Vitamin D and the intestine: Review and update

Critical Role for 24-Hydroxylation in Homeostatic Regulation of Vitamin D Metabolism

CONTEXT

The body has evolved homeostatic mechanisms to maintain free levels of Ca+2 and 1,25-dihydroxyvitamin D (1,25(OH)2D) within narrow physiological ranges. Clinical guidelines emphasize important contributions of parathyroid hormone (PTH) in maintaining this homeostasis.

OBJECTIVE

This work aimed to investigate mechanisms of homeostatic regulation of vitamin D (VitD) metabolism and to apply mechanistic insights to improve clinical assessment of VitD status.

METHODS

This crossover clinical trial studied community participants before and after VitD3 supplementation. Participants included 11 otherwise healthy individuals with VitD deficiency (25-hydroxyvitamin D [25(OH)D] ≤20 ng/mL). VitD3 supplements (50 000 IU once or twice a week depending on body mass index, for 4-6 weeks) were administered to achieve 25(OH)D of 30 ng/mL or greater.

RESULTS

VitD3 supplementation significantly increased mean 25(OH)D by 2.7-fold and 24,25-dihydroxyvitamin D (24,25(OH)2D) by 4.3-fold. In contrast, mean levels of PTH, fibroblast growth factor-23, and 1,25(OH)2D did not change. Mathematical modeling suggested that 24-hydroxylase activity was maximal for 25(OH)D 50 ng/mL or greater and achieved a minimum (∼90% suppression) with 25(OH)D less than 10 to 20 ng/mL. The 1,25(OH)2D/24,25(OH)2D ratio better predicted modeled 24-hydroxylase activity (h) (ρ = -0.85; P = .001) compared to total plasma 25(OH)D (ρ = 0.51; P = .01) and the 24,25(OH)2D/25(OH)D ratio (ρ = 0.37; P = .3).

CONCLUSION

Suppression of 24-hydroxylase provides a first line of defense against symptomatic VitD deficiency by decreasing metabolic clearance of 1,25(OH)2D. The 1,25(OH)2D/24,25(OH)2D ratio provides a useful index of VitD status since it incorporates 24,25(OH)2D levels, and therefore provides insight into 24-hydroxylase activity. When VitD availability is limited, this suppresses 24-hydroxylase activity-thereby decreasing the level of 24,25(OH)2D and increasing the 1,25(OH)2D/24,25(OH)2D ratio. Thus, an increased 1,25(OH)2D/24,25(OH)2D ratio signifies triggering of homeostatic regulation, which occurs at early stages of VitD deficiency.

Bioinformatics analysis of colorectal cancer transcriptomic data reveals novel prognostic signature and potential biomarker genes

OBJECTIVE

Colorectal cancer (CRC) is a type of digestive system cancer. At the molecular level, some factors, including genetic and epigenetic factors, as well as various signaling pathways such as oxidative stress and inflammation, play an active role in the onset of CRC. Genetic and epigenetic mutations, particularly in oncogenes and tumor suppressor genes, occur during colorectal adenocarcinoma development as a result of a change in gastrointestinal epithelial cell proliferation and self-renewal rates. This study aimed to determine the genes and molecular mechanisms that play a role in the emergence of this disease by analyzing the CRC data.

MATERIAL AND METHODS

Microarray data selected for bioinformatics analysis is Gene Expression data stored with the code GSE110224 in the National Center for Biotechnology Information (NCBI) Gene Expression Omnibus (GEO) database. Gene expression analysis, functional clustering analysis, enrichment analysis, and pathway analysis were performed using this data set.

RESULTS

Analysis of raw transcriptomic data revealed 1770 common DEGs in CRC. While the expression level of 769 of these genes increased, the expression level of 1001 genes decreased. A Protein-protein interaction (PPI) network was created from the first 25 genes with increased expression levels and 11 signature genes were identified. Increased expression of REG1A, MMP3, FOXQ1 and CEMIP genes and decreased expression of AQP8, CA1, CLDN8, PYY, CA4, CEACAM7 and SLC30A10 genes were observed.

CONCLUSIONS

This approach revealed a CRC-specific molecular profile and may provide some guidance for further investigation of potential biomarkers for diagnosis and prognosis prediction of CRC patients.

In Vivo Contribution of Cyp24a1 Promoter Vitamin D Response Elements

CYP24A1 is a multifunctional, P450 mitochondrial enzyme that catabolizes the vitamin D hormone (calcitriol, 1,25(OH)2D3), its precursor (calcifediol, 25(OH)D3), and numerous vitamin D metabolites. In the kidney, Cyp24a1 is induced by 1,25(OH)2D3 and fibroblast growth factor 23 (FGF23) and potently suppressed by PTH to control the circulating levels of 1,25(OH)2D3. Cyp24a1 is controlled by a pair of promoter proximal (PRO) vitamin D response elements (VDREs) that are aided by distal, downstream (DS) enhancers. The downstream 1 region of Cyp24a1 (DS1) enhancer is kidney-specific and responsible for PTH and FGF23 actions, and the downstream 2 region of Cyp24a1 enhancer responds to 1,25(OH)2D3 in all tissues. Despite this knowledge, in vivo contributions of the PRO VDREs to basal expression, FGF23 activation, and PTH suppression of Cyp24a1 remain unknown. In this study, we selectively mutated the PRO VDREs in the mouse to address these questions. We found mutation of the VDREs leads to a dramatic loss of VDR occupancy, a reduction of 1,25(OH)D3-induced kidney Cyp24a1 expression, and near elimination of intestinal Cyp24a1 induction. FGF23 induction of Cyp24a1 was reduced but not eliminated and still showed a synergistic increase with 1,25(OH)2D3. PTH suppression of Cyp24a1 was unchanged, despite minor reductions in total for phosphorylated cAMP-response element binding protein occupancy. Finally, VDR recruitment was dramatically reduced across the DS enhancers in the Cyp24a1 locus. Taken together, our data suggest a cooperative relationship between the DS and PRO enhancers in the regulation of Cyp24a1 by 1,25(OH)2D3 and FGF23 and points to the DS1 region as a crucial basal switch for Cyp24a1 activity that further defines the interconnected genomic control in vitamin D catabolism.

