- Email: [email protected]
Vitreous Levels of Interleukin-6 and Vascular Endothelial Growth Factor in Macular Edema with Central Retinal Vein Occlusion
Vitreous Levels of Interleukin-6 and Vascular Endothelial Growth Factor in Macular Edema with Central Retinal Vein Occlusion Hidetaka Noma, MD,1,2 Hideharu Funatsu, MD,1 Tatsuya Mimura, MD,3 Seiyo Harino, MD,4 Sadao Hori, MD5 Objective: To investigate whether interleukin (IL)-6 or vascular endothelial growth factor (VEGF) influences macular edema in patients with central retinal vein occlusion (CRVO). Design: Retrospective case-control study. Participants: Twenty-seven patients who had macular edema with CRVO and 16 patients with nonischemic ocular diseases (control group). Methods: Retinal ischemia was evaluated by measuring the area of capillary nonperfusion using fluorescein angiography and the public domain Scion Image program, and macular edema was examined by optical coherence tomography. Vitreous fluid samples were obtained at pars plana vitrectomy. VEGF and IL-6 levels in vitreous fluid and plasma were determined with enzyme-linked immunosorbent assay kits. Main Outcome Measures: Vitreous fluid levels of IL-6 and VEGF. Results: The vitreous fluid levels of VEGF (median: 435 pg/ml) and IL-6 (median: 51.2 pg/ml) were significantly higher in the patients with CRVO than in the control group (median: 62.4 pg/ml and 1.07 pg/ml, respectively; P ⫽ 0.0046 and P⬍0.0001, respectively). The vitreous fluid level of VEGF was significantly correlated with that of IL-6 (P ⫽ 0.0029). Vitreous fluid levels of both VEGF and IL-6 were significantly higher in patients with CRVO who had retinal ischemia than in those without ischemia (P⬍0.0001 and P ⫽ 0.0003, respectively). Vitreous fluid levels of VEGF and IL-6 were also significantly correlated with the severity of macular edema (P ⫽ 0.0014 and P ⫽ 0.0047, respectively). Conclusions: Both IL-6 and VEGF were elevated in the vitreous fluid of patients with ischemic CRVO and macular edema. VEGF may increase vascular permeability in patients with macular edema and CRVO, whereas IL-6 may also contribute by acting together with or via VEGF. Financial Disclosure(s): The author(s) have no proprietary or commercial interest in any materials discussed in this article. Ophthalmology 2009;116:87–93 © 2009 by the American Academy of Ophthalmology.
Central retinal vein occlusion (CRVO) is a common retinal vascular disease that often leads to macular edema, which is the most frequent cause of visual impairment in patients with CRVO.1–3 Accordingly, investigation of the cellular and molecular factors that underlie the occurrence of macular edema in patients with CRVO is of considerable importance. Expression of many cytokines is increased in the eyes of patients with CRVO, and cytokine levels are elevated in their ocular fluid.4 – 6 Some progress has been made in understanding the mechanisms responsible for the development of macular edema. Vascular endothelial growth factor (VEGF) causes a marked increase of vascular permeability7 by provoking conformational changes in the tight junctions of retinal vascular endothelial cells.8,9 Expression of VEGF is induced in retinal cells by hypoxia10 and interleukin (IL)-6,11 which is a multifunctional cytokine that can indirectly increase vascular permeability by inducing VEGF expression and directly increase endothelial permeability itself.11,12 We © 2009 by the American Academy of Ophthalmology Published by Elsevier Inc.
previously reported that the levels of both VEGF and IL-6 were elevated in the ocular fluid of patients who had macular edema associated with branch retinal vein occlusion.13–15 It was recently reported that intravitreal injection of bevacizumab, a full-length humanized monoclonal antibody targeting VEGF, is beneficial for patients with macular edema and CRVO.16,17 These findings suggest that both VEGF and IL-6 may contribute to the occurrence of macular edema in patients with CRVO. However, the levels of these cytokines in patients with CRVO and their relationship to the pathogenesis of macular edema are still poorly understood. Therefore, we measured the concentrations of VEGF and IL-6 in the vitreous fluid of patients with CRVO with macular edema and investigated the relation between the occurrence of macular edema and the vitreous levels of these 2 molecules. We found that vitreous levels of both VEGF and IL-6 were higher in patients with CRVO who had retinal ischemia than in patients without retinal ischemia, and that the vitreous levels of both molecules were ISSN 0161-6420/09/$–see front matter doi:10.1016/j.ophtha.2008.09.034
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Ophthalmology Volume 116, Number 1, January 2009 correlated with the severity of macular edema and showed a strong correlation with each other. These results suggest that VEGF and IL-6 may contribute to the onset and progression of macular edema in patients with CRVO, and that further investigation of the ocular cytokine network may help to improve our understanding of the pathogenesis of macular edema associated with CRVO.
Materials and Methods Subjects Undiluted vitreous fluid samples were harvested at the start of pars plana vitrectomy after written informed consent was obtained from each subject following an explanation of the purpose and potential adverse effects of the procedure. This study was performed in accordance with the Helsinki Declaration of 1975 (1983 revision). The institutional review boards of Tokyo Women’s Medical University and Hiroshima University approved the protocol for collection and testing of vitreous fluid and blood samples. Vitrectomy was performed as part of standard care because it has been reported that macular edema and visual acuity can be improved in patients with CRVO by this procedure.18,19 Forty-two consecutive patients with CRVO who presented to the hospitals of Tokyo Women’s Medical University or Hiroshima University between June of 2003 and August of 2007 were screened using the criteria listed below, and vitreous fluid samples were obtained from the 27 patients who were enrolled. The indication for pars plana vitrectomy was relief of vitreomacular traction to improve macular edema secondary to CRVO. Thus, the subjects did not include patients with mild CRVO because we performed vitrectomy for advanced macular edema. The inclusion criteria were (1) macular edema secondary to CRVO in patients who were scheduled for pars plana vitrectomy (including patients who had received retinal photocoagulation) and (2) best-corrected visual acuity of less than 20/50 before surgery. Fifteen of the 42 patients were excluded, with the reason being previous ocular surgery in 4 patients, diabetic retinopathy in 3 patients, iris rubeosis in 5 patients, and a history of ocular inflammation or vitreoretinal disease in 3 patients. Vitreous fluid samples were also obtained from 16 patients with nonischemic ocular diseases as a control group. These 16 control patients without CRVO included 11 patients with a macular hole and 5 patients with an idiopathic epiretinal membrane (CRVO was excluded as a cause of epiretinal membrane, and none of them had proliferative vitreoretinopathy). The CRVO group (16 men and 11 women) was aged 69.7 ⫾ 9.4 years (mean ⫾ standard deviation), and the control group (8 men and 8 women) was aged 65.1 ⫾ 6.5 years (Table 1). Fourteen of the 16 control subjects of this study were also used as control subjects in another study.14 None of the control patients had undergone retinal photocoagulation or cryotherapy for retinal tears, procedures that may potentially influence the VEGF level. The mean duration of CRVO was 3.6 ⫾ 1.6 months (range: 2–7 months). Pars plana vitrectomy was performed at Tokyo Women’s Medical University or Hiroshima University. Within 2.5 ⫾ 1.1 months (range: 1–5 months) before surgery, panretinal photocoagulation was done to prevent neovascular glaucoma in 14 eyes (mean: 950 shots; range: 298 –1711 shots). None of the subjects received treatment with anti-VEGF agents.
