Construction of a screening system for lipid-derived radical inhibitors and validation of hit compounds to target retinal and cerebrovascular diseases

Recent studies have highlighted the indispensable role of oxidized lipids in inflammatory responses, cell death, and disease pathogenesis. Consequently, inhibitors targeting oxidized lipids, particularly lipid-derived radicals critical in lipid peroxidation, which are known as radical-trapping antioxidants (RTAs), have been actively pursued. We focused our investigation on nitroxide compounds that have rapid second-order reaction rate constants for reaction with lipid-derived radicals. A novel screening system was developed by employing competitive reactions between library compounds and a newly developed profluorescence nitroxide probe with lipid-derived radicals to identify RTA compounds. A PubMed search of the top hit compounds revealed their wide application as repositioned drugs. Notably, the inhibitory efficacy of methyldopa, selected from these compounds, against retinal damage and bilateral common carotid artery stenosis was confirmed in animal models. These findings underscore the efficacy of our screening system and suggest that it is an effective approach for the discovery of RTA compounds.

Visual fatigue a comprehensive review of mechanisms of occurrence, animal model design and nutritional intervention strategies

When the eyes work intensively, it is easy to have eye discomfort such as blurred vision, soreness, dryness, and tearing, that is, visual fatigue. Visual fatigue not only affects work and study efficiency, but long-term visual fatigue can also easily affect physical and mental health. In recent years, with the popularization of electronic products, although it has brought convenience to the office and study, it has also caused more frequent visual fatigue among people who use electronic devices. Moreover, studies have reported that the number of people with visual fatigue is showing a trend of increasing year by year. The range of people involved is also extensive, especially students, people who have been engaged in computer work and fine instruments (such as microscopes) for a long time, and older adults with aging eye function. More and more studies have proposed that supplementation with the proper nutrients can effectively relieve visual fatigue and promote eye health. This review discusses the physiological mechanisms of visual fatigue and the design ideas of animal experiments from the perspective of modern nutritional science. Functional food ingredients with the ability to alleviate visual fatigue are discussed in detail.

Singlet oxygen-generating cell-adhesive glass surfaces for the fundamental investigation of plasma membrane-targeted photodynamic therapy

Recently, plasma membrane-targeted photodynamic therapy has attracted attention as an effective cancer immunotherapeutic strategy. However, the released photosensitizers do not only adhere to the plasma membrane but may also be internalized in the cytosol, in endosomes/lysosomes, hindering investigations of the effects of photosensitizers attached to the plasma membrane. In this study, we developed a cell culture dish with singlet oxygen-generating cell-adhesive glass surfaces that allows investigation of the effects of photosensitizers attached to the plasma membrane. For cell adhesion, poly[N-(3-aminopropyl)methacrylamide] conjugated with hematoporphyrin PA-HpD was immobilized on the glass surfaces. Singlet oxygen was produced from the PA-HpD-immobilized glass surface upon laser irradiation at 635 nm. When murine colon adenocarcinoma 26 (Colon-26) cells were cultured on the PA-HpD-immobilized surface, the cells were swollen and ruptured, leading to effective apoptotic cell death using laser irradiation at 635 nm. In addition, microvesicles of approximately 10 μm in diameter were released from the plasma membrane into the culture medium. These phenomena were due to the oxidation of lipids in the cellular membrane, caused by the plasma membrane-targeted photodynamic therapy. In contrast, these phenomena were not observed on poly[N-(3-aminopropyl)methacrylamide]-immobilized glass surfaces. These results indicate that cell culture dishes with singlet oxygen-generating cell-adhesive glass surfaces can be used to investigate fundamental mechanisms in plasma membrane-targeted photodynamic therapy.

Polyunsaturated Fatty Acids (PUFAs): Sources, Digestion, Absorption, Application and Their Potential Adjunctive Effects on Visual Fatigue

When the eyes are exposed to the environment, they are easily affected by strong light stimulation and harmful substances. At the same time, prolonged use of the eyes or incorrect eye habits can cause visual fatigue, which mainly manifests as eye dryness, soreness, blurred vision, and various discomforts. The main reason for this is a decline in the function of the eye, especially the cornea and retina on the surface of the eye, which have the greatest impact on the normal function of the eye. Research has found that supplementation with appropriate foods or nutrients can effectively strengthen the eye against external and internal stimuli, thereby alleviating or avoiding visual fatigue. Among these, supplementation with polyunsaturated fatty acids has been found to be effective at protecting eye health and relieving visual fatigue. This article summarizes the sources of polyunsaturated fatty acids (including the main dietary sources and internal synthesis), the mechanisms of digestion and absorption of polyunsaturated fatty acids in the body and the safety of polyunsaturated fatty acid applications. It also reviews the mechanism of action of polyunsaturated fatty acids in aiding the relief of visual fatigue based on the mechanism of impaired function or structure of the ocular surface and fundus in the hope of providing some reference and insight into the development and application of polyunsaturated fatty acids in functional foods for the relief of visual fatigue.

