Vitamin A: is it a risk factor for osteoporosis and bone fracture?

Vitamin A fortification: Recent advances in encapsulation technologies

Vitamin A is an essential micronutrient whose deficiency is still a major health concern in many regions of the world. It plays an essential role in human growth and development, immunity, and vision, but may also help prevent several other chronic diseases. The total amount of vitamin A in the human diet often falls below the recommended dietary allowance of approximately 900-1000 μ $ \umu $ g/day for a healthy adult. Moreover, a significant proportion of vitamin A may be degraded during food processing, storage, and distribution, thereby reducing its bioactivity. Finally, the vitamin A in some foods has a relatively low bioavailability, which further reduces its efficacy. The World Health Organization has recommended fortification of foods and beverages as a safe and cost-effective means of addressing vitamin A deficiency. However, there are several factors that must be overcome before effective fortified foods can be developed, including the low solubility, chemical stability, and bioavailability of this oil-soluble vitamin. Consequently, strategies are required to evenly disperse the vitamin throughout food matrices, to inhibit its chemical degradation, to avoid any adverse interactions with any other food components, to ensure the food is palatable, and to increase its bioavailability. In this review article, we discuss the chemical, physical, and nutritional attributes of vitamin A, its main dietary sources, the factors contributing to its current deficiency, and various strategies to address these deficiencies, including diet diversification, biofortification, and food fortification.

Emerging Cancer Epigenetic Mechanisms Regulated by All-Trans Retinoic Acid

All-trans retinoic acid (RA), which is the dietary bioactive derivative obtained from animal (retinol) and plant sources (beta-carotene), is a physiological lipid signal of both embryonic and postembryonic development. During pregnancy, either RA deficiency or an excessive RA intake is teratogenic. Too low or too high RA affects not only prenatal, but also postnatal, developmental processes such as myelopoiesis and mammary gland morphogenesis. In this review, we mostly focus on emerging RA-regulated epigenetic mechanisms involving RA receptor alpha (RARA) and Annexin A8 (ANXA8), which is a member of the Annexin family, as well as ANXA8 regulatory microRNAs (miRNAs). The first cancer showing ANXA8 upregulation was reported in acute promyelocytic leukemia (APL), which induces the differentiation arrest of promyelocytes due to defective RA signaling caused by RARA fusion genes as the PML-RARA gene. Over the years, ANXA8 has also been found to be upregulated in other cancers, even in the absence of RARA fusion genes. Mechanistic studies on human mammary cells and mammary glands of mice showed that ANXA8 upregulation is caused by genetic mutations affecting RARA functions. Although not all of the underlying mechanisms of ANXA8 upregulation have been elucidated, the interdependence of RA-RARA and ANXA8 seems to play a relevant role in some normal and tumorigenic settings.

Circulating serum level of retinoic acid and hip fractures among postmenopausal women

PURPOSE

The aim of this study was to evaluate the serum levels of retinoic acid (RA), an active form of vitamin A, in postmenopausal women with hip fractures from Zhengzhou, China.

METHODS

This was a case-control study from the Affiliated Hospital of Zhengzhou University. Serum samples were drawn from 375 postmenopausal women who were diagnosed as having hip fracture and 750 matched controls without fracture. Serum RA levels were evaluated as both a continuous variable and a categorical variable in quintiles.

RESULTS

The results showed that the serum levels of RA were significantly (P = .039) higher in patients with hip fracture compared with controls. In univariate and multivariate logistic regression analysis, for each 1 ng/mL increase of serum level of RA, the unadjusted and adjusted risk of hip fracture would be increased by 5% (odds ratio [OR] = 1.05; 95% confidence interval [CI] = 1.00-1.10; P = .035) and 2% (OR = 1.02; 95% CI = 0.95-1.11; P = .096), respectively. In multivariate models comparing the fifth with the third quintiles of RA, the RA was associated with hip fracture, and adjusted risk of hip fracture would be increased by 52% (OR = 1.52; 95% CI = 1.13-1.42; P = .011).

CONCLUSIONS

The results of our study suggest that subclinical higher levels of RA may increase the risk of hip fracture in postmenopausal women, particularly among the top quintile of serum RA. J Am Geriatr Soc 67:336-341, 2019.

