Relationship between vascular endothelial growth factor and interleukin-6 in diabetic retinopathy

Triamcinolone reduces neovascularization, capillary density and IGF-1 receptor phosphorylation in a model of oxygen-induced retinopathy

PURPOSE

To study the effects of intravitreous triamcinolone acetonide (TA) on neovascularization (NV), capillary density, and retinal endothelial cell (REC) viability in a model of oxygen-induced retinopathy (OIR).

METHODS

Newborn rats exposed to OIR underwent intravitreous injections (right eye) at day 14 to achieve intravitreous concentrations of: dexamethasone (DEX) (0.3 mg/mL), triamcinolone (TA; 0.4-4 mg/mL), or PBS. Animals were removed to room air and at day 18, retinal flatmounts were assayed for clock hours of NV, percent peripheral avascular retina, capillary density, apoptosis, and VEGF protein. At day 15, retinas were assayed for insulin-like growth factor (IGF)-1 receptor phosphorylation (IGF-1Rphos). Human RECs exposed to TA were assayed for trypan blue exclusion or activated caspase-3.

RESULTS

TA but not DEX or PBS reduced NV (ANOVA, P < 0.001), capillary density (ANOVA, P < 0.001), and systemic weight gain (ANOVA, P = 0.002). VEGF protein was not different between TA- and PBS-injected or noninjected groups. Apoptosis was not increased in vivo or in vitro between groups, but there was a dose-dependent toxic effect of TA on cultured RECs (P < 0.001). At day 15, retinas from the 4 mg/mL TA-injected OIR group had a trend toward reduced IGF-1Rphos compared with room air-raised PBS- or non-injected OIR groups.

CONCLUSIONS

TA caused dose-dependent reductions in NV, retinal vascularization, and systemic weight gain associated with a reduction in IGF-1Rphos. Long-term studies are needed to assess TA toxicity in vivo. TA doses should be carefully considered before administering the drug in diseases with ongoing retinal vascular development, such as retinopathy of prematurity.

Involvement of circulating endothelial progenitor cells and vasculogenic factors in the pathogenesis of diabetic retinopathy

PURPOSE

Retinal neovascularization in diabetes has been thought to follow the release of local angiogenic factors in the retina. We hypothesize that neovascularization of diabetic retinopathy is a systemic vasculogenesis rather than a local angiogenesis. Thus, we evaluate the concentrations of circulating endothelial progenitor cells (EPCs) and stem cell modulation factors such as vascular endothelial growth factor (VEGF), erythropoietin (Epo), and substance p (SP) in the peripheral blood of diabetic retinopathy patients.

METHODS

We studied 15 normal controls and 45 type II diabetic patients (no DR group (n=15), NPDR group (n=15), and PDR group (n=15)). We measured circulating CD34+mononuclear cells (CD34+MNCs), c-Kit+mononuclear cells (c-Kit+MNCs) by flow cytometry. VEGF, Epo, and SP in the peripheral blood were measured by ELISA.

RESULTS

The circulating CD34+MNCs and c-Kit+MNCs increased in the NPDR and PDR groups compared with the control group (P<0.01). Serum level of VEGF increased in the NPDR and PDR groups compared with the control group (P<0.05). The level of Epo elevated exclusively in the no DR group compared with the other three groups (P<0.01). Circulating SP level increased in the NPDR and PDR groups compared with the control group (P<0.05). SP and CD34+MNCs were shown to have increased correlation according to the diabetic retinopathy in the NPDR and PDR groups (r=0.440, P<0.05 and r=0.460, P<0.05, respectively).

CONCLUSIONS

The present study is the first to demonstrate that CD34+MNCs, c-Kit+MNCs and their modulator are elevated in diabetic retinopathy patients. Therefore, it is possible that circulating EPCs and serum Epo, VEGF, and SP may be involved in the progression of diabetic retinopathy.

