Coordination of mycotoxins with lanthanides in luminescent complexes

Authors: HOSSAIN, MD ZAKIR - Orise Fellow; Maragos, Chris

Submitted to: Mycotoxin Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/15/2019
Publication Date: 4/4/2019
Citation: Hossain, M.Z., Maragos, C.M. 2019. Coordination of mycotoxins with lanthanides in luminescent complexes. Mycotoxin Research. 35(3):279-292. https://doi.org/10.1007/s12550-019-00356-w.
DOI: https://doi.org/10.1007/s12550-019-00356-w

Interpretive Summary: Several toxins that are produced by fungi (mycotoxins) are known to avidly bind to certain metals forming chelates. The mycotoxins in this group include cyclopiazonic acid, a neurotoxin, tenuazonic acid (TeA) which is toxic to a variety of plants and animals, ochratoxin and citrinin, which are kidney toxins, and kojic acid, which is widely used as a skin-whitening agent. These toxins are found in a variety of commodities, foods, and cosmetics. While it is known that they chelate metals, for several of these toxins the mechanism by which they exert their toxic effects is not well understood. ARS scientists in Peoria, IL tested these mycotoxins to determine if fluorescent derivatives could be readily made to facilitate their detection. Two of them, TeA and CPA formed fluorescent complexes with lanthanide metals (terbium, europium), which greatly facilitated their detection. To determine how other, more common, metals might react, 10 metals were tested to see how well they would bind to TeA. Results demonstrated that TeA bound copper and aluminum very effectively, providing some insight into how this compound may exert its toxic effects.

Technical Abstract: The ability of several chelating mycotoxins to form coordination complexes with the lanthanide metals europium and terbium was explored. The mycotoxins examined included ochratoxin A, citrinin, cyclopiazonic acid (CPA), kojic acid, and tenuazonic acid (TeA). Of these compounds, TeA and CPA resulted in the greatest luminescence. Parameters influencing luminescence of TeA were investigated further. These included the type of lanthanide and its concentration, certain environmental factors, and the effect of competing metal cations. Of the two lanthanide metals, the terbium coordination complex (TeA-Tb3+) showed greater luminescence relative to the europium complex (TeA-Eu3+). The effects of solvent type, water content, and pH on the TeA-Tb3+ system suggested that optimal conditions for luminescence were in 90% methanol with 10% aqueous buffer at pH 3. In competitive assays, the luminescence of the TeA-Tb3+ complex decreased as the concentration of competing metal cations increased. Among the cations tested, Cu2+ was the best inhibitor followed by Al3+, Au3+, Fe3+, Co2+, Mn2+, Mg2+, and Ca2+. Two cations, Na+ and K+, showed no significant inhibition. This is the first report to describe the coordination of the metal-chelating mycotoxin TeA with lanthanides and the ability of TeA to serve as an “antenna” for the efficient transfer of energy to the lanthanide with resulting luminescence. Understanding the ability of mycotoxins such as TeA to chelate metals provides insight into how they exert their toxic effects.