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Biomedical subjects

B Chakrabarti

Publications and source records attributed to B Chakrabarti.

At least 19 recordsLinked to original sources
PubMed2006

Management of acute ventilatory failure.

Acute ventilatory failure is a challenging yet increasingly common medical emergency reflecting the growing burden of respiratory disease. It is not a diagnosis in itself but the end result of a diversity of disease processes culminating in arterial hypoxaemia and hypercapnia. This review focuses on key management issues including giving appropriate oxygen therapy, treatment of the underlying aetiology as well as any precipitant factors and provision of assisted ventilation if required. Ventilatory assistance can be provided both invasively and non-invasively and the indications for either or both forms of assisted ventilation are discussed. Further emphasis is needed regarding advanced directives of care and clinicians should be aware of ethical issues regarding assisted ventilation.

Acute Disease↗
PubMed2006

Pleural tuberculosis.

Pleural effusions in tuberculosis are commonly seen in young adults as an immunological phenomenon occurring soon after primary infection. However, the epidemiology and demographics of tuberculous pleurisy are changing due to the impact of HIV co-infection and the increasing number of pleural effusions seen as part of re-activation disease. Pleural biopsy for histology and culture is the mainstay of diagnosis with closed needle biopsy adequate in the majority of cases. Techniques such as PCR of biopsy specimens and the role of pleural fluid ADA are still being evaluated as a diagnostic aid. Tuberculous empyema is less commonly seen in the western world and the diagnostic yield from pleural fluid here is greater than in "primary" effusions. Treatment with appropriate antituberculous chemotherapy is generally successful though there is currently insufficient evidence to recommend the routine use of corticosteroids in this condition.

AIDS-Related Opportunistic Infections↗
PubMed2001

Radio-iodine (NaI131) therapy in hyperthyroidism.

Iodine131 is well recognised as an ideal isotope for treatment of hyperthyroidism. NaI131 therapy is considered as the simplest, safest, least expensive and most effective form of therapy for most patients. This form of therapy can be applied to all categories of patients except in pregnant and nursing mothers who are not willing to forgo breastfeeding. In contrary to the common belief, this form of therapy can also be used in children and adolescents. One common complication is hypothyroidism which can be easily treated but life long follow-up is essential which is, however, necessary in other modalities of treatment also. NaI131 therapy in hyperthyroidism can be instituted on outpatient basis. This form of therapy is available in several centres of Calcutta.

Antithyroid Agents↗
PubMed2000

Ciprofloxacin in children: is arthropathy a limitation?

Two hundred and nineteen children treated with Ciprofloxacin were observed for drug related adverse reactions (ADR). ADR was observed in 35/219 (15.98%) children, arthropathy in 2/219 (0.9%) children only. All the ADR were reversible even on continuation of therapy except one child with arthropathy and no permanent sequele or death occurred as a drug related ADR.

Adolescent↗
PubMed2000

Calculation of the first excited (1)S(e) state of the He atom using supersymmetric quantum mechanics and extension to the nth excitation

Usually the renormalized Numerov (RN) algorithm is used to solve the set of coupled differential equations of the few-body system, mainly for the ground state. The straightforward approach of this algorithm faces some serious problems of convergence to calculate the excited states. Here we present an alternative method using the supersymmetric quantum mechanics formalism to a multidimensional bound-state problem. The problem of convergence is avoided in this approach by searching for the ground state of the partner potential. Application of this formalism to the first excited (1)S(e) state of the He atom gives excellent results; it is much better than the conventional RN algorithm and the hyperspherical adiabatic approximation. We also indicate how the method can be generalized to the nth excited state.

Journal Article↗
PubMed1998

Intermolecular interaction of lens crystallins: from rotationally mobile to immobile states at high protein concentrations.

