PBDE-47 and PBDE mixture (DE-71) toxicities and liver transcriptomic changes at PND 22 after in utero/postnatal exposure in the rat.

Pentabromodiphenyl ethers (PBDE) are found in human tissue, in household dust, and in the environment, and a particular concern is the potential for the induction of cancer pathways from these fat-soluble persistent organic pollutants. Only one PBDE cancer study has been conducted and that was for a PBDE mixture (DE-71). Because it is not feasible to test all PBDE congeners in the environment for cancer potential, it is important to develop a set of biological endpoints that can be used in short-term toxicity studies to predict disease outcome after long-term exposures. In this study, PBDE-47 was selected as the test PBDE congener to evaluate and compare toxicity to that of the carcinogenic PBDE mixture. The toxicities of PBDE-47 and the PBDE mixture were evaluated at PND 22 in Wistar Han rat (Crl: WI (Han)) pups after in utero/postnatal exposure (0, 0.1, 15, or 50 mg/kg; dams, GD6-21; pups, PND 12-PND 21; oral gavage daily dosing). By PND 22, PBDE-47 caused centrilobular hypertrophy and fatty change in liver, and reduced serum thyroxin (T4) levels; similar effects were also observed after PBDE mixture exposure. Transcriptomic changes in the liver included induction of cytochrome p450 transcripts and up-regulation of Nrf2 antioxidant pathway transcripts and ABC membrane transport transcripts. Decreases in other transport transcripts (ABCG5 & 8) provided a plausible mechanism for lipid accumulation, characterized by a treatment-related liver fatty change after PBDE-47 and PBDE mixture exposure. The benchmark dose calculation based on liver transcriptomic data was generally lower for PBDE-47 than for the PBDE mixture. The up-regulation of the Nrf2 antioxidant pathway and changes in metabolic transcripts after PBDE-47 and PBDE mixture exposure suggest that PBDE-47, like the PBDE mixture (NTP 2016, TR 589), could be a liver toxin/carcinogen after long-term exposure.

Prevention of photocarcinogenesis and UV-induced immunosuppression in mice by topical tannic acid.

Topical application of tannic acid, a phenolic antioxidant derived from plants, was found to inhibit the cutaneous carcinogenesis and the immunosuppression induced by ultraviolet B (UVB) irradiation with no visible toxicity. BALB/cAnNTacfBR mice were treated with 200 micrograms of tannic acid three times weekly for two weeks before UV treatments began and throughout the experiment. UVB irradiation consisted of five 30-minute exposures per week to banks of six FS40 Westinghouse sunlamps. In the photocarcinogenesis study, mice received a total dose of approximately 1.09 x 10(6) J/m2. Skin cancer incidence in UV-irradiated mice was 75% at 26 weeks after the first UV exposure; tannic acid reduced this to 42%. Immunosuppression induced by UVB irradiation normally prevents the host from rejecting antigenic syngeneic UV-induced tumors. Immunosuppression in these experiments was measured by a passive transfer assay. Tumor challenges grew to an average of 88 +/- 20, 36 +/- 11, and 20 +/- 8 mm2 in naive recipients of splenocytes from UVB-irradiated mice, nonirradiated control mice, and UVB-irradiated mice treated with tannic acid, respectively. Thus topical tannic acid treatment prevented the transfer of enhanced tumor susceptibility with splenocytes from UVB-irradiated mice.

Inhibition of DFMO-induced audiogenic seizures by chlordiazepoxide.

Mice given 1% alpha-difluoromethylornithine (DFMO) in the drinking water for 5 weeks developed a hyperactive behavior characterized by uncontrolled running upon stimulation with noise. The running was followed by seizures and sometimes death. These behaviors are characteristic of audiogenic seizures. Strain differences in susceptibility to DFMO-induced audiogenic seizures were observed. The order of sensitivity to this DFMO effect was: C3HeB/FEJ = C3H/HeN > CBA/J = BALB/c. Chronic DFMO treatment was found to deplete whole brain putrescine and spermidine, but not spermine nor gamma-aminobutyric acid (GABA), in the 2 strains of mice analyzed, C3H/HeN and BALB/c. The audiogenic seizures were eliminated by pretreatment with the benzodiazepine, chlordiazepoxide (Librium) (40 mg/kg, ip) 105 minutes prior to testing for seizures.

