Retinal carotenoids can attenuate formation of A2E in the retinal pigment epithelium

Abstract

A2E, an important constituent of lipofuscin in human retinal pigment epithelium (RPE), is thought to mediate light-induced oxidative damage associated with aging and other ocular disorders. Ocular carotenoids in overlying retinal tissues were measured by HPLC and mass spectrometry and were correlated with levels of RPE A2E. We observed a statistically significant increase in total A2E levels in human RPE/choroid with age, and A2E levels in macular regions were approximately 1/3 lower than in peripheral retinal regions of the same size. There was a statistically significant inverse correlation between peripheral retina carotenoids and peripheral RPE/choroid A2E. Prospective carotenoid supplementation studies in Japanese quail demonstrated nearly complete inhibition of A2E formation and oxidation. These findings support current recommendations to increase dietary intake of xanthophyll carotenoids in individuals at risk for macular degeneration and highlight a new potential mechanism for their protective effects-inhibition of A2E formation and oxidation in the eye.

Fig 1

HPLC PDA-chromatograms (A and B) and full scan mass spectra (C, D, E, F) of the A2E and iso-A2E peaks from the RPE/choroids of a 14-year-old (A, C, & E) and a 74-year-old (B, D, & F) donor.

Fig 2

Agewise distribution of A2E levels in human whole RPE/choroid (A); 8-mm macular punches (B); and 8-mm peripheral retina punches (C). There was a significant increase observed with age (P < 0.001) in all cases.

Fig 3

Distribution of RPE/choroid A2E levels in relation to overlying retinal carotenoid levels in 8-mm macular punches (A) and 8-mm peripheral retina punches (B). There was a statistically significant inverse correlation between carotenoids in the peripheral retina and A2E levels in the underlying RPE-choroid (R= −0.36, N=40, P=0.02); however, this inverse relationship was not statistically significant between macular carotenoids and macular A2E (R= −0.28; N= 35; P= 0.10).

Fig 4

Manipulation of ocular carotenoid and A2E levels in response to dietary supplementation with lutein or zeaxanthin in Japanese quail for 16 weeks (N=4 for all groups). In the upper panel, dark grey bars represent total carotenoids, and light grey bars represent total lutein and zeaxanthin content in the respective groups. Control animals were on a low carotenoid diet for 16 weeks. The A2E levels in the RPE were significantly higher for the control group relative to the other three groups (P < 0.001). The A2E levels of other groups were not significantly different from each other.

Fig 5

Full scan mass spectra of the A2E extracted from RPE of experimental birds. Week 1 control diet (A); Week 10 control diet (B); Week 12 zeaxanthin-supplemented diet (C); Week 12 lutein-supplemented diet (D).