The effectiveness of a mixture of beta-carotene, alpha-tocopherol, glutathione, and ascorbic acid for cancer prevention

Comparative Impact of Various Fasting Periods on the Welfare of Sprague-Dawley Rats With or Without Supplementation

In nonclinical toxicology studies, lab animals are fasted typically overnight, to reduce variability in some clinical pathology parameters. However, fasting adds undue stress, and this is particularly concerning in rodents given their fast metabolic rates. Furthermore, as rodents are nocturnal animals, an overnight fasting may cause a protracted negative metabolic state even when the fasting has technically ended, given their minimal activity and food consumption during the day. Therefore, to evaluate the impacts of different fasting durations (±DietGel supplementation) on rats' welfare, we assessed the traditional and ancillary clinical pathology parameters in Sprague-Dawley rats, along with body weight, organ weight, and histopathology. Although most endpoints were comparable between the different fasting durations (±DietGel supplementation), the long fasting times (≥8 hr) without DietGel supplementation caused significant decreases in body weight, liver weight, liver glycogen content, serum glucose, triglyceride, and creatinine concentrations-all findings suggestive of a negative energy balance that could impact animal welfare and consequently, data quality; while the short fasting time (4 hr) and DietGel supplementation were associated with higher triglycerides variability. Hence, we propose that short fasting time should be adequate for most toxicology studies in rats, and long fasting times should only be accommodated with scientific justification.

Reduced Fasting Duration in Cynomolgus Monkeys Enhances Animal Welfare During Toxicology Studies

During toxicology studies, fasting animals prior to clinical pathology blood collection is believed to reduce variability in some clinical chemistry analytes. However, fasting adds stress to animals that are already stressed from the administration of potentially toxic doses of the test article. The purpose of this study was to assess the impacts of different fasting durations on cynomolgus monkeys' welfare during toxicology studies. To this end, we assessed the cynomolgus monkeys traditional and ancillary clinical pathology endpoints at different fasting times. We showed that most clinical pathology endpoints were largely comparable between different fasting times suggesting that cynomolgus monkeys could be fasted for as little as 4 hours for toxicology studies, as longer fasting times (up to 20 hours) resulted in stress, dehydration, and significant decreases in blood glucose- changes that impacts animal welfare. Shorter fasting times were associated with higher triglycerides variability among individual animals. Therefore, we propose that shorter fasting time (i.e., 4 hours) should be adequate for most toxicology studies except when: (1) parameters that could be affected by non-fasting conditions are important for safety and pharmacodynamic assessments (i.e., glucose and lipids) and (2) fasting would be needed for the bioavailability of an orally administered test article.

Structural Effects of pH Variation and Calcium Amount on the Microencapsulation of Glutathione in Alginate Polymers

Reduced glutathione (GSH) has a high antioxidant capacity and is present in nearly every cell in the body, playing important roles in nutrient metabolism, antioxidant defense, and regulation of cellular events. Conversely, alginate is a macromolecule that has been widely used in the food, pharmaceutical, biomedical, and textile industries due to its biocompatibility, biodegradability, nontoxicity, and nonimmunogenicity as well as for its capabilities of retaining water and stabilizing emulsions. The primary goal of this study was to characterize and optimize the formation of a molecular complex of calcium alginate with GSH using a computational approach. As methods, we evaluated the influence of varying the amount of calcium cations at two different pHs on the structural stability of Ca²⁺-alginate complexes and thus on GSH liberation from these types of nanostructures. The results showed that complex stabilization depends on pH, with the system having a lower Ca²⁺ amount that produces the major GSH release. The systems at pH 2.5 retain more molecules within the calcium-alginate complex, which release GSH more slowly when embedded in more acidic media. In conclusions, this study demonstrates the dependence of the amount of calcium and the stabilizing effect of pH on the formation and subsequent maintenance of an alginate nanostructure. The results presented in this study can help to develop better methodological frameworks in industries where the release or capture of compounds, such as GSH in this case, depends on the conditions of the alginate nanoparticle.

Carotenoids from Cyanobacteria: A Biotechnological Approach for the Topical Treatment of Psoriasis

In this study, five cyanobacteria strains (Alkalinema aff. pantanalense LEGE15481, Cyanobium gracile LEGE12431, Nodosilinea (Leptolyngbya) antarctica LEGE13457, Cuspidothrix issatschenkoi LEGE03282 and Leptolyngbya-like sp. LEGE13412) from the Blue Biotechnology and Ecotoxicology Culture Collection (LEGE CC) of CIIMAR were explored for their biotechnological potential in the treatment of psoriasis. Different extracts were characterized for their pigment profile by HPLC-PDA. The antioxidant potential of the extracts was assessed against the superoxide anion radical (O₂^•-). Their anti-inflammatory and antiproliferative potential was assessed in vitro using the macrophages RAW 264.7 and the human keratinocytes HaCaT as cell-line models, respectively. Terrestrial and freshwater strains presented the highest carotenoid content (33193-63926 μg/g dry extract), with all-trans-β-carotene, zeaxanthin, echinenone and lutein derivatives being the most abundant carotenoids. Acetone was the most effective solvent for pigment extraction. The acetone extracts presented the lowest IC₅₀ values (0.29-0.38 mg dry extract/mL) regarding O₂^•- scavenging, and revealed anti-inflammatory potential, with N. antarctica LEGE13457, A. pantanalense LEGE15481 and Leptolyngbya-like sp. LEGE13412 reducing the nitric oxide (NO) in RAW 264.7 cell culture medium in about 25% (p < 0.05). With the exception of A. pantanalense LEGE15481, all the extracts significantly reduced keratinocyte proliferation (p < 0.05), demonstrating a selective toxicity among the different cell lines. Overall, Leptolyngbya-like sp. LEGE13412 and N. antarctica LEGE13457 seem promising for further exploitation in the framework of psoriasis, due to their antioxidant, anti-inflammatory and antiproliferative potential.

Antioxidant Agents and Colorectal Carcinogenesis: Role of β-Carotene, Vitamin E and Vitamin C

In consideration of findings reported in the literature and of our study, we examined the correlation between antioxidants (β-carotene, vitamin C, vitamin E) and colorectal carcinogenesis. Although diagnostic progress has been made in the last decades, no significant improvements in death rates have been achieved in the western world. Exogenous factors might be responsible for a complex alteration process of normal colonic mucosa into adenoma and carcinoma. Free radicals and reactive oxygen metabolites, due to increased production or to reduced inactivation, following a decrease in the antioxidant burden in the mucosa, might cause damage to DNA, thereby resulting in genetic alterations. This might represent the cause of the transformation process: normal mucosa→ adenoma→ carcinoma. In a prospective study, we observed a reduction of β-carotene levels in normal colonic mucosa in patients with polyps and colorectal cancer. We also showed that β-carotene supplementation raises levels of this micronutrient in the colonic mucosa of these patients. Findings from the literature and our trials show a significant decrease in the antioxidant capacity of colorectal mucosa in patients affected by colorectal cancer, although there is a significant interindividual variability. Such results suggest a possible chemopreventive role of antioxidant agents in colorectal cancer.

