Radiation-Induced Crosslinking of Thymine with Cysteamine: Cysteamine Attachment to the Methyl Group of Thymine

5-S-Cysteaminemethyluracil (the product of cysteamine attachment to the methyl group of thymine) was isolated from irradiated solutions containing thymine and cysteamine and identified. This compound was formed in the reaction of thiyl radicals with 5-methyleneuracil-5-yl radicals formed by H-atom abstraction from the methyl group of thymine. This product was not formed in the presence of oxygen.     

A New HPLC Method with UV Detection for the Determination of Carnosol in Human Plasma and Application to a Pharmacokinetic Study

Chromatographia - This article aims to present a simple and sensitive, HPLC–UV method, which was developed to determine carnosol in human plasma samples. Chromatographic separation was...     

A GC-SIM-MS Method for the Determination of Butylidenephthalide in Rat Plasma and Tissue: Application to the Pharmacokinetic and Tissue Distribution Study

Abstract

Butylidenephthalide is one of the major active components isolated from Rhizoma Chuanxiong. This paper describes a simple, rapid, specific and sensitive method for the quantification of butylidenephthalide in rat plasma and tissue distribution using a liquid-liquid extraction procedure followed by capillary gas chromatography-selected ion monitoring mode-mass spectrometry (GC-SIM-MS) analysis. The calibration curves were linear over the concentration ranging from 0.02–10.0 µg/mL (r > 0.99) for plasma samples and 0.18–7.25 µg/g (r > 0.99) for the tissue samples. The limit of quantification (LOQ) was 1.0 ng/mL or 1.0 ng/g (ten times signal/noise ratio). Within- and between-day precisions expressed as the relative standard deviation (RSD) for the method were 2.39–2.98% and 2.97–4.26%, respectively. The methods of recovery for all samples were greater than 80% at the low, medium, and high concentrations. The method has been successfully applied to a pharmacokinetics study in rats after an oral administration of Butylidenephthalide with a dose of 20.0 mg/kg. The main pharmacokinetic parameters obtained were T _max  = (0.22 ± 0.06) h, C _max = (3 ± 1) µg/mL, AUC = (32 ± 6) h?µg/mL, and K _a  = (8.5 ± 0.8)/h. The results showed that the butylidenephthalide was easily absorbed. The concentrations of butylidenephthalide in rat kidney, lung, heart, and cerebellum were higher than those in other organs. To determine free fraction in serum, samples were filtered using ultrafiltration membranes with a molecular weight cut-off of 10,000 Da and extracted using liquid-liquid extraction. The extracts were evaporated and analyzed by GC-MS. The protein binding in rat plasma, human plasma, and human serum albumin were 83 ± 4%, 94 ± 3%, and 89 ± 3%, respectively.     

LC Method for the Determination of Meropenem in Cerebrospinal Fluid: Application to Therapeutic Drug Monitoring

A simple, rapid and accurate liquid chromatography method using ultrafiltration to pretreat cerebrospinal fluid (CSF) samples was developed to determine meropenem concentrations in human CSF in clinical settings. Meropenem in CSF samples was stabilized by mixing with 1 mol L^?1 3-morpholinopropanesulfonic acid buffer (pH 7.0) (1:1). The mixture was transferred to a Nanosep 10 K centrifugal filter device; after centrifugation, the filtrate was subjected to reversed-phase LC and the eluate was monitored at 300 nm. The retention time for meropenem was 5.8 min. The calibration curve of meropenem in human CSF was linear over 0.05–50 μg mL^?1. The intra-day and inter-day precision was 0.27–5.66 % and accuracy was 99.0–109.5 %. The limit of detection was 0.01 μg mL^?1. This method was successfully applied to neurosurgical patients, showing that it is applicable for therapeutic drug monitoring in patients receiving meropenem.     

