Pyroptosis in sepsis-associated acute kidney injury: mechanisms and therapeutic perspectives

Abstract

Sepsis-associated acute kidney injury (S-AKI) is a severe complication characterized by high morbidity and mortality, driven by multi-organ dysfunction. Recent evidence suggests that pyroptosis, a form of programmed cell death distinct from apoptosis and necrosis, plays a critical role in the pathophysiology of S-AKI. This review examines the mechanisms of pyroptosis, focusing on inflammasome activation (e.g., NLRP3), caspase-mediated processes, and the role of Gasdermin D in renal tubular damage. We also discuss the contributions of inflammatory mediators, oxidative stress, and potential therapeutic strategies targeting pyroptosis, including inflammasome inhibitors, caspase inhibitors, and anti-inflammatory therapies. Lastly, we highlight the clinical implications and challenges in translating these findings into effective treatments, underscoring the need for personalized medicine approaches in managing S-AKI. 

Introduction

Sepsis is a critical condition and a leading cause of mortality in hospitals. The Third International Consensus Definitions for Sepsis and Septic Shock defines sepsis as “life-threatening organ dysfunction caused by a dysregulated host response to infection”. Septic shock, a severe form of sepsis, is characterized by the need for vasopressors to maintain a mean arterial pressure (MAP) of at least 65 mmHg, along with serum lactate levels exceeding 2 mmol/L (18 mg/dL), in the absence of hypovolemia. This condition is associated with a mortality rate exceeding 40%. With the increasing incidence of sepsis, there is growing concern about its complications, including sepsis-associated acute kidney injury (S-AKI) [1, 2]. Studies have shown that acute kidney injury (AKI) is very common in patients with sepsis in the intensive care unit (ICU), with a risk of death as high as 48% [3, 4]. Acute kidney injury (AKI) is defined as an increase in serum creatinine levels of at least 50% within 7 days, an increase of at least 0.3 mg/dL within 2 days, or a decrease in urine output (oliguria) lasting at least 6 h. This definition follows the 2020 Consensus of the Kidney Disease: Improving Global Outcomes (KDIGO) [5, 6]. The onset of AKI in these patients notably worsens prognosis, leading to higher mortality rates and an increased risk of progression to chronic kidney disease (CKD) [7].

Sepsis-associated acute kidney injury (S-AKI) is characterized by a rapid decline in renal function, often resulting from a complex interplay of hemodynamic, inflammatory, and immune-related factors. Despite advancements in critical care medicine, the pathophysiology of S-AKI is still not well understood, and there are no effective treatments specifically targeting the underlying mechanisms. Current therapeutic strategies primarily focus on supportive care, including fluid management, vasopressors, and renal replacement therapy [8]. A deeper understanding of the molecular mechanisms underlying S-AKI is essential for developing new therapeutic strategies to reduce renal damage and enhance patient outcomes. Recent studies have highlighted pyroptosis, a type of programmed cell death that differs from apoptosis and necrosis, as a significant factor in the pathogenesis of sepsis and acute kidney injury (AKI) [9, 10].

Pyroptosis is characterized by a strong inflammatory response, marked by the activation of inflammasomes and the secretion of pro-inflammatory cytokines. This process plays a significant role in the extensive tissue damage commonly seen in sepsis [11, 12]. Gaining insights into the role of pyroptosis in S-AKI could pave the way for targeted therapies that modulate this cell death pathway, ultimately reducing renal injury in patients with sepsis [13]. Pyroptosis is a mode of programmed cell death that depends on the activation of cysteinyl aspartate specific proteinase (Caspase) and is accompanied by the release of large amounts of inflammatory factors [14]. Unlike apoptosis, which is a non-inflammatory phagocytosis, pyroptosis leads to inflammatory cell death, which is characterized by the formation of cytoplasmic membrane pores, cell swelling and destruction, cell membrane lysis, release of inflammatory factors, and the development of intrinsic immunity, which leads to cell death [15]. It is triggered by the activation of specific inflammasomes in response to pathogen-associated molecular patterns (PAMPs) or damage-associated molecular patterns (DAMPs) [16]. Once activated, inflammasomes recruit and activate caspase-1 or caspase-11 (in humans, caspase-4 and caspase-5 also participate), which cleave the Gasdermin D (GSDMD) protein [17].

