Calcitrol (1α,25-dihydroxyvitamin D3) inhibits androgen glucuronidation in prostate cancer cells

A Scoping Review of Vitamin D for Nonskeletal Health: A Framework for Evidence-Based Clinical Practice

BACKGROUND

Low serum 25-hydroxy-vitamin D [25(OH)D] levels are prevalent worldwide. Although the benefits of vitamin D supplementation have focused on skeletal disorders (eg, rickets, osteomalacia, osteoporosis), emerging evidence for nonskeletal health merits further discussion.

PURPOSE

The purpose of this review was to critically examine the vitamin D supplementation literature pertaining to nonskeletal health to help guide clinicians.

METHODS

A scoping review that included observational studies and randomized clinical trials (RCTs) was performed. Evidence from meta-analyses and individual RCTs are discussed, and controversies and future directions are considered.

FINDINGS

25(OH)D deficiency is a ubiquitous condition associated with multiple nonskeletal diseases, including cardiometabolic (heart disease, diabetes, and kidney disease), immune (HIV/AIDS and cancer), lung (from traditional chronic disorders to coronavirus disease 2019), and gut diseases. Vitamin D deficiency also affects health across the life span (children, pregnant, and elderly), mental illness, and reproduction in both men and women. In contrast, vitamin D supplementation does not necessarily improve major medical outcomes, even when low 25(OH)D levels are treated. Screening for 25(OH)D status remains an important practice, primarily for high-risk patients (eg, elderly, women with osteoporosis, people with low exposure to sunlight). It is reasonable to supplement with vitamin D to treat 25(OH)D deficiency, such that if beneficial nonskeletal health occurs, this may be considered as a coadjutant instead of the central tenet of the disease. Furthermore, optimizing dosing regimens is an important clinical consideration.

IMPLICATIONS

Although 25(OH)D deficiency is prevalent in nonskeletal diseases, there is no uniform evidence that vitamin D supplementation improves major medical outcomes, even when low 25(OH)D levels are corrected. Findings from RCTs warrant caution due to possible selection bias. Overall, vitamin D supplementation must be guided by circulating levels as a reasonable medical practice to correct 25(OH)D deficiency.

The Impact of Suboptimal 25-Hydroxyvitamin D Levels and Cholecalciferol Replacement on the Pharmacokinetics of Oral Midazolam in Control Subjects and Patients With Chronic Kidney Disease

The aim of this study was to investigate the impact of suboptimal 25-hydroxyvitamin D (25-VitD) and cholecalciferol (VitD3 ) supplementation on the pharmacokinetics of oral midazolam (MDZ) in control subjects and subjects with chronic kidney disease (CKD). Subjects with CKD (n = 14) and controls (n = 5) with suboptimal 25-VitD levels (<30 ng/mL) were enrolled in a 2-phase study. In phase 1 (suboptimal), subjects were administered a single oral dose of VitD3 (5000 IU) and MDZ (2 mg). In phase 2 (replete) subjects who achieved 25-VitD repletion after receiving up to 16 weeks of daily cholecalciferol were given the identical single oral doses of VitD3 and MDZ as in phase 1. Concentrations of MDZ and metabolites, 1'-hydroxymidazolam (1'-OHMDZ), and 1'-OHMDZ glucuronide (1'-OHMDZ-G) were measured by liquid chromatography-tandem mass spectrometry and pharmacokinetic analysis was performed. Under suboptimal 25-VitD, reductions in MDZ clearance and renal clearance of 47% and 87%, respectively, and a 72% reduction in renal clearance of 1'-OHMDZ-G were observed in CKD vs controls. In phase 1 versus phase 2, MDZ clearance increased in all control subjects, with a median (interquartile range) increase of 10.5 (0.62-16.7) L/h. No changes in MDZ pharmacokinetics were observed in subjects with CKD between phases 1 and 2. The effects of 25-VitD repletion on MDZ disposition was largely observed in subjects without kidney disease. Impaired MDZ metabolism and/or excretion alterations due to CKD in a suboptimal 25-VitD state may not be reversed by cholecalciferol therapy. Suboptimal 25-VitD may augment the reductions in MDZ and 1'-OHMDZ-G clearance values observed in patients with CKD.

