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* Institute of Pathophysiology, Medical University of Vienna, Austria and Strang Cancer Research Laboratory, The Rockefeller University, NY, NY 10021
3 To whom correspondence should be addressed. E-mail: heide.cross{at}meduniwien.ac.at.
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ABSTRACT |
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 TOP ABSTRACT LITERATURE CITED |
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KEY WORDS: • colonic vitamin D hydroxylases • dietary calcium and folate • vitamin D degradation • phytoestrogens • epigenetic regulation
Hypovitaminosis D and colorectal cancer.
The majority (
90%) of human colorectal cancer cases are sporadic nonfamilial cancers and their incidence is strongly associated with age, nutrition, and lifestyle. Epidemiological studies showed involvement of vitamin D; however, a molecular basis for this is still incompletely understood.
Whereas oily fish is an excellent nutritional source of vitamin D (1), intake of this traditional food has been reduced in many countries due to lifestyle changes. Consequently, sunlight is responsible for the majority of vitamin D production: in the skin, UV-B energy converts 7-dehydrocholesterol to vitamin D. In the liver, vitamin D is hydroxylated to 25-hydroxycholecalciferol (25-OH-D3)4, the major circulating form of the steroid. 25-OH-D3 has no intrinsic biological activity but serves as the substrate for further hydroxylation and thus it can be considered a prohormone. Serum levels of 25-OH-D3 are a direct reflection of sunlight exposure, of the use of sun blockers, and of skin pigmentation. The concentration of 25-OH-D3 in blood varies between 25 and 125 nmol/L in winter and 50 and 200 nmol/L in summer (2). Whereas there is agreement that vitamin D deficiency is defined by 25-OH-D3 concentrations below 40 nmol/L, vitamin D insufficiency, i.e., sub-optimal vitamin D supply, is considered to be reflected by 25-OH-D3 concentrations in the 40–80 nmol/L range. This is because a number of studies have shown that a fall of serum 25-OH-D3 levels into this range is associated with a rise of serum parathyroid hormone indicative of secondary hyperparathyroidism (2,3).
Hypovitaminosis D is a widespread phenomenon in the adults of Central and Western Europe and in North America, especially in dark-skinned adults who have reduced vitamin D synthesis due to high melanin concentrations in the skin. Low 25-(OH)-D3 levels are also frequently observed in housebound or hospitalized elderly people, and it is indeed an older age-group that is particularly prone to sporadic colorectal cancer.
In 1980, Garland et al. (4) proposed that vitamin D was a protective factor against colorectal cancer. They based this hypothesis on the observation that colon cancer mortality in the USA was highest in regions where the population was least exposed to solar radiation. The link between colorectal cancer incidence and solar radiation was later confirmed by several large studies comparing southern and northern parts of the USA (5). By 1989 the link between low serum 25-OH-D3 levels and colon cancer incidence was recognized (6). A recent metaanalysis (7) reported a 50% lower incidence of colorectal cancer in individuals with 
82 nmol/L serum 25-hydroxyvitamin D concentrations.
Although serum 25-OH-D3 concentration may vary in a relatively wide nanomolar range, the picomolar serum levels of the active vitamin D metabolite dihydroxycholecalciferol (1,25-(OH)2-D3) need to be stringently controlled to maintain calcium/phosphate homeostasis. Levels of 1,25-(OH)2-D3 are regulated through the hormone's synthesis and degradation. 25-(OH)-D3 is 1
-hydroxylated by 25-(OH)-D3–1-hydroxylase (CYP27B1) in the kidney to 1,25-(OH)2-D3. Under normal circumstances, renal CYP27B1 activity is regulated by serum calcium, phosphate, and parathyroid hormone. 1,25-(OH)2-D3 regulates its own synthesis and degradation through repression of CYP27B1 and induction of 25-OH-D3 24-hydroxylase (CYP24). CYP24 can completely catabolize 25-OH-D3 and 1,25-(OH)2-D3 via a multistep reaction process to the final degradation product, calcitroic acid (8).
