In the presence of ferritin, visible light induces lipid peroxidation of the porcine photoreceptor outer segment

Abstract

We studied the synergistic effect of visible light and ferritin on the lipid peroxidation on a fraction of porcine photoreceptor outer segment (POS). Reaction mixtures containing the POS fraction and horse spleen ferritin were irradiated under white fluorescent light mainly at 17,000 lx or incubated under dark conditions at 37 degrees C. The lipid peroxidation was evaluated by both the thiobarbituric acid method and the ferrous oxidation/xylenol orange method. The irradiation-induced lipid peroxidation was affected by some experimental factors such as the irradiation dose and acidity of the material. When the irradiation was stopped, the lipid peroxidation was also stopped; thereafter, the re-irradiation induced lipid peroxidation. Moreover, this lipid peroxidation was inhibited by desferrioxamine, an iron chelator, or by dimethylthiourea, a hydroxyl radical scavenger, suggesting that the lipid peroxidation involves hydroxyl radicals generated via the Fenton reaction by iron ion released from ferritin. The lipid peroxidation did not take place under dark conditions or in the absence of ferritin. This study suggested the possibility that the visible light-induced lipid peroxidation of the POS fraction in the presence of ferritin may participate in the etiology of human retinal degenerative diseases as the human retina is exposed to light for life.

Conversion of 7-ketocholesterol to oxysterol metabolites by recombinant CYP27A1 and retinal pigment epithelial cells

“…Recent studies also suggest that in the retina cholesterol oxidation could involve ferritin, which colocalizes with 7KCh ( 9 ). Ferritin was shown to release bound iron upon light exposure ( 41 ) and induce lipid peroxidation in photoreceptor outer segments ( 42 ). This mechanism is supported by identifi cation of a new form of ferritin, mitochondrial ferritin, which localizes in the mitochondrial matrix ( 43 ).…”

Photodamage Generates 7‐keto‐ and 7‐hydroxycholesterol in the Rat Retina via a Free Radical‐mediated Mechanism

“…Other investigators have previously observed that ferritin can catalyze lipid peroxidation in bovine photoreceptors in the presence of visible light (19). Moreover, exposure of ferritin to visible light promotes release of free iron (18).…”

“…The free radical mechanism requires a transition metal catalyst (typically Fe +2 or Cu +2 ). One biologically significant form of iron is ferritin, which has been shown to enhance lipid peroxidation in photoreceptor outer segment (POS) membranes in the presence of light (18,19), and also is relatively abundant in the retina (20,21). Hence, we suspect that ferritin may be implicated in the formation of 7KCh in the retina.…”

Genome-Wide Microarrray Analysis Reveals Roles for the REF-1 Family Member HLH-29 in Ferritin Synthesis and Peroxide Stress Response

“…Though difficult to interpret, our measurements of ftn-1 mRNA levels in hlh-29 mutants exposed to peroxide stress, support the possibility that RNAi against ftn-1 in these animals suppresses a toxic effect of excess ferritin. Recent reports in other systems show, for example, that increased ferritin levels in the presence of hydrogen peroxide [70], [71] or visible light [72] is detrimental to the cell because of increased lipid peroxidation. It is also possible that the increased sensitivity of hlh-29 ; ftn-1 (RNAi) mutants is the result of HLH-29′s influence on genes required for oxidative stress response.…”