Angio-Fibrotic Switch Table 2. Odds ratio (OR) and 95% confidence interval (95%CI) of the univariate ordinal logistic regression models with degree of neovascularization or fibrosis as outcome in the PDR population (N = 32), respectively. Variable Female gender Age Types of diabetes Degree of haemorrhage Degree of neovascularization Degree of fibrosis CTGF VEGF Ratio CTGF/log10(VEGF) doi:10.1371/journal.pone.0002675.t002 Contrast per year II vs. I 1 vs. 0 2 vs. 0 3 vs. 0 0 vs. 2 1 vs. 2 2 vs. 1 3 vs. 1 per unit increase per 10 fold increase per unit increase Degree of neovascularization Degree of fibrosis OR 0.97 1 1.27 0.7 2.79 1.64 1.84 0.88 1.05 94.3 1.19 [95% CI] [0.24–3.89] [0.95–1.06] [0.32–5.07] [0.08–6.25] [0.48–16.26] [0.22–12.01] [0.10–33.09] [0.05–16.15] [0.97–1.15] [3.92 – Inf] [0.86–1.65] P-value 0.965 0.939 0.74 0.592 0.61 0.235 0.005 0.283 OR 1.25 0.98 3.21 0.65 1 0.21 0.39 3.18 1.14 0.33 2.05 [95% CI] [0.32–4.89] [0.93–1.04] [0.77–13.37] [0.07–6.29] [0.19–5.16] [0.02–1.81] [0.02–8.61] [0.70–14.53] [1.03–1.27] [0.05–2.39] [1.18–3.54] P-value 0.746 0.568 0.109 0.497 0.233 0.014 0.27 0.01 influence on the bioavailability of CTGF as well [45–47]. Furthermore, several growth factors have been suggested to play a role in angiogenesis and fibrosis in ocular disease [5,6], which may also have influence on the presence and availability of VEGF and/or CTGF. Our findings suggest that the balance between VEGF and CTGF determines the angio-fibrotic switch. This concept predicts that a sharp decline of VEGF levels in a patient with active neovascularization due to PDR inhibits angiogenesis, cause the angio-fibrotic switch and temporarily increase fibrosis. In a non- systematic survey, we studied the clinical files of a small series of four PDR patients with active neovascularization treated with intravitreal bevacizumab, an anti-VEGF antibody, and/or pan- retinal laser. Pan-retinal photocoagulation is a therapy which destroys large areas of retina, and which is known to markedly reduce intra-ocular VEGF levels [26]. In these four patients, we did indeed observe regression of neovascularization and the predicted temporary increase in fibrosis. In another patient with branch retinal vein occlusion complicated by focal pre-retinal neovascularization, fibrosis did not follow laser treatment. This suggests that for the angio-fibrotic switch to occur, CTGF levels need to reach a threshold value and a sufficient number of target cells must be able to elicit the fibrotic response. Therefore, intra- ocular fibrosis appears to be a tightly regulated on-off response, like intra-ocular angiogenesis. Existing literature supports our general concept. The role of CTGF as pro-fibrotic factor is well-established in various organs such as skin and kidney [11–13,15,27–31,43,48–50] and recently in the retina as well [10,51]. Furthermore, mRNA and protein of CTGF is upregulated by VEGF in retinal endothelial cells [16–18] and co-localizes with VEGF in neovascular subretinal membranes of patients with age-related macular disease [23]. In these Figure 3. Fundus photographs of a patient with proliferative diabetic retinopathy and new vessels (nv) along the lower vascular arcade, before (A) and 8 months after (B) an injection with bevacizumab followed by pan-retinal photocoagulation. Note the increase in fibrosis (f) after anti-VEGF and laser treatment (B). doi:10.1371/journal.pone.0002675.g003 PLoS ONE | www.plosone.org 5 July 2008 | Volume 3 | Issue 7 | e2675