Identification of ochratoxin-N-acetyl-L-cysteine as a new ochratoxin A metabolite and potential biomarker in human urine

Ochratoxin A (OTA) is a nephrotoxic mycotoxin with nephrocarcinogenic potential found in a broad spectrum of food commodities. The mode of action of this compound, as well as its metabolism, is still not fully understood. To determine whether the conjugation of OTA with glutathione plays an important role in human OTA metabolism, an ochratoxin-glutathione conjugate (OTB-GSH), as well as the corresponding urinary metabolite ochratoxin-N-acetyl-l-cysteine (OTB-NAC), were synthesized and their structures confirmed by NMR spectroscopy. By means of synthesized stable isotope-labeled d(5)-OTB-GSH and d(5)-OTB-NAC references, a sensitive HPLC-MS/MS method has been developed and applied for the screening of human urine samples. OTB-NAC could be detected in 11 of the analyzed 18 urine samples and was quantified in 5 urine samples in the range between 0.023 and 0.176 ng mg(−1) creatinine. OTB-GSH has not been detected in the urine samples. In OTB-NAC positive samples, this metabolite contributed to a comparable concentration range to the total OTA excretion as the parent compound. This is the first direct analysis of an OTA phase 2 metabolite in humans. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s12550-019-00360-0) contains supplementary material, which is available to authorized users.