Age-Related Macular Degeneration and its Current Treatment Strategies: An Updated Review

Abstract

The retinal pigment epithelium (RPE), which is crucial for good vision, supports the health and function of photoreceptors or Bruch’s membrane (BM). The two most prevalent retinal vascular disorders that account for the majority of blindness in people in their working years and older are diabetic macular edema (DME) and neovascular age-related macular degeneration (nAMD). The blood-retinal barrier (BRB), cell differentiation, autophagy, growth factors (GFs), and other complex signaling pathways all play a role in maintaining morphology, and their disruption by harmful substances affects RPE function. It is urgent to gain a better understanding of the molecular mechanisms underlying the pathogenesis of AMD and identify potential targets as leads for creating potent therapies because there are currently no effective treatments for the early-AMD and late-AMD forms of the disease. For this reason, it is vital to identify molecular targets and therapies that can stop RPE deterioration in AMD and restore RPE function. Currently, the first-line treatment for nAMD and DME involves anti-vascular endothelial growth factor (VEGF) medications that inhibit VEGF family ligands, such as ranibizumab, bevacizumab (off-label usage), brolucizumab, and aflibercept. However, because nAMD and DME have complicated pathophysiological backgrounds, further research is still needed to determine the causes of non-response, resistance to anti-VEGF treatment, and disease relapses.

1. Introduction

The main factor in blindness among the elderly in industrialized nations is age-related macular degeneration (AMD), which causes central vision loss. Choroidoidal neovascularization (CNV) is a hallmark of neovascular age-related macular degeneration (nAMD). In people with nAMD, a complicated mechanism involving the signal protein vascular endothelial growth factor A (VEGF-A) promotes the formation of new blood vessels. Ranibizumab, bevacizumab, and aflibercept are examples of anti-VEGF medications that inhibit this protein [1, 2, 3]. Retinal vascular disease has been treated with anti-VEGF medication; however, because VEGF plays a role in pathophysiology, its efficacy is restricted. The anti-VEGF-A impact has several effects, including suppression of neovascularization, reduction of vascular permeability, and inhibition of endothelial proliferation. The identification of alternative targets has led to the discovery of the function of angiopoietin (Ang), which binds to tyrosine kinase (Tie-2) endothelium receptors in two different isoforms, Ang-1 and Ang-2, to control vasculogenesis (Figure 1) [4, 5]. AMD, the main cause of vision loss in the elderly, is frequently a precursor and driver of ocular degenerative illnesses, such as retinal pigment epithelium (RPE) phenotypic alteration [1, 2, 3].

Figure 1.

The relative mechanisms of action of drugs agents for maculopathy, including faricimab and brolucizumab. Faricimab is a bispecific antibody that functions by simultaneously inhibiting vascular endothelial growth factor a and angiopoietin-2. In the world of ophthalmology, brolucizumab represents an important development. When tested in the same laboratory under the same circumstances, brolucizumab bound to all VEGF-A isoforms with strong affinity, with a comparable but numerically greater affinity than aflibercept or ranibizumab.

A lack of effective treatments and a poor knowledge of its pathophysiology make AMD, the primary cause of visual impairment in the aging population [6]. AMD first manifests as atrophic changes in the RPE, followed by the development of lysosomal lipofuscin and extracellular drusen deposits. Geographic atrophy (GA), choroidal neovascularization (CNV), and fibrosis may result from injury brought on by long-term oxidative stress, protein aggregation, inflammation, and epithelial-mesenchymal transition of RPE [3, 6, 7]. More importantly, the epithelial-mesenchymal transition and oxidative stress are highly involved in the occurrence of AMD [8]. Numerous in vitro, in vivo, and clinical investigations have shown that several regulators are implicated in AMD. It is yet unknown how exactly these transcription factors or regulators affect RPE and cause AMD at the molecular level [7]. To better comprehend molecular processes, establish intercellular signal network profiles, and identify cellular function-specific biomarkers and therapeutic targets are required [9]. This chapter briefly addresses the mechanisms of epithelial-mesenchymal transition and oxidative stress in the altered functioning of ocular RPE cells, as well as the current prospective pharmaceutical therapies for AMD.

2. Retinal pigment epithelium and age-related macular degeneration

The choroid and photoreceptors are separated by a monolayer of highly polarized, terminally differentiated RPE (Figure 2) [3, 10]. The presence of tight connections, melanosomes, a basal nucleus, and basal proteins in morphologically polarized RPE can be explained by their arrangement apically. RPE and choroidal vasculature are distinguished by the extracellular matrix (ECM) membrane known as Bruch’s membrane (BM), which is basally situated and made up of several ECM proteins such collagen-IV, laminin, and fibronectin [3, 8, 11]. The maintenance of healthy retinal physiology and a variety of signaling cascades required for good vision are greatly influenced by RPE [12]. Additionally, they are crucial for the movement of nutrients from the choroid to the inner retinal membranes as well as for absorbing extra dispersed light to prevent photooxidation [8, 11]. Furthermore, it produces growth factors (GFs), which are crucial for the survival and development of the neuronal retina [13]. An outer blood-retinal barrier (BRB) is the RPE in the structural arrangements of the eyes [11]. For effective retinal homeostasis, the BRB is very crucial [10, 14]. Due to the necessity of cell connections like tight junctions and adherens junctions, the BRB is essential for maintaining proper visual acuity [15, 16]. Other oxidative changes, such as tyrosine nitration, which appears to be controlled by light in rat retina, are expected to be observed in drusen due to the high photooxidative stress in the retina (Figure 3) [17].

Figure 2.

The structure of the eye with the position of RPE and the layers of the retina has been shown schematically. The outer plexiform layer, outer nuclear membrane, outer limiting membrane, bipolar cells layer, rods-cones cells, and finally retinal pigment epithelial cells (RPE) make up the outer retinal layers. The RPE has tight connections and rests on the choroid’s Bruch’s membrane, serving as a barriers between the blood and the retina as well as performing a variety of other essential functions.

Figure 3.

Schematic representation of the normal retina, dry age-related macular degeneration, and wet age-related macular degeneration. Drusen, a debris-like substance that accumulates under the RPE on Bruch’s membrane over time. During a funduscopic eye examination, drusen can be seen. These deposits are known as either soft drusen or hard drusen, which are clinical terms that define their relative size, abundance, and morphology. Drusen may be prevalent in the peripheral retina of normal eyes even if the macula is usually devoid of them. It is thought to be a significant risk factor for AMD to have multiple or confluent soft drusen in the macula.

