Dietary calcium supplementation increases apoptosis in the distal murine colonic epithelium

Factors Associated with Colorectal Polyps in Middle-Aged and Elderly Populations

Colorectal polyps are the precursor lesions of most colorectal cancers. This study aimed to evaluate associations between bone mineral density (BMD), metabolic syndrome (MetS), and gastrointestinal diseases with colorectal polyps in middle-aged and elderly populations. A retrospective cross-sectional study was performed using data from the health examination database of a tertiary medical center in southern Taiwan in 2015. Subjects aged 50 years and older who had been assessed for metabolic factors and had undergone colonoscopy, upper gastrointestinal endoscopy, and dual energy X-ray absorptiometry scan (DEXA) were included. Factors associated with colorectal polyps were evaluated using univariate and multivariate logistic regression. In total, 1515 subjects were included, with mean age 60.1 years. Among them, 710 (46.9%) had colorectal polyps. Multivariate logistic regression analysis showed that high fasting glucose (OR = 1.08, p = 0.001), high triglycerides (OR = 1.02, p = 0.008), high total cholesterol (OR = 1.004, p = 0.009), reflux esophagitis (OR = 1.44, p = 0.002), duodenal polyps (OR = 1.75, p = 0.026), gastric ulcer (OR = 1.38, p = 0.024), duodenal ulcers (OR = 1.45, p = 0.028), osteopenia (OR = 1.48, p = 0.001), and MetS (OR = 1.46, p < 0.001) were independently associated with colorectal polyps. In conclusion, hyperglycemia, hypercholesterolemia, hypertriglyceridemia, MetS, duodenal polyps, gastric and duodenal ulcers, reflux esophagitis, and low BMD are independent risk factors associated with colorectal polyps in the middle-aged and elderly Taiwanese population.

Prognostic significance of osteopenia in patients with colorectal cancer: A retrospective cohort study

AIM

We examined the prognostic impact of osteopenia on the long-term outcomes of patients with colorectal cancer after laparoscopic colectomy along with other nutritional factors, including sarcopenia or the Glasgow Prognostic Score.

METHODS

This retrospective cohort study analyzed the data of 230 patients with stage Ⅰ-Ⅲ colorectal cancers who underwent surgical resection between November 2010 and December 2015. Osteopenia and sarcopenia were evaluated by measuring the average pixel density in the mid-vertebral core of the 11th thoracic vertebra on enhanced computed tomography and the psoas muscle mass area at the third lumbar vertebra, respectively. The overall survival and disease-free survival rates were analyzed using Cox proportional hazards model and Kaplan-Meier curves with the log-rank test.

RESULTS

Osteopenia was identified in 43 patients (18.7%). Univariate analysis showed that the disease-free survival rate was significantly worse in patients with stage II-III cancers, vascular invasion, carcinoembryonic antigen (CA) >5.0 ng/mL, CA19-9 > 37.0 U/mL, sarcopenia, and osteopenia (all P < .01). Multivariate analysis revealed that stage II-III cancers (P = .01), vascular invasion (P = .01), carcinoembryonic antigen >5.0 (P < .01), and osteopenia (P < .01) were significant independent disease-free survival predictors. In univariate analysis, the overall survival rate significantly decreased in patients with stage II-III cancers (P = .03), carcinoembryonic antigen >5.0 (P < .01), CA19-9 > 37.0 (P < .01), sarcopenia (P < .01), and osteopenia (P < .01). Multivariate analysis indicated that carcinoembryonic antigen >5.0 (P = .04), CA19-9 > 37.0 (P = .05), and osteopenia (P < .01) were significant independent predictors of overall survival.

CONCLUSION

Preoperative osteopenia could be a strong predictor of long-term outcomes in patients undergoing resection for colorectal cancer.

