Inhibition of crystallin ascorbylation by nucleophilic compounds in the hsvct2 mouse model of lenticular aging.
PURPOSE: Senile cataracts are associated with oxidation,
fragmentation, cross-linking, insolubilization, and yellow pigmentation
of lens crystallins. This process is partially explained by advanced
glycation end products (AGEs) from ascorbic acid (ASA), as the authors
unequivocally demonstrated in an hSVCT2 transgenic mouse. The authors
present the first pharmacologic intervention study against ascorbylation
in these mice. METHODS: Five groups of mice from 2 to 9 months of age
(10 mice/group) were fed a diet containing 0.1% (wt/wt) aminoguanidine,
pyridoxamine, penicillamine, and nucleophilic compounds NC-I and NC-II.
AGEs were determined in crystallin digests using high-performance liquid
chromatography, liquid chromatography-mass spectrometry, or gas
chromatography-mass spectrometry. Lens protein extract was incubated in
vitro with ASA or dehydroascorbic acid. RESULTS: The ASA level increased
approximately 10-fold in all groups and was unaffected by treatment.
AGEs were increased several-fold in transgenic compared with control
lenses. Body weight, food intake, lenticular glutathione, and glycated
lysine level were unaltered. In vitro, all compounds inhibited AGE
formation. In vivo, NC-I and NC-II significantly decreased protein
fluorescence at lambda(ex)335/(em)385 (P = 0.045, P = 0.017,
respectively) and lambda(ex)370/ (em)440 (P = 0.029, P = 0.007,
respectively). Other inhibitors had no effect. After 7 months, only NC-I
and NC-II induced a 50% reduction in pentosidine (P = NS for NC-I; P =
0.035 for NC-II). NC-I also decreased carboxymethyllysine (P = 0.032)
and carboxyethyllysine (P = NS). Fluorescent cross-link K2P was
decreased by NC-I, NC-II, aminoguanidine, and pyridoxamine (P = NS).
CONCLUSIONS: Pharmacologically blocking protein ascorbylation with
absorbable guanidino compounds is feasible and may represent a new
strategy for the delay of age-related nuclear sclerosis of the lens.
Invest Ophthalmol Vis Sci. 2008 Nov;49(11):4945-52