Target Values for 25-Hydroxy and 1,25-Dihydroxy Vitamin D Based on Their Associations with Inflammation and Calcium-Phosphate Metabolism

Target values for 25-hydroxy vitamin D and 1,25(OH)2D or 1,25-dihydroxy vitamin D remain a topic of debate among clinicians. We analysed data collected from December 2012 to April 2020 from two cohorts. Cohort A, comprising 455,062 subjects, was used to investigate the relationship between inflammatory indicators (white blood cell [WBC] count and C-reactive protein [CRP]) and 25(OH)D/1,25(OH)2D. Cohort B, including 47,778 subjects, was used to investigate the connection between 25(OH)D/1,25(OH)2D and mineral metabolism markers (phosphate, calcium, and intact parathyroid hormone [iPTH]). Quadratic models fit best for all tested correlations, revealing U-shaped relationships between inflammatory indicators and 25(OH)D and 1,25(OH)2D. Minimal CRP and WBC counts were observed at 1,25(OH)2D levels of 60 pg/mL and at 25(OH)D levels of 32 ng/mL, as well as of 42 ng/mL, respectively. iPTH correlated inversely with both 1,25(OH)2D and 25(OH)D, while phosphate as well as calcium levels positively correlated with both vitamin D forms. Calcium-phosphate product increased sharply when 25(OH)D was more than 50 ng/mL, indicating a possible risk for vascular calcification. Multiple regression analyses confirmed that these correlations were independent of confounders. This study suggests target values for 25(OH)D between 30-50 ng/mL and for 1,25(OH)2D between 50-70 pg/mL, based particularly on their associations with inflammation but also with mineral metabolism markers. These findings contribute to the ongoing discussion around ideal levels of vitamin D but require support from independent studies with data on clinical endpoints.

Chronic Atrophic Autoimmune Gastritis: The Evolving Role of Vitamin D

Vitamin D possesses a crucial role in preserving bone health, modulating the immune system responses, and supporting various physiological functions throughout the body. Chronic atrophic autoimmune gastritis (CAAG) constitutes an autoimmune condition marked by inflammation and damage to the stomach cells, often resulting in a decreased ability to absorb certain nutrients, including vitamin B12 and iron. Although, vitamin D is not directly affected by this condition, the sufficiency of this micronutrient seems to have important implications for overall health and management of the disease. The aim of the current review was to assess the incidence and related features of vitamin D deficiency in patients with CAAG and to elucidate the complex regulatory role of this nutrient, in an effort to improve patient outcomes. Vitamin D greatly contributes to the regulation of the immune system. In patients with CAAG, the immune system attacks the stomach lining; thus, the maintenance of a healthy and balanced immune response is important. In autoimmune conditions such as CAAG, where inflammation plays a decisive role in disease progression, vitamin D could potentially exert a role in managing and controlling the associated symptoms. Adequate vitamin D levels may help in regulating the immune response and reducing inflammation. In addition, patients with CAAG are at risk of nutrient deficiencies, including vitamin B12 and iron, which can lead to anemia and bone health issues. As vitamin D is critical for calcium absorption and bone health, assurance of sufficient levels of this micronutrient can be beneficial in preventing or mitigating bone-related complications. In conclusion, regular monitoring of vitamin D levels, among other nutrients, and appropriate supplementation, when necessary, can help improve overall health and well-being in these patients.

Increased calcium intake from skimmed milk in energy-restricted diets reduces glycation markers in adults with type 2 diabetes and overweight: A secondary analysis of a randomized clinical trial

The effect of calcium (Ca) on glycation markers is unknown. We hypothesized that increased Ca intake from skimmed milk associated with an energy-restricted diet intake will reduce glycation markers. This reduction will be associated with a greater improvement in markers of metabolic control in adults with type 2 diabetes, overweight, and low habitual Ca intake (<600 mg/d). In this secondary data analysis based on a crossover clinical trial, 14 adults were allocated into 2 groups: high calcium (shake containing 700 mg Ca/day) or low calcium (shake with 6.4 mg Ca/day), for 12 consecutive weeks per session. Energy-restricted diets were also prescribed (-500 kcal/d, 800 mg of dietary Ca/d) to all participants. Advanced glycation end products (AGEs), soluble receptor for AGEs (sRAGE), glycemic control, and lipid profile were assessed at baseline and after 12 weeks. High-calcium serum AGE concentrations and AGE/sRAGE ratio were lower at the end of the study. ΔAGE and ΔAGE/sRAGE ratio were both positively associated with Δtriglycerides, Δtotal cholesterol, Δtriglyceride-glucose index and variations, and Δvisceral adiposity index. ΔAGE/sRAGE was positively associated with Δfructosamine and Δhigh-density lipoprotein-cholesterol, and negatively associated with male sex. Consumption of approximately 1200 mg/day of calcium (3 servings of skim milk) reduced serum AGEs concentrations and the AGE/sRAGE ratio in individuals with diabetes. In general, positive changes in glycation markers are associated with lipid profile, insulin resistance, and adiposity markers worsening. ΔAGEs/ΔsRAGE ratio seems to be a better marker of metabolic status than ΔAGEs and ΔsRAGE alone. Registered in ClinicalTrials.gov (NCT02377076).

