Age, lipofuscin and melanin oxidation affect fundus near-infrared autofluorescence

Tatjana Taubitz; Yuan Fang; Antje Biesemeier; Sylvie Julien-Schraermeyer; Ulrich Schraermeyer

doi:10.1016/j.ebiom.2019.09.048

Age, lipofuscin and melanin oxidation affect fundus near-infrared autofluorescence

EBioMedicine. 2019 Oct:48:592-604. doi: 10.1016/j.ebiom.2019.09.048. Epub 2019 Oct 21.

Authors

Tatjana Taubitz¹, Yuan Fang², Antje Biesemeier³, Sylvie Julien-Schraermeyer², Ulrich Schraermeyer⁴

Affiliations

¹ Division of Experimental Vitreoretinal Surgery, Centre for Ophthalmology, University of Tübingen, Schleichstrasse 12/1, 72076 Tübingen, Germany. Electronic address: tatjana.taubitz@med.uni-tuebingen.de.
² Division of Experimental Vitreoretinal Surgery, Centre for Ophthalmology, University of Tübingen, Schleichstrasse 12/1, 72076 Tübingen, Germany.
³ Division of Experimental Vitreoretinal Surgery, Centre for Ophthalmology, University of Tübingen, Schleichstrasse 12/1, 72076 Tübingen, Germany; NMI Natural and Medical Sciences Institute at the University of Tübingen, Reutlingen, Germany.
⁴ Division of Experimental Vitreoretinal Surgery, Centre for Ophthalmology, University of Tübingen, Schleichstrasse 12/1, 72076 Tübingen, Germany; STZ OcuTox Preclinical Drug Assessment, Hechingen, Germany.

Abstract

Background: Fundus autofluorescence is a non-invasive imaging technique in ophthalmology. Conventionally, short-wavelength autofluorescence (SW-AF) is used for detection of lipofuscin, a byproduct of the visual cycle which accumulates with age or disease in the retinal pigment epithelium (RPE). Furthermore, near-infrared autofluorescence (NIR-AF) is used as a marker for RPE and choroidal melanin, but contribution of lipofuscin to the NIR-AF signal is unclear.

Methods: We employed fluorescence microscopy to investigate NIR-AF properties of melanosomes, lipofuscin and melanolipofuscin granules in histologic sections of wildtype and Abca4^-/- mouse eyes, the latter having increased lipofuscin, as well as aged human donor eyes. Differentiation between these pigments was verified by analytical electron microscopy. To investigate the influence of oxidative and photic stress we used an in vitro model with isolated ocular melanosomes and an in vivo phototoxicity mouse model.

Findings: We show that NIR-AF is not an intrinsic property of melanin, but rather increases with age and after photic or oxidative stress in mice and isolated melanosomes. Furthermore, when lipofuscin levels are high, lipofuscin granules also show NIR-AF, as confirmed by correlative fluorescence and electron microscopy in human tissue. However, lipofuscin in albino Abca4^-/- mice lacks NIR-AF signals.

Interpretation: We suggest that NIR-AF is derived from melanin degradation products that accumulate with time in lipofuscin granules. These findings can help to improve the interpretation of patient fundus autofluorescence data.

Funding: This work was supported by Bundesministerium für Bildung und Forschung, Deutsche Forschungsgemeinschaft and Chinese Scholarship Council. Major instrumentation used in this work was supported by Deutsche Forschungsgemeinschaft, the European Fund for Regional Development and the state of Baden-Württemberg.

Keywords: Aging; Lipofuscin; Melanin; Melanolipofuscin; Oxidative stress.

MeSH terms

Age Factors
Animals
Biomarkers
Choroid / metabolism
Disease Models, Animal
Female
Fluorescein Angiography
Fundus Oculi*
Humans
Lipofuscin / metabolism*
Macular Degeneration / diagnosis
Macular Degeneration / etiology
Macular Degeneration / metabolism
Male
Melanins / metabolism*
Melanosomes / metabolism
Mice
Mice, Knockout
Optical Imaging
Oxidation-Reduction*
Oxidative Stress
Protein Transport
Retinal Pigment Epithelium / metabolism
Tomography, Optical Coherence

Substances

Biomarkers
Lipofuscin
Melanins