Intestinal calcium transporter genes are upregulated by estrogens and the reproductive cycle through vitamin D receptor-independent mechanisms

The impact of inducible-whole body or intestine-specific Cyp24a1 gene knockout on vitamin D metabolism in mice

Expression of 25 hydroxyvitamin D 24 hydroxylase from the Cyp24a1 gene mediates 1,25 dihydroxyvitamin D (1,25(OH)2D) catabolism but gaps exist in our understanding of this enzyme's physiologic importance. Here, we used tamoxifen to induce Cyp24a1 gene knockout (KO) in adult mice (50 mg Tamoxifen /g BW, ip, 5 d, at 11 wks of age) or intestinal-epithelial-cell-specific knock-out mice (IEC KO) to evaluate the role of CYP24A1 in adult mice and the contribution of the intestine to vitamin D (Vit D) metabolism. At 12-wks mice were euthanized and serum was analyzed for Vit D metabolites by LC MS/MS while duodenal (Dd) and kidney (Kd) mRNA levels were quantified using qPCR. Adult Cyp24a1 KO mice had higher 25 hydroxyvitamin D (25(OH)D, + 185 %) and 1,25(OH)2D (+41.4 %) levels and reduced levels of 1,24,25(OH)3D (-53.7 %). No changes in serum Vit D metabolites were seen in adult mice lacking one Cyp24a1 allele (HT). In kidney, compensatory changes in Cyp27b1 mRNA (-85.3 % in KO, -36.5 % in HT) and Cyp24a1 mRNA (+147 % in KO, +43 % in HT) were observed. No changes in Dd Trpv6 or S100g mRNA were observed and Dd Cyp3a13 mRNA did not compensate for Cyp24a1 gene loss. Neither serum Vit D metabolites nor Dd Trpv6 and S100g mRNA were changed in IEC KO mice but there was a trend towards elevated renal Cyp24a1 mRNA (+61 %, p = 0.06). Our data in adult KO mice indicate that CYP24A1 has an important physiologic impact on Vit D metabolism while IEC KO data suggests that local degradation of the hormone by CYP24A1 is not a strong regulator of intestinal Vit D action or systemic vitamin D metabolism.

Effect of laying parity and sex ratio on reproduction performance and biochemical parameters of White Roman geese kept in an environmentally controlled house

1. This study aimed to investigate the effect of the first and third parities and one male: four females (1 M:4F) and 1 M:6F sex ratios of White Roman geese on their reproductive performance and biochemical parameters in an environmentally controlled house.2. Ganders (n = 136) and geese (n = 656) from the first and third parity were randomly placed into eight pens. These eight pens were assigned to one of four treatments in a 2 × 2 factorial arrangement (two sex ratio groups × two parity groups). The first and third parity treatment groups had 1 M:4F (each pen containing 20 ganders and 80 geese) and 1 M:6F (each pen containing 14 ganders and 84 geese) sex ratio treatment groups, respectively, replicated twice.3. Blood samples were collected from the geese at different time points: upon entering the house (ST), the beginning of the lighting regime of 7 L:17D for six weeks (LC6W), lighting adjustment to 9 L:15D for 6 weeks (9C6W), the peak of egg production (PEP) and the end of egg production (EEP).4. The first parity group had a longer laying period than the third parity (274 vs.191 days). First parity had a lower egg production rate than third parity during whole stage (18.7 vs. 25.4%). Fertility in 1 M:4F group was significantly higher than in 1 M:6F rate group (54.7 vs. 45.1%) at all periods.5. Plasma levels of total protein, albumin, globulin, triglycerides, calcium and phosphorus concentrations were significantly higher for whole laying period in first parity geese compared to third parity birds.

Antepartum high dietary supply of calcium affects bone homeostasis and offspring growth in dairy sheep and dairy goats

This study investigated the effects of high dietary Ca supplementation during the final 21 d antepartum on Ca and bone homeostasis in dairy sheep and goats, and the growth response of their suckling offspring. Multiparous dairy sheep (n = 5/group, 10 animals total) and goats (n = 6/group, 12 animals total) were randomly assigned to 2 experimental groups. Feeding occurred restrictively (2.3 kg DM/d*animal-1 antepartum for both species; 2.9 and 3.1 kg DM/d*animal-1 for sheep and goats postpartum, respectively) according to recommendations, except for Ca during antepartum feeding: 1 group received the basal diet based on hay and concentrate with extra CaCO3 (1.3% Ca in DM; 2.49-fold the recommendations) for 3 weeks antepartum, while the other group received just the basal diet (0.6% Ca in DM; 1.15-fold the recommendations). Experimental feeding ended with parturition and animals were henceforth fed according to Swiss recommendations for lactating sheep and goats and kept together with their suckling offspring. The observation period spanned from 21 d antepartum to 56 d postpartum. Animals were under continuous veterinary surveillance and monitored for signs of milk fever. Data collection comprised quantitative and functional parameters of Ca and bone homeostasis as well as birth weights and daily weight gain of suckling lambs and kids. Data were analyzed using repeated measures and endpoint mixed models. The response of quantitative markers indicated that high dietary Ca antepartum significantly increased fecal Ca concentrations until parturition, suggesting efficient physiological mechanisms to manage Ca overload through increasing fecal excretion. No significant differences were observed in serum Ca levels, urinary Ca excretion, or bone mineral density between the antepartum Ca feeding groups at any point during the observation period, indicating stable Ca homeostasis despite the dietary challenge. Differences in quantitative markers were noted between sheep and goats, including variations in serum and colostral Ca levels and bone mineral density, which largely aligned with results from earlier comparative studies. Serum 1,25-(OH)2 vitamin D (calcitriol) as well as markers of bone formation and resorption were monitored, revealing significant increases in serum osteocalcin postpartum in both goats and sheep fed high Ca antepartum. However, all other serum markers including calcitriol, remained unaffected by the feeding regimen but differed between sheep and goats, consistent with previous findings. All repeated measures were significantly affected by time, except for urinary Ca and bone-specific alkaline phosphatase activity in serum. Suckling offspring of sheep and goats in the high Ca group exhibited significantly reduced average daily weight gain compared with those in the 0.6% in DM Ca group, despite similar birth weights. We conclude that while dairy sheep and goats effectively managed high dietary Ca intake without overt signs of hypocalcemia or milk fever under these experimental conditions, the observed impacts on offspring growth and potential long-term physiological effects warrant further investigation. These findings contribute to the understanding of mineral nutrition in late-gestating dairy goats and sheep and highlight the need for further research on balanced dietary strategies to optimize health and productivity of dairy sheep and goats and their offspring.

Adaptations in Gastrointestinal Nutrient Absorption and its Determinants During Pregnancy in Monogastric Mammals: A Scoping Review

CONTEXT

Pregnancy increases nutrient demand, but how nutrient uptake and its determinants adapt to facilitate this is unclear.

OBJECTIVE

This review aimed to identify and characterize evidence and evidence gaps regarding changes in gastrointestinal nutrient absorption and its determinants during pregnancy in monogastric mammals.

DATA SOURCES

A scoping review of peer-reviewed sources was conducted across PubMed, Scopus, Web of Science, Embase, and ProQuest (theses and dissertations) databases.

DATA EXTRACTION

Data extracted included species, pregnancy stages and outcomes. Where sufficient data for a given outcome was available, relative values were summarized graphically or in tables, to allow comparison across pregnancy stages and/or small intestine regions. Searches identified 26 855 sources, of which only 159 were eligible. Mechanistic studies were largely restricted to rodents, and most compared non- and late-pregnant groups, with fewer studies including early- or mid-pregnant groups.

DATA ANALYSIS

During pregnancy, there is some evidence for greater capacity for glucose uptake but unchanged amino acid uptake, and good evidence for increased uptake of calcium, iron, and zinc, and slower gastrointestinal passage of nutrients. The available evidence indicates that acute glucose uptake, gastric emptying, and the activities of sucrase, maltase, and lactase do not change during pregnancy. Gaps in the knowledge include the effects of pregnancy on uptake of specific amino acids, lipids, and most minerals and vitamins.

CONCLUSION

The results indicate that the gastrointestinal tract adapts during pregnancy to facilitate increased nutrient absorption. Additional data is required in order to assess the underlying mechanisms for and impacts on the absorption of many nutrients, as well as to determine the timing of these adaptations.

