p53 in the anticancer mechanism of vitamin E

The Involvement of the Oxidative Stress Status in Cancer Pathology: A Double View on the Role of the Antioxidants

Oxygen-free radicals, reactive oxygen species (ROS) or reactive nitrogen species (RNS), are known by their "double-sided" nature in biological systems. The beneficial effects of ROS involve physiological roles as weapons in the arsenal of the immune system (destroying bacteria within phagocytic cells) and role in programmed cell death (apoptosis). On the other hand, the redox imbalance in favor of the prooxidants results in an overproduction of the ROS/RNS leading to oxidative stress. This imbalance can, therefore, be related to oncogenic stimulation. High levels of ROS disrupt cellular processes by nonspecifically attacking proteins, lipids, and DNA. It appears that DNA damage is the key player in cancer initiation and the formation of 8-OH-G, a potential biomarker for carcinogenesis. The harmful effect of ROS is neutralized by an antioxidant protection treatment as they convert ROS into less reactive species. However, contradictory epidemiological results show that supplementation above physiological doses recommended for antioxidants and taken over a long period can lead to harmful effects and even increase the risk of cancer. Thus, we are describing here some of the latest updates on the involvement of oxidative stress in cancer pathology and a double view on the role of the antioxidants in this context and how this could be relevant in the management and pathology of cancer.

Potential of diallyl sulfide bearing pH-sensitive liposomes in chemoprevention against DMBA-induced skin papilloma

Diallyl sulfide (DAS), an active component of garlic, possesses strong anti-neoplastic properties against various forms of cancer. In the present study, we have evaluated chemo-preventive effects of liposomized DAS (conventional egg PC and pH-sensitive liposomes) against DMBA-induced skin papilloma. Various liposome-based novel formulations of DAS (250 microg/mouse) were applied topically, after one hour of exposure to DMBA (52 microg/mouse/dose), to the animals. The animals were treated thrice weekly for the total period of 12 weeks. The efficacy of the various liposomal formulations of DAS was evaluated on the basis of parameters such as incidence of tumorogenesis and total numbers and sizes of induced tumor nodules. The liposomized DAS formulations also were assessed for their effect on the expression of p53wt, p53mut, and p21/Waf1. The results of the present study showed that liposomized DAS could effectively delay the onset of tumorogenesis and reduce the cumulative numbers and sizes of tumor papillomas in treated mice. Treatment of DMBA-exposed animals with the liposomal formulation of DAS ensued in upregulation of p53wt and p21/Waf1, while levels of p53mut expression reduced down. The promising chemo-preventive nature of liposomal DAS may form the basis for establishing effective means of controlling various forms of cancer, including skin papilloma.

Potential of diallyl sulfide bearing pH-sensitive liposomes in chemoprevention against DMBA-induced skin papilloma

Diallyl sulfide (DAS), an active component of garlic, possesses strong anti-neoplastic properties against various forms of cancer. In the present study, we have evaluated chemo-preventive effects of liposomized DAS (conventional egg PC and pH-sensitive liposomes) against DMBA-induced skin papilloma. Various liposome-based novel formulations of DAS (250 microg/mouse) were applied topically, after one hour of exposure to DMBA (52 microg/mouse/dose), to the animals. The animals were treated thrice weekly for the total period of 12 weeks. The efficacy of the various liposomal formulations of DAS was evaluated on the basis of parameters such as incidence of tumorogenesis and total numbers and sizes of induced tumor nodules. The liposomized DAS formulations also were assessed for their effect on the expression of p53wt, p53mut, and p21/Waf1. The results of the present study showed that liposomized DAS could effectively delay the onset of tumorogenesis and reduce the cumulative numbers and sizes of tumor papillomas in treated mice. Treatment of DMBA-exposed animals with the liposomal formulation of DAS ensued in upregulation of p53wt and p21/Waf1, while levels of p53mut expression reduced down. The promising chemo-preventive nature of liposomal DAS may form the basis for establishing effective means of controlling various forms of cancer, including skin papilloma.