The cleavage of GSDMD is a pivotal event in pyroptosis. The N-terminal fragment of GSDMD oligomerizes and forms pores in the cell membrane, leading to cell lysis and the release of intracellular contents, including pro-inflammatory cytokines such as interleukin-1β (IL-1β) and interleukin-18 (IL-18) [18, 19]. This release of inflammatory mediators further amplifies the immune response, contributing to tissue damage and organ dysfunction, particularly in conditions like sepsis [20]. Unlike other forms of cell death, pyroptosis serves a dual role: while it is an effective defense mechanism against pathogens by eliminating infected cells, its excessive or dysregulated activation can result in collateral damage to surrounding tissues [21]. In the context of sepsis, the systemic activation of pyroptosis is thought to exacerbate multi-organ dysfunction, including AKI [22]. Key molecular players in pyroptosis include caspases (such as caspase-1, caspase-11, and their human homologs), inflammasomes (e.g., NLRP3, AIM2), GSDMD, and the cytokines IL-1β and IL-18 [23]. In recent years, there has been increasing evidence that pyroptosis plays a critical role in the pathophysiology of sepsis-associated acute kidney injury [24,25,26]. The involvement of inflammasomes, particularly the NLRP3 inflammasome, has been highlighted in numerous experimental models of sepsis, where its activation correlates with renal inflammation, tubular injury, and dysfunction [27]. The kidney's unique architecture, particularly the high metabolic demands of the renal tubular epithelial cells, makes it highly susceptible to injury from pyroptosis [26, 28, 29]. The renal tubular cells are especially vulnerable to the effects of circulating PAMPs and DAMPs released during sepsis, which trigger inflammasome activation and subsequent pyroptotic cell death [30, 31]. This process is regulated by the PANoptosome [32], a multi-protein complex that senses pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs), leading to the activation of caspases, receptor-interacting protein kinases (RIPKs), and other inflammatory mediators [33].

As a result, pyroptosis contributes to tubular necrosis, impaired filtration, and ultimately, renal failure. Given the central role of pyroptosis in the progression of S-AKI, it represents an attractive target for therapeutic intervention. Inhibition of key components of the pyroptotic pathway, such as inflammasome activation, caspase-1, or Gasdermin D, has shown promise in reducing renal injury in experimental models [34, 35]. Furthermore, therapeutic strategies aimed at modulating the inflammatory response, such as the use of IL-1β inhibitors, have demonstrated potential in alleviating the severity of AKI in septic patients [36]. The aim of this review is to provide a comprehensive overview of the mechanisms by which pyroptosis contributes to the development of sepsis-associated AKI. By exploring the molecular pathways involved in pyroptosis, we seek to highlight potential therapeutic strategies that could be leveraged to mitigate renal damage in septic patients. Understanding these mechanisms is essential for the development of targeted treatments that address the underlying causes of S-AKI, rather than merely providing supportive care. This review will also examine current experimental therapies that focus on inhibiting pyroptosis and discuss their potential translation into clinical practice (Table 1).

Table 1 Pyroptosis during sepsis-associated acute kidney injury

Mechanisms of pyroptosis in sepsis-associated acute kidney injury

Pyroptosis is primarily mediated by the activation of inflammasomes, a group of multiprotein complexes that sense microbial infection and tissue damage. The most studied inflammasomes in the context of sepsis and acute kidney injury are NLRP3 (NOD-like receptor pyrin domain-containing 3) and AIM2 (absent in melanoma 2) [50]. These inflammasomes are activated in response to pathogen-associated molecular patterns (PAMPs) or damage-associated molecular patterns (DAMPs) [51]. Once activated, they recruit and activate caspases, primarily caspase-1, but also caspase-4, -5, and -11 in response to intracellular lipopolysaccharide (LPS) [52,53,54]. The activation of caspase-1 triggers the cleavage of Gasdermin D (GSDMD), a key protein responsible for pore formation in the plasma membrane. The N-terminal fragment of GSDMD inserts into the lipid bilayer, forming large pores that disrupt the cell membrane’s integrity [55]. These pores allow the release of cellular contents, including inflammatory cytokines, such as IL-1β and IL-18, into the extracellular space [56]. The result is cell lysis and the amplification of the local inflammatory response, which is particularly damaging in the kidneys during sepsis (Fig. 1).

Fig. 1

Mechanisms of pyroptosis leading to acute kidney injury in sepsis.Schematic representation of the mechanism by which bacterial lipopolysaccharide (LPS) activates the NLRP3 inflammasome pathway. Intracellularly, LPS triggers activation of the NLRP3 inflammasome through pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs), subsequently activating caspase-1, caspase-4, caspase-5 (in humans), and caspase-11 (in mice). Caspase enzymes cleave Gasdermin D (GSDMD), generating the GSDMD-N fragment, which forms pores in the cell membrane, leading to cell death and the release of pro-inflammatory cytokines such as IL-1β and IL-18. These cytokines attract neutrophils and macrophages, contributing to acute kidney injury (AKI) and causing vascular leakage and coagulation abnormalities

