To gain insight into melanoma pathogenesis, we characterized an insertional mouse mutant, TG3, that is predisposed to develop multiple melanomas. Physical mapping identified multiple tandem insertions of the transgene into intron 3 of Grm1 (encoding metabotropic glutamate receptor 1) with concomitant deletion of 70 kb of intronic sequence. To assess whether this insertional mutagenesis event results in alteration of transcriptional regulation, we analyzed Grm1 and two flanking genes for aberrant expression in melanomas from TG3 mice. We observed aberrant expression of only Grm1. Although we did not detect its expression in normal mouse melanocytes, Grm1 was ectopically expressed in the melanomas from TG3 mice. To confirm the involvement of Grm1 in melanocytic neoplasia, we created an additional transgenic line with Grm1 expression driven by the dopachrome tautomerase promoter. Similar to the original TG3, the Tg(Grm1)EPv line was susceptible to melanoma. In contrast to human melanoma, these transgenic mice had a generalized hyperproliferation of melanocytes with limited transformation to fully malignant metastasis. We detected expression of GRM1 in a number of human melanoma biopsies and cell lines but not in benign nevi and melanocytes. This study provides compelling evidence for the importance of metabotropic glutamate signaling in melanocytic neoplasia.

ABSTRACT:On the basis of the ability of capsaicin to activate the transient receptor potential vanilloid 1 receptor (TRPV1) expressed in nociceptive sensory neurons, topical and injectable high-concentration formulations are being developed as potential treatments for various pain syndromes. As much of the published literature on capsaicin is based on pepper extracts, which are typically a mixture of capsaicin and other capsaicinoids (including norhydrocapsaicin, dihydrocapsaicin, homocapsaicin and homodihydrocapsaicin), the purpose of this investigation was to study the in vitro metabolism of pure capsaicin. The metabolism of capsaicin was similar in human, rat, and dog microsomes and S9 fractions.In these assays, three major metabolites were detected and identified as 16-hydroxycapsaicin, 17-hydroxycapsaicin, and 16,17-dehydrocapsaicin. In addition to these three metabolites, rat microsomes and S9 fractions also produced vanillylamine and vanillin. Biotransformation of capsaicin was slow in human skin in vitro, with the majority of the applied capsaicin remaining unchanged and a small fraction being metabolized to vanillylamine and vanillic acid. These data suggest that the metabolism of capsaicin by cytochrome P450 enzymes in skin is minimal, relative to hepatic metabolism.Capsaicin is the most abundant pungent molecule produced by pepper plants and thereby represents an important ingredient in spicy foods consumed throughout the world. The capsaicin content of peppers ranges from 0.1 to 2.5 mg/g (Parrish, 1996), and the resulting average human capsaicin consumption is on the order of 0.5 to 4 mg/kg/day (EC Scientific Committee on Food, 2002, http://ec.europa.eu/food/fs/sc/scf/out120_en.pdf). In addition to its extensive role as a food additive, there is also substantial human exposure to capsaicin in the form of nonprescription (in the United States) or prescription (in the European Union) topical analgesics, self-defense products (e.g., pepper spray), and oral herbal supplements.Capsaicin is a highly selective agonist for the TRPV1 [formerly known as the vanilloid receptor 1 (VR1)]. TRPV1 is a ligand-gated, nonselective cation channel preferentially expressed on small-diameter sensory neurons, especially those nociceptors that specialize in the detection of painful or noxious sensations (C-fibers and to a lesser extent A␦-fibers) (Caterina et al., 1997;Szallasi and Blumberg, 1999). The initial effect of capsaicin is the activation of TRPV1-expressing nociceptors, resulting in a burning sensation, hyperalgesia, allodynia, and erythema (Szallasi and Blumberg, 1999); these events are followed by a reversible defunctionalization of nociceptive sensory axons (Bley, 2004). Defunctionalization of hyperactive nociceptors is thought to underlie the pain relief that follows topical application or intra-articular injections of capsaicin (Bley, 2004).Much of the published literature on capsaicin relates to extracts of capsaicin derived from peppers; these extracts are typically a mixture of capsaicin, norhydrocapsaicin...

