Acetaminophen-induced hepatotoxicity in mice is dependent on Tlr9 and the Nalp3 inflammasome

Abstract

Hepatocyte death results in a sterile inflammatory response that amplifies the initial insult and increases overall tissue injury. One important example of this type of injury is acetaminophen-induced liver injury, in which the initial toxic injury is followed by innate immune activation. Using mice deficient in Tlr9 and the inflammasome components Nalp3 (NACHT, LRR, and pyrin domain-containing protein 3), ASC (apoptosis-associated specklike protein containing a CARD), and caspase-1, we have identified a nonredundant role for Tlr9 and the Nalp3 inflammasome in acetaminophen-induced liver injury. We have shown that acetaminophen treatment results in hepatocyte death and that free DNA released from apoptotic hepatocytes activates Tlr9. This triggers a signaling cascade that increases transcription of the genes encoding pro-IL-1β and pro-IL-18 in sinusoidal endothelial cells. By activating caspase-1, the enzyme responsible for generating mature IL-1β and IL-18 from pro-IL-1β and pro-IL-18, respectively, the Nalp3 inflammasome plays a crucial role in the second step of proinflammatory cytokine activation following acetaminophen-induced liver injury. Tlr9 antagonists and aspirin reduced mortality from acetaminophen hepatotoxicity. The protective effect of aspirin on acetaminophen-induced liver injury was due to downregulation of proinflammatory cytokines, rather than inhibition of platelet degranulation or COX-1 inhibition. In summary, we have identified a 2-signal requirement (Tlr9 and the Nalp3 inflammasome) for acetaminophen-induced hepatotoxicity and some potential therapeutic approaches.

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

“…Previous reports have described apoptotic gDNA as the major activator of TLR9 in APAP-induced liver injury. 34 However, we and others 8 have provided evidence that mitDNA also plays a key role in immune system activation by TLR9 signaling during ALF.…”

Gut–Liver Axis: Role of Inflammasomes

“…6 Recent studies have revealed the expression of inflammasomes in innate immune cells including monocytes, macrophages, neutrophils, and dendritic cells. Furthermore, non-immune cells including hepatocytes, [57][58][59] stellate cells, 60 endothelial cells, 61,62 and myofibroblasts 63 also contain the functionally active inflammasome complex. Studies at the mRNA levels support the expression of NLRP1, 2, 3, 6, 10, 12, and NLRC4 in the liver.…”

Reply

“…1 Interestingly, all studies that investigated a role of the Nalp3 inflammasome and interleukin-1b (IL-1b) in APAP hepatotoxicity are in agreement that damage-associated-molecular patterns released from necrotic cells activate macrophages to generate cytokines, including pro-IL-1b. 1,3,4 All groups also agree that inhibition or deficiency of caspase-1 eliminates processing of pro-IL-1b to the active cytokine. 1,3,4 Most important, all agree that only a few pg/mL of IL-1b are actually produced during APAP hepatotoxicity.…”

“…1,3,4 Most important, all agree that only a few pg/mL of IL-1b are actually produced during APAP hepatotoxicity. 1,3,4 However, the fact that mice treated with 10,000-fold more recombinant IL-1b had no effect on APAPinduced liver injury clearly indicates that minor quantities of endogenously generated IL-1b have no impact on APAP hepatotoxicity. 4 …”

“…1 Except for the fact that the majority of Chinese people are obliged to pay a large part or even all of their medical costs, another important reason is that hepatitis B virus carriers still encounter discrimination in various aspects of their lives in China, as we mentioned in an article in The Lancet. 3 Therefore, on the one hand, China should be involved in the large-scale dissemination of scientific knowledge about hepatitis B and other liver diseases so as to eliminate the ingrained fear that leads to discrimination; on the other hand, it should plug more money into the health care budget, increase health financing available for the Chinese people, and ensure that more citizens obtain real benefits. Thus, more patients with liver disease can afford regular specialized examinations as well as preventive treatments.…”