Reactive oxygen species (ROS) generated by xanthine oxidase in the corneal epithelium and their potential participation in the damage of the corneal epithelium after prolonged use of contact lenses in rabbits

Recent Advances in Xanthine Oxidase Inhibitors

Uric acid is a product of purine nucleotide metabolism, and high concentrations of uric acid can lead to hyperuricemia, gout and other related diseases. Xanthine oxidase, the only enzyme that catalyzes xanthine and hypoxanthine into uric acid, has become a target for drug development against hyperuricemia and gout. Inhibition of xanthine oxidase can reduce the production of uric acid, so xanthine oxidase inhibitors are used to treat hyperuricemia and related diseases, including gout. In recent years, researchers have obtained new xanthine oxidase inhibitors through drug design, synthesis, or separation of natural products. This paper summarizes the research on xanthine oxidase inhibitors since 2015, mainly including natural products, pyrimidine derivatives, triazole derivatives, isonicotinamide derivatives, chalcone derivatives, furan derivatives, coumarin derivatives, pyrazole derivatives, and imidazole derivatives, hoping to provide valuable information for the research and development of novel xanthine oxidase inhibitors.

Arabinogalactan and hyaluronic acid in ophthalmic solution: Experimental effect on xanthine oxidoreductase complex as key player in ocular inflammation (in vitro study)

Dry eye syndrome is a common disease associated to eyes inflammation, irritation and tear film instability. The enzymatic complex of xanthine oxidoreductase (XOR) is involved in the generation of reactive oxygen species (ROS) and uric acid that, in the end, can cause reperfusion injuries, irritation and pathological conditions. Furthermore, in the eye, it has been proposed that oxygen free radicals might play a significant role in retinal ischemic damage. A new artificial drop formulation based on arabinogalactan and hyaluronic acid has been proposed in this article. The uric acid and the ROS formation have been monitored. The effect of the arabinogalactan, the hyaluronic acid and their mixture has been studied. The arabinogalactan entails a uric acid and ROS reduction of 27% and 38% respectively; no significant reduction of uric acid or ROS has been observed after the addition of hyaluronic acid alone. Notably the combination of arabinogalactan and hyaluronic acid involves the reduction of uric acid and ROS equal to 38% and 62%, namely. This study demonstrates that this artificial drop formulation can markedly reduce the uric acid and ROS formation in vitro; thus, the use of this formulation may contribute in the resolution of the dry eye syndrome.

Characterization and expression analysis of immune-related genes in the red swamp crayfish, Procambarus clarkii in response to lipopolysaccharide challenge

To learn more about red swamp crayfish related genes in response to bacterial infections, we investigated immune-related genes induced by lipopolysaccharide (LPS) in the hepatopancreas using high-throughput sequencing method. In present the study, a total of 55,107 unigenes were identified, with an average length of 678 bp. A total of 2215 differentially expressed genes (DEGs) were found, including 669 up-regulated genes and 1546 down-regulated genes. The result of Gene ontology (GO) analysis revealed that 3017 DEGs were enriched in 19 biological process subcategories, 17 cellular component subcategories and 15 molecular function subcategories. The top 20 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways showed that "ribosome" was the most abundant group, which had 34 DEGs. KEGG enrichment analysis identified several immune response pathways. Real-time quantitative reverse transcription-PCR (qRT-PCR) results exhibited that several immune responsive genes were greatly up-regulated following LPS stimulation as observed in the results of high-throughput sequencing. Overall, this study provides new insight into the immune defense mechanisms of P. clarkii against LPS infection.

The conservative cysteines in transmembrane domain of AtVKOR/LTO1 are critical for photosynthetic growth and photosystem II activity in Arabidopsis

Thylakoid protein vitamin K epoxide reductase (AtVKOR/LTO1) is involved in oxidoreduction. The deficiency of this compound causes pleiotropic defects in Arabidopsis thaliana, such as severely stunted growth, smaller sized leaves, and delay of flowering. Transgenic complementation of wild-type AtVKOR (VKORWT) to vkor mutant lines ultimately demonstrates that the phenotype changes are due to this gene. However, whether AtVKOR functions in Arabidopsis through its protein oxidoreduction is unknown. To further study the redox-active sites of AtVKOR in vivo, a series of plasmids containing cysteine-mutant VKORs were constructed and transformed into vkor deficient lines. Compared with transgenic AtVKORWT plants, the size of the transgenic plants with a single conservative cysteine mutation (VKORC109A, VKORC116A, VKORC195A, and VKORC198A) were smaller, and two double-cysteine mutations (VKORC109AC116A and VKORC195AC198A) showed significantly stunted growth, similar with the vkor mutant line. However, mutations of two non-conservative cysteines (VKORC46A and VKORC230A) displayed little obvious changes in the phenotypes of Arabidopsis. Consistently, the maximum and actual efficiency of photosystem II (PSII) in double-cysteine mutation plants decreased significantly to the level similar to that of the vkor mutant line both under normal growth light and high light. A significantly decreased amount of D1 protein and increased accumulation of reactive oxygen species were observed in two double-cysteine mutations under high light. All of the results above indicated that the conservative cysteines in transmembrane domains were the functional sites of AtVKOR in Arabidopsis and that the oxidoreductase activities of AtVKOR were directly related to the autotrophic photosynthetic growth and PSII activity of Arabidopsis thaliana.