Key molecular mediators in pyroptosis

Caspase-1 and caspase-11 activation

Caspase-1 is central to the canonical pathway of pyroptosis [57]. It is activated by inflammasomes, such as NLRP3, in response to microbial infections and other inflammatory signals. Once activated, caspase-1 cleaves pro-inflammatory cytokines, pro-IL-1β, and pro-IL-18, into their active forms, facilitating their release through the GSDMD-formed pores [58, 59]. In addition, caspase-1 cleaves Gasdermin D, leading to membrane pore formation and subsequent pyroptotic cell death [60]. Caspase-11 (in mice) or caspase-4 and caspase-5 (in humans) represent the non-canonical pyroptosis pathway, where intracellular LPS from gram-negative bacteria directly activates these caspases. This activation bypasses the need for inflammasome formation and directly leads to Gasdermin D cleavage, culminating in pyroptosis [61, 62]. In sepsis, Gram negative bacterial infections often release LPS, exacerbating inflammation and organ dysfunction. LPS is an endotoxin that is the main component of the outer membrane of Gram negative bacteria. In rodents, it mainly activates caspase-11, while in humans, it can activate caspase-4 and caspase-5, promoting cell death through non classical pyroptosis pathways [52, 63, 64], Research has shown that knockout of caspase-1 and caspase-11 genes can alleviate LPS induced sepsis AKI in mice [34, 41].

Gasdermin D and membrane pore formation

Gasdermin D (GSDMD) plays a pivotal role in executing pyroptosis [65]. Upon cleavage by caspase-1 or caspase-11, the N-terminal fragment of GSDMD translocates to the plasma membrane, where it oligomerizes and forms pores. These pores are large enough to allow the passive release of ions, water, and small molecules, leading to osmotic cell swelling and eventual rupture [66]. This disruption of cellular integrity not only causes cell death but also releases pro-inflammatory cytokines, which perpetuate the inflammatory cycle in septic organs, including the kidneys [67]. The uncontrolled activation of GSDMD has been shown to contribute to extensive tissue damage in organs affected by sepsis. In the kidneys, pyroptosis of tubular epithelial cells leads to tubular injury and dysfunction, which are hallmark features of AKI [68].

IL-1β and IL-18 release

IL-1β and IL-18 are potent pro-inflammatory cytokines that are key players in the immune response during sepsis [69,70,71]. These cytokines are synthesized as inactive precursors and require cleavage by caspase-1 to become active. Once cleaved, they are released through the Gasdermin D pores and act on nearby immune and non-immune cells, amplifying the inflammatory response [72]. In the context of sepsis-associated AKI, elevated levels of IL-1β and IL-18 contribute to local and systemic inflammation [73,74,75]. These cytokines recruit and activate immune cells, such as neutrophils and macrophages, which infiltrate the kidney and exacerbate tissue damage. Furthermore, IL-1β has been shown to induce endothelial dysfunction, a key factor in the pathogenesis of AKI, by promoting vascular leakage and coagulation abnormalities [76].

ZBP1

Recent studies have also identified Z-DNA binding protein 1 (ZBP1) as a critical regulator of pyroptosis in sepsis. ZBP1, a cytosolic nucleic acid sensor, recognizes Z-form nucleic acids derived from pathogens or endogenous sources, such as mitochondrial DNA (mtDNA) released during cellular stress [77]. In sepsis, ZBP1 activation by DAMPs triggers the formation of the PANoptosome [78], a multi-protein complex that integrates pyroptosis, apoptosis, and necroptosis pathways. ZBP1 recruits RIPK3 and caspase-8, which in turn activate the NLRP3 inflammasome and caspase-1, thereby executing instructions for pyroptosis [79, 80]. This process results in the release of pro-inflammatory cytokines, including IL-1β and IL-18 [81], which amplify the systemic inflammatory response and contribute to multi-organ dysfunction, including AKI [82]. Experimental studies have shown that ZBP1 deficiency in macrophages can reduce mitochondrial damage and inhibit glycolysis, thereby altering the metabolic status of macrophages. And reduce macrophage pyroptosis triggered by NLRP3 inflammasome activation. These changes significantly weakened the inflammatory signaling pathway between macrophages and endothelial cells, and alleviated endothelial dysfunction and cell damage [83].

Role of inflammatory mediators and oxidative stress in pyroptosis

Pyroptosis is a highly inflammatory form of cell death that plays a significant role in the pathogenesis of sepsis-associated acute kidney injury (S-AKI). This process is not only driven by inflammasomes and caspases but is also closely linked to the production of inflammatory mediators and oxidative stress. These factors exacerbate tissue damage, contribute to the activation of pyroptotic pathways, and perpetuate the cycle of inflammation and injury in sepsis. In this section, we explore the roles of NF-κB signaling, reactive oxygen species (ROS), and endotoxins in the regulation of pyroptosis in S-AKI.