Structural Analysis of Intracellular Lipid Radicals by LC/MS/MS Using a BODIPY-Based Profluorescent Nitroxide Probe

Free radical-mediated lipid peroxidation (LPO) induces the formation of numerous lipid radicals, which contribute to the development of several oxidative diseases. To understand the mechanism of LPO in biological systems and the significance of these radicals, identifying the structures of individual lipid radicals is imperative. In this study, we developed an analytical method based on liquid chromatography coupled with tandem mass spectrometry (LC/MS/MS) and a profluorescent nitroxide probe, N-(1-oxyl-2,2,6-trimethyl-6-pentylpiperidin-4-yl)-3-(5,5-difluoro-1,3-dimethyl-3H,5H-5l4-dipyrrolo[1,2-c:2',1'-f][1,3,2]diazaborinin-7-yl)propanamide (BDP-Pen), for the detailed structural analysis of lipid radicals. The MS/MS spectra of BDP-Pen-lipid radical adducts showed product ions and thus allow the prediction of the lipid radical structures and individual detection of isomeric adducts. Using the developed technology, we separately detected the isomers of arachidonic acid (AA)-derived radicals generated in AA-treated HT1080 cells. This analytical system is a powerful tool for elucidating the mechanism of LPO in biological systems.

Polyunsaturated Lipids in the Light-Exposed and Prooxidant Retinal Environment

The retina is an oxidative stress-prone tissue due to high content of polyunsaturated lipids, exposure to visible light stimuli in the 400–480 nm range, and high oxygen availability provided by choroidal capillaries to support oxidative metabolism. Indeed, lipids’ peroxidation and their conversion into reactive species promoting inflammation have been reported and connected to retinal degenerations. Here, we review recent evidence showing how retinal polyunsaturated lipids, in addition to oxidative stress and damage, may counteract the inflammatory response triggered by blue light-activated carotenoid derivatives, enabling long-term retina operation despite its prooxidant environment. These two aspects of retinal polyunsaturated lipids require tight control over their synthesis to avoid overcoming their protective actions by an increase in lipid peroxidation due to oxidative stress. We review emerging evidence on different transcriptional control mechanisms operating in retinal cells to modulate polyunsaturated lipid synthesis over the life span, from the immature to the ageing retina. Finally, we discuss the antioxidant role of food nutrients such as xanthophylls and carotenoids that have been shown to empower retinal cells’ antioxidant responses and counteract the adverse impact of prooxidant stimuli on sight.

Effect of relative configuration of TEMPO-type nitroxides on ascorbate reduction

2,2,6,6-Tetramethylpiperidin-N-oxyl (TEMPO)-type nitroxides are susceptible to bioreduction, leading to a loss of radical properties. Although it has been reported that the steric and electronic environments around the N-O moiety of nitroxides affect the reduction, how the relative configuration of nitroxide derivatives alters it is unclear. In this study, we investigated the effect of diastereomers on the radical properties of C2- and C4-disubstituted TEMPO-type nitroxides. We succeeded in isolating the diastereomers of the studied nitroxides for the first time. In addition, we compared the reactivities of nitroxide derivatives with different substituents at the C2 and C4 positions toward ascorbate reduction. We found that the bulky substituents at both C2 and C4 and the electronic effect of C4 affected the reduction of the isomers. C2- and C4-disubstituted nitroxides were administered to mice for electron spin resonance imaging to assess bioreduction in the brain. Similar to the reactivity to reduction in vitro, a difference in the bioreduction of diastereomers was observed in brain tissues. Our research strongly indicates that bioreduction can be controlled by changing the relative configuration, which can be used in the design of nitroxide derivatives for biological applications.

Detection and structural analysis of lipid-derived radicals in vitro and in vivo

Lipids can be oxidized by reactive oxygen species, resulting in lipid peroxidation and the formation of reactive metabolites such as lipid-derived electrophiles. These products have been reported to induce inflammation, angiogenesis, and ferroptosis. Lipid peroxidation can produce many different products, each of which performs a different function, and which can be challenging to detect in vivo. The initial products of lipid oxidation are lipid-derived radicals, which can cause extensive chain reactions leading to lipid peroxidation. Hence, the ability to detect lipid radicals may provide information about this important class of molecules and the mechanism by which they cause cellular and tissue damage in a wide range of oxidative conditions. In this review, we report recent scientific advances in the detection of lipid-derived radicals in vitro and in cultured cells. We also introduce the possibility of visualization and structural analysis of lipid-derived radicals generated not only in in cells but also in animal tissue samples from oxidative disease models, using fluorescence-based lipid radicals' detection probes. We anticipate that the various innovative techniques summarized in this paper will be applied and further developed to clarify the role of lipid peroxidation in the pathogenesis of oxidative stress-associated diseases.

