Effects of sodium L-ascorbate and related compounds on rat stomach carcinogenesis initiated by N-methyl-N'-nitro-N-nitrosoguanidine

Final Report on the Safety Assessment of Ascorbyl Palmitate, Ascorbyl Dipalmitate, Ascorbyl Stearate, Erythorbic Acid, and sodium Erythorbate

Ascorbyl Palmitate, Ascorbyl Dipalmitate, Ascorbyl Stearate, Erythorbic Acid, and Sodium Erythorbate are related ingredients that function as antioxidants in cosmetic formulations. Ascorbyl Palmitate, Ascorbyl Dipalmitate, and Ascorbyl Stearate are esters and diesters of ascorbic acid with long-chain fatty acids. Erythorbic Acid is a stereoisomer of ascorbic acid and Sodium Erythorbate is the sodium salt of Erythorbic Acid. Although all of these ingredients are used, uses of Ascorbyl Palmitate and Erythorbic Acid predominate, with combined uses in over a thousand cosmetic formulations at low concentrations. Ascorbyl Palmitate is used at concentrations between 0.01 and 0.2% , and Erythorbic Acid is used at concentrations of 0.5-1% . Ascorbyl Palmitate has vitamin C activity approximately equal to that of L-ascorbic acid, whereas Erythorbic Acid has only 5% activity. The esters are likely to penetrate the skin readily, but the acid and its salt are not likely to penetrate. These ingredients exhibit low acute oral toxicity in animals. In chronic feeding studies, decreased body weight gain, the formation of oxalate stones in the bladder, and hyperplasia were seen in rats fed high levels of Ascorbyl Palmitate. Ascorbyl Palmitate (10%) and Ascorbyl Dipalmitate (100%) were not irritating to the intact skin of albino rabbits. Ascorbic Acid (30 % ) itself caused barely perceptible erythema and Sodium Erythorbate powder caused no irritation to the intact and abraded skin of rabbits. In animal studies, Ascorbic acid was not a sensitizer, and Erythorbic Acid (10%) applied topically to porcine skin reduced ultraviolet B (UVB)-induced phototoxicity. In clinical studies, Ascorbyl Palmitate caused no dermal irritation or sensitization. These ingredients are minimally irritating to the eye. Sodium Erythorbate did not cause fetal or maternal toxicity or developmental toxicity in rats and mice fed high levels. Although these ingredients were generally negative in a wide range of genotoxicity tests, Erythorbic Acid and Sodium Erythorbate did produce isolated positive genotoxicity test results. As antioxidants, these ingredients have been studied in animals after initiation with various carcinogens. In some cases reductions in tumor incidence were seen, in others no effect was noted. In no case did treatment with these ingredients increase tumor incidence. The highest use concentrations of Erythorbic Acid and Sodium Erythorbate are in oxidative hair dyes, where they are completely consumed in the chemical reaction that takes place at mixing. The fatty acid esters of ascorbic acid are used at lower concentrations in leave-on formulations. In consideration of these uses and based on the available safety test data, Ascorbyl Palmitate, Ascorbyl Dipalmitate, Ascorbyl Stearate, Erythorbic Acid, and Sodium Erythorbate are safe for use as cosmetic ingredients in the present practices of use.

Nutrition and gastric cancer risk: an update

Data from epidemiologic, experimental, and animal studies indicate that diet plays an important role in the etiology of gastric cancer. High intake of fresh fruits and vegetables, lycopene and lycopene-containing food products, and potentially vitamin C and selenium may reduce the risk for gastric cancer. Data also suggest that high intake of nitrosamines, processed meat products, salt and salted foods, and overweight and obesity are associated with increased risk for gastric cancer. However, current data provide little support for an association of beta-carotene, vitamin E, and alcohol consumption with risk for gastric cancer.

The role of ascorbic acid in oral cancer and carcinogenesis

L-ascorbic acid is an essential dietary vitamin in humans, primates and certain mammals and is endogenously synthesised in some species. Epidemiological and ecological studies have shown that L-ascorbic acid has a protective effect against cancer, in particular non-hormone-dependent malignancies, such as oropharyngeal neoplasms. Experimental in vivo and in vitro studies, however, have yielded more controversial results, suggesting that the effects of L-ascorbic acid are dose- and perhaps, time-dependent with different effects depending on the species or organ studied. An update of the epidemiological and experimental evidence linking L-ascorbic acid to oral cancer and carcinogenesis is discussed together with a brief review of the possible mechanisms of action of L-ascorbic acid.

