ABSTRACT:In addition to primary human hepatocytes, hepatoma cell lines, and transfected nonhepatoma, hepatic cell lines have been used for pharmacological and toxicological studies. However, a systematic evaluation and a general report of the gene expression spectra of drug-metabolizing enzymes and transporters (DMETs) in these in vitro systems are not currently available. To fill this information gap and to provide references for future studies, we systematically characterized the basal gene expression profiles of 251 drugmetabolizing enzymes in untreated primary human hepatocytes from six donors, four commonly used hepatoma cell lines (HepG2, Huh7, SK-Hep-1, and Hep3B), and one transfected human liver epithelial cell line. A large variation in DMET expression spectra was observed between hepatic cell lines and primary hepatocytes, with the complete absence or much lower abundance of certain DMETs in hepatic cell lines. Furthermore, the basal DMET expression spectra of five hepatic cell lines are summarized, providing references for researchers to choose carefully appropriate in vitro models for their studies of drug metabolism and toxicity, especially for studies with drugs in which toxicities are mediated through the formation of reactive metabolites.

Triclosan has broad-spectrum anti-microbial activity against most gram-negative and gram-positive bacteria. It is widely used in personal care products, household items, medical devices, and clinical settings. Due to its extensive use, there is potential for humans in all age groups to receive life-time exposures to triclosan, and, indeed, triclosan has been detected in human tissues and the environment. Data gaps exist regarding the chronic dermal toxicity and carcinogenicity of triclosan, which is needed for the risk assessment of triclosan. The US Food and Drug Administration (FDA) nominated triclosan to the National Toxicology Program (NTP) for toxicological evaluations. Currently, the NTP is conducting several dermal toxicological studies to determine the carcinogenic potential of triclosan, evaluate its endocrine and developmental-reproductive effects, and investigate the potential UV-induced dermal formation of chlorinated phenols and dioxins of triclosan. This paper reviews data on the human exposure, environmental fate, efficacy of anti-microbial activity, absorption, distribution, metabolism and elimination, endocrine disrupting effects, and toxicity of triclosan.

This article is available online at http://dmd.aspetjournals.org ABSTRACT:UDP-glucuronosyltransferases (UGTs) have been implicated as important detoxifying enzymes for several major tobacco carcinogens. Because the aerodigestive tract is a primary target for exposure to tobacco smoke carcinogens, the major goal of the present study was to determine whether aerodigestive tract tissues exhibit glucuronidating activity against metabolites of benzo-[a]pyrene (BaP) and to explore the pattern of expression of UGT genes in a series of aerodigestive tract tissue specimens. Glucuronidation of the phenolic BaP metabolites 3-, 7-, and 9-hydroxyBaP was observed in all upper aerodigestive tract tissue microsome specimens tested, as determined by high-pressure liquid chromatography analysis. Glucuronidating activity toward the procarcinogenic BaP metabolite trans-BaP-7,8-dihydrodiol(؎) was also detected in aerodigestive tract tissues. By semiquantitative duplex reverse transcription-polymerase chain reaction analysis, UGT1A7 and UGT1A10 were shown to be well expressed in all aerodigestive tract tissues examined, including tongue, tonsil, floor of mouth, larynx, and esophagus. UGT1A8 and UGT1A6 were expressed primarily in larynx; no expression was observed for UGTs 1A1, 1A3, 1A4, 1A5, 1A9. Of the family 2B UGTs, only UGT2B4 and UGT2B17 exhibited significant levels of expression in aerodigestive tract tissues. Of the aerodigestive tract-expressing UGTs, only UGTs 1A7, 1A8, and 1A10 exhibited glucuronidating activity against 7-hydroxy-BaP, with UGT1A10 exhibiting the highest affinity as determined by kinetic analysis (K m ‫؍‬ 49 M). No UGT expression or glucuronidating activity was observed for any of the lung specimens analyzed in this study. These results suggest that several family 1 UGTs may potentially play an important role in BaP detoxification in the aerodigestive tract.

Usnic acid is a prominent secondary lichen metabolite that has been used for various purposes worldwide. Crude extracts of usnic acid or pure usnic acid have been marketed in the United States as dietary supplements to aid in weight loss. The US Food and Drug Administration (FDA) received 21 reports of liver toxicity related to the ingestion of dietary supplements that contain usnic acid. This prompted the FDA to issue a warning about one such supplement, LipoKinetix, in 2001 (http://www.cfsan.fda.gov/~dms/ds-lipo.html). Subsequently, usnic acid and Usnea barbata lichen were nominated by the National Toxicology Program (NTP) for toxicity evaluations. At present, a toxicological evaluation of usnic acid is being conducted by the NTP. This review focuses on the recent findings of usnic acid-induced toxicities and their underlying mechanisms of action. KeywordsWeight loss dietary supplement; usnic acid and Usnea barbata toxicity

The nicotine-derived tobacco-specific nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, is one of the most potent and abundant procarcinogens found in tobacco and tobacco smoke, and glucuronidation of its major metabolite, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), is an important mechanism for 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone detoxification. Substantial interindividual variability in urinary NNAL glucuronide formation has been observed in smokers and tobacco chewers. To determine whether genetic variations may play a role in this interindividual variability, NNAL-glucuronidating activities were analyzed in 78 human liver microsomal specimens and compared with the prevalence of missense polymorphisms in the two major NNALglucuronidating enzymes UGT1A4 and UGT2B7. In vitro assays using liver microsomal specimens from individual subjects demonstrated a 70-and 50-fold variability in NNAL-N-Gluc and NNAL-O-Gluc formation, respectively, and a 20-fold variability in the ratio of NNAL-N-Gluc: NNAL-O-Gluc formation. Microsomes from subjects with a homozygous polymorphic UGT1A4 24Thr /UGT1A4 24Thr genotype exhibited a significantly higher (P < 0.05) level of NNAL-N-Gluc activity compared with microsomes from subjects with the wild-type UGT1A4 24Pro /UGT1A4 24Pro genotype, and a significantly higher (P < 0.05) number of subjects with liver microsomes having high NNAL-N-Gluc formation activity contained the UGT1A4 24Thr /UGT1A4 24Thr genotype. Microsomes from subjects with the homozygous polymorphic UGT2B7 268Tyr /UGT2B7 268Tyr genotype exhibited a significantly lower level (P < 0.025) of NNAL-O-Gluc activity when compared with microsomes from subjects with the wild-type UGT2B7 268His /UGT2B7 268His genotype, and a significantly (P < 0.05) higher number of subjects with liver microsomes having low NNAL-OGluc formation activity contained the UGT2B7 268Tyr /UGT2B7 268Tyr genotype. These data suggest that the UGT1A4 codon 24 and UGT2B7 codon 268 polymorphisms may be associated with altered rates glucuronidation and detoxification of NNAL in vivo.