Abstract
Background and Aims: Recently, it has been suggested that heme oxygenase-1 (HO-1) can be involved in acute phase response (APR). The purpose of the current work was to study the expression of HO-1 during localized inflammation in rats using in vivo and in vitro approaches. Methods: APR was induced by intramuscular injection of turpentine oil (TO). HO-1 and interleukin-6 (IL-6) mRNA expression in internal organs and injected muscle was evaluated by Northern blot hybridization. Expression at the protein level was analyzed by Western blot, immunohistochemistry (IHC) and ELISA. Alternatively, rat primary hepatocytes (rPH) and Kupffer cells (KC) were isolated and cultured in the presence or absence of IL-6. Results: In the liver and injured muscle the HO-1 mRNA levels were dramatically increased by 4–6h after TO administration. HO-1 protein synthesis in the liver was also elevated. In other internal organs the level of HO-1 mRNA was only slightly up-regulated. IL-6 specific transcripts appeared only in the muscle and were in accordance with serum levels of IL-6. Both these events had profiles that strongly correlated with HO-1 expression in the liver and injured muscle. Moreover, in the muscle, as shown by IHC, HO-1 synthesis was attributed mainly to macrophages. After treatment with IL-6 induction of HO-1 mRNA expression was observed in rPH with a peak effect at 2–4h whereas in cultured KC HO-1 mRNA was up-regulated at later time points, suggesting that not only hepatocytes but also liver macrophages may be the target of serum IL-6 during APR. Conclusions: Our data demonstrate that during localized inflammation in rats the expression of HO-1 is strongly induced at early time points in injured muscle, were APR is initiated by IL-6 production, and in the liver, the major source of serum acute phase proteins. Thus, HO-1 seems to play an important role in cytoprotection of tissue macrophages and hepatocytes, which could become damaged during their clearance function.
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