibited in differentiated cells and the serotonin content goes down to the level present in undifferentiated cells, the sequestered proportion still remains at this high level. The total neurotransmitter content of a cell is, thus, an unreliable indicator of the sequestered amount.

Alanine↗

PubMed2005

Entrapment efficiency and release characteristics of polyethyleneimine-treated or -untreated calcium alginate beads loaded with propranolol-resin complex.

Propranolol-HCl-loaded calcium alginate (ALG) beads, propranolol-resin complex (resinate)-loaded calcium alginate (RALG) beads and polyethyleneimine (PEI)-treated RALG (RALG-PEI) beads were prepared by ionotropic gelation/polyelectrolyte complexation method. The beads were evaluated and compared in respect of drug entrapment efficiency (DEE) and release characteristics in simulated gastric fluid (SGF, 0.1(N) HCl, pH 1.2) and simulated intestinal fluid (SIF, phosphate buffer, pH 6.8). DEE of RALG beads was considerably higher than that of ALG beads containing unresinated drug. However, DEE of RALG beads decreased with increase in both gelation time and concentration of the gel forming Ca2+ ions due to drug displacement from resinate. PEI treatment of RALG beads further decreased DEE as the polycation also displaced the drug from the resinate. The release of drug from all the beads was slow and incomplete in SGF owing to considerably less swelling of the beads and the decrease in drug release from the beads followed the order: RALG-PEI<RALG<ALG. In contrast to rapid discharge of the drug by ALG beads in SIF, RALG beads provided marginal prolongation in drug release as both ALG and RALG beads swelled and eroded rapidly although at different rates. On the other hand, drug release from RALG-PEI beads in SIF was considerably prolonged for different periods of time depending upon the conditions of PEI treatment. Interaction of the polycation with alginate resulted in the formation of polyelectrolyte complex membrane as evident from scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and fourier-transform infrared spectroscopy (FTIR) studies. The membrane having reduced swelling and erosion properties behaved as a physical barrier to drug release. Kinetics of the drug release also confirmed the formation of physical barrier as anomalous transport type of release associated with. RALG beads tended to shift towards Fickian transport in case of RALG-PEI beads.

Alginates↗

PubMed2005

Quantitative measurement of the resolution and sensitivity of confocal microscopes using line-scanning fluorescence correlation spectroscopy.

Spatial resolution and the sensitivity to detect a fluorophore are the two most important optical parameters that characterize a confocal microscope. However, these are rather difficult to estimate quantitatively. We show that fluorescence correlation spectroscopy (FCS) provides an easy and reliable measure of these quantities. We modify existing schemes for performing FCS on a commercial confocal microscope to carry out these measurements, and provide an analysis routine that can yield the relevant quantities. Our method does not require any modification of the confocal microscope, yet it yields a robust measure of the resolution and sensitivity of the instrument.

Mathematics↗

PubMed2004

Live cell ultraviolet microscopy: a comparison between two- and three-photon excitation.

We compare conventional infrared laser based three-photon excitation with a visible laser based two-photon excitation scheme for imaging the ultraviolet fluorophore serotonin in solution and in live cells. To obtain a signal level of 1000 photons per second per mM serotonin solution, we need a back aperture power of 5 mW at 550 nm (for two-photon excitation) and 33 mW at 740 nm (for three-photon excitation). The detectivity of serotonin (defined as the concentration of serotonin that yields a signal equivalent to three times the standard deviation of the signal obtained from the buffer alone) is 12 microM for two-photon, and 220 microM for three-photon excitation. Surprisingly, for live cell imaging of vesicular serotonin in serotonergic cells, three-photon excitation appears to provide better image contrast than two-photon excitation. The origin of this is traced to the concentration-dependent shift of the serotonin emission spectrum.

Animals↗

PubMed2004

Cathepsin B-like proteolysis and MARCKS degradation in sub-lethal NMDA-induced collapse of dendritic spines.

Sub-lethal excitotoxic injury to dendrites can elicit loss or shrinkage of dendritic spines. Here, we used a cell culture model of sub-lethal NMDA-induced injury to investigate a role for proteolysis in spine collapse. Transient incubation with NMDA-induced spine collapse and spine F-actin loss within 10 min, an effect not mimicked by the actin assembly inhibitor latrunculin A. NMDA-induced spine collapse was significantly attenuated by preincubation with broad-spectrum cysteine protease inhibitors. Results obtained using several class-specific protease inhibitors suggested that this protective effect was due to specific blockade of cathepsin B/L type protease activity, since selective inhibitors of only these proteases significantly attenuated spine loss. Cathepsin B-like immunoreactivity was observed at synaptic sites, but lysosomes were not. Immunoblot analysis showed that MARCKS (myristoylated-alanine-rich C-kinase substrate), a known substrate of cathepsin B, was specifically degraded in response to intense NMDA receptor stimulation. This effect was blocked by preincubation with a cathepsin B-selective inhibitor. Together these data suggest a model in which NMDA-induced spine collapse involves cathepsin B-like proteolysis of MARCKS, and possibly other proteins that regulate the actin-based cytoskeleton.

