The eye is closely connected to the brain, a biological extension of it. It is therefore not surprising that various ophthalmological diseases such as glaucoma, cataract, macular degeneration, and diabetic retinopathy may be associated with Alzheimer's disease. Epidemiological studies suggest this. The common pathogenesis of ophthalmological and neurological diseases is conceivable. A recently published scientific article deals with this issue.1
In recent decades, the prevalence of neurodegenerative diseases has increased in aging societies. The scientific search for biomarkers that allow us to identify neurodegenerative diseases in their early stages has led us, among other things, to the Neurofilament Light Chain (NfL) biomarker. At the very beginning, the symptoms of a neurodegenerative disease can be quite subtle. But especially in this initial stage, the timely initiation of therapy can have a strong influence on the further course of the disease.
NfL is a new promising biomarker for neurodegenerative diseases. It could be detected in the cerebrospinal fluid and blood of patients with neurodegenerative diseases. Neurofilament light chains could be of great prognostic relevance in the future and could also be used as a screening tool.1-4
Neurofilaments are an important component of the neuronal cytoskeleton. They ensure the stability and structure of axons and are essential for nerve conduction velocity. Neurofilament light chains are a subunit of the neurofilaments and can only be measured to a small extent under physiological conditions. With increasing age, the concentration of neurofilament light chains also increases.
Damage to neurons, whether of neurodegenerative, inflammatory or vascular origin, is accompanied by a significantly increased neurofilament light chain concentration. Compared to healthy individuals, neurofilament light-chain concentrations are higher in the neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, corticobasal syndrome, Down's syndrome with dementia, frontotemporal dementia, and Lewy body dementia.1-4
A research group from Boston recently published a scientific study in which they were able to demonstrate the presence of this new biomarker in the vitreous body. A total of 77 vitreous samples (0.5-1ml per sample) from 63 patients with a median age of 56.2 years were examined in this prospective study. In addition, an ApoE (Apolipoprotein E Phenotypes) genotyping of the blood was performed. In the ApoE genotyping - in the presence of Alzheimer's disease - a section in exon 4 of the APOE gene is detected by a polymerase chain reaction. Using immunoassay, the research group has investigated the diagnostic significance of the presence of neurofilament light chains in the vitreous body.1
By means of immunoassay, the vitreous body samples were analyzed in detail. The search was done for neurofilament light chains, beta-amyloid, total tau protein, phosphorylated tau protein, inflammatory cytokines, chemokines, and vascular proteins. Neurofilament light chains were detected in all 77 vitreous samples. A neurofilament light chain value of ≥ 20 pg/ml was measured in about 72% of the samples. The median neurofilament light chain value was ≥ 68.65 pg/ml.1
This biomarker for neurodegenerative diseases had not been associated with ophthalmological diseases. Neither had it been associated with ApoE genotypes and systemic diseases. The NfL concentration in the vitreous body correlated positively with total tau protein, beta-amyloid 40, and 42, but not with phosphorylated tau protein 181. A positive correlation of the NfL concentration was also observed with the inflammatory cytokines interleukin 15, interleukin 16, and monocyte chemoattractant protein-1, Vascular endothelial growth factor C (VEGF-C), vascular endothelial growth factor receptor 1 (VEGFR1), vascular cell adhesion molecule 1 (VCAM-1), angiopoietin receptor 1 and intracellular adhesion molecule 1 (ICAM-1).1
This interesting scientific study was able to show an association between the vital NfL concentration and the total tau protein, beta-amyloid 40 and 42, inflammatory cytokines/chemokines, and vascular proteins. However, this method is currently not suitable for the verification of neurodegenerative disease, because there was no association with the ApoE genotypes and no neurodegenerative disease was clinically present in the presence of an increased measurable vitreal NfL concentration.
References:
1. Delaby C. et al (2020). Differential levels of neurofilament light protein in cerebrospinal fluid in patients with a wide range of neurodegenerative disorders. Sci Rep. 2020;10(1):9161 Published 2020 Jun 8.
2. Bäckström D. et al (2020). NfL as a biomarker for neurodegeneration and survival in Parkinson disease. Neurology Aug 2020, 95 (7) e827-e838.
3. Lin Y. et al. (2018). Levels of plasma neurofilament light chain and cognitive function in patients with Alzheimer's or Parkinson's disease. Sci Rep 8, 17368 (2018).
4. Subramanian M. L. et al. (2020). Neurofilament light chain in the vitreous humor of the eye. Alzheimer's Res Ther. 2020 Sep 17;12(1):111.