Analysis of the roles of dietary protein and calcium in fluoride-induced changes in T-lymphocyte subsets in rat

The roles of dietary protein (Pr) and calcium (Ca) levels on the changes in T-lymphocyte subsets induced by excessive fluoride (F) intake were assessed using rats that were malnourished for 120 days as a model. The CD⁴⁺ and CD⁸⁺ T-lymphocytes in the spleen tissue were determined by flow cytometry and immunofluorescence assay. The percentages of CD³⁺ , CD⁴⁺ , and CD⁸⁺ T-lymphocytes were reduced in the spleen of rats exposed to excessive F, and malnutrition aggravated these changes in the T-lymphocytes. In addition, the mRNA expression levels of IL-1β, IL-2, IL-6, TNF-α, and IFN-γ in the spleen were downregulated significantly. We also reported herein the increased apoptosis ratio following caspase-9 and caspase-3 upregulation in the spleen of rats exposed to excessive amount of F. Light and transmisison electron microscopy revealed the irregularly arranged lymphocytes, few lymph nodules and the apoptotic characteristic of lymphocytes, which are caused by the increased expression of caspase. In addition, Pr and Ca supplementation reversed the morphologic and T-lymphocytic changes in spleen under malnutrition. Taken together, our results revealed an endogenous caspase-mediated mechanism of regulating the apoptosis of the T-lymphocyte subsets, as well as the immune-related cytokine secretion, which reduces the immune function in F-induced rats. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 1587-1595, 2017.

Low bone mineral density linked to colorectal adenomas: a cross-sectional study of a racially diverse population

BACKGROUND

Epidemiologic studies suggest that lower bone mineral density (BMD) is associated with an increased risk for colorectal adenoma/cancer, especially in postmenopausal women. The aim of this study is to investigate the association between osteopenia and/or osteoporosis and colorectal adenomas in patients from a New York community hospital.

METHODS

We performed a cross-sectional observational study on 200 patients who underwent screening colonoscopies and bone density scan (dual-energy X-ray absorptiometry) at Nassau University Medical Center from November 2009 to March 2011. Among these, 83 patients were identified as osteoporosis (T score of -2.5 or below) and 67 were osteopenia (T score between -1.0 and -2.5). Logistic regression model was performed to assess the association between osteopenia and/or osteoporosis and colorectal adenomas.

RESULTS

Among the patients with osteopenia and osteoporosis, the mean ages were 59.1 years [standard deviation (SD) =8.9] and 61.5 (SD =8.9), respectively. There were 94.0%, 85.1% and 74.7% women, respectively, in normal BMD, osteopenia and osteoporosis groups. The prevalence of colorectal adenomas was 17.9% and 25.3% in the osteopenia and osteoporosis groups, respectively, and 18.0% in the normal BMD group. After adjustment for potential confounders including age, sex, race, body mass index (BMI), tobacco use, alcohol use, history of diabetes, hypertension, or dyslipidemia, osteoporosis was found to be associated with presence of colorectal adenomas more than 2, compared to the normal BMD group. No significant associations were found for the prevalence, size, and location of adenomas.

CONCLUSIONS

Our study suggests that osteoporosis is significantly associated with the presence of multiple colorectal adenomas. Prospective studies with a larger sample size are warranted in the future.

Dietary calcium supplementation enhances efficacy but also toxicity of EGFR inhibitor therapy for colon cancer

The inverse correlation between levels of dietary calcium and colorectal cancer (CRC) incidence has been extensively investigated. However, the impact of supplemental calcium on cancer therapy remains unknown. We used four models of CRC, Caco-2 and HCT116 human cancer cell lines and Apc (Min/+) and azoxymethane carcinogen-induced mouse models, to investigate the impact of a western-style diet low in calcium (0.05%) vs. a similar diet but supplemented with calcium (5%) on therapeutic targeting of the epidermal growth factor receptor (EGFR). We found that calcium supplementation combined with pharmacologic blockade of EGFR results in an additive effect on tumor growth inhibition in all models. Unexpectedly, the combined use of dietary calcium supplementation and EGFR inhibitors also resulted in elevated toxicity suggesting that careful consideration be given when combining dietary supplements with prescribed cancer therapies.

