Peroxiredoxin 6 attenuates ischemia‑ and hypoxia‑induced liver damage of brain‑dead donors

Serum metabolomics of hyperbilirubinemia and hyperuricemia in the Tibetan plateau has unique characteristics

Few studies have provided data on the metabolomics characteristics of metabolic diseases such as hyperuricemia and hyperbilirubinemia in the Tibetan plateau. In the current study, we sought to investigate the serum metabolomics characteristics of hyperbilirubinemia and hyperuricemia in the Tibetan plateau, with the aim to provide a basis for further research on their pathogenesis, prevention, and treatment. The study participants were born in low-altitude areas below 1000 m and had no prior experience living in a high-altitude area before entering Golmud, Tibet (average elevation: 3000 m) and Yushu, Qinghai (average elevation: 4200 m). Thirty-four participants with hyperbilirubinemia (18 in Golmud and 16 in Yushu), 24 participants with hyperuricemia, and 22 healthy controls were enrolled. The serum samples of subjects were separated and then sent to a local tertiary hospital for biochemical examination. Serum widely targeted technology, based on the ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) platform, was used to detect serum metabolites and differential metabolites. Compared to the healthy controls, hyperbilirubinemia patients from Golmud showed 19 differential metabolites, hyperbilirubinemia patients from Yushu showed 12 differential metabolites, and hyperuricemia patients from Yushu showed 23 differential metabolites. Compared to the hyperbilirubinemia patients from Golmud that is at a low altitude, the Yushu groups had 33 different metabolites. Differential metabolites are primarily classified into amino acids and their derivatives, nucleotides and their derivatives, organic acids and their derivatives, and lipids/fatty acids. These are related to metabolic pathways such as caffeine metabolism, arachidonic acid metabolism, and tyrosine metabolism. Hyperbilirubinemia and hyperuricemia in the Tibetan plateau have unique serum metabolomics characteristics. Glycine derivatives and arachidonic acid and its derivatives were associated with plateau hyperbilirubinemia, and vanillic acid and pentadecafluorooctanoic acid were associated with plateau hyperuricemia.

Effects of Three-Month Administration of High-Saturated Fat Diet and High-Polyunsaturated Fat Diets with Different Linoleic Acid (LA, C18:2n-6) to α-Linolenic Acid (ALA, C18:3n-3) Ratio on the Mouse Liver Proteome

The aim of the study was to evaluate the effect of different types of high-fat diets (HFDs) on the proteomic profile of mouse liver. The analysis included four dietary groups of mice fed a standard diet (STD group), a high-fat diet rich in SFAs (SFA group), and high-fat diets dominated by PUFAs with linoleic acid (LA, C18:2n-6) to α-linolenic acid (ALA, C18:3n-3) ratios of 14:1 (14:1 group) and 5:1 (5:1 group). After three months of diets, liver proteins were resolved by two-dimensional gel electrophoresis (2DE) using 17 cm non-linear 3-10 pH gradient strips. Protein spots with different expression were identified by MALDI-TOF/TOF. The expression of 13 liver proteins was changed in the SFA group compared to the STD group (↓: ALB, APOA1, IVD, MAT1A, OAT and PHB; ↑: ALDH1L1, UniProtKB-Q91V76, GALK1, GPD1, HMGCS2, KHK and TKFC). Eleven proteins with altered expression were recorded in the 14:1 group compared to the SFA group (↓: ARG1, FTL1, GPD1, HGD, HMGCS2 and MAT1A; ↑: APOA1, CA3, GLO1, HDHD3 and IVD). The expression of 11 proteins was altered in the 5:1 group compared to the SFA group (↓: ATP5F1B, FTL1, GALK1, HGD, HSPA9, HSPD1, PC and TKFC; ↑: ACAT2, CA3 and GSTP1). High-PUFA diets significantly affected the expression of proteins involved in, e.g., carbohydrate metabolism, and had varying effects on plasma total cholesterol and glucose levels. The outcomes of this study revealed crucial liver proteins affected by different high-fat diets.

