Benzo(a)pyrene reduces osteoclast and osteoblast activity in ex-vivo scales of zebrafish (Danio rerio [Hamilton-Buchanan, 1822]) and goldfish (Carassius auratus [Linnaeus, 1758])

Abstract

Environmental contaminants have previously been demonstrated to cause bone deformities mediated through the aryl hydrocarbon receptor (AhR) in fish and mammals. Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in the environment, many of them capable of activating AhR. In the present study, fish scales were utilized as a model system to examine possible AhR-mediated effects of PAHs on bone forming osteoblasts and bone resorptive osteoclasts, using the AhR-ligand benzo(a)pyrene (BaP) as a model compound. Elasmoid scales from goldfish and zebrafish were exposed to 0.005–50 μM BaP for up to 48 hr, and the activity of osteoblastic and osteoclastic markers were measured, as well as mRNA levels of bone related genes and cyp1a and cyp3a. Using the sp7:luciferase zebrafish assay, a decrease in sp7 promoter activation was observed at the two highest concentrations (5 and 50 μM). Gelatin zymography revealed significantly reduced activity of the osteoclastic protease matrix metalloproteinase 9 (Mmp9) at the highest concentration. Furthermore, transcriptional analysis showed a dose-dependent increase in cyp1a, however, no significant differential expression was observed for the bone related genes. The findings indicate that BaP might decrease differentiation and activation of osteoblasts, and reduce osteoclastic activity, and thus ultimately cause decreased bone formation. Further investigation is necessary in order to confirm the role of AhR in mediating these effects.