The vitamin D receptor (VDR) is a ligand-regulated transcription factor that binds to unique promoter sequences (i.e., vitamin D response elements) in target genes and it modulates their expression (see e.g., 9). The active vitamin D metabolite, in addition to regulating calcium/phosphate homeostasis and bone mineralization, induces in vitro cell cycle arrest, differentiation, and apoptosis in a variety of cancer cells, including those derived from colon (see e.g., 10). However, although mineral homeostasis is efficiently regulated by the picomolar serum concentrations of 1,25-(OH)2-D3, growth inhibition of cancer cells generally occurs only at a 1000-fold higher nanomolar concentration (10). In addition, a negative correlation of 1,25-(OH)2-D3 with tumor incidence has never been detected, not even at the highest physiological serum concentrations (6,11), whereas there is clear negative correlation with 25-OH-D3 levels. In addition, a recent human pilot study by Holt et al. (12) demonstrated for the first time that rectal crypt proliferation correlated inversely with serum 25-OH-D3 levels. These data support our hypothesis, published in 1997 (13), that because human colon cancer cells can synthesize 1,25-(OH)2-D3, they possess an intrinsic physiological defense which, if optimally functional, could prevent hyperproliferation and progression into malignancy. However, low serum 25-OH-D3 could result in colonic 1,25-(OH)2-D3 production that is insufficient for maintenance of autocrine/paracrine regulation of cellular growth and function. Because an optimized colonic synthesis of 1,25-(OH)2-D3 could contribute to prevention of cancer progression, it was essential that we characterized the regulatory aspects.
Extrarenal colonic 1,25-(OH)2-D3 synthesis. We have demonstrated that CYP27B1 is active both in colon cancer cell lines and in colonocytes freshly isolated from human tumors and the normal adjacent mucosa (13,14). Primary cultures established from human premalignant and malignant colonic tissue at diverse stages of malignancy display a mosaic pattern of VDR expression. In colon tissue derived from a large patient cohort, VDR and CYP27B1 mRNA expression was low in normal tissue, but rose early during colon tumor progression (14,15), potentially as a protection against growth promoting events. In late stage, high-grade colon cancer, there is an apparent failure of this protective system while, at the same time, there is increased expression of CYP24, which could cause rapid catabolism of 1,25-(OH)2-D3 at the tumor site, counteracting its local inhibition of tumor growth (16). We therefore hypothesized that, while the precursor of the active metabolite certainly had to reach adequate serum levels either through nutrition, substitution, or/and sun exposure (for review see 17), colonic synthesis of 1,25-(OH)2-D3 should be optimized as well, by increasing CYP27B1 and decreasing CYP24 expression and activity.
Regulation of the colonic vitamin D system in mice. The importance of the VDR for prevention of colonic hyperproliferation and of potential tumorigenesis was demonstrated in VDR-knockout mice (18). Complete loss of the VDR resulted in colonic hyperproliferation, cyclin D1 elevation, and a dramatic increase of DNA damage, as measured by 8-hydroxy-2'-deoxyguanosine accumulation, primarily in the distal colon. This suggests that growth control by 1,25-(OH)2-D3 is mainly effective in the mouse sigmoid colon and may be essential for normal growth of mucosal cells.
Recently we provided evidence in normal C57BL/6 mice that the catabolic CYP24 hydroxylase was present only minimally in the distal colon, but was strongly expressed in the proximal colon (19). This suggests a high potential for accumulation of 1,25-(OH)2-D3 in the sigmoid colon due to low degradation, which could protect against premalignant lesions.
Regulation by low nutritional calcium. Another nutritional factor that is inversely associated with colorectal cancer incidence is calcium. Risk reductions are in the range of 15–40% for the highest vs. the lowest intake categories; see e.g., (20,21).