Effects of chitinase-3-like protein 1 on brain death-induced hepatocyte apoptosis via PAR2-JNK-caspase-3

Hepatocyte apoptosis is a crucial factor affecting liver quality in brain-dead donors. The identification of key molecular proteins involved in brain-death (BD)-induced hepatocyte apoptosis may help determine an effective method for improving the quality of livers from brain-dead donors. In this study, we used in vivo and in vitro models to investigate the role of chitinase-3-like protein 1 (CHI3L1) in promoting liver cell apoptosis after BD. Chitin was used to inhibit CHI3L1 in a rat model of BD. Macrophage polarization of THP-1 cells and hypoxia/reoxygenation (H/R) of LO-2 cells were used to mimic BD-induced cell stress in liver. We found that CHI3L1 played a vital role in promoting liver cell apoptosis. Six hours after BD, CHI3L1 expression was significantly upregulated in liver macrophages and was associated with BD-induced M1 polarization of these cells. In liver cells cultured under H/R conditions, recombinant CHI3L1 activated the protease-activated receptor 2 (PAR2)/c-June N-terminal kinase (JNK) apoptotic pathway and aggravated apoptosis. Compared with the control group, chitin particles inhibited the expression of CHI3L1 in the liver of brain dead rats, thereby reducing activation of the hepatocyte surface receptor, PAR2, and its downstream JNK/caspase-3 signaling pathway, ultimately reducing hepatocyte apoptosis. In conclusion, our results indicate that CHI3L1 relies on a PAR2/JNK-mediated mechanism to promote BD-induced hepatocyte apoptosis.

Lack of the peroxiredoxin 6 gene causes impaired spatial memory and abnormal synaptic plasticity

Peroxiredoxin 6 (PRDX6) is expressed dominantly in the astrocytes and exerts either neuroprotective or neurotoxic effects in the brain. Although PRDX6 can modulate several signaling cascades involving cognitive functions, its physiological role in spatial memory has not been investigated yet. This study aims to explore the function of the Prdx6 gene in spatial memory formation and synaptic plasticity. We first tested Prdx6-/- mice on a Morris water maze task and found that their memory performance was defective, along with reduced long-term potentiation (LTP) in CA3-CA1 hippocampal synapses recorded from hippocampal sections of home-caged mice. Surprisingly, after the probe test, these knockout mice exhibited elevated hippocampal LTP, higher phosphorylated ERK1/2 level, and decreased reactive astrocyte markers. We further reduced ERK1/2 phosphorylation by administering MEK inhibitor, U0126, into Prdx6-/- mice before the probe test, which reversed their spatial memory deficit. This study is the first one to report the role of PRDX6 in spatial memory and synaptic plasticity. Our results revealed that PRDX6 is necessary for maintaining spatial memory by modulating ERK1/2 phosphorylation and astrocyte activation.

Mild hypothermia pretreatment extenuates liver ischemia-reperfusion injury through Rab7-mediated autophagosomes-lysosomes fusion

Liver ischemia-reperfusion (IR) injury is an unavoidable pathological process in transplantation, closely related to poor prognosis. To date, there has been no clear therapeutic measure. We previously reported that mild hypothermia (MH), a widely used therapy, can exert significant protective effect against liver IR injury. Among the multiple mechanisms underlying the therapeutic effect of MH, autophagy flux drew our special attention. In this study, we evaluated the role of autophagy flux in IR injury and thereby explored the relationship between MH and autophagy flux in IR injury. We developed in vivo and in vitro models for hepatic IR injury. By autophagy flux assay with Western blotting and immunofluorescence, we found that MH restricts heavy accumulation of autophagosomes (APs) during IR injury. Activation and blocking of the autophagy flux unraveled that accumulation of APs further aggravated IR injury. Further, MH reduces APs accumulation to restore autophagy flux by regulating the fusion of APs and lysosomes. Besides, MH upregulated the level of Rab7 protein expression that was seriously impaired during IR injury. Inhibition of Rab7 expression increased apoptosis of liver cells and reduced the degree of overlap between APs and lysosomes. The results were reversed upon activation of Rab7. In conclusion, MH can alleviate liver IR injury by regulating the Rab7-mediated APs-lysosomes fusion that reduces APs accumulation. This can provide a theoretical basis for the further application of MH in related clinical diseases.

Fecal Microbiota Transplantation Is a Promising Method to Restore Gut Microbiota Dysbiosis and Relieve Neurological Deficits after Traumatic Brain Injury

BACKGROUND

Traumatic brain injury (TBI) can induce persistent fluctuation in the gut microbiota makeup and abundance. The present study is aimed at determining whether fecal microbiota transplantation (FMT) can rescue microbiota changes and ameliorate neurological deficits after TBI in rats.

METHODS

A controlled cortical impact (CCI) model was used to simulate TBI in male Sprague-Dawley rats, and FMT was performed for 7 consecutive days. 16S ribosomal RNA (rRNA) sequencing of fecal samples was performed to analyze the effects of FMT on gut microbiota. Modified neurological severity score and Morris water maze were used to evaluate neurobehavioral functions. Metabolomics was used to screen differential metabolites from the rat serum and ipsilateral brains. The oxidative stress indices were measured in the brain.