Radioiodinated Nitroxide Derivative for the Detection of Lipid Radicals

Thus far, no accurate measurement technology has been developed to detect lipid alkyl radicals (lipid radicals), which cause lipid peroxidation. Therefore, we aimed to develop a nuclear medical imaging probe that can be taken up in the lipophilic site in cells such as biological membranes, by reacting specifically with the lipid radicals generated there. We designed and synthesized 4-(4-[¹²⁵I]iodobenzamido)-2,2,6,6-tetramethylpiperidine-1-oxyl, which shows high reactivity to lipid radicals with a high radiochemical yield and purity. Intracellular retention was found to increase significantly when lipid radicals were produced.

Cyanidin-3-glucoside attenuates 4-hydroxynonenal- and visible light-induced retinal damage in vitro and in vivo

4-Hydroxynonenal (HNE) is a highly reactive end-product of lipid peroxidation reaction that leads to retinal pigment epithelial (RPE) cell damage. Cyanidin-3-glucoside (C3G), the most abundant anthocyanin in the edible parts of plants, is a nutritional supplement used for preventing retinal damage. However, the protective effect of C3G against HNE-induced RPE cell damage remains to be elucidated. The protective mechanisms of C3G on ARPE-19 cells after HNE exposure were investigated in this study. Results showed that compared with HNE-treated cells, the viability of ARPE-19 cells was significantly (P < 0.05) increased after 1 and 5 μM C3G treatment. C3G exhibited a significant (P < 0.05) inhibitory effect on the expression of senescence-associated β-galactosidase in ARPE-19 cells. VEGF levels in the C3G groups were significantly (P < 0.05) decreased relative to those of the HNE-treated group. C3G also regulated the release of two inflammatory mediators, namely monocyte chemoattractant protein 1 and interleukine-8, in ARPE-19 cells after HNE treatment. Furthermore, C3G attenuated retinal cell apoptosis in pigmented rabbits induced by visible light. Therefore, our data showed that C3G has efficient protective effects on HNE-induced apoptosis, angiogenesis, and dysregulated cytokine production in ARPE-19 cells.

Blueberry Polyphenols Ameliorate Visible Light and Lipid-Induced Injury of Retinal Pigment Epithelial Cells

Although dietary polyphenols are known to be beneficial to vision, the protective distinctions among different types of polyphenols are unclear. In this work, the visual benefits of various blueberry polyphenols were evaluated using an in vitro model of visible light-lipid-induced injury of retinal pigment epithelial cells. Results showed that, at 10.0 μg/mL, the phenolic acid-rich fraction was superior in inhibiting cell death (93.6% ± 2.8% of cell viability). Anthocyanin- and flavonoid-rich fractions shared similar advantages in preventing the expression of senescence-associated β-galactosidase (34.8% ± 11.1% and 32.2% ± 9.7% of aged cells, respectively) and overexpression of vascular endothelial growth factor (51.8 ± 3.5 and 54.1 ± 6.5 pg/mL, respectively). The flavonoid-rich fraction also showed high activity in ameliorating phagocytosis (70.3% ± 12.6%) and cellular oxidative stress. These results were further confirmed by using the corresponding polyphenol standards. Improved inhibitory effects of polyphenol mixture on cell death and senescence-associated β-galactosidase expression were also observed. Therefore, various polyphenols play diverse roles and exert synergistic effects in nourishing the retina.

Progranulin protects the mouse retina under hypoxic conditions via inhibition of the Toll‑like receptor‑4‑NADPH oxidase 4 signaling pathway

To investigate the function of progranulin on the retina under hypoxic conditions, 8-week-old C57BL/6 mice were divided into normal condition and hypoxic condition groups (n=24 mice/group). The hypoxia model was established through intravitreal injection of 9 mM cobalt chloride. Subsequently, 10 mM progranulin and an equal amount of PBS were injected into the right and left eyes, respectively. Photoreceptor function was examined using electroretinogram (ERG) analysis. Morphological alterations were examined using immunofluorescence co-localization, retinal vascular inflammation was examined using the leukostasis assay, and signaling pathways were screened using immunoblotting. The results revealed that ERG amplitude was significantly lower under hypoxic conditions compared with under normal conditions. Furthermore, the amplitude was significantly reduced in the PBS-injected eyes compared with in the progranulin-injected eyes. Morphological examination demonstrated that the number of rods in the PBS-injected eyes was decreased compared with in the progranulin-injected eyes under hypoxic conditions. In addition, the arrangement of the cones was sparse and the morphology of the outer segments was short and small. Although the number of adherent leukocytes in the progranulin-injected eyes was higher in the hypoxic mice compared with in those under normal conditions, the number was only 52.31% of the number detected in the PBS-injected eyes. Analysis of the signaling pathways demonstrated that the protective effects of progranulin on retinas under hypoxic conditions were regulated by the Toll-like receptor 4 (TLR4)-NADPH oxidase 4 (NOX4) pathway, instead of the caspase and Wnt/β-catenin pathways. In conclusion, progranulin exerted protective effects on the function and morphology of photoreceptors in a hypoxic environment, and could reduce retinal vascular inflammation, through inhibition of the TLR4-NOX4 pathway.