Subclinical hypervitaminosis A in rat: measurements of bone mineral density (BMD) do not reveal adverse skeletal changes

Structural changes of erythrocyte membrane revealed by 3D confocal optical profilometer

We examined hematological changes influenced by the experimental hypervitaminosis A. The 3D confocal optical profilometer was applied for assessment of the erythrocytes' membrane structural changes influenced by an overdose of vitamin A. The blood smears were evaluated in terms of alterations of geometrical and optical parameters of erythrocytes for two groups of animals: oil base and retinol palmitate (n = 9 animals for each group). The results demonstrate that an overdose of retinol palmitate causes changes in the torus curvature and pallor of discocytes, their surface area and volume. The observed structural malformations of the shape of red blood cells become visible at the earlier preclinical stage of changes in animal state and behavior. With this in mind, the results of the study open a new area of research in the certain dysfunction diagnosis of red blood cells and have a great potential in the further development of new curative protocols.

Bone toxicity induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and the retinoid system: A causality analysis anchored in osteoblast gene expression and mouse data

Dioxin exposures impact on bone quality and osteoblast differentiation, as well as retinoic acid metabolism and signaling. In this study we analyzed associations between increased circulating retinol concentrations and altered bone mineral density in a mouse model following oral exposure to 2,3,7,8-tetrachlordibenzo-p-dioxin (TCDD). Additionally, effects of TCDD on differentiation marker genes and genes involved with retinoic acid metabolism were analysed in an osteoblast cell model followed by benchmark dose-response analyses of the gene expression data. Study results show that the increased trabecular and decreased cortical bone mineral density in the mouse model following TCDD exposure are associated with increased circulating retinol concentrations. Also, TCDD disrupted the expression of genes involved in osteoblast differentiation and retinoic acid synthesis, degradation, and nuclear translocation in directions compatible with increasing cellular retinoic acid levels. Further evaluation of the obtained results in relation to previously published data by the use of mode-of-action and weight-of-evidence inspired analytical approaches strengthened the evidence that TCDD-induced bone and retinoid system changes are causally related and compatible with an endocrine disruption mode of action.

Vitamin A and Bone Health: A Review on Current Evidence

Vitamin A is a fat-soluble micronutrient essential for growth, immunity, and good vision. The preformed retinol is commonly found in food of animal origin whereas provitamin A is derived from food of plant origin. This review summarises the current evidence from animal, human and cell-culture studies on the effects of vitamin A towards bone health. Animal studies showed that the negative effects of retinol on the skeleton were observed at higher concentrations, especially on the cortical bone. In humans, the direct relationship between vitamin A and poor bone health was more pronounced in individuals with obesity or vitamin D deficiency. Mechanistically, vitamin A differentially influenced the stages of osteogenesis by enhancing early osteoblastic differentiation and inhibiting bone mineralisation via retinoic acid receptor (RAR) signalling and modulation of osteocyte/osteoblast-related bone peptides. However, adequate vitamin A intake through food or supplements was shown to maintain healthy bones. Meanwhile, provitamin A (carotene and β-cryptoxanthin) may also protect bone. In vitro evidence showed that carotene and β-cryptoxanthin may serve as precursors for retinoids, specifically all-trans-retinoic acid, which serve as ligand for RARs to promote osteogenesis and suppressed nuclear factor-kappa B activation to inhibit the differentiation and maturation of osteoclasts. In conclusion, we suggest that both vitamin A and provitamin A may be potential bone-protecting agents, and more studies are warranted to support this hypothesis.

Ursolic Acid Prevents Retinoic Acid-Induced Bone Loss in Rats

OBJECTIVE

To examine the effects of ursolic acid (UA) on mitigating retinoic acid (RA)-induced osteoporosis in rats.