Vitamin E mediates cell signaling and regulation of gene expression

alpha-Tocopherol modulates two major signal transduction pathways centered on protein kinase C and phosphatidylinositol 3-kinase. Changes in the activity of these key kinases are associated with changes in cell proliferation, platelet aggregation, and NADPH-oxidase activation. Several genes are also regulated by tocopherols partly because of the effects of tocopherol on these two kinases, but also independently of them. These genes can be divided in five groups: Group 1. Genes that are involved in the uptake and degradation of tocopherols: alpha-tocopherol transfer protein, cytochrome P450 (CYP3A), gamma-glutamyl-cysteine synthetase heavy subunit, and glutathione-S-transferase. Group 2. Genes that are implicated with lipid uptake and atherosclerosis: CD36, SR-BI, and SR-AI/II. Group 3. Genes that are involved in the modulation of extracellular proteins: tropomyosin, collagen-alpha-1, MMP-1, MMP-19, and connective tissue growth factor. Group 4. Genes that are connected to adhesion and inflammation: E-selectin, ICAM-1 integrins, glycoprotein IIb, IL-2, IL-4, IL-1b, and transforming growth factor-beta (TGF-beta). Group 5. Genes implicated in cell signaling and cell cycle regulation: PPAR-gamma, cyclin D1, cyclin E, Bcl2-L1, p27, CD95 (APO-1/Fas ligand), and 5a-steroid reductase type 1. The transcription of p27, Bcl2, alpha-tocopherol transfer protein, cytochrome P450 (CYP3A), gamma-glutamyl-cysteine sythetase heavy subunit, tropomyosin, IL-2, and CTGF appears to be upregulated by one or more tocopherols. All the other listed genes are downregulated. Gene regulation by tocopherols has been associated with protein kinase C because of its deactivation by alpha-tocopherol and its contribution in the regulation of a number of transcription factors (NF-kappaB, AP1). A direct participation of the pregnane X receptor (PXR) / retinoid X receptor (RXR) has been also shown. The antioxidant-responsive element (ARE) and the TGF-beta-responsive element (TGF-beta-RE) appear in some cases to be implicated as well.

Vitamin E: Textbooks require updating

Vitamin E was discovered in 1922, but in more than 60 years many new findings have added to the early one. However, its description in many textbooks has not been proportionally updated. The result is an inaccurate, incomplete, and often incorrect description of the function of this vitamin. In some other textbooks, vitamin E is absolutely neglected. In almost all books the existence of vitamin E deficiency diseases is ignored. Recent findings on vitamin E molecular functions and its related diseases are described in this article.

Chemopreventive effect of dietary d-alpha-tocopheryl succinate supplementation on precancer colon aberrant crypt formation and vitamin E analogue levels in young and old rats

This study examined the effects of dietary d-alpha-tocopheryl succinate (TS) in female rats, 20 mo (OLD) or 2 mo (YNG) of age, on azoxymethane (AOM)-induced colonic aberrant crypt foci (ACF) and tissue distribution of d-alpha-tocopherol (alphaT), d-gamma-tocopherol (gammaT), and alphaTS. Rats were fed a commercial rodent chow supplemented with or without 1 (YNG) or 2 (OLD) g alphaTS/kg diet for 1 week prior to ip administration of AOM to induce colon ACF. The animals were sacrificed after 49 days of exposure. The results showed that OLD rats had significantly fewer ACF than YNG animals, and the percent body fat and serum triglycerides were significantly higher in the OLD group compared with the YNG. However, only OLD animals receiving alphaTS had significantly reduced numbers of larger ACF and significantly higher levels of colonic alphaT, gammaT, and alphaTS. These data support previous studies demonstrating that dietary alphaTS administration is protective against intestinal cancer. Also, this is the first study to show that alphaTS accumulates in most tissues following dietary exposure. We hypothesize that increased colon accumulation of fat-soluble vitamin E compounds and subsequent chemoprevention may be related to greater percent body fat and serum triglycerides in OLD animals receiving dietary TS.

