Activation of AMP-activated protein kinase during sepsis/inflammation improves survival by preserving cellular metabolic fitness

Lactate metabolism and acute kidney injury

ABSTRACT

Acute kidney injury (AKI) is a common clinically critical syndrome in hospitalized patients with high morbidity and mortality. At present, the mechanism of AKI has not been fully elucidated, and no therapeutic drugs exist. As known, glycolytic product lactate is a key metabolite in physiological and pathological processes. The kidney is an important gluconeogenic organ, where lactate is the primary substrate of renal gluconeogenesis in physiological conditions. During AKI, altered glycolysis and gluconeogenesis in kidneys significantly disturb the lactate metabolic balance, which exert impacts on the severity and prognosis of AKI. Additionally, lactate-derived posttranslational modification, namely lactylation, is novel to AKI as it could regulate gene transcription of metabolic enzymes involved in glycolysis or Warburg effect. Protein lactylation widely exists in human tissues and may severely affect non-histone functions. Moreover, the strategies of intervening lactate metabolic pathways are expected to bring a new dawn for the treatment of AKI. This review focused on renal lactate metabolism, especially in proximal renal tubules after AKI, and updated recent advances of lactylation modification, which may help to explore potential therapeutic targets against AKI.

Targeting the epigenetic regulation of ferroptosis: a potential therapeutic approach for sepsis-associated acute kidney injury

Sepsis is a syndrome of organ dysfunction caused by the invasion of pathogenic microorganisms. In clinical practice, patients with sepsis are prone to concurrent acute kidney injury, which has high morbidity and mortality rates. Thus, understanding the pathogenesis of sepsis-associated acute kidney injury is of significant clinical importance. Ferroptosis is an iron-dependent programmed cell death pathway, which is proved to play a critical role in the process of sepsis-associated acute kidney injury through various mechanisms. Epigenetic regulation modulates the content and function of nucleic acids and proteins within cells through various modifications. Its impact on ferroptosis has garnered increasing attention; however, the role of epigenetic regulation targeting ferroptosis in sepsis-associated acute kidney injury has not been fully elucidated. Growing evidence suggests that epigenetic regulation can modulate ferroptosis through complex pathway networks, thereby affecting the development and prognosis of sepsis-associated acute kidney injury. This paper summarizes the impact of ferroptosis on sepsis-associated acute kidney injury and the regulatory mechanisms of epigenetic regulation on ferroptosis, providing new insights for the targeted therapy of sepsis-associated acute kidney injury.

Potential relationship between cuproptosis and sepsis-acquired weakness: an intermediate role for mitochondria

Sepsis is defined as a life-threatening organ dysfunction caused by a dysregulated host response to infection. Skeletal muscle atrophy due to critical illness is a common phenomenon in the intensive care unit (ICU) and is referred to as ICU-acquired weakness (ICU-AW). The occurrence of ICU-AW in patients with sepsis is known as sepsis-acquired weakness (SAW). Furthermore, it is well known that maintaining normal muscle function closely relates to mitochondrial homeostasis. Once mitochondrial function is impaired, both muscle quality and function are affected. Copper plays a key role in mitochondrial homeostasis as a transition metal that regulates the function and stability of various enzymes. Copper is also involved in oxidation-reduction reactions, and intracellular copper overload causes oxidative stress and induces cell death. Previous studies have shown that excess intracellular copper induces cell death by targeting lipid-acylated proteins that regulate the mitochondrial tricarboxylic acid (TCA) cycle, which differs from the known canonical mechanisms of regulated cell death. Furthermore, inhibitors of cell death, such as apoptosis, necroptosis, pyroptosis and ferroptosis, are not effective in preventing copper-induced cell death. This new form of cell death has been termed "Cuproptosis"; however, the mechanism by which copper-induced cell death is involved in SAW remains unclear. In this paper, we review the possible relationship between cuproptosis and SAW. Cuproptosis may be involved in regulating the pathological mechanisms of SAW through mitochondria-related signaling pathways, mitochondria-related ferroptosis mechanisms, and mitochondria-related genes, and to provide new ideas for further investigations into the mechanism of SAW.

Pan AMPK activation protects tubules in rat ischemic acute kidney injury

Acute kidney injury (AKI) is characterized by an abrupt decline in kidney function and has been associated with excess risks of death, kidney disease progression, and cardiovascular events. The kidney has a high energetic demand with mitochondrial health being essential to renal function, and damaged mitochondria have been reported across AKI subtypes. 5' Adenosine monophosphate-activated protein kinase (AMPK) activation preserves cellular energetics through improvement of mitochondrial function and biogenesis when ATP levels are low, such as under ischemia-induced AKI. We developed a selective potent small molecule pan AMPK activator, compound 1, and tested its ability to increase AMPK activity and preserve kidney function during ischemia/reperfusion injury in rats. A single administration of compound 1 caused sustained activation of AMPK for at least 24 hours, protected against acute tubular necrosis, and reduced clinical markers of tubular injury such as NephroCheck and fractional excretion of sodium. Reduction in plasma creatinine and increased glomerular filtration rate indicated preservation of kidney function. Surprisingly, we observed a strong diuretic effect of AMPK activation associated with natriuresis both with and without AKI. Our findings demonstrate that activation of AMPK leads to protection of tubular function under hypoxic/ischemic conditions which holds promise as a potential novel therapeutic approach for AKI. SIGNIFICANCE STATEMENT: No approved pharmacological therapies currently exist for acute kidney injury. We developed compound 1, which dose-dependently activated 5' adenosine monophosphate-activated protein kinase in the kidney and protected kidney function and tubules after ischemic renal injury in the rat. This was accompanied by natriuresis in injured as well as uninjured rats.

New drugs on the horizon for acute kidney injury

PURPOSE OF REVIEW

Acute kidney injury (AKI) is a frequent and serious complication in critically ill patients. Currently, no effective therapy to prevent or treat AKI is available. This review highlights recently published developments on pharmacological treatments that aim to prevent AKI or to alleviate the severity of AKI in critical ill patients.

RECENT FINDINGS

Studies on pharmacological interventions aimed to improve hemodynamics, renal perfusion, to mediate inflammation-associated renal damage and to reduce oxidative stress are presented, including several observational studies and randomized trials focused on the potential renal protective effects in relevant patient populations. Different existing and novel compounds are being investigated for the effects on renal endpoints and several show potential to prevent or alleviate the occurrence of AKI. It is now acknowledged that different underlying pathophysiological processes are relevant in the development of AKI. Recognition of these sub-endotypes of AKI and knowledge of the therapeutic target of different compounds is of paramount importance to select the right patient for the right treatment at the right time.

SUMMARY

The discovery of reno-protective therapies is hampered by the timely detection and recognition of the overriding mechanism of AKI. Nevertheless, several compounds are under investigation, which hold promise for a future treatment.

The role of inflammatory response and metabolic reprogramming in sepsis-associated acute kidney injury: mechanistic insights and therapeutic potential

Sepsis represents a severe condition characterized by organ dysfunction resulting from a dysregulated host response to infection. Among the organs affected, the kidneys are particularly vulnerable, with significant functional impairment that markedly elevates mortality rates. Previous researches have highlighted that both inflammatory response dysregulation and metabolic reprogramming are crucial in the onset and progression of sepsis associated acute kidney injury (SA-AKI), making these processes potential targets for innovative therapies. This study aims to elucidate the pathophysiological mechanisms of renal injury in sepsis by perspective of inflammatory response dysregulation, with particular emphasis on pyroptosis, necroptosis, autophagy, and ferroptosis. Furthermore, it will incorporate insights into metabolic reprogramming to provide a detailed analysis of the mechanisms driving SA-AKI and explore potential targeted therapeutic strategies, providing solid theoretical framework for the development of targeted therapies for SA-AKI.

Targeting AMP-activated protein kinase in sepsis

Sepsis is a global health challenge marked by limited clinical options and high mortality rates. AMP-activated protein kinase (AMPK) is a cellular energy sensor that mediates multiple crucial metabolic pathways that may be an attractive therapeutic target in sepsis. Pre-clinical experimental studies have demonstrated that pharmacological activation of AMPK can offer multiple potential benefits during sepsis, including anti-inflammatory effects, induction of autophagy, promotion of mitochondrial biogenesis, enhanced phagocytosis, antimicrobial properties, and regulation of tight junction assembly. This review aims to discuss the existing evidence supporting the therapeutic potential of AMPK activation in sepsis management.

