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The primary challenge associated with the development of an LC/MS/MS-based assay for simultaneous determination of biogenic monoamine neurotransmitters such as norepinephrine (NE), dopamine (DA), serotonin (5-HT), and normetanephrine (NM) in rat brain microdialysates is to improve detection sensitivity. In this work, a UPLC/ MS/MS-based method combined with a diethyl labeling technique was developed for simultaneous determination of a panel of monoamines in rat prefrontal cortex microdialysates. The chromatographic run time is 3.5 min/ sample. The limits of detection of the UPLC/MS/MS-based method for NE, DA, 5-HT/ and NM, with/without diethyl labeling of monoamines, are 0.005/0.4 (30/2367 pM), 0.005/0.1 (33/653 pM), 0.005/0.2 (28/1136 pM), and 0.002/0.2 ng/mL (11/1092 pM), respectively. Diethyl labeling of amino groups of monoamines affords 20-100 times increased detection sensitivity of corresponding native monoamines during the UPLC/MS/MS analysis. This could result from the following: (1) improved fragmentation patterns; (2) increased hydrophobicity and concomitantly increased ionization efficiency in ESI MS and MS/MS analysis; (3) reduced matrix interference. This labeling reaction employs a commercially available reagent, acetaldehyde-d4, to label the amine groups on the monoamines via reductive amination. It is also simple, fast (approximately 25-min reaction time), specific, and quantitative under mild reaction conditions. Data are also presented from the application of this assay to monitor the drug-induced changes of monoamine concentrations in rat prefrontal cortex microdialysate samples followed by administration of SKF 81297, a selective D1 dopamine receptor agonist known to elevate the extracellular level of the neurotransmitters DA and NE in the central nervous system.

Thrombosis and its complications are the leading cause of death in patients with diabetes. Metformin, a first-line therapy for type 2 diabetes, is the only drug demonstrated to reduce cardiovascular complications in diabetic patients. However, whether metformin can effectively prevent thrombosis and its potential mechanism of action is unknown. Here we show, metformin prevents both venous and arterial thrombosis with no significant prolonged bleeding time by inhibiting platelet activation and extracellular mitochondrial DNA (mtDNA) release. Specifically, metformin inhibits mitochondrial complex I and thereby protects mitochondrial function, reduces activated platelet-induced mitochondrial hyperpolarization, reactive oxygen species overload and associated membrane damage. In mitochondrial function assays designed to detect amounts of extracellular mtDNA, we found that metformin prevents mtDNA release. This study also demonstrated that mtDNA induces platelet activation through a DC-SIGN dependent pathway. Metformin exemplifies a promising new class of antiplatelet agents that are highly effective at inhibiting platelet activation by decreasing the release of free mtDNA, which induces platelet activation in a DC-SIGN-dependent manner. This study has established a novel therapeutic strategy and molecular target for thrombotic diseases, especially for thrombotic complications of diabetes mellitus.

ABSTRACT:To assess the feasibility of using sandwich-cultured human hepatocytes (SCHHs) as a model to characterize transport kinetics for in vivo pharmacokinetic prediction, the expression of organic anion-transporting polypeptide (OATP) proteins in SCHHs, along with biliary efflux transporters, was confirmed quantitatively by liquid chromatography-tandem mass spectrometry. Rifamycin SV (Rif SV), which was shown to completely block the function of OATP transporters, was selected as an inhibitor to assess the initial rates of active uptake. The optimized SCHH model was applied in a retrospective investigation of compounds with known clinically significant OATP-mediated uptake and was applied further to explore drug-drug interactions (DDIs). Greater than 50% inhibition of active uptake by Rif SV was found to be associated with clinically significant OATP-mediated DDIs. We propose that the in vitro active uptake value therefore could serve as a cutoff for class 3 and 4 compounds of the Biopharmaceutics Drug Disposition Classification System, which could be integrated into the International Transporter Consortium decision tree recommendations to trigger clinical evaluations for potential DDI risks. Furthermore, the kinetics of in vitro hepatobiliary transport obtained from SCHHs, along with protein expression scaling factors, offer an opportunity to predict complex in vivo processes using mathematical models, such as physiologically based pharmacokinetics models.

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Although the strategic use of enzymatic digestion combined with isotope dilution mass spectrometry has been increasingly developed and used for the absolute quantification of therapeutic and endogenous proteins in the biopharmaceutical industry over the past several years, the lack of an appropriate internal standard has become the rate-limiting step in the development of a standardized analytical approach to provide bioanalytical support for both preclinical and clinical studies. In this study, we present a universal strategy for fast development and validation (within 1-2 weeks) of a method for absolute quantification of a therapeutic monoclonal antibody in biological matrices using differential dimethyl labeling coupled with UPLC-MS/MS. Differential dimethyl labeling of tryptic peptides generated from the purified therapeutic monoclonal antibody and those derived from proteins in cynomolgus monkey serum with either d(2)- or d(0)-formaldehyde provided a fast, cost-effective, and standardized approach to generate internal standards for any surrogate peptides that are used to quantify the therapeutic monoclonal antibody in biological matrices. This labeling reaction employs inexpensive and commercially available reagents, d(0)- or d(2)-formaldehyde, to globally label the N-terminus and epsilon-amino group of Lys in a peptide via reductive amination. Moreover, the process is simple, relatively fast (<2 h reaction time), specific, and quantitative under mild reaction conditions. The chromatographic run time is 6 min per sample. The linearity of the assay for the selected monoclonal antibody was established from 1.00 to 1000 mug/mL with accuracy and precision within 15% at all concentrations. The intraday and interday assay accuracy (%RE) and coefficient of variations (CV%) are all within 15% for all QCs (2.00, 4.00, 20.0, 100, 750 mug/mL) prepared in three different serum pools from male and female cynomolgus monkeys.

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