NF-κB signaling pathway in pyroptosis activation

NF-κB is a dimeric transcription factor in B lymphocytes regarded as a major regulator of inflammation [84] (Fig. 2). In the classical pathway of pyroptosis, activation of the NLRP3 inflammasome, consisting of NLRP3, ASC, and caspase-1, requires two steps: (I) an initiation step: activation of NF-κB after recognition of PAMPs and DAMPs by pattern recognition receptor, which enhances NLRP3 expression and synthesis; and (II) an activation step: recognition of NLRP3 agonists and inflammasome assembly [85, 86]. NF-κB functions in nearly all cells and tissues. It is involved in various pathophysiological reactions in the body [87], such as immunity and inflammation, which serves as a key factor for initiating inflammatory responses and regulating gene transcription,Activation of NF-κB signaling in the kidney accelerates inflammatory cell infiltration and triggers oxidative stress, ultimately leading to swelling of glomerular endothelial cells and necrosis of tubular epithelial cells, which will severely impair renal function [88]. Therefore, blocking NF-κB signaling can effectively reduce the damage caused by cellular death. Wang et al. [89] found that Resolvin D1 inhibited the NF-κB pathway in vivo and in vitro, resulting in human proximal renal tubular epithelial cells exhibiting higher cell viability and lower reactive oxygen species levels and apoptosis rates, suggesting that Resolvin D1 inhibits cellular cellular death and thus achieves the goal of treating or preventing sepsis-associated acute kidney injury. Sepsis-associated acute kidney injury, a condition in which renal function declines rapidly in a short period of time, is characterized by pathophysiological changes that disrupt renal cortex and medullary blood flow and cause tubule necrosis [7].These inflammatory factors are generally signal molecules and effectors that directly result in “inflammatory storm” through the NF-κB pathway, leading to cell damage.These inflammatory factors are generally signal molecules and effectors that directly result in “inflammatory storm” can through the NF-κB pathway, leading to cell damage. Chinese scholars Zhu et al. [90] found that Ang-(1–7) can inhibit the production of pro-inflammatory cytokines and maintain redox balance by regulating the NF-κB signaling pathway, thus inhibiting the occurrence of cellular pyroptosis and attenuating sepsis-associated acute kidney injury.The NF-κB signaling pathway plays a key role in inflammatory reactions and immune responses [91]. Numerous animal experiments have confirmed that NF-κB is pivotal in the pathophysiology of sepsis and sepsis shock [92, 93]. Zhang et al. [94] found that β-CM-7 attenuated sepsis-associated AKI through reducing inflammation and oxidative stress and by inhibition of nuclear factor (NF)-κB activities. For sepsis-associated AKI, new pharmacological studies related to the NF-κB pathway in pyroptosis have shown some results. For example, Polygonum cuspidatum Sieb.et Zucc. can alleviate oxidative stress, regulate the expression levels of apoptosis related proteins, and inhibit the production of inflammatory cytokines by inactivating nuclear factor kappa B (NF—κ B) signaling in vivo [95], and the Protein Kinase R Inhibitor C16 Alleviates Sepsis-Induced Acute Kidney Injury Through Modulation of the NF-κB and NLR Family Pyrin Domain-Containing 3 (NLPR3) Pyroptosis Signal Pathways [96]. The study also confirmed that macrophage migration inhibitory factor inhibits NLRP3 inflammasome release by regulating the NF—κ B pathway, which can improve sepsis induced AKI mediated cell pyroptosis [26].

Fig. 2

Two-step activation process of the NLRP3 inflammasome.In Step 1 (initiation), pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs), derived from viruses and bacteria, activate pattern recognition receptors, leading to the activation of NF-κB and upregulation of NLRP3 expression. In Step 2 (activation), NLRP3 agonists trigger the assembly of the NLRP3 inflammasome complex, which includes NLRP3, ASC, and caspase-1. This activation results in the formation of the functional inflammasome, initiating downstream inflammatory responses

Reactive oxygen specindrial dysfunction

Oxidative stress, particularly from the excessive production of reactive oxygen species (ROS), plays a significant role in the development of sepsis-associated acute kidney injury (S-AKI) [97] (Fig. 3). Mitochondria, the primary source of ROS during sepsis, contribute to cellular damage and the activation of inflammasomes, especially the NLRP3 inflammasome, which triggers pyroptosis [98]. Mitochondrial ROS (mtROS) is a key signaling molecule that can activate the NLRP3 inflammasome [99]. When ROS levels rise due to mitochondrial dysfunction, mtROS promotes the oligomerization of NLRP3, leading to the activation of caspase-1 [100]. This process cleaves Gasdermin D (GSDMD) and initiates pyroptosis. Additionally, the release of mitochondrial DNA (mtDNA) into the cytosol, indicative of mitochondrial damage, acts as a damage-associated molecular pattern (DAMP) that further enhances NLRP3 inflammasome activation [101]. In the context of sepsis, ROS not only contributes to inflammasome activation but also worsens tissue injury by causing oxidative damage to lipids, proteins, and DNA in renal tubular cells. This oxidative damage impairs mitochondrial function and disrupts cellular metabolism, leading to energy deficits in kidney cells and exacerbating tissue injury associated with acute kidney injury (AKI). Therapies targeting ROS, such as antioxidant treatments, have shown promise in reducing oxidative stress and inflammasome activation in experimental models of sepsis [102]. Liu et al. [103] found that Anemonin mitigated the levels of serum creatinine and urea nitrogen in the CLP-induced mouse sepsis model, reduced the renal tissue injury score, and attenuated OS, inflammation, and apoptosis levels in the kidney, Thus, it serves to protect the kidney. Li et al. [104] found that NOX4 is a potential therapeutic target in septic acute kidney injury by inhibiting mitochondrial dysfunction and inflammation, NOX4 prevents S-AKI by reducing ROS release, thereby inhibiting mitochondrial dysfunction, inflammation, and apoptosis. Liu et al. [105] found that frehmaglutinin D and rehmaionoside C ameliorate S-AKI by decreasing renal injury and inflammation, modulating immune cells, decreasing ROS levels, increasing ERα and ERβ protein expression, and decreasing TLR4, caspase 11, and IL-1β protein expression in mice.

