A role for vitamin A in the formation of ocular lipofuscin
Department of
Ophthalmology and School of Biological Sciences, University of
Manchester, Manchester
Correspondence to: Dr Mike Boulton, Department of Ophthalmology, Manchester Royal Eye Hospital, Oxford Road, Manchester M13 9WH.
Accepted for publication 28 July 1997
BACKGROUND
Lipofuscin granules in the retinal
pigment epithelium are lipid protein aggregates which are thought to
represent the lifelong accumulation of the non-degradable end products
from the phagocytosis of photoreceptor outer segments. Given the
increasing evidence for a key role for vitamin A in the formation of
ocular lipofuscin, the fluorophores generated by reacting vitamin A
with lipid were assessed.
METHODSReaction mixtures consisting of vitamin A
(retinol) or its aldehyde (retinal) and (a) isolated rod outer
segments, (b) the lipid extract of rod outer segments, (c) protein, or
(d) liposomes were incubated at either pH 4.5 or 7.0 for up to 42 days.
The fluorescence characteristics and mobility of the chloroform soluble fluorophores generated were compared with those extracted from purified
human lipofuscin. Finally, the effect of lysosomal degradation on
fluorophores generated in the above mixtures was assessed.
RESULTSMajor spectral changes were observed when
ROS or liposomes were incubated with retinal. These changes were pH
dependent and did not occur if retinal was replaced with retinol. A
number of the fluorophores generated exhibited similar fluorescence
characteristics and chromatographic mobility to those of lipofuscin.
Neither the presence of protein nor exposure to lysosomal enzymes had
any effect on the spectral profile or fluorophore mobility of the fluorophores generated.
CONCLUSIONSThese results suggest that some of the
chloroform soluble fluorophores of lipofuscin are formed as a direct
reaction product of retinal and lipid.
© 1997 by British Journal of Ophthalmology
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