Consequences of Inadequate Intakes of Vitamin A, Vitamin B12, Vitamin D, Calcium, Iron, and Folate in Older Persons

Purpose of Review

This review broadly discusses the consequences of inadequate consumption, by deficit or excess, of selected micronutrients on the quality of life and morbidity during aging, specifically considering increases in life expectancy and the costs of care in the older persons.

Recent Findings

A literature review of the periods 2012 to 2018, focusing on vitamins A, B₁₂, and D, calcium, iron and folate, was completed as these micronutrients are found to significantly affect the aging process. Causation and application of these micronutrients to disorders related to aging are controversial and mixed. This review highlights research needs and controversial points on the role of these micronutrients.

Summary

Micronutrient deficiencies are a common and avoidable contributor to decreased quality of life and healthcare costs in the older persons. Further research is needed to determine adequate intakes and innovative uses, including appropriate thresholds for improved health outcomes for this population.

Identification of potential target genes and related regulatory transcription factors in spontaneous hairline fracture induced by hypervitaminosis A

BACKGROUND

The aim was to research the molecular changes of bone cells induced by excessive dose of vitamin A, and analyze molecular mechanism underlying spontaneous fracture.

METHODS

The gene expression profile of GSE29859, including 4 cortical bone marrow samples with excessive doses of Vitamin A and 4 control cortical bone marrow samples, was obtained from the Gene Expression Omnibus (GEO) database. Differentially expressed genes (DGEs) between cortical bone marrow samples and control samples were screened out and pathway enrichment analysis was undertaken. Based on the MSigDB database, the potential regulatory transcription factors (TFs) were identified.

RESULTS

A total of 373 DEGs including 342 up- and 31 down-regulated genes were identified. These DEGs were significantly enriched in pathways of protein processing in endoplasmic reticulum, ubiquitin mediated proteolysis and glycerophospholipid metabolism. Finally, the most significant regulatory TFs were obtained, including E2F Transcription Factor 1 (E2F1), GA Binding Protein Transcription Factor (GABP), Nuclear Factor, Erythroid 2-Like 2 (NRF2) and ELK1, Member of ETS Oncogene Family (ELK1).

CONCLUSION

Key TFs including E2F1, GABP, NRF2 and ELK1 and their targets genes such as Ube2d3, Uba1, Phb2 and Tomm22 may play potential key roles in spontaneous fracture induced by hypervitaminosis A. The pathways of protein processing in endoplasmic reticulum, ubiquitin mediated proteolysis and glycerophospholipid metabolism may be key mechanisms involved in spontaneous fracture induced by hypervitaminosis A. Our findings will provide new insights for the target selection in clinical application to prevent spontaneous fracture induced by hypervitaminosis A.

Nuclear Receptors in Skeletal Homeostasis

Nuclear receptors are a family of transcription factors that can be activated by lipophilic ligands. They are fundamental regulators of development, reproduction, and energy metabolism. In bone, nuclear receptors enable bone cells, including osteoblasts, osteoclasts, and osteocytes, to sense their dynamic microenvironment and maintain normal bone development and remodeling. Our views of the molecular mechanisms in this process have advanced greatly in the past decade. Drugs targeting nuclear receptors are widely used in the clinic for treating patients with bone disorders such as osteoporosis by modulating bone formation and resorption rates. Deficiency in the natural ligands of certain nuclear receptors can cause bone loss; for example, estrogen loss in postmenopausal women leads to osteoporosis and increases bone fracture risk. In contrast, excessive ligands of other nuclear receptors, such as glucocorticoids, can also be detrimental to bone health. Nonetheless, the ligand-induced osteoprotective effects of many other nuclear receptors, e.g., vitamin D receptor, are still in debate and require further characterizations. This review summarizes previous studies on the roles of nuclear receptors in bone homeostasis and incorporates the most recent findings. The advancement of our understanding in this field will help researchers improve the applications of agonists, antagonists, and selective modulators of nuclear receptors for therapeutic purposes; in particular, determining optimal pharmacological drug doses, preventing side effects, and designing new drugs that are more potent and specific.