The primary cause of normal vision loss in older people is AMD. In general, it is described as the loss of RPE cells in the macular area [18, 19]. The macular area of the retina contains the greatest concentration of photoreceptors [20]. Due to its multifactorial nature, AMD is referred to as a multifactorial retinopathy. The factors that cause it include genetic predisposition, aberrant physiological inflammation, and oxidative stress (Figure 4) [19]. AMD is classified into two types: dry and wet. Progressive atrophy of the retinal pigment epithelium, choriocapillaris, and photoreceptors occurs in dry AMD, leading to slow but progressive loss of central vision. Drusen, or yellow lipid deposits under the macula, is an early symptom of AMD [8]. Wet AMD is distinguished by the formation of new yet aberrant blood vessels underneath the macula. Vascular endothelial growth factor (VEGF) is one of the growth factors involved in the formation of new choroidal arteries and the expansion of vascular permeability. Wet-AMD and dry-AMD are distinguished by CNV and GA, respectively [19, 21]. The term GA implies aberrant choriocapillaris, photoreceptor disruption, and RPE [19, 22]. CNV is defined as the creation of new blood vessels with scarring tissue around the RPE [23, 24]. This can cause early vision loss due to macular edema, hemorrhage, and scarring. Visual distortion (straight lines seem wavy), a central scotoma, or a blurry patch are frequent symptoms [8, 25, 26]. Furthermore, oxidative stress has been identified as the primary disease-causing factor in AMD [23]. Aside from oxidative stress, additional environmental variables including smoking, sunlight exposure, and inadequate dietary antioxidants also contribute to AMD development (Figure 4) [27, 28, 29].

Figure 4.

Diagrammatic representation of factors involved to alter fate of normal retinal pigment epithelium. The normal retinal pigment epithelium is prone to epithelial-mesenchymal transition or stress-mediated cell death, both of which are responsible for retinopathies such as age-related macular degeneration, under the impact of different stimuli such as photooxidation, oxidative stress, and altered growth hormones microenvironment.

3. Oxidative stress (OS) and age-related macular degeneration

The oxidative stress (OS) concept is built on an oxidation-reduction process [23]. OS is caused by an imbalance in the ratio of reactive oxygen species (ROS) generation to antioxidants [20, 30, 31]. The fact that ROS displayed critical biological processes such as cell proliferation, inflammation, apoptosis, certain gene expressions, survival, and migration explains the favorable influence of ROS in the simplest words [20, 32]. To sustain signal transduction and cell cycle control for healthy cellular homeostasis, ROS functions as a secondary messenger [20, 33, 34]. The intracellular concentration of ROS is essential for both the induction and inhibition of apoptosis [20, 35]. Recent research suggests that a decreased ROS concentration, particularly in the eye, aided in maintaining normal defenses against conditions that could threaten vision [36]. The ROS-mediated defense against pathogenic infection in the eye is provided by macrophages, neutrophils, and microglia [36]. A contributing element in age-related illnesses is the cumulative OS damage to essential macromolecules [37, 38]. Because of its increased oxygen tension, constant exposure to light, and presence of rich polyunsaturated fatty acids (PUFAs), the retina in particular is exceptionally susceptible to OS-induced harm [39]. According to observations, numerous ocular health conditions, including AMD and DR, have a significant association with OS [38, 40, 41]. Therefore, RPE is more likely to develop OS and cause a variety of degenerative disorders such as AMD, DR, and proliferative vitreoretinopathy (PVR) [42, 43, 44, 45]. One of the most significant pathogenic factors in AMD is oxidative stress, as previously mentioned. Due to physiological sources of oxidative stress, including the high metabolic activity of RPE cells and the phagocytosis of photoreceptor outer segments, as well as specific sources of photooxidative stress brought on by high UV exposure, RPE cells are exposed to an especially high oxidative cellular environment [46, 47]. Aging-related declines in the ability to neutralize ROS and lower autophagy ability expose degenerative RPE cells to particularly large accumulations of ROS [47].

Oxidized lipoproteins that affect RPE are one possible common target. It is well known that oxidized low-density lipoproteins preferentially collect in the macular area and are key participants in the etiology of AMD [48, 49]. By increasing the buildup of ROS, oxidized low-density lipoproteins play a significant role in oxidative stress and inflammation in AMD [50, 51]. ROS must be eliminated from the body for organisms to survive [34]. Antioxidants are essential for preventing the accumulation of ROS [20, 52]. To combat the harm caused by ROS, antioxidants are available naturally and are also found in the body [52]. By neutralizing the free radicals from blood, it shields the macromolecules by preventing the oxidation of cellular macromolecules [49, 52, 53, 54]. The antioxidants neutralize ROS by a variety of methods, including chelation, electron transfer, and hydrogen atom transfer from molecules [52, 55, 56].

4. Epithelial-mesenchymal transition (EMT) and age-related macular degeneration

Epithelial-mesenchymal transition (EMT), the trans-differentiation of epithelial cells into mesenchymal-like cells, plays a role in a number of biological processes, such as cell migration, wound healing, and development. Different substances, such as TGFβ, CTGF, epidermal growth factor, and fibroblast growth factor-2, cause EMT, which enhances cell motility and results in an invasive phenotype [8, 57, 58].

There are three different categories of EMT: type I, type II, and type III. In particular, type II-EMT is involved in retinopathy [8, 59]. Tissue fibrosis is caused by an unfavorable microenvironment and inappropriate stimulation of the pathological state [60]. Given that EMT is present in retinopathies and is particularly present in the RPE, it is believed to represent the fundamental underlying mechanism for severe retinal diseases. In particular, type II-EMT is involved in retinopathy [8, 61]. Epithelial cells must undergo a complex cellular reorganization and reprogramming the process that communicates new biochemical directives in order to become mesenchymal cells [62]. During EMT, desmosomes, adherent or tight junctions, and apical-basal polarity are all eliminated [63].

According to the in vivo investigation, the formation of mesenchymal cells in the vitreous cavity, which contributes to EMT, is mostly caused by the loss of cell-cell connections in RPE [64]. The RPE encounters altered apoptosis, dedifferentiation, and loss of epithelial polarity in pathological situations, which allows it to persist even in an abnormal microenvironment [12]. A few retinal disease symptoms, such as scarring and the development of the proliferative membrane, which compromise visual acuity, were evident during the clinical examination [65, 66]. Additionally, the in vitro research revealed that during the epithelial-mesenchymal transition of retinal pigment epithelium (RPE-EMT), the RPE demonstrates aberrant migratory ability, which is not desired for normal vision [64, 67, 68]. AMD, DR, rhegmatogenous retinal detachment (RRD), PVR, diabetic macular edema (DME), and GA are some of the oculopathies where EMT is implicated in RPE [66, 67, 69, 70, 71, 72, 73]. Clinical data also suggest that RPE fibrosis in PVR and DR [65, 66, 71].

