Abstract
Purpose: :
We strove to characterize the structures and behaviours of A2E photo-cleavage products that are generated subsequent to photooxidation.
Methods: :
Liquid chromatography (LC) coupled to electrospray ionization mass spectrometry (ESI-MS) together with tandem mass spectrometry (MS/MS) was employed to characterize photocleavage products of A2E. ARPE-19 cells that were grown on a fibronectin substrate were allowed to accumulate A2E and irradiated at 430 nm. Fibronectin was immunoprecipitated from homogenates of the cells and substrate and immunoblots were subsequently probed with polyclonal chicken antibody to advanced glycation end products (AGEs).
Results: :
A complex mixtures of A2E photo-products of various molecular weights were detected. Studies in which A2E was incubated with a singlet oxygen generator yielded results consistent with a mechanism involving bisretinoid photocleavage at sites of singlet molecular oxygen addition. Structural characterization revealed that A2E photodegradation releases methylglyoxal, a 72 Da reactive dicarbonyl with the capacity to form AGE. AGE adducts were detected at sites of blue light irradiation in association with the fibronectin substrate on which the cells were grown.
Conclusions: :
Photodegradation of A2E releases methylglyoxal, a low molecular weight reactive dicarbonyl that initiates AGE formation. Diffusion of A2E photocleavage products such as methylglyoxal is suggested by the observation that when cultured RPE cells that have accumulated A2E were irradiated (430 nm), the extracellular fibronectrin substrate on which the cells are grown becomes AGE-modified. Methylglyoxal is already known to be generated by carbohydrate and lipid oxidation; this is the first report of its production via bisretinoid photocleavage. It is significant that AGE-modified proteins are detected in drusen; drusen have been linked to AMD pathogenesis. These findings suggest a possible association between RPE bisretinoid lipofuscin photooxidation and drusen formation.
Keywords: ipofuscin • retinal pigment epithelium • drusen