Concentration dependent promoting effects of sodium L-ascorbate with the same total dose in a rat two-stage urinary bladder carcinogenesis

Clinical efficacy and safety of oral and intravenous vitamin C use in patients with malignant diseases

Background

Vitamin C, also called ascorbic acid, is a water-soluble antioxidant and free radical scavenger. It is required in the body for numerous metabolic functions and is involved in the development of proteins and connective tissue.

Methods

In April 2020, a systematic search was carried out on five electronic databases (Medline, Embase, Cochrane, Cinahl, PsycINFO) to find studies on the use, efficacy and safety of a complementary therapy with vitamin C in oncological patients.

Results

Out of the initial 23,195 search results, 21 studies with 1961 patients were included in this review. Five of the included studies (n = 417) were randomized controlled trials (RCTs). The remaining 16 studies belonged to a lower class of evidence. The patients who were treated with vitamin C suffered from various malignant diseases, some in an advanced and palliative stage. Vitamin C was applied intravenously or orally. It was either the only treatment or was combined with chemo- or radiotherapy. Endpoints included the development of the disease-related symptoms, quality of life, mortality, progression-free survival and safety of vitamin C. The studies were of moderate quality and showed either no effect of vitamin C or a positive trend, although this has rarely been statistically proven in group comparisons. No or only slight side effects with both oral and intravenous administration of vitamin C were reported.

Conclusion

Oral intake of vitamin C does not appear to have any effect in patients with malignancies. Data are heterogeneous for intravenous administration. There are no RCTs with statistical group comparisons.

Lack of urinary bladder carcinogenicity of sodium L-ascorbate in human c-Ha-ras proto-oncogene transgenic rats

Sodium L-ascorbate (Na-AsA) is widely known to be a tumor promoter of rat bladder carcinogenesis but tests negative in standard 2-year bioassays. In the present study, bladder-cancer-susceptible transgenic rats designated Hras128 were used to further examine the tumorigenicity of Na-AsA. A total of 40 7-week-old male transgenic (Tg) and 42 littermate nontransgenic (Non-tg) rats were divided into 4 groups and given powdered MF diet with or without 5% Na-AsA for 57 weeks. Tg rats showed significantly short survival compared with Non-tg, independent of Na-AsA treatment. Tg rats treated with Na-AsA showed a slightly higher incidence of carcinoma (29.6%) as compared to those without Na-AsA treatment (15.4%), but this was without statistical significance. Moreover, the total bladder tumor incidences, including papillomas, did not differ statistically (with Na-AsA, 37.0%; without Na-AsA, 30.8%). No bladder tumor was detected in Non-tg rats. Various kinds of other lesions in various organs were noted in Tg rats treated with or without Na-AsA treatment, but no intergroup differences were evident. In conclusion, Na-AsA did not show tumorigenicity in highly bladder-cancer-susceptible transgenic Hras128 rats. These results suggest that Na-AsA is a pure promoter but not a complete carcinogen in rats.

Skin tumor promotion by Vitamin E in mice: amplification by ionizing radiation and Vitamin C

We have shown previously that Vitamin E acts as a tumor promoter in 7,12-dimethylbenz(a)anthracene (DMBA) initiated mouse skin. We now show that high concentrations (80 micromol) of Vitamin E are required for promotion, and that 10-fold lower concentrations do not promote tumor formation. The same high concentration of the water-soluble anti-oxidant Vitamin C did not act as a tumor promoter, but did amplify the promoting effect of high, but not low, concentrations of Vitamin E. Oxidizing free radicals generated by beta-radiation exposure of the skin at the time of Vitamin E treatment also enhanced promotion by high (but not low) concentrations of Vitamin E. The results are consistent with a process whereby tumor promotion by the lipid-soluble Vitamin E occurs as a result of alpha-tocopherol acting as a free radical scavenger, with the formation and subsequent transfer of the alpha-tocopherol free radical center to the surrounding lipids, resulting in lipid oxidations.

Induction of transitional cell hyperplasia in the urinary bladder and aberrant crypt foci in the colon of rats treated with individual and a mixture of drinking water disinfection by-products

Cancer of the urinary bladder and colon are significant human health concerns. Epidemiological studies have suggested a correlation between these cancers and the chronic consumption of chlorinated surface water containing disinfection by-products (DBPs). The present study was designed to determine if exposure to DBPs would cause preneoplastic or neoplastic lesions in the urinary bladder and colon of rats, and what effect a mixture of DBPs would have on these lesions. Male and female Eker rats were treated via drinking water with low and high concentrations of potassium bromate, 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX), chloroform, or bromodichloromethane individually or in a mixture for 10 months. The urinary bladders and colons were examined for the presence of preneoplastic lesions. Cell proliferation in the urothelium was examined using immunohistochemical staining for bromodeoxyuridine. Aberrant crypt foci (ACF), as well as the number of individual crypts in each ACF, were identified and counted microscopically after staining with 0.2% methylene blue. Colon crypt cell proliferation and mitotic index were determined using immunohistochemical staining for proliferating cell nuclear antigen. Labeling indexes for the urinary bladder and colon were calculated based on the percentage of positively labeled cells. Treatment with the high dose of MX caused transitional epithelial hyperplasia and cell proliferation in the rat urinary bladder, and this effect was diminished in the high dose mixture animals. Treatment with 4 individual DBPs, as well as a mixture of them, caused the development of ACF, the putative preneoplastic lesion of colon cancer.

Beneficial and adverse effects of chemopreventive agents

The beneficial and adverse effects of some chemopreventive agents, such as Vitamins A, C, E, beta-carotene, indole-3-carbinol, capsaicin, garlic, and aloe are reviewed. Two large randomized trials with a lung cancer endpoint, the Alpha-Tocopherol, Beta-Carotene (ATBC) Prevention Study and the Beta-Carotene and Retinol Efficacy Trial (CARET), suggested that antioxidants might be harmful in smokers. However, the results of the Linxian study and of the ATBC or the CARET studies were significantly different in this respect, and therefore, the relationship between antioxidant and carcinogenesis remains open to debate. Indole-3-carbinol has cancer promoting activities in the colon, thyroid, pancreas, and liver, whereas capsaicin alters the metabolism of chemical carcinogens and may promote carcinogenesis at high doses. Organosulfur compounds and selenium from garlic have no or a little enhancing effect on cancer promotion stage. Information upon chemopreventive mechanisms that inhibit carcinogenesis is imperfect, although the causes and natures of certain human cancers are known. Therefore, definitive preventive guidelines should be carefully offered for various types of tumors, which properly consider ethnic variations, and the efficacies and the safety of chemopreventive agents.