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Biomedical subjects

S X Peng

Publications and source records attributed to S X Peng.

At least 19 recordsLinked to original sources
PubMed2003

Inhibition of nicotine-DNA adduct formation in mice by six dietary constituents.

Nicotine [3-(1-methyl-2-pyrrolidinyl)-pyridine] is a major alkaloid in tobacco products and has proven to be a potential genotoxic compound. Many natural dietary products can suppress the DNA adduction, and hence act as inhibitors of cancer. In this study, we investigated the inhibitory effects of curcumin, garlic squeeze, grapeseed extract, tea polyphenols, vitamin C, and vitamin E on nicotine-DNA adduction in vivo using an ultrasensitive method of accelerator mass spectrometry (AMS). The results demonstrated that all the dietary constituents induced marked dose-dependent decrease in nicotine-DNA adducts as compared with the control. The reduction rate reached about 50% for all agents, except garlic squeeze (40%), even at its highest dose level. Amongst the six agents, grapeseed extract exhibited the strongest inhibition to the DNA adduct formation. Therefore, we may arrive at a point that these dietary constituents are beneficial to prevent the harmful adduct formation, and thus to block the potential carcinogenesis induced by nicotine.

Animals↗
PubMed2001

Separation and identification methods for metalloproteinase inhibitors.

Metalloproteinase inhibitors are being explored for the treatment of a wide variety of human diseases including cancers, arthritis, cardiovascular disorders, human immunodeficiency virus infection, and central nervous system illnesses. This review provides an overview of various analytical sample preparation, separation, detection, and identification techniques employed for the quantitative and qualitative determination of these inhibitor compounds. Special emphasis is placed on biological sample preparation by automated solid-phase extraction, liquid-liquid extraction, and protein precipitation by centrifugation or filtration. Other sample preparation methodologies are also evaluated. Applications of high-performance liquid chromatography. gas chromatography, and capillary electrophoresis to the quantitative determination of metalloproteinase inhibitors are described. Examples of qualitative analysis of metalloproteinase inhibitors by hyphenated liquid chromatography with mass spectrometry and nuclear magnetic resonance are also presented. The advantages and limitations of these separation and identification methodologies as well as other less frequently employed techniques are assessed and discussed.

Chromatography, Gas↗
PubMed2001

Ion-exchange liquid chromatographic analysis of bisphosphonates by on-line post-column photochemical reaction and spectrophotometric detection.

A simple ion-exchange high-performance liquid chromatographic method was developed and employed for the analysis of bisphosphonate compounds in dosage formulations using on-line post-column photochemical reactions. The method used molybdate as the post-column reagent to react with the photolyzed bisphosphonate to form phosphomolybdate for enhanced spectrophotometric detection. A bisphosphonate compound, 2-thioethane-1,1-bisphophonic acid, was selected to evaluate the separation using both isocratic and gradient elution methods, along with the effects of other experimental parameters including mobile phase composition, flow-rate and post-column reagent concentration. The gradient elution method showed improved resolution and detection sensitivity compared to the isocratic elution method. The optimized gradient method was simple, reproducible, and specific to bisphosphonate compounds. It was successfully employed for the stability study of the bisphosphonate compound in pharmaceutical dosage formulations.

Calibration↗
PubMed2001

Development of new carboxylic acid-based MMP inhibitors derived from functionalized propargylglycines.

A series of carboxylic acids were prepared from a propargylglycine scaffold and tested for efficacy as matrix metalloproteinase (MMP) inhibitors. Detailed SAR for the series is reported for four enzymes within the MMP family. The inhibitors were typically potent against collagenase-3 (MMP-13) and gelatinase A (MMP-2), while they spared collagenase-1 (MMP-1) and only moderately inhibited stromelysin (MMP-3). Compound 40 represents a typical inhibition profile of a compound with reasonable potency. Introduction of polar groups was required in order to generate inhibitors with acceptable water solubility, and this often resulted in a loss of potency as in compound 63. High serum protein binding proved to be a difficult hurdle with many compounds such as 48 showing >99% binding. Some compounds such as 64 displayed approximately 90% binding, but no reliable method was discovered for designing molecules with low protein binding. Finally, selected data regarding the pharmacokinetic behavior of these compounds is presented.