Oral supplementation with liposomal glutathione elevates body stores of glutathione and markers of immune function

BACKGROUND/OBJECTIVES

Glutathione (GSH) is the most abundant endogenous antioxidant and a critical regulator of oxidative stress. Maintenance of optimal tissues for GSH levels may be an important strategy for the prevention of oxidative stress-related diseases. We investigated if oral administration of liposomal GSH is effective at enhancing GSH levels in vivo.

SUBJECTS/METHODS

A 1-month pilot clinical study of oral liposomal GSH administration at two doses (500 and 1000 mg of GSH per day) was conducted in healthy adults. GSH levels in whole blood, erythrocytes, plasma and peripheral blood mononuclear cells (PBMCs) were assessed in 12 subjects at the baseline and after 1, 2 and 4 weeks of GSH administration.

RESULTS

GSH levels were elevated after 1 week with maximum increases of 40% in whole blood, 25% in erythrocytes, 28% in plasma and 100% in PBMCs occurring after 2 weeks (P<0.05). GSH increases were accompanied by reductions in oxidative stress biomarkers, including decreases of 35% in plasma 8-isoprostane and 20% in oxidized:reduced GSH ratios (P<0.05). Enhancements in immune function markers were observed with liposomal GSH administration including Natural killer (NK) cell cytotoxicity, which was elevated by up to 400% by 2 weeks (P<0.05), and lymphocyte proliferation, which was elevated by up to 60% after 2 weeks (P<0.05). Overall, there were no differences observed between dose groups, but statistical power was limited due to the small sample size in this study.

CONCLUSIONS

Collectively, these preliminary findings support the effectiveness of daily liposomal GSH administration at elevating stores of GSH and impacting the immune function and levels of oxidative stress.

Glutathione and its antiaging and antimelanogenic effects

Background

Previous studies showed that supplementation of reduced form of glutathione (GSH, 500 mg/d) has a skin-lightening efficacy in humans. This study was designed to evaluate the influences of both GSH and oxidized form (GSSG), at doses lower than 500 mg/d, on improving skin properties.

Patients and methods

A randomized, double-blind, placebo-controlled, parallel, three-arm study was conducted. Healthy female subjects were equally randomized into three groups and took GSH (250 mg/d), GSSG (250 mg/d), or placebo orally for 12 weeks. At each visit at baseline and for 12 weeks, skin features including melanin index, wrinkles, and other relevant biophysical properties were measured. Blood samples were collected for safety monitoring.

Results

In generalized estimating equation analyses, melanin index and ultraviolet spots of all sites including face and arm when given GSH and GSSG tended to be lower than placebo. At some sites evaluated, subjects who received GSH showed a significant reduction in wrinkles compared with those taking placebo. A tendency toward increased skin elasticity was observed in GSH and GSSG compared with placebo. There were no serious adverse effects throughout the study.

Conclusion

We showed that oral glutathione, 250 mg/d, in both reduced and oxidized forms effectively influences skin properties. Overall, glutathione in both forms are well tolerated.

Antioxidant-Oxidant Index as a Biomarker in Oral Potentially Malignant Disorders and Oral Squamous Cell Carcinoma: A Biochemical Study

INTRODUCTION

Oxidative stress has been implicated in tumourigenesis by affecting the actions of various protein kinases and transcription factors, and resulting in damage to DNA structure by the deamination of nucleotides and the generation of free radicals. Derangements in the antioxidant defence mechanism have been considered in the pathogenesis of oral cancer.

AIM

To evaluate and compare the serum levels of nitric oxide and vitamin C in cases of Oral Potentially Malignant Disorders (OPMDs) and Oral Squamous Cell Carcinoma (OSCC) and healthy controls.

MATERIALS AND METHODS

Serum from 20 patients with OSCC, 20 patients with OPMDs and 10 healthy subjects were analyzed for levels of nitric oxide and vitamin C using UV spectrophotometry. Antioxidant-Oxidant Index (AOI) was calculated by calculating the ratio between the levels of nitric oxide and vitamin C.

RESULTS

The mean nitric oxide levels were elevated in OSCC group, as compared to OPMD and control group, whereas, mean serum vitamin C levels were reduced in OSCC group as compared to OPMDs and control group (statistically significant, p<0.05). There was significant increase in AOI from control group (0.023), OPMDs (0.167) and OSCC group (0.279) (p<0.05).

CONCLUSION

Assessment of levels of antioxidant oxidant markers are useful tools in monitoring the progression of OPMDs to OSCC. AOI is an objective tool to assess the oxidative stress in these patients.

Orthomolecular Oncology Review: Ascorbic Acid and Cancer 25 Years Later

The effect of ascorbic acid on cancer has been a subject of great controversy. This is a follow-up review of the 1979 article by Cameron, Pauling, and Leibovitz published in Cancer Research. In this updated version, the authors address general aspects of ascorbic acid and cancer that have been presented before, while reviewing, analyzing, and updating new existing literature on the subject. In addition, they present and discuss their own mechanistic hypothesis on the effect of ascorbic acid on the cancer cell. The objective of this review is to provide an updated scientific basis for the use of ascorbic acid, especially intravenously as adjuvant treatment in pharmacological nutritional oncology.

Randomized controlled trial of oral glutathione supplementation on body stores of glutathione

PURPOSE

Glutathione (GSH), the most abundant endogenous antioxidant, is a critical regulator of oxidative stress and immune function. While oral GSH has been shown to be bioavailable in laboratory animal models, its efficacy in humans has not been established. Our objective was to determine the long-term effectiveness of oral GSH supplementation on body stores of GSH in healthy adults.

METHODS

A 6-month randomized, double-blinded, placebo-controlled trial of oral GSH (250 or 1,000 mg/day) on GSH levels in blood, erythrocytes, plasma, lymphocytes and exfoliated buccal mucosal cells was conducted in 54 non-smoking adults. Secondary outcomes on a subset of subjects included a battery of immune markers.

