Vitamin A effects on vertebral bone tissue homeostasis in gilthead sea bream (Sparus aurata) juveniles

Vertebral deformities constitute a recurrent problem in farmed teleost fish species. Potential causes of skeletal deformities are associated with genetic, environmental and nutritional factors. Considering nutritional factors, previous studies have shown that nutritional vitamin A (VA) imbalance implied the appearance of vertebral deformities in marine fish larvae; however, information about the effects of VA on bone homeostasis in juveniles is scarce. A study of vertebral bone tissue homeostasis in gilthead sea bream (Sparus aurata) juveniles fed with two dietary VA levels was performed by means of histological (Haematoxylin-Eosin, Alcian blue PAS, Haematoxylin VOF and Picrosirius red staining) and histochemical (immunostaining for bone and matrix Gla protein; OC and MGP, respectively) approaches. Fish were fed with two diets containing 2.5 X 104 (control) and 2.3 x 106 (hypervitaminosis A group) IU total VA kg-1 during 6 months. Results showed that gilthead sea bream juveniles were not affected in terms of growth or survival rate by nutritional hypervitaminosis A, whereas the homeostasis of the vertebral bone was altered. Vertebral bodies from the control and VA fed fish showed differences in their morphological and biochemical composition at the growth zone of the vertebral end-plates. Picrosirius red staining revealed that vertebral end-plates and the trabecular bone layer from control and VA fed fish presented different diameter in collagen fibers. In addition, immunohistochemical analysis revealed increased protein levels of MGP and BGP in the notochord from gilthead sea bream juveniles fed hypervitaminosis A. Results suggest that hypervitaminosis A alter bone homeostasis through an accelerated bone mineralization, which might increase mechanical load between adjacent vertebrae and induce vertebral compression/fusion through a bone remodelling process.