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Biomedical subjects

B J Clark

Publications and source records attributed to B J Clark.

At least 19 recordsLinked to original sources
PubMed2006

Validation of high-performance liquid chromatography assay for quantification of formoterol in urine samples after inhalation using UV detection technique.

A novel high-performance liquid chromatography (HPLC) assay for the estimation of formoterol in urine samples was developed and validated. A solid phase extraction (SPE) using Oasis HLB was optimised to isolate formoterol from a urine matrix followed by HPLC with UV detection. This extraction procedure concentrated the final analyte forty times so that UV detection can be used to determine even a low concentration of formoterol in urine samples. The urinary assay was performed in accordance with FDA and ICH regulations for the validation of bioanalytical samples. The samples were injected onto a C18 Spherisorb (250 mm x 4.6 mm x 5 microm) analytical column maintained at 30 degrees C. The mobile phase consisted of 5 mM of potassium dihydrogen orthophosphate buffer (adjusted to pH 3 with ortho phosphoric acid):acetonitrile (ACN) (70:30, v/v), and the formoterol peak was detected at wavelength 214 nm. The extraction recovery of formoterol from the urine sample was >95%. The calibration curve was linear (r2=0.99) over formoterol concentrations ranging from 1.5 to 25 ng/mL (n=6). The method had an accuracy of >92% and intra and inter-day precision CV% of <3.9% and <2.2%, respectively, at three different concentrations low, medium and high (10, 15, 20 ng/mL). The limit of quantification (LOQ) for formoterol was found to be 1.50 ng/mL. The accuracy and precision at the LOQ level were 95% and %CV <3.7% (n=10), respectively. The method reported is simple, reliable, precise, and accurate and has the capacity to be used for determination of formoterol in urine samples.

Administration, Inhalation↗
PubMed2006

Optimising reversed-phase liquid chromatographic separation of an acidic mixture on a monolithic stationary phase with the aid of response surface methodology and experimental design.

An optimization strategy for the separation of an acidic mixture by employing a monolithic stationary phase is presented, with the aid of experimental design and response surface methodology (RSM). An orthogonal array design (OAD) OA(16) (2(15)) was used to choose the significant parameters for the optimization. The significant factors were optimized by using a central composite design (CCD) and the quadratic models between the dependent and the independent parameters were built. The mathematical models were tested on a number of simulated data set and had a coefficient of R(2) > 0.97 (n = 16). On applying the optimization strategy, the factor effects were visualized as three-dimensional (3D) response surfaces and contour plots. The optimal condition was achieved in less than 40 min by using the monolithic packing with the mobile phase of methanol/20 mM phosphate buffer pH 2.7 (25.5/74.5, v/v). The method showed good agreement between the experimental data and predictive value throughout the studied parameter space and were suitable for optimization studies on the monolithic stationary phase for acidic compounds.

Acids↗
PubMed2005

Experimental design for a basic mixture on a fluorinated packing. The effect of composition of the mobile phase.

An optimization methodology is introduced for investigating the separation and the retention behavior of analytes on a new fluorinated reversed-phase packing. Ten basic compounds were selected as test probes to study the predictive models developed by using SPSS and MATLAB software. A two-level orthogonal array design (OAD) was used to extract significant parameters. The significant factors were optimised using a central composite design to obtain the quadratic relationship between the dependent and the independent variables. Using this strategy, response surfaces were derived as the 3D and contour plots, and mathematical models were defined for the separation. The models had a satisfactory coefficient (R(2) > 0.97, n = 16). For the test compounds, the best separation condition was: MeCN/30 mM phosphate buffer pH 7.1(55.5:44.5, v/v) and 10 basic solutes were resolved in 22 min. The significant influence of the concentration of buffer shows that different mechanisms of separation for basic compounds on the fluorinated packing exist compared with a common ODS stationary phase.

Chromatography, High Pressure Liquid↗
PubMed2005

Determination of the bioavailability of gentamicin to the lungs following inhalation from two jet nebulizers.