RESULTS

TBI induced significance changes in the gut microbiome, including the alpha- and beta-bacterial diversity, as well as the microbiome composition at 8 days after TBI. On the other hand, FMT could rescue these changes and relieve neurological deficits after TBI. Metabolomics results showed that the level of trimethylamine (TMA) in feces and the level of trimethylamine N-oxide (TMAO) in the ipsilateral brain and serum was increased after TBI, while FMT decreased TMA levels in the feces, and TMAO levels in the ipsilateral brain and serum. Antioxidant enzyme methionine sulfoxide reductase A (MsrA) in the ipsilateral hippocampus was decreased after TBI but increased after FMT. In addition, FMT elevated SOD and CAT activities and GSH/GSSG ratio and diminished ROS, GSSG, and MDA levels in the ipsilateral hippocampus after TBI.

CONCLUSIONS

FMT can restore gut microbiota dysbiosis and relieve neurological deficits possibly through the TMA-TMAO-MsrA signaling pathway after TBI.

PP2Ac upregulates PI3K-Akt signaling and induces hepatocyte apoptosis in liver donor after brain death

Multiple research groups have demonstrated that the outcome of patients receiving liver grafts from brain death donors (DBD) is poorer when compared with patients receiving grafts from living donors. This might be due to an increased hepatocyte apoptosis induced after brain death (BD). In this work, we found that the activity of PP2A-Akt pathway is significantly increased in clinical donor ex vivo hepatocytes after BD by iTRAQ protein quantification analysis. The same results were confirmed in animal models. A time-dependent promotion of apoptosis was also found in DBD rabbit liver, as demonstrated by the increased levels of cleaved Caspase 3 and the decreased of Bcl-2. To further investigate the roles of PP2A and Akt in regulating apoptosis of hepatocytes after BD, we cultivated human liver cell line L02 with serum deprivation and hypoxia, to simulate the ischemic and hypoxic conditions of hepatocytes in DBD. Increased apoptosis and decreased viability were observed during the time in this model. Meanwhile PP2A activity and Akt activity were respectively increased and decreased. Notably, the proportion of Akt phosphorylation at Ser473 decreased, while other known targets of PP2A (p38, JNK and ERK) were not affected in terms of protein levels or phosphorylation. These results suggested that PP2A is involved in apoptotic induction of hepatocytes after brain death by specific suppression of Akt. This discovery was further confirmed with pharmaceutical and genetic methods. Our work implied potential targets for reducing liver cell apoptosis and improving organ donor quality after BD.

Peroxiredoxin 6 Is a Key Antioxidant Enzyme in Modulating the Link between Glycemic and Lipogenic Metabolism

Insulin action and often glucose-stimulated insulin secretion are reduced in obesity. In addition, the excessive intake of lipids increases oxidative stress leading to overt type 2 diabetes mellitus (T2DM). Among the antioxidative defense systems, peroxiredoxin 6 (PRDX6) is able to reduce H₂O₂ and short chain and phospholipid hydroperoxides. Increasing evidences suggest that PRDX6 is involved in the pathogenesis of atherosclerosis and T2DM, but its role in the etiopathology of obesity and its complications is still not known. Therefore, in the present study, we sought to investigate this association by using PRDX6 knockout mice (PRDX6^−/−). Metabolic parameters, like carbon dioxide (VCO₂) production, oxygen consumption (VO₂), and the respiratory exchange ratio (RER), were determined using metabolic cages. Intraperitoneal insulin and glucose tolerance tests were performed to evaluate insulin sensitivity and glucose tolerance, respectively. Liver and pancreas histochemical analyses were also evaluated. The expression of enzymes involved in lipid and glucose metabolism was analyzed by real-time PCR. Following 24 weeks of high-fat-diet (HFD), PRDX6^−/− mice showed weight gain and higher food and drink intake compared to controls. VO₂ consumption and VCO₂ production decreased in PRDX6^−/− mice, while the RER was lower than 0.7 indicating a prevalent lipid metabolism. PRDX6^−/− mice fed with HFD showed a further deterioration on insulin sensitivity and glucose-stimulated insulin secretion. Furthermore, in PRDX6^−/− mice, insulin did not suppress adipose tissue lipolysis with consequent hepatic lipid overload and higher serum levels of ALT, cholesterol, and triglycerides. Interestingly, in PRDX6^−/− mice, liver and adipose tissue were associated with proinflammatory gene upregulation. Finally, PRDX6^−/− mice showed a higher rate of nonalcoholic steatohepatitis (NASH) compared to control. Our results suggest that PRDX6 may have a functional and protective role in the development of obesity-related metabolic disorders such as liver diseases and T2DM and may be considered a potential therapeutic target against these illnesses.

