Abstract
A study was conducted to determine the enzymatic kinetic parameters Vmax, KM, and intrinsic clearance (CLint) for the hepatic in vitro production of aflatoxin B1-dihydrodiol (AFB1-dhd) from aflatoxin B1 (AFB1) in four commercial poultry species, ranging in sensitivity to AFB1 from highest (ducks) to lowest (chickens). Significant but small differences were seen for Vmax, while large significant differences were observed for KM. However, the largest inter-species differences were observed for the CLint parameter, with ducks being extraordinarily efficient in converting AFB1 into AFB1-dhd. Since AFB1-dhd is considered the metabolite responsible for the acute toxic effects of AFB1, the high hepatic production of AFB1-dhd from AFB1 in ducks is the possible biochemical explanation for the extraordinary high sensitivity of this poultry species to the adverse effects of AFB1.
Highlights
Since the discovery of aflatoxins[1] after the turkey “X” disease outbreak that killed over 100,000 turkey poults in Britain in 19602, it has been known that there are extremely large differences in sensitivity to aflatoxin B1 (AFB1) among commercial poultry species
The putative peak observed at 6.7 min Fig. 2a corresponded to a compound of 347 Da, which is consistent with the monoisotopic protonated mass of AFB1-dhd Fig. 2b
Regarding the CLint parameter, very large differences among the species evaluated were observed, with ducks being extraordinarily efficient in converting AFB1 into AFB1-dhd compared to the other poultry species investigated Fig. 3d
Summary
Since the discovery of aflatoxins[1] after the turkey “X” disease outbreak that killed over 100,000 turkey poults in Britain in 19602, it has been known that there are extremely large differences in sensitivity to aflatoxin B1 (AFB1) among commercial poultry species. The 100-fold difference between ducks and laying hens reflects the extreme tolerance to aflatoxins in adult chickens and the large sensitivity in ducks. The AFB1 metabolite responsible for the acute toxic effects of AFB1 has not been clearly identified but one possible candidate is the AFB1-exo-8,9-dihydrodiol (AFB1-dhd) that results from the nucleophilic trapping process of the AFB1-exo-8,9-epoxide by water[12,13], Fig. 1. For more than a decade our research group has been looking for biochemical differences in the hepatic biotransformation of AFB1 that could explain the in vivo differences in response to AFB1 among the main poultry species[8,18,19,20,21]. Parameters of AFB1-dhd production in liver microsomes that could explain the different in vivo sensitivity to AFB1 of resistant (chickens and quail), sensitive (turkeys) and highly sensitive (ducks) poultry species
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