Free radical generating mechanisms in the colon: their role in the induction and promotion of colorectal cancer?

Effects of different extraction methods on the structural and biological properties of Hericium coralloides polysaccharides

In current study, polysaccharides from Hericium coralloides were extracted by heat reflux, acid-assisted, alkali-assisted, enzyme-assisted, ultrasonic-assisted, cold water, pressurized hot water, hydrogen peroxide/ascorbic acid system and acid-chlorite delignification methods, which were named as HRE-P, ACE-P, AAE-P, EAE-P, UAE-P, CWE-P, PHE-P, HAE-P, and ACD-P, respectively. Their physicochemical properties, structural characteristics, and antioxidant activities were investigated and compared. Experimental outcomes indicated notable variations in the extraction yields, chemical compositions, monosaccharide constituents and molecular weights of the obtained nine polysaccharides. HRE-P demonstrated the highest activity against ABTS and OH radicals, CWE-P against ABTS, DPPH, and superoxide radicals, and UAE-P against DPPH radicals. In addition, UAE-P, CWE-P, and HAE-P exhibited better protective effects on L929 cells, when compared to the other obtained polysaccharides. Additionally, correlation analysis indicated that monosaccharide composition and total polyphenol content were two prominent variables influencing the bioactivity of H. coralloides polysaccharides.

Iron Supplementation Increases Tumor Burden and Alters Protein Expression in a Mouse Model of Human Intestinal Cancer

Iron supplements are widely consumed. However, excess iron may accelerate intestinal tumorigenesis. To determine the effect of excess iron on intestinal tumor burden and protein expression changes between tumor and normal tissues, ApcMin/+ mice were fed control (adequate) and excess iron (45 and 450 mg iron/kg diet, respectively; n = 9/group) for 10 wk. Tumor burden was measured, and two-dimensional fluorescence difference gel electrophoresis was used to identify differentially expressed proteins in tumor and normal intestinal tissues. There was a significant increase (78.3%; p ≤ 0.05) in intestinal tumor burden (mm2/cm) with excess iron at wk 10. Of 980 analyzed protein spots, 69 differentially expressed (p ≤ 0.05) protein isoforms were identified, representing 55 genes. Of the isoforms, 56 differed (p ≤ 0.05) between tumor vs. normal tissues from the adequate iron group and 23 differed (p ≤ 0.05) between tumors from the adequate vs. excess iron. Differentially expressed proteins include those involved in cell integrity and adaptive response to reactive oxygen species (including, by gene ID: ANPEP, DPP7, ITGB1, PSMA1 HSPA5). Biochemical pathway analysis found that iron supplementation modulated four highly significant (p ≤ 0.05) functional networks. These findings enhance our understanding of interplay between dietary iron and intestinal tumorigenesis and may help develop more specific dietary guidelines regarding trace element intake.

Obesity and cancer stem cells: Roles in cancer initiation, progression and therapy resistance

Obesity, the global pandemic since industrialization, is the number one lifestyle-related risk factor for premature death, which increases the incidence and mortality of various diseases and conditions, including cancer. In recent years, the theory of cancer stem cells (CSCs), which have the capacity for self-renewal, metastasis and treatment resistance, has been bolstered by increasing evidence. However, research on how obesity affects CSCs to facilitate cancer initiation, progression and therapy resistance is still in its infancy, although evidence has already begun to accumulate. Regarding the ever-increasing burden of obesity and obesity-related cancer, it is pertinent to summarize evidence about the effects of obesity on CSCs, as elucidating these effects will contribute to the improvement in the management of obesity-related cancers. In this review, we discuss the association between obesity and CSCs, with a particular focus on how obesity promotes cancer initiation, progression and therapy resistance through CSCs and the mechanisms underlying these effects. In addition, the prospect of preventing cancer and targeting the mechanisms linking obesity and CSCs to reduce cancer risk or to improve the survival of patients with cancer is considered.

Ultrasound-assisted extraction and properties of polysaccharide from Ginkgo biloba leaves

Response surface methodology (RSM) was used to optimize the ultrasound-assisted extraction conditions of Ginkgo biloba leaves polysaccharide (GBLP). The optimum extraction conditions for the ultrasound-assisted extraction of GBLP were obtained as liquid to material ratio of 30 mL/g, ultrasonic power of 340 W, and extraction time of 50 min. Under these conditions, the yield of GBLP was 5.37 %. Two chemically modified polysaccharides, CM-GBLP and Ac-GBLP, were obtained by carboxymethylation and acetylation of GBLP. The physicochemical properties of these three polysaccharides were comparatively studied and their in vitro antioxidant activities were evaluated comprehensively. The results showed that the solubility of the chemically modified polysaccharides was significantly enhanced and the in vitro antioxidant activity was somewhat improved. This suggests that carboxymethylation and acetylation are effective methods to enhance polysaccharide properties, but the results exhibited some uncontrollability. At the same time, GBLP has also shown high potential for research and application.

Nutritional Regulation of Intestinal Stem Cells

Dietary composition and calorie intake are major determinants of health and disease. Calorie restriction promotes metabolic changes that favor tissue regeneration and is arguably the most successful and best-conserved antiaging intervention. Obesity, in contrast, impairs tissue homeostasis and is a major risk factor for the development of diseases including cancer. Stem cells, the central mediators of tissue regeneration, integrate dietary and energy cues via nutrient-sensing pathways to maintain growth or respond to stress. We discuss emerging data on the effects of diet and nutrient-sensing pathways on intestinal stem cells, as well as their potential application in the development of regenerative and therapeutic interventions.

