Mechanisms of decreased Vitamin D 1alpha-hydroxylase activity in prostate cancer cells

Vitamin D regulates prostate cell metabolism via genomic and non-genomic mitochondrial redox-dependent mechanisms

Vitamin D deficiency has been associated with increased risk for aggressive prostate cancer (PCa). Prostate epithelium has a unique metabolism compared to other tissues. Normal prostate exhibits low levels of mitochondrial respiration and there is a metabolic switch to increased oxidative phosphorylation in PCa. 25-hydroxyvitamin D (25(OH)D) is the major circulating form of vitamin D and is used clinically to determine vitamin D status. Activation of 25(OH)D to the transcriptionally active form, 1,25(OH)₂D occurs via a reduction-oxidation (redox) reaction within the mitochondria that is catalyzed by the P450 enzyme, CYP27B1. We sought to determine if hydroxylation of 25(OH)D by CYP27B1 contributes to non-genomic activity of vitamin D by altering the redox-dependent state of the mitochondria in benign prostate epithelial cells. Exposure to 25(OH)D produced a transient pro-oxidant effect and change in mitochondrial membrane potential that was dependent on CYP27B1. Extended exposure ultimately suppressed mitochondrial respiration, consistent with a protective effect of 25(OH)D in supporting benign prostate metabolism. To model physiologically relevant changes in vitamin D, cells were cultured in constant 25(OH)D then changed to high or deficient concentrations. This model also incurred a biphasic effect with a pro-oxidant shift after short exposure followed by decreased respiration after 16 h. Several genes involved in redox cycling and Mitochondrial Health were regulated by 25(OH)D in these cells. These results indicate a secondary non-genomic mechanism for vitamin D to contribute to prostate cell health by supporting normal mitochondrial respiration.

Vitamin D Receptor Signaling and Cancer

The vitamin D receptor (VDR) binds the secosteroid hormone 1,25(OH)₂D₃ with high affinity and regulates gene programs that control a serum calcium levels, as well as cell proliferation and differentiation. A significant focus has been to exploit the VDR in cancer settings. Although preclinical studies have been strongly encouraging, to date clinical trials have delivered equivocal findings that have paused the clinical translation of these compounds. However, it is entirely possible that mining of genomic data will help to refine precisely what are the key anticancer actions of vitamin D compounds and where these can be used most effectively.

Hypovitaminosis D as predisposing factor for atrophic type A gastritis: a case-control study and review of the literature on the interaction of Vitamin D with the immune system

1,25-Dihydroxyvitamin D displays immunoregulatory and anti-inflammatory properties, and the cells involved in innate and adaptive immune response express the vitamin D receptor and can both produce and respond to this hormone. This article aims at describing the complex immune regulatory role of vitamin D and depicting whether a correlation exists between atrophic type A gastritis and hypovitaminosis. We studied 62 autoimmune gastritis (AIG) patients and compared them to 54 lymphocytic gastritis patients, 21 Helicobacter pylori gastritis patients and 212 healthy subjects. We also statistically analyzed vitamin D concentration in 36,384 outpatients referred to our clinical laboratories. 25-Hydroxyvitamin D levels, the measurable metabolite used to determine vitamin D status in plasma, were measured by a chemiluminescent method. Average level of 25-OHD in AIG subjects was 9.8 ± 5.6 ng/mL (95% confidence interval (CI) 8.4-11.2), 11.1 ± 8.4 (CI 7.5-14.7) in H. pylori gastritis patients, 22.2 ± 13.5 (CI 18.6-25.8) in nonspecific lymphocytic gastritis patients, 21.3 ± 12.2 (CI 19.7-22.9) in healthy subjects, and 21.8 ± 13.1 (CI 21.7-21.9) in the 36,384 outpatients. Vitamin D levels in AIG patients were significantly lower than in patients with nonspecific gastritis or in the general population, supporting the hypothesis that hypovitaminosis D might be a risk factor for the development of autoimmune diseases. The low vitamin D concentration in H. pylori gastritis patients might act as predisposing factor for a more severe Th1-type aggression to the stomach epithelium.