AIMS: To determine the bioavailability of gentamicin to the lung following inhalation from two jet nebulizers. METHODS: Serial urine samples were obtained from 10 volunteers after a 80 mg dose given orally, nebulized from a Pari LC + (PARI) and MicroNeb III (MN) devices, or after a 40 mg intravenous dose. In vitro aerodynamic characteristics of the nebulized doses were also determined. RESULTS: The mean (SD) absolute gentamicin lung bioavailalibility following delivery by PARI and MN devices was 1.4 (0.4) and 1.7 (0.5) %. The mass median aerodynamic diameter (MMAD) of the drug particles from the PARI and MN systems was 8.6 (0.6) and 6.7 (0.5) microm and the corresponding fine particle doses (FPD) were 10.2 (2.8) and 11.7 (1.5) mg. CONCLUSIONS: The MMAD and FPD data reflect the poor lung deposition of gentamicin identified by urinary excretion.

Administration, Inhalation↗
PubMed2005

Modeling the electrophoretic mobility of analytes in binary solvent electrolyte systems in capillary electrophoresis using an artificial neural network.

An artificial neural network (ANN) methodology was used to model the electrophoretic mobility of basic analytes in binary solvent electrolyte systems. The electrophoretic mobilities in pure solvent electrolytes, and the volume fractions of the solvents in mixtures were used as input. The electrophoretic mobilities in mixed solvent buffers were employed as the output of the network. The optimized topology of the network was 3-3-1. 32 experimental mobility data sets collected from the literature were employed to test the correlation ability and prediction capability of the proposed method. The mean percentage deviation (MPD) between the experimental and calculated values was used as an accuracy criterion. The MPDs obtained for different numerical analyses varied between 0.21% and 13.74%. The results were also compared with similar calculated mobilities which were derived from the best multiple linear model from the literature. From these results it was found that the ANN methodology is superior to the multiple linear model.

Adrenergic beta-Antagonists↗
PubMed2003

Calculation of electrophoretic mobility in ternary solvent electrolyte systems.

Electrophoretic mobility of salmeterol and phenylpropanolamine in capillary electrophoresis has been determined using acetate buffer containing different concentrations of water, methanol and acetonitrile. Maximum electrophoretic mobilities for salmeterol and phenylpropanolamine have been observed at water-methanol-acetonitrile (5:50:45, v/v) and (3:60:37, v/v), respectively, while minimum mobilities of both compounds occurred at methanol-acetonitrile (30:70, v/v). The generated experimental data have been used to evaluate a mathematical model to compute the electrophoretic mobility of the analytes. The proposed model reproduced the mobility data with mean percentage deviations within 1-4%.

Electrolytes↗
PubMed2003

Mathematical representation of electrophoretic mobility of basic drugs in ternary solvent buffers in capillary zone electrophoresis.

The electrophoretic mobilities of two beta-blocker drugs, i.e., labetalol and atenolol, have been determined in a mixed solvent background electrolyte system containing sodium acetate+acetic acid as buffering agent and different volume fractions of water, methanol and ethanol using capillary electrophoresis. The produced data and three other sets collected from a recent work are employed to study the accuracy and prediction capability of a mathematical model to calculate the electrophoretic mobility with respect to the volume fractions of the solvents in the mixture. The results show that the proposed model is able to correlate/predict the mobility within an acceptable error range and it is possible to use the model in industry to achieve the optimum solvent composition for the buffer where using a ternary solvent system is required. The average percentage deviations (APDs) obtained for correlated and predicted data points are 0.71-2.48 and 1.72-4.39%, respectively. The accuracy of the proposed model is compared with that of a mixture response surface method and the results show that the proposed model is superior from both correlation and prediction points of view. The possibility of calculation of the mobility of chemically related drugs in water-methanol-ethanol mixtures using the proposed model is also shown and the produced prediction APD is approximately 8%.

Electrophoresis, Capillary↗
PubMed2003

Electrophoretic behavior of alprenolol in mixed solvent electrolyte systems.

The electrophoretic mobilities of alprenolol have been determined in a mixed solvent background electrolyte system containing sodium acetate (40 mM)+acetic acid (40 mM) as buffering agent and different volume fractions of water, methanol and ethanol using capillary electrophoresis. The mobility of alprenolol has been used to test the prediction capability of a model trained by previously reported mobility data of five beta-blocker drugs at the same electrophoretic conditions. The average percentage mean deviations (APMD) between experimental and predicted values were used as an accuracy criterion. The APMD (+/-SD) obtained for alprenolol data in binary/ternary solvent electrolyte system employing the mobility values in mono-solvent buffers was 4.37 (+/-3.50)% and the corresponding value for an ab initio prediction method was 7.65 (+/-4.30)%.