The potential of TRP channels as new prognostic and therapeutic targets against prostate cancer progression

Prostate cancer (PCa) is the second deadliest cancer among men worldwide. Particularly critical is its development towards metastatic androgen-independent forms for which the current therapies are ineffective. Indeed, the 5-year relative survival for PCa drops dramatically to 34 % in the presence of metastases. The superfamily of Transient Receptor Potential (TRP) channels could answer the urgent request to identify new prognostic and therapeutic tools against metastatic PCa. Indeed, this class of ion channels revealed an appealing de-regulation during PCa development and its progression towards aggressive forms. Altered expression and/or functionality of several TRPs have been associated with the PCa metastatic cascade by significantly impacting tumor growth, invasiveness, and angiogenesis. In this review, we will dissect the contribution of TRP channels in such hallmarks of PCa and then discuss their applicability as new prognostic and therapeutic agents in the fight against metastatic PCa. In particular, the great potential of TRPM8, TRPV6, and TRPA1 in opening the way to new treatment perspectives will be highlighted.

Significance of Duodenal Prolactin Receptor Modulation by Calcium and Vitamin D in Sulpiride-Induced Hyperprolactinemia

Background and Objectives: Hyperprolactinemia, as a potential side-effect of some antipsychotic medications, is associated with decreased bone density and an increased risk of fractures. This study investigates whether calcium and vitamin D supplementation affects prolactin receptor (Prlr) gene expression in the duodenum, vertebrae, and kidneys of female rats with sulpiride-induced hyperprolactinemia. Materials and Methods: Twenty-one-week-old female Wistar rats were assigned to three groups: Group S consisted of ten rats who received sulpiride injections (10 mg/kg) twice daily for 6 weeks; Group D (10 rats) received daily supplementation of 50 mg calcium and 500 IU vitamin D along with sulpiride for the last 3 weeks; and Group C consisting of seven age-matched nulliparous rats serving as a control group. Real-time PCR was used to assess Prlr gene expression in the duodenum, vertebrae, and kidneys. Results: In Group S, Prlr gene expression was notably decreased in the duodenum (p < 0.01) but elevated in the vertebrae and kidneys compared to Group C. Conversely, Group D exhibited significantly increased Prlr expression in the duodenum (p < 0.01) alongside elevated expression in the vertebrae and kidneys. Conclusions: In sulpiride-induced hyperprolactinemia, decreased Prlr gene expression in the duodenum may lead to reduced intestinal calcium absorption. Consequently, prolactin may draw calcium from the skeletal system to maintain calcium balance, facilitated by increased Prlr gene expression in the vertebrae. However, vitamin D supplementation in sulpiride-induced hyperprolactinemia notably enhances Prlr gene expression in the duodenum, potentially ameliorating intestinal calcium absorption and mitigating adverse effects on bone health.

Dietary calcium is inversely associated with hepatitis B virus infection: an analysis of US National Health and Nutrition Examination Survey (NHANES) 2007-2020

BACKGROUND

There have been studies on the relationship between hepatitis B virus (HBV) infection and diet. We hypothesized HBV infection is related to dietary calcium intake, but the evidence is limited. This study aimed to examine whether dietary calcium intake is independently related to HBV infection in the United States population.

METHODS

A total of 20,488 participants aged over 20 years from the National Health and Nutrition Examination Survey (NHANES), conducted from 2007 to 2020, were included in this study. Pearson correlation was used to test the association between dietary calcium and serum calcium. The relationships of HBV infection with dietary calcium and serum calcium were assessed by logistic regression models.

RESULTS

There was a weak correlation between dietary calcium and serum calcium (r = 0.048). Logistic regression models indicated that HBV infection had a linear negative correlation with dietary calcium (OR 0.37; 95%CI 0.19, 0.76). For each additional 10 mg dietary calcium, the possibility of HBV infection was reduced by 63%. Hepatitis B positive participants had lower serum calcium content than negative participants. Stratified analysis shown the linear relationship between calcium and HBV infection varied among sex, race/ethnicity, and body mass index.

CONCLUSION

Our findings demonstrated HBV infection was linearly and inversely correlated with dietary calcium. The current study is expected to offer a fresh perspective on reducing HBV infection.

The Ca∗Cl/P Ratio: A Novel and More Appropriate Screening Tool for Normocalcaemic or Overt Primary Hyperparathyroidism

OBJECTIVE

The main purpose of this study was to explore the diagnostic performance of the Ca∗Cl/P ratio for primary hyperparathyroidism (PHPT), especially normocalcaemic PHPT (NPHPT), to assist health care providers in making reliable and rapid clinical identifications.

METHODS

From January 1, 2013, to March 31, 2023, 230 PHPT patients, including 65 with NPHPT and 230 sex- and age-matched controls, were enrolled in this retrospective study. Differences between hypercalcaemic PHPT (HPHPT) and NPHPT and between them and their respective controls were analyzed. The diagnostic accuracy of the Ca∗Cl/P ratio, Ca/P ratio, Cl/P ratio and albumin-corrected calcium was assessed by the area under the receiver operating characteristic curve.

RESULTS

Compared with corresponding controls, NPHPT and HPHPT patients both had significantly higher Ca ∗ Cl/P ratios (271.64 ± 51.74 vs 192.71 ± 26; 419.91 ± 139.11 vs 199.14 ± 36.75, P < .001). In the overall cohort, the ROC-AUC of the Ca∗Cl/P ratio (0.964, 95% CI = 0.943-0.979) for diagnosis of PHPT patients was superior to albumin-corrected calcium (0.959, 95% CI = 0.934-0.973), the Ca/P ratio (0.956, 95% CI = 0.934-0.973), and the Cl/P ratio (0.923, 95% CI = 0.895-0.946). A Ca ∗ Cl/P ratio above 239.17 mmol/L, with sensitivity (0.952), specificity (0.922), PPV (0.924), NPV (0.951) and accuracy (0.937), can distinguish PHPT patients from healthy individuals. Furthermore, the Ca ∗ Cl/P ratio yielded a sensitivity of 0.831, specificity of 0.938, PPV of 0.931, NPV of 0.847 and accuracy of 0.885 for NPHPT.

CONCLUSION

The Ca∗Cl/P ratio provides excellent diagnostic power for diagnosis of PHPT, especially NPHPT.

Novel Mutation in CYP2R1 Causing Vitamin D-Dependent Rickets Type 1b

Monogenic forms of rickets are being increasingly recognized. However, vitamin D-dependent rickets 1b (VDDR1b) due to CYP2R1 gene mutation is exceedingly rare. We report a 4.5-year-old girl and her younger sibling who presented with clinical, radiological, and biochemical features suggestive of nutritional rickets that did not resolve despite repeated therapeutic doses of vitamin D3. This led to evaluation for resistant rickets, which revealed a novel homozygous CYP2R1 c.50_51insTCGGCGGCGC; p.Leu18ArgfsTer79 variant in the affected siblings. The children were treated with oral calcium and cholecalciferol, dose titrated to maintain serum alkaline phosphatase, 25 hydroxy vitamin D, and parathyroid hormone levels in the normal range, with good clinical and radiological response. This case highlights the importance of genetic evaluation in patients with suspected nutritional rickets who have a family history of similar illness and require higher than usual doses of vitamin D for healing or relapse on stopping treatment. To the best of our knowledge this is the first case of VDDR1b reported from Asia.

Retrospective Analysis of Vitamin D Deficiency in an Adult Population of Arad County, Western Romania (2019-2022)

Vitamin D, a steroid hormone synthesized primarily in the skin upon exposure to ultraviolet light, is widely deficient across global populations. This study aimed to fill the data gap in Western Romania by measuring 25-hydroxy-vitamin D levels in a cohort of 7141 from Arad County. It was observed that women, younger adults (18-29 years), and older adults (70-79 years) had notably lower vitamin D levels compared to the average population. Additionally, there was a rise in vitamin D levels over the four-year span of 2018-2022, coinciding with the COVID-19 pandemic. Our research provides fresh data on those most susceptible to vitamin D deficiency and lays the groundwork for educational campaigns on vitamin D supplementation benefits.

Pectin Modulates Calcium Absorption in Polarized Caco-2 Cells via a Pathway Distinct from Vitamin D Stimulation

Pectin, a type of soluble fiber, promotes morphological changes in the small intestinal villi. Although its physiological significance is unknown, we hypothesized that changes in villus morphology enhance the efficiency of nutrient absorption in the small intestine and investigated the effect of pectin derived from persimmon on calcium absorption using polarized Caco-2 cells. In polarized Caco-2 cells, pectin altered the mRNA expression levels of substances involved in calcium absorption and the regulation of intracellular calcium concentration and significantly reduced calcium absorption. Although this was comparable to the results of absorption and permeability associated with the addition of active vitamin D, the simultaneous action of pectin and active vitamin D did not show any additive effects. Furthermore, as active vitamin D significantly increases the activity of intestinal alkaline phosphatase (ALP), which is known to be involved in the regulation of intestinal absorption of calcium and lipids, we also investigated the effect of pectin on intestinal ALP activity. As a result, it was found that, unlike the effect of active vitamin D, pectin significantly reduced intestinal ALP activity. These results suggest that pectin stimulates polarized Caco-2 cells through a mechanism distinct from the regulation of calcium absorption by vitamin D, modulating total calcium absorption from the elongated villi through morphological changes in the small intestine by suppressing it at the cellular level.