During a full clinical evaluation of AMD patients, non-apoptotic degraded RPE was discovered, which was hypothesized to be the outcome of epithelial-mesenchymal transition of retinal pigment epithelium [51, 74, 75]. According to a clinical examination, a lesion brought on by abnormal pathological fluid buildup resulted in hyperreflective foci (HRF) [76, 77]. As a result, the HRF and RPE-EMT are interconnected [78]. The other research also revealed that HRF is a byproduct of RPE, further illuminating the HRF-RPE-EMT connection [78, 79]. In addition, another study found a connection between HRF severity and AMD, including GA and CNV [80]. Intriguingly, HRF content is protectively suppressed by anti-VEGF in AMD patients [78, 81]. The prevalence of drusen-burden and aberrant pigment is taken into consideration by the Age-Related Eye Disease Study (AREDS) when assessing the severity of the disease condition. A higher risk of illness is indicated by more drusen as well as more depigmented RPE [82]. However, it is not yet known how their molecular mechanism contributes to the development of diseases.

5. Current treatment strategy of age-related macular degeneration

The major objective of nAMD therapy is to improve visual acuity. To accomplish this purpose, the damaged retina must prevent new blood vessel formation and minimize fluid leakage [83]. CNV is exacerbated by VEGF [84]. Antagonism of vascular endothelial growth factor has been found to decrease CNV in mouse and nonhuman primate models of neovascularization [85]. CNV can be delayed by inhibiting VEGF from attaching to its receptor, VEGF receptor-2, in blood vessels, which is the main proangiogenic pathway [85]. Antibodies that neutralize VEGF binding to its receptor (anti-VEGF drugs) diminish fluid leakage from the CNV, restrict growth, and result in CNV regression (Figure 5). The development of the anti-VEGF agent therapeutic class has substantially improved visual results and prognosis for people with nAMD [86, 87]. A variety of treatments have been utilized to treat neovascular AMD. Before the development of anti-VEGF antibody therapy, laser treatment, including laser coagulation and photodynamic therapy (PDT), was employed. Anti-VEGF medicines that block VEGF family ligands, including ranibizumab, bevacizumab (off-label usage), brolucizumab, and aflibercept, are being used as first-line therapy for nAMD and DME [88].

Figure 5.

Diagrammatic representation of mechanism of various drugs or compounds utilized for the treatment of retinopathies such as age-related macular degeneration. For the treatment of age-related macular degeneration, different compounds are utilized. the VEGF-inhibitors include substances such as aflibercept, ranibizumab (Lucentis), and pegaptanib. additional compounds, including non-lethal sodium iodate (NaI), bradykinin (BK), and glucosamine (Glc), downregulate the epithelial-mesenchymal transition of the retinal pigment epithelium by acting through different signaling pathways.

5.1 Ranibizumab

The first anti-VEGF medication, ranibizumab (Lucentis), a humanized recombinant monoclonal antibody fragment, was demonstrated to improve visual acuity (VA) in individuals with wet-AMD and DME. Based on MARINA and ANCHOR studies, it obtained regulatory permission for the use of ranibizumab [89, 90]. Furthermore, the release of ranibizumab (Lucentis; Genentech, South San Francisco, CA, USA) in 2006 was one of the most significant advancements in the treatment of CNV in AMD [1]. Ranibizumab inhibits cell proliferation, prevents the development of new blood vessels, and reduces vascular leakage [91]. Intravitreal ranibizumab treatment for 2 years prevented vision loss and improved mean visual acuity in patients with minimally classic or occult (no classic lesions) choroidal neovascularization secondary to age-related macular degeneration [92].

Ranibizumab was found to be more effective than verteporfin as an intravitreal therapy for primarily classic nAMD, with fewer significant ocular side effects based on one study of 1 year, the treatment increased visual acuity on average [92]. Ranibizumab has improved the treatment of nAMD and gives millions of people hope. Outcomes of clinical trials indicate that ranibizumab was efficacious and well tolerated in patients [91]. Razumab™ (the world’s first biosimilar ranibizumab) was well-tolerated and dramatically improved visual acuity in individuals with wet-AMD [93, 94]. Razumab™ (biosimilar ranibizumab), has been approved by the highest Indian regulatory authority “Drugs Controller General of India (DCGI)” for the treatment of neovascular wet-AMD, DME, macular edema following retinal vein occlusion (RVO), and visual impairment due to CNV secondary to pathologic myopia [94]. According to the findings of this study, lowered blood VEGF and TGFβ-1 concentrations were seen following combination therapy, suggesting that the condition is well managed and visual acuity is improved. Photodynamic therapy can block existing CNV, and ranibizumab is capable of resisting VEGF and suppressing CNV, therefore combining the two treatments appears to improve clinical effectiveness [94].

Based on clinical data, most guidelines prescribe three consecutive monthly intravitreal injections of ranibizumab [95, 96]. In other words, the pivotal trials MARINA, ANCHOR, and subsequently Pronto, SUSTAIN, and IVAN planned three loading doses of ranibizumab as the first therapy [89, 90, 97, 98, 99]. Their findings demonstrate that after the first three injections, visual acuity improves. The current ranibizumab product features summary recommendations to begin therapy with a loading phase consisting of three consecutive months of monthly injections of 0.5 mg ranibizumab. However, the comparisons of age-related macular degeneration treatment trials (CATT)-protocol recently discovered that after the first year, ranibizumab administered as needed without the use of three necessary loading doses was similar to ranibizumab given monthly [98, 100]. Ranibizumab is being studied further as a potential treatment for various conditions such as DME, retinal vein occlusion, and probable ocular histoplasmosis syndrome [89, 90].

In brief, the development of VEGF inhibitors has dramatically improved the prognosis of this life-threatening oculopathy, and ranibizumab, which targets VEGF-A, has become the gold standard in its therapy. Large randomized controlled studies, however, have revealed that ranibizumab therapy necessitates long-term treatment regimens and repeated intravitreal injections. This rigorous therapy is expensive for both the patient and the healthcare system. This burden, as well as the potential side effects of intraocular administration, is driving research toward individualized dosing strategies and multimodal treatment combinations aimed at combating the complex pathogenesis responsible for CNV and potentially reducing the frequency of retreatment required for optimal results [101].

