Calcium regulation of colonic crypt cell kinetics: evidence for a direct effect in mice

Prolonged Effect of Calcium Supplementation on Risk of Colorectal Adenomas in a Randomized Trial

BACKGROUND

Calcium supplementation has been shown to decrease the risk of recurrence of colorectal adenomas in randomized trials. However, the duration of this protective effect after cessation of active supplementation is not known.

METHODS

In the Calcium Polyp Prevention Study, 930 subjects with a previous colorectal adenoma were randomly assigned from November 1988 through April 1992 to receive placebo or 1200 mg of elemental calcium daily for 4 years. The Calcium Follow-up Study was an observational phase of the trial that tracked adenoma occurrence for an average of 7 years after the end of randomized treatment and gathered information regarding the use of medications, vitamins, and supplements during that time. We obtained follow-up information for 822 subjects, 597 of whom underwent at least one colonoscopy after the end of study treatment and are included in this analysis. Generalized linear models were used to compute relative risks (RRs) and 95% confidence intervals (CIs) for the effect of randomized calcium treatment on risk of adenoma recurrence during the first 5 years after study treatment ended and during the subsequent 5 years. Statistical tests were two-sided.

RESULTS

During the first 5 years after randomized treatment ended, subjects in the calcium group still had a substantially and statistically significantly lower risk of any adenoma than those in the placebo group (31.5% versus 43.2%; adjusted RR = 0.63, 95% CI = 0.46 to 0.87, P = .005) and a smaller and not statistically significant reduction in risk of advanced adenomas (adjusted RR = 0.85, 95% CI = 0.43 to 1.69, P = .65). However, the randomized treatment was not associated with the risk of any type of polyp during the next 5 years. The findings were broadly similar when the analysis was restricted to subjects who did not report use of any calcium supplements after the treatment phase of the trial ended.

CONCLUSION

The protective effect of calcium supplementation on risk of colorectal adenoma recurrence extends up to 5 years after cessation of active treatment, even in the absence of continued supplementation.

Roles for the calcium sensing receptor in primary and metastatic cancer

AIM

To review the role of the calcium sensing receptor (CASR) in colorectal, breast and parathyroid cancers and related cell lines, and to discuss the effects of CASR in the setting of bone metastases from breast cancer.

METHODS

We performed a literature search of the PubMed database of the National Library of Medicine (NLM) to identify articles concerning the CASR's involvement in different cancers. Further relevant papers were obtained from the references of those identified in the original search.

RESULTS

Loss of CASR expression is understood to be associated with abnormal differentiation and progression of colorectal carcinoma. It is expressed in both normal and malignant breast tissues and has been implicated in the vicious cycle of bone metastases through its interactions with the parathyroid hormone related peptide (PTHrP). In parathyroid tissue, CASR expression has been linked to proliferation of both parathyroid adenomas and carcinomas.

CONCLUSION

Apart from its role in calcium homeostasis, the CASR has many diverse functions in a variety of tissue types throughout the body, and is involved in various signalling pathways relating to cell proliferation and differentiation. CASR has been shown to be involved in the progression and spread of a variety of cancers such as colorectal, breast and parathyroid, and is likely to be the focus of much research to further elucidate its precise role.

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.

Calcium and colorectal cancer: some questions remain

There is convincing laboratory evidence that calcium reduces the risk of colorectal cancer, but previous epidemiologic studies have reported somewhat inconsistent results. A recent large prospective study confirms that higher calcium intake is associated with a modestly reduced risk of distal colorectal cancer. There was little additional risk reduction associated with consumers of more than 700 mg calcium/day. This study also suggests that certain subgroups, such as males, smokers, and people who consume low levels of vitamin D, may be at differential risk. Because colon cancer is a common disease, even a modest decrease in risk has the potential for preventing a substantial number of cases.