Overexpression of Pa_1_10620 encoding a mitochondrial Podospora anserina protein with homology to superoxide dismutases and ribosomal proteins leads to lifespan extension

In biological systems, reactive oxygen species (ROS) represent 'double edged swords': as signaling molecules they are essential for proper development, as reactive agents they cause molecular damage and adverse effects like degeneration and aging. A well-coordinated control of ROS is therefore of key importance. Superoxide dismutases (SODs) are enzymes active in the detoxification of superoxide. The number of isoforms of these proteins varies among species. Here we report the characterization of the putative protein encoded by Pa_1_10620 that has been previously annotated to code for a mitochondrial ribosomal protein but shares also sequence domains with SODs. We report that the gene is transcribed in P. anserina cultures of all ages and that the encoded protein localizes to mitochondria. In strains overexpressing Pa_1_10620 in a genetic background in which PaSod3, the mitochondrial MnSOD of P. anserina, is deleted, no SOD activity could be identified in isolated mitochondria. However, overexpression of the gene leads to lifespan extension suggesting a pro-survival function of the protein in P. anserina.

Antioxidant defenses in the ocular surface

The human eye is subjected constantly to oxidative stress due to daily exposure to sunlight, high metabolic activities, and oxygen tension. Reactive oxygen species generated from environmental insults and pathological conditions render the human eye particularly vulnerable to oxidative damage. The ocular surface composed of the tear film, the cornea, and the aqueous humor forms the first physical and biochemical barrier of the eye and plays a pivotal role in combating free radicals. These ocular compartments are enriched in certain antioxidants in the form of metabolic enzymes or small molecules. Such an antioxidant defense system in the ocular surface is essential for the maintenance of redox homeostasis in the eye and protection against oxidative damage. Herein, we review the properties and functions of key constituent antioxidants of the ocular surface.

Ultraviolet radiation: cellular antioxidant response and the role of ocular aldehyde dehydrogenase enzymes

Solar ultraviolet radiation (UVR) exposes the human eye to near constant oxidative stress. Evidence suggests that UVR is the most important environmental insult leading to the development of a variety of ophthalmoheliosis disorders. UVR-induced reactive oxygen species (ROS) are highly reactive with DNA, proteins, and cellular membranes, resulting in cellular and tissue damage. Antioxidant defense systems present in ocular tissues function to combat ROS and protect the eye from oxidative damage. Important enzymatic antioxidants are the superoxide dismutases, catalase, glutathione peroxidases, glutathione reductase, and members of the aldehyde dehydrogenase (ALDH) superfamily. Glutathione, ascorbic and uric acids, α-tocopherol, nicotinamide-adenine dinucleotide phosphate, and ferritin serve as small molecule, nonenzymatic antioxidants. Ocular tissues have high levels of these antioxidants, which are essential for the maintenance of reduction-oxidation homeostasis in the eye and protection against oxidative damage. ALDH1A1 and ALDH3A1, present abundantly in the cornea and lens, have been shown to have unique roles in the defense against UVR and the downstream effects of oxidative stress. This review presents the properties and functions of ocular antioxidants that play critical roles in the cellular response to UVR exposure, including a focused discussion of the unique roles that the ALDH1A1 and ALDH3A1 enzymes have as multifunctional ocular antioxidants.

Low levels of hydrogen peroxide stimulate corneal epithelial cell adhesion, migration, and wound healing

PURPOSE

Intracellular reactive oxygen species have been reported to associate with growth factor and integrin signalings in promoting cell adhesion in many cell types. This study is to explore if exogenous H(2)O(2) at low levels can be beneficial to cell adhesion, migration, and wound healing.

