6-Hydroxymelatonin protects against cyanide induced oxidative stress in rat brain homogenates
- Maharaj, Deepa S, Walker, Roderick B, Glass, Beverley D, Daya, Santylal
- Authors: Maharaj, Deepa S , Walker, Roderick B , Glass, Beverley D , Daya, Santylal
- Date: 2003
- Language: English
- Type: Article , text
- Identifier: vital:6405 , http://hdl.handle.net/10962/d1006478
- Description: Both 6-hydroxymelatonin and N-acetyl-N-formyl-5-methoxykynurenamine are photodegradants and enzymatic metabolites of melatonin and are known to retain equipotent activity against potassium cyanide-induced superoxide generation compared to melatonin. It is not clear whether one or both of these metabolites is responsible for this effect. The present study therefore investigates the possible manner in which 6-hydroxymelatonin protects against oxidative stress induced by cyanide in rat brain homogenates. We examined the ability of 6-hydroxymelatonin to scavenge KCN-induced superoxide anion generation as well as lipid peroxidation. In addition, we also examined the effect of this indole on lactate dehydrogenase activity (LDH) as well as mitochondrial electron transport using dichlorophenol–indophenol as an electron acceptor. The results of this study show that 6-hydroxymelatonin significantly reduces KCN-induced superoxide anion generation, which is accompanied by a commensurate reduction in lipid peroxidation. Partial reversal of the KCN-induced reduction in mitochondrial electron transport is accompanied by a similar reversal of mitochondrial LDH activity blunted by KCN. It can thus be proposed that 6-hydroxymelatonin is potentially neuroprotective against KCN-induced neurotoxicity.
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- Authors: Maharaj, Deepa S , Walker, Roderick B , Glass, Beverley D , Daya, Santylal
- Date: 2003
- Language: English
- Type: Article , text
- Identifier: vital:6405 , http://hdl.handle.net/10962/d1006478
- Description: Both 6-hydroxymelatonin and N-acetyl-N-formyl-5-methoxykynurenamine are photodegradants and enzymatic metabolites of melatonin and are known to retain equipotent activity against potassium cyanide-induced superoxide generation compared to melatonin. It is not clear whether one or both of these metabolites is responsible for this effect. The present study therefore investigates the possible manner in which 6-hydroxymelatonin protects against oxidative stress induced by cyanide in rat brain homogenates. We examined the ability of 6-hydroxymelatonin to scavenge KCN-induced superoxide anion generation as well as lipid peroxidation. In addition, we also examined the effect of this indole on lactate dehydrogenase activity (LDH) as well as mitochondrial electron transport using dichlorophenol–indophenol as an electron acceptor. The results of this study show that 6-hydroxymelatonin significantly reduces KCN-induced superoxide anion generation, which is accompanied by a commensurate reduction in lipid peroxidation. Partial reversal of the KCN-induced reduction in mitochondrial electron transport is accompanied by a similar reversal of mitochondrial LDH activity blunted by KCN. It can thus be proposed that 6-hydroxymelatonin is potentially neuroprotective against KCN-induced neurotoxicity.
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Analysis of chromameter results obtained from corticosteroid-induced skin blanching. I. Manipulation of data
- Smith, Eric W, Haigh, John M, Walker, Roderick B
- Authors: Smith, Eric W , Haigh, John M , Walker, Roderick B
- Date: 1998
- Language: English
- Type: text , Article
- Identifier: vital:6424 , http://hdl.handle.net/10962/d1006559
- Description: Purpose. One of the unresolved issues in the FDA Guidance document for topical corticosteroid bioequivalence testing is the method of manipulation suggested for the chromameter data. The purpose of this study was to manipulate the instrumental data from a typical blanching study in a number of ways to investigate the appropriateness of these procedures for comparison with the subjective visually-assessed results. Methods. The human skin blanching assay methodology routinely practiced in our laboratories was utilised and the vasoconstriction produced by two corticosteroid formulations of different potency was assessed visually and instrumentally by use of a Minolta chromameter. The instrumental data were corrected for zero-time and unmedicated site readings. In addition, Euclidean distances were calculated using all data generated by the instrument. Results. Individually the a-, b- and L-scale chromameter values are imprecise and there is negligible vasoconstriction response recorded for the moderately potent formulation. Arithmetical manipulation of the data as suggested by the FDA does not appear to improve the quality of the data in any way. Euclidean distance analysis more closely resembles the visual data and appears to have better precision. Conclusions. It is clear that mathematical correction of chromameter data is unnecessary, especially since the instrumental data are extremely imprecise. Furthermore, the assessment of each individual chromameter index does not adequately characterise the blanching response profile. It is therefore suggested that Euclidean distance may be a better measure on which to base an analysis of bioequivalence than the truncated data set methodology currently suggested by the FDA.