Ascorbic acid and gastrointestinal cancer

A literature review was made to critically evaluate the ability of ascorbic acid to modulate the incidence of gastrointestinal cancer. A comparison of preclinical, clinical, and epidemiological studies indicated that evidence for ascorbic acid as an inhibitor of carcinogenesis is stronger with regard to gastric cancer and weaker with regard to esophageal and colon/rectal cancer. Insufficient evidence currently exists regarding the oral cavity and the use of ascorbic acid in precancerous conditions such as polyposis and leukoplakia.

Modifying effects of various chemicals on tumor development in a rat wide-spectrum organ carcinogenesis model

The efficacy of a wide-spectrum organ carcinogenesis model for detection of modification potential of exogenous agents was investigated in F344 male rats. Groups of animals were sequentially injected with N-bis(2-hydroxypropyl)nitrosamine (1000 mg/kg body weight, i.p., in saline, twice in week 1), N-ethyl-N-hydroxyethylnitrosamine (1500 mg/kg body weight, i.g., in distilled water, twice in week 2) and 3,2'-dimethyl-4-aminobiphenyl (75 mg/kg body weight, s.c., in corn oil, twice in week 3) for wide-spectrum initiation of target organs and then given one of 10 test chemicals, comprising 6 hepatocarcinogens and 4 non-hepatocarcinogens, for 12 weeks. All 10 chemicals exerted modifying effects in their respective target organs. Enhancing influence could be detected in the liver and urinary bladder with 2-acetylaminofluorene, ethionine, and 3'-methyl-4-dimethylaminoazobenzene; in the liver and thyroid with 4,4'-diaminodiphenylmethane and phenobarbital; in the esophagus and urinary bladder with N-butyl-N-(4-hydroxybutyl)nitrosamine; in the forestomach and urinary bladder with butylated hydroxyanisole; in the liver with 7,12-dimethylbenz[a]anthracene and in the liver and lung with 3-methylcholanthrene. Inhibitory effects on development of glutathione S-transferase placental form-positive liver cell foci were observed with clofibrate. The results indicate that the present model can be reliably utilized as a whole body medium-term bioassay system for assessment of environmental cancer modifiers.

Effects of various bile acids and their sodium salts on development of pepsinogen-altered pyloric glands in rats

Effects of dietary bile acids and their sodium salts on the development of pepsinogen-altered pyloric glands (PAPG) were examined in male WKY/N Crj rats initially given a single dose of 160 mg/kg body weight of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) by gastric intubation. From week 3 the animals were administered basal diet containing 0.5% supplements of cholic acid (CA), deoxycholic acid (DCA), chenodeoxycholic acid (CDCA) or their sodium salts (Na-C, Na-DC and Na-CDC), or 5% ascorbic acid (ASA) or its salt (Na-AS) for 18 weeks. The concentration of DCA and Na-DC was reduced to 0.3% from week 12. At week 20, animals were killed and the numbers of immunohistochemically-demonstrated PAPG were determined. Values were significantly higher with Na-C and Na-CDC than with the corresponding parent acids, and in the Na-C case PAPG development was greater than with MNNG alone. In addition, Na-CDC itself induced the numbers of PAPG significantly. These results suggest that bile salts are possible intrinsic promoters of gastric carcinogenesis. They were without effect, however, on forestomach lesions.

Enhancing potential of 6 different carcinogens on multi-organ tumorigenesis after initial treatment with N-methyl-N-nitrosourea in rats