The role of the calcium-sensing receptor in cancer

The extracellular calcium-sensing receptor (CaR) is a versatile sensor of small, polycationic molecules ranging from Ca2+ and Mg2+ through polyarginine, spermine, and neomycin. The sensitivity of the CaR to changes in extracellular Ca2+ over the range of 0.05-5 mM positions the CaR as a key mediator of cellular responses to physiologically relevant changes in extracellular Ca2+. For many cell types, including intestinal epithelial cells, breast epithelial cells, keratinocytes, and ovarian surface epithelial cells, changes in extracellular Ca2+ concentration over this range can switch the cellular behaviour from proliferation to terminal differentiation or quiescence. As cancer is predominantly a disease of disordered balance between proliferation, differentiation, and apoptosis, disruptions in the function of the CaR could contribute to the progression of neoplastic disease. Loss of the growth suppressing effects of elevated extracellular Ca2+ have been demonstrated in parathyroid hyperplasias and in colon carcinoma, and have been correlated with changes in the level of CaR expression. Activation of the CaR has also been linked to increased expression and secretion of PTHrP (parathyroid hormone-related peptide), a primary causal factor in hypercalcemia of malignancy and a contributor to metastatic processes involving bone. Although mutation of the CaR does not appear to be an early event in carcinogenesis, loss or upregulation of normal CaR function can contribute to several aspects of neoplastic progression, so that therapeutic strategies directed at the CaR could potentially serve a supportive function in cancer management.

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.

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.

Dietary calcium supplementation increases apoptosis in the distal murine colonic epithelium

BACKGROUND

Increased dietary calcium might reduce colorectal cancer risk, possibly by reduction of colonic epithelial hyperproliferation, but not all studies have demonstrated this. Little is known about the effects of calcium on colonic apoptosis.

AIM

To quantify the effects of increasing calcium on apoptosis and cell proliferation in normal murine colonic crypt epithelium.

METHODS

Twenty one day old male C57B1/6 mice were fed either control AIN-76 diet (0.5% calcium wt/wt; n = 10) or the same supplemented with calcium carbonate (1.0% calcium; n = 10) for 12 weeks. Apoptotic cells in proximal and distal segments were counted and expressed as an apoptotic index (AI: frequency of apoptosis/100 longitudinal crypts). The bromodeoxyuridine (BrdU) labelling index was also determined. Differences were analysed by the student's t test.

RESULTS

In control animals, the AI was significantly higher in the caecum/proximal colon (mean, 28.6; SEM, 2.0) compared with the distal colon (mean, 19.9; SEM, 1.8; p = 0.004). In the calcium treated group, the AI in the caecum/proximal colon (mean, 30.6; SEM, 1.7) was similar to controls (p = 0.71) but the AI in the distal colon was significantly greater (mean, 32.6; SEM, 1.8; p = 0.001) than in control mice and was raised to values similar to those in the proximal colon. Calcium was also associated with reduced crypt cellularity and, in the proximal colon, a downward shift in the crypt position at which apoptosis occurred. There were no significant differences in the BrdU labelling index between groups or between proximal and distal colonic segments in each group.

CONCLUSIONS

Increased dietary calcium is associated with the induction of apoptosis in normal mouse distal colonic epithelium without affecting cell proliferation. This might contribute to its putative chemopreventive role in colorectal carcinogenesis. Whether this effect is direct or indirect requires further study.

Sigmoid colon cancer associated with primary hyperparathyroidism: report of a case

We present herein a case of sigmoid colon cancer associated with primary hyperparathyroidism (PHP). PHP is known to be associated with malignancy, and decreased intracolonic calcium (Ca) resulting from increased vitamin D (VD) levels may play a role in colorectal carcinogenesis. PHP was diagnosed in this patient by preoperative screening blood chemistry examination. The blood level of intact parathyroid hormone (PTH) was elevated and a parathyroid gland scintigram demonstrated abnormal uptake near the right lower lobe of the thyroid. There was no evidence of bone metastasis, and a sigmoid colectomy was performed with curative intent. The patient had an uneventful postoperative course without a critical elevation of the serum Ca level. This case report suggests that a relationship exists between PHP and colon cancer, and the possible mechanisms of this association are presented in our discussion.

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.