Animals↗

PubMed2003

The amyloid beta peptide (Abeta(1-40)) is thermodynamically soluble at physiological concentrations.

Precipitation of the 39-43-residue amyloid beta peptide (Abeta) is a crucial factor in Alzheimer's disease (AD). In normal as well as in AD-afflicted brain, the Abeta concentration is estimated to be a few nanomolar. Here we show that Abeta(1-40) precipitates in vitro only if the dissolved concentration is >14 microM. Using fluorescence correlation spectroscopy, we further show that the precipitation is complete in 1 day, after which the size distribution of Abeta monomer/oligomers in the solution phase becomes stationary in time and independent of the starting Abeta concentration. Mass spectra confirm that both the solution phase and the coexisting precipitate contain chemically identical Abeta molecules. Incubation at 68 degrees C for 1 h reduces the solubility by <12%. Together, these results show that the thermodynamic saturation concentration (C(sat)) of Abeta(1-40) in phosphate-buffered saline (PBS) at pH 7.4 has a well-defined lower limit of 15.5 +/- 1 microM. Divalent metal ions (believed to play a role in AD) at near-saturation concentrations in PBS reduce C(sat) only marginally (2 mM Mg(2+) by 6%, 2.5 microM Ca(2+) by 7%, and 4 microM Zn(2+) by 11%). Given that no precipitation is possible at concentrations below C(sat), we infer that coprecipitant(s), and not properties of Abeta(1-40) alone, are key factors in the in vivo aggregation of Abeta.

Alzheimer Disease↗

PubMed2003

Measuring size distribution in highly heterogeneous systems with fluorescence correlation spectroscopy.

Fluorescence correlation spectroscopy (FCS) is a sensitive and widely used technique for measuring diffusion. FCS data are conventionally modeled with a finite number of diffusing components and fit with a least-square fitting algorithm. This approach is inadequate for analyzing data obtained from highly heterogeneous systems. We introduce a Maximum Entropy Method based fitting routine (MEMFCS) that analyzes FCS data in terms of a quasicontinuous distribution of diffusing components, and also guarantees a maximally wide distribution that is consistent with the data. We verify that for a homogeneous specimen (green fluorescent protein in dilute aqueous solution), both MEMFCS and conventional fitting yield similar results. Further, we incorporate an appropriate goodness of fit criterion in MEMFCS. We show that for errors estimated from a large number of repeated measurements, the reduced chi(2) value in MEMFCS analysis does approach unity. We find that the theoretical prediction for errors in FCS experiments overestimates the actual error, but can be empirically modified to serve as a guide for estimating the goodness of the fit where reliable error estimates are unavailable. Finally, we compare the performance of MEMFCS with that of a conventional fitting routine for analyzing simulated data describing a highly heterogeneous distribution containing 41 diffusing species. Both methods fit the data well. However, the conventional fit fails to reproduce the essential features of the input distribution, whereas MEMFCS yields a distribution close to the actual input.

Algorithms↗

PubMed2003

Factor V Leiden detection by polymerase chain reaction-restriction fragment length polymorphism with mutagenic primers in a multiplex reaction with Pro G20210A--a novel technique.

Factor V Leiden (FVL) R506Q and Prothrombin G20210A are clinically important genetic mutations associated with increased susceptibility to venous thrombosis. The objective of our study was to design a polymerase chain reaction/restriction fragment length polymorphism (PCR/RFLP) reaction that allows simultaneous detection of these two mutations. The reaction can be used in routine diagnostic settings. We have analysed 4504 alleles for each mutation with a mutagenic primer-based PCR system with a low failure rate. The system eliminates the false positive FVL G1691A results associated with other PCR/RFLP caused by rare confounding mutations adjacent to restriction endonuclease recognition sites. This multiplex PCR/RFLP reaction is rapid, robust and dependable.

3' Untranslated Regions↗

PubMed2002

Laparoscopic management of ectopic pregnancy: a 5-year experience.