METHODS

Fifty female Sprague-Dawley rats were randomly divided into the control group (n=10) and the osteoporosis group (n=40). The 40 osteoporosis rats were induced by 75 mg/(kg•d) RA once daily for 2 weeks, and then were randomly assigned to vehicle control (model), low-, middle-, and high-dose UA [(UA-L, UA-M, UA-H; 30, 60, 120 mg/(kg•d), respectively] groups (10 rats each). UA were administered once daily to the rats from the 3rd weeks for up to 4 weeks by gavage. Bone turnover markers [serum alkaline phosphatase (ALP), osteocalcin (OCN), urine deoxypyridinoline (DPD)] and other parameters, including serum calcium (S-Ca), serum phosphorus (S-P), urine calcium (U-Ca), urine phosphorus (U-P), and bone mineral density (BMD) of the femur, 4th lumbar vertebra and tibia, bone biomechanical properties and trabecular microarchitecture, were measured.

RESULTS

The osteoporosis in rats was successfully induced by RA. Compared with the model group, UA-M and UA-H significantly reversed the RA-induced changes in S-P, U-Ca, U-P, ALP, OCN and urine DPD ratio and markedly enhanced the BMD of right femur, 4th lumbar vertebra and tibia (Plt;0.05 or Plt;0.01). Further, biomechanical test and microcomputed tomography evaluation also showed that UA-H drastically improved biomechanical properties and trabecular microarchitecture (Plt;0.05 or Plt;0.01).

CONCLUSION

UA could promote bone formation, increase osteoblastic activity and reduce osteoclastic activity in rats, indicating that UA might be a potential therapeutic of RA-induced acute osteoporosis.

Vitamin A decreases the anabolic bone response to mechanical loading by suppressing bone formation

Increased vitamin A consumption is associated with decreased cortical bone mass and increased fracture risk in humans. Rodent studies have demonstrated that hypervitaminosis A increases cortical bone resorption, whereas the importance of the effects on bone formation is less well defined. We used an experimental model of increased bone formation by loading of the tibiae to investigate the effect of vitamin A on bone formation. Control [retinol activity equivalents (RAE) 4.5 µg/g chow] or vitamin A (RAE 60 µg/g chow) diets were given to female C57BL/6N mice for 4 wk, after which the tibiae were subjected to axial loading on alternate days for 2 wk, while the diets were continued. Vitamin A inhibited the loading-induced increase in trabecular and cortical bone volume. This was attributed to inhibition of loading-induced increase in osteoblast number and activity, and expression of osteoblastic genes Sp7, Alpl, and Col1a1 in cortical bone. Vitamin A, loading, and combination thereof also resulted in site-specific effects on bone composition measured by Raman spectroscopy. In summary, a clinically relevant dose of vitamin A suppresses the loading-induced gain of bone mass by decreasing bone formation. These observations may have implications for regulation of bone mass caused by physical activity and the risk of osteoporosis in humans.-Lionikaite, V., Henning, P., Drevinge, C., Shah, F. A., Palmquist, A., Wikström, P., Windahl, S. H., Lerner, U. H. Vitamin A decreases the anabolic bone response to mechanical loading by suppressing bone formation.

Clinically relevant doses of vitamin A decrease cortical bone mass in mice

Excess vitamin A has been associated with decreased cortical bone thickness and increased fracture risk. While most studies in rodents have employed high dosages of vitamin A for short periods of time, we investigated the bone phenotype in mice after longer exposure to more clinically relevant doses. For 1, 4 and 10 weeks, mice were fed a control diet (4.5 µg retinyl acetate/g chow), a diet modeled from the human upper tolerable limit (UTL; 20 µg retinyl acetate/g chow) and a diet three times UTL (supplemented; 60 µg retinyl acetate/g chow). Time-dependent decreases in periosteal circumference and bone mineral content were noted with the supplemented dose. These reductions in cortical bone resulted in a significant time-dependent decrease of predicted strength and a non-significant trend toward reduced bone strength as analyzed by three-point bending. Trabecular bone in tibiae and vertebrae remained unaffected when vitamin A was increased in the diet. Dynamic histomorphometry demonstrated that bone formation was substantially decreased after 1 week of treatment at the periosteal site with the supplemental dose. Increasing amount of vitamin A decreased endocortical circumference, resulting in decreased marrow area, a response associated with enhanced endocortical bone formation. In the presence of bisphosphonate, vitamin A had no effect on cortical bone, suggesting that osteoclasts are important, even if effects on bone resorption were not detected by osteoclast counting, genes in cortical bone or analysis of serum TRAP5b and CTX. In conclusion, our results indicate that even clinically relevant doses of vitamin A have a negative impact on the amount of cortical bone.