The potential double-burden of vitamin A malnutrition: under- and overconsumption of fortified table sugar in the Guatemalan highlands

BACKGROUND/OBJECTIVES

In Guatemala, population-wide vitamin A fortification of table sugar has been operating for two decades. The objective of this study was to estimate the adequacy of vitamin A intakes in pregnant and lactating women from low-income, urban and rural communities.

SUBJECTS/METHODS

One or two previous-day dietary recalls were collected in a convenience sample of 234 pregnant and lactating women in the Western Highlands of Guatemala. Estimated daily intakes and main sources of total vitamin A, provitamin A and preformed vitamin A were calculated. Total intakes, adjusted for day-to-day variation, were examined in relation to estimated average requirements (EAR).

RESULTS

Median estimated 1-day total vitamin A intake was 1177 μg retinol activity equivalents (RAE) (interquartile range (IQR) 832-1782) in the urban site and 567 μg RAE (IQR 441-737) in the rural site. Women not meeting their status-specific vitamin A requirement were 3.5 times more common in the rural communities (31%) than in the urban confines (9%). In the urban area, 26 women (21%) had preformed vitamin A intakes above 1500 μg on the day of data collection. Preformed vitamin A accounted for a median of 83.9% and 60.9% of the daily total vitamin A intake in the urban and rural sites, respectively. Sugar was the principal source of vitamin A, contributing 512 μg RAE (IQR 343-749) in the urban site and 256 μg RAE (IQR 189-363 μg) in the rural area.

CONCLUSIONS

The vitamin A contribution from fortified sugar can be a determinant of reaching adequacy; nevertheless, a significant proportion of pregnant and lactating women do not meet the EAR, especially in the rural setting.

Vitamin A intake, serum vitamin D and bone mineral density: analysis of the Korea National Health and Nutrition Examination Survey (KNHANES, 2008-2011)

The association of high vitamin A intake and low bone mineral density (BMD) is still controversial. To determine the association of dietary vitamin A intake and serum 25-hydroxyvitamin D (25(OH)D) concentration with BMD, a total of 6481 subjects (2907 men and 3574 women) aged ≥50 years from the Korean National Health and Nutrition Examination Survey (2008–2011) were divided into groups according to dietary vitamin A intake (tertiles) and serum 25(OH)D (<50, 50–75, >75 nmol/L), and evaluated for BMD after adjusting for relevant variables. Mean dietary vitamin A intakes were 737 and 600 μg RE (Retinol Equivalents) in men and women, respectively. Total hip and femoral neck BMD in men and lumbar spine BMD in women were both positively correlated with dietary vitamin A intake in subjects with serum 25(OH)D >75 nmol/L. Among men with serum 25(OH)D <50 nmol/L, both the top (mean 1353 μg RE) and bottom (mean 218 μg RE) tertiles of dietary vitamin A intake had lower BMD than the middle group (mean 577 μg RE). In this population, BMD was the highest among men and women with serum 25(OH)D = 50–75 nmol/L and that there were no differences in BMD by vitamin A intake in these vitamin D adequate groups. This cross-sectional study indicates that vitamin A intake does not affect bone mineral density as long as the serum 25(OH)D concentration is maintained in the moderate level of 50–75 nmol/L.

Minireview: nuclear receptor regulation of osteoclast and bone remodeling

Osteoclasts are bone-resorbing cells essential for skeletal remodeling and regeneration. However, excessive osteoclasts often contribute to prevalent bone degenerative diseases such as osteoporosis, arthritis, and cancer bone metastasis. Osteoclast dysregulation is also associated with rare disorders such as osteopetrosis, pycnodysostosis, Paget's disease, and Gorham-Stout syndrome. The nuclear receptor (NR) family of transcription factors functions as metabolic sensors that control a variety of physiological processes including skeletal homeostasis and serves as attractive therapeutic targets for many diseases. In this review, we highlight recent findings on the new players and the new mechanisms for how NRs regulate osteoclast differentiation and bone resorption. An enhanced understanding of NR functions in osteoclastogenesis will facilitate the development of not only novel osteoprotective medicine but also prudent strategies to minimize the adverse skeletal effects of certain NR-targeting drugs for a better treatment of cancer and metabolic diseases.