A critical role for HNF4α in polymicrobial sepsis-associated metabolic reprogramming and death

In sepsis, limited food intake and increased energy expenditure induce a starvation response, which is compromised by a quick decline in the expression of hepatic PPARα, a transcription factor essential in intracellular catabolism of free fatty acids. The mechanism upstream of this PPARα downregulation is unknown. We found that sepsis causes a progressive hepatic loss-of-function of HNF4α, which has a strong impact on the expression of several important nuclear receptors, including PPARα. HNF4α depletion in hepatocytes dramatically increases sepsis lethality, steatosis, and organ damage and prevents an adequate response to IL6, which is critical for liver regeneration and survival. An HNF4α agonist protects against sepsis at all levels, irrespectively of bacterial loads, suggesting HNF4α is crucial in tolerance to sepsis. In conclusion, hepatic HNF4α activity is decreased during sepsis, causing PPARα downregulation, metabolic problems, and a disturbed IL6-mediated acute phase response. The findings provide new insights and therapeutic options in sepsis.

Metabolic reprogramming in septic acute kidney injury: pathogenesis and therapeutic implications

Acute kidney injury (AKI) is a frequent and severe complication of sepsis and is characterized by significant mortality and morbidity. However, the pathogenesis of septic acute kidney injury (S-AKI) remains elusive. Metabolic reprogramming, which was originally referred to as the Warburg effect in cancer, is strongly related to S-AKI. At the onset of sepsis, both inflammatory cells and renal parenchymal cells, such as macrophages, neutrophils and renal tubular epithelial cells, undergo metabolic shifts toward aerobic glycolysis to amplify proinflammatory responses and fortify cellular resilience to septic stimuli. As the disease progresses, these cells revert to oxidative phosphorylation, thus promoting anti-inflammatory reactions and enhancing functional restoration. Alterations in mitochondrial dynamics and metabolic reprogramming are central to the energetic changes that occur during S-AKI. In this review, we summarize the current understanding of the pathogenesis of metabolic reprogramming in S-AKI, with a focus on each cell type involved. By identifying relevant key regulatory factors, we also explored potential metabolic reprogramming-related therapeutic targets for the management of S-AKI.

Macrophage migration inhibitory factor (MIF) suppresses mitophagy through disturbing the protein interaction of PINK1-Parkin in sepsis-associated acute kidney injury

Damage to renal tubular epithelial cells (RTECs) signaled the onset and progression of sepsis-associated acute kidney injury (SA-AKI). Recent research on mitochondria has revealed that mitophagy plays a crucial physiological role in alleviating injury to RTECs and it is suppressed progressively by the inflammation response in SA-AKI. However, the mechanism by which inflammation influences mitophagy remains poorly understood. We examined how macrophage migration inhibitory factor (MIF), a pro-inflammatory protein, influences the PINK1-Parkin pathway of mitophagy by studying protein-protein interactions when MIF was inhibited or overexpressed. Surprisingly, elevated levels of MIF were found to directly bind to PINK1, disrupting its interaction with Parkin. This interference hindered the recruitment of Parkin to mitochondria and impeded the initiation of mitophagy. Furthermore, this outcome led to significant apoptosis of RTECs, which could, however, be reversed by an MIF inhibitor ISO-1 and/or a new mitophagy activator T0467. These findings highlight the detrimental impact of MIF on renal damage through its disruption of the interaction between PINK1 and Parkin, and the therapeutic potential of ISO-1 and T0467 in mitigating SA-AKI. This study offers a fresh perspective on treating SA-AKI by targeting MIF and mitophagy.

The AMPK activator ATX-304 alters cellular metabolism to protect against cisplatin-induced acute kidney injury

Acute kidney injury (AKI) disrupts energy metabolism. Targeting metabolism through AMP-activated protein kinase (AMPK) may alleviate AKI. ATX-304, a pan-AMPK activator, was evaluated in C57Bl/6 mice and tubular epithelial cell (TEC) cultures. Mice received ATX-304 (1 mg/g) or control chow for 7 days before cisplatin-induced AKI (CI-AKI). Primary cultures of tubular epithelial cells (TECs) were pre-treated with ATX-304 (20 µM, 4 h) prior to exposure to cisplatin (20 µM, 23 h). ATX-304 increased acetyl-CoA carboxylase phosphorylation, indicating AMPK activation. It protected against CI-AKI measured by serum creatinine (control 0.05 + 0.03 mM vs ATX-304 0.02 + 0.01 mM, P = 0.03), western blot for neutrophil gelatinase-associated lipocalin (NGAL) (control 3.3 + 1.8-fold vs ATX-304 1.2 + 0.55-fold, P = 0.002), and histological injury (control 3.5 + 0.59 vs ATX-304 2.7 + 0.74, P = 0.03). In TECs, pre-treatment with ATX-304 protected against cisplatin-mediated injury, as measured by lactate dehydrogenase release, MTS cell viability, and cleaved caspase 3 expression. ATX-304 protection against cisplatin was lost in AMPK-null murine embryonic fibroblasts. Metabolomic analysis in TECs revealed that ATX-304 (20 µM, 4 h) altered 66/126 metabolites, including fatty acids, tricarboxylic acid cycle metabolites, and amino acids. Metabolic studies of live cells using the XFe96 Seahorse analyzer revealed that ATX-304 increased the basal TEC oxygen consumption rate by 38%, whereas maximal respiration was unchanged. Thus, ATX-304 protects against cisplatin-mediated kidney injury via AMPK-dependent metabolic reprogramming, revealing a promising therapeutic strategy for AKI.

Physiologic disruption and metabolic reprogramming in infection and sepsis

Effective responses against severe systemic infection require coordination between two complementary defense strategies that minimize the negative impact of infection on the host: resistance, aimed at pathogen elimination, and disease tolerance, which limits tissue damage and preserves organ function. Resistance and disease tolerance mostly rely on divergent metabolic programs that may not operate simultaneously in time and space. Due to evolutionary reasons, the host initially prioritizes the elimination of the pathogen, leading to dominant resistance mechanisms at the potential expense of disease tolerance, which can contribute to organ failure. Here, we summarize our current understanding of the role of physiological perturbations resulting from infection in immune response dynamics and the metabolic program requirements associated with resistance and disease tolerance mechanisms. We then discuss how insight into the interplay of these mechanisms could inform future research aimed at improving sepsis outcomes and the potential for therapeutic interventions.

Metformin for sepsis-associated AKI: a protocol for the Randomized Clinical Trial of the Safety and FeasibiLity of Metformin as a Treatment for sepsis-associated AKI (LiMiT AKI)

INTRODUCTION

Acute kidney injury (AKI) is a common complication of sepsis associated with increased risk of death. Preclinical data and observational human studies suggest that activation of AMP-activated protein kinase, an ubiquitous master regulator of energy that can limit mitochondrial injury, with metformin may protect against sepsis-associated AKI (SA-AKI) and mortality. The Randomized Clinical Trial of the Safety and FeasibiLity of Metformin as a Treatment for sepsis-associated AKI (LiMiT AKI) aims to evaluate the safety and feasibility of enteral metformin in patients with sepsis at risk of developing SA-AKI.

METHODS AND ANALYSIS

Blind, randomised, placebo-controlled clinical trial in a single-centre, quaternary teaching hospital in the USA. We will enrol adult patients (18 years of age or older) within 48 hours of meeting Sepsis-3 criteria, admitted to intensive care unit, with oral or enteral access. Patients will be randomised 1:1:1 to low-dose metformin (500 mg two times per day), high-dose metformin (1000 mg two times per day) or placebo for 5 days. Primary safety outcome will be the proportion of metformin-associated serious adverse events. Feasibility assessment will be based on acceptability by patients and clinicians, and by enrolment rate.

