α-ketoglutarate attenuates ischemia-reperfusion injury of liver graft in rats

Glycogen synthase kinase-3β: A multifaceted player in ischemia-reperfusion injury and its therapeutic prospects

Ischemia-reperfusion injury (IRI) results in irreversible metabolic dysfunction and structural damage to tissues or organs, posing a formidable challenge in the field of organ implantation, cardiothoracic surgery, and general surgery. Glycogen synthase kinase-3β (GSK-3β) a multifunctional serine/threonine kinase, is involved in a variety of biological processes, including cell proliferation, apoptosis, and immune response. Phosphorylation of its tyrosine 216 and serine 9 sites positively and negatively regulates the activation and inactivation of the enzyme. Significantly, inhibition or inactivation of GSK-3β provides protection against IRI, making it a viable target for drug development. Though numerous GSK-3β inhibitors have been identified to date, the development of therapeutic treatments remains a considerable distance away. In light of this, this review summarizes the complicated network of GSK-3β roles in IRI. First, we provide an overview of GSK-3β's basic background. Subsequently, we briefly review the pathological mechanisms of GSK-3β in accelerating IRI, and highlight the latest progress of GSK-3β in multiorgan IRI, encompassing heart, brain, kidney, liver, and intestine. Finally, we discuss the current development of GSK-3β inhibitors in various organ IRI, offering a thorough and insightful reference for GSK-3β as a potential target for future IRI therapy.

Potentiation of the axis involving pentose phosphate pathway/NADPH oxidase/reactive oxygen species drives higher IL-10 production in monocytes of Sub-Saharan Africans

Cellular metabolism is a key determinant of immune cell function. Here we found that CD14+ monocytes from Sub-Saharan Africans produce higher levels of IL-10 following TLR-4 stimulation and are bioenergetically distinct from monocytes from Europeans. Through metabolomic profiling, we identified the higher IL-10 production to be driven by increased baseline production of NADPH oxidase-dependent reactive oxygen species, supported by enhanced pentose phosphate pathway activity. Together, these data indicate that NADPH oxidase-derived ROS is a metabolic checkpoint in monocytes that governs their inflammatory profile and uncovers a metabolic basis for immunological differences across geographically distinct populations.

[Latest Findings on the Role of α-Ketoglutarate in Metabolic Syndrome]

Alpha-ketoglutarate (α-KG), an endogenous intermediate of the tricarboxylic acid cycle, is involved in a variety of cellular metabolic pathways. It serves as an energy donor, a precursor of amino acid biosynthesis, and an epigenetic regulator. α-KG plays physiological functions in immune regulation, oxidative stress, and anti-aging as well. In recent years, it has been reported that the level of α-KG in the body is closely associated with metabolic syndrome, including obesity, hyperglycemia, and other pathological factors. Exogenous supplementation of α-KG improves obesity, blood glucose levels, and cardiovascular disease risks associated with metabolic syndrome. Furthermore, α-KG regulates the common pathological mechanisms of metabolic syndrome, suggesting the potential application prospect of α-KG in metabolic syndrome. In order to provide a theoretical basis for further exploration of the application of α-KG in metabolic syndrome, we focused on α-KG and metabolic syndrome in this article and summarized the latest research progress in the role of α-KG in improving the pathological condition and disease progression of metabolic syndrome. For the next step, researchers may focus on the co-pathogenesis of metabolic syndrome and investigate whether α-KG can be used to achieve the therapeutic goal of "homotherapy for heteropathy" in the treatment of metabolic syndrome.

α-Ketoglutarate for Preventing and Managing Intestinal Epithelial Dysfunction

The epithelium lining the intestinal tract serves a multifaceted role. It plays a crucial role in nutrient absorption and immune regulation and also acts as a protective barrier, separating underlying tissues from the gut lumen content. Disruptions in the delicate balance of the gut epithelium trigger inflammatory responses, aggravate conditions such as inflammatory bowel disease, and potentially lead to more severe complications such as colorectal cancer. Maintaining intestinal epithelial homeostasis is vital for overall health, and there is growing interest in identifying nutraceuticals that can strengthen the intestinal epithelium. α-Ketoglutarate, a metabolite of the tricarboxylic acid cycle, displays a variety of bioactive effects, including functioning as an antioxidant, a necessary cofactor for epigenetic modification, and exerting anti-inflammatory effects. This article presents a comprehensive overview of studies investigating the potential of α-ketoglutarate supplementation in preventing dysfunction of the intestinal epithelium.

