Phase-1 bioactivation mechanisms of aflatoxin through AhR, CAR and PXR nuclear receptors and the interactions with Nigella sativa seeds and thymoquinone in broilers

Abstract

Aflatoxins (AFs) are metabolised in two main phases in the liver. Cytochrome p450 enzyme (CYP) 1A1 and CYP2A6 are expressed through AhR, CAR and PXR nuclear receptors in phase-1 biotransformation of AFs. This study is the first to examine phase-1 biotransformation mechanisms of AF and the activity of Nigella sativa seed (NS) and its active ingredient thymoquinone (TQ) on these enzymes and receptors at the molecular level in broilers. Six groups of one day old broiler chicken (20 animals per group) were fed either control feed or a diet containing Aspergillus parasiticus NRRL 2999 culture material (total AFs 2 mg/kg), TQ (300 mg/kg), and NS (5%), either alone or as AF + TQ and AF + NS. Randomly selected from each group, 10 chicks were necropsied, and the livers were removed. Histopathological examination and serum biochemistry results revealed that AF caused hydropic and fatty degenerations, periportal inflammatory infiltrations, acinar arrangement, and biliary duct proliferation in livers and a significant increase at AST, ALT, ALP and GGT levels while significant decreases at serum cholesterol and total protein levels. These aflatoxicosis lesions and deteriorations in biochemistry levels were significantly ameliorated by NS or TQ (p < 0.05). AF was immunohistochemically found to increase strongly the nuclear receptors of AhR, PXR, CAR, and the enzyme activity of CYP1A1 and CYP2A6 responsible for its metabolism, leading to the emergence of toxic effects. Addition of TQ or NS to AF-containing diets improved the negative effects of AF on these receptors and enzymes significantly (p < 0.05). It was concluded that TQ and NS successfully alleviated liver injury by inhibiting or reducing the bioactivation of AF through phase-1 nuclear receptors and CYP-450 enzymes modulation.