The current research investigated the therapeutic effects of ranibizumab in patients with myopic CNV. A great improvement in BCVA was found, along with a significantly decreased CMT measured by OCT and aqueous humor contents of VEGF-A, VEGF-D, and endoglin, but significantly decreased content of EGF after consecutive intravitreal injections of ranibizumab. The results were similar to those from another study on the effects of ranibizumab in AMD cases [25]. The concentrations of cytokines may be quantitative indicators of the effects of ranibizumab in patients with myopic CNV. Ranibizumab demonstrated significant effects on CNV secondary to pathologic myopia by improving BCVA values, reducing CMT, and modulating cytokines associated with angiogenesis. For different individuals, different treatment projects should be chosen.
The myopic CNV group showed higher plasma concentration of VEGF-A than the control group, whereas EGF and angiopoietin-2 contents were decreased in the myopic CNV group by comparing with the control group. Moreover, compared to controls, aqueous humor content of FGF-2 increased, whereas those of EGF and VEGF-A decreased in the eyes of patients with myopic CNV.
VEGF concentration in the plasma is greater among patients with active CNV secondary to AMD than in healthy individuals [26]. However, there is no research on the plasma VEGF concentration among patients with myopic CNV. It is well known that VEGF is the most significant signaling protein taking part in both vasculogenesis and angiogenesis, and the rise of plasma VEGF is a prerequisite for CNV generation. Therefore, in the present research, it is reasonable to detect a higher plasma concentration of VEGF-A in the myopic CNV group. Based on past research, it is controversial whether the VEGF concentration in the aqueous humor is high in myopic CNV. Tong et al. disclosed that VEGF concentration in the aqueous humor grew significantly among patients with CNV secondary to AMD, polypoidal choroidal vasculopathy, and CNV secondary to pathologic myopia, compared to healthy controls [27]. In contrast, in research by Sawada et al., VEGF concentrations in the aqueous humor of the myopic CNV group were greatly lower than those in the control group, which is consistent with our results [28]. Vascular endothelial growth factor receptor VEGFR-2 is mainly located in the retinal blood vessel cells of the leakage area, which is related to vascular leakage, whereas VEGFR-3 is mainly located in deep retinal capillaries and is relevant to VEGFR-2. VEGF-A induces VEGFR-2 and VEGFR-3 expression in the ischemic area and leads to retinal leakage, thereby promoting the formation of new blood vessels [6]. We hypothesize that VEGF-A may be localized in a small subfoveal area in combination with VEGFR-2 and VEGFR-3, resulting in decreased levels in the aqueous humor during CNV formation.
EGF contents are greatly higher in the aqueous humor of patients with AMD [11]. However, in the current research, the result was different when patients with myopic CNV were the research focus. The EGFR primarily resides in the cell membrane, where it binds with a significant quantity of EGF. It transduces biological signals by invagination pinocytosis, leading to its internalization into the cytoplasm. Once internalized, EGF is degraded by lysosomes, and EGFR is subsequently recycled back to the membrane. The expression of transforming growth factor-α (TGF-α) will increase while CNV forms [29]. TGF-α and EGF have 33–44% homology in structure, and TGF-α may competitively inhibit the expression of EGF. This leads to a decrease in EGF level in the plasma and aqueous humor of patients with myopic CNV.
Angiopoietin-2 exerts a key effect on vessel maturation, angiogenesis, and vessel regression and is expressed most heavily in tumor tissue (especially in tumor neovascularization) but not in normal tissue [30]. Myopic CNV expresses a large quantity of angiopoietin-2 and angiopoietin receptor (TEK) restricted to CNV lesions; thus, we found lower contents of angiopoietin-2 in both the plasma and aqueous humor among patients with myopic CNV by comparing with the control group.
In the normal retina, the mRNA of FGF-2 and its receptor were discovered in the ganglion cell layer and kernel, and transient retinal ischemia induced the synthesis of FGF-2 mRNA [31]. In vitro studies have found that the complex of anti-VEGF antibody/anti-FGF-2 antibody could completely inactivate VEGF and FGF-2 in the retinal pigment epithelium containing CNV, better inhibiting the growth of vascular endothelial cells than simply adding anti-VEGF antibody [32]. Unlike VEGF-A, EGF, and angiopoietin-2, FGF-2 is not expressed in retinal capillary cells and is limited to CNV lesions, which may result in higher aqueous humor level of FGF-2 in patients with myopic CNV than in controls.
The present research showed lower aqueous humor concentrations of VEGF-A, VEGF-D, and endoglin after consecutive intravitreal injections of ranibizumab, which are anti-VEGF-A monoclonal antibodies [8]. There is little doubt that the concentration of VEGF-A decreases after intravitreal injection [33]. As a result, the atrophy of CNV will lower the aqueous humor concentrations of the other two cytokines. VEGF-D works in the processes of angiogenesis and lymphangiogenesis. As there are no lymphatic vessels in the eyes, the VEGF-D expressed by RPE is related to ocular angiogenesis [34]. VEGF-D can also upregulate VEGF-A expression and promote angiogenesis [35]. Previous studies have shown that endoglin has strong immunogenicity in the endothelial cells of CNV membranes [14]. In contrast, the aqueous humor contents of EGF increased after consecutive intravitreal injections of ranibizumab. The atrophy of CNV led to a decrease in TGF-α contents and weakened the inhibition of EGF. As a result, the aqueous humor content of EGF increased.
This study had some limitations. First, there was relatively low number of participants recruited into our research. Although the outcomes revealed statistical significance for some of the detected cytokines, more molecular mechanisms should be explored further. Second, we did not gather three aqueous humor samples from each patient, mainly due to the high price of ranibizumab and the economic burden. Some of the patients could not afford three consecutive intravitreal injections of ranibizumab. Third, caused by the restricted volume of the samples, all cytokines that may be related to myopic CNV was not detected. There are still a few molecules potentially associated with the disease that were not examined, such as TGF-β [36], matrix metalloproteinase [37], tumor necrosis factor [38], and pigment epithelium-derived factor [27]. Finally, we selected patients with cataracts as the control group, so the diopter did not match between the two groups.