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Biomedical subjects

R N Saha

Publications and source records attributed to R N Saha.

15 recordsLinked to original sources
PubMed2006

HATs and HDACs in neurodegeneration: a tale of disconcerted acetylation homeostasis.

Gradual disclosure of the molecular basis of selective neuronal apoptosis during neurodegenerative diseases reveals active participation of acetylating and deacetylating agents during the process. Several studies have now successfully manipulated neuronal vulnerability by influencing the dose and enzymatic activity of histone acetyltransferases (HATs) and histone deacetylases (HDACs), enzymes regulating acetylation homeostasis within the nucleus, thus focusing on the importance of balanced acetylation status in neuronal vitality. It is now increasingly becoming clear that acetylation balance is greatly impaired during neurodegenerative conditions. Herein, we attempt to illuminate molecular means by which such impairment is manifested and how the compromised acetylation homeostasis is intimately coupled to neurodegeneration. Finally, we discuss the therapeutic potential of reinstating the HAT-HDAC balance to ameliorate neurodegenerative diseases.

Acetylation↗
PubMed2006

New, sensitive and validated spectrofluorimetric method for the estimation of etoposide in bulk and pharmaceutical formulations.

A new, simple and sensitive spectrofluorimetric method was developed for the routine estimation of etoposide, an anticancer drug, in bulk and in pharmaceutical formulations. The medium selected for the estimation of etoposide was methanol : phosphate buffer (pH 7.4) in a ratio of 70 : 30 v/v. Excitation and emission wavelengths used were 240 and 324 nm respectively. The method was validated according to ICH and U.S.P guidelines. Linearity range was 200-1000 ng/ml with detection and quantitation limits of 23 ng/ml and 72 ng/ml respectively. Regression equation obtained was Fluorescence Intensity = 6.704 (Concentration in ng/ml) + 115.4. The drug was found to be stable and there was no interference from the excipients present in different formulations of etoposide.

Antineoplastic Agents, Phytogenic↗
PubMed2002

Determination of celecoxib in pharmaceutical formulations using UV spectrophotometry and liquid chromatography.

A new UV spectrophotometric method (UV method) and a reversed phase liquid chromatographic method (LC method) for the quantitative estimation of celecoxib, a selective COX-2 inhibitor, in pure form and in solid dosage form were developed in the present study. The linear regression equations obtained by least square regression method, were Abs=4.949 x 10(-2).Conc. (in microg/ml)+1.110 x 10(-2) for the UV method and Area under the curve=5.340 x 10(1).Conc. (in ng/ml)+3.144 x 10(2) for the LC method, respectively. The detection limit, as per the error propagation theory, was found to be 0.26 microg/ml and 25 ng/ml, respectively, for the UV and LC methods. The developed methods were employed with a high degree of precision and accuracy for the estimation of total drug content in three commercial capsule formulations of celecoxib. The results of analysis were treated statistically, as per International Conference on Harmonisation (ICH) guidelines for validation of analytical procedures, and by recovery studies. The results were found to be accurate, reproducible and free from interference and better than the earlier reported methods.

Calibration↗
PubMed2000

New Ultraviolet spectrophotometric method for the estimation of nimesulide.

Two simple and accurate ultraviolet (UV) spectrophotometric methods with better detection range for estimation of nimesulide in pure form and in solid dosage form were developed in the present studies using 50% v/v and 100% v/v acetonitrile as the solvent system. The linearity range of nimesulide in both the methods was found to be 10-50 micrograms/ml at a lambda max of 300 nm. The linear regression equations obtained by the least-square regression method are Abs = 1.33 x 10(-1).Conc + 1.89 x 10(-1) in 50% v/v acetonitrile and Abs = 1.05 x 10(-1).Conc + 1.14 x 10(-1) in 100% v/v acetonitrile. The detection limit as per the error propagation theory was found to be 0.46 microgram/ml and 1.04 micrograms/ml, respectively, in 50% v/v and 100% v/v acetonitrile. The developed methods were employed with high degree of precision and accuracy for the estimation of total drug content in three commercial tablet formulations of nimesulide. The results of the analysis were validated statistically and by recovery studies.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed1999

Simultaneous determination of tinidazole, furazolidone and diloxanide furoate in a combined tablet preparation by second-derivative spectrophotometry.

