Metabolomics analysis elucidates unique influences on purine / pyrimidine metabolism by xanthine oxidoreductase inhibitors in a rat model of renal ischemia-reperfusion injury

Xanthine oxidoreductase inhibition ameliorates high glucose-induced glomerular endothelial injury by activating AMPK through the purine salvage pathway

Xanthine oxidoreductase (XOR) contributes to reactive oxygen species production. We investigated the cytoprotective mechanisms of XOR inhibition against high glucose (HG)-induced glomerular endothelial injury, which involves activation of the AMP-activated protein kinase (AMPK). Human glomerular endothelial cells (GECs) exposed to HG were subjected to febuxostat treatment for 48 h and the expressions of AMPK and its associated signaling pathways were evaluated. HG-treated GECs were increased xanthine oxidase/xanthine dehydrogenase levels and decreased intracellular AMP/ATP ratio, and these effects were reversed by febuxostat treatment. Febuxostat enhanced the phosphorylation of AMPK, the activation of peroxisome proliferator-activated receptor (PPAR)-gamma coactivator (PGC)-1α and PPAR-α and suppressed the phosphorylation of forkhead box O (FoxO)3a in HG-treated GECs. Febuxostat also decreased nicotinamide adenine dinucleotide phosphate oxidase (Nox)1, Nox2, and Nox4 expressions; enhanced superoxide dismutase activity; and decreased malondialdehyde levels in HG-treated GECs. The knockdown of AMPK inhibited PGC-1α-FoxO3a signaling and negated the antioxidant effects of febuxostat in HG-treated GECs. Despite febuxostat administration, the knockdown of hypoxanthine phosphoribosyl transferase 1 (HPRT1) also inhibited AMPK-PGC-1α-FoxO3a in HG-treated GECs. XOR inhibition alleviates oxidative stress by activating AMPK-PGC-1α-FoxO3a signaling through the HPRT1-dependent purine salvage pathway in GECs exposed to HG conditions.

Possible Use of Non-purine Selective Xanthine Oxidoreductase Inhibitors for Prevention of Exercise-induced Acute Kidney Injury Associated with Renal Hypouricemia

Exercise-induced acute kidney injury (EIAKI) is frequently complicated with renal hypouricemia (RHUC). In patients with RHUC, limiting anaerobic exercise can prevent EIAKI. However, it is challenging to reduce exercise intensity in athletes. We herein report a 16-year-old Japanese football player with familial RHUC with compound heterozygous mutations in urate transporter 1 (URAT1) who presented with recurrent EIAKI. As prophylaxis (hydration during exercise) could not prevent EIAKI, febuxostat was initiated. EIAKI was not observed for 16 months despite exercising intensively. Hence, non-purine-selective xanthine oxidoreductase inhibitors may decrease the incidence of EIAKI in athletes with RHUC.

SGLT2 inhibitors improve kidney function and morphology by regulating renal metabolic reprogramming in mice with diabetic kidney disease

Diabetic kidney disease (DKD) is the leading cause of end-stage renal disease (ESRD) worldwide. SGLT2 inhibitors are clinically effective in halting DKD progression. However, the underlying mechanisms remain unclear. The serum and kidneys of mice with DKD were analyzed using liquid chromatography with tandem mass spectrometry (LC–MS/MS)-based metabolomic and proteomic analyses. Three groups were established: placebo-treated littermate db/m mice, placebo-treated db/db mice and EMPA-treated db/db mice. Empagliflozin (EMPA) and placebo (10 mg/kg/d) were administered for 12 weeks. EMPA treatment decreased Cys-C and urinary albumin excretion compared with placebo by 78.60% and 57.12%, respectively (p < 0.001 in all cases). Renal glomerular area, interstitial fibrosis and glomerulosclerosis were decreased by 16.47%, 68.50% and 62.82%, respectively (p < 0.05 in all cases). Multi-omic analysis revealed that EMPA treatment altered the protein and metabolic profiles in the db/db group, including 32 renal proteins, 51 serum proteins, 94 renal metabolites and 37 serum metabolites. Five EMPA-related metabolic pathways were identified by integrating proteomic and metabolomic analyses, which are involved in renal purine metabolism; pyrimidine metabolism; tryptophan metabolism; nicotinate and nicotinamide metabolism, and glycine, serine and threonine metabolism in serum. In conclusion, this study demonstrated metabolic reprogramming in mice with DKD. EMPA treatment improved kidney function and morphology by regulating metabolic reprogramming, including regulation of renal reductive stress, alleviation of mitochondrial dysfunction and reduction in renal oxidative stress reaction.

