Expressions of some molecular cancer risk factors and their modification by vitamins

The role of vitamin E in the prevention of cancer: a meta-analysis of randomized controlled trials

BACKGROUND

There are conflicting results in published randomized controlled trials (RCTs) on the role of vitamin E in the prevention of cancer. We conducted a meta-analysis of RCTs to evaluate the role of vitamin E in the prevention of cancer in adults.

METHODS

We included RCTs in which the outcomes of the intake of vitamin E supplement alone or with other supplements were compared to a control group. The primary outcomes were total mortality, cancer mortality, total incidence of cancer, and incidence of lung, stomach, esophageal, pancreatic, prostate, breast and thyroid cancers. All identified trials were reviewed independently by the two reviewers to determine whether trials should be included or excluded. The quality of all included studies was scored independently by the two reviewers.

RESULTS

Twelve studies, which included 167025 participants, met the inclusion criteria. There were no statistically significant differences in total mortality (relative risk, 0.99; 95% CI, 0.96-1.03) among the different groups of patients included in this meta-analysis. Vitamin E was associated with a significant reduction in the incidence of prostate cancer (relative risk, 0.85; 95% CI, 0.73-0.96, number needed to treat=500), but it did not reduce the incidence of any other types of cancer.

CONCLUSIONS

Vitamin E supplementation was not associated with a reduction in total mortality, cancer incidence, or cancer mortality, but it was associated with a statistically significant reduction in the incidence of prostate cancer. Vitamin E can be used in the prevention of prostate cancer in men who are at high risk of prostate cancer.

Effects of the antioxidative vitamins A, C and E on liver metastasis and intrametastatic lipid peroxidation in BOP-induced pancreatic cancer in Syrian hamsters

BACKGROUND/AIMS

Antioxidative vitamins are known to inhibit metastasis. Therefore we evaluated the impact of vitamins A (retinol), C (ascorbic acid) and E (alpha-tocopherol) on liver metastasis in a model of ductal pancreatic adenocarcinoma in hamster.

METHODS

One hundred and twenty male Syrian hamsters were randomized into 8 groups (Gr.) (n = 15). Gr. 1-4 were given 0.5 ml normal saline subcutaneously (s.c.) weekly, whereas Gr. 5-8 received 10 mg N-nitrosobis(2-oxopropyl)amine (BOP)/kg body weight s.c. for 3 months for tumor induction. In the 13th week Gr. 2 and 6 were administered retinol, Gr. 3 and 7 received ascorbic acid and Gr. 4 and 8 were given alpha-tocopherol orally. No treatment was performed in Gr. 1 and 5. After 24 weeks animals were sacrificed, pancreas and liver were histologically determined. Activities of glutathione-peroxidase (GSH-Px), superoxide dismutase (SOD) and concentration of thiobarbituric-acid-reactive substances (TBARS) were analyzed in hepatic tissue.

RESULTS

Retinol and alpha-tocopherol decreased the incidence of liver metastases (44.4 vs. 86.7%, p < 0.05). The number and size of liver metastases were significantly reduced by retinol. Activities of GSH-Px and SOD were increased and concentration of TBARS was decreased in NML and LiMe by all vitamins.

CONCLUSION

Obviously, antioxidative vitamins prevent oxidative stress in hepatocytes. This may be one mechanism decreasing liver metastasis in pancreatic cancer in the present trial.

The use of antioxidants with first-line chemotherapy in two cases of ovarian cancer

OBJECTIVE

Because of poor overall survival in advanced ovarian malignancies, patients often turn to alternative therapies despite controversy surrounding their use. Currently, the majority of cancer patients combine some form of complementary and alternative medicine with conventional therapies. Of these therapies, antioxidants, added to chemotherapy, are a frequent choice.