A second-derivative spectrophotometric procedure has been developed for the simultaneous determination of tinidazole (TD), furazolidone (FD) and diloxanide furoate (DF) in a commercial preparation. The method consists of the utilization of second-derivative absorption spectra of tablet extract in distilled water and then determination of the analyte concentration in the mixture was carried out using zero-crossing (ZC) and ratio-compensation (RC) techniques. Calibration graphs constructed at their wavelengths of determination were linear in the concentration range of TD (5-20 microg ml(-1)), FD (2.5-10 microg ml(-1)) and DF (7.5-15 microg ml(-1)). The results were found to be accurate and free from interference. The details of the statistical treatment of analytical data are also presented.

Antiprotozoal Agents↗
PubMed1992

Quantitative structure-activity relationship studies on benzodiazepine receptor binding: recognition of active sites in receptor and modelling of interaction.

A quantitative structure-activity relationship study was carried out for the binding of a series of 'classical' benzodiazepines (BZs) and some beta-carbolines with BZ receptors to investigate the active sites in the latter and the nature of the binding of compounds with them. Using the Hansch approach, an attempt was made to correlate binding affinities of compounds with various physico-chemical and electronic properties of substituents. The correlations obtained showed the main roles were played by the hydrophobic constant pi and the Hammett constant sigma (an electronic parameter) of various substituents. This led to the suggestion that BZ receptors have many additional hydrophobic, hydrogen bonding and polar sites other than those suggested by Hollinshead et al. (1990). From the present study, the Hollinshead model of interaction was found to be inadequate to account fully for the binding of all types of compounds.

Benzodiazepines↗
PubMed1991

QSAR studies on benzodiazepine receptor binding of purines and amino acid derivatives.

Quantitative structure-activity relationship (QSAR) studies are reported on the benzodiazepine receptor binding of a series of substituted 9-benzyl-6-dimethylamino-9H-purines and N-(indol-3-ylglyoxylyl)amino acid derivatives. The nitrogen of the five membered heterocyclic ring and the polar substituent in the aromatic ring, present in both series of compounds, form important centres in the binding interaction. We conclude that the receptor must possess a strong nucleophilic centre and a polar site, and that a hydrophobic pocket exists to accommodate hydrophobic moieties.

Algorithms↗
PubMed1990

A quantitative structure-activity relationship study on the inhibitory effects of local anesthetics on sodium flux, phosphoinositide breakdown, and binding to sodium channels.

The inhibitory effects of a series of nonspecific local anesthetics on batrachotoxin-elicited sodium flux, batrachotoxin-elicited phosphoinositide breakdown, and on the binding of [3H]batrachotoxin-A 20 alpha-benzoate to sodium channels in guinea pig cerebral cortical synaptoneurosomes are shown to be well-correlated with the molecular size and the hydrophobic character of the molecules. These correlations lead us to suggest that the drug-receptor interaction involves a dispersion interaction, and that the overall effects of local anesthetics is dependent upon their ability to reach the receptor site.

Anesthetics, Local↗
PubMed1990

Quantitative structure-activity relationships of salicylamide neuroleptic agents.

The in vitro antidopamine activity of substituted N-[(1-alkyl-2-pyrrolidinyl)methyl]-6-methoxysalicylamides was found to be well correlated with the hydrophobic and electronic nature of substituents at the 3-position, and with the steric nature of groups replacing the hydrogen atom of the salicyl hydroxy group. In contrast, only the hydrophobic and steric characteristics were found to be important in the in vivo activity of these neuroleptics. This difference suggests that different mechanisms are probably involved in their in vitro and in vivo actions, and that the relevant receptors are slightly different in structure. The in vitro results suggest that electron donation by the 3-substituent strengthens the formation of a hydrogen bond between the carbonyl group of the amide moiety and a hydrogen of the receptor.

Animals↗
PubMed1989

A quantitative structure-activity relationship study on some pyrazolo[4,5-c]quinolines acting as inhibitors of benzodiazepine-receptor binding.

