Neuroprotective effects of tempol acyl esters against retinal ganglion cell death in a rat partial optic nerve crush model

Ferroptosis in Glaucoma: A Promising Avenue for Therapy

Glaucoma, a blind-leading disease largely since chronic pathological intraocular high pressure (ph-IOP). Hitherto, it is reckoned incurable for irreversible neural damage and challenges in managing IOP. Thus, it is significant to develop neuroprotective strategies. Ferroptosis, initially identified as an iron-dependent regulated death that triggers Fenton reactions and culminates in lipid peroxidation (LPO), has emerged as a focal point in multiple tumors and neurodegenerative diseases. Researches show that iron homeostasis play critical roles in the optic nerve (ON) and retinal ganglion cells (RGCs), suggesting targeted treatments could be effective. In glaucoma, apart from neural lesions, disrupted metal balance and increased oxidative stress in trabecular meshwork (TM) are observed. These disturbances lead to extracellular matrix excretion disorders, known as sclerotic mechanisms, resulting in refractory blockages. Importantly, oxidative stress, a significant downstream effect of ferroptosis, is also a key factor in cell senescence. It plays a crucial role in both the etiology and risk of glaucoma. Moreover, ferroptosis also induces non-infectious inflammation, which exacerbate glaucomatous injury. Therefore, the relevance of ferroptosis in glaucoma is extensive and multifaceted. In this review, the study delves into the current understanding of ferroptosis mechanisms in glaucoma, aiming to provide clues to inform clinical therapeutic practices.

Design, synthesis and anti-hypoxia activity of HPN derivatives containing lipophilic long chains

OBJECTIVE

To design and synthesize long-chain substituted 2-[(4'-hydroxyethoxy) phenyl]-4,4,5,5-tetramethyl-2-imidazoline-1-oxyl 3-oxide (HPN) derivatives with enhanced anti-hypoxic activity.

METHODS

HPN derivatives 1, 3, 5 containing lipophilic long chains were synthesized via the alkylation of HPN with 6-bromohexan-1-ol, ethyl 6-bromohexanoate or 6-bromohexane, respectively using acetonitrile as the solvent and K ₂CO ₃ as the acid-binding agent at 60 ℃. Derivative 2 was synthesized via hydrolysis reactions of derivative 1 in the NaOH/CH ₃OH/H ₂O system. Using dichloromethane as the solvent and N, N'-diisopropylcarbodiimide as the dehydrating agent, HPN underwent esterification with hexanoic acid to obtain derivative 4. The structures of derivatives 1-5 were characterized by infrared spectroscopy, electron paramagnetic resonance and high resolution mass spectrometry. The purities of derivatives were detected by high performance liquid chromatography, and the lipid solubilities of derivatives were evaluated by calculating the oil-water partition coefficients (log P). Anti-hypoxia activities of HPN and its long-chain lipophilic derivatives 1-5 were evaluated using normobaric hypoxia test and acute decompression hypoxia test.

RESULTS

The structures of the derivatives were confirmed by infrared spectroscopy, electron paramagnetic resonance and high resolution mass spectroscopy. The yields of target derivatives were all above 92%, and the purities were all above 96%. The log P values of derivatives 1-5 were 2.78, 2.00, 2.04, 2.88 and 3.10, which were higher than that of HPN (0.97). Derivatives 1-5 significantly prolonged the survival time of mice at the dose of 0.3 mmol/kg in normobaric hypoxic test and reduced the mortality rate of acute decompression hypoxic mice to 60%, 70%, 60%, 70% and 40%, respectively.

CONCLUSIONS

The synthesis of derivatives 1-5 is convenient, and the yield is high. The synthesized derivatives especially derivative 5 show anti-hypoxic activity similar to or better than HPN at lower doses.

Bioavailability by design — Vitamin D3 liposomal delivery vehicles

Vitamin D3 deficiency has serious health consequences, as demonstrated by its effect on severity and recovery after COVID-19 infection. Because of high hydrophobicity, its absorption and subsequent redistribution throughout the body are inherently dependent on the accompanying lipids and/or proteins. The effective oral vitamin D₃ formulation should ensure penetration of the mucus layer followed by internalization by competent cells. Isothermal titration calorimetry and computer simulations show that vitamin D₃ molecules cannot leave the hydrophobic environment, indicating that their absorption is predominantly driven by the digestion of the delivery vehicle. In the clinical experiment, liposomal vitamin D₃ was compared to the oily formulation. The results obtained show that liposomal vitamin D₃ causes a rapid increase in the plasma concentration of calcidiol. No such effect was observed when the oily formulation was used. The effect was especially pronounced for people with severe vitamin D₃ deficiency.

Carnosine decreases retinal ganglion cell death in a mouse model of optic nerve crushing

PURPOSE

The objectives of this study were to investigate whether carnosine can increase retinal ganglion cell (RGC) survival in the mouse retina and to determine the possible association between nuclear factor-kappa B (NF-κB) mediated oxidative stress and neuroprotection of RGCs following optic nerve crushing (ONC).

METHODS

C57BL/6 J mice underwent ONC and were treated with carnosine (250 mg/kg) or saline intraperitoneally once daily until sacrifice. Peroxisome proliferator activated receptor (PPAR)-γ and glial fibrillary acidic protein (GFAP) expression were assessed at 1, 3, and 7 days after ONC. The effects of carnosine on the expression of PPAR-γ, GFAP, and NF-κB were assessed. To evaluate the effects of carnosine on mitochondrial biogenesis and function, we compared the expression of PPAR gamma coactivator-1α (PGC-1α) and mitochondrial transcription factor A (mtTFA) in retinas from mice that were treated with carnosine or saline at 3 days after ONC. RGC survival was assessed by labeling flat-mounted retinas with Brn3a at 2 weeks after ONC.

