Caffeic acid phenethyl ester reduces the secretion of vascular endothelial growth factor through the inhibition of the ROS, PI3K and HIF-1α signaling pathways in human retinal pigment epithelial cells under hypoxic conditions

Effects and potential mechanisms of exercise and physical activity on eye health and ocular diseases

In the field of eye health, the profound impact of exercise and physical activity on various ocular diseases has become a focal point of attention. This review summarizes and elucidates the positive effects of exercise and physical activities on common ocular diseases, including dry eye disease (DED), cataracts, myopia, glaucoma, diabetic retinopathy (DR), and age-related macular degeneration (AMD). It also catalogues and offers exercise recommendations based on the varying impacts that different types and intensities of physical activities may have on specific eye conditions. Beyond correlations, this review also compiles potential mechanisms through which exercise and physical activity beneficially affect eye health. From mitigating ocular oxidative stress and inflammatory responses, reducing intraocular pressure, enhancing mitochondrial function, to promoting ocular blood circulation and the release of protective factors, the complex biological effects triggered by exercise and physical activities reveal their substantial potential in preventing and even assisting in the treatment of ocular diseases. This review aims not only to foster awareness and appreciation for how exercise and physical activity can improve eye health but also to serve as a catalyst for further exploration into the specific mechanisms and key targets through which exercise impacts ocular health. Such inquiries are crucial for advancing innovative strategies for the treatment of eye diseases, thereby holding significant implications for the development of new therapeutic approaches.

Effects of Temperature, Metal Ions and Biosurfactants on Interaction Mechanism between Caffeic Acid Phenethyl Ester and Hemoglobin

Caffeic acid phenylethyl ester (CAPE) is a natural polyphenol extracted from propolis, which is reported to have several pharmacological effects such as antibacterial, antitumor, antioxidant and anti-inflammatory activities. Hemoglobin (Hb) is closely related to the transport of drugs, and some drugs, including CAPE, can lead to a change in Hb concentration. Herein, the effects of temperature, metal ions and biosurfactants on the interaction between CAPE and Hb were studied using ultraviolet-visible spectroscopy (UV-Vis), fluorescence spectroscopy, circular dichroism (CD), dynamic light scattering (DLS) and molecular docking analysis. The results showed that the addition of CAPE led to changes in the microenvironment of Hb amino acid residues as well as the secondary structure of Hb. Hydrogen bonding and van der Waals force were found to be the main driving forces for the interaction between CAPE and Hb through fluorescence spectroscopy and thermodynamic parameter data. The results of fluorescence spectroscopy also showed that lowering the temperature, adding biosurfactants (sodium cholate (NaC) and sodium deoxycholate (NaDC)) and the presence of Cu²⁺ increased the binding force between CAPE and Hb. These results provide useful data for the targeted delivery and absorption of CAPE and other drugs.

Therapeutic Potential of Honey and Propolis on Ocular Disease

Honey and propolis have recently become the key target of attention for treating certain diseases and promoting overall health and well-being. A high content of flavonoids and phenolic acids found in both honey and propolis contributes to the antioxidant properties to scavenge free radicals. Honey and propolis also exhibited antibacterial effects where they act in two ways, namely the production of hydrogen peroxide (H2O2) and gluconic acids following the enzymatic activities of glucose oxidase, which exerts oxidative damage on the bacteria. Additionally, the anti-inflammatory effects of honey and propolis are mainly by reducing proinflammatory factors such as interleukins and tumor necrosis factor alpha (TNF-α). Their effects on pain were discovered through modulation at a peripheral nociceptive neuron or binding to an opioid receptor in the higher center. The aforementioned properties of honey have been reported to possess potential therapeutic topical application on the exterior parts of the eyes, particularly in treating conjunctivitis, keratitis, blepharitis, and corneal injury. In contrast, most of the medicinal values of propolis are beneficial in the internal ocular area, such as the retina, optic nerve, and uvea. This review aims to update the current discoveries of honey and propolis in treating various ocular diseases, including their antioxidant, anti-inflammatory, antibacterial, and anti-nociceptive properties. In conclusion, research has shown that propolis and honey have considerable therapeutic promise for treating various eye illnesses, although the present study designs are primarily animal and in vitro studies. Therefore, there is an urgent need to translate this finding into a clinical setting.