5.2 Brolucizumab

Brolucizumab is a humanized, single-chain variable fragment (scFv) that inhibits VEGF-A [102, 103]. It is also known as “RTH258” (and was formerly known as “ESBA1008”). In other words, Brolucizumab is a newly created, humanized single-chain fragment of a monoclonal antibody that binds all VEGF-A isoforms and was recently authorized for the treatment of neovascular AMD [102, 103]. By producing equivalent therapeutic results with fewer clinic visits, intravitreal brolucizumab holds the potential to lessen the burden of therapy for individuals with nAMD. Its application to the management of more difficult maculopathies, such as DME, also seems promising [104]. These brolucizumab molecules are composed of a small protein fragment, about 26 kDa, that is formed by joining the heavy and light chain domains of a monoclonal antibody together with a flexible linker [102]. Single-chain variable fragments are a desirable form for pharmacologic treatment due to their small size and lack of a fragment crystallizable area [102]. Small molecules have shown better penetration into target tissues than full-sized immunoglobulin-G. This can lead to increased local efficacy, extended duration of action, and decreased systemic exposure, all of which can minimize side effects [87, 102].

Following an intravitreal injection of 1 or 6 mg of the medication into each of the two eyes of cynomolgus monkeys, the pharmacokinetics of Brolucizumab were examined in vivo. According to estimates made by the researchers, the concentration of brolucizumab in the central retina and choroid after delivery was 42 and 18%, respectively, of the vitreous concentration. The maximum concentration of brolucizumab in serum was found to be almost 3500 times lower than the concentration in the vitreous, and its serum clearance was 51.0 hours. According to these study findings, brolucizumab has a low systemic penetration rate and can enter the choroid through the retina. Intravitreal administration of brolucizumab in monkeys showed no ocular or systemic harm and only mild ocular inflammation [87]. Brolucizumab systemic exposure was shown to be limited, as in earlier studies. The quick systemic clearance by brolucizumab is thought to be due to its short molecular size and lack of an Fc-region [87, 104, 105].

These preclinical trials in nonhuman monkey species demonstrate brolucizumab as an anti-VEGF drug that has a minimal systemic concentration and little to no side effects, which might ease the treatment of nAMD patients burden because it would be given more rarely [87].

The MERLIN research, which began in 2018, compares the effectiveness of 6 mg brolucizumab with 2 mg-aflibercept delivered in a 4-week dose schedule following the loading phase in nAMD patients with persisting retinal fluid despite anti-VEGF therapy. MERLIN one-year data showed that brolucizumab was non-inferior to aflibercept in mean best corrected visual acuity change and had superior anatomic outcomes. In the brolucizumab group, however, 4-week treatment intervals were linked with a greater reported frequency of significant ocular adverse events such as ocular inflammation, retina vasculitis, and retina occlusion. As a result, Novartis stated that the MERLIN research will be terminated in May 2021 owing to patient safety concerns [106]. Ogura and colleagues presented the 96-week visual and anatomic results of brolucizumab treatment compared to aflibercept in Japanese eyes diagnosed with polypoidal choroidal vasculopathy in a HAWK research subanalysis [104, 106]. HAWK and HARRIER were two-year, randomized, double-masked, multicenter phase 3 studies that evaluated the safety and effectiveness of brolucizumab intravitreal injections for the treatment of nAMD to aflibercept [107, 108, 109]. The KESTREL and KITE trials were the first to compare the effectiveness of brolucizumab vs. aflibercept in DME patients. In 52-week findings from KITE and KESTREL, 6 mg-brolucizumab was shown to be non-inferior to 2 mg-aflibercept in mean Best Corrected Visual Acuity change from baseline (Table 1) [106, 125]. Similar phase III trials, TENAYA and LUCERNE, are randomized, double-masked, active comparator-controlled, and lasted 112 weeks when it came to faricimab treatment for nAMD. Throughout the trial, patients were randomized to either aflibercept or faricimab. Throughout weeks 40, 44, and 48, the mean change in best-corrected visual acuity (BCVA) from baseline was the main effectiveness objective. According to some investigations safety outcomes comprised the frequency and severity of retinal and other ocular adverse events [110, 112].

Name of the study (Name of the drug/treatment agent/year of study)	Type of the study (Type of oculopathy/retinopathy)	Outcome of the study/investigation	References
The BREW study (Brolucizumab, year-2020)	Real-world study (nAMD)	No inflammation or vasculitis No other adverse ocular outcome	[4]
The STAIRWAY study (Faricumab, year-2020)	Phase-II, Real-world study (nAMD)	No other adverse ocular	[110, 111]
The TENAYA and LUCERNE study (Faricumab, year-2020)	Phase-III, Real-world clinical trials (nAMD)	No retinal vasculitis No retinal occlusion	[112]
The BOURLEVARD study (Faricumab, year-2020)	Phase-III, Real-world randomized study (DME)	No adverse effects observed	[113]
Kushuhara et al., study (Faricumab, year-2023)	Real-world retrospective study (DME)	No adverse effects reported	[114]
The YOSHEMITE and RHINE study (Faricumab, year-2022)	Phase-III, Real-world clinical trials (DME)	Very few retinal adverse effects reported	[115]
The TRUCKEE study (Faricumab, year-2023)	Real-world study (Multicentre) (nAMD)	Intraocular inflammation reported	[110, 111]
Mukai et al., (Faricumab, year-2023)	Real-world study (nAMD-	RPE-detachment observed	[116]
Enrique study (Brolucizumab, year-2023)	Real-world study (Case study) (nAMD)	Intraocular inflammation reported Adverse ocular outcome observed	[117]
Bulirsch et al., (Brolucizumab, year-2021)	Real-world study (observational study) (nAMD)	Intraocular inflammation observed Retinal vasculitis observed	[118]
The REBA study	Real-world study (observational, multicentric study) (nAMD)	Vascular occlusions reported Macular hole observed	[119, 120]
The BRAILLE study (Brolucizumab, year-2021)	Real world study (non-randomized, uncontrolled study) (nAMD)	Subretinal hemorrhage RPE-tear observed No intraocular inflammation reported	[121]
Matsumoto et al., (Brolucizumab, year-2021)	Real-world study (Retrospective study) (nAMD)	Intraocular inflammation reported Adverse ocular outcome observed	[122]
Bilgic et al., The PROBE Study (Brolucizumab, year-2021)	Real-world study (observational) (nAMD)	No ocular adverse events reported	[119, 123]
Montesel et al. (Brolucizumab, year-2021)	Real-world study (observational, monocentric) (nAMD)	Few patients developed intraocular inflammation	[124]
Michalska-Małecka et al. (Brolucizumab, year-2021)	Real-world study (observational, monocentric) (nAMD)	No ocular adverse events reported	[125]
Tamashiro et al. (Brolucizumab, year-2022)	Real-world study (multicentre) (nAMD)	Inflammation of iris observed	[126]
Avaylon et al. (Brolucizumab, year-2022)	Real-world study(nAMD)	No ocular adverse events reported	[127]
Haensli et al. (Brolucizumab, year-2021)	Real-world study(nAMD)	Intraocular inflammation with ocular occlusion but no vision loss reported	[128]
Hussain et al. (Brolucizumab, year-2021)	Real-world study(nAMD)	No vascular inflammation reported	[129]
Awh et al. Brolucizumab, year-2022)	Real-world study (nAMD)	Intraocular inflammation observed additionally other retinal inflammation observed	[130]
Matsumoto et al. (Brolucizumab, year-2021)	Real-world study (Polypoidal choroidal vasculopathy)	Suppression of lesions	[122]
Fukuda et al. (Brolucizumab, year-2021)	Real-world study (Polypoidal choroidal vasculopathy)	Intraocular inflammation observed	[131]
Chakraborty et al. (Brolucizumab, year-2021)	Real-world study (DME)	No Intraocular inflammation reported	[121, 132]
The SΕΕ study (Brolucizumab)	Clinical trials (nAMD)	Occasional adverse ocular events observed	[102]
The OWL study (Brolucizumab)	Clinical trials (nAMD)	Positive treatment response observed	[133]
The OSΡRΕΥ study (aflibercept, Brolucizumab, year-2017)	Clinical trials (nAMD)	Adverse ocular events observed	[108, 109]
ΗΑWΚ and ΗΑRRΙΕR (aflibercept, Brolucizumab, year-2020)	Clinical trials, Phase-III (nAMD)	Well tolerated range of Brolucizumab observed	[108]
ΚΕSΤRΕL and ΚΙΤΕ (aflibercept, Brolucizumab, year-2022)	Clinical trials, Phase-III (DME)	Very low severe ocular adverse events reported	[125]