Antioxidant intake and bone status in a cross-sectional study of Brazilian women with osteoporosis

This study aimed to investigate the association between antioxidant intake and bone mineral density (BMD) in postmenopausal women with osteoporosis. We conducted a cross-sectional study with 150 women, mean age 68.7 (SD 9.1) years. BMD and body composition were obtained using dual-energy X-ray absorptiometry (DXA). We assessed anthropometric measures and dietary intake and applied an adapted Dietary Antioxidant Quality Score (a-DAQS) to evaluate the antioxidant consumption. 65.3% of women had higher scores on the a-DAQS. We found no relationship between the a-DAQS and BMD; however, we observed an inverse correlation between vitamin A and lumbar spine (LS) BMD in g/cm(2) (r = - 0.201; p = 0.013). An analysis of variance (ANOVA) test also showed that vitamin A was negatively associated with the LS BMD (F = 6.143; p = 0.013, but without significance when a multivariate analysis was applied. The a-DAQS did not have an association with BMD; however, Vitamin A showed a negative correlation with BMD, but such an association disappeared when the other antioxidants were taken together. Our findings encourage an antioxidant-based dietary approach to osteoporosis prevention and treatment, since the negative effect of vitamin A was neutralized by the intake of such nutrients.

Role of flavonoids on oxidative stress and mineral contents in the retinoic acid-induced bone loss model of rat

PURPOSE

Reactive oxygen species play a role in a number of degenerative conditions including osteoporosis. Flavonoids as phyto-oestrogens exert physiological effects against oxidative stress diseases. We developed a retinoic acid-induced bone loss model of rats to assess whether flavonoids and alendronate as positive control have role against oxidative stress and mineral contents in osteoporosis in vivo.

METHODS

Three-month-old female rats of the Y59 strain were given quercetin, chrysin, naringenin (100 mg kg(-1)) or alendronate (40 mg kg(-1), a positive control) immediately before retinoic acid treatment (80 mg kg(-1)) once daily for 14 days by a single intragastric (i.g.) application. In the second part of the study, we assessed the effect of those flavonoids on the skeletal system of healthy rats using single i.g. application on the respective flavonoids during 14 days. Twenty-four hours after the treatment, we analysed bone mineral density and the total content of bone calcium and phosphorus in the femur, the geometric and physical characteristics of thigh bones and lipid peroxidation and glutathione levels of liver and kidney cells.

RESULTS

All flavonoids improved the decrease in bone weight coefficient, the length and the diameter of the bone, the content of bone ash and calcium and phosphorus content induced by retinoic acid. Chrysin and quercetin showed promise as preventive agents. Flavonoids were superior to alendronate according to some criteria.

CONCLUSIONS

These results suggest that the dietary flavonoids could reduce retinoic acid-induced oxidative stress and bone loss and that flavonoids may be useful therapeutics for prevention of skeletal diseases.

Fish liver and seagull eggs, vitamin D-rich foods with a shadow: results from the Norwegian Fish and Game Study

SCOPE

Fish liver, fish liver oil, oily fish and seagull eggs have been major sources of vitamin D for the coastal population of Norway. They also provide dioxin and polychlorinated dioxin-like compounds (dl-compounds), which may interfere with vitamin D homeostasis. We investigated whether serum 25-hydroxyvitamin D (25(OH)D) might be compromised by concomitant intake of dl-compounds.

METHODS AND RESULTS

We studied 182 adults participating in the Norwegian Fish and Game Study. Participants who consumed fish liver and/or seagull eggs had higher dl-compound intake and blood concentrations than non-consumers (p < 0.001). Vitamin D intake was higher (p < 0.001), whereas serum 25(OH)D was lower (p = 0.029) in consumers than in non-consumers. Among non-consumers, vitamin D intake was associated with serum 25(OH)D (β=1.06; 95% CI: 0.48, 1.63). This association was weaker among consumers (β = 0.52; 95% CI: -0.05, 1.08), but strengthened when adjusted for retinol intake (β = 0.66; 95% CI: 0.12, 1.21). The association between vitamin D intake and serum 25(OH)D did not seem to be compromised by intake of dl-compounds.