Molecular Mechanisms of Iron Mediated Programmed Cell Death and Its Roles in Eye Diseases

Ferroptosis, a newly identified, iron-dependent type of programmed cell death, is active in several diseases, such as heart disease, brain damage, and cancer. Its main characteristics commonly involve excess iron accumulation, elevated lipid peroxides and reactive oxygen species, and reduced levels of glutathione and glutathione peroxidase 4 levels. The effects of ferroptosis in eye diseases cannot be underestimated, with ferroptosis becoming a research target in ocular disorders and emerging evidence from a series of in vivo and in vitro researches into ferroptosis revealing its role in eye conditions. However, no report provides comprehensive information on the pathophysiology of ferroptosis in eye diseases and its possible treatments. In the current review, we present an up-to-date overview of ferroptosis biology and its involvement in the pathological processes of ocular diseases. Furthermore, we pose several outstanding questions and areas for future research in this topic. We deem ferroptosis-associated cell death a pivotal new field of scientific study in ocular diseases and consider it a new therapeutic target in the treatment of some eye disorders.

Exploration of the Specific Pathology of HXMM Tablet Against Retinal Injury Based on Drug Attack Model to Network Robustness

Retinal degenerative diseases are related to retinal injury because of the activation of the complement cascade, oxidative stress-induced cell death mechanisms, dysfunctional mitochondria, chronic neuroinflammation, and production of the vascular endothelial growth factor. Anti-VEGF therapy demonstrates remarkable clinical effects and benefits in retinal degenerative disease patients. Hence, new drug development is necessary to treat patients with severe visual loss. He xue ming mu (HXMM) tablet is a CFDA-approved traditional Chinese medicine (TCM) for retinal degenerative diseases, which can alleviate the symptoms of age-related macular degeneration (AMD) and diabetic retinopathy (DR) alone or in combination with anti-VEGF agents. To elucidate the mechanisms of HXMM, a quantitative evaluation algorithm for the prediction of the effect of multi-target drugs on the disturbance of the disease network has been used for exploring the specific pathology of HXMM and TCM precision positioning. Compared with anti-VEGF agents, the drug disturbance of HXMM on the functional subnetwork shows that HXMM reduces the network robustness on the oxidative stress subnetwork and inflammatory subnetwork to exhibit the anti-oxidation and anti-inflammation activity. HXMM provides better protection to ARPE-19 cells against retinal injury after H₂O₂ treatment. HXMM can elevate GSH and reduce LDH levels to exhibit antioxidant activity and suppress the expression of IL-6 and TNF-α for anti-inflammatory activity, which is different from the anti-VEGF agent with strong anti-VEGF activity. The experimental result confirmed the accuracy of the computational prediction. The combination of bioinformatics prediction based on the drug attack on network robustness and experimental validation provides a new strategy for precision application of TCM.

Controlled Release of Caffeic Acid and Pinocembrin by Use of nPSi-βCD Composites Improves Their Antiangiogenic Activity

Although polyphenols have great pharmacological potential, the main disadvantage is that they have low bioavailability at the desired site. Thus, the use of biocompatible systems for drug delivery is a strategy that is currently gaining great interest. The objective of this study is to evaluate the effect of microencapsulation of caffeic acid and pinocembrin on the antioxidant and antiangiogenic activity of both polyphenols, by the use of nPSi-βCD composite microparticles. For this HUVEC, cells were exposed to H₂O₂ and to treatments with polyphenols in solution and loaded in the composite microparticle. The polyphenols were incorporated into a microparticle using nanoporous silicon, chitosan and a β-cyclodextrin polymer as the biomaterial. The evaluation of the antiangiogenic effect of the treatments with polyphenols in solution and microencapsulated was carried out through functional tests, and the changes in the expression of target genes associated with the antioxidant pathway and angiogenesis was performed through qPCR. The results obtained show that the caffeic acid and pinocembrin have an antioxidant and antiangiogenic activity, both in solution as microencapsulated. In the caffeic acid, a greater biological effect was observed when it was incorporated into the nPSi-βCD composite microparticle. Our results suggest that the nPSi-βCD composite microparticle could be used as an alternative oral drug administration system.

Receptor tyrosine kinases as a therapeutic target by natural compounds in cancer treatment

Background

Receptor tyrosine kinases (RTKs) are single-pass transmembrane proteins that play significant roles in regulating cellular processes, including cell division and growth. Overexpression and mutations of RTKs have been found in clinical manifestations of different forms of cancer. Therefore, RTKs have received considerable interest as a therapeutic biomarker in the treatment of cancer cells.

