Inhibition of Drug-Induced Liver Injury in Mice Using a Positively Charged Peptide That Binds DNA

Hepatic cell death occurs in response to diverse stimuli such as chemical and physical damage. The exposure of intracellular contents such as DNA during necrosis induces a severe inflammatory response that has yet to be fully explored therapeutically. Here, we sought means to neutralize the ability of extracellular DNA to induce deleterious tissue inflammation when drug-induced liver injury had already ensued. DNA exposure and inflammation were investigated in vivo in drug-induced liver injury using intravital microscopy. The necrotic DNA debris was studied in murine livers in vivo and in DNA debris models in vitro by using a positively charged chemokine-derived peptide (MIG30; CXCL9[74-103]). Acetaminophen-induced liver necrosis was associated with massive DNA accumulation, production of CXC chemokines, and neutrophil activation inside the injured tissue. The MIG30 peptide bound the healthy liver vasculature and, to a much greater extent, to DNA-rich necrotic tissue. Moreover, MIG30 bound extracellular DNA directly in vivo in a charge-dependent manner and independently of glycosaminoglycans and chemokines. Post-treatment of mice with MIG30 reduced mortality, liver damage, and inflammation significantly. These effects were not observed with a control peptide that does not bind DNA. Mechanistically, MIG30 inhibited the interaction between DNA and histones, and promoted the dissociation of histones from necrotic debris. MIG30 also inhibited the pro-inflammatory effect of CpG DNA, as measured by a reduction in CXCL8 production, indicating that MIG30 disturbs the ability of DNA to induce hepatic inflammation. Conclusion: The use of DNA-binding peptides reduces necrotic liver injury and inflammation, even at late timepoints.

Complement Receptors and Their Role in Leukocyte Recruitment and Phagocytosis

The complement system is deeply embedded in our physiology and immunity. Complement activation generates a multitude of molecules that converge simultaneously on the opsonization of a target for phagocytosis and activation of the immune system via soluble anaphylatoxins. This response is used to control microorganisms and to remove dead cells, but also plays a major role in stimulating the adaptive immune response and the regeneration of injured tissues. Many of these effects inherently depend on complement receptors expressed on leukocytes and parenchymal cells, which, by recognizing complement-derived molecules, promote leukocyte recruitment, phagocytosis of microorganisms and clearance of immune complexes. Here, the plethora of information on the role of complement receptors will be reviewed, including an analysis of how this functionally and structurally diverse group of molecules acts jointly to exert the full extent of complement regulation of homeostasis.

SnapShot:Macropinocytosis

Macropinocytosis is the bulk ingestion of extracellular fluids via large endocytic vacuoles. This SnapShot provides an overview of physiological macropinocytosis in immune surveillance and its pathogenic contribution during infection and cancer proliferation.

Dengue virus requires the CC-chemokine receptor CCR5 for replication and infection development

Dengue is a mosquito-borne disease that affects millions of people worldwide yearly. Currently, there is no vaccine or specific treatment available. Further investigation on dengue pathogenesis is required to better understand the disease and to identify potential therapeutic targets. The chemokine system has been implicated in dengue pathogenesis, although the specific role of chemokines and their receptors remains elusive. Here we describe the role of the CC-chemokine receptor CCR5 in Dengue virus (DENV-2) infection. In vitro experiments showed that CCR5 is a host factor required for DENV-2 replication in human and mouse macrophages. DENV-2 infection induces the expression of CCR5 ligands. Incubation with an antagonist prevents CCR5 activation and reduces DENV-2 positive-stranded (+) RNA inside macrophages. Using an immunocompetent mouse model of DENV-2 infection we found that CCR5(-/-) mice were resistant to lethal infection, presenting at least 100-fold reduction of viral load in target organs and significant reduction in disease severity. This phenotype was reproduced in wild-type mice treated with CCR5-blocking compounds. Therefore, CCR5 is a host factor required for DENV-2 replication and disease development. Targeting CCR5 might represent a therapeutic strategy for dengue fever. These data bring new insights on the association between viral infections and the chemokine receptor CCR5.

Calcium signalling from the type I inositol 1,4,5-trisphosphate receptor is required at early phase of liver regeneration

BACKGROUND & AIMS

Liver regeneration is a multistage process that unfolds gradually, with different mediators acting at different stages of regeneration. Calcium (Ca(2+) ) signalling is essential for liver regeneration. In hepatocytes, Ca(2+) signalling results from the activation of inositol 1,4,5-trisphosphate receptors (InsP3 R) of which two of the three known isoforms are expressed (InsP3 R-I and InsP3 R-II). Here, we investigated the role of the InsP3 R-I-dependent Ca(2+) signals in hepatic proliferation during liver regeneration.