METHODS

For this preliminary report, two patients with advanced epithelial ovarian cancer were studied. One patient had Stage IIIC papillary serous adenocarcinoma, and the other had Stage IIIC mixed papillary serous and seromucinous adenocarcinoma. Both patients were optimally cytoreduced prior to first-line carboplatinum/paclitaxel chemotherapy. Patient 2 had a delay in initiation of chemotherapy secondary to co-morbid conditions and had evidence for progression of disease prior to institution of therapy. Patient 1 began oral high-dose antioxidant therapy during her first month of therapy. This consisted of oral vitamin C, vitamin E, beta-carotene, coenzyme Q-10 and a multivitamin/mineral complex. In addition to the oral antioxidant therapy, patient 1 added parenteral ascorbic acid at a total dose of 60 grams given twice weekly at the end of her chemotherapy and prior to consolidation paclitaxel chemotherapy. Patient 2 added oral antioxidants just prior to beginning chemotherapy, including vitamin C, beta-carotene, vitamin E, coenzyme Q-10 and a multivitamin/mineral complex. Patient 2 received six cycles of paclitaxel/carboplatinum chemotherapy and refused consolidation chemotherapy despite radiographic evidence of persistent disease. Instead, she elected to add intravenous ascorbic acid at 60 grams twice weekly. Both patients gave written consent for the use of their records in this report.

RESULTS

Patient 1 had normalization of her CA-125 after the first cycle of chemotherapy and has remained normal, almost 3(1/2) years after diagnosis. CT scans of the abdomen and pelvis remain without evidence of recurrence. Patient 2 had normalization of her CA-125 after the first cycle of chemotherapy. After her first round of chemotherapy, the patient was noted to have residual disease in the pelvis. She declined further chemotherapy and added intravenous ascorbic acid. There is no evidence for recurrent disease by physical examination, and her CA-125 has remained normal three years after diagnosis.

CONCLUSION

Antioxidants, when added adjunctively, to first-line chemotherapy, may improve the efficacy of chemotherapy and may prove to be safe. A review of four common antioxidants follows. Because of the positive results found in these two patients, a randomized controlled trial is now underway at the University of Kansas Medical Center evaluating safety and efficacy of antioxidants when added to chemotherapy in newly diagnosed ovarian cancer.

Scientific rationale for using high-dose multiple micronutrients as an adjunct to standard and experimental cancer therapies

We have hypothesized that high-dose multiple micronutrients, including antioxidants, as an adjunct to standard (radiation therapy and chemotherapy) or experimental therapy (hyperthermia and immunotherapy), may improve the efficacy of cancer therapy by increasing tumor response and decreasing toxicity. Several in vitro studies and some in vivo investigations support this hypothesis. A second hypothesis is that antioxidants may interfere with the efficacy of radiation therapy and chemotherapy. This hypothesis is based on the concept that antioxidants will destroy free radicals that are generated during therapy, thereby protecting cancer cells against death. None of the published data on the effect of antioxidants in combination with radiation or chemotherapeutic agents on tumor cells supports the second hypothesis. Scientific rationale in support of a micronutrient protocol to be used as an adjunct to standard or experimental cancer therapy is presented.

Influence of antioxidative vitamins A, C and E on lipid peroxidation in BOP-induced pancreatic cancer in Syrian hamsters

Persistent oxidative stress is thought to play an important role in carcinogenesis. Vitamins may influence oxygen radical metabolism and thus inhibit tumor growth. In the present trial the effects of Vitamins (Vit.) A, C and E on neoplastic growth and lipid peroxidation in pancreatic tissue were evaluated on chemically-induced pancreatic adenocarcinoma in the Syrian hamster. The incidence of pancreatic cancer was decreased by Vit. A (64.3%) and Vit. C (71.4%) as compared to the control group (100%, P<0.05). All vitamins increased the activity of superoxidedismutase (SOD) in pancreatic carcinomas. Accumulation of vitamins in tumor cells seems to be responsible for high levels of SOD and consecutive intracellular increase of hydrogen peroxide levels. Since this effect is selectively toxic for tumor cells it might be one of the mechanisms decreasing the incidence of pancreatic cancer in our trial.

