Octreotide Protects the Mouse Retina against Ischemic Reperfusion Injury through Regulation of Antioxidation and Activation of NF-κB

Diabetes Renders Photoreceptors Susceptible to Retinal Ischemia-Reperfusion Injury

Purpose

Studies have suggested that photoreceptors (PR) are altered by diabetes, contributing to diabetic retinopathy (DR) pathology. Here, we explored the effect of diabetes on retinal ischemic injury.

Methods

Retinal ischemia-reperfusion (IR) injury was caused by elevation of intraocular pressure in 10-week-old BKS db/db type 2 diabetes mellitus (T2DM) mice or C57BL/6J mice at 4 or 12 weeks after streptozotocin (STZ)-induced type 1 diabetes mellitus (T1DM), and respective nondiabetic controls. Retinal neurodegeneration was evaluated by retinal layer thinning, TUNEL staining, and neuron loss. Vascular permeability was evaluated as retinal accumulation of circulating fluorescent albumin. The effects of pretreatment with a sodium-glucose co-transporter (SGLT1/2) inhibitor, phlorizin, were examined.

Results

Nondiabetic control mice exhibited no significant outer retinal layer thinning or PR loss after IR injury. In contrast, db/db mice exhibited significant outer retina thinning (49%, P < 0.0001), loss of PR nuclei (45%, P < 0.05) and inner segment (IS) length decline (45%, P < 0.0001). STZ-induced diabetic mice at 4 weeks showed progressive thinning of the outer retina (55%, by 14 days, P < 0.0001) and 4.3-fold greater number of TUNEL+ cells in the outer nuclear layer (ONL) than injured retinas of control mice (P < 0.0001). After 12 weeks of diabetes, the retinas exhibited similar outer layer thinning and PR loss after IR. Diabetes also delayed restoration of the blood-retinal barrier after IR injury. Phlorizin reduced outer retinal layer thinning from 49% to 3% (P < 0.0001).

Conclusions

Diabetes caused PR to become highly susceptible to IR injury. The ability of phlorizin pretreatment to block outer retinal thinning after IR suggests that the effects of diabetes on PR are readily reversible.

Oxidative stress in the eye and its role in the pathophysiology of ocular diseases

Oxidative stress occurs through an imbalance between the generation of reactive oxygen species (ROS) and the antioxidant defense mechanisms of cells. The eye is particularly exposed to oxidative stress because of its permanent exposure to light and due to several structures having high metabolic activities. The anterior part of the eye is highly exposed to ultraviolet (UV) radiation and possesses a complex antioxidant defense system to protect the retina from UV radiation. The posterior part of the eye exhibits high metabolic rates and oxygen consumption leading subsequently to a high production rate of ROS. Furthermore, inflammation, aging, genetic factors, and environmental pollution, are all elements promoting ROS generation and impairing antioxidant defense mechanisms and thereby representing risk factors leading to oxidative stress. An abnormal redox status was shown to be involved in the pathophysiology of various ocular diseases in the anterior and posterior segment of the eye. In this review, we aim to summarize the mechanisms of oxidative stress in ocular diseases to provide an updated understanding on the pathogenesis of common diseases affecting the ocular surface, the lens, the retina, and the optic nerve. Moreover, we discuss potential therapeutic approaches aimed at reducing oxidative stress in this context.

New insights in ferroptosis: Potential therapeutic targets for the treatment of ischemic stroke

Stroke is a common disease in clinical practice, which seriously endangers people's physical and mental health. The neurovascular unit (NVU) plays a key role in the occurrence and development of ischemic stroke. Different from other classical types of cell death such as apoptosis, necrosis, autophagy, and pyroptosis, ferroptosis is an iron-dependent lipid peroxidation-driven new form of cell death. Interestingly, the function of NVU and stroke development can be regulated by activating or inhibiting ferroptosis. This review systematically describes the NVU in ischemic stroke, provides a comprehensive overview of the regulatory mechanisms and key regulators of ferroptosis, and uncovers the role of ferroptosis in the NVU and the progression of ischemic stroke. We further discuss the latest progress in the intervention of ferroptosis as a therapeutic target for ischemic stroke and summarize the research progress and regulatory mechanism of ferroptosis inhibitors on stroke. In conclusion, ferroptosis, as a new form of cell death, plays a key role in ischemic stroke and is expected to become a new therapeutic target for this disease.