Protective effect of alpha-ketoglutarate against water-immersion restraint stress-induced gastric mucosal damage in mice

Gastric lesions have several aetiologies, among which stress is the most prominent. Therefore, identification of new therapies to prevent stress is of considerable importance. Alpha-ketoglutarate (α-kg) several beneficial effects and has shown promise in combating oxidative stress, inflammation, and premature aging. Thus, this study aimed to evaluate the protective effect of α-kg in a gastric damage model by water-immersion restraint stress (WIRS). Pretreatment with α-kg decreased stress-related histopathological scores of tissue oedema, cell loss, and inflammatory infiltration. The α-kg restored the percentage of type III collagen fibres. Mucin levels were preserved as well as the structure and area of the myenteric plexus ganglia were preserved after pretreatment with α-kg. Myeloperoxidase (MPO) levels and the expression of pro-inflammatory cytokines (TNF-α and IL-1β) were also reduced following α-kg pretreatment. Decreased levels of glutathione (GSH) in the stress group were restored by α-kg. The omeprazole group was used as standard drug e also demonstrated improve on some parameters after the exposition to WIRS as inflammatory indexes, GSH and mucin. Through this, was possible to observe that α-kg can protect the gastric mucosa exposed to WIRS, preserve tissue architecture, reduce direct damage to the mucosa and inflammatory factors, stimulate the production of type III collagen and mucin, preserve the myenteric plexus ganglia, and maintain antioxidant potential. Due to, we indicate that α-kg has protective activity of the gastric mucosa, demonstrating its ability to prevent damage associated with gastric lesions caused by stress.

Prediction of the mechanisms of action of Qutan Huoxue decoction in non-alcoholic steatohepatitis (NASH): a network pharmacology study and experimental validation

CONTEXT

Qutan Huoxue decoction (QTHX) is used to treat non-alcoholic steatohepatitis (NASH) with good efficacy in the clinic. However, the mechanism is not clear yet.

OBJECTIVE

This study investigates the mechanism of QTHX in the treatment of NASH.

MATERIALS AND METHODS

Potential pathways of QTHX were predicted by network pharmacology. Fourty Sprague Dawley (SD) rats (half normal diet, half high-fat diet) were fed six to eight weeks, primary hepatocytes and Kupffer cells were extracted and co-cultured by the 0.4-micron trans well culture system. Then, the normal co-cultured cells were treated by normal serum, the NASH co-cultured cells were treated with various concentrations of QTHX-containing serum (0, 5, 7.5 or 10 μg/mL) for 24 h. The expression of targets were measured with Activity Fluorometric Assay, Western blot and PCR assay.

RESULTS

Network pharmacology indicated that liver-protective effect of QTHX was associated with its anti-inflammation response, oxidative stress, and lipid receptor signalling. 10 μg/mL QTHX significantly reduced the inflammation response and lipid levels in primary hepatocytes (ALT: 46.43 ± 2.76 U/L, AST: 13.96 ± 1.08 U/L, TG: 0.25 ± 0.01 mmol/L, TC: 0.14 ± 0.05 mmol/L), comparing with 0 μg/mL NASH group (ALT: 148 ± 9.22 U/L, AST: 53.02 ± 2.30 U/L, TG: 0.74 ± 0.07 mmol/L, TC: 0.91 ± 0.07 mmol/L) (p < 0.01). Meanwhile, QTHX increased expression of SOCS1 and decreased expression of TLR4, Myd88, NF-κB.

CONCLUSIONS

The study suggested that QTHX treats NASH in rats by activating the SCOS1/NF-κB/TLR4 pathway, suggesting QTHX could be further developed as a potential liver-protecting agent.