RESULTS

GSH levels in blood increased after 1, 3 and 6 months versus baseline at both doses. At 6 months, mean GSH levels increased 30-35 % in erythrocytes, plasma and lymphocytes and 260 % in buccal cells in the high-dose group (P < 0.05). GSH levels increased 17 and 29 % in blood and erythrocytes, respectively, in the low-dose group (P < 0.05). In most cases, the increases were dose and time dependent, and levels returned to baseline after a 1-month washout period. A reduction in oxidative stress in both GSH dose groups was indicated by decreases in the oxidized to reduced glutathione ratio in whole blood after 6 months. Natural killer cytotoxicity increased >twofold in the high-dose group versus placebo (P < 0.05) at 3 months.

CONCLUSIONS

These findings show, for the first time, that daily consumption of GSH supplements was effective at increasing body compartment stores of GSH.

Improved survival in patients with end-stage cancer treated with coenzyme Q(10) and other antioxidants: a pilot study

This pilot study evaluated the survival of patients with end-stage cancer who received supplements of coenzyme Q(10) and a mixture of other antioxidants (e.g. vitamin C, selenium, folic acid and beta-carotene). During a period of 9 years, 41 patients who had end-stage cancer were included. Forty patients were followed until death and one patient was lost to follow-up and presumed dead. Primary cancers were located in the breast, brain, lungs, kidneys, pancreas, oesophagus, stomach, colon, prostate, ovaries and skin. The median predicted survival time was calculated from Kaplan-Meier curves for each patient at inclusion. Median predicted survival was 12 months (range 3 - 29 months), whereas median actual survival was 17 months (1 - 120 months), which is > 40% longer than the median predicted survival. Mean actual survival was 28.8 months versus 11.9 months for mean predicted survival. Ten patients (24%) survived for less time than predicted, whereas 31 (76%) survived for longer. Treatments were very well tolerated with few adverse effects.

Inhibition of oral carcinogenesis by citrus flavonoids

Six citrus flavonoids were tested for antineoplastic activity. The hamster cheek pouch model was utilized, and the solutions of the flavonoids (2.0-2.5%) and the solution of the carcinogen, 7,12-dimethylbenz[a]anthracene (0.5%), were applied topically to the pouches. The pouches of the positive controls were treated with the solvent used to dissolve the flavonoids and the solution of the carcinogen. The data show that 4 flavonoids (hesperetin, neohesperidin, tangeretin, and nobiletin) were inactive. The results with naringin and naringenin show that both of these flavonoids significantly lowered tumor number [5.00 (control group), 2.53 (naringin group), and 3.25 (naringenin group)]. Naringin also significantly reduced tumor burden [269 mm(3)(control group) and 77.1 mm(3)(naringin group)]. The data suggest that naringin and naringenin, 2 flavonoids found in high concentrations in grapefruit, may be able to inhibit the development of cancer.

Enhanced levels of glutathione and protein glutathiolation in rat tongue epithelium during 4-NQO-induced carcinogenesis

High glutathione (GSH) levels are commonly found in oral tumors and are thought to play an important role in tumorigenesis. While posttranslational binding of GSH to cellular proteins (protein glutathiolation) has recently been recognized as an important redox-sensitive regulatory mechanism, no data currently exist on this process during carcinogenesis. Our goal was to determine the effects of 4-nitroquinoline-N-oxide (4-NQO)-induced carcinogenesis on tongue levels of protein-bound and free GSH and related thiols in the rat. Male F-344 rats (6 weeks of age) were administered either 4-NQO (20 ppm) in drinking water or tap water alone (controls) for 8 weeks. Twenty-four weeks after cessation of 4-NQO, squamous cell carcinomas of the tongue were observed in all rats. The levels of both free and bound GSH in tumors, as well as in adjacent tissues, were 2- to 3-fold greater than in tongue epithelium from control rats (p < 0.05). Prior to tumor formation, at 8 weeks after cessation of 4-NQO, hyperplasia, dysplasia and carcinoma in situ were observed in 100%, 25% and 12.5% of 4-NQO-treated rats, respectively. At this early stage of carcinogenesis, levels of free and bound GSH were increased 50% compared with tongue tissues from control rats (p<0.05). Glutathione disulfide (GSSG) levels were also 2-fold greater in tongue tissues from 4-NQO treated vs. control rats (p<0.05). Altogether, these results suggest that protein glutathiolation, together with GSH and GSSG levels, are induced during oral carcinogenesis in the rat possibly as a result of enhanced levels of oxidative stress.

Animal models in oral cancer research

Biologically and clinically relevant animal models are essential in investigation of the progression of diseases and the elaboration of diagnostic or therapeutic protocols. The several rodent models used for in vivo evaluation for oral cancer employ chemical, transplantation and genetic (knockout and transgenic) induction methods. These models are described together with their advantages and disadvantages. Their optimization and application in future research may improve the early detection and treatment of oral cancer.

Synergy among phytochemicals within crucifers: does it translate into chemoprotection?

The association between cruciferous vegetables and cancer prevention has been linked to glucosinolate derivatives. These phytochemicals enhance endogenous detoxification, leading to inactivation of potential carcinogens before initiation occurs. Two derivatives, indole-3-carbinol (I3C) and 1-cyano-2-hydroxy-3-butene (crambene) were shown in rats to induce a synergistic enhancement of detoxification enzyme activity. To follow up on these findings, a short-term carcinogenicity study using aflatoxin B1 (AFB(1)) was performed in which male F344 rats were fed diets supplemented with these 2 compounds alone or in combination. Groups included a negative control group (no AFB(1), crambene, or I3C), a crambene group (diet 0.150% crambene), an I3C group (diet 0.165% I3C), a high-dose group (diet 0.150% crambene, 0.165% I3C) a low-dose group (diet 0.030% crambene, 0.033% I3C), and a positive control group (AFB(1) treatment only). AFB(1) was administered after 2 wk of dietary pretreatment. Liver sections were scored for lesions including karyomegaly, apoptosis, and biliary hyperplasia and evaluated for expression of the preneoplastic marker glutathione S-transferase-pi (GSTP). I3C and crambene groups were protected against AFB(1) toxicity whereas the low-dose group was not. The high-dose group had scores close to those of the negative controls. For log(10) transformed 2- and 3-dimensional GSTP data, the high-dose group demonstrated synergistic reduction in GSTP-positive area and an additive reduction in GSTP-positive volume compared with the crambene and I3C groups. The low-dose group had no effect. In conclusion, high combination dietary doses of I3C and crambene demonstrated enhanced protection from AFB(1). Low combination doses, as might be realistically in the diet, were not effective.