The role of folates in squamous cell carcinoma of the head and neck

The primary objective of this review is to explore the hypothesis that folate insufficiency may be important in the pathogenesis of squamous cell carcinomas of the head and neck (SCCHN) and that folate repletion may be an effective component of chemoprevention. The main results are that folate insufficiency disrupts DNA global and specific gene methylation patterns such that the activity of certain tumor suppressor genes such as p16 and possibly p53 may be lost. Folate pool imbalance and impaired repair mechanisms may contribute to DNA instability and strand breaks. Sensitive methods exist for identification of individuals with folate insufficiency in contrast to the relatively insensitive conventional serum or red cell folate assays with broad "normal" ranges. The impact of folate supplementation can thus be quantified. Folate imbalance may result from alterations in folate cellular uptake by the reduced folate carrier (RFC) and/or the folate receptor (FR) and polymorphisms in enzymes important in folate retention such as folylpolyglutamate synthetase and in folate modification such as methylene tetrahydrofolate reductase (MTHFR). Known predisposing factors for SCCHN such as alcohol and tobacco carcinogens may influence folate balance. Folate supplementation may reduce primary or secondary risk of cancer. Formal studies of folate sufficiency in persons at risk for or diagnosed and treated for SCCHN are needed to define the role of folate supplementation in the prevention of these cancers.

Modulation of p53 in 7,12-dimethylbenz[a]anthracene–induced skin tumors by diallyl sulfide in Swiss albino mice

Allium vegetables have been shown to have beneficial health effects against several chronic diseases including cancer. Diallyl sulfide (DAS), an organosulfur compound present in garlic, is well known for its chemopreventive properties in several tumor models. The pharmacologic role of DAS in prevention and treatment of cancer is well documented in the literature, but its molecular mechanism of action is not yet well defined. In the present study, modulation in p53 expression by topical application of DAS was recorded in 7,12-dimethylbenz[a]anthracene (DMBA)–induced skin tumors in Swiss albino mice. Western blot analysis and immunohistochemical protein detection, combined with multivariable flow cytometry, show that DAS application induces the expression of the wild-type (wt) p53 and down-regulates the expression of mutant (mut) p53. Immunoblotting analysis of tumors showed significant increase in levels of wtp53 by DAS application, whereas for mutp53 the DMBA-induced levels of protein were found to reduce to near normal levels with DAS application. The quantitative analysis of immunostained skin/tumor sections using image analysis and quantitative stereology showed 66.6% and 54.2% increases in wtp53 levels and 53.4% and 44.3% decreases in mutp53 levels in animals where DAS was applied 1 hour prior to or 1 hour after DMBA application, respectively. Flow cytometric analysis further confirmed modulation of wtp53 and mutp53 protein in DAS-supplemented tumors. The increase in the expression of wt tumor suppressor gene protein p53 was accompanied by elevation of the levels of cyclin-dependent kinase inhibitor p21/waf1. The percentage increase in the levels of p21/waf1 was found to be 72.9% and 61.3%, respectively, in DAS-supplemented groups before and after administration. These results thus show that DAS is a potential chemopreventive agent capable of modulating and regulating the tumor suppressor p53 along with its downstream effective molecule, p21/waf1. Thus, DAS can be a potential chemopreventive agent against skin tumor development.

The role of alpha-tocopherol in preventing disease: from epidemiology to molecular events

The function of vitamin E has been attributed to its capacity to protect the organism against the attack of free radicals by acting as a lipid based radical chain breaking molecule. More recently, alternative non-antioxidant functions of vitamin E have been proposed and in particular that of a "gene regulator". Effects of vitamin E have been observed at the level of mRNA or protein and could be consequent to regulation of gene transcription, mRNA stability, protein translation, protein stability and post-translational events. Given the high priority functions assigned to vitamin E, it can be speculated that it would be inefficient to consume it as a radical scavenger. Rather, it would be important to protect vitamin E through a network of cellular antioxidant defences, similarly to what occurs with proteins, nucleic acids and lipids.