Fundus Findings Patients were evaluated by careful biomicroscopic examination using a fundus contact lens. The fundus findings were confirmed preoperatively by standardized fundus color photography and flu-
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Table 1. Profile of Control Patients and Patients with Central Retinal Vein Occlusion
Gender Female Male Age (y) Hypertension No Yes Duration of CRVO (mo)
CRVO
Control
No.* (N ⫽ 27)
No.* (N ⫽ 16) P Value
11 (41%) 16 (59%) 69.7 ⫾ 9.4†
8 (50%) 8 (50%) 65.1 ⫾ 6.5†
10 (37%) 17 (63%) 3.6 ⫾ 1.6†
13 (81%) 3 (19%) ⫺
0.0912 0.0050 ⫺
CRVO ⫽ central retinal vein occlusion. *Number of patients with data. Mean ⫾ standard deviation.
†
orescein angiography, which were performed with a Topcon TRC50EX fundus camera, an image-net system (Tokyo Optical Co Ltd, Japan), and a preset lens with a slit-lamp. Both preoperative and operative fundus findings were recorded for each subject. A masked grader independently assessed ischemic retinal vascular occlusion by examination of fluorescein angiograms. Regions where photocoagulation had been performed were excluded when calculating the nonperfused area. The ischemic region of the retina was measured using the public domain Scion Image program, as reported previously.13–15 If the nonperfused area multiplied by the disc area gave a value of 10 or more, this was defined as indicating the presence of retinal ischemia.20 –22 Three patients were switched from the “ischemic” group to the “nonischemic” group after retinal photocoagulation, so the 27 patients with CRVO included 18 patients with retinal ischemia (12 men and 6 women aged 70.2 ⫾ 8.9 years) and 9 patients without ischemia (5 men and 4 women aged 68.6 ⫾ 10.7 years). Optical coherence tomography (Zeiss-Humphrey Ophthalmic Systems, Dublin, CA) was performed on each subject within 1 week before vitrectomy. The fundi were scanned with the measuring beam focused on horizontal and vertical planes crossing the central fovea, which was located on the fundus photograph. The location of the central fovea was determined from the fundus photograph and by each patient’s fixation. The subjects were limited to patients who could fix on the central landmark during optical coherence tomography. Cross-sectional images were collected by a single experienced examiner, and each examination was repeated until highly reproducible scans were obtained. We defined the thickness of the central fovea as the distance between the inner limiting membrane and the retinal pigment epithelium (including any serous retinal detachment), and measurements were automatically made by computer. The thickness of the neurosensory retina was defined as the distance between the inner and outer neurosensory retinal surfaces,23 and the severity of macular edema was graded from the measured retinal thickness. The average preoperative retinal thickness was 669 ⫾ 180 m, with a range of 280 to 990 m.
Sample Collection Samples of undiluted vitreous fluid (300 –500 L) were collected into sterile tubes at the time of surgery and rapidly frozen at ⫺80°C. Blood samples were collected simultaneously and centrifuged at 3000g for 5 minutes to obtain plasma, after which aliquots were stored at ⫺80°C until assay.
Noma et al 䡠 Macular Edema with Central Retinal Vein Occlusion Measurement of VEGF and IL-6 IL-6 and VEGF were measured in vitreous fluid samples (from the same eye) and in plasma by enzyme-linked immunosorbent assay using kits for human VEGF and IL-6 (R&D Systems, Minneapolis, MN).13–15 The VEGF kit detected 2 of the 4 VEGF isoforms, which were VEGF121 and VEGF165. The levels of these factors in the vitreous fluid samples and plasma were within the detection ranges of the assays, with the minimum detectable concentration being 15.6 pg/ml for VEGF (intra-assay coefficient of variation [CV] 5.5%, interassay CV 6.9%) and 0.156 pg/ml for IL-6 (intra-assay CV 5.4%, interassay CV 6.7%).
Statistical Analysis All analyses were performed with SAS System 9.1 software (SAS Inc., Cary, NC). Data are presented as the mean ⫾ standard deviation or as medians with interquartile ranges or frequencies. The Student t test was used to compare normally distributed unpaired continuous variables between the 2 groups, and the Mann–Whitney U test was used for other variables with a normal distribution. The chi-square or Fisher exact test was used to compare discrete variables. Wilcoxon’s signed-rank test was performed to compare paired continuous variables. To examine the relation between VEGF or IL-6 and the severity of macular edema, Spearman’s rank-order correlation coefficients were calculated. Two-tailed P values of less than 0.05 were considered to indicate a statistically significant difference.