The role of Kupffer cell activation in immune liver damage induced by trichloroethylene associated with the IFN-γ/STAT1 signaling pathway

Trichloroethylene (TCE) is a metal detergent commonly used in industry that can enter the human body through the respiratory tract and skin, causing occupational medicamentosa-like dermatitis due to TCE (OMDT) and multiple organ damage, including liver failure. However, the pathogenesis of liver injury remains unclear. Kupffer cells (KCs) are important tissue macrophages in the body because the polarization of KCs plays a crucial role in immune-mediated liver injury. However, the mechanism of KCs polarization in TCE-induced immune liver injury has not been thoroughly elucidated. In this study, we investigated the effect of TCE-induced KCs polarization on liver function and signal transduction pathways using the TCE sensitization model developed by our group. BALB/c mouse skin was exposed to TCE for sensitization, and an increase in the expression of M1 macrophage-specific markers (CD16/CD32, iNOS), M1 macrophage-specific cytokines IL-1β, and IFN-γ, P-JAK-1 and P-STAT1 levels were also found to be dramatically increased. When using low doses of gadolinium trichloride (GdCl₃), the expression of these proteins and mRNA was significantly reduced. This phenomenon indicates that GdCl₃ blocks TCE-induced polarization of KCs and suggests that the IFN-γ/STAT1 signaling pathway may be involved in the polarization process of KCs. These findings clarify the relationship between the polarization of KCs and immune liver injury and highlight the importance of further study of immune-mediated liver injury in TCE-sensitized mice.

Alpha-ketoglutarate alleviates cadmium-induced inflammation by inhibiting the HIF1A-TNFAIP3 pathway in hepatocytes

The threat to public health posed by rapidly increasing levels of cadmium (Cd) in the environment is receiving worldwide attention. Although, Cd is known to be absorbed into the body and causes non-negligible damage to the liver, the detailed mechanisms underlying its hepatoxicity are incompletely understood. In the present study, investigated the effect of TNFAIP3 and α-ketoglutarate (AKG) on Cd-induced liver inflammation and hepatocyte death. Male C57BL/6 mice were exposed to cadmium chloride (1.0 mg/kg) while being fed a diet with 2 % AKG for two weeks. We found that Cd induced hepatocyte injury and inflammatory infiltration. In addition, TNFAIP3 expression was inhibited in the liver tissues and cells of CdCl₂-treated mice. Mouse hepatocyte-specific TNFAIP3 overexpression by tail vein injection of an adeno-associated virus (AAV) vector effectively alleviated Cd-induced hepatic necrosis and inflammation, which was mediated by the NF-κB signaling pathway. Notably, this inhibitory effect of TNFAIP3 on Cd-induced liver injury was dependent on AKG. Exogenous addition of AKG prevented Cd exposure-induced increases in serum ALT, AST and LDH levels, production of pro-inflammatory cytokines, activation of the NF-κB signaling pathway, and even significantly reduced Cd-induced oxidative stress and hepatocyte death. Mechanistically, AKG exerted its anti-inflammatory effect by promoting the hydroxylation and degradation of HIF1A to reduce its Cd-induced overexpression in vivo and in vitro, avoiding the inhibition of the TNFAIP3 promoter by HIF1A. Moreover, the protective effect of AKG was significantly weaker in Cd-treated primary hepatocytes transfected with HIF1A pcDNA. Overall, our results reveal a novel mechanism of Cd-induced hepatotoxicity.

Cuproptosis-a potential target for the treatment of osteoporosis

Osteoporosis is an age-related disease of bone metabolism marked by reduced bone mineral density and impaired bone strength. The disease causes the bones to weaken and break more easily. Osteoclasts participate in bone resorption more than osteoblasts participate in bone formation, disrupting bone homeostasis and leading to osteoporosis. Currently, drug therapy for osteoporosis includes calcium supplements, vitamin D, parathyroid hormone, estrogen, calcitonin, bisphosphates, and other medications. These medications are effective in treating osteoporosis but have side effects. Copper is a necessary trace element in the human body, and studies have shown that it links to the development of osteoporosis. Cuproptosis is a recently proposed new type of cell death. Copper-induced cell death regulates by lipoylated components mediated via mitochondrial ferredoxin 1; that is, copper binds directly to the lipoylated components of the tricarboxylic acid cycle, resulting in lipoylated protein accumulation and subsequent loss of iron-sulfur cluster proteins, leading to proteotoxic stress and eventually cell death. Therapeutic options for tumor disorders include targeting the intracellular toxicity of copper and cuproptosis. The hypoxic environment in bone and the metabolic pathway of glycolysis to provide energy in cells can inhibit cuproptosis, which may promote the survival and proliferation of various cells, including osteoblasts, osteoclasts, effector T cells, and macrophages, thereby mediating the osteoporosis process. As a result, our group tried to explain the relationship between the role of cuproptosis and its essential regulatory genes, as well as the pathological mechanism of osteoporosis and its effects on various cells. This study intends to investigate a new treatment approach for the clinical treatment of osteoporosis that is beneficial to the treatment of osteoporosis.