Insights into the diagnosis and management of iron deficiency in inflammatory bowel disease

INTRODUCTION

Iron deficiency is a frequent comorbidity of chronic diseases such as inflammatory bowel disease that can severely impact the health and quality of life of affected individuals. It can exist as a silent condition and manifest in non-specific symptoms even in the absence of anemia. Even though iron deficiency anemia is the most common complication and extra-intestinal manifestation of inflammatory bowel disease, the majority of inflammatory bowel disease patients who are diagnosed with iron deficiency anemia are not treated. Areas covered: In this review, we discuss iron deficiency and iron deficiency anemia in patients with inflammatory bowel disease, and review diagnostic and therapeutic options. Expert commentary: We invite international gastroenterological societies and associations to refine the practice guidelines and include iron deficiency as a potential morbidity associated with IBD in analogy to arthritis, uveitis or any other extra intestinal manifestations. There should a more unanimous agreement among different societies on the specific diagnostic cutoff values for C-reactive protein levels, serum ferritin, and transferrin saturation in order to differentiate iron deficiency anemia from anemia of chronic disease.

Iron replacement therapy in inflammatory bowel disease patients with iron deficiency anemia: a systematic review and meta-analysis

BACKGROUND AND AIMS

Iron deficiency anemia (IDA) is a common problem in patients with Inflammatory Bowel Disease (IBD) and has a significant negative impact on quality of life. The aim was to compare the clinical efficacy of intravenous (IV) versus oral (PO) iron replacement in adult IBD with iron deficiency anemia (IDA).

METHODS

A systematic search for randomized controlled trials comparing the efficacy of IV versus PO iron therapy in the treatment of IDA in adult IBD patients. The primary outcome was the mean change in the hemoglobin at the end of study and secondary outcomes include mean change in ferritin, clinical disease activity index, quality of life score and the adverse reaction rate.

RESULTS

The search strategy identified 757 articles while only three industry-funded articles met the inclusion criteria for systematic review and meta-analysis. The total sample size was 333 patients with 203 patients receiving IV therapy. IV route was associated with a 6.8 g/L higher mean hemoglobin increment and 110 μg/L higher mean ferritin increment. The IBD activity index and Quality of Life scores were comparable between the two treatment groups. More adverse events were reported in the oral treatment group with the odds for discontinuation being 6.2 (CI 2.2, 17.1).

CONCLUSIONS

Intravenous iron treatment is better tolerated and more effective than oral iron treatment in improving ferritin. The higher hemoglobin gain with the IV route was small and of uncertain clinical significance. The combined sample size of the included studies was small and further clinical trials are required.

The relationship between 8-oxo-7,8-dihydro-2'-deoxyguanosine level and extent of cytosine methylation in leukocytes DNA of healthy subjects and in patients with colon adenomas and carcinomas

It has been known for a long time that DNA hypomethylation occurs in many human cancers and precancerous conditions. However, the mechanisms of hypomethylation are largely unknown. It is possible that endogenous 8-oxo-7,8-dihydroguanine (8-oxoGua) level may be linked to aberrant DNA methylation of adjacent cytosine and in this way influences carcinogenesis. Therefore, the aim of the present study was to assess a possible link between 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) background level and 5-methylcytosine content in DNA from human leukocytes of healthy subjects (n=105) as well as in patients with colon adenomas (n=39) and carcinomas (n=50). Our results demonstrated statistically significant negative correlation between background level of 8-oxodG and 5-methylcytosine content in DNA isolated from leukocytes of healthy donors (r=-0.3436, p=0.0003). The mean content of 5-methylcytosine was significantly lower, while 8-oxodG level was significantly higher in leukocytes DNA of patients with colon adenomas and carcinomas in comparison with healthy subjects. The mean values for 5-methylcytosine were: 3.59+/-0.173% (healthy subjects), 3.38+/-0.128% (patients with adenomas), 3.40+/-0.208% (colon cancer patients). The mean values of 8-oxodG in DNA were, respectively: 4.67+/-1.276, 5.72+/-1.787, 5.76+/-1.884 8-oxodG per 10(6) dG molecules. DNA from affected tissue (colon) suffered from significant, about 10% reduction in cytosine methylation in comparison with leukocytes of the paired subjects. Our work provides the first in vivo evidence suggesting that increased levels of 8-oxodG in DNA may lead to carcinogenesis not only via mispair/mutagenic potential of the modified base but also through its ability to influence gene expression by affecting DNA methylation.

Trace element concentration distributions in breast, lung and colon tissues

The concentrations of Fe, Cu, Zn and Se in cancerous and benign tissues of breast, lung and intestine (colon) have been determined. In the cases when the element concentration has not been determined in all samples the Kaplan-Meier method has been used for the reconstruction of the original concentration distributions and estimation of the true mean concentrations and medians. Finally, the log-rank test has been applied to compare the elemental concentration distributions between cancerous and benign tissues of the same organ, between cancerous tissues and between benign tissues taken from different organs. Comparing benign and malignant neoplastic tissues, statistically significant differences have been found between Fe and Se concentration distributions of breast as well as for Cu and Zn in the case of lung tissues and in the case of colon tissues for Zn. The concentrations of all elements have been found to be statistically different in cancer tissues as well as in benign ones when comparing the different organs, i.e. groups 'breast-colon' and 'breast-lung'. Concentrations of Fe and Cu have been found to be statistically different in lung and colon cancerous tissues. For benign tissues of lung and colon a statistically significant difference has been found only for Zn.