Fig. 3

Mechanism of sepsis-associated acute kidney injury (AKI) via mitochondrial dysfunction and pyroptosis.Sepsis triggers mitochondrial dysfunction in renal tubular cells, leading to the release of mitochondrial DNA (mtDNA) as a damage-associated molecular pattern (DAMP) and the production of mitochondrial reactive oxygen species (mtROS). The mtROS causes oxidative damage, activating the NLRP3 inflammasome pathway. Activation of NLRP3 promotes the cleavage of gasdermin D (GSDMD), leading to pyroptosis, an inflammatory form of cell death. The pyroptotic process exacerbates tissue damage in the kidney, ultimately resulting in AKI

Endotoxins anssociated molecular patterns (DAMPs)

In the chaos of sepsis, bacterial endotoxins and endogenous damage-associated molecular patterns (DAMPs) emerge as potent triggers of pyroptosis, a form of programmed cell death that signals distress [106]. Endotoxins like lipopolysaccharides (LPS), which are part of the outer membrane of gram-negative bacteria, surge into the bloodstream, powerfully activating the immune response. Meanwhile, DAMPs, released from injured cells and tissues, serve as urgent cries for help, intensifying the body’s inflammatory reaction [107] (Fig. 4). LPS engages TLR4 on the surfaces of both immune and non-immune cells, igniting the MyD88-dependent NF-κB pathway and unleashing pro-inflammatory cytokines into the fray [108]. Yet, LPS also has a more direct role, triggering pyroptosis through a non-canonical inflammasome pathway. Here, intracellular LPS is sensed by caspase-4 and caspase-5 in humans (or caspase-11 in mice), resulting in the cleavage of Gasdermin D [109]. This process forms membrane pores, a hallmark of pyroptosis, allowing the cell’s turmoil to spill out.

Fig. 4

The molecular mechanism by which lipopolysaccharide (LPS) induces acute kidney injury (AKI) through the TLR4 pathway. Upon LPS stimulation, TLR4 activates the NF-κB pathway via MyD-88, promoting the release of pro-inflammatory cytokines such as IL-1β and IL-18. Concurrently, LPS induces the release of DAMPs (e.g., uric acid, mtDNA, ATP), which activate the NLRP3 inflammasome. This activation leads to the stimulation of caspase-11 (in mice) and caspase-4/5 (in humans), which cleave GSDMD to generate the GSDMD-N fragment, forming pores in the cell membrane. This process induces pyroptosis, ultimately resulting in acute kidney injury (AKI)

DAMPs like ATP, uric acid, and mitochondrial DNA also flood the system during sepsis, recognized by pattern recognition receptors such as NLRP3 [110]. These molecules propel the activation of inflammasomes and caspases, leading to further pyroptotic cell death. The release of inflammatory cytokines IL-1β and IL-18 during this process fans the flames of systemic inflammation, contributing to multiorgan dysfunction, including acute kidney injury (AKI). The interplay between endotoxins and DAMPs creates a vicious cycle, perpetuating pyroptosis and tissue damage [111]. In the kidneys, this relentless activation results in the loss of tubular epithelial cells and disrupts normal renal function, a defining feature of sepsis-associated AKI.

Inflammatory mediators like NF-κB and pro-inflammatory cytokines, alongside oxidative stress from reactive oxygen species (ROS) and mitochondrial dysfunction, are central players in the activation of pyroptosis during sepsis-associated acute kidney injury. Endotoxins and DAMPs further amplify this inflammatory cascade, driving cell death and tissue destruction in the kidneys. By targeting these pathways, we may uncover therapeutic avenues to mitigate the severity of AKI in sepsis, offering hope in a time of crisis by modulating pyroptosis and its upstream activators.

