Changes in aqueous and vitreous inflammatory cytokine levels in neovascular age-related macular degeneration: a systematic review and meta-analysis

The role of the cytokine TNF-α in choroidal neovascularization: a systematic review

TNF-α is a multifunctional cytokine produced by macrophages and T cells. This proinflammatory substance is considered to play a crucial role in the inflammatory process associated with age-related macular degeneration (AMD). The current review aimed to describe evidence for an association between TNF-α and AMD reported in various studies. The MEDLINE, Embase, PubMed and Global Health databases were systematically searched to identify studies that investigated the role of TNF-α in AMD. A total of 24 studies were deemed eligible for the review. To better understand and integrate the evidence, the studies were categorised into four major groups in relation to the role of TNF-α in AMD: (1) those examining biological signalling pathways through which TNF-α exerts its effect; (2) investigating levels of TNF-α; (3) exploring the genetics underlying the role of TNF-α; and (4) assessing anti-TNF-α agents as potential treatments for AMD. TNF-α is thought to directly contribute to choroidal neovascularization (CNV) enhancement and has been shown to exert its effect by augmenting the inflammatory response through other signalling pathways. Additionally, different genes have been found to be associated with activities linked to TNF-α in AMD. Overall, measurement of systemic and local levels of TNF-α has not yielded consistent findings, with variable conclusions for the role of anti-TNF-α agents in remission of AMD symptoms. The role of TNF-α in neovascular AMD is not clear, and not all anti-TNF-α agents are safe. The potential of this cytokine in atrophic AMD has not been examined. Future studies should address these unresolved questions.

The central role of the NLRP3 inflammasome pathway in the pathogenesis of age-related diseases in the eye and the brain

With increasing age, structural changes occur in the eye and brain. Neuronal death, inflammation, vascular disruption, and microglial activation are among many of the pathological changes that can occur during ageing. Furthermore, ageing individuals are at increased risk of developing neurodegenerative diseases in these organs, including Alzheimer's disease (AD), Parkinson's disease (PD), glaucoma and age-related macular degeneration (AMD). Although these diseases pose a significant global public health burden, current treatment options focus on slowing disease progression and symptomatic control rather than targeting underlying causes. Interestingly, recent investigations have proposed an analogous aetiology between age-related diseases in the eye and brain, where a process of chronic low-grade inflammation is implicated. Studies have suggested that patients with AD or PD are also associated with an increased risk of AMD, glaucoma, and cataracts. Moreover, pathognomonic amyloid-β and α-synuclein aggregates, which accumulate in AD and PD, respectively, can be found in ocular parenchyma. In terms of a common molecular pathway that underpins these diseases, the nucleotide-binding domain, leucine-rich-containing family, and pyrin domain-containing-3 (NLRP3) inflammasome is thought to play a vital role in the manifestation of all these diseases. This review summarises the current evidence regarding cellular and molecular changes in the brain and eye with age, similarities between ocular and cerebral age-related diseases, and the role of the NLRP3 inflammasome as a critical mediator of disease propagation in the eye and the brain during ageing.

The Role of Inflammation in Age-Related Macular Degeneration: Updates and Possible Therapeutic Approaches

Age-related macular degeneration (AMD) is a common retinal disease characterized by complex pathogenesis and extremely heterogeneous characteristics. Both in "dry" and "wet" AMD forms, the inflammation has a central role to promote the degenerative process and to stimulate the onset of complications. AMD is characterized by several proinflammatory stimuli, cells and mediators involved, and metabolic pathways. Nowadays, inflammatory biomarkers may be unveiled and analyzed by means of several techniques, including laboratory approaches, histology, immunohistochemistry, and noninvasive multimodal retinal imaging. These methodologies allowed to perform remarkable steps forward for understanding the role of inflammation in AMD pathogenesis, also offering new opportunities to optimize the diagnostic workup of the patients and to develop new treatments. The main goal of the present paper is to provide an updated scenario of the current knowledge regarding the role of inflammation in "dry" and "wet" AMD and to discuss new possible therapeutic strategies.

Association of IL-4 with pachychoroid neovasculopathy

The purpose of this study was to identify the inflammatory cytokines that were associated with pachychoroid neovasculopathy (PNV). Seventy-five eyes of 75 patients with PNV, 145 eyes of 145 patients with neovascular age-related macular degeneration without pachyvessels, and 150 eyes of 150 normal subjects were examined for the levels of intraocular cytokines. In eyes with PNV, the levels of IL-1α, IL-1β, IL-2, IL-4, IL-10, and VEGF were significantly higher than that of the controls. Logistic regression analysis showed that the highest association with the pachyvessels was found for IL-4, IL-2, and IL-1α. In eyes with PNV, the levels of IL-4, IL-2, IL-5, IL-13, IL-1α, and IL-1β were significantly higher in eyes with both increased choroidal thickness and choroidal vessel diameter. The strongest correlation with the choroidal thickness and vessel diameter was observed for IL-4. In PNV eyes with polypoidal lesions, the levels of IL-4, IL-17, and TNFβ were significantly correlated with the number of polypoidal lesions. Of these cytokines, IL-4 was especially associated with the thickness of the choroidal vessels and the formation of polypoidal lesions. We conclude that IL-4 is most likely involved in establishing the clinical characteristics of PNV and polypoidal vascular remodeling.

