Neuroinflammation and neovascularization in diabetic eye diseases (DEDs): identification of potential pharmacotherapeutic targets

The goal of this review is to increase public knowledge of the etiopathogenesis of diabetic eye diseases (DEDs), such as diabetic retinopathy (DR) and ocular angiosarcoma (ASO), and the likelihood of blindness among elderly widows. A widow’s life in North India, in general, is fraught with peril because of the economic and social isolation it brings, as well as the increased risk of death from heart disease, hypertension, diabetes, depression, and dementia. Neovascularization, neuroinflammation, and edema in the ocular tissue are hallmarks of the ASO, a rare form of malignant tumor. When diabetes, hypertension, and aging all contribute to increased oxidative stress, the DR can proceed to ASO. Microglia in the retina of the optic nerve head are responsible for causing inflammation, discomfort, and neurodegeneration. Those that come into contact with them will get blind as a result of this. Advanced glycation end products (AGE), vascular endothelial growth factor (VEGF), protein kinase C (PKC), poly-ADP-ribose polymerase (PARP), metalloproteinase9 (MMP9), nuclear factor kappaB (NFkB), program death ligand1 (PDL-1), factor VIII (FVIII), and von Willebrand factor (VWF) are potent agents for ocular neovascularisation (ONV), neuroinflammation and edema in the ocular tissue. AGE/VEGF, DAG/PKC, PARP/NFkB, RAS/VEGF, PDL-1/PD-1, VWF/FVIII/VEGF, and RAS/VEGF are all linked to the pathophysiology of DEDs. The interaction between ONV and ASO is mostly determined by the VWF/FVIII/VEGF and PDL-1/PD-1 axis. This study focused on retinoprotective medications that can pass the blood-retinal barrier and cure DEDs, as well as the factors that influence the etiology of neovascularization and neuroinflammation in the eye.