- Full Text: false
- Authors: Smith, Eric W , Haigh, John M , Walker, Roderick B
- Date: 1998
- Language: English
- Type: text , Article
- Identifier: vital:6424 , http://hdl.handle.net/10962/d1006559
- Description: Purpose. One of the unresolved issues in the FDA Guidance document for topical corticosteroid bioequivalence testing is the method of manipulation suggested for the chromameter data. The purpose of this study was to manipulate the instrumental data from a typical blanching study in a number of ways to investigate the appropriateness of these procedures for comparison with the subjective visually-assessed results. Methods. The human skin blanching assay methodology routinely practiced in our laboratories was utilised and the vasoconstriction produced by two corticosteroid formulations of different potency was assessed visually and instrumentally by use of a Minolta chromameter. The instrumental data were corrected for zero-time and unmedicated site readings. In addition, Euclidean distances were calculated using all data generated by the instrument. Results. Individually the a-, b- and L-scale chromameter values are imprecise and there is negligible vasoconstriction response recorded for the moderately potent formulation. Arithmetical manipulation of the data as suggested by the FDA does not appear to improve the quality of the data in any way. Euclidean distance analysis more closely resembles the visual data and appears to have better precision. Conclusions. It is clear that mathematical correction of chromameter data is unnecessary, especially since the instrumental data are extremely imprecise. Furthermore, the assessment of each individual chromameter index does not adequately characterise the blanching response profile. It is therefore suggested that Euclidean distance may be a better measure on which to base an analysis of bioequivalence than the truncated data set methodology currently suggested by the FDA.
- Full Text: false
Analysis of macrolide antibiotics
- Kanfer, Isadore, Skinner, Michael F, Walker, Roderick B
- Authors: Kanfer, Isadore , Skinner, Michael F , Walker, Roderick B
- Date: 1998
- Language: English
- Type: Article , text
- Identifier: vital:7011 , http://hdl.handle.net/10962/d1008394 , http://www.sciencedirect.com/science/article/pii/S0021967398002763
- Description: The following macrolide antibiotics have been covered in this review: erythromycin and its related substances, azithromycin, clarithromycin, dirithromycin, roxithromycin, flurithromycin, josamycin, rokitamycin, kitasamycin, mycinamycin, mirosamycin, oleandomycin, rosaramicin, spiramycin and tylosin. The application of various thin-layer chromatography, paper chromatography, gas chromatography, high-performance liquid chromatography and capillary zone electrophoresis procedures for their analysis are described. These techniques have been applied to the separation and quantitative analysis of the macrolides in fermentation media, purity assessment of raw materials, assay of pharmaceutical dosage forms and the measurement of clinically useful macrolide antibiotics in biological samples such as blood, plasma, serum, urine and tissues. Data relating to the chromatographic behaviour of some macrolide antibiotics as well as the various detection methods used, such as bioautography, UV spectrophotometry, fluorometry, electrochemical detection, chemiluminescence and mass spectrometry techniques are also included.
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- Authors: Kanfer, Isadore , Skinner, Michael F , Walker, Roderick B
- Date: 1998
- Language: English
- Type: Article , text
- Identifier: vital:7011 , http://hdl.handle.net/10962/d1008394 , http://www.sciencedirect.com/science/article/pii/S0021967398002763
- Description: The following macrolide antibiotics have been covered in this review: erythromycin and its related substances, azithromycin, clarithromycin, dirithromycin, roxithromycin, flurithromycin, josamycin, rokitamycin, kitasamycin, mycinamycin, mirosamycin, oleandomycin, rosaramicin, spiramycin and tylosin. The application of various thin-layer chromatography, paper chromatography, gas chromatography, high-performance liquid chromatography and capillary zone electrophoresis procedures for their analysis are described. These techniques have been applied to the separation and quantitative analysis of the macrolides in fermentation media, purity assessment of raw materials, assay of pharmaceutical dosage forms and the measurement of clinically useful macrolide antibiotics in biological samples such as blood, plasma, serum, urine and tissues. Data relating to the chromatographic behaviour of some macrolide antibiotics as well as the various detection methods used, such as bioautography, UV spectrophotometry, fluorometry, electrochemical detection, chemiluminescence and mass spectrometry techniques are also included.