Vitamin D opposes multilineage cell differentiation induced by Notch inhibition and BMP4 pathway activation in human colon organoids

Understanding the mechanisms involved in colonic epithelial differentiation is key to unraveling the alterations causing inflammatory conditions and cancer. Organoid cultures provide an unique tool to address these questions but studies are scarce. We report a differentiation system toward enterocytes and goblet cells, the two major colonic epithelial cell lineages, using colon organoids generated from healthy tissue of colorectal cancer patients. Culture of these organoids in medium lacking stemness agents resulted in a modest ultrastructural differentiation phenotype with low-level expression of enterocyte (KLF4, KRT20, CA1, FABP2) and goblet cell (TFF2, TFF3, AGR2) lineage markers. BMP pathway activation through depletion of Noggin and addition of BMP4 resulted in enterocyte-biased differentiation. Contrarily, blockade of the Notch pathway using the γ-secretase inhibitor dibenzazepine (DBZ) favored goblet cell differentiation. Combination treatment with BMP4 and DBZ caused a balanced strong induction of both lineages. In contrast, colon tumor organoids responded poorly to BMP4 showing only weak signals of cell differentiation, and were unresponsive to DBZ. We also investigated the effects of 1α,25-dihydroxyvitamin D3 (calcitriol) on differentiation. Calcitriol attenuated the effects of BMP4 and DBZ on colon normal organoids, with reduced expression of differentiation genes and phenotype. Consistently, in normal organoids, calcitriol inhibited early signaling by BMP4 as assessed by reduction of the level of phospho-SMAD1/5/8. Our results show that BMP and Notch signaling play key roles in human colon stem cell differentiation to the enterocytic and goblet cell lineages and that calcitriol modulates these processes favoring stemness features.

The Molecular Mechanisms Underlying the Systemic Effects Mediated by Parathormone in the Context of Chronic Kidney Disease

Chronic kidney disease (CKD) stands as a prominent non-communicable ailment, significantly impacting life expectancy. Physiopathology stands mainly upon the triangle represented by parathormone-Vitamin D-Fibroblast Growth Factor-23. Parathormone (PTH), the key hormone in mineral homeostasis, is one of the less easily modifiable parameters in CKD; however, it stands as a significant marker for assessing the risk of complications. The updated "trade-off hypothesis" reveals that levels of PTH spike out of the normal range as early as stage G2 CKD, advancing it as a possible determinant of systemic damage. The present review aims to review the effects exhibited by PTH on several organs while linking the molecular mechanisms to the observed actions in the context of CKD. From a diagnostic perspective, PTH is the most reliable and accessible biochemical marker in CKD, but its trend bears a higher significance on a patient's prognosis rather than the absolute value. Classically, PTH acts in a dichotomous manner on bone tissue, maintaining a balance between formation and resorption. Under the uremic conditions of advanced CKD, the altered intestinal microbiota majorly tips the balance towards bone lysis. Probiotic treatment has proven reliable in animal models, but in humans, data are limited. Regarding bone status, persistently high levels of PTH determine a reduction in mineral density and a concurrent increase in fracture risk. Pharmacological manipulation of serum PTH requires appropriate patient selection and monitoring since dangerously low levels of PTH may completely inhibit bone turnover. Moreover, the altered mineral balance extends to the cardiovascular system, promoting vascular calcifications. Lastly, the involvement of PTH in the Renin-Angiotensin-Aldosterone axis highlights the importance of opting for the appropriate pharmacological agent should hypertension develop.

Anti-inflammatory effects of bay laurel (Laurus nobilis L.) towards the gut microbiome in dextran sodium sulfate induced colitis animal models

Bay laurel (Laurus nobilis L.) contains active antioxidative phenolic components that are beneficial to human health. However, none was examined and reported utilizing health effects related to inflammatory bowel diseases (IBD) mainly ulcerative colitis (UC) in correlation to gut microbiota (GM). Thus, the current study aimed to investigate the impacts of bay leaves on UC albino rats targeting on the GM composition and their metabolites production (i.e., short-chain fatty acids; SCFAs) for improving the gut barrier functions. UC models were induced by supplementing 5% DSS into their drinking water. The models were then divided randomly for the diet with 1%, 2%, and 3% of bay leaves, as well as two control studies (positive and negative). Colon-to-body weight ratio was used as an indicator for the presence of edema tissue. From the collected fecal samples at 0, 24 h, and final day, the population changes of gut microbiota (Lactobacillus, Bifidobacteria, Clostridium, and sulfate-reducing bacteria) and SCFAs production were evaluated using fluorescence in situ hybridization (FISH) and gas-liquid chromatography (GC). The colon-to-body weight ratio of the rat models consuming 2% and 3% bay leaves was found to be significantly lower with better recovery of colonic function. Models consuming 3% bay leaves showed the best treatment effects on GM compositions; promoting the growth of Bifidobacteria and Lactobacillus in addition to producing high butyric acid levels. Meanwhile, the number of Clostridium and SRB was significantly reduced. Conclusively, consuming bay leaves brought significant colon health benefits other than stimulating appetite for a better taste.

The role of vitamin D deficiency in the development of paediatric diseases

Children's Vitamin D (VitD) fortification and supplementation are diminishing due to less outdoor exercise and insufficient VitD intake (low exogenous intake and endogenous malabsorption induced by gastrointestinal disease). Consequently, children in many developed countries suffer from VitD deficiency, which may contribute to many paediatric disorders. Our review briefly introduced the metabolic process of VitD, summarized the role of VitD in paediatric diseases such as autism, obesity, rickets and asthma. We sought to identify the link between VitD deficiency and these diseases.

Structure-activity relationship studies on vitamin D-based selective SREBP/SCAP inhibitor KK-052

Vitamin D3 metabolites block lipid biosynthesis by promoting degradation of the complex of sterol regulatory element-binding protein (SREBP) and SREBP cleavage-activating protein (SCAP) independent of their effects on the vitamin D receptor (VDR). We previously reported the development of KK-052, the first vitamin D-based SREBP inhibitor that mitigates hepatic lipid accumulation without VDR-mediated calcemic action in mice. Herein we extend our previous work to synthesize KK-052 analogues. Various substituents were introduced to the phenyl ring of KK-052, and two KK-052 analogues were found to exhibit more potent SREBP/SCAP inhibitory activity than KK-052, whereas they all lack VDR activity. These new KK-052 analogues may be suited for further development as VDR-silent SREBP/SCAP inhibitors.

