Association between intestinal vitamin D receptor, calcium absorption, and serum 1,25 dihydroxyvitamin D in normal young and elderly women

Vitamin D Level Between Calcium-Phosphorus Homeostasis and Immune System: New Perspective in Osteoporosis

Vitamin D is a key molecule in calcium and phosphate homeostasis; however, increasing evidence has recently shown that it also plays a crucial role in the immune system, both innate and adaptive. A deregulation of vitamin D levels, due also to mutations and polymorphisms in the genes of the vitamin D pathway, determines severe alterations in the homeostasis of the organism, resulting in a higher risk of onset of some diseases, including osteoporosis. This review gives an overview of the influence of vitamin D levels on the pathogenesis of osteoporosis, between bone homeostasis and immune system.

Association between serum level of vitamin D (25-hydroxyvitamin D) and plasma level of vitamin D receptor with bacteriological index in leprosy patients

Macrophages respond against Mycobacterium leprae infection through interacting with vitamin D and vitamin D receptor (VDR). There has been no study analyzing the association between vitamin D and VDR with bacteriological index (BI) in leprosy patients in Indonesia. To analyze the serum level of 25- hydroxyvitamin D (25(OH)D) and plasma level of VDR as well as their association with BI in leprosy patients in Indonesia. This is a cross-sectional study. Serum level of 25(OH)D was assessed with in vitro chemiluminescent immunoassay. Plasma level of VDR was assessed with enzyme linked immunosorbent assay method. Median serum level of 25(OH)D was 12.68 ng/mL. There was no correlation between serum level of 25(OH)D and BI (r=0.033; p=0.869). Median plasma level of VDR was 1.36 ng/mL. There was no correlation between plasma level of VDR and BI (r=- 0.063; p=0.749) and no significant association between BI and serum level of 25(OH) and plasma level of VDR (R2=0.055). There was no association between serum level of 25(OH)D and plasma level of VDR with BI in leprosy patients.

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.

Effects of Dietary Vitamin D Deficiency on Markers of Skeletal Muscle Mitochondrial Biogenesis and Dynamics

We examined the effects of dietary vitamin D deficiency on markers of mitochondrial biogenesis and dynamics in rat soleus muscle. Male Wistar rats were fed a chow with no vitamin D (No-D; 0 IU/kg) or a moderate dose (Mod-D; 2,000 IU/kg) of vitamin D chow for 8 wk. Compared to the Mod-D group, at 8 wk the No-D group showed significantly lower serum 25(OH)D levels. Although vitamin D deficiency had no effect on body composition, the No-D rats showed significantly decreased levels of PGC-1α, a marker of skeletal muscle mitochondrial biogenesis, and DRP1, a marker of skeletal muscle mitochondrial fission. The change in the PGC-1α protein expression and the serum 25(OH)D concentrations were significantly correlated. The change in DRP1 protein expression and the serum 25(OH)D concentrations tended to be correlated. There was no significant between-group difference in markers of mitochondrial fusion (MFN2 and OPA1) and mitophagy (PARKIN) in soleus muscle, and no relationship with serum 25(OH)D concentrations. Collectively our findings suggest that dietary vitamin D deficiency decreased PGC-1α and DRP1 protein expression in rat soleus muscle.

Association of High Serum Chemerin with Bone Mineral Density Loss and Osteoporotic Fracture in Elderly Chinese Women

Background

Chemerin has been suggested to be a risk factor for osteoporosis; however, its relationship with osteoporotic fracture is poorly understood. Herein, we intend to explore the association between serum chemerin and osteoporotic fracture.

Methods

A total of 111 elderly women patients diagnosed with osteoporotic fracture were selected as the observation group, and 40 healthy subjects were enrolled as controls. Dual-energy X-ray absorptiometry, enzyme-linked immunosorbent assay, electrochemiluminescence immunoassay, and biochemical analysis were separately performed to determine body bone mineral density (BMD), chemerin levels, bone turnover markers, and other parameters. Pearson's correlation analysis was conducted to examine a relationship between chemerin and laboratory parameters. Moreover, the levels of chemokine-like receptor 1 (CMKLR), C-C motif chemokine receptor-like 2 (CCRL2), collagen type I alpha (COLA1), and runt-related transcription factor-2 (RUNX2) were confirmed by quantitative polymerase chain reaction, and the effect of chemerin on osteogenic differentiation of hFOB1.19 cells was indicated by tartrate-resistant acid phosphatase and alkaline phosphatase double staining.

Results

A higher level of chemerin was generally detected in patients with osteoporotic fracture compared with those without (P<0.05). Compared with controls, lower BMD levels and higher β-CTx and P1NP levels were detected in patients with osteoporotic fracture (all P<0.05). Interestingly, chemerin level was negatively correlated to BMD, but positively related to P1NP and β-CTx. Risk of osteoporotic fracture was 2.75-fold higher in subjects with each standard deviation increment of chemerin. Compared with controls, there were no significant differences in CMKLR1 and CCRL2 mRNA after incubation with osteogenic differentiation medium (all P>0.05), whereas there was a remarkable decrease of COLA1 and RUNX2 after incubation with chemerin for nine days (all P<0.05). Furthermore, prolonged incubation with chemerin enhanced osteoclast differentiation and maturation, consequently contributing to an increased risk of fracture.

Conclusion

Chemerin is a strong and independent risk factor for osteoporosis-related fracture among elderly Chinese women.

Exercise acutely increases vitamin D receptor expression in T lymphocytes in vitamin D-deficient men, independent of age

NEW FINDINGS

What is the central question of this study? Does exercise affect vitamin D receptor expression in T lymphocytes in young, middle-aged and older adults? What is the main finding and its importance? Moderate-intensity cycling exercise increases vitamin D receptor expression in vitamin D-deficient men, independent of age, presenting a strategy to combat the prevalence of vitamin D deficiency.

ABSTRACT

Vitamin D plays a key role in the modulation of the immune system, mediated through the intracellular vitamin D receptor (VDR). Exercise has been shown to influence the activity and availability of the VDR. The aim of this study was to investigate the effect of age on basal immune cell (T-lymphocyte) VDR expression and the subsequent effect of acute aerobic exercise to modulate VDR expression in peripheral T cells. Thirty-five men were included in the study (mean ± SD: age 44 ± 17 years and body mass index 25.7 ± 3.1 kg/m² ), separated into three age groups: 18-30 (n = 12), 31-45 (n = 11) and 60-75 years (n = 12). Participants completed two trials [control (CON) and aerobic exercise (AE)], with blood samples collected pre- and postexercise (0, 1 and 3 h). Peripheral blood T cells were isolated and analysed for VDR expression by flow cytometry. The results show that advanced age is associated with lower VDR expression in T cells (882 ± 274, 796 ± 243 and 594 ± 174 geomean in the 18-30, 31-45 and 60-75 year age groups, respectively). Acute AE was successful at acutely increasing VDR expression in T cells, irrespective of age. Advanced age corresponds to a lower T-cell VDR expression, which might be responsible for age-associated development of chronic conditions and autoimmunity. Exercise was successful in increasing VDR expression in T cells irrespective of age and independent of exercise-induced T-cell mobilization.

Vitamin D Deficiency is Associated with Handgrip Strength, Nutritional Status and T2DM in Community-Dwelling Older Mexican Women: A Cross-Sectional Study

The aim of this study was to evaluate the association between handgrip strength, nutritional status and vitamin D deficiency in Mexican community-dwelling older women. A cross sectional study in women ≥ 60 years-old was performed. Plasma 25-hydroxyvitamin D (25(OH)D) concentrations were measured by a quantitative immunoassay technique. Handgrip strength was assessed using a dynamometer, while nutritional status was assessed through the Full Mini Nutritional Assessment (Full-MNA). A total of 116 women participated in the study, their mean age was 70.3 ± 5.8 years; 49.1% of the study group had plasma 25(OH)D levels lower than 40 nmol/L [16 ng/mL]. Meanwhile, 28.45% of participants had low handgrip strength (<16 kg), and 23.1% were identified at risk of malnutrition/malnourished according with Full-MNA score. Women with 25(OH)D deficiency (<40 nmol/L [16 ng/mL]) were more likely to have low handgrip strength (OR = 2.64, p = 0.025) compared with those with higher 25(OH)D values. Additionally, being malnourished or at risk of malnutrition (OR = 2.53, p = 0.045) or having type 2 diabetes mellitus (T2DM) (OR = 2.92, p = 0.044) was also associated with low 25(OH)D. The prevalence of low plasma 25(OH)D concentrations was high among Mexican active older women. Low handgrip strength, being at risk of malnutrition/malnourished, or diagnosed with T2DM was also associated with Vitamin D deficiency.

