Xanthine Oxidoreductase Function Contributes to Normal Wound Healing

Emerging Roles of Xanthine Oxidoreductase in Chronic Kidney Disease

Xanthine Oxidoreductase (XOR) is a ubiquitous, essential enzyme responsible for the terminal steps of purine catabolism, ultimately producing uric acid that is eliminated by the kidneys. XOR is also a physiological source of superoxide ion, hydrogen peroxide, and nitric oxide, which can function as second messengers in the activation of various physiological pathways, as well as contribute to the development and the progression of chronic conditions including kidney diseases, which are increasing in prevalence worldwide. XOR activity can promote oxidative distress, endothelial dysfunction, and inflammation through the biological effects of reactive oxygen species; nitric oxide and uric acid are the major products of XOR activity. However, the complex relationship of these reactions in disease settings has long been debated, and the environmental influences and genetics remain largely unknown. In this review, we give an overview of the biochemistry, biology, environmental, and current clinical impact of XOR in the kidney. Finally, we highlight recent genetic studies linking XOR and risk for kidney disease, igniting enthusiasm for future biomarker development and novel therapeutic approaches targeting XOR.

Sulfide and transition metals - A partnership for life

Sulfide and transition metals often came together in Biology. The variety of possible structural combinations enabled living organisms to evolve an array of highly versatile metal-sulfide centers to fulfill different physiological roles. The ubiquitous iron‑sulfur centers, with their structural, redox, and functional diversity, are certainly the best-known partners, but other metal-sulfide centers, involving copper, nickel, molybdenum or tungsten, are equally crucial for Life. This review provides a concise overview of the exclusive sulfide properties as a metal ligand, with emphasis on the structural aspects and biosynthesis. Sulfide as catalyst and as a substrate is discussed. Different enzymes are considered, including xanthine oxidase, formate dehydrogenases, nitrogenases and carbon monoxide dehydrogenases. The sulfide effect on the activity and function of iron‑sulfur, heme and zinc proteins is also addressed.

Topical Allopurinol-Loaded Nanostructured Lipid Carriers: A Novel Approach for Wound Healing Management

Nanostructured lipid carriers (NLC) have been widely studied as delivery systems for a variety of routes, including the skin. Their composition results in an imperfect lipid matrix, allowing increased drug encapsulation. Allopurinol (AP), a xanthine oxidase inhibitor, is characterized by low water solubility and high melting point, which has hampered its use through the topical route. In this work, AP was incorporated in a NLC formulation to enhance drug-carrier association and skin delivery as a topical approach to treat wounds. AP-NLC system was characterized in terms of size, charge, rheological behavior, and in vitro skin permeation. The in vitro cytotoxicity was evaluated using HaCaT cells. The wound healing efficacy of the AP-NLC formulation on animal skin lesions was evaluated in male Wistar rats. The AP-NLC presented a mean size of 193 ± 15 nm with a PdI of 0.240 ± 0.02, zeta potential values around −49.6 mV, and an encapsulation efficiency of 52.2%. The AP-NLC formulation presented an adequate profile to be used topically, since epidermal and dermal drug retention were achieved. No reduction in HaCaT cells viability was observed at the tested concentrations (AP < 10 μg/mL). The in vivo application of the AP-NLC formulation resulted in the regeneration of skin lesions when compared with non-treated controls.

The Therapeutic Effects of Oral Intake of Hydrogen Rich Water on Cutaneous Wound Healing in Dogs

This study explored the effects of drinking Hydrogen-rich water (HRW) on skin wound healing in dogs. Eight circular wounds were analyzed in each dog. The experimental group was treated with HRW thrice daily, while the control group was provided with distilled water (DW). The wound tissues of dogs were examined histopathologically. The fibroblasts, inflammatory cell infiltration, the average number of new blood vessels, and the level of malondialdehyde (MDA) and superoxide dismutase (SOD) activity in the skin homogenate of the wound was measured using the corresponding kits. The expressions of Nrf-2, HO-1, NQO-1, VEGF, and PDGF were measured using the real-time fluorescence quantitative method. We observed that HRW wounds showed an increased rate of wound healing, and a faster average healing time compared with DW. Histopathology showed that in the HRW group, the average thickness of the epidermis was significantly lower than the DW group. The average number of blood vessels in the HRW group was higher than the DW group. The MDA levels were higher in the DW group than in the HRW group, but the SOD levels were higher in the HRW group than in the DW group. The results of qRT-PCR showed that the expression of each gene was significantly different between the two groups. HRW treatment promoted skin wound healing in dogs, accelerated wound epithelization, reduced inflammatory reaction, stimulated the expression of cytokines related to wound healing, and shortened wound healing time.