Mitochondria in innate immunity signaling and its therapeutic implications in autoimmune diseases

Autoimmune diseases are characterized by vast alterations in immune responses, but the pathogenesis remains sophisticated and yet to be fully elucidated. Multiple mechanisms regulating cell differentiation, maturation, and death are critical, among which mitochondria-related cellular organelle functions have recently gained accumulating attention. Mitochondria, as a highly preserved organelle in eukaryotes, have crucial roles in the cellular response to both exogenous and endogenous stress beyond their fundamental functions in chemical energy conversion. In this review, we aim to summarize recent findings on the function of mitochondria in the innate immune response and its aberrancy in autoimmune diseases such as rheumatoid arthritis, systemic lupus erythematosus, etc., mainly focusing on its direct impact on cellular metabolism and its machinery on regulating immune response signaling pathways. More importantly, we summarize the status quo of potential therapeutic targets found in the mitochondrial regulation in the setting of autoimmune diseases and wish to shed light on future studies.

Donor graft METTL3 gene transfer ameliorates rat liver transplantation ischemia-reperfusion injury by enhancing HO-1 expression in an m6A-dependent manner

Ischemia-reperfusion injury (IRI) is one of the most common complications in liver transplantation. METTL3 regulates inflammation and various cellular stress responses via modulating RNA m6A modification level. Here, the study aimed to investigate the role and mechanism of METTL3 in IRI after rat orthotopic liver transplantation. Firstly, m6A dot blot assay showed that total RNA m6A modification level in grafts was down-regulated, which echoed with the downregulation of METTL3. Furthermore, METTL3 pretreatment in donor significantly reduced liver grafts necrosis formation, apoptosis, improved liver function and depressed the proinflammatory cytokine/chemokine expression. Mechanistically, western blot and immunohistochemical showed that METTL3 inhibited apoptosis via upregulating HO-1. Moreover, MeRIP-qPCR assay revealed that METTL3 promoted HO-1 expression in an m6A-dependent manner. Additionally, METTL3 alleviated primary hepatocytes apoptosis by upregulating HO-1 under hypoxia/reoxygenation condition. Taken together, these results demonstrated that METTL3 exerted a cytoprotective role against IRI via inducing HO-1 in an m6A-dependent manner.

HPLC-MS-based untargeted metabolomic analysis of differential plasma metabolites and their associated metabolic pathways in reproductively anosmic black porgy, Acanthopagrus schlegelii

Olfaction, a universal form of chemical communication, is a powerful channel for animals to obtain social and environmental cues. The mechanisms by which fish olfaction affects reproduction, breeding and disease control are not yet clear. To evaluate metabolites profiles, plasma from anosmic and control black porgy during reproduction was analyzed by non-targeted metabolomics using ultra high-performance liquid chromatography-mass spectrometry and multivariate statistical analysis techniques, including principal component analysis and orthogonal partial least squares discriminant analysis. The metabolite profiles of anosmia and control groups were found to be significantly separated. Ten different differential metabolites, mainly including amino acids, such as isoleucine and methionine, and lipids, such as phosphatidylserine, were screened based on the combined analysis of variable importance in the projection and p values. In addition, six key differential metabolic pathways were analyzed using the Kyoto Encyclopedia of Genes and Genomes and enriched for four metabolic pathways including the citrate acid (TCA) cycle, tyrosine metabolism, arginine and proline metabolism, and arginine synthesis. The TCA cycle enhances fertility through the reduction of pyruvate kinase, and intermediate derivatives (acetyl CoA, malonyl CoA) act as signaling factors that regulate immune cell function. The tyrosine cycle can indirectly participate and promote reproduction in black porgy through melanin-concentrating hormone. Arginine and proline metabolism can promote reproduction by promoting growth hormone and enhance immunity in anosmic black porgy by stimulating T lymphocytes. Our metabolomic study revealed that anosmia in black porgy played an active role in immunity and reproduction and provided theoretical support for breeding and disease control.

