Increased Systemic C-Reactive Protein Is Associated With Choroidal Thinning in Intermediate Age-Related Macular Degeneration

C-reactive protein-complement factor H axis as a biomarker of activity in early and intermediate age-related macular degeneration

Purpose

To determine and compare the serum levels of complement Factor H (FH), monomeric C-Reactive Protein (mCRP) and pentameric C-Reactive protein (pCRP) in patients with age-related macular degeneration (AMD) and to correlate them with clinical, structural and functional parameters.

Methods

Cross-sectional observational study. One hundred thirty-nine individuals (88 patients and 51 healthy controls) from two referral centers were included and classified into three groups: early or intermediate AMD (n=33), advanced AMD (n=55), and age and sex matched healthy controls (n=51). Serum levels of FH, mCRP, and pCRP were determined and correlated with clinical and imaging parameters.

Results

Patients with intermediate AMD presented FH levels significantly lower than controls [186.5 (72.1-931.8) µg/mL vs 415.2 (106.1-1962.2) µg/mL; p=0.039] and FH levels <200 µg/mL were associated with the presence of drusen and pigmentary changes in the fundoscopy (p=0.002). While no differences were observed in pCRP and mCRP levels, and mCRP was only detected in less than 15% of the included participants, women had a significantly higher detection rate of mCRP than men (21.0% vs. 3.8%, p=0.045). In addition, the ratio mCRP/FH (log) was significantly lower in the control group compared to intermediate AMD (p=0.031). Visual acuity (p<0.001), macular volume (p<0.001), and foveal thickness (p=0.034) were significantly lower in the advanced AMD group, and choroidal thickness was significantly lower in advanced AMD compared to early/intermediate AMD (p=0.023).

Conclusion

Intermediate AMD was associated in our cohort with decreased serum FH levels together with increased serum mCRP/FH ratio. All these objective serum biomarkers may suggest an underlying systemic inflammatory process in early/intermediate AMD patients.

Correlation Between C-Reactive Protein and Lipid Analytes in Dry Age-Related Macular Degeneration: A Retrospective Study

INTRODUCTION

To date few studies have investigated the correlation between inflammatory markers and lipoproteins in the serum of age-related macular degeneration (AMD) patients, often reporting conflicting findings. This study aimed to investigate the correlation between lipid analytes and C-reactive protein (CRP) levels in individuals diagnosed with dry AMD.

METHODS

A standard clinical lipid panel (total cholesterol, triglycerides, high-density lipoprotein [HDL], and low-density lipoproteins) and CRP laboratory results were retrospectively collected from the medical records of patients with dry AMD and age- and sex-matched controls.

RESULTS

The study included 90 patients with dry AMD and 270 patients without AMD. In univariate analysis, CRP showed a higher mean value in cases than in controls. After adjusting for age and sex, CRP and triglyceride levels showed significant differences between cases and controls. Pearson's correlation analysis revealed a significant negative correlation between CRP and HDL levels in the dry AMD group (n=90). Other lipid analytes showed no significant correlations with CRP.

CONCLUSION

Our findings add to the growing body of evidence linking inflammation to AMD. Although it is unclear whether changes in serum CRP and triglyceride levels are the causes or effects, monitoring both analytes may be beneficial as an early disease predictor, especially in individuals with a family history of AMD. The negative correlation between CRP and HDL (i.e., inflammation and good cholesterol) may be targeted for future therapies.

Biomarkers for the Progression of Intermediate Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is a leading cause of severe vision loss worldwide, with a global prevalence that is predicted to substantially increase. Identifying early biomarkers indicative of progression risk will improve our ability to assess which patients are at greatest risk of progressing from intermediate AMD (iAMD) to vision-threatening late-stage AMD. This is key to ensuring individualized management and timely intervention before substantial structural damage. Some structural biomarkers suggestive of AMD progression risk are well established, such as changes seen on color fundus photography and more recently optical coherence tomography (drusen volume, pigmentary abnormalities). Emerging biomarkers identified through multimodal imaging, including reticular pseudodrusen, hyperreflective foci, and drusen sub-phenotypes, are being intensively explored as risk factors for progression towards late-stage disease. Other structural biomarkers merit further research, such as ellipsoid zone reflectivity and choriocapillaris flow features. The measures of visual function that best detect change in iAMD and correlate with risk of progression remain under intense investigation, with tests such as dark adaptometry and cone-specific contrast tests being explored. Evidence on blood and plasma markers is preliminary, but there are indications that changes in levels of C-reactive protein and high-density lipoprotein cholesterol may be used to stratify patients and predict risk. With further research, some of these biomarkers may be used to monitor progression. Emerging artificial intelligence methods may help evaluate and validate these biomarkers; however, until we have large and well-curated longitudinal data sets, using artificial intelligence effectively to inform clinical trial design and detect outcomes will remain challenging. This is an exciting area of intense research, and further work is needed to establish the most promising biomarkers for disease progression and their use in clinical care and future trials. Ultimately, a multimodal approach may yield the most accurate means of monitoring and predicting future progression towards vision-threatening, late-stage AMD.