Maternal Epidermal Growth Factor Promotes Neonatal Claudin-2 Dependent Increases in Small Intestinal Calcium Permeability

A higher concentration of calcium in breast milk than blood favors paracellular calcium absorption enabling growth during postnatal development. We aimed to determine whether suckling animals have greater intestinal calcium permeability to maximize absorption and to identify the underlying molecular mechanism. We examined intestinal claudin expression at different ages in mice and in human intestinal epithelial (Caco-2) cells in response to hormones or human milk. We also measured intestinal calcium permeability in wildtype, Cldn2 and Cldn12 KO mice and Caco-2 cells in response to hormones or human milk. Bone mineralization in mice was assessed by μCT. Calcium permeability across the jejunum and ileum of mice were 2-fold greater at 2 wk than 2 mo postnatal age. At 2 wk, Cldn2 and Cldn12 expression were greater, but only Cldn2 KO mice had decreased calcium permeability compared to wildtype. This translated to decreased bone volume, cross-sectional thickness, and tissue mineral density of femurs. Weaning from breast milk led to a 50% decrease in Cldn2 expression in the jejunum and ileum. Epidermal growth factor (EGF) in breast milk specifically increased only CLDN2 expression and calcium permeability in Caco-2 cells. These data support intestinal permeability to calcium, conferred by claudin-2, being greater in suckling mice and being driven by EGF in breast milk. Loss of the CLDN2 pathway leads to suboptimal bone mineralization at 2 wk of life. Overall, EGF-mediated control of intestinal claudin-2 expression contributes to maximal intestinal calcium absorption in suckling animals.

Role of Coactivator Associated Arginine Methyltransferase 1 (CARM1) in the Regulation of the Biological Function of 1,25-Dihydroxyvitamin D3

1,25-Dihydroxyvitamin D3 (1,25(OH)₂D₃), the hormonally active form of vitamin D, activates the nuclear vitamin D receptor (VDR) to mediate the transcription of target genes involved in calcium homeostasis as well as in non-classical 1,25(OH)₂D₃ actions. In this study, CARM1, an arginine methyltransferase, was found to mediate coactivator synergy in the presence of GRIP1 (a primary coactivator) and to cooperate with G9a, a lysine methyltransferase, in 1,25(OH)₂D₃ induced transcription of Cyp24a1 (the gene involved in the metabolic inactivation of 1,25(OH)₂D₃). In mouse proximal renal tubule (MPCT) cells and in mouse kidney, chromatin immunoprecipitation analysis demonstrated that dimethylation of histone H3 at arginine 17, which is mediated by CARM1, occurs at Cyp24a1 vitamin D response elements in a 1,25(OH)₂D₃ dependent manner. Treatment with TBBD, an inhibitor of CARM1, repressed 1,25(OH)₂D₃ induced Cyp24a1 expression in MPCT cells, further suggesting that CARM1 is a significant coactivator of 1,25(OH)₂D₃ induction of renal Cyp24a1 expression. CARM1 was found to act as a repressor of second messenger-mediated induction of the transcription of CYP27B1 (involved in the synthesis of 1,25(OH)₂D₃), supporting the role of CARM1 as a dual function coregulator. Our findings indicate a key role for CARM1 in the regulation of the biological function of 1,25(OH)₂D₃.

Effect of vitamin D metabolites on bone histomorphometry in healthy black and white women: An attempt to unravel the so-called vitamin D paradox in blacks

An apparent vitamin D paradox, characterized by lower serum 25-hydroxyvitamin D (25(OH)D) levels and higher bone mineral density, is present in black population. In contrast, blacks have higher serum 1,25-dihydroxyvitamin D (1,25(OH)₂D) levels. The effect of 1,25(OH)₂D on the skeleton is not fully understood. We examined serum 25(OH)D, 1,25(OH)₂D and bone histomorphometry in 50 black and white women (25 each) matched for age, menstrual status, and BMI. Histomorphometric indices related to bone structure, remodeling and mineralization were measured in cancellous bone in iliac bone biopsies. Data analyses led to the following results: 1) serum 25(OH)D was significantly lower and 1,25(OH)₂D was significantly higher in black than in white women, but neither blacks nor whites revealed significant correlation between these two vitamin D metabolites. 2) there was no significant difference in PTH levels between blacks and whites. 3) except for greater trabecular thickness (Tb.Th) in blacks, there were no significant differences in other histomorphometric variables between the two ethnic groups. 4) osteoid surface (OS/BS), unlabeled osteoid surface (ulOS/BS), and osteoblast surface (ObS/BS) significantly correlated with serum 1,25(OH)₂D levels. We conclude that lower serum 25(OH)D levels in blacks do not impair bone structure and remodeling, nor decrease bone mineralization. Higher serum 1,25(OH)₂D levels in blacks may help preserve bone mass by stimulating bone formation via increasing osteoblast number and function, but moderately inhibit terminal bone mineralization as shown by higher ulOS/BS.

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-D_9k, PMCA_1b 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 CFTR_inh-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 CFTR_inh-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.

Growth pattern in children with X-linked hypophosphatemia treated with burosumab and growth hormone

BACKGROUND

X-linked hypophosphatemia (XLH) is characterized by increased serum concentrations of fibroblast growth factor 23 (FGF23), hypophosphatemia and insufficient endogenous synthesis of calcitriol. Beside rickets, odonto- and osteomalacia, disproportionate short stature is seen in most affected individuals. Vitamin D analogs and phosphate supplements, i.e., conventional therapy, can improve growth especially when started early in life. Recombinant human growth hormone (rhGH) therapy in XLH children with short stature has positive effects, although few reports are available. Newly available treatment (burosumab) targeting increased FGF23 signaling leads to minimal improvement of growth in XLH children. So far, we lack data on the growth of XLH children treated with concomitant rhGH and burosumab therapies.