Introduction
New Delhi, India's capital city, is just a short drive away from Vrindavan and Mathura, two of the country's most hallways of public buildings [1][2][3]. A widow's life in North India can be fraught with peril on many levels, including the inability to be married again, social isolation, and an increased risk of death [4]. Polo Foundation, an NGO in Uttar Pradesh, India, surveyed the ashrams in Vrindavan and found that approximately 70% of the widows there have high blood pressure and high sugar levels. As a result of their hypertension, nearly all the widows had blood pressure readings of 173/97; 189/93; 159/99; etc. [5]. Several initiatives have been launched by the Indian state government of Uttarpradesh to assist widows living in various Ashrams. High blood pressure and diabetes can exacerbate diabetic eye diseases (DEDs).
Diabetic retinopathy is the most disabling complication of diabetes mellitus (DR). Continuous hyperglycemia damages the retina's microvascular system, resulting in diabetic retinopathy (DR), which can progress to ocular angiosarcoma (ASO) [6,7]. Early detection of DR by an automated technique is more helpful than manual detection because of developments in artificial intelligence [8]. Type 1 diabetics are 60% more likely than type 2 diabetics to develop DR during the first two decades of their diabetes. High blood pressure, high cholesterol, kidney disease, genetically accelerated diabetes, and blood sugar oscillations with haemorrhage or fluid accumulation in the retina are all factors that aggravate diabetic retinopathy [9]. More than 90% of diabetic people have had their vision saved by early identification of DR, which has been shown in numerous studies [10]. An ophthalmologist can diagnose DR manually or automatically using computer technologies [11]. More than 30 million Americans were diagnosed with diabetes in 2017, accounting for about 9.4% of the country's population. Diabetes treatment in the United States is estimated to cost $120 billion per year, accounting for more than 40% of total costs [12].
Common causes of ASO development include hypoxia, glaucoma, and autoimmune response, which are all linked to retinal microvascular dysfunction as well as supraorbital edema, exophthalmos, and conjunctivitis [13]. Neuroinflammation and ocular neovascularization (ONV) are the two primary causes of ASO. In synucleinopathies, neuroinflammation manifests itself as microglial activation, which may be a therapeutic target for slowing or stopping the degenerative process [14]. There are several synucleinopathies, a group of neurodegenerative diseases where alpha-synuclein protein fibrils are seen in the cytoplasm of certain neuronal and glial populations [15]. Haemangiosarcomas and lymphangiosarcomas are the two main subtypes of ASO [16]. All layers of the ocular tissues (sclera, choroid, and retina) are affected by the sugar-loaded blood, causing damage to small blood capillaries and making them more vulnerable [17]. Hypoxia and autoimmune responses are stimulated by the fluctuation in plasma glucose with the predicted HbA1c level. Due to a lack of oxygen, cells in hyperglycemic patients are more likely to suffer from macroalbuminuria [18,19]. Several inflammatory mediators have been identified as being involved in the pathophysiology of ONV and neuroinflammation, including cyclooxygenase enzyme (COX), interleukin-1 (IL-1), advanced glycation end products (AGE), vascular endothelial growth factor (VEGF), protein kinase C (PKC), poly-ADP-ribose polymerase (PARP), and metalloproteinase 9 (MMP9). Microaneurysms are the most dangerous clinical manifestations of ASO [20]. Inflammatory cells have been linked to the ASO where 'balloon-like protrusions of the capillary wall', cause further damage to the endothelium lining. After an ONV, diabetic macular edema (DME) might develop [21]. In DME, there is a rise in vascular penetrability and an accumulation of solid excretes in the macula. DME is a condition in which fluid (edema) builds up in the macula, a region of the retina [22]. The macula of the retina is essential for reading and recognizing faces because it gives clear forward vision. At any time in a person's life, the DME is the most common cause of ASO's visual issues [23].
Ocular angiosarcoma (ASO) was discovered in four senior horses by Moore et al. (1986), who theorized that ASO in horses is caused by the production of factor VIIIrelated antigen (VIII: RAG) by blood capillary endothelial cells [24]. The anti-hemophilia factor VIII (FVIII) and the associated antigen (FVIII-RAG) are found in the bloodstream as a single protein complex. Von Willebrand factor (VWF) is another name for FVIII-RAG [25,26]. Using cultivated endothelial cells, Li et al. (2003) found that VEGF(165) induction increased the quantity of FVIII through the overexpression of interleukin-1 (IL-1) [27]. As a result, in cases of ASO, the FVIII-VWF is an immunohistochemistry indicator of the emergence of ONV. MMP-9 activity in tear fluid was found to be integrally connected to tear fluid interleukin (IL)-1 levels in patients with ocular rosacea (a tear film abnormality) [28]. The STAT3/MMP9 signaling via VEGF was shown to be implicated in the etiology of angiosarcoma by Panda et al. (2022) in studies on cutaneous angiosarcoma [29]. Panda et al. (2021) used invivo inflammatory screening on Swiss albino rats and docking analysis to prove the NFkB/MMP9 signaling link during the development of inflammation [30].
Corneal limbi feature a rich distribution of capillaries and lymphatic vessels that act as the entry and exit sites for immune cells [31]. The immune cell types such as Langerhans cells (LCs), mast cells (MCs), and macrophages are present in the epithelial tissues of the eye [32]. Recent studies have revealed the role of LCs in terms of manufacturing different cytokines and other growth factors in corneal homeostasis and its pathologic states. The formation of LCs also depends on signals from interleukin-34 (IL-34) [33]. According to Foucher et al. (2015), macrophages stimulated by IL-34 secrete IL-1, which leads to ONV and neuroinflammation [34]. Cytokines such as IL, monocyte chemoattractant protein-1 (MCP-1) hepatocyte growth factor (HGF), granulocyte colony-stimulating factor (GCSF), IFN-γ, and TNF-α are released collectively in hyperinflammatory conditions, are referred to as a cytokine storm [35,36]. Recent research has connected pro-angiogenic VEGF genes, such as vascular endothelial growth factor (VEGF), to the PD-L1/PD-1 pathways in many malignant tumours [37]. PD-L1 was found in approximately 66% of angiosarcoma samples with membrane-specific antibodies. The PD-L1/PD-1 axis promotes tumor development by inhibiting anti-tumor antibodies and mediating immunological tolerance. The adaptive immune system's anti-tumor actions can be maintained by limiting the linkage between PD-L1 and PD-1 [38].
Scientists depicted the different stages of DR with the following characteristic features [13,20,31].