Association between inflammatory cytokines in the aqueous humor and hyperreflective foci on optical coherence tomography in patients with neovascular age-related macular degeneration and polypoidal choroidal vasculopathy

Purpose

To investigate the associations between cytokine levels in the aqueous humor (AH) and hyperreflective foci (HF) on spectral-domain optical coherence tomography (SD-OCT) in neovascular age-related macular degeneration (nAMD) and polypoidal choroidal vasculopathy (PCV).

Methods

The prospective study included 63 eyes with nAMD, 44 with PCV, and 43 with cataracts (Controls). AH samples were obtained before anti-vascular endothelial growth factor (VEGF) therapy or cataract surgery. Cytokines interleukin 6 (IL-6), IL-8, IL-10, interferon-inducible protein 10 (IP-10), monocyte chemotactic protein 1 (MCP-1), and VEGF were measured by multiplex bead assay. Best-corrected visual acuity (BCVA), central macular thickness (CMT), and the number of HF were evaluated at baseline and 1 month after anti-VEGF treatment.

Results

No significances difference in IL-6 and IL-8 levels were noted among the three groups (P = 0.370 and P = 0.067). VEGF, IP-10, and IL-10 levels were significantly higher in nAMD and PCV groups than in Controls (all P < 0.05). In nAMD, HF was positively correlated with VEGF (rs = 0.300, P = 0.025) and in eyes with HF group, VEGF and IL-10 were significantly higher than those without HF (P = 0.008 and P = 0.022). In PCV, no correlation was observed between HF and cytokines (all P > 0.05). After anti-VEGF treatment, patients with HF in nAMD and PCV were predisposed to worse visual outcomes (P = 0.022 and P = 0.015) and a significantly greater reduction in CMT (P = 0.001 and P = 0.057). And nAMD patients with HF were more sensitive to anti-VEGF treatment than those without HF (P = 0.029).

Conclusions

In the nAMD group, HF was positively correlated with VEGF. Patients in nAMD with HF had elevated levels of VEGF and IL-10 and responded favorably to anti-VEGF. HF might serve as an inflammatory biomarker and a predictive factor for therapeutic efficacy in patients with nAMD.

Lower CXCR3 expression in both patients with neovascular AMD and advanced stages of chronic myeloproliferative blood cancers

Purpose

Peripheral T cell CXCR3 expression has been found uniquely lower in patients having neovascular age-related macular degeneration (nAMD) than in healthy individuals. The CXCR3-axis has been shown to have angiostatic and antifibrotic properties. We have recently investigated systemic markers in patients with myeloproliferative neoplasms (MPNs) because of their higher prevalence of AMD, and we have observed higher systemic chronic low-grade inflammation and immunosenescence signs in MPNs with drusen (MPNd) compared to those with normal retinas (MPNn). The MPNs evolve in a biological continuum from early cancer-stages (essential thrombocytosis, polycythemia vera) to the advanced myelofibrosis stage. Especially myelofibrosis is characterized by bone marrow angiogenesis and fibrosis, similarly to retinal observations in nAMD. We speculate if we can find lower CXCR3 expression in MPNs, particularly myelofibrosis and if differences are seen between MPNd and MPNn. We also wanted to compare expression in nAMD and intermediate (i)AMD.

Methods

Patients in this cross-sectional study were 29 nAMD, 28 iAMD, 35 MPNd, and 27 MPNn. We performed flowcytometry on blood to measure CXCR3 expression.

Results

CD8+CXCR3 expression in nAMD was 6,1%, significantly lower than in iAMD 16%, MPNd 11%, MPNn 12% (p-values<0.05). Similar results were seen for CD4+CXCR3 expression. We also found CXCR3 expression decreasing over the MPN-continuum. For instance, in myelofibrosis, intermediate monocytes expression was 6.2%, significantly lower than 18% in ET and 18% in PV (p-values<0.05).

Conclusions

We find CXCR3 downregulation on T-cells and some monocyte subset in nAMD compared to iAMD, MPNd, and MPNn, in line with previous nAMD studies. We also find CXCR3 downregulation in most monocyte subsets over the MPN continuum. Systemic leukocyte CXCR3 expression could both be involved in changes seen in the retina and the bone marrow. Further understanding the CXCR3-axis in AMD and MPNs may elucidate underlying pathogenic mechanisms and reveal new targets for treatment.

Changes in aqueous and vitreous inflammatory cytokine levels in proliferative diabetic retinopathy: a systematic review and meta-analysis

BACKGROUND

Diabetic retinopathy is a major complication of diabetes mellitus, where in its most advanced form ischemic changes lead to the development of retinal neovascularization, termed proliferative diabetic retinopathy (PDR). While the development of PDR is often associated with angiogenic and inflammatory cytokines, studies differ on which cytokines are implicated in disease pathogenesis and on the strength of these associations. We therefore conducted a systematic review and meta-analysis to quantitatively assess the existing body of data on intraocular cytokines as biomarkers in PDR.