Anti-PANoptosis is involved in neuroprotective effects of melatonin in acute ocular hypertension model

Acute ocular hypertension (AOH) is the most important characteristic of acute glaucoma, which can lead to retinal ganglion cell (RGC) death and permanent vision loss. So far, approved effective therapy is still lacking in acute glaucoma. PANoptosis (pyroptosis, apoptosis, and necroptosis), which consists of three key modes of programmed cell death-apoptosis, necroptosis, and pyroptosis-may contribute to AOH-induced RGC death. Previous studies have demonstrated that melatonin (N-acetyl-5-methoxytryptamine) exerts a neuroprotective effect in many retinal degenerative diseases. However, whether melatonin is anti-PANoptotic and neuroprotective in the progression of acute glaucoma remains unclear. Thus, this study aimed to explore the role of melatonin in AOH retinas and its underlying mechanisms. The results showed that melatonin treatment attenuated the loss of ganglion cell complex thickness, retinal nerve fiber layer thickness, and RGC after AOH injury, and improved the amplitudes of a-wave, b-wave, and oscillatory potentials in the electroretinogram. Additionally, the number of terminal deoxynucleotidyl transferase dUTP nick-end labeling-positive cells was decreased, and the upregulation of cleaved caspase-8, cleaved caspase-3, Bax, and Bad and downregulation of Bcl-2 and p-Bad were inhibited after melatonin administration. Meanwhile, both the expression and activation of MLKL, RIP1, and RIP3, along with the number of PI-positive cells, were reduced in melatonin-treated mice, and p-RIP3 was in both RGC and microglia/macrophage after AOH injury. Furthermore, melatonin reduced the expression of NLRP3, ASC, cleaved caspase-1, gasdermin D (GSDMD), and cleaved GSDMD, and decreased the number of Iba1/interleukin-1β-positive cells. In conclusion, melatonin ameliorated retinal structure, prevented retinal dysfunction after AOH, and exerted a neuroprotective effect via inhibition of PANoptosis in AOH retinas.

Relevance of Peptide Homeostasis in Metabolic Retinal Degenerative Disorders: Curative Potential in Genetically Modified Mice

The mammalian retina contains approximately 30 neuropeptides that are synthetized by different neuronal cell populations, glia, and the pigmented epithelium. The presence of these neuropeptides leaves a mark on normal retinal molecular processes and physiology, and they are also crucial in fighting various pathologies (e.g., diabetic retinopathy, ischemia, age-related pathologies, glaucoma) because of their protective abilities. Retinal pathologies of different origin (metabolic, genetic) are extensively investigated by genetically manipulated in vivo mouse models that help us gain a better understanding of the molecular background of these pathomechanisms. These models offer opportunities to manipulate gene expression in different cell types to help reveal their roles in the preservation of retinal health or identify malfunction during diseases. In order to assess the current status of transgenic technologies available, we have conducted a literature survey focused on retinal disorders of metabolic origin, zooming in on the role of retinal neuropeptides in diabetic retinopathy and ischemia. First, we identified those neuropeptides that are most relevant to retinal pathologies in humans and the two clinically most relevant models, mice and rats. Then we continued our analysis with metabolic disorders, examining neuropeptide-related pathways leading to systemic or cellular damage and rescue. Last but not least, we reviewed the available literature on genetically modified mouse strains to understand how the manipulation of a single element of any given pathway (e.g., signal molecules, receptors, intracellular signaling pathways) could lead either to the worsening of disease conditions or, more frequently, to substantial improvements in retinal health. Most attention was given to studies which reported successful intervention against specific disorders. For these experiments, a detailed evaluation will be given and the possible role of converging intracellular pathways will be discussed. Using these converging intracellular pathways, curative effects of peptides could potentially be utilized in fighting metabolic retinal disorders.

Somatostatin and Its Receptors in Myocardial Ischemia/Reperfusion Injury and Cardioprotection

Little is known about the role of the neuropeptide somatostatin (SST) in myocardial ischemia/reperfusion injury and cardioprotection. Here, we investigated the direct cardiocytoprotective effect of SST on ischemia/reperfusion injury in cardiomyocyte cultures, as well as the expression of SST and its receptors in pig and human heart tissues. SST induced a bell-shaped, concentration-dependent cardiocytoprotection in both adult rat primary cardiomyocytes and H9C2 cells subjected to simulated ischemia/reperfusion injury. Furthermore, in a translational porcine closed-chest acute myocardial infarction model, ischemic preconditioning increased plasma SST-like immunoreactivity. Interestingly, SST expression was detectable at the protein, but not at the mRNA level in the pig left ventricles. SSTR1 and SSTR2, but not the other SST receptors, were detectable at the mRNA level by PCR and sequencing in the pig left ventricle. Moreover, remote ischemic conditioning upregulated SSTR1 mRNA. Similarly, SST expression was also detectable in healthy human interventricular septum samples at the protein level. Furthermore, SST-like immunoreactivity decreased in interventricular septum samples of patients with ischemic cardiomyopathy. SSTR1, SSTR2, and SSTR5 but not SST and the other SST receptors were detectable at the mRNA level by sequencing in healthy human left ventricles. In addition, in healthy human left ventricle samples, SSTR1 and SSTR2 mRNAs were expressed especially in vascular endothelial and some other cell types as detected by RNA Scope® in situ hybridization. This is the first demonstration that SST exerts a direct cardiocytoprotective effect against simulated ischemia/reperfusion injury. Moreover, SST is expressed in the heart tissue at the peptide level; however, it is likely to be of sensory neural origin since its mRNA is not detectable. SSTR1 and SSTR2 might be involved in the cardioprotective action of SST, but other mechanisms cannot be excluded.