Chronic kidney disease: Which role for xanthine oxidoreductase activity and products?

The present review explores the role of xanthine oxidoreductase (XOR) in the development and progression of chronic kidney disease (CKD). Human XOR is a multi-level regulated enzyme, which has many physiological functions, but that is also implicated in several pathological processes. The main XOR activities are the purine catabolism, which generates uric acid, and the regulation of cell redox state and cell signaling, through the production of reactive oxygen species. XOR dysregulation may lead to hyperuricemia and oxidative stress, which could have a pathogenic role in the initial phases of CKD, by promoting cell injury, hypertension, chronic inflammation and metabolic derangements. Hypertension is common in CKD patients and many mechanisms inducing it (upregulation of renin-angiotensin-aldosterone system, endothelial dysfunction and atherosclerosis) may be influenced by XOR products. High XOR activity and hyperuricemia are also risk factors for obesity, insulin resistance, type 2 diabetes and metabolic syndrome that are frequent CKD causes. Moreover, CKD is common in patients with gout, which is characterized by hyperuricemia, and in patients with cardiovascular diseases, which are associated with hypertension, endothelial dysfunction and atherosclerosis. Although hyperuricemia is undoubtedly related to CKD, controversial findings have been hitherto reported in patients treated with urate-lowering therapies.

Analysis of Purine Metabolism to Elucidate the Pathogenesis of Acute Kidney Injury in Renal Hypouricemia

Renal hypouricemia is a disease caused by the dysfunction of renal urate transporters. This disease is known to cause exercise-induced acute kidney injury, but its mechanism has not yet been established. To analyze the mechanism by which hypouricemia causes renal failure, we conducted a semi-ischemic forearm exercise stress test to mimic exercise conditions in five healthy subjects, six patients with renal hypouricemia, and one patient with xanthinuria and analyzed the changes in purine metabolites. The results showed that the subjects with renal hypouricemia had significantly lower blood hypoxanthine levels and increased urinary hypoxanthine excretion after exercise than healthy subjects. Oxidative stress markers did not differ between healthy subjects and hypouricemic subjects before and after exercise, and no effect of uric acid as a radical scavenger was observed. As hypoxanthine is a precursor for adenosine triphosphate (ATP) production via the salvage pathway, loss of hypoxanthine after exercise in patients with renal hypouricemia may cause ATP loss in the renal tubules and consequent tissue damage.

Allopurinol Lowers Serum Urate but Does Not Reduce Oxidative Stress in CKD

Xanthine oxidase (XO) contributes to oxidative stress and vascular disease. Hyperuricemia and gout are common in patients with chronic kidney disease (CKD), a population at increased risk of vascular disease. We evaluated effects of allopurinol on serum XO activity and metabolome of CKD patients who had participated in a randomized double-blind clinical trial of allopurinol vs. placebo. XO activity was measured in participants' serum. XO expression in venous endothelial cells was evaluated via immunofluorescence. Gas chromatography mass spectrometry (GC/MS) was utilized for metabolomics analysis. We found that in patients with stage 3 CKD and hyperuricemia, allopurinol lowered serum urate while increasing serum xanthine levels. Allopurinol, however, did not significantly suppress measured serum XO activity. Of note, baseline serum XO activity was low. Additionally, neither baseline serum XO activity nor XO protein expression were associated with measures of vascular dysfunction or with systemic or endothelial biomarkers of oxidative stress. Allopurinol affected several pathways, including pentose phosphate, pyrimidine, and tyrosine metabolism. Our findings suggest that circulating XO does not contribute to vascular disease in CKD patients. In addition to inhibition of XO activity, allopurinol was observed to impact other pathways; the implications of which require further study.