It has been assumed that vitamin D and calcium insufficiency contribute to the development of colon cancer by different pathogenic mechanisms (for review see 22). However, there is increasing evidence that calcium and vitamin D status act largely together in control of colon epithelial cell proliferation (for review see 23): Calcium supplementation was effective only in patients with physiologically normal 25-OH-D3 concentrations. In the Polyp Prevention Study Group trial, supplementation of calcium with vitamin D during follow-up was inversely associated with adenoma recurrence, and even more so with multiple recurrences (24,25).
An interaction between nutritional calcium and vitamin D in protection against colorectal cancer may be due to the ability of luminal calcium to suppress degradation of 1,25-(OH)2-D3 synthesized in colonocytes. We have shown in mice that low dietary calcium (the AIN76A rodent diet was modified to contain 0.4 mg/g calcium) resulted in dramatically reduced fecal calcium content and in hyperproliferation of the colon mucosa. At the same time, expression of the cyclin-dependent kinase inhibitor p21 was reduced by 50%. Colonic CYP27B1 was not modified by low dietary calcium, whereas in contrast, CYP24 expression was doubled, but only in the ascending colon (19). Renal CYP27B1, as expected, was enhanced and CYP24 expression was reduced (19).
To investigate other prominent risk factors of the human Western style diet on expression of the vitamin D system, we used the NWD (New Western Diet)1 diet. This diet is based on the semisynthetic AIN76A diet (5% fat, 0.025µg/g vitamin D, 5 mg/g calcium and 2 µg/g folic acid with respect to nutrient density equivalents), but had previously been modified to contain high fat (20%), low calcium (0.5 mg/g), and vitamin D (0.00275 µg/g), as well as low folic acid (0.23 µg/g). In mice, this NWD1 diet led to hyperproliferation and hyperplasia, depletion of apoptotic crypt cells and single crypt dysplastic lesions (26–28), and eventually to colonic tumors without carcinogen exposure (29).
In C57/BL6 mice, the NWD1 diet upregulated CYP24 mRNA expression (evaluated by real time RT-PCR), but only in the proximal colon. This is similar to our results with low nutritional calcium alone (19), which indicates that the additional risk factors were not necessary to affect the colon adversely. Neither CYP27B1 nor VDR mRNA were modified significantly.
The NWD2 diet is similar to NWD1 except that both calcium and vitamin D are increased to nutrient-density equivalents of maximum levels recommended in human daily intakes in the USA (0.0575 µg/g and 7 mg/g, respectively); however, folic acid is still low. CYP24 mRNA expression of the proximal colon was reduced to that of the AIN76-fed control group, without change in the distal colon. The high levels of calcium and vitamin D in NWD2 decreased CYP27B1 and VDR mRNA expression, but only in the distal colon. This might be related to the well known antimitotic action of enhanced calcium and vitamin D ingestion (22) and suggests that, similar to the human colon during hyperproliferation and incipient malignancy (15), the mouse colon responds to the NWD1 stress diet with enhanced proliferation and increased CYP27B1 and VDR mRNA expression.
The third diet used in our study was NWD3. It is similar to NWD1, but the folic acid concentration is higher, equivalent to that in the AIN76A diet. In mice fed this diet, expression of CYP24 mRNA in the proximal colon was even lower than in the NWD2 group. In addition, CYP27B1 and VDR mRNA expression was significantly lower than that in the AIN76A-fed mice, again only in the distal colon.
These findings indicate a distinct, site-specific regulation of the vitamin D system by nutrients, especially by high dietary calcium and by folate. Optimal nutrition could decrease degradation of 1,25-(OH)2-D3 in the proximal colon, while in the distal colon, the ability to synthesize enhanced levels of 1,25-(OH)2-D3 may depend on the proliferative status of the mucosa. However, it also suggests that increasing the availability of methyl donors could compensate for decreased levels of dietary vitamin D and calcium, which indicates epigenetic regulation of the vitamin D system.