The tumorigenic activity of manufactured gas plant residue (MGP) was evaluated in female A/J mice using a F0927 basal gel diet system. Adulterated diets containing MGP (0.10% or 0.25%) or benzo[a]pyrene (B[alpha]P; 16 or 98 ppm) were fed for 260 days. A negative control group was maintained on a nonadulterated basal gel diet. Mice dosed with a single ip injection of 1.79 mg of B[a]P in a tricaprylin vehicle and maintained on a NIH-07 pellet diet were positive controls. In addition, a nontreated group of mice and a group dosed with vehicle only were maintained on a NIH-07 pellet diet and used as negative controls. Animal body weight and consumption of MGP and B[a]P were monitored throughout the study. Ingestion of a 0.10 or 0.25% MGP adulterated diet resulted in 70 and 100% of the mice developing lung tumors with a multiplicity of 1.19 and 12.17 tumors/mouse, respectively. Mice maintained on a 0.10% MGP diet consumed 0.7 g of MGP containing 1.8 mg of B[a]P while those fed a 0.25% MGP diet ingested 1.5 g of MGP containing 4.2 mg of B[a]P. The incidence of lung tumors in mice fed only B[a]P was considerably lower than that observed for animals fed a MGP diet. A diet containing 98 ppm B[a]P produced a significant incidence of tumor-bearing mice with 52% developing lung tumors. The multiplicity observed in these animals, however, was not significant at 0.59 tumors/mouse. A diet containing 16 ppm B[a]P did not produce a significant tumorigenic response in lung. Animals fed a 16 or 98 ppm B[a]P diet consumed a total of 11 and 67 mg of B[a]P, respectively. A single ip dose of B[alpha]P (1.79 mg in 0.25 mL of tricaprylin) resulted in 100% lung tumorigenesis with a multiplicity of 15.79 tumors/mouse. In contrast to observed induction of lung tumors, no forestomach tumors were detected in any animal fed a 0.10 or 0.25% MGP adulterated diet. However, ingestion of a diet containing only 16 or 98 ppm of B[a]P resulted in 20 and 100% of the mice developing forestomach tumors, respectively. The multiplicity for forestomach tumors was 0.24 and 4.22 tumors/mouse, respectively. The incidence of forestomach carcinomas in tumor bearing mice was 8 and 52%, respectively. The ip administration of 1.79 mg of B[a]P resulted in an 83% forestomach tumor incidence having a multiplicity of 1.83 tumors/mouse. Forestomach carcinomas were induced in 34% of the mice exhibiting forestomach tumors. These data indicate that chronic ingestion of MGP- or B[a]P-adulterated diets produces significant differences in the tumorigenic response of female A/J mouse forestomach and lung tissues.

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2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and related chemicals induce cytochrome P450 1A (CYP1A) gene expression and, at sufficient exposures, cause toxicity. Human health risks from such exposures are typically estimated from animal studies. We tested whether animal models predict human sensitivity by characterizing CYP1A gene expression in cultures of fresh hepatocytes from human donors, rats, and rhesus monkeys and HepG2 human hepatoma cells. We exposed the cells to three aryl hydrocarbon receptor (AhR) ligands of current environmental interest and measured 7-ethoxyresorufin-O-deethylase (EROD) activity and concentrations of CYP1A1 and CYP1A2 mRNA. We found that human cells are about 10-1000 times less sensitive to TCDD, 3,3',4,4',5-pentachlorobiphenyl (PCB 126), and Aroclor 1254 than rat and monkey cells, that relative potencies among these chemicals are different across species, and that gene expression thresholds exist for these chemicals. Newly calculated rat-human interspecies relative potency factors for PCB 126 were more than 100 times lower than the current rodent-derived value. We propose that human-derived values be used to improve the accuracy of estimates of human health risks.