The role of cytokines and trophic factors in epiretinal membranes: Involvement of signal transduction in glial cells

Idiopathic epiretinal membranes (ERMs) in the macular region can cause a reduction in vision and sometimes recurs after surgical removal, but its pathogenic mechanisms are still unknown. On the other hand, the presence of secondary ERMs has been associated with various clinical conditions including proliferative diabetic retinopathy (PDR) and proliferative vitreoretinopathy (PVR). Recent studies have shown a significant association between clinical grades of PDR or PVR, and the expression levels of specific cytokines and/or growth factors in the vitreous fluid. Expression of these factors and their receptors are also observed in secondary ERMs. ERMs are composed of many cell types such as retinal pigment epithelial cells and vascular endothelial cells, however the role of glial cells is yet unclear. Interestingly, glial cells in ERMs express some trophic factor receptors and transcription factors, such as NF-kappaB, suggesting an involvement of glial signal transduction in the pathogenesis of ERMs. In this review, we summarize recent progress regarding the clinical and laboratory findings of ERMs.

Risk evaluation of outcome of vitreous surgery based on vitreous levels of cytokines

AIM

To ascertain whether vitreous and plasma levels of vascular endothelial growth factor (VEGF), interleukin-6 (IL-6) and fundus findings could predict the outcome of vitreous surgery in patients with proliferative diabetic retinopathy (PDR).

METHODS

Vitreous fluid samples were obtained during vitreoretinal surgery from 73 consecutive eyes with PDR. The levels of VEGF and IL-6 in vitreous fluid and plasma were determined by enzyme-linked immunosorbent assay. Patients were prospectively followed for 6 months and the postoperative outcome was analysed by logistic regression analysis.

RESULTS

No improvement and/or progression of PDR occurred in 23 (32%) of the 73 eyes (progression group). The vitreous levels of VEGF and IL-6 were significantly higher in eyes from the progression group than in eyes with regression of PDR (regression group) (P=0.0032 and 0.0088, respectively). Multivariate logistic regression analysis showed that higher vitreous levels of VEGF were associated with the progression of PDR after vitreous surgery (odds ratio 2.72, P=0.0003).

CONCLUSIONS

High vitreous levels of VEGF identified as a significant risk factor for the outcome of vitreous surgery in patients with PDR. A model was developed to predict the probability of PDR progression and measurement of the vitreous level of VEGF may be useful for predicting the outcome of surgery.

Determination of vitreous interleukin-1 (IL-1) and tumour necrosis factor (TNF) levels in proliferative diabetic retinopathy

We measured interleukin-1 beta (IL-1beta) and tumour necrosis factor-alpha (TNF-alpha) in the vitreous humour and serum of patients with proliferative diabetic retinopathy (PDR), in order to determine the role of these cytokines in the pathogenesis of the disease. Vitreous and serum samples were collected from 21 patients with PDR who were undergoing pars plana vitrectomy. Control vitreous samples were obtained from cadavers and control serum samples from healthy subjects. The cytokines were measured by enzyme-linked immunosorbent assay. Vitreous IL-1beta and TNF-alpha concentrations in patients with PDR exceeded those of controls (P<0.05), as did serum IL-1beta and TNF-alpha. We suggest that increased vitreous IL-1beta and TNF-alpha levels may play a significant role in the pathogenesis of PDR, which features abnormal cell proliferation and neovascularisation.

Risk evaluation of outcome of vitreous surgery for proliferative diabetic retinopathy based on vitreous level of vascular endothelial growth factor and angiotensin II

AIMS

To ascertain whether measurement of the vitreous fluid levels of vascular endothelial growth factor (VEGF) or angiotensin II (Ang II) could predict the outcome of vitreous surgery in patients with proliferative diabetic retinopathy (PDR).

METHODS

A prospective observational case study was performed in 61 consecutive patients (61 eyes) with PDR who underwent vitreoretinal surgery. Vitreous fluid samples were obtained during surgery. The VEGF level in vitreous fluid and plasma was determined by enzyme linked immunosorbent assay, while the Ang II level was measured by radioimmunoassay. Patients were prospectively followed for 6 months and the postoperative outcome was analysed by logistic regression analysis.

RESULTS

No improvement and/or progression of PDR was seen in 15 (25%) of the 61 eyes. Vitreous levels of VEGF and Ang II were significantly higher in eyes with progression of PDR than in eyes with regression of PDR (p = 0.0044, and p = 0.0178, respectively). Multivariate logistic regression analysis showed that the vitreous VEGF level increased along with the progression of PDR after vitreous surgery (odds ratio 2.48, p = 0.0008).

