n-3 PUFA and alpha-tocopherol control of tumor cell proliferation

N-3 Long Chain Fatty Acids Supplementation, Fatty Acids Desaturase Activity, and Colorectal Cancer Risk: A Randomized Controlled Trial

INTRODUCTION

n-3 long-chain polyunsaturated fatty acids (LCPUFA) have anti-inflammatory effects and may reduce colorectal cancer risk. The purpose of this study was to evaluate the effects of n-3 LCPUFA supplementation on markers of rectal cell proliferation and apoptosis and examine how genetic variation in desaturase enzymes might modify this effect.

METHODS

We conducted a randomized, double-blind, control six-month trial of 2.5 grams of n-3 LCPUFA per day compared to olive oil. Study participants had a history of colorectal adenomas. Randomization was stratified based on the gene variant rs174535 in the fatty acid desaturase 1 enzyme (FADS1). Our primary outcome was change in markers of rectal epithelial proliferation and apoptosis.

RESULTS

A total of 141 subjects were randomized. We found no difference in apoptosis markers between participants randomized to n-3 LCPUFA compared to olive oil (P = 0.41). N-3 LCPUFA supplementation increased cell proliferation in the lower colonic crypt compared to olive oil (P = 0.03) however baseline indexes of proliferation were different between the groups at randomization. We found no evidence that genotype modified the effect.

CONCLUSIONS

Our study did not show evidence of a proliferative or pro-apoptotic effect on n-3 LCPUFA supplementation on rectal mucosa regardless of the FADS genotype.ClinicalTrials.gov Identifier: NCT01661764Supplemental data for this article is available online at https://dx.doi.org/10.1080/01635581.2021.1955286.

Effects of fish oil supplementation on eicosanoid production in patients at higher risk for colorectal cancer

Fish oil supplementation may represent a potential chemopreventive agent for reducing colorectal cancer risk. The mechanism of action of fish oil is unknown but presumed to be related to eicosanoid modification. The purpose of this study was to evaluate the effects of fish oil supplementation on the levels of urinary and rectal eicosanoids. We conducted a randomized, double-blind, controlled trial of 2.5 g of fish oil per day compared with olive oil supplementation over a 6-month period. Study participants had a history of colorectal adenomas. Randomization was stratified based on the gene variant rs174535 in the fatty acid desaturase 1 enzyme (FADS1), which affects tissue levels of arachidonic acid. A total of 141 participants were randomized. Urinary prostaglandin E2 metabolite (PGE-M) was measured at baseline, 3, and 6 months and rectal prostaglandin E2 (PGE2) at baseline and 6 months. Repeated-measures linear regression was used to determine the effect of the intervention on each outcome measure. Overall, fish oil supplementation was found to reduce urinary PGE-M production compared with olive oil (P=0.03). Fish oil did not reduce rectal PGE2 overall; however, it did significantly reduce PGE2 in the subgroup of participants not using aspirin or NSAIDs (P=0.04). FADS1 genotype did not seem to modify effects of fish oil on PGE2 production. We conclude that fish oil supplementation has a modest but beneficial effect on eicosanoids associated with colorectal carcinogenesis, particularly in those not taking aspirin or NSAIDs.

Natural Products for Cancer Prevention: Clinical Update 2016

OBJECTIVES

To present a clinical update of natural products for cancer prevention and provide oncology nurses with an evidence-based review of natural products for patient counseling and education.

DATA SOURCES

Clinical trials published in PubMed.

CONCLUSION

In the past 4 years since the publication of the original review there have been minimal changes in the conclusions of the published literature on the use of natural products for cancer prevention. To date, clinical trials have not demonstrated conclusive benefit of using natural products for cancer prevention, and current guidelines do not recommend their use. This review provides an update on published and ongoing trials and can serve as an updated resource for nurses. Evidence-based natural products databases can help nurses stay current with the scientific literature and be effective educators and health coaches for their patients, who can be influenced by marketing of unregulated products.

IMPLICATIONS FOR NURSING PRACTICE

Patients often discuss the use of natural products with nurses. Nurses have an opportunity to educate and coach patients in effective preventive lifestyle practices.