Therapeutic perspectives

Sepsis-associated acute kidney injury (S-AKI) presents a daunting clinical challenge, marked by high rates of mortality and morbidity. At the heart of this crisis lies pyroptosis, a pro-inflammatory form of programmed cell death that significantly contributes to the development of S-AKI. Given its crucial role, targeting the key components of the pyroptosis pathway emerges as a promising strategy to alleviate kidney damage and enhance patient outcomes in the context of sepsis. This section will explore various therapeutic approaches, including the inhibition of inflammasomes, caspases, and Gasdermin D, along with anti-inflammatory therapies, antioxidant strategies, and innovative new treatments.

Inhibition of inflammasomes

The NLRP3 inflammasome is one of the most well-characterized inflammasomes and is closely associated with pyroptosis [112]. Excessive activation of NLRP3 in response to pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs) is implicated in the pathophysiology of sepsis and AKI [113]. Thus, inhibiting the NLRP3 inflammasome represents a potential therapeutic approach for S-AKI. One promising small molecule inhibitor is MCC950, which specifically targets NLRP3 activation [114]. Preclinical studies have demonstrated that MCC950 effectively suppresses the release of pro-inflammatory cytokines such as IL-1β and IL-18, reducing inflammation and kidney damage in experimental models of AKIly, colchicine, a drug traditionally used to treat gout, has been shown to inhibit NLRP3 and is currently being investigated for its anti-inflammatory properties in various conditions, including sepsis. By the NLRP3 inflammasome, these inhibitors could potentially mitigate pyroptosis, thereby reducing renal injury in sepsis patients. However, further clinical trials are necessary to evaluate the efficacy and safety of these agents in S-AKI.

Caspase inhibitors

Caspase-1 and caspase-11 play pivotal roles in the drama of pyroptosis, orchestrating the cleavage of Gasdermin D (GSDMD) and the release of pro-inflammatory cytokines. By inhibiting these enzymes, we could potentially limit the destructive cascade of pyroptosis and its detrimental effects on the kidneys during sepsis. Kayagaki et al. [115] found that caspase-11 cleaves gasdermin D, and the resulting amino-terminal fragment promotes both pyroptosis and NLRP3-dependent activation of caspase-1 in a cell-intrinsic manner and identify gasdermin D as a critical target of caspase-11 and a key mediator of the host response.

VX-765, a selective caspase-1 inhibitor, has shown promise in preclinical sepsis models. wen et al. found VX-765 ameliorates kidney injury and renal fibrosis in diabetic patients by modulating caspase-1-mediated sepsis and inflammation and reducing the occurrence of acute kidney injury [116]. In a study focused on diabetic nephropathy, the combination of VX765 was found to decrease the expression of the NLRP3 inflammasome in HBZY-1 cells subjected to high glucose conditions, effectively preventing the release of IL-1β [117], it works by dampening the maturation of IL-1β, effectively reducing inflammation and kidney damage in experimental AKI. Similarly, caspase inhibitors have been explored in animal studies, demonstrating protective effects against kidney injury associated by sepsis. These inhibitors present a hopeful avenue for preventing the harmful consequences of pyroptosis in sepsis-associated AKI. However, translating these findings from the lab to human trials is a crucial journey that lies ahead. AcYVAD-cmk and z-VAD-fmk are irreversible selective inhibitors of Caspase 1 and broad-spectrum inhibitors of Caspases 1, 4, 5, and 11, respectively, which inactivate Caspases by covalent bonding to cysteines in the catalytic site [118].

Gasdermin D inhibition

Gasdermin D (GSDMD) is a cytoplasmic protein encoded by the GSDMD gene within the gasdermin family and serves as the ultimate executor of pyroptosis [119]. Inhibiting GSDMD could directly block pyroptosis, shielding the kidneys from damage during sepsis.

Recent studies have delved into developing selective GSDMD inhibitors that prevent pore formation and curb the release of inflammatory mediators. Camila Meirelles S. Silva found that during sepsis, activation of the caspase-11/GSDMD pathway controls NET release by neutrophils during sepsis, Gasdermin D inhibition prevents multiple organ dysfunction during sepsis by blocking NET formation [63], Inhibiting GSDMD could directly block pyroptosis, shielding the kidneys from damage during sepsis. Tan et al. [120] found that the release of eCIRP from living macrophages occurs through GSDMD pores, suggesting that targeting GSDMD may serve as a novel therapeutic strategy to inhibit eCIRP-mediated inflammation in sepsis. In animal models of sepsis, inhibiting GSDMD has been linked to reduced kidney injury and improved survival rates, Kang et al. [121] demonstrated that myeloid lineage cell-specific Gpx4 depletion caused a marked increase in caspase-11- and caspase-1-mediated GSDMD cleavage, ausing cell swelling (oncosis) and eventual lysis, suggesting that lipid peroxidation may serve as an accelerator of inflammasome activation and pyroptosis. While research on GSDMD inhibitors is still in its infancy, these agents represent a promising frontier in the battle against pyroptosis and inflammation in sepsis-associated AKI. Selective inhibition of GSDMD offers a more direct approach, potentially minimizing off-target effects compared to inflammasome or caspase inhibitors. Yet, further studies are essential to evaluate the long-term safety and efficacy of these innovative therapies.