Phytochemicals for the prevention of breast and endometrial cancer

Although there is evidence that phytochemicals decrease the incidence of breast and endometrial cancer, many observations are only phenomenologic, and much work needs to be done to explore basic mechanisms and the strategic exploitation of their interactions. The multiplicity of phytochemical actions at different sites in the process of tumorigenesis may eventually lead to the development of a multiagent strategy designed to maximize the complementary effects of different agents. A number of effects with possible relevance to cancer chemoprevention have been excluded from this review, including effects of phytochemicals on the immune response; the question of dietary restriction, which has a profound effect on tumorigenesis; the relatively low methionine levels in some phytochemicals such as soy, which may limit the synthesis of polyamines necessary for tumor growth [151]; and the fact that diets higher in plant products are usually lower in fat and result in leaner individuals with less potential for the synthesis of estradiol in adipose tissue. Also, many studies dealing solely with in vitro mutagenesis were excluded.

Vitamin E (d-alpha-tocopheryl succinate) decreases mitotic accumulation in gamma-irradiated human tumor, but not in normal, cells

Previous studies have shown that treatment of tumor cells in vitro with d-alpha-tocopheryl succinate (alpha-TS), a most effective form of vitamin E, alone or in combination with X-irradiation, reduced the growth of these cells more than that produced by individual agents. However, it is unknown whether alpha-TS, alone or in combination with gamma-irradiation, would produce similar effects on normal cells. To study this, we have compared the effects of alpha-TS on three human tumor cell lines, HeLa (cervical carcinoma), OVGI (ovarian carcinoma), and A549 (lung carcinoma), with the effects on three human normal fibroblast lines, GM2149, AG1522, and HF19. Results showed that alpha-TS treatment of HeLa cells for 20 hours caused inhibition of growth in a dose-dependent manner, but normal human fibroblasts treated similarly with alpha-TS did not show such an effect. alpha-TS treatment for 20 hours also decreased mitotic accumulation in all three tumor cell lines but did not produce such an effect in any of the normal fibroblasts. As expected, gamma-irradiation with 1 Gy decreased mitotic accumulation in human tumor cells and normal fibroblasts; however, alpha-TS treatment for 24 hours before, during, and after irradiation for the entire experimental period further decreased mitotic accumulation in human tumor cells but not in normal cells. These data suggest that effects of alpha-TS, alone or in combination with gamma-irradiation, are selective for tumor cells. Therefore, existing fear that antioxidants such as vitamin E may protect cancer cells from free radical damage during radiation therapy is not justified.

High doses of multiple antioxidant vitamins: essential ingredients in improving the efficacy of standard cancer therapy

Numerous articles and several reviews have been published on the role of antioxidants, and diet and lifestyle modifications in cancer prevention. However, the potential role of these factors in the management of human cancer have been largely ignored. Extensive in vitro studies and limited in vivo studies have revealed that individual antioxidants such as vitamin A (retinoids), vitamin E (primarily alpha-tocopheryl succinate), vitamin C (primarily sodium ascorbate) and carotenoids (primarily polar carotenoids) induce cell differentiation and growth inhibition to various degrees in rodent and human cancer cells by complex mechanisms. The proposed mechanisms for these effects include inhibition of protein kinase C activity, prostaglandin E1-stimulated adenylate cyclase activity, expression of c-myc, H-ras, and a transcription factor (E2F), and induction of transforming growth factor-beta and p21 genes. Furthermore, antioxidant vitamins individually or in combination enhance the growth-inhibitory effects of x-irradiation, chemotherapeutic agents, hyperthermia, and biological response modifiers on tumor cells, primarily in vitro. These vitamins, individually, also reduce the toxicity of several standard tumor therapeutic agents on normal cells. Low fat and high fiber diets can further enhance the efficacy of standard cancer therapeutic agents; the proposed mechanisms for these effects include the production of increased levels of butyric acid and binding of potential mutagens in the gastrointestinal tract by high fiber and reduced levels of growth promoting agents such as prostaglandins, certain fatty acids and estrogen by low fat. We propose, therefore, a working hypothesis that multiple antioxidant vitamin supplements together with diet and lifestyle modifications may improve the efficacy of standard and experimental cancer therapies.

