Yoichi Katoh

Inhibition of benzo[a]pyrene-induced mutagenesis in Chinese hamster V79 cells by hemin and related compounds

The inhibitory effects of hemin and related compounds on the mutagenicity of benzo[a]pyrene (BP) were investigated in Chinese hamster V79 cells co-cultivated with X-irradiated hamster embryo cells. Mutant V79 cells were selected by their resistance to ouabain. The mutation frequency induced by BP was substantially inhibited dose dependently by hemin. The mutagenicity of BP (1 microgram/ml) on V79 cells was reduced to 6.5% by hemin, 52% by biliverdin, 73% by protoporphyrin and 85% by chlorophyllin at the highest concentration of the compounds tested (15 microM).

Morphological transformation, sister chromatid exchange and mutagenesis assay of betel constituents

Betel quid, a masticatory widely used in Sri Lanka, consists of Jaffna tobacco, the nuts and leaves of betel plants and calcium hydroxide. An ethyl acetate extract of Jaffna tobacco induced morphological transformation of hamster embryo cells. The extract also induced sister chromatid exchanges inn virally transformed and phytohaemagglutinin (PHA)-stimulated human lymphocytes. The induction of sister chromatid exchanges was potentiated by addition of rat liver homogenate. The extract did not induce ouabain-resistant mutation of V79 cells. Extracts of betel nuts and leaves gave negative results in assay of morphological transformation, sister chromatid exchange and mutagenesis.

Higher efficiency of hamster hepatocytes than rat hepatocytes for detecting dimethylnitrosamine and diethylnitrosamine in hepatocyte-mediated Chinese hamster V79 cell mutagenesis assay.

The mutagenicities of dimethylnitrosamine (DMN) and diethylnitrosamine (DEN) on Chinese hamster V79 cells were examined by cocultivation of the cells with primary cultures of rat hepatocytes or hamster hepatocytes. Mutations in V79 cells were selected by resistance to ouabain. The mutation frequencies induced by all doses of DMN (1, 5, 10 and 50 micrograms/ml) and DEN (10, 50, 100 and 500 g/ml) were substantially higher on cocultivation with hamster hepatocytes than with rat hepatocytes. Thus it is proposed that hamster hepatocytes are useful for detecting mutagenesis in V79 cells induced by nitrosamines.

In vitro transformation of hamster chondrocytes by 4-nitroquinoline 1-oxide

Hamster sternal chondrocytes were transfored morphologically in vitro 29-51 days after exposure to 4-nitroquinoline 1-oxide for 3 h. The transformed chondrocytes were randomly oriented, piled up and grew continuously. These cells produced nodules when transferred to the cheek pouch of a hamster. Histologically, these nodules revealed chondromatous patterns. Untreated cells in the control cultures failed to produce nodules.

In vitro transformation of hamster embryo cells by 3-(N-salicyloyl) amino-1,2,4-triazole

The in vitro carcinogenic activities of 3-(N-salicyloyl)amino-1,2,4-triazole (SAT) and its two components, 3-amino-1,2,4-triazole and phenyl salicylate were examined in a transformation assay with cryopreserved hamster embryo cells. SAT induced morphological transformation at certain doses between 10 microgram/ml and 100 microgram/ml in each of 5 repeated experiments, but gave a negative result in the Salmonella mutation assay. 3-Amino-1,2,4-triazole also induced transformation in 3 repeated experiments. Phenyl salicylate did not induce transformation at any of the doses tested in 3 consecutive experiments.

EPIDERMAL METAPLASIA OF THE CORNEAL ANTERIOR EPITHELIUM IN THE CHICK EMBRYO

The corneal anterior epithelium of younger chick embryos can be changed into a keratinized epidermis, when it is cultured in vitro combined with 6 1/2‐day dorsal dermis. Even if a Millipore filter is inserted between the corneal anterior epithelium and underlying dorsal dermis, the epithelium undergoes similar metaplastic changes. In older embryos, however, the epithelium gradually loses the competence for the keratinization. Cultivation of cornea (anterior epithelium, stroma and endothelium) of 6 1/2‐ or 10‐day embryos results in maintenance of its original pattern, and the epithelium fails to differentiate into a keratinized epidermis. The dermis isolated from 8 1/2‐day dorsal or 12 1/2‐day tarsometatarsal skin is not so effective in inducing the epidermal metaplasia. The mesenchyme of 5 1/2‐day proventriculus or 5 1/2‐day gizzard fails to bring about any endodermal metaplasia of the corneal epithelium. The corneal stroma, on the other hand, has no inhibitory action on the keratinization of the epidermis obtained from 6 1/2‐day dorsal skin.

AN ABNORMAL REGENERATION OF HYDRA INDUCED WITH THEOPHYLLINE AND OTHER XANTHINE DERIVATIVES

Morphogenesis, the mode of pattern formation, is one of the major problems in develop mental biology, as is differentiation, which involves the structural and functional specialization of individual cells. Hydra, a fresh-water coelenterate, offers a convenient experimental model for studying pattern formation, as the animal has several characteristic properties; a relatively simple from, a remarkable regenerative ability, and a rigid polarity. If a piece is cut from the gastric region of a hydra,distal structures(hyp0stome and tentacles) always regenerate from its distal end, while proximal structures (peduncle and basal disc) are formed from its proximal end, so that the original polarity is maintained (Fig.1). However, when