Anti-inflammatory therapies

Targeting the pro-inflammatory cytokines IL-1β and IL-18, key players in pyroptosis, represents another therapeutic strategy [122]. By neutralizing these cytokines, we may reduce systemic inflammation and halt the progression of AKI during sepsis.

Anakinra is a recombinant human interleukin-1 (IL-1) receptor antagonist [123], has been investigated for various inflammatory conditions, including sepsis [124]. Clinical studies suggest that anakinra can mitigate inflammation and enhance outcomes for sepsis patients [125]. Although specific trials focusing on sepsis-associated AKI are limited, anakinra holds promise as a therapeutic agent against pyroptosis and its downstream effects. Beyond IL-1β, blocking IL-18 has also been explored as a potential strategy. Animal studies indicate that IL-18 inhibitors can lessen kidney damage and inflammation in AKI models [126]. Anti-inflammatory therapies, particularly those targeting pyroptosis, provide a systemic approach to diminishing inflammation and improving renal outcomes in sepsis.

Antioxidant therapies

Oxidative stress, fueled by an overproduction of reactive oxygen species (ROS), significantly contributes to the activation of inflammasomes and pyroptosis in sepsis-induced AKI [127]. Consequently, antioxidant therapies aimed at reducing oxidative stress may help mitigate pyroptosis and safeguard kidney function.

Mitochondrial-targeted antioxidants like MitoQ and SkQ1 show promise in alleviating oxidative damage and inflammasome activation in preclinical models. By scavenging ROS and preserving mitochondrial integrity, these antioxidants can prevent the onset of pyroptosis and lessen renal injury. Xia et al. [128] found that honokiol enhances the antioxidant properties of HO-1 in rats subjected to cecal ligation and puncture (CLP) and mitigates the morphological changes in the kidneys of these rats. They concluded that honokiol plays a protective role in sepsis-induced acute kidney injury (AKI) by modulating oxidative stress levels and the expression of inflammatory cytokines in the kidneys.

Additionally, antioxidants like N-acetylcysteine (NAC) have been investigated for their potential to reduce oxidative stress and inflammation in sepsis. For example, pretreatment with NAC significantly reduced pathological damage to kidney tissues in septic rats, lowered serum creatinine and blood urea nitrogen levels, and decreased plasma neutrophil gelatinase-associated lipocalin and kidney injury molecule-1 levels. Additionally, it reduced the expression of tumor necrosis factor-alpha, interleukin (IL)-1β, IL-6, and IL-8 [129]. While NAC has shown some benefits in mitigating organ damage, its specific effects on sepsis-associated AKI warrant further exploration. Antioxidant therapies hold potential as complementary treatments for sepsis-associated AKI by addressing the upstream mechanisms of pyroptosis activation, although clinical evidence supporting their use in this context remains limited.

Emerging novel therapeutic targets

Beyond traditional small molecules and biologics, innovative approaches such as RNA-based therapies and CRISPR-based gene editing are emerging as exciting avenues for modulating pyroptosis and enhancing outcomes in sepsis-associated AKI [66, 130]. RNA-based therapies, including small interfering RNA (siRNA) and microRNA (miRNA), have demonstrated the ability to silence genes involved in inflammasome activation and pyroptosis. siRNA targeting NLRP3 or caspase-1 has shown protective effects in experimental sepsis models. For instance, Jin et al. [131] found that siRNA interference against NF-κB p65 was able to decrease the expression of NF-κB and further inhibit the early phasic excessive inflammatory reaction in sepsis, which may alleviate ALI. Pavan et al. [132] found that Apoptotic loss of immune effector cells such as CD4 T and B cells is a key component in the loss of immune competence in sepsis,Antiapoptotic siRNA-based therapy markedly decreased lymphocyte apoptosis and prevented the loss of splenic CD4 T and B cells. Steven et al. [133] found that Bim siRNA decreases lymphocyte apoptosis and improves survival in sepsis. siRNA targeting NLRP3 or caspase-1 has shown protective effects in experimental sepsis models. Similarly, miRNAs that regulate inflammation and cell death pathways offer promising new therapeutic interventions, MicroRNAs (miRNAs) have been demonstrated to regulate Toll-like receptor (TLR) responses and NF-κB activity, thereby modulating the dysregulated inflammatory response observed in sepsis [134, 135]. Several microRNAs, including miR-125b, miR-146a, miR-15a, and miR-16, have been shown to inhibit NF-κB activation in sepsis by downregulating the expression of TRAF6 and IRAK [136,137,138,139].

