LC-MS/MS-based quantification of clinically relevant intestinal uptake and efflux transporter proteins

Interspecies variability in expression of hepatobiliary transporters across human, dog, monkey, and rat as determined by quantitative proteomics

We quantified, by liquid chromatography tandem mass spectrometry, transporter protein expression of BSEP, MATE1, MRP3, MRP4, NTCP, and OCT1 in our human liver bank (n = 55) and determined the relationship between protein expression and sex, age and genotype. These data complement our previous work in the same liver bank where we quantified the protein expression of OATPs, BCRP, MDR1, and MRP2. In addition, we quantified and compared the interspecies differences in expression of the hepatobiliary transporters, corresponding to the above human transporters, in liver tissue and hepatocytes of male beagle dogs, cynomolgus monkeys, Sprague-Dawley rats, and Wistar rats. In all the species, the sinusoidal OATPs/Oatps were the most abundant hepatic transporters. However, there were notable interspecies differences in the relative abundance of the remaining transporters. For example, the next most abundant transporter in humans and monkeys was OCT1/Oct1, whereas it was Mrp2 and Ntcp in dogs/Wistar rats and Sprague-Dawley rats, respectively. In contrast, the protein expression of the efflux transporters BCRP/Bcrp, MDR1/Mdr1, MRP3/Mrp3, MRP4/Mrp4, and MATE1/Mate1 was much lower across all the species. For most transporters, the expression in the liver tissues was comparable to that in the unplated cryopreserved hepatocytes. These data on human liver transporter protein expression complete the picture of the expression of major human hepatobiliary transporters important in drug disposition and toxicity. In addition, the data on expression of the corresponding hepatobiliary transporters in preclinical species will be helpful in interpreting and extrapolating pharmacokinetic, pharmacological, and toxicological results from preclinical studies to humans.

Optimized approaches for quantification of drug transporters in tissues and cells by MRM proteomics

Drug transporter expression in tissues (in vivo) usually differs from that in cell lines used to measure transporter activity (in vitro). Therefore, quantification of transporter expression in tissues and cell lines is important to develop scaling factor for in vitro to in vivo extrapolation (IVIVE) of transporter-mediated drug disposition. Since traditional immunoquantification methods are semiquantitative, targeted proteomics is now emerging as a superior method to quantify proteins, including membrane transporters. This superiority is derived from the selectivity, precision, accuracy, and speed of analysis by liquid chromatography tandem mass spectrometry (LC-MS/MS) in multiple reaction monitoring (MRM) mode. Moreover, LC-MS/MS proteomics has broader applicability because it does not require selective antibodies for individual proteins. There are a number of recent research and review papers that discuss the use of LC-MS/MS for transporter quantification. Here, we have compiled from the literature various elements of MRM proteomics to provide a comprehensive systematic strategy to quantify drug transporters. This review emphasizes practical aspects and challenges in surrogate peptide selection, peptide qualification, peptide synthesis and characterization, membrane protein isolation, protein digestion, sample preparation, LC-MS/MS parameter optimization, method validation, and sample analysis. In particular, bioinformatic tools used in method development and sample analysis are discussed in detail. Various pre-analytical and analytical sources of variability that should be considered during transporter quantification are highlighted. All these steps are illustrated using P-glycoprotein (P-gp) as a case example. Greater use of quantitative transporter proteomics will lead to a better understanding of the role of drug transporters in drug disposition.

Qualitative de novo analysis of full length cDNA and quantitative analysis of gene expression for common marmoset (Callithrix jacchus) transcriptomes using parallel long-read technology and short-read sequencing

The common marmoset (Callithrix jacchus) is a non-human primate that could prove useful as human pharmacokinetic and biomedical research models. The cytochromes P450 (P450s) are a superfamily of enzymes that have critical roles in drug metabolism and disposition via monooxygenation of a broad range of xenobiotics; however, information on some marmoset P450s is currently limited. Therefore, identification and quantitative analysis of tissue-specific mRNA transcripts, including those of P450s and flavin-containing monooxygenases (FMO, another monooxygenase family), need to be carried out in detail before the marmoset can be used as an animal model in drug development. De novo assembly and expression analysis of marmoset transcripts were conducted with pooled liver, intestine, kidney, and brain samples from three male and three female marmosets. After unique sequences were automatically aligned by assembling software, the mean contig length was 718 bp (with a standard deviation of 457 bp) among a total of 47,883 transcripts. Approximately 30% of the total transcripts were matched to known marmoset sequences. Gene expression in 18 marmoset P450- and 4 FMO-like genes displayed some tissue-specific patterns. Of these, the three most highly expressed in marmoset liver were P450 2D-, 2E-, and 3A-like genes. In extrahepatic tissues, including brain, gene expressions of these monooxygenases were lower than those in liver, although P450 3A4 (previously P450 3A21) in intestine and P450 4A11- and FMO1-like genes in kidney were relatively highly expressed. By means of massive parallel long-read sequencing and short-read technology applied to marmoset liver, intestine, kidney, and brain, the combined next-generation sequencing analyses reported here were able to identify novel marmoset drug-metabolizing P450 transcripts that have until now been little reported. These results provide a foundation for mechanistic studies and pave the way for the use of marmosets as model animals for drug development in the future.