Vitamin D, Calcium, Parathyroid Hormone, and Sex Steroids in Bone Health and Effects of Aging

Bone health of the elderly is a major global health concern, since about 1 in 3 women and 1 in 5 men suffer from bone loss and fractures, often called osteoporosis, in old age. Bone health is a complex issue affected by multiple hormones and minerals. Among all the hormones involved in bone health, calcitriol (also vitamin D), parathyroid, and sex hormones (especially estrogen) have been discussed in this review paper. We have discussed the metabolism of these hormones and their effects on bone health. Vitamin D can be obtained from diet or formed from 7-dehydrocholesterol found under the skin in the presence of sunlight. The active form, calcitriol, causes dimerization of vitamin D receptor and acts on the bones, intestine, and kidney to regulate the level of calcium in blood. Similarly, parathyroid hormone is secreted when the serum level of calcium is low. It helps regulate the level of blood calcium through calcitriol. Sex hormones regulate bone modeling at an early age and remodeling later in life. Loss of ovarian function and a decrement in the level of production of estrogen are marked by bone loss in elderly women. In the elderly, various changes in the calcium and vitamin D metabolism, such as decrease in the production of vitamin D, decrease in dietary vitamin D, decreased renal production, increased production of excretory products, decrease in the level of VDR, and decreased calcium absorption by the intestines, can lead to bone loss. When the elderly are diagnosed with osteoporosis, medications that directly target bone such as bisphosphonates, RANK ligand inhibitors, estrogen and estrogen analogues, estrogen receptor modulators, and parathyroid hormone receptor agonists are used. Additionally, calcium and vitamin D supplements are prescribed.

Genetic, environmental and biomarker considerations delineating the regulatory effects of vitamin D on central nervous system function

Studies show that vitamin D (vit-D) (25(OH)D), the bioactive metabolite (1,25(OH)2D3) and vit-D receptors (vit-D receptor; protein disulphide isomerase, family A member 3) are expressed throughout the brain, particularly in regions pivotal to learning and memory. This has led to the paradigm that avoiding vit-D deficiency is important to preserve cognitive function. However, presently, it is not clear if the common clinical measure of serum 25(OH)D serves as a robust surrogate marker for central nervous system (CNS) homeostasis or function. Indeed, recent studies report CNS biosynthesis of endogenous 25(OH)D, the CNS expression of the CYP group of enzymes which catalyse conversion to 1,25(OH)2D3 and thereafter, deactivation. Moreover, in the periphery, there is significant ethnic/genetic heterogeneity in vit-D conversion to 1,25(OH)2D3 and there is a paucity of studies which have actually investigated vit-D kinetics across the cerebrovasculature. Compared with peripheral organs, the CNS also has differential expression of receptors that trigger cellular response to 1,25(OH)2D3 metabolites. To holistically consider the putative association of peripheral (blood) abundance of 25(OH)D on cognitive function, herein, we have reviewed population and genetic studies, pre-clinical and clinical intervention studies and moreover have considered potential confounders of vit-D analysis.

The vitamin D receptor expression in skeletal muscle of women with distal radius fracture

We evaluated the vitamin D receptor (VDR) expression in the forearm flexor muscle of women with distal radius fracture. High VDR expression was associated with low appendicular lean mass index.

INTRODUCTION

We aimed to evaluate the relationship between the VDR expression in the muscle cell and the muscle mass in women with a distal radius fracture (DRF).

METHODS

We prospectively recruited 45 women over 50 years of age (mean age, 66 years) with DRF and acquired biopsy of the forearm flexor muscle. The muscle cross-sectional area (CSA) and VDR expression were measured using immunohistochemistry staining. The clinical parameters including grip strength, gait speed, body mass index (BMI), bone mineral density (BMD), and serum vitamin D levels were compared between patients grouped by appendicular lean mass index and were correlated with the VDR expression.

RESULTS

Twelve patients (27%) showed a decreased appendicular lean mass index, less than the cut-off value of 5.4 kg/m2 which was suggested by the Asian Working Group for Sarcopenia. Patients with a low appendicular lean mass index had significantly lower muscle CSA (p = 0.037), but a higher VDR expression (p = 0.045) than those with higher indices. VDR expression was negatively correlated with BMI (r = - 0.417, p = 0.004) and appendicular lean mass index (r = - 0.316, p = 0.044).

CONCLUSIONS

DRF patients with low appendicular lean mass index presented high VDR expression and low CSA in forearm muscle cells. This suggests that the VDR expression might be upregulated in the attempt to compensate for the decreasing muscle mass. Further studies are necessary to explore the role of VDR in the progression of sarcopenia.

Expression of vitamin D receptor in the subsynovial connective tissue in women with carpal tunnel syndrome

Studies suggest that low vitamin D levels are associated with carpal tunnel syndrome. We aimed to evaluate whether level of vitamin D receptor expression in the endothelial cells of the subsynovial connective tissue is associated with clinical features of carpal tunnel syndrome. We obtained the subsynovial connective tissue from 52 women with carpal tunnel syndrome during surgery and performed immunohistochemical analysis of vitamin D receptors in the endothelial cells of the subsynovial connective tissue. We explored correlation of vitamin D receptor expression with clinical features of carpal tunnel syndrome, such as age, symptom duration, symptom severity and electrophysiological severity. Diverse range of vitamin D receptor expression was observed. Vitamin D receptor expression was independently associated with distal motor latency. This suggests that vitamin D receptor expression may be associated with disease progression, as prolonged distal motor latency reflects severity of the disease. Further studies are necessary to explore the role of vitamin D and vitamin D receptors in patients with carpal tunnel syndrome.

LEVEL OF EVIDENCE

IV.

Is there a role for vitamin D in supporting cognitive function as we age?

Globally, an estimated 46 million people are currently living with dementia and this figure is projected to increase 3-fold by 2050, highlighting this major public health concern and its substantial associated healthcare costs. With pharmacological treatment yet to reach fruition, the emphasis on evidence-based preventative lifestyle strategies is becoming increasingly important and several modifiable lifestyle factors have been identified that may preserve cognitive health. These include good cardiovascular health, physical activity, low alcohol intake, smoking and a healthy diet, with growing interest in vitamin D. The aim of the present paper is to review the evidence supporting the potential roles of vitamin D in ageing and cognitive health in community-dwelling older adults. Furthermore, to describe the utility and challenges of cognitive assessments and outcomes when investigating vitamin D in this context. Evidence indicates that serum 25-hydroxyvitamin D (25(OH)D) may impact brain health. There is a biological plausibility from animal models that vitamin D may influence neurodegenerative disorders, through several mechanisms. Epidemiological evidence supports associations between low serum 25(OH)D concentrations and poorer cognitive performance in community-dwelling older populations, although an optimal 25(OH)D level for cognitive health could not be determined. The effect of raising 25(OH)D concentrations on cognitive function remains unclear, as there is a paucity of interventional evidence. At a minimum, it seems prudent to aim to prevent vitamin D deficiency in older adults, with other known common protective lifestyle factors, as a viable component of brain health strategies.

Changes in vitamin D endocrinology during aging in adults

Worldwide, vitamin D deficiency is a common finding. Within individuals 25-hydroxyvitamin D (25OH)D) concentrations remain fairly stable over time although large differences in individual longitudinal changes exist. During aging vitamin D metabolism and activity changes in several different ways. Intestinal resistance to 1,25(OH)2D develops which hampers intestinal calcium uptake. Vitamin D receptor number decreases with aging in several organs involved in calcium metabolism and 1alpha-hydroxylase activity decreases mainly due to a decrease in renal function reducing vitamin D activation. Effects of 1,25(OH)2D on cell proliferation and differentiation may influence potential anti-cancer effects whereas regulation of telomere length may result in longevity. In older individuals, vitamin D supplementation has positive effects on fracture risk, number of falls and physical function. Supplementation in older populations warrants specific attention. Effects on "non-classical" outcomes may be revealed by ongoing large randomized clinical trials with high doses of vitamin D.