Table 1.

List of treatment agents/drugs utilized for retinopathy condition.

Experimental research on non-human primates has demonstrated that brolucizumab binds to all VEGF-A isoforms. According to Gaudreault and coworkers, it has been demonstrated to prevent VEGF from binding to its receptor, VEGFR2 [134]. The suggested dosage of brolucizuab is 6 mg (0.05 mL of solution, or 120 mg/mL) for the treatment of both DME and non-alcoholic AMD. Intravitreal injections into the vitreous cavity are used to deliver brolucizumab. It is advised to have injections into the afflicted eye or eyes once a month for the first three loading doses. Based on the clinician’s assessment of the patient”s condition, a dosage interval of 8–12 weeks is advised subsequently [108]. According to the European Society of Retina Specialists (EURETINA) guidelines, fluid on an OCT scan indicates an active illness that has to be treated with an anti-VEGF medication. Brolucizumab has been shown in other trials to be beneficial in patients whose subretinal fluid did not resolve after prior anti-VEGF therapy. Studies using brolucizumab have demonstrated higher rates of fluid resolution and more persistent decreases in central subfield thickness, suggesting morphological and structural benefits [4, 109, 118].

As previously noted, injection frequency may be decreased without sacrificing therapeutic efficacy when using brolucizumab, an intravitreal anti-VEGF medication approved for the treatment of nAMD and DME [135]. The FDA, USA authorized brolucizumab in October 2019 for the treatment of neovascular AMD. Two phase 3 randomized clinical studies, HAWK and HARRIER, were conducted concurrently to examine brolucizumab [136]. The BCVA change from baseline at week 48 served as the main outcome [107, 108, 109]. As of week 96, in the HAWK and HARRIER investigations, conjunctival bleeding, impaired visual acuity, cataracts, vitreous floaters, dry eye, and eye discomfort were the most common ocular adverse events (>5% of patients for the whole research group). While 47% of brolucizumab patients in the HARRIER trial reported experiencing at least one ocular adverse event, 61% of patients in the HAWK trial reported experiencing at least one ocular adverse event. The eye inflammation, uveitis, chorioretinitis, iridocyclitis, keratitis precipitates, anterior chamber cell, vitreous haze, retinal vasculitis, anterior chamber flare, and vitritis were adverse outcomes associated with intraocular inflammation. In the HAWK trial, the most frequent conditions were uveitis (2.2%) and iritis (2.5%) (Table 1) [105].

In brief, both individuals with newer to treatment and switch therapy patients respond well to intravitreal brolucizumab therapy. The drug, however, does entail an insignificant but evident risk [119]. Patients with nAMD may have less treatment burden as a result of the preclinical and clinical results on brolucizumab, which show maintained disease management with longer injection intervals [87]. With concentrated molar dose, brolucizumab has proven to be a highly effective therapeutic molecule that outperforms other anti-VEGFs licensed for the treatment of patients with nAMD in terms of clarity of vision, fluid adjustment, and duration of impact. Additionally, there is evidence that brolucizumab can lessen treatment burden by permitting longer injection intervals with sustained disease control, as demonstrated by the OSPREY study and the key studies HAWK and HARRIER. By lessening the burden of medication, improving patient adherence, and assisting in the management of patients who are under control with the anti-VEGFs that are already on the market, this is anticipated to enhance long-term results. In the upcoming years, more data on the clinical effectiveness of brolucizumab and its influence on clinical practice in other anti-VEGF-responsive diseases are anticipated, underscoring the potential of compound significance in applications other than nAMD [87, 102, 108].