ETHICS AND DISSEMINATION

This study has been approved by the Institutional Review Board. All patients or surrogates will provide written consent prior to enrolment and any study intervention. Metformin is a widely available, inexpensive medication with a long track record for safety, which if effective would be accessible and easy to deploy. We describe the study methods using the Standard Protocol Items for Randomized Trials framework and discuss key design features and methodological decisions. LiMiT AKI will investigate the feasibility and safety of metformin in critically ill patients with sepsis at risk of SA-AKI, in preparation for a future large-scale efficacy study. Main results will be published as soon as available after final analysis.

TRIAL REGISTRATION NUMBER

NCT05900284.

The protective mechanism of SIRT3 and potential therapy in acute kidney injury

Acute kidney injury (AKI) is a complex clinical syndrome with a poor short-term prognosis, which increases the risk of the development of chronic kidney diseases and end-stage kidney disease. However, the underlying mechanism of AKI remains to be fully elucidated, and effective prevention and therapeutic strategies are still lacking. Given the enormous energy requirements for filtration and absorption, the kidneys are rich in mitochondria, which are unsurprisingly involved in the onset or progression of AKI. Accumulating evidence has recently documented that Sirtuin 3 (SIRT3), one of the most prominent deacetylases highly expressed in the mitochondria, exerts a protective effect on AKI. SIRT3 protects against AKI by regulating energy metabolism, inhibiting oxidative stress, suppressing inflammation, ameliorating apoptosis, inhibiting early-stage fibrosis and maintaining mitochondrial homeostasis. Besides, a number of SIRT3 activators have exhibited renoprotective properties both in animal models and in vitro experiments, but have not yet been applied to clinical practice, indicating a promising therapeutic approach. In this review, we unravel and summarize the recent advances in SIRT3 research and the potential therapy of SIRT3 activators in AKI.

Surviving Sepsis Campaign Research Priorities 2023

OBJECTIVES

To identify research priorities in the management, epidemiology, outcome, and pathophysiology of sepsis and septic shock.

DESIGN

Shortly after publication of the most recent Surviving Sepsis Campaign Guidelines, the Surviving Sepsis Research Committee, a multiprofessional group of 16 international experts representing the European Society of Intensive Care Medicine and the Society of Critical Care Medicine, convened virtually and iteratively developed the article and recommendations, which represents an update from the 2018 Surviving Sepsis Campaign Research Priorities.

METHODS

Each task force member submitted five research questions on any sepsis-related subject. Committee members then independently ranked their top three priorities from the list generated. The highest rated clinical and basic science questions were developed into the current article.

RESULTS

A total of 81 questions were submitted. After merging similar questions, there were 34 clinical and ten basic science research questions submitted for voting. The five top clinical priorities were as follows: 1) what is the best strategy for screening and identification of patients with sepsis, and can predictive modeling assist in real-time recognition of sepsis? 2) what causes organ injury and dysfunction in sepsis, how should it be defined, and how can it be detected? 3) how should fluid resuscitation be individualized initially and beyond? 4) what is the best vasopressor approach for treating the different phases of septic shock? and 5) can a personalized/precision medicine approach identify optimal therapies to improve patient outcomes? The five top basic science priorities were as follows: 1) How can we improve animal models so that they more closely resemble sepsis in humans? 2) What outcome variables maximize correlations between human sepsis and animal models and are therefore most appropriate to use in both? 3) How does sepsis affect the brain, and how do sepsis-induced brain alterations contribute to organ dysfunction? How does sepsis affect interactions between neural, endocrine, and immune systems? 4) How does the microbiome affect sepsis pathobiology? 5) How do genetics and epigenetics influence the development of sepsis, the course of sepsis and the response to treatments for sepsis?

CONCLUSIONS

Knowledge advances in multiple clinical domains have been incorporated in progressive iterations of the Surviving Sepsis Campaign guidelines, allowing for evidence-based recommendations for short- and long-term management of sepsis. However, the strength of existing evidence is modest with significant knowledge gaps and mortality from sepsis remains high. The priorities identified represent a roadmap for research in sepsis and septic shock.

Advances in metabolic reprogramming of renal tubular epithelial cells in sepsis-associated acute kidney injury

Sepsis-associated acute kidney injury presents as a critical condition characterized by prolonged hospital stays, elevated mortality rates, and an increased likelihood of transition to chronic kidney disease. Sepsis-associated acute kidney injury suppresses fatty acid oxidation and oxidative phosphorylation in the mitochondria of renal tubular epithelial cells, thus favoring a metabolic shift towards glycolysis for energy production. This shift acts as a protective mechanism for the kidneys. However, an extended reliance on glycolysis may contribute to tubular atrophy, fibrosis, and subsequent chronic kidney disease progression. Metabolic reprogramming interventions have emerged as prospective strategies to counteract sepsis-associated acute kidney injury by restoring normal metabolic function, offering potential therapeutic and preventive modalities. This review delves into the metabolic alterations of tubular epithelial cells associated with sepsis-associated acute kidney injury, stressing the importance of metabolic reprogramming for the immune response and the urgency of metabolic normalization. We present various intervention targets that could facilitate the recovery of oxidative phosphorylation-centric metabolism. These novel insights and strategies aim to transform the clinical prevention and treatment landscape of sepsis-associated acute kidney injury, with a focus on metabolic mechanisms. This investigation could provide valuable insights for clinicians aiming to enhance patient outcomes in the context of sepsis-associated acute kidney injury.

The metabolic pathway regulation in kidney injury and repair

Kidney injury and repair are accompanied by significant disruptions in metabolic pathways, leading to renal cell dysfunction and further contributing to the progression of renal pathology. This review outlines the complex involvement of various energy production pathways in glucose, lipid, amino acid, and ketone body metabolism within the kidney. We provide a comprehensive summary of the aberrant regulation of these metabolic pathways in kidney injury and repair. After acute kidney injury (AKI), there is notable mitochondrial damage and oxygen/nutrient deprivation, leading to reduced activity in glycolysis and mitochondrial bioenergetics. Additionally, disruptions occur in the pentose phosphate pathway (PPP), amino acid metabolism, and the supply of ketone bodies. The subsequent kidney repair phase is characterized by a metabolic shift toward glycolysis, along with decreased fatty acid β-oxidation and continued disturbances in amino acid metabolism. Furthermore, the impact of metabolism dysfunction on renal cell injury, regeneration, and the development of renal fibrosis is analyzed. Finally, we discuss the potential therapeutic strategies by targeting renal metabolic regulation to ameliorate kidney injury and fibrosis and promote kidney repair.

Colistin Effects on Emphysematous Lung in an LPS-Sepsis Model

Emphysema is prevalent in various respiratory diseases like Chronic Obstructive Pulmonary Disease (COPD) and cystic fibrosis. Colistin and vasoconstrictive drugs are crucial for treating these patients when diagnosed with sepsis in the ICU. This study examines colistin impact in ether-induced emphysematous septic and non-septic animals, focusing on lung pathophysiology and inflammatory responses, including IL-1β, TNF-α, AMPK, caspase-3, cyclin-D1, and colistin levels in lung tissue. All animals exhibited significant emphysematous changes, accentuated by LPS-induced septic conditions, validating the emphysema model and highlighting the exacerbating effect of sepsis on lung pathology. Colistin, alone or with vasoconstrictive drugs, stimulated immune responses through increased inflammatory cell infiltration and the presence of lymphocytes, indicating potential immunomodulatory effects. Vasoconstriction did not alter the effects of colistin or sepsis but correlated with increased colistin levels in the lungs of septic animals. These observations suggest a potential interplay between vasoconstrictive drugs and colistin distribution/metabolism, leading to enhanced local concentrations of colistin in the lung microenvironment. The findings suggest the need for further investigations to optimize colistin and vasoconstrictive drug delivery in critically ill patients with lung pathologies. Understanding these complexities may guide more effective management of inflammatory responses and lung pathologies in these critical conditions.