The mutagenic versus protective role of vitamin A on the induction of chromosomal aberration in human lymphocyte cultures

The present study was carried out to evaluate the role of vitamin A (VA) on the induction of chromosomal aberrations (CA) in lymphocyte culture system and to investigate its modulating effect on chromosomal damage induced by gamma irradiation. Lymphocyte cultures from five healthy normal adult males were either treated with VA at a dose level of 2.0, 8.0 or 24.0 microg/ml or exposed to gamma-irradiation of 3.0 Gy, then followed immediately by a treatment with one of the above mentioned doses of VA. Non-treated cultures and cultures exposed to gamma-irradiation served as control for the two sets of experiments. Cultures were set up in duplicates and incubated for 48 h for assessment of CA. Treatment with VA alone increased CA demonstrating a dose-response effect. Addition of VA to gamma-irradiated cultures resulted in an inverse protective effect as the low dose of 2 microg/ml reduced the CA induced by radiation to about 1/3 rd whereas a dose of 8 microg/ml had a protective effect of 40% of the total damage and the large dose of 24 microg/ml had no or little effect. These results suggest that a proportion of the added VA may interfere with the radiation induced free radicals and other reactive metabolites which elevate CA. On the other hand, excessive amounts of VA increased toxicity and reduced effect on repair enzymes.

Cancer prevention studies: past, present, and future directions

In spite of extensive research on vitamins and diet, a consistent beneficial role of vitamin supplements, together with diet modification in human cancer prevention, has not been demonstrated. Published results of human intervention trials with vitamin supplements have been contradictory. This review critically, but briefly, evaluates (a) current concepts of human carcinogenesis, (b) effects of vitamins on biochemical parameters that are pertinent to cancer prevention, and (c) whether past or current protocols for intervention trials among high-risk populations adopt specific scientific rationales that are based on laboratory and human epidemiology studies. In addition, we propose a novel experimental design for intervention trials among high-risk human populations that is based on sound scientific principles derived from laboratory and human epidemiologic data on vitamins, diet, lifestyle, and cancer prevention. Such trials would answer a fundamental public health issue of today: Does supplementation with multiple vitamins, together with diet and lifestyle modifications, reduce the risk of cancer?

Basis and consequences of primary and secondary prevention of gastrointestinal tumors

Carcinomas of the gastrointestinal tract (GI) are among the most common malignancies with regard to their incidence and mortality. Nutritional factors play an important role in the tumor development. The strength of their influence varies with the localization in the GI tract. Epidemiological studies focusing on GI cancer incidence or mortality as an endpoint necessitate large numbers of subjects to achieve significant results. Generally, a low energy and fat intake and a high intake of antioxidative vitamins (vitamin C, E, beta-carotene) and secondary plant metabolites (especially polyphenols) appear to be protective in GI carcinogenesis. Moderate drinking of alcohol and increased consumption of whole grain products, as opposed to highly refined carbohydrates, may help to reduce the risk of colon cancer. The recommended type of diet is low in fat, especially in saturated fatty acids, includes monounsaturated fatty acids, and includes moderate amounts of polyunsaturated fatty acids (no more than 10% of calories). Moderate consumption of salt and of highly salted, smoked, and barbecued foods should be encouraged. Obesity should be avoided by trying to match energy intake with expenditure while increasing physical activity levels. The mechanisms by which nutritional factors act especially on molecular events still remain to be examined. The use of molecular biomarkers will help us better understand cancer development as well as the role and significance of nutritional factors in this process.

Disease heterogeneity: does it impact our ability to detect dietary associations with breast cancer?

It is generally believed that breast cancer is a multistage process and that multiple and varying genetic events occur on the pathway to disease. We hypothesize that disease heterogeneity has an impact on our ability to identify risk factors. If a genetic alteration occurred in 50% of cases and a risk factor was associated only with that specific alteration, a risk estimate of 1.6 would be detected rather than the true risk estimate of 2.5 if analyses had been limited to those cases with the genetic alteration. Based on the literature we know that many genetic alterations occur in less than 50% of breast tumors. Thus, if environmental factors are related to some, but not all genetic alterations, we are decreasing our ability to identify potentially important risk factors. We therefore hypothesize that identification of dietary factors associated with breast cancer has been hampered by our inability to identify and capture the unique disease pathways which exist and contribute to the heterogeneity of common cancers such as breast cancer.