Iron and colorectal cancer risk in the α-tocopherol, β-carotene cancer prevention study

In vitro and in vivo studies have associated iron with both the initiation and promotional stages of carcinogenesis. We investigated whether iron was associated with colorectal cancer in a nested case-control study within the alpha-tocopherol, beta-carotene cancer prevention study cohort. Exposure was assessed at baseline, using a 276-item food frequency questionnaire and a fasting serum sample. The study included 130 colorectal cancer cases (73 colon cancers and 57 rectal cancers) and 260 controls. Conditional logistic regression was used to estimate odds ratios (ORs) and 95% confidence intervals (CIs). Supplemental iron intake was only reported for 4 cases and 18 controls; therefore, we were unable to obtain meaningful results for this variable. Comparing the highest to the lowest quartiles, there was an inverse association between serum ferritin and colorectal cancer risk (OR = 0.4, 95% CI = 0.2-0.9) and a suggestion of an inverse association between dietary iron and colorectal cancer risk (OR = 0.4, 95% CI = 0.1-1.1). In addition, serum ferritin, serum iron and transferrin saturation were all inversely associated with colon cancer risk specifically (OR = 0.2, 95% CI = 0.1-0.7, p trend = 0.02; OR = 0.2, 95% CI = 0.1-0.9, p trend = 0.05; OR = 0.1, 95% CI = 0.02-0.5, p trend = 0.003, respectively), whereas serum unsaturated iron binding capacity was positively associated with colon cancer risk (OR = 4.7, 95% CI = 1.4-15.1, p trend = 0.009). In summary, we found a significant inverse association between several serum iron indices and colon cancer risk.

Health promotion by flavonoids, tocopherols, tocotrienols, and other phenols: direct or indirect effects? Antioxidant or not?

Foods and beverages rich in phenolic compounds, especially flavonoids, have often been associated with decreased risk of developing several diseases. However, it remains unclear whether this protective effect is attributable to the phenols or to other agents in the diet. Alleged health-promoting effects of flavonoids are usually attributed to their powerful antioxidant activities, but evidence for in vivo antioxidant effects of flavonoids is confusing and equivocal. This may be because maximal plasma concentrations, even after extensive flavonoid intake, may be low (insufficient to exert significant systemic antioxidant effects) and because flavonoid metabolites tend to have decreased antioxidant activity. Reports of substantial increases in plasma total antioxidant activity after flavonoid intake must be interpreted with caution; findings may be attributable to changes in urate concentrations. However, phenols might exert direct effects within the gastrointestinal tract, because of the high concentrations present. These effects could include binding of prooxidant iron, scavenging of reactive nitrogen, chlorine, and oxygen species, and perhaps inhibition of cyclooxygenases and lipoxygenases. Our measurements of flavonoids and other phenols in human fecal water are consistent with this concept. We argue that tocopherols and tocotrienols may also exert direct beneficial effects in the gastrointestinal tract and that their return to the gastrointestinal tract by the liver through the bile may be physiologically advantageous.

Dietary iron affects inflammatory status in a rat model of colitis

Iron deficiency anemia is a common feature in inflammatory bowel disease, and oral supplementation is one of the mainstay therapies. However, there is some concern that oral iron supplementation may lead to oxidative stress and exacerbation of inflammation. Our objective was to study the effect of severely deficient, moderately deficient, normal and high iron status on oxidative stress and the course of inflammation in a rat model of colitis induced by 2,4,6-trinitrobenzene sulfonic acid (TNBS). The rats were randomly assigned to receive the low-iron diet for 3 (moderately iron-deficient group, n = 16) or 5 (severely iron-deficient group, n = 16) wk, the normal iron diet for 2 wk (normal iron group, n = 16) or the high-iron diet for 2 wk (high-iron group, n = 16). Malondialdehyde concentration, electroparamagnetic resonance measurement, myeloperoxidase activity, and histological analysis were used to evaluate oxidative stress. Noncolitic rats in the high-iron group had higher oxidative stress parameters than those in the other groups. The induction of colitis resulted in severe inflammatory changes in the high-iron and severely iron-deficient groups, and produced higher histological scores in the colon of the normal and high-iron groups. Iron overload, oxidative stress, and inflammation were lower in the moderately iron-deficient group compared with the other 3 groups. In conclusion, we suggest that low rather than normal or high iron supplementation should be considered for the treatment of iron deficiency in inflammatory bowel disease.

Antiproliferative effect of 1,4-phenylenebis(methylene)selenocyanate (p-XSC) on colonic epithelium of patients with adenomatous polyps in vitro

We have consistently shown that the organoselenium compound 1,4-phenylenebis(methylene)selenocyanate (p-XSC) is a superior cancer chemopreventive agent and less toxic than selenite or certain naturally-occurring selenoamino acids. To elucidate the effects of p-XSC on human colonic mucosa, biopsies from endoscopically normal sigmoid colon of 30 patients with adenomatous polyps were incubated with p-XSC at concentrations of 1, 2 and 5 micromol/l dissolved in dimethylsulphoxide (DMSO). Biopsies incubated with DMSO or pure culture medium served as a control. Proliferating cells were labelled by bromodeoxyuridine immunohistochemistry and the labelling index (LI) was computed. Upper crypt labelling index (LI of crypt compartments 4+5) and Phih value, which are both discriminators of the expansion of the proliferative zone, were significantly lower after incubation with 1 and 5 micromol/l p-XSC, respectively (LI 4+5: 0.8 and 1.0; Phih value: 2.1 and 2.4), as compared with DMSO (LI 4+5: 3.6 and 4.5; Phih value: 7.0 and 8.3) or culture medium (LI 4+5: 3.3 and 4.5; Phih value: 7.2 and 8.1) (P<0.005 and P<0.05 by Friedman's block test). A trend towards lower levels of LI 4+5 (P=0.059) and Phih value (P=0.075) were seen after 2 micromol/l p-XSC incubation compared with DMSO. Since hyperproliferation of colonic crypt cells with expansion of the proliferative zone is regarded as a biomarker of increased cancer risk, the antiproliferative effects of p-XSC especially on upper crypt LI and Phih value may indicate a possible protective effect of this organoselenium compound in the prevention of human colon cancer development.