CONCLUSION

A high vitreous fluid VEGF level is associated with a significant risk of postoperative progression of PDR. The vitreous level of VEGF at the time of surgery may be a useful predictor of the outcome.

Inflammatory markers and retinopathy in pregnancies complicated with Type I diabetes

AIM

The relation of maternal cytokine levels to retinopathy progression during diabetic pregnancy is a less studied subject. Therefore, we investigated levels of systemic proinflammatory markers, C-reactive peptide (CRP), interleukin-6 (IL-6) and circulating vascular cell adhesion molecule-1 (VCAM-1) during pregnancy and postpartum in relation to the progression of diabetic retinopathy (DR).

METHODS

A prospective follow-up study of 39 pregnant women with Type I diabetes and eight nondiabetic pregnant women was performed. DR was graded from fundus photographs. Plasma levels of systemic proinflammatory markers were measured by immunofluorometric assay (CRP) and by enzyme-linked immunosorbent assay (IL-6 and VCAM-1) in the first, second (diabetics only), third trimester of pregnancy, and 3 and 6 months postpartum (diabetics only).

RESULTS

Our diabetic women had good glycaemic control (HbA1c 6.9 +/- 0.8). The levels of IL-6, VCAM-1, and CRP did not differ between diabetic and nondiabetic women throughout pregnancy and postpartum (repeated measures ANOVA between the groups). An association between CRP and progression of retinopathy was observed in diabetic women (P = 0.037). Additional evidence of inter-relationship could be revealed as CRP was higher in those diabetic women with worse glycaemic control (HbA1c) (P = 0.038).

CONCLUSIONS

During pregnancy and postpartum, levels of proinflammatory factors (IL-6, CRP, VCAM-1) seem to be generally similar in Type I diabetic women compared to nondiabetic controls. However, CRP levels were higher in those diabetic women with progression of retinopathy and in those with worse glycaemic control.

Aqueous humor levels of cytokines are related to vitreous levels and progression of diabetic retinopathy in diabetic patients

BACKGROUND

Cytokine levels are elevated in the ocular fluid of diabetic patients. It is unclear whether aqueous humor levels of vascular endothelial growth factor (VEGF) and interleukin-6 (IL-6) are related to the vitreous fluid levels of these substances and to the progression of diabetic retinopathy.

METHODS

Aqueous humor and vitreous fluid samples were obtained during cataract and vitreous surgery from ten eyes of ten patients with diabetic macular edema and 26 eyes of 26 patients with proliferative diabetic retinopathy (PDR). The VEGF and IL-6 levels in aqueous humor, vitreous fluid, and plasma were measured by enzyme-linked immunosorbent assay.

RESULTS

VEGF and IL-6 levels in aqueous humor were significantly correlated with those in vitreous fluid (rho=0.793 and rho=0.737, respectively). VEGF levels in aqueous humor and vitreous fluid were significantly correlated with the corresponding IL-6 levels (rho=0.631 and rho=0.687, respectively). The aqueous and vitreous levels of VEGF were significantly correlated with the severity of diabetic retinopathy (rho=0.659 and rho=0.771, respectively). Aqueous and vitreous levels of IL-6 were also significantly correlated with the severity of diabetic retinopathy (rho=0.742 and rho=0.746, respectively). Aqueous and vitreous levels of both VEGF and IL-6 were significantly higher in the patients with active PDR than those in quiescent PDR.

CONCLUSIONS

Our results suggest that there is a significant relationship between VEGF and IL-6 levels in aqueous humor and in vitreous fluid. Measurement of the aqueous levels of VEGF and IL-6 may be useful to analyze the pathogenesis of diabetic retinopathy and to predict disease activity.

Pathogenesis of diabetic retinopathy and the renin-angiotensin system

Despite the beneficial effects of good glycaemic control, loss of vision because of diabetic retinopathy (DR) still occurs. Recent studies have suggested that hypertension is a risk factor for the development and progression of DR and that blood pressure reduction can delay the progression of retinopathy. The renin-angiotensin system is activated by chronic hyperglycaemia, and the vitreous fluid level of angiotensin II (AII) is elevated in patients with proliferative diabetic retinopathy and diabetic macular oedema. AII increases vascular permeability and promotes neovascularization. It has been suggested that an autocrine-paracrine relationship may exist between AII and vascular endothelial growth factor in the ocular tissues. Accordingly, angiotensin-converting enzyme inhibitors or AII Type 1 (AT1) receptor blockers may be useful therapeutic agents for preventing the progression of DR.

