Protective effects of SS31 on t‑BHP induced oxidative damage in 661W cells

Application research of novel peptide mitochondrial-targeted antioxidant SS-31 in mitigating mitochondrial dysfunction

Due to the pivotal role of mitochondria in the generation of adenosine triphosphate (ATP) and the regulation of cellular homeostasis, mitochondrial dysfunction may exert a profound impact on various physiological systems, potentially precipitating a spectrum of distinct diseases. Consequently, research pertaining to mitochondrial therapeutics has assumed increasing significance, warranting heightened scrutiny. In recent years, the field of mitochondrial therapy has witnessed noteworthy advancements, with active exploration into diverse pharmacological agents aimed at ameliorating mitochondrial function. Elamipretide (SS-31), a novel synthetic mitochondrial-targeted antioxidant, has emerged as a promising candidate with extensive therapeutic potential. Its notable attributes encompass the mitigation of oxidative stress, the suppression of inflammatory processes, the maintenance of mitochondrial dynamics, and the prevention of cellular apoptosis. As such, SS-31 may emerge as a viable choice for the treatment of mitochondrial dysfunction-related ailments in the foreseeable future. This article extensively expounds upon the superiority of SS-31 over natural antioxidants and traditional mitochondrial-targeted antioxidants, delves into its mechanisms of modulating mitochondrial function, and comprehensively summarizes its applications in alleviating mitochondrial dysfunction-associated disorders. Furthermore, we offer a comprehensive outlook on the expansive prospects of SS-31's future development and application.

Mitochondrial-Targeted Antioxidant Peptide SS31 Prevents RPE Cell Death under Oxidative Stress

This work aims at investigating the protective effects of the mitochondria-targeted peptide SS31, on mitochondria function, preventing human retinal pigment epithelial cell-19 (ARPE-19) cell apoptosis. The ARPE-19 cells were subjected to 24 h of intervention with H2O2 of various concentrations (0, 100, 150, 200, 250, 300, and 500 μmol/L). Various concentrations of SS31 (10 nM, 100 nM, and 1 μmol/L) pretreated the cells for 2 h. The MTT assay determined cell viability. ARPE-19 cell apoptosis was observed by 4',6-diamidino-2-phenylindole (DAPI) staining under fluorescence microscope and detected by Annexin-V/PI staining under flow cytometry. The measurement of reactive oxygen species (ROS) release level used MitoSOX Red (a mitochondrial superoxide indicator) and the probe 2'-7'dichlorofluorescin diacetate (DCFH-DA). And with the use of a JC-1 probe, the mitochondrial membrane potential (MMP; ΔΨm) was analyzed. Reverse transcription polymerase chain reaction (RT-PCR) and real-time PCR were responsible for measuring the levels of apoptosis related genes (Bcl-2, Bax, and Caspase-3). The cell viability increased significantly with SS31 pretreated (P < 0.05). In the SS31 + H2O2 group, the fluorescence of the cell nuclei with DAPI staining was weaker than H2O2 along group accordance with the decreased ratio of apoptotic cells (P < 0.05). The ROS generation decreased in SS31 pretreated group, with the increased ΔΨm. The RT-PCR result showed decreased Bax gene and Caspase-3 gene expression with SS31 pretreatment, while increased antiapoptotic gene Bcl-2 (P < 0.05). We provide evidence that SS31 promotes resilience of RPE cells to oxidative stress by stabilizing mitochondrial function.