Adrenergic beta-Antagonists↗
PubMed2002

Calculation of electrophoretic mobility in mixed solvent buffers in capillary zone electrophoresis using a mixture response surface method.

The electrophoretic mobilities of three beta-blocker drugs, practolol, timolol and propranolol, have been measured in electrolyte systems with mixed binary and ternary water-methanol-ethanol solvents with acetic acid/sodium acetate as buffer using capillary electrophoresis. The highest mobilities for the analytes studied have been observed in pure aqueous, the lowest values in ethanolic buffers. The measured electrophoretic mobilities have been used to evaluate the accuracy of a mathematical model based on a mixture response surface method that expresses the mobility as a function of the solvent composition. Mean percentage error (MPE) has been computed considering experimental and calculated mobilities as an accuracy criterion. The obtained MPE for practolol, timolol and propranolol in the binary mixtures are between 0.9 and 2.6%, in the ternary water-methanol-ethanol solvent system the MPE was about 2.7%. The MPE values resulting from the proposed equation lie within the experimental relative standard deviation values and can be considered as an acceptable error.

Adrenergic beta-Antagonists↗
PubMed2002

Nonaqueous capillary electrophoretic analysis of hexetidine in a commercial liquid formulation.

A non-aqueous capillary electrophoresis method has been proposed to analyse hexetidine and its degradation products in a commercial liquid pharmaceutical formulation. The separation was achieved using a 37 cm fused silica capillary with a 75 microns internal diameter, an electrolyte of 120 mM sodium acetate buffer in methanol, at 16 kV and 25 degrees C. The results show that the proposed method is able to resolve hexetidine from its degradation products and/or impurities.

Antifungal Agents↗
PubMed2001

7,12-Dimethylbenz[a]anthracene inhibition of steroid production in MA-10 mouse Leydig tumor cells is not directly linked to induction of CYP1B1.

Testosterone, which is essential for spermatogenesis, is synthesized in the Leydig cells of the testis. This study addresses whether male reproductive toxicity from exposure to polycyclic or polychlorinated aromatic hydrocarbons, such as 7,12-dimethylbenz[a]anthracene (DMBA) or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), may be due to direct effects on Leydig cell function. Using a cell-based assay, the effects of TCDD, benz[a]anthracene (BA), and DMBA on steroid production and cytochrome P4501B1 (CYP1B1) expression in treated MA-10 mouse Leydig tumor cells or primary cultures of rat Leydig cells was determined. (Bu)(2)cAMP-stimulated steroid production was inhibited approximately 25% and approximately 80% by DMBA treatment of MA-10 cells and rat Leydig cells, respectively, while BA or TCDD were without effect. Conversely, male Sprague-Dawley rats treated with TCDD displayed a 75% decrease in serum testosterone levels, while DMBA-treated rats had circulating testosterone levels comparable to control rats. Injection of human chorionic gonadotropin (hCG) 1 h prior to euthanasia restored testosterone levels in TCDD-treated rats to 79% of the hCG-stimulated levels in control rats. Steady-state levels of CYP1B1 mRNA, as detected by RT-PCR, are present in the MA-10 cells and treatment with TCDD, BA, DMBA, or the cAMP analog (Bu)(2)cAMP induced CYP1B1 mRNA expression levels. CYP1B1 was constitutively expressed in rat testis, adrenal, liver, and kidney tissues while CYP1A1 was undetectable. TCDD treatment induced CYP1B1 expression in the adrenal and liver and CYP1A1 in the kidney and liver. DMBA treatment induced only CYP1A1 levels in kidney and liver. In sum, DMBA or a reactive DMBA metabolite, but not TCDD, has a direct effect on steroidogenesis in isolated Leydig cells. CYP1B1 expression levels, however, cannot be directly correlated to potential in vitro or in vivo toxic effects of TCDD or DMBA.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed2001

Selective and quantitative analysis of 4-hydroxybenzoate preservatives by microemulsion electrokinetic chromatography.