The objective of this study was to review our management of ectopic pregnancy with the introduction of a laparoscopic service to the obstetrics and gynaecology department at South Cleveland Hospital. A retrospective analysis of 210 cases of ectopic pregnancy managed from May 1995 to May 2000 including operative findings and surgical data were collected prospectively over the past 5 years. All our women with an ectopic pregnancy were treated surgically. One hundred and seventy-seven (84.3%) patients were managed successfully laparoscopically with no major intraoperative or postoperative complications. Thirty-three (15.7%) women were managed by laparotomy for various reasons. Salpingectomy was the main (80%) procedure performed either by laparoscopy or by laparotomy. Thirty-five (16.7%) women were treated conservatively by salpingostomy. Of these 22.9% achieved a successful pregnancy and delivery. Half of our patients were managed by senior registrars. The estimated blood loss, the need for blood transfusion and the length of hospital stay following laparoscopic treatment were significantly less than those in laparotomy group. This study demonstrated that laparoscopic management of ectopic pregnancy is the most beneficial procedure with maximum safety and efficiency when the laparoscopic service is added to the unit.

Adult↗

PubMed2001

A direct-method ab initio phasing of a protein, cupredoxin amicyanin, at 1.31 A resolution.

The direct-methods program MULTAN88 has been applied successfully to redetermine the structure of a protein, cupredoxin amicyanin, containing 808 non-H atom sites, one Cu atom and 132 ordered water molecules in the asymmetric unit using data at 1.31 A resolution. Starting with initially random phases, useful phase sets selected by figures of merit could be obtained from multiple trials. The E maps corresponding to the best eight phase sets in order of combined figures of merit (CFOM2) revealed a distorted tetrahedral geometry around the Cu site. The phase estimates from the metal and a few neighbouring atoms in the initial E map corresponding to the set with the highest CFOM2 could be improved by the density-modification procedure PERP and led to an interpretable electron-density map.

Azurin↗

PubMed2001

Localization and stability of introns spliced from the Pem homeobox gene.

RNA splicing generates two products in equal molar amounts, mature mRNAs and spliced introns. Although the mechanism of RNA splicing and the fate of the spliced mRNA products have been well studied, very little is known about the fate and stability of most spliced introns. Research in this area has been hindered by the widely held view that most vertebrate introns are too unstable to be detectable. Here, we report that we are able to detect all three spliced introns from the coding region of the Pem homeobox gene. By using a tetracycline (tet)-regulated promoter, we found that the half-lives of these Pem introns ranged from 9 to 29 min, comparable with those of short lived mRNAs such as those encoding c-fos and c-myc. The half-lives of the Pem introns correlated with both their length and 5' to 3' orientation in the Pem gene. Subcellular fractionation analysis revealed that spliced Pem introns and pre-mRNA accumulated in the nuclear matrix, high salt-soluble, and DNase-sensitive fractions within the nucleus. Surprisingly, we found that all three of the spliced Pem introns were also in the cytoplasmic fraction, whereas Pem pre-mRNAs, U6 small nuclear RNA, and a spliced intron from another gene were virtually excluded from this fraction. This indicates either that spliced Pem introns are uniquely exported to the cytoplasm for degradation or they reside in a unique soluble nuclear fraction. Our study has implications for understanding the regulation of RNA metabolism, as the stability of introns and the location of their degradation may dictate the following: (i) the stability of nearby mRNAs that compete with spliced introns for rate-limiting nucleases, (ii) the rate at which free nucleotides are available for further rounds of transcription, and (iii) the rate at which splicing factors are recycled.

Animals↗

PubMed2001

Effects on levels of glutathione and some related enzymes in tissues after an acute arsenic exposure in rats and their relationship to dietary protein deficiency.

Arsenic is a potent toxin, carcinogen and modulator of antioxidant defense system. In this study, male rats of Wistar strain, maintained on either 18% or 6% protein (casein) diet, received an acute i.p. exposure to sodium arsenite (As3+) at its LD50 dose (15.86 mg/kg body weight). One hour after the arsenic exposure, glutathione (GSH) concentration was significantly depleted and lipid peroxidation was increased. A relationship between any two of tissue arsenic concentrations, GSH levels and lipid peroxidation values was observed only for liver when the proportional changes of respective parameters in either of the dietary groups of animals were compared. This suggests that, in liver, arsenic metabolism appears dependant upon the GSH concentration. Acute arsenic exposure significantly increased the glutathione peroxidase (GPx) activity in liver of both dietary groups and in kidney of only the 18% protein-fed group of animals. The glutathione-S-transferase (GST) activity significantly decreased in liver of the 18% protein-fed animals while GST increased in kidney of both the 18% and the 6% protein-fed groups. No significant change in glutathione reductase (GR) or glucose-6-phosphate dehydrogenase (G6PDH) activity was observed. In the present investigation, liver as a whole seems to be more affected in terms of GSH level and GST activity. The mode of responses of GPx and GR activities as well as the unaltered G6PDH activity might result in arsenic-induced GSH depletion and increase in lipid peroxidation. The animals of the 6% protein-fed group, appeared to be affected less in terms of tissue arsenic concentration, GSH level and GST activity. lipid peroxidation,

Acute Disease↗

PubMed2001

Clinical appraisal of Ascaris lumbricoides, with special reference to surgical complications.

