High-mobility group box 1 (HMGB1) is a nuclear factor that is released extracellularly as a late mediator of lethality in sepsis as well as after necrotic, but not apoptotic, death. Here we demonstrate that in contrast to the delayed role of HMGB1 in the systemic inflammation of sepsis, HMGB1 acts as an early mediator of inflammation and organ damage in hepatic ischemia reperfusion (I/R) injury. HMGB1 levels were increased during liver I/R as early as 1 h after reperfusion and then increased in a time-dependent manner up to 24 h. Inhibition of HMGB1 activity with neutralizing antibody significantly decreased liver damage after I/R, whereas administration of recombinant HMGB1 worsened I/R injury. Treatment with neutralizing antibody was associated with less phosphorylation of c-Jun NH2-terminal kinase and higher nuclear factor–κB DNA binding in the liver after I/R. Toll-like receptor 4 (TLR4)-defective (C3H/Hej) mice exhibited less damage in the hepatic I/R model than did wild-type (C3H/HeOuj) mice. Anti-HMGB1 antibody failed to provide protection in C3H/Hej mice, but successfully reduced damage in C3H/Ouj mice. Together, these results demonstrate that HMGB1 is an early mediator of injury and inflammation in liver I/R and implicates TLR4 as one of the receptors that is involved in the process.

Endogenous ligands from damaged cells, so-called damage-associated molecular pattern molecules, can activate innate immunity via TLR4 signaling. Hepatic warm ischemia and reperfusion (I/R) injury and inflammation is largely TLR4 dependent. We produced TLR4 chimeric mice to assess whether the TLR4-dependent injury required TLR4 expression on liver parenchymal or nonparenchymal cells. Chimeric mice were produced by adoptive transfer of donor bone marrow cells into irradiated recipient animals using reciprocal combinations of TLR4 wild-type (WT; C3H/HeOuj) and TLR4 mutant (C3H/HeJ) mouse bone marrow. Wild-type chimeric mice bearing TLR4 mutant hemopoietic cells and TLR4 mutant mice transplanted with their own bone marrow-derived cells were protected from hepatic I/R and exhibited decreased JNK and NF-κB activation compared with WT chimeric mice transplanted with their own bone marrow. In contrast, TLR4 mutant mice transplanted with TLR4 WT bone marrow were not protected from liver I/R and demonstrated pronounced increases in JNK and NF-κB activation when compared with autochthonous transplanted mutant mice. In addition, depletion of phagocytes taking up gadolinium chloride failed to provide any additional protection to TLR4 mutant mice, but substantially reduced damage in WT mice after hepatic I/R. Together, these results demonstrate that TLR4 engagement on actively phagocytic nonparenchymal cells such as Kupffer cells is required for warm I/R-induced injury and inflammation in the liver.

Recent basic and clinical research has revealed that hydrogen is an important physiological regulatory factor with antioxidant, anti-inflammatory and anti-apoptotic protective effects on cells and organs. Therapeutic hydrogen has been applied by different delivery methods including straightforward inhalation, drinking hydrogen dissolved in water and injection with hydrogen-saturated saline. This review summarizes currently available data regarding the protective role of hydrogen, provides an outline of recent advances in research on the use of hydrogen as a therapeutic medical gas in diverse models of disease and discusses the feasibility of hydrogen as a therapeutic strategy. It is not an overstatement to say that hydrogen's impact on therapeutic and preventive medicine could be enormous in the future.

Carbon monoxide (CO), a byproduct of heme catabolism by heme oxygenase (HO), confers potent antiinflammatory effects. Here we demonstrate that CO derived from HO-1 inhibited Toll-like receptor (TLR) 2, 4, 5, and 9 signaling, but not TLR3-dependent signaling, in macrophages. Ligand-mediated receptor trafficking to lipid rafts represents an early event in signal initiation of immune cells. Trafficking of TLR4 to lipid rafts in response to LPS was reactive oxygen species (ROS) dependent because it was inhibited by diphenylene iodonium, an inhibitor of NADPH oxidase, and in gp91phox-deficient macrophages. CO selectively inhibited ligand-induced recruitment of TLR4 to lipid rafts, which was also associated with the inhibition of ligand-induced ROS production in macrophages. TLR3 did not translocate to lipid rafts by polyinosine-polycytidylic acid (poly(I:C)). CO had no effect on poly(I:C)-induced ROS production and TLR3 signaling. The inhibitory effect of CO on TLR-induced cytokine production was abolished in gp91phox-deficient macrophages, also indicating a role for NADPH oxidase. CO attenuated LPS-induced NADPH oxidase activity in vitro, potentially by binding to gp91phox. Thus, CO negatively controlled TLR signaling pathways by inhibiting translocation of TLR to lipid rafts through suppression of NADPH oxidase–dependent ROS generation.

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