Acute liver failure (ALF) is a severe syndrome with a mortality rate of up to 80%. It is characterized by the rapid deterioration of liver function (Antoniades et al., 2008; Vaquero et al., 2003). To date, there are no effective intervention targets or breakthrough drugs available for ALF, other than liver transplantation, which is costly and dependent on donor availability. Hence, it is necessary to explore possible targets for the treatment of this life-threatening disease.

Macrophages are stimulated by endotoxemia to release a significant amount of pro-inflammatory cytokines such as interleukin (IL)− 1β and tumor necrosis factor (TNF)-α, leading to a systemic inflammatory response (SIRS) and multiorgan failure in ALF (Antoniades et al., 2008, Han, 2002, Vaquero et al., 2003). The depletion of macrophages by gadolinium has been shown to protect mice from acetaminophen-induced acute liver failure while transferring macrophages leads to disease relapse (Biagioli et al., 2020). These findings highlight the crucial role of macrophages in the pathogenesis of ALF. Additionally, IL-1β is a key cytokine that significantly contributes to inflammation amplification and disease progression in ALF. Blocking IL-1β with IL-1-receptor antagonist or IL-1β siRNA has been found to reduce the severity of D-galactosamine (D-GalN)/ lipopolysaccharide (LPS) induced-ALF (Ding et al., 2021, Ilyas et al., 2016), further confirming the impact of IL-1β. Therefore, identifying new targets that interfere with the upstream process of the IL-1β pathway in macrophages represents a viable strategy for ALF treatment.

Pyroptosis represents a distinct form of programmed cell death characterized by an inflammatory response and is different from necrosis and apoptosis (Xia et al., 2019). The process involves the formation of pores on the plasma membrane, resulting in cell swelling and membrane disruption. Pyroptosis can occur through two pathways: canonical and non-canonical. In the canonical pathway, the Nod-like receptor protein 3 (NLRP3) inflammasome is assembled, consisting of an intracellular sensor (typically an NLR), a precursor procaspase-1, and an adaptor apoptosis-associated speck-like protein. This assembly leads to the activation of caspase-1, which then cleaves gasdermin D (GSDMD) in response to various microbial pathogens and molecules. Additionally, caspase-1 cleaves pro IL-1β and pro IL-18 to generate mature IL-1β and IL-18. Cleaved GSDMD forms transmembrane pores, which subsequently lead to the release of IL-1β and IL-18 and eventually, cell lysis (Broz and Dixit, 2016, Fink and Cookson, 2006, Li et al., 2023). In the non-canonical pathway, mouse caspase-11 (caspase-4 or 5 in humans) is directly activated by cytosolic LPS, triggering pyroptosis through GSDMD cleavage (Shi et al., 2014). While pyroptosis of macrophages serves as an important defense mechanism against microbial pathogens, uncontrolled pyroptosis can exacerbate the inflammatory response and cause severe tissue damage (Labbe and Saleh, 2008, Wu et al., 2019). Notably, the depletion or inhibition of key proteins associated with pyroptosis, including the NLRPs inflammasome, caspase-11, and GSDMD, has been shown to alleviate the inflammatory response in the liver and prolong the survival of mice with ALF, underlining the critical role of macrophages pyroptosis in the context of ALF (Carty et al., 2019; Gehrke et al., 2018; Li et al., 2019; Wang et al., 2022; Xu et al., 2021).

Succinate dehydrogenase (SDH), also known as mitochondrial complex II, catalyzes the oxidation of succinate to fumarate while reducing ubiquinone to ubiquinol, thereby connecting the tricarboxylic acid cycle and the electron transport chain (Sun et al., 2005). SDH consists of four subunits, namely SDHA, SDHB, SDHC, and SDHD. Recent studies have reported that SDHA or SDHB expression levels are positively associated with inflammation in epithelium or endothelium tissues (Chen et al., 2021; Vohwinkel et al., 2021). Moreover, SDH activity of macrophage increases in inflammatory conditions accompanied by an increase in the secretion of pro-inflammatory cytokines IL-1β, IL-6, IL-18, and TNF-α and a decrease in the release of anti-inflammatory cytokine IL-10 (Azzimato et al., 2021, Koenis et al., 2018, Mills et al., 2016). Inhibition of SDH activity in macrophages impedes inflammatory response and alleviates the severity of sepsis and renal ischemia-reperfusion injury, implying that the overactivation of SDH in macrophages promotes inflammation (Beach et al., 2020, Mills et al., 2016). The inflammatory effects of SDH activity are primarily attributed to increased oxidation of succinate, stabilization of hypoxic inducible factor-1α, and elevated ROS production (Mills et al., 2016; Tannahill et al., 2013). Furthermore, one study has elucidated that the production of ROS promotes macrophage pyroptosis by GSDMD oligomerization (Evavold et al., 2021). Given the role of SDH in ROS production, we speculated that increased SDH activity on macrophages may promote pyroptosis by GSDMD oligomerization.

The objective of this study was to examine the impact of SDH activity in macrophages on inflammation using a well-characterized D-GalN/LPS-induced ALF mouse model and elucidate the underlying mechanism associated with this phenomenon. Our findings showed a significant augmentation of SDH activity specifically in liver macrophages during ALF. Notably, inhibiting SDH activity using dimethyl malonate (DMM) provided protection against ALF in mice by reducing GSDMD oligomer production and subsequent pyroptosis.