Oral calcium and vitamin D supplements differentially alter exploratory, anxiety-like behaviors and memory in male rats

Oral calcium and calcium plus vitamin D supplements are commonly prescribed to several groups of patients, e.g., osteoporosis, fracture, and calcium deficiency. Adequate and steady extracellular calcium levels are essential for neuronal activity, whereas certain forms of calcium supplement (e.g., CaCO3) probably interfere with memory function. However, it was unclear whether a long-term use of ionized calcium (calcium chloride in drinking water ad libitum), vitamin D supplement (oral gavage) or the combination of both affected anxiety and memory, the latter of which was probably dependent on the hippocampal neurogenesis. Here, we aimed to determine the effects of calcium and/or vitamin D supplement on the anxiety- and memory-related behaviors and the expression of doublecortin (DCX), an indirect proxy indicator of hippocampal neurogenesis. Eight-week-old male Wistar rats were divided into 4 groups, i.e., control, calcium chloride-, 400 UI/kg vitamin D3-, and calcium chloride plus vitamin D-treated groups. After 4 weeks of treatment, anxiety-, exploration- and recognition memory-related behaviors were evaluated by elevated pulse-maze (EPM), open field test (OFT), and novel object recognition (NOR), respectively. The hippocampi were investigated for the expression of DCX protein by Western blot analysis. We found that oral calcium supplement increased exploratory behavior as evaluated by OFT and the recognition index in NOR test without any effect on anxiety behavior in EPM. On the other hand, vitamin D supplement was found to reduce anxiety-like behaviors. Significant upregulation of DCX protein expression was observed in the hippocampus of both calcium- and vitamin D-treated rats, suggesting their positive effects on neurogenesis. In conclusion, oral calcium and vitamin D supplements positively affected exploratory, anxiety-like behaviors and/or memory in male rats. Thus, they potentially benefit on mood and memory in osteoporotic patients beyond bone metabolism.

Vitamin D and malabsorptive gastrointestinal conditions: A bidirectional relationship?

This paper is one of the outcomes of the 5th International Conference "Controversies in Vitamin D" held in Stresa, Italy from 15 to 18 September 2021 as part of a series of annual meetings which was started in 2017. The scope of these meetings is to discuss controversial issues about vitamin D. Publication of the outcomes of the meeting in international journals allows a wide sharing of the most recent data with the medical and academic community. Vitamin D and malabsorptive gastrointestinal conditions was one of the topics discussed at the meeting and focus of this paper. Participants to the meeting were invited to review available literature on selected issues related to vitamin D and gastrointestinal system and to present their topic to all participants with the aim to initiate a discussion on the main outcomes of which are reported in this document. The presentations were focused on the possible bidirectional relationship between vitamin D and gastrointestinal malabsorptive conditions such as celiac disease, inflammatory bowel diseases (IBDs) and bariatric surgery. In fact, on one hand the impact of these conditions on vitamin D status was examined and on the other hand the possible role of hypovitaminosis D on pathophysiology and clinical course of these conditions was also evaluated. All examined malabsorptive conditions severely impair vitamin D status. Since vitamin D has known positive effects on bone this in turn may contribute to negative skeletal outcomes including reduced bone mineral density, and increased risk of fracture which may be mitigated by vitamin D supplementation. Due to the immune and metabolic extra-skeletal effects there is the possibility that low levels of vitamin D may negatively impact on the underlying gastrointestinal conditions worsening its clinical course or counteracting the effect of treatment. Therefore, vitamin D status assessment and supplementation should be routinely considered in all patients affected by these conditions. This concept is strengthened by the existence of a possible bidirectional relationship through which poor vitamin D status may negatively impact on clinical course of underlying disease. Sufficient elements are available to estimate the desired threshold vitamin D level above which a favourable impact on the skeleton in these conditions may be obtained. On the other hand, ad hoc controlled clinical trials are needed to better define this threshold for obtaining a positive effect of vitamin D supplementation on occurrence and clinical course of malabsorptive gastrointestinal diseases.

Intestinal Vitamin D Receptor Is Dispensable for Maintaining Adult Bone Mass in Mice With Adequate Calcium Intake

1,25-Dihydroxyvitamin D3 (1,25(OH)2D3)-mediated intestinal calcium (Ca) absorption supplies Ca for proper bone mineralization during growth. We tested whether vitamin D receptor (VDR)-mediated 1,25(OH)2D3 signaling is critical for adult Ca absorption and bone by using mice with inducible Vdr gene knockout in the whole intestine (villin-CreERT2+/- × Vdrf/f, WIK) or in the large intestine (Cdx2-CreERT2+/- ×Vdrf/f, LIK). At 4-month-old, Vdr alleles were recombined (0.05 mg tamoxifen/g BW, intraperitoneally [i.p.], 5 days) and mice were fed diets with either 0.5% (adequate) or 0.2% (low) Ca. Ca absorption was examined after 2 weeks while serum 1,25(OH)2D3, bone mass, and bone microarchitecture were examined after 16 weeks. Intestinal and renal gene expression was measured at both time points (n = 12/genotype/diet/time point). On the 0.5% Ca diet, all phenotypes in WIK and LIK mice were similar to the controls. Control mice adapted to the 0.2% low-Ca diet by increasing renal Cyp27b1 mRNA (3-fold), serum 1,25(OH)2D3 level (1.9-fold), and Ca absorption in the duodenum (Dd, + 131%) and proximal colon (PCo, + 28.9%), which prevented bone loss. In WIK mice, low-Ca diet increased serum 1,25(OH)2D3 (4.4-fold) but Ca absorption remained unaltered in the Dd and PCo. Consequently, significant bone loss occurred in WIK mice (e.g., cortical thickness, Ct.Th, -33.7%). LIK mice adapted to the low-Ca diet in the Dd but not the PCo, and the effect on bone phenotypes was milder (e.g., Ct.Th, -13.1%). Our data suggest intestinal VDR in adult mice prevents bone loss under low Ca intake but is dispensable under adequate calcium intake.

Biochemistry and pathophysiology of the Transient Potential Receptor Vanilloid 6 (TRPV6) calcium channel

TRPV6 is a Transient Receptor Potential Vanilloid (TRPV) cation channel with high selectivity for Ca²⁺ ions. First identified in 1999 in a search for the gene which mediates intestinal Ca²⁺ absorption, its far more extensive repertoire as a guardian of intracellular Ca²⁺ has since become apparent. Studies on TRPV6-deficient mice demonstrated additional important roles in placental Ca²⁺ transport, fetal bone development and male fertility. The first reports of inherited deficiency in newborn babies appeared in 2018, revealing its physiological importance in humans. There is currently strong evidence that TRPV6 also contributes to the pathogenesis of some common cancers. The recently reported association of TRPV6 deficiency with non-alcoholic chronic pancreatitis suggests a role in normal pancreatic function. Over time and with greater awareness of TRPV6, other disease-associations are likely to emerge. Powerful analytical tools have provided invaluable insights into the structure and operation of TRPV6. Its roles in Ca²⁺ signaling and carcinogenesis, and the use of channel inhibitors in cancer treatment are being intensively investigated. This review first briefly describes the biochemistry and physiology of the channel, and analytical methods used to investigate these. The focus subsequently shifts to the clinical disorders associated with abnormal expression and the underlying pathophysiology. The aims of this review are to increase awareness of this channel, and to draw together findings from a wide range of sources which may help to formulate new ideas for further studies.

Vasoactive intestinal peptide and cystic fibrosis transmembrane conductance regulator contribute to the transepithelial calcium transport across intestinal epithelium-like Caco-2 monolayer

Vasoactive intestinal peptide (VIP) as a neurocrine factor released by enteric neurons has been postulated to participate in the regulation of transcellular active calcium transport across intestinal epithelium, but the preceding evidence is scant and inconclusive. Herein, transepithelial calcium flux and epithelial electrical parameters were determined by Ussing chamber technique with radioactive tracer in the intestinal epithelium-like Caco-2 monolayer grown on Snapwell. After 3-day culture, Caco-2 cells expressed mRNA of calcium transporters, i.e., TRPV6, calbindin-D9k, PMCA1b and NCX1, and exhibited transepithelial resistance of ~200 Ω cm2, a characteristic of leaky epithelium similar to the small intestine. VIP receptor agonist was able to enhance transcellular calcium flux, whereas VIP receptor antagonist totally abolished calcium fluxes induced by 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]. Since the intestinal cystic fibrosis transmembrane conductance regulator (CFTR) could be activated by VIP and calciotropic hormones, particularly parathyroid hormone, we sought to determine whether CFTR also contributed to the 1,25(OH)2D3-induced calcium transport. A selective CFTR inhibitor (20-200 μM CFTRinh-172) appeared to diminish calcium fluxes as well as transepithelial potential difference and short-circuit current, both of which indicated a decrease in electrogenic ion transport. On the other hand, 50 μM genistein-a molecule that could rapidly activate CFTR-was found to increase calcium transport. Our in silico molecular docking analysis confirmed direct binding of CFTRinh-172 and genistein to CFTR channels. In conclusion, VIP and CFTR apparently contributed to the intestinal calcium transport, especially in the presence of 1,25(OH)2D3, thereby supporting the existence of the neurocrine control of intestinal calcium absorption.