Review article: loss of the calcium-sensing receptor in colonic epithelium is a key event in the pathogenesis of colon cancer

The calcium-sensing receptor (CaSR) is expressed abundantly in normal colonic epithelium and lost in colon cancer, but its exact role on a molecular level and within the carcinogenesis pathway is yet to be described. Epidemiologic studies show that inadequate dietary calcium predisposes to colon cancer; this may be due to the ability of calcium to bind and upregulate the CaSR. Loss of CaSR expression does not seem to be an early event in carcinogenesis; indeed it is associated with late stage, poorly differentiated, chemo-resistant tumors. Induction of CaSR expression in neoplastic colonocytes arrests tumor progression and deems tumors more sensitive to chemotherapy; hence CaSR may be an important target in colon cancer treatment. The CaSR has a complex role in colon cancer; however, more investigation is required on a molecular level to clarify its exact function in carcinogenesis. This review describes the mechanisms by which the CaSR is currently implicated in colon cancer and identifies areas where further study is needed.

Higher bone mineral density is associated with a decreased risk of colorectal adenomas

Bone mineral density (BMD) is a biomarker for cumulative exposure to multiple factors including estrogen, calcium, vitamin D and physical activity, which have all been independently associated with colorectal cancer. Furthermore, higher levels of BMD have been inversely associated with colorectal cancer risk, particularly in postmenopausal women. However, no prior studies have examined the potential association between BMD and colorectal adenomas, which are precursor lesions to most colorectal cancers. Therefore, we evaluated the association between BMD, which was measured using a whole body, dual-energy X-ray absorptiometry scan and colorectal adenomas in 167 patients who underwent colonoscopy screening. We found that patients in the highest tertile of total body BMD (>1.294 g/cm(2)) and in the middle tertile (≥1.167 to ≤1.294 g/cm(2)) compared to those with a total body BMD in the lowest tertile (<1.167 g/cm(2)) had a lower risk of colorectal adenomas (highest vs. lowest tertile: OR = 0.29 (0.10-0.84); middle vs. lowest tertile: OR=0.26 (0.08-0.80); p-trend=0.02). Stratification by gender revealed that this association was more pronounced in women (highest (>1.280 g/cm(2)) vs. lowest (<1.130 g/cm(2)) tertile: OR=0.08 (0.01-0.70); middle (≥1.130 to ≤1.280 g/cm(2)) vs. lowest tertile: OR=0.15 (0.04-0.94); p-trend=0.02) even after excluding hormone replacement therapy users (highest (>1.295 g/cm(2)) and middle (≥1.132 to ≤1.295 g/cm(2)) vs. lowest (<1.132 g/cm(2)) tertile: OR=0.17 (0.03-0.97); p-trend=0.04). Our results show, for the first time, that BMD is inversely associated with colorectal adenomas, particularly in women. Although additional larger, prospective studies are needed, our results suggest that BMD may be a biomarker for colorectal cancer precursor lesions.

Dietary microparticles and their impact on tolerance and immune responsiveness of the gastrointestinal tract

Dietary microparticles are non-biological bacterial-sized particles of the gastrointestinal lumen that occur due to endogenous formation (calcium phosphate) or following oral exposure (exogenous microparticle). In the UK, about 40 mg (10(12)) of exogenous microparticles are ingested per person per day, through exposure to food additives, pharmaceutical/supplement excipients or toothpaste constituents. Once ingested, exogenous microparticles are unlikely to pass through the gastrointestinal tract without adsorbing to their surfaces some ions and molecules of the intestinal lumen. Both entropy and ionic attraction drive such interactions. Calcium ions are especially well adsorbed by dietary microparticles which then provide a positively charged surface for the attraction (adsorption) of other organic molecules such as lipopolysaccharides, peptidoglycans or protein antigen from the diet or commensal flora. The major (but not only) sites of microparticle entry into intestinal tissue are the M-cell rich lymphoid aggregates (termed Peyer's patches in the small bowel). Indeed, it is well established that this is an efficient transport route for non-biological microparticles although it is unclear why. We hypothesise that this pathway exists for "endogenous microparticles" of calcium phosphate, with immunological and physiological benefit, and that "exogenous dietary microparticles", such as titanium dioxide and the silicates, hijack this route. This overview focuses on what is known of these microparticles and outlines their potential role in immune tolerance of the gut (endogenous microparticles) or immune activation (exogenous microparticles) and inflammation of the gut.