New method to study oxidative damage and antioxidants in the human small bowel: effects of iron application

Iron may induce oxidative damage to the intestinal mucosa by its catalyzing role in the formation of highly reactive hydroxyl radicals. This study aimed to determine iron-induced oxidative damage provoked by a single clinical dosage of ferrous sulfate and to elucidate the antioxidant defense mechanisms in the human small intestine in vivo. A double-lumen perfusion tube was positioned orogastrically into a 40-cm segment of the proximal small intestine in six healthy volunteers (25 +/- 5 yr). The segment was perfused with saline and subsequently with saline containing 80 mg iron as ferrous sulfate at a rate of 10 ml/min. Intestinal fluid samples were collected at 15-min intervals. Thiobarbituric acid reactive substances concentrations as an indicator of lipid peroxidation increased significantly from 0.07 microM (range, 0-0.33 microM) during saline perfusion to 3.35 microM (range, 1.19-7.27 microM) during iron perfusion (P < 0.05). Nonprotein antioxidant capacity increased significantly from 474 microM (range, 162-748 microM) to 1,314 microM (range, 674-1,542 microM) (P < 0.05). These data show that a single dosage of ferrous sulfate induces oxidative damage and the subsequent release of an antioxidant in the small intestine in vivo in healthy volunteers.

Effect of oxidants on small intestinal brush border membranes and colonic apical membranes--a comparative study

This study compares composition of the rat small intestinal brush border membranes (BBM) and colonic apical membranes (CAM) and their susceptibility to in vitro exposure to various oxidants. Differences were observed between BBM and CAM in their lipid composition, sugar content, alkaline phosphatase (ALP) activity and cholesterol/phospholipid ratio. BBM and CAM were exposed to superoxide generated by xanthine+xanthine oxidase (X-XO) or peroxides such as tertiary butyl hydroperoxide (tBuOOH) and hydrogen peroxide (H(2)O(2)) and alterations in ALP activity, peroxidation parameters and membrane lipids were analyzed. Exposure of BBM and CAM to superoxide resulted in decrease in ALP activity and increase in peroxidation parameters such as protein carbonyl content, malondialdehyde and conjugated diene. Superoxide exposure also resulted in lipid alterations specifically in certain phospholipids. These alterations were prevented either by superoxide dismutase or by allopurinol. Peroxides did not have any significant effect. These results suggest that both BBM and CAM are susceptible to superoxide, which can bring about peroxidation and degradation of membrane lipids specifically, certain phospholipids.

Selenium reduces hemoglobin-induced epithelial damage to intestinal mucosa

Modified hemoglobins are being considered as possible "blood substitutes." Experiments were performed to determine whether diaspirin cross-linked hemoglobin (DBBF-Hb) produces epithelial damage and whether this is reduced by selenium (Se). Anesthetized Sprague-Dawley rats, half of which received 2 x 10(-6) g/ml Se, daily for 3 weeks, in their drinking water, were injected with a 5 ml bolus of 10 mg/ml DBBF-Hb. Control animals received saline (5 animals per group). After 30 minutes, the intestine was perfusion-fixed for light and electron microscopy. Eighty villi per rat were assigned an epithelial integrity index (E.I.), ranging from 1 (intact) to 3 (some cell-cell and cell-basement membrane separation). In non-Se rats, E.I. was significantly compromised by DBBF-Hb, compared to HBS-BSA (2.47+/-0.57 (SD) vs. 1.36+/-0.49, p<0.001). In Se rats, neither injection with DBBF-Hb or HBS-BSA caused epithelial damage (1.03+/-0.17 vs. 1.07+/-0.26). Mast cell degranulation per villus (MCD) was measured in 60 villi per rat. In non-Se rats, MCD was significantly greater after DBBF-Hb than after HBS-BSA injection (1.83+/-1.42 vs. 0.2+/-0.4). Supplementary Se did not reduce this effect. In fact, MCD was significantly increased in both sets of rats compared to their non-Se counterparts (3.27+/-2.40 and 1.48+/-1.70 for DBBF-Hb and HBS-BSA, respectively). Since mast cell mediators damage cells, Se must protect the mucosal epithelium in some way.

Serum and colon mucosa micronutrient antioxidants: differences between adenomatous polyp patients and controls

OBJECTIVES

Micronutrient antioxidants, by virtue of their free radical scavenging properties, are potential chemopreventive agents against colon cancer. Yet, little is known about the actual concentration of these antioxidants in colonic mucosa. It is also not known whether a relationship exists between serum and mucosal tissue antioxidant levels. Previous studies evaluating the occurrence of polyps after supplementation with vitamin E and beta-carotene have yielded mixed results. The aim of this study was to determine the concentrations of seven micronutrient antioxidants (alpha- and gamma-tocopherol, lutein, beta-cryptoxanthin, lycopene, and alpha- and beta-carotene) in colonic mucosa and to determine whether serum levels of each antioxidant could predict levels of that antioxidant in the right and left colon of patients with normal mucosa or in those with adenomatous polyps.

METHODS

Mucosal tissue concentrations and serum levels of antioxidants were determined in 10 patients with adenomatous polyps and 15 control subjects (GI patients with normal colonic mucosa). Mucosal tissue samples were obtained from both the right and left colon in all patients.

RESULTS

Patients with polyps similar serum antioxidant status similar to that of control. However, polyp patients had significantly lower concentrations of all seven antioxidants in both the right (p < 0.0070) and left colon (p < 0.0026) than did controls. Finally, serum antioxidant levels predict right and left colon antioxidant levels in controls but not in patients with polyps.

