Fibrous membranes in diabetic retinopathy and bevacizumab

Cell-Matrix Interactions in the Eye: From Cornea to Choroid

The extracellular matrix (ECM) plays a crucial role in all parts of the eye, from maintaining clarity and hydration of the cornea and vitreous to regulating angiogenesis, intraocular pressure maintenance, and vascular signaling. This review focuses on the interactions of the ECM for homeostasis of normal physiologic functions of the cornea, vitreous, retina, retinal pigment epithelium, Bruch's membrane, and choroid as well as trabecular meshwork, optic nerve, conjunctiva and tenon's layer as it relates to glaucoma. A variety of pathways and key factors related to ECM in the eye are discussed, including but not limited to those related to transforming growth factor-β, vascular endothelial growth factor, basic-fibroblastic growth factor, connective tissue growth factor, matrix metalloproteinases (including MMP-2 and MMP-9, and MMP-14), collagen IV, fibronectin, elastin, canonical signaling, integrins, and endothelial morphogenesis consistent of cellular activation-tubulogenesis and cellular differentiation-stabilization. Alterations contributing to disease states such as wound healing, diabetes-related complications, Fuchs endothelial corneal dystrophy, angiogenesis, fibrosis, age-related macular degeneration, retinal detachment, and posteriorly inserted vitreous base are also reviewed.

APOPTOSIS AND ANGIOFIBROSIS IN DIABETIC TRACTIONAL MEMBRANES AFTER VASCULAR ENDOTHELIAL GROWTH FACTOR INHIBITION: Results of a Prospective Trial. Report No. 2

PURPOSE

We sought to characterize the angiofibrotic and apoptotic effects of vascular endothelial growth factor (VEGF)-inhibition on fibrovascular epiretinal membranes in eyes with traction retinal detachment because of proliferative diabetic retinopathy.

METHODS

Membranes were excised from 20 eyes of 19 patients (10 randomized to intravitreal bevacizumab, 10 controls) at vitrectomy. Membranes were stained with antibodies targeting connective tissue growth factor (CTGF) or VEGF and colabeled with antibodies directed against endothelial cells (CD31), myofibroblasts, or retinal pigment epithelium markers. Quantitative and colocalization analyses of antibody labeling were obtained through immunofluorescence confocal microscopy. Masson trichrome staining, cell counting of hematoxylin and eosin sections, and terminal dUTP nick-end labeling staining were performed.

RESULTS

High levels of fibrosis were observed in both groups. Cell apoptosis was higher (P = 0.05) in bevacizumab-treated membranes compared with controls. The bevacizumab group had a nonsignificant reduction in colocalization in CD31-CTGF and cytokeratin-VEGF studies compared with controls. Vascular endothelial growth factor in extracted membranes was positively correlated with vitreous levels of VEGF; CTGF in extracted membranes was negatively correlated with vitreous levels of CTGF.

CONCLUSION

Bevacizumab suppresses vitreous VEGF levels, but does not significantly alter VEGF or CTGF in diabetic membranes that may be explained by high baseline levels of fibrosis. Bevacizumab may cause apoptosis within fibrovascular membranes.

Bevacizumab modulates the process of fibrosis in vitro

BACKGROUND

Fibrosis is the most common side effect after anti-vascular epithelial growth factor (VEGF) therapy (intravitreal bevacizumab) for retinal or choroidal neovascularization. This study was to investigate the efficacy of bevacizumab on the expressions of fibrosis-related cytokines in human umbilical vein endothelial cells (HUVECs) in vitro.

METHODS

Cultured HUVECs were divided into groups of controls (group 1), hypoxia (group 2) and hypoxia combined with bevacizumab (group 3). No treatment was given in group 1. In group 2, cobalt(II) chloride (CoCl₂) (200 μm) was added to the medium. In group 3, in addition to CoCl₂, bevacizumab was mixed in the medium, with a final concentration of 0.25 mg/mL, roughly equal to the concentration used clinically. The expressions of connective tissue growth factor (CTGF), transforming growth factor-β₂ (TGF-β₂) and basic fibroblast growth factor-2 (bFGF-2) were evaluated by SYBR green real-time polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay at 6 h, 12 h, 24 h and 48 h. Matrix metalloproteinases (MMP)-2 was detected by SYBR green real-time PCR and Western blotting at each time point.

