Reaction-kinetic parameters of glycidamide as determinants of mutagenic potency.
Values for reaction-kinetic parameters of electrophiles can be used to predict mutagenic potency. One approach employs the Swain-Scott relationship for comparative kinetic studies of electrophilic agents reacting with nucleophiles. In this way glycidamide (GA), the putatively mutagenic/carcinogenic metabolite of acrylamide, was assessed by determining the rates of reaction with different nucleophiles. The rate constants (kNu) were determined using the "supernucleophile" cob(I)alamin [Cbl(I)] as an analytical tool. The Swain-Scott parameters for GA were compared with those of ethylene oxide (EO). The substrate constants, s values, for GA and for EO were found to be 1.0 and 0.93, respectively. The reaction rates at low values of nucleophilic strength (n=1-3), corresponding to oxygens in DNA, were determined to be 2-3.5 times higher for GA compared to EO. GA was also more reactive than EO towards other nucleophiles (n=0-6.4). The mutagenic potency of GA was determined in Chinese hamster ovary cells (hprt mutations in CHO-AA8 cells per dose unit with gamma-radiation as reference standard). The potency of GA was estimated to be about three mutations per 10(5) cells and mMh corresponding to about 40 rad-equ./mMh. A preliminary comparison of the mutagenic potency (per mMh and as rad-equivalents) of GA and EO shows an approximately seven times higher potency for GA. A higher mutagenic potency of GA compared to EO is compatible with expectation from reaction-kinetic data of the two compounds. The data confirmed that GA is not a strong mutagen, which is in line with what is expected for simple oxiranes. The present study shows the value of cob(I)alamin for the determination of reaction-kinetic parameters and their use for prediction of mutagenic potency.
Silvari
V
V
Department of Environmental Chemistry, Stockholm University, S-10691 Stockholm, Sweden.
Haglund
J
J
Jenssen
D
D
Golding
B T
BT
Ehrenberg
L
L
Törnqvist
M
M
D000818:Animals; D002460:Cell Line; D006224:Cricetinae; D003412:Cricetulus; D004305:Dose-Response Relationship, Drug; D004852:Epoxy Compounds / Q000737:chemistry* / Q000633:toxicity; D005027:Ethylene Oxide / Q000737:chemistry / Q000633:toxicity; D007700:Kinetics; D008954:Models, Biological; D009153:Mutagens / Q000737:chemistry* / Q000633:toxicity; D009154:Mutation; D014805:Vitamin B 12 / Q000737:chemistry
D004852:Epoxy Compounds; D009153:Mutagens; C071834:glycidamide; D005027:Ethylene Oxide; D014805:Vitamin B 12