Low dietary calcium levels modulate mucosal caspase expression and increase disease activity in mice with dextran sulfate sodium induced colitis

Dietary calcium (Ca) positively modulates the susceptibility to colon cancer, but its effects on related or earlier colonic pathologies, such as inflammation and mucosal dysregulation, are poorly understood. We tested the effects of differing dietary Ca levels on acute dextran sulfate sodium (DSS)-induced colitis in mice. BALB/c mice received a normal Ca (NCa) diet (0.5% Ca), a high Ca (HCa) diet (1.5% Ca), a low Ca (LCa) diet (0.05% Ca), or a very low Ca (VLCa) diet (0.009% Ca) for 3 wk. Mucosal caspases 1, 3, and 9 were assessed by Western blotting, and the histological crypt score was assessed by microscopy. Half of the mice in each group received DSS (1.5%) for 20 d in their drinking water, and disease activity was assessed. Increasing or lowering dietary Ca increased mucosal caspases (P < 0.0001 vs. NCa). Crypt scores increased with decreasing dietary Ca levels (P < 0.0001, r = -0.675), indicating that elevated caspases in LCa groups reflected early subclinical inflammation. DSS-induced disease activity was higher in mice fed low dietary Ca levels [P < 0.0001, VLCa and DSS vs. NCa and DSS (NCaDSS) and P < 0.005, LCa and DSS vs. NCaDSS], and mice from the VLCa group were moribund within 11 d of DSS administration. Those in the HCa group did not differ greatly from controls. Together, these data indicate that Ca protects against DSS-induced colitis in mice. The mechanisms are unclear, but the calcium-sensing receptor and/or luminal precipitates of calcium phosphate microparticles may be involved. Whether these observations can be extended to patients with colitis or infectious diarrhea deserves consideration.

Adiposity-related protection of intestinal tumorigenesis: interaction with dietary calcium

Although high-calcium diets have been reported to reduce the risk of colorectal cancer, our preliminary data with the adenomatous polyposis coli (Apc) Min mutation (Min/+;Apc(Min/+)) mouse shows a paradoxical increase in intestinal tumor loads (> 65%) with high calcium diets. Since we previously demonstrated that increasing dietary calcium reduces adiposity, and Apc(Min/+) mice on high calcium diets exhibited profound loss of adipose tissue, we hypothesized that loss of an adipose tissue-derived tumor suppressor factor(s) resulted in increased tumor susceptibility in animals on the high calcium diet. Accordingly, tumor prone Apc(Min/+) mice were crossed with obesity prone lethal yellow agouti (A(y)/a) mice to generate obese A(y)/Apc(Min/+) mice. Low (0.2%), normal (0.5%), and high (1.2%) calcium diets were fed to both A(y)/Apc(Min/+) mice and Apc(Min/+) mice from 35-40 days until 90 days of age (n=21/strain, n=7/diet group). The high calcium diet reduced weight gain in both strains (P < 0.01) and reduced fat pad mass by 46-57% in A(y)/Apc(Min/+)(P < 0.004) and by 65-82% in Apc(Min/+)(P < 0.03).Apc(Min/+) mice on the high calcium diet exhibited an increase in tumor number (76 vs. 29, P=0.009), but this effect was not seen in the A(y)/Apc(Min/+) mice. beta-Catenin and cyclin D1 gene expression were significantly induced with high calcium diet in intestinal tumor tissue of Apc(Min/+) mice but not in A(y)/Apc(Min/+) mice. We conclude that the differential effect of dietary calcium on intestinal tumorigenesis in lean vs. obese Apc(Min/+) may result from the loss of adipose-derived protective factor(s) due to the substantial loss of body fat in Apc(Min/+) mice fed a high calcium dairy diet, increasing beta-catenin and cyclin D1 in tumors.

