Primary open-angle glaucoma remains a global issue, lacking a definitive treatment. Increased intraocular pressure (IOP) is considered the primary risk factor of the disease and it can be caused by fibrotic-like changes in the trabecular meshwork (TM) such as increased tissue stiffness and outflow resistance. Previously, we demonstrated that the sigma-1 receptor (S1R) agonist fluvoxamine (FLU) has anti-fibrotic properties in the kidney and lung. In this study, the localization of the S1R in TM cells was determined, and the anti-fibrotic efficacy of FLU was examined in both mouse and human TM cells. Treatment with FLU reduced the F-actin rearrangement, inhibited cell proliferation and migration induced by the platelet-derived growth factor and decreased the levels of fibrotic proteins. The protective role of the S1R in fibrosis was confirmed by a more pronounced increase in alpha smooth muscle actin and F-actin bundle and clump formation in primary mouse S1R knockout TM cells. Furthermore, FLU demonstrated its protective effects by increasing the production of nitric oxide and facilitating the degradation of the extracellular matrix through the elevation of cathepsin K. These findings suggest that the S1R could be a novel target for the development of anti-fibrotic drugs and offer a new therapeutic approach for glaucoma.

The trabecular meshwork (TM) route is the principal outflow egress of the aqueous humor. Actin cytoskeletal remodeling in the TM and extracellular matrix (ECM) deposition increase TM stiffness, outflow resistance, and elevate intraocular pressure (IOP). These alterations are strongly linked to transforming growth factor-β2 (TGFβ2), a known profibrotic cytokine that is markedly elevated in the aqueous humor of glaucomatous eyes. Sigma-1 receptor (S1R) has been shown to have neuroprotective effects in the retina, but data are lacking about its role in the TM. In this study, we identified the presence of S1R in mouse TM tissue and investigated the effect of an S1R agonist fluvoxamine (FLU) on TGFβ2-induced human TM cells regarding cell proliferation; ECM-related functions, including F-actin reorganization; and the accumulation of ECM elements. TGFβ2 increased the proliferation, cytoskeletal remodeling, and protein levels of fibronectin, collagen type IV, and connective tissue growth factor, and decreased the level of matrix metalloproteinase-2. Most importantly, FLU reversed all these effects of TGFβ2, suggesting that S1R agonists could be potential candidates for preserving TM function and thus maintaining normal IOP.

Diabetic kidney disease (DKD) is the leading cause of chronic kidney disease. Current treatments for DKD do not halt renal injury progression, highlighting an urgent need for therapies targeting key disease mechanisms. Our previous studies demonstrated that activating the Sigma-1 receptor (S1R) with fluvoxamine (FLU) protects against acute kidney injury by inhibiting inflammation and ameliorating the effect of hypoxia. Based on these, we hypothesized that FLU might exert a similar protective effect in DKD. Diabetes was induced in male Wistar rats using streptozotocin, followed by a seven-week FLU treatment. Metabolic and renal parameters were assessed along with a histological analysis of glomerular damage and fibrosis. The effects of FLU on inflammation, hypoxia, and fibrosis were tested in human proximal tubular cells and normal rat kidney fibroblasts. FLU improved renal function and reduced glomerular damage and tubulointerstitial fibrosis. It also mitigated inflammation by reducing TLR4, IL6, and NFKB1 expressions and moderated the cellular response to tubular hypoxia. Additionally, FLU suppressed TGF-β1-induced fibrotic processes and fibroblast transformation. These findings suggest that S1R activation can slow DKD progression and protect renal function by modulating critical inflammatory, hypoxic, and fibrotic pathways; therefore, it might serve as a promising novel drug target for preventing DKD.

Background/Objectives: Fluvoxamine (FLU) is a selective serotonin reuptake inhibitor and one of the most potent agonists of the sigma-1 receptor. Emerging evidence shows that FLU exerts protective effects in multiple organs, making it a promising candidate for topical ocular therapy. Developing an FLU eyedrop for glaucoma can address a significant treatment gap with potentially fewer side effects compared with conventional therapies. To optimise formulation development, precise quantification of FLU in ocular compartments such as aqueous humour, as well as systemic circulation, is essential to characterise drug absorption, ocular bioavailability, and safety. Methods: We developed and validated a UHPLC-MS method for FLU detection in aqueous humour and serum using simple sample preparation steps. Results: The 11-min-long reverse phase chromatography followed by SRM-based mass spectrometry detection provides a highly selective and sensitive FLU detection method. Our method was proved to be linear in the 0.0625–1.5 µg/mL range and was validated according to the EMA guidelines. Conclusions: The simplicity of sample preparation, the tolerable matrix effects, and the favourable detection parameters provide a robust tool for preclinical pharmacokinetic and pharmacodynamic studies of FLU’s ocular protective effects.

Background/Objectives: Diabetes mellitus (DM) is associated with a doubled prevalence of elevated intraocular pressure (IOP) caused by trabecular meshwork (TM) dysfunction. Chronic hyperglycaemia leads to oxidative stress and fibrotic remodeling of the TM. We previously identified the Sigma-1 receptor (S1R) as a novel anti-fibrotic target by demonstrating that its agonist, fluvoxamine (FLU), is protective in diabetes-related renal fibrosis. Here, we investigate its potential to mitigate ocular fibrosis. Methods: First, we wanted to verify in different in vivo models (high-fat diet/streptozotocin (HFD/STZ) rats, db/db mice) that type 2 DM (T2DM) leads to fibrotic remodeling of the TM. Then, in vitro, we assessed the effect of FLU (15 µM) on hyperglycaemia-induced (HG, 25 µM) fibrosis, oxidative stress and endogenous nitric oxide (NO) production. Results: In T2DM models, excessive accumulation of collagen, α-smooth muscle actin (αSMA), fibronectin (Fn) and F-actin was observed in the eyes. Ocular fibrosis was accompanied by IOP elevation (13.7 vs. 18.7 mmHg) in db/db mice. In human TM cells (HTM5), FLU decreased HG-induced cell proliferation (14% vs. 24%) and upregulated S1R protein expression. Furthermore, FLU suppressed the expressions of key fibrotic elements, including transforming growth factor-β2 (TGF-β2) by 37%, Fn by 49%, collagen type 1 (COL1A1) and type 4 (COL4A1) by 24% and 45%, respectively. FLU also reversed HG-induced F-actin accumulation by 39% and enhanced intracellular NO levels by 34%. Crucially, FLU decreased ROS generation by half, demonstrating its protective effect against HG-induced oxidative stress. Conclusions: These findings highlight the potential of S1R activation as a promising therapeutic target to alleviate hyperglycaemia-induced injury to the TM by modulating multiple molecular pathways.