Results The vitreous fluid level of VEGF (median [interquartile range]) was significantly higher in the patients with CRVO (435 pg/ml [55.8 – 1643]) than in the control subjects (62.4 pg/ml [39.0 – 62.4]; P ⫽ 0.0046; Fig 1A). The vitreous fluid level of IL-6 was also significantly higher in the patients with CRVO (51.2 pg/ml [25.3–127]) than in the controls (1.07 pg/ml [0.77–1.58]; P⬍0.0001; Fig 1B). In the patients with CRVO, there was a significant correlation between the vitreous levels of VEGF and IL-6 ( ⫽ 0.5862, P ⫽ 0.0029) (Fig 2). Vitreous fluid levels of both VEGF and IL-6 were significantly higher in patients with CRVO with ischemia than in those without ischemia (P⬍0.0001 and P ⫽ 0.0003, respectively) (Fig 3A and B). In addition, the vitreous levels of both factors were significantly correlated with the severity of macular edema in the patients with CRVO (VEGF, ⫽ 0.6277, P ⫽ 0.0014; IL-6, ⫽ 0.5543, P ⫽ 0.0047) (Fig 4A and B). There was a significant difference of the VEGF level between the 11 patients with ischemic CRVO who received retinal photocoagulation and the 7 patients without retinal photocoagulation (P ⫽ 0.0109). In contrast, there was no significant difference of IL-6 between the ischemic patients with CRVO with and without retinal photocoagulation (P ⫽ 0.4135). The vitreous level of VEGF was not significantly related to either the extent or the timing of retinal photocoagulation in 14 eyes ( ⫽ ⫺0.0747, P ⫽ 0.7810 and ⫽ ⫺0.3022, P ⫽ 0.1779, respectively). Vitreous levels of IL-6 also showed no significant correlation with the extent or timing of photocoagulation ( ⫽ ⫺0.0736, P ⫽ 0.7874 and ⫽ 0.1473, P ⫽ 0.7131, respectively). Vitreous fluid levels of both VEGF and IL-6 were significantly higher than the corresponding plasma levels in the patients with CRVO (74.7 pg/ml [15.6 –234] and 1.20 pg/ml [1.13–1.84], P ⫽ 0.0010 and P⬍0.0001, respectively) (Table 2). No correlation was observed between the vitreous and plasma levels of VEGF ( ⫽ 0.1758, P ⫽ 0.4129) or IL-6 ( ⫽ ⫺0.2224, P ⫽ 0.2533). In addition, the plasma level of VEGF was significantly higher in hypertensive patients than in those without hypertension (P ⫽
Figure 1. A, VEGF levels in vitreous fluid of control patients and patients with macular edema and CRVO (*P ⫽ 0.0046). B, IL-6 levels in vitreous fluid of control patients and patients with CRVO with macular edema (*P⬍0.0001).
0.0459), but plasma IL-6 showed no significant difference between patients with and without hypertension (P ⫽ 0.1841).
Discussion Our previous study14 showed that vitreous fluid levels of both IL-6 and VEGF were correlated with the severity of
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Ophthalmology Volume 116, Number 1, January 2009 (Fig 3). This finding is supported by previous studies showing that VEGF mRNA expression by retinal pericytes increases as hypoxia becomes more severe,10 whereas IL-6 mRNA expression by cultured endothelial cells exposed to hypoxic condi-
Figure 2. Relation between the vitreous levels of VEGF and IL-6 in patients with macular edema and CRVO ( ⫽ 0.5862, P ⫽ 0.0029).
macular edema in patients with branch retinal vein occlusion. We also demonstrated that the vitreous level of IL-6 was significantly correlated with that of VEGF.14 Furthermore, levels of both VEGF and IL-6 were higher in the vitreous fluid than in the plasma.14 It has been reported that pars plana vitrectomy is one of the potential techniques for the treatment of macular edema and improvement of visual acuity in CRVO,18,19 whereas retinal photocoagulation is ineffective for improving visual acuity in patients with nonperfused CRVO and macular edema.21 Therefore, in this study, we performed pars plana vitrectomy in patients with CRVO with macular edema and investigated the relationship between vitreous fluid levels of VEGF or IL-6 and macular edema in ischemic and nonischemic CRVO. To investigate the sources of VEGF and IL-6, we measured both vitreous fluid and plasma levels. We found that the levels of both VEGF and IL-6 were higher in the vitreous fluid than in the corresponding plasma samples, whereas there was no correlation between the vitreous and plasma levels of either VEGF or IL-6. These results suggest that VEGF and IL-6 in the vitreous fluid came from an intraocular source rather than from the systemic circulation, a conclusion supported by previous reports that VEGF10,24 and IL-625 are produced by ocular cells. The present study also showed that the plasma level of VEGF was significantly higher in hypertensive patients than in those without hypertension, a finding that agrees with the report of Belgore et al.26 This suggests that upregulation of VEGF production by hypertension may be involved in the pathogenesis of CRVO. The present study showed that vitreous levels of both VEGF and IL-6 were significantly higher in patients with CRVO than in control subjects. In addition, the vitreous levels of VEGF and IL-6 were significantly higher in patients with CRVO with retinal ischemia than in those without ischemia
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Figure 3. Correlation between the presence of retinal ischemia and the vitreous levels of VEGF and IL-6. Retinal ischemia was evaluated by calculating the nonperfused area of the retina using the public domain Scion Image program. Vitreous levels of VEGF (A) and IL-6 (B) were significantly higher in patients who had CRVO with ischemia than in those without ischemia (*P⬍0.0001 and *P ⫽ 0.0003, respectively).
Noma et al 䡠 Macular Edema with Central Retinal Vein Occlusion
Figure 4. Correlation between the severity of macular edema and vitreous fluid levels of VEGF and IL-6. The severity of macular edema was evaluated by optical coherence tomography. Higher vitreous levels of VEGF (A) and IL-6 (B) were significantly associated with more severe edema ( ⫽ 0.6277, P ⫽ 0.0014 and ⫽ 0.5543, P ⫽ 0.0047, respectively).
tions also increases in a time-dependent manner.27–29 Thus, we hypothesized that the elevation of intraocular VEGF and IL-6 levels may contribute to the occurrence of macular edema associated with CRVO. In this study, we measured the foveal thickness by optical coherence tomography to assess the severity of macular edema in our patients with CRVO and demonstrated that vitreous fluid levels of VEGF and IL-6 were significantly correlated with the severity of macular edema (Fig 4). In addition, the vitreous levels of these 2 molecules showed a significant correlation. Production of VEGF is induced by
hypoxia,10 and VEGF increases endothelial permeability by causing changes to tight junctions.8,9 In patients with CRVO, breakdown of the blood-retinal barrier occurs because of damage to capillary endothelial cells.30 Accordingly, it seems likely that vascular occlusion induces the expression of VEGF via hypoxia in patients with CRVO, resulting in breakdown of the blood-retinal barrier and increased vascular permeability. This hypothesis is supported by a previous report that the intravitreous injection of VEGF induces retinal edema, dilated and tortuous vessels, and capillary closure in adult primates,31 as well as by recent reports that treatment with an anti-VEGF monoclonal antibody (bevacizumab) is effective for macular edema in CRVO.16,17 IL-6 has been reported to increase endothelial permeability in vitro by promoting the rearrangement of actin filaments (which changes the shape of endothelial cells) in a dose- and time-dependent manner.12 It is also possible that IL-6 induces an increase of VEGF production in patients with CRVO, thus contributing to macular edema. That is, both VEGF and IL-6 may directly increase vascular permeability, or IL-6 may indirectly increase vascular permeability via upregulation of VEGF. Accordingly, further investigations are needed to define the ocular interaction between IL-6 and VEGF, as well as the role of IL-6 in the pathogenesis of macular edema in patients with CRVO. The present study showed that patients with ischemic CRVO who received retinal photocoagulation before surgery had lower VEGF levels than those without photocoagulation. This result is in agreement with previous reports4 and is supported by previous findings that scatter photocoagulation reverses tissue hypoxia in miniature pigs with experimental vasoproliferative microangiopathy32 and that hyperoxia reduces VEGF production in the ischemic retina.33 However, in 14 patients who received retinal photocoagulation before surgery, the vitreous levels of VEGF and IL-6 were not significantly correlated with the extent or timing of photocoagulation. Laser photocoagulation has been shown to increase the expression of cytokines, including VEGF, by cultured human retinal pigment epithelial (RPE) cells, but upregulation of VEGF production was observed at the early period of 6 hours after photocoagulations and then VEGF returned to its basal level by 72 hours.34 In contrast, Itaya et al35 reported that the peak VEGF level occurs on day 3 in vivo, coinciding with the peak of macrophage infiltration, and that the difference from in vitro data may arise because recruited macrophages contribute more to the upregulation of VEGF than RPE cells or because secretion of VEGF may be induced by macroTable 2. Vitreous Fluid and Plasma Levels of Vascular Endothelial Growth Factor and Interleukin-6 in Patients with Central Retinal Vein Occlusion
VEGF (pg/ml) IL-6 (pg/ml)
Vitreous Fluid
Plasma
P Value
435 (55.8–1643) 51.2 (25.3–127)
74.7 (15.6–234) 1.20 (1.13–1.84)
0.0010 ⬍0.0001
IL ⫽ interleukin; VEGF ⫽ vascular endothelial growth factor. Data are medians with interquartile ranges.