Effects of vitamin D on drugs: Response and disposal

Vitamin D supplementation and vitamin D deficiency are common in clinical experience and in daily life. Vitamin D not only promotes calcium absorption and immune regulation, but also changes drug effects (pharmacodynamics and adverse reactions) and drug disposal in vivo when combined with various commonly used clinical drugs. The extensive physiological effects of vitamin D may cause synergism effects or alleviation of adverse reactions, and vitamin D's affect on drugs in vivo disposal through drug transporters or metabolic enzymes may also lead to changes in drug effects. Herein, the effects of vitamin D combined with commonly used drugs were reviewed from the perspective of drug efficacy and adverse reactions. The effects of vitamin D on drug transport and metabolism were summarized and analyzed. Hopefully, more attention will be paid to vitamin D supplementation and deficiency in clinical treatment and drug research and development.

Evaluation of vitamin D biosynthesis and pathway target genes reveals UGT2A1/2 and EGFR polymorphisms associated with epithelial ovarian cancer in African American Women

An association between genetic variants in the vitamin D receptor (VDR) gene and epithelial ovarian cancer (EOC) was previously reported in women of African ancestry (AA). We sought to examine associations between genetic variants in VDR and additional genes from vitamin D biosynthesis and pathway targets (EGFR, UGT1A, UGT2A1/2, UGT2B, CYP3A4/5, CYP2R1, CYP27B1, CYP24A1, CYP11A1, and GC). Genotyping was performed using the custom-designed 533,631 SNP Illumina OncoArray with imputation to the 1,000 Genomes Phase 3 v5 reference set in 755 EOC cases, including 537 high-grade serous (HGSOC), and 1,235 controls. All subjects are of African ancestry (AA). Logistic regression was performed to estimate odds ratios (OR) and 95% confidence intervals (CI). We further evaluated statistical significance of selected SNPs using the Bayesian False Discovery Probability (BFDP). A significant association with EOC was identified in the UGT2A1/2 region for the SNP rs10017134 (per allele OR = 1.4, 95% CI = 1.2-1.7, P = 1.2 × 10-6 , BFDP = 0.02); and an association with HGSOC was identified in the EGFR region for the SNP rs114972508 (per allele OR = 2.3, 95% CI = 1.6-3.4, P = 1.6 × 10-5 , BFDP = 0.29) and in the UGT2A1/2 region again for rs1017134 (per allele OR = 1.4, 95% CI = 1.2-1.7, P = 2.3 × 10-5 , BFDP = 0.23). Genetic variants in the EGFR and UGT2A1/2 may increase susceptibility of EOC in AA women. Future studies to validate these findings are warranted. Alterations in EGFR and UGT2A1/2 could perturb enzyme efficacy, proliferation in ovaries, impact and mark susceptibility to EOC.

The UDP-Glycosyltransferase (UGT) Superfamily: New Members, New Functions, and Novel Paradigms