Therapeutic efficacy of green tea polyphenols on cellular thiols in 4-Nitroquinoline 1-oxide-induced oral carcinogenesis

In cancer, a high flux of oxidants not only depletes the cellular thiols, but damages the whole cell as well. Epidemiological studies suggest green tea may mitigate cancers in human and animal models for which several mechanisms have been proposed. In the present investigation, the levels of cellular thiols such as reduced glutathione (GSH), oxidised glutathione (GSSG), protein thiols (PSH), total thiols, lipid peroxidation product conjugated dienes and the activity of gamma glutamyl transferase (GGT) were assessed in tongue and oral cavity. In 4-Nitroquinoline 1-oxide- (4-NQO) induced rats, there was a decrease in the levels of GSH, PSH and total thiols and an increase in the levels of GSSG, conjugated dienes and the activity of GGT. On supplementation of green tea polyphenols (GTP) for 30 days (200 mg/kg) for the oral cancer-induced rats, there was a moderate increase in the levels of GSH, PSH and total thiols and a decrease in the levels of GSSG, conjugated dienes and the activity of GGT. Thus, GTP reduces the oxidant production thereby maintains the endogenous low molecular weight cellular thiols in oral cancer-induced rats. From the results, it can be concluded that GTP supplementation enhances the cellular thiol status thereby mitigate oral cancer.

Antioxidative and Cardioprotective Effects of Phyllanthus urinaria L. on Doxorubicin-Induced Cardiotoxicity

Cardiac toxicity is a major adverse effect caused by doxorubicin (DOX) therapy. Many recent studies have shown that DOX toxicity involves generation of reactive oxygen species (ROS). Although protection or alleviation of DOX toxicity can be achieved by administration of antioxidant vitamins such as ascorbic acid and vitamin E, their cardioprotective effect remains controversial. Thus alternative naturally occurring antioxidants may potentially be candidates for antioxidant therapy. In this study, we investigated the antioxidative and cytoprotective effects of Phyllanthus urinaria (PU) against DOX toxicity using H9c2 cardiac myoblasts. The total antioxidant capacity of PU (1 mg/ml) was 5306.75+/-461.62 FRAP value (microM). DOX IC50 values were used to evaluate the cytoprotective effects of PU ethanolic extract (1 or 10 microg/ml) in comparison with those of ascorbic acid (VIT C, 100 microM) and N-acetylcysteine (NAC, 100 microM). PU treatments (1 or 10 microg/ml) dose dependently caused rightward DOX IC50 shifts of 2.8- and 8.5-fold, respectively while treatments with VIT C and NAC increased DOX IC50 by 3.3- and 4.2-fold, respectively. Additionally, lipid peroxidation and caspase-3 activity were parameters used to evaluate cytoprotective effect. All antioxidants completely inhibited cellular lipid peroxidation and caspase-3 activation induced by DOX (1 microM). Endogenous antioxidant defense such as total glutathione (tGSH), catalase and superoxide dismutase (SOD) activity was also modulated by the antioxidants. PU treatment alone dose dependently increased tGSH, and this effect was retained in the presence of DOX. Similar effect was observed in the assessment of catalase and SOD enzyme activity. The nuclear factor kappaB (NFkappaB) transcription factor assay demonstrated that all antioxidants significantly inhibited DOX-induced NFkappaB activation. Our results suggest that PU protection against DOX cardiotoxicity was mediated through multiple pathways and this plant may serve as an alternative source of antioxidants for prevention of DOX cardiotoxicity.

Prooxidant effects of β-carotene in cultured cells

There is a growing body of interest on the role of beta-carotene and other carotenoids in human chronic diseases, including cancer. While epidemiological evidence shows that people who ingest more dietary carotenoids exhibit a reduced risk for cancer, results from intervention trials indicate that supplemental beta-carotene enhances lung cancer incidence and mortality among smokers. A possible mechanism which can explain the dual role of beta-carotene as both a beneficial and a harmful agent in cancer as well as in other chronic diseases is its ability in modulating intracellular redox status. beta-Carotene may serve as an antioxidant or as a prooxidant, depending on its intrinsic properties as well as on the redox potential of the biological environment in which it acts. This review summarizes the available evidence for a prooxidant activity of beta-carotene in cultured cells, focusing on biochemical and molecular markers of oxidative stress, which have been reported to be enhanced by the carotenoid.

Effects of dietary fish oil on fatty acids and eicosanoids in metastasizing human breast cancer cells

We examined the relationships between the suppressive effects of dietary fish oil on growth and metastasis of MDA-MB-435 human breast cancer cells in female nude mice and the primary tumor phospholipid fatty acid concentrations, phospholipase A2 activity, and eicosanoid levels. Mice (n = 120) were fed a 23% (wt/wt) corn oil (CO) linoleic acid (LA)-rich diet for seven days before and after 10(6) tumor cells were injected into a mammary fat pad, and then the mice receive one of three isocaloric diets containing 23% total fat but different proportions of CO and menhaden oil (MO) (18% CO-5% MO, 11.5% CO-11.5% MO, 5% CO-18% MO) or a 23% fat diet containing 18% deodorized fish oil supplemented with tocopherol and tert-butylhydroquinone antioxidants (FAO). Primary tumor growth rate was significantly greater in mice fed the 18% CO diet than in the three diets containing higher levels of fish oil (all p < 0.05). The 18% MO diet, but not the 11.5% MO or the 18% FAO diet, suppressed the development of lung metastases compared with the 18% CO diet. Increasing the proportion of MO relative to CO in the diets produced corresponding increases in the primary tumor phospholipid eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) concentrations and reductions in LA and arachidonic acid. There was a significant positive correlation between the LA concentration in these tumors and the extent of lung metastasis (r = 0.504). Tumor phospholipase A2 activity was unaffected by dietary MO intake. Prostaglandin E2 concentration was inversely correlated with phospholipid EPA (r = -0.484) and DHA (r = -0.439), but there was no relationship with lung metastasis. Tumor leukotriene B4 and 5-hydroxyeicosatetraenoic acid levels were not reduced by dietary MO. The 18% FAO- and the 18% MO-fed mice showed similar relationships for the phospholipid fatty acids and prostaglandin E2, despite the lack of effect on metastasis. The strong correlation between phospholipid LA levels and metastasis and the lack of an association with tumor eicosanoids suggest that the 18% MO diet inhibited metastasis because dietary LA was replaced by other fatty acids.