Gut Microbiota-Derived Glutamine Attenuates Liver Ischemia/Reperfusion Injury via Macrophage Metabolic Reprogramming

BACKGROUND & AIMS

Many studies have revealed crucial roles of the gut microbiota and its metabolites in liver disease progression. However, the mechanism underlying their effects on liver ischemia/reperfusion (I/R) injury remain largely unknown. Here, we investigate the function of gut microbiota and its metabolites in liver I/R injury.

METHODS

C57BL/6 mice was pretreated with an antibiotic cocktail. Then, we used multi-omics detection methods including 16s rRNA sequencing, ultra-performance liquid chromatography coupled to tandem mass spectrometry (UPLC-MS/MS) to explore the changes of gut microbiota and metabolites in both feces and portal blood to reveal the mechanism of their protective effect in liver I/R injury.

RESULTS

We found that antibiotic pretreatment (ABX) could significantly reduce the severity of I/R-induced hepatic injury, and this effect could be transferred to germ-free mice by fecal microbiota transplantation (FMT), suggesting a protective role of the gut microbiota depletion. During I/R, the rates of serum α-ketoglutarate (αKG) production and glutamate reduction, downstream products of gut microbiota-derived glutamine, were more significant in the ABX mice. Then, we showed that αKG could promote alternative (M2) macrophage activation through oxidative phosphorylation, and oligomycin A could inhibit M2 macrophage polarization and reversed this protective effect.

CONCLUSIONS

These findings show that the gut microbiota and its metabolites play critical roles in hepatic I/R injury by modulating macrophage metabolic reprogramming. Potential therapies that target macrophage metabolism, including antibiotic therapies and novel immunometabolism modulators, can be exploited for the treatment of liver I/R injury.

The role of immunomodulatory metabolites in shaping the inflammatory response of macrophages

Macrophage activation has long been implicated in a myriad of human pathophysiology, particularly in the context of the dysregulated capacities of an unleashing intracellular or/and extracellular inflammatory response. A growing number of studies have functionally coupled the macrophages' inflammatory capacities with dynamic metabolic reprogramming which occurs during activation, albeit the results have been mostly interpreted through classic metabolism point of view; macrophages take advantage of the rewired metabolism as a source of energy and for biosynthetic precursors. However, a specific subset of metabolic products, namely immune-modulatory metabolites, has recently emerged as significant regulatory signals which control inflammatory responses in macrophages and the relevant extracellular milieu. In this review, we introduce recently highlighted immuno-modulatory metabolites, with the aim of understanding their physiological and pathological relevance in the macrophage inflammatory response. [BMB Reports 2022; 55(11): 519-527].

The role of immunomodulatory metabolites in shaping the inflammatory response of macrophages

Macrophage activation has long been implicated in a myriad of human pathophysiology, particularly in the context of the dysregulated capacities of an unleashing intracellular or/and extracellular inflammatory response. A growing number of studies have functionally coupled the macrophages' inflammatory capacities with dynamic metabolic reprogramming which occurs during activation, albeit the results have been mostly interpreted through classic metabolism point of view; macrophages take advantage of the rewired metabolism as a source of energy and for biosynthetic precursors. However, a specific subset of metabolic products, namely immune-modulatory metabolites, has recently emerged as significant regulatory signals which control inflammatory responses in macrophages and the relevant extracellular milieu. In this review, we introduce recently highlighted immuno-modulatory metabolites, with the aim of understanding their physiological and pathological relevance in the macrophage inflammatory response. [BMB Reports 2022; 55(11): 519-527].

Alpha-Ketoglutarate Attenuates Colitis in Mice by Increasing Lactobacillus Abundance and Regulating Stem Cell Proliferation via Wnt-Hippo Signaling

SCOPE

Inflammatory bowel disease is an inflammatory gastrointestinal disorder associated with intestinal barrier damage, cell proliferation disorder, and dysbiosis of the intestinal microbiota. It remains unknown whether alpha-ketoglutarate (α-KG) can alleviate colitis in mice.