AMPK activation coupling SENP1-Sirt3 axis protects against acute kidney injury

Acute kidney injury (AKI) is a critical clinical condition that causes kidney fibrosis, and it currently lacks specific treatment options. In this research, we investigate the role of the SENP1-Sirt3 signaling pathway and its correlation with mitochondrial dysfunction in proximal tubular epithelial cells (PTECs) using folic acid (FA) and ischemia-reperfusion-induced (IRI) AKI models. Our findings reveal that Sirt3 SUMOylation site mutation (Sirt3 KR) or pharmacological stimulation (metformin) protected mice against AKI and subsequent kidney inflammation and fibrosis by decreasing the acetylation level of mitochondrial SOD2, reducing mitochondrial reactive oxygen species (mtROS), and subsequently restoring mitochondrial ATP level, reversing mitochondrial morphology and alleviating cell apoptosis. In addition, AKI in mice was similarly alleviated by reducing mtROS levels using N-acetyl-L-cysteine (NAC) or MitoQ. Metabolomics analysis further demonstrated an increase in antioxidants and metabolic shifts in Sirt3 KR mice during AKI, compared with Sirt3 wild-type (WT) mice. Activation of the AMPK pathway using metformin promoted the SENP1-Sirt3 axis and protected PTECs from apoptosis. Hence, the augmented deSUMOylation of Sirt3 in mitochondria, activated through the metabolism-related AMPK pathway, protects against AKI and subsequently mitigated renal inflammation and fibrosis through Sirt3-SOD2-mtROS, which represents a potential therapeutic target for AKI.

Critical-Illness: Combined Effects of Colistin and Vasoactive Drugs: A Pilot Study

Colistin is often used as a last resort for treating multidrug-resistant infections, particularly in critically ill patients in intensive care units. Nonetheless, its side effects, including myopathy, require careful monitoring. Vasoconstrictive drugs are also used in intensive care to increase blood pressure and improve blood flow to vital organs, which can be compromised in critically ill patients. The exact mechanism of colistin-induced muscle toxicity is of significant interest due to its potential intensive-care clinical implications. Colistin alone or in combination with vasoconstrictive agents was administrated in non-septic and LPS-induced septic animals for 10 days. Histopathological evaluation of the gastrocnemius muscle and dot-blot protein tissue analysis were performed. Increased intramuscular area, de-organization of the muscle fibers and signs of myopathy were observed in colistin-treated animals. This effect was ameliorated in the presence of vasoconstrictive drugs. Administration of colistin to septic animals resulted in a decrease of AMPK and cyclin-D1 levels, while it had no effect on caspase 3 levels. Vasoconstrictive drugs' administration reversed the effects of colistin on AMPK and cyclin D1 levels. Colistin's effects on muscle depend on septic state and vasoconstriction presence, highlighting the need to consider these factors when administering it in critically ill patients.

Human Resistin Induces Cardiac Dysfunction in Pulmonary Hypertension

Background Cardiac failure is the primary cause of death in most patients with pulmonary arterial hypertension (PH). As pleiotropic cytokines, human resistin (Hresistin) and its rodent homolog, resistin-like molecule α, are mechanistically critical to pulmonary vascular remodeling in PH. However, it is still unclear whether activation of these resistin-like molecules can directly cause PH-associated cardiac dysfunction and remodeling. Methods and Results In this study, we detected Hresistin protein in right ventricular (RV) tissue of patients with PH and elevated resistin-like molecule expression in RV tissues of rodents with RV hypertrophy and failure. In a humanized mouse model, cardiac-specific Hresistin overexpression was sufficient to cause cardiac dysfunction and remodeling. Dilated hearts exhibited reduced force development and decreased intracellular Ca2+ transients. In the RV tissues overexpressing Hresistin, the impaired contractility was associated with the suppression of protein kinase A and AMP-activated protein kinase. Mechanistically, Hresistin activation triggered the inflammation mediated by signaling of the key damage-associated molecular pattern molecule high-mobility group box 1, and subsequently induced pro-proliferative Ki67 in RV tissues of the transgenic mice. Intriguingly, an anti-Hresistin human antibody that we generated protected the myocardium from hypertrophy and failure in the rodent PH models. Conclusions Our data indicate that Hresistin is expressed in heart tissues and plays a role in the development of RV dysfunction and maladaptive remodeling through its immunoregulatory activities. Targeting this signaling to modulate cardiac inflammation may offer a promising strategy to treat PH-associated RV hypertrophy and failure in humans.

ADENOSINE MONOPHOSPHATE-ACTIVATED PROTEIN KINASE PHOSPHORYLATION MEDIATED BY SIRTUIN 5 ALLEVIATES SEPTIC ACUTE KIDNEY INJURY

ABSTRACT

Background : Our previous studies have shown that ameliorating mitochondrial damage in renal tubular epithelial cells (RTECs) can alleviate septic acute kidney injury (SAKI). It is reported that AMPK phosphorylation (p-AMPK) could ameliorate mitochondrial damage in renal tissue and Sirtuin 5 (SIRT5) overexpression significantly enhanced the level of p-AMPK in bovine preadipocytes. However, the role of SIRT5-mediated phosphorylation of AMPK in SAKI needs to be clarified. Methods : WT/SIRT5 gene knockout mouse model of cecal ligation and puncture-induced SAKI and a human kidney 2 cell model of LPS-induced SAKI were constructed. An AMPK chemical activator and SIRT5 overexpression plasmid were used. Indexes of mitochondrial structure and function, level of p-AMPK, and expression of SIRT5 protein in renal tissue and RTECs were measured. Results : After sepsis stimulation, the p-AMPK level was decreased, mitochondrial structure was disrupted, and ATP content was decreased. Notably, an AMPK activator alleviated SAKI. Sirtuin 5 gene knockout significantly aggravated SAKI, while SIRT5 overexpression alleviated mitochondrial dysfunction after LPS stimulation, as manifested by the increase of p-AMPK level, the alleviation of mitochondrial structure damage, the restoration of ATP content, the decrease of proapoptotic protein expression, as well as the reduction of reactive oxygen species generation. Conclusions : Upregulation of SIRT5 expression can attenuate mitochondrial dysfunction in RTECs and alleviate SAKI by enhancing the phosphorylation of AMPK.

Sepsis-associated acute kidney injury: consensus report of the 28th Acute Disease Quality Initiative workgroup

Sepsis-associated acute kidney injury (SA-AKI) is common in critically ill patients and is strongly associated with adverse outcomes, including an increased risk of chronic kidney disease, cardiovascular events and death. The pathophysiology of SA-AKI remains elusive, although microcirculatory dysfunction, cellular metabolic reprogramming and dysregulated inflammatory responses have been implicated in preclinical studies. SA-AKI is best defined as the occurrence of AKI within 7 days of sepsis onset (diagnosed according to Kidney Disease Improving Global Outcome criteria and Sepsis 3 criteria, respectively). Improving outcomes in SA-AKI is challenging, as patients can present with either clinical or subclinical AKI. Early identification of patients at risk of AKI, or at risk of progressing to severe and/or persistent AKI, is crucial to the timely initiation of adequate supportive measures, including limiting further insults to the kidney. Accordingly, the discovery of biomarkers associated with AKI that can aid in early diagnosis is an area of intensive investigation. Additionally, high-quality evidence on best-practice care of patients with AKI, sepsis and SA-AKI has continued to accrue. Although specific therapeutic options are limited, several clinical trials have evaluated the use of care bundles and extracorporeal techniques as potential therapeutic approaches. Here we provide graded recommendations for managing SA-AKI and highlight priorities for future research.

Renoprotective effects of ferulic acid mediated by AMPKα1 against lipopolysaccharide-induced damage

The kidney is susceptible to lipopolysaccharide (LPS)-induced damage with sepsis, and renal dysfunction is a leading cause of mortality in patients with sepsis. However, the renoprotective effects of ferulic acid (FA) during sepsis and the underlying mechanism remain unclear. This study explored these renoprotective effects using NRK-52E cells and mice with LPS-induced renal damage. The results showed that after LPS challenge, NRK-52E cell viability decreased, whereas lactate dehydrogenase, caspase-3 activity, apoptosis, the release of the inflammatory cytokines, and reactive oxygen species generation increased. Further, the activities of endogenous enzymatic and non-enzymatic antioxidant systems, and energy metabolism were inhibited, mitochondrial membrane potential was lost, mitochondrial permeability transition pores opened, renal blood flow and excretory functions were reduced, and the morphology and ultrastructure of renal tissue were seriously damaged in mice exposed to LPS. FA pretreatment upregulated AMP-activated protein kinase (AMPK) α1 expression and phosphorylation and significantly reversed the aforementioned functional, enzymological, and morphological indexes in vivo and in vitro. However, these renoprotective effects of FA were attenuated by compound C, an AMPK inhibitor. In conclusion, FA pretreatment can upregulate AMPKα1 expression and phosphorylation, inhibit inflammatory cytokine release and oxidative stress, improve mitochondrial function and energy supply, alleviate apoptosis, and ultimately protect renal tissue against LPS damage.