Cellular and molecular effects of vitamin D on carcinogenesis

Epidemiologic data suggest that the incidence and severity of many types of cancer inversely correlates with indices of vitamin D status. The vitamin D receptor (VDR) is highly expressed in epithelial cells at risk for carcinogenesis including those resident in skin, breast, prostate and colon, providing a direct molecular link by which vitamin D status impacts on carcinogenesis. Consistent with this concept, activation of VDR by its ligand 1,25-dihydroxyvitamin D (1,25D) triggers comprehensive genomic changes in epithelial cells that contribute to maintenance of the differentiated phenotype, resistance to cellular stresses and protection of the genome. Many epithelial cells also express the vitamin D metabolizing enzyme CYP27B1 which enables autocrine generation of 1,25D from the circulating vitamin D metabolite 25-hydroxyvitamin D (25D), critically linking overall vitamin D status with cellular anti-tumor actions. Furthermore, pre-clinical studies in animal models has demonstrated that dietary supplementation with vitamin D or chronic treatment with VDR agonists decreases tumor development in skin, colon, prostate and breast. Conversely, deletion of the VDR gene in mice alters the balance between proliferation and apoptosis, increases oxidative DNA damage, and enhances susceptibility to carcinogenesis in these tissues. Because VDR expression is retained in many human tumors, vitamin D status may be an important modulator of cancer progression in persons living with cancer. Collectively, these observations have reinforced the need to further define the molecular actions of the VDR and the human requirement for vitamin D in relation to cancer development and progression.

Vitamin D metabolism and action in the prostate: implications for health and disease

Prostate cancer (PCa) is the second most common cancer in men worldwide. Epidemiological, molecular, and cellular studies have implicated vitamin D deficiency as a risk factor for the development and/or progression of PCa. Studies using cell culture systems and animal models suggest that vitamin D acts to reduce the growth of PCa through regulation of cellular proliferation and differentiation. However, although preclinical studies provide a strong indication for anti-cancer activity, proof of therapeutic benefits in men is still lacking. The anti-proliferative and pro-differentiating properties of vitamin D have been attributed to calcitriol [1,25(OH)(2)D(3)], the hormonally active form of vitamin D, acting through the vitamin D receptor (VDR). Metabolism of vitamin D in target tissues is mediated by two key enzymes: 1α-hydroxylase (CYP27B1), which catalyzes the synthesis of calcitriol from 25(OH)D and 24-hydroxylase (CYP24), which catalyzes the initial step in the conversion of calcitriol to less active metabolites. Many factors affect the balance of calcitriol synthesis and catabolism and several maneuvers, like combination therapy of calcitriol with other drugs, have been explored to treat PCa and reduce its risk. The current paper is an overview addressing some of the key factors that influence the biological actions of vitamin D and its metabolites in the treatment and/or prevention of PCa.

Regulation of vitamin D metabolism

Fundamental to understanding the way in which perturbations in the vitamin D endocrine system can affect human health is an appreciation of the steps involved in the production of the well-recognized active hormonal form, 1,25-dihydroxyvitamin D(3). Thus this paper focuses first on the nature and regulation of the two enzymes responsible for the production of 1,25-dihydroxyvitamin D(3), the 25-hydroxylase in the liver and the 1α-hydroxylase in the kidney. The most important regulators of the 1α-hydroxylase in the kidney are 1,25-dihydroxyvitamin D(3) itself, parathyroid hormone and FGF23. The extent and importance of extra-renal, 1,25-dihydroxyvitamin D(3) synthesis is then considered. Finally the features of the 24R-hydroxylase, which produces 24R,25-dihydroxyvitamin D(3) in the kidney and is induced by and inactivated, 1,25-dihydroxyvitamin D(3)in target cells are described.