Vitamin E: the evidence for multiple roles in cancer

There is accumulating evidence that vitamin E may have different roles in the prevention and treatment of cancer. The purpose of this review is to summarize and evaluate this evidence and to suggest future avenues of research. A comprehensive literature review of vitamin E and cancer was conducted. Articles were organized into the following categories: 1) cancer prevention, 2) direct antineoplastic activity, 3) augmentation of chemotherapy effects, and 4) attenuation or treatment of chemotherapy toxicity. The evidence was systematically evaluated using guidelines developed by the U.S. Preventative Services Task Force. There is evidence to suggest that those individuals with higher serum vitamin E levels and those receiving vitamin E supplementation have a decreased risk of some cancers, including lung, prostate, stomach, and gastrointestinal carcinoma. However, these results differed depending on the study design and the population studied. There is insufficient evidence to support anticancer activity and attenuation of chemotherapy toxicity by vitamin E. Vitamin E is likely to be important in the prevention of some cancers. The therapeutic role of vitamin E is poorly understood. Further research will be required before routine use of vitamin E in patients with cancer can be advocated in the clinical setting.

Vitamin E and its role in the prevention of atherosclerosis and carcinogenesis: a review

Epidemiological and experimental studies suggest that antioxidants like vitamin E (alpha-tocopherol) may play an important role in prevention of chronic disease. Several observational surveys have linked populations with a large intake of vitamin E with reduced incidence of heart disease. These observations have been strengthened by the demonstration of strong antioxidant activity by vitamin E in cellular, molecular and animal experiments. These results have highlighted a potential role for vitamin E supplementation in the prevention of chronic disease in humans. Interestingly however, large-scale clinical trials of vitamin E and other antioxidants in preventing specific disease processes (e.g., coronary artery disease) have generated conflicting and mixed outcomes. In this review, the role of vitamin E in the prevention of atherosclerosis and carcinogenesis has been carefully examined with particular emphasis on salient human studies (clinical trials) and their limitations. In addition, pertinent biochemical, physiological and metabolic features of vitamin E have also been incorporated. A list of common natural food sources of vitamin E has been provided. Important in vitro and animal studies related to the antiatherosclerotic and anticarcinogenic actions of vitamin E have been discussed in detail. Finally, the direction of future investigations in primary and secondary prevention of chronic diseases by vitamin E supplementation has been outlined.

Susceptibility and biomarker knowledge for improvement of environmental health

At the international level, environmental health problems are usually most serious in countries that have the least resources to deal with the problems. Therefore, international efforts have been initiated to achieve equitable environmental health globally. One approach is to conduct international collaborative studies. This approach has been successful in the building of scientific infrastructure in these countries so that they can address their own environmental health concerns and to sustain the environmental health programs. Using liver and oral cancers as models for discussion, examples of success in the identification of etiology and the mechanisms for the diseases are provided. For example, biomarkers are used to provide early warning signals for the disease. In addition, the application of the collected information for developing disease prevention and intervention programs is presented. Expertise in genetic susceptibility is used to provide a more precise understanding of the cancer process. With the precise knowledge, the information can potentially be used to screen for high-risk individuals and to develop "designer" intervention procedures against specific biochemical defects. Success in disease prevention is dependent upon multidisciplinary collaborations at the local and international levels.

Cancer chemopreventive effects of oral feeding alpha-tocopherol on ultraviolet light B induced photocarcinogenesis of hairless mouse

Ultraviolet light is the most common cause of skin cancers in humans and several effects of ultraviolet light B (UVB: 290-320 nm) are thought to contribute to skin photocarcinogenesis. The generation of free radicals and related oxidants produced by UVB exposure, result in photocarcinogenesis by directly damaging DNA. On the other side, activating of transcription factor, activator protein 1 (AP-1) induced by UVB exposure causes tumor promotion. alpha-tocopherol has two principal physiological activities and one is an antioxidant activity through which alpha-tocopherol protects unsaturated fatty acids, protein and DNA from oxidation. The other activity is to stabilize the structure of the biomembrane. In addition to these two activities, it has been recently established that alpha-tocopherol plays important roles in cell signal transduction. In course of these studies, we examined such effects of alpha-tocopherol on UVB induced skin photocarcinogenesis in hairless mice. These results indicate that oral feeding of alpha-tocopherol including diet exhibited a marked inhibitory effects on both tumor incidence and multiplicity in UVB induced mouse skin photocarcinogenesis.

