Idiopathic epiretinal membrane and idiopathic macular hole are two of the most common vitreomacular interface disease. Many studies, involving the measurements of intraocular cytokines, usually employed iERM and iMH as controls for retinal pathologies such as proliferative diabetic retinopathy, uveitis, retinal vein occlusion, and high myopia[5, 7, 8, 19]. However, the comparative data of the vitreal cytokine levels in patients with ERMs and MHs are very sparse. In present study, we found the no difference in the vitreal cytokine profiles between Asian patients with iERM and those with iMH. According to our study results, the vitreous fluid in the eyes of patients with either iERM or iMH can be served as controls in further researches.
iERM, as one of the vitreous macular traction diseases, its pathophysiology mechanism remains unclear. A generally received opinion is that age-related vitreoretinal interface change and pathologic cell proliferation result in vertical or horizontal traction force to the macula[20, 21]. A number of cellular factors are involved in cell recognition and signal transduction during the occurrence and development of iERM formation, among which, TGF-β2 is the most extensively studied factor[6, 20, 22]. The concentration of vitreal TGF-β2 level we measured is 587.05 ± 88.89 pg/ml, while already published data is 327.98 ± 99.58 and 951.06 ± 593.25. The discrepancy between this data could be due to differences in the tested methods and test kits.
Our data suggested that before Bonferroni correction, the TGF-β2 levels in the vitreous fluids of the patients with iERM were significantly higher than those in iMH (p = 0.01). These findings were similar to those reported by Ludovico Iannetti, whose research found that TGF-β2 and nerve growth factor (NGF) were associated with idiopathic ERMs. However, in our research, the statistical difference disappeared after Bonferroni correction. In addition to iERM or iMH, Iannetti et al once used primary retinal detachment (within 72 hours of retinal detachment onset) as control group. Ideally then, the human vitreous of healthy subjects should be used as the control. However, in clinical practice, vitreous sample from healthy subjects cannot be obtained because of the ethic issue. The present study demonstrates that the cytokine expression profile between patients with iERM and patients with iMH is similar, which means that like iMH, iERM can be reliably used as control groups.
Before our CONCEPT trial, we thoroughly retrieved the published literatures on vitreous cytokines during the past decade. Considering the compatibility of different cytokines in single commercial bead array, we finally investigated 48 cytokines using multiplex bead array method and other 4 cytokines with ELISA. Here, a total of 52 cytokines were included in the present study, covering most of the published factors associated with intraocular diseases and some new cytokines in other related diseases, such as asthma and Alzheimer's disease. And these cytokines can be classified into four main groups: the inflammatory factors and chomkines, the promoting angiogenesis factors, and the fibrogenic cytokines, which corresponding respectively to inflammatory, neovascular, and fibrotic retinopathy.
There were published studies focusing on the protein or cytokine profiles of vitreous from patients with iERM and iMH but yielding opposite conclusion[15, 16, 23]. Nakul Mandal et al demonstrated that none of the 330 protein spots changed significantly between the iERM and iMH groups using comparative proteomic experiments. On the contrary, Souska Zandi et al employed ELISA and multiplex technology while Zhang et al employed one-dimensional gel fractionation and liquid chromatography–tandem mass spectrometry analyses, and both found some of the differently expressed cytokines between ERM and MH. Several issues should be kept in mind to interpret the controversial findings between ours and others. Firstly, the expression of cytokines may be duration related. The average course of iERM in our study was 1.95 months, while the duration of iERM in Souska Zandi’s study was unknown. What we know is that the subjects whose courses were more than 6 months constitute 94% of the ERM group in the Souska Zandi’s study and 62% of those in our study. Besides, in 31.9% of the measured patients in Souska Zandi’s study, the cytokine concentrations lay below the lower cutoff level. Though half of the lower cutoff value was used for subsequent calculation, the result would be still in error. Third, the race might also be involved in the difference of cytokine levels in the vitreous. The above mentioned studies were conducted in Switzerland, in Europe, and in USA, while our patients were all Asian populations.
We acknowledge that this study has several limitations. First, the number of patients included is limited. More cases are required in future to confirm the results. Second, we did not compare the vitreous cytokines among the two macular diseases and vitreous floaters. However, the safety and efficiency of vitrectomy over Nd:YAG laser for floaters remains to be demonstrated. Thus, most studies involving the cytokines measurements still employed iERM or iMH as “negtive” controls. [5, 7, 8, 19]. Third, we did not include ERM or MH eyes with high myopia. ERM and MH are two of the main complications of pathological myopia. It will be interesting to investigate the vitreous cytokines between emmetropic and myopic eyes in conditions of ERM or MH.
In conclusion, the current research provides substantial evidence that the cytokine in the vitreous show similar expression in iERM group and iMH group. This prospective control study is the first one that demonstrates Asian patients with iERM and iMH can be chosen as “negative” control. These results provide theoretical foundation for the future clinical design methods. Further investigations with more participants should be conducted to verify these findings.