Vitamin d, sunlight and prostate cancer risk

Prostate cancer is the second common cancer in men worldwide. The prevention of prostate cancer remains a challenge to researchers and clinicians. Here, we review the relationship of vitamin D and sunlight to prostate cancer risk. Ultraviolet radiation of the sunlight is the main stimulator for vitamin D production in humans. Vitamin D's antiprostate cancer activities may be involved in the actions through the pathways mediated by vitamin D metabolites, vitamin D metabolizing enzymes, vitamin D receptor (VDR), and VDR-regulated genes. Although laboratory studies including the use of animal models have shown that vitamin D has antiprostate cancer properties, whether it can effectively prevent the development and/or progression of prostate cancer in humans remains to be inconclusive and an intensively studied subject. This review will provide up-to-date information regarding the recent outcomes of laboratory and epidemiology studies on the effects of vitamin D on prostate cancer prevention.

Life course sun exposure and risk of prostate cancer: population-based nested case-control study and meta-analysis

There is currently no means of primary prevention for prostate cancer. Increased exposure to ultraviolet-radiation may be protective, but the literature is inconclusive. We investigated associations of life course exposure to sunlight with prostate cancer. The study design was a UK-wide nested case-control study, based on 1,020 prostate specific antigen-detected cases and 5,044 matched population controls and a systematic review with meta-analysis. Men with olive/brown skin (OR = 1.47; 95% CI: 1.00 to 2.17), men who burnt rarely/never (OR = 1.11; 0.95 to 1.29) and men with the lowest levels of intense sun exposure in the 2 years prior to diagnosis (OR = 1.24; 1.03 to 1.50) had an increased prostate cancer risk. However, amongst men with prostate cancer, spending less time outside was associated with a reduced risk of advanced cancer (OR = 0.49; 0.27 to 0.89) and high Gleason grade (OR = 0.62; 0.43 to 0.91), and men who burnt rarely/never had a reduced risk of advanced cancer (OR = 0.71; 0.47 to 1.08). The meta-analysis provided weak evidence that men with the lowest (versus highest) sunlight exposure had an increased prostate cancer risk (4 studies, random-effects pooled relative risk = 1.13; 0.98 to 1.29) and higher advanced or fatal prostate cancer risk (6 studies, random-effects pooled relative risk = 1.14; 0.98 to 1.33). Our data and meta-analyses provide limited support for the hypothesis that increased exposure to sunlight may reduce prostate cancer risk. The findings warrant further investigation because of their implications for vitamin D chemoprevention trials.

From vitamin D to hormone D: fundamentals of the vitamin D endocrine system essential for good health

New knowledge of the biological and clinical importance of the steroid hormone 1alpha,25-dihydroxyvitamin D(3) [1alpha,25(OH)(2)D(3)] and its receptor, the vitamin D receptor (VDR), has resulted in significant contributions to good bone health. However, worldwide reports have highlighted a variety of vitamin D insufficiency and deficiency diseases. Despite many publications and scientific meetings reporting advances in vitamin D science, a disturbing realization is growing that the newer scientific and clinical knowledge is not being translated into better human health. Over the past several decades, the biological sphere of influence of vitamin D(3), as defined by the tissue distribution of the VDR, has broadened at least 9-fold from the target organs required for calcium homeostasis (intestine, bone, kidney, and parathyroid). Now, research has shown that the pluripotent steroid hormone 1alpha,25(OH)(2)D(3) initiates the physiologic responses of >/=36 cell types that possess the VDR. In addition to the kidney's endocrine production of circulating 1alpha,25(OH)(2)D(3,) researchers have found a paracrine production of this steroid hormone in >/=10 extrarenal organs. This article identifies the fundamentals of the vitamin D endocrine system, including its potential for contributions to good health in 5 physiologic arenas in which investigators have clearly documented new biological actions of 1alpha,25(OH)(2)D(3) through the VDR. As a consequence, the nutritional guidelines for vitamin D(3) intake (defined by serum hydroxyvitamin D(3) concentrations) should be reevaluated, taking into account the contributions to good health that all 36 VDR target organs can provide.