UDP-glycosyltransferases (UGTs) catalyze the covalent addition of sugars to a broad range of lipophilic molecules. This biotransformation plays a critical role in elimination of a broad range of exogenous chemicals and by-products of endogenous metabolism, and also controls the levels and distribution of many endogenous signaling molecules. In mammals, the superfamily comprises four families: UGT1, UGT2, UGT3, and UGT8. UGT1 and UGT2 enzymes have important roles in pharmacology and toxicology including contributing to interindividual differences in drug disposition as well as to cancer risk. These UGTs are highly expressed in organs of detoxification (e.g., liver, kidney, intestine) and can be induced by pathways that sense demand for detoxification and for modulation of endobiotic signaling molecules. The functions of the UGT3 and UGT8 family enzymes have only been characterized relatively recently; these enzymes show different UDP-sugar preferences to that of UGT1 and UGT2 enzymes, and to date, their contributions to drug metabolism appear to be relatively minor. This review summarizes and provides critical analysis of the current state of research into all four families of UGT enzymes. Key areas discussed include the roles of UGTs in drug metabolism, cancer risk, and regulation of signaling, as well as the transcriptional and posttranscriptional control of UGT expression and function. The latter part of this review provides an in-depth analysis of the known and predicted functions of UGT3 and UGT8 enzymes, focused on their likely roles in modulation of levels of endogenous signaling pathways.

Regulation of UDP-Glucuronosyltransferase 2B15 by miR-331-5p in Prostate Cancer Cells Involves Canonical and Noncanonical Target Sites

UGT2B15 is an important androgen-metabolizing UDP-glucuronosyltransferase (UGT) and the mechanisms controlling its expression are of considerable interest. Recent studies showed that miR-376c regulates UGT2B15 in prostate cancer cells via a canonical target site in the 3' untranslated region (3'UTR). The UGT2B15 3'UTR also contains a canonical miR-331-5p target site; previous work indicated that deleting this site reduced, but did not abolish, the ability of miR-331-5p to repress a luciferase reporter carrying the UGT2B15 3'UTR We report here the discovery and characterization of a second, noncanonical miR-331-5p target site in the UGT2B15 3'UTR miR-331-5p-mediated repression of a UGT2B15 3'UTR-reporter was partly inhibited by mutating either of the two miR-331-5p target sites separately, but completely abolished by mutating the two sites simultaneously, indicating that the two sites act cooperatively. miR-331-5p mimics significantly reduced both UGT2B15 mRNA levels and glucuronidation activity in prostate cancer cells, confirming that the native transcript is a miR-331-5p target. Transfection of either miR-331-5p or miR-376c mimics repressed the activity of the UGT2B15 3'UTR-reporter; however, cotransfection of both microRNAs (miRNAs) further reduced activity, indicating cooperative regulation by these two miRNAs. A significant negative correlation between miR-331 and UGT2B15 mRNA levels was observed in a tissue RNA panel, and analysis of The Cancer Genome Atlas (TCGA) hepatocellular carcinoma data set provided further evidence that miR-331 may play an important role in regulation of UGT2B15 in vivo. There was no significant correlation between miR-331 and UGT2B15 mRNA levels in the TCGA prostate adenocarcinoma cohort, which may reflect the complexity of androgen-mediated regulation in determining UGT2B15 levels in prostate cancer. Finally, we show that miR-331-5p does not regulate UGT2B17, providing the first evidence for a post-transcriptional mechanism that differentially regulates these two important androgen-metabolizing UGTs.

Endocrine Disrupting Chemicals Mediated through Binding Androgen Receptor Are Associated with Diabetes Mellitus

Endocrine disrupting chemicals (EDCs) can mimic natural hormone to interact with receptors in the endocrine system and thus disrupt the functions of the endocrine system, raising concerns on the public health. In addition to disruption of the endocrine system, some EDCs have been found associated with many diseases such as breast cancer, prostate cancer, infertility, asthma, stroke, Alzheimer’s disease, obesity, and diabetes mellitus. EDCs that binding androgen receptor have been reported associated with diabetes mellitus in in vitro, animal, and clinical studies. In this review, we summarize the structural basis and interactions between androgen receptor and EDCs as well as the associations of various types of diabetes mellitus with the EDCs mediated through androgen receptor binding. We also discuss the perspective research for further understanding the impact and mechanisms of EDCs on the risk of diabetes mellitus.

