Subclinical hypervitaminosis A in rat: Measurements of bone mineral density (BMD) do not reveal adverse skeletal changes
Introduction
It has long been known that large doses of retinol (Vitamin A) are severely toxic to the rat appendicular skeleton [1], [2], [3]. In humans, a high dietary intake of Vitamin A is associated with an increased risk of hip fracture [4], [5]. The active metabolite retinoic acid binds and activates the retinoid acid receptors (RARs) which, like the Vitamin D receptor belong to the family of steroid hormone receptors. Upon ligand binding, these receptors bind to specific sequences in the genome, thus functioning as transcription factors in the nucleus [6]. The different RAR subtypes are all expressed in osteoblasts [7], [8], [9] and a bone-resorptive effect of Vitamin A has been reported from in vitro studies [10], [11], [3], [12]. Therefore, it is likely that Vitamin A can exert a direct toxic effect on bone tissue via its active metabolite retinoic acid. However, also indirect mechanisms, via interaction with other agents of importance for bone metabolism, such as Vitamin D, have been proposed. We have previously shown that the acute serum-calcium-increasing effect of a single dose of Vitamin D can be antagonized by retinyl palmitate in man [13], but the relationship is still hardly studied in humans. In rat, an excessive intake of Vitamin A diminishes the curative effect of Vitamin D on rickets [14] and an increased intake of Vitamin D has been shown to alleviate the symptoms of hypervitaminosis A [15]. An antagonism of Vitamin D action on bone and intestine by Vitamin A has been confirmed in vivo in rat [16].
However, the relevant mechanisms for the action of Vitamin A on the skeleton, especially at moderately increased dietary intake levels, are still poorly defined. We recently demonstrated a negative effect on bone strength, evident as decreased three-point bending breaking force of the femur, in rats with subclinical hypervitaminosis A [17]. To begin to investigate possible mechanisms for Vitamin A action, we extended our study on rats.
Section snippets
Animals and experimental design
Animals and experimental design have been described previously [17]. All animal experiments were approved by the local ethical committee for animal experiments. Briefly, 45 female Sprague-Dawley rats, 3 months of age, were obtained from Möllegaards Breeding Centre, Ltd. (Skensved, Denmark). They were kept in groups of five animals in polycarbonate cages with hardwood chips as bedding in a room maintained at 21 ± 1 °C (relative humidity 50 ± 5%), using a 12 h light:dark cycle with the light cycle
Evaluation of retinoid uptake and Vitamin A intoxication
To verify Vitamin A uptake and storage in the rats, retinoids in liver, kidney and serum were analyzed using high-performance liquid chromatography (HPLC) as presented in detail previously [17].
Analyses of Vitamin D, E and K
All serum samples were analyzed within the same assay to avoid interassay variations. Analyses of fat-soluble vitamins were done by AS Vitas (Oslo, Norway, www.vitas.no) using high-performance liquid chromatography (HPLC), which was performed with a HP 1100 liquid chromatograph (Agilent Technologies,
Evaluation of retinoid uptake and Vitamin A intoxication
Serum retinyl esters were elevated 4- and 20-fold and the total amount of liver retinoid increased 3- and 7-fold in the 10 × C and 50 × C group, as reported previously [17]. Neither average food intake nor final body weights were significantly different between groups; 0.05, 0.05, and 0.06 g food/g rat and 321.5 ± 6.4, 328 ± 5.7 and 319.5 ± 4.3 g/rat among C, 10 × C and 50 × C rats, respectively.
Effects on bone geometry
Bone dimensions of humerus are presented in Table 1. In the 50 × C group the diameter was decreased (−4.1%, p < 0.05)
Discussion
In the present study, we have investigated the mechanisms of Vitamin A action on bone tissue in rats with subclinical hypervitaminosis A. We hereby show that in the rats with the highest Vitamin A intake (50 × C group), the volume and diameter, but not the BMD, as measured at the diaphysis with pQCT, of the long bones are affected. Moreover, we show for the first time that subclinical hypervitaminosis A in rats leads to a reduction in serum levels of both Vitamins D and E.
In a previous study on
Acknowledgments
This work was supported by grants from the Swedish Medical Research Council, Torsten and Ragnar Söderberg Foundation, and Agricultural Sciences and Spatial Planning (grant 216/2004-2088).
References (44)
Interactions of retinoid binding proteins and enzymes in retinoid metabolism
Biochim. Biophys. Acta
(1999)- et al.
Reverse transcription-polymerase chain reaction assay demonstrates that the 9-cis retinoic acid receptor alpha is expressed in human osteoblasts
Biochem. Biophys. Res. Commun.
