Abstract
Aflatoxin M1 (AFM1) is a hydroxylated metabolite of aflatoxin B1 (AFB1). After it is formed, it is secreted in the milk of mammals. Despite the potential risk of human exposure to AFM1, data reported in literature on the metabolism, toxicity, and bioavailability of this molecule are limited and out of date. The aim of the present research was to study the absorption profile of AFM1 and possible damage to tight junctions (TJ) of the intestinal Caco-2/TC7 clone grown on microporous filter supports. These inserts allowed for the separation of the apical and basolateral compartments which correspond to the in vivo lumen and the interstitial space/vascular systems of intestinal mucosa respectively. In this study, the Caco-2/TC7 cells were treated with different AFM1 concentrations (10–10,000 ng/kg) for short (40 min) and long periods of time (48 h). The AFM1 influx/efflux transport and effects on TJ were evaluated by measuring trans-epithelial electrical resistance and observing TJ protein (Zonula occludens-1 and occludin) localization. The results showed that: (i) when introduced to the apical and basolateral compartments, AFM1 was poorly absorbed by the Caco-2/TC7 cells but its transport across the cell monolayer occurred very quickly (Papp value of 105.10 ± 7.98 cm/s × 10−6). (ii) The integrity of TJ was not permanently compromised after exposure to the mycotoxin. Viability impairment or barrier damage did not occur either. The present results contribute to the evaluation of human risk exposure to AFM1, although the AFM1 transport mechanism need to be clarified.
Highlights
The results showed that: (i) when introduced to the apical and basolateral compartments, Aflatoxin M1 (AFM1) was poorly absorbed by the Caco-2/TC7 cells but its transport across the cell monolayer occurred very quickly (P app value of 105.10 ± 7.98 cm/s × 10−6). (ii) The integrity of tight junctions (TJ) was not permanently compromised after exposure to the mycotoxin
EFFECTS ON TJ Trans-epithelial electrical resistance Trans-epithelial electrical resistance values in Experiment 1 were recorded before the treatment and after exposure for 6 and 24 h to different concentrations of AFM1
Caco-2/TC7 cells were exposed to different concentrations of AFM1 (1,000–10,000 ng/kg) in both Ap and Bl compartments www.frontiersin.org and distribution between compartments was determined after 48 h by HPLC analysis
Summary
Aflatoxin B1 (AFB1), the most potent hepatocarcinogen known in mammals (Creppy, 2002), is biotransformed into aflatoxin M1 (AFM1) at the hepatic level by microsomal cytochrome P450 (Van Egmond, 1989) and can be secreted in the milk of mammals (Holzapfel et al, 1966; Applebaum et al, 1982; Van Egmond, 1989; Wood, 1991; Neal et al, 1998). Human exposure to AFM1 is partly from consumption of contaminated milk and dairy products and partly from endogenous production through AFB1 metabolism in the liver (Neal et al, 1998). The potential presence of AFM1 in milk and its by-products represents a worldwide concern as these products are primarily consumed by infants and children who are more susceptible to the adverse effects of mycotoxins (Boudra et al, 2007). The US Food and Drug Administration (FDA) has established an action level of 500 ng/kg in whole, low fat, and skim milk (FDA, 2005)
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