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Ophthalmology Volume 116, Number 1, January 2009 phage-RPE interactions. Furthermore, it was reported that changes of the VEGF mRNA level in the burned area of the retina after laser photocoagulation in miniature pigs were confined to RPE cells, with mRNA expression being low immediately after photocoagulation and returning to normal by 42 days.36 Moreover, after photocoagulation of the rabbit retina, the level of IL-6 was reported to increase at 24 hours and then return to baseline by 72 hours.37 However, the kinetics of IL-6 in human vitreous fluid after photocoagulation have been unclear. These reports and our results suggest that any increase of VEGF or IL-6 expression in the retina after photocoagulation is transient, and that both might decrease again relatively early. Further investigations will be needed to clarify the relationship between the extent and timing of photocoagulation and the vitreous levels of VEGF or IL-6. We found that the vitreous fluid levels of both IL-6 and VEGF were higher in patients who had ischemic CRVO with macular edema than in patients who had nonischemic CRVO. Vitreous levels of both IL-6 and VEGF were significantly correlated with the severity of macular edema in patients with CRVO. In addition, there was a significant correlation between the vitreous levels of these 2 molecules. Our findings suggest that VEGF increases vascular permeability in patients with CRVO with macular edema and that IL-6 also contributes to increased vascular permeability by acting together with or via VEGF. Acknowledgment. We thank Katsunori Shimada (Department of Biostatistics, STATZ Corporation, Tokyo) for assistance with the statistical analysis.
References 1. Zegarra H, Gutman FA, Conforto J. The natural course of central retinal vein occlusion. Ophthalmology 1979;86:1931– 42. 2. Hayreh SS. Classification of central retinal vein occlusion. Ophthalmology 1983;90:458 –74. 3. Gutman FA, Zegarra H. Macular edema secondary to occlusion of the retinal veins. Surv Ophthalmol 1984;28:462–70. 4. Aiello LP, Avery RL, Arrigg PG, et al. Vascular endothelial growth factor in ocular fluid of patients with diabetic retinopathy and other retinal disorders. N Engl J Med 1994;331: 1480 –7. 5. Chen KH, Wu CC, Roy S, et al. Increased interleukin-6 in aqueous humor of neovascular glaucoma. Invest Ophthalmol Vis Sci 1999;40:2627–32. 6. Pe’er J, Folberg R, Itin A, et al. Vascular endothelial growth factor upregulation in human central retinal vein occlusion. Ophthalmology 1998;105:412– 6. 7. Dvorak HF, Brown LF, Detmar M, Dvorak AM. Vascular permeability factor/vascular endothelial growth factor, microvascular hyperpermeability, and angiogenesis. Am J Pathol 1995;146:1029 –39. 8. Vinores SA, Derevjanik NL, Ozaki H, et al. Cellular mechanisms of blood-retinal barrier dysfunction in macular edema. Doc Ophthalmol 1999;97:217–28. 9. Gardner TW, Antonetti DA, Barber AJ, et al, Penn State Retina Research Group. The molecular structure and function of the inner blood-retinal barrier. Doc Ophthalmol 1999;97:229 –37. 10. Aiello LP, Northrup JM, Keyt BA, et al. Hypoxic regulation of vascular endothelial growth factor in retinal cells. Arch Ophthalmol 1995;113:1538 – 44.