Vegetables, fruits, related dietary antioxidants, and risk of squamous cell carcinoma of the esophagus: a case-control study in Uruguay

In 1998-1999, a case-control study on esophageal cancer was conducted in Uruguay. For this purpose, 111 cases with squamous cell carcinoma of the esophagus and 444 controls with conditions unrelated to tobacco smoking, alcohol drinking, or recent changes in the diet were frequency matched on age, gender, residence, and urban/rural status. Vegetables and, more markedly, fruits were associated with strong reductions in risk. On the other hand, 12 of 15 dietary antioxidants displayed significant inverse associations with esophageal cancer risk. The strongest effect was observed for high intake of beta-cryptoxanthin (odds ratio = 0.16, 95% confidence interval = 0.08-0.36). Also, alpha-carotene, lycopene, and beta-sitosterol were associated with significant reductions in risk. Most antioxidants lost their effect when they were further adjusted for a term for all vegetables and fruits. beta-Carotene showed an increased risk with high intakes. On the other hand, vegetables and fruits remained as significant variables after adjustment for each antioxidant, suggesting that other substances or other mechanisms could explain this effect.

Suplementação de vitaminas na prevenção de câncer

Este trabalho constitui uma revisão de dados epidemiológicos sobre a relação entre o consumo de vitaminas e prevenção de câncer. Estudos observacionais evidenciam uma associação inversa consistente entre a ingestão de frutas e hortaliças e risco de câncer, e um efeito protetor das vitaminas C, E e dos carotenóides contra certos tipos de câncer. Resultados de estudos de intervenção, na prevenção primária de câncer, são contraditórios, sendo que em dois desses estudos o beta-caroteno, suplementado em doses consideradas farmacológicas, isolado ou associado à vitamina E ou à vitamina A, mostrou-se deletério para tabagistas. Ao contrário, a ingestão de doses mais fisiológicas de antioxidantes parece ser mais eficaz, sendo que a ação sinérgica dessas substâncias na quimioprevenção de câncer já foi demonstrada tanto em modelo in vivo de carcinogênese quanto em estudo epidemiológico de intervenção. Como estratégia de prevenção de câncer preconiza-se o consumo de dietas ricas em frutas e hortaliças, que aportem cerca de 150 mg de vitamina C, 30 mg de vitamina E e 4 mg de carotenóides. A ingestão de quantidades mais elevadas, na forma de suplementos, não está recomendada.

Experimental basis for cancer prevention by vitamin E

Recent clinical trials have demonstrated the significant cancer preventive potential of vitamin E in many different cancer sites, ranging from oral and pharyngeal cancer to prostate cancer. There is an extensive experimental basis for this clinical cancer inhibition. The experimental background includes animal studies (experimental pathology, immunology and molecular biology, synergism, selectivity and safety), in vitro biochemical studies, and human studies (epidemiology and biomarkers, prevention of many pathologic entities other than cancer).

Experimental oral carcinoma of the tongue and buccal mucosa: possible biologic markers linked to cancers at two anatomic sites

The application of the carcinogen 7,12-dimethylbenz(a)anthracene (DMBA) can initiate and promote the development of oral squamous cell carcinoma of the tongue and buccal mucosa. In this study the level of expression of various markers related to the development of programmed cell death (PCD) in the respective oral carcinomas was analyzed. Sixteen male and female Syrian hamsters (Mesocrietus auratus) were treated with 0.05% DMBA for 16 weeks. Immunohistochemistry was used to observe the expression of p53, proliferating cell nuclear antigen (PCNA), Bcl-2, and nucleosome formation. Single-strand conformational polymorphism (SSCP) for exons 2-9 and sequence analysis of exon 9 of the p53 gene from normal buccal or tongue mucosa as well as the squamous cell carcinomas from the buccal mucosa or the tongue were determined. p53 (wild type) expression was significantly reduced in the tongue dysplastic mucosa or squamous cell carcinoma. The SSCP disclosed banding shifts or new bands in exons 2/3, 4, 8, and 9 for the tongue or buccal oral carcinomas (five of each). In exon 9 the mutation in codon 307 (ala)GCC-GTC(val) was present in the tongue but not in the buccal carcinoma. Other markers included the level of PCNA. PCNA was initially lower in the premalignant tongue lesions but increased in oral squamous cell carcinoma at both sites. In contrast, the amount of nucleosome formation in the tongue carcinomas was less than the level noted for buccal cancers but premalignant dysplasias in the tongue mucosa exhibited higher levels. The inhibitor of PCD, Bcl-2 was lower for dysplasias and carcinomas of the tongue compared to similar lesions of the buccal mucosa. These results indicate that oral carcinomas of different anatomical sites can exhibit differences in growth, oncogene mutation expression, and the development of PCD. The differences in Bcl-2 and nucleosome formation may signify their influence on oncogene expression and growth potential for developing transformed clones and established oral carcinomas.

Dietary antioxidants and lung cancer risk: a case-control study in Uruguay

To examine the protective role of dietary antioxidants (carotenoids, vitamin C, vitamin E, glutathione, and flavonoids) in lung cancer risk, a case-control study involving 541 cases of lung cancer and 540 hospitalized controls was carried out in Uruguay. The relevant variables were energy adjusted using the residuals method and then categorized in quartiles. Adjusted odds ratios (ORs) for antioxidants were calculated through unconditional logistic regression. With the exception of lycopene and vitamin C, the remaining antioxidants were associated with significant reductions in risk of lung cancer. Of particular interest was the inverse association between dietary glutathione and lung cancer [OR of quartile with highest intake compared with lowest quartile = 0.42, 95% confidence interval (CI) = 0.27-0.63]. Also, carotenoids and vitamin E were associated with significant reductions in risk of lung cancer (OR = 0.43, 95% CI = 0.29-0.64 for total carotenoids and OR = 0.50, 95% CI = 0.39-0.85 for vitamin E). A joint effect for high vs. low intakes of beta-carotene and glutathione was associated with a significant reduction in risk (OR = 0.32, 95% CI = 0.22-0.46). It could be concluded that dietary antioxidants are associated with a significant protective effect in lung carcinogenesis and that the inverse association for glutathione persisted after controlling for total vegetables and fruits.