Octreotide inhibits secretion of IGF-1 from orbital fibroblasts in patients with thyroid-associated ophthalmopathy via inhibition of the NF-κB pathway

PURPOSE

We investigated the effect of octreotide, a long-acting somatostatin (SST) analogue, on IGF-1 secretion and its possible mechanism of action in orbital fibroblasts (OFs) from patients with thyroid-associated ophthalmopathy (TAO).

MATERIALS AND METHODS

OFs were isolated from the orbital fat of patients with TAO or healthy individuals. The expression level of insulin-like growth factor (IGF)-1, at the protein and mRNA level, was determined with ELISA and quantitative RT-PCR, respectively. The expression pattern of somatostatin receptor (SSTR) 2, which has the highest affinity for octreotide, was examined by flow cytometry. The activity of NF-κB pathway was determined by examining the levels of phosphorylation of IKKα/β and p65, and degradation of IκB via western blot analysis, and by measuring the activity of NF-kB-dependent luciferase via transfection with plasmids containing luciferase and NF-κB binding site.

RESULTS

OFs from patients with TAO showed significantly higher levels of IGF-1 secretion and NF-κB activity even in the absence of stimulation, compared to those from controls. Treatment with octreotide reduced the level of IGF-1 secretion in OFs from patients with TAO, but not in OFs from controls. OFs from patients with TAO expressed higher levels of SSTR2 on the cell surface, compared to controls. In addition, the expression of IGF-1 at the protein and mRNA level was dependent on the activity of NF-κB pathway in OFs from patients with TAO. Furthermore, treatment with octreotide reduced on the activity of NF-κB pathway in OFs from patients with TAO.

CONCLUSION

OFs from patients with TAO showed significantly higher levels of IGF-1 secretion via up-regulation of NF-κB activity. Treatment with octreotide inhibited the secretion of IGF-1 by reducing the NF-κB pathway in OFs, which expressed higher levels of SSRT2 on the cell surface, from patients with TAO.

Targeting autophagy to modulate hepatic ischemia/reperfusion injury: A comparative study between octreotide and melatonin as autophagy modulators through AMPK/PI3K/AKT/mTOR/ULK1 and Keap1/Nrf2 signaling pathways in rats

Hepatic ischemia-reperfusion (HIR) injury is a common pathophysiological process in many clinical settings. This study was designed to compare the protective role of octreotide (somatostatin analogue, OCT) and melatonin (N-acetyl-5-methoxytryptamine, MLT) through the modulation of autophagy against HIR injury in rats. Male albino rats were divided into sham, HIR, OCT at three doses (50, 75, and 100 μg/kg), MLT, MLT + OCT75, compound C (AMPK inhibitor, CC), and CC + OCT75 groups. Ischemia was induced for 30 min followed by 24 h reperfusion. Biochemical, histopathological, immunohistochemical, lipid peroxidation, ELISA, qPCR, and western blot techniques were performed in our study. Liver autophagy was restored by OCT at doses (50 or 75 μg/kg) as indicated by elevating the expressions of Beclin-1, ATG7, and LC3 accompanied by the reduction of p62 expression through induction of AMPK/S317-ULK1 and inhibition of PI3K/AKT/mTOR/S757-ULK1 signaling pathways. As well, OCT maintained the integrity of the Keap1-Nrf2 system for the normal hepatic functions via controlling the Keap1 turnover through autophagy in a p62-dependent manner, resulting in upholding a series of anti-oxidant and anti-inflammatory cascades. These effects were abolished by compound C. On the other hand, MLT showed a decrease in the autophagy markers via inhibiting AMPK/pS317-ULK1 and activating PI3K/AKT/mTOR/pS757-ULK1 pathways. Autophagy inhibition with MLT markedly reversed the hepatoprotective effects of OCT75 after HIR injury. Finally, our results proved for the first time that OCT75 was more effective than MLT as it was sufficient to induce protective autophagy in our HIR model, which led to the induction of Nrf2-dependent AMPK/autophagy pathways.

Octreotide and melatonin alleviate inflammasome-induced pyroptosis through inhibition of TLR4-NF-κB-NLRP3 pathway in hepatic ischemia/reperfusion injury

BACKGROUND AND AIM

The Toll-like receptor 4 (TLR4)/nuclear factor kappa B (NF-κB)/NLRP3 inflammasome signaling pathway is essential in the pathogenesis of hepatic ischemia/ reperfusion (HIR) injury. Pyroptosis is a proinflammatory programmed cell death that is related to several diseases. Thus, the purpose of this study was to examine whether pretreatment with octreotide (somatostatin analogue, OCT) at different doses or OCT at 75μg/kg combined with melatonin (N-acetyl-5-methoxytryptamine, MLT) can alleviate HIR injury via targeting NLRP3 inflammasome-induced pyroptosis in a TLR4/MyD88/NF-κB dependent manner.