The conformation of lens crystallins in vivo or in a highly concentrated solution is not well established. Most studies were carried out in dilute solutions in which protein-protein interaction is minimal. In order to see whether there is conformational change (tertiary and secondary structures) when crystallin solutions are brought to high concentrations, we have performed the following molecular spectroscopic measurements: circular dichroism (CD) and Fourier transform infrared (FTIR). Near-UV CD measurements showed a more than two-fold increase in CD intensity (molar ellipticity) for the total water-soluble (WS) protein from young calf lens nucleus in a highly concentrated solution (> 300 mg/ml in a 0.01-mm cell), when compared with a dilute solution (1000-fold dilution in a 10-mm cell). The individual crystallins in concentrated solutions also showed an increase in CD intensity, but of different magnitude: alpha-crystallin > beta-crystallin > gamma-crystallin. The increased CD indicates that lens crystallins are in a more compact structure in highly concentrated solutions; they likely undergo a transition from a mobile to an immobile state. Change in near-UV CD usually is caused by restricted mobility of aromatic side groups, particularly Trp. The transition involves not only a change in protein tertiary and/or quaternary structure, but also in protein backbone structure. The change of protein backbone structure was drawn from FTIR measurements. FTIR spectra, sensitive to the secondary structure in the amide I region, could be measured for a highly concentrated solution for which far-UV CD measurement is not feasible. The secondary structure that showed prominent change for alpha-crystallin in a highly concentrated solution was beta-conformation: increase in beta-turn with a concomitant decrease of alpha-helix structure.

Animals↗
PubMed1997

Heat-induced conformational change and increased chaperone activity of lens alpha-crystallin.

PURPOSE: Alpha-crystallin is the major structural protein of the eye lens known to have chaperone-like activity. Our objective is to elucidate the nature of the thermal transition that alpha-crystallin undergoes at 60 degrees C and the effect of this transition on the chaperone activity. METHODS: FPLC size exclusion chromatography, far- and near-ultraviolet circular dichroism, and tryptophan (Trp) and 1-anilino-8-naphthalenesulfonate (ANS) fluorescence were used to study conformational change. Turbidity of dithiothreitol (DTT)-reduced insulin was used to study chaperone activity. RESULTS: The thermal transition was identified as a conformational change in mainly tertiary (partial unfolding) and quaternary high-molecular-weight (HMW) aggregation structures, along with a loss of 10 percentage points of secondary structure (beta-sheet). Initial partial perturbation in tertiary structure increased chaperone activity, but the increase was less in the HMW aggregate. Similar results were observed in in vivo-formed HMW alpha-crystallin. CONCLUSIONS: The conformational change and HMW aggregation of alpha-crystallin observed at 60 degrees C, as well as in vivo-formed HMW aggregates, increased chaperone activity.

Anilino Naphthalenesulfonates↗
PubMed1996

Evidence of cross-link formation of vitreous collagen during experimental ocular inflammation.

PURPOSE: To determine the mechanisms of vitreous changes during ocular inflammation. METHODS: We investigated vitreous changes, with special emphasis on collagen, in an experimental model of ocular inflammation induced by intravitreal injection of endotoxin (Escherichia coli) in rabbits. RESULTS: Inflammation caused gel contraction and loss of elasticity, accompanied by release of a water-like liquid from the gel, and increases in the amount of insoluble material and high-molecular-weight components of vitreous collagen, presumably due to extensive cross-links of the collagen molecules. Those changes were partially inhibited by intravitreal injection of superoxide dismutase. CONCLUSIONS: The cross-links of vitreous collagen may promote vitreous gel contraction and release of a water-like liquid from the gel. Superoxide anion may play a role in this process.

Animals↗
PubMed1996

Vitreous changes during ocular inflammation induced by interleukin 1 beta.

To determine the mechanisms of vitreous changes during ocular inflammation, we investigated these changes, focusing on the collagen, in an experimental model of ocular inflammation induced by intravitreal injection of interleukin 1 beta in rabbits. Inflammation caused gel contraction, with release of a watery liquid from the gel, and increases in the amount of insoluble material and high-molecular-weight components of the vitreous collagen, presumably due to extensive cross-links of the collagen molecules. The cross-links of vitreous collagen may promote vitreous gel contraction and the release of watery liquid from the gel.