Ascorbic acid recycling in Nb2 lymphoma cells: implications for tumor progression

Analysis of cultured rat "Nb2 lymphoma" cell lines, showing different degrees of malignant progression, can lead to identification of phenotypic changes associated with this phenomenon in T-cell cancers. In the present study we have compared the metastatic sublines, Nb2-11 and Nb2-SFJCD1, with regard to ascorbate and glutathione recycling, important processes in cellular protection from oxidative stresses. Whereas the Nb2-11 subline is prolactin (PRL)-dependent, the genetically related Nb2-SFJCD1 subline is growth factor-independent and shows more chromosomal alterations, indicative of more advanced progression. The Nb2-SFJCD1 cells, compared to the Nb2-11 cells, were less sensitive to toxic effects of dehydroascorbate, a potentially toxic oxidation product of ascorbate. Results were consistent with a significantly higher production of reducing equivalents (e.g., NADPH, GSH) and an accelerated reduction of dehydroascorbate by homogenates of Nb2-SFJCD1 cells. However, the increased resistance was apparently not directly related to the cellular uptake and reduction of dehydroascorbate by whole cells, which was similar in both cell lines. Observations indicate that Nb2 lymphoma cells, in their progression to malignancy, can acquire an enhanced capability to protect themselves from oxidative damage assisting them in withstanding the oxidative stress that anti-neoplastic drugs can cause. The adaptation may also be a mechanism that is utilized by tumor cells in suppressing apoptosis and other protective cellular functions facilitating, or potentiating, a tumor cell's ability to become more metastatic. However, the mechanism leading to this augmented capacity of Nb2 lymphoma cells to resist oxidative stress in not known and is the subject for further study.

Supplementation with canthaxanthin affects plasma and tissue distribution of alpha- and gamma-tocopherols in mice

The effects of oral doses of canthaxanthin on tissue distribution of alpha- and gamma-tocopherols were investigated in three experiments in male and female Balb/c mice. Mice were assigned to receive canthaxanthin [7 or 14 microg/(g body weight.d)] or placebo (olive oil) by gavage for different periods of time (0, 1, 2, 4 and 6 wk). A 2 wk-treatment with canthaxanthin resulted in incorporation of the carotenoid in all tissues analyzed, including liver, spleen, kidney, lung and heart. In liver, the maximum accumulation of the carotenoid was reached after 2 wk of dosing in female mice and after 6 wk in male mice. Canthaxanthin incorporation was accompanied by changes in alpha- and gamma-tocopherol concentrations in plasma and tissues. These included the following: 1) a significant increase (P < 0.001) in alpha-tocopherol concentration in spleen (21 and 27% in male and female mice, respectively) after 2 wk and in liver ( approximately 50% in both male and female mice) after 6 wk; 2) a significant decrease in gamma-tocopherol concentration in plasma (P < 0.05) and tissues (P < 0.001) after 2 wk of treatment. In female mice, this decrease was 55% in plasma, 43% in liver, 44% in kidney, 71% in lung and 70% in heart. In male mice, the decrease was observed only in plasma (30%), kidney (54%) and heart (46%). In liver, the decrease in gamma-tocopherol concentration was both dose- and time-dependent and significantly (P < 0.001) greater in female than in male mice. We conclude that dietary administration of canthaxanthin modifies tocopherol status in murine tissues.

Prooxidant actions of carotenoids in biologic systems

The potential for carotenoids to modulate chronic disease risk is currently under investigation, and renewed interest has been placed on achieving a better understanding of the mechanisms of action of carotenoids in biologic systems. Available data currently show that the antioxidant activity of these compounds may shift into prooxidant activity, depending on the redox potential of the carotenoid molecules as well as on the biologic environment in which they act. The prooxidant potency of these compounds is determined by several factors, including oxygen tension, carotenoid concentration, and interactions with other antioxidants. Prooxidant activity can induce either beneficial or harmful results in biologic systems and influence the development of human chronic diseases.

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.

Mechanisms of cancer inhibition by anti-oxidant nutrients

The cancer inhibitory properties of anti-oxidant micronutrients have been well established in experimental animal models and cell culture studies. Human studies have also tended to indicate an inhibition of various forms of cancer and the regression of some precancerous lesions. The biological mechanisms for cancer inhibition and regression are now gradually becoming understood, and the anti-oxidant nutrients appear to act through a number of pathways common to most of the agents studied. These various micronutrients appear to act through a complex group of "common pathways" of anticancer activity based upon three major mechanisms: (1) tumour inhibition by immune cytokines; (2) stimulation of cancer suppressor genes, such as "wild type" p53, and diminished expression or dysregulation of oncogenes such as mutant p53 and H-ras; (3) inhibition of tumour angiogenesis through the inhibition of angiogenesis-stimulating factors such as TGF alpha. Retinoid action differs, in some respects, from other micronutrient anticancer mechanisms and appears to relate to its stimulation of cellular differentiation and resultant apoptosis of neoplastic cells. Combinations of anti-oxidant nutrients have been shown to be synergistic in their anticancer activity, probably due to their optimal anticancer activity at different oxygen potentials. Selectivity in the action on cancer cells, as opposed to normal cells, is a major feature of the anti-oxidant micronutrients.

Verification in syngeneic hamsters of in vitro transformation of hamster oral mucosa by 7,12-dimethylbenz(a)anthracene

The carcinogen 7,12-dimethylbenz(a)anthracene (DMBA) has been used to induce oral carcinogenesis of the hamster buccal mucosa in an experimental model that exhibits many of the genetic, biochemical and pathological features of human oral squamous cell carcinoma. To complement this in vivo process we have established an in vitro transformation procedure that involved the treatment of normal hamster oral mucosal keratinocytes (NHKs) with DMBA. Uptake of DMBA in NHKs was verified by observing autofluorescence of DMBA in the oral mucosal cells. Treatment doses ranged from 5, 50 and 200 ng and the NHKs were generally treated with DMBA for 1-14 days. The 200 ng dose proved to be toxic to these cells. The 5 and 50 ng treatments were found to maintain the viability of the NHKs and demonstrate anchorage-independent agarose growth, producing 18 and 40 colonies, respectively, after 14 days of treatment. Characterisation assays included determinations for cellular growth through plating efficiency, counting of cell colony number, and 3H-thymidine incorporation. Differentiation was ascertained by counting cornified cells, specification of either high or low molecular weight keratins, the percentage of cells expressing gamma glutamyl-transpeptidase (GGT), the level of p53 expression, and a determination of cell cycle. After 24 h the plating efficiency of the NHKs was found to be slightly increased following treatment with a 5 or 50 ng dose of DMBA compared to the untreated NHKs. After 14 days of incubation these doses also enhanced the number of colonies formed by the NHKs (e.g. plating efficiency). In contrast, the number of cornified cells was reduced in these colonies, while immunohistochemistry disclosed an increase in the number of NHKs expressing low molecular weight keratins, significantly lower levels of high molecular weight keratins and high levels for GGT. Flow cytometric analysis verified an increase in p53 expression (e.g. p53 wild type, 19% and p53 mutant, 66%). Cell cycle analysis of NHKs treated with DMBA (5 ng) demonstrated a shift in the number of cells in S phase (17.2%) and G2 + mitosis (11.0%). Cells from this DMBA treatment group were injected into syngeneic hamster recipient buccal pouches (10 x 10(6) cells/0.25 ml). Squamous carcinomas grew in four of six hamster buccal pouches as determined by histopathological analysis. The in vitro assay system will enhance our ability to define the genetic and molecular changes related to chemical carcinogenesis and oral malignant transformation.