Vitamin D, calcium homeostasis and aging

Osteoporosis is characterized by low bone mass and microarchitecture deterioration of bone tissue, leading to enhanced bone fragility and consequent increase in fracture risk. Evidence is accumulating for an important role of calcium deficiency as the process of aging is associated with disturbed calcium balance. Vitamin D is the principal factor that maintains calcium homeostasis. Increasing evidence indicates that the reason for disturbed calcium balance with age is inadequate vitamin D levels in the elderly. In this article, an overview of our current understanding of vitamin D, its metabolism, and mechanisms involved in vitamin D-mediated maintenance of calcium homeostasis is presented. In addition, mechanisms involved in age-related dysregulation of 1,25(OH)₂D₃ action, recommended daily doses of vitamin D and calcium, and the use of vitamin D analogs for the treatment of osteoporosis (which remains controversial) are reviewed. Elucidation of the molecular pathways of vitamin D action and modifications that occur with aging will be an active area of future research that has the potential to reveal new therapeutic strategies to maintain calcium balance.

What Does It Cost to Improve Household Diets in Nepal? Using the Cost of the Diet Method to Model Lowest Cost Dietary Changes

BACKGROUND

In Nepal, limited availability and affordability of nutritious foods contribute to malnutrition.

OBJECTIVES

To identify nutrient deficiencies in commonly consumed diets and model lowest cost changes that could improve diet quality in 3 agroecological zones of Nepal.

METHODS

In August to September 2014, we collected market price and women's food frequency data from 3 representative villages in Nepal's mountains (Mahat Gaun, Jumla, n = 181 households), hills (Sitapur, Arghakhanchi, n = 166), and terai (Saigaun, Banke, n = 232) and verified local diets during women's group discussions. Using the Cost of the Diet method, we compared models of the most nutritious version of a commonly consumed diet given locally available foods ("common diet") with the cheapest possible diet meeting nutrient requirements, including foods not currently available ("optimal diet").

RESULTS

The household common diet lacks sufficient vitamin B12, riboflavin, and calcium in the mountains; B6, B12, calcium, and iron in the hills; vitamin A, calcium, and iron in the terai. Adding fish to the mountain and hill diets and increasing dark green leafy vegetable consumption in all zones yielded nutritional adequacy. Optimal diets are more expensive than the common diet in the mountains and hills but less expensive in the terai.

CONCLUSION

The modeled lowest cost diet commonly eaten in 3 Nepalese communities lacks key nutrients. Policies and interventions that increase market availability and consumption of vitamin B12- and calcium-rich fish and dark green leafy vegetables could improve local diets, particularly in the mountains and hills.

Gene-by-diet interactions influence calcium absorption and bone density in mice

Dietary calcium (Ca) intake is needed to attain peak bone mineral density (BMD). Habitual low Ca intake increases intestinal Ca absorption efficiency to protect bone mass, but the mechanism controlling, and the impact of genetics on, this adaptive response is not clear. We fed 11 genetically diverse inbred mouse lines a normal (0.5%) or low (0.25%) Ca diet from 4 to 12 weeks of age (n = 8 per diet per line) and studied the independent and interacting effects of diet and genetics on Ca and bone metabolism. Significant genetic variation was observed in all bone, renal, and intestinal phenotypes measured including Ca absorption. Also, adaptation of Ca absorption and bone parameters to low dietary Ca was significantly different among the lines. Ca absorption was positively correlated to femur BMD (r = 0.17, p = 0.02), and distal femur bone volume/tissue volume (BV/TV) (r = 0.34, p < 0.0001). Although Ca absorption was correlated to 1,25 dihydroxyvitamin D (1,25(OH)2 D) (r = 0.35, p < 0.0001), the adaptation of Ca absorption to low Ca intake did not correlate to diet-induced adaptation of 1,25(OH)2 D across the 11 lines. Several intestinal proteins have been proposed to mediate Ca absorption: claudins 2 and 12, voltage gated Ca channel v1.3 (Cav1.3), plasma membrane Ca ATPase 1b (PMCA1b), transient receptor potential vanilloid member 6 (TRPV6), and calbindin D9k (CaBPD9k). Only the mRNA levels for TRPV6, CaBPD9k, and PMCA1b were related to Ca absorption (r = 0.42, 0.43, and 0.21, respectively). However, a significant amount of the variation in Ca absorption is not explained by the current model and suggests that novel mechanisms remain to be determined. These observations lay the groundwork for discovery-focused initiatives to identify novel genetic factors controlling gene-by-diet interactions affecting Ca/bone metabolism.

Vitamin D and aging

Age-related changes affect vitamin D metabolism and increase the requirement for vitamin D in the elderly. Also there is an age related decrease in calcium absorption and a higher calcium intake is needed. Increasing calcium from dietary sources may be better than supplements, and requires increasing the intake of dairy products or other and calcium-fortified foods. Evidence suggests that vitamin D and calcium nutrition can be improved in the elderly by increasing the vitamin D intake to 800 IU daily together with a total calcium intake of 1000 mg daily. This combination is a simple, inexpensive strategy that can reduce fractures in institutionalized individuals by 30%.

Allelic variations in coding regions of the vitamin D receptor gene in dairy cows and potential susceptibility to periparturient hypocalcaemia

Periparturient hypocalcaemia (milk fever) is a disorder of Ca metabolism in dairy cattle primarily affecting multiparous cows. The major reasons for the rapid decrease of blood Ca concentration after calving are the prompt increase of Ca secretion into the colostrum and the delayed activation of Ca regulation mechanisms including calcitriol, a metabolite of vitamin D. In man, vitamin D receptor (VDR) gene polymorphisms are reported to be associated with disturbances of Ca metabolism, whereas data confirming the same in dairy cows are still missing. Moreover, polymorphisms that only affect non-coding regions are sometimes difficult to ascribe to a specific disorder as pathways and unequivocal links remain elusive. Therefore, the idea of the present study was to investigate in a small group of dairy cows with documented clinical records whether polymorphisms in the coding regions of the VDR gene existed and whether these potentially found variations were correlated with the incidence of periparturient hypocalcaemia. For this purpose, blood DNA was isolated from 26 dairy cows in their 4th to 6th lactation, out of which 17 had experienced hypocalcaemia at least once, whereas 9 cows had never undergone periparturient hypocalcaemia in their lifetime. The 10 VDR exons and small parts of adjacent introns were sequenced and compared with the Bos taurus VDR sequence published on NCBI based on the DNA of one Hereford cow. In total, 8 sequence alterations were detected in the fragments, which were primarily heterozygous. However, only 4 of them were really located on exons thereby potentially causing changes of the encoded amino acid of the VDR protein, but were not correlated with the incidence of periparturient hypocalcaemia. Certainly, this lack of statistical correlation could be due to the small number of animals included; anyhow, it was not encouraging enough to initiate a larger study with hundreds of cows and document blood Ca levels post partum for at least four lactations.

Evidence in favor of a severely impaired net intestinal calcium absorption in patients with (early-stage) chronic kidney disease

INTRODUCTION

Calcium and phosphorus are essential to many vital physiological processes. Little is known about the net and fractional intestinal absorption of calcium and phosphorus in patients with chronic kidney disease (CKD) and their clinical and hormonal determinants.

METHODS

Blood and 24-hour urine samples were collected in 20 healthy volunteers (HV) and 72 stable CKD stage 1-4 patients and analyzed for parameters of mineral metabolism including calcidiol, calcitriol, and parathyroid hormone (PTH). Dietary intake was assessed by dietary history.

RESULTS

The 24-hour urinary calcium excretion, as opposed to the phosphorus excretion, showed a stepwise decrease across CKD stages (median of 219, 84, 40, and 22 mg/day in HV and patients with CKD stages 1-2, 3 and 4, respectively). Younger age, high serum calcitriol, and high estimated GFR were associated with a high 24-hour urinary calcium excretion. High serum calcitriol levels and dietary phosphorus intake were associated with a high 24-hour urinary phosphorus excretion. The fractional intestinal calcium absorption, as estimated by the urinary-to-ingested calcium ratio, decreased across CKD stages.

CONCLUSIONS

The 24-hour urinary excretion of calcium, as opposed to phosphorus, is markedly decreased in CKD, even in early-stage disease. This is partly explained by low calcitriol levels and older age. Assuming a neutral calcium balance at the time of urine collection, we infer that net intestinal calcium absorption may be severely impaired in CKD.

Worsening severity of vitamin D deficiency is associated with increased length of stay, surgical intensive care unit cost, and mortality rate in surgical intensive care unit patients

BACKGROUND

Vitamin D deficiency is the most common nutritional deficiency in the United States. It is seldom measured or recognized, and rarely is treated, particularly in critically ill patients. The purpose of this study was to investigate the prevalence and impact of vitamin D deficiency in surgical intensive care unit patients. We hypothesized that severe vitamin D deficiency increases the length of stay, mortality rate, and cost in critically ill patients admitted to surgical intensive care units.

