Inhibition of oral carcinogenesis by glutathione

Lower tumorigenesis without life extension in rats receiving lifelong deep ocean minerals

Naturally occurring tumor in animals receiving high minerals from deep oceans (DOM: hardness 600 mg/L) from 6 months of age until natural death was firstly assessed in 200 Sprague Dawley rats, randomized into four groups: Control (C), DOM (D), Fructose (F), and Fructose + DOM (FD). Fructose drink contained 11% fructose. Tumor incidence (necropsy at death) in the D group was ~40% lower than that in the C group (P < .05), together with lower body mass gain and greater locomotive activity during their initial 18 months (P < .05) but not during later life. X‐ray image analysis on abnormal solid tissue among survivors at 18 and 24 months of age confirms a similar trend, exhibiting ~50% and ~65% lower tumor incidence than the C and F groups, respectively. Reduced‐to‐oxidized glutathione ratio (GSH/GSSG) declined with age for the first three quarters of life on all groups (P < .05), followed by a resurgence during end‐life among survivors at 24 months. This resurgence is markedly associated with lower tumor expansion but unrelated with DOM supplementation. Our results demonstrate valuable application of minerals and trace elements from deep oceans, as a vastly available natural source, on tumor suppression during normal aging.

In vitro effect of oxidized and reduced glutathione peptides on angiotensin converting enzyme purified from human plasma

Angiotensin converting enzyme (ACE, peptidyldipeptidase A, EC 3.4.15.1) plays an important role in the regulation of blood pressure. In this study, ACE was purified from human plasma by affinity chromatography in single step. The enzyme purified in 5367-fold from human plasma and specific activity was found to be 1208 EU/mg protein. The purity and molecular weight of ACE were determined by SDS-PAGE, which indicated two bands at around 60 kDa and 70 kDa on the gel. Effect of oxidized glutathione (GSSG) peptide and reduced glutathione (GSH) peptide on purified ACE activity were also investigated in which lisinopril was used as reference inhibitor. GSSG showed activation effect on ACE activity whereas GSH provided inhibition effect. In the lights of activity (%) versus activator graph for GSSG and activity (%) versus inhibitor graphs for GSH and lisinopril; IC₅₀ values for GSH and lisinopril were determined to be 16.2 μM and 0.781 nM, respectively. Type of inhibition for GSH and lisinopril from graph Lineweaver-Burk was found to be reversible non-competitive inhibition and K_i constants for GSH and lisinopril were calculated as 11.7 μM and 0.662 nM, respectively.

Selective Extraction and Antioxidant Properties of Thiol-Containing Peptides in Soy Glycinine Hydrolysates

A highly selective procedure to extract thiol-containing peptides (TCPs) from complicated soy glycinin hydrolysates (SGHs) was described. This procedure included the reduction of disulfide bonds by 1,4-dithiothreitol (DTT) and enrichment of TCPs through Thiopropyl-Sephrose 6B covalent chromatography. TCPs were confirmed using a strategy based on mass shift after differential alkylation of sulfhydryl groups with iodoacetamide and N-ethylmaleimide by matrix-assisted laser desorption ionization mass spectrometry (MALDI-TOF-MS). The antioxidant activities of TCPs were evaluated using chemical assays. DTT reduction increased the concentration of sulfhydryl groups from 1.8 μmol/g to 113.8 μmol/g. The efficiency of the extraction was improved by optimizing the loading of sample, extraction and desorption time and the content of desorption reagent. Both of the adsorption and desorption process were found to fit a pseudo-second order model. MALDI-TOF-MS showed that 36 of the 45 extracted peptides were TCPs. The EC50 of TCPs for DPPH, hydroxyl radical, and superoxide anion radical was 0.1, 1.49 and 0.084 mg/mL, respectively. The reducing power of TCPs (0.2 mg/mL) was of 0.375. These results suggest that the combination of DTT reduction and Thiopropyl-Sepharose 6B covalent chromatograph was a successful pathway to extract TCPs from SGHs and the TCPs could be used as potential antioxidants.

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.

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.