Alpha-tocopheryl succinate, the most effective form of vitamin E for adjuvant cancer treatment: a review

In 1982, it was established that alpha-tocopheryl succinate (alpha-TS) was the most effective form of vitamin E in comparison to alpha-tocopherol, alpha-tocopheryl acetate and alpha-tocopheryl nicotinate in inducing differentiation, inhibition of proliferation and apoptosis in cancer cells, depending upon its concentration. During the last two decades, several studies have confirmed this observation in rodent and human cancer cells in culture and in vivo (animal model). The most exciting aspect of this alpha-TS effect is that it does not affect the proliferation of most normal cells. In spite of several studies published on the anti-cancer properties of alpha-TS, the value of this form of vitamin E has not drawn significant attention from researchers and clinicians. Therefore, a critical review on the potential role of alpha-TS in the management of cancer is needed. In addition, such a review can also provide in-depth analysis of existing literature on this subject. alpha-TS treatment causes extensive alterations in gene expression; however, only some can be attributed to differentiation, inhibition of proliferation and apoptosis. alpha-TS also enhances the growth-inhibitory effect of ionizing radiation, hyperthermia, some chemotherapeutic agents and biological response modifiers on tumor cells, while protecting normal cells against some of their adverse effects. Thus, alpha-TS alone or in combination with dietary micronutrients can be useful as an adjunct to standard cancer therapy by increasing tumor response and possibly decreasing some of the toxicities to normal cells.

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).

Induction of apoptosis in human breast cancer cells by tocopherols and tocotrienols

The apoptosis-inducing properties of RRR-alpha-, beta-, gamma-, and delta-tocopherols, alpha-, gamma-, and delta-tocotrienols, RRR-alpha-tocopheryl acetate (vitamin E acetate), and RRR-alpha-tocopheryl succinate (vitamin E succinate) were investigated in estrogen-responsive MCF7 and estrogen-nonresponsive MDA-MB-435 human breast cancer cell lines in culture. Apoptosis was characterized by two criteria: 1) morphology of 4,6-diamidino-2-phenylindole-stained cells and oligonucleosomal DNA laddering. Vitamin E succinate, a known inducer of apoptosis in several cell lines, including human breast cancer cells, served as a positive control. The estrogen-responsive MCF7 cells were more susceptible than the estrogen-nonresponsive MDA-MB-435 cells, with concentrations for half-maximal response for tocotrienols (alpha, gamma, and delta) and RRR-delta-tocopherol of 14, 15, 7, and 97 micrograms/ml, respectively. The tocotrienols (alpha, gamma, and delta) and RRR-delta-tocopherol induced MDA-MB-435 cells to undergo apoptosis, with concentrations for half-maximal response of 176, 28, 13, and 145 micrograms/ml, respectively. With the exception of RRR-delta-tocopherol, the tocopherols (alpha, beta, and gamma) and the acetate derivative of RRR-alpha-tocopherol (RRR-alpha-tocopheryl acetate) were ineffective in induction of apoptosis in both cell lines when tested within the range of their solubility, i.e., 10-200 micrograms/ml. In summary, these studies demonstrate that naturally occurring tocotrienols and RRR-delta-tocopherol are effective apoptotic inducers for human breast cancer cells.

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.