Inhibition of colon cancer growth by docosahexaenoic acid involves autocrine production of TNFα

The omega-3 polyunsaturated fatty acid docosahexaenoic acid (DHA) has anti-inflammatory and anti-cancer properties. Among pro-inflammatory mediators, tumor necrosis factor α (TNFα) plays a paradoxical role in cancer biology with induction of cancer cell death or survival depending on the cellular context. The objective of the study was to evaluate the role of TNFα in DHA-mediated tumor growth inhibition and colon cancer cell death. The treatment of human colorectal cancer cells, HCT-116 and HCT-8 cells, with DHA triggered apoptosis in autocrine TNFα-dependent manner. We demonstrated that DHA-induced increased content of TNFα mRNA occurred through a post-transcriptional regulation via the down-regulation of microRNA-21 (miR-21) expression. Treatment with DHA led to nuclear accumulation of Foxo3a that bounds to the miR-21 promoter triggering its transcriptional repression. Moreover, inhibition of RIP1 kinase and AMP-activated protein kinase α reduced Foxo3a nuclear-cytoplasmic shuttling and subsequent increase of TNFα expression through a decrease of miR-21 expression in DHA-treated colon cancer cells. Finally, we were able to show in HCT-116 xenograft tumor-bearing nude mice that a DHA-enriched diet induced a decrease of human miR-21 expression and an increase of human TNFα mRNA expression limiting tumor growth in a cancer cell-derived TNFα dependent manner. Altogether, the present work highlights a novel mechanism for anti-cancer action of DHA involving colon cancer cell death mediated through autocrine action of TNFα.

Prostaglandin E3 metabolism and cancer

The anticancer activity of n-3 fatty acids, especially those derived from fish, such as eicosapentaenoic acid (EPA) and docosahexaenoic acid) (DHA), has been studied for centuries. While there is a growing body of evidence that EPA and DHA may influence cancer initiation and development through targeting multiple events of tumor development, the underlying mechanisms responsible for these activities are still not fully understood. A number of studies have suggested that the anticancer activities of EPA and DHA are associated with their effects on eicosanoid metabolism by which they inhibit prostaglandin E2 (PGE2) production. In contrast to DHA, EPA can function as a substrate for cyclooxygenases (COXs) to synthesize unique 3-series prostaglandin compounds, especially PGE3. With advance technology in mass spectrometry, there is renewed interest in studying the role of PGE3 in EPA elicited anti-proliferative activity in various cancers, with some promising results. Here, we summarize the regulation of PGE3 synthesis in cancer cells and its role in EPA elicited anticancer activity. The development of PGE3 and its metabolites as potential biomarkers for future clinical evaluation of EPA and fish oil in cancer care is discussed.

Natural products for cancer prevention

OBJECTIVES

To review the clinical trial literature on the use and effects of natural products for cancer prevention.

DATA SOURCES

Clinical trials published in PubMed.

CONCLUSION

There is a growing body of literature on the use of natural products for cancer prevention. To date, few trials have demonstrated conclusive benefit. Current guidelines recommend against the use of natural products for cancer prevention.

IMPLICATIONS FOR NURSING PRACTICE

Clinicians should ask patients about their use of natural products and motivations for use. If patients are using natural products for cancer prevention, they should be counseled on the current guidelines, as well as their options for other cancer prevention strategies.

Dietary n-3 polyunsaturated fatty acids and the paradox of their health benefits and potential harmful effects