5.3 Faricimab

The FDA approved faricimab, also known as RG7716 in preclinical testing, in January 2021 for the treatment of nAMD and DME. Faricimab is the first bispecific monoclonal antibody created for intravitreal administration [137]. Unlike conventional monospecific antibodies, bispecific heterodimeric antibodies may attach to two distinct targets because they contain independent light chains in each of the fragment antigen-binding (Fab) domains. During the drug design phase, a knob and hole mechanism between the heavy chains was used to achieve these properties utilizing the CrossMAb CH1-CL technology, which was first described in 2011 [138]. Due to its distinct structural characteristics, faricimab has one VEGF-binding domain and one Ang-2-binding domain, enabling simultaneous and independent neutralization [88, 137, 139, 140]. Similar to this, the FDA, USA approved faricimab-svoa (Vabysmo™, Genentech, San Francisco, CA) in January 2022 for the treatment of DME and nAMD. This medication has simultaneous and independent binding on both VEGF-A and angiopoietin-2 (Ang-2) [111]. It is hypothesized that the anti-Ang 2 impact will increase vascular stability and desensitize the vessels to the effects of VEGF-A. One chance to target two mediators of retinal vascular disease with a single molecule was provided by the use of monoclonal antibodies in anti-VEGF treatment. With CrossMAb (Roche, Basel, Switzerland), a patented method that enables the antibody to have two distinct antigen-binding domains (Fab), these bispecific antibodies may be created. Facitimab, formerly known as RG7716, was developed with the aid of CrossMAb [4, 5, 141, 142]. As was previously noted, faricimab has been shown to be able to inhibit VEGF-A and the detrimental effects of Ang-2 on human vascular endothelial cells in vitro. Additionally, compared to VEGF and Ang-2 inhibitors used separately, the combined reduction of VEGF and Ang-2 activity significantly decreased vascular permeability and retinal edema, neuronal death, and macrophage infiltration of neovascular lesions in JR5558 mice with spontaneous CNV [88]. Intravitreal faricimab was able to significantly reduce the levels of pro-inflammatory IL-6 in the aqueous humor and was more effective than ranibizumab in decreasing leaky lesions in monkeys with laser-induced CNV [143]. In replication research, Foxton and associates confirmed similar results [88, 143].

Faricimab is administered intravitreally at a dosage of 6 mg from 0.05 mL of a 120 mg/mL solution. One regimen for nAMD is 6 mg intravitreal every 4 weeks for the first four doses, then the same dose 8 or 12 weeks later depending on the results of optical coherence tomography (OCT) and visual acuity assessments [110]. Faricimab has been tested in a number of clinical studies to determine its safety and effectiveness. YOSEMITE and RHINE are phase III clinical studies of faricimab in individuals with DME who have never received anti-VEGF therapy. The primary effectiveness outcome is the mean change from baseline in best-corrected visual acuity averaged across weeks 48, 52, and 56 [144]. BOULEVARD and STAIRWAY are faricimab phase II clinical studies for DME and nAMD, respectively. Faricimab phase III studies RHINE and YOSEMITE are underway in DME. Similarly, faricimab phase III trials in nAMD are TENAYA and LUCERNE [4, 110, 111]. BOULEVARD is a phase II, 36-week, randomized, and double-blinded, multicenter study of 229 DME patients who have not previously received therapy. The 6.0 mg faricimab cohort showed better letter improvement in visual perception, a decrease in central subfield thickness, and an improvement in the diabetic retinopathy severity score. The findings showed that combined suppression of Ang-2 and VEGF-A might improve visual gain and have a longer duration in individuals with DME [112, 113, 145].

In brief, targeting the angiopoietin/Tie (Ang/Tie) signaling cascade beyond the VEGF pathway may be a promising therapeutic technique that has the ability to address some of the previously described complications. Faricimab is a novel bispecific antibody that targets both VEGF-A and the Ang-Tie/pathway. Faricimab can sustain clinical effectiveness with more prolonged treatment regimens compared to aflibercept (12 or 16 weeks) with a favorable safety profile, according to results from phase III studies TENAYA and LUCERNE (nAMD) and RHINE and YOSEMITE (DME) profile [112, 146]. In comparison to earlier anti-VEGF medications, faricimab is believed to have a more enduring impact and inhibits both VEGF-A and Ang-2. Faricimab injection, like all intravitreal anti-VEGF injections, can cause thromboembolic events, endophthalmitis, hypersensitivity, retinal detachment, vitreous hemorrhage, subconjunctival hemorrhage, and elevated intraocular pressure, among other possible side effects. In about 8–10% of instances, the potential immunogenicity of the drug may result in an occurrence of an anti-faricimab immunoglobulin. The usage of this medication in pregnant women has not been thoroughly studied. Effective contraception is suggested for women of reproductive potential who use this medication, as the impact of the drug on human fertility is uncertain. After the final faricimab dose, the contraception should be used for at least three more months [146, 147].

5.4 Aflibercept

Aflibercept is a new recombinant fusion protein composed of VEGF receptor (R1) and VEGFR2 extracellular domains fused to the Fc-region of human immunoglobulin G1. It binds all VEGF isoforms and has a greater affinity for VEGF-A/B. Aflibercept’s effectiveness was evaluated in two randomized, double-blind, multicenter, active-controlled studies in patients with choroidal neovascularization owing to exudative age-related macular degeneration (AMD) [1, 103]. The findings of phase 1 and 2 studies demonstrated effective short-term suppression of choroidal neovascularization in individuals with exudative age-related macular degeneration and revealed that aflibercept had longer durability when compared to other anti-VEGF medications [1].

Aflibercept was studied in multiple preclinical trials before entering clinical trials. In these investigations, VEGF-Trap inhibited the growth of bovine vascular endothelial cells in a manner analogous to ranibizumab [148]. The effectiveness of aflibercept in preventing CNV formation was subsequently evaluated in rodent and non-human primate models [149, 150]. In adult rats with CNV caused by subretinal Matrigel injection, two systemic treatments of aflibercept, 2 days before and 6 days after Matrigel administration, inhibited the formation of CNV. Aflibercept, on the other hand, inhibited collagen production and thus prevented the creation of new neovascular lesions and the regression of existing lesions, leukocyte infiltration, and the development of fibrosis in CNV that developed over 10 days [149]. Another study found that subcutaneous and intravitreal aflibercept inhibited CNV growth in mice with laser photocoagulation-induced BM-damage. Aflibercept’s inhibitory impact on CNV development after subcutaneous injection in transgenic mice with enhanced VEGF expression inside the photoreceptor layer was also verified. This experiment also demonstrated the protective properties of aflibercept against BRB by limiting its damage in the presence of increased VEGF concentrations in the vitreous, both after administration of recombinant VEGF and in transgenic mice with VEGF overexpression [150].