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Evaluation of the proposed FDA pilot-dose response methodology for topical corticosteroid bioeqivalence testing [authors' reply in Letters to the Editor]
- Smith, Eric W, Walker, Roderick B, Haigh, John M, Kanfer, Isadore
- Authors: Smith, Eric W , Walker, Roderick B , Haigh, John M , Kanfer, Isadore
- Date: 1998
- Language: English
- Type: text , Article
- Identifier: vital:6423 , http://hdl.handle.net/10962/d1006558
- Description: Reply to: Letter to the Editor by Singh GJ; Fleischer N; Lesko L; Williams R - relating to original article in Pharmaceutical Research (USA), Mar 1997, vol. 14, pp. 303-308.
- Full Text: false
- Authors: Smith, Eric W , Walker, Roderick B , Haigh, John M , Kanfer, Isadore
- Date: 1998
- Language: English
- Type: text , Article
- Identifier: vital:6423 , http://hdl.handle.net/10962/d1006558
- Description: Reply to: Letter to the Editor by Singh GJ; Fleischer N; Lesko L; Williams R - relating to original article in Pharmaceutical Research (USA), Mar 1997, vol. 14, pp. 303-308.
- Full Text: false
Evaluation of the proposed FDA pilot-dose response methodology for topical corticosteroid bioequivalence testing
- Demana, Patrick H, Smith, Eric W, Walker, Roderick B, Haigh, John M, Kanfer, Isadore
- Authors: Demana, Patrick H , Smith, Eric W , Walker, Roderick B , Haigh, John M , Kanfer, Isadore
- Date: 1997
- Language: English
- Type: Article
- Identifier: vital:6356 , http://hdl.handle.net/10962/d1006047
- Description: The American FDA has recently released a Guidance document for topical corticosteroid bioequivalence testing. The purpose of this study was to evaluate the recommendations of this document for appropriateness. The new specifications require a dose-vasoconstriction response estimation by the use of a Minolta chromameter in a preliminary pilot study to determine the parameters for use in a pivotal bioequivalence study. Methods. The visually-assessed human skin blanching assay methodology routinely practiced in our laboratories was modified to comply with the requirements of the pilot study so that visual and chromameter data could be compared. Two different cream formulations, each containing 0.12% betamethasone 17-valerate, were used for this comparison. Results. Visual data showed the expected rank order of AUC values for most dose durations whereas the chromameter data did not show similar results. The expected rank order of AUC values for both chromameter and visual data was not observed at very short dose durations. In fitting the data to pharmacodynamic models, equivalent goodness of fit criteria were obtained when several different parameter estimates were used in the model definition, however the visual data were best described by the sigmoid E[subscript max] model while the chromameter data were best described by the simple E[subscript max] model. Conclusions. The E[subscript max] values predicted by the models were close to the observed values for both data sets and, in addition, excellent correlation between the AUC values and the maximum blanching response (R[subscript max]) (r > 0.95) was noted for both methods of assessment. The chromameter ED[subscript 50] values determined in this study were approximately 2 hours for both preparations. At this dose duration the instrument would not be sensitive enough to distinguish between weak blanching responses and normal skin for bioequivalence assessment purposes.
- Full Text: false
- Authors: Demana, Patrick H , Smith, Eric W , Walker, Roderick B , Haigh, John M , Kanfer, Isadore
- Date: 1997
- Language: English
- Type: Article
- Identifier: vital:6356 , http://hdl.handle.net/10962/d1006047
- Description: The American FDA has recently released a Guidance document for topical corticosteroid bioequivalence testing. The purpose of this study was to evaluate the recommendations of this document for appropriateness. The new specifications require a dose-vasoconstriction response estimation by the use of a Minolta chromameter in a preliminary pilot study to determine the parameters for use in a pivotal bioequivalence study. Methods. The visually-assessed human skin blanching assay methodology routinely practiced in our laboratories was modified to comply with the requirements of the pilot study so that visual and chromameter data could be compared. Two different cream formulations, each containing 0.12% betamethasone 17-valerate, were used for this comparison. Results. Visual data showed the expected rank order of AUC values for most dose durations whereas the chromameter data did not show similar results. The expected rank order of AUC values for both chromameter and visual data was not observed at very short dose durations. In fitting the data to pharmacodynamic models, equivalent goodness of fit criteria were obtained when several different parameter estimates were used in the model definition, however the visual data were best described by the sigmoid E[subscript max] model while the chromameter data were best described by the simple E[subscript max] model. Conclusions. The E[subscript max] values predicted by the models were close to the observed values for both data sets and, in addition, excellent correlation between the AUC values and the maximum blanching response (R[subscript max]) (r > 0.95) was noted for both methods of assessment. The chromameter ED[subscript 50] values determined in this study were approximately 2 hours for both preparations. At this dose duration the instrument would not be sensitive enough to distinguish between weak blanching responses and normal skin for bioequivalence assessment purposes.