(1993) - et al.
Transcriptional regulation by transforming growth factor beta of the expression of retinoic acid and retinoid X receptor genes in osteoblastic cells is mediated through AP-1
J. Biol. Chem.
(1996) - et al.
Stimulation by retinoids of the natriuretic peptide system of osteoblastic MC3T3-E1 cells
Biochem. Biophys. Res. Commun.
(1996) - et al.
Hypervitaminosis A and calcium-regulating hormones in the rat
J. Nutr.
(1986) - et al.
Bone resorption activity of all-trans retinoic acid is independent of Vitamin D in rats
J. Nutr.
(2003) - et al.
Concerning the toxicity of Vitamin A
J. Nutr.
(1938) - et al.
Vitamin A antagonizes the action of Vitamin D in rats
J. Nutr.
(1999) - et al.
Subclinical hypervitaminosis A causes fragile bones in rats
Bone
(2002) - et al.
Effects of the antiestrogenic environmental pollutant 3,3′,4,4′ 5-pentachlorobiphenyl (PCB #126) in rat bone and uterus: diverging effects in ovariectomized and intact animals
Toxicol. Appl. Pharmacol.
(1999)
Bone tissue composition, dimensions and strength in female rats given an increased dietary level of vitamin A or exposed to 3,3′,4, 4′ 5-pentachlorobiphenyl (PCB126) alone or in combination with Vitamin C
Toxicology
Change of bone tissue composition and impaired bone strength in rats exposed to 3,3′,4,4′ 5-pentachlorobiphenyl (PCB126)
Toxicology
Torsional testing and peripheral quantitative computed tomography in rat humerus
Bone
Mechanical validation of a tomographic (pQCT) index for noninvasive estimation of rat femur bending strength
Bone
Serum Vitamin A concentration and the risk of hip fracture among women 50–74 years old in the United States: a prospective analysis of the NHANES I follow-up study
Am. J. Med.
Changes in serum osteocalcin, plasma phylloquinone, and urinary gamma-carboxyglutamic acid in response to altered intakes of dietary phylloquinone in human subjects
Am. J. Clin. Nutr.
Serum Vitamin K level and bone mineral density in post-menopausal women
Int. J. Gynaecol. Obstet.
Dietary Vitamin K intakes are associated with hip fracture but not with bone mineral density in elderly men and women
Am. J. Clin. Nutr.
Interactions of Vitamins A, D3, E, and K in the diet of broiler chicks
Poult. Sci.
Effects and interactions of dietary levels of Vitamins A and E and cholecalciferol in broiler chickens
Poult. Sci.
Hypervitaminosis A in the rat
J. Nutr.
Retinoid-induced hemorrhaging and bone toxicity in rats fed diets deficient in Vitamin K
Toxicol. Appl. Pharmacol.
Cited by (24)
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
2021, Reproductive ToxicologyCitation Excerpt :The identified associations extend previous findings from the same mouse experiment [36,38] and strengthen the hypothesis of a causal relationship between the observed TCDD-induced changes in bone properties and circulating retinol concentrations, which has been proposed both in experimental [81] and human studies (reviewed by [82]). The mouse results are also in line with associations between excess vitamin A intake and observations of harder and more brittle bone [26], increase of trabecular bone content [83], and lower mechanical strength [29,30] in rodent studies. It can be argued that the observed TCDD-induced elevation in circulating retinol concentrations, per se are mediating the associated bone tissue modulations observed in the study.
Animal Models of Bone Diseases-A
2013, Animal Models for the Study of Human DiseaseHigh dietary intake of retinol leads to bone marrow hypoxia and diaphyseal endosteal mineralization in rats
2011, BoneCitation Excerpt :These results suggest a local endosteal/marrow increase in mineralization in hypervitaminosis A animals. We have previously shown experimentally that a subclinical dose of vitamin A for three months causes weakening of bones in rats, without reduction or slight increase of BMD, depending on the method of calculation [14]. Here we show that three times this subclinical dose of vitamin A in food induces a measurable reduction in both diaphyseal cortical area and bone strength after only 8 days in younger male rats.
Mineral density and biomechanical properties of bone tissue from male Arctic foxes (Vulpes lagopus) exposed to organochlorine contaminants and emaciation
2009, Comparative Biochemistry and Physiology - C Toxicology and PharmacologySelenium and vitamins status in Saudi children
2006, Clinica Chimica Acta
- 1
P.M. Lind. and S. Johansson contributed equally to this study.