Prolonged overdose of all-trans retinoic acid enhances bone sensitivity in castrated mice

OBJECTIVES

Intake of multivitamin preparations is very common in developed countries. However, excessive intake of vitamin A was associated with increased bone fragility. The aim of this study was to determine if chronic administration of the active metabolite of vitamin A all-trans-retinoic acid (ATRA) in slight excess is associated with changes of bone turnover and density in intact and castrated mice.

METHOD

Three mo old male mice (C57B1/6) intact and castrated were injected intraperitonealy with 10 mg/kg/d of the ATRA or vehicle (control) once daily for 3 wk. The bone density, ash weights, calcium, and phosphorus content of the femur were measured. Plasma tartrate-resistant acid phosphatase (Tr-ACP) and serum bone alkaline phosphatase (B-ALP) were determined.

RESULTS

ATRA decreased bone density in both groups; however, this effect was more pronounced in castrated animals (1.487 ± 0.04 to 1,360 ± 0.05 g/cm(3)) than in intact mice (1.570 ± 0.03 to 1.510 ± 0.03 g/cm(3)). Bone density correlated with decreased B-ALP and increased Tr-ACP in ATRA-treated mice. ATRA treatment led to significantly lower thickness of cortical bone both in the intact and castrated animals.

CONCLUSION

Our results indicate that repeated administration of ATRA in slight excess leads to significant bone loss both in intact and castrated mice. This effect was more pronounced in testosterone-deficient animals. Testosterone deficiency as occurs following castration may sensitize the bone to resorption mediated by ATRA. Therefore, chronic vitamin A administration may be a risk factor for osteoporosis, especially in older and testosterone-depleted subjects.

Acyclic retinoid targets platelet-derived growth factor signaling in the prevention of hepatic fibrosis and hepatocellular carcinoma development

Hepatocellular carcinoma (HCC) often develops in association with liver cirrhosis, and its high recurrence rate leads to poor patient prognosis. Although recent evidence suggests that peretinoin, a member of the acyclic retinoid family, may be an effective chemopreventive drug for HCC, published data about its effects on hepatic mesenchymal cells, such as stellate cells and endothelial cells, remain limited. Using a mouse model in which platelet-derived growth factor (PDGF)-C is overexpressed (Pdgf-c Tg), resulting in hepatic fibrosis, steatosis, and eventually, HCC development, we show that peretinoin significantly represses the development of hepatic fibrosis and tumors. Peretinoin inhibited the signaling pathways of fibrogenesis, angiogenesis, and Wnt/β-catenin in Pdgf-c transgenic mice. In vitro, peretinoin repressed the expression of PDGF receptors α/β in primary mouse hepatic stellate cells (HSC), hepatoma cells, fibroblasts, and endothelial cells. Peretinoin also inhibited PDGF-C-activated transformation of HSCs into myofibroblasts. Together, our findings show that PDGF signaling is a target of peretinoin in preventing the development of hepatic fibrosis and HCC.

Adverse effects of antioxidative vitamins

High doses of synthetic antioxidative vitamins: A, E, C and β-carotene are often used on long-term basis in numerous preventive and therapeutic medical applications. Instead of expected health effects, the use of those vitamins may however lead to cases of hypervitaminosis and even to intoxication. The article points out main principles of safety which are to be observed during supplementation with antioxidative vitamins. Toxic effects resulting from erroneous administration of high doses of those substances on organs and systems of the organism are also discussed. Attention is drawn to interactions of antioxidative vitamins with concomitantly used drugs, as well as intensification of adverse effects caused by various exogenous chemical factors. Moreover, the article presents the evaluation of supplementation with these vitamins, which was performed in large studies.