Regulation of uridine diphosphate-glucuronosyltransferase 2B15 expression during ovulation in the rat

Uridine diphosphate-glucuronosyltransferase 2B15 (UGT2B15) conjugates 5α-androstane-3α, 17β-diol (3α-diol) to 3α-diol glucuronide (3α-diol G) in steroid target tissues. The present study investigated the regulation of UGT2B15 expression during the ovulatory process in the rat. Real-time PCR analysis revealed that treatment of immature rats with equine chorionic gonadotropin followed by human chorionic gonadotropin transiently stimulated UGT2B15 gene expression in granulosa cells of preovulatory follicles within 6 h. The progesterone receptor antagonist RU486 suppressed the gonadotropin-induced UGT2B15 expression. The expression of UGT2B15 and the levels of 3α-diol G were transiently increased by luteinizing hormone (LH) treatment in cultured preovulatory follicles. The LH-stimulated UGT2B15 mRNA level in cultured preovulatory follicles was inhibited by inhibitors of adenylyl cyclase, phosphoinositide 3-kinase and mitogen-activated protein kinase. Furthermore, a vitamin D receptor agonist (calcitriol) suppressed the LH-stimulated UGT2B15 expression in a dose-dependent manner. Taken together, these results indicate that gonadotropins transiently stimulate UGT2B15 expression and activity in preovulatory follicles, and UGT2B15 mRNA levels are regulated by the progesterone receptor and vitamin D receptor.

UDP-glucuronosyltransferases (UGTs) and their related metabolic cross-talk with internal homeostasis: A systematic review of UGT isoforms for precision medicine

UDP-glucuronosyltransferases (UGTs) are the primary phase II enzymes catalyzing the conjugation of glucuronic acid to the xenobiotics with polar groups for facilitating their clearance. The UGTs belong to a superfamily that consists of diverse isoforms possessing distinct but overlapping metabolic activity. The abnormality or deficiency of UGTs in vivo is highly associated with some diseases, efficacy and toxicity of drugs, and precisely therapeutic personality. Despite the great effects and fruitful results achieved, to date, the expression and functions of individual UGTs have not been well clarified, the inconsistency of UGTs is often observed in human and experimental animals, and the complex regulation factors affecting UGTs have not been systematically summarized. This article gives an overview of updated reports on UGTs involving the various regulatory factors in terms of the genetic, environmental, pathological, and physiological effects on the functioning of individual UGTs, in turn, the dysfunction of UGTs induced disease risk and endo- or xenobiotic metabolism-related toxicity. The complex cross-talk effect of UGTs with internal homeostasis is systematically summarized and discussed in detail, which would be of great importance for personalized precision medicine.

New insights into the androgen biotransformation in prostate cancer: A regulatory network among androgen, androgen receptors and UGTs

Androgen, as one kind of steroid hormones, is pivotal in the hormone-sensitive cancer, such as prostate cancer (PCa). The synthesis, elimination, and bioavailability of androgen in prostate cells have been proved to be a main cause of the carcinogenesis, maintenance and deterioration of PCa. This review illustrates the outlines of androgen biotransformation, and further discusses the different enzymes, especially UDP-glucuronyltransferases (UGTs) embedded in both benign and malignant prostate cells, which catalyze the reactions. Although many inhibitors of the enzymes responsible for the synthesis of androgens have been developed into drugs to fight against PCa, the elimination procedures metabolized by the UGTs are less emphasized. Thus the regulatory network among androgen, androgen receptors (AR) and UGTs is carefully reviewed in this article, indicating the determinant effects of UGTs on prostatic androgens and the regulation of AR. Finally, the hypothesis is also put forward that the regulators of UGTs may be developed to accelerate the androgen elimination and benefit PCa therapy.

