Neurofilament light chain in the vitreous humor of the eye

Subramanian et al. Alzheimer's Research & Therapy https://doi.org/10.1186/s13195-020-00677-4 (2020) 12:111 RESEARCH Open Access Neurofilament light chain in the vitreous humor of the eye Manju L. Subramanian1* , Viha Vig1, Jaeyoon Chung2, Marissa G. Fiorello1, Weiming Xia3,4, Henrik Zetterberg5,6,7,8, Kaj Blennow5,6, Madeleine Zetterberg9, Farah Shareef10, Nicole H. Siegel1, Steven Ness1, Gyungah R. Jun2 and Thor D. Stein11,12,13 Abstract Background: Neurofilament light chain (NfL) is a promising biomarker of neurodegeneration in the cerebrospinal fluid and blood. This study investigated the presence of NfL in the vitreous humor and its associations with amyloid beta, tau, inflammatory cytokines and vascular proteins, apolipoprotein E (APOE) genotypes, Mini-Mental State Examination (MMSE) scores, systemic disease, and ophthalmic diseases. Methods: This is a single-site, prospective, cross-sectional cohort study. Undiluted vitreous fluid (0.5–1.0 mL) was aspirated during vitrectomy, and whole blood was drawn for APOE genotyping. NfL, amyloid beta (Aβ), total Tau (tTau), phosphorylated Tau (p-Tau181), inflammatory cytokines, chemokines, and vascular proteins in the vitreous were quantitatively measured by immunoassay. The main outcome measures were the detection of NfL levels in the vitreous humor and its associations with the aforementioned proteins. Linear regression was used to test the associations of NfL with other proteins, APOE genotypes, MMSE scores, and ophthalmic and systemic diseases after adjustment for age, sex, education level, and other eye diseases. Results: NfL was detected in all 77 vitreous samples. NfL was not found to be associated with ophthalmic conditions, APOE genotypes, MMSE scores, or systemic disease (p > 0.05). NfL levels were positively associated with increased vitreous levels of Aβ40 (p = 7.7 × 10−5), Aβ42 (p = 2.8 × 10−4), and t-tau (p = 5.5 × 10−7), but not with ptau181 (p = 0.53). NfL also had significant associations with inflammatory cytokines such as interleukin-15 (IL-15, p = 5.3 × 10−4), IL-16 (p = 2.2 × 10−4), monocyte chemoattractant protein-1 (MCP1, p = 4.1 × 10−4), and vascular proteins such as vascular endothelial growth factor receptor-1 (VEGFR1, p = 2.9 × 10−6), Vegf-C (p = 8.6 × 10−6), vascular cell adhesion molecule-1 (VCAM-1, p = 5.0 × 10−4), Tie-2 (p = 6.3 × 10−4), and intracellular adhesion molecular-1 (ICAM-1, p = 1.6 × 10−4). Conclusion: NfL is detectable in the vitreous humor of the eye and significantly associated with amyloid beta, ttau, and select inflammatory and vascular proteins in the vitreous. Additionally, NfL was not associated with patients’ clinical eye condition. Our results serve as a foundation for further investigation of NfL in the ocular fluids to inform us about the potential utility of its presence in the eye. Keywords: Alzheimer’s disease, Vitreous humor, Neuro-filament light chain, Ocular biomarkers, Amyloid beta, Tau * Correspondence: 1 Department of Ophthalmology, Boston Medical Center, Boston University School of Medicine, 85 E Concord St. #8813, Boston, MA 02118, USA Full list of author information is available at the end of the article © The Author(s). 2020 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Subramanian et al. Alzheimer's Research & Therapy (2020) 12:111 Page 2 of 12 Background Neurodegenerative diseases have risen in prevalence over the last few decades with the growth of an aging population in Western society [1]. Of the two most common neurodegenerative diseases, Alzheimer’s disease (AD) alone affects 5.5 million Americans while Parkinson’s disease (PD) now affects over 1 million individuals in the USA [2]. Although the diagnosis of neurodegenerative diseases is often based on clinical presentation supported by diagnostic testing during later stages, early diagnosis remains a challenge. There is a need for reliable biomarkers that can serve as a mechanism for early diagnosis, prognostic assessment, and measurable response to treatment for AD and other neurological disorders. More recently, neurofilament light chain (NfL), a promising biomarker of neurodegeneration, has been identified in the cerebrospinal fluid (CSF) and blood as a potential screening tool and prognostic indicator, and it may now be on the brink of clinical applicability [3]. NfL is a subunit of neurofilaments (Nfs), which are proteins exclusively located in the neuronal cytoplasm to provide structural stability and maintain the integrity of neurons and speed of impulses. Large axons need and express both NfL and Nfs. Under normal circumstances, NfL is persistently released at low levels, and with increasing age, higher levels are seen in older individuals [4]. Higher levels of NfL are also seen in both the cerebrospinal fluid (CSF) and blood in those with neurodegenerative, inflammatory, or vascular injury of neurons, in several different neurological diseases, including multiple sclerosis (MS), AD, frontotemporal dementia (FTD), amyotrophic lateral sclerosis (ALS), atypical Parkinsonian disorders (APDs), and traumatic brain injury (TBI). In addition to other biomarkers such as amyloid beta (Aβ) and tau protein, elevated levels of NfL in both the CSF and blood have been shown to differentiate healthy controls from subjects with AD with reliable accuracy [3, 5–9]. Although NfL is not yet being used as a screening tool in the clinical setting, the ability of serum NfL to detect and differentiate people suffering from neurodegenerative diseases from healthy controls has made it an important research subject in the last few decades [10]. The eye is a window to the brain, and they both share a common embryological origin and vasculature [11– 17]. Eye diseases such as cataracts, glaucoma, macular degeneration, and diabetic retinopathy have been associated with AD in epidemiological studies, indicating that eye disease and AD possibly share common risk factors and pathological mechanisms at the molecular le (...truncated)