Inhibition of crystallin ascorbylation by nucleophilic compounds in the hSVCT2 mouse model of lenticular aging.
OBJECTIVE
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.
Fan
Xingjun
X
Department of Pathology, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106, USA.
Monnier
Vincent M
VM
D000375:Aging / Q000378:metabolism*; D000818:Animals; D000975:Antioxidants / Q000493:pharmacokinetics; D001205:Ascorbic Acid / Q000493:pharmacokinetics*; D002386:Cataract / Q000378:metabolism* / Q000517:prevention & control; D002851:Chromatography, High Pressure Liquid; D003459:Crystallins / Q000378:metabolism*; D008401:Gas Chromatography-Mass Spectrometry; D017127:Glycation End Products, Advanced / Q000378:metabolism; D007908:Lens, Crystalline / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D013050:Spectrometry, Fluorescence
D000975:Antioxidants; D003459:Crystallins; D017127:Glycation End Products, Advanced; D001205:Ascorbic Acid