The Role of Vitamin D and Vitamin D Binding Protein in Chronic Liver Diseases

Vitamin D (calciferol) is a fat-soluble vitamin that has a significant role in phospho-calcium metabolism, maintaining normal calcium levels and bone health development. The most important compounds of vitamin D are cholecalciferol (vitamin D3, or VD3) and ergocalciferol (vitamin D2, or VD2). Besides its major role in maintaining an adequate level of calcium and phosphate concentrations, vitamin D is involved in cell growth and differentiation and immune function. Recently, the association between vitamin D deficiency and the progression of fibrosis in chronic liver disease (CLD) was confirmed, given the hepatic activation process and high prevalence of vitamin D deficiency in these diseases. There are reports of vitamin D deficiency in CLD regardless of the etiology (chronic viral hepatitis, alcoholic cirrhosis, non-alcoholic fatty liver disease, primary biliary cirrhosis, or autoimmune hepatitis). Vitamin D binding protein (VDBP) is synthesized by the liver and has the role of binding and transporting vitamin D and its metabolites to the target organs. VDBP also plays an important role in inflammatory response secondary to tissue damage, being involved in the degradation of actin. As intense research during the last decades revealed the possible role of vitamin D in liver diseases, a deeper understanding of the vitamin D, vitamin D receptors (VDRs), and VDBP involvement in liver inflammation and fibrogenesis could represent the basis for the development of new strategies for diagnosis, prognosis, and treatment of liver diseases. This narrative review presents an overview of the evidence of the role of vitamin D and VDBP in CLD, both at the experimental and clinical levels.

Does Vitamin D Insufficiency Influence Prebiotic Effect on Calcium Absorption and Bone Retention?

Higher calcium (Ca) absorption would partially compensate for Ca intake below requirements for bone health. Previously, we found that GOS/FOS prebiotic mixture (PM) increases Ca absorption in the colon and retention in bone. Ca absorption and retention are regulated by vitamin D (VD). Hence, it is relevant to explore whether VD insufficiency influences the effect of the PM in the colon. The effect of the PM on Ca, phosphate (IP), and magnesium (Mg) absorption and retention under conditions of VD sufficiency and insufficiency (VDInsuff) was compared using a preclinical model of VDInsuff and low bone mass. Ovariectomized rats were fed isocaloric semisynthetic diets according to AIN-93 M. The diets varied in Ca (0.5% or 0.3%), VD [100 IU% (+ D) or 0 IU% (- D)], and PM (2.5% or 0%) content. The following eight groups were studied: + D0.5; + D0.3; + DPM0.5; + DPM0.3; - D0.5; - D0.3; - DPM0.5; and - DPM0.3. Irrespective of Ca content, VDInsuff did not affect the prebiotic effect of the PM on caecum pH, lactobacillus colony growth, or Mg absorption but significantly decreased its effect on colonic crypt length and cell/crypt and Ca and IP absorption. The PM failed to counterbalance the pro-inflammatory effect of VDInsuff. Moreover, bone retention i.e., bone mineral content and density, bone volume, and bone quality parameters were significantly lower (p < 0.05) and bone turnover significantly was higher (p < 0.05). Although the PM is a useful tool to improve mineral absorption and bone retention, it would seem important to monitor VD nutritional status to ensure the full prebiotic effect in the large intestine.

Vitamin D-Mediated Regulation of Intestinal Calcium Absorption

Vitamin D is a critical regulator of calcium and bone homeostasis. While vitamin D has multiple effects on bone and calcium metabolism, the regulation of intestinal calcium (Ca) absorption efficiency is a critical function for vitamin D. This is necessary for optimal bone mineralization during growth, the protection of bone in adults, and the prevention of osteoporosis. Intestinal Ca absorption is regulated by 1,25 dihydroxyvitamin D (1,25(OH)2 D), a hormone that activates gene transcription following binding to the intestinal vitamin D receptor (VDR). When dietary Ca intake is low, Ca absorption follows a vitamin-D-regulated, saturable pathway, but when dietary Ca intake is high, Ca absorption is predominately through a paracellular diffusion pathway. Deletion of genes that mediate vitamin D action (i.e., VDR) or production (CYP27B1) eliminates basal Ca absorption and prevents the adaptation of mice to low-Ca diets. Various physiologic or disease states modify vitamin-D-regulated intestinal absorption of Ca (enhanced during late pregnancy, reduced due to menopause and aging).

The contribution of regulated colonic calcium absorption to the maintenance of calcium homeostasis

Calcium absorption and secretion can occur along the length of the small and large intestine. To date, the focus of research into intestinal calcium absorption has been the small intestine, the site contributing the majority of intestinal calcium absorption. However, evidence that the colon contributes as much as 10% of enteral calcium transport has been available for decades. Transcellular calcium absorption and bidirectional paracellular calcium flux contributing to either net absorption or secretion have been observed in the colon, depending on the physiological state. Moreover, the calcium transport pathways contributing to colonic absorption or secretion are regulated by a variety of hormones, including calcitriol, plasma calcium and dietary factors, including prebiotics. Herein we review historical and recent research highlighting the role of colonic calcium transport in overall maintenance of calcium balance, and suggest these data are consistent with the colon being a site of significant regulated transepithelial calcium transport.

Vitamin D Deficiency in Women with Breast Cancer: A Correlation with Osteoporosis? A Machine Learning Approach with Multiple Factor Analysis

Breast cancer (BC) is the most frequent malignant tumor in women in Europe and North America, and the use of aromatase inhibitors (AIs) is recommended in women affected by estrogen receptor-positive BCs. AIs, by inhibiting the enzyme that converts androgens into estrogen, cause a decrement in bone mineral density (BMD), with a consequent increased risk of fragility fractures. This study aimed to evaluate the role of vitamin D3 deficiency in women with breast cancer and its correlation with osteoporosis and BMD modifications. This observational cross-sectional study collected the following data regarding bone health: osteoporosis and osteopenia diagnosis, lumbar spine (LS) and femoral neck bone mineral density (BMD), serum levels of 25-hydroxyvitamin D3 (25(OH)D3), calcium and parathyroid hormone. The study included 54 women with BC, mean age 67.3 ± 8.16 years. Given a significantly low correlation with the LS BMD value (r2 = 0.30, p = 0.025), we assessed the role of vitamin D3 via multiple factor analysis and found that BMD and vitamin D3 contributed to the arrangement of clusters, reported as vectors, providing similar trajectories of influence to the construction of the machine learning model. Thus, in a cohort of women with BC undergoing Ais, we identified a very low prevalence (5.6%) of patients with adequate bone health and a normal vitamin D3 status. According to our cluster model, we may conclude that the assessment and management of bone health and vitamin D3 status are crucial in BC survivors.

Calcium selective channel TRPV6: Structure, function, and implications in health and disease

Calcium-selective channel TRPV6 (Transient Receptor Potential channel family, Vanilloid subfamily member 6) belongs to the TRP family of cation channels and plays critical roles in transcellular calcium (Ca2+) transport, reuptake of Ca2+ into cells, and maintaining a local low Ca2+ environment for certain biological processes. Recent crystal and cryo-electron microscopy-based structures of TRPV6 have revealed mechanistic insights on how the protein achieves Ca2+ selectivity, permeation, and inactivation by calmodulin. The TRPV6 protein is expressed in a range of epithelial tissues such as the intestine, kidney, placenta, epididymis, and exocrine glands such as the pancreas, prostate and salivary, sweat, and mammary glands. The TRPV6 gene is a direct transcriptional target of the active form of vitamin D and is efficiently regulated to meet the body's need for Ca2+ demand. In addition, TRPV6 is also regulated by the level of dietary Ca2+ and under physiological conditions such as pregnancy and lactation. Genetic models of loss of function in TRPV6 display hypercalciuria, decreased bone marrow density, deficient weight gain, reduced fertility, and in some cases alopecia. The models also reveal that the channel plays an indispensable role in maintaining maternal-fetal Ca2+ transport and low Ca2+ environment in the epididymal lumen that is critical for male fertility. Most recently, loss of function mutations in TRPV6 gene is linked to transient neonatal hyperparathyroidism and early onset chronic pancreatitis. TRPV6 is overexpressed in a wide range of human malignancies and its upregulation is strongly correlated to tumor aggressiveness, metastasis, and poor survival in selected cancers. This review summarizes the current state of knowledge on the expression, structure, biophysical properties, function, polymorphisms, and regulation of TRPV6. The aberrant expression, polymorphisms, and dysfunction of this protein linked to human diseases are also discussed.

