Heme oxygenase-1 induction by cobalt protoporphyrin enhances fever and inhibits pyrogenic tolerance to lipopolysaccharide

• We examine the effect of HO-1 induction on fever and pyrogenic tolerance to LPS.
• Induction of HO-1 accelerated and enhanced the early stage of LPS induced fever.
• Induction of HO-1 attenuates the development of pyrogenic tolerance to LPS.
• HO-1 acts as physiological regulator of the febrile response intensity to infections.

Heme oxygenase-1 (HO-1) is an enzyme that catalyzes degradation of the heme and regulates its availability for newly synthetized hemeproteins such as cyclooxygenases, NO synthases and cytochrome P450. Moreover, HO-1 activity modulates synthesis of cytokines and prostaglandins. All of these factors are well-defined components of fever and pyrogenic tolerance mechanisms. We examine the effect of HO-1 induction and activation using cobalt protoporphyrin (CoPP) on changes in body temperature (Tb), plasma levels of interleukin-6 (IL-6), prostaglandin E2 (PGE2) and HO-1 protein in the course of these processes. Intraperitoneally (i.p.) pre-treatment of rats with CoPP (5 mg kg−1) significantly accelerated and enhanced the early stage of lipopolysaccharide (LPS)-induced fever and shortened a post-fever recovery to normal temperature. Pre-treatment with CoPP significantly potentiated the increase in plasma IL-6, PGE2 and HO-1 levels measured 4 h after the LPS administration. Furthermore, induction of HO-1 attenuated the development of pyrogenic tolerance to repeated injections of LPS. Based on these data we conclude that heme oxygenase-1 may act as a physiological regulator of the febrile response intensity to bacterial infections.