Vitamin D and Placental-Decidual Function

The active form of vitamin D (1,25-dihydroxyvitamin D(3), 1,25[OH](2)D(3)) has well-established effects on bone metabolism and mineral homeostasis. However, recently it has become clear that 1,25(OH)(2)D(3) has potent antiproliferative and immunomodulatory actions that are not immediately linked to its role as a skeletal regulator. Both the nuclear receptor for 1,25(OH)(2)D(3) (vitamin D receptor, VDR) and the vitamin D-activating enzyme 1alpha-hydroxylase are expressed in a wide variety of nonclassic tissues, highlighting the potential for local autocrine-paracrine responses rather than traditional endocrine effects. Prominent among the tissues that express 1alpha-hydroxylase is the placenta-decidua, and this has raised important questions concerning the potential role of locally generated 1,25(OH)(2)D(3) as a modulator of fetal-placental development and function. When bound to the VDR, 1,25(OH)(2)D(3) regulates key target genes associated with implantation, such as HOXA10, whereas the potent immunosuppressive effects of 1,25(OH)(2)D(3) suggest a role in implantation tolerance. These observations are further supported by data from our group showing increased expression of 1alpha-hydroxylase and VDR in first-trimester trophoblast and decidua from human pregnancies. Studies by other groups have reported abnormal expression of 1alpha-hydroxylase in preeclamptic pregnancies, revealing a potential role for 1,25(OH)(2)D(3) as a regulator of placentation. The effect of vitamin D on reproduction has been further endorsed by murine gene knockout models for 1alpha-hydroxylase and VDR, both of which are infertile. These observations and others are discussed in this article in which we postulate an active role for 1,25(OH)(2)D(3) in placenta-decidua. In particular, we describe how induction of the vitamin D-activating enzyme 1alpha-hydroxylase in early gestation might provide a mechanism by which environmental or dietary vitamin D can influence fetal-placental development.

Extra-renal 25-hydroxyvitamin D3-1alpha-hydroxylase in human health and disease

Although ectopic expression of 25-hydroxyvitamin D(3)-1alpha-hydroxylase (1alpha-OHase) has been recognized for many years, the precise function of this enzyme outside the kidney remains open to debate. Three specific aspects of extra-renal 1alpha-OHase have attracted most attention: (i) expression and regulation in non-classical tissues during normal physiology; (ii) effects on the immune system and inflammatory disease; (iii) expression and function in tumors. The most well-recognized manifestation of extra-renal 1alpha-OHase activity remains that found in some patients with granulomatous diseases where locally synthesized 1alpha,25(OH)(2)D(3) has the potential to spill-over into the general circulation. However, immunohistochemistry and mRNA analyses suggest that 1alpha-OHase is also expressed by a variety of normal human tissues including the gastrointestinal tract, skin, vasculature and placenta. This has promoted the idea that autocrine/paracrine synthesis of 1,25(OH)(2)D(3) contributes to normal physiology, particularly in mediating the potent effects of vitamin D on innate (macrophage) and acquired (dendritic cell) immunity. We have assessed the capacity for synthesis of 1,25(OH)(2)D(3) in these cells and the functional significance of autocrine responses to 1alpha-hydroxylase. Data suggest that local synthesis of 1,25(OH)(2)D(3) may be a preferred mode of response to antigenic challenge in many tissues.

Effects of 25-hydroxyvitamin D3 and 1,25-dihydroxyvitamin D3 on cytokine production by human decidual cells