Regulation of the vitamin D system in mouse colon by phytoestrogens. Considerable evidence is accumulating for a protective effect of estrogens against colorectal cancer incidence. In colon cancer animal models, male rodents have a higher tumor load and increased aberrant crypt formation rates (30). At all ages, women are less likely than men to develop colon cancer, and postmenopausal hormone replacement therapy (HRT) reduces even further colon cancer risk by up to 25%. Potter et al. (31) demonstrated lower risk of adenomatous polyps of the large bowel with HRT. The large study by the Women's Health Initiative Investigators on the physiological effects of HRT showed that its only positive effects were reduction in incidence of colorectal cancer and of osteoporosis (32).
There are at least two distinct estrogen receptors in the human body: estrogen receptor (ER)- and ER-ß. In the normal human colon, ER-ß is widely regarded to be the predominant subtype (see e.g., 33). It has been suggested that ER-ß may mediate signals which would protect the colon against tumorigenesis (34).
A dramatic reduction in hormone-related tumors, such as those of the breast or prostate, has been linked to consumption of an Asian diet containing soy products. This effect, to a lesser extent, is also apparent for colorectal cancer. Soy products are rich in phytoestrogens, and these substances are potentially selective estrogen receptor modulators. Phytoestrogens bind with high affinity to ER-ß and could therefore have a protective effect in the colon. We demonstrated in mice that genistein, a prominent phytoestrogen in soy, can induce CYP27B1 expression and reduce that of CYP24 (35). A suppression of CYP24 expression by soy was even more pronounced in mice fed low dietary calcium; proliferation of colonocytes was enhanced and CYP24 expression was induced (36).
Conclusion. Based on studies in mice and in human tissue, we suggest a model for separate nutritional regulation of the renal and the colonic vitamin D system (Fig. 1). Insufficiency of serum 25-OH-D3, which is prevalent in many countries, could give rise to reduced 1,25-(OH)2-D3 synthesis in colonocytes, and consequently to impaired mitotic control. High intake of calcium and soy could improve colonic accumulation of 1,25-(OH)2-D3, due to enhanced expression of the synthesizing hydroxylase CYP27B1 and suppression of the catabolic CYP24 hydroxylase. This does not occur with renal vitamin D hydroxylases. It is provocative that increased folate consumption results in modulation of the expression of all components of the vitamin D system in a site-specific manner. Nutritional folate can serve as a methyl donor for epigenetic regulation of gene expression. We therefore suggest that both vitamin D hydroxylases and the VDR are under epigenetic control, an observation which could have considerable influence on the future of colon tumor prevention.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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2 Financially supported by grants from the Austrian National Bank and by a grant from the American Institute of Cancer Research, Washington DC.
4 Abbreviations used: ER, estrogen receptor; HRT, hormone replacement therapy; NWD, New Western Diet; 1,25-(OH)2-D3, dihydroxycholecalciferol; 25-OH-D3, hydroxycholecalciferol; VDR, vitamin D receptor.
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LITERATURE CITED |
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TOPABSTRACTLITERATURE CITED |
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1. Nakamura K, Nashimoto M, Hori Y, Yamamoto M. Serum 25-hydroxyvitamin D concentrations and related dietary factors in peri- and postmenopausal Japanese women. Am J Clin Nutr. 2000;71:1161–65.
2. Dawson-Hughes B, Harris SS, Dallal GE. Plasma calcidiol, season, and serum parathyroid hormone concentrations in healthy elderly men and women. Am J Clin Nutr. 1997;65:67–71.
3. Pasco JA, Henry MJ, Kotowicz MA, Sanders KM, Seeman E, Pasco JR, Schneider HG, Nicholson GC. Seasonal periodicity of serum vitamin D and parathyroid hormone, bone resorption, and fractures: the Geelong Osteoporosis Study. J Bone Miner Res. 2004;19:752–58.[Medline]
4. Garland CF, Garland FC. Do sunlight and vitamin D reduce the likelihood of colon cancer? Int J Epidemiol. 1980;9:227–31.
