Role of the Nalp3 inflammasome in acetaminophen-induced sterile inflammation and liver injury

P2X7 receptor-mediated purinergic signaling promotes liver injury in acetaminophen hepatotoxicity in mice

Inflammation contributes to liver injury in acetaminophen (APAP) hepatotoxicity in mice and is triggered by stimulation of immune cells. The purinergic receptor P2X7 is upstream of the nod-like receptor family, pryin domain containing-3 (NLRP3) inflammasome in immune cells and is activated by ATP and NAD that serve as damage-associated molecular patterns. APAP hepatotoxicity was assessed in mice genetically deficient in P2X7, the key inflammatory receptor for nucleotides (P2X7-/-), and in wild-type mice. P2X7-/- mice had significantly decreased APAP-induced liver necrosis. In addition, APAP-poisoned mice were treated with the specific P2X7 antagonist A438079 or etheno-NAD, a competitive antagonist of NAD. Pre- or posttreatment with A438079 significantly decreased APAP-induced necrosis and hemorrhage in APAP liver injury in wild-type but not P2X7-/- mice. Pretreatment with etheno-NAD also significantly decreased APAP-induced necrosis and hemorrhage in APAP liver injury. In addition, APAP toxicity in mice lacking the plasma membrane ecto-NTPDase CD39 (CD39-/-) that metabolizes ATP was examined in parallel with the use of soluble apyrase to deplete extracellular ATP in wild-type mice. CD39-/- mice had increased APAP-induced hemorrhage and mortality, whereas apyrase also decreased APAP-induced mortality. Kupffer cells were treated with extracellular ATP to assess P2X7-dependent inflammasome activation. P2X7 was required for ATP-stimulated IL-1β release. In conclusion, P2X7 and exposure to the ligands ATP and NAD are required for manifestations of APAP-induced hepatotoxicity.

RETRACTED: Molecular forms of HMGB1 and keratin-18 as mechanistic biomarkers for mode of cell death and prognosis during clinical acetaminophen hepatotoxicity

BACKGROUND & AIMS

Full length keratin-18 (FL-K18) and High Mobility Group Box-1 (HMGB1) represent circulating indicators of necrosis during acetaminophen (APAP) hepatotoxicity in vivo. In addition, the caspase-cleaved fragment of K18 (cK18) and hyper-acetylated HMGB1 represent serum indicators of apoptosis and immune cell activation, respectively. The study aim was to assess their mechanistic utility to establish the balance between apoptosis, necrosis, and immune cell activation throughout the time course of clinical APAP hepatotoxicity.

METHODS

HMGB1 (total, acetylated) and K18 (apoptotic, necrotic) were identified and quantified by novel LC-MS/MS assays in APAP overdose patients (n=78).

RESULTS

HMGB1 (total; 15.4±1.9ng/ml, p<0.01, acetylated; 5.4±2.6ng/ml, p<0.001), cK18 (5649.8±721.0U/L, p<0.01), and FL-K18 (54770.2±6717.0U/L, p<0.005) were elevated in the sera of APAP overdose patients with liver injury compared to overdose patients without liver injury and healthy volunteers. HMGB1 and FL-K18 correlated with alanine aminotransferase (ALT) activity (R(2)=0.60 and 0.58, respectively, p<0.0001) and prothrombin time (R(2)=0.62 and 0.71, respectively, p<0.0001). Increased total and acetylated HMGB1 and FL-K18 were associated with worse prognosis (King's College Criteria) or patients that died/required liver transplant compared to spontaneous survivors (all p<0.05-0.001), a finding not reflected by ALT and supported by ROC analysis. Acetylated HMGB1 was a better predictor of outcome than the other markers of cell death.

CONCLUSIONS

K18 and HMGB1 represent blood-based tools to investigate the cell death balance clinical APAP hepatotoxicity. Activation of the immune response was seen later in the time course as shown by the distinct profile of acetylated HMGB1 and was associated with worse outcome.

Regulation of alternative macrophage activation in the liver following acetaminophen intoxication by stem cell-derived tyrosine kinase

Stem cell-derived tyrosine kinase (STK) is a transmembrane receptor reported to play a role in macrophage switching from a classically activated/proinflammatory phenotype to an alternatively activated/wound repair phenotype. In the present studies, STK⁻/⁻ mice were used to assess the role of STK in acetaminophen-induced hepatotoxicity as evidence suggests that the pathogenic process involves both of these macrophage subpopulations. In wild type mice, centrilobular hepatic necrosis and increases in serum transaminase levels were observed within 6h of acetaminophen administration (300 mg/kg, i.p.). Loss of STK resulted in a significant increase in sensitivity of mice to the hepatotoxic effects of acetaminophen and increased mortality, effects independent of its metabolism. This was associated with reduced levels of hepatic glutathione, rapid upregulation of inducible nitric oxide synthase, and prolonged induction of heme oxygenase-1, suggesting excessive oxidative stress in STK⁻/⁻ mice. F4/80, a marker of mature macrophages, was highly expressed on subpopulations of Kupffer cells in livers of wild type, but not STK⁻/⁻ mice. Whereas F4/80⁺ macrophages rapidly declined in the livers of wild type mice following acetaminophen intoxication, they increased in STK⁻/⁻ mice. In wild type mice hepatic expression of tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-12, products of classically activated macrophages, increased after acetaminophen administration. Monocyte chemotactic protein-1 (MCP-1) and its receptor, CCR2, as well as IL-10, mediators involved in recruiting and activating anti-inflammatory/wound repair macrophages, also increased in wild type mice after acetaminophen. Loss of STK blunted the effects of acetaminophen on expression of TNFα, IL-1β, IL-12, MCP-1 and CCR2, while expression of IL-10 increased. Hepatic expression of CX3CL1, and its receptor, CX3CR1 also increased in STK⁻/⁻ mice treated with acetaminophen. These data demonstrate that STK plays a role in regulating macrophage recruitment and activation in the liver following acetaminophen administration, and in hepatotoxicity.