Synthesis, Characterization, and Specific Localization of Mitochondrial-Targeted Antioxidant Peptide SS31 Probe

The aim of this study is to investigate the targeting efficiency of FITC-SS31 to mitochondria in both normal and H2O2-induced oxidative damaged 661W cells, characterizing the properties of FITC-SS31 in the biological assays. The purity and molecular weight of FITC-SS31 were identified using HPLC and MS. MTT and LDH assays were used to evaluate the cytotoxicity and cell permeability. The binding ability of FITC-SS31 to cells was demonstrated by flow cytometry. The colocalization of FITC-SS31 and MitoTracker both in normal and oxidative cells was analyzed by a laser confocal microscope. We detected the DEGs between SS31+H2O2 and H2O2-alone-treated cells by RNA seq. GO and KEGG analyses were performed to predict the functional gene of SS31. The molecular weight of FITC-SS31 was 1142.2 with the 97.76% purity. The flow cytometry results showed that the MFI (mean fluorescence intensity) of FITC-SS31 in normal cells in the 4 h probe treatment group was higher than that in the 2 h and the 0 h group. The MFI in the 2 h probe treatment group was much higher than that in the 4 h and 0 h groups in damaged cells. The positive rate of 10 μM FITC-SS31 was higher than that of 1 μM and 5 μM. Fluorescein imaging analysis confirmed that FITC-SS31 was overlapped with MitoTracker. Through the analysis, DEGs were highly expressed in "localization, organelle, antioxidant activity, binding" functions and enriched in "AMPK signaling pathway, MAPK targets/nuclear events mediated by MAP kinase pathway and PI3K-Akt signaling pathway." It is speculated that SS31 exerts an antioxidant effect through one of these pathways. We hypothesized that SS31 could play a more efficient role in the pathological cells in the half-life period to avoid cell death due to oxidative damage. The functions of the DEGs in SS31+H2O2 and H2O2-alone samples are related to the localization and antioxidant activity of SS31. DEGs are mostly enriched in the AMPK signaling pathway, which needs further studies.

ACTH(6-9)PGP Peptide Protects SH-SY5Y Cells from H2O2, tert-Butyl Hydroperoxide, and Cyanide Cytotoxicity via Stimulation of Proliferation and Induction of Prosurvival-Related Genes

Stabilized melanocortin analog peptide ACTH(6-9)PGP (HFRWPGP) possesses a wide range of neuroprotective activities. However, its mechanism of action remains poorly understood. In this paper, we present a study of the proproliferative and cytoprotective activity of the adrenocorticotropic hormone fragment 6-9 (HFRW) linked with the peptide prolyine-glycyl-proline on the SH-SY5Y cells in the model of oxidative stress-related toxicity. The peptide dose-dependently protected cells from H2O2, tert-butyl hydroperoxide, and KCN and demonstrated proproliferative activity. The mechanism of its action was the modulation of proliferation-related NF-κB genes and stimulation of prosurvival NRF2-gene-related pathway, as well as a decrease in apoptosis.

Protective Effect of Mitochondrially Targeted Peptide Against Oxidant Injury of Cone Photoreceptors Through Preventing Necroptosis Pathway

Retinopathy is an eye disease caused by the death of retinal cells in the macular area and the surrounding choroid. As the retinal rod cell dysfunction and death lead to the loss of night vision, the disease will lead to visual dysfunction and blindness as the disease progresses. Because of the irreversible nature of cell death, gene therapy has become a research hotspot in the field of retinopathy. But the technology is still in animal studies or clinical trials, and more research is needed to prove its feasibility. In this study, oxidative damage cell model was established and divided into a control group, H₂O₂ group, SS31 +NEC1 group, SS31 +H₂O₂ group, and SS31 +NEC1 +H₂O₂ group, for different interventions. The cell survival rate of the H₂O₂ group was significantly increased compared with those of the SS31 + H₂O₂ group, SS31 +NEC1 +H₂O₂ group, and NEC1 +H₂O₂ group. Nec1 combined treatment significantly reduced reactive oxygen species (ROS) production compared with that in the H₂O₂ group. The level of MDA in the SS31 group, Nec-1 group and combined treatment of SS31 +NEC1 group decreased significantly compared with the H₂O₂ group. The proportion of cells with decreased mitochondrial membrane potential in the H₂O₂ group significantly increased, and the rate of positivity for propidium iodide (PI) of 661W cells in the H₂O₂ group and the control group significantly increased. Nine hours after H₂O₂ treatment of 661W cells, the RIP3 expression level began to increase, and peaked at 24 h. The level of RIP3 in the H₂O₂ group was significantly increased, while this level was downregulated in the SS31 and NEC1 treatment groups. Therefore, this study suggests that SS31 has a partial protective effect on 661W cells by inhibiting necrosis, which has certain guiding significance for the treatment of retinal diseases.