RESULTS

Thirty-six patients received burosumab for at least 1 year after switching from conventional therapy. Of these, 23 received burosumab alone, while the others continued rhGH therapy after switching to burosumab. Children treated with burosumab alone showed a minimal change in height SDS after 1 year (mean ± SD 0.0 ± 0.3 prepubertal vs. 0.1 ± 0.3 pubertal participants). In contrast, rhGH clearly improved height during the first year of treatment before initiating burosumab (mean ± SD of height gain 1.0 ± 0.4); patients continued to gain height during the year of combined burosumab and rhGH therapies (mean ± SD height gain 0.2 ± 0.1). As expected, phosphate serum levels normalized upon burosumab therapy. No change in serum calcium levels, urinary calcium excretion, or 25-OHD levels was seen, though 1,25-(OH)₂D increased dramatically under burosumab therapy.

CONCLUSION

To our knowledge, this is the first study on growth under concomitant rhGH and burosumab treatments. We did not observe any safety issue in this cohort of patients which is one of the largest in Europe. Our data suggest that continuing treatment with rhGH after switching from conventional therapy to burosumab, if the height prognosis is compromised, might be beneficial for the final height.

Changes in Metabolic Parameters in Patients with Diabetic Kidney Disease Depending on the Status of D3

BACKGROUND

Type 2 diabetes is a metabolic disease characterized by hyperglycemia as a result of insulin resistance and decreased insulin secretion. A relatively large number of patients with this type of diabetes have abdominal obesity, which also affects insulin resistance development. Chronic hyperglycemia can lead to damage and dysfunction of various organs, and a striking example is diabetic nephropathy. Diabetic nephropathy is a specific kind of kidney damage that occurs due to complications of diabetes and is accompanied by the formation of diffuse or nodular glomerulosclerosis, which can lead to terminal renal failure and requires immediate substitution through renal therapy or renal transplantation. Diabetic nephropathy is diagnosed with albuminuria and a decrease in the rate of glomerular filtration.

METHODS

This review was based on a literature search for the most important evidence of vitamin D as a possible method of prevention for obesity, type 2 diabetes, and diabetic nephropathy. Collected published articles were summarized according to their overall themes.

RESULTS

In this review, we considered vitamin D as a possible method of treatment for type 2 diabetes, as well as its complications, including diabetic nephropathy.

CONCLUSION

Studies show that vitamin D inhibits the renin-angiotensin-aldosterone system, resulting in improved renal function in diabetic nephropathy. Vitamin D also has antiinflammatory, antiproliferative, and anti-metastatic effects, which improve endothelial function.

Epigenomic effects of vitamin D in colorectal cancer

Vitamin D regulates a plethora of physiological processes in the human body and has been proposed to exert several anticancer effects. Epigenetics plays an important role in regulating vitamin D actions. In this review, we highlight the recent advances in the understanding of different epigenetic factors such as lncRNAs, miRNAs, methylation and acetylation influenced by vitamin D and its downstream targets in colorectal cancer to find more potential therapeutic targets. We discuss how vitamin D exerts anticancer properties through interactions between the vitamin D receptor and genes (e.g., SLC30A10), the microenvironment, microbiota and other factors in colorectal cancer. Developing therapeutic approaches targeting the vitamin D signaling system will be aided by a better knowledge of the epigenetic impact of vitamin D.

An emerging role of vitamin D3 in amino acid absorption in different intestinal segments of on-growing grass carp (Ctenopharyngodon idella)

Vitamin D3 (VD3), an essential nutrient for animals, has been demonstrated to stimulate the uptake of certain amino acids. However, the role of VD3 in the intestine, the primary site for digestion and absorption of nutrients, remains poorly characterized. Here, the grass carp (Ctenopharyngodon idella) was studied to assess the influence of different doses of VD3 (15.2, 364.3, 782.5, 1,167.9, 1,573.8, and 1,980.1 IU/kg) on growth performance, intestinal morphology, digestive absorption, amino acid transport, and potential signaling molecule levels in a feeding experiment. As a result, dietary VD3 improved growth performance, intestinal structure, and digestive and brush border enzyme activities. Additionally, most intestinal free amino acids and their transporters were upregulated after VD3 intake, except for Ala, Lys, Asp, Leu, solute carrier (SLC) 7A7, SLC1A5, and SLC1A3 mRNA in different segments, Leu and SLC6A14 mRNA in the proximal intestine, and SLC7A5 mRNA in the mid and distal intestine. In the crucial target of rapamycin (TOR) signal pathway of amino acid transport, the gene and protein expression of TOR, S6 kinase 1, and activating transcription factor 4 were elevated, whereas 4E-binding protein 1 was decreased, further suggesting an advanced amino acid absorption capacity in the fish due to VD3 supplementation. Based on percentage weight gain, feed efficiency, and trypsin activity, the VD3 requirements of on-growing grass carp were estimated to be 968.33, 1,005.00, and 1,166.67 IU/kg, respectively. Our findings provide novel recommendations for VD3 supplementation to promote digestion and absorption capacities of fish, contributing to the overall productivity of aquaculture.

Interdisciplinary management of FGF23-related phosphate wasting syndromes: a Consensus Statement on the evaluation, diagnosis and care of patients with X-linked hypophosphataemia

X-linked hypophosphataemia (XLH) is the most frequent cause of hypophosphataemia-associated rickets of genetic origin and is associated with high levels of the phosphaturic hormone fibroblast growth factor 23 (FGF23). In addition to rickets and osteomalacia, patients with XLH have a heavy disease burden with enthesopathies, osteoarthritis, pseudofractures and dental complications, all of which contribute to reduced quality of life. This Consensus Statement presents the outcomes of a working group of the European Society for Clinical and Economic Aspects of Osteoporosis, Osteoarthritis and Musculoskeletal Diseases, and provides robust clinical evidence on management in XLH, with an emphasis on patients' experiences and needs. During growth, conventional treatment with phosphate supplements and active vitamin D metabolites (such as calcitriol) improves growth, ameliorates leg deformities and dental manifestations, and reduces pain. The continuation of conventional treatment in symptom-free adults is still debated. A novel therapeutic approach is the monoclonal anti-FGF23 antibody burosumab. Although promising, further studies are required to clarify its long-term efficacy, particularly in adults. Given the diversity of symptoms and complications, an interdisciplinary approach to management is of paramount importance. The focus of treatment should be not only on the physical manifestations and challenges associated with XLH and other FGF23-mediated hypophosphataemia syndromes, but also on the major psychological and social impact of the disease.