High-Throughput mRNA Sequencing Reveals Potential Therapeutic Targets of Febuxostat in Secondary Injury After Intracerebral Hemorrhage

Febuxostat is a urate-lowering medication for the treatment of patients with gout. This study was performed to elucidate the effects and underlying mechanisms of febuxostat on neuronal injury induced by intracerebral hemorrhage (ICH) in mice. The results showed that the administration of febuxostat improved neurological severity scores and blood–brain barrier (BBB) permeability. Moreover, febuxostat attenuated neuronal cell death and cytokine levels compared with the ICH group. Next, we conducted a transcriptome analysis of the neuroprotective effects of febuxostat. The overlapping significant differentially expressed genes (DEGs) were identified. Gene ontology (GO) analysis revealed that the overlapping significant DEGs were most enriched in five items. The intersecting DEGs of the aforementioned five pathways were Wisp1, Wnt7b, Frzb, and Pitx2. In addition, GO terms and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways revealed that DEGs were mainly involved in the wnt signaling pathway. Furthermore, the expression of Wisp1 and Wnt7b in the perihematomal region at 72 h post-ICH was observed. The results showed that both Wisp1 and Wnt7b were increased in the ICH group and were decreased by the administration of febuxostat. Taken together, the study showed that febuxostat protected against secondary brain injury after ICH and the Wnt7b-Wisp1 pathway was closely related to neuroprotective effects.

Hypoxanthine Reduces Radiation Damage in Vascular Endothelial Cells and Mouse Skin by Enhancing ATP Production via the Salvage Pathway

An effective method that can protect radiation-damaged tissues from apoptosis and promote tissue repair has not been reported to date. Hypoxanthine (Hx) is an intermediate metabolite in the purine degradation system that serves as a substrate for ATP synthesis via the salvage pathway. In this study, we focused on the transient decrease in intracellular ATP concentration after radiation exposure and examined the protective effect of Hx against radiation-induced tissue damage. Human umbilical vein endothelial cells were X irradiated, and the cell viability and incidence of apoptosis and DNA double-strand breaks (DSBs) were evaluated at different Hx concentrations. We found that in the presence of 2-100 μM Hx, the percentages of DSBs and apoptotic cells after 2, 6 and 10 Gy dose of radiation significantly decreased, whereas cell viability increased in a concentration-dependent manner. Moreover, the addition of Hx increased the levels of AMP, ADP, and ATP in the cells at 2 h postirradiation, suggesting that Hx was used for adenine nucleotide synthesis through the salvage pathway. Administration of a xanthine oxidoreductase inhibitor to a mouse model of radiation dermatitis resulted in increased blood Hx levels that inhibited severe dermatitis and accelerated recovery. In conclusion, the findings provide evidence that increasing the levels of Hx to replenish ATP could be an effective strategy to reduce radiation-induced tissue damage and elucidating the detailed mechanisms underlying the protective effects of Hx could help develop new protective strategies against radiation.

Preclinical models versus clinical renal ischemia reperfusion injury: A systematic review based on metabolic signatures

Despite decennia of research and numerous successful interventions in the preclinical setting, renal ischemia reperfusion (IR) injury remains a major problem in clinical practice, pointing toward a translational gap. Recently, two clinical studies on renal IR injury (manifested either as acute kidney injury or as delayed graft function) identified metabolic derailment as a key driver of renal IR injury. It was reasoned that these unambiguous metabolic findings enable direct alignment of clinical with preclinical data, thereby providing the opportunity to elaborate potential translational hurdles between preclinical research and the clinical context. A systematic review of studies that reported metabolic data in the context of renal IR was performed according to the PRISMA guidelines. The search (December 2020) identified 35 heterogeneous preclinical studies. The applied methodologies were compared, and metabolic outcomes were semi-quantified and aligned with the clinical data. This review identifies profound methodological challenges, such as the definition of IR injury, the follow-up time, and sampling techniques, as well as shortcomings in the reported metabolic information. In light of these findings, recommendations are provided in order to improve the translatability of preclinical models of renal IR injury.