Exosomes derived from neural progenitor cells preserve photoreceptors during retinal degeneration by inactivating microglia

Retinal degeneration (RD) is one of the most common causes of visual impairment and blindness and is characterized by progressive degeneration of photoreceptors. Transplantation of neural stem/progenitor cells (NPCs) is a promising treatment for RD, although the mechanisms underlying the efficacy remain unclear. Accumulated evidence supports the notion that paracrine effects of transplanted stem cells is likely the major approach to rescuing early degeneration, rather than cell replacement. NPC-derived exosomes (NPC-exos), a type of extracellular vesicles (EVs) released from NPCs, are thought to carry functional molecules to recipient cells and play therapeutic roles. In present study, we found that grafted human NPCs (hNPCs) secreted EVs and exosomes in the subretinal space (SRS) of RCS rats, an RD model. And direct administration of mouse neural progenitor cell-derived exosomes (mNPC-exos) delayed photoreceptor degeneration, preserved visual function, prevented thinning of the outer nuclear layer (ONL), and decreased apoptosis of photoreceptors in RCS rats. Mechanistically, mNPC-exos were specifically internalized by retinal microglia and suppressed their activation in vitro and in vivo. RNA sequencing and miRNA profiling revealed a set of 17 miRNAs contained in mNPC-exos that markedly inhibited inflammatory signal pathways by targeting TNF-α, IL-1β, and COX-2 in activated microglia. The exosomes derived from hNPC (hNPC-exos) contained similar miRNAs to mNPC-exos that inhibited microglial activation. We demonstrated that NPC-exos markedly suppressed microglial activation to protect photoreceptors from apoptosis, suggesting that NPC-exos and their contents may be the mechanism of stem cell therapy for treating RD.

SS31 Ameliorates Sepsis-Induced Heart Injury by Inhibiting Oxidative Stress and Inflammation

Sepsis-induced myocardial dysfunction (SIMD), lack of effective treatment, accounts for high mortality of sepsis. Mitochondrion-targeted antioxidant peptide SS31 has been revealed to be responsible for certain cardiovascular disease by ameliorating oxidative stress injury. But whether it protects a septic heart remains little known. This study sought to prove that SS31 was capable of improving sepsis-induced myocardial dysfunction dramatically. C57BL/6 mice were intraperitoneally administered lipopolysaccharide (LPS), exposed to systemic inflammation. Thirty-five C57BL/6 mice were randomly divided into four groups: sham group, LPS group (5 mg/kg), SS31 group (5 mg/kg), and SS31 + LPS group (treatment group). Heart tissues were harvested for pathological examination at the indicated time points. H9C2 cell were treated with LPS with or without the presence of SS31 (10 μM) at 37 °C to assess the effect on cardiomyocytes at the indicated time points. SS31 restored myocardial morphological damage and suppressed inflammatory response as evidenced by significantly decreasing the mRNA levels of IL-6, IL-1β, and TNF-α in vitro and in vivo. In addition, myocardial energy deficiency secondary to sepsis was remarkedly ameliorated by SS31. Furthermore, we found that SS-31 normalized the activity of malondialdehyde, glutathione peroxidase, and superoxide dismutase in vitro and in vivo, and maintained mitochondrial membrane potential (MMP) as well. And western blot was applied to measure the expressions of p-p38MAPK, p-JNK1/2, p-ERK, p62, and NF-κB p65; the results illuminated that the cardioprotective effect of SS31 was partly linked to NF-κB. In conclusion, SS31 therapy effectively protected the heart against LPS-induced cardiac damage.