VEGF-Trap has also been studied for its capacity to prevent and cure laser-induced CNV in cynomolgus monkeys [151]. The results demonstrated that aflibercept, delivered weekly intravenously at doses of 3 and 10 mg/kg, as well as intravitreal at doses of 50, 250, and 500 g at two-week intervals, effectively protected the investigated eyes from developing CNV. Furthermore, it was demonstrated during the trial that a single intravitreal injection of aflibercept at a dosage of 500 g reversed neovascular alterations generated by laser 2 weeks earlier and strongly reduced the establishment of advanced vascular leakage sites [88, 151]. In the real world, aflibercept has equivalent effects to ranibizumab for treatment-naive nAMD and may be more beneficial for individuals with poorer initial visual acuity [152]. In a cohort of neovascular AMD patients resistant to chronic bevacizumab and/or ranibizumab injections, switching to intravitreal aflibercept treatment can result in considerable visual improvement in the near term and persistent decrease of central macular thickness over a year of follow-up [103].

5.5 Pegaptanib

Pegaptanib (Macugen; OSI/Eyetech Pharmaceuticals, New York, NY, USA) was the first VEGF inhibitor to get FDA clearance for CNV in AMD in 2004. Pegaptanib is an RNA aptamer with excellent affinity and specificity for human VEGF [153]. However, the medication did not bind to other active VEGF isoforms like VEGF121. However, the results of the investigation were encouraging, with 70% of patients losing fewer than three lines of vision compared to 55% of controls (p 0.001) [1, 153]. In 2004, the FDA authorized Macugen™ (Pegaptanib sodium) as the first anti-VEGF therapy for AMD. Pegaptanib, an aptamer that binds to the heparin-binding site of VEGF-165, prevents it from connecting with its endothelial cell receptor. The Fab portion of an anti-VEGF isoform-A antibody was used to create Lucentis™ [154]. It was authorized for use in AMD patients because it retained 95% of vision while improving visual gain [155]. Avastin™ (bevacizumab), derived from the same antibody as Lucentis™, is being used to treat AMD [92]. Anecortave acetate (Retaane™), a steroid, squalene, triamcinolone, Visudyne™, and other VEGF inhibitors are now being researched in vivo and in vitro [155, 156, 157].

5.6 Other regulators of epithelial-mesenchymal transition and age-related macular degeneration

Lampalizumab, a drug in clinical trials, has been demonstrated to be ineffective against AMD and GA [158]. Laser photocoagulation, intravenous anti-VEGF, and other steroid medicines are used to treat ocular diseases. Pan-retinal photocoagulation (PRP) is used to treat PDR. PRP has been demonstrated to have various beneficial benefits, including lessening the chance of blindness later in life, and is thus commonly used as a therapy [159]. Several phase-III trials in the developed world have indicated that anti-VEGF is better than other therapies in lowering the risk of later-life vision loss and, more interestingly, improvement of vision gain in DME [158, 160, 161]. Many intravenous steroids are useful in DME, although their adverse effects are unknown [162, 163]. However, anti-VEGF is not advised for those who are unable to maintain frequent checkups. As an adverse effect of steroid medication, cataracts and glaucoma may develop. Anti-VEGF medication still fails to work in 40–50% of eyes with DME, necessitating the adoption of a non-invasive, non-surgical, and more durable remedy [164]. The production of new nucleotides was hindered by the anticancer medication methotrexate [165]. According to patient-based research, methotrexate can help persons with PVR and AMD with vision improvement [51, 166, 167]. Interestingly, phase 3 clinical studies for the treatment of PVR are being conducted using the methotrexate analog (ADX-2191) [168]. When utilized to treat AMD under in vivo testing, the anti-diabetic drug metformin was discovered to have a favorable association with sustaining mitochondrial health [158, 169]. The use of a light spectrum to regulate the physiological activity of tissues or cells is known as photobiomodulation (PBM) [170]. PBM is another kind of PRP. Retinopathies and PBM treatment have recently been linked clinically [171]. Despite the fact that laser therapy has many clear advantages, it cannot be considered the best option for treating sub-foveal lesions since there are significant dangers associated with vision loss in old age, particularly in the sub-foveal region, as well as a high chance of recurrence [172]. However, it can still be considered useful for treating tiny lesions in wet-AMD [173]. Because AMD is defined as either “dry” or “wet,” PRP, photodynamic therapy, and anti-neovascular therapy can be used to prevent vision loss, but there is presently no therapy for dry-AMD [155].

According to research on antioxidants in peripheral blood, AMD patients had higher levels of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px), and reduced GSH in their platelets as well as GSH-Px, (R-GSH), and glutathione transferase (GST) in their RBCs [174]. There is no long-term treatment for AMD at present [175, 176]. Antioxidants may be used to modify ROS-mediated apoptosis, according to several studies [38]. Antioxidants and zinc supplements have been found to slow down the course of retinopathy [38, 177]. Additionally, the National Health and Nutrition Examination Survey (NHANES) reported a favorable correlation between antioxidant-rich dietary consumption and the suppression of AMD [178].

The decline in antioxidants causes aberrant neovascularization, as shown in AMD [20, 43]. It is interesting to note that phytochemical treatment aided in maintaining cellular SOD status [179]. More intriguingly, evidence from recent studies shows that the antioxidant homologs were effective in restoring the antioxidant state [175, 180]. Antioxidants may help prevent vision loss in roughly 20–25% of injured eyes. It may be possible to develop more effective treatment plans by researching significant biological processes, hereditary factors, and metabolic procedures that are thought to be implicated in AMD. As already mentioned, epidemiological research conducted over the past 40 years has found a number of risk factors linked to AMD, including heredity, age, smoking, and obesity [181]. In 1992, the AREDS examined several AMD patients who were given antioxidant treatment or a placebo. These individuals were then categorized as having wet-AMD in one eye or mild, moderate, or severe dry-AMD in both eyes. The findings of this study, which took around 6–7 years to complete, were released in 2001 [182, 183]. According to these results, patients who got antioxidant treatment instead of a placebo had a decreased probability of developing advanced AMD. Unexpectedly, it was also demonstrated that patients still had early AMD [155].

It has been proven via numerous in vivo and in vitro experimental research that nicotinamide (NAM) suppresses TGFβ-induced EMT in human adult-retinal pigment epithelial stem cells (RPESC) [184, 185, 186, 187, 188]. Bone morphogenetic proteins (BMPs) demonstrated an anti-fibrotic impact in both in vivo and in vitro investigations, with BMP7 in particular contributing to the maintenance of RPE differentiation and the inhibition of TGFβ-2-induced EMT [189]. The diabetic drug pioglitazone is frequently administered. The main RPE of monkeys did not exhibit EMT-like features due to the PPAR-gamma, an agonist of pioglitazone, necessitating more investigation [66].