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11. Cohen T, Nahari D, Cerem LW, et al. Interleukin 6 induces the expression of vascular endothelial growth factor. J Biol Chem 1996;271:736 – 41. 12. Maruo N, Morita I, Shirao M, Murota S. IL-6 increases endothelial permeability in vitro. Endocrinology 1992;131: 710 – 4. 13. Noma H, Funatsu H, Yamasaki M, et al. Pathogenesis of macular edema with branch retinal vein occlusion and intraocular levels of vascular endothelial growth factor and interleukin-6. Am J Ophthalmol 2005;140:256 – 61. 14. Noma H, Minamoto A, Funatsu H, et al. Intravitreal levels of vascular endothelial growth factor and interleukin-6 are correlated with macular edema in branch retinal vein occlusion. Graefes Arch Clin Exp Ophthalmol 2006;244: 309 –15. 15. Noma H, Funatsu H, Yamasaki M, et al. Aqueous humour levels of cytokines are correlated to vitreous levels and severity of macular oedema in branch retinal vein occlusion. Eye 2008;22:42– 8. 16. Iturralde D, Spaide RF, Meyerle CB, et al. Intravitreal bevacizumab (Avastin) treatment of macular edema in central retinal vein occlusion: a short-term study. Retina 2006;26: 279 – 84. 17. Pai SA, Shetty R, Vijayan PB, et al. Clinical, anatomic, and electrophysiologic evaluation following intravitreal bevacizumab for macular edema in retinal vein occlusion. Am J Ophthalmol 2007;143:601– 6. 18. Tachi N, Hashimoto Y, Ogino N. Vitrectomy for macular edema combined with retinal vein occlusion. Doc Ophthalmol 1999;97:465–9. 19. Leizaola-Fernandez C, Suarez-Tata L, Quiroz-Mercado H, et al. Vitrectomy with complete posterior hyaloid removal for ischemic central retinal vein occlusion: series of cases. BMC Ophthalmol [serial online] 2005;5:10. Available at: http:// www.biomedcentral.com/1471–2415/5/10. Accessed September 13, 2008. 20. Baseline and early natural history report: the Central Vein Occlusion Study. Arch Ophthalmol 1993;111:1087–95. 21. Evaluation of grid pattern photocoagulation for macular edema in central vein occlusion: the Central Vein Occlusion Study Group M report. Ophthalmology 1995;102:1425–33. 22. Central Vein Occlusion Study Group. Natural history and clinical management of central retinal vein occlusion. Arch Ophthalmol 1997;115:486 –91. 23. Otani T, Kishi S. Tomographic assessment of vitreous surgery for diabetic macular edema. Am J Ophthalmol 2000;129:487–94. 24. Lutty GA, McLeod DS, Merges C, et al. Localization of vascular endothelial growth factor in human retina and choroid. Arch Ophthalmol 1996;114:971–7. 25. Planck SR, Dang TT, Graves D, et al. Retinal pigment epithelial cells secrete interleukin-6 in response to interleukin-1. Invest Ophthalmol Vis Sci 1992;33:78 – 82. 26. Belgore FM, Blann AD, Li-Saw-Hee FL, et al. Plasma levels of vascular endothelial growth factor and its soluble receptor (SFlt-1) in essential hypertension. Am J Cardiol 2001;87: 805–7, A9. 27. Yan SF, Tritto I, Pinsky D, et al. Induction of interleukin 6 (IL-6) by hypoxia in vascular cells: central role of the binding site for nuclear factor-IL-6. J Biol Chem 1995;270: 11463–71. 28. Ali MH, Schlidt SA, Chandel NS, et al. Endothelial permeability and IL-6 production during hypoxia: role of ROS in signal transduction. Am J Physiol 1999;277:L1057– 65. 29. Pearlstein DP, Ali MH, Mungai PT, et al. Role of mitochondrial oxidant generation in endothelial cell responses to hypoxia. Arterioscler Thromb Vasc Biol 2002;22:566 –73.
Noma et al 䡠 Macular Edema with Central Retinal Vein Occlusion 30. Chahal PS, Fallon TJ, Kohner EM. Measurement of bloodretinal barrier function in central retinal vein occlusion. Arch Ophthalmol 1986;104:554 –7. 31. Tolentino MJ, Miller JW, Gragoudas ES, et al. Intravitreous injections of vascular endothelial growth factor produce retinal ischemia and microangiopathy in an adult primate. Ophthalmology 1996;103:1820 – 8. 32. Pournaras CJ, Tsacopoulos M, Strommer K, et al. Scatter photocoagulation restores tissue hypoxia in experimental vasoproliferative microangiopathy in miniature pigs. Ophthalmology 1990;97:1329 –33. 33. Pournaras CJ, Miller JW, Gragoudas ES, et al. Systemic hyperoxia decreases vascular endothelial growth factor gene expression in ischemic primate retina. Arch Ophthalmol 1997;115:1553–8.
34. Ogata N, Ando A, Uyama M, Matsumura M. Expression of cytokines and transcription factors in photocoagulated human retinal pigment epithelial cells. Graefes Arch Clin Exp Ophthalmol 2001;239:87–95. 35. Itaya M, Sakurai E, Nozaki M, et al. Upregulation of VEGF in murine retina via monocyte recruitment after retinal scatter laser photocoagulation. Invest Ophthalmol Vis Sci 2007;48: 5677– 83. 36. Xiao M, McLeod D, Cranley J, et al. Growth factor staining patterns in the pig retina following retinal laser photocoagulation. Br J Ophthalmol 1999;83:728 –36. 37. Er H, Doganay S, Turkoz Y, et al. The levels of cytokines and nitric oxide in rabbit vitreous humor after retinal laser photocoagulation. Ophthalmic Surg Lasers 2000;31:479 – 83.
Footnotes and Financial Disclosures Originally received: May 8, 2008. Final revision: September 5, 2008. Accepted: September 22, 2008.
4
Manuscript no. 2008-556.
1
Department of Ophthalmology, Yachiyo Medical Center, Tokyo Women’s Medical University, Chiba, Japan.
2
Department of Ophthalmology and Visual Science, Graduate School of Biomedical Sciences, Hiroshima University, Hiroshima, Japan.
3
Department of Ophthalmology, Yodogawa Christian Hospital, Osaka, Japan. Department of Ophthalmology, Tokyo Women’s Medical University, Tokyo, Japan. Financial Disclosure(s): The authors have no proprietary or commercial interest in any materials discussed in this article.
5
Department of Ophthalmology, University of Tokyo Graduate School of Medicine, Tokyo, Japan.
Correspondence: Hidetaka Noma, MD, Department of Ophthalmology, Yachiyo Medical Center, Tokyo Women’s Medical University, 477–96, Owada-shinden, Yachiyo, Chiba 276 – 8524, Japan. E-mail: [email protected].
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Central retinal vein occlusion (CRVO) is a common retinal vascular disease that often leads to macular edema, which is the most frequent cause of visual impairment in patients with CRVO.1–3 Accordingly, investigation of the cellular and molecular factors that underlie the occurrence of macular edema in patients with CRVO is of considerable importance. Expression of many cytokines is increased in the eyes of patients with CRVO, and cytokine levels are elevated in their ocular fluid.4 – 6 Some progress has been made in understanding the mechanisms responsible for the development of macular edema. Vascular endothelial growth factor (VEGF) causes a marked increase of vascular permeability7 by provoking conformational changes in the tight junctions of retinal vascular endothelial cells.8,9 Expression of VEGF is induced in retinal cells by hypoxia10 and interleukin (IL)-6,11 which is a multifunctional cytokine that can indirectly increase vascular permeability by inducing VEGF expression and directly increase endothelial permeability itself.11,12 We © 2009 by the American Academy of Ophthalmology Published by Elsevier Inc.
previously reported that the levels of both VEGF and IL-6 were elevated in the ocular fluid of patients who had macular edema associated with branch retinal vein occlusion.13–15 It was recently reported that intravitreal injection of bevacizumab, a full-length humanized monoclonal antibody targeting VEGF, is beneficial for patients with macular edema and CRVO.16,17 These findings suggest that both VEGF and IL-6 may contribute to the occurrence of macular edema in patients with CRVO. However, the levels of these cytokines in patients with CRVO and their relationship to the pathogenesis of macular edema are still poorly understood. Therefore, we measured the concentrations of VEGF and IL-6 in the vitreous fluid of patients with CRVO with macular edema and investigated the relation between the occurrence of macular edema and the vitreous levels of these 2 molecules. We found that vitreous levels of both VEGF and IL-6 were higher in patients with CRVO who had retinal ischemia than in patients without retinal ischemia, and that the vitreous levels of both molecules were ISSN 0161-6420/09/$–see front matter doi:10.1016/j.ophtha.2008.09.034
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Ophthalmology Volume 116, Number 1, January 2009 correlated with the severity of macular edema and showed a strong correlation with each other. These results suggest that VEGF and IL-6 may contribute to the onset and progression of macular edema in patients with CRVO, and that further investigation of the ocular cytokine network may help to improve our understanding of the pathogenesis of macular edema associated with CRVO.