Alkynes↗
PubMed2001

Fully automated 96-well liquid-liquid extraction for analysis of biological samples by liquid chromatography with tandem mass spectrometry.

A fully automated high-throughput liquid-liquid extraction (LLE) methodology has been developed for preparation of biological samples using a 96-well LLE plate and a 96-channel robotic liquid handling workstation. The 96-well LLE plate is made of a 96-well filter plate filled with inert diatomaceous earth particles, allowing continuous and efficient extraction of analytes between the aqueous biological sample and the organic extraction solvent. Two carboxylic acid-based protease inhibitor compounds with high and low levels of plasma protein binding were chosen for the development and application of the automated methodology. The LLE extracts of the plasma samples of the two compounds were analyzed by high-performance liquid chromatography with electrospray (ESI) tandem mass spectrometry (LC-MS/MS). The LC-MS/MS method was developed using a rapid gradient LC separation, followed by sample introduction through an ionspray interface in the negative ion mode and tandem mass spectrometric detection with selected reaction monitoring. In the optimized LLE method, a formate buffer solution was first loaded into a 96-well filter plate packed with inert diatomaceous earth material. Then crude plasma samples and a water-immiscible organic solvent, methyl ethyl ketone, were sequentially added to the LLE plate so that LLE would occur in the interface between the two liquid phases on the surface of individual particles in each well. The organic eluate containing extracted analytes was evaporated and reconstituted for LC-MS/MS analysis. This fully automated LLE methodology avoids several disjointed steps involved in a manual or semiautomated LLE method, leading to significantly reduced sample preparation time, increased sample throughput, and clean sample extracts for improved ESI-MS/MS detection. The automated LLE methodology is universal and can be employed for sample preparation of other biological fluids. The complete bioanalytical method, based on the automated LLE and fast gradient LC-MS/MS, was validated and successfully applied to the quantitative analysis of protease inhibitors in rat plasma.

Animals↗
PubMed2000

Development of new hydroxamate matrix metalloproteinase inhibitors derived from functionalized 4-aminoprolines.

A series of hydroxamates was prepared from an aminoproline scaffold and tested for efficacy as matrix metalloproteinase (MMP) inhibitors. Detailed SAR for the series is reported for five enzymes within the MMP family, and a number of inhibitors, such as compound 47, display broad-spectrum activity with sub-nanomolar potency for some enzymes. Modifications of the P1' portion of the molecule played a key role in affecting both potency and selectivity within the MMP family. Longer-chain aliphatic substituents in this region of the molecule tended to increase potency for MMP-3 and decrease potency for MMP-1, as exemplified by compounds 48-50, while aromatic substituents, as in compound 52, generated broad-spectrum inhibition. The data is rationalized based upon X-ray crystal data which is also presented. While the in vitro peroral absorption seemed to be less predictable, it tended to decrease with longer and more hydrophilic substituents. Finally, a rat model of osteoarthritis was used to evaluate the efficacy of these compounds, and a direct link was established between their pharmacokinetics and their in vivo efficacy.

Animals↗
PubMed2000

Automated 96-well SPE and LC-MS-MS for determination of protease inhibitors in plasma and cartilage tissues.

Bioanalytical methods based on automated solid-phase extraction (SPE) and high-performance liquid chromatography with electrospray tandem mass spectrometry (LC-MS-MS) have been developed and utilized for the determination of MMP inhibitors in plasma and cartilage tissues. The SPE methods were automated using a 96-well extraction plate and a 96-channel programmable liquid-handling workstation. The LC-MS-MS methods were developed using a rapid gradient LC separation, followed by sample introduction through an ionspray interface in the positive ion mode and tandem mass spectrometric detection with selected reaction monitoring. In the optimized SPE methods, crude plasma or ground cartilage supernatant samples were loaded onto an SPE plate to remove proteins and other interfering components in the matrixes to render relatively clean extracts for LC-MS-MS analysis. Compared to the simple plasma protein precipitation method, the automated SPE method afforded significant time-saving in sample preparation and improved sensitivity in MS detection. The methods were validated and successfully applied to the analysis of protease inhibitors in plasma and cartilage tissues.

Animals↗
PubMed2000

Automated high-throughput liquid-liquid extraction for initial purification of combinatorial libraries.