There is some evidence to support the toxicity of polyunsaturated fatty acids (PUFAs) and their oxidative products, suggesting their involvement in the pathogenesis of different chronic diseases, including cancer. It has been shown that products of PUFA oxidation may exert a carcinogenic action by forming mutagenic adducts with DNA. However, a large amount of evidence accumulated over several decades has indicated the beneficial effects of administration of n-3 PUFAs in the prevention and therapy of a series of diseases. In particular, there is much evidence that n-3 PUFAs exert anti-inflammatory and antineoplastic effects, whereas n-6 PUFAs promote inflammation and carcinogenesis. In our tissues, both of the two classes of PUFAs can be converted into bioactive products, incorporated into membrane phospholipids or bound to membrane receptors, where they may alter, often in opposite ways, transduction pathways and affect important biological processes, such as cell death and survival, inflammation, and neo-angiogenesis. In the present review, we intend to shed light on the paradox of the coexisting healthy and toxic effects of n-3 PUFAs, focusing on their possible pro-oxidant cytotoxic and carcinogenic effect, in order to understand if their increased intake, recommended by a number of health agencies worldwide and promoted by nutraceutical producers, may or may not represent a hazard to human health.

Fish consumption and markers of colorectal cancer risk: a multicenter randomized controlled trial

BACKGROUND

Diet is a major factor in the etiology of colorectal cancer, with high fish consumption possibly decreasing colorectal cancer risk, as was shown in several observational studies. To date, no intervention trials have examined the possible beneficial effects of fish intake on colorectal cancer risk.

OBJECTIVE

The objective was to investigate the effects of a 6-mo intervention with oil-rich or lean fish on apoptosis and mitosis within the colonic crypt.

DESIGN

In a multicenter, randomized, controlled intervention trial, patients with colorectal polyps, inactive ulcerative colitis, or no macroscopic signs of disease were recruited (n = 242) and randomly allocated to receive dietary advice plus either 300 g oil-rich fish (salmon) per week (n = 82), 300 g lean fish (cod) per week (n = 78), or only dietary advice (DA) (n = 82). Apoptosis and mitosis were measured in colonic biopsy samples collected before and after intervention (n = 213).

RESULTS

The total number of apoptotic cells per crypt did not increase in the salmon or cod group: -0.10 (95% CI: -0.36, 0.16) and -0.06 (95% CI: -0.32, 0.20), respectively, compared with the DA group. The total number of mitotic cells per crypt decreased nonsignificantly in the salmon group (-0.87; 95% CI: -2.41, 0.68) and in the cod group (-1.04; 95% CI: -2.62, 0.53) compared with the DA group. Furthermore, the distribution of mitosis within the crypt did not significantly change in either group.

CONCLUSION

An increase in the consumption of either oil-rich or lean fish to 2 portions weekly over 6 mo does not markedly change apoptotic and mitotic rates in the colonic mucosa. This trial was registered at www.clinicaltrials.gov as NCT00145015.

Antineoplastic effects of n-3 polyunsaturated fatty acids in combination with drugs and radiotherapy: preventive and therapeutic strategies

Many data support the beneficial effect of n-3 polyunsaturated fatty acids (PUFAs) as chemopreventive and chemotherapeutic agents in the treatment of several chronic pathologies including cancer. Different molecular mechanisms have been proposed to explain their effects, including alterations in arachidonic acid oxidative metabolism and metabolic conversion of n-3 PUFAs to novel discovered bioactive derivatives; modification of oxidative stress; changes in cell membrane fluidity and structure and altered metabolism and function of membrane proteins. Considerable knowledge has been recently gathered on the possible beneficial effects of n-3 PUFAs administered in combination with different antineoplastic drugs and radiotherapy against melanoma, leukemia, neuroblastoma, and colon, breast, prostate, and lung cancer. The efficacy of these combinations has been demonstrated both in vivo and in vitro, and clinical trials have also been conducted. The aim of this review is to analyze all the n-3 PUFA combinations investigated so far, their efficacy, and the possible molecular mechanisms involved. It would be highly auspicable that the detailed analysis of the literature in this field could further support the common use of n-3 PUFAs in combination with other chemopreventive agents and warrant more clinical investigations designed to test the effectiveness of n-3 PUFA treatments coupled with conventional antineoplastic therapies.