Main body of the abstract

Comprehensive data on RTKs, pharmacological and biological properties of natural compounds were systematically searched up to 2021 using relevant keywords from various databases, such as Google Scholar, PubMed, Web of Science, and Scopus. The scientific search by various standard electronic resources and databases unveils the effectiveness of medicinal plants in the treatment of various cancers. In vitro and in vivo studies suggested that bioactive compounds such as flavonoids, phenols, alkaloids, and many others can be used pharmacologically as RTKs inhibitors (RTKI) either by competing with ATP at the ATP binding site of the tyrosine kinase domain or competing for the receptor extracellular domain. Additionally, studies conducted on animal models indicated that inhibition of RTKs catalytic activity by natural compounds is one of the most effective ways to block the activation of RTKs signaling cascades, thereby hampering the proliferation of cancer cells. Furthermore, various pharmacological experiments, transcriptomic, and proteomic data also reported that cancer cells treated with different plants extracts or isolated phytochemicals exhibited better anticancer properties with minimal side effects than synthetic drugs. Clinically, natural compounds have demonstrated significant anti-proliferative effect via induction of cell apoptosis in cancer cell lines.

Short conclusion

An in-depth knowledge of the mechanism of inhibition and structural characterization of RTKs is important to the design of novel and selective RTKIs. This review focuses on the molecular mechanisms and structures of natural compounds RTKI targeting vascular endothelial growth factor, epidermal growth factor receptor, insulin receptor, and platelet-derived growth factor while also giving future directions to ameliorate the scientific burden of cancer.

Graphic abstract

Recent progresses in the pharmacological activities of caffeic acid phenethyl ester

The past decades have seen a growing interest in natural products. Caffeic acid phenethyl ester (CAPE), a flavonoid isolated from honeybee propolis, has shown multiple pharmacological potentials, including anti-cancer, anti-inflammatory, antioxidant, antibacterial, antifungal, and protective effects on nervous systems and multiple organs, since it was found as a potent nuclear factor κB (NF-κB) inhibitor. This review summarizes the advances in these beneficial effects of CAPE, as well as the underlying mechanisms, and proposes that CAPE offers an opportunity for developing therapeutics in multiple diseases. However, clinical trials on CAPE are necessary and encouraged to obtain certain clinically relevant conclusions.

Complement family member CFI polymorphisms and AMD susceptibility from a comprehensive analysis

The complement factor I (CFI) gene polymorphisms have been reported to age-related macular degenerative (AMD) risk, nevertheless, above association is not consistent. We investigated a meta-analysis to evaluate the conclusions between CFI polymorphisms (rs10033900 and rs2285714) and AMD risk. An identification was covered with the PubMed and other databases through February 8, 2020. Odds ratios (OR) and 95% confidence intervals (CI) were used to assess the strength of associations. After a comprehensive search, 11 different articles (12 case–control studies for total AMD and 11 case–control studies about neovascular disease/geographic atrophy in AMD) were retrieved. Individuals carrying C-allele or CC genotype of rs10033900 polymorphism may have a decreased risk to be AMD disease. For example, there has a significantly decreased relationship between rs10033900 polymorphism and AMD both in the whole group, Caucasian population and population-based source of control. Moreover, a similar trend in subgroup of genotype method group by MALDI-TOF MS was detected. To classify the type of AMD in further, decreased association was also observed in both neovascular disease and geographic atrophy AMD. No association was found about rs2285714 polymorphism. Our present groundbreaking study suggests that the CFI rs10033900 polymorphism is potentially associated with the risk of AMD development.

The Pluripotent Activities of Caffeic Acid Phenethyl Ester

Caffeic acid phenethyl ester (CAPE) is a strong antioxidant extracted from honey bee-hive propolis. The mentioned compound, a well-known NF-κB inhibitor, has been used in traditional medicine as a potent anti-inflammatory agent. CAPE has a broad spectrum of biological properties including anti-viral, anti-bacterial, anti-cancer, immunomodulatory, and wound-healing activities. This review characterizes published data about CAPE biological properties and potential therapeutic applications, that can be used in various diseases.

New insights into oxidative stress and immune mechanisms involved in age-related macular degeneration tackled by novel therapies

The prevalence of age-related macular degeneration (AMD) has increased in the last years. Although anti-VEGF agents have improved the prognosis of exudative AMD, dry AMD has still devastating effects on elderly people vision. Oxidative stress and inflammation are mechanisms involved in AMD pathogenesis and its progression. Molecular pathways involving epidermal growth factor receptor (EGFR), bone morphogenetic protein (BMP4) and the nuclear erythroid related factor 2 (Nrf2) are behind oxidative stress in AMD due to their participation in antioxidant cellular pathways. As a consequence of the disbalance produced in the antioxidant mechanisms, there is an activation of innate and adaptative immune response with cell recruitment, changes in complement factors expression, and modification of cellular milieu. Different therapies are being studied to treat dry AMD based on the possible effects on antioxidant molecular pathways or their action on the immune response. There is a wide range of treatments presented in this review, from natural antioxidant compounds to cell and gene therapy, based on their mechanisms. Finally, we hypothesize that alpha-1-antitrypsin (AAT), an anti-inflammatory and immunomodulatory molecule that can also modulate antioxidant cellular defenses, could be a good candidate for testing in AMD. This article is part of the special ssue on 'The Quest for Disease-Modifying Therapies for Neurodegenerative Disorders'.