5. Emerson JC, Weiss NS. Colorectal cancer and solar radiation. Cancer Causes Control. 1992;3:95–9.[Medline]
6. Garland CF, Comstock GW, Garland FC, Helsing KJ, Shaw EK, Gorham ED. Serum 25-hydroxyvitamin D and colon cancer: eight-year prospective study. Lancet. 1989;2:1176–78.[Medline]
7. Gorham ED, Garland CF, Garland FC, Grant WB, Mohr SB, Lipkin M, Newmark HL, Giovannucci E, Wei M, Holick MF. Vitamin D and prevention of colorectal cancer. J. Steroid Biochem Mol Biol. 2005;97:179–94.
8. Sakaki T, Sawada N, Komai K, Shiozawa S, Yamada S, Yamamoto K, Ohyama Y, Inouye K. Dual metabolic pathway of 25-hydroxyvitamin D3 catalyzed by human CYP24. Eur J Biochem. 2000;267:6158–65.[Medline]
9. Jurutka PW, Whitfield GK, Hsieh JC, Thompson PD, Haussler CA, Haussler MR. Molecular nature of the vitamin D receptor and its role in regulation of gene expression. Rev Endocr Metab Disord. 2001;2:203–16.[Medline]
10. Cross HS, Pavelka M, Slavik J, Peterlik M. Growth control of human colon cancer cells by vitamin D and calcium in vitro. J Natl Cancer Inst. 1992;84:1355–57.
11. Tangrea J, Helzlsouer K, Pietinen P, Taylor P, Hollis B, Virtamo J, Albanes D. Serum levels of vitamin D metabolites and the subsequent risk of colon and rectal cancer in Finnish men. Cancer Causes Control. 1997;8:615–25.[Medline]
12. Holt PR, Arber N, Halmos B, Forde K, Kissileff H, McGlynn KA, Moss SF, Kurihara N, Fan K, et al. Colonic epithelial cell proliferation decreases with increasing levels of serum 25-hydroxy vitamin D. Cancer Epidemiol Biomarkers Prev. 2002;11:113–19.
13. Cross HS, Peterlik M, Reddy GS, Schuster I. Vitamin D metabolism in human colon adenocarcinoma-derived Caco-2 cells: expression of 25-hydroxyvitamin D3–1alpha-hydroxylase activity and regulation of side-chain metabolism. J Steroid Biochem Mol Biol. 1997;62:21–8.[Medline]
14. Bareis P, Bises G, Bischof MG, Cross HS, Peterlik M. 25-hydroxy-vitamin D metabolism in human colon cancer cells during tumor progression. Biochem Biophys Res Commun. 2001;285:1012–17.[Medline]
15. Cross HS, Bareis P, Hofer H, Bischof MG, Bajna E, Kriwanek S, Bonner E, Peterlik M. 25-Hydroxyvitamin D(3)-1alpha-hydroxylase and vitamin D receptor gene expression in human colonic mucosa is elevated during early cancerogenesis. Steroids. 2001;66:287–92.[Medline]
16. Cross HS, Bises G, Lechner D, Manhardt T, Kallay E. The Vitamin D endocrine system of the gut-Its possible role in colorectal cancer prevention. J Steroid Biochem Mol Biol. 2005;97:121–8.[Medline]
17. Calvo MS, Whiting SJ, Barton CN. Vitamin D intake: a global perspective of current status. J Nutr. 2005;135:310–16.
18. Kallay E, Pietschmann P, Toyokuni S, Bajna E, Hahn P, Mazzucco K, Bieglmayer C, Kato S, Cross HS. Characterization of a vitamin D receptor knockout mouse as a model of colorectal hyperproliferation and DNA damage. Carcinogenesis. 2001;22:1429–35.
19. Kallay E, Bises G, Bajna E, Bieglmayer C, Gerdenitsch W, Steffan I, Kato S, Armbrecht HJ, Cross HS. Colon-specific regulation of vitamin D hydroxylases - a possible approach for tumor prevention. Carcinogenesis. 2005;26:1581–89.