Over a period of 4 years (January 1993-December 1997), 509 patients were treated for abdominal colic with or without intestinal obstruction and a history of passage of adult roundworms either in the stool or in vomitus. All patients were below the age of 10 years, the youngest 6 months old, and were treated successfully with antispasmodics and normal saline enemas. When the pain subsided, an anthelminthic drug was given. Of 209 patients admitted to the hospital, 105 responded to conservative management and 104 (50%) required surgical intervention. The procedures included squeezing out of worms, resection and anastomosis, and treatment of other pathologies like acute appendicitis, tubercular stricture of the small intenstine, etc. Five patients died in the postoperative period due to various complications. There were no deaths among those treated by conservative management. Early recognition of the condition can prevent serious surgical complications and morbidity.

Animals↗

PubMed2001

Comparison of antibiogram, virulence genes, ribotypes and DNA fingerprints of Vibrio cholerae of matching serogroups isolated from hospitalised diarrhoea cases and from the environment during 1997-1998 in Calcutta, India.

This study identified 17 matching serogroups of Vibrio cholerae belonging to serogroups other than O1 and O139 isolated from human cases and from the environment during a concurrent clinical and environmental study conducted in Calcutta, a cholera endemic area. Isolates within these matching serogroups were compared by various phenotypic and genotypic traits to determine if the environment was the source of the organisms associated with the disease. Clinical strains of V. cholerae were resistant to a greater number of drugs and exhibited multi-drug resistance compared with their environmental counterparts. Except for the presence of the genes for the El Tor haemolysin and the regulatory element ToxR in most of the strains of V. cholerae examined, non-O1, non-O139 V. cholerae strains lacked most of the other known virulence traits associated with toxigenic V. cholerae O1 or O139. Restriction fragment-length polymorphism of virulence-associated genes, ribotypes and DNA fingerprints of strains of matched serogroups showed considerable diversity, although some gene polymorphisms and ribotypes of a few strains of different serogroups were similar. It is concluded that despite sharing the same serogroup, environmental and clinical isolates were genetically heterogeneous and were of different lineages.

Blotting, Southern↗

PubMed2001

Irradiation selectively inhibits expression from the androgen-dependent Pem homeobox gene promoter in sertoli cells.

How radiation blocks spermatogenesis in certain strains of rats, such as LBNF(1), is not known. Because the block depends on androgen, we propose that androgen affects Sertoli cell function in irradiated LBNF(1) rats, resulting in the failure of spermatogonial differentiation. To begin to identify genes that may participate in this irradiation-induced blockade of spermatogenesis, we investigated the expression of several Sertoli genes in response to irradiation. The expression of the PEM: homeobox gene from its androgen-dependent Sertoli-specific proximal promoter (Pp) was dramatically reduced more than 100-fold in response to irradiation. In contrast, most other genes and gene products reported to be localized to the Sertoli cell, including FSH receptor (FSHR), androgen receptor (AR), SGP1, and the transcription factor CREB, did not exhibit significant changes in expression, whereas transferrin messenger RNA (mRNA) expression dramatically increased in response to irradiation. Irradiation also decreased Pp-driven PEM: mRNA levels in mouse testes (approximately 10-fold), although higher doses of irradiation than in rats were required to inhibit PEM: gene expression in testes of mice, consistent with their greater radioresistance. The decrease in Pem gene expression in mouse testis was also selective, as the expression of CREB, GATA-1, and SGP1 were little affected by irradiation. We conclude that the dramatic irradiation-triggered reduction of Pem expression in Sertoli cells is a conserved response that may be a marker for functional changes in response to irradiation.

Androgens↗

PubMed2000

Aggregation and Polymerization of Amphiphilic Macromonomers with a Double Bond at the Hydrophilic Terminal.

Macromonomers with general formula C(n)[EO](m)-CO-CH=CH(2) were synthesized by endcapping corresponding Brij compounds with acryloyl chloride. Their aggregation behavior evaluated against the parent Brij compounds, the saturated and triblock analogs advocate that the terminal double bond is protected by the partially looped PEG chain. The homo- and copolymerization behavior in aqueous media is consistent with this possibility. Copyright 2000 Academic Press.

Journal Article↗