Stages of DR
DR is divided into four stages.
A. Stage 1-DR: There are small balloon-like bulges in the ocular tissue visible at this stage of the sickness called microaneurysms. Fluid leakage into the ocular tissue can occur as a result of these tiny aneurysms expanding. The retina has at least one microaneurysm. B. Stage 2-DR: Optic neuroinflammation may develop and become distorted as the disease advances. There are distinct changes in the appearance of the eye in Stages 1 and 2, however, the two stages are not mutually exclusive. C. Stage 3-DR: The choroid and retina are deprived of oxygen-rich blood because of the obstruction of several more blood capillaries. Angiogenesis and inflammation can be stimulated by growth factors secreted by these tissues. D. Late stage DR or ASO: Retinal growth factors at this stage induce new blood vessels sprouting from the retina's inner surface and into the vitreous gel, which encases the eye. Blood vessels are prone to rupture and bleeding because they are so delicate. In the same way, that wallpaper peels off a wall, scar tissue forms (sclerosis), shrinks and separates from retinal tissue. An irreversible retinal detachment caused vision loss. Thrombosis in ocular blood vessels causes scar tissue to form on the sclera (sclerosis).

DED leading to vision loss: pathophysiology and diagnosis
In DED (DR + ASO), retinal microvasculature and neurons are damaged by oxidative stress. Retinal blood flow was diminished and nerve cells in the retina malfunctioned as a result of the initial modification that produced vision loss as a result of DED. The retinal neuropile, a protective layer that shields the retina from contaminants, was also broken by the breach in the blood-retinal barrier. Persistent oxidative stress damages the microvasculature, including the endothelial smooth muscle cells. A gradual loss of neurons and neuroglial cells occurs as the retina's blood capillaries stiffen with time, leading to balloon-like structures, microscopic aneurysms from capillary walls, and the influx of inflammation cells. Additionally, ONV is linked to elevated LDL cholesterol and ocular hypertension. Because of the activation of Protein Kinase C and some other signaling pathway intermediates, oxidative stress promotes pericyte death [39]. As DED progressed, several patients had difficulty seeing any vision changes. Microaneurysms in the retinal posterior pole were first discovered in the early twentieth century by the use of established techniques like ophthalmoscopy and fluorescein angiography. Optical coherence tomography (OCT) is currently being used to identify the ONV. Using an OCT, one can scan all of the eye's surface and the retina [40]. Tonometry testing can also be used to determine intraocular pressure. The pupil dilates when loops are placed on the eye's surface, making it possible for a doctor to examine the retina and optic nerve. One way to determine a person's overall eye health is to perform an eye chart exam. The eye chart test measures a person's visual acuity [41]. The retina may be examined by the doctor during a comprehensive dilated eye exam for the following reasons: I) Fatty deposits or leaky blood vessel symptoms. II) Edema of the macula. III) Lens modifications. IV) Injury in the optic nerve.

Molecular pathways of DED
In this review, the major molecular mechanisms of DED are discussed. It is considered that the DED developed as a result of oxidative stress, aging, the biosynthesis of hexosamine, and activation of the major signaling pathways such as DAG/PKC signaling, the RAGE/AGE signaling pathway, RAS signaling, VEGF-FVIII/VWF signaling, and the PD-L1/PD-1 axis.
It was shown that the polyol pathway under oxidative stress produced fructose, which was phosphorylated and broken down into fructose-3-phosphate and 3-deoxyglucosone, respectively. The dynamic glycosylating agents play a role in the AGE formation process [53]. Reactive carbonyl species such as glyoxal (GO), methylglyoxal (MGO), and 3-deoxy glucosulose (3-DG) were formed as a result of the lipid peroxidation process, and these compounds were subsequently employed to create AGEs. Products such as Schiff's bases or imines or amadori products are formed by the reaction between the reducing sugar and the free amino group of protein ( Fig. 1) [54].

RAGE-AGE signaling
The AGE-specific receptor is the most important signaling receptor, often abbreviated as RAGE. An increase in inflammatory signaling is triggered when AGEs are attached to their receptor, which is known as the RAGE-AGE axis [55]. NF-kB and AP-1 phosphorylation or activation are connected to the AGE-RAGE axis via RAS/MAPK/ERK1/2 signaling pathways. The JAK/STAT signal transduction pathway, which is connected to the AGE-RAGE axis, generated phosphorylated NF-kB (pNF-kB) and phosphorylated STAT3 (pSTAT3). The pNF-kB and pSTATs are responsible for the formation of MMP9 and VEGF. MMP9 and VEGF are important in both ONV and neuroinflammation ( Fig. 1) [56].