Co-expression of CYP27B1 enzyme with the 1.5kb CYP27B1 promoter-luciferase transgene in the mouse

The renal enzyme 25-hydroxyvitamin D 1alpha-hydroxylase (CYP27B1), responsible for the synthesis of circulating. 1,25-dihydroxyvitamin D (1,25D), is also expressed in a number of non-renal tissues. The regulation of CYP27B1 expression by the short flanking promoter outside the kidney is, however, largely unknown. We have used a transgenic mice expressing the 1.5kb promoter of the human CYP27B1 gene fused to the firefly luciferase gene in order to investigate tissue-specific CYP27B1 expression. These transgenic animals demonstrated co-localised luciferase and endogenous CYP27B1 expression in kidney proximal convoluted tubular cells. Strong co-expression of luciferase and CYP27B1 also occurred in neurons and Purkinje cells of the cerebellum and in Leydig and Sertoli cells of the testes. Other tissues to exhibit CYP27B1-promoter directed luciferase activity included lung, prostate, trabecular bone and jejunum as well as the choroid epithelium. The tissue specific changes in luciferase activity were age-related. These findings demonstrate that the proximal 1.5kb 5' flanking region of the CYP27B1 gene directs the expression of CYP27B1 in a number of known and novel tissues in a specific manner.

Hypothesis--ultraviolet-B irradiance and vitamin D reduce the risk of viral infections and thus their sequelae, including autoimmune diseases and some cancers

Many viral infections reach clinical significance in winter, when it is cold, relative humidity is lowest and vitamin D production from solar ultraviolet-B irradiation is at its nadir. Several autoimmune diseases, such as multiple sclerosis, type 1 diabetes mellitus and asthma, are linked to viral infections. Vitamin D, through induction of cathelicidin, which effectively combats both bacterial and viral infections, may reduce the risk of several autoimmune diseases and cancers by reducing the development of viral infections. Some types of cancer are also linked to viral infections. The cancers with seemingly important risk from viral infections important in winter, based on correlations with increasing latitude in the United States, an index of wintertime solar ultraviolet-B dose and vitamin D, are bladder, prostate, testicular and thyroid cancer, Hodgkin's and non-Hodgkin's lymphoma, and, perhaps, gastric cancer. The evidence examined includes the role of viruses in the etiology of these diseases, the geographic and seasonal variation of these diseases, and the time of life when vitamin D is effective in reducing the risk of disease. In general, the evidence supports the hypothesis. However, further work is required to evaluate this hypothesis.

Calcium intake and vitamin D metabolism and action, in healthy conditions and in prostate cancer

An association between Ca intake and the risk of prostate cancer has been reported in some but not all epidemiological studies. Assuming that a pathophysiological relationship would underlie this association, a favoured hypothesis proposes that relatively high Ca consumption could promote prostate cancer by reducing the production of 1,25-dihydroxyvitamin D (1,25(OH)2D; calcitriol), the hormonal form of vitamin D. The present review analyses the plausibility of this hypothesis by considering the quantitative relationships linking Ca intake to 1,25(OH)2D production and action in healthy conditions and in prostate cancer. Changes in the plasma level of 1,25(OH)2D in response to Ca intake are of very small magnitude as compared with the variations required to influence the proliferation and differentiation of prostate cancer cells. In most studies, 1,25(OH)2D plasma level was not found to be reduced in patients with prostate cancer. The possibility that the level of 1,25(OH)2D in prostate cells is decreased with a high-Ca diet has not been documented. Furthermore, a recent randomised placebo-controlled trial did not indicate that Ca supplementation increases the relative risk of prostate cancer in men. In conclusion, the existence of a pathophysiological link between relatively high Ca intake and consequent low production and circulation level of 1,25(OH)2D that might promote the development of prostate cancer in men remains so far an hypothesis, the plausibility of which is not supported by the analysis of available clinical data.

