Eye-Light on Age-Related Macular Degeneration: Targeting Nrf2-Pathway as a Novel Therapeutic Strategy for Retinal Pigment Epithelium

Abstract

Age-related macular degeneration (AMD) is a common disease with a multifactorial aetiology, still lacking effective and curative therapies. Among the early events triggering AMD is the deterioration of the retinal pigment epithelium (RPE), whose fundamental functions assure good health of the retina. RPE is physiologically exposed to high levels of oxidative stress during its lifespan; thus, the integrity and well-functioning of its antioxidant systems are crucial to maintain RPE homeostasis. Among these defensive systems, the Nrf2-pathway plays a primary role. Literature evidence suggests that, in aged and especially in AMD RPE, there is an imbalance between the increased pro-oxidant stress, and the impaired endogenous detoxifying systems, finally reverberating on RPE functions and survival. In this in vitro study on wild type (WT) and Nrf2-silenced (siNrf2) ARPE-19 cells exposed to various AMD-related noxae (H 2 O 2 , 4-HNE, MG132 + Bafilomycin), we show that the Nrf2-pathway activation is a physiological protective stress response, leading downstream to an up-regulation of the Nrf2targets HO1 and p62, and that a Nrf2 impairment predisposes the cells to a higher vulnerability to stress. In search of new pharmacologically active compounds potentially useful for AMD, four nature-inspired hybrids (NIH) were individually characterized as Nrf2 activators, and their pharmacological activity was investigated in ARPE-19 cells. The Nrf2 activator dimethyl-fumarate (DMF; 10 mM) was used as a positive control. Three out of the four tested NIH (5 mM) display both direct and indirect antioxidant properties, in addition to cytoprotective effects in ARPE-19 cells under pro-oxidant stimuli. The observed pro-survival effects require the presence of Nrf2, with the exception of the lead compound NIH1, able to exert a still significant, albeit lower, protection even in siNrf2 cells, supporting the concept of the existence of both Nrf2-dependent and independent pathways mediating pro-survival effects. In conclusion, by using some pharmacological tools as well as a reference compound, we dissected the role of the Nrf2-pathway in ARPE-19 stress response, suggesting that the Nrf2 induction represents an efficient defensive strategy to prevent the stressinduced damage.

Targeting Cytokine Release Through the Differential Modulation of Nrf2 and NF-κB Pathways by Electrophilic/Non-Electrophilic Compounds

“…As shown in Figure 2A, compounds 1, 2, as well as CURC, significantly induced Nrf2 nuclear translocation, whereas compounds 3 and 4 did not increase Nrf2 nuclear content (Figure 2A). Such results are consistent with our previous work (Simoni et al, 2017;Serafini et al, 2019;Catanzaro et al, 2020), where the ability of compounds 1 and 2, but not 3, to activate the Nrf2 pathway in SH-SY5Y and ARPE-19 cells suggested that the addition of Keap1 nucleophilic cysteines to (pro)electrophilic portions of the molecule could represent the initiating event. The finding that the newly synthesized molecule, compound 4, was also unable to induce Nrf2 nuclear translocation corroborates this hypothesis.…”

“…Consistently with our previous data on a different cellular model (Simoni et al, 2016;Simoni et al, 2017;Serafini et al, 2019;Catanzaro et al, 2020), all the compounds were well-tolerated, with a slight reduction of cell viability of about 10% observed for compounds 3 and 4 ( Figure 1). Based on these results and according to our previous investigations (Simoni et al, 2017;Serafini et al, 2019;Catanzaro et al, 2020), all further experiments were conducted using the concentration of 5 mM.…”

“…Thus, we studied a set of previously synthesized compounds (1, 2, and 3), for which the ability to induce the Nrf2 pathway was strictly related to the (pro)electrophilic character of the molecule in THP-1 cells, a widely used cellular model for the immune modulation approach (Chanput et al, 2014). In agreement with previous results (Simoni et al, 2017;Serafini et al, 2019;Catanzaro et al, 2020), a significant effect was detected for the Nrf2 inducers 1 and 2, carrying a catechol moiety and/or an a,b-unsaturated carbonyl group, while no effect was observed for compound 3, lacking both (pro)-electrophilic features ( Table 1). The same lack of effect was observed for compound 4, which was included in the study to exclude possible oxidative activation into electrophilic metabolites such as quinone methide, which could provide an additional site for adduct formation.…”

Oxidative Stress and Vascular Dysfunction in the Retina: Therapeutic Strategies

“…Zyla et al showed that Tecfidera ® is effective in preventing or delaying recurrences of optic neuritis in patients with optic neuritis during RRMS in a retrospective study [ 262 ]. Dimethyl fumarate represented an efficient defensive strategy by activating the Nrf2 pathway to prevent the ROS-induced injury in RPE cells [ 263 ]. Wan et al suggested that trimetazidine has antioxidative and anti-inflammatory effects by activating the Nrf2/heme oxygenase-1 (HO-1) pathway, contributing to the therapeutic effects against IOP-induced retinal damage [ 264 ].…”

Neuroprotective Properties of Dimethyl Fumarate Measured by Optical Coherence Tomography in Non-inflammatory Animal Models

“…In AMD, one of the most common vision-threatening diseases, the RPE is physiologically exposed to high levels of oxidative stress during its lifespan. For the well-functioning of its antioxidant systems, the Nrf2-pathway plays an important role ( 24 ). Both approaches led to a prominent degradation of retinal tissue.…”