Pathobiological Mechanisms of Endothelial Dysfunction Induced by tert-Butyl Hydroperoxide via Apoptosis, Necrosis and Senescence in a Rat Model

Background: Endothelial dysfunction is one of the underlying causes for vascular diseases. tert-Butyl hydroperoxide (t-BHP), a short-chain lipid hydroperoxide analog, has been reported to cause adverse effects in different systems. However, the adverse actions of t-BHP on inducing endothelial dysfunction are unclear and remain under investigation. Aim of the present study was to identify the pathobiological mechanisms of t-BHP in rat aortic endothelial cells and thoracic aorta. Methods: Primary cultured cells were treated with vehicle or t-BHP (50, 100, 250, 500, and 1,000 μM). Cells were harvested and specific analyses regarding cellular apoptosis, necrosis, and senescence were conducted. Additionally, t-BHP (0.1, 0.2, and 0.4 mmol/kg body weight) or vehicle were administered to male rats (the young group at 6 weeks of age and the mature adult group at 24 weeks of age) daily through intraperitoneal injections. At 10 days after the first drug treatment apoptotic endothelial toxicity was evaluated by biochemical, histological, and immunofluorescent staining analyses. Results: Dose-dependent effects of t-BHP were observed for the reduction of cell viability, deterioration of cell toxicity, initiation of cell cycle arrest, and triggering of apoptosis and necrosis. Moreover, increase of cells stained positive for senescence-associated beta-galactosidase (SA-β-Gal), amelioration of telomerase activity, and precipitations of necrotic, cell cycle, and apoptotic signaling regulatory proteins were also found in the in vitro model. In the in vivo study, results indicated that t-BHP at higher doses enlarged the intima-medial thickness of descending aorta in the mature adult group, but led to aortic narrowing in the young group. Increased injuries were observed by upregulating endothelial apoptosis- and senescence-positive staining, along with caspase-3 activity and down-regulating telomerase activity. Conclusion: These results confirmed that t-BHP impaired aortic endothelial cell survival at least partially by the activation of p53-mediated signaling pathways, inhibition of cell cycle regulatory proteins, and initiation of cellular senescence-related signaling pathways. In conclusion, t-BHP was found to be a major trigger for impairing aortic endothelial cell survival and deteriorating vascular dysfunction in experimental practice.

Mitochondria-Targeted Peptide SS31 Attenuates Renal Tubulointerstitial Injury via Inhibiting Mitochondrial Fission in Diabetic Mice

Objective

Renal tubular injury is an early characteristic of diabetic nephropathy (DN) that is related to mitochondrial dysfunction. In this study, we explore the effects and mechanisms of mitochondria-targeted peptide SS31 on renal tubulointerstitial injury in DN.

Method

40 C57BL/6 mice were randomly divided into control group, STZ group, STZ+SS31 group, and STZ+normal saline group. SS31 was intraperitoneally injected to the mice every other day for 24 weeks. Renal lesions and the expression of Drp1, Mfn1, Bcl-2, Bax, Caspase1, IL-1β, and FN were detected. In in vitro studies, HK-2 cells were incubated with different concentrations of D-glucose (5, 30 mM) or combined with SS31 and Drp1 inhibitor Midivi1. Mitochondrial ROS, membrane potential, and morphology have been detected to evaluate the mitochondrial function.

Results

Compared with diabetic mice, the levels of serum creatinine and microalbuminuria were significantly decreased in the SS31 group. Renal tubulointerstitial fibrosis, oxidative stress, and apoptosis were observed in diabetic mice, while the pathological changes were reduced in the SS31-treatment group. SS31 could decrease the expression of Drp1, Bax, Caspase1, IL-1β, and FN in the renal tissue of diabetic mice, while increasing the expression of Mfn1. Additionally, mitochondria exhibit focal enlargement and crista swelling in renal tubular cells of diabetic mice, while SS31 treatment could partially block these changes. An in vitro study showed that pretreatment with SS31 or Drp1 inhibitor Mdivi1 could restore the level of mitochondrial ROS, the membrane potential levels, and the expressions of Drp1, Bax, Caspase1, IL-1β, and FN in HK-2 cells under high-glucose conditions.