Xanthine Oxidoreductase Inhibitors Suppress the Onset of Exercise-Induced AKI in High HPRT Activity Urat1-Uox Double Knockout Mice

BACKGROUND

Hereditary renal hypouricemia type 1 (RHUC1) is caused by URAT1/SLC22A12 dysfunction, resulting in urolithiasis and exercise-induced AKI (EIAKI). However, because there is no useful experimental RHUC1 animal model, the precise pathophysiologic mechanisms underlying EIAKI have yet to be elucidated. We established a high HPRT activity Urat1-Uox double knockout (DKO) mouse as a novel RHUC1 animal model for investigating the cause of EIAKI and the potential therapeutic effect of xanthine oxidoreductase inhibitors (XOIs).

METHODS

The novel Urat1-Uox DKO mice were used in a forced swimming test as loading exercise to explore the onset mechanism of EIAKI and evaluate related purine metabolism and renal injury parameters.

RESULTS

Urat1-Uox DKO mice had uricosuric effects and elevated levels of plasma creatinine and BUN as renal injury markers, and decreased creatinine clearance observed in a forced swimming test. In addition, Urat1-Uox DKO mice had increased NLRP3 inflammasome activity and downregulated levels of Na⁺-K⁺-ATPase protein in the kidney, as Western blot analysis showed. Finally, we demonstrated that topiroxostat and allopurinol, XOIs, improved renal injury and functional parameters of EIAKI.

CONCLUSIONS

Urat1-Uox DKO mice are a useful experimental animal model for human RHUC1. The pathogenic mechanism of EIAKI was found to be due to increased levels of IL-1β via NLRP3 inflammasome signaling and Na⁺-K⁺-ATPase dysfunction associated with excessive urinary urate excretion. In addition, XOIs appear to be a promising therapeutic agent for the treatment of EIAKI.

Protective Effect of Topiroxostat on Myocardial Injury Induced by Lipopolysaccharide

BACKGROUND

Myocardial injury induced by sepsis is the most common cause of death. Topiroxostat has been found to have organ protective effects, but its role in septic shock-related cardiomyocyte damage is still unclear and needs further study.

MATERIAL AND METHODS

An endotoxemic shock model in rats was constructed. After topiroxostat treatment, hemodynamic parameters, myocardial injury marker enzymes, oxidative stress, myocardial injury, and apoptosis were measured by polyphysiograph, enzyme-linked immunosorbent assay, hematoxylin and eosin staining, TUNEL staining, and western blot. During in vitro experiments, the effect of topiroxostat on cell vitality, oxidative stress, inflammatory factors, apoptosis-related markers, phosphorylated-p65 (p-p65) and p65 expressions were measured by 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), flow cytometry, enzyme-linked immunosorbent assay, quantitative real-time polymerase chain reaction, and western blot.

RESULTS

Topiroxostat improved myocardial dysfunction and superoxide dismutase activity while suppressing levels of creatine kinase, lactate dehydrogenase and malondialdehyde in serum of endotoxemic shock rats. Additionally, topiroxostat augmented dry-wet weight ratios of the hearts in rats. Meanwhile, topiroxostat was proved to alleviate interstitial edema and apoptosis in myocardial tissues of endotoxemic shock rats. During in vitro experiments, topiroxostat pretreatment elevated lipopolysaccharide (LPS)-induced H9c2 cell vitality, and alleviated oxidative stress and inflammation. Moreover, topiroxostat pretreatment downregulated apoptosis-related markers, p-p65, and p-p65/p65 levels in LPS-induced H9c2 cells.

CONCLUSIONS

Topiroxostat attenuated LPS-induced myocardial injury via repressing apoptosis and oxidative stress.

Association of Coronary Artery Disease and Metabolic Syndrome: Usefulness of Serum Metabolomics Approach

Introduction

Individuals with metabolic syndrome (MetS) are at increasing risk of coronary artery disease (CAD). We investigated the common metabolic perturbations of CAD and MetS via serum metabolomics to provide insight into potential associations.