A functional trinucleotide repeat polymorphism in the 5'-untranslated region of the glutathione biosynthetic gene GCLC is associated with increased risk for lung and aerodigestive tract cancers

Glutathione (GSH), the major intracellular antioxidant, protects against cancer development by detoxifying carcinogens and free radicals and strengthening the immune system. Recently, a GAG-trinucleotide repeat polymorphism in the 5'-untranslated region of the gene for the rate-limiting enzyme for GSH biosynthesis, γ-glutamine cysteine ligase (GCL), was shown to be associated with lowered GCL activity and GSH levels in vitro and in vivo. We tested the hypothesis that this functional polymorphism in GCL is associated with the risk for lung and aerodigestive tract cancers. To this end, we conducted a case-control study that included 375 lung cancer cases, 200 aerodigestive tract cancer cases, and 537 controls. GAG repeat genotype (4, 7, 8, 9, and 10 repeat alleles) was determined by capillary electrophoresis of PCR products from the repeat region of the GCL catalytic subunit (GCLC). Odds ratios (OR) were calculated by logistic regression and adjusted for risk factors, including age, sex, body mass index, and smoking history. The GAG-7/7 genotype was associated with a 1.9-fold increased risk of lung cancer and 2.6-fold increased risk of aerodigestive tract cancer compared to the wild-type GAG-9/9 (P < 0.05). Similarly, the GAG-7 allele was associated with an increased risk of lung cancer (OR = 1.5, P = 0.01) and aerodigestive tract cancer (OR = 2.3, P < 0.001) compared to subjects without GAG-7 allele. These findings suggest that GSH synthesis affects the risk of lung and aerodigestive tract cancers, and further implicates a role for oxidative stress in the development of these cancers.

Cajanus indicus leaf protein: Beneficial role in experimental organ pathophysiology. A review

The herb, Cajanus indicus L, has been and is popular for its medicinal value in India and other countries for long. The herb is mainly cultivated for the seeds which are used as pulses and are rich in proteins. People of rural India and some neighboring countries use the aqueous extract of the leaves of the herb against poor liver function and recently it has been found that the extract is not only useful against liver damage but also beneficial for renal failure and a number of other pathophysiological conditions. Intraperitoneal administration of the aqueous protein fraction of the leaves has shown hepatoprotective activity in mice. The protein fraction revealed the presence of a 43kDa protein having antioxidant and other protective properties in organ pathophysiology. The purified protein, CI-protein, scavenges free radicals generated by different free radical inducers and helps providing cytoprotection. Amino acid sequence of CI-protein has some structural similarity with plastocyanin, an electron carrier protein in photosynthesis. The protein has also been found to be active against a number of organ dysfunction inducer chemicals and drugs, like carbon tetrachloride, thioacetamide and acetaminophen. Signal transduction studies suggest that CI-protein exerts its protective action by free radical scavenging and antioxidative properties; it activates NF-κB and Akt without any involvement of ERK1/ERK2 and STAT-3 in acetaminophen induced hepatic pathophysiology. Besides, it reduces both drug and toxin induced cytotoxicity by decreasing the formation and/or scavenging of free radicals involving cytochrome P450, taking part in detoxification of xenobiotics.

Blood iron, glutathione, and micronutrient levels and the risk of oral cancer

The risk of oral cavity cancer was determined in relation to serological levels of iron; vitamins A, B2, C, E; zinc; thiamin; and glutathione (GSH). The study included 65 hospitalized patients with oral cancer and 85 matched controls. In comparing the highest to the lowest tertiles, the risk was odds ratio (OR) = 0.3 [95% confidence interval (CI) = 0.1-0.6] for iron; 3.2 (95% CI = 1.3-8.1) for total iron binding capacity (TIBC), which measures the concentration of the iron delivery protein transferrin; and 0.4 (95% CI = 0.2-0.9) for transferrin saturation (iron/TIBC x 100). These associations were stronger in never smokers than in ever smokers. The risk associated with the iron storage protein ferritin was significantly elevated, but this association could reflect disease-related inflammation or comorbidity. The OR for GSH was 0.4 (95% CI = 0.1-0.9), and the OR for GSH reductase activity coefficient (indicative of riboflavin deficiency) was 1.6 (95% CI = 1.3-3.7). These findings suggest that mild iron deficiency and low GSH levels, which are associated with increased oxidative stress, increase the risk of oral cavity cancer.

