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 d5-OTB-GSH and d5-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.

Occurrence of the Ochratoxin A Degradation Product 2'R-Ochratoxin A in Coffee and Other Food: An Update.

Food raw materials can contain the mycotoxin ochratoxin A (OTA). Thermal processing of these materials may result in decreased OTA levels but also in the formation of the thermal isomerization product 2'R-ochratoxin A (2'R-OTA). So far, only 2'R-OTA levels reported from 15 coffee samples in 2008 are known, which is little when compared to the importance of coffee as a food and trading good. Herein, we present results from a set of model experiments studying the effect of temperatures between 120 °C and 270 °C on the isomerization of OTA to 2'R-OTA. It is shown that isomerization of OTA starts at temperatures as low as 120 °C. At 210 °C and above, the formation of 25% 2'R-OTA is observed in less than one minute. Furthermore, 51 coffee samples from France, Germany, and Guatemala were analyzed by HPLC-MS/MS for the presence of OTA and 2'R-OTA. OTA was quantified in 96% of the samples, while 2'R-OTA was quantifiable in 35% of the samples. The highest OTA and 2'R-OTA levels of 28.4 µg/kg and 3.9 µg/kg, respectively, were detected in coffee from Guatemala. The OTA:2'R-OTA ratio in the samples ranged between 2.5:1 and 10:1 and was on average 5.5:1. Besides coffee, 2'R-OTA was also for the first time detected in a bread sample and malt coffee powder.