Animals↗
PubMed1995

Serum-induced collagen gel contraction.

PURPOSE: To understand the molecular events underlying disease-related vitreous gel contraction, the effect of serum components on collagen was investigated. METHODS: Bovine vitreous or dermal collagen was incubated with a mixture of transglutaminase (TG; factor XIIIa) and fibronectin (FN), and the biochemical changes of collagen were monitored by gel electrophoresis. In addition, serum-induced changes in the volume of the collagen gel were monitored. RESULTS: Gel electrophoresis revealed a new high-molecular-weight band (M(r) 240,000) presumably due to intermolecular cross-links of collagen peptides and FN. The serum components also were shown to cause a significant decrease in the volume of the collagen gel. CONCLUSION. Collagen gel contraction could be attributed to the collagen-FN-collagen cross-links catalyzed by TG.

Animals↗
PubMed1994

Human placental aldose reductase: role of Cys-298 in substrate and inhibitor binding.

Steady-state kinetic and inhibition properties of human placental aldose reductase carboxymethylated at Cys-298 were investigated. A comparison of the primary deuterium kinetic isotope effect on the reduced and the carboxymethylated enzymes suggests that carboxymethylation did not affect the reaction sequence of substrate binding and release. Values of DV/KD-glyceraldehyde greater than DV suggest that steps in the reaction scheme subsequent to hydride transfer, particularly the release of NADP may be rate limiting. Carboxymethylation of Cys-298 was also found to affect NADPH and aldehyde binding to the enzyme. Carboxymethylation had little effect on the secondary structure of the enzyme, but a comparison of the circular dichroic spectra of the reduced and carboxymethylated enzyme, suggests a weakened interaction between the nicotinamide and 2'-monophosphoadenosine 5'-diphosphoribose of NADPH, and the carboxymethylated enzyme. Interaction between Cys-298 and NADPH appears to determine the rate of isomerization of the E:NADP binary complex and carboxymethylation-induced decrease in kcat may be due to slower isomerization of the E:NADP binary complex. The carboxymethylated enzyme was less sensitive than the reduced enzyme to most aldose reductase inhibitors including sorbinil (d-6-fluoro-spiro[chroman-4,4'-imidazolidine]-2',5'-dione), except tolrestat (N-methyl-N-[(5-trifluromethyl-6-methoxy-1-naphthalenyl)- thiomethyl]glycine) and quercetin. On the basis of these observations it is suggested that Cys-298 may form a part of the 'S'-inhibitor binding site of the enzyme and may be responsible for tight binding of NADPH.

Aldehyde Reductase↗
PubMed1994

Molecular mechanisms of photochemically induced posterior vitreous detachment.

Vitreous gel contraction and syneresis, commonly associated with age- and disease-related posterior vitreous detachment (PVD), were induced by a hematoporphyrin (HP)-photosensitized reaction. Calf vitreous gel was irradiated by white light in the presence of HP. Gel weights of the vitreous samples after 24 h of irradiation decreased by 14%, the irradiated control without HP by 8% and the control with HP stored in the dark by 8%. No significant difference in vitreous gel compressibility was found between the irradiated controls and the irradiated samples. In separate experiments, collagen gel in a glass capillary and hyaluronic acid (HA) were irradiated with white light in the presence of HP. The control collagen gel (irradiated without HP and stored in the dark with HP) decreased in length by 0.6% after 96 h, the experimental gel with HP decreased in length by 1.3 and 1.9% after 24- and 96-hour irradiation by visible light, respectively. The irradiated HA monitored by high-performance liquid chromatography showed a molecular weight decrease in the HP-treated polymer. Because the HP-sensitized reaction predominantly produces singlet oxygen, collagen gel contraction and HA degradation, in this case, are likely caused by this active oxygen species.