Peroxiredoxin6 in Endothelial Signaling

Peroxiredoxins (Prdx) are a ubiquitous family of highly conserved antioxidant enzymes with a cysteine residue that participate in the reduction of peroxides. This family comprises members Prdx1–6, of which Peroxiredoxin 6 (Prdx6) is unique in that it is multifunctional with the ability to neutralize peroxides (peroxidase activity) and to produce reactive oxygen species (ROS) via its phospholipase (PLA₂) activity that drives assembly of NADPH oxidase (NOX2). From the crystal structure, a C47 residue is responsible for peroxidase activity while a catalytic triad (S32, H26, and D140) has been identified as the active site for its PLA₂ activity. This paradox of being an antioxidant as well as an oxidant generator implies that Prdx6 is a regulator of cellular redox equilibrium (graphical abstract). It also indicates that a fine-tuned regulation of Prdx6 expression and activity is crucial to cellular homeostasis. This is specifically important in the endothelium, where ROS production and signaling are critical players in inflammation, injury, and repair, that collectively signal the onset of vascular diseases. Here we review the role of Prdx6 as a regulator of redox signaling, specifically in the endothelium and in mediating various pathologies.

Associations of Oxidative Stress and Postoperative Outcome in Liver Surgery with an Outlook to Future Potential Therapeutic Options

Several types of surgical procedures have shown to elicit an inflammatory stress response, leading to substantial cytokine production and formation of oxygen-based or nitrogen-based free radicals. Chronic liver diseases including cancers are almost always characterized by increased oxidative stress, in which hepatic surgery is likely to potentiate at least in the short term and hereby furthermore impair the hepatic redox state. During liver resection, intermittent inflow occlusion is commonly applied to prevent excessive blood loss but resulting ischemia and reperfusion of the liver have been linked to increased oxidative stress, leading to impairment of cell functions and subsequent cell death. In the field of liver transplantation, ischemia/reperfusion injury has extensively been investigated in the last decades and has recently been in the scientific focus again due to increased use of marginal donor organs and new machine perfusion concepts. Therefore, given the intriguing role of oxidative stress in the pathogenesis of numerous diseases and in the perioperative setting, the interest for a therapeutic antioxidative agent has been present for several years. This review is aimed at giving an introduction to oxidative stress in surgical procedures in general and then examines the role of oxidative stress in liver surgery in particular, discussing both transplantation and resection. Results from studies in the animal and human settings are included. Finally, potential therapeutic agents that might be beneficial in reducing the burden of oxidative stress in hepatic diseases and during surgery are presented. While there is compelling evidence from animal models and a limited number of clinical studies showing that oxidative stress plays a major role in both liver resection and transplantation and several recent studies have suggested a potential for antioxidative treatment in chronic liver disease (e.g., steatosis), the search for effective antioxidants in the field of liver surgery is still ongoing.

Peroxiredoxin6, a Multitask Antioxidant Enzyme Involved in the Pathophysiology of Chronic Noncommunicable Diseases

SIGNIFICANCE

Chronic noncommunicable diseases (NCDs) are the leading causes of disability and death worldwide. NCDs mainly comprise diabetes mellitus, cardiovascular diseases, chronic obstructive pulmonary disease, cancer, and neurological degenerative diseases, which kill more than 80% of population, especially the elderly, worldwide. Recent Advances: Several recent theories established NCDs as multifactorial diseases, where a combination of genetic, epigenetic, and environmental factors contributes to their pathogenesis. Nevertheless, recent findings suggest that the common factor linking all these pathologies is an increase in oxidative stress and the age-related loss of the antioxidant mechanisms of defense against it. Impairment in mitochondrial homeostasis with consequent deregulation in oxidative stress balance has also been suggested.

CRITICAL ISSUES

Therefore, antioxidant proteins deserve particular attention for their potential role against NCDs. In particular, peroxiredoxin(Prdx)6 is a unique antioxidant enzyme, belonging to the Prdx family, with double properties, peroxidase and phospholipase activities. Through these activities, Prdx6 has been shown to be a powerful antioxidant enzyme, implicated in the pathogenesis of different NCDs. Recently, we described a phenotype of diabetes mellitus in Prdx6 knockout mice, suggesting a pivotal role of Prdx6 in the pathogenesis of cardiometabolic diseases.