The advantages of applying a whole-body concept to the assessment of carcinogenic potential of compounds in a two-stage model after initiation by N-methyl-N-nitrosourea (MNU) were investigated. Male, 6-week-old F344 rats were injected with MNU (20 mg/kg, i.p.) twice a week for 4 weeks and they then received 3,2'-dimethyl-4-aminobiphenyl (DMAB) (50 mg/kg, s.c., once a week), N,N'-dibutylnitrosamine (DBN) (0.05%, in drinking water), N-bis(2-hydroxypropyl)nitrosamine (DHPN) (0.1%, in drinking water), diethylstilbestrol (DES) (2.5 ppm, in diet), sodium o-phenylphenate (S.OPP) (2%, in diet) or captafol (0.15%, in diet) for 20 weeks. All six carcinogens enhanced the incidences of preneoplastic and neoplastic lesions in their respective target organs: liver, pancreas, small intestine and urinary bladder with DMAB; liver, esophagus, forestomach and urinary bladder with DBN; thyroid, lung, liver, esophagus, forestomach, small intestine and urinary bladder with DHPN; liver and forestomach with DES; and thyroid, forestomach, kidney and urinary bladder with S.OPP; liver and forestomach with captafol. The results suggested that prior treatment with MNU sensitized the tissues to the organotropic carcinogenic potential of chemicals given thereafter for as short a period as 20 weeks. Thus, this system could be utilized as a whole-body medium-term bioassay system for the screening of environmental carcinogens, bridging the gap between in vitro mutagenicity and long-term carcinogenicity tests.

Antioxidants--carcinogenic and chemopreventive properties

Synthetic and naturally occurring antioxidants have a wide variety of biological actions in rodents in addition to their primary antioxidant activity. Some of the included biological effects are of direct interest in relation to studies of carcinogenicity and/or modulation of carcinogenesis. Since the synthetic antioxidant BHA was first found to exert carcinogenic potential in rat and hamster forestomach epithelium, many other synthetic and naturally occurring antioxidants have been examined for their ability to induce proliferative activity in the alimentary canal. These studies have revealed that caffeic acid and sesamol are also tumorigenic for rat forestomach epithelium, whereas catechol and p-methylcatechol induce neoplasia in rat glandular stomach epithelium. Although the proliferative response is very rapid, with inflammation and ulceration, it takes a very long time before carcinomas develop. The proliferative lesions in the forestomach induced by BHA or caffeic acid are largely reversible, in contrast to those induced by genotoxic carcinogens, which generally persist and develop into cancer. Therefore, chronic irritation is considered to be responsible for the induction of stomach cancer by antioxidants. Butylated hydroxyanisole can undergo oxidative metabolism in vitro, and some of the metabolites formed have the potential for binding to proteins. Neither BHA nor its metabolites binds to DNA in vivo, but protein binding in the forestomach was greater than 10 times higher than that in the glandular stomach. It is thus conceivable that BHA is oxidatively metabolized in the forestomach epithelium (possibly entering into redox cycling), and reactive metabolites including semiquinone radicals or active oxygen species are responsible for the carcinogenesis by a mechanism involving binding to macromolecules. Many antioxidants have been shown to modify carcinogenesis, and as a rule, they inhibit the initiation stage by reducing the interaction between carcinogen and DNA. However, both promotion and inhibition have been reported for second-stage carcinogenesis, depending on the organ site, species of animal, or initiating carcinogen. They can also block reaction of amine and nitrite to form nitrosamines or reduce TPA promotion of skin carcinogenesis. Generally high doses of antioxidants are required for carcinoma induction or modification of chemical carcinogenesis. The significance of the reported tumorigenicity and strong promoting activity of antioxidants for forestomach epithelium of animals to the development of human cancer appears limited mainly because humans do not have a forestomach. The carcinogenic and strong promoting activities of catechol and its structurally related compounds on rat glandular stomach epithelium are of greater concern because this tissue is directly analogous to human gastric epithelium.(ABSTRACT TRUNCATED AT 400 WORDS)

Forestomach carcinogens: possible mechanisms of action

A brief review indicates that a considerable number of compounds induce forestomach tumours in different species. Naturally occurring forestomach tumours are rare (an incidence of less than 1%) in rats and mice, but they do occur in hamsters with incidences up to 12%. Most forestomach carcinogens are known to be genotoxic, although a few non-genotoxic substances are also able to induce this type of tumour. The promoting and inhibiting action of substances in a two-stage forestomach tumour model is described. Morphologically the development of tumours is characterized by early lesions such as epithelial damage, hyperplasia and hyperkeratosis, which at a later stage progress to strong diffuse hyperplasia, dysplasia, papilloma and squamous-cell carcinoma. Possible mechanisms of action of non-genotoxic forestomach carcinogens are described, and the relevance to man is discussed. Since humans have no squamous epithelium in the stomach, the potential risk from non-genotoxic forestomach carcinogens involves exposure of the mouth, pharynx and oesophagus at dose levels that exert irritating action. It seems very unlikely that exposure to concentrations far below those having irritating potential is hazardous to man.