RESULTS

The expression levels of PPAR-γ and GFAP were upregulated in saline-treated retinas for 7 days after ONC, with maximal expression at 3 days, and carnosine treatment effectively attenuated this upregulation. In addition, upregulation of NF-κB, PGC-1α and mtTFA expression was also observed in saline-treated retinas after ONC, and this upregulation was blocked by carnosine treatment, resulting in a significant difference between carnosine-treated and saline-treated retinas after ONC. Immunohistochemical staining for Brn3a also showed that carnosine treatment protected against RGC loss after ONC.

CONCLUSIONS

Inhibition of NF-κB expression and oxidative stress by carnosine treatment plays a significant role in the prevention of RGC loss after ONC. The results also highlight the potential of carnosine as a neuroprotective agent against RGC loss in optic neuropathy.

Tryptophan and Kynurenine Pathway Metabolites in Animal Models of Retinal and Optic Nerve Damage: Different Dynamics of Changes

Kynurenines, products of tryptophan (TRP) metabolism, display neurotoxic (e.g., 3-hydroxykynurenine; 3-HK), or neuroprotective (e.g., kynurenic acid; KYNA) properties. Imbalance between the enzymes constituting the kynurenine pathway (KP) plays a role in several disease, including neurodegeneration. In this study, we track changes in concentrations of tryptophan and its selected metabolites after damage to retinal ganglion cells and link this data with expression of KP enzymes. Brown-Norway rats were subjected to intravitreal N-methyl-D-aspartate (NMDA) injection or partial optic nerve crush (PONC). Retinas were collected 2 and 7 days after the completion of PONC or NMDA injection. Concentrations of TRP, kynurenine (KYN), and KYNA were determined by high performance liquid chromatography (HPLC). Data on gene expression in the rat retina were extracted from GEO, public microarray experiments database. Two days after NMDA injection concentration of TRP decreased, while KYN and KYNA increased. At day 7 compared to day 2 decrease of KYN, KYNA and further reduction of TRP concentration were observed, but on day 7 KYN concentration was still elevated when compared to controls. At day 2 and 7 after NMDA injection no statistically significant alterations of 3-HK were observed. TRP and 3-HK concentration was higher in PONC group than in controls. However, both KYN and KYNA were lower. At day seven concentration of TRP, 3-HK, and KYN was higher, whereas concentration of KYNA declined. In vivo experiments showed that retinal damage or optic nerve lesion affect TRP metabolism via KP. However, the pattern of changes in metabolite concentrations was different depending on the model. In particular, in PONC KYNA and KYN levels were decreased and 3-HK elevated. These observations correspond with data on expression of genes encoding KP enzymes assessed after optic nerve crush or transection. After intraorbital optic nerve crush downregulation of KyatI and KyatIII between 24 h and 3 days after procedure was observed. Kmo expression was transiently upregulated (12 h after the procedures). After intraorbital optic nerve transsection (IONT) Kmo expression was upregulated after 48 h and 7 days, KyatI and KyatIII were downregulated after 12, 48 h, 7 days and upregulated after 15 days. Collected data point to the conclusion that development of therapeutic strategies targeting the KP could be beneficial in diseases involving retinal neurodegeneration.

Rapid repeatable in vivo detection of retinal reactive oxygen species

Oxidative injuries, such as those related to reactive oxygen species (ROS), have been implicated in various retinal and optic nerve disorders. Many ROS detection methods have been developed. Although widely utilized, many of these methods are useful only in post mortem tissues, or require relatively expensive equipment, or involve intraocular injection. In the present study, we demonstrated and characterized a chemiluminescent probe L-012 as a noninvasive, in vivo ROS detection agent in the mouse retina. Using optic nerve crush (ONC) and retinal ischemia/reperfusion (I/R) as injury models, we show that L-012 produced intensive luminescent signals specifically in the injured eyes. Histological examination showed that L-012 administration was safe to the retina. Additionally, compounds that reduce tissue superoxide levels, apocynin and TEMPOL, decreased injury-induced L-012 chemiluminescence. The decrease in L-012 signals correlated with their protective effects against retinal I/R-induced morphological and functional changes in the retina. Together, these data demonstrate the feasibility of a fast, simple, reproducible, and non-invasive detection method to monitor in vivo ROS in the retina. Furthermore, the results also show that reduction of ROS is a potential therapeutic approach for protection from these retinal injuries.

Searching for protein binding sites from Molecular Dynamics simulations and paramagnetic fragment-based NMR studies

Hotspot delineation on protein surfaces represents a fundamental step for targeting protein-protein interfaces. Disruptors of protein-protein interactions can be designed provided that the sterical features of binding pockets, including the transient ones, can be defined. Molecular Dynamics, MD, simulations have been used as a reliable framework for identifying transient pocket openings on the protein surface. Accessible surface area and intramolecular H-bond involvement of protein backbone amides are proposed as descriptors for characterizing binding pocket occurrence and evolution along MD trajectories. TEMPOL induced paramagnetic perturbations on (1)H-(15)N HSQC signals of protein backbone amides have been analyzed as a fragment-based search for surface hotspots, in order to validate MD predicted pockets. This procedure has been applied to CXCL12, a small chemokine responsible for tumor progression and proliferation. From combined analysis of MD data and paramagnetic profiles, two CXCL12 sites suitable for the binding of small molecules were identified. One of these sites is the already well characterized CXCL12 region involved in the binding to CXCR4 receptor. The other one is a transient pocket predicted by Molecular Dynamics simulations, which could not be observed from static analysis of CXCL12 PDB structures. The present results indicate how TEMPOL, instrumental in identifying this transient pocket, can be a powerful tool to delineate minor conformations which can be highly relevant in dynamic discovery of antitumoral drugs.