No abstract

Cytochrome P450 (P450) and uridine 59-diphospho-glucuronosyltransferase (UGT) enzymes mediate a major proportion of phase I and phase II metabolism of xenobiotics. In vitro-in vivo extrapolation (IVIVE) of hepatic clearance in conjunction with physiologicallybased pharmacokinetics (PBPK) has become common practice in drug development. However, prediction of xenobiotic kinetics in virtual populations requires knowledge of both enzyme abundances and the extent to which these correlate. A multiplexed quantification concatemer (QconCAT) strategy was used in this study to quantify the expression of several P450 and UGT enzymes simultaneously and to establish correlations between various enzyme abundances in 24 individual liver samples (ages 27-66, 14 male ), expressed as mean 6 S.D. Previous reports of correlations in expression of various P450 (CYP3A4/CYP3A5*1/*3, CYP2C8/CYP2C9, and CYP3A4/CYP2B6) were confirmed. New correlations were demonstrated between UGTs [including UGT1A6/UGT1A9 (r s = 0.82, P < 0.0001) and UGT2B4/UGT2B15 (r s = 0.71, P < 0.0001)]. Expression of some P450 and UGT enzymes were shown to be correlated [including CYP1A2/UGT2B4 (r s = 0.67, P = 0.0002)]. The expression of CYP3A5 in individuals with *1/*3 genotype (n = 11) was higher than those with *3/*3 genotype (n = 10) (P < 0.0001). No significant effect of gender or history of smoking or alcohol use on enzyme expression was observed; however, expression of several enzymes declined with age. The correlation matrix produced for the first time by this study can be used to generate more realistic virtual populations with respect to abundance of various enzymes.

Cytochrome P450 is a family of enzymes that catalyze reactions involved in the metabolism of drugs and other xenobiotics. These enzymes are therefore important in pharmacologic and toxicologic studies, and information on their abundances is of value in the process of scaling in vitro data to in vivo metabolic parameters. A meta-analysis was applied to data on the abundance of human hepatic cytochrome P450 enzymes in Caucasian adult livers (50 studies). Despite variations in the methods used to measure the abundance of enzymes, agreement between the studies in 26 different laboratories was generally good. Nonetheless, some heterogeneity was detected (Higgins and Thompson heterogeneity test). More importantly, large interindividual variability was observed in the collated data. Positive correlations between the expression levels of some cytochrome P450 enzymes were found in the abundance data, including the following pairs: CYP3A4/CYP3A5*1/*3 (Rs = 0.70, P < 0.0001, n = 52), CYP3A4/CYP2C8 (Rs = 0.68, P < 0.0001, n = 134), CYP3A4/CYP2C9 (Rs = 0.55, P < 0.0001, n = 71), and CYP2C8/CYP2C9 (Rs = 0.55, P < 0.0001, n = 99). These correlations can be used to demonstrate common genetic transcriptional mechanisms.

The Blood-Brain Barrier (BBB) maintains brain homeostasis by controlling traffic of molecules from the circulation into the brain. This function is predominantly dependent on proteins expressed at the BBB, especially transporters and tight junction proteins. Alterations to the level and function of BBB proteins can impact on the susceptibility of the central nervous system to exposure to xenobiotics in the systemic circulation with potential consequent effects on brain function. In this study, expression profiles of drug transporters and solute carriers in the BBB were assessed in tissues from healthy individuals (n=12), Alzheimer's patients (n=5) and Dementia with Lewy Bodies patients (n=5), using targeted, AMRT (Accurate Mass Retention Time) and global proteomic methods. A total of 66 transporters were quantified, 19 for the first time in the BBB. A further 20 novel transporters were identified but not quantified. The global proteomic method identified another 3333 BBB proteins. Transporter abundances, taken together with the scaling factor microvessel protein content per unit tissue (BMvPGB also measured here) can be used in quantitative systems pharmacology models predicting drug disposition in the brain and permitting dose adjustment (precision dosing) in special populations of patients, such as those with dementia. Even in this small study, we see differences in transporter profile between healthy and diseased brain tissue.