Multi-targeted therapy of cancer by omega-3 fatty acids

Omega-3 (n-3) and omega-6 (n-6) polyunsaturated fatty acids (PUFAs) are essential fatty acids necessary for human health. Currently, the Western diet contains a disproportionally high amount of n-6 PUFAs and low amount of n-3 PUFAs, and the resulting high n-6/n-3 ratio is thought to contribute to cardiovascular disease, inflammation, and cancer. Studies in human populations have linked high consumption of fish or fish oil to reduced risk of colon, prostate, and breast cancer, although other studies failed to find a significant association. Nonetheless, the available epidemiological evidence, combined with the demonstrated effects of n-3 PUFAs on cancer in animal and cell culture models, has motivated the development of clinical interventions using n-3 PUFAs in the prevention and treatment of cancer, as well as for nutritional support of cancer patients to reduce weight loss and modulate the immune system. In this review, we discuss the rationale for using long-chain n-3 PUFAs in cancer prevention and treatment and the challenges that such approaches pose in the design of clinical trials.

Hypothalamic integration of immune function and metabolism

The immune and neuroendocrine systems are closely involved in the regulation of metabolism at peripheral and central hypothalamic levels. In both physiological (meals) and pathological (infections, traumas and tumors) conditions immune cells are activated responding with the release of cytokines and other immune mediators (afferent signals). In the hypothalamus (central integration), cytokines influence metabolism by acting on nucleus involved in feeding and homeostasis regulation leading to the acute phase response (efferent signals) aimed to maintain the body integrity. Peripheral administration of cytokines, inoculation of tumor and induction of infection alter, by means of cytokine action, the normal pattern of food intake affecting meal size and meal number suggesting that cytokines acted differentially on specific hypothalamic neurons. The effect of cytokines-related cancer anorexia is also exerted peripherally. Increase plasma concentrations of insulin and free tryptophan and decrease gastric emptying and d-xylose absorption. In addition, in obesity an increase in interleukin (IL)-1 and IL-6 occurs in mesenteric fat tissue, which together with an increase in corticosterone, is associated with hyperglycemia, dyslipidemias and insulin resistance of obesity-related metabolic syndrome. These changes in circulating nutrients and hormones are sensed by hypothalamic neurons that influence food intake and metabolism. In anorectic tumor-bearing rats, we detected upregulation of IL-1beta and IL-1 receptor mRNA levels in the hypothalamus, a negative correlation between IL-1 concentration in cerebro-spinal fluid and food intake and high levels of hypothalamic serotonin, and these differences disappeared after tumor removal. Moreover, there is an interaction between serotonin and IL-1 in the development of cancer anorexia as well as an increase in hypothalamic dopamine and serotonin production. Immunohistochemical studies have shown a decrease in neuropeptide Y (NPY) and dopamine (DA) and an increase in serotonin concentration in tumor-bearing rats, in first- and second-order hypothalamic nuclei, while tumor resection reverted these changes and normalized food intake, suggesting negative regulation of NPY and DA systems by cytokines during anorexia, probably mediated by serotonin that appears to play a pivotal role in the regulation of food intake in cancer. Among the different forms of therapy, nutritional manipulation of diet in tumor-bearing state has been investigated. Supplementation of tumor bearing rats with omega-3 fatty acid vs. control diet delayed the appearance of tumor, reduced tumor-growth rate and volume, negated onset of anorexia, increased body weight, decreased cytokines production and increased expression of NPY and decreased alpha-melanocyte-stimulating hormone (alpha-MSH) in hypothalamic nuclei. These data suggest that omega-3 fatty acid suppressed pro-inflammatory cytokines production and improved food intake by normalizing hypothalamic food intake-related peptides and point to the possibility of a therapeutic use of these fatty acids. The sum of these data support the concept that immune cell-derived cytokines are closely related with the regulation of metabolism and have both central and peripheral actions, inducing anorexia via hypothalamic anorectic factors, including serotonin and dopamine, and inhibiting NPY leading to a reduction in food intake and body weight, emphasizing the interconnection of the immune and neuroendocrine systems in regulating metabolism during infectious process, cachexia and obesity.