Materials and Methods Subjects Undiluted vitreous fluid samples were harvested at the start of pars plana vitrectomy after written informed consent was obtained from each subject following an explanation of the purpose and potential adverse effects of the procedure. This study was performed in accordance with the Helsinki Declaration of 1975 (1983 revision). The institutional review boards of Tokyo Women’s Medical University and Hiroshima University approved the protocol for collection and testing of vitreous fluid and blood samples. Vitrectomy was performed as part of standard care because it has been reported that macular edema and visual acuity can be improved in patients with CRVO by this procedure.18,19 Forty-two consecutive patients with CRVO who presented to the hospitals of Tokyo Women’s Medical University or Hiroshima University between June of 2003 and August of 2007 were screened using the criteria listed below, and vitreous fluid samples were obtained from the 27 patients who were enrolled. The indication for pars plana vitrectomy was relief of vitreomacular traction to improve macular edema secondary to CRVO. Thus, the subjects did not include patients with mild CRVO because we performed vitrectomy for advanced macular edema. The inclusion criteria were (1) macular edema secondary to CRVO in patients who were scheduled for pars plana vitrectomy (including patients who had received retinal photocoagulation) and (2) best-corrected visual acuity of less than 20/50 before surgery. Fifteen of the 42 patients were excluded, with the reason being previous ocular surgery in 4 patients, diabetic retinopathy in 3 patients, iris rubeosis in 5 patients, and a history of ocular inflammation or vitreoretinal disease in 3 patients. Vitreous fluid samples were also obtained from 16 patients with nonischemic ocular diseases as a control group. These 16 control patients without CRVO included 11 patients with a macular hole and 5 patients with an idiopathic epiretinal membrane (CRVO was excluded as a cause of epiretinal membrane, and none of them had proliferative vitreoretinopathy). The CRVO group (16 men and 11 women) was aged 69.7 ⫾ 9.4 years (mean ⫾ standard deviation), and the control group (8 men and 8 women) was aged 65.1 ⫾ 6.5 years (Table 1). Fourteen of the 16 control subjects of this study were also used as control subjects in another study.14 None of the control patients had undergone retinal photocoagulation or cryotherapy for retinal tears, procedures that may potentially influence the VEGF level. The mean duration of CRVO was 3.6 ⫾ 1.6 months (range: 2–7 months). Pars plana vitrectomy was performed at Tokyo Women’s Medical University or Hiroshima University. Within 2.5 ⫾ 1.1 months (range: 1–5 months) before surgery, panretinal photocoagulation was done to prevent neovascular glaucoma in 14 eyes (mean: 950 shots; range: 298 –1711 shots). None of the subjects received treatment with anti-VEGF agents.
Fundus Findings Patients were evaluated by careful biomicroscopic examination using a fundus contact lens. The fundus findings were confirmed preoperatively by standardized fundus color photography and flu-
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Table 1. Profile of Control Patients and Patients with Central Retinal Vein Occlusion
Gender Female Male Age (y) Hypertension No Yes Duration of CRVO (mo)
CRVO
Control
No.* (N ⫽ 27)
No.* (N ⫽ 16) P Value
11 (41%) 16 (59%) 69.7 ⫾ 9.4†
8 (50%) 8 (50%) 65.1 ⫾ 6.5†
10 (37%) 17 (63%) 3.6 ⫾ 1.6†
13 (81%) 3 (19%) ⫺
0.0912 0.0050 ⫺
CRVO ⫽ central retinal vein occlusion. *Number of patients with data. Mean ⫾ standard deviation.
†
orescein angiography, which were performed with a Topcon TRC50EX fundus camera, an image-net system (Tokyo Optical Co Ltd, Japan), and a preset lens with a slit-lamp. Both preoperative and operative fundus findings were recorded for each subject. A masked grader independently assessed ischemic retinal vascular occlusion by examination of fluorescein angiograms. Regions where photocoagulation had been performed were excluded when calculating the nonperfused area. The ischemic region of the retina was measured using the public domain Scion Image program, as reported previously.13–15 If the nonperfused area multiplied by the disc area gave a value of 10 or more, this was defined as indicating the presence of retinal ischemia.20 –22 Three patients were switched from the “ischemic” group to the “nonischemic” group after retinal photocoagulation, so the 27 patients with CRVO included 18 patients with retinal ischemia (12 men and 6 women aged 70.2 ⫾ 8.9 years) and 9 patients without ischemia (5 men and 4 women aged 68.6 ⫾ 10.7 years). Optical coherence tomography (Zeiss-Humphrey Ophthalmic Systems, Dublin, CA) was performed on each subject within 1 week before vitrectomy. The fundi were scanned with the measuring beam focused on horizontal and vertical planes crossing the central fovea, which was located on the fundus photograph. The location of the central fovea was determined from the fundus photograph and by each patient’s fixation. The subjects were limited to patients who could fix on the central landmark during optical coherence tomography. Cross-sectional images were collected by a single experienced examiner, and each examination was repeated until highly reproducible scans were obtained. We defined the thickness of the central fovea as the distance between the inner limiting membrane and the retinal pigment epithelium (including any serous retinal detachment), and measurements were automatically made by computer. The thickness of the neurosensory retina was defined as the distance between the inner and outer neurosensory retinal surfaces,23 and the severity of macular edema was graded from the measured retinal thickness. The average preoperative retinal thickness was 669 ⫾ 180 m, with a range of 280 to 990 m.
Sample Collection Samples of undiluted vitreous fluid (300 –500 L) were collected into sterile tubes at the time of surgery and rapidly frozen at ⫺80°C. Blood samples were collected simultaneously and centrifuged at 3000g for 5 minutes to obtain plasma, after which aliquots were stored at ⫺80°C until assay.