The Essential Role of the Choriocapillaris in Vision: Novel Insights from Imaging and Molecular Biology

The choriocapillaris, a dense capillary network located at the posterior pole of the eye, is essential for supporting normal vision, supplying nutrients, and removing waste products from photoreceptor cells and the retinal pigment epithelium. The anatomical location, heterogeneity, and homeostatic interactions with surrounding cell types make the choroid complex to study both in vivo and in vitro. Recent advances in single-cell RNA sequencing, in vivo imaging, and in vitro cell modeling are vastly improving our knowledge of the choroid and its role in normal health and in age-related macular degeneration (AMD). Histologically, loss of endothelial cells (ECs) of the choriocapillaris occurs early in AMD concomitant with elevated formation of the membrane attack complex of complement. Advanced imaging has allowed us to visualize early choroidal blood flow changes in AMD in living patients, supporting histological findings of loss of choroidal ECs. Single-cell RNA sequencing is being used to characterize choroidal cell types transcriptionally and discover their altered patterns of gene expression in aging and disease. Advances in induced pluripotent stem cell protocols and 3D cultures will allow us to closely mimic the in vivo microenvironment of the choroid in vitro to better understand the mechanism leading to choriocapillaris loss in AMD.

Deletion of the Pedf gene leads to inflammation, photoreceptor loss and vascular disturbances in the retina

Retinal diseases are often accompanied by inflammation, vascular abnormalities, and neurodegeneration that decrease vision. Treatment with exogenous PEDF is widely shown to alleviate these conditions leading us to hypothesize that loss of function of the PEDF gene disrupts these pathways and leads to visual loss. Measurements were carried out by detailed phenotyping of PEDF null mice to assess expression of immunomodulators, glia activation, systemic inflammation, vascular disturbances, and visual sensitivity often associated with retinal pathologies. With a deletion of the Pedf gene, there was increased expression of several immune modulators in Pedf^-/- retinas and serum with IL-2 and GM-CSF upregulated in both. Increases in retina glia activation and macrophage infiltration, levels of serum c-reactive protein (CRP), numbers of white and red blood cells and platelets and decreased blood glucose levels were all features associated with PEDF null mice. With PEDF gene deletion, there was also a notable increase in apoptosis in early developing retinas (PN3), reduced thickness of the photoreceptor layer, swelling of the inner plexiform layer, reduced retinal sensitivity and steady-state reduced activation of Erk and Akt, two signaling pathways used by PEDF. There is a substantial body of animal data emphasizing utility of PEDF treatment in homeostatic regulation of retinal diseases, including diabetic retinopathy and age-related macular degeneration but there is little agreement or evidence on the role of endogenous PEDF in retinal diseases. Our findings strongly support the concept that a deletion of the PEDF gene makes the retina vulnerable to diseases, and argue that endogenous PEDF plays a critical role in limiting pathological events in the retina.

Plasma C-C Chemokine Concentrations in Intermediate Age-Related Macular Degeneration

Purpose: To determine the relationship between plasma concentrations of the C-C chemokines CCL2, CCL3, CCL4, and CCL5 and intermediate age-related macular degeneration (iAMD) patients compared with control inidividuals to further define the inflammatory pathways associated with age-related macular degeneration.

Methods: The concentrations of CCL2, CCL3, CCL4, and CCL5 were measured using multiplex assays in plasma collected from 210 patients with iAMD and 102 control individuals with no macular degeneration as defined by multi-modal imaging. Non-inflammatory data included in the analysis were: age, sex, family history of AMD, history of smoking, body mass index, presence of reticular pseudo-drusen and cardiovascular disease. Median concentrations as well as a cutoff value for each chemokine were compared between the two groups.

Results: The median concentrations of CCL2 and CCL4 did not differ between control and iAMD groups, however, CCL2 was elevated in iAMD when a cutoff comparison was used (p < 0.05). Median CCL3 and CCL5 concentrations were significantly decreased in the macular degeneration group compared with controls (p < 0.001) as well as when a cutoff value comparison was used. CCL3 and CCL5 were negatively correlated in cases and positively correlated in controls.

Conclusions: Plasma CCL3 and CCL5 concentrations were significantly decreased and CCL2 concentrations were increased in patients with iAMD compared with controls, suggesting a role for C-C chemokines in the systemic inflammatory processes associated with disease development.