The active form of vitamin D, 1,25-dihydroxyvitamin D(3) (1,25[OH](2)D(3)) is a potent immunomodulatory seco-steroid. We have demonstrated that several components of vitamin D metabolism and signaling are strongly expressed in human uterine decidua from first trimester pregnancies, suggesting that locally produced 1,25(OH)(2)D(3) may exert immunosuppressive effects during early stages of gestation. To investigate this further, we used primary cultures of human decidual cells from first and third trimester pregnancies to demonstrate expression and activity of the enzyme that catalyzes synthesis of 1,25(OH)(2)D(3), 1alpha-hydroxylase (CYP27B1). Synthesis of 1,25(OH)(2)D(3) was higher in first trimester decidual cells (41 +/- 11.8 fmoles/h/mg protein) than in third trimester cells (8 +/- 4.4 fmoles/h/mg protein; P < 0.05). Purification of decidual cells followed by quantitative RT-PCR analysis showed that CYP27B1 was expressed by both CD10(+VE) stromal-enriched and CD10(-VE) stromal-depleted cells, with higher levels of mRNA in first trimester pregnancies. Expression of CYP27B1 correlated with TLR4 and IDO. Functional responses to 1,25(OH)(2)D(3) were studied using CD56(+VE) natural killer (NK) cells isolated from first trimester decidua. Decidual NK cells treated with 1,25(OH)(2)D(3) or precursor 25-hydroxyvitamin D(3) (25OHD(3)) for 28 h showed decreased synthesis of cytokines, such as granulocyte-macrophage colony stimulating factor 2 (CSF2), tumor necrosis factor, and interleukin 6, but increased expression of mRNA for the antimicrobial peptide cathelicidin antimicrobial peptide. These data indicate that human decidual cells are able to synthesize active 1,25(OH)(2)D(3), particularly in early gestation, and this may act in an autocrine/paracrine fashion to regulate both acquired and innate immune responses at the fetal-maternal interface.

Biological actions of extra-renal 25-hydroxyvitamin D-1alpha-hydroxylase and implications for chemoprevention and treatment

The Vitamin D-activating enzyme 25-hydroxyvitamin D-1alpha-hydroxylase (1alpha-hydroxylase) is now known to be expressed in a much wider range of tissues that previously thought, suggesting a role for 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)), which is more in keeping with a cytokine than a hormone. In this capacity, the function of 1alpha-hydroxylase in tumors is far from clear. Studies from several groups including ours have shown altered expression of 1alpha-hydroxylase in different types of neoplasm including breast, prostate and colon cancers. However, functional analysis of Vitamin D metabolism in cancer is complicated by the heterogenous composition of tumors. Immunohistochemical analysis of breast tumors has shown that 1alpha-hydroxylase is expressed by both epithelial cells and by tumor-infiltrating macrophages, suggesting an immunomodulatory component to 1,25(OH)(2)D(3) production in some types of cancer. The demonstration of 1alpha-hydroxylase activity in tumors and their equivalent normal tissues has implications for both the treatment and prevention of cancers. For example, in tumors chemotherapy options may include the use of non-1alpha-hydroxylated Vitamin D analogs to increase local concentrations of active metabolites without systemic side-effects. The role of 1alpha-hydroxylase in protection against cancer is likely to be more complicated and may involve anti-tumor immune responses.

Expression of 11beta-hydroxysteroid dehydrogenase type 1 permits regulation of glucocorticoid bioavailability by human dendritic cells

Glucocorticoids (GCs) exert powerful anti-inflammatory effects that may relate in part to their ability to restrict the differentiation and function of dendritic cells (DCs). Although these inhibitory effects are dependent upon GCs binding to nuclear glucocorticoid receptors (GRs), fine-tuning of GR signaling is achieved by prereceptor interconversion of cortisol that binds GRs with high affinity and cortisone that does not. We show for the first time that human monocyte-derived DCs are able to generate cortisol as a consequence of up-regulated expression of the enzyme 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1). Immature DCs demonstrate selective enhancement of 11beta-HSD1 reductase activity, leading to increased conversion of inactive cortisone to active cortisol. Enhancement of GC bioavailability is maintained or increased upon terminal differentiation induced by signals associated with innate immune activation. In marked contrast, maturation induced by CD40 ligation leads to a sharp reduction in cortisol generation by DCs. The differentiation of DCs from monocyte precursors is inhibited at physiologic concentrations of inactive cortisone, an effect that requires activity of the 11beta-HSD1 enzyme. In conclusion, prereceptor regulation of endogenous GCs appears to be an important determinant of DC function and represents a potential target for therapeutic manipulation.