Antioxidant micronutrients and breast cancer

We reviewed epidemiologic evidence on the relationship between four antioxidant micronutrients (vitamin A, vitamin C, vitamin E, and selenium) and breast cancer risk. Available data support a modest protective effect of vitamin A, although more studies are needed to examine further this association and to assess the relative contributions of preformed vitamin A (retinol) and carotenoids. In addition, the possibility that some other component of vitamin A-rich foods may account for this observed association should be explored. Data on the relationship between vitamins C and E and breast cancer risk are limited and inconsistent, and further information is necessary. A substantial body of evidence indicates a lack of any appreciable effect of selenium intake on breast cancer risk, at least within the range of human diets. Future observational studies should ideally be prospective in design, as prospective studies are less prone to selection and recall bias than are case-control studies, and should address methodologic issues such as confounding by other micronutrients and appropriate storage conditions of blood specimens. Although hypotheses relating micronutrient intake to risk of breast cancer should be tested in randomized trials, ethical and logistical constraints make these studies difficult to perform.

A prospective study of the intake of vitamins C, E, and A and the risk of breast cancer

BACKGROUND

Although it has been hypothesized that large intakes of the antioxidant vitamins C, E, and A reduce the risk of breast cancer, few prospective data are available.

METHODS

We prospectively studied 89,494 women who were 34 to 59 years old in 1980 and who did not have cancer. Their intakes of vitamins C, E, and A from foods and supplements were assessed at base line and in 1984 with the use of a validated semiquantitative food-frequency questionnaire.

RESULTS

Breast cancer was diagnosed in 1439 women during eight years of follow-up. After multivariate adjustment for known risk factors, the relative risk among women in the highest quintile group for intake of vitamin C as compared with the risk among those in the lowest quintile group was 1.03 (95 percent confidence interval, 0.87 to 1.21); for vitamin E, after vitamin A intake had been controlled for, the relative risk was 0.99 (95 percent confidence interval, 0.83 to 1.19). In contrast, among women in the highest quintile group for intake of total vitamin A the relative risk was 0.84 (95 percent confidence interval, 0.71 to 0.98; P for trend = 0.001). Among women in the lowest quintile group for intake of vitamin A from food, consumption of vitamin A from supplements was associated with a reduced risk (P = 0.03). The significant inverse association of vitamin A intake with the risk of breast cancer was also found on study of data based on the 1984 questionnaire and four years of follow-up.

CONCLUSIONS

Large intakes of vitamin C or E did not protect women in our study from breast cancer. A low intake of vitamin A may increase the risk of this disease; any benefit of vitamin A supplements may be limited to women with diets low in vitamin A.

Vegetables, fruit, and cancer. II. Mechanisms

The epidemiologic literature on the relationship between vegetable and fruit consumption and human cancer at a variety of sites was reviewed systematically in Part I. It was concluded that consumption of higher levels of vegetables and fruit is associated consistently, although not universally, with a reduced risk of cancer at most sites, and particularly with epithelial cancers of the alimentary and respiratory tracts. Possible mechanisms by which vegetable and fruit intake might alter risk of cancer are addressed here. A large number of potentially anticarcinogenic agents are found in these food sources, including carotenoids, vitamins C and E, selenium, dietary fiber, dithiolthiones, glucosinolates and indoles, isothiocyanates, flavonoids, phenols, protease inhibitors, plant sterols, allium compounds, and limonene. These agents have both complementary and overlapping mechanisms of action, including the induction of detoxification enzymes, inhibition of nitrosamine formation, provision of substrate for formation of antineoplastic agents, dilution and binding of carcinogens in the digestive tract, alteration of hormone metabolism, antioxidant effects, and others. It appears extremely unlikely that any one substance is responsible for all the associations seen. Possible adverse effects of vegetable and fruit consumption are also examined. One way to consider the relationships reviewed here is to hypothesize that humans are adapted to a high intake of plant foods that supply substances crucial to the maintenance of the organism, but only some of which are currently called 'essential nutrients.' Cancer may be the result of reducing the level of intake of foods that are metabolically necessary--it may be a disease of maladaptation.