RESULTS

Both messenger RNA and protein levels of CTGF, bFGF, TGF-β₂ and MMP-2 in group 2 were higher than group 1 (P < 0.05). In group 3, the expressions of CTGF, bFGF, TGF-β₂ and MMP-2 were upregulated compared with group 2 (P < 0.05).

CONCLUSIONS

Bevacizumab at clinical doses can exert pro-fibrotic effects on HUVECs by upregulating the expressions of CTGF, bFGF, TGF-β₂ and MMP-2. This may be involved in fibrosis after anti-VEGF therapy.

Functional and molecular characterization of ex vivo cultured epiretinal membrane cells from human proliferative diabetic retinopathy

Characterization of the cell surface marker phenotype of ex vivo cultured cells growing out of human fibrovascular epiretinal membranes (fvERMs) from proliferative diabetic retinopathy (PDR) can give insight into their function in immunity, angiogenesis, and retinal detachment. FvERMs from uneventful vitrectomies due to PDR were cultured adherently ex vivo. Surface marker analysis, release of immunity- and angiogenesis-pathway-related factors upon TNF α activation and measurement of the intracellular calcium dynamics upon mechano-stimulation using fluorescent dye Fura-2 were all performed. FvERMs formed proliferating cell monolayers when cultured ex vivo, which were negative for endothelial cell markers (CD31, VEGFR2), partially positive for hematopoietic- (CD34, CD47) and mesenchymal stem cell markers (CD73, CD90/Thy-1, and PDGFR β ), and negative for CD105. CD146/MCAM and CD166/ALCAM, previously unreported in cells from fvERMs, were also expressed. Secretion of 11 angiogenesis-related factors (DPPIV/CD26, EG-VEGF/PK1, ET-1, IGFBP-2 and 3, IL-8/CXCL8, MCP-1/CCL2, MMP-9, PTX3/TSG-14, Serpin E1/PAI-1, Serpin F1/PEDF, TIMP-1, and TSP-1) were detected upon TNF α activation of fvERM cells. Mechano-stimulation of these cells induced intracellular calcium propagation representing functional viability and role of these cells in tractional retinal detachment, thus serving as a model for studying tractional forces present in fvERMs in PDR ex vivo.

Altered vascular microenvironment by bevacizumab in diabetic fibrovascular membrane

PURPOSE

The purpose of this study was to evaluate the impact of intravitreal bevacizumab (IVB) on three cellular components (vascular endothelial cells, pericytes, and myofibroblasts) of the vascular microenvironment in fibrovascular membranes (FVMs) of patients with proliferative diabetic retinopathy.

METHODS

Immunohistological studies with antibodies of CD34, αSMA, and transforming growth factor-β were performed on 20 surgical specimens obtained during a pars plana vitrectomy from 8 IVB-treated eyes, whereas 12 remained untreated. Four different indexes of vascular phenotype (vascular area, vascular major axis, CD34 endothelial area, and blood vessel density) and αSMA expression in vascular and stromal components were quantitatively analyzed.

RESULTS

The intraluminal area of blood vessels, CD34 endothelial area, and the blood vessel density in IVB-treated FVMs were significantly less than in untreated FVMs. The number of CD34 blood vessels in IVB-treated FVMs was similar to that in untreated FVMs. Intravitreal bevacizumab could not affect vascular and stromal αSMA area significantly. However, the ratio of vascular αSMA area/CD34 area was significantly higher in IVB-treated FVMs than in untreated FVMs. Transforming growth factor-β expression could be observed in the IVB-treated FVM.