Conclusion

SS31 protected renal tubulointerstitial injury in diabetic mice through a decrease in mitochondrial fragmentation via suppressing the expression of Drp1 and increasing the expression of Mfn1.

Rescue of Retinal Degeneration in rd1 Mice by Intravitreally Injected Metformin

Retinitis pigmentosa (RP) is a progressive hereditary retinal degenerative disease in which photoreceptor cells undergo degeneration and apoptosis, eventually resulting in irreversible loss of visual function. Currently, no effective treatment exists for this disease. Neuroprotection and inflammation suppression have been reported to delay the development of RP. Metformin is a well-tested drug used to treat type 2 diabetes, and it has been reported to exert beneficial effects in neurodegenerative diseases, such as Parkinson’s disease and Alzheimer’s disease. In the present study, we used immunofluorescence staining, electroretinogram (ERG) recordings and RNA-Seq to explore the effects of metformin on photoreceptor degeneration and its mechanism in rd1 mice. We found that metformin significantly reduced apoptosis in photoreceptors and delayed the degeneration of photoreceptors and rod bipolar cells in rd1 mice, thus markedly improving the visual function of rd1 mice at P14, P18, and P22 when tested with a light/dark transition test and ERG. Microglial activation in the outer nuclear layer (ONL) of the retina of rd1 mice was significantly suppressed by metformin. RNA-Seq showed that metformin markedly downregulated inflammatory genes and upregulated the expression of crystallin proteins, which have been demonstrated to be important neuroprotective molecules in the retina, revealing the therapeutic potential of metformin for RP treatment. αA-crystallin proteins were further confirmed to be involved in the neuroprotective effects of metformin in a Ca²⁺ ionophore-damaged 661W photoreceptor-like cell line. These data suggest that metformin exerts a protective effect in rd1 mice via both immunoregulatory and new neuroprotective mechanisms.

Mitochondria-targeted antioxidant peptide SS-31 mediates neuroprotection in a rat experimental glaucoma model

To investigate the neuroprotective effects of the mitochondria-targeted antioxidant Szeto-Schiller peptide 31 (SS-31) in a rat experimental glaucoma model, SS-31 was intraperitoneally (IP) injected into Sprague-Dawley rats, followed by intracameral injection of polystyrene microspheres to induce elevated intraocular pressure (IOP). After 6 weeks, electroretinography (ERG) and flash visual-evoked potentials (F-VEPs) were recorded to assess retinal function. Hematoxylin-eosin staining was performed on retinal cross-sections to measure ganglion cell complex (GCC) thickness. Apoptotic retinal cells were assessed by TUNEL staining. Brn3a-positive retinal ganglion cells (RGCs) were counted in retinal flat mounts via immunofluorescence. The retinal total SOD, SOD2, and MDA expression levels were assessed in retinal tissue homogenates. The cyt c, Bax, and Bcl-2 protein levels in rat retinas were detected by western blot analysis. Bax and Bcl-2 expressions were also evaluated using immunohistochemistry in paraffinized sections. Our results showed that the rats that received microsphere injection developed elevated IOP. SS-31 ameliorated the reductions in the a- and b-wave amplitudes on ERG and the F-VEP amplitude in glaucomatous eyes. GCC thickness was preserved, TUNEL-positive cells were decreased in the retina, and Brn3a-positive RGCs were increased in the SS-31-treated glaucoma group compared with those in the non-treated glaucoma group. SS-31 significantly reduced MDA levels and increased SOD2 levels after glaucoma induction. Significant suppression of cyt c release, upregulation of Bcl-2, and downregulation of Bax were observed following SS-31 administration. In summary, SS-31 exerts neuroprotective effects in this experimental glaucoma model by inhibiting mitochondrial dysfunction and therefore represents a promising therapeutic agent for glaucoma.