Noma et al 䡠 Macular Edema with Central Retinal Vein Occlusion Measurement of VEGF and IL-6 IL-6 and VEGF were measured in vitreous fluid samples (from the same eye) and in plasma by enzyme-linked immunosorbent assay using kits for human VEGF and IL-6 (R&D Systems, Minneapolis, MN).13–15 The VEGF kit detected 2 of the 4 VEGF isoforms, which were VEGF121 and VEGF165. The levels of these factors in the vitreous fluid samples and plasma were within the detection ranges of the assays, with the minimum detectable concentration being 15.6 pg/ml for VEGF (intra-assay coefficient of variation [CV] 5.5%, interassay CV 6.9%) and 0.156 pg/ml for IL-6 (intra-assay CV 5.4%, interassay CV 6.7%).
Statistical Analysis All analyses were performed with SAS System 9.1 software (SAS Inc., Cary, NC). Data are presented as the mean ⫾ standard deviation or as medians with interquartile ranges or frequencies. The Student t test was used to compare normally distributed unpaired continuous variables between the 2 groups, and the Mann–Whitney U test was used for other variables with a normal distribution. The chi-square or Fisher exact test was used to compare discrete variables. Wilcoxon’s signed-rank test was performed to compare paired continuous variables. To examine the relation between VEGF or IL-6 and the severity of macular edema, Spearman’s rank-order correlation coefficients were calculated. Two-tailed P values of less than 0.05 were considered to indicate a statistically significant difference.
Results The vitreous fluid level of VEGF (median [interquartile range]) was significantly higher in the patients with CRVO (435 pg/ml [55.8 – 1643]) than in the control subjects (62.4 pg/ml [39.0 – 62.4]; P ⫽ 0.0046; Fig 1A). The vitreous fluid level of IL-6 was also significantly higher in the patients with CRVO (51.2 pg/ml [25.3–127]) than in the controls (1.07 pg/ml [0.77–1.58]; P⬍0.0001; Fig 1B). In the patients with CRVO, there was a significant correlation between the vitreous levels of VEGF and IL-6 ( ⫽ 0.5862, P ⫽ 0.0029) (Fig 2). Vitreous fluid levels of both VEGF and IL-6 were significantly higher in patients with CRVO with ischemia than in those without ischemia (P⬍0.0001 and P ⫽ 0.0003, respectively) (Fig 3A and B). In addition, the vitreous levels of both factors were significantly correlated with the severity of macular edema in the patients with CRVO (VEGF, ⫽ 0.6277, P ⫽ 0.0014; IL-6, ⫽ 0.5543, P ⫽ 0.0047) (Fig 4A and B). There was a significant difference of the VEGF level between the 11 patients with ischemic CRVO who received retinal photocoagulation and the 7 patients without retinal photocoagulation (P ⫽ 0.0109). In contrast, there was no significant difference of IL-6 between the ischemic patients with CRVO with and without retinal photocoagulation (P ⫽ 0.4135). The vitreous level of VEGF was not significantly related to either the extent or the timing of retinal photocoagulation in 14 eyes ( ⫽ ⫺0.0747, P ⫽ 0.7810 and ⫽ ⫺0.3022, P ⫽ 0.1779, respectively). Vitreous levels of IL-6 also showed no significant correlation with the extent or timing of photocoagulation ( ⫽ ⫺0.0736, P ⫽ 0.7874 and ⫽ 0.1473, P ⫽ 0.7131, respectively). Vitreous fluid levels of both VEGF and IL-6 were significantly higher than the corresponding plasma levels in the patients with CRVO (74.7 pg/ml [15.6 –234] and 1.20 pg/ml [1.13–1.84], P ⫽ 0.0010 and P⬍0.0001, respectively) (Table 2). No correlation was observed between the vitreous and plasma levels of VEGF ( ⫽ 0.1758, P ⫽ 0.4129) or IL-6 ( ⫽ ⫺0.2224, P ⫽ 0.2533). In addition, the plasma level of VEGF was significantly higher in hypertensive patients than in those without hypertension (P ⫽
Figure 1. A, VEGF levels in vitreous fluid of control patients and patients with macular edema and CRVO (*P ⫽ 0.0046). B, IL-6 levels in vitreous fluid of control patients and patients with CRVO with macular edema (*P⬍0.0001).
0.0459), but plasma IL-6 showed no significant difference between patients with and without hypertension (P ⫽ 0.1841).
Discussion Our previous study14 showed that vitreous fluid levels of both IL-6 and VEGF were correlated with the severity of
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Ophthalmology Volume 116, Number 1, January 2009 (Fig 3). This finding is supported by previous studies showing that VEGF mRNA expression by retinal pericytes increases as hypoxia becomes more severe,10 whereas IL-6 mRNA expression by cultured endothelial cells exposed to hypoxic condi-
Figure 2. Relation between the vitreous levels of VEGF and IL-6 in patients with macular edema and CRVO ( ⫽ 0.5862, P ⫽ 0.0029).
macular edema in patients with branch retinal vein occlusion. We also demonstrated that the vitreous level of IL-6 was significantly correlated with that of VEGF.14 Furthermore, levels of both VEGF and IL-6 were higher in the vitreous fluid than in the plasma.14 It has been reported that pars plana vitrectomy is one of the potential techniques for the treatment of macular edema and improvement of visual acuity in CRVO,18,19 whereas retinal photocoagulation is ineffective for improving visual acuity in patients with nonperfused CRVO and macular edema.21 Therefore, in this study, we performed pars plana vitrectomy in patients with CRVO with macular edema and investigated the relationship between vitreous fluid levels of VEGF or IL-6 and macular edema in ischemic and nonischemic CRVO. To investigate the sources of VEGF and IL-6, we measured both vitreous fluid and plasma levels. We found that the levels of both VEGF and IL-6 were higher in the vitreous fluid than in the corresponding plasma samples, whereas there was no correlation between the vitreous and plasma levels of either VEGF or IL-6. These results suggest that VEGF and IL-6 in the vitreous fluid came from an intraocular source rather than from the systemic circulation, a conclusion supported by previous reports that VEGF10,24 and IL-625 are produced by ocular cells. The present study also showed that the plasma level of VEGF was significantly higher in hypertensive patients than in those without hypertension, a finding that agrees with the report of Belgore et al.26 This suggests that upregulation of VEGF production by hypertension may be involved in the pathogenesis of CRVO. The present study showed that vitreous levels of both VEGF and IL-6 were significantly higher in patients with CRVO than in control subjects. In addition, the vitreous levels of VEGF and IL-6 were significantly higher in patients with CRVO with retinal ischemia than in those without ischemia
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Figure 3. Correlation between the presence of retinal ischemia and the vitreous levels of VEGF and IL-6. Retinal ischemia was evaluated by calculating the nonperfused area of the retina using the public domain Scion Image program. Vitreous levels of VEGF (A) and IL-6 (B) were significantly higher in patients who had CRVO with ischemia than in those without ischemia (*P⬍0.0001 and *P ⫽ 0.0003, respectively).