METHODS

Rats were randomized into sham, HIR, OCT (50, 75, and 100 µg/kg), MLT, and MLT + OCT75 groups. Ischemia was induced via occlusion of the portal triad for 30 min followed by 24 h reperfusion.

RESULTS

OCT pretreatment at doses (50 or 75 μg/kg), MLT alone, and MLT + OCT75 significantly ameliorated the biochemical with histopathological changes, oxidative stress, inflammation, apoptosis, then augmented anti-oxidant and anti-apoptotic markers through downregulation of HMGB1, TLR4, MyD88, TRAF-6, p-IκBα (S32), p-NF-κBp65 (S536), NLRP3, ASC, caspase-1(p20), and GSDMD-N expressions compared with HIR group.

CONCLUSION

OCT at doses (50 or 75 µg/kg) showed for the first time a hepatoprotective effect against HIR injury via inhibiting TLR4-NLRP3-mediated pyroptosis in rats. As well, OCT75 was more effective than OCT50 or MLT alone, and its effect was not enhanced after the addition of MLT, through downregulation of TLR4/MyD88/NF-κB/NLRP3 inflammasome pathway.

Oxidative Stress and Vascular Dysfunction in the Retina: Therapeutic Strategies

Many retinal diseases, such as diabetic retinopathy, glaucoma, and age-related macular (AMD) degeneration, are associated with elevated reactive oxygen species (ROS) levels. ROS are important intracellular signaling molecules that regulate numerous physiological actions, including vascular reactivity and neuron function. However, excessive ROS formation has been linked to vascular endothelial dysfunction, neuron degeneration, and inflammation in the retina. ROS can directly modify cellular molecules and impair their function. Moreover, ROS can stimulate the production of inflammatory cytokines, such as tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6) causing inflammation and cell death. However, there are various compounds with direct or indirect antioxidant activity that have been used to reduce ROS accumulation in animal models and humans. In this review, we report on the physiological and pathophysiological role of ROS in the retina with a special focus on the vascular system. Moreover, we present therapeutic approaches for individual retinal diseases targeting retinal signaling pathways involving ROS.

Octreotide and lanreotide decrease ovarian ischemia-reperfusion injury in rats by improving oxidative and nitrosative stress

AIM

To investigate the protective effect of octreotide and lanreotide on ovarian damage in experimental ovarian ischemia-reperfusion injury.

METHODS

Fifty-six rats were separated into seven groups; group 1: sham group, group 2: surgical control group with 3-h torsion and detorsion, group 3: 0.02 mg/kg s.c. octreotide 30 min before 3-h torsion, group 4; octreotide just after detorsion for 7 days, group 5: octreotide 30 min before torsion and just after detorsion for 7 days, group 6: single time 20 mg/kg s.c. lanreotide before torsion, group 7: single time lanreotide just after detorsion.

RESULTS

All histopathological scores except congestion were significantly lower in group 1 than other groups. In addition, hemorrhage (group 2 vs 4: P < 0.05), degeneration (group 2 vs 4: P < 0.05, group 2 vs 5: P < 0.01 and group 2 vs 6: P < 0.05) and total damage score (group 2 vs 4: P < 0.05, group 2 vs 5: P < 0.05, group 2 vs 6: P < 0.05 and group 2 vs 7: P < 0.05) were significantly lower than other groups. Moreover, ovarian tissue total oxidant status and oxidative stress index levels were significantly decreased in groups 5 (both P < 0.05) and 7 (both P < 0.05) when compared to group 2. Furthermore, tissue levels of peroxynitrite were significantly higher in group 2 than groups 1, 3 and 5 (all P < 0.05).

CONCLUSIONS

Octreotide and lanreotide have a protective role against ischemia-reperfusion damage in rat torsion detorsion model by improving histopathological and biochemical findings including tissue levels of total oxidant status, oxidative stress index and peroxynitrite.

Thioredoxin 1 Plays a Protective Role in Retinas Exposed to Perinatal Hypoxia-Ischemia

Thioredoxin family proteins are key modulators of cellular redox regulation and have been linked to several physiological functions, including the cellular response to hypoxia-ischemia. During perinatal hypoxia-ischemia (PHI), the central nervous system is subjected to a fast decrease in O₂ and nutrients with a subsequent reoxygenation that ultimately leads to the production of reactive species impairing physiological redox signaling. Particularly, the retina is one of the most affected tissues, due to its high oxygen consumption and exposure to light. One of the main consequences of PHI is retinopathy of prematurity, comprising changes in retinal neural and vascular development, with further compensatory mechanisms that can ultimately lead to retinal detachment and blindness. In this study, we have analyzed long-term changes that occur in the retina using two well established in vivo rat PHI models (perinatal asphyxia and carotid ligation model), as well as the ARPE-19 cell line that was exposed to hypoxia and reoxygenation. We observed significant changes in the protein levels of the cytosolic oxidoreductase thioredoxin 1 (Trx1) in both animal models and a cell model. Knock-down of Trx1 in ARPE-19 cells affected cell morphology, proliferation and the levels of specific differentiation markers. Administration of recombinant Trx1 decreased astrogliosis and improved delayed neurodevelopment in animals exposed to PHI. Taken together, our results suggest therapeutical implications for Trx1 in retinal damage induced by hypoxia-ischemia during birth.