METHODS

A comprehensive search of the literature without year limitation was conducted to January 18, 2021, which identified 341 studies assessing vitreous or aqueous cytokine levels in PDR, accounting for 10379 eyes with PDR and 6269 eyes from healthy controls. Effect sizes were calculated as standardized mean differences (SMD) of cytokine concentrations between PDR and control patients.

RESULTS

Concentrations (SMD, 95% confidence interval, and p-value) of aqueous IL-1β, IL-6, IL-8, MCP-1, TNF-α, and VEGF, and vitreous IL-2, IL-4, IL-6, IL-8, angiopoietin-2, eotaxin, erythropoietin, GM-CSF, GRO, HMGB-1, IFN-γ, IGF, IP-10, MCP-1, MIP-1, MMP-9, PDGF-AA, PlGF, sCD40L, SDF-1, sICAM-1, sVEGFR, TIMP, TNF-α, and VEGF were significantly higher in patients with PDR when compared to healthy nondiabetic controls. For all other cytokines no differences, failed sensitivity analyses or insufficient data were found.

CONCLUSIONS

This extensive list of cytokines speaks to the complexity of PDR pathogenesis, and informs future investigations into disease pathogenesis, prognosis, and management.

Changes in aqueous and vitreous inflammatory cytokine levels in diabetic macular oedema: a systematic review and meta-analysis

Diabetic macular oedema (DME) is considered a chronic inflammatory disease associated with aberrations in many intraocular cytokines. Studies assessing the role of these cytokines as biomarkers in the diagnosis and management of DME have demonstrated inconsistent findings. We quantitatively summarized data related to 116 candidate aqueous and vitreous inflammatory cytokines as biomarkers in DME. A systematic search without year limitation was performed up to 19 October 2020. Studies were included if they provided data on aqueous or vitreous cytokine concentrations in patients with DME. Effect sizes were generated as standardized mean differences (SMDs) of cytokine concentrations between patients with DME and controls. Data were extracted from 128 studies that included 4163 study eyes with DME and 1281 control eyes. Concentrations (standard mean difference, 95% confidence interval and p-value) of aqueous IL-6 (1.28, 0.57-2.00, p = 0.004), IL-8 (1.06, 0.74-1.39, p < 0.00001), MCP-1 (1.36, 0.57-2.16, p = 0.0008) and VEGF (1.31, 1.01-1.62, p < 0.00001) and vitreous VEGF (2.27, 1.55-2.99, p < 0.00001) were significantly higher in patients with DME (n = 4163) compared to healthy controls (n = 1281). No differences, failed sensitivity analyses or insufficient data were found between patients with DME and healthy controls for the concentrations of the remaining cytokines. This analysis implicates multiple cytokine biomarker candidates other than VEGF in DME and clarifies previously reported inconsistent associations. As the therapeutic options for DME expand to include multiple agents with multiple targets, it will be critical to manage the treatment burden with tailored therapy that optimizes outcomes and minimizes treatment burden. Intraocular cytokines have the promise of providing a robust individualized assessment of disease status and response to therapy. We have identified key candidate cytokines that may serve as biomarkers in individualized treatment algorithms.

Imaging Hyperreflective Foci as an Inflammatory Biomarker after Anti-VEGF Treatment in Neovascular Age-Related Macular Degeneration Patients with Optical Coherence Tomography Angiography

Purpose

To investigate the hyperreflective foci (HRF) as an inflammatory biomarker using optical coherence tomography angiography (OCTA) in neovascular age-related macular degeneration (AMD) patients after antivascular endothelial growth factor (anti-VEGF) treatment and its association with the retinal microcapillary density.

Methods

Twenty-five eyes from 25 patients with neovascular AMD were included in the study. All eyes were imaged with OCTA at baseline (M0) and after 3 consecutive injections (M3; injection performed each month) of anti-VEGF. The number of HRF in the superficial capillary plexus (SCP), deep capillary plexus (DCP), and outer retina was counted. The vascular density of the fovea, parafovea, and the whole macula, as well as the area of the foveal avascular zone (FAZ), was measured.

Results

The mean interval between baseline and follow-up with OCTA was 93.08 ± 5.00 (range, 85-101) days. Compared with the baseline, the number of HRF significantly decreased in DCP (7.52 ± 3.06 vs. 3.76 ± 1.48, P < 0.01) and outer retina (12.04 ± 4.91 vs. 5.88 ± 3.32, P < 0.01) after treatment. There was no significant difference for HRF number in the SCP, the vascular density (containing foveal, parafoveal, and whole macular), and FAZ area before and after treatments.

Conclusion

The number of HRF in DCP and outer retina might serve as an inflammatory biomarker in patients with neovascular AMD. The reduced HRF possibly represents the alleviation of inflammation after anti-VEGF treatment in patients with AMD.