Literature Review: The Neuroprotective Role of the Mitochondria-Targeted Antioxidant Peptide SS-31 in Rat Experimental Glaucoma Models
Release time:
2025-12-28
In glaucoma research, accurate and reliable measurement of intraocular pressure (IOP) is crucial for assessing model success and treatment efficacy. In this 2019 study, scientists used the Icare Tonolab rebound tonometer, specifically designed for small animals, to continuously monitor IOP changes in rats, thereby establishing a reliable foundation for subsequent evaluation of neuroprotective effects.
Research Background:
Glaucoma is a progressive neurodegenerative disease with a complex pathogenesis and is the second leading cause of irreversible blindness worldwide. According to statistics from 2010, there were approximately 60.5 million glaucoma patients globally, and this number is expected to increase to 80 million by 2020. The characteristic pathological change in glaucoma is the progressive loss of retinal ganglion cells (RGCs) and their axons, which gradually leads to visual field defects. Elevated intraocular pressure (IOP) is considered the primary risk factor for glaucoma, and conventional clinical treatments primarily focus on lowering IOP. It is noteworthy that some patients exhibit normal intraocular pressure, while others still experience progressive visual field defects despite effective control of IOP through medication or surgical interventions. Therefore, it is essential to explore other factors related to the pathogenesis. Mitochondrial dysfunction and oxidative stress are significant contributors to neurodegeneration and retinal ganglion cell death in glaucoma.
Research Objective
To investigate the neuroprotective effect of the mitochondria-targeted antioxidant peptide SS-31 (Szeto-Schiller peptide 31) in an experimental rat glaucoma model, researchers administered SS-31 via intraperitoneal (IP) injection to Sprague-Dawley rats, followed by induction of elevated intraocular pressure (IOP) through anterior chamber injection of polystyrene microbeads. Six weeks later, retinal function was assessed via electroretinogram (ERG) and flash visual evoked potential (F-VEP) recordings. Hematoxylin-eosin staining of retinal cross-sections was used to measure the thickness of the ganglion cell complex (GCC), TUNEL staining to detect retinal cell apoptosis, and whole-mount retinal immunohistochemistry to count Brn3a-positive retinal ganglion cells (RGCs). Additionally, total superoxide dismutase (SOD), SOD2, and malondialdehyde (MDA) expression levels were measured in retinal tissue homogenates, Western blot was performed to analyze cytochrome c (cyt c), Bax, and Bcl-2 protein levels in the retina, and paraffin section immunohistochemistry was used to evaluate the expression of Bax and Bcl-2.
Research Methods
This study utilized 68 male Sprague-Dawley (SD) rats (6 weeks old; 150-180 g) provided by the Experimental Animal Center of Southwest Medical University (Luzhou, China). All animals were housed indoors under a fixed 12/12-hour light/dark cycle with free access to food and water. Experimental procedures strictly adhered to the ARVO Statement for the Use of Animals in Ophthalmic and Vision Research and the animal experiment guidelines of Southwest Medical University. The 68 rats were randomly divided into four groups: (1) Glaucoma group (Group A): 17 rats receiving anterior chamber injection of 10 μm polystyrene microbeads; (2) Glaucoma + SS-31 group (Group B): 17 rats receiving anterior chamber injection of microbeads combined with intraperitoneal injection of SS-31; (3) Control group (Group C): 17 normal rats receiving no intervention; (4) Control + SS-31 group (Group D): 17 normal rats receiving only intraperitoneal injection of SS-31. Rats were anesthetized via intraperitoneal injection of 5 mg/kg pentobarbital sodium (Huaxia, Chengdu, China) combined with topical anesthesia using oxybuprocaine hydrochloride (Santen, Osaka, Japan). Rats in Groups A and B received an intracameral injection of 5 μl of 10 μm polystyrene microbeads (FluoSpheres; Invitrogen, Carlsbad, USA) into the right eye using a 33-gauge Hamilton syringe. Four weeks after the initial injection, the procedure was repeated. Following the injection, topical levofloxacin eye drops (Cravit, Santen Pharmaceutical, Osaka, Japan) were applied. Intraocular pressure (IOP) of the right eye was measured six times over 4 to 7 minutes in awake rats using the Tonolab rebound tonometer (Icare Finland Oy, Helsinki, Finland), designed specifically for rodents. Rats in Groups B and D received daily intraperitoneal injections of SS-31 (3 mg/kg; ChinaPeptides Co., Ltd., Hangzhou, China) for 7 weeks. All rats were euthanized, and samples from the right eye were collected. After completing the SS-31 administration, electroretinogram (ERG) was performed using the Reti-com system (Roland, Los Angeles, USA). This electrophysiological technique objectively assesses retinal function, particularly suited for analyzing retinal ganglion cell activity in neurodegenerative diseases such as glaucoma.
Research Results
Following the initial microsphere injection, intraocular pressure (IOP) exhibited a sustained and gradual upward trend. Pre-injection baseline IOP remained within the normal range (9.67±0.67 to 9.96±0.59 mmHg), with no significant differences observed among the four groups (P>0.05 vs. Group C). Post-injection, Groups A and B showed sustained elevated IOP throughout the observation period, while the non-injection groups (Groups C and D) maintained stable levels. There were no significant differences in IOP between Groups C and D from week 1 to week 7 post-operation, with all eyes maintaining stable IOP levels; similarly, no significant differences were noted in IOP changes between Groups A and B during the same 1-7 week period post-operation. At week 4 post-operation, the peak IOP in Group A reached 16.42±1.35 mmHg, while in Group B it was 16.78±1.98 mmHg, with no significant difference between the two groups' peak IOP values. SS-31 Restores Electroretinogram (ERG) and Flash Visual Evoked Potential (F-VEP) Amplitudes To evaluate the impact of SS-31 on retinal and visual pathway function, ERG and F-VEP assessments were conducted weekly for 7 weeks following SS-31 treatment. Changes in ERG for each group are shown in the accompanying figure. In this model, the amplitudes of the a-wave (369±18.65 μV) and b-wave (882±120.23 μV) in Group A rats were significantly lower than those in Group C (P=0.0001). The a-wave and b-wave amplitudes in Group C were 555.5±20.86 μV and 1443±64.08 μV, respectively, while in Group D they were 560±21.63 μV and 1455±162.94 μV. No significant differences in a-wave or b-wave amplitudes were found between Groups C and D (P=0.639 and P=0.857, respectively). These results suggest that SS-31 may mitigate electrophysiological abnormalities in the glaucoma model by protecting retinal function, although the specific mechanisms require further validation through histological analysis. SS-31 Improves Inner Retinal Ganglion Cell Complex (GCC) Thickness The effect of 7-week SS-31 treatment on the inner retinal layer was assessed by measuring GCC thickness. The GCC thickness in Groups C and D was 50.23±1.29 μm and 50.25±1.49 μm, respectively, with no significant difference between the two groups.
Research Conclusion
In summary, SS-31 demonstrated retinal neuroprotective effects in this experimental glaucoma model by inhibiting the activation of retinal apoptotic proteins and enhancing the activity of antioxidant enzymes. These results indicate that SS-31 or its analogs may serve as effective targeted agents for the treatment of glaucomatous optic neuropathy.
This mechanism is likely closely related to its mitochondria-targeted antioxidant properties, which mitigate oxidative damage to retinal ganglion cells (RGCs) by improving mitochondrial function. Future studies could further explore its clinical translational potential and synergistic effects with other neuroprotective therapies.
Source of literature ：https://academic.oup.com/abbs/article/51/4/411/5366303
Related News