Expression of splice variants of 1alpha-hydroxylase in mcf-7 breast cancer cells

1,25-Dihydroxyvitamin D(3) (calcitriol) is the most active natural metabolite of Vitamin D(3). It has strong antiproliferative and differentiating effects on various cell types including breast cancer cells. 25-Hydroxyvitamin D(3)-1alpha-hydroxylase (1alpha-hydroxylase, CYP27B1) is one of the key enzymes in the formation of calcitriol. It has been found in breast cancer cells suggesting an autocrine regulation of formation of calcitriol in these cells. Alternative splicing of the encoding genes for this enzyme can possibly play a role in regulating the enzyme level and can explain tissue specific variations of 1alpha-hydroxylase activity. Splice variants containing intron 1 may encode for truncated proteins with deletion of protein domains which are essential for its enzymatic activity. In order to obtain more information on the abundance of 1alpha-hydroxylase splice variants, we performed a highly specific nested touchdown PCR in MCF-7 cells. The full-length sequence of 1alpha-hydroxylase and two different splice variants of this enzyme containing intron 1 were isolated. By Western blot technique we then confirmed the protein products of the full-length enzyme and its splice variants. We hypothesize that that the expression of splice variants can lead to a quantitatively lower expression of the mRNA of the full-length enzyme. The abundance of less active 1alpha-hydroxylase protein variants can alter the local synthesis of calcitriol in the cells and may explain variations of enzymatic activity in different cells and tissues.

Evidence for auto/paracrine actions of vitamin D in bone: 1alpha-hydroxylase expression and activity in human bone cells

Vitamin D is an important regulator of mineral homeostasis and bone metabolism. 1Alpha-hydroxylation of 25-(OH)D3 to form the bioactive vitamin D hormone, 1alpha,25-(OH)2D3, is classically considered to take place in the kidney. However, 1alpha-hydroxylase has been reported at extrarenal sites. Whether bone is a 1alpha,25-(OH)2D3 synthesizing tissue is not univocal. The aim of this study was to investigate an autocrine/paracrine function for 1alpha,25-(OH)2D3 in bone. We show that 1alpha-hydroxylase is expressed in human osteoblasts, as well as the vitamin D binding protein receptors megalin and cubilin. Functional analyses demonstrate that after incubation with the 1alpha-hydroxylase substrate 25-(OH)D3, the osteoblasts can produce sufficient 1alpha,25-(OH)2D3 to modulate osteoblast activity, resulting in induced alkaline phosphatase (ALP) activity, osteocalcin (OC) and CYP24 mRNA expression, and mineralization. The classical renal regulators of 1alpha-hydroxylase, parathyroid hormone, and ambient calcium do not regulate 1alpha-hydroxylase in osteoblasts. In contrast, interleukin (IL)-1beta strongly induces 1alpha-hydroxylase. Besides the bone-forming cells, we demonstrate 1alpha-hydroxylase activity in the bone resorbing cells, the osteoclasts. This is strongly dependent on osteoclast inducer RANKL. This study showing expression, activity, and functionality of 1alpha-hydroxylase unequivocally demonstrates that vitamin D can act in an auto/paracrine manner in bone.

Differential expression of aquaporin 7 in adipose tissue of lean and obese high fat consumers

Aquaporin 7 (AQP7) is an aquaglyceroprotein responsible for the secretion and uptake of glycerol from the adipocyte. The modulation of the expression of this membrane transport protein might play an important role in the susceptibility to the development of obesity. The aim of the present study was to compare the AQP7 gene expression in subcutaneous abdominal fat in lean vs. obese high fat intakers with a similar daily physical activity pattern. Twelve young men, 6 lean (BMI=23.2+/-0.4kg/m(2)) and 6 obese (35.0+/-1.1kg/m(2)) with a similar habitual dietary intake of fat (45.5+/-2.5 vs. 43.5+/-1.7% daily energy from fat for lean and obese, respectively) and physical activity (16.0+/-5.7 vs. 17.2+/-5.1 METsh/week for lean and obese, respectively), were recruited. Subcutaneous abdominal fat biopsies were obtained and total RNA was extracted and purified. Pools of RNA from lean and obese individuals were probed into Affymetrix GeneChip Human U133A. The microarray analysis revealed that AQP7 gene was down-regulated in obese compared to lean subjects. The results of the microarray analysis were confirmed by real-time PCR studies. In summary, our data show that the AQP7 gene is differentially expressed in adipose tissue of lean and obese individuals. The down-regulation of the AQP7 gene could be implicated in the susceptibility to obesity by reducing glycerol release and promoting the accumulation of lipids in the adipose tissue.