METHODS

We performed a prospective observational study of vitamin D status on 258 consecutive patients admitted to the Surgical Intensive Care Unit at Grady Memorial Hospital between August 2009 and January 2010. Vitamin D levels (25 [OH]2 vitamin-D3) were measured by high-pressure liquid chromatography and tandem mass spectrometry. Vitamin D deficiency was defined as follows: severe deficiency was categorized as less than 13 ng/mL; moderate deficiency was categorized as 14 to 26 ng/mL; mild deficiency was categorized as 27 to 39 ng/mL; and normal levels were categorized as greater than 40 ng/mL.

RESULTS

Of the 258 patients evaluated, 70.2% (181) were men, and 29.8% (77) were women; 57.6% (148) were African American and 32.4% (109) were Caucasian. A total of 138 (53.5%) patients had severe vitamin D deficiency, 96 (37.2%) had moderate deficiency, 18 (7.0%) had mild deficiency, and 3 (1.2%) of the patients had normal vitamin D levels. The mean length of stay in the Surgical Intensive Care Unit for the severe vitamin D-deficient group was 13.33 ± 19.5 days versus 7.29 ± 15.3 days and 5.17 ± 6.5 days for the moderate and mild vitamin D-deficient groups, respectively, which was clinically significant (P = .002). The mean treatment cost during the patient stay in the surgical intensive care unit was $51,413.33 ± $75,123.00 for the severe vitamin D-deficient group, $28,123.65 ± $59,752.00 for the moderate group, and $20,414.11 ± $25,714.30 for the mild vitamin D-deficient group, which also was clinically significant (P = .027). More importantly, the mortality rate for the severe vitamin D-deficient group was 17 (12.3%) versus 11 (11.5%) in the moderate group (P = .125). Because no deaths occurred in the mildly or normal vitamin D-deficient groups, we compared the mortality rate between severe/moderate and mild/normal vitamin D groups (P = .047).

CONCLUSIONS

In univariate analysis, severe and moderate vitamin D deficiency was related inversely to the length of stay in the surgical intensive care unit (r = .194; P = .001), related inversely to surgical intensive care unit treatment cost (r = .194; P = .001) and mortality (r = .125; P = .023), compared with the mild vitamin D-deficient group, after adjusting for age, sex, race, and comorbidities (myocardial infarctions, acute renal failure, and pneumonia); the length of stay, surgical intensive care unit cost, and mortality remained significantly associated with vitamin D deficiency.

Trpv6 mediates intestinal calcium absorption during calcium restriction and contributes to bone homeostasis

Energy-dependent intestinal calcium absorption is important for the maintenance of calcium and bone homeostasis, especially when dietary calcium supply is restricted. The active form of vitamin D, 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)], is a crucial regulator of this process and increases the expression of the transient receptor potential vanilloid 6 (Trpv6) calcium channel that mediates calcium transfer across the intestinal apical membrane. Genetic inactivation of Trpv6 in mice (Trpv6(-/-)) showed, however, that TRPV6 is redundant for intestinal calcium absorption when dietary calcium content is normal/high and passive diffusion likely contributes to maintain normal serum calcium levels. On the other hand, Trpv6 inactivation impaired the increase in intestinal calcium transport following calcium restriction, however without resulting in hypocalcemia. A possible explanation is that normocalcemia is maintained at the expense of bone homeostasis, a hypothesis investigated in this study. In this study, we thoroughly analyzed the bone phenotype of Trpv6(-/-) mice receiving a normal (approximately 1%) or low (approximately 0.02%) calcium diet from weaning onwards using micro-computed tomography, histomorphometry and serum parameters. When dietary supply of calcium is normal, Trpv6 inactivation did not affect growth plate morphology, bone mass and remodeling parameters in young adult or aging mice. Restricting dietary calcium had no effect on serum calcium levels and resulted in a comparable reduction in bone mass accrual in Trpv6(+/+) and Trpv6(-/-) mice (-35% and 45% respectively). This decrease in bone mass was associated with a similar increase in bone resorption, whereas serum osteocalcin levels and the amount of unmineralized bone matrix were only significantly increased in Trpv6(-/-) mice. Taken together, our findings indicate that TRPV6 contributes to intestinal calcium transport when dietary calcium supply is limited and in this condition indirectly regulates bone formation and/or mineralization.

Inflammatory bowel diseases, celiac disease, and bone

The article summarizes the current knowledge on the pathogenesis, clinical aspects and treatment of bone problems in the major inflammatory bowel diseases (Crohn's disease and ulcerative colitis) and celiac disease. It presents the physiological relationship between intestine and bone as well as the alterations determined by disease-disrupted intestinal integrity. Two hypotheses about the pathogenetic mechanisms of bone metabolism derangements and bone loss are discussed: the classical one, that indicates calcium malabsorption as the main culprit, and the new one, that emphasizes the role of inflammation. The article summarizes the available epidemiological data about osteopenia/osteoporosis and fragility fractures in these chronic intestinal diseases and presents the state-of-the-art treatment options.

Role of calcium malabsorption in the development of secondary hyperparathyroidism after biliopancreatic diversion

Secondary hyperparathyroidism (SH) is a frequent metabolic complication of bariatric surgery. Around 70%of patients who undergo biliopancreatic diversion (BPD) have this complication in the long term. The aim of this study was to evaluate the relative influence of vitamin D deficiency and calcium malabsorption in the development of SH in patients who underwent BPD. We reviewed the mean values of PTH throughout the post-operative follow-up and of related biochemical data (25-hydroxyvitamin D, calcium, magnesium) of 121 patients who underwent BPD at our institute from November 1996 to November 2004 (mean follow-up 66 months). Mean PTH correlated negatively with mean 25-hydroxyvitamin D (r=-0.27, p=0.003) and with urinary calcium(r=-0.19, p=0.047), and positively with age (r=0.22, p=0.018). However, a high mean PTH was found in 48.7% patients with mean 25-hydroxyvitamin D >or=30 ng/ml and in 80.0% patients with mean 25-hydroxyvitamin D between 20 and 30 ng/ml. The mean PTH was normal in 5 patients without calcium supplements at present, and progressively increased in parallel to the calcium dose in the rest of patients, although mean 25-hydroxyvitamin D levels were not related to the calcium dose. Our data suggest that individual differences in active and/or passive calcium absorption determine intractable SH after BPD in around half of the patients who have normal levels of 25-hydroxyvitamin D and in 80% of patients with 25-hydroxyvitamin D levels between 20 and 30 ng/ml after BPD, worsening with age.

Vitamin D receptor amounts across different segments of the gastrointestinal tract in Brown Swiss and Holstein Frisean cows of different age

During different stages of lactation, different requirements of calcium have to be met depending on the milk amount. Vitamin D receptors (VDR) regulate calcium homeostasis by increasing the entry of Ca into blood from bone stores and dietary sources. The purpose of this study was to investigate if age and breed of cows influence VDR amounts across different segments of the gastrointestinal tract. Thirty-six cows were used (18 Brown Swiss, 18 Holstein Friesan, both > 5.5 years or < 4.5 years). Tissue specimens of the intestines were collected from the cows. Formaldehyde-fixed and microwave-treated paraffin sections were used for VDR immunohistochemistry employing a biotinylated monoclonal rat antibody and streptavidin peroxidase technique. The results showed that nuclei and cytoplasm of enterocytes stained positively for VDRs. Strongest immunoreactions were observed in intermediate and basal glandular cells. No significant differences were observed between the different groups. Vitamin D receptors immunoreactivities were prominent in duodenal mucosa, lower in jejunum and in colon, decreased further in ileum and were lowest in caecum. Decreases in number of positively marked cells and staining intensities resulted in reduced immunoreactions. The results of this study indicate that VDR are highly expressed at the site of maximal intestinal calcium absorption. No significant influence of age and breed was observed. The animals used were not in a negative Ca balance. The cows were all in the stage of late or mid lactation. During these periods, the Ca requirements are low and the diets are high in Ca concentration; and the animals are adapted to these circumstances. Passive absorption in adult animals seems to dominate when Ca intake is adequate or high. The active absorption may play a considerably more significant role during the peripartal period, when Ca homeostatic mechanisms are challenged because of tremendous Ca demand at the initiation of lactation.