Relationships Between Neurodegeneration and Vascular Damage in Diabetic Retinopathy

Diabetic retinopathy (DR) is a common complication of diabetes and constitutes a major cause of vision impairment and blindness in the world. DR has long been described exclusively as a microvascular disease of the eye. However, in recent years, a growing interest has been focused on the contribution of neuroretinal degeneration to the pathogenesis of the disease, and there are observations suggesting that neuronal death in the early phases of DR may favor the development of microvascular abnormalities, followed by the full manifestation of the disease. However, the mediators that are involved in the crosslink between neurodegeneration and vascular changes have not yet been identified. According to our hypothesis, vascular endothelial growth factor (VEGF) could probably be the most important connecting link between the death of retinal neurons and the occurrence of microvascular lesions. Indeed, VEGF is known to play important neuroprotective actions; therefore, in the early phases of DR, it may be released in response to neuronal suffering, and it would act as a double-edged weapon inducing both neuroprotective and vasoactive effects. If this hypothesis is correct, then any retinal stress causing neuronal damage should be accompanied by VEGF upregulation and by vascular changes. Similarly, any compound with neuroprotective properties should also induce VEGF downregulation and amelioration of the vascular lesions. In this review, we searched for a correlation between neurodegeneration and vasculopathy in animal models of retinal diseases, examining the effects of different neuroprotective substances, ranging from nutraceuticals to antioxidants to neuropeptides and others and showing that reducing neuronal suffering also prevents overexpression of VEGF and vascular complications. Taken together, the reviewed evidence highlights the crucial role played by mediators such as VEGF in the relationship between retinal neuronal damage and vascular alterations and suggests that the use of neuroprotective substances could be an efficient strategy to prevent the onset or to retard the development of DR.

Neuroprotective Potential of Pituitary Adenylate Cyclase Activating Polypeptide in Retinal Degenerations of Metabolic Origin

Pituitary adenylate cyclase-activating polypeptide (PACAP1-38) is a highly conserved member of the secretin/glucagon/VIP family. The repressive effect of PACAP1-38 on the apoptotic machinery has been an area of active research conferring a significant neuroprotective potential onto this peptide. A remarkable number of studies suggest its importance in the etiology of neurodegenerative disorders, particularly in relation to retinal metabolic disorders. In our review, we provide short descriptions of various pathological conditions (diabetic retinopathy, excitotoxic retinal injury and ischemic retinal lesion) in which the remedial effect of PACAP has been well demonstrated in various animal models. Of all the pathological conditions, diabetic retinopathy seems to be the most intriguing as it develops in 75% of patients with type 1 and 50% of patients with type 2 diabetes, with concomitant progression to legal blindness in about 5%. Several animal models have been developed in recent years to study retinal degenerations and out of these glaucoma and age-related retina degeneration models bear human recapitulations. PACAP neuroprotection is thought to operate through enhanced cAMP production upon binding to PAC1-R. However, the underlying signaling network that leads to neuroprotection is not fully understood. We observed that (i) PACAP is not equally efficient in the above conditions; (ii) in some cases more than one signaling pathways are activated; (iii) the coupling of PAC1-R and signaling is stage dependent; and (iv) PAC1-R is not the only receptor that must be considered to interpret the effects in our experiments. These observations point to a complex signaling mechanism, that involves alternative routes besides the classical cAMP/protein kinase A pathway to evoke the outstanding neuroprotective action. Consequently, the possible contribution of the other two main receptors (VPAC1-R and VPAC2-R) will also be discussed. Finally, the potential medical use of PACAP in some retinal and ocular disorders will also be reviewed. By taking advantage of, low-cost synthesis technologies today, PACAP may serve as an alternative to the expensive treatment modelities currently available in ocular or retinal conditions.

Neuroprotective Peptides in Retinal Disease

In the pathogenesis of many disorders, neuronal death plays a key role. It is now assumed that neurodegeneration is caused by multiple and somewhat converging/overlapping death mechanisms, and that neurons are sensitive to unique death styles. In this respect, major advances in the knowledge of different types, mechanisms, and roles of neurodegeneration are crucial to restore the neuronal functions involved in neuroprotection. Several novel concepts have emerged recently, suggesting that the modulation of the neuropeptide system may provide an entirely new set of pharmacological approaches. Neuropeptides and their receptors are expressed widely in mammalian retinas, where they exert neuromodulatory functions including the processing of visual information. In multiple models of retinal diseases, different peptidergic substances play neuroprotective actions. Herein, we describe the novel advances on the protective roles of neuropeptides in the retina. In particular, we focus on the mechanisms by which peptides affect neuronal death/survival and the vascular lesions commonly associated with retinal neurodegenerative pathologies. The goal is to highlight the therapeutic potential of neuropeptide systems as neuroprotectants in retinal diseases.