The Vitamin D endocrine system of the gut--its possible role in colorectal cancer prevention

While Vitamin D insufficiency in the US and European population is rising, epidemiological studies suggest an inverse correlation between low serum levels of 25-hydroxyvitamin D(3) (25-OH-D(3)) and colorectal cancer incidence. The antimitotic, prodifferentiating and proapoptotic active metabolite 1alpha,25-dihydroxyvitamin D(3) (1,25-(OH)(2)-D(3)) is synthesized also by colonocytes, since these possess Vitamin D synthesizing (CYP27B1) and catabolic (CYP24) hydroxylases similar to the kidney. Early during colon tumor progression, expression of CYP27B1 and of the Vitamin D receptor increases, suggesting an autocrine/paracrine growth control in colon tissue as a physiological restriction against tumor progression. However, in human adenocarcinomas expression of the catabolic CYP24 is also enhanced when compared with adjacent normal mucosa. Therefore, to maintain colonic accumulation of 1,25-(OH)(2)-D(3) its catabolism needs to be restricted. Our studies in mice show that low nutritional calcium causes hyperproliferation of colon crypts and significant elevation of CYP24 expression, which can be completely abrogated by soy feeding. We suggest that phytoestrogens in soy, known to be estrogen receptor modulators, are responsible for decreased CYP24 expression. These results and our observation that 17beta-estradiol can elevate CYP27B1 expression in rectal tissue of postmenopausal women, may underlie the observed protective effect of estrogens against colorectal cancer in females.

Genistein potentiates the growth inhibitory effects of 1,25-dihydroxyvitamin D3 in DU145 human prostate cancer cells: role of the direct inhibition of CYP24 enzyme activity

In a search for improved therapies for prostate cancer, we investigated the effect of genistein in combination with 1alpha-25-dihydroxyvitamin D3 [1,25(OH)2D3], on the growth of DU145 human prostate cancer cells. DU145 cells were very resistant to the growth inhibitory action of 1,25(OH)2D3 or genistein when administered individually. However, the combination caused a significant growth inhibition seen at lower concentrations of both agents. 1,25(OH)2D3 induces the expression of the CYP24 gene, which codes for the enzyme that initiates the catabolism of 1,25(OH)2D3. We showed for the first time that genistein at low doses (50-100 nM) directly inhibited CYP24 at the enzyme level. Addition of genistein to mitochondrial preparations inhibited CYP24 enzyme activity in a noncompetitive manner. CYP24 inhibition by genistein increased the half-life of 1,25(OH)2D3 thereby augmenting the homologous up-regulation of the vitamin D receptor (VDR) both at the mRNA and protein levels. Genistein co-treatment enhanced 1,25(OH)2D3-mediated transactivation of the vitamin D responsive reporters OC-Luc and OP-Luc transfected into DU145 cells. Consistent with the growth inhibition due to the combination treatment, significant changes in the expression of genes involved in growth arrest and apoptosis were seen. We conclude that genistein potentiates the antiproliferative actions of 1,25(OH)2D3 in DU145 cells by two mechanisms: (i) an increase in the half-life of 1,25(OH)2D3 due to the direct inhibition of CYP24 enzyme activity and (ii) an amplification of the homologous up-regulation of VDR. Together these two effects lead to a substantial enhancement of the cellular responses to the growth inhibitory and pro-apoptotic signaling by 1,25(OH)2D3.