Classical and Non-Classical Roles for Pre-Receptor Control of DHT Metabolism in Prostate Cancer Progression

Androgens play an important role in prostate cancer (PCa) development and progression. Accordingly, androgen deprivation therapy remains the front-line treatment for locally recurrent or advanced PCa, but patients eventually relapse with the lethal form of the disease termed castration resistant PCa (CRPC). Importantly, castration does not eliminate androgens from the prostate tumor microenvironment which is characterized by elevated tissue androgens that are well within the range capable of activating the androgen receptor (AR). In this mini-review, we discuss emerging data that suggest a role for the enzymes mediating pre-receptor control of dihydrotestosterone (DHT) metabolism, including AKR1C2, HSD17B6, HSD17B10, and the UGT family members UGT2B15 and UGT2B17, in controlling intratumoral androgen levels, and thereby influencing PCa progression. We review the expression of steroidogenic enzymes involved in this pathway in primary PCa and CRPC, the activity and regulation of these enzymes in PCa experimental models, and the impact of genetic variation in genes mediating pre-receptor DHT metabolism on PCa risk. Finally, we discuss recent data that suggests several of these enzymes may also play an unrecognized role in CRPC progression separate from their role in androgen inactivation.

Serum 25-hydroxyvitamin D concentrations and risk of prostate cancer: results from the Prostate Cancer Prevention Trial

BACKGROUND

Epidemiologic studies have reported inconsistent associations of vitamin D and prostate cancer risk; however, few have adequately controlled for detection bias related to prostate-specific antigen (PSA) screening, and the results of many studies may be affected by occult prostate cancers among controls.

METHODS

Data for this nested case-control analysis (n = 1,695 cases/1,682 controls) are from the Prostate Cancer Prevention Trial. Baseline serum was analyzed for 25-hydroxyvitamin D [25(OH)D]. The presence or absence of cancer was subsequently determined by prostate biopsy. Polytomous logistic regression models were used to estimate associations of 25(OH)D with risk of total, Gleason 2-6, Gleason 7, and Gleason 8-10 prostate cancer. Results are presented for placebo and finasteride arms separately and combined.

RESULTS

There were no associations of serum 25(OH)D with total prostate cancer risk. For Gleason 2-6 cancers, results were inconsistent across treatment arms with a suggestion of increased risk in the placebo arm only; however, there was no dose-response relationship. For Gleason 8-10 prostate cancers, 25(OH)D concentrations were associated with a linear decrease in risk among combined treatment arms [quartile 4 vs. 1: OR, 0.55; 95% confidence interval (CI), 0.32-0.94; P(trend) = 0.04]. These findings were somewhat stronger among men ≥65 versus 55-64 years at baseline (quartile 4 vs. 1: OR, 0.40; 95% CI, 0.18-0.88 vs. OR, 0.73; 95% CI, 0.35-1.52, respectively; P(interaction) = 0.52).

CONCLUSIONS

Higher serum 25(OH)D may modestly increase risk of Gleason 2-6 disease and more substantially reduce risk of Gleason 8-10 prostate cancer.

IMPACT

Vitamin D may have different effects for different stages of prostate cancers.

Transcriptional regulation of human UDP-glucuronosyltransferase genes

Glucuronidation is an important metabolic pathway for many small endogenous and exogenous lipophilic compounds, including bilirubin, steroid hormones, bile acids, carcinogens and therapeutic drugs. Glucuronidation is primarily catalyzed by the UDP-glucuronosyltransferase (UGT) 1A and two subfamilies, including nine functional UGT1A enzymes (1A1, 1A3-1A10) and 10 functional UGT2 enzymes (2A1, 2A2, 2A3, 2B4, 2B7, 2B10, 2B11, 2B15, 2B17 and 2B28). Most UGTs are expressed in the liver and this expression relates to the major role of hepatic glucuronidation in systemic clearance of toxic lipophilic compounds. Hepatic glucuronidation activity protects the body from chemical insults and governs the therapeutic efficacy of drugs that are inactivated by UGTs. UGT mRNAs have also been detected in over 20 extrahepatic tissues with a unique complement of UGT mRNAs seen in almost every tissue. This extrahepatic glucuronidation activity helps to maintain homeostasis and hence regulates biological activity of endogenous molecules that are primarily inactivated by UGTs. Deciphering the molecular mechanisms underlying tissue-specific UGT expression has been the subject of a large number of studies over the last two decades. These studies have shown that the constitutive and inducible expression of UGTs is primarily regulated by tissue-specific and ligand-activated transcription factors (TFs) via their binding to cis-regulatory elements (CREs) in UGT promoters and enhancers. This review first briefly summarizes published UGT gene transcriptional studies and the experimental models and tools utilized in these studies, and then describes in detail the TFs and their respective CREs that have been identified in the promoters and/or enhancers of individual UGT genes.