Chemoprevention of colorectal cancer

This review summarizes the principles of cancer chemoprevention and discusses the evidence from epidemiologic and experimental studies and preclinical and clinical trials of potential colorectal chemopreventive agents. The putative mechanisms of action of the drugs in chemoprevention and their potential to reduce the incidence and mortality rate of colorectal neoplasms are discussed. The future of colorectal chemoprevention will depend on important new insights into molecular carcinogenesis of colorectal cancer, application of molecular markers as surrogate endpoints, and ultimately on therapeutic targets of prevention in clinical trials.

The paradoxical role of lipid peroxidation on carcinogenesis and tumor growth: a commentary

Lipid peroxidation has been shown to both enhance carcinogenesis and to have an anticarcinogenic effect. This paradox is of great relevance to the fields of free radical biology, biochemistry, pathology, nutrition and oncology among others and needs to be addressed. A proper understanding of this issue can be a key to more effective treatment of malignant tumors in the near future.

Vitamin E inhibits experimental carcinogenesis and tumour angiogenesis

In an experiment in which vitamin E inhibited carcinogenesis, it was found that tumour angiogenesis and tumour growth-factor alpha (TGF alpha) expression were also inhibited. Forty male golden hamsters were divided into four equal groups. Group 1 animals had the left buccal pouches painted three times weekly with 7,12-dimethylbenz(a)anthracene (DMBA) for 14 weeks. Group 2 animals had the same procedure of DMBA applications but also received alpha tocopherol. Groups 3 and 4 were vitamin E and untreated controls. Angiogenesis was studied with factor 8-related antigen (F8-RA) which identifies endothelial cells. TGF alpha was studied with the appropriate antibody. Staining was effected by the standard avidin-biotin horseradish peroxidase system. Mean tumour volume was significantly lower in the DMBA-vitamin E group compared to the tumour control group. Angiogenesis was significantly inhibited in the DMBA-vitamin E group and TGF alpha expression was also inhibited. It is suggested that inhibition of tumour angiogenesis by vitamin E may be an additional mechanism for the anticancer action of vitamin E.

Glutathione inhibits experimental oral carcinogenesis, p53 expression, and angiogenesis

Previous studies have shown that reduced glutathione (GSH) inhibits experimental oral carcinogenesis in the hamster buccal pouch model. To gain further understanding of molecular mechanisms in the anticancer effect of GSH, these studies examined levels of p53 protein expression. 7,12-Dimethylbenz[a]anthracene (DMBA) was applied to the buccal pouches of 20 Syrian Golden hamsters (Mesocricetus auratus) in a 0.5% solution in mineral oil thrice weekly for 14 weeks. In 10 animals, 10 mg/kg reduced glutathione (GSH) in 0.5 ml of mineral oil was administered by mouth thrice weekly on days alternate to the DMBA painting. An additional 20 animals served as DMBA-untreated and GSH controls. At the termination of the experimental period, there were fewer tumors in the DMBA-GSH than in the DMBA tumor control group, and the tumors were smaller (tumor burden 315 vs. 3,040 mm3). Histologically, the DMBA-GSH group showed a marked reduction in dysplasia, carcinoma in situ, and invasive epidermoid carcinoma sites. Immunohistochemically, by use of monoclonal antibodies for wild-type p53 (PAb 246), changes were observed in protein expression levels at dysplastic sites and within the malignant tumors. Staining for p53 protein was slightly increased in dysplasia and squamous cell carcinoma in the tumor control animals (painted with DMBA) compared with the untreated controls that were free of tumors. In the GSH and DMBA treatment group, p53 protein expression levels were strongly increased in dysplastic and tumor sites. The significant inhibition of oral carcinogenesis associated with the administration of GSH was correlated with the increased levels of the wild-type p53 tumor suppressor gene, suggesting its possible use as a biomarker for GSH chemoprevention. The inhibition of oral carcinogenesis by reduced GSH was also related to a very significant inhibition of tumor angiogenesis, defined by factor VIII staining. Thus angiogenesis inhibition may be an additional mechanism for antioxidant chemoprevention, and this suggests another possible biomarker for antioxidant chemoprevention.

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.

Pentachlorophenol-induced oxidative DNA damage in mouse liver and protective effect of antioxidants

8-Hydroxydeoxyguanosine (8-OH-dG) was determined as a marker of oxidative DNA damage in male B6C3F1 mice treated with the hepatocarcinogen pentachlorophenol (PCP). A single oral administration of PCP (0-80 mg/kg) significantly and dose-dependently increased the 8-OH-dG level specifically in the liver at 6 hr. Repeated doses (0-80 mg/kg) over 5 days caused a further increase. Elevation of the 8-OH-dG level caused by a single dose of PCP (60 mg/kg) was not affected by ip injection of buthionine sulfoximine (2 mmol/kg), an inhibitor of GSH synthesis, or aminotriazole (1 g/kg), an inhibitor of catalase, showing no clear evidence for enhancement by the oxidative stress due to reduction of antioxidative factors under these experimental conditions. However, examination of the effects of natural antioxidants on repeated PCP treatment (60 mg/kg/day, for 5 days) revealed that oral administration of vitamin E and diallyl sulfide 3 hr before each PCP challenge significantly protected against elevation of hepatic 8-OH-dG levels. beta-Carotene did not have any effect. Ellagic acid, epigallocatechin gallate and vitamin C demonstrated partial protection. These findings indicate that PCP causes oxidative DNA damage in the target organ liver which can be blocked by a number of antioxidant agents.