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 D3 Treatment Alters Thyroid Functional Morphology in Orchidectomized Rat Model of Osteoporosis

Vitamin D plays an essential role in prevention and treatment of osteoporosis. Thyroid hormones, in addition to vitamin D, significantly contribute to regulation of bone remodeling cycle and health. There is currently no data about a possible connection between vitamin D treatment and the thyroid in the context of osteoporosis. Middle-aged Wistar rats were divided into: sham operated (SO), orchidectomized (Orx), and cholecalciferol-treated orchidectomized (Orx + Vit. D₃; 5 µg/kg b.m./day during three weeks) groups (n = 6/group). Concentration of 25(OH)D in serum of the Orx + Vit. D₃ group increased 4 and 3.2 times (p < 0.0001) respectively, compared to Orx and SO group. T_4, TSH, and calcitonin in serum remained unaltered. Vit. D₃ treatment induced changes in thyroid functional morphology that indicate increased utilization of stored colloid and release of thyroid hormones in comparison with hormone synthesis, to maintain hormonal balance. Increased expression of nuclear VDR (p < 0.05) points to direct, TSH independent action of Vit. D on thyrocytes. Strong CYP24A1 immunostaining in C cells suggests its prominent expression in response to Vit. D in this cell subpopulation in orchidectomized rat model of osteoporosis. The indirect effect of Vit. D on bone, through fine regulation of thyroid function, is small.

A robust method for simultaneous measurement of serum 25(OH)D, 1,25(OH)2 D, and 24,25(OH)2 D by liquid chromatography-tandem mass spectrometry with efficient separation of 3-epi analogs, 23R,25(OH)2 D3 , and 4β,25(OH)2 D3

BACKGROUND

This study aimed to establish a robust, simple method to detect 25-hydroxyvitamin D₃ (25(OH)D₃ ), 25-hydroxyvitamin D₂ (25(OH)D₂ ), 1,25-dihydroxyvitamin D₃ (1,25(OH)₂ D₃ ), 1,25-dihydroxyvitamin D₂ (1,25(OH)₂ D₂ ), 24,25-dihydroxyvitamin D₃ (24,25(OH)₂ D₃ ), and 24,25-dihydroxyvitamin D₂ (24,25(OH)₂ D₂ ) simultaneously with efficient separation of 3-epi 25(OH)D₃ , 3-epi 24,25(OH)₂ D₃ , 23R,25(OH)₂ D₃ , and 4β,25-dihydroxyvitamin D₃ (4β,25(OH)₂ D₃ ) by liquid chromatography-tandem mass spectrometry (LC-MS/MS).

METHOD

This method was validated according to procedures established by Clinical and Laboratory Standards Institute (CLSI) and then applied in healthy population to determine the distribution of the vitamin D metabolites by LC-MS/MS.

RESULTS

The total-run CV% of 25(OH)D₃ , 25(OH)D₂ , 24,25(OH)₂ D₃ , 24,25(OH)₂ D₂ , 1,25(OH)₂ D₃ , and 1,25(OH)₂ D₂ were 6.30%-8.40%, 5.00%-8.40%, 5.90%-9.00%, 5.60%-9.00%, 5.60%-8.00%, and 7.00%-9.70%, respectively. The linearity correlation coefficients r of these six vitamin D metabolites were >0.99. The matrix effects of 25(OH)D₃ , 25(OH)D₂ , 24,25(OH)₂ D₃ , 24,25(OH)₂ D₂ , 1,25(OH)₂ D₃ , and 1,25(OH)₂ D₂ were 90.6%-103.3%, 97.3%-106.3%, 90.7%-106.3%, 100.7%-114.5%, 97.9%-104.6%, and 97.0%-111.0%. The trueness values of 25(OH)D₃ , 25(OH)D₂ , and 24,25(OH)₂ D₃ were 93.8%-103.0%, 101.0%, and 96.3%-100%, respectively.

CONCLUSION

This study successfully established an efficient, accurate, robust method for simultaneous measurement of serum 25(OH)D, 1,25(OH)₂ D, and 24,25(OH)₂ D by LC-MS/MS with efficient separation of 3-epi analogs, 23R,25(OH)₂ D₃ , and 4β,25(OH)₂ D₃ .

Higher Genetically Predicted Triglycerides, LDL, and HDL Increase the Vitamin D Deficiency: A Mendelian Randomization Study

Introduction

It has been proven that high body mass index (BMI) levels can cause vitamin D deficiency, but the mechanism is still unclear. Therefore, this study attempts to explain this phenomenon from the perspective of blood lipid by using mendelian randomization (MR).

Methods

Genome-wide association studies (GWAS) summary datasets for serum lipids were obtained from the Global Lipids Genetics Consortium (GLGC). Vitamin D deficiency outcome data were acquired from the UK Biobank samples. Single-variable MR (SVMR) and multi-variable MR (MVMR) analyses were conducted using the TwoSampleMR package based on R 4.0.3. The four main methods were the random-effect inverse-variance weighted (IVW), MR-Egger, weighted-median method, and weighted mode.

Results

In the SVMR of serum lipid/apolipoprotein levels on serum vitamin D level, it was found that elevated serum triacylglycerol (IVW, OR = 0.85, 95%CI:0.81-0.89, P < 0.001), low-density lipoprotein (LDL) (IVW, OR = 0.93, 95%CI:0.90-0.95, P < 0.001), and high-density lipoprotein (HDL) (IVW, OR = 0.95, 95%CI:0.91-0.98, P < 0.001) levels all had a causal relationship with vitamin D deficiency, but significant pleiotropy was detected in the triacylglycerol (P = 0.001) and HDL (P = 0.003) analysis. MVMR analysis results were consistent with SVMR.

