Carcinogen-Induced DNA Damage and Cellular Alterations in F344 Rat Colon Organ Cultures23

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Abstract
Optimized culture conditions were used to achieve prolonged survival of colon mucosa from conventional inbred F344 strain rats. Up to 21 days in culture, a high percentage of expiants had viable mucosa with intact crypt columns and maintained active replicative DNA synthesis in the proliferative zone of the crypts. An acute 4-hour in vitro exposure to 0.5 mM of the colon-selective carcinogens 1,2-dimethylhydrazine dihydrochloride (DMH) and N-methyl-N′-nitro-N-nitrosoguanidine (MNNG) produced 26 and 78% suppressions of replicative DNA synthesis, respectively, whereas the same exposure to the liver carcinogen dimethylnitrosamine produced only a 5% suppression. The thymidine-labeling index of DMH-exposed cells was lower than that of control cells at 1 day and then increased above the control values 7–21 days later. MNNG exposure produced pronounced morphologic changes in the crypt columns. MNNG-exposed cultures that were transplanted into the mammary fat pads of syngeneic female rats produced hypercellular cysts different from those formed by nonex-posed fragments. These findings indicate that the acute and persistent effects of colon carcinogens can be studied directly on the target tissue in organ culture.