The epidemiology and toxicology of TCDD

Industrial chemicals and the horse

Poisoning resulting from exposure to a wide variety of industrial chemicals is not a common occurrence in horses, but it does happen on occasion. A wide range of toxicosis can occur from a wide range of industrial pollutants, such as dioxin, carbon tetrachloride, and tetrachloroethylene, to heavy metals, such as cadmium and zinc. The equine practitioner must consider industrial chemical toxicosis in differential diagnoses and work with a reputable veterinary diagnostic laboratory to confirm or rule out industrial chemical poisoning.

Inhibition of postconfluent focus production in cultures of MCF-7 human breast cancer cells by 2,3,7,8-tetrachlorodibenzo-p-dioxin

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a potent inducer of differentiation and an antiestrogen, is shown to suppress in vitro postconfluent cell accumulation in the estrogen-dependent MCF-7 human breast tumor cell line. This dose-responsive suppression is apparent by 14 days of exposure with an EC50 between 10(-10) and 10(-11) M TCDD, and is characterized by reduced cell density (approximately 60% of controls after 14 days). This was attributed to a reduced formation in TCDD-treated cultures of multicellular foci which are characteristic of cancer cell growth in vitro (less than 1/mm2 compared to control levels of 40/mm2). Preconfluent cell growth and viability of MCF-7 cells is not affected by 10(-9) M TCDD. These results suggest that the principle of TCDD's activity may be useful in the study and possibly the management of estrogen-dependent breast tumors.