Calcium, dietary, and lifestyle factors in the prevention of colorectal adenomas

BACKGROUND

Many studies have suggested a role for calcium in reducing the risk of colorectal adenomas and cancer but its effectiveness may be dependent on interactions with other dietary and/or lifestyle factors. We examined the association between calcium and prevalence of adenomas and assessed whether the association was stronger in biologically plausible subgroups.

METHODS

Cross-sectional data from 222 cases and 479 adenoma-free controls who underwent colonoscopies and completed food frequency and lifestyle questionnaires were used in the analyses. Multivariable logistic regression was used to estimate the association between calcium and prevalence of adenomas. Stratified analyses and the likelihood ratio test were used to examine effect modification by various demographic, lifestyle, and behavioral factors.

RESULTS

Overall, little association was observed comparing total calcium intake of > or = 900 mg/day to < 500 mg/day (adjusted odds ratio [OR] = 0.85, 95% confidence interval [CI]: 0.53-1.37). However, stronger associations were observed in patients with lower fat intake and in those who regularly (> or = 15 times/month) took nonsteroidal antiinflammatory drugs (NSAIDs). Specifically, total calcium intake of > or = 900 mg/day was associated with a lower prevalence of adenomas among patients with lower fat intake (OR = 0.47, 95% CI: 0.25-0.91) but not among those with higher fat intake (OR = 1.20, 95% CI: 0.61-2.35; P-value for interaction = .01). For NSAIDs, the associations were OR = 0.37 (95% CI: 0.16-0.86) for regular NSAID users and OR = 1.27 (95% CI: 0.73-2.22) with infrequent or nonuse of NSAIDs, respectively (P = .06).

CONCLUSIONS

The data suggest that a lower-fat diet and regular NSAID use may enhance calcium's effectiveness as a colorectal cancer preventive agent.

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Interaction of Calcium Supplementation and Nonsteroidal Anti-inflammatory Drugs and the Risk of Colorectal Adenomas

BACKGROUND

Calcium and aspirin have both been found to be chemopreventive against colorectal neoplasia. However, the joint effect of the two agents has not been well investigated.

METHODS

To explore the separate and joint effects of calcium and aspirin/nonsteroidal anti-inflammatory drugs (NSAID), we used data from two large randomized clinical trials among patients with a recent history of colorectal adenomas. In the Calcium Polyp Prevention Study, 930 eligible subjects were randomized to receive placebo or 1,200 mg of elemental calcium daily for 4 years. In the Aspirin/Folate Polyp Prevention Study, 1,121 eligible subjects were assigned to take placebo, 81 mg of aspirin, or 325 mg of aspirin daily for 3 years. In each study, subjects completed a validated food frequency questionnaire at enrollment and were asked periodically about medications and supplements used. Recurrent adenomas and advanced adenomas were the end points considered. We used generalized linear models to assess the separate and combined effects of aspirin (or NSAIDs) and calcium supplementation (or dietary calcium) and the interactions between these exposures.

RESULTS

In the Calcium Trial, subjects randomized to calcium who also were frequent users of NSAIDs had a reduction of risk for advanced adenomas of 65% [adjusted risk ratio (RR), 0.35; 95% confidence interval (95% CI), 0.13-0.96], and there was a highly significant statistical interaction between calcium treatment and frequent NSAID use (P(interaction) = 0.01). Similarly, in the Aspirin Trial, 81 mg aspirin and calcium supplement use together conferred a risk reduction of 80% for advanced adenomas (adjusted RR, 0.20; 95% CI, 0.05-0.81); there was a borderline significant statistical interaction between the two treatments (P(interaction) = 0.09). In this trial, we found similar trends when we considered baseline dietary calcium intake instead of calcium supplements. For all adenomas considered together, the interactive patterns were not consistent.

CONCLUSION

Data from two different randomized clinical trials suggest that calcium and NSAIDs may act synergistically to lower the risk of advanced colorectal neoplastic polyps.