Integrated analysis of lncRNA and mRNA in liver of Megalobrama amblycephala post Aeromonas hydrophila infection

Background

As non-coding RNA molecules of more than 200 bp in length, long non-coding RNAs (lncRNAs) play a variety of roles in biological processes, including regulating the immune responses to bacterial infections. In recent years, there have been many in-depth studies on mammalian lncRNAs, but the relevant studies in fish are very limited. Meanwhile, since lncRNAs are not conserved among species, it is difficult to apply the existing results directly to unstudied species.

Results

To obtain the information of lncRNAs in Megalobrama amblycephala, one of the most economically important freshwater fish in China, also to better understand the biological significance of lncRNAs in the immunity system, the fish liver at 0, 4, 12, 24, and 72 h post Aeromonas hydrophila infection (hpi) were obtained for lncRNA-sequencing (lncRNA-seq). A total of 14,849 lncRNAs were identified, and 2196 lncRNAs showed significant differences at different time points post A. hydrophila infection. Gene Ontology (GO) annotation and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses showed that the target genes of the differentially expressed lncRNAs were enriched in several pathways related to immune such as apoptosis, inflammation, and immune response. Time-specific modules were then identified, using weighted correlation network analysis (WGCNA), and 28 modules significantly correlated with different time point after infection were found. Furthermore, four immune-related genes and six lncRNAs in the time-specific modules were subsequently verified by RT-qPCR.

Conclusions

The above findings reveal the discovery of widespread differentially expressed lncRNAs in the M. amblycephala liver post A. hydrophila infection, suggesting that lncRNAs might participate in the regulation of host response to bacterial infection, enriching the information of lncRNAs in teleost and providing a resources basis for further studies on the immune function of lncRNAs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07969-5.

Formation and degradation of lipid droplets in human adipocytes and the expression of aldehyde oxidase (AOX)

Lipid droplet (LD) binding proteins in mammary glands and in adipocytes were previously compared and striking similar sets of these specific proteins demonstrated. Xanthine oxidoreductase (XOR) together with perilipins and the lactating mammary gland protein butyrophilin play an important role in the secretion process of LDs into milk ducts. In contrast, in adipose tissue and in adipocytes, mainly perilipins have been described. Moreover, XOR was reported in mouse adipose tissue and adipocyte culture cells as “novel regulator of adipogenesis”. This obvious coincidence of protein sets prompted us to revisit the formation of LDs in human-cultured adipocytes in more detail with special emphasis on the possibility of a LD association of XOR. We demonstrate by electron and immunoelectron microscopy new structural details on LD formation in adipocytes. Surprisingly, by immunological and proteomic analysis, we identify in contrast to previous data showing the enzyme XOR, predominantly the expression of aldehyde oxidase (AOX). AOX could be detected tightly linked to LDs when adipocytes were treated with starvation medium. In addition, the majority of cells show an enormous interconnected, tubulated mitochondria network. Here, we discuss that (1) XOR is involved—together with perilipins—in the secretion of LDs in alveolar epithelial cells of the lactating mammary gland and is important in the transcytosis pathway of capillary endothelial cells. (2) In cells, where LDs are not secreted, XOR cannot be detected at the protein level, whereas in contrast in these cases, AOX is often present. We detect AOX in adipocytes together with perilipins and find evidence that these proteins might direct LDs to mitochondria. Finally, we here report for the first time the exclusive and complementary localization of XOR and AOX in diverse cell types.

