Effect of dietary calcium on the colonic luminal environment

Negative effects of divalent mineral cations on the bioaccessibility of carotenoids from plant food matrices and related physical properties of gastro-intestinal fluids

Proposed interaction of divalent cations, bile acids, and fatty acids in the intestine, resulting in precipitation and entrapment of carotenoids.

Damage to the intestinal epithelial barrier by antibiotic pretreatment of salmonella-infected rats is lessened by dietary calcium or tannic acid

Perturbation of the intestinal microbiota by antibiotics predisposes the host to food-borne pathogens like Salmonella. The effects of antibiotic treatment on intestinal permeability during infection and the efficacy of dietary components to improve resistance to infection have not been studied. Therefore, we investigated the effect of clindamycin on intestinal barrier function in Salmonella-infected rats. We also studied the ability of dietary calcium and tannic acid to protect against infection and concomitant diarrhea and we assessed intestinal barrier function. Rats were fed a purified control diet including the permeability marker chromium EDTA (CrEDTA) (2 g/kg) or the same diet supplemented with calcium (4.8 g/kg) or tannic acid (3.75 g/kg). After adaptation, rats were orally treated with clindamycin for 4 d followed by oral infection with Salmonella enteritidis. Two additional control groups were not treated with antibiotics and received either saline or Salmonella. Urine and feces were collected to quantify intestinal permeability, diarrhea, cytotoxicity of fecal water, and Salmonella excretion. In addition, Salmonella translocation was determined. Diarrhea, CrEDTA excretion, and cytotoxicity of fecal water were higher in the clindamycin-treated infected rats than in the non-clindamycin-treated infected control group. Intestinal barrier function was less in the Salmonella-infected rats pretreated with antibiotics compared with the non-clindamycin- treated rats. Both calcium and tannic acid reduced infection-associated diarrhea and inhibited the adverse intestinal permeability changes but did not decrease Salmonella colonization and translocation. Our results indicate that calcium protects against intestinal changes due to Salmonella infection by reducing luminal cytotoxicity, whereas tannic acid offers protection by improving the mucosal resistance.

Supplemental calcium attenuates the colitis-related increase in diarrhea, intestinal permeability, and extracellular matrix breakdown in HLA-B27 transgenic rats

We have shown in several controlled rat and human infection studies that dietary calcium improves intestinal resistance and strengthens the mucosal barrier. Reinforcement of gut barrier function may alleviate inflammatory bowel disease (IBD). Therefore, we investigated the effect of supplemental calcium on spontaneous colitis development in an experimental rat model of IBD. HLA-B27 transgenic rats were fed a purified high-fat diet containing either a low or high calcium concentration (30 and 120 mmol CaHPO4/kg diet, respectively) for almost 7 wk. Inert chromium EDTA (CrEDTA) was added to the diets to quantify intestinal permeability by measuring urinary CrEDTA excretion. Relative fecal wet weight was determined to quantify diarrhea. Colonic inflammation was determined histologically and by measuring mucosal interleukin (IL)-1beta. In addition, colonic mucosal gene expression of individual rats was analyzed using whole-genome microarrays. The calcium diet significantly inhibited the increase in intestinal permeability and diarrhea with time in HLA-B27 rats developing colitis compared with the control transgenic rats. Mucosal IL-1beta levels were lower in calcium-fed rats and histological colitis scores tended to be lower (P = 0.08). Supplemental calcium prevented the colitis-induced increase in the expression of extracellular matrix remodeling genes (e.g. matrix metalloproteinases, procollagens, and fibronectin), which was confirmed by quantitative real-time PCR and gelatin zymography. In conclusion, dietary calcium ameliorates several important aspects of colitis severity in HLA-B27 transgenic rats. Reduction of mucosal irritation by luminal components might be part of the mechanism. These results show promise for supplemental calcium as effective adjunct therapy for IBD.

Effect of calcium supplementation on the risk of large bowel polyps

BACKGROUND

Clinical trials have shown that calcium supplementation modestly decreases the risk of colorectal adenomas. However, few studies have examined the effect of calcium on the risk of different types of colorectal lesions or dietary determinants of this effect.

METHODS

Our analysis used patients from the Calcium Polyp Prevention Study, a randomized, double-blind, placebo-controlled chemoprevention trial among patients with a recent colorectal adenoma. Nine hundred thirty patients were randomly assigned to calcium carbonate (1200 mg/day) or placebo. Follow-up colonoscopies were conducted approximately 1 and 4 years after the qualifying examination. We used general estimating equation (GEE) and generalized linear regression analyses to compute risk ratios and 95% confidence intervals (CIs) to assess the effect of calcium treatment versus placebo on the risk of hyperplastic polyps, tubular adenomas, and more advanced lesions. Additionally, we used GEE analyses to compare the calcium treatment effects for various types of polyps with that for tubular adenomas. We also examined the interaction between calcium treatment and baseline intake of dietary calcium, fat, and fiber. All P values were obtained using Wald tests based on the corresponding models. All tests of statistical significance were two-sided.