Increased expression of 25-hydroxyvitamin D-1alpha-hydroxylase in dysgerminomas: a novel form of humoral hypercalcemia of malignancy

Humoral hypercalcemia of malignancy (HHM) is a common paraneoplastic disorder usually associated with increased synthesis of parathyroid hormone-related peptide (PTHrP). Unlike non-cancer forms of hypercalcemia, HHM does not routinely involve increased circulating levels of the active form of vitamin D, 1,25-dihydroxyvitamin D3 (1,25(OH)2D3). Dysgerminomas are a notable exception to this rule, previous reports having described hypercalcemia with elevated serum 1,25(OH)2D3. To investigate the etiology of this form of HHM we have characterized expression and activity of the enzyme that catalyzes synthesis of 1,25(OH)2D3, 25-hydroxyvitamin D-1alpha-hydroxylase (1alpha-hydroxylase), in a collection of 12 dysgerminomas. RT-PCR analyses indicated that mRNA for 1alpha-hydroxylase was increased 222-fold in dysgerminomas compared to non-tumor ovarian tissue. Parallel enzyme assays in tissue homogenates showed that dysgerminomas produced fivefold higher levels of 1,25(OH)2D3 compared to normal ovarian tissue. Immunolocalization studies indicated that 1alpha-hydroxylase was expressed by both tumor cells and by macrophages within the inflammatory cell infiltrate associated with dysgerminomas. The immunological nature of the increased 1,25(OH)2D3 production observed in dysgerminomas was further emphasized by correlation between expression of 1alpha-hydroxylase and the endotoxin recognition factors CD14 and toll-like receptor 4 (TLR4). These data suggest that inflammatory mechanisms associated with dysgerminomas are the underlying cause of the increased expression and activity of 1alpha-hydroxylase associated with these tumors. We further postulate that this autocrine/paracrine action of 1alpha-hydroxylase may lead to increased circulating levels of 1,25(OH)2D3 and a form of HHM which is distinct from that seen with PTHrP-secreting tumors.

Vitamin D and placental-decidual function

The active form of vitamin D (1,25-dihydroxyvitamin D(3), 1,25[OH](2)D(3)) has well-established effects on bone metabolism and mineral homeostasis. However, recently it has become clear that 1,25(OH)(2)D(3) has potent antiproliferative and immunomodulatory actions that are not immediately linked to its role as a skeletal regulator. Both the nuclear receptor for 1,25(OH)(2)D(3) (vitamin D receptor, VDR) and the vitamin D-activating enzyme 1alpha-hydroxylase are expressed in a wide variety of nonclassic tissues, highlighting the potential for local autocrine-paracrine responses rather than traditional endocrine effects. Prominent among the tissues that express 1alpha-hydroxylase is the placenta-decidua, and this has raised important questions concerning the potential role of locally generated 1,25(OH)(2)D(3) as a modulator of fetal-placental development and function. When bound to the VDR, 1,25(OH)(2)D(3) regulates key target genes associated with implantation, such as HOXA10, whereas the potent immunosuppressive effects of 1,25(OH)(2)D(3) suggest a role in implantation tolerance. These observations are further supported by data from our group showing increased expression of 1alpha-hydroxylase and VDR in first-trimester trophoblast and decidua from human pregnancies. Studies by other groups have reported abnormal expression of 1alpha-hydroxylase in preeclamptic pregnancies, revealing a potential role for 1,25(OH)(2)D(3) as a regulator of placentation. The effect of vitamin D on reproduction has been further endorsed by murine gene knockout models for 1alpha-hydroxylase and VDR, both of which are infertile. These observations and others are discussed in this article in which we postulate an active role for 1,25(OH)(2)D(3) in placenta-decidua. In particular, we describe how induction of the vitamin D-activating enzyme 1alpha-hydroxylase in early gestation might provide a mechanism by which environmental or dietary vitamin D can influence fetal-placental development.

Differential regulation of vitamin D receptor and its ligand in human monocyte-derived dendritic cells

