The major mutagenic base lesion in DNA caused by exposure to reactive oxygen species is 8-hydroxyguanine or 7,8-dihydro-8-oxoguanine (8-OH-G). Products of the human MMH͞OGG1 gene are known to catalyze in vitro the reactions repairing this DNA lesion. To analyze the function of Mmh in vivo, we generated a mouse line carrying a mutant Mmh allele by targeted gene disruption. Mmh homozygous mutant mice were found to have a physically normal appearance, but to have lost nicking activity in liver extracts for substrate DNA containing 8-OH-G, exhibiting a 3-fold increased accumulation of this adduct at 9 weeks of age compared with wild-type or heterozygous mice. Further elevation to 7-fold was observed in 14-week-old animals. Substantial increase of spontaneous mutation frequencies was clearly identified in Mmh mutant mice bearing transgenic gpt genes. These results indicate that exposure of DNA to endogenous oxidative species continuously produces the mutagenic adduct 8-OH-G in mice, and Mmh plays an essential role in repair of this DNA damage.

BACKGROUND. An anomalous junction of the pancreaticobiliary duct (AJPBD) was thought to be an important risk factor for gallbladder carcinoma in Japan. In this report, we compared K-rus and p53 mutations in Stage I gallbladder carcinomas (GC) of patients with AJPBD with those in patients without AJPBD. METHODS. We examined 6 GC of patients with AJPBD and 20 GC of patients without AJPBD. lmmunohistochemistry was performed for p53 protein. K-rus and p53 mutations were examined using genomic DNA extracted from the cancer regions. The methods of polymerase chain reaction (PCR) single strand conformation polymor-phism analysis were performed for mutations in exons 5-8 of p53. The methods of PCR restriction fragment length polymorphism were performed for mutation in codon 12 of K-ras. RESULTS. p53 positivity was 67% in GC of patients with AJPBD and 65% in GC of patients without AJPBD. p53 mutations were found in exons 7 and 8 in GC of patients with AJPBD and in exons 5, 6, and 7 in GC of patients without AJPBD. The incidence of K-rus mutation in GC of patients with AJPBD (50%) was greater than that in patients without AJPBD (6%) iP < 0.05). CONCLUSIONS. These results suggest that K-rczs mutation may be important in the early stage of carcinogenesis of the gallbladder mucosa with AJPBD, and that p53 mutations may also contribute to the early stage of carcinogenesis of the gallblad-der mucosa, regardless of AJPBD.

The decomposition processes of alkali or alkaline earth carbonates with a large excess of carbon, and the reverse Boudouard reaction given by over metal carbonates, were compared. The carbonates of CO 2 /C ] 2CO Li`, Na`, K`, Cs`, Sr2`and Ba2`generated CO exclusively by an intermolecular redox reaction given byThe reverse Boudouard reaction over these metal carbonates at 700 ¡C proceeded CO 3 2~] C ] 2CO ] O2~. at a steady rate until just before the carbon was completely consumed, and in the cases of Li`, Sr2`and Ba2`, the rates agreed with the initial rates of the intermolecular redox reaction. On the other hand, the rates over the carbonates of Na`, K`and Cs`, the oxides of which undergo a disproportionation reaction to produce gas-phase metal and liquid-phase metal peroxide, were much higher than the initial rates of the intermolecular redox reaction. This discrepancy can be explained by the presence of a catalytic process on the metal-covered surface of the silica wool that was used for preventing the highly basic gas-phase metals from escaping.

Cyclooxygenase (COX)-2, one enzyme isoform responsible for producing prostanoids from arachidonic acid, contributes to colon carcinogenesis. Recently, genetic disruption of COX-1, the other isoform, was shown to decrease the number of intestinal polyps and prostaglandin E(2) levels in intestinal mucosa, like the case with COX-2 gene disruption, in Min mice. We therefore investigated whether a COX-1 selective inhibitor, mofezolac, suppresses intestinal carcinogenesis in rodents. F344 male rats, receiving azoxymethane (AOM, 15 mg/kg body wt) s.c. injections at 5 and 6 weeks of age, were fed a diet containing 600 or 1200 p.p.m. mofezolac for 4 weeks. The number of aberrant crypt foci (ACFs) per rat and the bromodeoxyuridine labeling index of the crypt epithelium were dose-dependently decreased by administration of mofezolac, the value for the former at 1200 p.p.m. being 60% of control value. When Apc gene knockout mice (APC1309 mice) were given 600 or 1200 p.p.m. mofezolac in their diet for 8 weeks, the numbers of intestinal polyps were also dose-dependently decreased, with reduction to 59% of that in the control diet group at the higher dose. Nimesulide, a COX-2 selective inhibitor used as positive control, showed similar suppressive effects on the development of ACFs in AOM-treated rats and polyps in Apc gene knockout mice. The data indicate that both COX-1 and COX-2 can contribute to intestinal tumorigenesis.