CONCLUSION

Intravitreal bevacizumab might primarily affect blood vessels, and the effects on pericytes and myofibroblasts might be secondary. Intravitreal bevacizumab treatment regulates vascular microenvironment by the contraction of blood vessels, the increasing pericyte ratio, and transforming growth factor-β expression in FVMs of patients with proliferative diabetic retinopathy.

Thioredoxin Interacting Protein (TXNIP) and Pathogenesis of Diabetic Retinopathy

Chronic hyperglycemia (HG)-associated reactive oxygen/nitrogen species (ROS/RNS) stress and low grade inflammation are considered to play critical roles in the development of diabetic retinopathy (DR). Excess glucose metabolic flux through the aldose reductase/polyol pathway, advanced glycation end product (AGE) formation, elevated hexosamine biosynthesis pathway (HBP), diacyl glycerol/PKC activation, and mitochondrial ROS generation are all implicated in DR. In addition, endoplasmic reticulum stress/unfolded protein response (er-UPR) and deregulation of mitochondrial quality control by autophagy/mitophagy are observed causing cellular bioenergetic deficiency and injury. Recently, a pro-oxidant and pro-apoptotic thioredoxin interacting protein (TXNIP) was shown to be highly upregulated in DR and by HG in retinal cells in culture. TXNIP binds to thioredoxin (Trx) inhibiting its oxidant scavenging and thiolreducing capacity. Hence, prolonged overexpression of TXNIP causes ROS/RNS stress, mitochondrial dysfunction, inflammation and premature cell death in DR. Initially, DR was considered as microvascular complications of endothelial dysfunction and pericyte loss characterized by capillary basement membrane thickening, pericyte ghost, blood retinal barrier leakage, acellular capillary and neovascularization. However, it is currently acknowledged that neuro-glia are also affected by HG in diabetes and that neuronal injury, glial activation, innate immunity/sterile inflammation, and ganglion apoptosis occur early in DR. In addition, retinal pigment epithelium (RPE) becomes dysfunctional in DR. Since TXNIP is induced by HG in most cells, its effects are not restricted to a particular cell type in DR. However, depending on the metabolic activity and anti-oxidant capacity, some cells may be affected earlier by TXNIP than others. Identification of TXNIP sensitive cells and elucidating the underlying mechanism(s) will be critical for preventing pre-mature cell death and progression of DR.

Treatment of proliferative diabetic retinopathy with anti-VEGF agents

Proliferative diabetic retinopathy (PDR) is the most common cause of severe visual loss in people with diabetes. Although panretinal photocoagulation (PRP) remains the gold standard of care to date, several combinations of new treatment modalities have emerged. These approaches can be used to increase the extent of treatment, expedite the effect of laser treatment and provide alternate measures when laser delivery is difficult or impossible, especially in patients with vitreous haemorrhage. Currently, most of the research in this field is focussed on inhibitors of vascular endothelial growth factor (VEGF), referred to herein as anti-VEGF agents. Although limited by their short-lived effects and a lack of established protocols, anti-VEGF agents are widely available, especially for the treatment of aggressive PDR. This review analyses published studies using anti-VEGF agents alone or as an adjunct to other therapies in the treatment of PDR.

Retro-mode imaging of fibrovascular membrane in proliferative diabetic retinopathy after intravitreal bevacizumab injection

The F10 is a new commercially available scanning laser confocal ophthalmoscope (SLO) that can perform multiple functions. We determined the usefulness of noninvasive evaluation of proliferative diabetic retinopathy (PDR) pathologies before and after intravitreal injection of bevacizumab (IVB) using the new indirect viewing system of the retro-mode function of the F10 SLO, and compared the images histologically with surgically excised fibrovascular membrane from two cases. In PDR, neovascular vessels in fibrovascular membrane were clearly seen with the retro-mode, even after IVB and without blood flow. The F10 SLO may be useful in evaluating neovascular vessels in fibrovascular membrane in PDR and for determining the precise retinal changes in diabetic retinopathy.