Interaction of the Emerging Mycotoxins Beauvericin, Cyclopiazonic Acid, and Sterigmatocystin with Human Serum Albumin

Abstract

Beauvericin (BEA), cyclopiazonic acid (CPA), and sterigmatocystin (STC) are emerging mycotoxins. They appear as contaminants in food and animal feed, leading to economic losses and health risks. Human serum albumin (HSA) forms stable complexes with certain mycotoxins, including ochratoxins, alternariol, citrinin, and zearalenone. HSA binding can influence the toxicokinetics of xenobiotics, and albumin can also be considered and applied as a relatively cheap affinity protein. Therefore, we examined the potential interactions of BEA, CPA, and STC with HSA employing fluorescence spectroscopy, ultracentrifugation, ultrafiltration, and molecular modeling. Spectroscopic and ultracentrifugation studies demonstrated the formation of low-affinity BEA-HSA (K_a ≈ 10³ L/mol) and moderately strong CPA-HSA and STC-HSA complexes (K_a ≈ 10⁴ L/mol). In ultrafiltration experiments, CPA slightly displaced each site marker (warfarin, naproxen, and camptothecin) tested, while BEA and STC did not affect significantly the albumin binding of these drugs. Modeling studies suggest that CPA occupies Sudlow's site I, while STC binds to the Heme site (FA1) on HSA. Considering the interactions of CPA with the site markers, the CPA-HSA interaction may have toxicological importance.

Keywords: albumin–ligand interaction; beauvericin; cyclopiazonic acid; human serum albumin; sterigmatocystin.

Figure 1

Chemical structures of beauvericin (BEA), cyclopiazonic acid (CPA), and sterigmatocystin (STC).

Figure 2

Fluorescence emission spectra of HSA (2.0 μM) in the presence of the increasing concentrations of BEA (A), CPA (B), and STC (C) in PBS (pH 7.4; λ_ex = 295 nm). Stern–Volmer plots of CPA–HSA and STC–HSA complexes (D; λ_ex = 295 nm, λ_em = 340 nm).

Figure 3

Concentrations of warfarin (A), naproxen (B), and camptothecin (C) in the filtrate after ultrafiltration (MWCO: 30 kDa). Samples contained warfarin and HSA (1.0 and 5.0 μM, respectively) or naproxen and HSA (1.0 and 1.5 μM, respectively), or camptothecin and HSA (1.0 and 1.5 μM, respectively) in the absence and presence of mycotoxins (20 μM) in PBS (pH 7.4; * p < 0.05; BEA, beauvericin; CPA, cyclopiazonic acid; STC, sterigmatocystin; WAR, warfarin; NAP, naproxen; CPT, camptothecin; HSA, human serum albumin).

Figure 4

Blind docking results of CPA (sticks colored by docking ranks) on HSA (gray cartoon) with the representative binding positions of different ranks (left panel). In the right panel, a close-up of the binding mode in regard to rank 1 is demonstrated, representing the best energy score in the inset with interacting HSA residues (sticks colored by atom types).

Figure 5

Blind docking results of STC (sticks colored by docking ranks) on HSA (gray cartoon) with the representative binding positions of different ranks (left panel). In the right panel, a close-up of the binding mode in regard to rank 1 is demonstrated, representing the best energy score in the inset with interacting HSA residues (sticks colored by atom types).