Conclusion

By using single-variable mendelian randomization and multi-variable mendelian randomization methods, we identified that the elevated serum triacylglycerol, LDL, and HDL levels all had a causal relationship with vitamin D deficiency. Taking into account the significant pleiotropy demonstrated in this study, the conclusions of this study should be treated with caution.

Physiology of Calcium Homeostasis: An Overview

Calcium plays a key role in skeletal mineralization and several intracellular and extracellular homeostatic networks. It is an essential element that is only available to the body through dietary sources. Daily acquisition of calcium depends, in addition to the actual intake, on the hormonally regulated state of calcium homeostasis through three main mechanisms: bone turnover, intestinal absorption, and renal reabsorption. These procedures are regulated by a group of interacting circulating hormones and their key receptors. This includes parathyroid hormone (PTH), PTH-related peptide, 1,25-dihydroxyvitamin D, calcitonin, fibroblast growth factor 23, the prevailing calcium concentration itself, the calcium-sensing receptor, as well as local processes in the bones, gut, and kidneys.

Claudin-2 and claudin-12 form independent, complementary pores required to maintain calcium homeostasis

Calcium (Ca2+) homeostasis is maintained through coordination between intestinal absorption, renal reabsorption, and bone remodeling. Intestinal and renal (re)absorption occurs via transcellular and paracellular pathways. The latter contributes the bulk of (re)absorption under conditions of adequate intake. Epithelial paracellular permeability is conferred by tight-junction proteins called claudins. However, the molecular identity of the paracellular Ca2+ pore remains to be delineated. Claudins (Cldn)-2 and -12 confer Ca2+ permeability, but deletion of either claudin does not result in a negative Ca2+ balance or increased calciotropic hormone levels, suggesting the existence of additional transport pathways or parallel roles for the two claudins. To test this, we generated a Cldn2/12 double knockout mouse (DKO). These animals have reduced intestinal Ca2+ absorption. Colonic Ca2+ permeability is also reduced in DKO mice and significantly lower than single-null animals, while small intestine Ca2+ permeability is unaltered. The DKO mice display significantly greater urinary Ca2+ wasting than Cldn2 null animals. These perturbations lead to hypocalcemia and reduced bone mineral density, which was not observed in single-KO animals. Both claudins were localized to colonic epithelial crypts and renal proximal tubule cells, but they do not physically interact in vitro. Overexpression of either claudin increased Ca2+ permeability in cell models with endogenous expression of the other claudin. We find claudin-2 and claudin-12 form partially redundant, independent Ca2+ permeable pores in renal and colonic epithelia that enable paracellular Ca2+ (re)absorption in these segments, with either one sufficient to maintain Ca2+ balance.

New Approaches to Assess Mechanisms of Action of Selective Vitamin D Analogues

Recent studies of transcription have revealed an advanced set of overarching principles that govern vitamin D action on a genome-wide scale. These tenets of vitamin D transcription have emerged as a result of the application of now well-established techniques of chromatin immunoprecipitation coupled to next-generation DNA sequencing that have now been linked directly to CRISPR-Cas9 genomic editing in culture cells and in mouse tissues in vivo. Accordingly, these techniques have established that the vitamin D hormone modulates sets of cell-type specific genes via an initial action that involves rapid binding of the VDR-ligand complex to multiple enhancer elements at open chromatin sites that drive the expression of individual genes. Importantly, a sequential set of downstream events follows this initial binding that results in rapid histone acetylation at these sites, the recruitment of additional histone modifiers across the gene locus, and in many cases, the appearance of H3K36me3 and RNA polymerase II across gene bodies. The measured recruitment of these factors and/or activities and their presence at specific regions in the gene locus correlate with the emerging presence of cognate transcripts, thereby highlighting sequential molecular events that occur during activation of most genes both in vitro and in vivo. These features provide a novel approach to the study of vitamin D analogs and their actions in vivo and suggest that they can be used for synthetic compound evaluation and to select for novel tissue- and gene-specific features. This may be particularly useful for ligand activation of nuclear receptors given the targeting of these factors directly to genetic sites in the nucleus.

Vitamin D Receptor Gene Single Nucleotide Polymorphisms and Association With Vitamin D Levels and Endoscopic Disease Activity in Inflammatory Bowel Disease Patients: A Pilot Study

BACKGROUND

Inflammatory bowel diseases (IBDs) comprise a heterogenous group of chronic gastrointestinal disorders that are multifactorial in etiology. Experimental in vitro and in vivo studies suggest that intestinal vitamin D receptor (VDR) signaling plays a role in modulating the immune response in IBD as a cause and/or a consequence of chronic inflammation.

AIM

The aim of this study is to study the associations between vitamin D receptor gene single nucleotide polymorphisms(SNPs), vitamin D levels, and endoscopic disease activity in IBD.

METHODS

This is a cross-sectional analysis of IBD patients who underwent endoscopic evaluation at a tertiary care hospital. Demographic variables, IBD disease type and location, medical therapies, vitamin D levels, and endoscopic disease activity were collected. Colonic biopsies obtained were investigated for the presence of VDR SNPs: ApaI, TaqI, BsmI, FokI, and Tru9I.

RESULTS

Patients in endoscopic remission had higher vitamin D levels compared with those with inflammation found on endoscopy (P = <0.001). Patients with lower vitamin D levels were homozygous for Fok ancestral alleles (P = 0.0045). With regard to endoscopic disease activity, we found no differences in mutations of any of the VDR SNPs in our sample.

CONCLUSIONS

The association between the presence of the ancestral FokI and lower vitamin D levels suggests a multifactorial etiology for vitamin D deficiency in IBD. Higher vitamin D levels in those in endoscopic remission compared with lower levels in those with active inflammation suggests that the impact of VDR gene SNP on disease activity may be overcome with replacement therapy.

