Specific modulatory effect of arachidonic acid on bone cytokine mRNA expression

Background. A significantly higher arachidonic acid (AA) content in plasma and erythrocyte phospholipids of patients with idiopathic calcium nephrolitiasis was reported, A relationship was found between plasma phospholipid AA level, serum calciotropic hormone values and intestinal, renal and bone calcium metabolism alterations, which have been observed to constitute the main causes of idiopathic hypercalciuria. To confirm a causal Link between phospholipid AA content and high bone turnover, we evaluated the effects of AA on the expression of the main cytokines involved in bone remodeling. Methods. The mRNA of cytokines expressed in human osteosarcoma cell Line MG-63 was assayed by total RNA extraction and kinetic comparative RT-PCR, We used Western Blot analysis to assay which signaling pathway was involved in AA-induced cytokine expression. Results. Cell treatment with AA induced an increase in IL-1 alpha, IL-1 beta, TNF-alpha and M-CSF expression, while eicosapentaenoic acid had no effect on mRNA expression of cytokines. The AA effect on cytokine expression was inhibited when Calphostin C, an inhibitor of Protein Kinase C (PKC), was added to the cultures, AA was able to activate a PKC-alpha isoenzyme, Conclusions, These results show a specific PKC-mediated effect of AA on some cytokine expression in osteoblastic cells, suggesting a link between plasma phospholipid AA level and bone turnover in renal stone formers, These findings may open new approaches to the relationship between lipids and primary or secondary bone diseases and their treatment.