Calcium, vitamin D, and apoptosis in the rectal epithelium

OBJECTIVE

Decreased apoptosis in the colon is potentially an early indicator of colon cancer risk and may be influenced by calcium and vitamin D. This report describes the associations of calcium intake and 25-hydroxyvitamin D levels with apoptosis in colorectal epithelium.

METHODS

Consecutive patients undergoing colonoscopies were recruited for a study designed to examine risk and etiologic factors for colorectal adenomas. Diet was assessed by food frequency questionnaire, and in one subpopulation, serum 25-hydroxyvitamin D levels were measured using an enzyme immunoassay. Apoptosis was scored from normal rectal mucosal pinch biopsies. Linear and logistic regression analyses were used to examine associations between calcium, serum vitamin D, and apoptotic scores. Data were available for 498 and 280 patients for the calcium and vitamin D analyses, respectively.

RESULTS

Associations of calcium intake and vitamin D with apoptosis were modified by adenoma case-status. In an adjusted logistic regression model, patients with adenomas in the highest versus lowest tertile of dietary calcium intake had 3.4 times higher odds [95% confidence interval (CI), 0.9-12.9] of elevated apoptotic scores. In adenoma-free patients, high calcium intake was not related to apoptosis (OR, 1.2; 95% CI, 0.6-2.7). In contrast, the highest level of 25-hydroxyvitamin D was associated with higher apoptosis in adenoma-free patients (OR, 2.6; 95% CI, 1.1-6.2) and slightly lower levels in patients with adenomas (OR, 0.6; 95% CI, 0.2-2.2).

CONCLUSION

These results are consistent with a calcium and vitamin D-mediated apoptotic mechanism in colon carcinogenesis.

Colorectal cancer and the relationship between genes and the environment

Colorectal cancer (CRC) is a significant cause of morbidity and mortality in developed countries, with both genetic and environmental factors contributing to the etiology and progression of the disease. Several risk factors have been identified, including positive family history, red meat intake, smoking, and alcohol intake. Protective factors include vegetables, calcium, hormone replacement therapy, folate, nonsteroidal anti-inflammatory drugs, and physical activity. The interaction between these environmental factors, in particular diet and genes, is an area of growing interest. Currently, oncogenes, tumor suppressor genes, and mismatch repair genes are believed to play an essential role in colorectal carcinogenesis. When considering the genetics of CRC, only 10% of cases are inherited and only 2-6% can be ascribed to the highly penetrant genes, such as APC, hMLH and hMSH2. Lower penetrance genes combined with a Western-style diet contribute to the majority of sporadic CRCs. The purpose of this article is to give a brief overview of the epidemiologic studies that have been conducted and present the major findings. Here, we examine the molecular events in CRC, with particular focus on the interaction between genes and environment, and review the most current research in this area.

Relationship between serum calcium and CA 19-9 levels in colorectal cancer

AIM: To examine the calcium metabolism of colorectal cancer (CRC) in patients with colorectal cancer and control patients.

METHODS: Seventy newly diagnosed CRC patients were included. The healthy control group was age and gender matched (n = 32). Particular attention was devoted to the relationship between serum calcium of patients, and levels of AFP, CEA, carbohydrate antigen 19-9 (CA 19-9) (that could be considered as prognostic factors). Furthermore, the Ca-sensing receptor (CaSR) gene A986S polymorphism was investigated in these patients, as well as the relationship between different CaSR genotypes and the data stated above.

RESULTS: A lower level of ionized calcium (also corrected for albumin) was found in the serum of CRC patients with normal 25 (OH) vitamin D levels. The ionized calcium concentration was inversely correlated with the serum level of CA 19-9. There was no difference in the distribution of CaSR genotypes, between CRC patients and general population. The genotypes did not correlate with other data examined.

CONCLUSION: Based on these results, lower levels of serum calcium might be a pathogenic and prognostic factor in colorectal cancer.