Methods

Non-targeted serum metabolomics analyses were performed using ultra high-performance liquid chromatography coupled with Q Exactive hybrid quadrupole-orbitrap high-resolution accurate mass spectrometry (UHPLC-Q-Orbitrap HRMS) in samples from 492 participants (272 CAD vs. 121 healthy controls (HCs) as cohort 1, 55 MetS vs. 44 HCs as cohort 2). Cross-sectional data were obtained when the participants were recruited from the First Affiliated Hospital of Zhengzhou University. Multivariate statistics and Student's t test were applied to obtain the significant metabolites [with variable importance in the projection (VIP) values >1.0 and p values <0.05] for CAD and MetS. Logistic regression was performed to investigate the association of identified metabolites with clinical cardiac risk factors, and the association of significant metabolic perturbations between CAD and MetS was visualized by Cytoscape software 3.6.1. Finally, the receiver operating characteristic (ROC) analysis was evaluated for the risk prediction values of common changed metabolites.

Results

Thirty metabolites were identified for CAD, mainly including amino acids, lipid, fatty acids, pseudouridine, niacinamide; 26 metabolites were identified for MetS, mainly including amino acids, lipid, fatty acids, steroid hormone, and paraxanthine. The logistic regression results showed that all of the 30 metabolites for CAD, and 15 metabolites for MetS remained significant after adjustments of clinical risk factors. In the common metabolic signature association analysis between CAD and MetS, 11 serum metabolites were significant and common to CAD and MetS outcomes. Out of this, nine followed similar trends while two had differing directionalities. The nine common metabolites exhibiting same change trend improved risk prediction for CAD (86.4%) and MetS (90.9%) using the ROC analysis.

Conclusion

Serum metabolomics analysis might provide a new insight into the potential mechanisms underlying the common metabolic perturbations of CAD and MetS.

Topiroxostat ameliorates oxidative stress and inflammation in sepsis-induced lung injury

Sepsis-induced lung injury was the most common cause of death in patients. Topiroxostat, a novel xanthine oxidoreductase inhibitors, possessed obvious organ protectives effects. Xanthine oxidase played a vital role in acute lung injury. The study aimed to investigate the roles of Topiroxostat in sepsis-induced lung injury. The sepsis rats were established using cecum ligation and perforation. The lung damage induced by sepsis was evaluated by Hematoxylin and Eosin staining and lung tissue wet to dry ratio. The oxidative stress was detected by measurement of reactive oxygen species, malondialdehyde, myeloperoxidase and superoxide dismutase (SOD). The pro-inflammatory mediators, tumor necrosis factor-α, interleukin (IL)-1β, IL-6 and monocyte chemotactic protein 1, were measured by Enzyme-Linked Immunosorbent Assay. The cell apoptosis in lung was detected by TUNNEL staining and western blot analysis of apoptosis-related proteins including pro-apoptosis proteins, Bax, cleaved caspase9, cleaved caspase3 and anti-apoptosis protein Bcl2. The results showed that Topiroxostat significantly reduced lung damage, along with decreased oxidative stress, inflammation response and apoptosis in sepsis rats. Topiroxostat exerted markedly protective effects in sepsis-induced lung injury and could be an antioxidant in treating sepsis-induced lung injury.

Antioxidant-Based Therapy Reduces Early-Stage Intestinal Ischemia-Reperfusion Injury in Rats

Intestinal ischemia-reperfusion injury (i-IRI) is a rare disorder with a high mortality rate, resulting from the loss of blood flow to an intestinal segment. Most of the damage is triggered by the restoration of flow and the arrival of cytokines and reactive oxygen species (ROS), among others. Inactivation of these molecules before tissue reperfusion could reduce intestinal damage. The aim of this work was to analyze the preventive effect of allopurinol and nitroindazole on intestinal mucosal damage after i-IRI. Wag/RijHsd rats were subjected to i-IRI by clamping the superior mesenteric artery (for 1 or 2 h) followed by a 30 min period of reperfusion. Histopathological intestinal damage (HID) was assessed by microscopic examination of histological sections obtained from injured intestine. HID was increased by almost 20% by doubling the ischemia time (from 1 to 2 h). Nitroindazole reduced HID in both the 1 and 2 h period of ischemia by approximately 30% and 60%, respectively (p < 0.001). Our preliminary results demonstrate that nitroindazole has a preventive/protective effect against tissue damage in the early stages of i-IRI. However, to better understand the molecular mechanisms underlying this phenomenon, further studies are needed.