Hexosamine biosynthesis and its linkage to ONV and neurodegeneration
An increase in tissue levels of the hexosamine precursor has been linked to vascular disease in the eye. Glycolysis, which begins with glucose-6 phosphate and progresses to fructose-6 phosphate and pathway, is responsible for the majority of glucose digestion [57]. A small percentage (between 3 and 5 percent) of fructose-6-phosphate is diverted from glycolysis and used as a source of the amino acid Glucosamine-6-phosphate (Glucosamine-6P). The enzyme Glucosamine-6-phosphate N-acetyltransferase (GNA1/GNPNAT1) subsequently transforms the glucosamine-6P to N-acetylglucosamine-6-phosphate (GlcNAc-6P). The following enzyme, phosphoglucomutase (PGM3/ AGM1), was involved in the conversion of GlcNAc-6P to GlcNAc-1P. UDP-N-acetylhexosamine pyrophosphorylase (UAP/AGX1) utilised energy from the nucleic acid metabolism pathway to assist in the conversion of GlcNAc-1P to uridine diphosphate N-acetylglucosamine (UDP-GlcNAc). The hexosamine production route may exacerbate retinal neurodegeneration by increasing apoptosis, which may be triggered by abnormalities in the remainder of the glycolytic

Oxidative stress on the eye
In a two-step metabolic pathway, glucose is transformed to sorbitol, which is then oxidised to fructose. The synthesis of fructose, a by product of glucose metabolism, is aided by two enzymes: aldose reductase (AR) and sorbitol dehydrogenase (SDH) (Fig. 2) [42]. NADPH is used as a cofactor by the AR in the conversion of glucose to sorbitol [43,44]. NAD + acted as a cofactor for the enzyme sorbitol dehydrogenase (SDH), which catalysed the conversion of sorbitol to fructose [45,46]. Glutathione reductase (GR) requires NADPH as a cofactor for the formation of reduced glutathione (GSH). The free radical scavenger GSH is a strong antioxidant system found in mammalian tissues. As a result of AR's increased reliance on NADPH, little or no GR was available for glutathione reduction [47]. Lower levels of GSH (a free radical scavenger) were found in the absence of these cofactors, which in turn led to increased oxidative stress. The superoxide free radicals are produced during the oxidation of sorbitol to fructose. Low GSH levels and high levels of superoxide free radicals are the most common causes of retinal damage (SFig. 1) [48].

Oxidative stress-poly (ADP-ribose) polymerase (PARP) axis
The nucleus of vascular endothelial cells in the retina and ganglion cell layer was the source of PARP production. As a result of exposure to DNA-damaging stimuli such as oxidative and nitrous oxide stressors, PARP becomes activated [49,50]. Polymers of ADP-ribose were formed when PARP catalysed the NAD + substrate. Activated PARP-polymer was theorised. Toxic DNA damage triggered vascular dysfunction and cell death by the PARP polymer. Researchers established a relationship between NFkB and PARP polymer activity. In the presence of oxidative stress, more PARP polymers are generated and bound to the NFkB p50 and p65 subunits [51]. The p50 subunit is more attractive to PARP than the p65 subunit. NFkB transcription and binding affinity to the retinal endothelium are increased as a result of PARP activation, and this is particularly true in rods. Retinal tissue inflammation occurs when NFkB is bound to the retinal tissue. Inflammation in the eye is reduced by PARP inhibitors, according to a study published by Lan et al. (2012) (SFig.1) [52].

Oxidative stress-AGEs axis
Increased levels of advanced glycation end products (AGEs) in tissues were linked to oxidative stress, and impaired carbohydrate, protein, and lipid balance. In human tissues, carboxymethyl lysine (CML), carboxyethyl lysine (CEL), and pentosidine are the three most common AGEs, respectively. of PKC increases production of the vasoconstrictor endothelin 1 (ET-1) [62]. ASO is fueled by a TXA2/PGI2 imbalance and ET-1.