SLC7A11 Reduces Laser-Induced Choroidal Neovascularization by Inhibiting RPE Ferroptosis and VEGF Production

In age-related macular degeneration (AMD), one of the principal sources of vascular endothelial growth factor (VEGF) is retinal pigment epithelium (RPE) cells under hypoxia or oxidative stress. Solute carrier family 7 member 11 (SLC7A11), a key component of cystine/glutamate transporter, regulates the level of cellular lipid peroxidation, and restrains ferroptosis. In our study, we assessed the role of SLC7A11 in laser-induced choroidal neovascularization (CNV) and explored the underlying mechanism. We established a mouse model of CNV to detect the expression level of SLC7A11 and VEGF during disease progression. We found the expression of the SLC7A11 protein in RPE cells peaked at 3 days after laser treatment, which was correlated with the expression of VEGF. Intraperitoneal injection of SLC7A11 inhibitor expanded the area of CNV. We examined functional proteins related to oxidative stress and Fe²⁺ and found laser-induced ferroptosis accompanied by increased Fe²⁺ content and GPX4 expression in the RPE-choroidal complex after laser treatment. We verified the expression of SLC7A11 in the ARPE19 cell line and the effects of its inhibitors on cell viability and lipid peroxidation in vitro. Application of SLC7A11 inhibitor and SLC7A11 knockdown increased the level of lipid peroxidation and reduced the cell viability of ARPE19 which can be rescued by ferroptosis inhibitors ferrostatin-1 (Fer-1) and liproxstatin-1 (Lip-1). Conversely, SLC7A11 overexpression induced resistance to erastin or RSL3-induced ferroptosis. Moreover, we tested the possible regulatory transcription factor NF-E2-related factor 2 (NRF2) of SLC7A11 by Western blot. Knock-down of NRF2 decreased the expression of SLC7A11. Our study suggests that SLC7A11 plays a key role in the laser-induced CNV model by protecting RPE cells from ferroptosis. SLC7A11 provides a new therapeutic target for neovascular AMD patients.

Red Wine Extract Inhibits VEGF Secretion and Its Signaling Pathway in Retinal ARPE-19 Cells to Potentially Disrupt AMD

Age-related macular degeneration (AMD) is a degenerative disease of the retina where the molecular mechanism involves the production of vascular endothelial growth factor (VEGF), a factor of poor prognosis of the progression of the disease. Previous studies have shown that resveratrol, a polyphenol of grapevines, can prevent VEGF secretion induced by stress from retinal cells. Considering the fundamental role played by VEGF in development and progression of AMD, we investigate the potential effect of red wine extract (RWE) on VEGF secretion and its signaling pathway in human retinal cells ARPE-19. To examine the effect of RWE in ARPE-19, a quantitative and qualitative analysis of the RWE was performed by HPLC MS/MS. We show for the first time that RWE decreased VEGF-A secretion from ARPE-19 cells and its protein expression in concentration-dependent manner. RWE-induced alteration in VEGF-A production is associated with a down of VEGF-receptor 2 (VEGF-R2) protein expression and its phosphorylated intracytoplasmic domain. Subsequently, the activation of kinase pathway is disturbing and RWE prevents the phosphorylation of MEK and ERK 1/2 in human retinal cells ARPE-19. Finally, this study sheds light on the interest that the use of polyphenolic cocktails could represent in a prevention strategy.

Cardiovascular Effects of Caffeic Acid and Its Derivatives: A Comprehensive Review