METHODS

Primary rabbit corneal epithelial cells treated with 0-70 μM H(2)O(2) were tested for viability by MTT assay, adhesion by centrifugation assay, focal contacts of vinculin and F-actin by immunofluorescence, activated Src(pY416), EGF receptor (pY845), vinculin(pY1065), FAK(pY397), and FAK(pY576) by immunoblotting. Cell migration was examined with 0-50 μM H(2)O(2) using the scratch wound technique. Corneal wound healing of ex vivo pig model and in vivo mouse model was examined using H(2)O(2) with and without antioxidant N-acetylcysteine (NAC).

RESULTS

Compared with the untreated control, H(2)O(2) at 10-50 μM stimulated cell viability and facilitated adhesion and migration with clear induction of vinculin-rich focal adhesions and F-actin-containing stress fibers by increasing activated Src, FAK(pY576), and vinculin(pY1065). H(2)O(2) also increased phosphorylation of EGFR(Y845) parallel to that of activated Src, but both were eliminated by NAC and PP1 (Src inhibitor). Finally, H(2)O(2) induced faster wound healing in cornea both in vitro and in vivo, but the healing was diminished by NAC.

CONCLUSIONS

These findings suggest that H(2)O(2) at low levels promotes cell adhesion, migration, and wound healing in cornea cells or tissue, and the interaction of H(2)O(2) with Src plays a major role.

Protective effect of 4-coumaric acid from UVB ray damage in the rabbit eye

UV-induced oxidation damage seems to play a major role in a number of specific pathological conditions of intraocular tissues, such as cataract formation and retinal degeneration. Therefore, antioxidant and/or scavenger compounds might protect the eyes from UV-induced cellular damage. We previously reported that 4-coumaric acid (4-CA) is able to protect rabbit corneal-derived cells (SIRC) from UVB-induced oxidation damage. In this study we evaluated the protective effect of 4-CA against UVB-induced cell damage in rabbit cornea in vivo. Twelve male New Zealand albino rabbits were used; four rabbits were used as a control and received vehicle in one eye and 4-CA acid in the contralateral eye; eight rabbits were exposed to UVB rays (79.2mJ/cm(2)) and three days before to UV exposure each animal received 1 drop/day of vehicle in one eye and 1 drop/day of vehicle containing 4-CA (164ng) in the contralateral eye. Corneal and sclera tissues were removed and 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo) levels were measured. Superoxide dismutase (SOD) and xanthine oxidase (XO) activities were determined in aqueous humour. UVB-induced vessel hyper-reactivity was strongly reduced at 4 and 24h after UVB exposure after local treatment with 4-CA, 8-oxodGuo levels, a marker of oxidative DNA damage, were significantly increased (P<0.05) in sclera and cornea by UVB irradiation, but when 4-CA was administered to the conjunctiva in a buffered solution once a day for 3d before and 6d after UVB exposure, levels of 8-oxodGuo were similar to controls and significantly reduced (P<0.05) compared to UVB-treated corneas. XO activity in the aqueous humour was significantly increased. The administration of 4-CA for 3d before and 6d after UVB irradiation induced a small but significant (P<0.05) reduction of XO compared with control eyes. Our results indicate that the administration of 4-CA protects eye tissues, thus reducing the harmful effect of UVB radiation at low concentration, probably through its free radical scavenging and antioxidant properties. Therefore, 4-CA may be useful in protecting the eye from free radical damage following UVB exposure from sunlight, UV lamps and welding torches.

NOX enzymes as novel targets for drug development

The members of the NOX/DUOX family of NADPH oxidases mediate such physiologic functions as host defense, cell signaling, and thyroid hormone biosynthesis through the generation of reactive oxygen species (ROS), including superoxide anion and hydrogen peroxide. Moreover, ROS are involved in a broad range of fundamental biochemical and cellular processes, and data accumulated in recent years indicate that the NOX enzymes comprise one of the most important biological sources of ROS. Given the high biochemical reactivity of ROS, it is not surprising that they have been implicated in a wide variety of pathologies and diseases. Prominent among the settings that feature ROS-mediated tissue injury are disorders associated with inflammation, aging, and progressive degenerative changes in cells and organ systems, and it appears that essentially no organ system is exempt. Among the disorders currently believed to be mediated at least in part by NOX-derived ROS are hypertension, aortic aneurysm, myocardial infarction (and other ischemia-reperfusion disorders), pulmonary fibrosis and hypertension, amyotropic lateral sclerosis, Alzheimer's disease, Parkinson's disease, ischemic stroke, diabetic nephropathy, and renal cell carcinoma. Several small-molecule and peptide inhibitors of the NOX enzymes have been useful in experimental studies, but issues of specificity, potency, and toxicity militate against any of the existing published compounds as candidates for drug development. Given the broad array of disease targets documented in recent work, the time is here for vigorous efforts to develop clinically useful inhibitors of the NOX enzymes. As most (though not all) NOX-related diseases appear to be mediated by a single member of the NOX family, agents with isoform specificity will be preferred, although broadly active NOX inhibitors may prove to be useful in some settings.