RESULTS

The calcium risk ratio for hyperplastic polyps was 0.82 (95% CI = 0.67 to 1.00), that for tubular adenomas was 0.89 (95% CI = 0.77 to 1.03), and that for histologically advanced neoplasms was 0.65 (95% CI = 0.46 to 0.93) compared with patients assigned to placebo. There were no statistically significant differences between the risk ratio for tubular adenomas and that for other types of polyps. The effect of calcium supplementation on adenoma risk was most pronounced among individuals with high dietary intakes of calcium and fiber and with low intake of fat, but the interactions were not statistically significant.

CONCLUSION

Our results suggest that calcium supplementation may have a more pronounced antineoplastic effect on advanced colorectal lesions than on other types of polyps.

Calcium inhibits colon carcinogenesis in an experimental model in the rat

Different dietary factors can affect colorectal cancer incidence. However, the effect of increased levels of dietary calcium on neoplasms is unclear. The present study was designed to examine the effect of a low calcium supplement on experimental colon carcinogenesis induced by parenteral administration of dimethylhydrazine (DMH). One hundred and twenty 10-week-old Sprague-Dawley rats were divided into five groups of equal sex distribution. The 10 rats in group A (control group) received no treatment; the 30 rats in group B (DMH group) were injected subcutaneously with 18 weekly doses of 21 mg/kg DMH; the 20 rats in group C (EDTA control group) received EDTA solution only; the 30 rats in group D (calcium group) received calcium at 3.2 g/l by adding calcium lactate to the drinking water from the start until the conclusion of the experiment; and the 30 rats in group E (DMH + calcium group) received oral calcium supplements at the same dose as the rats in group D (calcium group) and the same DMH injections as the rats in group B (DMH group). The rats were sacrificed at 25-34 weeks. In group E, we observed a significant diminution in the number of tumours (P = 0.01); an increase in the number of tumour-free animals (P = 0.006); a change in tumour location towards the distal colon (P < 0.025); more adenomas (P = 0.02); and a diminution of adenocarcinomas and mucinous carcinomas, although this was not significant. We conclude that a low dietary calcium supplement in rats inhibits colon cancer carcinogenesis induced by DMH, and changes tumour location towards the distal colon.

Factors influencing the development of sigmoid colon cancer. Bacteriologic and biochemical studies

BACKGROUND

Cancer of the sigmoid colon is especially sensitive to environmental factors such as food. The authors have conducted a series of studies with food as the external environmental factor and intestinal microflora as the internal environment factor in relation to sigmoid colon carcinogenesis.

METHODS

Thirteen males who had previously undergone surgery for sigmoid colon cancer, and who later developed new epithelial neoplasia of the colon, were chosen as the high risk (HR) group. Fourteen males of similar age, whose large bowel was entirely normal by total colonoscopy, were chosen as the control (CONT) group. Food constituents were analyzed by a dietician. Fecal bile acids, cholesterol metabolites, degradation products of amino acids, pH, water content, and bacterial flora were quantitatively analyzed.

RESULTS

Although the HR group consumed slightly more carbon hydrate, fiber, and calcium, as a whole, there was no significant difference in food constituents, especially animal fat, between the two groups. Concentrations of bile acids and cholesterol metabolites were not different between the groups, with the exception of a higher level of cholestanol in the HR group. Succinic, lactic, propionic, and isovaleric acids were abundant in the HR group. Fecal pH and amounts of hydrogen sulfide and cresol also were higher in the HR group. The total amount of bacteria, lecithinase-negative Clostridia, and Lactobacillus, were also more abundant in the HR group.

CONCLUSIONS

The feces of the HR group was abundant in such substances as sigmoid colon cancer promoters, and appeared unrelated to food constituents. Resident flora of the HR group were abundant in enzymatically active anaerobes. Because agents carcinogenic to the colon and rectum exist ubiquitously, microflora play a key role in sigmoid colon carcinogens by producing promoters.

