The translocator protein (TSPO), an evolutionarily conserved protein located on the outer mitochondrial membrane, is typically expressed at low levels in the central nervous system under normal physiological conditions. However, its expression can increase in response to various pathological conditions, such as neurodegenerative diseases and neuroinflammation. Retinitis pigmentosa (RP) refers to a group of inherited degenerative diseases of the retina; the progression of the pathology is linked to a chronic inflammatory state that leads to the progressive loss of photoreceptors and ultimately to blindness. One of the key processes contributing to the gradual loss of photoreceptors is neuroinflammation, a mechanism in which the TSPO plays a newly studied role. In this context, TSPO could be an excellent target. In the current study, rd10 mice of both sexes were treated with a TSPO ligand, PIGA1138, as an ophthalmic suspension (1 mg/mL) from post-natal day (P)18 to P30, P60, and P90. Retinal function was evaluated through electroretinography, while visual acuity was assessed using the Prusky Water Maze task. Additionally, molecular analyses were performed to assess TSPO expression, alongside examinations of retinal morphology. Results showed significant retinal preservation, reduced photoreceptor loss, and improved retinal responses, suggesting preserved visual function. These findings highlight PIGA1138’s potential in mitigating retinal degeneration and preserving function in retinal diseases like RP.

Saffron, branded as Repron^®, is effective in slowing the progression of several neurodegenerative diseases. Its production, however, requires specific cultivation techniques and procedures that, together with low yields, make it expensive. To address this challenge, hydroponic cultivation has been adopted. Previous studies have shown that hydroponically cultivated saffron and Repron^® share comparable chemical compositions and neuroprotective effects under oxidative stress conditions. In this study, we evaluated the protective properties of extracts derived from Crocus sativus L. waste, compared with those of saffron derived from stigmas. Human retinal pigment epithelium (ARPE-19) cells were pre-treated with extracts of various plant waste fractions before being subjected to three stress conditions: H₂O₂-induced oxidative stress (500 μM, 3 h), lipopolysaccharide (LPS; 0.25 mg/mL, 24 h), and hyperglycemia (25 mM glucose, 96 h). Saffron Repron^® served as a positive control. The results revealed that the extract derived from C. sativus waste had superior protective effects against oxidative stress and inflammation by preserving the state of the mitochondria and tight junctions (ZO-1); conversely, the tepal extract alone was more effective under hyperglycemic conditions by also modulating acrolein levels. These results suggest that different plant fractions contain bioactive compounds with specific protective actions, which together lead to increased cell survival.

Background: Hyperglycemia contributes to diabetic retinopathy by promoting oxidative stress, inflammatory signaling, retinal pigment epithelial (RPE) dysfunction, and vascular endothelial growth factor A (VEGF-A) secretion. Saffron Repron® (sR), selected (and patented) according to its chemical composition, has been shown to activate neuroprotective responses. This study investigated whether sR pretreatment modulates high glucose-induced oxidative damage, antioxidant and inflammatory signaling, VEGF-A secretion, and paracrine endothelial activation in ARPE-19 cells. Methods: ARPE-19 cells were pretreated with sR (40 μg/mL for 24 h), washed, and exposed to high-glucose (HG) (25 mM) for 24 or 96 h. Cell viability and cytotoxicity were assessed using colorimetric assays, reactive oxygen species (ROS) using a luminescence assay, superoxide dismutase 2 (SOD2), nuclear factor erythroid 2–related factor 2 (NRF2), KEAP1, nuclear factor kappa B (NF-κB), and IκBα expression by western blotting, catalase activity by spectrophotometry, and VEGF-A secretion by bioluminescent immunoassay. Human microvascular endothelial cells (HMEC-1) were exposed to ARPE-19 conditioned media for 24 h, after which viability and ROS levels were evaluated. Data were analyzed using one-way analysis of variance followed by Tukey’s post-hoc test. Results: sR alone did not substantially affect basal ARPE-19 viability or VEGF-A secretion. HG increased cytotoxicity and ROS levels at 24 h and reduced viability, while increasing the cytotoxicity/viability ratio and ROS levels at 96 h. sR reduced HG-induced cytotoxicity, restored viability at 96 h, and normalized ROS levels. However, SOD2 expression and catalase activity were reduced by HG and/or sR, indicating that sR-mediated ROS reduction was not associated with induction of these antioxidant defenses. Total NRF2 expression and the NRF2/KEAP1 ratio remained unchanged, although sR prevented HG-induced KEAP1 upregulation at 24 h. HG altered the NF-κB/IκBα balance and increased VEGF-A secretion at both time points; sR did not prevent increase in VEGF-A at 24 h but significantly reduced the HG-induced increase at 96 h. Conditioned media from HG-treated ARPE-19 cells increased HMEC-1 viability and ROS levels, whereas media from sR-pretreated HG cells attenuated these effects. Conclusions: Pretreatment with sR protects ARPE-19 cells from HG-induced cytotoxicity and oxidative stress primarily by reducing ROS levels rather than by inducing NRF2/SOD2-associated antioxidant responses. sR pretreatment also attenuated the pro-oxidative paracrine effects of HG-exposed ARPE-19 RPE model on endothelial cells, supporting further investigation of its potential protective effects in models of hyperglycemic retinal stress.

Introduction: Diabetic retinopathy (DR) is characterized by early retinal neurodegeneration accompanied by progressive alterations of the retinal microvasculature, both exacerbated by hyperglycemia-induced oxidative stress and inflammation. Mitochondrial dysfunction critically contributes to neuronal loss and vascular impairment. The 18 kDa Translocator Protein (TSPO) is a mitochondrial outer membrane protein whose expression is increased in activated retinal glial cells and represents a promising target to modulate neuroinflammation and oxidative stress. This study evaluates the therapeutic potential of the TSPO ligand PIGA-1138 in experimental models of DR. Methods: PIGA-1138 (3 µM in vitro; 10 mg/kg/day, i.p., in vivo) was evaluated in high glucose (HG)-exposed 661W retinal cells and in streptozotocin (STZ, 150 mg/kg)-induced diabetic C57BL/6J mice. Cell viability, mitochondrial function, oxidative stress, and Nrf2, HO-1, and SOD1 expression were assessed in vitro. Retinal function and morphology were evaluated in vivo by electroretinography (ERG), visual acuity testing, and optical coherence tomography (OCT) at 30 and 60 days after diabetes induction. Results: PIGA-1138 significantly improved cell viability, reducing apoptosis (TUNEL p ≤ 0.01), preserving mitochondrial membrane potential (MitoRed p ≤ 0.01), reducing oxidative damage, and enhancing Nrf2 nuclear translocation together with HO-1 (p ≤ 0.05) and SOD1 (p ≤ 0.01) expression in HG-treated retinal cells. In diabetic mice, treatment preserved ERG responses and limited retinal thinning at 60 days (p ≤ 0.01), while showing a trend toward preserving visual acuity. Conclusions: Targeting mitochondrial TSPO with PIGA-1138 attenuates key hallmarks of DR by mitigating oxidative stress, suppressing neuroinflammation, and preserving retinal structure and function. These findings support TSPO as a potential disease-modifying target for DR.