LC Method for Quantification of Lutein in Rat Plasma: Validation, and Application to a Pharmacokinetic Study

A reversed-phase LC method has been developed for quantitative analysis of lutein in rat plasma and applied to a study of the pharmacokinetics of lutein in rats. From a variety of compounds and solvents tested, astaxanthin was selected as the internal standard. n-Hexane was found to be the best solvent for extracting lutein from plasma. LC analysis of the extracts was performed on a C₁₈ column equipped with a guard pre-column. Linearity was good (r > 0.99) over the range 10–100 ng mL^?1. Recovery from plasma was 82.7–92.9% the intra-day and inter-day precision were always better than 3%. The limits of detection (LOD) and quantification (LOQ) were 2.5 and 8.3 ng mL^?1, respectively. The LC method was used to quantify lutein and zeaxanthin in rat plasma in a 36-h pharmacokinetic study in which experimental rats received a single oral dose of lutein (20 mg kg^?1). The results are presented.     

A Rapid and Sensitive LC−MS/MS Method for the Quantitation of Physalin A with Special Consideration to Chemical Stability in Rat Plasma: Application to a Pharmacokinetic Study

Physalin A is a promising natural product with excellent anti-inflammatory and anti-tumor activities. However, the pharmacokinetic profile of physalin A is still unclear. In this study, a rapid and sensitive analytical method based on LC–MS/MS for the quantitation of physalin A in rat plasma with special consideration to its chemical stability was developed and validated. To avoid the degradation of physalin A, the separation of plasma was conducted at 4 °C directly after the blood samples were collected. Meanwhile, plasma samples were immediately precipitated with acetonitrile containing tolbutamide (internal standard, IS) and the pH of the supernatant was adjusted to 1.5 with formic acid. Chromatographic separation of physalin A and IS was achieved on an ACQUITY UPLC BEH-C18 column (2.1 × 50 mm, 1.7 μm) using 0.1% formic acid and acetonitrile as mobile phase delivered at 0.3 mL/min in a gradient elution mode. Physalin A and IS were detected through negative ion electrospray ionization in multiple reaction monitoring (MRM) mode. The MS/MS ion transitions for physalin A and IS were m/z 525.1–148.9 and m/z 269.8–169.9, respectively. The developed method showed good linearity over the range of 2.00–400 ng/mL. This method was successfully applied to the pharmacokinetic study of physalin A in rats following its intragastric administration and the findings were beneficial for future studies of physalin A.     

LC Method for the Determination of Rhaponticin in Rat Plasma, Faeces and Urine for Application to Pharmacokinetic Studies

A simple liquid chromatography (LC) method has been developed and validated to determine rhaponticin in rat plasma, faeces and urine. Chromatographic separation was achieved through mobile phase consisting of acetonitrile and water at a flow rate of 1.0 mL min^?1. Rhaponticin was quantified using UV detection at 324 nm. The assay was linear over the concentration range of 50–4,000 ng mL^?1 for plasma, faeces and urine. The intra- and inter-day RSD were less than 10%. The plasma, faeces and urine rhaponticin levels were monitored in rats after oral administration. This simple LC method appears to be useful in the pharmacokinetic investigation of rhaponticin.     

LC-MS/MS Method for the Quantitation of Cefotetan in Human Plasma and Its Application to Pharmacokinetic Study

A rapid and sensitive liquid chromatography-tandem mass spectrometry（LC-MS/MS） method for the de- termination of cefotetan in human plasma was developed and validated. After the protein precipitation of sample with acetonitrile, the analyte and internal standard（IS）, tramadol, were separated on a Zorbax XDB C8 column using ace- tonitrile/1%（volume fraction） formic acid（volume ratio 35：65, pH=2.5） as mobile phase at a flow rate of 1.0 mL/min with a 1 ： 1 split. The detection was performed by electrospray ionization with positive ion mode, followed by multiple reaction monitoring of the transitions for cefotetan at m/z 576.3→460.2（quantifier） and m/z 576.3→432.2（qualifier） and for IS at m/z 264.1→58.1. Cefotetan and IS were eluted at 1.86 and 1.87 rain, respectively. The assay was linear over the concentration range of 0.1-100 gg/mL for 20 μL of human plasma only with intra- and inter-day preci- sions（expressed as the relative standard deviation） of less than 6.62% and accuracies（as relative error） of ＋1.31%. The method was applied to the pharmacokinetic study of a l-h intravenous infusion of 1.0 g of cefotetan disodium for human volunteers（n=6）.     