CONCLUSIONS

Patients with adenomatous polyps have low levels of micronutrient antioxidants in their colon mucosa. Because the serum levels of these antioxidants were similar in controls and polyp patients, our findings suggest an increased level of free radical activity in patients with polyps compared to normal subjects.

Oxygen free radical generating mechanisms in the colon: do the semiquinones of vitamin K play a role in the aetiology of colon cancer?

It is proposed that bile acids (deoxycholic acid), the K vitamins, iron(II) complexes and oxygen interact to induce an oncogenic effect in the colon by the generation of free radicals. In the relatively low oxidising/reducing conditions of the colonic lumen the K vitamins exist in the reduced form; however, if absorbed into the mucosa they have the capacity to be chemically oxidised and to enter into a redox cycle yielding oxygen radicals. The semiquinone radical of K(1) (phylloquinone) has been stabilised in bile acid mixed micelles and investigated by electron paramagnetic resonance spectroscopy and quantum chemical calculations. The estimated half-life of the radical was about 30 min which confirms a remarkably high stability in aqueous micellar solution. A model is presented in which the reduced K vitamins may initiate superoxide radical, O2(-*) generation leading to Fe(II) mediated Fenton reactions in the stem colon cells.

Iron-induced oxidative damage in colon carcinoma (Caco-2) cells

Intestinal epithelial cells have an active apical iron uptake system that is involved in the regulated absorption of iron. By the action of this system, intestinal cells acquire increasing amounts of iron with time. Since intracellular reactive iron is a source of free radicals and a possible cause of colon carcinoma, this study analyzed the oxidative damages generated by iron accumulation in Caco-2 cells. Cells cultured with increasing concentrations of iron increased both total intracellular iron and the reactive iron pool, despite an active IRE/IRP system, which regulates intracellular iron levels. Increasing concentrations of iron resulted in increased protein oxidative damage, as shown by the immunoreactivity for 4-hydroxy-2-nonenal-modified proteins, and markedly induced DNA oxidation determined by 8-hydroxy-2'-deoxyguanidine production. Iron also impaired cell viability, resulting in increased cell death after 6 days of culture. In summary, iron accumulation by intestinal Caco-2 cells correlated with oxidative damage to proteins and DNA. Oxidative damage finally resulted in loss of cell viability. The Fe-induced oxidative damage observed may be relevant in understanding the cascade of events associated with iron-mediated colon carcinogenesis.

The gastrointestinal tract: a major site of antioxidant action?

Diets rich in fruits and vegetables delay the onset of many age-related diseases, and contain a complex mixture of antioxidants (including ascorbate, carotenoids, vitamin E and other phenolics such as the flavonoids). However, diet also contains pro-oxidants, including iron, copper, H2O2, haem, lipid peroxides and aldehydes. Nitrite is frequently present in diet, leading to generation of reactive nitrogen species in the stomach. In considering the biological importance of dietary antioxidants, attention has usually focussed on those that are absorbed through the gastrointestinal tract into the rest of the body. In the present paper we develop the argument that the high levels of antioxidants present in certain foods (fruits, vegetables, grains) and beverages (e.g. green tea) play an important role in protecting the gastrointestinal tract itself from oxidative damage, and in delaying the development of stomach, colon and rectal cancer. Indeed, carotenoids and flavonoids do not seem to be as well absorbed as vitamins C and E. Hence their concentrations can be much higher in the lumen of the GI tract than are ever achieved in plasma or other body tissues, making an antioxidant action in the GI tract more likely. Additional protective mechanisms of these dietary constituents (e.g. effects on intercellular communication, apoptosis, cyclooxygenases and telomerase) may also be important.

Evaluation of fecal mutagenicity and colorectal cancer risk

Colorectal cancer is one of the most common internal malignancies in Western society. The cause of this disease appears to be multifactorial and involves genetic as well as environmental aspects. The human colon is continuously exposed to a complex mixture of compounds, which is either of direct dietary origin or the result of digestive, microbial and excretory processes. In order to establish the mutagenic burden of the colorectal mucosa, analysis of specific compounds in feces is usually preferred. Alternatively, the mutagenic potency of fecal extracts has been determined, but the interpretation of these more integrative measurements is hampered by methodological shortcomings. In this review, we focus on exposure of the large bowel to five different classes of fecal mutagens that have previously been related to colorectal cancer risk. These include heterocyclic aromatic amines (HCA) and polycyclic aromatic hydrocarbons (PAH), two exogenous factors that are predominantly ingested as pyrolysis products present in food and (partially) excreted in the feces. Additionally, we discuss N-nitroso-compounds, fecapentaenes and bile acids, all fecal constituents (mainly) of endogenous origin. The mutagenic and carcinogenic potency of the above mentioned compounds as well as their presence in feces, proposed mode of action and potential role in the initiation and promotion of human colorectal cancer are discussed. The combined results from in vitro and in vivo research unequivocally demonstrate that these classes of compounds comprise potent mutagens that induce many different forms of genetic damage and that particularly bile acids and fecapentaenes may also affect the carcinogenic process by epigenetic mechanisms. Large inter-individual differences in levels of exposures have been reported, including those in a range where considerable genetic damage can be expected based on evidence from animal studies. Particularly, however, exposure profiles of PAH and N-nitroso compounds (NOC) have to be more accurately established to come to a risk evaluation. Moreover, lack of human studies and inconsistency between epidemiological data make it impossible to describe colorectal cancer risk as a result of specific exposures in quantitative terms, or even to indicate the relative importance of the mutagens discussed. Particularly, the polymorphisms of genes involved in the metabolism of heterocyclic amines are important determinants of carcinogenic risk. However, the present knowledge of gene-environment interactions with regard to colorectal cancer risk is rather limited. We expect that the introduction of DNA chip technology in colorectal cancer epidemiology will offer new opportunities to identify combinations of exposures and genetic polymorphisms that relate to increased cancer risk. This knowledge will enable us to improve epidemiological study design and statistical power in future research.