RAS signaling
RAS was given precedence over ONV in the study of the renin-angiotensin system. Angiotensin-converting enzyme (ACE) concentrations increased in ONV, assisting in the conversion of angiotensin 1 (AT-1) to angiotensin 2 (AT-2) [63]. Consequently, the retinal blood AT-2 concentration rose in direct proportion. The Angiotensin 2 receptor (AT-2R) in the retina commences its activity after connecting with the AT-2. The interaction boosted the expression of VEGF in the retinal vasculature during ONV by activating the NFkB (SFig.3). Diabetic retinopathy can be treated using AT-2R blockers, which have been proven to be effective in clinical trials [64,42].

VEGF-FVIII/VWF signaling
Platelet activation and aggregation occurs as a result of oxidative stress-induced vascular damage, and the coagulation mechanism is activated to stabilise the bleeding. An protein glycosylation pathway [58]. Proteoglycans and glycoproteins are formed during the conversion of N-acetyl glucosamine-1 to UDP-N-acetyl glucosamine (SFig.2) [59].

DAG/PKC signaling
The protein kinase c (PKC) enzyme found in 13 different mammalian organs has been linked to ONV through genetic studies (STable 1). For cells, insulin resistance and microvascular issues are all controlled by PKC isozymes [60]. Vascular dysfunction and ASO aetiology have been connected to the traditional isoforms of PKC such as PKC, 1/2 and PKC. DAG and calcium ions are the primary activators of the vast majority of PKC. Phosphatidic acid is converted to DAG via a series of intermediary metabolites generated by the cytoplasmic breakdown of glucose 6P [61]. A variety of proteins, including VEGF, MMP, STATs, NF-kB and inflammatory mediators, are produced more quickly when PKC isoforms are used in conjunction with their respective transduction systems to do so. An abundance of these protein components in retinal tissue is likewise linked to both the ASO and the DME. Thromboxane A2 (TXA2) and prostacyclin (PGI2) are disrupted when PKC is activated, resulting in blood vessel constriction and thrombosis. Activation Fig. 1 Synthesis of AGEs and RAGE/AGE axis In human tissues, CML, CEL, and pentosidine are the three most common AGEs, respectively. Glyoxal (GO), methylglyoxal (MGO), and 3-deoxy glucosulose (3-DG) are reactive carbonyl species that combine to create AGEs. Oxidative stress on the retina promotes the AGE-RAGE axis, which was linked to ONV and eye neuroinflammation through activation of NF-kB. The NF-kB and AP-1 phosphorylation or activation are connected to the AGE-RAGE axis via RAS/MAPK/ ERK1/2 signaling pathways. The JAK/STAT signal transduction pathway, which is connected to the AGE-RAGE axis, generated phosphorylated NF-kB (pNF-kB) and phosphorylated STAT3 (pSTAT3). The pNF-kB and pSTATs are responsible for the formation of MMP9 and VEGF. The ONV as well as neuroinflammation depend heavily on MMP9 and VEGF.
The IL-1 family regulates the innate immune response. The majority of research has focused on IL-1's impact on VEGF, the main regulator of angiogenesis and permeability, but there was some evidence that IL-1 can regulate other pro-angiogenic growth factors (Fig. 2). When interleukin1 (IL-1) was overexpressed, activated VEGF took part in the proteolytic cleavage of FVIII-VWF, resulting in the generation of plasma-bound free activated FVIII (FVIIIa). To put it another way, the VWF is critical for platelet aggregation and thrombus development in the eye's blood vessels. Endothelial mesenchymal transformation (EMT) was induced when corneal endothelial cells (CEC) were activated with IL-1, important part of platelet activation and aggregation is a complex between FVIII and VWF. Due to vascular damage and elevated levels of oxidative stress, the endothelium matrix becomes more adherent to VWF, which in turn promotes adhesion. The platelet plug might form as a result of the VWF being linked to platelets in the bloodstream. At the adhesion site, Volkswagen binds to Volkswagen receptors, increasing the local concentration of FVIII dramatically [65]. The FVIII was involved in a complex formation with the VWF (FVIII-VWF). The IL-1 family of cytokines is also known to play a role in ONV, either directly or through the activation of proangiogenic proteins like VEGF. Fig. 2 The pathway of platelet aggregation and neuroinflammationThe FVIII was involved in a complex formation with the VWF (FVIII-VWF). When interleukin1 (IL-1) was overexpressed, activated VEGF took part in the proteolytic cleavage of FVIII-VWF, resulting in the generation of plasma-bound free activated FVIII (FVIIIa). DAG and calcium ions are the primary activators of the vast majority of PKC. Phosphatidic acid is converted to DAG via a series of intermediary metabolites generated by the cytoplasmic breakdown of glucose 6P. A variety of proteins, including VEGF, MMP9, NF-kB and inflammatory mediators, are produced more quickly when PKC isoforms are used in conjunction with their respective transduction systems to do so. An abundance of these protein components in retinal tissue is likewise linked to both the ONV and neuroinflammation. Thromboxane A2 (TXA2) and prostacyclin (PGI2) are disrupted when PKC is activated, resulting in blood vessel constriction and thrombosis. Activation of PKC increases production of the vasoconstrictor endothelin 1 (ET-1). Platelet aggregation is fueled by a TXA2/PGI2 imbalance and ET-1. explain why persons with neuroinlammatory illnesses who carry this variant tend to experience a more severe course of neuroinflammation [70]. Overexpression of PD-L1 is the cause of primary angiosarcoma, which was confirmed by the aforementioned theory. 66% of angiosarcoma samples were positive for PD-L1 [71]. Recently, research has linked the PDL1/PD-1 pathways in a number of malignant tumours to pro-angiogenic VEGF genes, such as vascular endothelial growth factor (VEGF) [72]. Anti-tumor antibodies are inhibited by the PD-L1/PD-1 axis, which promotes tumour growth by promoting immunological tolerance. PD-1 and PD-L1 monoclonal antibodies have shown promising results in early clinical trials in patients with refractory malignancies [73]. When PD1 binds to PDL1, it can reduce T cell-mediated immune recognition, leading to a lack of immunoreaction and even T lymphocytes death. Tumorinfiltrating CD4+/CD8 + T cells are often suppressed, along with mediators notably TNF, IFN-, and IL-2 [74]. This allows tumors to evade the immune response. By blocking PD-1 and PD-L1, a tumor's immune system can proliferate T cells and mount an effective defense against the tumor (Fig. 3) [75].