Noma et al 䡠 Macular Edema with Central Retinal Vein Occlusion
Figure 4. Correlation between the severity of macular edema and vitreous fluid levels of VEGF and IL-6. The severity of macular edema was evaluated by optical coherence tomography. Higher vitreous levels of VEGF (A) and IL-6 (B) were significantly associated with more severe edema ( ⫽ 0.6277, P ⫽ 0.0014 and ⫽ 0.5543, P ⫽ 0.0047, respectively).
tions also increases in a time-dependent manner.27–29 Thus, we hypothesized that the elevation of intraocular VEGF and IL-6 levels may contribute to the occurrence of macular edema associated with CRVO. In this study, we measured the foveal thickness by optical coherence tomography to assess the severity of macular edema in our patients with CRVO and demonstrated that vitreous fluid levels of VEGF and IL-6 were significantly correlated with the severity of macular edema (Fig 4). In addition, the vitreous levels of these 2 molecules showed a significant correlation. Production of VEGF is induced by
hypoxia,10 and VEGF increases endothelial permeability by causing changes to tight junctions.8,9 In patients with CRVO, breakdown of the blood-retinal barrier occurs because of damage to capillary endothelial cells.30 Accordingly, it seems likely that vascular occlusion induces the expression of VEGF via hypoxia in patients with CRVO, resulting in breakdown of the blood-retinal barrier and increased vascular permeability. This hypothesis is supported by a previous report that the intravitreous injection of VEGF induces retinal edema, dilated and tortuous vessels, and capillary closure in adult primates,31 as well as by recent reports that treatment with an anti-VEGF monoclonal antibody (bevacizumab) is effective for macular edema in CRVO.16,17 IL-6 has been reported to increase endothelial permeability in vitro by promoting the rearrangement of actin filaments (which changes the shape of endothelial cells) in a dose- and time-dependent manner.12 It is also possible that IL-6 induces an increase of VEGF production in patients with CRVO, thus contributing to macular edema. That is, both VEGF and IL-6 may directly increase vascular permeability, or IL-6 may indirectly increase vascular permeability via upregulation of VEGF. Accordingly, further investigations are needed to define the ocular interaction between IL-6 and VEGF, as well as the role of IL-6 in the pathogenesis of macular edema in patients with CRVO. The present study showed that patients with ischemic CRVO who received retinal photocoagulation before surgery had lower VEGF levels than those without photocoagulation. This result is in agreement with previous reports4 and is supported by previous findings that scatter photocoagulation reverses tissue hypoxia in miniature pigs with experimental vasoproliferative microangiopathy32 and that hyperoxia reduces VEGF production in the ischemic retina.33 However, in 14 patients who received retinal photocoagulation before surgery, the vitreous levels of VEGF and IL-6 were not significantly correlated with the extent or timing of photocoagulation. Laser photocoagulation has been shown to increase the expression of cytokines, including VEGF, by cultured human retinal pigment epithelial (RPE) cells, but upregulation of VEGF production was observed at the early period of 6 hours after photocoagulations and then VEGF returned to its basal level by 72 hours.34 In contrast, Itaya et al35 reported that the peak VEGF level occurs on day 3 in vivo, coinciding with the peak of macrophage infiltration, and that the difference from in vitro data may arise because recruited macrophages contribute more to the upregulation of VEGF than RPE cells or because secretion of VEGF may be induced by macroTable 2. Vitreous Fluid and Plasma Levels of Vascular Endothelial Growth Factor and Interleukin-6 in Patients with Central Retinal Vein Occlusion
VEGF (pg/ml) IL-6 (pg/ml)
Vitreous Fluid
Plasma
P Value
435 (55.8–1643) 51.2 (25.3–127)
74.7 (15.6–234) 1.20 (1.13–1.84)
0.0010 ⬍0.0001
IL ⫽ interleukin; VEGF ⫽ vascular endothelial growth factor. Data are medians with interquartile ranges.
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Ophthalmology Volume 116, Number 1, January 2009 phage-RPE interactions. Furthermore, it was reported that changes of the VEGF mRNA level in the burned area of the retina after laser photocoagulation in miniature pigs were confined to RPE cells, with mRNA expression being low immediately after photocoagulation and returning to normal by 42 days.36 Moreover, after photocoagulation of the rabbit retina, the level of IL-6 was reported to increase at 24 hours and then return to baseline by 72 hours.37 However, the kinetics of IL-6 in human vitreous fluid after photocoagulation have been unclear. These reports and our results suggest that any increase of VEGF or IL-6 expression in the retina after photocoagulation is transient, and that both might decrease again relatively early. Further investigations will be needed to clarify the relationship between the extent and timing of photocoagulation and the vitreous levels of VEGF or IL-6. We found that the vitreous fluid levels of both IL-6 and VEGF were higher in patients who had ischemic CRVO with macular edema than in patients who had nonischemic CRVO. Vitreous levels of both IL-6 and VEGF were significantly correlated with the severity of macular edema in patients with CRVO. In addition, there was a significant correlation between the vitreous levels of these 2 molecules. Our findings suggest that VEGF increases vascular permeability in patients with CRVO with macular edema and that IL-6 also contributes to increased vascular permeability by acting together with or via VEGF. Acknowledgment. We thank Katsunori Shimada (Department of Biostatistics, STATZ Corporation, Tokyo) for assistance with the statistical analysis.
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Footnotes and Financial Disclosures Originally received: May 8, 2008. Final revision: September 5, 2008. Accepted: September 22, 2008.
4
Manuscript no. 2008-556.
1
Department of Ophthalmology, Yachiyo Medical Center, Tokyo Women’s Medical University, Chiba, Japan.
2
Department of Ophthalmology and Visual Science, Graduate School of Biomedical Sciences, Hiroshima University, Hiroshima, Japan.
3
Department of Ophthalmology, Yodogawa Christian Hospital, Osaka, Japan. Department of Ophthalmology, Tokyo Women’s Medical University, Tokyo, Japan. Financial Disclosure(s): The authors have no proprietary or commercial interest in any materials discussed in this article.
5
Department of Ophthalmology, University of Tokyo Graduate School of Medicine, Tokyo, Japan.
Correspondence: Hidetaka Noma, MD, Department of Ophthalmology, Yachiyo Medical Center, Tokyo Women’s Medical University, 477–96, Owada-shinden, Yachiyo, Chiba 276 – 8524, Japan. E-mail: [email protected].
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