Protective Effect of Melatonin against Oxidative Stress-Induced Apoptosis and Enhanced Autophagy in Human Retinal Pigment Epithelium Cells

Age-related macular degeneration (AMD) affects the retinal macula and results in loss of vision, and AMD is the primary cause of blindness and severe visual impairment among elderly people worldwide. AMD is characterized by the accumulation of drusen in the Bruch's membrane and dysfunction of retinal pigment epithelial (RPE) cells and photoreceptors. The pathogenesis of AMD remains unclear, and no effective treatment exists. Accumulating evidence indicates that oxidative stress plays a critical role in RPE cell degeneration and AMD. Melatonin is an antioxidant that scavenges free radicals, and it has anti-inflammatory, antitumor, and antiangiogenic effects. This study investigated the antioxidative, antiapoptotic, and autophagic effects of melatonin on oxidative damage to RPE cells. We used hydrogen peroxide (H₂O₂) to stimulate reactive oxygen species production to cause cell apoptosis in ARPE-19 cell lines. Our findings revealed that treatment with melatonin significantly inhibited H₂O₂-induced RPE cell damage, decreased the apoptotic rate, increased the mitochondrial membrane potential, and increased the autophagy effect. Furthermore, melatonin reduced the Bax/Bcl-2 ratio and the expression levels of the apoptosis-associated proteins cytochrome c and caspase 7. Additionally, melatonin upregulated the expression of the autophagy-related proteins LC3-II and Beclin-1 and downregulated the expression of p62. Thus, melatonin's effects on autophagy and apoptosis can protect against H₂O₂-induced oxidative damage in human RPE cells. Melatonin may have multiple protective effects on human RPE cells against H₂O₂-induced oxidative damage.

Nanoparticle-Mediated Delivery of Neuroprotective Substances for the Treatment of Diabetic Retinopathy

BACKGROUND

Diabetic retinopathy (DR) is a major complication of diabetes, characterized by extensive vascular pathology leading to vision loss. Neuronal suffering and death are also present in the diabetic retina as a result of different molecular mechanisms that are compromised or modified in response to high glucose. The aim of this paper is to highlight recent data indicating that neurodegeneration is likely to play a primary role in the development of DR and that strategies based on nanomedicine may be exploited to deliver neuroprotection to the retina.

METHODS

An extensive analysis of the publications dealing with the role of neuroprotection in DR and with nanoparticle-mediated drug delivery to the retina has been conducted using PubMed, with particular attention to the most recent papers.

RESULTS

There are important limitations related to possible systemic side effects of neuroprotective substances and to drug bioavailability in the retina such as, for instance, the amount of drug reaching the retina, the need of keeping to a minimum the number of administrations (especially, for example, in the case of intraocular injections) and the need of assuring a long-lasting, graded intraocular drug delivery. In recent years, a variety of investigations have been aimed at the exploitation of approaches of nanomedicine to enhance the pharmacokinetics and pharmacodynamic activity of intraocularly delivered drugs. In particular, we provide some preliminary results that we have obtained about the feasibility of delivering magnetic nanoparticles functionalized with a neuroprotectant to mouse eyes through intraocular injections.

CONCLUSION

We propose that nanoparticles functionalized with neuroprotective substances may be used to protect the diabetic retina, thus causing an impact in the design of future pharmacologic treatments for DR.

Activation inhibitors of nuclear factor kappa B protect neurons against the NMDA-induced damage in the rat retina

We reported that high-mobility group Box-1 (HMGB1) was involved in excitoneurotoxicity in the retina. HMGB1 is known to activate nuclear factor kappa B (NF-κB). However, the role of NF-κB in excitotoxicity is still controversial. Here, we demonstrated that NF-κB activation induced by NMDA led to the retinal neurotoxicity. Male Sprague-Dawley rats were used, and NMDA (200 nmol/eye) and bovine HMGB1 (15 μg/eye) were intravitreally injected. Triptolide (500 pmol/eye), BAY 11-7082 (500 pmol/eye), and IMD-0354 (7.5 nmol/eye), NF-κB inhibitors, were co-injected with NMDA or HMGB1. Retinal sections were obtained seven days after intravitreal injection. Cell loss in the ganglion cell layer was observed in the HMGB1- and the NMDA-treated retina. All of the NF-κB inhibitors used in this study reduced the damage. BAY 11-7082 reduced the expression of phosphorylated NF-κB 12 h after NMDA injection, upregulation of GFAP immunoreactivity induced by NMDA 12 and 48 h after NMDA injection, and the number of TUNEL-positive cells 48 h after NMDA injection. The results suggest that NF-κB activation is one of the mechanisms of the retinal neuronal death that occurs 48 h after NMDA injection or later. Prevention of NF-kB activation is a candidate for the treatment of retinal neurodegeneration associated with excitotoxicity.