PD-L1/PD-1 axis
The 40 kDa transmembrane protein PD-L1 belong to B7 ligand family found in a wide range of healthy tissues comprising natural killer (NK) cells, macrophages, myeloid dendritic (MDC) cells, B cells, and epithelial (EC) cells [67]. The checkpoint protein PD-1 belongs to CD28 family are also expressed by B cells, monocytes, and MDC. Recent studies have shown that the PD-L1/PD-1axis may play an important role in the interaction of tumour cells with the host immune response. Prognostic and predictive biomarker PD-L1 has been found to be expressed in the vast majority of human solid tumours, and its expression has been linked to poor prognosis [68]. The protein programmed death-ligand 1 (PD-L1) is predominantly expressed on microglial cells and astrocytes in the vicinity of the meninges, especially in regions with the greatest inflammatory response [69]. PD-L1 activity is also enhanced on the endothelium enclosing infiltrates. A genetic variant in the programmed death 1 (PD-1) gene has been linked to a partial impairment in PD-1-mediated suppression of T-cell activation, which may (ranibizumab), Aflibercept, and Eylea (ranibizumab). RISE (clinicaltrials.gov ID: NCT00473330), RIDE (clinicaltrials.gov ID: NCT00473330), and RIDE (clinicaltrials.gov ID: NCT00473330) have performed the most comprehensive clinical trials on ranibizumab (clinicaltrials.gov ID: NCT00473382). Monthly injections of ranibizumab are used to treat DME. According to the results of a clinical trial, three drugs, Avastin, Lucentis, and Eylea, are effective in treating ASO and DME [78].

AGE inhibitors
A powerful AGE-RAGE interaction boosted ONV by increasing the synthesis of VEGF. Researchers have shown that AGEs inhibitors are effective against the ONV in animal studies. Researchers have developed and examined many AGEs inhibitors, including alagebrium, aminoguanidine, pyridoxamine, OPB-9195, and ALT-946. To decrease or halt the advancement of ASO, AGE-RAGE exercise was minimized or prevented by such drugs [79].