CRISPR-based strategies present another cutting-edge approach to targeting genes associated with pyroptosis. By editing the genes that drive inflammasome activation or pyroptosis, CRISPR technology could provide a precise and durable therapeutic solution for sepsis-associated AKI. However, the application of CRISPR in sepsis and AKI is still in its early research stages, necessitating further studies to assess its feasibility and safety. CRISPR-Cas9 technology can use for Gene screening, Gene knockout and Gene knockin, for instance, Using CRISPR-Cas9 technology, specific sequences of mutated DNA can be deleted to treat patients with disease caused by mutant mtDNA [140], scientise modified murine iPSCs using CRISPR/Cas9 to insert anti-inflammatory molecules (e.g. IL-1Ra or chimeric human sTNFR1-murine IgG) in the Ccl2 locus, the inserted naturally occurring cytokine antagonists within the Ccl2 locus mitigated the inflammatory effects of physiologic concentrations of IL-1 and TNF-α when the iPSCs were cultured in monolayer [141]. However, the application of CRISPR in sepsis and AKI is still in its early research stages, necessitating further studies to evaluate its feasibility and safety.

Clinical Implications and challenges

As the understanding of pyroptosis and its role in sepsis-induced acute kidney injury (S-AKI) advances, significant clinical implications and challenges arise regarding the translation of these findings into effective therapies. This section explores the barriers to clinical application, the potential for biomarkers in monitoring disease progression, and the promise of personalized medicine approaches.

Translation of preclinical findings to clinical settings

Despite the promising results from preclinical studies targeting pyroptosis, translating these findings into clinical settings poses numerous challenges. One significant limitation is the heterogeneity of sepsis, which can result in varying responses to therapies among patients. This variability complicates the design of clinical trials and the interpretation of results. Furthermore, many experimental therapies, such as inflammasome inhibitors or caspase blockers, face challenges related to drug delivery, particularly in systemic diseases like sepsis, where effective tissue targeting is crucial.

Additionally, potential off-target effects and the risk of adverse reactions can arise with the systemic administration of these therapies. Ensuring safety and efficacy in a clinical context requires comprehensive evaluation through robust clinical trials, which are often time-consuming and costly. Overcoming these hurdles is essential for the successful integration of pyroptosis-targeted therapies into standard clinical practice.

Biomarkers for pyroptosis in AKI

Identifying reliable biomarkers for pyroptosis in the context of S-AKI could significantly enhance the clinical management of patients. Biomarkers such as circulating levels of IL-1β, IL-18, or even components of the NLRP3 inflammasome hold potential for indicating pyroptosis activity in the kidneys during sepsis. These biomarkers may aid in diagnosing S-AKI, assessing disease severity, and monitoring the response to therapies targeting pyroptosis.

The utility of such biomarkers extends beyond diagnosis; they can provide insights into patient prognosis. For instance, elevated levels of IL-18 have been associated with poor outcomes in sepsis patients, suggesting that monitoring these markers could help clinicians make informed decisions regarding treatment strategies. Identifying and validating specific pyroptosis-related biomarkers could ultimately lead to better patient stratification and improved clinical outcomes.

Personalized medicine approaches

Personalized medicine offers a promising approach to enhancing the effectiveness of therapies targeting pyroptosis in S-AKI. By stratifying patients based on their pyroptosis biomarker profiles, clinicians can tailor treatment strategies to individual patient needs, potentially improving outcomes. For example, patients exhibiting high levels of IL-1β or IL-18 might benefit more from therapies aimed at inhibiting these cytokines, while others might respond better to inflammasome inhibitors.

Moreover, the prospective use of combination therapies that target multiple cell death pathways could further enhance treatment efficacy. Given the complex interplay between pyroptosis, apoptosis, and necroptosis in the context of sepsis, combining agents that modulate these pathways may offer synergistic benefits. For instance, co-administration of inflammasome inhibitors with antioxidants could address both inflammatory and oxidative stress components, potentially leading to improved renal protection in S-AKI.

Conclusion

Pyroptosis is pivotal in the development of sepsis-induced acute kidney injury, highlighting the urgency of addressing this condition. Key molecular mediators, including inflammasomes, caspases, and GSDMD, have emerged as promising targets for therapeutic intervention. Preclinical studies have shown that pyroptosis inhibitors can significantly reduce renal damage and inflammation in sepsis models, yet translating these findings into clinical practice poses considerable challenges. Future research should prioritize refining these therapies, identifying suitable biomarkers for effective patient stratification, and overcoming obstacles related to drug delivery and safety. As we navigate these hurdles, therapies targeting pyroptosis could represent a groundbreaking and effective strategy for alleviating the burden of S-AKI in critically ill patients, offering hope for improved outcomes and quality of life.