A novel target for the promotion of dermal wound healing: Ryanodine receptors

Ryanodine receptors have an important role in the regulation of intracellular calcium levels in the nervous system and muscle. It has been described that ryanodine receptors influence keratinocyte differentiation and barrier homeostasis. Our goal was to examine the role of ryanodine receptors in the healing of full-thickness dermal wounds by means of in vitro and in vivo methods. The effect of ryanodine receptors on wound healing, microcirculation and inflammation was assessed in an in vivo mouse wound healing model, using skin fold chambers in the dorsal region, and in HaCaT cell scratch wound assay in vitro. SKH-1 mice were subjected to sterile saline (n = 36) or ryanodine receptor agonist 4-chloro-m-cresol (0.5 mM) (n = 42) or ryanodine receptor antagonist dantrolene (100 μM) (n = 42). Application of ryanodine receptor agonist 4-chloro-m-cresol did not influence the studied parameters significantly, whereas ryanodine receptor antagonist dantrolene accelerated the wound closure. Inhibition of the calcium channel also increased the vessel diameters in the wound edges during the process of healing and increased the blood flow in the capillaries at all times of measurement. Furthermore, application of dantrolene decreased xanthine-oxidoreductase activity during the inflammatory phase of wound healing. Inhibition of ryanodine receptor-mediated effects positively influence wound healing. Thus, dantrolene may be of therapeutic potential in the treatment of wounds.

Xanthine Oxidoreductase: A Novel Therapeutic Target for the Treatment of Chronic Wounds?

Significance: Chronic wounds are a major burden to patients and to healthcare systems worldwide. These wounds are difficult to heal and treatment is often lengthy and expensive. This has led to research efforts focussed on the wound environment attempting to understand the underlying pathological mechanisms of impaired wound healing. While some of this research has translated to advancements in wound therapies and implementation of new treatment options, chronic wounds remain a significant challenge to treat. Thus, identification of effective, low-cost, advanced wound therapies that enhance healing rates of these problematic wounds is still essential. Recent Advances and Critical Issues: Xanthine oxidoreductase (XOR), a molybdoflavin enzyme, is emerging as an important source of reactive oxygen species (ROS) in various pathologies, including diabetes and chronic wounds. XOR has recently been shown to be upregulated in chronic wounds, stimulating the overproduction of ROS during dysfunctional wound healing. XOR-induced ROS can amplify and potentiate inflammation in the wound environment further delaying wound closure. Future Directions: The detrimental role of XOR in impaired healing indicates it may be a therapeutic target. Targeted inhibition of XOR has been shown to reduce the expression and activity of this enzyme in diabetic wound models. In turn, this resulted in a significant decrease in ROS levels in the wound environment and improved wound healing. Therefore, repurposing existing XOR inhibitors that are approved for human use may be able to restore homeostasis at the wound site and enable damaged tissue to return to normal healing.

Chitosan nanoparticles loaded hydrogels promote skin wound healing through the modulation of reactive oxygen species

This study developed a novel bioactive chitosan nanoparticle loaded calcium alginate hydrogel to regulate inflammation and neovascularization for accelerated wound healing in vivo. It was found that chitosan nanoparticles loaded calcium alginate hydrogel exhibited remarkable antibacterial activity. Through the modulation of generation of ROS, it promoted the synthesis and secretion of IL-6 in vascular endothelial cell (VEC), suggesting its potential proinflammatory activation. Further, it promoted VEC invasion, metastasis and neovascularization to accelerate wound healing.

Reactive Oxygen Species and NOX Enzymes Are Emerging as Key Players in Cutaneous Wound Repair

Our understanding of the role of oxygen in cell physiology has evolved from its long-recognized importance as an essential factor in oxidative metabolism to its recognition as an important player in cell signaling. With regard to the latter, oxygen is needed for the generation of reactive oxygen species (ROS), which regulate a number of different cellular functions including differentiation, proliferation, apoptosis, migration, and contraction. Data specifically concerning the role of ROS-dependent signaling in cutaneous wound repair are very limited, especially regarding wound contraction. In this review we provide an overview of the current literature on the role of molecular and reactive oxygen in the physiology of wound repair as well as in the pathophysiology and therapy of chronic wounds, especially under ischemic and hyperglycemic conditions.

Xanthine dehydrogenase downregulation promotes TGFβ signaling and cancer stem cell-related gene expression in hepatocellular carcinoma

Xanthine dehydrogenase (XDH), a rate-limiting enzyme involved in purine metabolism, has an essential role in inflammatory cascades. Researchers have known for decades that XDH activity is decreased in some cancers, including hepatocellular carcinoma (HCC). However, the role of XDH in cancer pathogenesis has not been fully explored. In this study, we showed that low XDH mRNA levels were correlated with higher tumor stages and poorer prognoses in patients with HCC. Knocking down or inhibiting XDH promoted migration and invasion but not proliferation of HCC cells. The abovementioned phenotypic changes are dependent on increases in epithelial-mesenchymal transition marker gene expression and transforming growth factor-β-Smad2/3 signaling activity in HCC. XDH overexpression suppressed HCC cell invasion in vitro and in vivo. In addition, the expression and activity of XDH were associated with the expression of CSC-related genes, such as CD44 or CD133, in HCC cells. These data suggest that downregulated XDH expression may be a useful clinical indicator and contribute to the development and progression of HCC.