By a quantitative structure-activity relationship (QSAR) study, the ability of a series of 1-arylpyrazolo[4,5-c]quinolin-4-ones to displace specific [3H]-flunitrazepam from bovine brain membranes is shown to be significantly correlated with steric and hydrophobic constants of aryl subtituents, suggesting that substituents of 2- and 6-positions produce dominant steric effects and that those of 3- and 5-positions are involved in strong hydrophobic interaction with the receptor.

Animals↗
PubMed1988

A quantitative structure-activity relationship study of 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase inhibitors.

A quantitative structure-activity relationship study has been made of some 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors. The HMG-CoA reductase inhibition activities of mevinolin analogs and 6-substituted 4-hydroxypyran-2 ones have been mostly found to be significantly correlated with the molecular size of substituents. In one case, however, the inhibition potency was found to be related to the hydrophobicity of molecules. These findings led us to suggest that the enzyme HMG-CoA reductase possesses an active site which is involved in dispersion interaction and another site which is involved in hydrophobic interaction with inhibitor molecules, depending upon the proper orientation of the latter towards these sites. Furthermore, the results indicate that both active sites possess limited steric bulk tolerance.

Chemical Phenomena↗
PubMedDate not supplied

Oral controlled release formulation of diclofenac sodium by microencapsulation with ethyl cellulose.

The aim of this study was to formulate and evaluate microencapsulated controlled release preparations of diclofenac sodium (DFS) using different proportions of ethyl cellulose (EC) as the retardant material to extend the release. The formulated microcapsules were then compressed into tablets to obtain controlled release oral formulations. Phase separation-coacervation technique was employed to prepare microcapsules of DFS using different proportions of EC in cyclohexane. Physical characteristics of microcapsules and their tablets, in vitro release pattern of the designed microcapsules and their tablets prepared from them were studied using USP dissolution apparatus (USP 2000) type 2 (paddle method) in triple distilled water. The prepared microcapsules were white, free flowing and spherical in shape, with the particle size varying from 49.94-52.72 microm. The duration of DFS release from microcapsules was found to be directly proportional to the proportion of EC and, thus, coat thickness. All tablets were of good quality with respect to appearance, drug content uniformity, hardness, weight variation, friability and thickness uniformity. In vitro release study of the tabletted microcapsules in triple distilled water showed a zero order release kinetics and extended release beyond 24 h. A good correlation was obtained between drug release (t(60)) and proportion of EC in the microcapsules. In the case of tabletted microcapsules, very good correlation could be established between t(60), proportion of EC, weight of the tablets and between release rate constant (K) and proportion of EC. All the formulations were highly stable and possessed reproducible release kinetics across the batches.

Administration, Oral↗
PubMedDate not supplied

A comparative study of controlled release matrix tablets of diclofenac sodium, ciprofloxacin hydrochloride, and theophylline.

The need for controlled release formulations for diclofenac sodium, ciprofloxacin, and theophylline is well recognized. In our study, controlled release tablets of the three drugs were formulated by the matrix-embedding technique using ethyl cellulose as retardant. Tablets of all the drugs were of good physical quality with respect to appearance, drug content uniformity, hardness, weight variation, and friability. In vitro release rate studies showed that ethyl cellulose extended the release of the three drugs to 12 hr or more. Release patterns from formulations of the three drugs followed Higuchi's square root kinetics. At pH 6.8, the release rate was higher in all three drugs, probably due to increased solubility of the drugs and/or increased swelling of ethyl cellulose at the higher pH. The formulations were highly stable and possessed reproducible release kinetics across batches.

Ciprofloxacin↗
PubMedDate not supplied

Design and study of rifampicin oral controlled release formulations.

Oral controlled release formulations of rifampicin have been developed by using hydroxypropyl methylcellulose polymer at different ratios. From in vitro release data, we found that the release was extended with an increase of polymer proportion from 20% to 40%. However, increase in polymer beyond 40% resulted in no significant change in the release rate. There was a distinct difference in the release rate and release character due to variation in the compression force. The release kinetics were analyzed using Ritger and Peppas exponential equation. Stability studies at ambient storage conditions for 1 year showed that formulations were stable.

Algorithms↗