There has been considerable interest in the glycation of lens proteins as a causative mechanism of both diabetic and senile cataract. The long half life of the lens proteins predict that glycated molecules should accumulate in the lens, and may play a role in the formation of the high molecular weight protein aggregates seen in aged lenses and cataracts. After 10 years of research there has been little progress on identification and quantitation of glycated products, and no direct evidence for protein crosslinking has been forthcoming. We have been studying glycation of lens proteins by ascorbic acid as opposed to glucose. When ascorbic acid is oxidized to dehydroascorbic acid, a rapid glycation and crosslinking occurs which resembles that seen in cataract. Specific amino acid adducts have been isolated, and several of these are present at relatively high concentrations in the water-insoluble fraction from human lens tissue. We intend to obtain more definitive data in the work outlined here by identifying the degradation products of ascorbic acid and studying the rate of formation of each under the conditions present in the lens. The isolation and identification of 5 different lysine adducts is planned, as well as their identification as modified amino acids in cataract extracts. Several approaches will also be taken in an attempt to identify the nature of the crosslink formed between crystallins. Experiments are also designed to see if ascorbic acid can play a role in the generation of oxygen free radicals, and to estimate whether this is a viable mechanism for additional protein damage in vivo.

Agency
National Institute of Health (NIH)
Institute
National Eye Institute (NEI)
Type
Research Project (R01)
Project #
5R01EY007070-07
Application #
3263955
Study Section
Visual Sciences A Study Section (VISA)
Project Start
1987-08-01
Project End
1995-07-31
Budget Start
1993-08-01
Budget End
1994-07-31
Support Year
7
Fiscal Year
1993
Total Cost
Indirect Cost
Name
University of Missouri-Columbia
Department
Type
Schools of Medicine
DUNS #
112205955
City
Columbia
State
MO
Country
United States
Zip Code
65211
Bhattacharyya, Jaya; Shipova, Ekaterina V; Santhoshkumar, Puttur et al. (2007) Effect of a single AGE modification on the structure and chaperone activity of human alphaB-crystallin. Biochemistry 46:14682-92
Cheng, Rongzhu; Feng, Qi; Argirov, Ognyan K et al. (2005) K2P--a novel cross-link from human lens protein. Ann N Y Acad Sci 1043:184-94
Cheng, Rongzhu; Lin, Bin; Ortwerth, Beryl J (2002) Rate of formation of AGEs during ascorbate glycation and during aging in human lens tissue. Biochim Biophys Acta 1587:65-74
Linetsky, M; James, H L; Ortwerth, B J (1999) Spontaneous generation of superoxide anion by human lens proteins and by calf lens proteins ascorbylated in vitro. Exp Eye Res 69:239-48
Prabhakaram, M; Ortwerth, B J (1994) Determination of glycation crosslinking by the sugar-dependent incorporation of [14C]lysine into protein. Anal Biochem 216:305-12
Nagaraj, R H; Prabhakaram, M; Ortwerth, B J et al. (1994) Suppression of pentosidine formation in galactosemic rat lens by an inhibitor of aldose reductase. Diabetes 43:580-6
Li, E Y; Feather, M S (1994) The degradation of L-threose at Maillard reaction conditions. Carbohydr Res 256:41-7
Ortwerth, B J; Speaker, J A; Prabhakaram, M et al. (1994) Ascorbic acid glycation: the reactions of L-threose in lens tissue. Exp Eye Res 58:665-74
Ortwerth, B J; Olesen, P R; Sharma, K K et al. (1993) Chemical modification of alpha crystallin. Exp Eye Res 56:107-14
Prabhakaram, M; Ortwerth, B J (1992) Glycation of MP26 and MP22 in bovine lens membranes. Biochem Biophys Res Commun 185:496-504

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