Peptide-modified chitosan hydrogels promote skin wound healing by enhancing wound angiogenesis and inhibiting inflammation

Cutaneous wound healing following trauma is a complex and dynamic process involving multiple overlapping events following trauma. Two critical elements affecting skin wound healing are neovascularization and inflammation. A nascent vessel can provide nutrition and oxygen to a healing wound. Therefore, treatments strategies that enhance angiogenesis and inhibit inflammation can promote skin wound healing. Previous studies have shown that the SIKVAV peptide (Ser-Ile-Lys-Val-Ala-Val) from laminin can promote angiogenesis in vitro. This study evaluated the effects of peptide SIKVAV-modified chitosan hydrogels on skin wound healing. We established skin wounds established in mice and treated them with SIKVAV-modified chitosan hydrogels. H&E staining showed that peptide-modified chitosan hydrogels accelerated the reepithelialization of wounds compared with the negative and positive controls. Immunohistochemistry analysis demonstrated that more myofibroblasts were deposited at wounds treated with peptide-modified chitosan hydrogels that at those treated with negative and positive controls. In addition, peptide-modified chitosan hydrogels promoted angiogenesis as well as keratinocyte proliferation and differentiation, but inhibited inflammation in skin wounds. Taken together, these results suggest that SIKVAV-modified chitosan hydrogels are a promising treatment component for healing-impaired wounds.

Pathways and Genes Associated with Immune Dysfunction in Sheep Paratuberculosis

Multibacillary and paucibacillary paratuberculosis are both caused by Mycobacterium avium subspecies paratuberculosis. Multibacillary lesions are composed largely of infected epithelioid macrophages and paucibacillary lesions contain T cells but few bacteria. Multibacillary disease is similar to human lepromatous leprosy, with variable/high levels of antibody and a dysfunctional immune response. Animals with paucibacillary disease have high cell-mediated immunity and variable levels of antibody. This study aims to characterize the immunological dysfunction using TruSeq analysis of the ileocaecal lymph node that drains disease lesions. Immune dysfunction is highlighted by repression of TCR/CD3 genes, T cell co-receptors/co-stimulators, T cell activation and signal-transduction genes. Inflammation was an acute phase response and chronic inflammation, with little evidence of acute inflammation. The high levels of immunoglobulin and plasma cell transcripts is consistent with the anti-MAP antibody responses in paratuberculosis sheep. Also notable was the overwhelming reduction in mast cell transcripts, potentially affecting DC activation of the immune response. This study also shows that there were no fundamental differences in the gene expression patterns in multibacillary and paucibacillary disease, no shift in T cell genes from Th1 to Th2 pattern but rather an incremental decline into immune dysfunction leading to multibacillary pathology.

My Continuing Evolution as a Surgeon-Scientist: A Decade after the Jacobson Promising Investigator Award

THE SECOND JOAN L AND JULIUS H JACOBSON PROMISING INVESTIGATOR AWARDEE, EDITH TZENG MD, FACS: In 2005, the Surgical Research Committee of the American College of Surgeons was tasked with selecting the recipient of a newly established award, "The Joan L and Julius H Jacobson Promising Investigator Award." According to the Jacobsons, the award funded by Dr Jacobson should be given at least once every 2 years to a surgeon investigator at "the tipping point," who can demonstrate that his or her research shows the promise of leading to a significant contribution to the practice of surgery and patient safety. Every year, the Surgical Research Committee receives many excellent nominations and has the difficult task of selecting one awardee. The first awardee was Michael Longaker MD, FACS, who 10 years later reflected on the award and the impact it had on his career.¹ This year, Edith Tzeng, MD, FACS, the second Jacobson awardee, reflects on her 10-year journey after receiving the award. Dr Tzeng is now a national and international figure in the field of vascular surgery and has studied the effect of nitric oxide and carbon monoxide on intimal hyperplasia. Kamal MF Itani, MD, FACS and Leigh Neumayer, MD, FACS, on behalf of the Surgical Research Committee of the American College of Surgeons.