Glutamine prevents DMBA-induced squamous cell cancer

The etiology of oral squamous cell carcinoma has been linked to environmental carcinogens, such as activated aromatic heterocyclic radicals and epoxides. Our previous work on implantable and 7,12-dimethylbenz[a]anthracene (DMBA)-induced breast cancer showed that oral glutamine (GLN) inhibited tumor growth possibly through stimulation of host - and selective inhibition of tumor glutathione (GSH). This finding was associated with up-regulation of NK cell activity, decreased IGF-1 and TGF-beta in the circulation and downregulation of PI-3K/Akt antiapoptotic signaling in tumors. The present study was designed to investigate the effect of topically applied GLN on DMBA-induced hamster buccal pouch squamous cell carcinoma. Histopathological alterations in buccal pouches were studied by light microscopy. GLN and GSH levels in blood and buccal mucosa were determined using specific enzyme assays. The protein expression of bax, bcl-2 and PARP was determined by western blotting. H-ras and p53 genes were examined for presence of mutations using direct DNA sequencing. Fourteen weeks after DMBA application none of the GLN-supplemented animals developed tumors, while all of the control animals had well developed squamous cell carcinomas. The inhibition of DMBA-carcinogenesis by GLN application was associated with increased arterial GLN and GSH, elevated buccal mucosa GSH as well as induction of bax and PARP, and inhibition of bcl-2. H-ras and p53 were wild type. The results from this study in combination with our previous data suggest that the chemopreventive effects of GLN are exerted by enhancing the antioxidant status of the body and activation of apoptosis.

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.

Effects of ceramide inhibition on experimental radiation-induced oral mucositis

OBJECTIVE

Oral mucositis (OM) is a common toxicity of ionizing radiation (IR), which is used as treatment for head and neck cancer. Ceramide-mediated apoptosis may contribute to the pathogenesis of mucositis. In response to IR or other cellular stresses, ceramide production occurs either by the hydrolytic action of sphingomyelinase (SMase) or de novo via ceramide synthase.

STUDY DESIGN

Male golden Syrian hamsters (10 per group) exposed to a single dose of 40 Gy ionizing radiation (day 0) were treated with subcutaneous 0.2 mL injections of either neutral SMase, acidic SMase, or ceramide synthase inhibitor (5 mmol/L glutathione, 5 micromol/L desipramine, or 1 micromol/L fumonisin B1, respectively) from day -1 to day 16. A control group was treated with saline. Two blinded examiners assessed clinical OM development from day 6 to day 26. Two animals per group were killed on days 3, 10, and 16 for immunohistochemical detection of ceramide expression in both the epithelium and in the connective tissue.

RESULTS

The group exposed to fumonisin B1 exhibited a statistically significant reduction in mean daily weight gain, mean mucositis score, duration of mucositis, and expression of ceramide in the epithelium on day 3 as well as in the connective tissue on days 10 and 16 relative to control. Immunohistologic analysis also revealed significant differences in ceramide expression on days 3 and 16 for animals treated with glutathione in both the epithelial and connective tissue when compared to the control.

CONCLUSIONS

These results suggest that IR triggers early de novo ceramide production and that inhibition of this process attenuates OM on a clinical level.

Lethal synergistic effect of cigarette smoke and saliva in an in vitro model: does saliva have a role in the development of oral cancer?

Exposure of oral mucosal cells to cigarette smoke induces oral cancer, presumably via the injurious effect of free radicals. To explore the effects of cigarette smoke on cells in the presence of saliva, we used peripheral blood lymphocytes (PBL) and exposed them to cigarette smoke, alone or in the presence of saliva. After 80 min exposure to cigarette smoke alone, a time-dependent cellular loss and survival rate of 52% was observed. By contrast, following the exposure of the lymphocytes to cigarette smoke in the presence of saliva, less than 20% of the cells survived. Saliva secreted from the submandibular/sublingual (Sm/Sl) glands was highly cytotoxic, while saliva secreted from the parotid glands was only moderately cytotoxic. Redox active iron ions in saliva and aldehydes in cigarette smoke were shown to play the major injurious roles in this synergistic phenomenon. The salivary-borne redox active iron ions participate in Fenton and Haber-Weiss reactions to transform low-reactive free radicals, which originate from cigarette smoke into highly-reactive .OH(-)-free radicals. In light of these results, a comprehensive mechanism for the induction of oral cancer by cigarette smoke is suggested where saliva may be a pivotal player.

Synergistic effect of cigarette smoke and saliva on lymphocytes—the mediatory role of volatile aldehydes and redox active iron and the possible implications for oral cancer