Dipeptidyl peptidase II (DPPII), a review

An increasing number of biological processes appear to be regulated by Pro-specific N-terminal processing. The proline-specific dipeptidyl peptidases (DPPs) like DPPIV, fibroblast activation protein alpha (FAP), DPPII, DPP8 and DPP9, because of their preference for cleavage after X-Pro in vitro, are likely to be involved in many of these processes. These DPPs are emerging as an important protease family with roles in the regulation of signaling by peptide hormones. Dipeptidyl peptidase II (DPPII, E.C. 3.4.14.2) is an intracellular protease that localizes to the vesicular system. It releases, preferably at acidic pH, N-terminal dipeptides from oligopeptides with Pro or Ala in the penultimate position. Despite the fact that the physiological role of DPPII still has not been elucidated, several suggestions were made on possible functions of the enzyme depending on its localization in different cells, body fluids and organs. DPPII was a.o. suggested to be involved in the processes of cell differentiation and in the protection from cell death, and to have a role in the degradation of collagen fragments, myofibrillar proteins and short neuropeptides. Moreover, changes in the level and distribution of the enzyme provided clues indicating additional roles in disease-related processes. Here we review the DPPII literature, aiming to bring more clarity in the disperse data on this subject and give a state of the art on DPPII research.

Comparative histochemical and immunohistochemical study on xanthine oxidoreductase/xanthine oxidase in mammalian corneal epithelium

We have previously found that xanthine oxidase (one form of xanthine oxidoreductase that generates reactive oxygen species, such as superoxide radicals and hydrogen peroxide) is present in corneal epithelium of normal rabbit eye. It was suggested that the reactive oxygen species contribute to additional eye damage related to prolonged continuous contact lens wear and irradiation of the eye with UV-B light. To further explore the potential danger of xanthine oxidase as a source of reactive oxygen species, we have examined in the present paper whether xanthine oxidoreductase and xanthine oxidase are present in corneal epithelium of other mammalian species, employing immunohistochemical and enzyme histochemical methods. In corneal epithelium of normal eyes of ox, pig, guinea-pig, and rat xanthine oxidoreductase activity was detected by the tetrazolium salt reduction method and xanthine oxidase activity was localized by a method based on cerium ions capturing hydrogen peroxide. For the immunohistochemical demonstration of the enzymes, rabbit anti-bovine xanthine oxidase antibody, rabbit anti-human xanthine oxidase antibody and monoclonal mouse anti-human xanthine oxidase/xanthine dehydrogenase/aldehyde oxidase antibody were used. The immunohistochemical and enzyme histochemical results show that xanthine oxidoreductase and xanthine oxidase are present both as proteins and as active enzymes in the corneal epithelium of all animals studied. It is hypothesized that under various pathological states, xanthine oxidase-generated reactive oxygen species might contribute to eye damage.

The polysaccharide from Tamarindus indica (TS-polysaccharide) protects cultured corneal-derived cells (SIRC cells) from ultraviolet rays

The aim of this work was to investigate the possible protective effect of a new viscosising agent, TS-polysaccharide, on corneal-derived cells (SIRC) exposed to ultraviolet-B rays. To verify this, SIRC cells were first exposed, in the absence or in the presence of TS-polysaccharide (1% w/v), for 9 s at the UV-B source and then post-incubated for 45 min at 37 degrees C. After this period the hydrogen peroxide (H(2)O(2)) accumulated in the medium and the concentration of 8-hydroxy-2'-deoxy-guanosine (8-OHdG) in cell DNA was measured. In addition, the amount of (3)H-methyl-thymidine incorporated in cellular DNA was evaluated after 18 h from irradiation. Our results show that cells exposed to UV-B rays accumulate H(2)O(2), and have higher levels of 8OHdG and a lower amount of (3)H-methyl-thymidine incorporated in DNA than control cells. In the presence of TS-polysaccharide, the H(2)O(2) and 8-OHdG accumulation, and the (3)H-methyl-thymidine incorporation were significantly reduced with respect to the values measured in cells exposed in the absence of the polysaccharide. We propose a protective role of the polysaccharide in reducing UV-B derived DNA damage to eye cells. This finding could be of some clinical importance when the polysaccharide is used as a delivery system for ophthalmic preparations.