" Commandeuring" Xenobiotic Metabolism: Advances in Understanding Xenobiotic Metabolism

Abstract

The understanding of how exogenous chemicals (xenobiotics) are metabolized, distributed, and eliminated is critical to determine the impact of the chemical and its metabolites to the (human) organism. This is part of the research and educational discipline ADMET (absorption, distribution, metabolism, elimination, and toxicity). Here, we review the work of Jan Commandeur and colleagues who have not only made a significant impact in understanding of phase I and phase II metabolism of several important compounds but also contributed greatly to the development of experimental techniques for the study of xenobiotic metabolism. Jan Commandeur's work has covered a broad area of research, such as the development of online screening methodologies, the use of a combination of enzyme mutagenesis and molecular modeling for structure-activity relationship (SAR) studies, and the development of novel probe substrates. This work is the bedrock of current activities and brings the field closer to personalized (cohort-based) pharmacology, toxicology, and hazard/risk assessment.

Figure 1

Reaction scheme representing regioisomer formation of GSH conjugation-dependent metabolism of TCE. Enzymes involved: (a) glutathione-S-transferases, (b) γ-glutamyltransferase, (c) cysteinyl–glycine dipeptidase, (d) β-lyase, (e) cysteine-conjugated N-acetyltransferase, (f) aminoacylase.

Figure 2

Different strategies for the screening of activity and/or affinity in complex mixtures. The upper portion (A) depicts a fractionation approach in which the gradient HPLC eluent after mixing with a postcolumn makeup gradient is collected in a microtiter plate, which is subsequently analyzed by the appropriate bioassays (e.g., receptor binding or enzyme inhibition assays). The lower portion (B) depicts the general scheme of a HRS setup. After gradient HPLC with postcolumn makeup gradient, the total flow is split to a bioassay and a parallel HPLC effluent readout. In the bioassay, HPLC effluent is first mixed in a reaction coil with the target protein (in this case a receptor), and subsequently, in the second reaction, coil mixed with a probe allows bioassay readout. When the system is operated in flow injection analysis (FIA) mode, the samples are introduced into the carrier solution by the autoinjector directly.

Figure 3

Reaction scheme of fotemustine metabolism.

Figure 4

Chemical structures of burimamide (thiourea group) versus cimetidine (cyanoguanidine group).

Figure 5

Reaction mechanism of the bioactivation of APAP to NAPQI and subsequent detoxification to GSH adducts.

Figure 6

Oxidative (CYP) versus conjugative (GST) metabolic route for 1,2-DBE metabolism.

Figure 7

Urinary excretion of acetone and propanal determined every 12 h in urine fractions of four groups of male Wistar rats. Open circles, dotted line: control group. Closed circles, solid line: treated with 0.5 mL/kg body weight of CCl₄. Adapted with permission from De Zwart et al. 1998.

Figure 8

Computer model of the active site of CYP1A2, showing the location of residues 298/299 at the CPR/Cyt. B5 interaction site and residues 406/83 at the substrate entrance/product egress channel. The heme center is shown in gray stick mode. Residue I386 is located near the heme group in the substrate recognition site, and R456, which is involved in heme anchoring, is located below the heme group.

Figure 9

Active site of the homology model of CYP2D6 (Keizers et al. 2004), showing the active site residues F120, E216, D301 and F483. The pink ball at the bottom represents the heme iron atom. In yellow, the substrate dextromethorphan is depicted.

Figure 10

Time dependence of dextromethorphan metabolism by BM3 mutants M11 (open circles), M05 (open squares), M01 (closed squares), and M02 (open triangles). Enzymatic activity in nmol product/nmol enzyme is plotted against reaction time in seconds. Adapted with permission from van Vugt-Lussenburg et al. 2007.