CONCLUSION

To secure adequate vitamin D status while keeping the intake of dioxins and dl-polychlorinated biphenyls low, a healthy diet should include both supplemental vitamin D and oily fish. Despite high nutrient content, dietary fish liver and seagull eggs should be restricted, due to dl-compounds and possible vitamin A-D antagonism.

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.

Cortical and trabecular bone, bone mineral density, and resistance to ex vivo fracture are not altered in response to life-long vitamin A supplementation in aging rats

High vitamin A (VA) intakes have been correlated with increased risk of bone fracture. Over 50% of the U.S. adult population reports use of dietary supplements, which can result in VA intakes > 200% of the RDA. In this study, 2 experiments were designed to determine the effect of dietary VA on cortical and trabecular bone properties and resistance to ex vivo fracture. In Expt. 1, we investigated whether orally administered VA accumulates in bone. Seven-week-old rats were treated daily with VA (6 mg/d for 14 d). Total retinol increased in both the tibia and femur (P < 0.01). In Expt. 2, we conducted a longitudinal study in which rats were fed 1 of 3 levels of dietary VA (marginal, adequate, and supplemented, equal to 0.35, 4, and 50 μg retinol/g diet, respectively) from weaning until the ages of 2-3 mo (young), 8-10 mo (middle-age), and 18-20 mo (old). Tibial trabecular and cortical bone structure, bone mineral density, and resistance to fracture were measured using micro-computed tomography and material testing system analysis, respectively. The VA-marginal diet affected measures of cortical bone dimension, suggesting bone remodeling was altered. VA supplementation increased medullary area and decreased cortical thickness in young rats (P < 0.05), but these changes were not present during aging. VA supplementation did not affect resistance to fracture or bone mineral content in old rats. From these results, we conclude that VA-marginal status affects trabecular bone more than cortical bone, and VA supplementation at a moderate level over the lifetime is unlikely to increase the risk of age-related bone fracture in rats.

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.

Mineral density and biomechanical properties of bone tissue from male Arctic foxes (Vulpes lagopus) exposed to organochlorine contaminants and emaciation

We investigated the impact from dietary OC (organochlorine) exposure and restricted feeding (emaciation) on bone mineral density (BMD; g hydroxy-apatite cm(-2)) in femoral, vertebrate, skull and baculum osteoid tissue from farmed Arctic blue foxes (Vulpes lagopus). For femur, also biomechanical properties during bending (displacement [mm], load [N], energy absorption [J] and stiffness [N/mm]) were measured. Sixteen foxes (EXP) were fed a wet food containing 7.7% OC-polluted minke whale (Balaenoptera acutorostrata) blubber in two periods of body fat deposition (Aug-Dec) and two periods of body fat mobilisation (Jan-July) in which the food contained less energy and only 2% blubber. SigmaOC food concentration in the food containing 7.7% whale blubber was 309 ng/g wet mass. This corresponded to a SigmaOC exposure of ca. 17 microg/kg body mass/d and a responding SigmaOC residue in subcutaneous adipose tissue of ca. 1700 ng/g live mass in the 8 EXP fat foxes euthanized after 16 months. A control group (CON) composed of 15 foxes were fed equal daily caloric amounts of clean pork (Sus scrofa) fat. After 16 months, 8 EXP and 7 CON foxes were euthanized (mean body mass=9.25 kg) while the remaining 8 EXP and 8 CON foxes were given restricted food rations for 6 months resulting in a body weight reduction (mean body mass=5.46 kg). The results showed that only BMD(skull) vs. BMD(vertebrae) were significantly correlated (R=0.68; p=0.03; n=10) probably due to a similar composition of trabecular and cortical osteoid tissue. No difference in any of the BMD measurements or femoral biomechanical properties was found between EXP and CON foxes although BMD baculum was 1.6-folds lower in the EXP group. However, lean summer foxes had significantly lower femoral biomechanical properties measured as displacement (mm), energy absorption (J) and time (s) biomechanical properties than fat winter foxes (all p<0.004). This indicates lower stiffness and softer bones from fasting which is in agreement with previous studies. Further, it should be kept in mind when studying bone tissues in Arctic mammals also in order to avoid confounding effects from body condition.