Identification of the functional vitamin D response elements in the human MDR1 gene

P-glycoprotein, encoded by the multidrug resistance 1 (MDR1) gene, is an efflux transporter and plays an important role in pharmacokinetics. The expression of MDR1 is induced by a variety of compounds, of which 1alpha,25-dihydroxyvitamin D(3) is known to be an effective inducer. However, it remains unclear how 1alpha,25-dihydroxyvitamin D(3) regulates the expression of MDR1. In this study, we demonstrated that the vitamin D receptor (VDR) induces MDR1 expression in a 1alpha,25-dihydroxyvitamin D(3)-dependent manner. Luciferase assays revealed that the region between -7.9 and -7.8k bp upstream from the transcription start site of the MDR1 is responsible for the induction by 1alpha,25-dihydroxyvitamin D(3). Electrophoretic mobility shift assays revealed that several binding sites for the VDR/retinoid X receptor alpha (RXRalpha) heterodimer are located between the -7880 and -7810 bp region, to which the three molecules of VDR/RXRalpha are able to simultaneously bind with different affinities. Luciferase assays using mutated constructs revealed that the VDR-binding sites of DR3, DR4(I), MdC3, and DR4(III) contribute to the induction, indicating that these binding sites act as vitamin D response elements (VDREs). The contribution of each VDRE to the inducibility was different for each response element. An additive effect of the individual VDREs on induced luciferase activity by 1alpha,25-dihydroxyvitamin D(3) was also observed. These results indicate that the induction of MDR1 by 1alpha,25-dihydroxyvitamin D(3) is mediated by VDR/RXRalpha binding to several VDREs located between -7880 and -7810bp, in which every VDRE additively contributes to the 1alpha,25-dihydroxyvitamin D(3) response.

Heat shock protein 90beta: a novel mediator of vitamin D action

We investigated the role of Heat shock protein 90 (Hsp90) in vitamin D action in Caco-2 cells using geldanamycin (GA) to block Hsp90 function and RNA interference to reduce Hsp90beta expression. When cells were exposed to GA, vitamin D-mediated gene expression and transcriptional activity were inhibited by 69% and 54%, respectively. Gel shift analysis indicated that GA reduced vitamin D-mediated DNA binding activity of the vitamin D receptor (VDR). We tested the specific role of Hsp90beta by knocking down its expression with stably expressed short hairpin RNA. Vitamin D-induced gene expression and transcriptional activity were reduced by 90% and 80%, respectively, in Hsp90beta-deficient cells. Nuclear protein for VDR and RXRalpha, its heterodimer partner, were not reduced in Hsp90beta-deficient cells. These findings indicate that Hsp90beta is needed for optimal vitamin D responsiveness in the enterocyte and demonstrate a specific role for Hsp90beta in VDR signaling.

Calcium metabolism and vitamin D in the extreme longevity

Skeletal remodelling is a continuous process during life and is still active also in extreme senescence. In the elderly, bone resorption often prevails over bone formation, causing bone loss and fragility. Elderly subjects are exposed to the risk of fractures, and loss of self-sufficiency, if considering that the proximal femur is the most frequently involved site. Bone remodelling can maintain circulating calcium within physiological ranges, at the expense of a substantial loss of this ion from the skeleton, particularly during senescence. Calcium metabolism is regulated at cellular/molecular level by a network of cytokines, growth factors, systemic hormones that act on bone in paracrine/autocrine/systemic fashion. Among the molecules involved in bone metabolism, parathyroid hormone (PTH) and vitamin D present some peculiar aspects during senescence. The osteometabolic features in a consistent group of centenarians have been evaluated. It results that a severe hypovitaminosis D was present in 99 out of 104 centenarians (25-OH vitamin D below 5 nmol/L), and that it plays an important role as a factor inducing a vicious circle involving hypocalcemia, secondary hyperparathyroidism, together with biochemical features indicating a consistent bone loss. Serum C-terminal cross-linking telopeptide, a specific marker of bone resorption was elevated in 92% of these subjects. Moreover, it has been found that several femoral fractures had occurred after 90 years of age. These data offer a rational for the possible prevention of elevated bone turnover, bone loss and consequently the reduction of osteoporotic fractures and fractures-induced disability, in the oldest olds, through the simple supplementation with calcium and vitamin D.

Immunohistochemical Demonstration of Vitamin D Receptor Distribution in Goat Intestines

Vitamin D (VD) plays an important role in calcium homeostasis. 1,25-Dihydroxycholecalciferol or calcitriol modulates gene transcription via nuclear VD receptors (VDR). In the intestines, VD promotes calcium resorption via VDR. VDR has not been systematically assessed within the intestine in any species. We therefore present a semiquantitative immunohistochemical study of the distribution patterns of VDR in goat intestines. Intestinal tissue probes were collected from 5 lambs and 5 non-lactating non-pregnant dams, fixed in formalin, embedded in paraffin and assessed for VDR. Nuclear VDR immunoreaction was scored semiquantitatively. VDR exhibited a segment-specific distribution pattern. Goblet cells were always devoid of VDR. Enterocytes within the surface epithelium and the superficial crypts generally demonstrated only a weak immunoreaction along the length of the intestine, while basally and/or intermediately located crypt epithelial cells exhibited strong VDR immunoreactions in the duodenum, jejunum and colon descendens. The difference in VDR staining between deep and superficial locations was most prominent in the duodenum and less evident in the jejunum, ileum and colon descendens. Results demonstrate that VDR distribution exhibits cell type-, segment- and location-specific patterns in the goat. Data may serve as a basis for future experiments on the role of VDR in Ca metabolism.

Calcium channel TRPV6 expression in human duodenum: different relationships to the vitamin D system and aging in men and women

Intestinal absorption of calcium affects bone mineralization and varies greatly. In human duodenum, expression of the calcium channel TRPV6 was directly related to blood 1,25-dihydroxyvitamin D in men, but effects of age with lower median vitamin D receptor levels were more significant in women.

INTRODUCTION

The TRPV6 calcium channel/transporter is implicated in animal studies of intestinal calcium absorption, but in humans, its role and relationship to differences in mineral metabolism is unclear. We aimed to characterize TRPV6 expression in human intestine including defining relationships to the vitamin D endocrine system.

MATERIALS AND METHODS

TRPV6 transcript expression was determined in endoscopic mucosal biopsies obtained from normal duodenum. Expression was compared with that in ileum and with in situ hybridization in archival tissues and related to sequence variants in genomic DNA. TRPV6 expression was related in 33 subjects to other transcripts involved in calcium absorption including the vitamin D receptor (VDR) and to blood vitamin D metabolites including 1,25-dihydroxyvitamin D [1,25(OH)(2)D].

RESULTS

TRPV6 transcripts were readily detected in duodenum but not in ileum. Expression was highest in villous epithelial cells. Sequence variants in the coding and upstream regions of the gene did not affect TRPV6 expression. The relationship between duodenal TRPV6 expression and 1,25(OH)(2)D differed in men and women. In men, linear regression showed a strong association with 1,25(OH)(2)D (r = 0.87, p < 0.01), which was unaffected by age. In women, there was no significant overall relationship with 1,25(OH)(2)D, but there was a significant decrease with age (r = -0.69, p < 0.001). Individual expression of TRPV6 and VDR was significantly correlated. The group of older women (>50) had lower median levels of both TRPV6 and VDR transcripts than younger women (p < 0.001 and 0.02, respectively).

CONCLUSIONS

Duodenal TRPV6 expression is vitamin D dependent in men, but not in older women, where expression of TRPV6 and VDR are both reduced. These findings can explain, at least in part, the lower fractional calcium absorption seen in older postmenopausal women.

Dietary inulin intake and age can significantly affect intestinal absorption of calcium and magnesium in rats: a stable isotope approach

BACKGROUND

previous studies have shown that non-digestible inulin-type fructan intake can increase intestinal mineral absorption in both humans and animals. However, this stimulatory effect on intestinal absorption may depend on experimental conditions such as duration of fermentable fiber intake, mineral diet levels and animals' physiological status, in particular their age.

OBJECTIVES

the aim of this study was to determine the effect of inulin intake on Ca and Mg absorption in rats at different age stages.

METHODS

eighty male Wistar rats of four different ages (2, 5, 10 and 20 months) were randomized into either a control group or a group receiving 3.75% inulin in their diet for 4 days and then 7.5% inulin for three weeks. The animals were fed fresh food and water ad libitum for the duration of the experiment. Intestinal absorption of Ca and Mg was determined by fecal monitoring using stable isotopic tracers. Ca and Mg status was also assessed.