Erythropoietin and a nonerythropoietic peptide analog promote aortic endothelial cell repair under hypoxic conditions: role of nitric oxide

The cytoprotective effects of erythropoietin (EPO) and an EPO-related nonerythropoietic analog, pyroglutamate helix B surface peptide (pHBSP), were investigated in an in vitro model of bovine aortic endothelial cell injury under normoxic (21% O₂) and hypoxic (1% O₂) conditions. The potential molecular mechanisms of these effects were also explored. Using a model of endothelial injury (the scratch assay), we found that, under hypoxic conditions, EPO and pHBSP enhanced scratch closure by promoting cell migration and proliferation, but did not show any effect under normoxic conditions. Furthermore, EPO protected bovine aortic endothelial cells from staurosporine-induced apoptosis under hypoxic conditions. The priming effect of hypoxia was associated with stabilization of hypoxia inducible factor-1α, EPO receptor upregulation, and decreased Ser-1177 phosphorylation of endothelial nitric oxide synthase (NOS); the effect of hypoxia on the latter was rescued by EPO. Hypoxia was associated with a reduction in nitric oxide (NO) production as assessed by its oxidation products, nitrite and nitrate, consistent with the oxygen requirement for endogenous production of NO by endothelial NOS. However, while EPO did not affect NO formation in normoxia, it markedly increased NO production, in a manner sensitive to NOS inhibition, under hypoxic conditions. These data are consistent with the notion that the tissue-protective actions of EPO-related cytokines in pathophysiological settings associated with poor oxygenation are mediated by NO. These findings may be particularly relevant to atherogenesis and postangioplasty restenosis.

Dual and Opposing Roles of Xanthine Dehydrogenase in Defense-Associated Reactive Oxygen Species Metabolism in Arabidopsis

While plants produce reactive oxygen species (ROS) for stress signaling and pathogen defense, they need to remove excessive ROS induced during stress responses in order to minimize oxidative damage. How can plants fine-tune this balance and meet such conflicting needs? Here, we show that XANTHINE DEHYDROGENASE1 (XDH1) in Arabidopsis thaliana appears to play spatially opposite roles to serve this purpose. Through a large-scale genetic screen, we identified three missense mutations in XDH1 that impair XDH1's enzymatic functions and consequently affect the powdery mildew resistance mediated by RESISTANCE TO POWDERY MILDEW8 (RPW8) in epidermal cells and formation of xanthine-enriched autofluorescent objects in mesophyll cells. Further analyses revealed that in leaf epidermal cells, XDH1 likely functions as an oxidase, along with the NADPH oxidases RbohD and RbohF, to generate superoxide, which is dismutated into H2O2 The resulting enrichment of H2O2 in the fungal haustorial complex within infected epidermal cells helps to constrain the haustorium, thereby contributing to RPW8-dependent and RPW8-independent powdery mildew resistance. By contrast, in leaf mesophyll cells, XDH1 carries out xanthine dehydrogenase activity to produce uric acid in local and systemic tissues to scavenge H2O2 from stressed chloroplasts, thereby protecting plants from stress-induced oxidative damage. Thus, XDH1 plays spatially specified dual and opposing roles in modulation of ROS metabolism during defense responses in Arabidopsis.

Xanthine Oxidoreductase-Derived Reactive Species: Physiological and Pathological Effects

Xanthine oxidoreductase (XOR) is the enzyme that catalyzes the oxidation of hypoxanthine to xanthine and xanthine to uric acid and is widely distributed among species. In addition to this housekeeping function, mammalian XOR is a physiological source of superoxide ion, hydrogen peroxide, and nitric oxide, which can function as second messengers in the activation of various pathways. This review intends to address the physiological and pathological roles of XOR-derived oxidant molecules. The cytocidal action of XOR products has been claimed in relation to tissue damage, in particular damage induced by hypoxia and ischemia. Attempts to exploit this activity to eliminate unwanted cells via the construction of conjugates have also been reported. Moreover, different aspects of XOR activity related to phlogosis, endothelial activation, leukocyte activation, and vascular tone regulation, have been taken into consideration. Finally, the positive and negative outcomes concerning cancer pathology have been analyzed because XOR products may induce mutagenesis, cell proliferation, and tumor progression, but they are also associated with apoptosis and cell differentiation. In conclusion, XOR activity generates free radicals and other oxidant reactive species that may result in either harmful or beneficial outcomes.