Vitamin D as a Potential Preventive Agent For Young Women's Breast Cancer

Clinical studies backed by research in animal models suggest that vitamin D may protect against the development of breast cancer, implicating vitamin D as a promising candidate for breast cancer prevention. However, despite clear preclinical evidence showing protective roles for vitamin D, broadly targeted clinical trials of vitamin D supplementation have yielded conflicting findings, highlighting the complexity of translating preclinical data to efficacy in humans. While vitamin D supplementation targeted to high-risk populations is a strategy anticipated to increase prevention efficacy, a complimentary approach is to target transient, developmental windows of elevated breast cancer risk. Postpartum mammary gland involution represents a developmental window of increased breast cancer promotion that may be poised for vitamin D supplementation. Targeting the window of involution with short-term vitamin D intervention may offer a simple, cost-effective approach for the prevention of breast cancers that develop postpartum. In this review, we highlight epidemiologic and preclinical studies linking vitamin D deficiency with breast cancer development. We discuss the underlying mechanisms through which vitamin D deficiency contributes to cancer development, with an emphasis on the anti-inflammatory activity of vitamin D. We also discuss current evidence for vitamin D as an immunotherapeutic agent and the potential for vitamin D as a preventative strategy for young woman's breast cancer.

Rickets in Children: An Update

Rickets refers to a deficient mineralization of the growth plate cartilage, predominantly affecting longer bones. Despite the fact that preventive measures are available, it is still a common disease worldwide; nutritional rickets, due to vitamin D deficiency or dietary calcium inadequate intake, remains the most common form. Medical history, physical examination, radiologic features and biochemical tests are essential for diagnosis. Although recent studies suggest hypophosphatemia as the leading alteration, rickets is classically divided into two categories: calcipenic rickets and phosphopenic rickets. Knowledge of this categorization and of respective clinical and laboratory features is essential for rapid diagnosis and correct management. The aim of this review is to analyze the epidemiological, pathogenetic, clinical, and therapeutic aspects of the different forms of rickets, describing the novelties on this “long-lived” disease.

Two novel CYP2R1 mutations in a family with vitamin D-dependent rickets type 1b

PURPOSE

Vitamin D-dependent rickets type 1b (VDDR1b) is a very rare autosomal recessive disorder caused by mutations in CYP2R1 that produces 25-hydroxylase. To date only five mutations in CYP2R1 have been identified. This study has reported the genetic results and the clinical characteristics of a family with VDDR1b and compared this family to the other families with VDDR1b in literature.

METHODS

After two probands were diagnosed with VDDR1b, all other family members were evaluated. Serum calcium, phosphorus, alkaline phosphatase, parathyroid hormone, 25-hydroxy vitamin D, and 1.25-dihydroxy vitamin D levels were measured in all family members. All individuals were evaluated radiographically, and a genetic analysis was done in all family members. The other families with VDDR1b in literature were reviewed.

RESULTS

Two novel mutations [c.367 + 1G > C and p.E339Q (c.1015G > C)] were identified. The clinic and laboratory findings were strikingly different among the members of this family regardless of the mutation and the number of alleles affected. The families having different mutations in literature had also extensive variation in both the clinical and the laboratory findings.

CONCLUSION

The current study further expands CYP2R1 mutation spectrum. The findings of both the current and the previous studies suggest that VDDR1b is a more complex disorder than the known autosomal recessive inheritance model and the phenotype may show an extensive variation regardless of the mutation type and the gene dosage.

Intestinal Calcium Absorption

In this article, we focus on mammalian calcium absorption across the intestinal epithelium in normal physiology. Intestinal calcium transport is essential for supplying calcium for metabolism and bone mineralization. Dietary calcium is transported across the mucosal epithelia via saturable transcellular and nonsaturable paracellular pathways, both of which are under the regulation of 1,25-dihydroxyvitamin D₃ and several other endocrine and paracrine factors, such as parathyroid hormone, prolactin, 17β-estradiol, calcitonin, and fibroblast growth factor-23. Calcium absorption occurs in several segments of the small and large intestine with varying rates and capacities. Segmental heterogeneity also includes differential expression of calcium transporters/carriers (e.g., transient receptor potential cation channel and calbindin-D_9k ) and the presence of favorable factors (e.g., pH, luminal contents, and gut motility). Other proteins and transporters (e.g., plasma membrane vitamin D receptor and voltage-dependent calcium channels), as well as vesicular calcium transport that probably contributes to intestinal calcium absorption, are also discussed. © 2021 American Physiological Society. Compr Physiol 11:1-27, 2021.

Lessons Learned from Hereditary 1,25-Dihydroxyvitamin D-Resistant Rickets Patients on Vitamin D Functions

We summarize here lessons learned from studies on skeletal and extra-skeletal functions of vitamin D in hereditary 1,25-dihydroxyvitamin D-resistant rickets (HVDRR) patients with a mutant, nonfunctioning vitamin D receptor (VDR). During childhood, HVDRR patients are dependent on intestinal VDR, demonstrate low intestinal fraction calcium absorption, and have a bone calcium accretion rate that leads to hypocalcemia and rickets. After puberty, there is recovery in intestinal calcium absorption and in bone calcium accretion and structure. HVDRR monocytes and lymphocytes show impairment in the expression of antimicrobial proteins and demonstrate a proinflammatory cytokine profile. However, HVDRR patients do not exhibit increased rates of infections or inflammatory diseases. Vitamin D deficiency is associated with asthmatic exacerbations. Surprisingly, HVDRR patients do not usually develop asthma. They have normal allergic tests and lung functions and are protected against provoked bronchial hyperactivity. HVDRR patients have decreased IL-5 levels in their exhaled breath condensate. Given that IL-5 is a key cytokine in the development of airway inflammation and hyperactivity and that VDR is important for IL-5 generation, it is plausible that low lung IL-5 protects HVDRR patients from asthma. Vitamin D metabolites have suppressive effects on the renin angiotensin system. However, no HVDRR patient showed hypertension or echocardiographic pathology, and their renin angiotensin metabolites were normal. The VDR is expressed throughout the reproductive system, suggesting a role in reproduction. However, the reproductive history of HVDRR patients is normal despite the lack of a normal VDR. HVDRR patients provide a unique opportunity to study the role of the VDR and the role of vitamin D in various human systems.

Molting method alternative and detection of estrogen receptors by immunohistochemical methods on molted layers

Three experiments were designed to evaluate the effects of different molting methods on the growth performance, detection of estrogen receptors (ERs), and immunohistochemical properties of some tissues in pre-, during, and post-molting of layers. In experiment 1, 302 Hy-line W-36 were reared from 75 to 76 weeks. In experiment 2, a total of 252 Hy-line W-36 were randomly allocated to 7 groups, with 6 replications and 6 birds in each. Hens fed in the E and D groups reached 30% of loss weight sooner (P < 0.05). Egg production was also sooner stopped in the FW group than in other ones (P < 0.05). In experiment 3, after inducing molting, each group in experiment 2 was divided into 2 groups with and without Humulus lupulus (Hop). The E group feed intake was increased, as compared to groups F and C (P < 0.05). A significant increase in egg weight was found by applying Hop and molting methods (P < 0.05). Days for return to the initial egg production and 10% egg laying were significantly decreased in the birds fed by Hop in the E and D groups (P < 0.05). The W-D, N-D, W-E, and N-E groups sooner returned to 50% egg laying, in comparison to other treatments (P < 0.05). Plasma estrogen and ERs were decreased by the molting programs, as compared with pre-molting; however, Hop increased their post-molting. After the molting period, egg production and ERs were increased significantly, as compared with the pre-molting period. To conclude, the white button mushroom residual, through decreasing ERs, could be used successfully for forced molting, and Hop could lead to a good performance by increasing ERs in the second laying cycle.

