AGE-RELATED ACCUMULATION OF HYL-1,2,3,4-TETRAHYDRO-BETA-CARBOLINE-3-CARBOXYLIC ACID IN HUMAN LENS

A fluorescent beta-carboline, hyl-1,2,3,4-tetrahydro-beta-carboline-3- carboxylic acid (MTCA) was identified in human normal lenses and catar actous lenses. The mean total amounts of MTCA in normal lenses (n = 7) , diabetic cataractous lenses (n = 15), and senile cataractous lenses (n = 15) were 0.64 +/- 0.76 ng, 1.79 +/- 0.94 ng, and 3.66 +/- 1.04 ng , respectively. The MTCA levels in human lenses increased linearly wit h the age of the lenses, and there was a significant correlation betwe en the total amount of MTCA in human lenses and the age of the lens. I n all types of lenses, the concentrations of MTCA in the insoluble-pro tein fraction [pg (mg protein)(-1)] were significantly higher than tho se in the water-soluble protein fraction. These results suggest that M TCA may be one of the age-related fluorogens. In vitro experiments rev ealed that MTCA, a condensation reaction product of tryptophan with ac etaldehyde, can be formed in the mixture of tryptophan and glucose by low temperature heating. Furthermore, the MTCA levels in the homogenat e of cataractous lenses were significantly increased with the heating time, when the homogenate without addition of glucose and tryptophan w as heated at 60 degrees C. This indicates that enough material such as tryptophan for MTCA formation is present in human cataractous lenses. Therefore, it may be that MTCA is formed in human lens. However, we c an not rule out the possibility that MTCA in the lens may be derived f rom other sources, and deposited in the lens since MTCA is reported to be present in various foodstuffs and alcoholic beverages. (C) 1996 Ac ademic Press Limited