Oral squamous cell carcinoma (SCC) is most induced by exposure of the oral epithelial cells to tobacco products such as cigarette smoke. This exposure always occurs in the presence of saliva and presumably is induced by free radicals. To explore the effects of CS on cells in the presence of saliva, we used peripheral blood lymphocytes (PBL) and exposed them to CS, alone or in the presence of saliva. We discovered that after 80min, exposure of the lymphocytes to CS alone resulted in a time-dependent cellular loss with a survival rate of 56%, while following lymphocyte exposure to CS in the presence of saliva, less than 15% of the cells survived. This was accompanied by concomitant accumulation of cellular protein carbonyls which could be protected by the exogenous addition of uric acid or glutathione, but not by the addition of ascorbate (Asc), N-acetyl-l-cystein (NAC) or desferal (DES). Exposure of the lymphocytes to aldehydes present in CS, such as acrolein and croton-aldehyde, also resulted in the elevation of protein carbonyls, which was ameliorated primarily by the addition of glutathione. However, lymphocyte exposure to acroline in the presence of saliva did not show the same synergism in cell death observed as when the lymphocytes were exposed to CS and saliva. Thus, we postulated the existence of another mechanism and examined the role of redox active iron as an additional explanation for this synergism. In fact, it was found that in the presence of saliva and ascorbate there was a marked decrease in the lymphocyte survival rate; this was reversed by the addition of the iron chelator desferal. In light of these results, a comprehensive mechanism for the induction of oral cancer by cigarette smoke is suggested, stressing the role of a pivotal player in the process leading to oral cancer which has never been previously considered in this regard - the saliva.

Lipoic Acid as a Potential First Agent for Protection from Mycotoxins and Treatment of Mycotoxicosis

Mycotoxins--toxic substances produced by fungi or molds--are ubiquitous in the environment and are capable of damaging multiple biochemical mechanisms, resulting in a variety of human symptoms referred to collectively as "mycotoxicosis." In fact, mycotoxins mimic multiple xenobiotics, not only with respect to their ultimate damage, but also in their routes of detoxification. This suggests potential therapeutic options for the challenging treatment of mycotoxicosis. In this brief review, the author examines the use of lipoic acid as an example of an inexpensive and available nutrient that has been shown to protect against, or reverse, the adverse health effects of mycotoxins.

Timing of oral glutamine on DMBA-induced tumorigenesis

INTRODUCTION

A single dose of oral 7,12-dimethylbenz(a)anthracene (DMBA) in pubertal rats causes breast tumors by 11 weeks and is associated with ablation of the normal gut glutathione (GSH) production for up to 4 weeks. We hypothesized that glutamine (GLN), known to restore the gut GSH production inhibited by DMBA, given only during this 4-week period, would prevent breast cancer initiation.

METHODS

160 Female Sprague-Dawley rats were divided to 10 groups (n = 16/group): Long Term (LT): DMBA + GLN, DMBA + FA, DMBA + H2O, OIL + GLN, OIL + FA, OIL + H2O; Short Term (ST): DMBA + GLN, DMBA + FA, OIL + GLN, OIL + FA At age 50 days old, rats received a one-time dose of 100 mg/kg DMBA or sesame oil. LT rats were gavaged daily with isonitrogenous GLN, (FA), or water (H2O) the entire study. ST rats were gavaged with GLN, freamine, or H2O the first 4 weeks and then H2O the remaining 7 weeks. All rats were pair-fed defined chow. Rats were sacrificed at 11 weeks, observed for tumors, blood assayed for GLN, GSH, gut GLN and GSH and uptake or production calculated using labeled C-14-PAH.

RESULTS

ST and LT GLN were equally effective in preventing tumor formation. GLN doubled gut GSH production in LT animals as compared to all other groups (P < 0.05). Control rats developed no tumors and had superior gut GSH production as compared with tumor-bearing rats.

CONCLUSIONS

Oral GLN when given only during the 4 weeks of known gut GSH ablation had the same tumor prevention efficacy as prolonged GLN administration. Not previously reported, GLN appears to affect the initiation of tumor formation in this model.

Effect of 7,12-dimethylbenz[a]anthracene (DMBA) on gut glutathione metabolism

BACKGROUND

One mechanism of the mammary carcinogenesis of 7,12-dimethylbenz[a]anthracene (DMBA) is thought to be the generation of reactive oxygen species known to play an important role in initiation and progression. We hypothesized that DMBA would disrupt gut glutathione (GSH) metabolism and this disruption would correlate with mammary cell carcinogenesis.

METHODS

Sixty-four Sprague-Dawley rats were randomized to the DMBA versus control groups. At age 50 days, rats were gavaged with a one-time dose of 20 mg DMBA or sesame oil. Rats from each group were sacrificed at 1 week (n = 16), 2 weeks (n = 16), 4 weeks (n = 16), and 11 weeks (n = 16). Tumor appearance, arterial and gut GSH concentration, and gut GSH extraction were measured over time.

RESULTS

Gut GSH extraction (normally negative; production) was significantly depressed over the time points, even showing uptake (positive extraction) at Weeks 1 and 2. Tumors developed in all animals in the DMBA group by Week 11.

CONCLUSIONS

A one-time oral administration of DMBA has a significant and prolonged depressive effect on gut GSH production that has not previously been described. These data support the hypothesis that the carcinogenic effect of DMBA is mediated, at least in part, by oxidative damage and that the disruption of gut GSH metabolism may play a greater role in carcinogenesis than previously realized.

