Dual effectiveness of Alternaria but not Fusarium mycotoxins against human topoisomerase II and bacterial gyrase

Abstract

Type II DNA-topoisomerases (topo II) play a crucial role in the maintenance of DNA topology. Previously, fungi of the Alternaria genus were found to produce mycotoxins that target human topo II. These results implied the question why a fungus should produce secondary metabolites that target a human enzyme. In the current work, the homology between human topo II and its bacterial equivalent, gyrase, served as basis to study a potential dual inhibition of both enzymes by mycotoxins. A total of 15 secondary metabolites produced by fungi of the genera Alternaria and Fusarium were assessed for their impact on topo II of human and bacterial origin in the decatenation and the supercoiling assay, respectively. In line with the theory of dual topo II inhibition, six of the tested Alternaria mycotoxins were active against both enzymes, the dibenzo-α-pyrones alternariol (AOH) and alternariol monomethyl ether (AME), as well as the perylene-quinones altertoxin I (ATX I) and II (ATX II), alterperylenol (ALP) and stemphyltoxin III (STTX III). The Alternaria metabolites altersetin (ALN), macrosporin (MAC), altenusine (ALS) and pyrenophorol (PYR) impaired the function of human topo II, but did not show any effect on gyrase. The potency to inhibit topo II activity declined in the row STTX III (initial inhibitory concentration 10 µM) > AOH (25 µM) = AME (25 µM) = ALS (25 µM) = ATX II (25 µM) > ALN (50 µM) = ATX I (50 µM) > ALP (75 µM) = PYR (75 µM) > MAC (150 µM). Inhibition of gyrase activity was most pronounced for AOH and AME (initial inhibitory concentration 10 µM) followed by ATX II (25 µM) > ATX I = ALP = STTX III (50 µM). In contrast, none of the investigated Fusarium mycotoxins deoxynivalenol (DON), fumonisin B1, fusarin C and moniliformin, as well as the Alternaria metabolite tentoxin, had any impact on the activity of neither human nor bacterial topo II.Electronic supplementary materialThe online version of this article (doi:10.1007/s00204-016-1855-z) contains supplementary material, which is available to authorized users.

Chemotaxonomy of Mycotoxigenic Small-Spored Alternaria Fungi – Do Multitoxin Mixtures Act as an Indicator for Species Differentiation?

“…Recently, the potency of ATs to inhibit the human type II DNA-topoisomerase and its bacterial equivalent, gyrase, was reported, whereby the human enzyme inhibition increased gradually from ALP (75 μM) over ATX-I (50 μM), AOH, AME, and ATX-II (25 μM) to STTX-III (10 μM). The bacterial enzyme was inhibited increasingly from STTX-III, ATX-I, and ALP (50 μM) followed by ATX-II (25 μM) to AOH and AME (10 μM) ( Jarolim et al, 2017 ). The occurrence of those mycotoxin mixtures has already been linked to stronger adverse impacts and synergistic effects on human and animal health than indicated by a single mycotoxin.…”

Functional impairment triggered by altertoxin II (ATXII) in intestinal cells in vitro: cross-talk between cytotoxicity and mechanotransduction

“…Due to the presence of an epoxide group at the perylene quinone scaffold, ATXII is known to be a relatively reactive compound (Aichinger et al 2018; Fleck et al 2014a). In this light, it is prone not only to the activation of the Nrf2/ARE pathway (Jarolim et al 2017), but also to direct reaction with diverse cell structures (Fleck et al 2012; Jarolim et al 2016). To verify if the effect of the toxin on membrane fluidity was related to oxidation/reaction processes involving the epoxide moiety of the molecule, experiments were performed in the presence of the antioxidant NAC (Oommen et al 2016; Raza et al 2016).…”

“…Alternaria alternata proliferates on food items and can contaminate commodities which may also reach the market (Walravens et al 2016). Alternaria mycotoxins can differ greatly in structure and their biological targets span from the regulation of DNA topology to the estrogenic cascade (Aichinger et al 2017; Jarolim et al 2016; Lehmann et al 2006; Vejdovszky et al 2017a). Among these, the perylene quinone type mycotoxin altertoxin II (ATXII) is one of the more potent ones with respect to genotoxicity (Fleck et al 2016; Pahlke et al 2016; Schwarz et al 2012).…”

Tracking emerging mycotoxins in food: development of an LC-MS/MS method for free and modified Alternaria toxins

“…The mechanisms behind its mode of action could not be clarified so far. Nevertheless, genotoxicity was observed at comparatively low concentrations, but no enhanced levels of reactive oxygen species, glutathione depletion, or topoisomerase inhibition [11, 12]. Besides, AOH, AME, and some of their metabolites additionally exhibit estrogenic potential [13, 14] which may be enhanced by combinatory toxic effects [15–17].…”