Inhibition of progression of aberrant crypt foci and colon tumor development by vitamin E and beta-carotene in rats on a high-risk diet

In this study we evaluated the effect of dietary administration of a high-fat, low-fiber diet (HRD) supplemented with Vitamin E, beta-carotene or folic acid and wheat bran on the growth of pre-existing aberrant crypt foci (ACF) that had been induced in Fischer-344 rats exposed to azoxymethane (AOM) and a HRD for 10 weeks. The rats (25 rats/dietary group) were fed a HRD for 2 weeks and were then given 2 subcutaneous injections of AOM (15 mg/kg body weight) while the rats continued on the HRD. After 6 weeks, rats were either maintained on the HRD (control) or crossed over to a HRD containing non-toxic levels of either Vitamin E, beta-carotene, folic acid or wheat bran. At 10, 14 and 18 weeks after the initiation of the experiment, 5 rats from each group were killed and the number of aberrant crypt foci (ACF) with different multiplicities were compared between groups. The dietary intervention was continued for 30 weeks to determine whether the inhibitory effect on the growth of ACF influenced the subsequent development of colonic tumors. The results revealed that vitamin E and beta-carotene caused a significant decrease in the number of ACF of different multiplicities when compared to the effect of the HRD alone. The decrease in the number of ACF due to folic acid and wheat bran appeared to be much smaller and in most cases was not significant. However, there was also a significant decrease in the incidence of colonic tumors and tumor multiplicity in both the vitamin E and beta-carotene groups that was not seen in the control group. The reports clearly demonstrates the ability of vitamin E and beta-carotene to inhibit the growth of colonic ACF, even in the presence of the strong promoting effect of high levels of dietary fat, using a post-initiation experimental design.

Vitamin E enhances the lymphatic transport of beta-carotene and its conversion to vitamin A in the ferret

BACKGROUND/AIMS

beta-Carotene and alpha-tocopherol may have either antagonistic or synergistic effects on each other's absorption and metabolism. The effects of both physiological and pharmacological concentrations of alpha-tocopherol on the absorption and metabolism of beta-carotene in ferret intestine were determined.

METHODS

A high concentration of beta-carotene was perfused through the upper portion of the small intestine of ferrets in vivo with varying levels of alpha-tocopherol. The effluent of a mesenteric lymph duct cannulation, the intestinal mucosal scraping, and portal vein blood were sampled and analyzed by high-performance liquid chromatography.

RESULTS

The lymphatic transport of beta-carotene was enhanced 4-fold by alpha-tocopherol at a physiological dose and 12-21-fold at a pharmacological dose. The lymphatic transport of alpha-tocopherol was linearly (r = 0.8; P < 0.05) related to the luminal alpha-tocopherol concentration even in the presence of a high concentration of beta-carotene. Furthermore, alpha-tocopherol increased the conversion of beta-carotene into retinol in the intestine in a dose-dependent manner.

CONCLUSIONS

alpha-Tocopherol has a positive effect on the intestinal absorption of intact beta-carotene and may modulate the metabolic conversion of beta-carotene into retinoids.

Vitamin E succinate potentiates the inhibitory effect of prostaglandins on oral squamous carcinoma cell proliferation

Previous studies have shown that prostaglandin E2 (PGE2) and vitamin E succinate can act in an additive manner to inhibit the proliferation of human oral squamous carcinoma cells (SCC-25). The initial studies on the additive anticancer activity of PGE2 and vitamin E succinate have been extended to include antineoplastic PGs, delta 12-PGJ2 and PGJ2. Treatment of oral squamous carcinoma cells (SCC-15) with delta 12-PGJ2, PGJ2, and vitamin E succinate, individually, caused significant concentration-dependent inhibition of cell proliferation to various degrees. PGJ2 was most potent and caused an inhibition that corresponded to 85.55% at 10(-5) M. Addition of 1 microM of vitamin E succinate to delta 12-PGJ2 or PGJ2 resulted in a significant increase in the inhibitory potency of the lower concentrations of the two PGs. These results suggest a novel role for a mixture of PGs and vitamin E as potent antitumor proliferative agents.

Accumulation of beta-carotene in normal colorectal mucosa and colonic neoplastic lesions in humans

The quantity of beta-carotene (BC) accumulated in colonic polyps and colonic cancerous tissue in humans in situ was determined relative to the quantity accumulated in normal colon and rectal tissue. Serum concentration of BC, retinol, and alpha-tocopherol and tissue BC concentration were determined by high-performance liquid chromatography in samples obtained before and after oral supplementation with BC (30 mg/day). The serum BC and retinol concentrations significantly increased in response to supplementation in control, polyp, and cancer patients, but there was no change in serum alpha-tocopherol concentration. The BC concentration in tissue (colon, rectum, and tumor) of cancer patients was significantly less than that in tissue samples from control and polyp patients. Relative to baseline values, BC accumulated to a significant extent in tissues from all patients, including polyp and tumor tissue, during supplementation. The results indicate that BC does accumulate in colonic neoplastic tissue in humans and may potentially be utilized to augment cytotoxicity of chemotherapeutics or to prevent malignant transformation of cells.

Antioxidants and carcinogenesis

It is established beyond doubt that free radicals in tissues and cells can damage DNA, proteins, carbohydrates and lipids. These potentially deleterious reactions are at least partly controlled by antioxidants capable of scavenging free radicals. It is widely believed that a proper balance between free radicals and antioxidants is essential for the health of an organism. A vast body of observational epidemiological studies has suggested that high intake of dietary or supplemental antioxidants protects against ischaemic heart disease, various types of cancer and several other diseases. Final proof for the beneficial effects of antioxidants can, however, be obtained from controlled studies. Conflicting results of the first three major clinical trials force us to postpone conclusions of the usefulness of antioxidant supplements in disease prevention until the other on-going trials have been published.

Chemopreventive potential of dietary bioflavonoids against 20-methylcholanthrene-induced tumorigenesis

The effect of dietary supplementation of flavonoidal compounds such as quercetin, rutin, luteolin and (+)-catechin on the incidence of fibrosarcoma induced by 20-methylcholanthrene (20-MC) in male Swiss albino mice was observed. Subcutaneous injection of 20-MC produced 100% tumor incidence and the onset of tumor appeared within 7 weeks, while flavonoid-treated mice (1% quercetin- and luteolin-mixed diets) produced tumors in the 9th week, and the tumor incidences in mice treated with quercetin- and luteolin-mixed diets were 52% and 60%, respectively. Subcutaneous administration of 20-MC along with the flavonoidal compounds (quercetin, luteolin) was found to have significant effect on tumor expression. The compounds rutin and (+)-catechin did not influence tumor expression in both experiments. Elevated levels of lipid peroxides, cytochrome P450 and decreased activity of glutathione-S-transferase (GST) were observed in the tumor bearing animals. Test-diet-treated animals showed reduction in the lipid peroxides and cytochrome P450, and increased activity of GST (P < 0.001). In vitro [3H]thymidine incorporation showed the inhibition of DNA synthesis in fibrosarcoma cells by the flavonoids. The possible mode of action of the flavonoidal compounds may be through their influence on the initiation and promotion phases of the carcinogenic process coupled with enhancement of the detoxification process.