Substituted Two- to Five-Ring Polycyclic Aromatic Compounds Are Potent Agonists of Atlantic Cod (Gadus morhua) Aryl Hydrocarbon Receptors Ahr1a and Ahr2a

Polycyclic aromatic hydrocarbons (PAHs) are among the most toxic and bioavailable components found in petroleum and represent a high risk to aquatic organisms. The aryl hydrocarbon receptor (Ahr) is a ligand-activated transcription factor that mediates the toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and other planar aromatic hydrocarbons, including certain PAHs. Ahr acts as a xenosensor and modulates the transcription of biotransformation genes in vertebrates, such as cytochrome P450 1A (cyp1a). Atlantic cod (Gadus morhua) possesses two Ahr proteins, Ahr1a and Ahr2a, which diverge in their primary structure, tissue-specific expression, ligand affinities, and transactivation profiles. Here, a luciferase reporter gene assay was used to assess the sensitivity of the Atlantic cod Ahrs to 31 polycyclic aromatic compounds (PACs), including two- to five-ring native PAHs, a sulfur-containing heterocyclic PAC, as well as several methylated, methoxylated, and hydroxylated congeners. Notably, most parent compounds, including naphthalene, phenanthrene, and partly, chrysene, did not act as agonists for the Ahrs, while hydroxylated and/or alkylated versions of these PAHs were potent agonists. Importantly, the greater potencies of substituted PAH derivatives and their ubiquitous occurrence in nature emphasize that more knowledge on the toxicity of these environmentally and toxicologically relevant compounds is imperative.

Erythropoietic activity and interferon production in LCM virus-infected nude mice

The distinct haemopoietic lesions induced in ordinary mice during acut LCM virus infection are not mediated either by immunopathological mechanisms or by a direct cytopathogenetic effect of the virus. Medication has recently been artibuted to the high interferon activity found in mice with acute LCM virus infection. In this work, erythropoietic activity and interferon production have been studied in LCM virus-infected nude mice. Compared with ordinary mice, nude mice displayed a more moderate suppression of erythropoiesis and a very poor interferon response. Erythropoietic activity of thymus-transplanted nude mice was not significantly suppressed during the infection, and interferon responsiveness was not restored either by thymus-transplantation or by transfer of large numbers of spleen lymphocytes. The observations support the hypothesis that interferon plays a decisive role in the induction of haemopoietic diorders of mice with acute LCM virus infection. The puzzling question as to why nude mice and reconstituted nude mice are incapable of mounting a normal interferon response is discussed briefly.