Quantitative targeted proteomics for membrane transporter proteins: method and application

Although global proteomics has shown promise for discovery of many new proteins, biomarkers, protein modifications, and polymorphisms, targeted proteomics is emerging in the proteomics research field as a complement to untargeted shotgun proteomics, particularly when a determined set of low-abundance functional proteins need to be measured. The function and expression of proteins related to drug absorption, distribution, metabolism, and excretion (ADME) such as cytochrome P450 enzymes and membrane transporters are of great interest in biopharmaceutical research. Since the variation in ADME-related protein expression is known to be a major complicating factor encountered during in vitro-in vivo and in vivo-in vivo extrapolations (IVIVE), the accurate quantification of the ADME proteins in complex biological systems becomes a fundamental element in establishing IVIVE for pharmacokinetic predictions. In this review, we provide an overview of relevant methodologies followed by a summary of recent applications encompassing mass spectrometry-based targeted quantifications of membrane transporters.

Green tea ingestion greatly reduces plasma concentrations of nadolol in healthy subjects

This study aimed to evaluate the effects of green tea on the pharmacokinetics and pharmacodynamics of the β-blocker nadolol. Ten healthy volunteers received a single oral dose of 30 mg nadolol with green tea or water after repeated consumption of green tea (700 ml/day) or water for 14 days. Catechin concentrations in green tea and plasma were determined. Green tea markedly decreased the maximum plasma concentration (C(max)) and area under the plasma concentration-time curve (AUC(0-48)) of nadolol by 85.3% and 85.0%, respectively (P < 0.01), without altering renal clearance of nadolol. The effects of nadolol on systolic blood pressure were significantly reduced by green tea. [(3)H]-Nadolol uptake assays in human embryonic kidney 293 cells stably expressing the organic anion-transporting polypeptides OATP1A2 and OATP2B1 revealed that nadolol is a substrate of OATP1A2 (Michaelis constant (K(m)) = 84.3 μmol/l) but not of OATP2B1. Moreover, green tea significantly inhibited OATP1A2-mediated nadolol uptake (half-maximal inhibitory concentration, IC(50) = 1.36%). These results suggest that green tea reduces plasma concentrations of nadolol possibly in part by inhibition of OATP1A2-mediated uptake of nadolol in the intestine.

Mass spectrometry-based targeted proteomics as a tool to elucidate the expression and function of intestinal drug transporters

Intestinal transporter proteins affect the oral bioavailability of many drugs in a significant manner. In order to estimate or predict their impact on oral drug absorption, data on their intestinal expression levels are needed. So far, predominantly mRNA expression data are available which are not necessarily correlated with the respective protein content. All available protein data were assessed by immunoblotting techniques such as Western blotting which both possess a number of limitations for reliable protein quantification. In contrast to this, mass spectrometry-based targeted proteomics may represent a promising alternative method to provide comprehensive protein expression data. In this review, we will summarize so far available intestinal mRNA and protein expression data for relevant human multidrug transporters. Moreover, recently observed mass spectrometry-based targeted proteomic data will be presented and discussed with respect to potential functional consequences. Associated to this, we will provide a short tutorial how to set up these methods and emphasize critical aspects in method development. Finally, potential limitations and pitfalls of this emerging technique will be discussed. From our perspective, LC-MS/MS-based targeted proteomics represents a valuable new method to comprehensively analyse the intestinal expression of transporter proteins. The resulting expression data are expected to improve our understanding about the intestinal processing of drugs.

Mass spectrometry-based targeted proteomics as a tool to elucidate the expression and function of intestinal drug transporters

Intestinal transporter proteins affect the oral bioavailability of many drugs in a significant manner. In order to estimate or predict their impact on oral drug absorption, data on their intestinal expression levels are needed. So far, predominantly mRNA expression data are available which are not necessarily correlated with the respective protein content. All available protein data were assessed by immunoblotting techniques such as Western blotting which both possess a number of limitations for reliable protein quantification. In contrast to this, mass spectrometry-based targeted proteomics may represent a promising alternative method to provide comprehensive protein expression data. In this review, we will summarize so far available intestinal mRNA and protein expression data for relevant human multidrug transporters. Moreover, recently observed mass spectrometry-based targeted proteomic data will be presented and discussed with respect to potential functional consequences. Associated to this, we will provide a short tutorial how to set up these methods and emphasize critical aspects in method development. Finally, potential limitations and pitfalls of this emerging technique will be discussed. From our perspective, LC-MS/MS-based targeted proteomics represents a valuable new method to comprehensively analyse the intestinal expression of transporter proteins. The resulting expression data are expected to improve our understanding about the intestinal processing of drugs.