Does the nutrition profile of vitamins, fatty acids and microelements counteract the negative impact from organohalogen pollutants on bone mineral density in Greenland sledge dogs (Canis familiaris)?

There is a great need for understanding the impact from dietary OHCs (organohalogen compounds) on bone mineral composition - and thereby osteoporosis - in especially arctic wildlife such as polar bears (Ursus maritimus) as well as humans. For that purpose, we measured BMD (bone mineral density) by DXA scanning (g/cm(-2)) in 15 age and weight normalized sledge dog (Canis familiaris) bitches and their 26 pups divided into a control group (n=26) given 50-200 g/day clean pork (Suis scrofa) fat and a treated group (n=15) given 50-200 g/day OHC polluted minke whale (Balaenoptera acutorostrata) blubber as main lipid sources. The results showed that BMD increased significantly with age (linear regression: p<0.0001, r(2)=0.83, n=41) while no sex difference was found in the F-generation (two-way ANOVA: all p>0.3). No differences in BMD(femur) or BMD(vertebrae) between exposed and control individuals in the bitch generation were found (linear mixed effect model: both p>0.38). Likewise, no difference between exposed and control subadults and juveniles in the F-generation was found (two-way ANOVA: all p>0.33). Correlation analyses between BMD(femur), BMD(vertebrae) and groups of OHCs, respectively, did not show any statistically significant relationships nor a clear or decreasing trend (Pearson's: p: 0.07-0.78; r: -0.2-0.59; n: 10-18). As the groups were similar regarding genetics, age and sex are the only factors that can explain this observation. Either the pollutants did not have an impact on BMD using the present time frame and OHC concentrations (threshold levels not reached), or the difference in food composition (mainly vitamins and n3 fatty acids) conceal the potential OHC impact on BMD. Such information is important when evaluating the positive and negative health consequences from eating polluted marine species.

Selenium and vitamins status in Saudi children

BACKGROUND

Selenium is an essential element, and a cofactor required to maintain glutathione peroxidase activity. Its deficiency may induce modification in the cellular antioxidative status and the appearance of different diseases. Previous studies in Al-Kharj reported low selenium levels in the soil and the milk of lactating mothers living in that area.

METHODS

A cross-sectional study was carried out to determine the status of selenium, dl-alpha-tocopherol, and all-trans-retinol in 513 Saudi children living in Al-Kharj district using serum and toenail samples.

RESULTS

The prevalence of children with serum selenium below the threshold limit of clinical importance in coronary and cardiovascular diseases (45 microg/l) was only 1.4%, while 53.4% of the tested children had toenail selenium >0.56 microg/g, which is considered a low level as indicated in a previous study. DL-alpha-tocopherol deficiency (<0.5 mg/dl) was found only in 3.1%. However, none of the children in this study had a severe all-trans-retinol deficiency (<10 microg/dl) and the percentage of children with marginal deficiency <20 microg/dl was 5.5%.

CONCLUSION

It seems that the geographical location of primary health care units (PHCUs) is the most important factor in influencing the selenium status of these children. This implies variations in food habits. Serum and toenail selenium concentrations were significantly related which can both reflect dietary selenium intake. Although our results suggest an adequate vitamin A status, we found interestingly that 10.9% of the children had retinol >50 microg/dl. This suggests that a high dietary intake of vitamin A might have a harmful effect. Further work is necessary to determine whether the hypervitaminosis A in children reflects an excessive dietary intake of retinol. A significant negative association was also found between dl-alpha-tocopherol and all-trans-retinol and malonaldehyde (MDA) levels in the serum of children population. This confirms their role in reducing oxidative stress.