Caffeic acid (CA) and its phenethyl ester (CAPE) are naturally occurring hydroxycinnamic acids with an interesting array of biological activities; e.g., antioxidant, anti-inflammatory, antimicrobial and cytostatic. More recently, several synthetic analogs have also shown similar properties, and some with the advantage of added stability. The actions of these compounds on the cardiovascular system have not been thoroughly explored despite presenting an interesting potential. Indeed the mechanisms underlying the vascular effects of these compounds particularly need clarifying. The aim of this paper is to provide a comprehensive and up-to-date review on current knowledge about CA and its derivatives in the cardiovascular system. Caffeic acid, CAPE and the synthetic caffeic acid phenethyl amide (CAPA) exhibit vasorelaxant activity by acting on the endothelial and vascular smooth muscle cells. Vasorelaxant mechanisms include the increased endothelial NO secretion, modulation of calcium and potassium channels, and modulation of adrenergic receptors. Together with a negative chronotropic effect, vasorelaxant activity contributes to lower blood pressure, as several preclinical studies show. Their antioxidant, anti-inflammatory and anti-angiogenic properties contribute to an important anti-atherosclerotic effect, and protect tissues against ischemia/reperfusion injuries and the cellular dysfunction caused by different physico-chemical agents. There is an obvious shortage of in vivo studies to further explore these compounds' potential in vascular physiology. Nevertheless, their favorable pharmacokinetic profile and overall lack of toxicity make these compounds suitable for clinical studies.

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.

Development of an in vitro 3D choroidal neovascularization model using chemically induced hypoxia through an ultra-thin, free-standing nanofiber membrane

Choroidal neovascularization (CNV) is the pathological growth of new blood vessels in the sub-retinal pigment epithelial (RPE) space from the choroid through a break in the Bruch's membrane (BM). Despite its importance in studying biological processes and drug discovery, the development of an in vitro CNV model that achieves the physiological structures of native RPE-BM-choroidal capillaries (CC) is still challenging. Here, we develop a novel 3D RPE-BM-CC complex biomimetic system on an ultra-thin, free-standing nanofiber membrane. The thickness of the pristine nanofiber membrane is 2.17 ± 0.81 μm, and the Matrigel-coated nanofiber membrane attains a permeability coefficient of 2.95 ± 0.25 × 10^-6 cm/s by 40 kDa FITC-dextran, which is similar to the physiological value of the native BM. On the in vitro 3D RPE-BM-CC complex system, we demonstrate endothelial cell invasion across the 3D RPE-BM-CC complex and the mechanism of the invasion by imposing a hypoxic condition, which is thought to be the major pathological cause of CNV. Furthermore, alleviation of the invasion is achieved by treating with chrysin and anti-VEGF antibody. Thus, the in vitro 3D RPE-BM-CC complex biomimetic system can recapitulate essential features of the pathophysiological environment and be employed for the screening of drug candidates to reduce the number of costly and time-consuming in vivo tests or clinical trials.

Use of nPSi-βCD Composite Microparticles for the Controlled Release of Caffeic Acid and Pinocembrin, Two Main Polyphenolic Compounds Found in a Chilean Propolis

Propolis is widely recognized for its various therapeutic properties. These are attributed to its rich composition in polyphenols, which exhibit multiple biological properties (e.g., antioxidant, anti-inflammatory, anti-angiogenic). Despite its multiple benefits, oral administration of polyphenols results in low bioavailability at the action site. An alternative to face this problem is the use of biomaterials at nano-micro scale due to its high versatility as carriers and delivery systems of various drugs and biomolecules. The aim of this work is to determine if nPSi-βCD microparticles are a suitable material for the load and controlled release of caffeic acid (CA) and pinocembrin (Pin), two of the main components of a Chilean propolis with anti-atherogenic and anti-angiogenic activity. Polyphenols and nPSi-βCD microparticles cytocompatibility studies were carried out with human umbilical vein endothelial cells (HUVECs). Results from physicochemical characterization demonstrated nPSi-βCD microparticles successfully retained and controlled release CA and Pin. Furthermore, nPSi-βCD microparticles presented cytocompatibility with HUVECs culture at concentrations of 0.25 mg/mL. These results suggest that nPSi-βCD microparticles could safely be used as an alternate oral delivery system to improve controlled release and bioavailability of CA or Pin-and eventually other polyphenols-thus enhancing its therapeutic effect for the treatment of different diseases.

Caffeic Acid Phenethyl Ester Rescues Pulmonary Arterial Hypertension through the Inhibition of AKT/ERK-Dependent PDGF/HIF-1α In Vitro and In Vivo

