An overview of aflatoxin B1 biotransformation and aflatoxin M1 secretion in lactating dairy cows

Abstract

Milk is considered a perfect natural food for humans and animals. However, aflatoxin B1 (AFB1) contaminating the feeds fed to lactating dairy cows can introduce aflatoxin M1 (AFM1), the main toxic metabolite of aflatoxins into the milk, consequently posing a risk to human health. As a result of AFM1 monitoring in raw milk worldwide, it is evident that high AFM1 concentrations exist in raw milk in many countries. Thus, the incidence of AFM1 in milk from dairy cows should not be underestimated. To further optimize the intervention strategies, it is necessary to better understand the metabolism of AFB1 and its biotransformation into AFM1 and the specific secretion pathways in lactating dairy cows. The metabolism of AFB1 and its biotransformation into AFM1 in lactating dairy cows are drawn in this review. Furthermore, recent data provide evidence that in the mammary tissue of lactating dairy cows, aflatoxins significantly increase the activity of a protein, ATP-binding cassette super-family G member 2 (ABCG2), an efflux transporter known to facilitate the excretion of various xenobiotics and veterinary drugs into milk. Further research should focus on identifying and understanding the factors that affect the expression of ABCG2 in the mammary gland of cows.

Keywords: Aflatoxin B1; Aflatoxin M1; Biotransformation; Dairy cow; Milk safety.

Fig. 1

The metabolism and biotransformation pathways of AFB1 in lactating dairy cows. AFB1 = aflatoxin B1; AFBO = AFB1-8; 9-epoxide (highly toxic; mutagenic; and carcinogenic); AFB-GSH = aflatoxin glutathione adduction; AFL = aflatoxicol; AFM1 = aflatoxin M1 (highly toxic and excreted in milk); AFP1 = aflatoxin P1; AFQ1 = aflatoxin Q1. Dashed box, detoxification pathways in dairy cows. Dotted arrow, metabolic pathway needs to further validation.