PKC inhibitors
It has been found that PKC-1/2 is highly expressed in the ocular tissue. Although many molecular mechanisms are known to contribute to the onset of DEDs, stimulation of PKC, particularly the beta form of PKC (PKC-β), is linked to both early-stage and late signs of DR. Ruboxistaurin mesylate (LY333531), a PKC-β inhibitor, has been shown in investigations to be beneficial in reducing retinopathy development, proliferation, and vascular abnormalities [80].
NFkB inhibitorsAs a result of retinal NFkB overexpression during oxidative stress, endothelial cell proliferation was triggered. ASO is connected with proliferation and ONV. Multiple anti-oxidants including dehydroxymethylepoxyquinomicin (DHMEQ) suppressed NFkB expression in eye tissue by decreasing the synthesis of VEGF and angiotensin II. The NFkB gene's transcription and affinity for binding to the retinal endothelium are boosted by PARP activation. Neuroinflammation resulted when NFkB was interacted with the retinal tissue. NF-κB inflammatory signaling undoubtedly contribute to DEDs, and treatment approaches may specifically target NF-κB genes. Although there are currently no therapeutically accessible inhibitors of particular NF-κB pathways, work is still being done to investigate how current medicines such as thiazolidinediones (PPARγ activator) affect the NF-B pathway and to generate more specific anti-NF-κB medications [81].

Glycemic control
Diabetic retionopathy has been proven in numerous clinical trials to be delayed or prevented by insulin injections, according to the DCCT and UKPDS. According to the data, vigorous therapy with oral hypoglycemic medicines minimizes the chance of acquiring or worsening ASO. Clinical trials in non-diabetic patients (20 numbers) with full-thickness wounds (National Clinical Trial number: NCT02396888) were undertaken, and the angiogenesis suppression effect of insulin solution was detected (National Library of Medicine) [76].

Aldose reductase inhibitors (ARIs)
Sorbitol levels in the retinal tissue are elevated due to AR enzyme activity, resulting in oxidative stress. Sorbinil's aldose reductase inhibitory activity, which was initially known as ARI, was confirmed in clinical trials. ARIs work by lowering tissue or organ oxidative stress. ARIs with unique structures, such as ARI-809, tolerestat, epalrestat, fidarestat, zenarestat, zopolrestat, ponarestat, and ranirestat, were synthesised and their ability to suppress ASO was demonstrated following that discovery (STable 1). Some drugs, such ARI-809 and tolerestat, have a greater impact when taken orally. The anti-VEGF activity of Fidarestat is also well-documented. Chronic and persistent inflammation aids in the formation of malignant tumours.. Aldose reductase [AR; AKR1B1], a member of the aldo-keto reductase superfamily of proteins, is now known to integrate inflammatory signals induced by growth hormones, cytokines, carcinogens, and other substances. AR reduced the production of lipid-derived aldehydes and derivatives such glutathionyl 1,4-dihydroxynonanol (GS-DHN), which have been linked to the activation of transcription factors like NF-B and AP-1. Inflammatory cytokines and growth factors increase cell proliferation, which is a fundamental step in the process of carcinogenesis. In both in vitro and in vivo experiments, scientists have discovered that blocking AR inhibits the growth of cancer cells [77].

Anti-VEGF drugs
A VEGF inhibitor injection will be used to reduce VEGF production and the subsequent growth of abnormal retinal vascular tissue. Treatment of ASO is now allowed by the USFDA with Avastin (bevacizumab), Lucentis tiny vacuum pump, scar tissue can be removed or a detached retina can be repaired [86].

PD-L1/PD-1 inhibitors
Currently available anti-PD1/PDL1 medication blocks the interaction across PD1 and PDL1, successfully activating suppressed immune cells and setting off an immune reaction against tumours. In order to manage haematological and solid tumours, the Food and Drug Administration (FDA) recently authorized six antibodies that either targeting PD1 (nivolumab, pembrolizumab, and cemiplimab) or PDL1 (atezolizumab, Durvalumab, and avelumab). Researchers observed that by boosting T cell function and suppressing PD1, monoclonal antibodies greatly reduced cytotoxicity, shrank tumour growth, and massively increased patient life expectancy [87].