Role of carotenoid β-cryptoxanthin in bone homeostasis

Bone homeostasis is maintained through a balance between osteoblastic bone formation and osteoclastic bone resorption. Aging induces bone loss due to decreased osteoblastic bone formation and increased osteoclastic bone resorption. Osteoporosis with its accompanying decrease in bone mass is widely recognized as a major public health problem. Nutritional factors may play a role in the prevention of bone loss with aging. Among various carotenoids (carotene and xanthophylls including beta (β)-cryptoxanthin, lutein, lycopene, β-carotene, astaxanthin, and rutin), β-cryptoxanthin, which is abundant in Satsuma mandarin orange (Citrus unshiu MARC.), has been found to have a stimulatory effect on bone calcification in vitro. β-cryptoxanthin has stimulatory effects on osteoblastic bone formation and inhibitory effects on osteoclastic bone resorption in vitro, thereby increasing bone mass. β-cryptoxanthin has an effect on the gene expression of various proteins that are related osteoblastic bone formation and osteoclastic bone resororption in vitro. The intake of β-cryptoxanthin may have a preventive effect on bone loss in animal models for osteoporosis and in healthy human or postmenopausal women. Epidemiological studies suggest a potential role of β-cryptoxanthin as a sustainable nutritional approach to improving bone health of human subjects. β-Cryptoxanthin may be an osteogenic factor in preventing osteoporosis in human subjects.

Nutrition, bone, and aging: an integrative physiology approach

Osteoporosis, a condition associated with significant morbidity and mortality, is prevalent in the growing elderly population. Aging is associated with characteristic changes in the complex pathways of bone remodeling and in patterns of food intake. Whereas the traditional focus of nutritional supplementation for protection of bone health has centered around calcium and vitamin D, a multitude of nutrients have been identified with effects on bone, both individually and in combination. An integrative physiology approach can assist in formulating a deeper understanding of the complex interactions of nutrition and aging with bone, with the goal of identifying modifiable risk factors for the prevention of bone loss.

Retinol may counteract the negative effect of cadmium on bone

Cadmium and high vitamin A intake are both proposed risk factors for low bone mineral density (BMD), but potential interactions have not been studied. Within the Women's Health in the Lund Area, a population-based study in southern Sweden, we measured retinol in serum among 606 women aged 54-64 y. Data on BMD were measured by DXA at the distal forearm. Parathyroid hormone (PTH), bone alkaline phosphatase (bALP), and osteocalcin in serum and deoxypyridinoline (DPD) and cadmium in urine were available. Associations were evaluated using multivariable-adjusted linear regression analysis. Serum retinol concentrations (median, 1.9; range, 0.97-4.3 μmol/L) were inversely associated with the bone formation markers bALP and osteocalcin (P ≤ 0.04) and with PTH (P = 0.07) and tended to be positively associated with BMD (P = 0.08) but not with the bone resorption marker DPD, indicating different effects on bone compared to urinary cadmium (median, 0.66; range, 0.12-3.6 nmol/mmol creatinine). Women with serum retinol less than the median and cadmium greater than the median had lower BMD than those with retinol greater than the median and cadmium less than the median (P = 0.016 among all women and P = 0.010 among never-smokers). Our findings suggest that adequate vitamin A status may counteract the adverse association between cadmium and BMD.

Retinoic acid inhibits NFATc1 expression and osteoclast differentiation

Ingestion of excess vitamin A appears to correlate with an increased fracture risk, an outcome that is likely mediated by retinoic acids (RAs); these are vitamin A metabolites that have dramatic effects on skeletal development. We studied the impacts of RA and isoform-specific RA receptor (RAR) agonists (α, β, and γ) on osteoclast formation (osteoclastogenesis) in two model systems: RAW264.7 cells and murine bone marrow-derived monocytes. The pan-RAR agonists, all-trans and 9-cis RA, inhibited receptor activator of nuclear factor kappa B ligand (RANKL)-mediated osteoclast differentiation in a concentration-dependent manner. Isoform-specific RAR agonists (α, β, and γ) also inhibited osteoclastogenesis, with the RARα agonist producing the most consistent reductions in both osteoclast number and size and total area covered. Inhibition of osteoclastogenesis correlated with reductions in expression, DNA binding, and nuclear abundance of nuclear factor of activated T cells c1 (NFATc1), a transcription factor critical for osteoclastogenesis. The upregulation of three NFATc1-responsive genes, cathepsin K, dendritic cell-specific transmembrane protein and osteoclast-associated receptor were similarly reduced following RA or RAR agonist exposure. These results suggest that RA blocks in vitro RANKL-mediated osteoclastogenesis by decreasing NFATc1 function.