RESULTS

absorption of Ca and Mg was significantly lower in the aged rats (10 and 20 mo) than in the young and adult rat groups. As expected, inulin intake increased Ca and Mg absorption in all four rat groups. However, inulin had a numerically greater effect on Ca absorption in aged rats than in younger rats whereas its effect on Mg absorption remained similar across all four rat age groups.

CONCLUSION

the extent of the stimulatory effect of inulin on absorption of Ca may differ according to animal ages. Further studies are required to explore this effect over longer inulin intake periods, and to confirm these results in humans.

D-hormone analog alfacalcidol: an update on its role in post-menopausal osteoporosis and rheumatoid arthritis management

Alfacalcidol (1-alpha-hydroxyvitamin D3) is a non-endogenous analog of vitamin D which can bypass the renal and intestinal regulatory mechanisms that control the production of calcitriol (1,25-hydroxyvitamin D3, the active form of vitamin D, D-Hormone). Alfacalcidol may be metabolized into calcitriol with a limited risk of hypercalcemia. Alfacalcidol and calcitriol have been evaluated in animal and human studies assessing their effects on bone mineral density and fracture rates. More recently, they have been shown to produce beneficial effects in muscle, immune system, and autoimmune diseases, including rheumatoid arthritis. This paper discusses the therapeutic efficacy of alfacalcidol in reports in which it has been proposed as an interesting alternative to vitamin D or calcitriol. Some recent findings about general metabolism and regulation of vitamin D and its analogs are discussed. The biological and clinical effects of alfacalcidol in post-menopausal osteoporosis are reviewed, followed by critical appraisal of its efficacy in preventing bone loss and falls in the elderly. The last two sections discuss the role of D analogs in regulating the immune system, with particular regard to rheumatoid arthritis. The main results of this review show that alfacalcidol may have a wider range of therapeutic applicability, beyond simply restricting it to patients in hemodialysis or peritoneal dialysis with high serum levels of intact PTH.

Effect of age on calcium absorption in postmenopausal women

BACKGROUND

It is assumed that calcium absorption decreases with age, but this is not well documented. We report a study that addresses this issue.

OBJECTIVE

The aim was to establish the extent and timing of any age-related change in calcium absorption in postmenopausal women.

DESIGN

We measured radiocalcium absorption (alpha) in 262 healthy postmenopausal women aged 40-87 y. We also measured the serum vitamin D metabolites, parathyroid hormone (PTH), and other biochemical variables.

RESULTS

Radiocalcium absorption decreased with age (P = 0.018); it was 28% lower in the 25 women aged >75 y than in the rest (P < 0.001). It was significantly related to serum 1,25-dihydroxyvitamin D [1,25(OH)(2)D] in the whole set and in both the younger and older subsets, but it was not related to either 25-dihydroxyvitamin D [25(OH)D] or PTH or to any other measured variable. No decrease in 1,25(OH)(2)D was seen with age to account for the decrease in calcium absorption, so radiocalcium absorption corrected for serum 1,25(OH)(2)D decreased significantly after age 75 y. On multivariate analysis, the serum 1,25(OH)(2)D concentration was a positive function of 25(OH)D (P < 0.001), albumin (P = 0.010), and PTH (P = 0.012) and a negative function of serum creatinine (P = 0.003). PTH was a negative function of calculated ionized calcium (P = 0.004) and 25(OH)D (P = 0.009) and a positive function of weight (P = 0.011) and age (P = 0.028).

CONCLUSIONS

A late age-related decrease in calcium absorption is seen in postmenopausal women in addition to the decline that occurs at menopause. This decrease could be due to a decline in either the active calcium transport or diffusion component of the calcium absorption system.

Duodenal expression of the epithelial calcium transporter gene TRPV6: is there evidence for Vitamin D-dependence in humans?

Intestinal absorption of dietary calcium is regulated by 1,25-dihydroxycholecalciferol (1,25(OH)(2)D(3)) in humans and in experimental animals but interspecies differences in responsiveness to 1,25(OH)(2)D(3) are found, possibly due to differences in the promoters of genes for intestinal calcium transport proteins or of the Vitamin D receptor (VDR). The epithelial calcium transporter, known as ECAC2 or CAT1, the product of the TRPV6 gene expressed in proximal intestinal enterocytes, is the first step in calcium absorption and studies in mice have shown that its expression is Vitamin D-dependent. In contrast in man, we showed that duodenal TRPV6 mRNA expression was independent of blood 1,25(OH)(2)D(3), although in Caco-2 cells, 1,25(OH)(2)D(3)-dependent changes have been demonstrated. We sought to explain these findings. A consensus Vitamin D response element in the mouse gene is absent in the human gene. We re-analysed our duodenal expression data according to a CDX2-site polymorphism in the VDR promoter. Mean TRPV6 expression was the same, but there was evidence of different responsiveness to 1,25(OH)(2)D(3). In the GG genotype group, but not the AG, duodenal TRPV6 expression increased with 1,25(OH)(2)D(3). We postulate that lower levels of expression of VDR in the GG group produce greater sensitivity to 1,25(OH)(2)D(3).

Vitamin D receptor expression in human muscle tissue decreases with age

Intracellular 1,25-dihydroxyvitamin D receptor (VDR) is expressed in human skeletal muscle tissue. However, it is unknown whether VDR expression in vivo is related to age or vitamin D status, or whether VDR expression differs between skeletal muscle groups.

INTRODUCTION

We investigated these factors and their relation to 1,25-dihydroxyvitamin D receptor (VDR) expression in freshly removed human muscle tissue.

MATERIALS AND METHODS

We investigated biopsy specimens of the gluteus medius taken at surgery from 20 female patients undergoing total hip arthroplasty (mean age, 71.6 +/- 14.5; 72% > 65 years) and biopsy specimens of the transversospinalis muscle taken at surgery from 12 female patients with spinal operations (mean age, 55.2 +/- 19.6; 28% > 65 years). The specimens were obtained by immunohistological staining of the VDR using a monoclonal rat antibody to the VDR (Clone no. 9A7). Quantitative VDR expression (number of VDR positive nuclei) was assessed by counting 500 nuclei per specimen and person. Serum concentrations of 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D were assessed at day of admission to surgery.

RESULTS

All muscle biopsy specimens stained positive for VDR. In the univariate analyses, increased age was associated with decreased VDR expression (r = 0.5: p = 0.004), whereas there were no significant correlations between VDR expression and 25-hydroxyvitamin D or 1,25-dihydroxyvitamin D levels. VDR expression did not differ between patients with hip and spinal surgery. In the multivariate analysis, older age was a significant predictor of decreased VDR expression after controlling biopsy location (gluteus medius or the transversospinalis muscle), and 25-hydroxyvitamin D levels (linear regression analysis: beta-estimate = -2.56; p = 0.047).

CONCLUSIONS

Intranuclear immunostaining of the VDR was present in muscle biopsy specimens of all orthopedic patients. Older age was significantly associated with decreased VDR expression, independent of biopsy location and serum 25-hydroxyvitamin D levels.

Effect of growth and maturation on membrane-initiated actions of 1,25-dihydroxyvitamin D3?II: Calcium transport, receptor kinetics, and signal transduction in intestine of female chickens

We recently reported (Larsson and Nemere [2003]: Endocrinology 144:1726) the effects of growth and maturation on 1,25(OH)2D3-membrane initiated effects in the intestine of male chickens. Here we extend our observations to studies on females with two stages of high calcium demand: growth (7-14 weeks) and egg laying (28-58 weeks). The rapid stimulatory effect of 130 pM 1,25(OH)2D3 on calcium transport was assessed as a physiological response in perfused duodena of 7-, 14-, 28-, and 58-week-old chickens, and determined to be 308%, 184%, 170%, and 153%, respectively, of corresponding controls after 40 min. Saturation analyses of [3H]1,25(OH)2D3 binding to nuclear vitamin D receptor (VDR) indicated an absence of cooperative binding, no changes in dissociation constant (Kd) with age, and an increase in maximum binding capacity (Bmax) between 7-week birds and older age groups. Analyses of saturable binding of [3H]1,25(OH)2D3 to the membrane associated rapid response steroid binding protein (1,25D3-MARRS bp) in basal lateral membranes (BLM), indicated cooperative binding, and an increase in both Bmax and Kd with age. No changes in the age-related expression of 1,25D3-MARRS bp were found, as judged by Western analyses, suggesting that a shift in ligand binding to lower affinity membrane components accounted for the increase in calculated Bmax. Basal levels of protein kinase C (PKC) activity decreased with age, as did hormone enhancement of activity. Basal levels of protein kinase A (PKA) activity remained constant with age, while the magnitude of hormone stimulation increased. Comparison of dose-response curves for ion transport and kinase activities in 7-week chicks suggested that PKC mediates phosphate transport while PKA mediates calcium transport. Thus, the age-related loss of calcium transport is most likely related to loss of PKC-mediated phosphate transport.