The mitochondrial antioxidant SS-31 increases SIRT1 levels and ameliorates inflammation, oxidative stress and leukocyte-endothelium interactions in type 2 diabetes

There is growing focus on mitochondrial impairment and cardiovascular diseases (CVD) in type 2 diabetes (T2D), and the development of novel therapeutic strategies in this context. It is unknown whether mitochondrial-targeting antioxidants such as SS-31 protect sufficiently against oxidative damage in diabetes. We aimed to evaluate if SS-31 modulates SIRT1 levels and ameliorates leukocyte-endothelium interactions, oxidative stress and inflammation in T2D patients. Anthropometric and metabolic parameters were studied in 51 T2D patients and 57 controls. Production of mitochondrial reactive oxygen species (ROS), mitochondrial membrane potential, glutathione content, leukocyte-endothelium interactions, NFκB-p65, TNFα and SIRT1 levels was measured in leukocytes treated or not with SS-31. We observed increased mitochondrial ROS production that was restored by SS-31 treatment. SS-31 also increased mitochondrial membrane potential, glutathione content, SIRT1 levels and leukocyte rolling velocity and reduced rolling flux and adhesion in T2D patients. NFκB-p65 and TNFα, which were enhanced in diabetic patients, were also reduced by SS-31 treatment. Our results reveal that SS-31 exerts beneficial effects on the leukocytes of T2D patients by reducing oxidative stress, leukocyte-endothelium interactions, NFκB and TNFα and by increasing SIRT1 levels. These actions support its use as a potential agent against CVD risk.

Lipid (per) oxidation in mitochondria: an emerging target in the ageing process?

Lipids are essential for physiological processes such as maintaining membrane integrity, providing a source of energy and acting as signalling molecules to control processes including cell proliferation, metabolism, inflammation and apoptosis. Disruption of lipid homeostasis can promote pathological changes that contribute towards biological ageing and age-related diseases. Several age-related diseases have been associated with altered lipid metabolism and an elevation in highly damaging lipid peroxidation products; the latter has been ascribed, at least in part, to mitochondrial dysfunction and elevated ROS formation. In addition, senescent cells, which are known to contribute significantly to age-related pathologies, are also associated with impaired mitochondrial function and changes in lipid metabolism. Therapeutic targeting of dysfunctional mitochondrial and pathological lipid metabolism is an emerging strategy for alleviating their negative impact during ageing and the progression to age-related diseases. Such therapies could include the use of drugs that prevent mitochondrial uncoupling, inhibit inflammatory lipid synthesis, modulate lipid transport or storage, reduce mitochondrial oxidative stress and eliminate senescent cells from tissues. In this review, we provide an overview of lipid structure and function, with emphasis on mitochondrial lipids and their potential for therapeutic targeting during ageing and age-related disease.

Transplanted olfactory ensheathing cells restore retinal function in a rat model of light-induced retinal damage by inhibiting oxidative stress

There is still not an effective treatment for continuous retinal light exposure and subsequent photoreceptor degeneration. Olfactory ensheathing cell (OEC) transplantation has been shown to be neuroprotective in spinal cord, and optic nerve injury and retinitis pigmentosa. However, whether OECs protect rat photoreceptors against light-induced damage and how this may work is unclear. Thus, to elucidate this mechanism, purified rat OECs were grafted into the subretinal space of a Long-Evans rat model with light-induced photoreceptor damage. Light exposure decreased a- and b- wave amplitudes and outer nuclear layer (ONL) thickness, whereas the ONL of rats exposed to light for 24 h after having received OEC transplants in their subretinal space was thicker than the PBS control and untreated groups. A- and b- wave amplitudes from electroretinogram of OEC-transplanted rats were maintained until 8 weeks post OEC transplantation. Also, transplanted OECs inhibited formation of reactive oxygen species in retinas exposed to light. In vitro experiments showed that OECs had more total antioxidant capacity in a co-cultured 661W photoreceptor cell line, and cells were protected from damage induced by hydrogen-peroxide. Thus, transplanted OECs preserved retinal structure and function in a rat model of light-induced degeneration by suppressing retinal oxidative stress reactions.