Retinoids stimulate periosteal bone resorption by enhancing the protein RANKL, a response inhibited by monomeric glucocorticoid receptor

Increased vitamin A (retinol) intake has been suggested to increase bone fragility. In the present study, we investigated effects of retinoids on bone resorption in cultured neonatal mouse calvarial bones and their interaction with glucocorticoids (GC). All-trans-retinoic acid (ATRA), retinol, retinalaldehyde, and 9-cis-retinoic acid stimulated release of (45)Ca from calvarial bones. The resorptive effect of ATRA was characterized by mRNA expression of genes associated with osteoclast differentiation, enhanced osteoclast number, and bone matrix degradation. In addition, the RANKL/OPG ratio was increased by ATRA, release of (45)Ca stimulated by ATRA was blocked by exogenous OPG, and mRNA expression of genes associated with bone formation was decreased by ATRA. All retinoid acid receptors (RARα/β/γ) were expressed in calvarial bones. Agonists with affinity to all receptor subtypes or specifically to RARα enhanced the release of (45)Ca and mRNA expression of Rankl, whereas agonists with affinity to RARβ/γ or RARγ had no effects. Stimulation of Rankl mRNA by ATRA was competitively inhibited by the RARα antagonist GR110. Exposure of calvarial bones to GC inhibited the stimulatory effects of ATRA on (45)Ca release and Rankl mRNA and protein expression. This inhibitory effect was reversed by the glucocorticoid receptor (GR) antagonist RU 486. Increased Rankl mRNA stimulated by ATRA was also blocked by GC in calvarial bones from mice with a GR mutation that blocks dimerization (GR(dim) mice). The data suggest that ATRA enhances periosteal bone resorption by increasing the RANKL/OPG ratio via RARα receptors, a response that can be inhibited by monomeric GR.

The gastric sleeve: losing weight as fast as micronutrients?

Background

Recently, the laparoscopic sleeve gastrectomy (LSG) has become popular as a single-stage procedure for the treatment of morbid obesity and its co-morbidities. However, the incidence of micronutrient deficiencies after LSG have hardly been researched.

Methods

From January 2005 to October 2008, 60 patients underwent LSG. All patients were instructed to take daily vitamin supplements. Patients were tested for micronutrient deficiencies 6 and 12 months after surgery.

Results

Anemia was diagnosed in 14 (26%) patients. Iron, folic acid, and vitamin B12 deficiency was found in 23 (43%), eight (15%), and five (9%) patients, respectively. Vitamin D and albumin deficiency was diagnosed in 21 (39%) and eight (15%) patients. Hypervitaminosis A, B1, and B6 were diagnosed in 26 (48%), 17 (31%), and 13 (30%) patients, respectively.

Conclusions

Due to inadequate intake and uptake of micronutrients, patients who underwent LSG are at serious risk for developing micronutrient deficiencies. Moreover, some vitamins seem to increase to chronic elevated levels with possible complications in the long-term. Multivitamins and calcium tablets should be regarded only as a minimum and supplements especially for iron, vitamin B12, vitamin D, and calcium should be added to this regimen based on regular blood testing.

High dietary intake of retinol leads to bone marrow hypoxia and diaphyseal endosteal mineralization in rats

Vitamin A (retinol) is the only molecule known to induce spontaneous fractures in laboratory animals and we have identified retinol as a risk factor for fracture in humans. Since subsequent observational studies in humans and old animal data both show that high retinol intake appears to only have small effects on bone mineral density (BMD) we undertook a mechanistic study of how excess retinol reduces bone diameter while leaving BMD essentially unaffected. We fed growing rats high doses of retinol for only 1 week. Bone analysis involved antibody-based methods, histology, pQCT, biomechanics and bone compartment-specific PCR together with Fourier Transform Infrared Spectroscopy of bone mineral. Excess dietary retinol induced weakening of bones with little apparent effect on BMD. Periosteal osteoclasts increased but unexpectedly endosteal osteoclasts disappeared and there was a reduction of osteoclastic serum markers. There was also a lack of capillary erythrocytes, endothelial cells and serum retinol transport protein in the endosteal/marrow compartment. A further indication of reduced endosteal/marrow blood flow was the increased expression of hypoxia-associated genes. Also, in contrast to the inhibitory effects in vitro, the marrow of retinol-treated rats showed increased expression of osteogenic genes. Finally, we show that hypervitaminotic bones have a higher degree of mineralization, which is in line with biomechanical data of preserved stiffness in spite of thinner bones. Together these novel findings suggest that a rapid primary effect of excess retinol on bone tissue is the impairment of endosteal/marrow blood flow leading to hypoxia and pathological endosteal mineralization.

