The damage-associated molecular pattern HMGB1 is released early after clinical hepatic ischemia/reperfusion.

OBJECTIVE AND BACKGROUND: Activation of sterile inflammation after hepatic ischemia/reperfusion (I/R) culminates in liver injury. The route to liver damage starts with mitochondrial oxidative stress and cell death during early reperfusion. The link between mitochondrial oxidative stress, damage-associate molecular pattern (DAMP) release, and sterile immune signaling is incompletely understood and lacks clinical validation. The aim of the study was to validate this relation in a clinical liver I/R cohort and to limit DAMP release using a mitochondria-targeted antioxidant in I/R-subjected mice. METHODS: Plasma levels of the DAMPs high-mobility group box 1 (HMGB1), mitochondrial DNA, and nucleosomes were measured in 39 patients enrolled in an observational study who underwent a major liver resection with (N = 29) or without (N = 13) intraoperative liver ischemia. Circulating cytokine and neutrophil activation markers were also determined. In mice, the mitochondria-targeted antioxidant MitoQ was intravenously infused in an attempt to limit DAMP release, reduce sterile inflammation, and suppress I/R injury. RESULTS: In patients, HMGB1 was elevated following liver resection with I/R compared to liver resection without I/R. HMGB1 levels correlated positively with ischemia duration and peak post-operative transaminase (ALT) levels. There were no differences in mitochondrial DNA, nucleosome, or cytokine levels between the two groups. In mice, MitoQ neutralized hepatic oxidative stress and decreased HMGB1 release by ±50%. MitoQ suppressed transaminase release, hepatocellular necrosis, and cytokine production. Reconstituting disulfide HMGB1 during reperfusion reversed these protective effects. CONCLUSION: HMGB1 seems the most pertinent DAMP in clinical hepatic I/R injury. Neutralizing mitochondrial oxidative stress may limit DAMP release after hepatic I/R and reduce liver damage

Extracellular histones, cell-free DNA, or nucleosomes: differences in immunostimulation

In inflammation, extensive cell death may occur, which results in the release of chromatin components into the extracellular environment. Individually, the purified chromatin components double stranded (ds)DNA and histones have been demonstrated, both in vitro and in vivo, to display various immunostimulatory effects, for example, histones induce cytotoxicity and proinflammatory signaling through toll-like receptor (TLR)2 and 4, while DNA induces signaling through TLR9 and intracellular nucleic acid sensing mechanisms. However, DNA and histones are organized in nucleosomes in the nucleus, and evidence suggests that nucleosomes are released as such in inflammation. The cytotoxicity and proinflammatory signaling induced by nucleosomes have not been studied as extensively as the separate effects brought about by histones and dsDNA, and there appear to be some marked differences. Remarkably, little distinction between the different forms in which histones circulate has been made throughout literature. This is partly due to the limitations of existing techniques to differentiate between histones in their free or DNA-bound form. Here we review the current understanding of immunostimulation induced by extracellular histones, dsDNA and nucleosomes, and discuss the importance of techniques that in their detection differentiate between these different chromatin component

DNA and factor VII-activating protease protect against the cytotoxicity of histones

Circulating histones have been implicated as major mediators of inflammatory disease because of their strong cytotoxic effects. Histones form the protein core of nucleosomes; however, it is unclear whether histones and nucleosomes are equally cytotoxic. Several plasma proteins that neutralize histones are present in plasma. Importantly, factor VII-activating protease (FSAP) is activated upon contact with histones and subsequently proteolyzes histones. We aimed to determine the effect of FSAP on the cytotoxicity of both histones and nucleosomes. Indeed, FSAP protected against histone-induced cytotoxicity of cultured cells in vitro. Upon incubation of serum with histones, endogenous FSAP was activated and degraded histones, which also prevented cytotoxicity. Notably, histones as part of nucleosome complexes were not cytotoxic, whereas DNA digestion restored cytotoxicity. Histones in nucleosomes were inefficiently cleaved by FSAP, which resulted in limited cleavage of histone H3 and removal of the N-terminal tail. The specific isolation of either circulating nucleosomes or free histones from sera of Escherichia coli challenged baboons or patients with meningococcal sepsis revealed that histone H3 was present in the form of nucleosomes, whereas free histone H3 was not detected. All samples showed signs of FSAP activation. Markedly, we observed that all histone H3 in nucleosomes from the patients with sepsis, and most histone H3 from the baboons, was N-terminally truncated, giving rise to a similarly sized protein fragment as through cleavage by FSAP. Taken together, our results suggest that DNA and FSAP jointly limit histone cytotoxicity and that free histone H3 does not circulate in appreciable concentrations in sepsi