Animals↗
PubMed1994

Mechanisms of photo-induced vitreous liquefaction.

To understand the mechanisms of photo-induced vitreous liquefaction, this study investigated the effects of free radicals on collagen and hyaluronic acid (HA). Bovine vitreous collagen or HA was irradiated by visible light in the presence of riboflavin (RF) as a photosensitizer. The changes in the molecular weight of collagen and HA were monitored by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and high-performance liquid chromatography, respectively. Free radicals were shown to cause an increase in the high-molecular-weight components and insolubilization of the vitreous collagen and a decrease in the molecular weight of HA. The change in molecular properties of the vitreous collagen could be attributed to extensive crosslinks of the molecules. Since RF is present in the vitreous, which is irradiated by visible light over a lifetime, both cross-links of vitreous collagen and degradation of HA may contribute to age-related vitreous liquefaction.

Animals↗
PubMed1994

[Spectral transmittance of normal human crystalline lens].

The spectral transmittance and non-tryptophan fluorescence of human crystalline lenses were evaluated. Eleven eye bank lenses and three lenses of prematurity of retinopathy patients were investigated. All lenses absorbed the short wavelength light below 430 nm strongly. The transmission of the short wavelength visible light decreased gradually with age. There was a positive correlation between the fluorescence intensity ratio of non-tryptophan to tryptophan fluorescence and the logarithm of age. It was thought that the generation of non-tryptophan fluorescence might be a first-order chemical reaction.

Adult↗
PubMed1994

Cross-linking of dermal collagen induced by singlet oxygen.

Changes were studied in dermal collagen induced by singlet oxygen, which was generated by a bilirubin-photosensitized reaction. An increase in the ratio of high-molecular-weight components (beta- and r-components) against the alpha-chain of collagen after irradiation manifested in sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Sodium azide, a singlet oxygen quencher, inhibits the alteration of the molecular size by the photochemical reaction. These data suggest that chronic sunlight irradiation may contribute to cross-links of dermal collagen.

Animals↗
PubMed1994

Differential domain folding/unfolding of gamma-crystallins: existence of two distinct groups.

High resolution calorimetry and spectral measurements have been employed to examine folding/unfolding behaviour of gamma-crystallins which are known to contain two homologous domains. Results have been analyzed in terms of selective unfolding of domains, interdomain interactions, conformational stability and the existence of intermediates in the order-disorder transition equilibrium. Both spectral and thermotropic data indicate that, in terms of structural hierarchy, these proteins can be divided into two distinct groups, gamma II and gamma IIIB belonging to one and gamma IIIA and gamma IVA to the other. The unfolding/folding characteristics of these two groups are distinctly different. Equilibrium unfolding of gamma II and gamma IIIB is biphasic indicating the existence of an intermediate in which one domain unfolds and the other remains in the native form. The absence of a cooperative transition in gamma IIIA and gamma IVA in acidic urea has also been attributed to a structured intermediate, most likely a molten globule, which may not be thermodynamically as distinct as of the former group. The difference in the equilibrium folding/unfolding transition of these two groups has been explained by subtle differences in the packing arrangement of their two domains and interactions between them. Since the intermediates, under certain circumstances, are known to aggregate, they are likely to play a critical role in the etiology of human cataract formation.

Animals↗
PubMed1993

Evidence for singlet oxygen-induced cross-links and aggregation of collagen.

Singlet oxygen, generated by a hematoporphyrin-photosensitized reaction, was shown to cause insolubilization and an increase in molecular weight of acid soluble type I collagen and vitreous collagen as manifested in sodium dodecyl sulfate polyacrylamide gel electrophoresis. No such changes in the molecular properties of collagen could be observed when the irradiation was carried out in the presence of sodium azide, a singlet oxygen quencher. The increase in molecular weight and insolubilization of the collagen solution was attributed to extensive cross-links in the protein molecules.

Animals↗