Interaction of vitamin D with membrane-based signaling pathways

Many studies in different biological systems have revealed that 1α,25-dihydroxyvitamin D₃ (1α,25(OH)₂D₃) modulates signaling pathways triggered at the plasma membrane by agents such as Wnt, transforming growth factor (TGF)-β, epidermal growth factor (EGF), and others. In addition, 1α,25(OH)₂D₃ may affect gene expression by paracrine mechanisms that involve the regulation of cytokine or growth factor secretion by neighboring cells. Moreover, post-transcriptional and post-translational effects of 1α,25(OH)₂D₃ add to or overlap with its classical modulation of gene transcription rate. Together, these findings show that vitamin D receptor (VDR) cannot be considered only as a nuclear-acting, ligand-modulated transcription factor that binds to and controls the transcription of target genes. Instead, available data support the view that much of the complex biological activity of 1α,25(OH)₂D₃ resides in its capacity to interact with membrane-based signaling pathways and to modulate the expression and secretion of paracrine factors. Therefore, we propose that future research in the vitamin D field should focus on the interplay between 1α,25(OH)₂D₃ and agents that act at the plasma membrane, and on the analysis of intercellular communication. Global analyses such as RNA-Seq, transcriptomic arrays, and genome-wide ChIP are expected to dissect the interactions at the gene and molecular levels.

Vitamin D receptor agonist EB1089 is a potent regulator of prostatic "intracrine" metabolism

BACKGROUND

A contributing factor to the emergence of castrate resistant prostate cancer (CRPC) is the ability of the tumor to circumvent low circulating levels of testosterone during androgen deprivation therapy (ADT), through the production of "intracrine" tumoral androgens from precursors including cholesterol and dehydroepiandrosterone (DHEA). As these processes promote AR signaling and prostate cancer progression their modulation is required for disease prevention and treatment.

METHODS

We evaluated the involvement of the vitamin D receptor ligand EB1089 in the regulation of genes with a role in androgen metabolism using the androgen dependent cell lines LNCaP and LAPC-4. EB1089 regulation of androgen metabolism was assessed using QRT-PCR, luciferase promoter assays, western blotting, enzyme activity assays, and LC-MS analyses.

RESULTS

EB1089 induced significant expression of genes involved in androgen metabolism in prostate cancer cells. Real-Time PCR analysis revealed that VDR mediated significant regulation of CYP3A4, CYP3A5, CYP3A43, AKR1C1-3, UGT2B15/17, and HSD17B2. Data revealed potent regulation of CYP3A4 at the level of mRNA, protein expression and enzymatic activity, with VDR identified as the predominant regulator. Inhibition of CYP3A activity using the specific inhibitor ritonavir resulted in alleviation of the anti-proliferative response of VDR ligands in prostate cancer cells. Mass spectrometry revealed that overexpression of CYP3A protein in prostate cancer cells resulted in a significant increase in the oxidative inactivation of testosterone and DHEA to their 6-β-hydroxy-testosterone and 16-α-hydroxy-DHEA metabolites, respectively.

CONCLUSIONS

These data highlight a potential application of VDR-based therapies for the reduction of growth-promoting androgens within the tumor micro-environment.

