Quantitative real-time reverse transcription-polymerase chain reaction analysis of drug metabolizing and cytoprotective genes in psoriasis and regulation by ultraviolet radiation

There are unpredictable inter-individual differences in response to ultraviolet radiation, used in the treatment of psoriasis and other common skin diseases. It is therefore essential that we attempt to identify phenotypic markers that correlate with individual treatment outcomes. Exposure of human skin to ultraviolet radiation results in the generation of reactive intermediates and oxidative stress. Hepatic drug metabolizing and cytoprotective genes are induced as an adaptive response to xenobiotics and reactive intermediates; as several of these genes are present in skin, we hypothesized that their cutaneous expression and regulation may be implicated in responses to ultraviolet radiation. We used quantitative real-time reverse transcription–polymerase chain reaction to investigate interindividual differences in the cutaneous expression of a variety of drug metabolizing and cytoprotective genes, including cytochrome P450s, glutathione S-transferases and drug transporters, and investigated the regulation of gene expression by ultraviolet radiation and in lesional psoriatic skin. We confirmed significant induction of cyclooxygenase 2 (mean 3.63-fold, range 0.14–22.6, p<0.0001) by ultraviolet radiation and showed more modest (≈2-fold) inductions of glutathione peroxidase, and novel inductions of glutathione S-transferase P1 and the drug transporter multidrug resistance associated protein-1. Glutathione S-transferase P1 (3.74-fold, 1.3–33.1, p< 0.0001) and multidrug resistance associated protein-1 (4.06-fold, 1.3–24.8, p<0.0001) were also significantly increased in psoriatic plaque, as were P450 CYP2E1 (3.64-fold, 1–28.9 p<0.0001) and heme oxygenase-1 (10.19-fold, 2.9–49.7, p<0.0001), implying a differential adaptive response to oxidant exposure in lesional psoriatic skin. We found considerable interindividual variation in constitutive gene expression and inducibility, indicating that these genes may be associated with individuality in response to ultraviolet radiation

Trichloroethylene biotransformation and its role in mutagenicity, carcinogenicity and target organ toxicity

Metabolism is critical for the mutagenicity, carcinogenicity, and other adverse health effects of trichloroethylene (TCE). Despite the relatively small size and simple chemical structure of TCE, its metabolism is quite complex, yielding multiple intermediates and end-products. Experimental animal and human data indicate that TCE metabolism occurs through two major pathways: cytochrome P450 (CYP)-dependent oxidation and glutathione (GSH) conjugation catalyzed by GSH S-transferases (GSTs). Herein we review recent data characterizing TCE processing and flux through these pathways. We describe the catalytic enzymes, their regulation and tissue localization, as well as the evidence for transport and inter-organ processing of metabolites. We address the chemical reactivity of TCE metabolites, highlighting data on mutagenicity of these end-products. Identification in urine of key metabolites, particularly trichloroacetate (TCA), dichloroacetate (DCA), trichloroethanol and its glucuronide (TCOH and TCOG), and N-acetyl-S-(1,2-dichlorovinyl)-L-cysteine (NAcDCVC), in exposed humans and other species (mostly rats and mice) demonstrates function of the two metabolic pathways in vivo. The CYP pathway primarily yields chemically stable end-products. However, the GST pathway conjugate S-(1,2-dichlorovinyl)glutathione (DCVG) is further processed to multiple highly reactive species that are known to be mutagenic, especially in kidney where in situ metabolism occurs. TCE metabolism is highly variable across sexes, species, tissues and individuals. Genetic polymorphisms in several of the key enzymes metabolizing TCE and its intermediates contribute to variability in metabolic profiles and rates. In all, the evidence characterizing the complex metabolism of TCE can inform predictions of adverse responses including mutagenesis, carcinogenesis, and acute and chronic organ-specific toxicity