Modifying effects of carotenoids on superoxide and nitric oxide generation from stimulated leukocytes

Excessive and prolonged generation of superoxide (O2-) and nitric oxide (NO) from inflammatory leukocytes is associated with several lifestyle-related diseases, including cancer. In the present study, we screened 19 natural carotenoids for their modifying effects on O2- and NO generation from differentiated human promyelocytic HL-60 cells and mouse macrophage RAW 264.7 cells, respectively. Of the carotenoids tested, halocynthiaxanthin, isolated from oysters, showed the highest suppressive effect on the generation of both free radicals. The inhibitory potencies of certain carotenoids on radical generation markedly exceeded that of beta-carotene. In addition, some important structural moieties regulating radical generation suppression are discussed.

Measurement of DNA damage by the comet assay in rat embryos grown in media containing high concentrations of vitamin K(1)

It has been suggested that vitamin K(1) (phylloquinone) can cause genetic damage in rapidly dividing cells and that this should be considered in the risk/benefit analysis of the prophylactic use of vitamin K(1) in the newborn. Usual intramuscular administration of 1mg of vitamin K(1) to the newborn gives peak plasma levels of 1-2 microg/ml (approximately 2-4 microM). To investigate the possible harmful effects of high concentrations of vitamin K(1), rat embryos undergoing rapid cell division in the organogenic period were cultured for 46 hours in rat sera containing either 1, 10 or 100 microg of added vitamin K(1) per ml (2, 22 or 222 microM). At the end of the culture period the embryos were dissociated and the cells examined for evidence of DNA damage using the alkaline version of the comet assay. Control embryos were cultured in sera without added vitamin K(1) and positive controls were control embryos exposed to hydrogen peroxide at the end of the culture period. The results did not show any evidence of DNA damage in the vitamin K(1) exposed embryos. The positive controls showed a significant increase in tail length, moment and inertia. In conclusion, under the experimental conditions used, high concentrations of vitamin K(1) did not induce primary DNA damage in cells from rat embryos grown in vitro.

Trace element levels in drinking water and the incidence of colorectal cancer

We determined the levels of 15 elements in drinking water from 34 water treatment plants in Aomori Prefecture and studied how element levels relate to colorectal cancer incidence by district. Colorectal cancer incidence was calculated from the data of Aomori Colorectal Cancer Registry. Multiple regression analysis was performed by using age-adjusted incidences of rectal cancer and colon cancer by gender as object variables and each element level as an explanatory variable. The standardized partial regression coefficient was significant in gold (p < 0.01), magnesium (p < 0.01), selenium (p < 0.01) and tin (p < 0.05) for age-adjusted rectal cancer incidence in men as objective variable; in gold (p < 0.05), calcium (p < 0.01) and phosphorus (p < 0.01) with age-adjusted colon cancer incidence in men as the objective variable; and in sodium (p < 0.05), phosphorus (p < 0.05), tin (p < 0.05) and strontium (p < 0.01) with age-adjusted colon cancer incidence in women as the objective variable. These results confirm the need to further study trace elements in drinking water and food, and relationship to colorectal carcinogenesis.

Oral ferrous sulfate supplements increase the free radical-generating capacity of feces from healthy volunteers

BACKGROUND

Most dietary iron remains unabsorbed and hence may be available to participate in Fenton-driven free radical generation in conjunction with the colonic microflora, leading to the production of carcinogens or direct damage to colonocytes.

OBJECTIVE

Our aims were to measure the proportion of fecal iron available to participate in free radical generation and to determine the effect of an oral supplement of ferrous sulfate on free radical generation.

DESIGN

Eighteen healthy volunteers recorded their food intake and collected fecal samples before, during, and after 2 wk of supplementation (19 mg elemental Fe/d). Total, free, and weakly chelated fecal iron were measured and free radical production was determined by using an in vitro assay with dimethyl sulfoxide as a free radical trap.

RESULTS

Fecal iron increased significantly during the period of supplementation and returned to baseline within 2 wk. The concentration of weakly bound iron in feces (approximately 1.3% of total fecal iron) increased from 60 micromol/L before to 300 micromol/L during supplementation, and the production of free radicals increased significantly (approximately 40%). Higher-carbohydrate diets were associated with reduced free radical generation.

CONCLUSION

Unabsorbed dietary iron may increase free radical production in the colon to a level that could cause mucosal cell damage or increased production of carcinogens.

Nonsteroidal anti-inflammatory drugs, short-chain fatty acids, and reactive oxygen metabolism in human colorectal cancer cells

Nonsteroidal anti-inflammatory drugs (NSAIDs) and short-chain fatty acids are effective suppressors of colorectal cancer that may work in part by accentuating apoptosis of transformed cells. Since reactive oxygen species (ROS) can play an important role in regulating cell growth and cell death, we determined the effect of the NSAIDs indomethacin and salicylic acid, and the short-chain fatty acids butyrate and propionate on ROS metabolism in the HT-29 human colorectal carcinoma cell line. We find that all of these agents increase cellular peroxide generation, as determined by two independent assays. Arachidonic acid was also found to increase ROS generation, and could synergize with indomethacin in this reaction. The NSAIDs and short-chain fatty acids under study all possess a carboxyl group, and this carboxyl group is essential for salicylic acid's ability to increase ROS production. Although the two NSAIDs examined increase peroxide production, they were both found to suppress superoxide generation by vitamin K3 (menadione), a redox cycling compound similar to those found in the colon. The short-chain fatty acids did not have this activity. The ability of these NSAIDs and short-chain fatty acids to alter cellular ROS metabolism may contribute to their chemopreventive activity.