An automated high-throughput liquid-liquid extraction (LLE) methodology has been developed and utilized for the initial purification of the combinatorial library samples containing unreacted amines and other water-soluble byproducts or impurities. Various extraction solvents were evaluated along with different extraction devices. The LLE method was automated using 96-well-format plates and a robotic liquid-handling workstation. In the optimized LLE method, crude combinatorial library samples were dissolved in a water-immiscible organic solvent, butyl acetate, and added to each well in a 96-well-format plate packed with an inert support material coated with hydrochloric acid. Separation occurs based on the partitioning of the compounds between two liquid phases. Product recovery, purity, and amine removal efficiency were determined by HPLC with and without precolumn derivatization. The automated method was successfully applied to the cleanup of some representative combinatorial library samples with greater than 98% amine removal and an average product purity of 90%. The application of the automated high-throughput LLE method should greatly reduce the labor, time, and cost associated with the purification of combinatorial libraries.

Amines↗
PubMed2000

Hyphenated HPLC-NMR and its applications in drug discovery.

Hyphenated HPLC-NMR is a fast growing technology, allowing rapid and detailed structural characterization of unknown mixtures. The technical aspects of the technology are reviewed on the basis of system configuration, operation, solvent suppression, HPLC and NMR optimization, and detection. The combined use of HPLC-NMR and HPLC-MS is also described and discussed. Various applications of HPLC-NMR and integrated HPLC-NMR-MS in drug discovery, especially in the separation and structure elucidation of drug impurities, reaction mixtures, degradation products, in vitro and in vivo metabolites, and combinatorial library samples, are illustrated.

Chromatography, High Pressure Liquid↗
PubMed1999

Simultaneous determination of enantioselective plasma protein binding of aminohydantoins by ultrafiltration and chiral high-performance liquid chromatography.

Chiral HPLC methods were developed and utilized for the simultaneous determination of plasma protein binding of enantiomers of two racemic aminohydantoin compounds. Reversed-phase HPLC with the use of a polysaccharide-type chiral stationary phase column was employed for the separation and quantitation of the enantiomers of the two compounds with detection limits in the range 5-10 ng/ml in the plasma matrix. The chiral HPLC methods were selective, sensitive and reproducible. The R and S enantiomers of both compounds were baseline-resolved under the chromatographic conditions employed. Ultrafiltration techniques were applied to determining the plasma protein binding for each enantiomer in rat, dog and human plasma. The results clearly show stereoselective binding of the two enantiomers of each compound with higher protein binding of the R enantiomer than the S enantiomer in rat, dog and human plasma. Binding association constants were also determined to be in the range 1.01-14.0 x 10(4) M(-1) at 37 degrees C. Both the protein binding percentage and binding association constant were enantioselective and species-dependent. Such information is important for a clear understanding of the differences in biological activity as well as in pharmacokinetic and pharmacodynamic properties between the two enantiomers of each compound in the drug discovery and development process.

Animals↗
PubMed1999

Gas chromatographic-mass spectrometric analysis of hydroxylamine for monitoring the metabolic hydrolysis of metalloprotease inhibitors in rat and human liver microsomes.

A gas chromatographic-mass spectrometric (GC-MS) method was developed for the analysis of hydroxylamine (HA) in supernatants obtained from liver microsomes. HA monitoring was used to determine the metabolic hydrolysis of two hydroxamic acid-based matrix metalloprotease inhibitors in rat and human liver microsomes. The hydrolysis of the hydroxamic acids to their corresponding carboxylic acids releases HA as a common metabolic product. HA was derivatized to acetone oxime by addition of acetone to the liver microsomal supernatant, followed by direct injection of the supernatant into the GC-MS, with detection of the oxime by selected-ion-monitoring. The method is simple, reproducible, and sensitive for the determination of the hydrolysis of hydroxamic acid compounds, where hydrolysis is the major metabolic pathway. The methodology can be used for rank ordering and selecting hydroxamic acid analogs based on their susceptibility to hydrolysis.

Animals↗
PubMed1999

Direct determination of stability of protease inhibitors in plasma by HPLC with automated column-switching.