Estrogen Regulates Duodenal Calcium Absorption Through Differential Role of Estrogen Receptor on Calcium Transport Proteins

BACKGROUND AND AIMS

Intestinal calcium absorption from the diet plays important role in maintaining calcium homeostasis in the body. Estrogen exerts wide physiological and pathological effects in the human. Previous studies have shown that estrogen is involved in the intestinal calcium absorption. In this study, we made investigation on the mechanism of estrogen action on duodenal calcium absorption.

METHODS

The experiments were performed in mice, human, and human duodenal epithelial cells, SCBN cells. Murine duodenal calcium absorption was measured by using single pass perfusion of the duodenum in vivo. The calcium absorption of SCBN cells was evaluated by calcium imaging system. The expression of calcium transport proteins, transient receptor potential cation channel (TRPV6) and plasma membrane calcium pump (PMCA1b), in the duodenum or SCBN cells were analyzed by western blot.

RESULTS

The duodenal calcium absorption in ovariectomized mice was significantly decreased, compared with control female mice, which returned to control level after 17β-estradiol replacement treatment. Estrogen regulated the expressions of TRPV6 and PMCA1b in murine and human duodenal mucosae and SCBN cells. The further results from SCBN cells showed that 17β-estradiol regulated calcium influx through the respective effects of estrogen receptor (ER) ɑ and β on TRPV6 and PMCA1b.

CONCLUSION

Estrogen regulates duodenal calcium absorption through differential role of ERɑ and ERβ on duodenal epithelial cellular TRPV6 and PMCA1b. The study further elucidates the mechanism of estrogen on the regulation of intestinal calcium absorption.

Anti-Tumor Effect of Vitamin D Combined with Calcium on Lung Cancer: A Systematic Review and Meta-Analysis

Although many studies have demonstrated the impact of vitamin D and calcium on lung cancer, it remains the discrepancy for the effect of vitamin D and calcium on lung cancer. In this study, we aimed to verify the roles of vitamin D and calcium in the incidence and prognosis of lung cancer. A systematic literature search was performed by February 29, 2020. The relative risks (RRs) and hazard ratio (HRs) were pooled to evaluate the risk for the incidence and mortality of lung cancer. A total of 58,625 lung cancer cases from 40 studies were included. The risk (RR: 0.915, 95% Cl: 0.849-0.986) and mortality (RR: 0.718, 95% Cl: 0.530-0.973) of lung cancer were significantly decreased due to high circulating 25(OH)D level. Although the separate intake of vitamin D (RR: 0.909, 95% Cl: 0.801-1.031) and calcium (RR: 0.890, 95% Cl: 0.741-1.070) did not exhibit a protective effect on lung cancer, the combination supplement of vitamin D and calcium significantly decreased the incidence of lung cancer (RR: 0.811, 95% Cl: 0.659-0.999). High level of serum 25(OH)D could play the preventive role in lung cancer. Furthermore, vitamin D could be supplemented together with calcium against lung cancer.

Diagnosis and Management of Vitamin D Dependent Rickets

The term "vitamin D dependent rickets" describes a group of genetic disorders that are characterized by early-onset rickets due to the inability to maintain adequate concentrations of active forms of vitamin D or a failure to respond fully to activated vitamin D. Although the term is now admittedly a pathophysiological misnomer, there remains clinical relevance for its continued use, as patients have a lifelong "dependency" on administration of specialized regimens of vitamin D replacement. This review provides an update on the molecular bases for the three forms of vitamin D dependent rickets, and summarizes current protocols for management of affected subjects.

Review: Regulation of gastrointestinal and renal transport of calcium and phosphorus in ruminants

In comparison to monogastric animals, ruminants show some peculiarities in respect to the regulation of mineral homeostasis, which can be regarded as a concerted interplay between gastrointestinal absorption, renal excretion and bone mobilisation to maintain physiological Ca and phosphate (Pi) concentrations in serum. Intestinal absorption of Ca or Pi is mediated by two general mechanisms: paracellular, passive transport dominates when luminal Ca or Pi concentrations are high and transcellular. The contribution of active transport becomes more important when dietary Ca or Pi supply is restricted or the demand increased. Both pathways are modulated directly by dietary interventions, influenced by age and regulated by endocrine factors such as 1,25-dihydroxyvitamin D3. Similar transport processes are observed in the kidney. After filtration, Ca and Pi are resorbed along the nephron. However, as urinary Ca and Pi excretion is very low in ruminants, the regulation of these renal pathways differs from that described for monogastric species, too. Furthermore, salivary secretion, as part of endogenous Pi recycling, and bone mobilisation participate in the maintenance of Ca and Pi homeostasis in ruminants. Saliva contains large amounts of Pi for buffering rumen pH and to ensure optimal conditions for the rumen microbiome. The skeleton is a major reservoir of Ca and Pi to compensate for discrepancies between demand and uptake. But alterations of the regulation of mineral homeostasis induced by other dietary factors such as a low protein diet were observed in growing ruminants. In addition, metabolic changes, for example, at the onset of lactation have pronounced effects on gastrointestinal mineral transport processes in some ruminant species. As disturbances of mineral homeostasis do not only increase the risk of the animals to develop other diseases, but are also associated with protein and energy metabolism, further research is needed to improve our knowledge of its complex regulation.

Structure and function of the calcium-selective TRP channel TRPV6

Epithelial calcium channel TRPV6 is a member of the vanilloid subfamily of TRP channels that is permeable to cations and highly selective to Ca²⁺ ; it shows constitutive activity regulated negatively by Ca²⁺ and positively by phosphoinositol and cholesterol lipids. In this review, we describe the molecular structure of TRPV6 and discuss how its structural elements define its unique functional properties. High Ca²⁺ selectivity of TRPV6 originates from the narrow selectivity filter, where Ca²⁺ ions are directly coordinated by a ring of anionic aspartate side chains. Divalent cations Ca²⁺ and Ba²⁺ permeate TRPV6 pore according to the knock-off mechanism, while tight binding of Gd³⁺ to the aspartate ring blocks the channel and prevents Na⁺ from permeating the pore. The iris-like channel opening is accompanied by an α-to-π helical transition in the pore-lining transmembrane helix S6. As a result of this transition, the intracellular halves of the S6 helices bend and rotate by about 100 deg, exposing different residues to the channel pore in the open and closed states. Channel opening is also associated with changes in occupancy of the transmembrane domain lipid binding sites. The inhibitor 2-aminoethoxydiphenyl borate (2-APB) binds to TRPV6 in a pocket formed by the cytoplasmic half of the S1-S4 transmembrane helical bundle and shifts open-closed channel equilibrium towards the closed state by outcompeting lipids critical for activation. Ca²⁺ inhibits TRPV6 via binding to calmodulin (CaM), which mediates Ca²⁺ -dependent inactivation. The TRPV6-CaM complex exhibits 1:1 stoichiometry; one TRPV6 tetramer binds both CaM lobes, which adopt a distinct head-to-tail arrangement. The CaM C-terminal lobe plugs the channel through a unique cation-π interaction by inserting the side chain of lysine K115 into a tetra-tryptophan cage at the ion channel pore intracellular entrance. Recent studies of TRPV6 structure and function described in this review advance our understanding of the role of this channel in physiology and pathophysiology and inform new therapeutic design.

Vitamin D and the intestine: Review and update

The central role of vitamin D in calcium homeostasis is to increase calcium absorption from the intestine. This article describes the early work that served as the foundation for the initial model of vitamin D mediated calcium absorption. In addition, other research related to the role of vitamin D in the intestine, including those which have challenged the traditional model and the crucial role of specific calcium transport proteins, are reviewed. More recent work identifying novel targets of 1,25(OH)₂D₃ action in the intestine and highlighting the importance of 1,25(OH)₂D₃ action across the proximal/distal and crypt/villus axes in the intestine is summarized.

Anomalous bone changes in ovariectomized type 2 diabetic rats: inappropriately low bone turnover with bone loss in an estrogen-deficient condition

Estrogen deprivation accelerates bone resorption, leading to imbalance of bone remodeling and osteoporosis in postmenopausal women. In the elderly, type 2 diabetes mellitus (T2DM) frequently coexists as an independent factor of bone loss. However, little is known about the skeletal changes in a combined condition of estrogen deficiency and T2DM. Herein, we performed ovariectomy (OVX) in nonobese Goto-Kakizaki (GK) T2DM rats to examine changes associated with calcium and phosphate metabolism and bone microstructures and strength. As expected, wild-type (WT) rats subjected to ovariectomy (OVX-WT) had low trabecular bone volume and serum calcium with increased dynamic histomorphometric and serum bone markers, consistent with the high turnover state. T2DM in GK rats also led to low trabecular volume and serum calcium. However, the dynamic histomorphometric markers of bone remodeling were unaffected in these GK rats, indicating the distinct mechanism of T2DM-induced bone loss. Interestingly, OVX-GK rats were found to have anomalous and unique changes in bone turnover-related parameters, i.e., decreased osteoblast and osteoclast surfaces with lower COOH-terminal telopeptide of type I collagen levels compared with OVX-WT rats. Furthermore, the levels of calciotropic hormones, i.e., parathyroid hormone and 1,25(OH)2D3, were significantly decreased in OVX-GK rats. Although the OVX-induced bone loss did not further worsen in GK rats, a three-point bending test indicated that OVX-GK bones exhibited a decrease in bone elasticity. In conclusion, T2DM and estrogen deficiency both led to microstructural bone loss, the appearance of which did not differ from each factor alone. Nevertheless, the combination worsened the integrity and suppressed the turnover, which might eventually result in adynamic bone disease.