Prevention of photocarcinogenesis by dietary vitamin E.

Ultraviolet B (UV-B) irradiation of C3H/HeN mice induces skin cancer. In this study, the ability of dietary d-alpha-tocopheryl acetate to reduce photocarcinogenesis was tested in this murine model. Skin cancers developed in 67.5% of UV-B-irradiated mice by 31 weeks after the first UV exposure. Supplementation with 100 or 200 IU of d-alpha-tocopheryl acetate per kilogram of diet led to a reduction of the incidence to 46% and 19%, respectively. The latter value was significantly different from that found in mice fed the basal diet (p = 0.039, one-sided P value by log-rank test). Skin levels of alpha-tocopherol varied with the dietary dose of d-alpha-tocopheryl acetate. No toxicity was evident in unirradiated mice fed the vitamin E-supplemented diet, but 40% of the UV-B-irradiated mice fed 200 IU of vitamin E per kilogram of diet died by 31 weeks after the first UV-B treatment. Decreased relative spleen weight was observed in the UV-B-irradiated mice fed the vitamin E-supplemented diet. In summary, oral d-alpha-tocopheryl acetate prevented photocarcinogenesis, but at doses that were toxic to inbred C3H/HeN mice after exposure to 8.6 x 10(5) J/m2 of UV-B irradiation.

Prolactin-stimulated mitogenesis in the Nb2 rat lymphoma cell: lack of protoporphyrin IX effects.

Pharmacological characterization of the Nb2 cell peripheral-type benzodiazepine receptor (PBR) was determined using selected 1,4-benzodiazepines, PK 11195, and protoporphyrin IX (PPIX) to compete for specific [3H] Ro5-4864 binding. These data suggest that PPIX possesses an affinity for the Nb2 cell PBR (Ki = 142 nM). We have previously reported that the peripheral benzodiazepine ligands, Ro5-4864 and PK 11195, modulate prolactin-stimulated mitogenesis in the Nb2 cell(1). In contrast, PPIX, a putative endogenous ligand for the PBR had no effect on prolactin-stimulated mitogenesis in the Nb2 cell over the concentration range from 10(-15) M to 10(-6) M. Taken together these data show that PPIX has an affinity for the Nb2 cell PBR but does not modulate prolactin-stimulated mitogenesis at concentrations which should bind to the Nb2 cell PBR.

Peripheral benzodiazepine binding sites in Nb 2 node lymphoma cells: effects on prolactin-stimulated proliferation and ornithine decarboxylase activity.

[3H]Ro 5-4864 binds to Nb 2 node lymphoma cells in a specific saturable and reversible fashion. Scatchard analysis of specific binding data reveals a single, homogeneous class of whole cell binding sites with a Kd of 3.94 +/- 0.22 nM and a Bmax value of 155 +/- 11 fmol (Ro 5-4864 bound)/2 x 10(6) cells. Ro 5-4864, a reported peripheral benzodiazepine receptor agonist both inhibits (10(-6) M) and potentiates (10(-9) M) the mitogenic action of prolactin on the Nb 2 node lymphoma cells. Interestingly, PK 11195, an antagonist, potentiates (10(-9) M) the mitogenic activity of prolactin in these cells. The actions of both Ro 5-4864 and PK 11195 seem to be mediated through a common receptor type since a 10(-6) M concentration of either agent will block the others potentiating action. Furthermore, the simultaneous addition of a 10(-9) M concentration of Ro 5-4864 and PK 11195 does not further increase the effect on prolactin stimulated mitogenesis. Clonazepam, a central benzodiazepine receptor agonist has no effect on prolactin-stimulated mitogenesis in this system. These data suggest that the Nb 2 node lymphoma cells possess a peripheral-type benzodiazepine receptor. In these cells, this receptor seems to serve the function of modulating the ability of the growth factor, prolactin to initiate the mitogenic process. These studies also suggest that Ro 5-4864 is functioning as a partial agonist rather than a 'pure' agonist for the peripheral benzodiazepine receptor in this system.