Ceroid/lipofuscin-loaded human fibroblasts show increased susceptibility to oxidative stress

To test whether the possibly enhanced sensitivity of aged cells to oxidativ e stress may depend on their content of ceroid/lipofuscin, AG-1518 human fi broblasts with various amounts of the pigment accumulated due to prolonged cultivation under normobaric hyperoxia were exposed to acute oxidative stre ss (2.5 mu M naphthazarin, 15 min) and then returned to standard culture co nditions. Twenty-four hours after the naphthazarin treatment, 37% of the ce lls were still vital, whereas others had undergone oxidative stress-induced apoptosis with ensuing postapoptotic necrosis. The average amount of ceroi d/lipofuscin within the surviving cells was only about half of that of the initial population of cells, as measured before the naphthazarin exposure. This finding suggests that ceroid/lipofuscin-rich cells have an increased s ensitivity to oxidative stress. The ceroid/lipofuscin quantity strongly pos itively correlated with the size of the acidic compartment (as evaluated by uptake of the weakly basic lysosomotropic fluorochrome acridine orange) an d with its content of the lysosomal protease cathepsin D, as assayed by imm unocytochemistry. We hypothesize that the enhanced sensitivity of ceroid/li pofuscin-loaded cells to oxidative: stress may be caused by the increased a mounts of lysosomal enzymes, known as mediators of oxidative damage, and/or by catalysis of intralysosomal oxidative reactions by lipofuscin-associate d iron. (C) 1999 Elsevier Science Inc. All rights reserved.