Downregulation of TRPV6 channel activity by cholesterol depletion in Jurkat T cell line

Transient receptor potential vanilloid 6 (TRPV6) channels are key players in calcium metabolism of healthy and cancerous cells. Nevertheless, the mechanisms controlling abundance of these channels in plasma membrane of the cells to regulate Ca2+ transport is still poorly understood. In this study, we provide the first evidence that TRPV6 calcium channels and Ca 2+ influx in Jurkat T cell line are modulated by cholesterol, a main lipid component of the plasma membrane. Using patch-clamp technique, we found that activity of TRPV6 channels decreased by cholesterol sequestration with methyl-β-cyclodextrin (MβCD). Continuous measurement of intracellular Ca2+ revealed a reduction of Ca2+ influx into Jurkat cells following cholesterol depletion. Immunofluorescence and immunoelectron microscopy analyses of MβCD-treated cells detected the lower surface expression of the TRPV6 proteins in comparison with control cells. In general, our data showed that cholesterol regulates TRPV6 channel activity and TRPV6-mediated Ca2+ influx in cells, apparently affecting the localization and density of the calcium channels in the plasma membrane of Jurkat T cells.

Current evidence for vitamin D in intestinal function and disease

Vitamin D activity is associated with the modulation of a wide variety of biological systems, in addition to its roles in calcium homeostatic mechanisms. While vitamin D is well known to promote gastrointestinal calcium absorption, vitamin D also plays a role in attenuating and/or preventing the progression of several gastrointestinal diseases including Crohn’s disease, ulcerative colitis, and colorectal cancer, and may also play a role in chemotherapy-induced intestinal mucositis. The pro-differentiation, immunomodulatory, and anti-inflammatory effects of vitamin D, which has been reported in numerous circumstances, are key potential mechanisms of action in the prevention of gastrointestinal disorders. While the debate of the effectiveness of vitamin D to treat bone pathologies continues, the clinical importance of vitamin D therapy to prevent gastrointestinal disorders should be investigated given current evidence, using both nutritional and pharmaceutical intervention approaches.

Impact statement

The non-skeletal functions of vitamin D play an important role in health and disease. The anti-inflammatory properties and maintenance of intestinal function fulfilled by vitamin D impact other systems in the body though downstream processing. This review provides insight into the mechanisms underpinning the potential benefits of vitamin D in both maintaining intestinal homeostasis and associated diseased states.

Age-related changes in the shell gland and duodenum in relation to shell quality and bone strength in commercial laying hen hybrids

Background

During the production period of laying hens, the number of cracked eggshells increases and the skeleton becomes brittle. Both these problems are related to ageing of the hen and cause economic problems for egg producers and impaired animal welfare. This study investigated key factors in the shell gland and duodenum related to eggshell quality and bone strength in laying hens during the production period. Five Lohmann Selected Leghorn (LSL) and five Lohmann Brown (LB), common hybrids in commercial egg production, were euthanized at 21, 29, 49 and 70 weeks (wk) of age. Blood samples for analysis of total calcium were taken at euthanization. Right femur and humerus were used for bone strength measurements and tissue samples from shell gland and duodenum were processed for morphology, immunohistochemical localisation of oestrogen receptors (ERα, ERβ), plasma membrane calcium ATPase (PMCA) and histochemical localisation of carbonic anhydrases (CA). Eggs were collected for shell quality measurements.

Results

At age 49 week, shell and bone strength had both deteriorated, but the hens were then able to maintain the level until 70 week of age and femur bone strength even improved. The main physiological findings associated with the effects seen at 49 week were reduced gland density and a shift in balance between ERα and ERβ in the shell gland, which coincided with a reduction in CA activity in the duodenum. Somewhat surprisingly, capillary density and capillaries with CA activity both increased in the shell gland over time, the latter possibly mediated via ERβ. These findings were independent of hybrid. PMCA was found in both shell gland and duodenum, but appeared unrelated to the age-related changes in shell and bone quality.

Conclusions

In hens around half-way through the production period, both shell quality and bone strength had deteriorated. Decreased gland density and a shift in the balance between ERα and ERβ in the shell gland, co-occurring with a dramatic drop in duodenal CA activity, are suggested as possible factors involved in age-related changes in shell and bone quality.

Electronic supplementary material

The online version of this article (10.1186/s13028-019-0449-1) contains supplementary material, which is available to authorized users.

Intestinal clock system regulates skeletal homeostasis

The circadian clock network is an evolutionarily conserved system involved in the regulation of metabolic homeostasis; however, its impacts on skeletal metabolism remain largely unknown. We herein demonstrated that the circadian clock network in the intestines plays pivotal roles in skeletal metabolism such that the lack of the Bmal1 gene in the intestines (Bmal1Int-/- mice) caused bone loss, with bone resorption being activated and bone formation suppressed. Mechanistically, Clock protein interaction with the vitamin D receptor (VDR) accelerated its binding to the VDR response element by enhancing histone acetylation in a circadian-dependent manner, and this was lost in Bmal1Int-/- mice because nuclear translocation of Clock required the presence of Bmal1. Accordingly, the rhythmic expression of VDR target genes involved in transcellular calcium (Ca) absorption was created, and this was not observed in Bmal1Int-/- mice. As a result, transcellular Ca absorption was impaired and bone resorption was activated in Bmal1Int-/- mice. Additionally, sympathetic tone, the activation of which suppresses bone formation, was elevated through afferent vagal nerves in Bmal1Int-/- mice, the blockade of which partially recovered bone loss by increasing bone formation and suppressing bone resorption in Bmal1Int-/- mice. These results demonstrate that the intestinal circadian system regulates skeletal bone homeostasis.

Maternal vitamin D deficiency and developmental origins of health and disease (DOHaD)

Vitamin D is an essential nutrient that is metabolized in the body to generate an active metabolite (1,25(OH)2D) with hormone-like activity and highly diverse roles in cellular function. Vitamin D deficiency (VDD) is a prevalent but easily preventable nutritional disturbance. Emerging evidence demonstrates the importance of sufficient vitamin D concentrations during fetal life with deficiencies leading to long-term effects into adulthood. Here, we provide a detailed review and perspective of evidence for the role of maternal VDD in offspring long term health, particularly as it relates to Developmental Origins of Health and Disease (DOHaD). We focus on roles in neurobehavioral and cardiometabolic disorders in humans and highlight recent findings from zebrafish and rodent models that probe potential mechanisms linking early life VDD to later life health outcomes. Moreover, we explore evidence implicating epigenetic mechanisms as a mediator of this link. Gaps in our current understanding of how maternal VDD might result in deleterious offspring outcomes later in life are also addressed.

Longitudinal changes in serum vitamin D binding protein and free 25-hydroxyvitamin D in a multiracial cohort of pregnant adolescents

Serum free 25-hydroxyvitamin D (25(OH)D) rather than total 25(OH)D may better indicate vitamin D status during pregnancy given the pregnancy-associated increase in serum vitamin D binding protein (DBP) concentration. Our aims were to assess changes in DBP and free 25(OH)D across gestation and to determine whether free compared with total 25(OH)D more strongly correlates with markers of vitamin D and calcium metabolism during pregnancy. This ancillary study included 58 pregnant adolescents (53% African American, 47% White) who completed a vitamin D3 supplementation study in Rochester, NY. Blood was collected at entry, mid-study, and delivery (median 17, 29, and 40 weeks' gestation). Mixed-effects regression was used to test for differences in DBP, directly measured free 25(OH)D, and other serum markers by study visit and race. Free and total 25(OH)D were evaluated in relation to serum PTH, 1,25(OH)2D, 24,25(OH)2D, and calcium. The mean DBP concentration was above nonpregnant reference values at entry and increased across gestation (P < 0.0001). Total 25(OH)D explained most of the variance in free 25(OH)D (r ≥ 0.67; P < 0.0001). Holding total 25(OH)D constant, each 100 mg/L increase in DBP was associated with a 0.4 pg/mL decrease in free 25(OH)D (P < 0.01). The percent free 25(OH)D was inversely related to both DBP and total 25(OH)D at each visit. Regardless of race or visit, total 25(OH)D was a stronger correlate of PTH, 1,25(OH)2D, and 24,25(OH)2D, and neither total nor free 25(OH)D was related to serum calcium. African Americans had lower total 25(OH)D (P <  0.0001), but free 25(OH)D did not significantly differ by race (P =  0.2). In pregnant adolescents, DBP concentration was elevated and inversely associated with percent free 25(OH)D, but measured free 25(OH)D provided no advantage over total 25(OH)D as a predictor of PTH, 1,25(OH)2D, 24,25(OH)2D, or calcium. The clinical relevance of the small racial difference in percent free 25(OH)D requires further investigation.