METHODS AND RESULTS

Six-week-old male C57BL/6 mice supplemented with or without 0.5% α-KG (delivered in the form of sodium salt) are subjected to drinking water or 2.5% DSS to induce colitis. The results show that α-KG administration is attenuated the severity of colitis, as is indicated by reduced body-weight loss, colon shortening and colonic hyperplasia, and repressed proinflammatory cytokine secretion in DSS-challenged mice. Additionally, DSS-induced increases in malondialdehyde (MDA) and hydrogen peroxide (H₂ O₂ ), and decreases in glutathione (GSH) levels are attenuated by α-KG administration. Further study shows that the protective effect of α-KG is associated with restoring gut barrier integrity by enhancing the expression of tight junction proteins, increasing Lactobacillus levels, and regulating gut hyperplasia by the Wnt-Hippo signaling pathway in DSS-induced colitis.

CONCLUSION

Collectively, the data provided herein demonstrate that α-KG administration is attenuated mucosal inflammation, barrier dysfunction, and gut microflora dysbiosis. This beneficial effect is associated with increased Lactobacillus levels and regulated colon hyperplasia by the Wnt-Hippo signaling pathway.

Identification of serum metabolites enhancing inflammatory responses in COVID-19

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is characterized by a strong production of inflammatory cytokines such as TNF and IL-6, which underlie the severity of the disease. However, the molecular mechanisms responsible for such a strong immune response remains unclear. Here, utilizing targeted tandem mass spectrometry to analyze serum metabolome and lipidome in COVID-19 patients at different temporal stages, we identified that 611 metabolites (of 1,039) were significantly altered in COVID-19 patients. Among them, two metabolites, agmatine and putrescine, were prominently elevated in the serum of patients; and 2-quinolinecarboxylate was changed in a biphasic manner, elevated during early COVID-19 infection but levelled off. When tested in mouse embryonic fibroblasts (MEFs) and macrophages, these 3 metabolites were found to activate the NF-κB pathway that plays a pivotal role in governing cytokine production. Importantly, these metabolites were each able to cause strong increase of TNF and IL-6 levels when administered to wildtype mice, but not in the mice lacking NF-κB. Intriguingly, these metabolites have little effects on the activation of interferon regulatory factors (IRFs) for the production of type I interferons (IFNs) for antiviral defenses. These data suggest that circulating metabolites resulting from COVID-19 infection may act as effectors to elicit the peculiar systemic inflammatory responses, exhibiting severely strong proinflammatory cytokine production with limited induction of the interferons. Our study may provide a rationale for development of drugs to alleviate inflammation in COVID-19 patients.

Potential clinical applications of alpha‑ketoglutaric acid in diseases (Review)

As an intermediate of the tricarboxylic acid cycle, also known as 2‑oxoglutarate, α‑ketoglutaric acid (AKG) plays an important role in maintaining physiological functions and cell metabolism. AKG is involved in both energy metabolism, and carbon and nitrogen metabolism; thus, exhibiting a variety of functions. Moreover, AKG plays an important role in various systems of the body. Results of previous research indicated that AKG may act as a regulator in the progression of a variety of diseases; thus, it exhibits potential as a novel drug for the clinical treatment of age‑related diseases. The present review aimed to summarize the latest research progress and potential clinical applications of AKG and provided novel directions and scope for future research.

Disrupted Alpha-Ketoglutarate Homeostasis: Understanding Kidney Diseases from the View of Metabolism and Beyond

Alpha-ketoglutarate (AKG) is a key intermediate of various metabolic pathways including tricarboxylic acid (TCA) cycle, anabolic and catabolic reactions of amino acids, and collagen biosynthesis. Meanwhile, AKG also participates in multiple signaling pathways related to cellular redox regulation, epigenetic processes, and inflammation response. Emerging evidence has shown that kidney diseases like diabetic nephropathy and renal ischemia/reperfusion injury are associated with metabolic disorders. In consistence with metabolic role of AKG, further metabolomics study demonstrated a dysregulated AKG level in kidney diseases. Intriguingly, earlier studies during the years of 1980s and 1990s indicated that AKG may benefit wound healing and surgery recovery. Recently, interests on AKG are arising again due to its protective roles on healthy ageing, which may shed light on developing novel therapeutic strategies against age-related diseases including renal diseases. This review will summarize the physiological and pathological properties of AKG, as well as the underlying molecular mechanisms, with a special emphasis on kidney diseases.

