The mycotoxin alternariol suppresses lipopolysaccharide-induced inflammation in THP-1 derived macrophages targeting the NF-κB signalling pathway.

Alternariol (AOH) is a secondary metabolite formed by black mold of the genus Alternaria alternata. Due to limited hazard and occurrence data, AOH is still considered as an "emerging mycotoxin" and, as such, not monitored and regulated yet. Recent studies indicate immunosuppressive effects in vitro by altering the expression of CD molecules and proinflammatory cytokines, which are indispensable in mounting an innate immune response. However, the mode of action by which AOH exerts its immunosuppressive effects has not been unraveled yet. The present study aimed to characterise the impact of AOH on the nuclear factor kappa B (NF-κB) pathway, the expression of NF-κB target cytokines and involved regulatory microRNAs (miRNAs). In THP-1 derived macrophages, AOH (1-20 µM) was found to suppress lipopolysaccharide (LPS)-induced NF-κB pathway activation, decrease secretion of the proinflammatory cytokines IL-8, IL-6, TNF-α and to induce secretion of the anti-inflammatory IL-10. Thereby, a distinct pattern of cytokine mRNA levels was monitored, varying between short- and long-term exposure. Concomitantly, AOH (2-20 µM) affected the transcription levels of miR-146a and miR-155 in LPS-stimulated THP-1 derived macrophages dose-dependently by down- and upregulation, respectively. In contrast, transcription of miR-16 and miR-125b, two other immune-related miRNAs, was not modulated. In the absence of a LPS stimulus, AOH (20 µM) did not affect basal NF-κB activity, but increased IL-10 transcription. Collectively, our results indicate, that AOH itself does not induce a proinflammatory immune response in human macrophages; however, in an inflamed environment it possesses the ability to repress inflammation by targeting the NF-κB signalling pathway and regulatory miRNAs.