Future directions in the prevention of prostate cancer

The high global incidence of prostate cancer has led to a focus on chemoprevention strategies to reduce the public health impact of the disease. Early studies indicating that selenium and vitamin E might protect against prostate cancer encouraged large-scale studies that produced mixed clinical results. Next-generation prostate cancer prevention trials validated the impact of 5α-reductase inhibitors in hormone-responsive prostate cancer, and these results were confirmed in follow-up studies. Other interventions on the horizon, involving both dietary and pharmacological agents, hold some promise but require further investigation to validate their efficacy. In this Review, we discuss the clinical and preclinical evidence for dietary and pharmacological prevention of prostate cancer and give an overview of future opportunities for chemoprevention.

Nuclear receptors and endobiotics glucuronidation: the good, the bad, and the UGT

The recent progresses in molecular biology and pharmacology approaches allowed the characterization of a series of nuclear receptors (NRs) as efficient regulators of uridine diphosphate glucuronosyltransferase (UGT) genes activity. These regulatory processes ensure an optimized UGT expression in response to specific endo- and/or exogenous stimuli. Many of these NRs are activated by endobiotics that also are substrates for UGTs. Thus, by activating their receptors, these endogenous substances control their own conjugation, leading to the concept that glucuronidation is an important part of feed-forward/feedback mechanisms by which bioactive molecules control their own concentrations. On the other hand, numerous studies have established the pharmacological relevance of NR-UGT regulatory pathways in the response to therapeutic ligands. The present review article aims at providing a comprehensive view of the physiological and pharmacological importance of the NR regulation of the expression and activity of endobiotics-conjugating UGT enzymes. Selected examples will illustrate how the organism profits from the feed-forward/feedback mechanisms involving NR-UGT pathways, but also how such regulatory processes are involved in the initiation and/or progression of several pathological situations. Finally, we will discuss how the present pharmacopeia involves NR-dependent regulation of endobiotics glucuronidation, and whether the unexploited NR-UGT axes could serve as pharmacological targets for novel therapeutics to restore endobiotics homeostasis.

The regulation of UDP-glucuronosyltransferase genes by tissue-specific and ligand-activated transcription factors

Elucidation of the mechanisms regulating UGT genes is of prime importance if the adverse effects of interactions between drugs primarily eliminated by glucuronidation are to be minimized, and if UGT expression is to be manipulated for therapeutic effect. The factors controlling UGT gene expression in the liver include the liver-enriched transcription factors, HNF-1alpha and HNF-4alpha, several members of the nuclear-receptor family (CAR, PXR, FXR, LXR, and PPAR), the arylhydrocarbon receptor, and transcription factors involved in stress responses (Nrf2, Maf). HNF-1alpha, in concert with the intestine-specific transcription factor, Cdx2, and Sp1 regulate UGT gene expression in the gastrointestinal tract, whereas the genes for the major androgen-glucuronidating enzymes, UGT2B15 and UGT2B17, are upregulated by estrogens in breast cell lines and downregulated by androgens in prostate-derived cells. Despite this knowledge, the complex interactions between these transcription factors and their coregulators has not been determined, and the mechanisms regulating UGT gene expression in organs and tissues, other than the liver, gastrointestinal tract, breast, and prostate, remain to be elucidated.

The human UGT1A3 enzyme conjugates norursodeoxycholic acid into a C23-ester glucuronide in the liver