Vitamin D-VDR (vitamin D receptor) alleviates glucose metabolism reprogramming in lipopolysaccharide-induced acute kidney injury

Background: Our previous study showed that vitamin D (VD)-vitamin D receptor (VDR) plays a nephroprotective role in lipopolysaccharide (LPS)-induced acute kidney injury (AKI). Recently, glucose metabolism reprogramming was reported to be involved in the pathogenesis of AKI. Objective: To investigate the role of VD-VDR in glucose metabolism reprogramming in LPS-induced AKI. Methods: We established a model of LPS-induced AKI in VDR knockout (VDR-KO) mice, renal proximal tubular-specific VDR-overexpressing (VDR-OE) mice and wild-type C57BL/6 mice. In vitro, human proximal tubular epithelial cells (HK-2 cells), VDR knockout and VDR overexpression HK-2 cell lines were used. Results: Paricalcitol (an active vitamin D analog) or VDR-OE reduced lactate concentration, hexokinase activity and PDHA1 phosphorylation (a key step in inhibiting aerobic oxidation) and simultaneously ameliorated renal inflammation, apoptosis and kidney injury in LPS-induced AKI mice, which were more severe in VDR-KO mice. In in vitro experiments, glucose metabolism reprogramming, inflammation and apoptosis induced by LPS were alleviated by treatment with paricalcitol or dichloroacetate (DCA, an inhibitor of p-PDHA1). Moreover, paricalcitol activated the phosphorylation of AMP-activated protein kinase (AMPK), and an AMPK inhibitor partially abolished the protective effect of paricalcitol in LPS-treated HK-2 cells. Conclusion: VD-VDR alleviated LPS-induced metabolic reprogramming in the kidneys of AKI mice, which may be attributed to the inactivation of PDHA1 phosphorylation via the AMPK pathway.

Exploring the Muscle Metabolomics in the Mouse Model of Sepsis-Induced Acquired Weakness

Background/Aim

We aimed to identify the differentially expressing metabolites (DEMs) in the muscles of the mouse model of sepsis-induced acquired weakness (sepsis-AW) using liquid chromatography-mass spectrometry (LC-MS).

Materials and Methods

Sepsis by cecal ligation puncture (CLP) with lower limb immobilization was used to produce a sepsis-AW model. After this, the grip strength of the C57BL/6 male mice was investigated. The transmission electron microscopy was utilized to determine the pathological model. LC-MS was used to detect the metabolic profiles within the mouse muscles. Additionally, a statistically diversified analysis was carried out.

Results

Compared to the sepsis group, 30 DEMs, including 17 upregulated and 13 down-regulated metabolites, were found in the sepsis-AW group. The enriched metabolic pathways including purine metabolism, valine/leucine/isoleucine biosynthesis, cGMP-PKG pathway, mTOR pathway, FoxO pathway, and PI3K-Akt pathway were found to differ between the two groups. The targeted metabolomics analysis explored significant differences between four amino acid metabolites (leucine, cysteine, tyrosine, and serine) and two energy metabolites (AMP and cAMP) in the muscles of the sepsis-AW experimental model group, which was comparable to the sepsis group.

Conclusion

The present work identified DEMs and metabolism-related pathways within the muscles of the sepsis-AW mice, which offered valuable experimental data for diagnosis and identification of the pathogenic mechanism underlying sepsis-AW.

Phosphodiesterase-4 Inhibitor Roflumilast-Mediated Protective Effect in Sepsis-Induced Late-Phase Event of Acute Kidney Injury: A Narrative Review

Severe infections such as viral, bacterial, or fungal sepsis can cause an inflammatory response in the host, leading to organ failure and septic shock—phosphodiesterase-4 (PDE-4) inhibiting related agents from suppressing cyclic adenosine monophosphate (cAMP) degradation. Regulatory organisations have approved some substances in this category to reduce the risk of chronic obstructive pulmonary disease (COPD) exacerbations in patients with chronic bronchitis and a history of COPD exacerbations. Roflumilast has been shown to alleviate inflammatory responses, thus regulating airway inflammation. Additionally, roflumilast therapy dramatically enhanced B-cell lymphoma 2 (Bcl-2) expression, an anti-apoptotic marker lowered in septic animals. Previous research has indicated that roflumilast may help reverse sepsis-induced liver and lung harm, but whether it is also effective in reversing sepsis-induced renal impairment remains unknown. Therefore, this review determines whether roflumilast protects against renal dysfunction, inflammatory response, and apoptosis in sepsis-induced kidney damage. Additionally, we discussed the molecular mechanism through which roflumilast exerts its protective effect to uncover a possible treatment agent for sepsis-induced renal impairment.

Mitochondrial Sirt3 serves as a biomarker for sepsis diagnosis and mortality prediction

The purpose of this study is to determine whether the levels of serum Sirt3 correlate with disease severity and perfusion indicators in septic patients, as well as to assess the clinical value of Sirt3 as a potential novel marker for sepsis diagnosis and mortality prediction. A total of 79 patients in the ICU were included in the study, of which 28 were postoperatively noninfectious and the remaining 51 patients were all diagnosed with sepsis during the study period. The levels of Sirt3 were detected and dynamically monitored by enzyme-linked adsorption method, Pearson or Spearman coefficient for correlation analysis between Sirt3 and clinical indicators, ROC curve for evaluation of diagnosis and mortality prediction, Kaplan-Meier method for the significance of Sirt3 in 28-day survival. The serum levels of Sirt3 were lower in the sepsis patients on day 1 (P < 0.0001), and the septic shock group had lower Sirt3 levels than the sepsis group (P = 0.013). Sirt3 had good negative correlations with SOFA scores both in sepsis and septic shock groups (Pearson: r² = - 0.424, - 0.518; P = 0.011, 0.040), and Sirt3 correlated strongly with ScvO₂ in the septic shock group (Pearson: r² = - 0.679, P = 0.004) and with PCT in the sepsis group (Pearson: r² = - 0.409, P = 0.015). Sirt3 not only performed well in identifying sepsis (AUC = 0.995, 95% CI 0.987-1, P < 0.0001) but also greatly enhanced lactate's specificity in detecting septic shock (from 91.43 to 94.29%). Patients in the low Sirt3 group had higher ScvO₂, lactate, APACHE II score, SOFA score, longer ICU stays, and worse indicators of inflammation (TNF-α, IL-6) and infection (PCT) than those in the high Sirt3 group (P < 0.05). Additionally, Sirt3 can predict mortality of sepsis (AUC = 0.746, 95% CI 0.571-0.921, P = 0.022), patients with serum Sirt3 < 10.07 pg/ml have a lower 28-day survival (log-rank P = 0.008). Low serum levels of Sirt3 are significantly correlated with the disease severity. At the same time, Sirt3 increases the sensitivity of lactate to detect "cellular hypoxia" in septic shock. Sirt3 is a promising biomarker for the diagnosis of sepsis and predicting mortality risk in septic patients.

Anti-Hyperglycemic Agents in the Adjuvant Treatment of Sepsis: Improving Intestinal Barrier Function

Intestinal barrier injury and hyperglycemia are common in patients with sepsis. Bacteria translocation and systemic inflammatory response caused by intestinal barrier injury play a significant role in sepsis occurrence and deterioration, while hyperglycemia is linked to adverse outcomes in sepsis. Previous studies have shown that hyperglycemia is an independent risk factor for intestinal barrier injury. Concurrently, increasing evidence has indicated that some anti-hyperglycemic agents not only improve intestinal barrier function but are also beneficial in managing sepsis-induced organ dysfunction. Therefore, we assume that these agents can block or reduce the severity of sepsis by improving intestinal barrier function. Accordingly, we explicated the connection between sepsis, intestinal barrier, and hyperglycemia, overviewed the evidence on improving intestinal barrier function and alleviating sepsis-induced organ dysfunction by anti-hyperglycemic agents (eg, metformin, peroxisome proliferators activated receptor-γ agonists, berberine, and curcumin), and summarized some common characteristics of these agents to provide a new perspective in the adjuvant treatment of sepsis.

