title: Endogenous Tetrapyrroles Influence Leukocyte Responses to Lipopolysaccharide in Human Blood: Pre-Clinical Evidence Demonstrating the Anti-Inflammatory Potential of Biliverdin.
abstract: Sepsis is associated with abnormal host immune function in response to pathogen exposure, including endotoxin (lipopolysaccharide; LPS). Cytokines play crucial roles in the induction and resolution of inflammation in sepsis. Therefore, the primary aim of this study was to investigate the effects of endogenous tetrapyrroles, including biliverdin (BV) and unconjugated bilirubin (UCB) on LPS-induced cytokines in human blood. Biliverdin and UCB are by products of haem catabolism and have strong cytoprotective, antioxidant and anti-inflammatory effects. In the present study, whole human blood supplemented with BV and without was incubated in the presence or absence of LPS for 4 and 8 hours. Thereafter, whole blood was analysed for gene and protein expression of cytokines, including IL-1β, IL-6, TNF, IFN-γ, IL-1Ra and IL-8. Biliverdin (50 μM) significantly decreased the LPS-mediated gene expression of IL-1β, IL-6, IFN-γ, IL-1Ra and IL-8 (P<0.05). Furthermore, BV significantly decreased LPS-induced secretion of IL-1β and IL-8 (P<0.05). Serum samples from human subjects and, wild type and hyperbilirubinaemic Gunn rats were also used to assess the relationship between circulating bilirubin and cytokine expression/production. Significant positive correlations between baseline UCB concentrations in human blood and LPS-mediated gene expression of IL-1β (R=0.929), IFN-γ (R=0.809), IL-1Ra (R=0.786) and IL-8 (R=0.857) were observed in blood samples (allP<0.05). These data were supported by increased baseline IL-1β concentrations in hyperbilirubinaemic Gunn rats (P<0.05). Blood samples were also investigated for complement receptor-5 (C5aR) expression. Stimulation of blood with LPS decreased gene expression of C5aR (P<0.05). Treatment of blood with BV alone and in the presence of LPS tended to decrease C5aR expression (P=0.08). These data indicate that supplemented BV inhibits theex vivoresponse of human blood to LPS. Surprisingly, however, baseline UCB was associated with heighted inflammatory response to LPS. This is the first study to explore the effects of BV in a preclinical human model of inflammation and suggests that BV could represent an anti-inflammatory target for the prevention of LPS mediated inflammationin vivo.
authors.affiliation: Heart Foundation Research Centre, Griffith Health Institute, Griffith University, Gold Coast, QLD, Australia.
authors.forename: Kavita
authors.initials: K
authors.lastname: Bisht
authors.affiliation: Griffith Enterprise, Griffith University, Nathan, QLD, Australia.
authors.forename: Jens
authors.initials: J
authors.lastname: Tampe
authors.affiliation: School of Health Sciences, University of Tasmania, Launceston, Tasmania, Australia.
authors.forename: Cecilia
authors.initials: C
authors.lastname: Shing
authors.affiliation: Heart Foundation Research Centre, Griffith Health Institute, Griffith University, Gold Coast, QLD, Australia.
authors.forename: Bhavisha
authors.initials: B
authors.lastname: Bakrania
authors.affiliation: Gold Coast University Hospital Intensive Care Unit and Gold Coast University Hospital Critical Care Research Group, Gold Coast, QLD, Australia.
authors.forename: James
authors.initials: J
authors.lastname: Winearls
authors.affiliation: Critical Care Research Group, The Prince Charles Hospital, University of Queensland, QLD, Australia.
authors.forename: John
authors.initials: J
authors.lastname: Fraser
authors.affiliation: Emerging Field Oxidative Stress and DNA Stability and Research Platform Active Aging, Department of Nutritional Science, University of Vienna, Vienna, Austria.
authors.forename: Karl-Heinz
authors.initials: KH
authors.lastname: Wagner
authors.affiliation: Heart Foundation Research Centre, Griffith Health Institute, Griffith University, Gold Coast, QLD, Australia ; Gold Coast University Hospital Intensive Care Unit and Gold Coast University Hospital Critical Care Research Group, Gold Coast, QLD, Australia.
authors.forename: Andrew C
authors.initials: AC
authors.lastname: Bulmer
keywords: Cytokine; Inflammation; Lipopolysaccharide; Tetrapyrroles