High glucose enhances interleukin-6-induced vascular endothelial growth factor 165 expression via activation of gp130-mediated p44/42 MAPK-CCAAT/enhancer binding protein signaling in gingival fibroblasts

Diabetic patients are susceptible to severe inflammatory periodontitis manifesting as swollen gingiva with bleeding, but the underlying mechanism is not well understood. Our purpose was to determine the effect of a high glucose (HG) condition on the interleukin-6/soluble interleukin-6 receptor (IL-6/sIL-6R)-induced activation of signaling and vascular endothelial growth factor (VEGF) expression in human gingival fibroblasts (HGFs). In this study, HGFs were cultured for at least two passages under a normal glucose (NG; 5.5 mM) condition or high glucose (25 mM) condition. Importantly, the HG condition significantly induced expression of gp130 mRNA in HGFs compared with levels in control cells. Consistent with the expression of its mRNA, the HG condition also increased the expression of gp130 protein, and phosphorylation of the tyrosine residue by gp130 was enhanced significantly by IL-6/sIL-6R stimulation. Furthermore, the HG condition enhanced the IL-6/sIL-6R-induced phosphorylation of p44/42 MAPK and led to subsequent activation of CCAAT/enhancer binding protein in nuclei. In contrast, there was no significant difference in phosphorylation of JNK between the HG and NG condition. Interestingly, HGFs increased IL-6/sIL-6R-induced VEGF165 mRNA expression and VEGF165 secretion under the HG condition compared with levels under the NG condition. In contrast, the induction of VEGF165 secretion was partially inhibited by PD98059 (selective p44/42 MAPK inhibitor) under the HG condition. In addition, the VEGF165 secretion was completely inhibited by the combination of PD98059 and SP600125 (JNK inhibitor). Our findings suggest that the HG condition indirectly increases VEGF expression via activation of gp130-mediated p44/42 MAPK-CCAAT/enhancer binding protein signaling in HGFs. Thus, elevated VEGF secretion in HGFs under the HG condition may play a role in the development of the severe periodontitis observed in diabetic patients.

Vitreous levels of interleukin-6 and vascular endothelial growth factor are related to diabetic macular edema

PURPOSE

To investigate whether interleukin-6 (IL-6) or vascular endothelial growth factor (VEGF) is related to diabetic macular edema (DME) in subjects without posterior vitreous detachment (PVD).

DESIGN

Retrospective case-control study.

PARTICIPANTS

Twenty-six subjects who had DME without PVD and 12 subjects who had nondiabetic ocular disease (the control group).

METHODS

Vitreous fluid samples were obtained at vitreoretinal surgery, and the IL-6 and VEGF levels in vitreous fluid and plasma were measured by enzyme-linked immunosorbent assay.

MAIN OUTCOME MEASURES

Vitreous levels of IL-6 and VEGF in DME subjects without PVD.

RESULTS

The vitreous levels of both IL-6 and VEGF were significantly higher in the subjects with DME than in control subjects (P<0.0001 and P<0.0001, respectively). The vitreous level of IL-6 was significantly correlated with that of VEGF (P<0.0001). Vitreous levels of both IL-6 and VEGF were significantly higher in subjects with hyperfluorescent DME than in those with minimally fluorescent DME (P = 0.0008 and P = 0.0038, respectively).

CONCLUSIONS

We found that the levels of both IL-6 and VEGF were elevated in the vitreous fluid of subjects with hyperfluorescent DME. Our results suggest that IL-6 and VEGF may promote an increase of vascular permeability in DME subjects without PVD. Interleukin-6 may possibly induce an increase of vascular permeability through a paracrine effect on VEGF in these subjects.