METHODS

Partial hepatectomy (HX) in combination with knockdown of InsP3 R-I (AdsiRNA-I) was used to evaluate the role of InsP3 R-I on liver regeneration and hepatocyte proliferation, as assessed by liver to body mass ratio, PCNA expression, immunoblots and measurements of intracellular Ca(2+) signalling.

RESULTS

AdsiRNA-I efficiently infected the liver as demonstrated by the expression of β-galactosidase throughout the liver lobules. Moreover, this construct selectively and efficiently reduced the expression of InsP3 R-I, as evaluated by immunoblots. Expression of AdsiRNA-I in liver decreased peak Ca(2+) amplitude induced by vasopressin in isolated hepatocytes 2 days after HX. Reduced InsP3 R-I expression prior to HX also delayed liver regeneration, as measured by liver to body weight ratio, and reduced hepatocyte proliferation, as evaluated by PCNA staining, at the same time point. At later stages of regeneration, control hepatocytes showed a decreased expression of InsP3 R, as well as reduced InsP3 R-mediated Ca(2+) signalling, events that did not affect liver growth.

CONCLUSION

Together, these results show that InsP3 R-I-dependent Ca(2+) signalling is an early triggering pathway required for liver regeneration.

Treadmill exercise induces neutrophil recruitment into muscle tissue in a reactive oxygen species-dependent manner. An intravital microscopy study

Intense exercise is a physiological stress capable of inducing the interaction of neutrophils with muscle endothelial cells and their transmigration into tissue. Mechanisms driving this physiological inflammatory response are not known. Here, we investigate whether production of reactive oxygen species is relevant for neutrophil interaction with endothelial cells and recruitment into the quadriceps muscle in mice subjected to the treadmill fatiguing exercise protocol. Mice exercised until fatigue by running for 56.3±6.8 min on an electric treadmill. Skeletal muscle was evaluated by intravital microscopy at different time points after exercise, and then removed to assess local oxidative stress and histopathological analysis. We observed an increase in plasma lactate and creatine kinase (CK) concentrations after exercise. The numbers of monocytes, neutrophils, and lymphocytes in blood increased 12 and 24 hours after the exercise. Numbers of rolling and adherent leukocytes increased 3, 6, 12, and 24 hours post-exercise, as assessed by intravital microscopy. Using LysM-eGFP mice and confocal intravital microscopy technology, we show that the number of transmigrating neutrophils increased 12 hours post-exercise. Mutant gp91^phox-/- (non-functional NADPH oxidase) mice and mice treated with apocynin showed diminished neutrophil recruitment. SOD treatment promoted further adhesion and transmigration of leukocytes 12 hours after the exercise. These findings confirm our hypothesis that treadmill exercise increases the recruitment of leukocytes to the postcapillary venules, and NADPH oxidase-induced ROS plays an important role in this process.

Connexin and pannexin (hemi)channels in the liver

The liver was among the first organs in which connexin proteins have been identified. Hepatocytes harbor connexin32 and connexin26, while non-parenchymal liver cells typically express connexin43. Connexins give rise to hemichannels, which dock with counterparts on adjacent cells to form gap junctions. Both hemichannels and gap junctions provide pathways for communication, via paracrine signaling or direct intercellular coupling, respectively. Over the years, hepatocellular gap junctions have been shown to regulate a number of liver-specific functions and to drive liver cell growth. In the last few years, it has become clear that connexin hemichannels are involved in liver cell death, particularly in hepatocyte apoptosis. This also holds true for hemichannels composed of pannexin1, a connexin-like protein recently identified in the liver. Moreover, pannexin1 hemichannels are key players in the regulation of hepatic inflammatory processes. The current paper provides a concise overview of the features of connexins, pannexins and their channels in the liver.

Purinergic signalling during sterile liver injury

The liver plays a vital role in the organism, and thousands of patients suffer and even die from hepatic complications every year. Viral hepatitis is one of the most important causes of liver-related pathological processes. However, sterile liver diseases, such as drug-induced liver injury, cirrhosis and fibrosis, are still a worldwide concern and contribute significantly to liver transplantation statistics. During hepatocyte death, several genuine intracellular contents are released to the interstitium, where they will trigger inflammatory responses that may boost organ injury. Intracellular purines are key molecules to several metabolic pathways and regulate cell bioenergetics. However, seminal studies in early 70s revealed that purines may also participate in cell-to-cell communication, and more recent data have unequivocally demonstrated that the purinergic signalling plays a key role in the recognition of cell functionality by neighbouring cells and also by the immune system. This new body of knowledge has pointed out that several promising therapeutic opportunities may rely on the modulation of purine release and sensing during diseases. Here, we review the most recent data on the physiological roles of purinergic signalling and how its imbalance may contribute to injury progression during sterile liver injury.