Inhibition of growth in oral squamous carcinoma cells by cyclopentenone prostaglandins: comparison with chemotherapeutic agents

Four cyclopentenone prostaglandins (CPPGs) and PGE2 caused significant dose-dependent inhibition in growth of human oral squamous carcinoma cells (SCC-15). The rank order of their potency was PGJ2>PGA1>16, 16-dimethyl PGA1>PGA2>PGE2. In a follow-up experiment it was found that the mean per cent inhibition in cell growth by PGJ2 and delta12-PGJ2 at 10(-5) M was 61.22 and 63.81, while that of 5-fluorouracil and methotrexate was 36.67 and 38.86, respectively. delta12-PGJ2 and PGJ2 induced significant dose-dependent inhibition in nuclear DNA synthesis (i.e. cell proliferation). Combining vitamin E succinate with lower concentrations of CPPGs enhanced significantly their inhibitory effect on nuclear DNA synthesis of cancer cells.

Vitamin E and human health: rationale for determining recommended intake levels

The recent literature provides strong evidence that vitamin E intakes much higher than the current recommendations can contribute to and/or improve human health. In fact, the available data indicate that at higher-than-current recommended intake levels, vitamin E affects several functions related to human health. For example, Vitamin E is required to protect polyunsaturated fatty acids (PUFAs) against auto-oxidation. The amount of vitamin E needed to protect PUFAs against oxidative damage is at least 0.4-0.8 mg vitamin E per gram PUFAs and may be in excess of 1.5 mg/g when diets contain higher-than-average levels of long-chain PUFAs. Based upon studies of vitamin E kinetics and metabolism, a daily vitamin E intake of 135-150 IU is suggested. Important functions such as protection against oxidative damage, immune response, and the propensity of platelets to adhere to the vessel wall are related to vitamin E intakes. Vitamin E intake of 40 IU/d was the least amount demonstrated to inhibit low-density lipoprotein oxidation; a dose-dependent effect was seen up to 800 IU/d. Vitamin E intakes of at least 60 IU/d enhanced immune responses and intakes of 200 IU-400 IU/d decreased platelet adhesion to the vessel wall. Based upon the effects of modulating these functions, it is hypothesized that vitamin E plays a pivotal role in the prevention of cardiovascular diseases. Indeed, many observational studies have reported vitamin E to reduce the risk of cardiovascular disease. Recent intervention studies corroborate these findings. Of equal importance, there is a solid body of literature that demonstrates that these and much higher vitamin E intakes are safe.

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.

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.

Altered cytokeratin expression in carcinogenesis inhibition by antioxidant nutrients

Epidermoid carcinomas were induced in hamster buccal pouches with use of 7.12 dimethylbenz[a]anthracene (DMBA). In five animals that served as tumor controls (Group 1), right buccal pouches were painted with DMBA (0.5% solution in mineral oil) thrice weekly for 14 weeks. In five animals (Group 2), right buccal pouches were painted with DMBA and reduced glutathione (GSH) was administered systemically by mouth. Five animals (Group 3) received vitamin E instead of glutathione. An additional 20 animals (Groups 4, 5, 6, and 7) were untreated, vehicle, glutathione, and vitamin E controls, respectively. Glutathione and vitamin E were given in doses of 10 mg/kg in 0.5 ml of mineral oil thrice weekly on days alternate to DMBA painting. Treatment by GSH and vitamin E reduced the number and size of tumors that were formed. Histopathologically, there were also fewer sites of dysplasia, carcinoma in situ, and early invasive epidermoid carcinoma than in the tumor control animals. The formalin-fixed and paraffin-embedded buccal pouch sections were stained immunohistochemically with use of monoclonal antibodies for cytokeratins. These included high-molecular-weight keratins (50,000-68,000 mol wt) 10, 13, and 8 (k10, k13, and k8, respectively). Oral carcinomas and dysplastic sites exhibited basal and suprabasal (spinous layer) high levels of k10, k13, and k8 staining. Treatment with GSH or vitamin E increased the suprabasal staining for high-molecular-weight keratins and reduced the protein expression for k10, k13, or k8. This pattern of staining was observed in dysplastic as well as in carcinoma sites. These results indicate that cytokeratin protein expression could contribute to a common biomarker analysis for chemoprevention.