Treatment with sodium (S)-2-hydroxyglutarate prevents liver injury in an ischemia-reperfusion model in female Wistar rats

Background

Ischemia-reperfusion (IR) injury is one of the leading causes of early graft dysfunction in liver transplantation. Techniques such as ischemic preconditioning protect the graft through the activation of the hypoxia-inducible factors (HIF), which are downregulated by the EGLN family of prolyl-4-hydroxylases, a potential biological target for the development of strategies based on pharmacological preconditioning. For that reason, this study aims to evaluate the effect of the EGLN inhibitor sodium (S)-2-hydroxyglutarate [(S)-2HG] on liver IR injury in Wistar rats.

Methods

Twenty-eight female Wistar rats were divided into the following groups: sham (SH, n = 7), non-toxicity (HGTox, n = 7, 25 mg/kg of (S)-2HG, twice per day for two days), IR (n = 7, total liver ischemia: 20 minutes, reperfusion: 60 minutes), and (S)-2HG+IR (HGIR, n = 7, 25 mg/kg of (S)-2HG, twice per day for two days, total liver ischemia as the IR group). Serum ALT, AST, LDH, ALP, glucose, and total bilirubin were assessed. The concentrations of IL-1β, IL-6, TNF, malondialdehyde, superoxide dismutase, and glutathione peroxidase were measured in liver tissue, as well as the expression of Hmox1, Vegfa, and Pdk1, determined by RT-qPCR. Sections of liver tissue were evaluated histologically, assessing the severity of necrosis, sinusoidal congestion, and cytoplasmatic vacuolization.

Results

The administration of (S)-2HG did not cause any alteration in the assessed biochemical markers compared to SH. Preconditioning with (S)-2HG significantly ameliorated IR injury in the HGIR group, decreasing the serum activities of ALT, AST, and LDH, and the tissue concentrations of IL-1β and IL-6 compared to the IR group. IR injury decreased serum glucose compared to SH. There were no differences in the other biomarkers assessed. The treatment with (S)-2HG tended to decrease the severity of hepatocyte necrosis and sinusoidal congestion compared to the IR group. The administration of (S)-2HG did not affect the expression of Hmox1 but decreased the expression of both Vegfa and Pdk1 compared to the SH group, suggesting that the HIF-1 pathway is not involved in its mechanism of hepatoprotection. In conclusion, (S)-2HG showed a hepatoprotective effect, decreasing the levels of liver injury and inflammation biomarkers, without evidence of the involvement of the HIF-1 pathway. No hepatotoxic effect was observed at the tested dose.

The Regulatory Role of α-Ketoglutarate Metabolism in Macrophages

Macrophages are multifunctional immune cells whose functions depend on polarizable phenotypes and the microenvironment. Macrophages have two phenotypes, including the M1 proinflammatory phenotype and the M2 anti-inflammatory phenotype, which play important roles in many inflammatory responses and diseases. α-Ketoglutarate is a key metabolite of the TCA cycle and can regulate the phenotype of macrophage polarization to exert anti-inflammatory effects in many inflammation-related diseases. In this review, we primarily elucidate the metabolism, regulatory mechanism, and perspectives of α-ketoglutarate on macrophages. The regulation of macrophage polarization by α-ketoglutarate may provide a promising target for the prevention and therapy of inflammatory diseases and is beneficial to animal health.

Macrophage Polarization and Liver Ischemia-Reperfusion Injury

Ischemia-reperfusion injury refers to organ damage caused by the previous insufficient supply of oxygen and nutrients and the involvement of metabolic by-products after blood flow is restored. Liver ischemia-reperfusion injury (IRI) has become a hot research in recent years, because it occurs in many clinical scenarios. After the introduction of liver transplantation and vascular control techniques in liver surgery, liver ischemia-reperfusion injury is considered to be an important factor affecting postoperative mortality and morbidity. As the largest immune organ in the human body, liver contain a lot of immune cells such as resident macrophages (Kupffer cells), dendritic cells, natural killer cells, and natural killer T cells which play a key role in ischemia-reperfusion injury. Among those, macrophage-mediated excessive inflammatory response is considered to be an important factor in liver ischemia-reperfusion injury. The prominent feature of liver injury is an increase in the number of macrophages in liver due to the infiltration of blood monocytes and differentiation into monocyte-derived macrophages. Liver macrophages can be divided into M1 macrophages which can promote inflammation progress and M2 macrophages that inhibit inflammation progress according to their different phenotypes and functions. Both of them can regulate liver aseptic inflammation, and play an important role in triggering, maintaining, and improving liver ischemia-reperfusion injury. This review summarizes studies of macrophage polarization on liver ischemia-reperfusion injury in recent years, to provide potential ideas for translation application in future clinical management.