Novel effects of phytoestrogenic soy isoflavones on serum calcium and chloride in premenopausal women: A 2-year double-blind, randomized, placebo-controlled study

BACKGROUND

Soy phytoestrogens are potential alternatives to postmenopausal hormone replacement therapy (HRT). Adverse effects of HRT such as myocardial infarction, stroke, and pulmonary embolism are mediated by calcium-induced signaling.

OBJECTIVE

To determine whether soy isoflavones affect serum calcium in healthy female subjects.

DESIGN

In a double-blind trial, 197 premenopausal women were randomly assigned to either isoflavone (N = 99) or placebo pills (N = 98) 5 days per week for up to 2 years, plus prenatal vitamins. Isoflavone pills contained 60 mg genistein, 60 mg daidzein and 16.6 mg glycitein (expressed as aglycone equivalents). All pills contained 15 mg riboflavin as an adherence marker. Blood chemistries and urinary daidzein, genistein and riboflavin were measured multiple times during the luteal phase before and during treatment.

RESULTS

Analysis of the adherent population (N = 83 per group), revealed significantly strong associations between urinary levels of isoflavones and serum concentrations of calcium (regression coefficients 0.082 for daidzein and 0.229 for genistein, all P < 0.01) and chloride (regression coefficient, -1.537 for genistein, P < 0.0001), mediated in part by albumin. The effects amounted to mean changes of +0.24 mg/dL for calcium and -1.45 mEq/L for chloride, with each visit for subjects excreting the most vs. the least amounts of isoflavones. These associations were not evident in the intention-to-treat analysis (N = 197) that did not assess expected variations in isoflavone levels within and between subjects from metabolism and adherence.

CONCLUSIONS

These novel and strong effects of soy isoflavones on calcium homeostasis have important implications for long term effects of these natural substances on cardiovascular diseases.

Intestinal calcium transport and its regulation in thalassemia: interaction between calcium and iron metabolism

Osteoporosis and derangement of calcium homeostasis are common complications of thalassemia. Despite being an important process for bone and calcium metabolism, little is known about intestinal calcium transport in thalassemia. Recent reports of decreases in both intestinal calcium transport and bone mineral density in thalassemic patients and animal models suggested that defective calcium absorption might be a cause of thalassemic bone disorder. Herein, the possible mechanisms associated with intestinal calcium malabsorption in thalassemia are discussed. This includes alterations in the calcium transporters and hormonal controls of the transcellular and paracellular intestinal transport systems in thalassemia. In addition, the effects of iron overload on intestinal calcium absorption, and the reciprocal interaction between iron and calcium transport in thalassemia are elaborated. Understanding the mechanisms underlining calcium malabsorption in thalassemia would lead to development of therapeutic agents and mineral supplements that restore calcium absorption as well as prevent osteoporosis in thalassemic patients.

5α-dihydrotestosterone reduces renal Cyp24a1 expression via suppression of progesterone receptor

Androgens act in concert with vitamin D to influence reabsorption of calcium. However, it is unclear whether androgens directly regulate vitamin D homeostasis or control other cellular events that are related to vitamin D metabolism. To examine whether the expression of vitamin D-related genes in mouse kidney is driven by androgens or androgen-dependent effects, the androgen receptor and other sex steroid receptors were monitored in orchidectomized mice treated with 5α-dihydrotestosterone (DHT). Our results revealed that exposing orchidectomized mice to DHT inhibited the expression of progesterone receptor (Pgr) with or without estrogen receptor α expression, the latter was confirmed by ER-positive (MCF7 and T47D) or -negative (PCT) cells analysis. The loss of Pgr in turn decreased the expression of renal 24-hydroxylase via transcriptional regulation because Cyp24a1 gene has a progesterone receptor-binding site on promoter. When male kidneys preferentially hydroxylate 25-hydroxyvitamin D₃ using 24-hydroxylase rather than 25-hydroxyvitamin D₃-1-alpha hydroxylase, DHT suppressed the Pgr-mediated 24-hydroxylase expression, and it is important to note that DHT increased the blood 25-hydroxyvitamin D₃ levels. These findings uncover an important link between androgens and vitamin D homeostasis and suggest that therapeutic modulation of Pgr may be used to treat vitamin D deficiency and related disorders.

Intestinal microbiota: a potential target for the treatment of postmenopausal osteoporosis

Postmenopausal osteoporosis (PMO) is a prevalent metabolic bone disease characterized by bone loss and structural destruction, which increases the risk of fracture in postmenopausal women. Owing to the high morbidity and serious complications of PMO, many efforts have been devoted to its prophylaxis and treatment. The intestinal microbiota is the complex community of microorganisms colonizing the gastrointestinal tract. Probiotics, which are dietary or medical supplements consisting of beneficial intestinal bacteria, work in concert with endogenous intestinal microorganisms to maintain host health. Recent studies have revealed that bone loss in PMO is closely related to host immunity, which is influenced by the intestinal microbiota. The curative effects of probiotics on metabolic bone diseases have also been demonstrated. The effects of the intestinal microbiota on bone metabolism suggest a promising target for PMO management. This review seeks to summarize the critical effects of the intestinal microbiota and probiotics on PMO, with a focus on the molecular mechanisms underlying the pathogenic relationship between bacteria and host, and to define the possible treatment options.

Expression of transcellular and paracellular calcium and magnesium transport proteins in renal and intestinal epithelia during lactation

Significant alterations in maternal calcium (Ca2+) and magnesium (Mg2+) balance occur during lactation. Ca2+ is the primary divalent cation mobilized into breast milk by demineralization of the skeleton and alterations in intestinal and renal Ca2+ transport. Mg2+ is also concentrated in breast milk, but the underlying mechanisms are not well understood. To determine the molecular alterations in Ca2+ and Mg2+ transport in the intestine and kidney during lactation, three groups of female mice consisting of either nonpregnant controls, lactating mice, or mice undergoing involution were examined. The fractional excretion of Ca2+, but not Mg2+, rose significantly during lactation. Renal 1-α hydroxylase and 24-OHase mRNA levels increased markedly, as did plasma 1,25 dihydroxyvitamin D levels. This was accompanied by significant increases in intestinal expression of Trpv6 and S100g in lactating mice. However, no alterations in the expression of cation-permeable claudin-2, claudin-12, or claudins-15 were found in the intestine. In the kidney, increased expression of Trpv5 and Calb1 was observed during lactation, while no changes in claudins involved in Ca2+ and Mg2+ transport (claudin-2, claudin-14, claudin-16, or claudin-19) were found. Consistent with the mRNA expression, expression of both calbindin-D28K and transient receptor potential vanilloid 5 (TRPV5) proteins increased. Colonic Trpm6 expression increased during lactation, while renal Trpm6 remained unaltered. In conclusion, proteins involved in transcellular Ca2+ and Mg2+ transport pathways increase during lactation, while expression of paracellular transport proteins remained unchanged. Increased fractional Ca2+ excretion can be explained by vitamin D-dependent intestinal hyperabsorption and bone demineralization, despite enhanced transcellular Ca2+ uptake by the kidney.

The Plasma Membrane Calcium ATPases and Their Role as Major New Players in Human Disease

The Ca²⁺ extrusion function of the four mammalian isoforms of the plasma membrane calcium ATPases (PMCAs) is well established. There is also ever-increasing detail known of their roles in global and local Ca²⁺ homeostasis and intracellular Ca²⁺ signaling in a wide variety of cell types and tissues. It is becoming clear that the spatiotemporal patterns of expression of the PMCAs and the fact that their abundances and relative expression levels vary from cell type to cell type both reflect and impact on their specific functions in these cells. Over recent years it has become increasingly apparent that these genes have potentially significant roles in human health and disease, with PMCAs1-4 being associated with cardiovascular diseases, deafness, autism, ataxia, adenoma, and malarial resistance. This review will bring together evidence of the variety of tissue-specific functions of PMCAs and will highlight the roles these genes play in regulating normal physiological functions and the considerable impact the genes have on human disease.