Pulmonary arterial hypertension (PAH) is characterized by pulmonary arterial proliferation and remodeling, resulting in a specific increase in right ventricle systolic pressure (RVSP) and, ultimately right ventricular failure. Recent studies have demonstrated that caffeic acid phenethyl ester (CAPE) exerts a protective role in NF-κB-mediated inflammatory diseases. However, the effect of CAPE on PAH remains to be elucidated. In this study, monocrotaline (MCT) was used to establish PAH in rats. Two weeks after the induction of PAH by MCT, CAPE was administrated by intraperitoneal injection once a day for two weeks. Pulmonary hemodynamic measurements and pulmonary artery morphological assessments were examined. Our results showed that administration of CAPE significantly suppressed MCT-induced vascular remodeling by decreasing the HIF-1α expression and PDGF-BB production, and improved in vivo RV systolic performance in rats. Furthermore, CAPE inhibits hypoxia- and PDGF-BB-induced HIF-1α expression by decreasing the activation of the AKT/ERK pathway, which results in the inhibition of human pulmonary artery smooth muscle cells (hPASMCs) proliferation and prevention of cells resistant to apoptosis. Overall, our data suggest that HIF-1α is regarded as an alternative target for CAPE in addition to NF-κB, and may represent a promising therapeutic agent for the treatment of PAH diseases.

Caffeic acid phenethyl ester (CAPE) possesses pro-hypoxia and anti-stress activities: bioinformatics and experimental evidences

Honeybee propolis and its bioactive component, caffeic acid phenethyl ester (CAPE), are known for a variety of therapeutic potentials. By recruiting a cell-based reporter assay for screening of hypoxia-modulating natural drugs, we identified CAPE as a pro-hypoxia factor. In silico studies were used to probe the capacity of CAPE to interact with potential hypoxia-responsive proteins. CAPE could not dock into hypoxia inducing factor (HIF-1), the master regulator of hypoxia response pathway. On the other hand, it was predicted to bind to factor inhibiting HIF (FIH-1). The active site residue (Asp201) of FIH-1α was involved in hydrogen bond formation with CAPE and its analogue, caffeic acid methyl ester (CAME), especially in the presence of Fe and 2-oxoglutaric acid (OGA). We provide experimental evidence that the low doses of CAPE, that did not cause cytotoxicity or anti-migratory effect, activated HIF-1α and inhibited stress-induced protein aggregation, a common cause of age-related pathologies. Furthermore, by structural homology search, we explored and found candidate compounds that possess stronger FIH-1 binding capacity. These compounds could be promising candidates for modulating therapeutic potential of CAPE, and its recruitment in treatment of protein aggregation-based disorders.

BMP‑6 protects retinal pigment epithelial cells from oxidative stress‑induced injury by inhibiting the MAPK signaling pathways

Worldwide, neovascular age‑related macular degeneration (nAMD) is one of the most common causes of blindness in the elderly. In particular, degeneration of retinal pigment epithelial (RPE) cells represents the main pathological process in the development of nAMD, and oxidative stress serves a major role. The present study aimed to investigate the association between bone morphogenetic protein 6 (BMP‑6) and nAMD. BMP‑6 concentration was significantly reduced in patients with wet nAMD compared with in the control group. Furthermore, the present study investigated the protective effects of BMP‑6 on RPE cells following oxidative stress‑induced injury. Cell Counting Kit‑8 assay and terminal deoxynucleotidyl transferase dUTP nick‑end labeling staining demonstrated that BMP‑6 increased RPE cell viability, which was decreased following treatment with hydrogen peroxide (H2O2), and reduced H2O2‑induced apoptosis. In addition, western blotting revealed that BMP‑6 reversed the decrease in pro‑caspase‑3 levels and the dysregulation of the B‑cell lymphoma 2 (Bcl‑2)/Bcl‑2‑associated X protein (Bax) balance caused by H2O2. In addition, alterations in c‑Jun N‑terminal protein kinase (JNK) and p38 mitogen‑activated protein kinase (MAPK) expression were examined, and pretreatment with BMP‑6 was demonstrated to reduce H2O2‑induced activation of JNK and p38 MAPK. Conversely, the effects of BMP‑6 were attenuated by its inhibitor noggin. In conclusion, the present study demonstrated that BMP‑6 may protect RPE cells from oxidative stress injury to a certain extent, which may be associated with alterations in the MAPK signaling pathway. However, the specific mechanism of action underlying this effect requires further investigation. Overall, the present study laid a foundation for exploring novel nAMD treatment methods.