Association of Metformin Use During Hospitalization and Mortality in Critically Ill Adults With Type 2 Diabetes Mellitus and Sepsis

OBJECTIVES

Whether metformin exposure is associated with improved outcomes in patients with type 2 diabetes mellitus and sepsis.

DESIGN

Retrospective cohort study.

SETTING

Patients admitted to ICUs in 16 hospitals in Pennsylvania from October 2008 to December 2014.

PATIENTS

Adult critical ill patients with type 2 diabetes mellitus and sepsis.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

We conducted a retrospective cohort study to compare 90-day mortality in diabetic patients with sepsis with and without exposure to metformin during hospitalization. Data were obtained from the electronic health record of a large healthcare system in Pennsylvania from October 2008 to December 2014, on patients admitted to the ICU at any of the 16 hospitals within the system. The primary outcome was mortality at 90 days. The absolute and adjusted odds ratio (OR) with 95% CI were calculated in a propensity score-matched cohort. Among 14,847 patients with type 2 diabetes mellitus and sepsis, 682 patients (4.6%) were exposed to metformin during hospitalization and 14,165 (95.4%) were not. Within a total of 2,691 patients subjected to propensity score-matching at a 1:4 ratio, exposure to metformin (n = 599) was associated with decreased 90-day mortality (71/599, 11.9% vs 475/2,092, 22.7%; OR, 0.46; 95% CI, 0.35-0.60), reduced severe acute kidney injury (50% vs 57%; OR, 0.75; 95% CI, 0.62-0.90), less Major Adverse Kidney Events at 1 year (OR, 0.27; 95% CI, 0.22-0.68), and increased renal recovery (95% vs 86%; OR, 6.43; 95% CI, 3.42-12.1).

CONCLUSIONS

Metformin exposure during hospitalization is associated with a decrease in 90-day mortality in patients with type 2 diabetes mellitus and sepsis.

Transition of acute kidney injury to chronic kidney disease: role of metabolic reprogramming

Acute kidney injury (AKI) is a global public health concern associated with high morbidity and mortality. Although advances in medical management have improved the in-hospital mortality of severe AKI patients, the renal prognosis for AKI patients in the later period is not encouraging. Recent epidemiological investigations have indicated that AKI significantly increases the risk for the development of chronic kidney disease (CKD) and end-stage renal disease (ESRD) in the future, further contributing to the economic burden on health care systems. The transition of AKI to CKD is complex and often involves multiple mechanisms. Recent studies have suggested that renal tubular epithelial cells (TECs) are more prone to metabolic reprogramming during AKI, in which the metabolic process in the TECs shifts from fatty acid β-oxidation (FAO) to glycolysis due to hypoxia, mitochondrial dysfunction, and disordered nutrient-sensing pathways. This change is a double-edged role. On the one hand, enhanced glycolysis acts as a compensation pathway for ATP production; on the other hand, long-term shut down of FAO and enhanced glycolysis lead to inflammation, lipid accumulation, and fibrosis, contributing to the transition of AKI to CKD. This review discusses developments and therapies focused on the metabolic reprogramming of TECs during AKI, and the emerging questions in this evolving field.

TRPM7 silencing modulates glucose metabolic reprogramming to inhibit the growth of ovarian cancer by enhancing AMPK activation to promote HIF-1α degradation

BACKGROUND

Tumor cell metabolic reprogramming is crucial for the malignant behavior of cancer cells by promoting their proliferation. However, little is known on how transient receptor potential 7 (TRPM7) modulates metabolic reprogramming in ovarian cancer.

METHODS

The effects of TRPM7 silencing on transcriptome profile, glucose uptake, lactic acid production, extracellular acidification rate (ECAR), oxygen consumption rate (OCR), intracellular ROS and ATP levels, and NAD+/NADH ratios in ovarian cancer cells were examined. The impacts of TRPM7 silencing on the levels of glycolysis-related HK2, PDK1 and oxidative phosphorylation (OXPHOS)-related IDH3B and UQCRC1, HIF-1α expression and AMPK phosphorylation were determined in ovarian cancer. The effect of AMPK activity on HIF-1α ubiquitination degradation was investigated in ovarian cancer cells.

RESULTS

Compared with the control, TRPM7 silencing suppressed the proliferation of ovarian cancer cells by shifting preferable glycolysis to OXPHOS. In parallel, TRPM7 silencing decreased the glucose uptake of tumor-bearing mice and TRPM7 levels were negatively correlated with IDH3B and UQCRC1, but positively with HK2 and PDK1 expression in ovarian cancer tissues. Mechanistically, TRPM7 silencing significantly increased AMPK phosphorylation and decreased HIF-1α protein levels in ovarian cancer, particularly in HIF-1α silencing cells. The shifting from glycolysis to OXPHOS by TRPM7 silencing was abrogated by HIF-1α over-expression and impaired by inhibiting AMPK activity in ovarian cancer cells. Moreover, enhanced AMPK activation inhibited glycolysis, which was abrogated by HIF-1α over-expression in ovarian cancer cells. Moreover, the enhanced AMPK activation promoted HIF-1α ubiquitination degradation.

CONCLUSIONS

TRPM7 silencing enhanced AMPK activation to shift glycolysis to oxidative phosphorylation by promoting HIF-1α ubiquitination degradation in ovarian cancer. Hence, TRPM7 may be a therapeutic target for intervention of ovarian cancer.

Towards an ecological definition of sepsis: a viewpoint

In critically ill patients with sepsis, there is a grave lack of effective treatment options to address the illness-defining inappropriate host response. Currently, treatment is limited to source control and supportive care, albeit with imminent approval of immune modulating drugs for COVID-19-associated lung failure the potential of host-directed strategies appears on the horizon. We suggest expanding the concept of sepsis by incorporating infectious stress within the general stress response of the cell to define sepsis as an illness state characterized by allostatic overload and failing adaptive responses along with biotic (pathogen) and abiotic (e.g., malnutrition) environmental stress factors. This would allow conceptualizing the failing organismic responses to pathogens in sepsis with an ancient response pattern depending on the energy state of cells and organs towards other environmental stressors in general. Hence, the present review aims to decipher the heuristic value of a biological definition of sepsis as a failing stress response. These considerations may motivate a better understanding of the processes underlying "host defense failure" on the organismic, organ, cell and molecular levels.

The Programmed Cell Death of Macrophages, Endothelial Cells, and Tubular Epithelial Cells in Sepsis-AKI

Sepsis is a systemic inflammatory response syndrome caused by infection, following with acute injury to multiple organs. Sepsis-induced acute kidney injury (AKI) is currently recognized as one of the most severe complications related to sepsis. The pathophysiology of sepsis-AKI involves multiple cell types, including macrophages, vascular endothelial cells (ECs) and renal tubular epithelial cells (TECs), etc. More significantly, programmed cell death including apoptosis, necroptosis and pyroptosis could be triggered by sepsis in these types of cells, which enhances AKI progress. Moreover, the cross-talk and connections between these cells and cell death are critical for better understanding the pathophysiological basis of sepsis-AKI. Mitochondria dysfunction and oxidative stress are traditionally considered as the leading triggers of programmed cell death. Recent findings also highlight that autophagy, mitochondria quality control and epigenetic modification, which interact with programmed cell death, participate in the damage process in sepsis-AKI. The insightful understanding of the programmed cell death in sepsis-AKI could facilitate the development of effective treatment, as well as preventive methods.