FUTURE DIRECTIONS

Increasing awareness on the role of antioxidant defenses in the pathogenesis of NCDs may open novel therapeutic approaches to reduce the burden of this pandemic phenomenon. However, knowledge of the role of Prdx6 in NCD prevention and pathogenesis is still not clarified.

The Role of Peroxiredoxin 6 in Cell Signaling

Peroxiredoxin 6 (Prdx6, 1-cys peroxiredoxin) is a unique member of the peroxiredoxin family that, in contrast to other mammalian peroxiredoxins, lacks a resolving cysteine and uses glutathione and π glutathione S-transferase to complete its catalytic cycle. Prdx6 is also the only peroxiredoxin capable of reducing phospholipid hydroperoxides through its glutathione peroxidase (Gpx) activity. In addition to its peroxidase activity, Prdx6 expresses acidic calcium-independent phospholipase A₂ (aiPLA₂) and lysophosphatidylcholine acyl transferase (LPCAT) activities in separate catalytic sites. Prdx6 plays crucial roles in lung phospholipid metabolism, lipid peroxidation repair, and inflammatory signaling. Here, we review how the distinct activities of Prdx6 are regulated during physiological and pathological conditions, in addition to the role of Prdx6 in cellular signaling and disease.

Label-Free Quantitative Proteomics in a Methylmalonyl-CoA Mutase-Silenced Neuroblastoma Cell Line

Methylmalonic acidemias (MMAs) are inborn errors of metabolism due to the deficient activity of methylmalonyl-CoA mutase (MUT). MUT catalyzes the formation of succinyl-CoA from methylmalonyl-CoA, produced from propionyl-CoA catabolism and derived from odd chain fatty acids β-oxidation, cholesterol, and branched-chain amino acids degradation. Increased methylmalonyl-CoA levels allow for the presymptomatic diagnosis of the disease, even though no approved therapies exist. MMA patients show hyperammonemia, ketoacidosis, lethargy, respiratory distress, cognitive impairment, and hepatomegaly. The long-term consequences concern neurologic damage and terminal kidney failure, with little chance of survival. The cellular pathways affected by MUT deficiency were investigated using a quantitative proteomics approach on a cellular model of MUT knockdown. Currently, a consistent reduction of the MUT protein expression was obtained in the neuroblastoma cell line (SH-SY5Y) by using small-interfering RNA (siRNA) directed against an MUT transcript (MUT siRNA). The MUT absence did not affect the cell viability and apoptotic process in SH-SY5Y. In the present study, we evaluate and quantify the alterations in the protein expression profile as a consequence of MUT-silencing by a mass spectrometry-based label-free quantitative analysis, using two different quantitative strategies. Both quantitative methods allowed us to observe that the expression of the proteins involved in mitochondrial oxido-reductive homeostasis balance was affected by MUT deficiency. The alterated functional mitochondrial activity was observed in siRNA_MUT cells cultured with a propionate-supplemented medium. Finally, alterations in the levels of proteins involved in the metabolic pathways, like carbohydrate metabolism and lipid metabolism, were found.

Epigallocatechin-3-gallate protects against hepatic ischaemia-reperfusion injury by reducing oxidative stress and apoptotic cell death

Objective

To investigate the protective effects of epigallocatechin-3-gallate (EGCG), a major polyphenol source in green tea, against hepatic ischaemia–reperfusion injury in mice.

Methods

The partial hepatic ischaemia–reperfusion injury model was created by employing the hanging-weight method in C57BL/6 male mice. EGCG (50 mg/kg) was administered via an intraperitoneal injection 45 min before performing the reperfusion. A number of markers of inflammation, oxidative stress, apoptosis and liver injury were measured after the ischaemia–reperfusion injury had been induced.

Results

The treatment groups were: sham-operated (Sham, n = 10), hepatic ischaemia–reperfusion injury (IR, n = 10), and EGCG with ischaemia–reperfusion injury (EGCG-treated IR, n = 10). Hepatic ischaemia–reperfusion injury increased the levels of biochemical and histological markers of liver injury, increased the levels of malondialdehyde, reduced the glutathione/oxidized glutathione ratio, increased the levels of oxidative stress and lipid peroxidation markers, decreased B-cell lymphoma 2 levels, and increased the levels of Bax, cytochrome c, cleaved caspase-3, and cleaved caspase-9. Pretreatment with EGCG ameliorated all of these changes.

Conclusion

The antioxidant and antiapoptotic effects of EGCG protected against hepatic ischaemia–reperfusion injury in mice.