Anti-neovascularization effects of DMBT in age-related macular degeneration by inhibition of VEGF secretion through ROS-dependent signaling pathway

Choroidal neovascularization (CNV) is the hallmark of late-staged wet age-related macular degeneration (AMD). Vascular endothelial growth factor (VEGF) is a key component in the development and progression of wet AMD. DMBT, 6,6'-bis(2,3-dimethoxybenzoyl)-α,α-D-trehalose, had been proved that it could suppress tumor angiogenesis and metastasis by inhibiting production of VEGF. But the effects of DMBT on CNV were not known. This study was to investigate effects and mechanisms of DMBT on CNV in vitro and in vivo. Results showed that DMBT could inhibit migration and tube formation of RF/6A cells under ARPE-19 hypoxia conditioned medium. DMBT could reduce lesion area in laser-induced CNV model mice. ELISA and Western blotting assay showed that DMBT markedly inhibited secretion of VEGF in vitro and in vivo. Furthermore, DMBT restrained ROS level under hypoxia via suppressing Nrf2/HO-1 pathway. DMBT effectively suppressed hypoxia-induced the up-regulation of p-Akt, p-NF-κB, and HIF-1α. These results suggest that DMBT can inhibit CNV by down-regulation of VEGF in retina through Akt/NF-κB/HIF-1α and ERK/Nrf2/HO-1/HIF-1α pathway. DMBT might be a promising lead molecule for anti-CNV and serve as a therapeutic agent to inhibit CNV.

Effects of Novel Nitric Oxide-Releasing Molecules against Oxidative Stress on Retinal Pigmented Epithelial Cells

Oxidative stress is a hallmark of retinal degenerations such as age-related macular degeneration and diabetic retinopathy. Enhancement of heme oxygenase-1 (HO-1) activity in the retina would exert beneficial effects by protecting cells from oxidative stress, therefore promoting cell survival. Because a crosstalk exists between nitric oxide (NO) and HO-1 in promotion of cell survival under oxidative stress, we designed novel NO-releasing molecules also capable to induce HO-1. Starting from curcumin and caffeic acid phenethyl ester (CAPE), two known HO-1 inducers, the molecules were chemically modified by acylation with 4-bromo-butanoyl chloride and 2-chloro-propanoyl chloride, respectively, and then treated in the dark with AgNO₃ to obtain the nitrate derivatives VP10/12 and VP10/39. Human retinal pigment epithelial cells (ARPE-19) subjected to H₂O₂-mediated oxidative stress were treated with the described NO-releasing compounds. VP10/39 showed significant (p < 0.05) antioxidant and protecting activity against oxidative damage, in comparison to VP10/12, which in turn showed at 100 μM concentration a slight but significant cell toxicity. Only VP10/39 significantly (p < 0.05) induced HO-1 in ARPE-19, most likely through covalent bond formation at Cys151 of the Keap1-BTB domain, as revealed from molecular docking analysis. In conclusion, the present data indicate VP10/39 as a promising candidate to protect ARPE-19 cells against oxidative stress.

The PI3K/Akt pathway: a critical player in intervertebral disc degeneration

Intervertebral disc degeneration (IDD) is thought to be the primary cause of low back pain, a severe public health problem worldwide. Current therapy for IDD aims to alleviate the symptoms and does not target the underlying pathological alternations within the disc. Activation of the phosphatidylinositol 3-kinase (PI3K)/Akt pathway protects against IDD, which is attributed to increase of ECM content, prevention of cell apoptosis, facilitation of cell proliferation, induction or prevention of cell autophagy, alleviation of oxidative damage, and adaptation of hypoxic microenvironment. In the current review, we summarize recent progression on activation and negative regulation of the PI3K/Akt signaling pathway, and highlight its impact on IDD. Targeting this pathway could become an attractive therapeutic strategy for IDD in the near future.

Caffeic acid phenethyl ester upregulates N-myc downstream regulated gene 1 via ERK pathway to inhibit human oral cancer cell growth in vitro and in vivo

SCOPE

Caffeic acid phenethyl ester (CAPE), a bioactive component of propolis, is considered as a new anti-cancer agent. Oral squamous cell carcinoma (OSCC) is the most common oral cancer with unsatisfying survival. N-myc downstream regulated family genes (NDRGs) involve in numerous physiological processes. We investigated the anti-cancer effect of CAPE on OSCC and related mechanisms.

METHODS AND RESULTS

Cell proliferation assay, western blot, gene transfection and knockdown, and reporter assay were applied. We showed that CAPE attenuated OSCC cell proliferation and invasion in vitro, and safely and effectively inhibited OSCC cell growth in a xenograft animal model. CAPE treatment induced NDRG1, but not NDRG2 and NDRG3, expression in OSCC cells as determined by western blot, RT-qPCR, and reporter assay. The 5'-deletion assay demonstrated that CAPE increased NDRG1 promoter activity depending on the region of -128 to +46 of the 5'-flanking of NDRG1 gene. NDRG1 gene knockdown attenuated CAPE anti-growth effect on OSCC cells. CAPE activated mitogen-activated protein kinase (MAPK) signaling pathway. The extracellular signal regulated kinase (ERK) inhibitor (PD0325901) and ERK1 knockdown blocked CAPE-induced NDRG1 expression in OSCC cells.