Altered responsiveness to extracellular ATP enhances acetaminophen hepatotoxicity

BACKGROUND

Adenosine triphosphate (ATP) is secreted from hepatocytes under physiological conditions and plays an important role in liver biology through the activation of P2 receptors. Conversely, higher extracellular ATP concentrations, as observed during necrosis, trigger inflammatory responses that contribute to the progression of liver injury. Impaired calcium (Ca2+) homeostasis is a hallmark of acetaminophen (APAP)-induced hepatotoxicity, and since ATP induces mobilization of the intracellular Ca2+ stocks, we evaluated if the release of ATP during APAP-induced necrosis could directly contribute to hepatocyte death.

RESULTS

APAP overdose resulted in liver necrosis, massive neutrophil infiltration and large non-perfused areas, as well as remote lung inflammation. In the liver, these effects were significantly abrogated after ATP metabolism by apyrase or P2X receptors blockage, but none of the treatments prevented remote lung inflammation, suggesting a confined local contribution of purinergic signaling into liver environment. In vitro, APAP administration to primary mouse hepatocytes and also HepG2 cells caused cell death in a dose-dependent manner. Interestingly, exposure of HepG2 cells to APAP elicited significant release of ATP to the supernatant in levels that were high enough to promote direct cytotoxicity to healthy primary hepatocytes or HepG2 cells. In agreement to our in vivo results, apyrase treatment or blockage of P2 receptors reduced APAP cytotoxicity. Likewise, ATP exposure caused significant higher intracellular Ca2+ signal in APAP-treated primary hepatocytes, which was reproduced in HepG2 cells. Quantitative real time PCR showed that APAP-challenged HepG2 cells expressed higher levels of several purinergic receptors, which may explain the hypersensitivity to extracellular ATP. This phenotype was confirmed in humans analyzing liver biopsies from patients diagnosed with acute hepatic failure.

CONCLUSION

We suggest that under pathological conditions, ATP may act not only an immune system activator, but also as a paracrine direct cytotoxic DAMP through the dysregulation of Ca2+ homeostasis.

Chemokines and mitochondrial products activate neutrophils to amplify organ injury during mouse acute liver failure

Acetaminophen (APAP) is a safe analgesic and antipyretic drug. However, APAP overdose leads to massive hepatocyte death. Cell death during APAP toxicity occurs by oncotic necrosis, in which the release of intracellular contents can elicit a reactive inflammatory response. We have previously demonstrated that an intravascular gradient of chemokines and mitochondria-derived formyl peptides collaborate to guide neutrophils to sites of liver necrosis by CXC chemokine receptor 2 (CXCR2) and formyl peptide receptor 1 (FPR1), respectively. Here, we investigated the role of CXCR2 chemokines and mitochondrial products during APAP-induced liver injury and in liver neutrophil influx and hepatotoxicity. During APAP overdose, neutrophils accumulated into the liver, and blockage of neutrophil infiltration by anti-granulocyte receptor 1 depletion or combined CXCR2-FPR1 antagonism significantly prevented hepatotoxicity. In agreement with our in vivo data, isolated human neutrophils were cytotoxic to HepG2 cells when cocultured, and the mechanism of neutrophil killing was dependent on direct contact with HepG2 cells and the CXCR2-FPR1-signaling pathway. Also, in mice and humans, serum levels of both mitochondrial DNA (mitDNA) and CXCR2 chemokines were higher during acute liver injury, suggesting that necrosis products may reach remote organs through the circulation, leading to a systemic inflammatory response. Accordingly, APAP-treated mice exhibited marked systemic inflammation and lung injury, which was prevented by CXCR2-FPR1 blockage and Toll-like receptor 9 (TLR9) absence (TLR9(-/-) mice).

CONCLUSION

Chemokines and mitochondrial products (e.g., formyl peptides and mitDNA) collaborate in neutrophil-mediated injury and systemic inflammation during acute liver failure. Hepatocyte death is amplified by liver neutrophil infiltration, and the release of necrotic products into the circulation may trigger a systemic inflammatory response and remote lung injury.