Biological and pharmacological effects of carbon monoxide in humans

Background Inhalation of 250 ppm carbon monoxide (CO) produced marked anti-inflammatory effects in mice receiving endotoxin intraperitoneally. Among other cytokines, the tumor necrosis factor (TNF) alpha response was markedly reduced. (Otterbein et al, 2000) Endotoxin (LPS)-infusion in healthy volunteers provides a well standardized model to safely study inflammatory responses and pharmacodynamics of anti-inflammatory drugs. (Pernerstorfer et al, 1999) Trial objective Pilot trial: To compare with placebo effects of CO inhalation, i.e. to clarify if CO (i) has anti-inflammatory effects (reduces TNF generation) in whole blood incubated with LPS ex vivo, (ii) To document the safety and tolerability of CO inhalation. Main trial : To compare with placebo the effects of CO-inhalation on inflammatory responses after LPS challenge in vivo. Trial design The pilot trial is a subject- and analyst- blinded randomized, placebo-controlled, 4-way cross-over trial with a wash out period of one week and escalating dosages of CO in humans. The main trial is also a subject- and analyst- blinded randomized, placebo-controlled, 2-way cross-over trial with a wash out period of six weeks employing an optimal concentration of CO in healthy humans. Outcome parameters Primary: TNF levels Secondary: other cytokines measured on the protein or molecular level, HbCO-blood levels Methods of evaluation Enzyme immuno-assays, quantitative polymerase chain reaction (PCR) Trial rationale As CO may become a cheap and useful anti-inflammatory drug to fight inflammatory conditions in the lung or systemic inflammation, we aim to reproduce the anti-inflammatory effects of CO observed in vitro and in mice.

Severe sepsis still carries a mortality rate from 30-50 percent despite advances in intensive care medicine and antimicrobial therapy. Infectious agents and inflammatory cytokines, which are endogenously produced substances that regulate our "normal" defense system, lead to changes in the blood clotting system with an overall activation and hypercoagulate state. Simultaneously white blood cells are activated and the overall hypercoagulatory and hyperinflammatory response contribute to vascular injury, septic shock and death. Carbon monoxide (CO), the main product of heme degradation, has been shown to exert direct anti-inflammatory effects in different animal models. For instance, mice challenged with lipopolysaccharide (LPS), a noninfectious component of the bacterial wall, had a less pronounced inflammatory response if they were pretreated with carbon monoxide. In this project, we pretreated 13 healthy volunteers with carbon monoxide and synthetic air for one hour and compared the inflammatory response after intravenous LPS administration. Unfortunately, we could not observe any difference in the inflammatory or coagulatory response between both periods. Thus, our data cannot support a direct anti-inflammatory role of CO in this setting. Putative reasons for these conflicting results are that there are substantial differences between mice and humans, and these species differences must be considered when further developing CO as a medicinal product.