20. Garland C, Shekelle RB, Barrett-Connor E, Criqui MH, Rossof AH, Paul O. Dietary vitamin D and calcium and risk of colorectal cancer: a 19-year prospective study in men. Lancet. 1985;1:307–9.[Medline]
21. Cho E, Smith-Warner SA, Spiegelman D, Beeson WL, van den Brandt PA, Colditz GA, Folsom AR, Fraser GE, Freudenheim JL, et al. Dairy foods, calcium, and colorectal cancer: a pooled analysis of 10 cohort studies. J Natl Cancer Inst. 2004;96:1015–22.
22. Lamprecht SA, Lipkin M. Chemoprevention of colon cancer by calcium, vitamin D and folate: molecular mechanisms. Nat Rev Cancer. 2003;3:601–14.[Medline]
23. Peterlik M, Cross HS. Vitamin D and calcium deficits predispose for multiple chronic diseases. Eur J Clin Invest. 2005;35:290–304.[Medline]
24. Grau MV, Baron JA, Sandler RS, Haile RW, Beach ML, Church TR, Heber D. Vitamin D, calcium supplementation, and colorectal adenomas: results of a randomized trial. J Natl Cancer Inst. 2003;95:1765–71.
25. Hartman TJ, Albert PS, Snyder K, Slattery ML, Caan B, Paskett E, Iber F, Kikendall JW, Marshall J, et al. The association of calcium and vitamin D with risk of colorectal adenomas. J Nutr. 2005;135:252–59.
26. Newmark HL, Lipkin M, Maheshwari N. Colonic hyperplasia and hyperproliferation induced by a nutritional stress diet with four components of Western-style diet. J Natl Cancer Inst. 1990;82:491–96.
27. Newmark HL, Lipkin M. Calcium, vitamin D, and colon cancer. Cancer Res. 1992;52:2067s–70s.[Medline]
28. Risio M, Lipkin M, Newmark H, Yang K, Rossini FP, Steele VE, Boone CW, Kelloff GJ. Apoptosis, cell replication, and Western-style diet-induced tumorigenesis in mouse colon. Cancer Res. 1996;56:4910–16.
29. Newmark HL, Yang K, Lipkin M, Kopelovich L, Liu Y, Fan K, Shinozaki HA. Western-style diet induces benign and malignant neoplasms in the colon of normal C57Bl/6 mice. Carcinogenesis. 2001;22:1871–75.
30. Ochiai M, Watanabe M, Kushida H, Wakabayashi K, Sugimura T, Nagao M. DNA adduct formation, cell proliferation and aberrant crypt focus formation induced by PhIP in male and female rat colon with relevance to carcinogenesis. Carcinogenesis. 1996;17:95–8.
31. Potter JD, Bostick RM, Grandits GA, Fosdick L, Elmer P, Wood J, Grambsch P, Louis TA. Hormone replacement therapy is associated with lower risk of adenomatous polyps of the large bowel: the Minnesota Cancer Prevention Research Unit Case-Control Study. Cancer Epidemiol Biomarkers Prev. 1996;5:779–84.[Abstract]
32. Women's Health Initiative Investigators. Risks and benefits of estrogen plus progestin in healthy postmenopausal women. JAMA. 2002;288:321–33.
33. Campbell-Thompson M, Lynch IJ, Bhardwaj B. Expression of estrogen receptor (ER) subtypes and ERbeta isoforms in colon cancer. Cancer Res. 2001;61:632–40.
34. Foley EF, Jazaeri AA, Shupnik MA, Jazaeri O, Rice LW. Selective loss of estrogen receptor beta in malignant human colon. Cancer Res. 2000;60:245–48.
35. Kallay E, Adlercreutz H, Farhan H, Lechner D, Bajna E, Gerdenitsch W, Campbell M, Cross HS. Phytoestrogens regulate vitamin D metabolism in the mouse colon: relevance for colon tumor prevention and therapy. J Nutr. 2002;132:3490S–93S.
36. Cross HS, Kallay E, Lechner D, Gerdenitsch W, Adlercreutz H, Armbrecht HJ. Phytoestrogens and vitamin D metabolism: a new concept for the prevention and therapy of colorectal, prostate, and mammary carcinomas. J Nutr. 2004;134:1207S–12S.
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