Nitosamines are members of the N-nitroso family. Exposure to nitrosamines, especially dimethylnitrosamine (DMN) comes from a wide variety of dietary and industrial sources. Industrial exposures to DMN, are most prevalent in rubber and metal working industries. DMN is the most prevalent nitrosamine and is a model compound which exhibits toxicity, mostly in the liver. In laboratory animals, exposure to DMN results in centrolobular necrosis of the liver, as it does in humans. Following oral administration, DMN is rapidly absorbed from the upper small intestine and distributed throughout the body. Along with the organ damage caused by DMN, it also has been shown to have effects on antibody-forming cells, host surveillance, cell-mediated immunity, and hematopoiesis. Some of the effects can be traced to actions of cytokines and/or macrophages. This research proposal will determine whether tumor necrosis factor-alpha (TNF-alpha) is necessary for the hepatotoxicity caused by chronic administration of DMN. The hypothesis will be tested by administering DMN to mice in which receptors for TNF-alpha have been deleted from the genome by insertional recombination. Individual TNF-alpha receptors can be reintroduced by bone marrow transplant to generate mice with TNF-tx receptors on bone marrow derived leukocytes but not liver cells. Hepatic necrosis and-inflammatory cell infiltration will be measured by microscopic examination as an indication of DMN-induced toxicity. Changes in cytokines and acute phase proteins amounts will also be monitored as an indication of toxicity. If TNF-alpha is necessary for the DMN-induced hepatotoxicity then in mice without receptors for TNF-alpha there should be an amelioration of necrosis and cellular infiltration. Experiments using mice having no receptors for TNF-alpha but getting bone marrow transplant from mice with receptors will determine whether TNF-alpha receptors on immunocytes or on hepatocytes are necessary for DMN-induced toxicity. The experiments described in this proposal will add significant mechanistic data to the pathway of chemical-induced liver damage.