Innovations and Emerging Therapies to Combat Renal Cell Damage: NAD+ As a Drug Target

Significance: Acute kidney injury (AKI) is a common and life-threatening complication in hospitalized and critically ill patients. It is defined by an abrupt deterioration in renal function, clinically manifested by increased serum creatinine levels, decreased urine output, or both. To execute all its functions, namely excretion of waste products, fluid/electrolyte balance, and hormone synthesis, the kidney requires incredible amounts of energy in the form of adenosine triphosphate. Recent Advances: Adequate mitochondrial functioning and nicotinamide adenine dinucleotide (NAD+) homeostasis are essential to meet these high energetic demands. NAD+ is a ubiquitous essential coenzyme to many cellular functions. NAD+ as an electron acceptor mediates metabolic pathways such as oxidative phosphorylation (OXPHOS) and glycolysis, serves as a cosubstrate of aging molecules (i.e., sirtuins), participates in DNA repair mechanisms, and mediates mitochondrial biogenesis. Critical Issues: In many forms of AKI and chronic kidney disease, renal function deterioration has been associated with mitochondrial dysfunction and NAD+ depletion. Based on this, therapies aiming to restore mitochondrial function and increase NAD+ availability have gained special attention in the last two decades. Future Directions: Experimental and clinical studies have shown that by restoring mitochondrial homeostasis and increasing renal tubulo-epithelial cells, NAD+ availability, AKI incidence, and chronic long-term complications are significantly decreased. This review covers some general epidemiological and pathophysiological concepts; describes the role of mitochondrial homeostasis and NAD+ metabolism; and analyzes the underlying rationale and role of NAD+ aiming therapies as promising preventive and therapeutic strategies for AKI. Antioxid. Redox Signal. 35, 1449-1466.

Release of HMGB1 in Podocytes Exacerbates Lipopolysaccharide-Induced Acute Kidney Injury

Objective

Acute kidney injury (AKI) usually occurs during sepsis. Inflammation factors, such as high-mobility group box 1 (HMGB1), are dramatically upregulated under septic conditions. In our current work, the functions of HMGB1 in AKI were explored.

Methods

An AKI model was induced by the lipopolysaccharide (LPS) challenge in C57 mice. Podocytes were challenged by LPS for different durations. Subsequently, podocytes transfected with HMGB1 siRNA were exposed to LPS for 24 h. The expressions of supernatant HMGB1 and cellular active caspase-3 were examined by Western blotting analysis. To explore the effect of HMGB1 on tubular epithelial cells (TECs), HK-2 cells were exposed to HMGB1 at various concentrations for 24 h. Epithelial-mesenchymal transition (EMT) of HK-2 cells was evaluated by Western blotting analysis. Mitochondrial division and apoptosis of HK-2 cells were assessed by MitoTracker Red and Western blotting analysis, respectively.

Results

Compared with the sham control group, the expression of HMGB1 was increased in the kidney of AKI mice. Moreover, the expression of supernatant HMGB1 was increased in LPS-challenged podocytes compared with the control group. Knockdown of HMGB1 attenuated LPS-induced podocyte injury. Besides, EMT in TECs was triggered by HMGB1. Mitochondrial damage and apoptosis of HK-2 cells exposed to HMGB1 were markedly elevated compared with the control group.

Conclusions

Collectively, HMGB1 release in podocytes was induced by LPS, subsequently leading to exacerbated AKI.

Metabolic Reprogramming and Host Tolerance: A Novel Concept to Understand Sepsis-Associated AKI

Acute kidney injury (AKI) is a frequent complication of sepsis that increases mortality and the risk of progression to chronic kidney disease. However, the mechanisms leading to sepsis-associated AKI are still poorly understood. The recognition that sepsis induces organ dysfunction in the absence of overt necrosis or apoptosis has led to the consideration that tubular epithelial cells (TEC) may deploy defense mechanisms to survive the insult. This concept dovetails well with the notion that the defense against infection does not only depend on the capacity of the immune system to limit the microbial load (known as resistance), but also on the capacity of cells and tissues to limit tissue injury (known as tolerance). In this review, we discuss the importance of TEC metabolic reprogramming as a defense strategy during sepsis, and how this cellular response is likely to operate through a tolerance mechanism. We discuss the fundamental role of specific regulatory nodes and of mitochondria in orchestrating this response, and how this opens avenues for the exploration of targeted therapeutic strategies to prevent or treat sepsis-associated AKI.

Tubeimoside I protects against sepsis-induced cardiac dysfunction via SIRT3

Sepsis-induced cardiac dysfunction (SICD) is one of the key complications in sepsis and it is associated with adverse outcomes and increased mortality. There is no effective drug to treat SICD. Previously, we reported that tubeimoside I (TBM) improved survival of septic mice. The aim of this study is to figure out whether TBM ameliorates SICD. Also, SIRT3 was reported to protects against SICD. Our second aim is to confirm whether SIRT3 plays essential roles in TBM's protective effects against SICD. Our results demonstrated that TBM could alleviate SICD and SICD's key pathological factor, inflammation, oxidative stress, and apoptosis were all reduced by TBM. Notably, SICD induced a significant decrease in cardiac SIRT3 expression, while TBM treatment could reverse SIRT3 expression. To clarify whether TBM provides protection via SIRT3, we injected a specific SIRT3 inhibitor 3-(1H-1,2,3-triazol-4-yl) pyridine (3-TYP) into mice before TBM treatment. Then the cardioprotective effects of TBM were largely abolished by 3-TYP. This suggests that SIRT3 plays an essential role in TBM's cardioprotective effects. In vitro, TBM also protected H9c2 cells against LPS-induced injury, and siSIRT3 diminished these protective effects. Taken together, our results demonstrate that TBM protects against SICD via SIRT3. TBM might be a potential drug candidate for SICD treatment.

Sepsis-Associated Acute Kidney Injury

Sepsis-associated acute kidney injury (S-AKI) is a common and life-threatening complication in hospitalized and critically ill patients. It is characterized by rapid deterioration of renal function associated with sepsis. The pathophysiology of S-AKI remains incompletely understood, so most therapies remain reactive and nonspecific. Possible pathogenic mechanisms to explain S-AKI include microcirculatory dysfunction, a dysregulated inflammatory response, and cellular metabolic reprogramming. In addition, several biomarkers have been developed in an attempt to improve diagnostic sensitivity and specificity of S-AKI. This article discusses the current understanding of S-AKI, recent advances in pathophysiology and biomarker development, and current preventive and therapeutic approaches.

Protective Effect of Sirtuin 3 on CLP-Induced Endothelial Dysfunction of Early Sepsis by Inhibiting NF-κB and NLRP3 Signaling Pathways

It has been revealed that widespread vascular endothelial dysfunction occurs in septic shock, ultimately resulting in multiple organ failure. The mitochondrial deacetylase sirtuin 3 (SIRT3) is essential in the regulation of metabolism, anti-inflammation, and anti-oxidation. The purpose of this study is to investigate whether SIRT3 is associated with the pathological progression of endothelial dysfunction in sepsis. Septic shock model was induced by cecal ligation and puncture (CLP) surgery on wild-type C57BL/6 mice. We activated and inhibited the function of SIRT3 with honokiol (HKL) and 3-TYP, respectively, and then biochemical, inflammatory, and endothelial function parameters of vascular tissue and survival were determined after CLP. CLP significantly activated NF-κB and NLRP3 pathways and decreased survival rate, endothelium-dependent relaxation function, and expression of Ser1177 phosphorylation of endothelial nitric oxide synthase (p-eNOS). The activation of SIRT3 significantly attenuated the increases of NF-κB and NLRP3 pathways and the declines of p-eNOS, endothelium-dependent relaxation function, and survival rate in septic mice. However, it presented exactly opposite results if SIRT3 was suppressed. We suggested that SIRT3 had a critical protective effect against vascular inflammation and endothelial dysfunction in early sepsis. Our data support a potential therapeutic target in vascular dysfunction and septic shock.