Bile acids, fibre and colon cancer: the story unfolds

Are the changes in faecal bile acid concentrations the cause of colorectal cancer or one of its effects? This is an area of controversy mainly due to the lack of a clear explanation as to how the bile acid concentrations are controlled under different circumstances. This review presents an outline of the evidence that bile acids are both a causal factor in colorectal cancer and that their concentrations are affected by it in a synergistic manner. It also offers an explanation of how some dietary fibre protects against colorectal cancer.

Increases in the concentrations of available iron in response to dietary iron supplementation are associated with changes in crypt cell proliferation in rat large intestine

High concentrations of iron in the diet have been shown to increase chemically induced colorectal tumors in rats. It is therefore important to understand the influence of dietary iron on the concentration of unabsorbed iron in the large intestine and its distribution between soluble and insoluble pools in the luminal compartment. We sought to investigate this issue and to establish whether iron modifies mucosal cell proliferation, which is thought to influence initiation and progression through the adenoma carcinoma sequence. In the first experiment, four groups of seven rats were fed diets at two concentrations of iron, 29 and 102 mg/kg, with or without the addition of 2.5 g phytic acid/kg. The concentrations of iron in the contents of the large bowel extractable with water ("free iron") or a buffered EDTA solution ("exchangeable iron") were determined. The concentration of freely soluble iron increased approximately 100% with iron supplementation in both the cecum and the colon, and there was an approximately five- to sixfold increase in exchangeable iron at both sites (P < 0. 05). In a second experiment with identical feeding conditions, there was a significantly greater number of cell divisions per crypt in the colon of the high iron group and a significantly greater number of cell divisions in the upper part of the crypt in the cecum. The concentrations of free and exchangeable iron observed in colonic contents in this study are consistent with those reported by others to increase free radical production in fecal material. Further studies are required to determine whether the small changes in crypt cytokinetics are a consequence of oxidative mucosal damage.

Tocopherols and the etiology of colon cancer

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

Secondary bile acid induced DNA damage in HT29 cells: are free radicals involved?

Increased bile acid secretion, as a consequence of a high fat diet, results in the increased production of bile acids that may escape the enterohepatic circulation, and be subsequently metabolised by the colonic micro-flora to form the co-mutagenic and co-carcinogenic secondary bile acids. The potential of the secondary bile acids lithocholate (LOC) and deoxycholate (DOC), to induce DNA damage, in the colonocyte cell line HT29, at physiological concentrations both individually and in a 2:1 ratio was assessed. Results indicated significant levels of DNA damage induced by both bile acids, with LOC having the greater DNA damaging capacity. The potential role of vitamin A, and the antioxidant vitamin E, in reducing this damage was determined, over a range of vitamin concentrations. Both vitamins reduced the bile acid induced DNA damage. Vitamin A displayed a dose response relationship, whereas vitamin E reduced DNA damage close to negative control values at all concentrations above 50 microM. These results indicate a protective role for Vitamins A and E, against the DNA damaging capacity of LOC and DOC.

Variability of neoplastic parameters in colon tumours, and its significance in diagnostic practice

We have reviewed the value of individual variability in the reaction of tissues to treatment with carcinogens, and the manifestation of this variability in different morphological (histological, morphometric, and ultrastructural), histochemical and immunohistochemical parameters generated in tumorous tissues. Moreover, we also reviewed data in the literature on individual variability in the manifestation of some biochemical and immunochemical markers which are accumulated in the serum of tumour-bearing patients and which are characteristic for the different phases of tumourigenesis. The high variability of different tumorous parameters suggests that none can be utilized alone as a conclusive marker of neoplasia and that only their combined use can give objective information. We also reviewed the impact of this variability in the evaluation of various pathological methods to detect different stages of neoplastic transformation in the colon. It has been concluded that none of the present approaches can be absolutely conclusive and without false results, and that objective information regarding early cancerous changes may be obtained only by use of combined analyses utilizing several laboratory methods. The diagnostic procedures should be based on the complex utilization of all appropriate methods using the quantitative interpretation of the obtained data. Multivariate analysis of many parameters should be very effective for the prediction of therapeutic results.

The SOS chromotest: a review

The SOS chromotest is reviewed through over 100 publications corresponding to the testing of 751 chemicals. 404 (54%) of these chemicals present a genotoxic activity detectable in the SOS chromotest. Their SOS inducing potencies span more than 8 orders of magnitude. For 452 compounds, the results obtained in the SOS chromotest could be compared to those obtained in the Ames test. It was found that 373 (82%) of these compounds give similar responses in both tests (236 positive and 137 negative responses). Thus the discrepancies between both tests concern 79 compounds (18%). A case by case analysis shows that many of these compounds are at the same time very weak SOS inducers and very weak mutagens. Thus we think that, most of the time, the discrepancies between the two tests may be accounted for by differences in the interpretation of the results rather than by the experimental results themselves. However, there are some compounds which are clearly SOS inducers but devoid of mutagenic activity in the Ames test (such as quinoline-1-oxide) and to a larger extent, clearly mutagenic compounds which do not induce the SOS response in the SOS chromotest (such as benzidine, cyclophosphamide, acridines, ethidium bromide). We also analyzed the correlation between SOS induction, mutagenesis and carcinogenesis according to the classification of Lewis. For 65 confirmed carcinogens (class 1), the sensitivity, i.e., the capacity to identify carcinogens, was 62% with the SOS chromotest and 77% with the Ames test. For 44 suspected carcinogens (class 2), the sensitivity was 66% with the SOS chromotest and 68% with the Ames test. Thus, we confirmed previous observations made on 83 compounds that there is a close correlation between the results given by both bacterial tests. The capacity of the Ames test to identify carcinogens is higher than that of the SOS chromotest. However, because the number of false positive compounds was lower in the SOS chromotest, the specificity, i.e., the capacity to discriminate between carcinogens and non-carcinogens of the SOS chromotest, appeared higher than that of the Ames test. Thus, the results of the SOS chromotest and of the Ames test can complement each other. The SOS chromotest is one of the most rapid and simple short-term test for genotoxins and is easily adaptable to various conditions, so that it could be used as an early--perhaps the earliest--test in a battery.