The functions of dendritic cells (DCs) are tightly regulated such that protective immune responses are elicited and unwanted immune responses are prevented. 1 alpha 25-dihydroxyvitamin D(3) (1 alpha 25(OH)(2)D(3)) has been identified as a major factor that inhibits the differentiation and maturation of DCs, an effect dependent upon its binding to the nuclear vitamin D receptor (VDR). Physiological control of 1 alpha 25(OH)(2)D(3) levels is critically dependent upon 25-hydroxyvitamin D(3)-1 alpha-hydroxylase (1 alpha OHase), a mitochondrial cytochrome P450 enzyme that catalyzes the conversion of inactive precursor 25-hydroxyvitamin D(3) (25(OH)D(3)) to the active metabolite 1 alpha 25(OH)(2)D(3). Using a human monocyte-derived DC (moDC) model, we have examined the relationship between DC VDR expression and the impact of exposure to its ligand, 1 alpha 25(OH)(2)D(3). We show for the first time that moDCs are able to synthesize 1 alpha 25(OH)(2)D(3) in vitro as a consequence of increased 1 alpha OHase expression. Following terminal differentiation induced by a diverse set of maturation stimuli, there is marked transcriptional up-regulation of 1 alpha OHase leading to increased 1 alpha OHase enzyme activity. Consistent with this finding is the observation that the development and function of moDCs is inhibited at physiological concentrations of the inactive metabolite 25(OH)D(3). In contrast to 1 alpha OHase, VDR expression is down-regulated as monocytes differentiate into immature DCs. Addition of 1 alpha 25(OH)(2)D(3) to moDC cultures at different time points indicates that its inhibitory effects are greater in monocyte precursors than in immature DCs. In conclusion, differential regulation of endogenous 1 alpha 25(OH)(2)D(3) ligand and its nuclear receptor appear to be important regulators of DC biology and represent potential targets for the manipulation of DC function.

The ontogeny of 25-hydroxyvitamin D(3) 1alpha-hydroxylase expression in human placenta and decidua

In addition to its classical calciotropic effects, the active form of vitamin D, 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) is a potent anti-proliferative/immunomodulatory secosteroid. The enzyme that catalyzes the synthesis of 1,25(OH)(2)D(3), 1alpha-hydroxylase (1alpha-OHase), is expressed in many human tissues, highlighting its possible role as an autocrine/paracrine activator of vitamin D. Immunohistochemical and RNA analyses were used to characterize the ontogeny of 1alpha-OHase expression in human placenta and decidua. Protein for 1alpha-OHase was detectable in trophoblast and decidua; the latter being stronger in decidualized stromal cells than macrophages, with no staining of lymphocytes. Quantitative reverse transcriptase-polymerase chain reaction was used to assess changes in mRNA expression for 1alpha-OHase at different gestations: first (mean, 9.1 +/- 1.5 weeks); second (mean, 14 +/- 1.8 weeks), and third trimester (mean, 39.3 +/- 2.5 weeks). 1alpha-OHase expression in decidua was approximately 1000-fold higher in first (95% confidence limits, 611 to 1376) and second (95% confidence limits, 633 to 1623) trimester biopsies when compared with the third trimester (95% confidence limits, 0.36 to 2.81) (both P < 0.001). In placenta, 1alpha-OHase expression was 80-fold higher in the first (range, 42 to 137) and second (range, 30 to 199) trimester when compared with third trimester biopsies (0.6 to 1.6) (both P < 0.001). Similar results were obtained by semiquantitative IHC. Parallel analysis of the receptor for 1,25(OH)(2)D(3) (vitamin D receptor) indicated that, as with 1alpha-OHase, highest levels of expression occurred in first trimester decidua. However, changes in vitamin D receptor mRNA expression across gestation were less pronounced than 1alpha-OHase. These spatiotemporal data emphasize the potential importance of 1alpha-OHase during early fetoplacental life and, in particular, suggest an autocrine/paracrine immunomodulatory function for the enzyme.

A survey of emergency vascular service provision

Recommendations exist for the optimal management of vascular surgical emergency patients. A telephone survey of on-call surgical registrars was performed to assess the current state of emergency vascular service provision across the Wessex and South West regions in the UK. Of the 24 hospitals surveyed, 10 had formal on-call arrangements for vascular surgical cover, 14 had informal arrangements where the general surgical consultant on-call provided cover and could contact a vascular surgeon if they were available and 3 hospitals had no such arrangements. No difficulties had been experienced by the on-call staff surveyed with any of the existing arrangements. Only 5 of the hospitals had formal on-call arrangements for interventional radiologists. We conclude that current emergency vascular service provision is suboptimal compared to national guidelines and patients may be subject to unequitable access to services. This may not be tenable in the new era of clinical governance.