Cardioprotective time-window of Penehyclidine hydrochloride postconditioning: A rat study

Pharmacological postconditioning offers a clinical perspective for all patients with ischemic heart disease. Penehyclidine hydrochloride (PHC) is a new type of anticholinergic drug. We previously reported that PHC preconditioning protects against I/R injury in rat hearts in vivo. Ischemic heart disease often occurs suddenly, so postconditioning is more significant than preconditioning. However, studies evaluating myocardial protective effects of PHC postconditioning are unavailable. We explored the effects and time-window of cardioprotection of PHC postconditioning in myocardial I/R injury. PHC was administered by intravenous at various times (t = -5, 0, 5, 10, 15, or 30min) after the onset of reperfusion in addition to I/R rat. We observed five different indicators including infarct size, inflammatory response, myocardial enzyme, oxidative stress, and Ca²⁺ overload to quantify the effect of cardioprotection. Evans blue and TTC staining were used to measure myocardial infarct size. The expression of NF-κ B and IκB-α was analyzed using Western blot. ELISA was conducted to detect inflammatory and anti-inflammatory mediators. The Ca²⁺ level was determined using assay kit. PHC postconditioning (from -5 to 10min after the onset of reperfusion) significantly reduced infarct size, downregulated NF-κ B expression, and decreased the release of inflammatory mediators, while significantly upregulating IκB-α expression and increasing the release of anti-inflammatory mediators. All PHC postconditioning groups significantly reduced Ca²⁺ level. PHC postconditioning is cardioprotective over a larger time-window (from -5 to 10min after the onset of reperfusion). The probable mechanism is inhibition of NF-кB regulated inflammatory response pathway.

Occludin downregulation in high glucose is regulated by SSTR2 via the VEGF/NRP1/Akt signaling pathway in RF/6A cells

Occludin is a tight junction protein that forms the permeability barrier, which is typically disturbed in ischemic associated diseases. The aim of the present study was to determine whether somatostatin receptor 2 (SSTR₂) in RF/6A cells is involved in the modulation of the downregulation of occludin induced by high glucose, and to evaluate the implicated molecules. RF/6A cells were maintained in Dulbecco's modified Eagle medium and treated with 0 or 30 mM D-glucose. SSTR₂ agonist octreotide (OCT), OCT with SSTR₂ antagonist cycle-somatostatin (c-SOM) and neuropilin 1 (NRP1) inhibitor ATWLPPR, respectively, were administered to RF/6A cells under high glucose conditions. Cell apoptosis was evaluated by terminal deoxynucleotidyl transferase dUTP nick-end labeling. Western blot analysis was used to detect the protein expression level of SSTR₂, occludin, vascular endothelial growth factor (VEGF), protein kinase B (Akt), phosphorylated Akt (p-Akt), extracellular signal-related kinases (ERK) and p-ERK proteins. The amount of VEGF released was determined by ELISA. Notably, the level of occludin reduced significantly under high glucose conditions. The results indicated that the administration of OCT prevented the reduction of occludin induced by high glucose, and co-administration with c-SOM reversed the effect of OCT. Increased VEGF secretion and expression of VEGF, p-Akt and p-ERK in RF/6A cells induced by high glucose were inhibited by OCT. ATWLPPR also prevented the downregulation of occludin, but did not inhibit p-Akt and p-ERK levels under high glucose conditions. The current study concluded that the activation of SSTR₂ prevents high glucose-induced occludin downregulation in RF/6A cells, and VEGF, NRP1, p-Akt and p-ERK were implicated in this process. The pharmacological effects of SSTR₂ targeting to endothelium may be used to assess the role of resistance of permeability and anti-inflammation.

Protective roles of bioactive peptides during ischemia-reperfusion injury: From bench to bedside

Ischemia-reperfusion (I/R) is a well-known pathological condition which may lead to disability and mortality. I/R injury remains an unresolved and complicated situation in a number of clinical conditions, such as cardiac arrest with successful reanimation, as well as ischemic events in brain and heart. Peptides have many attractive advantages which make them suitable candidate drugs in treating I/R injury, such as low toxicity and immunogenicity, good solubility property, distinct tissue distribution pattern, and favorable pharmacokinetic profile. An increasing number of studies indicate that peptides could protect against I/R injury in many different organs and tissues. Peptides also face several therapeutic challenges that limit their clinical application. In this review, we present the mechanisms of action of peptides in reducing I/R injury, as well as further discuss modification strategies to improve the functional properties of bioactive peptides.