CE-MS for metabolomics: Developments and applications in the period 2018-2020

Capillary electrophoresis-mass spectrometry (CE-MS) is now a mature analytical technique in metabolomics, notably for the efficient profiling of polar and charged metabolites. Over the past few years, (further) progress has been made in the design of improved interfacing techniques for coupling CE to MS; also, in the development of CE-MS approaches for profiling metabolites in volume-restricted samples, and in strategies that further enhance the metabolic coverage. In this article, which is a follow-up of a previous review article covering the years 2016-2018 (Electrophoresis 2019, 40, 165-179), the main (technological) developments in CE-MS methods and strategies for metabolomics are discussed covering the literature from July 2018 to June 2020. Representative examples highlight the utility of CE-MS in the fields of biomedical, clinical, microbial, plant and food metabolomics. A complete overview of recent CE-MS-based metabolomics studies is given in a table, which provides information on sample type and pretreatment, capillary coatings, and MS detection mode. Finally, some general conclusions and perspectives are given.

Xanthine oxidase inhibition attenuates doxorubicin-induced cardiotoxicity in mice

Accumulating evidence suggests that high serum uric acid (UA) is associated with left ventricular (LV) dysfunction. Although xanthine oxidase (XO) activation is a critical regulatory mechanism of the terminal step in ATP and purine degradation, the pathophysiological role of cardiac tissue XO in LV dysfunction remains unclear. We herein investigated the role and functional significance of tissue XO activity in doxorubicin-induced cardiotoxicity. Either doxorubicin (10 mg/kg) or vehicle was intraperitonially administered in a single injection to mice. Mice were treated with or without oral XO-inhibitors (febuxostat 3 mg/kg/day or topiroxostat 5 mg/kg/day) for 8 days starting 24 h before doxorubicin injection. Cardiac tissue XO activity measured by a highly sensitive assay with liquid chromatography/mass spectrometry and cardiac UA content were significantly increased in doxorubicin-treated mice at day 7 and dramatically reduced by XO-inhibitors. Accordingly, XO-inhibitors substantially improved LV ejection fraction (assessed by echocardiography) and LV developed pressure (assessed by ex vivo Langendorff heart perfusion) impaired by doxorubicin administration. This was associated with an increase in XO-derived hydrogen peroxide production with concomitant upregulation of apoptotic and ferroptotic pathways, all of which were reduced by XO-inhibitors. Furthermore, metabolome analyses revealed enhanced purine metabolism in doxorubicin-treated hearts, and XO-inhibitors suppressed the serial metabolic reaction of hypoxanthine-xanthine-UA, the paths of ATP and purine degradation. In summary, doxorubicin administration induces cardiac tissue XO activation associated with impaired LV function. XO-inhibitors attenuate doxorubicin-induced cardiotoxicity through inhibition of XO-derived oxidative stress and cell death signals as well as the maintenance of cardiac energy metabolism associated with modulation of the purine metabolic pathway.

Febuxostat, a Xanthine Oxidoreductase Inhibitor, Decreases NLRP3-dependent Inflammation in Macrophages by Activating the Purine Salvage Pathway and Restoring Cellular Bioenergetics

The nucleotide-binding oligomerization domain-like receptor family, pyrin domain-containing 3 (NLRP3) inflammasome mediates caspase-1 activation and IL-1β processing and is implicated in autoinflammatory as well as other chronic inflammatory diseases. Recent studies have demonstrated that xanthine oxidoreductase (XOR) inhibition attenuated IL-1β secretion in activated macrophages, but the detailed mechanism of inhibition remains unclear. In this study, we report that febuxostat, an inhibitor of XOR, suppressed NLRP3 inflammasome-mediated IL-1β secretion and cell death by two mechanisms: in a mitochondrial ROS (mitoROS)-dependent and mitoROS-independent manner. MitoROS-independent effects of febuxostat were mediated by an increase of intracellular ATP and improved mitochondrial energetics via the activation of purine salvage pathway. Our findings suggest that cellular bioenergetics are important in regulating NLRP3 activation, and XOR inhibition may be clinically relevant in NLRP3-related inflammatory diseases.