Nutrition and Bone: It is More than Calcium and Vitamin D

Unlike pharmacological agents that are taken for proscribed periods of time, food and nutrient intakes have the possibility of affecting bone health over the entire lifespan. While deficiencies or excesses of individual nutrients have been shown to affect bone, it is likely that individual foods or dietary patterns have important effects related to skeletal health. While biochemical mechanisms exist to relate a deficiency of vitamin K to altered bone metabolism, clinical trials related to supplementation of this nutrient have been confusing. It is likely that these disparate results are related to the fact that interactions of nutrients have not been considered or the possibility that suboptimal nutrient status is a marker of poor nutritional status. Vitamin A excess has been postulated to be related to high fracture risk; however, it is likely that retinol is not the best marker for the proposed interaction. Altering whole food patterns, such as the Dietary Approaches to Stop Hypertension diet, have demonstrated beneficial effects on bone metabolism. Individuals who select some vegetarian patterns may need to consider supplementation with nutrients such as calcium and protein. Future studies should center on whole food and dietary patterns and their relationship to bone metabolism and fracture risk.

Recent progress in stable isotope methods for assessing vitamin metabolism

PURPOSE OF REVIEW

Recent developments in mass spectrometric methodology, in particular the widespread adoption of liquid chromatography/mass spectrometry, have presented investigators with new opportunities to investigate micronutrient absorption and metabolism. This review focuses on recent reports of the use of stable isotope techniques to facilitate research into vitamin uptake and utilization in humans.

RECENT FINDINGS

Stable isotopes are used principally in two ways, as analytical standards in isotope dilution assays and as tracers in studies of physiology. There have been a number of advances in both fields recently for almost all of the vitamins. In particular, the effects of food preparation and meal composition on vitamin bioavailability are being probed more widely than before.

SUMMARY

A considerable amount of method development has been reported. We now have the opportunity to consolidate our understanding of vitamin metabolism to better inform the dietary recommendations for optimal health.

Ligands for retinoic acid receptors are elevated in osteoarthritis and may contribute to pathologic processes in the osteoarthritic joint

OBJECTIVE

Vitamin A derivatives, including all-trans-retinoic acid (ATRA), have a well-established role during skeletal development and limb formation and have been shown to have profound effects on chondrocyte phenotype. The aim of this study was to elucidate the effects of retinoids and components of the retinoid metabolic pathway on chondrocyte phenotype in the tibiofemoral joints of patients with osteoarthritis (OA), to show that the retinoids can have multiple effects relevant to the OA disease process.

METHODS

Human explant tissue and a chondrocyte-like cell line were treated with ATRA, and the responses of 4 key markers of chondrocyte phenotype were analyzed. In addition, the effects of ATRA on a number of novel genes associated with OA were assessed using a low-density microarray containing 80 disease marker genes.

RESULTS

Vitamin A metabolite levels were elevated in synovial fluid, serum, and cartilage from patients with OA. Expression profiling of a retinoic acid receptor alpha coactivator protein, P/CAF, demonstrated elevated expression in patients with OA, suggesting the potential for increased signaling via the retinoid receptors in the disease. ATRA increased the levels of matrix metalloproteinase 13 and aggrecanase activity in human cartilage explants and in a human chondrocyte cell line. Furthermore, ATRA altered the expression of a wide range of relevant genes, including the types I, II, IX, and XI collagen genes, toward a nonchondrogenic and OA-like phenotype.

CONCLUSION

These results suggest that retinoid signaling could have a central role in OA, and that components of the pathway may provide potential disease biomarkers or targets for therapeutic intervention.