There is convincing evidence that cellular prooxidant states--that is, increased concentrations of active oxygen and organic peroxides and radicals--can promote initiated cells to neoplastic growth. Prooxidant states can be caused by different classes of agents, including hyperbaric oxygen, radiation, xenobiotic metabolites and Fenton-type reagents, modulators of the cytochrome P-450 electron-transport chain, peroxisome proliferators, inhibitors of the antioxidant defense, and membrane-active agents. Many of these agents are promoters or complete carcinogens. They cause chromosomal damage by indirect action, but the role of this damage in carcinogenesis remains unclear. Prooxidant states can be prevented or suppressed by the enzymes of the cellular antioxidant defense and low molecular weight scavenger molecules, and many antioxidants are antipromoters and anticarcinogens. Finally, prooxidant states may modulate the expression of a family of prooxidant genes, which are related to cell growth and differentiation, by inducing alterations in DNA structure or by epigenetic mechanisms, for example, by polyadenosine diphosphate-ribosylation of chromosomal proteins.

Our data show that one ROI species, H2O2 acts as a messenger in the TNF- and okadaic acid-induced post-translational activation of NF-kappa B. Superoxide is only indirectly involved, as a source for H2O2. These data explain the inhibitory effects of many antioxidative compounds on the activation of NF-kappa B and its target genes. H2O2 is overproduced in response to various stimuli, and normal levels of catalase appear insufficient to remove it completely. H2O2 can therefore accumulate and act as an intracellular messenger molecule in the response to pathogens.

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Hepatoceliular carcinoma (HCC) represents a major cause of mortality in certain areas ofthe world. Contamination offood with the mycotoxin aflatoxin B1 (AFB1) has been implicated as an etiological factor in certain regions of eastern Asia and subSaharan Africa (1, 2). Indeed, recent studies suggest that hepatitis B virus and AFB1 may exert a synergistic effect (3). Approximately 50%6 of HCC in high AFB1 regions (4, 5), but only 20%o in low AFB1 regions, harbors mutations in the p53 tumor suppressor gene, and the spectrum of mutations is quite different (6, 7). More than half of the tumors from high AFB1 regions contain G --T transversions in the third position of codon 249 (AGG), resulting in the replacement of arginine by serine (4-8). In contrast, mutations are distributed throughout the highly conserved domains IV and V of p53 in HCC from low AFB1 regions and no prevalence of G --T transversions is observed (9, 10). These results indicate that the substitution of arginine 249 by serine in the p53 protein is not required for hepatocarcinogenesis in man. Though G --T transversions are in agreement with the mutational specificity of AFB1 (11, 12) and other carcinogens forming bulky DNA adducts (13,14), there is no convincing explanation for the prevalence of mutations in codon 249, which almost never harbors mutations in other forms of human cancer. Many factors determine the mutability of a particular gene sequence, in addition to the chemical properties of the ultimate mutagen, and it is difficult to predict on the basis of model experiments. Among them, sequence context, local DNA conformation, chromatin structure, transcriptional activity, and repairability are recognized to play a role. Therefore, we have directly evaluated the mutability to The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.AFB1 of codons 247-250 in human hepatocarcinoma cells HepG2 by genotypic analysis using Msp I and Hae III restriction fragment length polymorphism/polymerase chain reaction (RFLP/PCR) (15-17). Our results indicate that AFB1 induces the transversion of G --T in the third position of codon 249, with the highest frequency producing the same mutation that is found almost exclusively in HCC from high AFB1 regions in east Asia and Africa. Our results support the notion that AFB1 represents a causative carcinogen in hepatocarcinogenesis in these regions of the world. MATERIALS AND METHODSHepG2 human hepatocarcinoma cells were grown in minimum essential medium supplemented with 10% fetal calf serum to =60% confluency before treatment for 30 min with AFB1 (0.5 ug/ml) in the presence of rat liver microsomes as described (18)(19)(20). The medium was replaced and cell growth continued for 0 hr or for 96 hr, respectively. Despite AFB1 treatment, the cell number doubled within 96 hr. Control cultures were sham-treated only with rat liver microsomes.

Oxidants are toxic, but at low doses they can stimulate rather than inhibit the growth of mammalian cells and play a role in the etiology of cancer and fibrosis. The effect of oxidants on cells is modulated by multiple interacting antioxidant defense systems. We have studied the individual roles and the interaction of Cu,Zn-superoxide dismutase (SOD) and catalase (CAT) in transfectants with human cDNAs of mouse epidermal cells JB6 clone 41. Since only moderate increases in these enzymes are physiologically meaningful, we chose the following five clones for in-depth characterization: CAT 4 and CAT 12 with 2.6-fold and 4.2-fold increased catalase activities, respectively, SOD 15 and SOD 3 with 2.3-fold and 3.6-fold increased Cu,Zn-SOD activities, respectively, and SOCAT 3 with a 3-fold higher catalase activity and 1.7-fold higher Cu,Zn-SOD activity than the parent JB6 clone 41. While the increases in enzyme activities were moderate, the human cDNAs were highly expressed in the transfectants. As demonstrated for the clone SOD 15, this discordance between message concentrations and enzyme activities may be due to the low stability of the human Cu,Zn-SOD mRNA in the mouse recipient cells. According to immunoblots the content of Mn-SOD was unaltered in the transfectants. While the activities of glutathione peroxidase were comparable in all strains, the concentrations of reduced glutathione (GSH) were significantly lower in SOD 3 and SOD 15. This decrease in GSH may reflect a chronic prooxidant state in these Cu,Zn-SOD overproducers.(ABSTRACT TRUNCATED AT 250 WORDS)