Chromatographic methods for the determination of toxicants in faeces

Modern chromatographic techniques and their application in the determination of toxic compounds in faeces are reviewed. Faecal analysis may be of importance in toxicokinetic studies of xenobiotics in order to determine factors such as metabolism, body burden and major routes of elimination. Compounds of interest include various food constituents, drugs and occupational or environmental factors. Further, various mutagenic or carcinogenic compounds which are excreted by faeces have been indicated to represent risk factors for colorectal cancer. In this context, the chromatographic determination of the endogenously generated fecapentaenes and bile acids, both postulated etiological factors in colorectal carcinogenesis, is reviewed. For fecapentaene determination, several high-performance liquid chromatographic (HPLC) methods are available; however, the applicability of some of these methods is limited owing to insufficient separation of various isomeric forms or discrimination between fecapentaenes and their precursors. For the determination of bile acids in faeces, many chromatographic procedures have been reported, and the characteristics of the most relevant methods are compared and discussed. It is concluded that separation by gas chromatography (GC) in combination with mass spectrometry provides the highest selectivity and sensitivity. A relatively rapid alternative analysis for the determination of total and aqueous faecal bile acids is proposed. Further, methods for the determination of polycyclic aromatic hydrocarbons (PAHs) are reviewed. Although the use of radiolabelled PAHs in animal studies has many advantages, it cannot be applied for human biological monitoring and HPLC and GC provide sensitive alternatives. An HPLC method for the determination of non-metabolized PAHs in faeces is described.

Effects of N'methyl-N'-nitro-N-nitrosoguanidine and deoxycholic acid on the content of free radicals in rat serum

The aim of this study was to determine whether changes in serum free radicals may be useful for the early detection of precancerous conditions in the rat colon after treatment with a direct carcinogen (N-Methyl-N'-Nitro-N-Nitrosoguanidine, MNNG) and a secondary bile acid (deoxycholic acid, DCA) as a tumor promoter. It was shown that a significant increase in the concentrations of free radicals in sera of rats following their treatment with MNNG and DCA was observed as early as the 18th week after the beginning of the treatment. Since our results have shown that these alterations occurred in parallel with neoplastic transformations in the rat colon, it suggests that the increase in serum free radicals reflected the precancerous situation in the animals and may be useful in the early detection of cancer development. The possible role of free radicals in deoxycholate-induced liver toxicity was discussed.

Prognostic factors in colorectal cancer

The prognostic power of the extent of tumour invasion is indisputable; Dukes' classification has repeatedly been proven to be strongly correlated with patient survival. Modifications have led only to confusion, resulting in caution being required in the classification of patients with Dukes' A tumours. In the UK, the American tumour node metastasis and Australian clinicopathological systems are frequently considered too complex for routine clinical use. Meanwhile, Jass's classification may be complicated by observer variation between pathologists, and recent evidence suggests that it offers no advantage over that of Dukes. All the conventional staging systems also fail to take the skill of the surgeon into account when determining outcome. Attempts at quantifying tumour structure have not heralded the expected major advance. For instance, the expense and uncertain prognostic value of tumour DNA content assessed by flow cytometry are likely to restrict widespread use of this technique. It may soon be possible, however, to provide optimum treatment for patients based on individual tumour doubling times. Classification using knowledge of how a small number of cells in the tumour have the ability to invade locally, enter blood vessels and metastasize would also provide important prognostic information on which treatment could be based. Until then, the ease of use and high prognostic power of Dukes' classification ensure that, after 60 years, it is still the 'gold standard' against which all other prognostic classifications in colorectal cancer should be assessed.

The isoquinoline sulfonamide H7 attenuates radiation-mediated protein kinase C activation and delays the onset of x-ray-induced G2 arrest

Protein kinase C activation by ionizing radiation in human tumor cell lines participates in the transcriptional activation of genes which may be associated with the phenotypic response of cells to x-rays. We gamma-irradiated cell line RIT-3 (radiation-induced human sarcoma) and quantified the phosphorylating capacity of protein kinase C. Protein kinase C activity increased rapidly and transiently in these cells. The selective protein kinase C inhibitor H7 attenuated radiation-mediated protein kinase C activation when added to cells prior to irradiation. To determine whether protein kinase C activation is associated with radiation-induced G2 arrest, we analyzed the cell cycle distribution of cells following gamma-irradiation. Following irradiation, RIT-3 cells rapidly progressed through G1 and S and subsequently underwent a dose dependent G2 arrest. At concentrations which are selective for protein kinase C inhibition, H7 delayed the onset of radiation-induced G2 arrest. However, there was no difference in the duration of G2 arrest following the addition of inhibitor as compared to cells irradiated without inhibitor. We propose that protein kinase C activation by ionizing radiation is associated with radiation-mediated cell cycle regulation.