A Versatile Method to Prepare Protein Nanoclusters for Drug Delivery

Nanocarriers based on natural biomaterials such as peptides and proteins have shown great advantages in the field of nanomedicine. However, the complicated preparation process and possible denaturation of proteins may limit their further applications. Herein, a novel method is developed to prepare protein nanocluster drug delivery system based on the self‐aggregated property of proteins under the isoelectric point condition. The crosslinked protein nanoclusters, prepared by adding modified natural crosslinking agent polysaccharide, exhibit excellent stability and autofluorescent property in physiological conditions. Hemoglobin, a model protein, is chosen for preparation of drug‐loaded nanoclusters. The as‐prepared nanoclusters demonstrate a pH‐responsive drug release behavior and can successfully deliver drugs into cancer cells. Moreover, this approach can be extended to various proteins, exemplifying the universal applicability of our new preparation method for protein‐based nanoparticles.     

Development and Validation of an HPLC–UV Method for the Determination of Insulin in Rat Plasma: Application to Pharmacokinetic Study

A simple, sensitive high performance liquid chromatographic method with UV detection was developed and validated for determination of insulin in rat plasma, using methyl paraben as an internal standard. Insulin was extracted from plasma by a liquid–liquid extraction with a mixture of dichloromethane and n-hexane (1:1, v/v) followed by an acidic back extraction. Chromatographic separation was achieved isocratically with a Phenomenex® C₁₈ analytical column (150 × 4.6 mm ID, 5 μm) at ambient room temperature. The calibration curves were linear within a concentration range of 0.7–8.4 μg mL^?1 (r ² = 0.9994). The inter-day and intra-day accuracy and precision were ≤3.33 and ≤5.55%. The limit of detection (LOD) and limit of quantification (LOQ) were 0.35 and 0.7 μg mL^?1. The average recovery was 87.86% for insulin and 83.52% for methyl paraben. Insulin containing plasma samples were stable at ?20 °C for 7 days. Validated HPLC method was successfully applied to a pharmacokinetic study of insulin in streptozotocin induced diabetic rats.     

A Sensitive LC�CMS�CMS Method for Simultaneous Quantification of Two Structural Isomers, Hyperoside and Isoquercitrin: Application to Pharmacokinetic Studies

We report the development and validation of a rapid, specific, and sensitive liquid chromatographic?Ctandem mass spectrometric (LC?CMS?CMS) method for analysis and pharmacokinetic study, in rats, of hyperoside and isoquercitrin, two bioactive structural isomers present in the leaves of Apocynum venetum L. After simple deproteinization by addition of acetonitrile, the analytes were separated on a C₁₈ column. Detection was by tandem mass spectrometry in multiple reaction monitoring mode. The method was linear over the concentration range 3.9?C195 ng mL^?1 for both hyperoside and isoquercitrin. Intra-day and inter-day precision for both hyperoside and isoquercitrin were <13.1%, and relative errors were all within 7.1% at all QC levels. The method was used to study the pharmacokinetic performance of the compounds after oral administration of an extract of Apocynum venetum L. leaves to rats.     

LC Method for Determination of Ginkgolic Acids in Mice Plasma and Its Application to a Pharmacokinetic Study

A sensitive and simple LC method for the quantification of ginkgolic acids in mice plasma has been developed. Following acetonitrile deproteinization, samples were separated on a SinoChrom ODS-AP C₁₈ column. The mobile phase was 3% (v/v) acetic acid water solution–methanol (8:92, v/v) at a flow rate of 1.0 mL min⁻¹. Detection was at 310 nm. Calibration curve was linear over the range of 0.25–50 μg mL⁻¹ with intra- and inter-day precisions (RSD%) of less than 9.5%. The extraction recovery ranged from 87.0 to 90.2% (RSD 2.4–6.4%) for ginkgolic acids. The method was successfully applied to the pharmacokinetic study of ginkgolic acids in mice after oral dosing of 1.0 g kg⁻¹.