Retinoprotective drugs
Phytoconstituents from a family of herbal medications known as neuroprotective herbal medicines have been shown to penetrate the blood-brain barrier and work [88]. Additional herbal remedies that can cross the blood-retinal barrier (BRB) and protect the eye and optic nerve from neurodegeneration were found by searching multiple databases in addition to those already mentioned. A number of databases have found herbal remedies that are used to treat neuropathy and protect the renal system from oxidative stress. Several synthetic, peptide, and herbal medicines with clinically demonstrated retinoprotective effects and the ability to cross BRB were examined (STable 2, 3). In light of the information presented above, ASO therapy's primary goal is to manage ONV and neuroinflammation. An important feature of ONV therapy is to focus on targeting the vascular endothelial growth factor (VEGF), a family of five related glycoproteins that play a vital role in the creation and development of new blood vessels in both normal immunological and inflammation responses. VEGF aids in the proliferation of endothelial cells, the opening of blood vessels, and the formation of new blood vessels. As a result, the principal treatment technique for neovascular eye illnesses is the inhibition of VEGF activity. The National Institutes of Healthsponsored Diabetic Retinopathy Clinical Research Network (DRCR.net) conducted a randomised clinical trial to compare intravitreous anti-VEGF drugs for treating visionimpairing DR (Table 1).

PARP inhibitors
Cell nuclei contain the active form of the PARP enzyme when organs or tissues are repeatedly exposed to oxidative stress. Active PARP has been directly linked to the production of additional free radicals via stimulating PKC and hexosamine. Reduced VEGF and NFkB expression by PARP inhibitors such as isoquinoline derivatives, PJ-34, and GPI-15427 reduced the ONV and edema in the damaged eye. In the treatment of ASO, PARP inhibitors may be more effective than other anti-ASO therapies [82].

Antioxidant therapy
Antioxidant molecules act as a booster with proteins or chemical compounds during the treatment of non-communicable diseases (NCD). The ASO, in particular, is produced by the accumulation of free radicals (ROS and RNS) in the ocular tissue. As a result of the oxidative stress, many metabolic pathways are reactivated and dysregulated, including PKC, NFkB, and PARP. VEGF expression in the vascular endothelium is reduced by alpha-lipoic acid and taurine. Nutritional supplements like vitamin C and E, beta carotene, and N-acetyl cysteine, reduced the activation of NFkB and caspase 3. By lowering AGE and ROS generation, Benfotiamine is effective in preventing retinal damage in animal experiments [83].

Stem cell therapy
Bone marrow-derived cells (stem cells) have significant potential in the repair function of endothelial cells. For the treatment of ASO, intravitreal stem cell injection therapy may be an excellent option [84].

NSAIDs therapy
Nonsteroidal anti-inflammatory medicines (NSAIDs) may have a limited role in the treatment of ASO, despite the lack of research into their efficacy. NSAIDS that work by inhibiting the enzyme cyclooxygenase (COX) to prevent the synthesis of eicosanoids includes valdecoxib and diclofenac [85].

Virectomy
A vitrectomy is a surgical procedure that removes the vitreous gel from the centre of the eye. The operation is carried either under local or general anaesthesia to address significant bleeding into the vitreous. Using ports (temporary watertight holes) inserted into the eye by a surgeon and a achandra Reddy; Figure and

Declarations
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Consent for publication All authors read and approved the final manuscript.

Competing interests
The authors declare no competing interests.

Discussion
Permanent vision loss is the most severe outcome of DEDs, which is marked by increased ONV, vascular tissue growth, and leukocyte infiltration in the retinal vasculature. An overview of intermediate proteins and growth factors that are involved in DED pathogenesis has been presented here. DEDs can be effectively managed with the help of the medicine or approach that was evaluated as a means of treatment. VEGF plays a dual role in DED formation. On the one hand, it is linked to the ONV, and on the other, it cleaves the FVIII-VWF complex in the endothelial cells, causing platelet aggregation and thrombosis. DAG and calcium ions activate the vast majority of PKCs in the body. By interrupting the thromboxane A2/prostacyclin (PGI2) axis, activation of PKC promotes ONV. It has also been shown that PKC activation increased the production of the vasoconstrictor endothelin 1 (ET-1). DED is fueled by a TXA2/ PGI2 imbalance and ET-1. However, despite extensive testing in laboratories, the majority of drugs are still unproven in terms of efficacy and/or safety. Researchers in this study revealed that anti-VEGF drugs worked well in the therapy and suppression of DEDs.