A fluorescent carcinogen, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in human lens

A fluorescent carcinogen, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) has been identified in both human normal lenses and cataractous lenses. The total amounts of PhIP in normal lenses were 50.7 +/- 36.0 pg (n = 7) while those of PhIP in senile and diabetic cataractous lenses were 143 +/- 29.2 pg (n = 10) and 148 +/- 55.0 pg (n = 10), respectively. Although it was not possible to strictly compare the contents of PhIP among normal, senile and diabetic lenses, due to the limited numbers of normal lenses available, the mean total amounts of PhIP in normal lenses were the lowest among normal, senile and cataractous lenses when allowing for differences in age. Furthermore, there was a significant correlation between total amounts of PhIP in human lenses, and age of the lens, suggesting that the content of PhIP in human lens is increased with age. In all types of lenses, the concentrations of PhIP in the insoluble-protein fraction (pg mg-1 protein) were significantly higher than those in the water-soluble protein fraction. In addition, PhIP was formed when bovine lens was incubated at 37 degrees C under the presence of creatinine and glucose for various time periods, and the yield of PhIP during incubation was found to be time-dependent. The results from our study suggest that PhIP may be one of the age-related fluorogens in the human lens.