     

Application of the JKR Method to the Measurement of Adhesion to Langmuir-Blodgett Cellulose Surfaces

The JKR method has been applied for studying adhesion between poly(dimethylsiloxane) (PDMS) caps and Langmuir–Blodgett cellulose surfaces including the substrate, hydrophobized mica, and two flat mineral surfaces, bare mica and glass. The self-adhesion of PDMS caps and oxidized PDMS caps are included as a reference to compare with literature data. The results of the measurements have been compared with previous studies using the surface force apparatus and similar systems. A satisfactory agreement is obtained for simple systems showing no, or very limited, hysteresis between loading and unloading curves. In several cases, however, a large hysteresis is found between loading and unloading curves, with a larger adhesion measured from the pull-off force than from the JKR-curve determined on loading. This is, for instance, the case for PDMS against cellulose. The situation is analogous to that found in wetting studies showing a large hysteresis between advancing and receding contact angles.     

Development of High Performance Liquid Chromatography Method for Costunolide and Dehydrocostuslactone in Mice Plasma and Tissues:Application to Pharmacokinetic Study

A simple and sensitive high performance liquid chromatographic (HPLC) method for simultaneous determination of costunolide and dehydrocostuslactone in mice plasma and tissues was developed and validated. Costunolide and dehydrocostuslactone were extracted into acetonitrile and separated using an isocratic mobile phase, on a Hypersil ODS C18 column. The effluent was monitored by UV detector at 210 nm and at a flow rate of 1.0 mL· min^?1 and 25°C. The linearity ranges of proposed method were 0.223–8.920 µg·mL^?1 for costunolide and 0.227–9.080 µg·mL^?1 for dehydrocostuslactone. The intra‐day and inter‐day RSD of the assay method for the two components were less than 5%, and mean recovery was within the 86.5% to 101.8% range. The method was found to be precise, accurate, and specific during the study. The method was successfully applied for pharmacokinetic study of costunolide and dehydrocostuslactone after application of ethanol extraction of Muxiang (EEM) in mice.     

Mathematical Modeling of Drug Release from Microemulsions: Theory in Comparison with Experiments

The topic of this paper is the study of the drug release from a drug-loaded microemulsion by reverting to a new mathematical model overcoming some drawbacks of previously proposed models. In particular, attention is focused on the mathematical expression of the drug fluxes existing between the oil and water phases during drug release. Indeed, not only the drug release kinetics, but also the drug oil-water partition coefficient strongly depend on these fluxes. Two microemulsion are considered: the first is composed by water, Tween80 as surfactant, and Triacetin as oil phase, while the second is composed by water, Tween80 as surfactant, and a Triacetin-benzylic alcohol mixture (1 : 1) as oil phase. Both of them are loaded by Nimesulide, an oil-soluble drug of considerable industrial relevance. The drug release is performed by resorting to a permeation experiment (Franz cells apparatus) as it demonstrated to be the most reliable methodology. The good agreement between the experimental permeation data and the model best-fitting ensures that the most important phenomena ruling this kind of drug release were properly accounted for by the new proposed model. Copyright 2000 Academic Press.     

Development and Validation of a Liquid Chromatographic Method for the Determination of Leflunomide: Application to in vitro Drug Metal Interactions

Leflunomide is a leading drug for the treatment of rheumatoid arthritis. The principle aim of this study was to develop and validate an RP‐HPLC method for the determination of leflunomide in bulk and pharmaceutical dosage form using diclofenac sodium as an internal standard. For this purpose, chromatography was accomplished on a Purospher Start, C₁₈ (5 (m, 12.5 cm×0.46 cm) column at ambient temperature. Methanol:water (80:20, V/V) solvent system was selected as mobile phase, the pH of which was adjusted to 3.4 by ortho‐phosphoric acid and delivered at a flow rate of 1.2 mL·min⁻¹. Seperation of leflunomide and diclofenac sodium was carried out on a Purospher Start, C₁₈ equipped with a UV‐visible detector at 248 nm. The suitability of the method for the quantitative determination of the drugs is proven by validation in accordance with the requirements laid down by the International Conference on Harmonization (ICH) guidelines. The method was accurate (99.55%–100.03%), specific, linear (R²>0.999) and precise (intra‐day precision 0.023%–0.93% and inter‐day precision 0.26%–0.944%) in the range of 0.5–20 (g·mL⁻¹. The minimum limit of detection and quantification in pharmaceutical formulation were 0.05 and 0.15 (g·mL⁻¹, respectively. Thus the proposed method is simple, accurate, reproducible and suitable for the routine analysis of leflunomide in pharmaceutical formulations and was applied to study in vitro drug‐metal interactions.     

