Carcinogenicity testing is indispensable for identifying environmental carcinogens and for evaluating the safety of drugs in the process of development. Conventional 2-year rodent bioassays are one of the most resource-consuming tests in terms of animals, time, and costs. Development of rapid carcinogenicity testing systems that can assess carcinogenicity within a short period has become a social demand and is essential to improve efficacy in the identification of environmental carcinogens as well as in the development of new drugs. In this review we introduce the rapid carcinogenicity testing system using transgenic (Tg) mice carrying the human prototype c-Ha-ras gene, namely rasH2 mouse (CB6F1-TgHras2 mouse is the same mouse). The studies have been conducted to validate the rasH2 mouse as a model for the rapid carcinogenicity testing system. Our current validation studies revealed that rasH2 mice are able to detect various types of mutagenic carcinogens within 6 months. The rasH2 mice may also be able to detect various nonmutagenic carcinogens. The validation studies also revealed that rasH2 mice are generally much more susceptible to both mutagenic and nonmutagenic carcinogens than control non-Tg mice. No significant tumor induction has been observed in rasH2 mice with either mutagenic or nonmutagenic noncarcinogens. More rapid onset and higher incidence of more malignant tumors can be expected with a high probability after treatment with various carcinogens in the rasH2 mice than in control non-Tg mice. The rasH2 mouse appears to be a promising candidate as an animal model for development of a rapid carcinogenicity testing system.

Carcinogenicity testing is indispensable for identifying environmental carcinogens and for evaluating the safety of drugs in the process of development. Conventional 2-year rodent bioassays are one of the most resource-consuming tests in terms of animals, time, and costs. Development of rapid carcinogenicity testing systems that can assess carcinogenicity within a short period has become a social demand and is essential to improve efficacy in the identification of environmental carcinogens as well as in the development of new drugs. In this review we introduce the rapid carcinogenicity testing system using transgenic (Tg) mice carrying the human prototype c-Ha-ras gene, namely rasH2 mouse (CB6F1-TgHras2 mouse is the same mouse). The studies have been conducted to validate the rasH2 mouse as a model for the rapid carcinogenicity testing system. Our current validation studies revealed that rasH2 mice are able to detect various types of mutagenic carcinogens within 6 months. The rasH2 mice may also be able to detect various nonmutagenic carcinogens. The validation studies also revealed that rasH2 mice are generally much more susceptible to both mutagenic and nonmutagenic carcinogens than control non-Tg mice. No significant tumor induction has been observed in rasH2 mice with either mutagenic or nonmutagenic noncarcinogens. More rapid onset and higher incidence of more malignant tumors can be expected with a high probability after treatment with various carcinogens in the rasH2 mice than in control non-Tg mice. The rasH2 mouse appears to be a promising candidate as an animal model for development of a rapid carcinogenicity testing system. Environ Health Perspect 1 06(Suppl 1 ):57-69 (1998). http.//ehpnetl.niehs.nih.gov/ docs/1998/Suppl-1/57-69yamamoto/abstract.html

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This study examines histologically the degeneration and subsequent regeneration processes of human hair follicles whose bulb is severely damaged. Human scalp hair follicles were isolated and grafted onto immunodeficient mice after their bulb was amputated. On day 14, thickening and corrugation of the vitreous membrane, apoptosis of follicular keratinocytes, and regression of the lower portion of the follicles were observed. By day 20, mesenchymal cells had accumulated around the lower end of the follicles. From day 14 through 50, the follicular regression and apoptosis continued, and between days 30 and 40 the follicles became maximally shortened, and the vitreous membrane disappeared. By day 50 the lower end of the follicles had become cup-shaped, and the cup surrounded an aggregate of mesenchymal cells that corresponded to the dermal papilla. By day 60, all the grafted follicles had developed into anagen VI follicles, and the apoptosis had ceased. These results indicate that human scalp hair follicles whose bulb is completely destroyed enter into dystrophic telogen after restoration of the dermal papilla, then into anagen, and that the duration of the dystrophic telogen is shorter than that of the normal hair cycle.