Norursodeoxycholic acid (norUDCA) exhibits efficient anti-cholestatic properties in an animal model of sclerosing cholangitis. norUDCA is eliminated as a C(23)-ester glucuronide (norUDCA-23G) in humans. The present study aimed at identifying the human UDP-glucuronosyltransferase (UGT) enzyme(s) involved in hepatic norUDCA glucuronidation and at evaluating the consequences of single nucleotide polymorphisms in the coding region of UGT genes on norUDCA-23G formation. The effects of norUDCA on the formation of the cholestatic lithocholic acid-glucuronide derivative and of rifampicin on hepatic norUDCA glucuronidation were also explored. In vitro glucuronidation assays were performed with microsomes from human tissues (liver and intestine) and HEK293 cells expressing human UGT enzymes and variant allozymes. UGT1A3 was identified as the major hepatic UGT enzyme catalyzing the formation of norUDCA-23G. Correlation studies using samples from a human liver bank (n = 16) indicated that the level of UGT1A3 protein is a strong determinant of in vitro norUDCA glucuronidation. Analyses of the norUDCA-conjugating activity by 11 UGT1A3 variant allozymes identified three phenotypes with high, low, and intermediate capacity. norUDCA is also identified as a competitive inhibitor for the hepatic formation of the pro-cholestatic lithocholic acid-glucuronide derivative, whereas norUDCA glucuronidation is weakly stimulated by rifampicin. This study identifies human UGT1A3 as the major enzyme for the hepatic norUDCA glucuronidation and supports that some coding polymorphisms affecting the conjugating activity of UGT1A3 in vitro may alter the pharmacokinetic properties of norUDCA in cholestasis treatment.

Bone health maintenance in survivors of breast and prostate cancer

Many therapeutic regimens used for the treatment of breast and prostate cancer survivors are associated with bone loss and adverse skeletal events. The purpose of this review is to identify mechanisms of treatment-induced bone loss and adverse skeletal events in this population. Furthermore, this review emphasizes the importance of screening for baseline risk factors for adverse skeletal events. Once these risk factors are identified, early evaluation and treatment of bone health is warranted. This article reviews an approach to the management of bone health in breast and prostate cancer survivors, including a discussion regarding lifestyle interventions, calcium and vitamin D supplementation, as well as the indications for initiation of bisphosphonate therapy. This article also reviews potential new agents, such as cathepsin K inhibitors and RANKL inhibitors, for the reduction of bone loss in high-risk populations.

The promiscuous receptor

OBJECTIVE

To determine the effectiveness of vitamin D therapy in patients with asymptomatic, prostate-specific antigen (PSA)-progression of prostate cancer.

PATIENTS AND METHODS

Twenty-six patients with locally advanced or metastatic prostate cancer were treated with vitamin D. Vitamin D therapy was discontinued on disease progression as assessed by symptoms or serum PSA increase. The response to therapy was judged from changes in PSA level from the pretreatment baseline to 3 months after starting vitamin D therapy.

RESULTS

Of the 26 patients, five (20%) responded to vitamin D; the mean (range) reduction in PSA level was 45.3 (15.9-95.1)%, and mean duration of response was 4-5 months. Patients in whom the PSA level was stabilized, but not reduced, after vitamin D treatment had a duration of response of up to 36 months. Treatment was well tolerated and was not associated with elevation of serum calcium levels. There was no significant correlation between response to therapy and stage of disease, Gleason grade, previous treatments or PSA level at diagnosis or initiation of vitamin D therapy.

CONCLUSION

Vitamin D therapy is an effective and well tolerated treatment for patients with asymptomatic progressive prostate cancer, and is a useful addition to the therapeutic options.

Vitamin D, vitamin D analogs (deltanoids) and prostate cancer

'Vitamin D' is a generic term for a family of secosteroids, members of which bind to the vitamin D receptor. Calcitriol, the active form of vitamin D, has antiproliferative effects on many tumor cells. However, clinical use of calcitriol in cancer prevention or therapy is limited because it induces hypercalcemia at the necessary supraphysiological doses. The anti-tumor effects of vitamin D analogs (deltanoids) have been researched extensively; more than 3000 deltanoids have now been described. Prostate cancer is more common in northern geographic regions; mortality decreases with exposure to sunlight. As UV light is necessary for vitamin D synthesis in the skin, it has long been dogma that vitamin D is involved. This review concerns deltanoids that have been assessed for use in treating or preventing prostate cancer.