Piperine inhibits aflatoxin B1 production in Aspergillus flavus by modulating fungal oxidative stress response

Aspergillus flavus, a soil-borne pathogen, represents a danger for humans and animals since it produces the carcinogenic mycotoxin Aflatoxin B1 (AFB1). Approaches aiming the reduction of this fungal contaminant mainly involve chemicals that may also be toxic. Therefore, identification and characterization of natural anti-aflatoxigenic products represents a sustainable alternative strategy. Piperine, a major component of black and long peppers, has been previously demonstrated as an AFB1-inhibitor; nevertheless its mechanism of action was yet to be elucidated. The aim of the present study was to evaluate piperine's molecular mechanism of action in A. flavus with a special focus on oxidative stress response. For that, the entire AFB1 gene cluster as well as a targeted gene-network coding for fungal stress response factors and cellular receptors were analyzed. In addition to this, fungal enzymatic activities were also characterized. We demonstrated that piperine inhibits aflatoxin production and fungal growth in a dose-dependent manner. Analysis of the gene cluster demonstrated that almost all genes participating in aflatoxin's biosynthetic pathway were down regulated. Exposure to piperine also resulted in decreased transcript levels of the global regulator veA together with an over-expression of genes coding for several basic leucine zipper (bZIP) transcription factors such as atfA, aftB and ap-1 and genes belonging to superoxide dismutase and catalase's families. Furthermore, this gene response was accompanied by a significant enhancement of catalase enzymatic activity. In conclusion, these data demonstrated that piperine inhibits AFB1 production while positively modulating fungal antioxidant status in A. flavus.