Rapamycin, a mTOR suppressor, demonstrated anti-RPE-EMT effects both in vivo and in vitro [67]. According to the in vivo mouse model research, combined treatment with bevacizumab (anti-VEGF) and shRNA (anti-CTGF) led to better vascularizations than either drug alone [190]. Dichloroacetate (DCA), an analog of pyruvate, was shown by Shukal and colleagues to have anti-RPE-EMT effects (TGFβ-2-induced EMT) that are mediated by suppressing the MAPK/Erk and PI3K/Akt signaling pathways [191]. The COX-2 antagonist (NS-398) was shown to be an anti-CNV drug in both in vivo and in vitro studies by maintaining VEGF and TGFβ expression in the RPE-ECM [192]. Clinical investigations have revealed that anti-VEGFs, anti-inflammatory factors, TGF-receptor inhibitors, PPAR-gamma agonists, and retinoic acid receptor-gamma (RAR-gamma) inhibitors all have therapeutic promise in preventing EMT in RPE [10, 78].

6. Future prospects

Although drusen are a well-established risk factor for AMD, nothing is known regarding their molecular makeup or method of production [17]. The disintegration of the BRB, the breakdown of tight junctions, and the noteworthy feature of AMD are only a few of the ways that OS has an impact on RPE cells [193]. The delayed and increasing function of OS makes it difficult to pinpoint the specific etiology of AMD [19]. Numerous in vitro investigations demonstrated that OS-induced damage in retinal tissue resembled AMD [175, 194, 195, 196]. Recent understandings from in vivo and in vitro experiments show that inducers, suppressors, and even miRNA may modify the RPE-EMT [78]. Even after more than 40 years of research, there are still gaps in the concrete diagnostic candidate for the management of retinopathies [78]. Although the precise mechanism affecting EMT cascades is yet unknown, research conducted in vitro generally indicates that altering cell density, passages, and serum deprivation induces “anti-EMT” effects in epithelial cells, especially if, and if so, to what extent, anti-fibrosis methods may affect RPE [51]. Therefore, there is a critical need for the development and improvement of therapeutic methods that could enable more satisfactory disease management and lower treatment burden, leading to a better quality of life for patients. This is because there is an increasing incidence of both nAMD and DME, both of which are associated with a marked impact on the health status of the global population.

With concentrated molar dosing and robust gains in visual acuity, superior fluid resolution, and longer effect durability than other anti-VEGFs approved for the treatment of patients with nAMD, brolucizumab has been developed into a highly effective therapeutic molecule [102, 108]. In addition, the OSPREY study and the critical HAWK and HARRIER studies show that brolucizumab can lessen the burden of therapy by enabling longer injection intervals with long-lasting disease control [102, 108]. By lessening the burden of therapy, boosting patient compliance, and assisting in the management of uncontrolled patients with the currently available anti-VEGFs, this is anticipated to enhance long-term results. In the upcoming years, more data on brolucizumab’s clinical effectiveness and its effects on clinical practice in other anti-VEGF-responsive diseases are anticipated, demonstrating the drug’s potential benefits beyond nAMD [105]. A minority of patients with neovascular age-related macular degeneration who display recurrent or resistant intraretinal or subretinal fluid after numerous injections with either bevacizumab or ranibizumab may benefit from aflibercept treatment [197].

After receiving a ranibizumab injection, minor and transient side effects may last for a few days. These include floaters, conjunctival hemorrhage, a feeling of a foreign body, and discomfort. Each injection has a negligible risk of endophthalmitis, a severe eye infection, of around 1 in 2000 individuals. Increased blurriness, eye discomfort, increased redness, and periocular edema are some of the signs and symptoms of endophthalmitis. An ophthalmologist must address this dangerous problem urgently. Other issues include vitreous hemorrhage, retinal detachment, and lens damage that can need surgical correction [197]. Due to the fact that the only available treatment for subretinal fibrosis is invasive surgery, it is crucial to understand the molecular pathways behind abnormal retinal wound healing in order to create non-invasive drug-based treatments [51, 198].

7. Conclusion

Inhibit epithelial-mesenchymal transition of retinal pigment epithelium is the exclusive focus of current in vivo and in vitro research, but it is crucial to comprehend how stress and RPE-EMT interact molecularly. There is an urgent need for treatments for retinopathies, which are the main factor in the loss of eyesight for millions of individuals. In conclusion, because they have a broader spectrum of activity than VEGF-A, therapy drugs including pegaptanib, ranibizumab, aflibercept, brolucizumab, and faricimab are beneficial therapeutic choices for individuals with retinal vascular disorders. The treatment load on patients and treatment facilities is decreased by intravitreal anti-angiogenic medicines, which have a sustained clinical action following intravitreal administration and enable appropriate disease management with concurrently lower injection frequency. The development of novel therapeutic strategies for nAMD and DME using cutting-edge pharmacotherapy that targets alternative pathways is crucial in the fight against the worldwide epidemic of blindness and visual impairment brought on by DME and nAMD due to the alarming prognosis of both conditions’ rising incidence.

Conflict of interest

There are no conflicts of interest to report among the authors. The final draft was approved by all the authors.

Abbreviations

AMD	age-related macular degeneration
AREDS	age-related eye disease study
BCVA	best-corrected visual acuity
BK	bradykinin
BMP7	bone morphogenic protein 7
BRB	blood-retinal barrier
CAT	catalase
CNV	choroidal neovascularization
DME	diabetic macula edema
DR	diabetic retinopathy
ECM	extracellular matrix
EGF	epidermal growth factor
EGFR	epidermal growth factor (EGF) and its receptor
EMT	epithelial-mesenchymal transition
Glc-N	glucosamine
GR	glutathione reductase
GSH-Px	glutathione peroxidase
KRT8	keratin 8
LPO	lipid peroxidation
MAPKs	mitogen-activated protein kinases
MCT1	monocarboxylate transporters 1
MIF	macrophage migration inhibitory factors
mTOR	mammalian target of rapamycin
n-AMD	neovascular-age-related macular degeneration
NHANES	National Health and Nutrition Examination Survey
OCT	optical coherence tomography
OS	oxidative stress
PBM	photo biomodulation
PPAR	peroxisome proliferator-activated receptor
PPAR-γ	peroxisome proliferator-activated receptor
PVR	proliferative vitreoretinopathy
RAR-γ	retinoic acid receptor gamma
ROCK	rho-associated protein kinase
RPE	retinal pigment epithelium
RPESC	retinal pigment epithelial stem cell
Shh	sonic hedgehog
SOD	superoxide dismutase
TGFβ	transforming growth factor β
VEGF	vascular endothelial growth factor