Dimethyl-2-oxoglutarate improves redox balance and mitochondrial function in muscle pericytes of individuals with diabetes mellitus

AIMS/HYPOTHESIS

Treatment of vascular complications of diabetes remains inadequate. We reported that muscle pericytes (MPs) from limb muscles of vascular patients with diabetes mellitus display elevated levels of oxidative stress causing a dysfunctional phenotype. Here, we investigated whether treatment with dimethyl-2-oxoglutarate (DM-2OG), a tricarboxylic acid cycle metabolite with antioxidant properties, can restore a healthy metabolic and functional phenotype.

METHODS

MPs were isolated from limb muscles of diabetes patients with vascular disease (D-MPs) and from non-diabetic control participants (ND-MPs). Metabolic status was assessed in untreated and DM-2OG-treated (1 mmol/l) cells using an extracellular flux analyser and anion-exchange chromatography-mass spectrometry (IC-MS/MS). Redox status was measured using commercial kits and IC-MS/MS, with antioxidant and metabolic enzyme expression assessed by quantitative RT-PCR and western blotting. Myogenic differentiation and proliferation and pericyte-endothelial interaction were assessed as functional readouts.

RESULTS

D-MPs showed mitochondrial dysfunction, suppressed glycolytic activity and reduced reactive oxygen species-buffering capacity, but no suppression of antioxidant systems when compared with ND-MP controls. DM-2OG supplementation improved redox balance and mitochondrial function, without affecting glycolysis or antioxidant systems. Nonetheless, this was not enough for treated D-MPs to regain the level of proliferation and myogenic differentiation of ND-MPs. Interestingly, DM-2OG exerted a positive effect on pericyte-endothelial cell interaction in the co-culture angiogenesis assay, independent of the diabetic status.

CONCLUSIONS/INTERPRETATION

These novel findings support the concept of using DM-2OG supplementation to improve pericyte redox balance and mitochondrial function, while concurrently allowing for enhanced pericyte-endothelial crosstalk. Such effects may help to prevent or slow down vasculopathy in skeletal muscles of people with diabetes. Graphical abstract.

IL-4 Alleviates Ischaemia-Reperfusion Injury by Inducing Kupffer Cells M2 Polarization via STAT6-JMJD3 Pathway after Rat Liver Transplantation

Background

Liver ischaemia-reperfusion injury (IRI) remains a problem in liver transplantation. Interleukin-4 (IL-4) has been found to reduce liver IRI, but the exact mechanism remains unclear.

Methods

Donor livers were infused with recombinant IL-4 or normal saline during cold storage, and the hepatocellular apoptosis and the inflammatory response were detected. The effect of IL-4 treatment on Kupffer cells (KCs) polarization and expression of the STAT6-JMJD3 pathway was evaluated in vivo and in vitro. KCs in donor livers were depleted by clodronate liposome treatment or JMJD3 was inhibited by GSK-J4 before liver transplantation to determine whether the protective effect of IL-4 treatment was dependent on KCs.

Results

IL-4 treatment decreased sALT and sAST levels and alleviated hepatocellular apoptosis and inflammation at 6 h after liver transplantation. IL-4 treatment induced KCs alternatively activated (M2) polarization in vitro. KCs in donor livers were depleted by clodronate liposome treatment or JMJD3 was inhibited by GSK-J4 before liver transplantation to determine whether the protective effect of IL-4 treatment was dependent on KCs. in vivo and in vitro. KCs in donor livers were depleted by clodronate liposome treatment or JMJD3 was inhibited by GSK-J4 before liver transplantation to determine whether the protective effect of IL-4 treatment was dependent on KCs.

Conclusions

IL-4 treatment-induced KCs M2 polarization was dependent on the STAT6-JMJD3 pathway and protected liver grafts from IRI after liver transplantation.