Lipofuscin-mediated photic stress inhibits phagocytic activity of ARPE-19 cells; effect of donors’ age and antioxidants

Abstract

The risk of chronic oxidative stress in the retinal pigment epithelium (RPE) increases with age due to accumulation of the photoreactive age pigment lipofuscin (LFG). Here, we asked whether sublethal and weakly lethal photic stress, induced by irradiation of ARPE-19 cells containing phagocytised LFG, affected the cell specific phagocytic activity, which is critically important for proper functioning and survival of the retina, and if natural antioxidants could modify the observed outcomes. ARPE-19 cells preloaded with LFG isolated from human donors of different age or containing LFG enriched with zeaxanthin and α-tocopherol (LFG-A), were irradiated with blue light. Phagocytosis of fluorescein-5-isothiocyanate (FITC)-labelled photoreceptor outer segments was determined by flow cytometry. Photoreactivity of LFG and LFG-A was analysed by measuring photoconsumption of oxygen and photogeneration of singlet oxygen mediated by the granules. LFG-mediated photic stress in ARPE-19 cells induced significant inhibition of their specific phagocytosis. The inhibitory effect increased with age of LFG donors and was reduced by enrichment of the granules with antioxidants. Oxygen consumption and generation of singlet oxygen induced by the photoexcited LFG increased with donor’s age and was partially quenched by antioxidants. Although the phototoxic potential of lipofuscin increased with age, natural antioxidants reduced photoreactivity of LFG and their efficiency to induce oxidative stress. This study has demonstrated, for the first time, that mild oxidative stress, mediated by the age pigment lipofuscin, impairs specific phagocytic activity of RPE, and that natural antioxidants can protect this important cellular function by reducing lipofuscin photoreactivity.

Keywords:

• Lipofuscin
• photic stress
• antioxidants
• phagocytosis of POS
• EPR oximetry
• time-resolved singlet oxygen detection

Acknowledgements

The authors thank Professor H. Halpern of the University of Chicago for providing us with the mHCTPO spin probe and F. Hoffmann–La Roche Ltd (Basel, Switzerland) for the generous gift of zeaxanthin. This work was supported by research grant MAESTRO 4 2013/08/A/NZ1/00194 from the Poland National Science Center. The Faculty of Biochemistry, Biophysics and Biotechnology of the Jagiellonian University is a beneficiary of structural funds from European Union Grant POIG.02.01.00-12-064/08 – “Molecular biotechnology for health”.

Disclosure statement

The authors declare no conflict of interest. The authors alone are responsible for the content.

Funding

This work was supported by Poland National Science Centre (MAESTRO 4 2013/08/A/NZ1/00194).