Vitamin D Is Necessary for Murine Gastric Epithelial Homeostasis

Unlike other organs, the importance of VD in a normal stomach is unknown. This study focuses on understanding the physiological role of vitamin D in gastric epithelial homeostasis. C57BL/6J mice were divided into three groups that were either fed a standard diet and kept in normal light/dark cycles (SDL), fed a standard diet but kept in the dark (SDD) or fed a vitamin D-deficient diet and kept in the dark (VDD). After 3 months, sera were collected to measure vitamin D levels by LC-MS/MS, gastric tissues were collected for immunohistochemical and gene expression analyses and gastric contents were collected to measure acid levels. The VDD group showed a significant decrease in the acid-secreting parietal cell-specific genes Atp4a and Atp4b when compared with the controls. This reduction was associated with an increased expression of an antral gastrin hormone. VDD gastric tissues also showed a high proliferation rate compared with SDL and SDD using an anti-BrdU antibody. This study indicates the requirement for normal vitamin D levels for proper parietal cell functions.

Hormonal regulation of biomineralization

Biomineralization is the process by which organisms produce mineralized tissues. This crucial process makes possible the rigidity and flexibility that the skeleton needs for ambulation and protection of vital organs, and the hardness that teeth require to tear and grind food. The skeleton also serves as a source of mineral in times of short supply, and the intestines absorb and the kidneys reclaim or excrete minerals as needed. This Review focuses on physiological and pathological aspects of the hormonal regulation of biomineralization. We discuss the roles of calcium and inorganic phosphate, dietary intake of minerals and the delicate balance between activators and inhibitors of mineralization. We also highlight the importance of tight regulation of serum concentrations of calcium and phosphate, and the major regulators of biomineralization: parathyroid hormone (PTH), the vitamin D system, vitamin K, fibroblast growth factor 23 (FGF23) and phosphatase enzymes. Finally, we summarize how developmental stresses in the fetus and neonate, and in the mother during pregnancy and lactation, invoke alternative hormonal regulatory pathways to control mineral delivery, skeletal metabolism and biomineralization.

Maternal and fetal vitamin D and their roles in mineral homeostasis and fetal bone development

During pregnancy, female physiology adapts to meet the additional mineral demands of the developing fetus. Meanwhile, the fetus actively transports minerals across the placenta and maintains high circulating levels to mineralize the rapidly developing skeleton. Most of this mineral is accreted during the last trimester, including 30 g of calcium, 20 g of phosphate and 0.8 g of magnesium. Given the dependence of calcium homeostasis on vitamin D and calcitriol in the adult and child, it may be expected that vitamin D sufficiency would be even more critical during pregnancy and fetal development. However, the pregnant mother and fetus appear to meet their mineral needs independent of vitamin D. Adaptations in maternal mineral and bone metabolism during pregnancy appear to be invoked independent of maternal vitamin D, while fetal mineral metabolism and skeletal development appear to be protected from vitamin D deficiency and genetic disorders of vitamin D physiology. This review discusses key data from both animal models and human studies to address our current knowledge on the role of vitamin D and calcitriol during pregnancy and fetal development.

Vitamin D Effects on Cell Differentiation and Stemness in Cancer

Vitamin D₃ is the precursor of 1α,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃), a pleiotropic hormone that is a major regulator of the human genome. 1,25(OH)₂D₃ modulates the phenotype and physiology of many cell types by controlling the expression of hundreds of genes in a tissue- and cell-specific fashion. Vitamin D deficiency is common among cancer patients and numerous studies have reported that 1,25(OH)₂D₃ promotes the differentiation of a wide panel of cultured carcinoma cells, frequently associated with a reduction in cell proliferation and survival. A major mechanism of this action is inhibition of the epithelial–mesenchymal transition, which in turn is largely based on antagonism of the Wnt/β-catenin, TGF-β and EGF signaling pathways. In addition, 1,25(OH)₂D₃ controls the gene expression profile and phenotype of cancer-associated fibroblasts (CAFs), which are important players in the tumorigenic process. Moreover, recent data suggest a regulatory role of 1,25(OH)₂D₃ in the biology of normal and cancer stem cells (CSCs). Here, we revise the current knowledge of the molecular and genetic basis of the regulation by 1,25(OH)₂D₃ of the differentiation and stemness of human carcinoma cells, CAFs and CSCs. These effects support a homeostatic non-cytotoxic anticancer action of 1,25(OH)₂D₃ based on reprogramming of the phenotype of several cell types.

Role of glucuronidated 25-hydroxyvitamin D on colon gene expression in mice

25-Hydroxyvitamin D₃-3β-glucuronic acid (25OHD-Gluc) is produced in the liver and is a constituent of human blood and bile. Bacterial glucuronidases (GUS) in mammalian digestive microbiota cleave glucuronide conjugates, such as 25OHD-Gluc, and release the free aglycone (i.e., 25OHD) inside the intestinal lumen. We hypothesized that 25OHD-Gluc would elicit a VDR-dependent mRNA response in the colon after cleavage by gut microbiota. The activity of 25OHD-Gluc was investigated by measuring expression of cytochrome P450 24A1 (Cyp24) mRNA both in vitro and in vivo. In cell culture, Caco2 cells responded to 25OHD-Gluc, whereas HT29 cells did not. When coincubated with GUS, both cell lines elicited a robust response as indicated by a 5 Ct (32-fold) increase in Cyp24 mRNA. In vitamin D-sufficient mice, we found that both oral and subcutaneous administration of 1 nmol 25OHD-Gluc induced expression of Cyp24 mRNA in the colon whereas 25OHD did not. In contrast, 25OHD, but not 25OHD-Gluc, was active in the duodenum. When the jejunum was surgically ligated to block flow of digesta to the colon, neither oral nor subcutaneous administration of 2 nmol 25OHD-Gluc was able to induce expression of Cyp24 in the colon. Our findings suggest that 25OHD-Gluc, a vitamin D metabolite found in bile, induces VDR-mediated responses in the colon by crossing the apical membrane of the colon epithelium.NEW & NOTEWORTHY We found that 25OHD-Gluc, an endogenously produced metabolite, is delivered to the colon via bile to induce vitamin D-mediated responses in the colon.