The role of the intestine in bone homeostasis

The intestine is critical for calcium absorption and skeletal mineralization. Nutritional factors affect the dietary intake of calcium and its bioavailability in the intestine. Individuals differ considerably in their ability to absorb calcium but the reasons for this physiological variation are not fully understood although much is now known about the effects of vitamin D metabolites and the molecular steps in calcium absorption. Bone changes are found in many intestinal disorders including lactose intolerance, coeliac disease, short bowel syndrome, small intestinal bacterial overgrowth and Crohn's disease.

Vitamin D and bone health in postmenopausal women

Osteoporosis, a disease of increased skeletal fragility, is becoming increasingly common as the U.S. population ages. Adequate vitamin D and calcium intake is the cornerstone of osteoporosis prevention and treatment. Age-related changes in vitamin D and calcium metabolism increase the risk of vitamin D insufficiency and secondary hyperparathyroidism. Although longitudinal data have suggested a role of vitamin D intake in modulating bone loss in perimenopausal women, studies of vitamin D and calcium supplementation have failed to support a significant effect of vitamin D and calcium during early menopause. There is a clearer benefit in vitamin D and calcium supplementation in older postmenopausal women. Vitamin D intake between 500 and 800 IU daily, with or without calcium supplementation, has been shown to increase bone mineral density (BMD) in women with a mean age of approximately 63 years. In women older than 65, there is even more benefit with vitamin D intakes of between 800 and 900 IU daily and 1200-1300 mg of calcium daily, with increased bone density, decreased bone turnover, and decreased nonvertebral fractures. The decreases in nonvertebral fractures may also be influenced by vitamin D-mediated decreases in body sway and fall risk. There are insufficient available data supporting a benefit from vitamin D supplementation alone, without calcium, to prevent osteoporotic fracture in postmenopausal women.

Role of the vitamin D-endocrine system in the pathophysiology of postmenopausal osteoporosis

Impaired calcium absorption and impaired adaptation to a low calcium diet are common features of aging in women and these processes are even more severely impaired in patients with osteoporotic fractures. The calcium absorption defects are associated with several abnormalities of the vitamin D-endocrine system including secondary hyperparathyroidism, intestinal resistance to 1,25-dihydroxyvitamin D (1,25(OH)(2)D) action, decreased 1,25(OH)(2)D production due to impaired 25(OH)D 1alpha-hydroxylase activity, and, in some elderly persons, nutritional deficiency of vitamin D. However, in postmenopausal women, most of these abnormalities are normalized by administration of physiologic replacement dosages of estrogen and, thus, appear to be secondary consequences of estrogen deficiency. Nonetheless, a minority of them, especially nutritional vitamin D deficiency and impaired 25(OH)D 1alpha-hydroxylase activity late in life, appear to be primary and are independent of estrogen deficiency.

Effects of vitamin D metabolites on intestinal calcium absorption and bone turnover in elderly women

BACKGROUND

The relative importance of vitamin D metabolites in the regulation of gut calcium absorption has not been well studied in elderly women living in an environment with abundant sunlight.

OBJECTIVE

The objective was to examine the determinants of active gut calcium absorption ( +/- SD: 42 +/- 11%) after an overnight fast with the use of a low (10 mg) calcium load.

DESIGN

One hundred twenty elderly women aged 74.7 +/- 2.6 y underwent an active calcium absorption test with a radioactive calcium tracer, dietary analysis, and measurement of markers of bone turnover and calcium metabolism.

RESULTS

The mean serum 25-hydroxyvitamin D [25(OH)D] concentration at the time of the calcium absorption test was 68 +/- 29 nmol/L. Gut calcium absorption was correlated with 25(OH)D but not 1,25-dihydroxyvitamin D (calcitriol), the free calcitriol index, or dietary calcium intake. After adjustment for age, calcitriol concentration, and dietary calcium intake, the significant determinant of fractional calcium absorption was the 25(OH)D concentration (r = 0.34, P = 0.001). When body weight was included in the regression, both 25(OH)D (beta = 1.20 x 10(-3)) and calcitriol (beta = 1.00 x 10(-3)) were significantly correlated with calcium absorption. Despite the strong relation between 25(OH)D and gut calcium absorption, there was no relation with other aspects of bone turnover or calcium metabolism.

CONCLUSION

These data suggest that at low calcium loads, 25(OH)D is a more important determinant of gut calcium absorption than is calcitriol in elderly women exposed to abundant sunlight, but that this relation has little effect on overall calcium metabolism.

Increased vitamin D receptor level enhances 1,25-dihydroxyvitamin D3-mediated gene expression and calcium transport in Caco-2 cells

Altered vitamin D receptor (VDR) level has been proposed to explain differences in intestinal responsiveness to 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]. We tested whether the enterocyte VDR level influences 1,25(OH)2D3-mediated gene expression and transepithelial calcium (Ca) transport in the human intestinal cell line Caco-2. Cells were stably transfected with a human metallothionein (hMT) IIA promoter-human VDR (hVDR) complementary DNA (cDNA) transgene that overexpressed hVDR in response to heavy metals. In MTVDR clones, induction of 25-hyroxyvitamin D3-24-hydroxylase (24-OHase) messenger RNA (mRNA) expression by 1,25(OH)2D3 (10(-9) M, 4 h) was correlated to metal-induced changes in nuclear VDR level (r2 = 0.99). In MTVDR clones, basal VDR level was 2-fold greater and 1,25(OH)2D3-mediated Ca transport (10(-7) M, 24 h) was 43% higher than in parental Caco-2 cells. Treatment of MTVDR clones with Cd (1 microM, 28 h) increased VDR level by 68%, significantly enhanced 1,25(OH)2D3-mediated Ca transport by 24%, and increased accumulation of calbindin D9K mRNA by 76% relative to 1,25(OH)2D3 alone. These observations support the hypothesis that the enterocyte VDR level is an important modulator of intestinal responsiveness to 1,25(OH)2D3.

Effect of estrogen on intestinal strontium absorption in postmenopausal women

OBJECTIVES

there is considerable uncertainty about the underlying cause of decreased intestinal calcium absorption that occurs in postmenopausal women. In a previous study, estrogen treatment did not result in an increased intestinal calcium absorption using strontium as a marker. A possible explanation could be that the calcium/strontium load given to the women was too high ( approximately 600 mg Ca), which might result in an insensitive test with respect to the possible stimulation of active strontium transport by estrogen. Therefore, the purpose of this study was to reinvestigate the effect of estrogen on active intestinal strontium absorption using a load of 2.5 mmol of strontium only.

METHODS

the effect of estrogen on intestinal strontium absorption was measured in eight normal postmenopausal women. The study included two baseline strontium absorption tests, which were performed with an interval of 10 days for calculating the within subject variation (SER). Thereafter the effect of 2 months of estrogen treatment on intestinal strontium absorption was assessed. Fractional absorption (FC(240)) and the area under the concentration time curve (AUC) 4 h after an oral strontium load of 2.5 mmol were calculated.

RESULTS

the within subject SER of FC(240) and AUC(0-240) were 2.3+/-0.76 and 1.2+/-0.41, respectively. FC(240) and AUC(0-240) of strontium were unchanged after treatment with estrogen.

CONCLUSIONS

in normal postmenopausal women, we did not find a modulating effect of short-term treatment with a (supra) physiological dose of estrogen on intestinal calcium absorption as measured by the strontium absorption test.

Polymorphisms in the vitamin D receptor gene and bone mass, bone turnover and osteoporotic fractures

BACKGROUND

Vitamin D is essential for normal bone metabolism. Polymorphisms in exon 2, intron 8 and exon 9 of the vitamin D receptor (VDR) gene have previously been found to be associated with bone mass and bone turnover.

MATERIALS AND METHODS

We examined the effect of these polymorphisms, separately and in combination, on bone mineral density (BMD), bone turnover, and the prevalence of osteoporotic fractures in 192 osteoporotic patients and 207 normal controls. The four polymorphisms were determined by RFLP using Fok I (T2-C), Bsm I (intron 8), Apa I (intron 8) and Taq I (T1055-C) after PCR.