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).

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.

Alcohol and cancer

A great number of epidemiological data have identified chronic alcohol consumption as a significant risk factor for upper alimentary tract cancer, including cancer of the oropharynx, larynx, and the esophagus, and for the liver. In contrast to those organs, the risk by which alcohol consumption increases cancer in the large intestine and in the breast is much smaller. However, although the risk is lower, carcinogenesis can be enhanced with relatively low daily doses of ethanol. Considering the high prevalence of these tumors, even a small increase in cancer risk is of great importance, especially in those individuals who exhibit a higher risk for other reasons. The epidemiological data on alcohol and other organ cancers are controversial and there is at present not enough evidence for a significant association. Although the exact mechanisms by which chronic alcohol ingestion stimulates carcinogenesis are not known, experimental studies in animals support the concept that ethanol is not a carcinogen, but under certain experimental conditions is a cocarcinogen and/or (especially in the liver) a tumor promoter. The metabolism of ethanol leads to the generation of acetaldehyde and free radicals. These highly reactive compounds bind rapidly to cell constituents and possibly to DNA. Acetaldehyde decreases DNA repair mechanisms and the methylation of cytosine in DNA. It also traps glutathione, an important peptide in detoxification. Furthermore, it leads to chromosomal aberrations and seems to be associated with tissue damage and secondary compensatory hyperregeneration. More recently, the finding of considerable production of acetaldehyde by gastrointestinal bacteria was reported. Other mechanisms by which alcohol stimulates carcinogenesis include the induction of cytochrome P4502E1, associated with an enhanced activation of various procarcinogens present in alcoholic beverages, in association with tobacco smoke and in diets, a change in the metabolism and distribution of carcinogens, alterations in cell cycle behavior such as cell cycle duration leading to hyperregeneration, nutritional deficiencies such as methyl, vitamin A, folate, pyrridoxalphosphate, zinc and selenium deficiency, and alterations of the immune system, eventually resulting in an increased susceptibility to certain viral infections such as hepatitis B virus and hepatitis C virus. In addition, local mechanisms in the upper gastrointestinal tract and in the rectum may be of particular importance. Such mechanisms lead to tissue injury such as cirrhosis of the liver, a major prerequisite for hepatocellular carcinoma. Thus, all these mechanisms, functioning in concert, actively modulate carcinogenesis, leading to its stimulation.

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.

Bionutrition and oral cancer in humans

Tobacco (smoking and smokeless) use and excessive consumption of alcohol are considered the main risk factors for oral cancer (ICD9 140-149). Conspicuous national and international variations in oral cancer incidence and mortality rates, as well as observations in migrant populations, raise the possibility that diet and nutritional status could be an important etiologic factor in oral carcinogenesis. As shown in this report, abuse of alcohol and tobacco has serious nutritional implications for the host, and generates increased production of reactive free radicals as well as eliciting immunosuppression. Maintenance of optimal competence of the immune system is critical for cancer surveillance. Active oxygen species and other reactive free radicals mediate phenotypic and genotypic alterations that lead from mutation to neoplasia. Consequently, the most widely used chemopreventive agents against oral cancer (e.g., vitamins A, E, C, and beta-carotene) are anti-oxidants/free radical scavengers. These anti-oxidants, both natural and synthetic, neutralize metabolic products (including reactive oxygen species), interfere with activation of procarcinogens, prevent binding of carcinogens to DNA, inhibit chromosome aberrations, restrain replication of the transformed cell, suppress actions of cancer promoters, and may even induce regression of precancerous oral lesions such as leukoplakia and erythroplakia. Malnutrition is characterized by marked tissue depletion of anti-oxidant nutrients, including GSH (gamma-glutamyl-cysteinyl-glycine), a key cellular anti-oxidant as well as a modulator of T-cell activation. GSH or its precursor cysteine inhibits activation of the nuclear transcription factor kB(NFkB), and has been shown to be protective against chemically induced oral cancer and leukoplakia. Alcohol-, tobacco-, and/or malnutrition-induced immunosuppression promotes impaired salivary gland function and oral mucosal immunity, a prominent reduction in the number of helper CD4 cells with less marked changes in number of suppressor T-cells, and depressed NK cell activity, among others. These suggest a breakdown in capacity or the malnourished to mount effective tumor surveillance. This review article underscores the compounding but important roles of nutritional/dietary factors in the long-established causal link between abuse of alcohol and tobacco (smoking and smokeless) and oral cancer.