Luminal and humoral influences on human rectal epithelial cytokinetics

Multiple genetic and environmental steps may underpin the development of human colorectal neoplasia, and experimental evidence suggests that promoters of colorectal cancer also induce colorectal epithelial cell hyperplasia. In vitro crypt cell production rate (CCPR) was measured to determine the effect of calcium, epidermal growth factor (EGF), vitamin D3 metabolites and synthetic analogues on human rectal epithelial cell proliferation. In a double-blind trial of oral calcium supplementation, CCPR was reduced by 49% in patients with familial adenomatous polyposis (FAP), but there was no effect on established neoplasia. In control tissue, the active form of vitamin D3 (1,25(OH)2D3) reduced rectal CCPR by 57% at 1 microM, 55% at 10 nM and 45% at 100 pM. Likewise, in tissue taken from patients with FAP, 1,25(OH)2D3 reduced CCPR by 52%. Vitamin D3 has profound effects on calcium metabolism, but synthetic analogues can avoid these. The effects of a synthetic analogue (MC-903) on human rectal CCPR were therefore studied. MC-903 (10(-7) M) reduced CCPR in control tissue by 51%, and in FAP tissue by 52% at 10(-6) M and 51% at 10(-7) M. In addition, MC-903 and a related analogue, EB 1089, produced a clear-cut dose-dependent inhibition of both HT-29 and Caco2 colorectal cancer cells maintained in culture. Hence, vitamin D3 and its analogues can reduce the rate of cell proliferation in normal, premalignant and malignant colorectal epithelial cells and might therefore have future therapeutic uses as chemoprotective or chemotherapeutic agents. Lastly, EGF increases CCPR by 102% in FAP tissue that expresses the EGF receptor. Thus, human colorectal cell proliferation is influenced by a variety of luminal and humoral agents and a greater understanding of these actions should help plan future treatments.

Calcipotriol inhibits rectal epithelial cell proliferation in ulcerative proctocolitis

Vitamin D3 reduces human rectal crypt cell production rate (CCPR) and may thereby protect against colorectal cancer. Cell turnover is increased in ulcerative proctocolitis, which might therefore respond to vitamin D3 metabolites. This study investigated the effect of calcipotriol, a synthetic vitamin D3 analogue that avoids hypercalcaemia, on human rectal CCPR in ulcerative proctocolitis. Paired rectal biopsy specimens from seven patients with severe disease were established in organ culture with or without calcipotriol (1 x 10(-6) M). After 15 hours, vincristine (0.6 microgram/ml) was added to induce metaphase arrest, and CCPR was determined by linear regression analysis of accumulated metaphases. Compared with values in 17 controls with incidental anal conditions, median rectal CCPR was 28% higher in ulcerative proctocolitis: 5.90 (5.00-9.50) v 4.80 (2.85-7.07) cells/crypt/hour (p < 0.01). Calcipotriol reduced CCPR by 62% in patients with ulcerative proctocolitis, from 5.90 (5.00-9.50) to 2.21 (0.81-3.22) cells/crypt/hour (median with range) p < 0.01. Thus calcipotriol can dampen the hyperproliferative state in ulcerative proctocolitis and could have a therapeutic role in the control of this inflammatory condition.

Oral calcium inhibits rectal epithelial proliferation in familial adenomatous polyposis

Calcium reduces colorectal cell turnover and might therefore protect against neoplasia. The inhibitory effects of dietary calcium were tested in a double-blind controlled trial in patients with familial adenomatous polyposis who had undergone previous abdominal colectomy and ileorectal anastomosis. Patients received supplemental calcium carbonate (1500 mg/day) or placebo tablets for 6 months; sigmoidoscopy was performed before and after treatment. Rectal biopsies were maintained in short-term organ culture, and crypt cell production rate (CCPR) was measured stathmokinetically. A total of 25 patients completed the trial; polyp counts were obtained before and after treatment in all and CCPR values in 16. Calcium treatment reduced the mean (s.e.m.) CCPR from 4.72 (0.48) to 2.42 (0.48) cells per crypt per h (P < 0.05), while values for placebo were unchanged (5.46 (1.21) versus 5.08 (1.17) cells per crypt per h). Calcium had no demonstrable effect on the number, size or distribution of rectal polyps. The ability of oral calcium supplementation to suppress rectal epithelial proliferation supports its potential to prevent development of colorectal carcinoma in high-risk individuals.

Effects of dietary calcium and phosphate on the intestinal interactions between calcium, phosphate, fatty acids, and bile acids

Luminal free fatty acids and bile acids may damage the colonic epithelium and stimulate proliferation, which may increase the risk of colon cancer. It has been suggested that only soluble calcium ions (Ca2+) precipitate fatty acids and bile acids, thus reducing their lytic activity. Consequently, precipitation of luminal Ca2+ by dietary phosphate should inhibit these effects. To evaluate the proposed antagonistic effects of dietary calcium and phosphate, we studied the intestinal interactions between calcium, phosphate, fatty acids, and bile acids in rats fed purified diets that differed only in the concentrations of calcium and phosphate. Increased dietary calcium drastically decreased the solubility of fatty acids in the ileum, colon, and faeces, as well as the solubility of bile acids in the colon and faeces. Although dietary calcium strongly increased the total faecal fatty acid concentration and hardly affected the total faecal bile acid concentration, the fatty acid and bile acid concentrations in faecal water were drastically decreased by dietary calcium. Consequently, the lytic activity of faecal water was decreased. Dietary phosphate did not interfere with these intestinal effects of calcium. These results indicate that dietary phosphate does not inhibit the protective effects of dietary calcium on luminal solubility and the lytic activity of fatty and bile acids.