Influence of inflammation on the efficacy of mesenchymal stem cell transplantation for acute liver injury

AIM: To evaluate the influence of inflammatory reaction on the survival of transplanted mesenchymal stem cells (MSCs) and on the efficacy of MSC transplantation for acute liver injury.

METHODS: Sixteen Chinese experimental mini-pigs were randomly divided into two groups: control group and MSC transplantation group. All the animals were given 0.25 g/kg and 0.35 g/kg of D-galactosamine (D-gal) to induce acute liver injury with inflammatory reaction of varying degrees. In the control group, 100 mL of normal saline was injected into the liver via the portal vein 24 h after model induction. In the MSC transplantation group, 8 × 10⁷ MSCs (in 40 mL PBS) were injected into the liver via the portal vein. Liver function, serum inflammatory markers, survival of MSCs and pathological changes were examined after injection.

RESULTS: Serum levels of inflammation factors (IL-1, TNF-alpha) were significantly higher in the high-concentration D-gal group than in the low-concentration group. For animals given low-concentration D-gal, serum ALT, TB and NH3 differed significantly between the MSC transplantation group and control group (D2: 232.6 ± 57.6 vs 334.4 ± 42.3, 12.2 ± 3.3 vs 16.0 ± 1.2, 79.7 ± 9.3 vs 127.8 ± 28.2, all P < 0. 05). In contrast, for animals given high-concentration D-gal, there was no difference in the above parameters between the MSC transplantation group and control group. Hepatic engraftment of MSCs in the mild inflammation group was obviously different from that in the severe inflammation group, and the growth of hepatocytes was significantly improved in the mild inflammation group compared to the severe inflammation group.

CONCLUSION: MSC transplantation is at least partially useful for the management of acute liver injury. Severe inflammatory reaction is harmful to hepatic engraftment of MSCs, while mild inflammatory reaction is useful for the transplanted cells.

Nucleotide-binding oligomerization domain-like receptors and inflammasomes in the pathogenesis of non-microbial inflammation and diseases

The nucleotide-binding oligomerization domain (NOD)-like receptor (NLR) or nucleotide-binding domain leucine-rich repeat-containing family of genes plays an important role in the development of innate immune responses. Some family members are known to form multiprotein complexes known as inflammasomes that regulate the processing and secretion of proinflammatory mediators, such as interleukin-1β and interleukin-18. Activity of the inflammasome is triggered not only by microbial infection, but also by a wide range of both exogenous and endogenous noninfectious stimuli. Consequently, the dysregulation of inflammasome activity is associated with numerous proinflammatory, non-microbial human diseases. The discovery of NLRP3 gene mutations in autoinflammatory diseases such as Muckle-Wells syndrome has led to the association of NLRs in the pathogenesis of many non-microbial diseases that include arthritis, neurodegenerative disorders, metabolic disorders (obesity and diabetes), cardiovascular disease (atherosclerosis, myocardial infarction), inflammatory bowel disease, kidney disease and hypersensitivity dermatitis. A number of NLRs are also associated with human disease in the absence of inflammasome activity, suggesting additional roles for NLRs in the regulation of inflammation and disease. This review serves to provide a summary of NLR-associated diseases and, where possible, the mechanisms behind the associations.

Mouse strain-dependent caspase activation during acetaminophen hepatotoxicity does not result in apoptosis or modulation of inflammation

The mechanisms of acetaminophen (APAP)-mediated hepatic oncotic necrosis have been extensively characterized. However, it was recently demonstrated that fed CD-1 mice have a transient caspase activation which initiates apoptosis. To evaluate these findings in more detail, outbred (Swiss Webster, SW) and inbred (C57BL/6) mice were treated with APAP with or without pan-caspase inhibitor and compared to the apoptosis model of galactosamine (GalN)/endotoxin (ET). Fasted or fed APAP-treated C57BL/6 mice showed no evidence of caspase-3 processing or activity. Interestingly, a minor, temporary increase in caspase-3 processing and activity (150% above baseline) was observed after APAP treatment only in fed SW mice. The degree of caspase-3 activation in SW mice after APAP was minor compared to that observed in GalN/ET-treated mice (1600% above baseline). The pancaspase inhibitor attenuated caspase activation and resulted in increased APAP-induced injury (plasma ALT, necrosis scoring). The caspase inhibitor did not affect apoptosis because regardless of treatment only <0.5% of hepatocytes showed consistent apoptotic morphology after APAP. In contrast, >20% apoptotic cells were observed in GalN/ET-treated mice. Presence of the caspase inhibitor altered hepatic glutathione levels in SW mice, which could explain the exacerbation of injury. Additionally, the infiltration of hepatic neutrophils was not altered by the fed state of either mouse strain.

CONCLUSION

Minor caspase-3 activation without apoptotic cell death can be observed only in fed mice of some outbred strains. These findings suggest that although the severity of APAP-induced liver injury varies between fed and fasted animals, the mechanism of cell death does not fundamentally change.