The epidemiology of vitamin D and cancer incidence and mortality: a review (United States)

In vitro and animal studies indicate that vitamin D may have anti-cancer benefits, including against progression and metastasis, against a wide spectrum of cancers. Supporting an anti-cancer effect of vitamin D is the ability of many cells to convert 25(OH)D, the primary circulating form of vitamin D, into 1,25(OH)2D, the most active form of this vitamin. No epidemiologic studies have directly measured vitamin D concentrations or intakes on risk of total cancer incidence or mortality. However, higher rates of total cancer mortality in regions with less UV-B radiation, and among African-Americans and overweight and obese people, each associated with lower circulating vitamin D, are compatible with a benefit of vitamin D on mortality. In addition, poorer survival from cancer in individuals diagnosed in the months when vitamin D levels are lowest suggests a benefit of vitamin D against late stages of carcinogenesis. The only individual cancer sites that have been examined directly in relation to vitamin D status are colorectal, prostate and breast cancers. For breast cancer, some data are promising for a benefit from vitamin D but are far too sparse to support a conclusion. The evidence that higher 25(OH)D levels through increased sunlight exposure or dietary or supplement intake inhibit colorectal carcinogenesis is substantial. The biologic evidence for an anti-cancer role of 25(OH)D is also strong for prostate cancer, but the epidemiologic data have not been supportive. Although not entirely consistent, some studies suggest that higher circulating 1,25(OH)2D may be more important than 25(OH)D for protection against aggressive, poorly-differentiated prostate cancer. A possible explanation for these divergent results is that unlike colorectal tumors, prostate cancers lose the ability to hydroxylate 25(OH)D to 1,25(OH)2D, and thus may rely on the circulation as the main source of 1,25(OH)2D. The suppression of circulating 1,25(OH)2D levels by calcium intake could explain why higher calcium and milk intakes appear to increase risk of advanced prostate cancer. Given the potential benefits from vitamin D, further research should be a priority.

Sun exposure, vitamin D receptor gene polymorphisms, and risk of advanced prostate cancer

Substantial experimental evidence indicates that the hormonal form of vitamin D promotes the differentiation and inhibits the proliferation, invasiveness, and metastasis of human prostatic cancer cells. Results from epidemiologic studies of vitamin D status and/or vitamin D receptor (VDR) polymorphisms and prostate cancer risk have been mixed. We conducted a population-based, case-control study of advanced prostate cancer among men ages 40 to 79 years from the San Francisco Bay area. Interview data on lifetime sun exposure and other risk factors were collected for 905 non-Hispanic White men (450 cases and 455 controls). Using a reflectometer, we measured constitutive skin pigmentation on the upper underarm (a sun-protected site) and facultative pigmentation on the forehead (a sun-exposed site) and calculated a sun exposure index from these measurements. Biospecimens were collected for 426 cases and 440 controls. Genotyping was done for VDR polymorphisms in the 5' regulatory region (Cdx-2), exon 2 (FokI), and the 3' region (TaqI and BglI). Reduced risk of advanced prostate cancer was associated with high sun exposure determined by reflectometry [odds ratio (OR), 0.51; 95% confidence interval (95% CI), 0.33-0.80] and high occupational outdoor activity (OR, 0.73; 95% CI, 0.48-1.11). Significant risk reductions with the high-activity alleles FokI FF or Ff, TaqI tt, and BglI BB genotypes and a nonsignificant reduction with Cdx-2 AG or AA genotype were observed in the presence of high sun exposure, with ORs ranging from 0.46 to 0.67. Our findings support the hypothesis that sun exposure and VDR polymorphisms together play important roles in the etiology of prostate cancer.

Designing the Selenium and Vitamin E Cancer Prevention Trial (SELECT)

Prostate cancer continues to be a major health threat, especially among African American men. The Selenium and Vitamin E Cancer Prevention Trial (SELECT), which opened on July 25, 2001, was planned to study possible agents for the prevention of prostate cancer in a population of 32,400 men in the United States, including Puerto Rico, and Canada. SELECT is a phase III randomized, placebo-controlled trial of selenium (200 microg/day from L-selenomethionine) and/or vitamin E (400 IU/day of all rac alpha-tocopheryl acetate) supplementation for a minimum of 7 years (maximum of 12 years) in non-African American men at least 55 years of age and African American men at least 50 years of age. SELECT is a large, simple trial that conforms as closely as possible with community standards of care. This commentary discusses the design problems the SELECT investigators had to resolve in developing the trial, including the role of prostate cancer screening, the best forms and doses of the study agents, and estimation of the event (prostate cancer) rate of men on the placebo arm.