In vivo studies have shown significant toxicity to retinal function and cellular morphology in ApoE-deficient mice fed a high-cholesterol diet.
14 Moreover, oxysterols, primarily 7kCh, are toxic in vitro to RPE cells
41 and cells derived from neuroretinas.
21,41 Human RPE cell degeneration is one of the initial events that occur in AMD.
61–63 The present study used ARPE-19 cells to examine the effects of 7kCh on mitochondrial DNA integrity and function because ARPE-19 cells have structural and functional properties characteristic of human RPE cells in vivo
40 and can internalize LDL and ox-LDL in large quantities in vitro and in vivo.
42 There is controversy on whether 7kCh should be mixed with LDL in the in vitro experiments. Rodriguez et al.
42 studied cell toxicity using oxysterols mixed with LDL, which aided with the internalization of the complex. However, other studies show that 7kCh without LDL could induce caspase activities, apoptosis, and cell death.
41,64,65 It has been suggested that 7kCh could be internalized into the cells, perhaps through carriers in the serum. We have not evaluated the effects of 7kCh using primary RPE cells or other cell lines, but other investigators have. Joffre et al.
66 report increases in ROS levels and mitochondrial dysfunction in primary porcine RPE cells treated with 7kCh. Rodriguez et al.
26 show that 7kCh is the most cytotoxic of the oxysterols using the ARPE-19 cell model. Reports show that 7kCh induces apoptosis involving caspase-3, caspase-8, and caspase-12 pathways in rat R28 cells, HMVEC cells, and ARPE-19 cells.
50,67,68 In addition, 7kCh, localized to the choriocapillaris and Bruch's membrane, induces VEGF levels, which might play a role in neovascularization.
69