Serum levels of polyunsaturated fatty acids and risk of colorectal cancer: a prospective study

To examine the relation between serum fatty acids and risk of colorectal cancer, the authors conducted a nested case-control study of 169 colorectal cancer cases and 481 controls matched by age and enrollment area as part of the Japan Collaborative Cohort Study. Serum samples were donated by subjects at baseline (between 1988 and 1990) and were stored at -80 degrees C until 2002. Serum fatty acid levels were measured by using gas chromatography and were expressed as the weight percentage of total lipids. Conditional logistic regression analyses adjusted for lifestyle factors revealed that total omega-3 polyunsaturated fatty acids (odds ratio = 0.24, 95% confidence interval: 0.08, 0.76), alpha-linolenic acid (odds ratio = 0.39, 95% confidence interval: 0.16, 0.91), docosapentaenoic acid (odds ratio = 0.30, 95% confidence interval: 0.11, 0.80), and docosahexaenoic acid (odds ratio = 0.23, 95% confidence interval: 0.07, 0.76) all showed a significantly decreased risk for the highest versus the lowest quartile levels for colorectal cancer in men. For women, a weak negative association was observed between docosapentaenoic acid and colorectal cancer risk, although it was not statistically significant. No adverse effects of high serum levels of omega-6 polyunsaturated fatty acids on colorectal cancer risk were detected.

N-3 fatty acids and lipid peroxidation in breast cancer inhibition

Long-chain n-3 fatty acids (FA) consistently inhibit the growth of human breast cancer (BC) cells both in culture and in grafts in immunosuppressed mice. Large cohort studies have, however, failed to confirm a protective effect for fish oils rich in n-3 FA against BC risk. The present review examines new evidence on biological mechanisms which may be involved in the inhibition of mammary carcinogenesis by long-chain n-3 FA, focusing on an apoptotic effect by its lipid peroxidation products. Dietary intake of n-3 FA leads to their incorporation into cell membrane lipids. Increased apoptosis in human BC cells following exposure to long-chain n-3 FA such as eicosapentaenoic and docosahexaenoic acids is generally ascribed to their inhibition of cyclooxygenase 2 which promotes mammary carcinogenesis. In addition however, long-chain n-3 FA are particularly likely to activate peroxisome proliferator-activated receptor (PPAR)-gamma, a key regulator of lipid metabolism but also capable of modulating proliferative activity in a variety of cells including mammary cells. Expression of PPAR-gamma in the nucleus is activated by second messengers such as J series prostaglandins and the latter have been shown to cause apoptosis in vivo in explants of human BC cells in immunosuppressed mice. In mammary tumours, it is observed that long-chain FA not only increase apoptosis, but also increase lipid peroxidation, and the apoptotic effect can be reversed by antioxidants. The rationale for use of n-3 FA dietary supplements in counteracting BC progression needs to be tested clinically in a phase 2 pilot study, while at the same time, the effect on whole-body lipid peroxidation needs to be monitored. Dietary supplements of fish oil rich in n-3 FA are proposed for premenopausal women over the age of 40 years who are shown to be at increased BC risk. Biological markers in breast tissue of BC progression will be monitored, and observed changes related to serial plasma levels of isoprostanes as a measure of whole-body lipid peroxidation.

Ornithine decarboxylase and thymidine kinase activities and polyamine levels from selected organs of adult miniature swine receiving three concentrations of dietary menhaden oil