Increased concentration of pentosidine, an advanced glycation end product, and interleukin-6 in the vitreous of patients with proliferative diabetic retinopathy

To investigate the relationship between advanced glycation end products (AGEs) and interleukin-6 (IL-6) in the development of diabetic retinopathy, we determined the concentrations of pentosidine, a well-characterized AGE, and IL-6 in the vitreous of 62 patients with proliferative diabetic retinopathy (PDR) and 50 non-diabetic control subjects. We also investigated the effect of AGEs on the production of IL-6 by human retinal Müller cells. The levels of pentosidine and IL-6 in the vitreous of patients with PDR were significantly higher compared with controls. In patients with PDR with vitreous hemorrhage (VH), the mean vitreous concentration of IL-6 was significantly higher than that in PDR patients without VH. There was a strong positive correlation between the vitreous levels of pentosidine and IL-6. Levels of IL-6 were strikingly higher in the vitreous compared with the serum and there was no correlation between IL-6 concentrations in the two fluids. Treatment of Müller cells with AGEs for 48 h resulted in a dose-dependent increase of IL-6 in the culture medium. These results suggest that increased formation of AGEs in the vitreous may be involved in the development of diabetic retinopathy by inducing the production of IL-6 from retinal Müller cells.

Prediction of macular edema exacerbation after phacoemulsification in patients with nonproliferative diabetic retinopathy

PURPOSE

To ascertain whether the aqueous humor levels of vascular endothelial growth factor (VEGF), interleukin-6 (IL-6), and protein can predict the postoperative exacerbation of macular edema in patients with nonproliferative diabetic retinopathy (NPDR) after phacoemulsification surgery for cataract.

SETTING

Department of Ophthalmology, Diabetes Center, Tokyo Women's Medical University, Tokyo, Japan.

METHODS

This prospective study included 104 consecutive patients (104 eyes) with NPDR who had cataract surgery. The concentrations of VEGF and IL-6 in aqueous humor specimens obtained during cataract surgery were measured by enzyme-linked immunosorbent assay. Patients were followed for 6 months to assess the postoperative exacerbation of macular edema.

RESULTS

Ninety patients (87%) achieved a visual acuity of 20/40 or better. Exacerbation of macular edema was seen in 30 eyes (29%) after 6 months. Hypertension and the aqueous levels of VEGF, IL-6, and protein were significantly correlated with the exacerbation of macular edema (odds ratio 1.16, 1.33, 1.27, and 1.28, respectively). In contrast, there was no correlation between the exacerbation of macular edema and other systemic factors. Multivariate logistic regression analysis showed that the aqueous VEGF level increase of 100 pg/mL increased the macular edema after phacoemulsification surgery (odds ratio 1.53).

CONCLUSIONS

A high VEGF level in the aqueous humor predicted a significant risk for the postoperative exacerbation of macular edema. A model was developed to predict the risk exacerbation.

Angiotensin II and vascular endothelial growth factor in the vitreous fluid of patients with diabetic macular edema and other retinal disorders

PURPOSE

To investigate the correlation between angiotensin II (AII) or vascular endothelial growth factor (VEGF) levels in the vitreous fluid and the severity of diabetic macular edema (DME).

DESIGN

A case-control study.

METHODS

Vitreous fluid samples were obtained at the time of vitreoretinal surgery from 20 eyes of 20 patients with DME, 6 eyes of 6 diabetic patients without retinopathy, and 14 eyes of 14 nondiabetic patients. The VEGF levels in vitreous fluid and plasma were determined by enzyme-linked immunosorbent assay, while AII levels were measured by radioimmunoassay.

RESULTS

The vitreous concentration of VEGF was significantly higher in patients with DME than in nondiabetic patients or diabetic patients without retinopathy (P <.0001 and P <.0001, respectively). Vitreous levels of AII were also higher in patients with DME than in nondiabetic patients (P =.0082). The vitreous concentration of AII was significantly correlated with that of VEGF (P =.0022). Vitreous concentrations of both AII and VEGF were significantly higher in patients with hyperfluorescent DME than in those with hypofluorescent (P =.0228 and P =.0068, respectively).

CONCLUSIONS

We found that the levels of both AII and VEGF were elevated in the vitreous fluid of patients with hyperfluorescein DME. Our results suggest that both AII and VEGF are related to the increase of vascular permeability in DME.