- Full Text: false
Role of percutaneous penetration enhancers
- Walker, Roderick B, Smith, Eric W
- Authors: Walker, Roderick B , Smith, Eric W
- Date: 1996
- Language: English
- Type: text , Article
- Identifier: vital:6446 , http://hdl.handle.net/10962/d1006633
- Description: It is clear that scientists are now only beginning to comprehend the complexity of transdermal drug delivery. Elucidation of the biochemical composition and functioning of the intrinsic diffusional barrier of the stratum corneum has prompted investigation of chemical and physical means of enhancing the percutaneous penetration of poorly absorbed drugs. Chemical enhancers that aid absorption of co-administered moieties are currently believed to improve solubility within the stratum corneum or increase lipid fluidity of the intracellular bilayers. Alternatively,the use of ionto- or phonophoresis may facilitate the absorption of some drug molecules by physical alteration of the barrier. The role of penetration enhancer inclusion in topical formulations has been well documented and will undoubtedly, in the future, permit the delivery of broader classes of drugs through the stratum corneum.
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- Authors: Walker, Roderick B , Smith, Eric W
- Date: 1996
- Language: English
- Type: text , Article
- Identifier: vital:6446 , http://hdl.handle.net/10962/d1006633
- Description: It is clear that scientists are now only beginning to comprehend the complexity of transdermal drug delivery. Elucidation of the biochemical composition and functioning of the intrinsic diffusional barrier of the stratum corneum has prompted investigation of chemical and physical means of enhancing the percutaneous penetration of poorly absorbed drugs. Chemical enhancers that aid absorption of co-administered moieties are currently believed to improve solubility within the stratum corneum or increase lipid fluidity of the intracellular bilayers. Alternatively,the use of ionto- or phonophoresis may facilitate the absorption of some drug molecules by physical alteration of the barrier. The role of penetration enhancer inclusion in topical formulations has been well documented and will undoubtedly, in the future, permit the delivery of broader classes of drugs through the stratum corneum.
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Sensitive high-performance liquid chromatographic determination of cyclizine and its demethylated metabolite, norcyclizine, in biological fluids using coulometric detection
- Walker, Roderick B, Kanfer, Isadore
- Authors: Walker, Roderick B , Kanfer, Isadore
- Date: 1995
- Language: English
- Type: text , Article
- Identifier: vital:6452 , http://hdl.handle.net/10962/d1006640 , http://dx.doi.org/10.1016/0378-4347(95)00202-T
- Description: An accurate, sensitive, selective and reproducible high-performance liquid chromatographic method with coulometric detection for the determination of cyclizine and its inactive demethylated metabolite, norcyclizine, in biological fluids has been developed. The drugs were separated using a custom packed reversed-phase C18 analytical column and phosphate buffer (0.05 M, pH 3)-acetonitrile (7:3) as mobile phase. The dual electrode coulometric detector was operated in the "oxidative-screen" mode with the upstream electrode (detector 1) set at 0.55 V and the downstream electrode (detector 2) set at 0.90 V. Serum and urine samples were prepared for analysis by solid-phase extraction, followed by a simple phase-separation step. The limit of quantitation was 1 ng/ml for both cyclizine and norcyclizine in serum and urine.
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- Authors: Walker, Roderick B , Kanfer, Isadore
- Date: 1995
- Language: English
- Type: text , Article
- Identifier: vital:6452 , http://hdl.handle.net/10962/d1006640 , http://dx.doi.org/10.1016/0378-4347(95)00202-T
- Description: An accurate, sensitive, selective and reproducible high-performance liquid chromatographic method with coulometric detection for the determination of cyclizine and its inactive demethylated metabolite, norcyclizine, in biological fluids has been developed. The drugs were separated using a custom packed reversed-phase C18 analytical column and phosphate buffer (0.05 M, pH 3)-acetonitrile (7:3) as mobile phase. The dual electrode coulometric detector was operated in the "oxidative-screen" mode with the upstream electrode (detector 1) set at 0.55 V and the downstream electrode (detector 2) set at 0.90 V. Serum and urine samples were prepared for analysis by solid-phase extraction, followed by a simple phase-separation step. The limit of quantitation was 1 ng/ml for both cyclizine and norcyclizine in serum and urine.
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