A microemulsion electrokinetic chromatography (MEEKC) method has been developed and validated for the determination of 4-hydroxybenzoates and their impurities. These materials are commonly known as parabens and are widely used as preservatives in foods, cosmetics and pharmaceuticals. The method was shown to be selective and quantitative for the methyl, ethyl, propyl and butyl esters of 4-hydroxybenzoic acid. An internal standard, 4-hydroxyacetophenone, was employed to improve injection precision and detector linearity. In addition, 4-hydroxybenzoic acid, the major degradent, could also be monitored at the 0.1% (m/m) level. The method was successfully validated for assay and detection of the impurities in 4-hydroxybenzoic acid methyl ester and 4-hydroxybenzoic acid propyl ester samples and for the determination of 4-hydroxybenzoic acid methyl ester in a liquid pharmaceutical formulation. The determination of paraben content by MEEKC in a liquid sample was consistent with HPLC analysis. This work is the first reported validated MEEKC method and shows that the methodology can be successfully implemented into routine quality control testing.

Chromatography, Micellar Electrokinetic Capillary↗
PubMed2001

Association of chromosome 22q11 deletion with isolated anomalies of aortic arch laterality and branching.

OBJECTIVES: The purpose of this study was to determine the frequency of chromosome 22q11 deletions in patients with isolated anomalies of the aortic arch and its branches. BACKGROUND: Chromosome 22q11 deletions are often present in patients with certain forms of congenital cardiovascular disease, including tetralogy of Fallot, truncus arteriosus and interruption of the aortic arch. Among patients with these anomalies, chromosome 22q11 deletion is more common in those with abnormal aortic arch laterality or branching. METHODS: We studied 66 patients with isolated anomalies of the aortic arch and no associated intracardiac defects for deletions within chromosome 22q11, using fluorescence in situ hybridization with the cosmid probe N25 (D22S75). Arch anomalies included: double aortic arch (n = 22); right aortic arch with aberrant left subclavian artery (n = 28); right aortic arch with mirror-image branching and a vascular ring formed by a left-sided ductus from the descending aorta (n = 5); right aortic arch with mirror-image branching and no vascular ring (n = 4); and left aortic arch with aberrant right subclavian artery (n = 7). In addition, four patients had a cervical aortic arch, four had aortic coarctation and six had hypoplasia/atresia of the proximal pulmonary arteries. RESULTS: Chromosome 22q11 deletions were found in 16 patients (24%) across the full spectrum of anomalies studied. Among the morphologic variables analyzed, only hypoplasia/atresia of the proximal pulmonary arteries correlated with the deletion (p = 0.03). Among patients with a double arch, the frequency of chromosome 22q11 deletion was higher in those with an atretic minor arch than it was in those with a patent minor arch (p = 0.02). CONCLUSIONS: Chromosome 22q11 deletion is associated with isolated anomalies of laterality or branching of the aortic arch in 24% of cases in our series. These findings should alert the clinician to consider deletion screening in patients with isolated anomalies of the aortic arch.

Aorta, Thoracic↗
PubMed2001

Elements involved in the regulation of the StAR gene.

The steroidogenic acute regulatory protein (StAR) mediates the transfer of cholesterol from the outer to the inner mitochondrial membrane, the regulated step in steroidogenesis. A most interesting facet of this protein is the manner in which its expression is acutely regulated. In this regard, a number of studies have concentrated on the search for consensus cis regulatory elements within its promoter, and, more importantly, on whether these elements are involved in its expression. This short review will summarize some of the findings that have been reported concerning the nature of how the expression of this gene is regulated.

Animals↗
PubMed2001

Solubility prediction of salmeterol xinafoate in water--dioxane mixtures.

The mole fraction solubility of salmeterol xinafoate was determined in various concentrations of dioxane in aqueous binary mixture. Maximum solubility was observed in 90% v/v dioxane and solubility parameter of the solute was estimated from solubility peak equal to 24.99 MPa(0.5). The predicting capability of four different cosolvency models was also evaluated employing a five data point training set. The solubility data at other cosolvent concentrations were predicted using the trained models, with percentage average errors for 28 drug solubility data sets in water-cosolvent mixtures lying between 12.5 and 15.0%. Further predictive model is proposed for accurate solubility predictions based on a minimum number of experiments. The percentage average error where tested was 10.6%.

Albuterol↗