Shozo Takayama

Carcinogenicities of heterocyclic amines in cooked food.

Mutagenic heterocyclic amines in cooked foods were carcinogenic to mice, rats and/or monkeys, when they were given orally continuously. The most common target organ was the liver, but in CDF1 mice lung tumors, forestomach tumors, lymphomas/leukemias, and blood vessel tumors in the brown adipose tissues were also induced. In F344 rats, in addition to liver tumors, tumors in the Zymbal gland, skin, clitoral gland, small and large intestines, oral cavity, and mammary gland were also induced. Monkeys given IQ developed metastatic hepatocellular carcinomas.

Induction of lymphoma in CDF1 mice by the food mutagen, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine.

The mutagenic compound, 2‐amino‐l‐methyl‐6‐phenylimidazo[4,5‐b]pyridine (PhIP), originally isolated from cooked beef, was tested for carcinogenicity in CDF1 mice of both sexes. When PhIP was given in the diet at a concentration of 0.04%, high incidences and early appearances of lymphomas were observed in both sexes during the 579‐day experiment.

A two-stage mouse skin carcinogenesis study of lyngbyatoxin A

SummaryA strong skin irritant, lyngbyatoxin A, isolated from the marine blue-green alga Lyngbya majuscula is structurally related to teleocidin. Since lyngbyatoxin A statisfied our short-term screening tests for possible tumor promoters, viz. irritation of mouse ear, induction of ornithine decarboxylase (ODC) in mouse skin, and adhesion of human promyelocytic leukemia cells (HL-60), a two-stage carcinogenesis experiment was carried out. Tumor incidences in the groups treated with 7,12-dimethylbenz(a)anthracene (DMBA) plus lyngbyatoxin A and with DMBA plus 12-O-tetradecanoylphorbol-13-acetate (TPA) were 86.7% and 93.3% in week 30, respectively. The average number of tumors per mouse was 3.7 in the former group and 10.5 in the latter group. This paper reports for the first time the potent tumor-promoting activity of lyngbyatoxin A and also the histological examination of tumors.

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).

Sulfate conjugation of benzo[a]pyrene metabolites and derivatives

Abstract Sulfate conjugation of benzo[a]pyrene(BP) metabolites and derivatives was studied. The reaction sequence consisted of two steps; activation of sulfate ion to 3′-phosphoadenosine-5′-phosphosulfate and transfer of the activated sulfate to the BP-derivatives. Both reactions were carried out by enzymes located in the rat liver 105 000 g supernatant. The reactions required MgCl2. Phenol and quinone derivatives were generally good substrates for sulfate conjugation and different reactivities were observed with the dihydrodiol derivatives. Sulfate conjugates were more polar than their parent BP-derivatives and except for quinone conjugates were easily extracted with ethyl acetate. The role of sulfate conjugation in BP carcinogenesis is discussed.

Induction of enzyme-altered islands in rat liver by tryptophan pyrolysis products.

SummaryTwo new γ-carboline derivatives, 3-amino-1,4-dimethyl-5H pyrido[4,3-b]indole (Trp-P-1) and 3-amino-1-methyl-5H pyrido[4,3-b]indole (Trp-P-2), isolated from the pyrolysis products of tryptophan, were found to be potent mutagens. When weanling rats were injected with Trp-P-1 and then given diet containing phenobarbital, they developed enzyme-altered islands in the liver. Since these islands are considered to be formed by immediate progeny of “initiated cells” and cell precursors in hepatocarcinogenesis, Trp-P-1 may well be carcinogenic in rat liver.

Effects of long-term oral administration of DDT on nonhuman primates

Abstract Because of reports on tumorigenic activity in different animal species exposed to DDT a decision was made in 1969 to evaluate the long-term effects of DDT on 24 cynomolgus and rhesus monkeys. DDT (20 mg/kg) was given in the diet for 130 months, followed by an observation period that ended in 1994. The two cases of malignant tumor detected in the DDT group included a metastatic hepatocellular carcinoma in a 233-month-old male and a well-differentiated adenocarcinoma of the prostate in a 212-month-old monkey. Benign tumors detected in the DDT group included three cases of leiomyoma, two of which were uterine and one, esophageal. No tumor was detected in the control group of 17 monkeys. Fatty changes in the liver were observed in 52.9% of the DDT group and 29.4% of the control group. More specific signs of hepatotoxicity were documented microscopically in seven DDT monkeys. Severe tremors and histological evidence of CNS and spinal cord abnormalities were observed in six DDT monkeys. The present findings show clear evidence of hepatic and CNS toxicity following long-term DDT administration to cynomolgus and rhesus monkeys. However, the two cases involving malignant tumors of different types are inconclusive with respect to a carcinogenic effect of DDT in nonhuman primates.

Activated c-raf gene in a rat hepatocellular carcinoma induced by 2-amino-3-methylimidazo[4,5-f]quinoline

A rat hepatocellular carcinoma, IQ7, induced by 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) gave two transformants of NIH 3T3 cells on DNA mediated gene transfer. One of these transformants was examined further and secondary and tertiary transformants were obtained. The secondary transformant was tumorigenic in nude mice. The activated oncogene in this primary transformant was identified as rat c-raf by Southern blot analysis.

OVARIAN NEOPLASIA IN ORNAMENTAL HYBRID CARP (NISHIKIGOI) IN JAPAN

Massive abdominal enlargements were observed in 21 adult carp 4--6 years old living in the breeding ponds of carp fisheries in northern Japan. The abdominal enlargement rapidly increased, and the affected fish died within a few months. At necropsy, single or multiple tumors, 1.5--25 cm (average, 10.6 cm) in diameter, were found in the abdominal cavity. Ovarian tissue was identified close to the tumors in 15 cases, and there was no evidence of anatomic continuity between the tumors and other viscera. It seems likely that all of these tumors arose in the ovaries. Histologically, the 21 tumors observed exhibited great variation, but they were composed mainly of various types of cells similar to those of human dysgerminoma, granulosatheca cell tumors, or embryonal carcinomas. Squamous cell nests were found with mesenchymal elements in one tumor. Thus, ovarian tumors in carp may have diverse histogenetic origins and probably arise both from germ cells and from ovarian mesenchyme. Areas of cellular pleomorphism, which suggested a malignant character, were seen in some of the tumors, but no evidence on metastasis was found. Tumor-bearing carp had generally been raised in ponds supplied by wells or underground springs in mountainous areas. Evidence of a possible environmental factors(s) is yet to be demonstrated.

Metabolic activation of 3-amino-5H-pyrido[4,3-b]indole, a highly mutagenic principle in tryptophan pyrolysate, by rat liver enzymes

3-Amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2), a mutagenic principle in tryptophan pyrolysates, binds to DNA after metabolic activation by rat liver enzymes. The enzymes for activation of Trp-P-2 were found in both microsomes and the cytosol. The reaction required NADPH and ATP, metabolic and was inhibited by 7,8-benzoflavone. Considerable binding was observed with only microsomes as enzyme source, but further addition of cytosol enhanced the binding, enhancement depending on the amount of cytosol added. Inducers for microsomal mixed-function oxidases induced activating enzyme(s) for Trp-P-2, 3-methylcholanthrene being most effective, followed by polychlorinated biphenyls and then phenobarbital.