Dietary pectin and calcium inhibit colonic proliferation in vivo by differing mechanisms

Diet plays an important role in promoting and/or preventing colon cancer; however, the effects of specific nutrients remain uncertain because of the difficulties in correlating epidemiological and basic observations. Transmissible murine colonic hyperplasia (TMCH) induced by Citrobacter rodentium, causes significant hyperproliferation and hyperplasia in the mouse distal colon and increases the risk of subsequent neoplasia. We have recently shown that TMCH is associated with an increased abundance of cellular beta-catenin and its nuclear translocation coupled with up-regulation of its downstream targets, c-myc and cyclin D1. In this study, we examined the effects of two putatively protective nutrients, calcium and soluble fibre pectin, on molecular events linked to proliferation in the colonic epithelium during TMCH. Dietary intervention incorporating changes in calcium [high (1.0%) and low (0.1%)] and alterations in fibre content (6% pectin and fibre-free) were compared with the standard AIN-93 diet (0.5% calcium, 5% cellulose), followed by histomorphometry and immunochemical assessment of potential oncogenes. Dietary interventions did not alter the time course of Citrobacter infection. Both 1.0% calcium and 6% pectin diet inhibited increases in proliferation and crypt length typically seen in TMCH. Neither the low calcium nor fibre-free diets had significant effect. Pectin diet blocked increases in cellular beta-catenin, cyclin D1 and c-myc levels associated with TMCH by 70%, whereas neither high nor low calcium diet had significant effect on these molecules. Diets supplemented with either calcium or pectin therefore, exert anti-proliferative effects in mouse distal colon involving different molecular pathways. TMCH is thus a diet-sensitive model for examining the effect of specific nutrients on molecular characteristics of the pre-neoplastic colonic epithelium.

Chemoprevention of colon cancer by calcium, vitamin D and folate: molecular mechanisms

Recent findings have indicated that dietary calcium, vitamin D and folate can modulate and inhibit colon carcinogenesis. Supporting evidence has been obtained from a wide variety of preclinical experimental studies, epidemiological findings and a few human clinical trials. Important molecular events and cellular actions of these micronutrients that contribute to their tumour-modulating effects are discussed. They include a complex series of signalling events that affect the structural and functional organization of colon cells.

Bacterial enterotoxins are associated with resistance to colon cancer

One half million patients suffer from colorectal cancer in industrialized nations, yet this disease exhibits a low incidence in under-developed countries. This geographic imbalance suggests an environmental contribution to the resistance of endemic populations to intestinal neoplasia. A common epidemiological characteristic of these colon cancer-spared regions is the prevalence of enterotoxigenic bacteria associated with diarrheal disease. Here, a bacterial heat-stable enterotoxin was demonstrated to suppress colon cancer cell proliferation by a guanylyl cyclase C-mediated signaling cascade. The heat-stable enterotoxin suppressed proliferation by increasing intracellular cGMP, an effect mimicked by the cell-permeant analog 8-br-cGMP. The antiproliferative effects of the enterotoxin and 8-br-cGMP were reversed by L-cis-diltiazem, a cyclic nucleotide-gated channel inhibitor, as well as by removal of extracellular Ca(2+), or chelation of intracellular Ca(2+). In fact, both the enterotoxin and 8-br-cGMP induced an L-cis-diltiazem-sensitive conductance, promoting Ca(2+) influx and inhibition of DNA synthesis in colon cancer cells. Induction of this previously unrecognized antiproliferative signaling pathway by bacterial enterotoxin could contribute to the resistance of endemic populations to intestinal neoplasia, and offers a paradigm for targeted prevention and therapy of primary and metastatic colorectal cancer.

