Abstract 5701: Determination of new biomarkers to monitor the dietary consumption of isothiocyanates

Abstract

Abstract Background. Isothiocyanates (ITCs) found in cruciferous vegetables have demonstrated cancer preventive activity in animals. Increased dietary intake of ITCs has been shown to be associated with a reduced cancer risk in humans. ITCs exert their cancer chemopreventive action by multiple mechanisms, for example, by modulating the activities of phase I and phase II drug metabolism enzymes, by inhibiting the cell cycle and histone deacetylase, and by causing apoptotic cell death. In cells, protein adducts account for most of total cellular ITC-uptake at 4h after treatment. The time course of this protein binding correlates well with the inhibition of proliferation and the induction of apoptosis. In animal studies, glutathione conjugates are the major products of ITCs. The major urinary excretion products of ITCs in human are N-acetyl cysteine conjugates. Urinary metabolites might provide the exposure history of the last 24h, if the urine of the full next day is collected. Therefore, stable biomarkers such as reaction products with blood proteins are needed which reflect a larger time span of the ITC-exposure history. Results. We developed a method to determine serum albumin adducts of allyl isothiocyanate (AITC), benzylisothiocyanate (BITC), phenylethyl isothiocyanate (PEITC), and sulforaphane (SFN) in humans. The feasibility of the method was tested on biological samples collected previously for a diet-study. The volunteers were randomly assigned to three groups: Group A (n=29): the diet was rich in flavonoids, but not supplemented. Group B (n=29), the diet was a normal iso-caloric diet with an adequate administration of fruit and vegetables. Group C (n=27): the diet was based on supplementation of the normal diet with additional flavonoids in the form of green tea and soy products. All subjects were male smokers. Blood samples were collected at the beginning and after 4 weeks. After enzymatic digestion of albumin we determined the adducts of the ITCs with lysine (Lys) using LC-MS/MS and isotope dilution method. At the beginning of the study (and after 4 weeks) 5.9% (2.4%), 83.5% (96.5%), 11.8% (15.3%), and 31.8% (32.9%) samples were found positive for AITC-Lys, BITC-Lys, PEITC-Lys, and SFN-Lys respectively. Significant differences among the groups were found at the beginning of the study. SFN-Lys levels in group C were significantly higher than in group A and B, and BITC-levels in group C were significantly lower than in group A and B. These differences disappear after 4 weeks. Conclusions. This new method enables to quantify ITC adducts in blood proteins from large prospective studies about diet and cancer. Protein adducts are involved in the chemopreventive effects of ITCs. Therefore, blood protein adducts are a potential surrogate marker for the effects of ITCs at the cellular level. This new technique will improve the assessment of ITC exposure and the power of studies on the relationship between ITC intake and cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5701.