CONCLUSION

CAPE activated MAPK signaling pathway and increased NDRG1 expression through phosphorylation of ERK1/2 to repress OSCC cells growth.

4-isothiocyanate-2, 2, 6, 6-tetramethyl piperidinooxyl inhibits angiogenesis by suppressing VEGFR2 and Tie2 phosphorylation

Reactive oxygen species (ROS) are involved in the signaling pathway and are triggered by angiogenic factors, including vascular endothelial growth factor and angiopoietins. 4-isothiocyanate-2, 2, 6, 6-tetramethyl piperidinooxyl (4-ISO-Tempo) is one of the nitroxides that exhibits antioxidant activity. However, the anti-angiogenic effect of 4-ISO-Tempo remains unknown. The aim of this study was to investigate the effect of 4-ISO-Tempo on tumor proliferation and angiogenesis as well as its underlying mechanisms. Our results revealed that 4-ISO-Tempo significantly inhibited the viability of neoplastic and endothelial cells. Furthermore, the effective concentration of 4-ISO-Tempo on human microvascular endothelial cell 1 (HMEC-1) was lower than that on human lung adenocarcinoma A549 and human colon cancer SW620 cells. This suggested that endothelial cells were more sensitive to 4-ISO-Tempo than tumor cells. Furthermore, we demonstrated that 4-ISO-Tempo also suppressed secretion of matrix metalloproteinase (MMP)-2 and MMP-9, and migration and tube formation of HMEC-1 cells. The mechanism is attributed to the decreasing ROS generation and further phosphorylation of vascular endothelial growth factor receptor 2 and Tie2. Our findings suggest that 4-ISO-Tempo should be investigated for its usefulness in anti-angiogenesis therapies.

Mining for genes related to choroidal neovascularization based on the shortest path algorithm and protein interaction information

BACKGROUND

Choroidal neovascularization (CNV) is a serious eye disease that may cause visual loss, especially for older people. Many factors have been proven to induce this disease including age, gender, obesity, and so on. However, until now, we have had limited knowledge on CNV's pathogenic mechanism. Discovering the genes that underlie this disease and performing extensive studies on them can help us to understand how CNV occurs and design effective treatments.

METHODS

In this study, we designed a computational method to identify novel CNV-related genes in a large protein network constructed using the protein-protein interaction information in STRING. The candidate genes were first extracted from the shortest paths connecting any two known CNV-related genes and then filtered by a permutation test and using knowledge of their linkages to known CNV-related genes.

RESULTS

A list of putative CNV-related candidate genes was accessed by our method. These genes are deemed to have strong relationships with CNV.

CONCLUSIONS

Extensive analyses of several of the putative genes such as ANK1, ITGA4, CD44 and others indicate that they are related to specific biological processes involved in CNV, implying they may be novel CNV-related genes.

GENERAL SIGNIFICANCE

The newfound putative CNV-related genes may provide new insights into CNV and help design more effective treatments. This article is part of a Special Issue entitled "System Genetics" Guest Editor: Dr. Yudong Cai and Dr. Tao Huang.

Caffeic Acid phenethyl ester is a potential therapeutic agent for oral cancer

Head and neck cancers, which affect 650,000 people and cause 350,000 deaths per year, is the sixth leading cancer by cancer incidence and eighth by cancer-related death worldwide. Oral cancer is the most common type of head and neck cancer. More than 90% of oral cancers are oral and oropharyngeal squamous cell carcinoma (OSCC). The overall five-year survival rate of OSCC patients is approximately 63%, which is due to the low response rate to current therapeutic drugs. In this review we discuss the possibility of using caffeic acid phenethyl ester (CAPE) as an alternative treatment for oral cancer. CAPE is a strong antioxidant extracted from honeybee hive propolis. Recent studies indicate that CAPE treatment can effectively suppress the proliferation, survival, and metastasis of oral cancer cells. CAPE treatment inhibits Akt signaling, cell cycle regulatory proteins, NF-κB function, as well as activity of matrix metalloproteinase (MMPs), epidermal growth factor receptor (EGFR), and Cyclooxygenase-2 (COX-2). Therefore, CAPE treatment induces cell cycle arrest and apoptosis in oral cancer cells. According to the evidence that aberrations in the EGFR/phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) signaling, NF-κB function, COX-2 activity, and MMPs activity are frequently found in oral cancers, and that the phosphorylation of Akt, EGFR, and COX-2 correlates to oral cancer patient survival and clinical progression, we believe that CAPE treatment will be useful for treatment of advanced oral cancer patients.