Determination of the endogenous OATP1B biomarkers glycochenodeoxycholate-3-sulfate and chenodeoxycholate-24-glucuronide in human and mouse plasma by a validated UHPLC-MS/MS method

Glycochenodeoxycholate-3-sulfate (GCDCA-S) and chenodeoxycholate-24-glucuronide (CDCA-24G) are bile acid metabolites that potentially serve as endogenous biomarkers for drug-drug interactions mediated by the hepatic uptake transporters OATP1B1 and OATP1B3. We developed and validated a novel UHPLC-MS/MS method for the quantitative determination of GCDCA-S and CDCA-24G in mouse and human plasma with a lower limit of quantitation of 0.5 ng/mL. Chromatographic separation was achieved on an Accucore aQ column (50 mm × 2.1 mm, dp = 2.6 μm) maintained at 20 °C and a gradient mobile phase comprising 2 mM ammonium acetate in water and methanol. The extraction recoveries of GCDCA-S and CDCA-24G were >80 %, and linear (r2 > 0.99) calibration curves ranged 0.5-100 ng/mL (CDCA-24G and GCDCA-S in mouse plasma) or 0.5-1000 ng/mL (GCDCA-S in mouse plasma). Values for precision (CV < 11.6 %) and accuracy bias (10.9 %) of analyte-spiked quality control samples verified that water was an acceptable matrix to prepare calibrators. This method was successfully applied to establish baseline activity of OATP1B1/OATP1B3 in humans and mice and establish the in vivo effects of OATP1B1/OATP1B3 inhibitors rifampin and micafungin.

Current progress in identifying endogenous biomarker candidates for drug transporter phenotyping and their potential application to drug development

Drug transporters play important roles in the elimination of various compounds from the blood. Genetic variation and drug-drug interactions underlie the pharmacokinetic differences for the substrates of drug transporters. Some endogenous substrates of drug transporters have emerged as biomarkers to assess differences in drug transporter activity-not only in animals, but also in humans. Metabolomic analysis is a promising approach for identifying such endogenous substrates through their metabolites. The appropriateness of metabolites is supported by studies in vitro and in vivo, both in animals and through pharmacogenomic or drug-drug interaction studies in humans. This review summarizes current progress in identifying such endogenous biomarkers and applying them to drug transporter phenotyping.

Mass isotopomer-guided decluttering of metabolomic data to visualize endogenous biomarkers of drug toxicity

Metabolomics offers the opportunity to uncover endogenous biomarkers that can lead to metabolic pathways and networks and that underpin drug toxicity mechanisms. A novel protocol is presented and discussed that is applicable to drugs which generate urinary metabolites when administered to mice sensitive to its toxicity. The protocol would not apply to drugs that are not metabolized or eliminated by a different route. Separate stable isotope-labeled and unlabeled drug administration to mice is made together with collection of urines from control animals. Untargeted mass spectrometry-based metabolomic analysis of these three urine groups is conducted in addition to principal components analysis (PCA). In the case of unlabeled acetaminophen and [acetyl-²H₃]acetaminophen, each given at a hepatotoxic dose (400 mg/kg i.p.) to the sensitive mouse strain (wild-type 129), the PCA loadings plot showed a distribution of ions in the shape of a "fallen-Y" with the deuterated metabolites in one arm and the paired nondeuterated metabolites in the other arm of the fallen-Y. Ions corresponding to the endogenous toxicity biomarkers sat in the mouth of the fallen-Y. This protocol represents an innovative means to separate endogenous biomarkers from drug metabolites, thereby aiding the identification of biomarkers of drug toxicity. For acetaminophen, increased hepatic oxidative stress, mitochondrial damage, Ca²⁺ signaling, heme catabolism, and saturation of glucuronidation, together with decreased fatty acid β-oxidation and cellular energy dysregulation were all implied from the discovered biomarkers. The protocol can be applied to other drugs and may now be translated to clinical studies.

Investigation of the protective effect of Paeonia lactiflora on Semen Strychni-induced neurotoxicity based on monitoring nine potential neurotoxicity biomarkers in rat serum and brain tissue

Semen Strychni has been widely used as a traditional Chinese herb medicine, but its clinical use was limited for its potential neurotoxicity and nephrotoxicity. This study aimed to investigate S. Strychni-induced neurotoxicity and the neuro-protective effect of Paeonia lactiflora based on monitoring nine potential neurotoxicity biomarkers in rat serum and brain tissue. A sensitive liquid chromatography-tandem mass spectrometry method was developed and validated to monitor serotonin, tryptophan, dopamine, tyrosine and glutamate in serum and five brain regions (prefrontal cortex, hippocampus, striatum, cerebellum and hypothalamus). Analytes were separated on a CAPCELL CORE PC column (150 mm × 2 mm, 2.7 μm) with a gradient program of acetonitrile-water (0.2 % formic acid) and a total runtime of 7.5 min. In addition, enzyme-linked immunosorbent assay was conducted to determine four kinds of protein (tryptophan hydroxylase, tyrosine hydroxylase, endogenous brain-derived neurotrophic factor and nerve growth factor). Results demonstrated that the administration of S. Strychni could cause certain endogenous substances disorder. These analytes were found significantly changed (p < 0.05) in serum (except glutamate) and in certain tested brain regions in S. Strychni extract group. Pretreatment of P. lactiflora could significantly reverse the S. Strychni-induced neurotoxicity and normalize the levels of such endogenous substances. The study could be further used in predicting and monitoring neurotoxicity caused by other reasons, and it was expected to be useful for improving clinical use of S. Strychni through pretreatment with P. lactiflora.