Automated column-switching HPLC methods were developed and utilized for the direct analyses of three hydroxamic acid based metalloprotease inhibitors in rat plasma. These column-switching methods involved the use of a restricted-access media (RAM) precolumn and a column-switching valve, allowing the complete automation of sample preparation and HPLC. The plasma samples were directly injected onto a precolumn packed with SPS/ODS stationary phase and then backflushed onto an ODS analytical column using a 6-port column-switching device. The drug stability in rat plasma was determined using both the automated and traditional HPLC methods. The results obtained from the automated column-switching methods were in good agreement with those from traditional methods that involve sequential protein precipitation, liquid extraction, solvent evaporation, and sample reconstitution. In addition to the elimination of labor-intensive and time-consuming sample preparation procedures, the column-switching methods allowed on-line analyte enrichment and accurate determination of drug stability in plasma with detection limits in the range of 10-20 ng/ml(-1). This work represents, for the first time, a drug stability study in plasma by automated column-switching HPLC technique with the use of a RAM column. Our column-switching methods can be readily adapted to any existing HPLC system with minimal hardware modification.

Animals↗
PubMed1999

Application of LC-NMR and LC-MS to the identification of degradation products of a protease inhibitor in dosage formulations.

LC-NMR and LC-MS were applied to the characterization of six degradation products of a protease inhibitor, N-hydroxy-1,3-di-[4-ethoxybenzenesulphonyl]-5,5-dimethyl-[1,3]c yclohexyldiazine-2-carboxamide, in a dosage formulation. A reversed-phase HPLC method was developed for the separation of the parent compound and its six degradation products. LC-MS was then utilized to obtain the molecular weight and fragmentation information using an electrospray ionization (ESI) interface in the positive ion mode. LC-NMR was employed to acquire detailed structural information using a selective solvent suppression pulse sequence in the stop flow mode. This work demonstrated the usefulness of this integrated approach for the rapid and unambiguous identification of drug compounds and their degradation products in dosage formulations.

Chromatography, High Pressure Liquid↗
PubMed1998

Direct pharmaceutical analysis of bisphosphonates by capillary electrophoresis.

Bisphosphonate compounds have been studied as a class of potential drugs for the treatment of various bone diseases. However, the analyses of these compounds are problematic because most of them do not contain strong chromophores. Based on the unique structures of these compounds, we have employed a capillary electrophoresis (CE) technique for the characterization of these compounds in pharmaceutical dosage formulations. In this study, two CE methods were developed for the determination of a bisphosphonate compound, 2-thioethane-1,1-bisphosphonic acid. The first method involved the use of an uncoated column, a phosphate buffer, and hydrostatic injection with direct UV absorbance detection. The method showed excellent resolution and precision with a reasonable detection limit of 30 microg/ml. Sensitivity was further improved using a glycerol-coated column, together with a phosphate buffer of higher concentration and electrokinetic injection under sample stacking conditions. This modified method revealed a significant improvement in sensitivity with a detection limit of about 50 ng/ml. Both methods demonstrated high simplicity and excellent reproducibility and were successfully applied to the quantitative analyses of pharmaceutical dosing solutions.

Chemistry, Pharmaceutical↗
PubMed1998

Permeability of articular cartilage to matrix metalloprotease inhibitors.

PURPOSE: To develop an in vitro cartilage permeation model for cartilage permeability study and to evaluate the effects of molecular hydrophilicity and cartilage location on the permeability of articular cartilage to matrix metalloprotease inhibitors. METHODS: An in vitro cartilage permeation model was developed and utilized to determine the permeability of articular cartilage to the matrix metalloprotease inhibitors of different hydrophilicity. Permeability coefficients were obtained by measuring the steady-state flux of the inhibitor compounds. HPLC methods were also developed and employed for the analysis of drug levels in assay media. RESULTS: The relationship between permeability and hydrophilicity of drug molecules was examined. Results indicated that the permeability coefficient increased with increasing hydrophilicity of the molecule. Additionally, the relationship between the permeability and the location of the cartilage section within the animal joint was investigated. Our results showed that the drug molecules penetrated faster in the surface layer cartilage than in the deep layer cartilage. CONCLUSIONS: Increasing the hydrophilicity of a molecule would increase its permeability across articular cartilage. The in vitro cartilage permeation model developed could be used to rank order drug compounds according to their cartilage permeability profiles and to aid in drug selection and development.

Animals↗