Primary prevention: phytoprevention and chemoprevention of colorectal cancer

Considering the various stages of carcinogenesis and the numerous tumor types and available chemoprevention agents, knowledge of the etiology and the type of cancer to be treated, or possibly prevented, and understanding of the mechanisms by which agents exert their chemoprevention benefits may provide for improved strategy in designing therapeutic regimens. Because cancer usually develops over a 10- to 20-year period, it may be necessary for some agents to be provided before or early in the initiation steps of carcinogenesis to have beneficial effects. On the other hand, some agents may be more suitable for CRC prevention if provided at a later stage of carcinogenesis. Gene array, genomics, and proteomics are useful tools in advancing our understanding of the molecular events involved in carcinogenesis and in identifying markers of risk and surrogate end-points for colorectal cancer progression. These techniques may also serve for screening, identifying, and providing treatment targets for high-risk patients populations. Treatment could be developed depending on a patient's individual needs and genomic tumor profile. Clinical markers and surrogate end-points should be considered, together with molecular measurements, to more accurately assess risk. NSAIDs and COXIBs are clinically recognized as chemoprevention agents, and clinical trials evaluating their efficacy are ongoing. Treatment protocols, including dose and timing, remain to be determined, however. DFMO may best be used in combination with other chemoprevention agents. Dietary fiber and calcium supplements, as part of an overall low-fat diet, may decrease CRC risk. Long-term compliance with this regimen may be necessary to effect a beneficial outcome. Folate holds promise but needs further investigation, especially because its beneficial effects may depend on cancer type. Phytochemicals have been identified as strong candidates for use as agents to prevent colorectal cancer in cell culture and in rodent models of carcinogenesis. Their potential as chemoprevention agents must be demonstrated in clinical trials. In vitro and animal studies indicated that combination therapy may be a promising strategy over the monotherapy approach; clinical trials addressing the safety and efficacy of some combinations (DFMO/sulindac, fiber/calcium) are underway. The gastrointestinal tract and other organs are constantly exposed to a mixture of potentially toxic compounds and molecules considered favorable to health. Homeostasis between stress-mediated by toxic compounds and defensive mechanisms, is key for the maintenance of health and the prevention of disease. Whereas aggressive pharmacologic treatment may be necessary for patients at high risk for cancer, dietary supplements may be useful for populations at normal risk. The message for cancer prevention in the general population may well remain: keep a balanced healthy diet, eating a variety from all food groups, as part of a healthy lifestyle that includes moderate exercise.

Msh2 deficiency increases the mutation frequency in all parts of the mouse colon

The Msh2 DNA mismatch repair gene is one of five genes implicated in the pathogenesis of hereditary nonpolyposis colorectal cancer (HNPCC). To address the possible mechanisms of the site-specific occurrence of HNPCC, the effect of Msh2 deficiency on mutations in different parts of the colon was investigated using the BC-1(lacI)/Msh2 double transgenic mouse. Compared to the Msh2(+/+) mice, Msh2(-/-) mice had an 8-9-fold increase of mutation frequency (MF) in the lacI gene from the cecum and the proximal and distal colon. The mutational spectra were also significantly different between Msh2(+/+) and Msh2(-/-) mice, with a significant increase in the frequency of -1 frameshifts and G:C-->A:T base substitutions in the repair-deficient mice. However, in spite of the site-specific predisposition of HNPCC in humans, we found no significant difference in the MF or mutation spectrum between the three parts of the colon in Msh2(+/+), Msh2(+/-), or Msh2(-/-) mice. In addition, 11 independent mutants harboring complex mutations within the lacI gene were recovered in the Msh2(-/-) mice. Interestingly, while the Msh2(+/-) mice displayed an overall MF similar to that observed in the wild-type mice, sequencing revealed a significantly different mutational spectrum between Msh2(+/+) and Msh2(+/-) mice, mainly characterized by an increase in -1 frameshifts. Due to the prevalence of frameshift mutations in HNPCC patients, this haploinsufficiency effect of the Msh2 gene in safeguarding genomic integrity may have important implications for human carrier status.

Cellular mechanisms of calcium and vitamin D in the inhibition of colorectal carcinogenesis

Convincing evidence is available showing that dietary calcium and vitamin D impede the development of colonic carcinogenesis. The major cellular modes of action of calcium and vitamin D which can contribute to the inhibition of colonic neoplasia are reviewed in this article. These consist of complex series of signaling events induced by the chemopreventive agents acting at various tiers of colonic cell organization.