Cytochrome P450 enzymes involved in the metabolism of aflatoxin B1 in chickens and quail

Abstract

A study was conducted to identify the cytochrome P450 (CYP, CYP450) enzyme orthologs involved in the bioactivation of aflatoxin B(1) (AFB(1)) into the highly toxic metabolite known as aflatoxin-8,9-epoxide (AFBO) in quail and chicken hepatic microsomes. The strategies used included the use of specific CYP450 inhibitors and the correlation of prototype substrate activities with AFBO production. Additionally, the presence of the enzymes was qualitatively determined using an immunoblotting technique. The results showed that both quail and chicken microsomes have CYP1A1, CYP1A2, CYP2A6, and CYP3A4 enzymatic activity. A strong relationship between CYP1A1 and CYP2A6 activities and AFB(1) bioactivation was found in both species. Inhibition studies provided more evidence for the role of CYP2A6 in the bioactivation of AFB(1). The immunoblot results showed clear bands for the CYP2A6 and CYP3A4 orthologs in both species. The results of the present study indicate that CYP2A6 and, to a lesser extent, CYP1A1 are responsible for the bioactivation of AFB(1) into AFBO in both quail and chicken hepatic microsomes.

Hepatocellular carcinoma and the risk of occupational exposure

“…This could be caused by the aflatoxin ability to determine the mutation of the p53 tumor suppressor gene, which in normal conditions induces the apoptosis processes [74][75][76][77] . The risk of HCC increases when the exposure occurs in the presence of HBV infection, as occurs in the Chinese population [78][79][80][81][82][83][84][85][86][87][88][89][90][91][92][93][94][95][96] .…”

Biotransformation of Aflatoxin B1 and Its Relationship with the Differential Toxicological Response to Aflatoxin in Commercial Poultry Species

“…The results of the studies conducted with the CYP3A4 turkey ortholog indicate that the turkey enzyme is not sensitive to the CYP3A4 human inhibitor troleandomycin but that it is sensitive to erythromycin and 17 -ethynylestradiol. If this lack of sensitivity to troleandomycin also applies for the duck CYP3A4 ortholog, this could explain the results of Diaz et al (2010b) previously described. In regards to the findings of Rawal et al (2010b), it is important to note that the fact that a cloned gene expressed in a heterologous system (e.g.…”

“…In contrast with turkeys, however, CYP3A4 does appear to play a role on AFB1 bioactivation in ducks (Diaz et al, 2010b). Duck microsomes show a high correlation between nifedipine oxidation and AFB1 epoxidation (Table 1) but the use of the specific human CYP3A4 inhibitor troleandomycin did not reduce AFBO production (Diaz et al, 2010b). A recent study reports the cloning of a turkey CYP3A37 expressed in E. coli able to biotransform AFB1 into AFQ1 (and to a lesser extent to AFBO) with an amino acid sequence homology of 76% compared with the human CYP3A4 (Rawal et al, 2010b).…”

“…This finding is of interest since CYP3A4 has been shown to be an activator of aflatoxins B1 and G1 in humans and other species (Parkinson & Ogilvie, 2008); however, in humans, CYP3A enzymes can form the AFBO only at relatively high substrate concentrations (Ramsdell et al, 1991). In contrast with turkeys, however, CYP3A4 does appear to play a role on AFB1 bioactivation in ducks (Diaz et al, 2010b). Duck microsomes show a high correlation between nifedipine oxidation and AFB1 epoxidation (Table 1) but the use of the specific human CYP3A4 inhibitor troleandomycin did not reduce AFBO production (Diaz et al, 2010b).…”

“…In contrast, in humans, at least three CYP450s had been identified as responsible for AFB1 bioactivation to AFBO (CYP1A2, CYP2A6 and CYP3A4) (Omiecinski et al, 1999;Hasler et al, 1999), and there was evidence that the CYP3A4 human enzyme was the most efficient . In view of this lack of information a series of studies were conducted by our group (Diaz et al, 2010a(Diaz et al, , 2010b(Diaz et al, , 2010c in order to investigate which specific avian CYP450 orthologs were responsible for the bioactivation of AFB1 into AFBO. These studies were conducted by using specific human CYP450 inhibitors ( -naphthoflavone for CYP1A1/2, furafylline for CYP1A2, 8-methoxypsoralen for CYP2A6 and troleandomycin for CYP3A4), by correlating AFBO formation with human prototype substrate activity (ethoxyresorufin O-deethylation for CYP1A1/2, methoxyresorufin Odeethylation for CYP1A2, coumarin 7-hydroxylation for CYP2A6 and nifedipine oxidation for CYP3A4) and by investigating the presence of ortholog proteins in avian liver by immunoblot using antibodies specific against human CYP1A1, CYP1A2, CYP2A6 and CYP3A4.…”