Sensitivity—enhanced Experiments for the Measurement of J and Dipolar Coupling Constants

A sensitivity-enhanced IPAP NMR experiment was described in this paper,which separates the ^1H-^15N doublets into two different spectra to alleviate the problem of resonance overlaps and achieve the accurate measurement of J and residual dipolar coupling constants in proteins.This experiment offered 20%-60% sensitivity enhancement over the original IPAP experiment,and therefore produced more measurable resonances.Pulsed field gradient was used for coherence selection.Water-flip-back approach was used for water suppression.The sensitivity-enhanced IPAP experiment was employed in the measurement of ^1JNH and ^1DNH constants of the protein UBC9.     

A Simple UPLC/MS-MS Method for Simultaneous Determination of Lenvatinib and Telmisartan in Rat Plasma,and Its Application to Pharmacokinetic Drug-Drug Interaction Study

Lenvatinib is a multi-targeted tyrosine kinase inhibitor that inhibits tumor angiogenesis, but hypertension is the most common adverse reaction. Telmisartan is an angiotensin receptor blocker used to treat hypertension. In this study, a simple ultra-performance liquid chromatography-tandem mass spectrometry method was developed for the simultaneous determination of lenvatinib and telmisartan, and it was applied to the pharmacokinetic drug interaction study. Plasma samples were treated with acetonitrile to precipitate protein. Water (containing 5 mM of ammonium acetate and 0.1% formic acid) and acetonitrile (0.1% formic acid) were used as the mobile phases to separate the analytes with gradient elution using a column XSelect HSS T3 (2.1 mm × 100 mm, 2.5 μm). Multiple reaction monitoring in the positive ion mode was used for quantification. The method was validated and the precision, accuracy, matrix effect, recovery, and stability of this method were reasonable. The determination of analytes was not interfered with by other substances in the blank plasma, and the calibration curves of lenvatinib and telmisartan were linear within the range of 0.2–1000 ng/mL and 0.1–500 ng/mL, respectively. The results indicate that lenvatinib decreased the systemic exposure of telmisartan. Potential drug interactions were observed between lenvatinib and telmisartan.     

Labetalol Analysis in Human Plasma Using Liquid Chromatography with Electrochemical Detection: Application to Pharmacokinetic Studies

Abstract

Labetalol determination in human plasma by a sensitive (to 2.5 ng/ml) and selective method using liquid chromatography with electrochemical detection is described. Plasma is extracted with diethyl ether under mildly basic (pH 9) conditions, back-extracted into an aqueous acidic buffer, then injected directly on column. Standard curves using propranolol as an internal standard are linear for concentrations from 2.5 to 200 ng/ml. Within-day and between-day reproducibility is satisfactory with coefficient of variation less than 8% for all concentrations. Sample recovery from the extraction is complete at all concentrations. Utility of the method is demonstrated by a pharmacokinetic study in a hypertensive volunteer who received 43.75 mg labetalol by 10 minute intravenous infusion.     

Supercritical Fenton Oxidation: A New Method for Total Organic Carbon Measurement

A new method for total organic carbon (TOC) measurement was established based on supercritical Fenton oxidation. The organic pollutants in wastewater were oxidized to carbon dioxide in supercritical water by Fenton reagents that was detected using a nondispersive infrared detector. The influence of temperature from 380 to 480°C, oxidant coefficient from 1 to 20, pH from 2.2 to 5.2, and Fe²⁺ concentration from 0.2 to 0.8?mg?L^?1 was characterized; the optimal conditions were at 420°C, an oxidant coefficient n?≥?5, a pH of 4.4, and Fe²⁺ concentration of 0.8?mg?L^?1. Using these parameters, the recovery of potassium hydrogen phthalate exceeded 98.2%. The introduction of Fenton oxidation based on supercritical water lowered the temperature and reduced the oxidant coefficient required for TOC determination.