RESULTS

We did not find any association between the Fok I polymorphism and bone mass, bone turnover or prevalence of osteoporotic fractures. We found that BB + Bb-genotypes were more frequent in patients with osteoporotic fractures (chi2 = 3.50, P = 0. 06). Furthermore, BMD of the intertrochanteric region (P < 0.0001, ANOVA) as well as the total hip (P < 0.01, ANOVA) were higher in individuals with the bb-genotype. The Apa I and the Taq I polymorphisms were not distributed differently among osteoporotic patients and normal controls. Apa I was not associated with differences in BMD. BMD of the intertrochanteric region was higher in individuals with the TT-genotype compared with individuals with the Tt- or tt-genotypes (P < 0.01, ANOVA), while no differences could be demonstrated in BMD of the lumbar spine, femoral neck, trochanter or Wards triangle. Combining the genotypes generally reflected the differences caused by the Bsm I polymorphism.

CONCLUSION

We have found that the B-allele of the Bsm I polymorphism in the 3' untranslated region of the VDR was associated with low BMD at the hip, and tended to be associated with osteoporotic fractures. The translation initiation polymorphism in the VDR does not affect BMD and is not associated with osteoporotic fractures in men or women.

Vitamin D receptor gene Fok1 polymorphism predicts calcium absorption and bone mineral density in children

The vitamin D receptor (VDR) gene has been implicated as one of the major genetic components of osteoporosis. We evaluated the relationship between markers of mineral status and restriction fragment length polymorphisms of the VDR gene in 72 healthy children age 7-12 years. Using stable isotope techniques and dual-energy X-ray absorptiometry, we measured dietary calcium absorption, bone calcium deposition rates, and total body bone mineral density (BMD). The Fok1 polymorphism at the VDR translation initiation site was significantly associated with BMD (p = 0.02) and calcium absorption (p = 0.04). Children who were FF homozygotes had a mean calcium absorption that was 41.5% greater than those who were ff homozygotes and 17% greater absorption than Ff heterozygotes. BMD was 8.2% greater in the FF genotype than the ff genotype and 4.8% higher than the Ff genotype. These results suggest a substantial relationship between the VDR gene and bone metabolism at one or more levels, including dietary absorption of calcium and BMD in growing children.

Determinants of peak bone mass: clinical and genetic analyses in a young female Canadian cohort

Peak bone mass has been shown to be a significant predictor of risk for osteoporosis. Previous studies have demonstrated that skeletal mass accumulation is under strong genetic control, and efforts have been made to identify candidate loci. Determinants of peak bone mass also include diet, physical activity, hormonal status, and other clinical factors. The overall contribution of these factors, genetic and nongenetic, and their interaction in determining peak bone density status have not been delineated. Six hundred and seventy-seven healthy unrelated Caucasian women ages 18-35 years were assessed. A detailed, standardized interview was conducted to evaluate lifestyle factors, menstrual and reproductive history, medical conditions, medication use, and family history of osteoporosis. Bone mineral density (BMD) was measured at the lumbar spine (L2-L4) and the femoral neck (hip) using dual-energy X-ray absorptiometry. Genotyping of the vitamin D receptor (VDR) locus at three polymorphic sites (BsmI, ApaI, and TaqI) was performed. In bivariate analyses, BMD at the lumbar spine and hip was positively correlated with weight, height, body mass index (BMI), and level of physical activity, both now and during adolescence, but negatively correlated with a family history of osteoporosis. Hip, but not spine BMD, correlated positively with dietary intake of calcium, and negatively with amenorrhea of more than 3 months, with caffeine intake, and with age. Spine, but not hip BMD, correlated positively with age and with number of pregnancies. VDR haplotype demonstrated significant associations with BMD at the hip, level of physical activity currently, and BMI. In multivariate analysis, independent predictors of greater BMD (at the hip or spine) were: age (younger for the hip, older for the spine), greater body weight, greater height (hip only), higher level of physical activity now and during adolescence, no family history of osteoporosis, and VDR genotype (hip only). Weight, age, level of physical activity, and family history are independent predictors of peak BMD. Of these factors, weight accounts for over half the explained variability in BMD. VDR alleles are significant independent predictors of peak femoral neck, but not lumbar spine BMD, even after adjusting for family history of osteoporosis, weight, age, and exercise. However, the overall contribution of this genetic determinant is modest. Taken together, these factors explained approximately 17% and 21% of the variability in peak spine and hip BMD, respectively, in our cohort. Future research should be aimed at further evaluation of genetic determinants of BMD. Most importantly, understanding the critical interactive nature between genes and the environment will facilitate development of targeted strategies directed at modifying lifestyle factors as well as earlier intervention in the most susceptible individuals.

Expression of genes involved in calcium absorption in human duodenum

BACKGROUND

The role of vitamin D metabolites in the regulation of expression of genes involved in dietary calcium absorption by the human intestine remains poorly understood despite much work in animals.

MATERIALS AND METHODS

To investigate this, we measured the expression of transcripts for two of these genes, calbindin-D9k and the basolateral membrane calcium pumping ATPase, PMCA1, in duodenal endoscopic biopsies from 40 subjects. Northern blots were hybridized with previously characterized probes, and the signal was quantified by phosphor imaging. These transcript levels were related to circulating vitamin D metabolites and also analysed according to the vitamin D receptor gene TaqI polymorphism determined in DNA from blood.

RESULTS

Plasma 1,25-dihydroxycholecalciferol correlated significantly with calbindin-D9k RNA (r = 0.4, P < 0.02) but not with PMCA1. Plasma 25-OH-cholecalciferol was not correlated with transcripts for either gene and, furthermore, the mean levels of these transcripts did not differ significantly when grouped by vitamin D receptor genotype.

CONCLUSION

In normal humans, 1, 25-dihydroxycholecalciferol has a small but significant relationship to duodenal expression of calbindin-D9k, but not to PMCA1 expression.

Evidence for involvement of 17beta-estradiol in intestinal calcium absorption independent of 1,25-dihydroxyvitamin D3 level in the Rat

The sex steroid 17beta-estradiol (17beta-E2) has a broad range of actions, including effects on calcium and bone metabolism. This study with 3-month-old Brown Norway rats was designed to investigate the role of 17beta-E2 in the regulation of calcium homeostasis. Rats were divided in four groups, sham-operated, ovariectomized (OVX), and OVX supplemented with either a 0.025-mg or 0.05-mg 17beta-E2 pellet implanted subcutaneously. After 4 weeks, in none of the groups was serum calcium, phosphate, or parathyroid hormone altered compared with the sham group, while only in the OVX rats was a significant reduction in urinary calcium found. Bone mineral density and osteocalcin were modified, as can be expected after OVX and 17beta-E2 supplementation. OVX resulted in a nonsignificant increase in serum 1,25-dihydroxyvitamin D3 (1,25(OH)2D3). Supplementation with either one of the 17beta-E2 dosages resulted in an 80% reduction of 1,25(OH)2D3 and only a 20% reduction in 25-hydroxyvitamin D3 levels. OVX, as well as supplementation with 17beta-E2, did not affect serum levels of vitamin D binding protein. As a consequence, the estimated free 1,25(OH)2D3 levels were also significantly decreased in the 17beta-E2-supplemented group compared with the sham and OVX groups. Next, the consequences for intestinal calcium absorption were analyzed by the in situ intestinal loop technique. Although the 1,25(OH)2D3 serum level was increased, OVX resulted in a significant decrease in intestinal calcium absorption in the duodenum. Despite the strongly reduced 1,25(OH)2D3 levels (18. 1 +/- 2.1 and 16.4 +/- 2.2 pmol/l compared with 143.5 +/- 29 pmol/l for the OVX group), the OVX-induced decrease in calcium absorption could partially be restored by supplementation with either 0.025 mg or 0.05 mg of 17beta-E2. None of the treatments resulted in a significant change in calcium handling in the jejunum, although the trends were similar as those observed in the duodenum. 17beta-E2 did not change the VDR levels in both the intestine and the kidney. In conclusion, the present study demonstrates that 17beta-E2 is positively involved in intestinal calcium absorption, and the data strengthen the assertion that 17beta-E2 exerts this effect independent of 1,25(OH)2D3. In general, 17beta-E2 not only affects bone turnover but also calcium homeostasis via an effect on intestinal calcium absorption. (J Bone Miner Res 1999;14:57-64)