Mature, female swine were randomly assigned to one of seven dietary groups. Swine in groups 1-3 were fed a cholesterol-rich diet for 55 days while the remaining groups remained on a basal swine diet. At the end of the cholesterol(Chol)-preloading period the swine in groups 1-7 were placed on menhaden oil (MO) and/or corn oil (CO) as follows: groups 1 and 4, 15% CO (control); groups 2 and 5, 0.75% MO+14.25% CO; groups 3 and 7, 15% MO; and group 6, 7.5% MO+7.5% CO. Animals were killed at the end of the approximately 6-month feeding period and portions of liver, pancreas and colon mucosa were analyzed for both ornithine decarboxylase (ODC) and thymidine kinase (TK) activity while polyamine levels were measured in the liver and pancreas. Statistical analyses were carried out by one-way and two-way ANOVA and by trend analysis. In the pancreas, the highest MO group (group 7) had significantly higher ODC levels when compared with the CO control (group 4) and the next to highest MO group (group 6) (one-way ANOVA)-all non-cholesterol preloaded groups. Using a two-way ANOVA (Chol-by-MO), liver ODC was significantly lower in the CO control when compared with the lowest and highest MO groups (groups 5 and 7, respectively), again in the non-cholesterol-preloaded animals. In the colon, the swine in the Chol-low MO group (group 2) had significantly lower TK activity than the Chol/CO control group (group 1) and Chol/Hi MO group (group 3) (one-way ANOVA) and also had significantly lower activity than all groups except the CO control (group 4) (two-way ANOVA). Liver acetylputrescine in the lowest and highest MO groups (groups 5 and 7, respectively) was significantly higher than in the CO group (group 4). Liver spermidine in the Chol-Hi MO group (group 3) was significantly higher than the Chol-Lo MO group (group 2), while the highest MO group (group 7) had a statistically higher level than the other non-cholesterol groups (groups 4-6) (one-way ANOVA). Liver spermine was significantly higher in the Chol-Hi MO group (group 3) when compared to the CO control (group 1) and the Chol-Lo MO group (group 2) (one-way ANOVA). Pancreatic putrescine in the CO control (group 4) was significantly higher than all other groups (two-way ANOVA) while spermine from the 2 Chol-MO groups (groups 2 and 3) was higher than the Chol-CO control (group 1) (one-way ANOVA). Using trend analysis, liver TK, putrescine and spermidine increased in the non-cholesterol preloaded groups with increasing dietary MO, similar to the increase seen in ODC. Thus, of the three organs studied, only liver responded to menhaden oil with changes in both ODC itself or some of its metabolic engendered products and thymidine kinase; at least for one of the parameters, ODC, change associated with dietary MO was dependent on whether the swine were preloaded with cholesterol.

Antioxidant status and lipid peroxidation in colorectal cancer

Colon carcinogenesis is a multistep process where oxygen radicals were found to enhance carcinogenesis at all stages: initiation, promotion, and progression. Since insufficient capacity of protective antioxidant system can result in cancer, the aim of this study was to examine the activity of antioxidant enzymes (superoxide dismutase, catalase, glutathione peroxidase, and glutathione reductase) and the levels of reduced glutathione, vitamin C, and vitamin E. The lipid peroxidation products were also determined by measuring malondialdehyde and 4-hydroxynonenal levels in colorectal cancer tissue collected from 55 patients. In these cases the activity of superoxide dismutase, glutathione peroxidase, and glutathione reductase was significantly increased while the activity of catalase was significantly decreased in cancer tissue. However, the level of nonenzymatic antioxidant parameters (glutathione, vitamin C, and vitamin E) was significantly decreased in cancer tissue. Further lipid peroxidation was enhanced during cancer development, manifested by a significant increase in malondialdehyde and 4-hydroxynonenal levels. The obtained results indicate significant changes in antioxidant capacity of colorectal cancer tissues, which lead to enhanced action of oxygen radicals, resulting in lipid peroxidation.

Fish oil blocks azoxymethane-induced rat colon tumorigenesis by increasing cell differentiation and apoptosis rather than decreasing cell proliferation

The purpose of this study was to determine whether the protective effect of fish oil against colon carcinogenesis is due to decreased proliferation, increased differentiation and/or increased apoptosis. Male Sprague Dawley rats (n = 260) were fed one of two oils (corn or fish) and two fibers (pectin or cellulose), plus or minus the carcinogen azoxymethane (AOM). Rats were killed at wk 18 (n = 80) or 36 (n = 180) for cytokinetic measurements. In vivo cell proliferation was measured by incorporation of bromodeoxyuridine into DNA, differentiation by binding of Dolichos biflorus agglutinin and apoptosis by immunoperoxidase detection of digoxigenin labeled genomic DNA. Fish oil resulted in a lower adenocarcinoma incidence (56.1 vs. 70.3%) compared with corn oil. There was no effect of fat or fiber on number of proliferative cells/crypt column in either the proximal or distal colon. In contrast, fish oil resulted in a greater degree of differentiation compared with corn oil in both colonic sites. In addition, fish oil resulted in a higher number of apoptotic cells/crypt column in both the proximal and distal colon as compared with corn oil. AOM treatment increased the ratio of proliferative cells/crypt column to apoptotic cells/crypt column in both the proximal and distal colon compared with saline controls. Fish oil, however, resulted in a lower ratio in both sites in the colon as compared with corn oil. These results suggest that an increase in apoptosis and differentiation, rather than a decrease in proliferation, accounts for the protective effect of fish oil against experimentally induced colon tumorigenesis.