Peroxisome proliferator-activated receptor γ (PPARγ) mediates the protective effect of quercetin against myocardial ischemia-reperfusion injury via suppressing the NF-κB pathway

Quercetin plays an important role in myocardial ischemia and reperfusion injury (IRI). However, the underlying mechanism for the protective effect of quercetin is largely unclear. In this study, we explored the protected effects of quercetin against myocardial IRI and its molecular mechanisms. Quercetin, GW9962 (PPARγ antagonist) or PPARγ-siRNA was administered alone or in combination prior to myocardial IRI in mice or to hypoxia and reoxygenation (H/R) treatment in H9C2 cells. Infarct size was evaluated by TTC staining after reperfusion. Myocardial injury was assessed by the serum levels of AST, CK-MB, cardiac troponin T (cTnT) and LDH. Cardiac function was measured by echocardiography. Oxidative stress injury was evaluated by analyses of inducible nitric oxide synthase (iNOS), MDA, SOD and glutathione peroxidase (GSH-PX) levels and by reactive oxygen species (ROS) detection. Myocardium apoptosis was evaluated by TUNEL staining, cleaved caspase-3 and Annexin V/PI detection. Moreover, activation of the NF-κB pathway was reflected by phosphorylation of IκB (p-IκB) and nuclear translocation of NF-κB p65. We reported that pretreatment of quercetin significantly improved cardiac function, diminished myocardial injury and reduced the infarct size. Myocardium oxidative damage and apoptosis were remarkably improved by quercetin treatment in vivo and in vitro. Quercetin also suppressed the activation of the NF-κB pathway induced by myocardial IRI. GW9662 or PPARγ knockdown partially attenuated these cardioprotective effects of quercetin during myocardial IRI. In conclusion, our findings suggest that quercetin ameliorated IRI-induced heart damage via PPARγ activation and the underlying mechanism might involve the inhibition of NF-κB pathway by PPARγ activation.

Vitexin exerts cardioprotective effect on chronic myocardial ischemia/reperfusion injury in rats via inhibiting myocardial apoptosis and lipid peroxidation

PURPOSE

The aim of this study was to explore the cardioprotective effect of vitexin on chronic myocardial ischemia/reperfusion injury in rats and potential mechanisms.

METHODS

A chronic myocardial ischemia/reperfusion injury model was established by ligating left anterior descending coronary for 60 minutes, and followed by reperfusion for 14 days. After 2 weeks ischemia/reperfusion, cardiac function was measured to assess myocardial injury. The level of ST segment was recorded in different periods by electrocardiograph. The change of left ventricular function and myocardial reaction degree of fibrosis of heart was investigated by hematoxylin and eosin (HE) staining and Sirius red staining. Endothelium-dependent relaxations due to acetylcholine were observed in isolated rat thoracic aortic ring preparation. The blood samples were collected to measure the levels of MDA, the activities of SOD and NADPH in serum. Epac1, Rap1, Bax and Bcl-2 were examined by using Western Blotting.

RESULTS

Vitexin exerted significant protective effect on chronic myocardial ischemia/reperfusion injury, improved obviously left ventricular diastolic function and reduced myocardial reactive fibrosis degree in rats of myocardial ischemia. Medium and high-dose vitexin groups presented a significant decrease in Bax, Epac1 and Rap1 production and increase in Bcl-2 compared to the I/R group. It may be related to preventing myocardial cells from apoptosis, improving myocardial diastolic function and inhibiting lipid peroxidation.

CONCLUSIONS

Vitexin is a cardioprotective herb, which may be a promising useful complementary and alternative medicine for patients with coronary heart disease.

Penehyclidine Hydrochloride Preconditioning Provides Cardioprotection in a Rat Model of Myocardial Ischemia/Reperfusion Injury

To investigate the impacts and related mechanisms of penehyclidine hydrochloride (PHC) on ischemia/reperfusion (I/R)-induced myocardial injury. A rat model of myocardial I/R injury was established by the ligation of left anterior descending coronary artery for 30 min followed by 3 h perfusion. Before I/R, the rats were pretreated with or without PHC. Cardiac function was measured by echocardiography. The activities/levels of myocardial enzymes, oxidants and antioxidant enzymes were detected. Evans blue/TTC double staining was performed to assess infarct size. Cardiomyocyte apoptosis was evaluated by TUNEL assay. The release of inflammatory cytokines and inflammatory mediators was detected by ELISA. Western blot was performed to analyze the expression of COX-2, IκB, p-IκB and NF-κB. Meanwhile, the rats were given a single injection of H-PHC before I/R. The effects of PHC on myocardial infarct and cardiac function were investigated after 7 days post-reperfusion. We found that PHC remarkably improved cardiac function, alleviated myocardial injury by decreasing myocardial enzyme levels and attenuated oxidative stress in a dose-dependent manner. Additionally, PHC preconditioning significantly reduced infarct size and the apoptotic rate of cardiomyocytes. Administration of PHC significantly decreased serum TNF-α, IL-1β, IL-6 and PGE₂ levels and myocardium COX-2 level. Meanwhile, the expression levels of p-IκB and NF-κB were downregulated, while IκB expression was upregulated. H-PHC also exerted long-term cardioprotection in a rat model of I/R injury by decreasing infarct size and improving cardiac function. These results suggest that PHC can efficiently protect the rats against I/R-induced myocardial injury.