Mechanism and application of metformin in kidney diseases: An update

Metformin is an oral antihyperglycemic drug widely used to treat type 2 diabetes mellitus (T2DM), acting via indirect activation of 5' Adenosine monophosphate-activated Protein Kinase (AMPK). Beyond the anti-diabetic effect, accumulative pieces of evidence have revealed that metformin also everts a beneficial effect in diverse kidney diseases. In various acute kidney diseases (AKI) animal models, metformin protects renal tubular cells from inflammation, apoptosis, reactive oxygen stress (ROS), endoplasmic reticulum (ER) stress, epithelial-mesenchymal transition (EMT) via AMPK activation. In diabetic kidney disease (DKD), metformin also alleviates podocyte loss, mesangial cells apoptosis, and tubular cells senescence through AMPK-mediated signaling pathways. Besides, metformin inhibits cystic fibrosis transmembrane conductance regulator (CFTR)-mediated fluids secretion and the mammalian target of rapamycin (mTOR)-involved cyst formation negatively regulated by AMPK in autosomal dominant polycystic kidney disease (APDKD). Furthermore, metformin also contributes to the alleviation of urolithiasis and renal cell carcinoma (RCC). As the common pathway for chronic kidney disease (CKD) progressing towards end-stage renal disease (ESRD), renal fibrosis is ameliorated by metformin, to a great extent dependent on AMPK activation. However, clinical data are not always consistent with preclinical data, some clinical investigations showed the unmeaningful even detrimental effect of metformin on T2DM patients with kidney diseases. Most importantly, metformin-associated lactic acidosis (MALA) is a vital issue restricting the application of metformin. Thus, we conclude the application of metformin in kidney diseases and uncover the underlying molecular mechanisms in this review.

Inhibition of aerobic glycolysis alleviates sepsis‑induced acute kidney injury by promoting lactate/Sirtuin 3/AMPK‑regulated autophagy

Metabolism reprogramming influences the severity of organ dysfunction, progression to fibrosis, and development of disease in acute kidney injury (AKI). Previously we showed that inhibition of aerobic glycolysis improved survival rates and protected septic mice from kidney injury. However, the underlying mechanisms remain unclear. In the present study, it was revealed that sepsis or lipopolysaccharide (LPS) enhanced aerobic glycolysis as evidenced by increased lactate production and upregulated mRNA expression of glycolysis-related genes in kidney tissues and human renal tubular epithelial (HK-2) cells. The aerobic glycolysis inhibitor 2-deoxy-D-glucose (2-DG) downregulated glycolysis, and improved kidney injury induced by sepsis. 2-DG treatments increased the expression of sirtuin 3 (SIRT3) and phosphorylation-AMP-activated protein kinase (p-AMPK), following promoted autophagy and attenuated apoptosis of tubular epithelial cells in septic mice and in LPS-treated HK-2 cells. However, the glycolysis metabolite lactate downregulated SIRT3 and p-AMPK expression, inhibited autophagy and enhanced apoptosis in LPS-treated HK-2 cells. Furthermore, pharmacological blockade of autophagy with 3-methyladenine (3-MA) partially abolished the protective effect of 2-DG in sepsis-induced AKI. These findings indicated that inhibition of aerobic glycolysis protected against sepsis-induced AKI by promoting autophagy via the lactate/SIRT3/AMPK pathway.

Targeting acute kidney injury in COVID-19

As of 15 August 2020, Coronavirus disease 2019 (COVID-19) has been reported in >21 million people world-wide and is responsible for more than 750,000 deaths. The occurrence of acute kidney injury (AKI) in patients hospitalized with COVID-19 has been reported to be as high as 43%. This is comparable to AKI in other forms of pneumonia requiring hospitalization, as well as in non-infectious conditions like cardiac surgery. The impact of AKI on COVID-19 outcomes is difficult to assess at present but, similar to other forms of sepsis, AKI is strongly associated with hospital mortality. Indeed, mortality is reported to be very low in COVID-19 patients without AKI. Given that AKI contributes to fluid and acid-base imbalances, compromises immune response and may impair resolution of inflammation, it seems likely that AKI contributes to mortality in these patients. The pathophysiologic mechanisms of AKI in COVID-19 are thought to be multifactorial including systemic immune and inflammatory responses induced by viral infection, systemic tissue hypoxia, reduced renal perfusion, endothelial damage and direct epithelial infection with Severe Acute Respiratory Syndrome Coronavirus 2. Mitochondria play a central role in the metabolic deregulation in the adaptive response to the systemic inflammation and are also found to be vital in response to both direct viral damage and tissue reperfusion. These stress conditions are associated with increased glycolysis and reduced fatty acid oxidation. Thus, there is a strong rationale to target AKI for therapy in COVID-19. Furthermore, many approaches that have been developed for other etiologies of AKI such as sepsis, inflammation and ischemia-reperfusion, have relevance in the treatment of COVID-19 AKI and could be rapidly pivoted to this new disease.

Dexmedetomidine Enhances Autophagy via α2-AR/AMPK/mTOR Pathway to Inhibit the Activation of NLRP3 Inflammasome and Subsequently Alleviates Lipopolysaccharide-Induced Acute Kidney Injury

Background

Acute kidney injury (AKI) is a severe complication of sepsis; however, no effective drugs have been found. Activation of the nucleotide-binding domain-like receptor protein 3 (NLRP3) inflammasome is a major pathogenic mechanism of AKI induced by lipopolysaccharide (LPS). Autophagy, a process of intracellular degradation related to renal homeostasis, effectively restricts inflammatory responses. Herein, we explored the potential protective mechanisms of dexmedetomidine (DEX), which has confirmed anti-inflammatory effects, on LPS-induced AKI.

Methods

AKI was induced in rats by injecting 10 mg/kg of LPS intraperitoneally (i.p.). Wistar rats received intraperitoneal injections of DEX (30 µg/kg) 30 min before an intraperitoneal injection of LPS. Atipamezole (ATI) (250 µg/kg) and 3-methyladenine (3-MA) (15 mg/kg) were intraperitoneally injected 30 min before the DEX injection.

Results

DEX significantly attenuated renal injury. Furthermore, DEX decreased activation of the NLRP3 inflammasome and expression of interleukins 1β and 18. In addition, autophagy-related protein and gene analysis indicated that DEX could significantly enhance autophagy. Finally, we verified the pharmacological effects of DEX on the 5′-adenosine monophosphate-activated protein kinase (AMPK)/mechanistic target of rapamycin (mTOR) pathway. Atip and 3-MA significantly reversed the protective effects of DEX.

Conclusions

Our results suggest that the protective effects of DEX were mediated by enhanced autophagy via the α₂-adrenoreceptor/AMPK/mTOR pathway, which decreased activation of the NLRP3 inflammasome. Above all, we verified the renal protective effects of DEX and offer a new treatment strategy for AKI.

Metformin Suppresses the Proliferation and Promotes the Apoptosis of Colon Cancer Cells Through Inhibiting the Expression of Long Noncoding RNA-UCA1

PURPOSE

LncRNA-UCA1 has been proven to facilitate the proliferation and metastasis of colon cancer. Whether metformin inhibits the progression of colon cancer by suppressing lncRNA-UCA1 remains unknown. In this research, we aimed to explore the role of Metformin playing in pathogenesis of colon cancer.

MATERIALS AND METHODS

Using qRT-PCR, we measured the expression of five tumor-promoting lncRNAs in SW480 and SW620 colon cancer cells. Then, we conducted Western blotting and immunohistochemistry to evaluate the effects of MET or UCA1 knockdown or the combined MET+ UCA1 knockdown on the activities of the PI3K/AKT and ERK pathways in vitro and in tumor tissues obtained from tumor-bearing nude mice.

RESULTS

The results from CCK-8 assays showed that MET dose-dependently and time-dependently inhibited the viability of the colon cancer cells in vitro. Flow cytometry revealed that MET promoted the apoptosis of the SW480 and SW620 cells. qRT-PCR showed that lncRNA-UCA1 had the highest expression among the five lncRNAs. Suppressing UCA1 expression by siRNA or shRNA could further enhance the metformin-mediated anticancer effects against colon cancer in vitro and in vivo. Metformin decreased the UCA1 expression and further inhibited the proliferation and promoted the apoptosis of the colon cancer cells, which were associated with inactivation of the PI3K/AKT and ERK signaling pathways in vitro and in the tumor tissues obtained from the mice.

CONCLUSION

These results indicated that metformin has potential anticancer properties and revealed the anticancer mechanisms of metformin against colon cancer via regulating lncRNA-UCA1.