A fish oil-derived concentrate enriched in eicosapentaenoic and docosahexaenoic acid as ethyl esters inhibits the formation and growth of aberrant crypt foci in rat colon

It was examined whether the fish oil derived n-3 fatty acid concentrate K85 (51.0% of eicosapentaenoic acid, 35.3% of docosahexaenoic acid and 7.7% of other n-3 fatty acids, all as ethyl esters) could inhibit the initial formation of aberrant crypt foci and the later growth of pre-existing aberrant crypt foci in the colon of male F344 rats treated with the carcinogens dimethylhydrazine or azoxymethane, the proximate metabolite of dimethylhydrazine. Given intragastrically 5 times a week, K85 caused a dose-dependent reduction of the initial (week 0-6) formation of aberrant crypt foci induced by azoxymethane (2 x 15 mg/kg body weight/injection the first two weeks). The number of aberrant crypt foci was reduced by 36% (P < 0.001) with 3.0 g K85/kg body weight/dose, the largest dose tested. The reduction was most pronounced (46%, P = 0.009) among the fastest growing aberrant crypt foci (foci with 3 or more aberrant crypts). When given in a later phase of the carcinogenesis (week 17-23) a similar intragastric treatment with K85 caused a dose-dependent reduction of the growth of pre-existing aberrant crypt foci induced by dimethylhydrazine (3 x 20 mg/kg body weight/injection the first week). The crypt multiplicity (aberrant crypt/focus) was reduced by 22% (P = 0.016) with 2.24 g K85/kg body weight/dose, the largest dose tested. This was sufficient to completely block the growth of the pre-existing aberrant crypt foci in the treatment period. The arrest of crypt multiplication was further documented by the 63% reduction (P = 0.03) of the large aberrant crypt foci (foci with 9 or more aberrant crypts). The total number of aberrant crypt foci was not affected.

Tocopherols and the etiology of colon cancer

Colorectal cancer is the second most common cause of cancer deaths in the United States for both sexes. Considerable evidence suggests that the risk of this cancer is increased by the mutagenic actions of free radicals, which are produced during oxidation reactions. Dietary factors, the intestinal flora (bacteria), and endogenously produced metabolites contribute to the production of free radicals in the colon. Dietary antioxidants, such as vitamin E, should reduce the levels of these harmful oxidation products. In the absence of vitamin E, polyunsaturated fats can be oxidized in the colon to produce mutagens, such as lipid hydroperoxides and malondialdehyde. Furthermore, fecal bacteria can generate a high flux of reactive oxygen species (e.g., the superoxide radical [O2*-]) at the surface of the intestinal lumen, and inflammatory cells in close proximity to the colon can produce reactive nitrogen species (e.g., nitrogen dioxide [NO2]). Increasing evidence suggests that the different chemical (e.g., alpha- and gamma-tocopherol) and stereochemical (e.g., RRR- and all-racemic-alpha-tocopherol) forms of vitamin E have distinct biologic potencies, pharmacokinetics, and different abilities to prevent neoplastic transformation. This review considers and evaluates recent studies relating vitamin E and oxidative stress to colon cancer, emphasizing the distinct roles of alpha- and gamma-tocopherols. In addition, recent findings on the antioxidant/pro-oxidant status of the digesta (ingested food) are discussed with respect to the use of antioxidants in chemo-prevention trials for colon cancer.