Cooperation of Factor VII-Activating Protease and Serum DNase I in the Release of Nucleosomes From Necrotic Cells

Objective. Removal of dead cells is essential in the maintenance of tissue homeostasis, and efficient removal prevents exposure of intracellular content to the immune system, which could lead to autoimmunity. The plasma protease factor VII-activating protease (FSAP) can release nucleosomes from late apoptotic cells. FSAP circulates as an inactive single-chain protein, which is activated upon contact with either apoptotic cells or necrotic cells. The purpose of this study was to investigate the role of FSAP in the release of nucleosomes from necrotic cells. Methods. Necrotic Jurkat cells were incubated with serum, purified 2-chain FSAP, and/or DNase I. Nucleosome release was analyzed by flow cytometry, and agarose gel electrophoresis was performed to detect DNA breakdown. Results. Incubation with serum released nucleosomes from necrotic cells. Incubation with FSAP-deficient serum or serum in which FSAP was inhibited by a blocking antibody was unable to release nucleosomes from necrotic cells, confirming that FSAP is indeed the essential serum factor in this process. Together with serum DNase I, FSAP induced the release of DNA from the cells, the appearance of nucleosomes in the supernatant, and the fragmentation of chromatin into eventually mononucleosomes. Conclusion. FSAP and DNase I are the essential serum factors that cooperate in necrotic cell DNA degradation and nucleosome release. We propose that this mechanism may be important in the removal of potential autoantigen

A psychophysical and neuroimaging analysis of genital hedonic sensation in men

Current understanding of human genital-brain interactions relates primarily to neuroendocrine and autonomic control, whereas interactions during sexual stimulation remain largely unexplored. Here we present a systematic approach towards identifying how the human brain encodes sensory genital information. Using a validated affective touch paradigm and functional magnetic resonance imaging, we found that hedonic responses to discriminatory versus affective tactile stimulation were distinctly different for both penile shaft and forearm. This suggests that, as with other body sites, genital skin contains small diameter mechanoreceptive nerve fibres that signal pleasant touch. In the brain, secondary somatosensory cortex (S2) distinguished between affective and discriminative touch for the penile shaft, but not for the forearm. Frenulum stimulation induced the greatest reports of subjective pleasure and led to the greatest deactivation of the default-mode network. This study represents a first pass at investigating, in humans, the relationship between innervation of genital surfaces, hedonic feelings, and brain mechanisms, in a systematic way

The damage-associated molecular pattern HMGB1 is released early after clinical hepatic ischemia/reperfusion

Objective and background: Activation of sterile inflammation after hepatic ischemia/reperfusion (I/R) culminates in liver injury. The route to liver damage starts with mitochondrial oxidative stress and cell death during early reperfusion. The link between mitochondrial oxidative stress, damage-associate molecular pattern (DAMP) release, and sterile immune signaling is incompletely understood and lacks clinical validation. The aim of the study was to validate this relation in a clinical liver I/R cohort and to limit DAMP release using a mitochondria-targeted antioxidant in I/R-subjected mice. Methods: Plasma levels of the DAMPs high-mobility group box 1 (HMGB1), mitochondrial DNA, and nucleosomes were measured in 39 patients enrolled in an observational study who underwent a major liver resection with (N = 29) or without (N = 13) intraoperative liver ischemia. Circulating cytokine and neutrophil activation markers were also determined. In mice, the mitochondria-targeted antioxidant MitoQ was intravenously infused in an attempt to limit DAMP release, reduce sterile inflammation, and suppress I/R injury. Results: In patients, HMGB1 was elevated following liver resection with I/R compared to liver resection without I/R. HMGB1 levels correlated positively with ischemia duration and peak post-operative transaminase (ALT) levels. There were no differences in mitochondrial DNA, nucleosome, or cytokine levels between the two groups. In mice, MitoQ neutralized hepatic oxidative stress and decreased HMGB1 release by ±50%. MitoQ suppressed transaminase release, hepatocellular necrosis, and cytokine production. Reconstituting disulfide HMGB1 during reperfusion reversed these protective effects. Conclusion: HMGB1 seems the most pertinent DAMP in clinical hepatic I/R injury. Neutralizing mitochondrial oxidative stress may limit DAMP release after hepatic I/R and reduce liver damage.</p