| Summary: | Sulforaphane was synthesised with an overall yield of 15%, essentially via 1-methylsulfinylphthalimidobutane, which was oxidised to the sulfoxide moiety. Sulforaphane was a competitive inhibitor of CYPO2E1 in acetone-induced Sprague-Dawley rat microsomes (Ki 37.9 4.5 M), as measured by the p-nitrophenol hydroxylase assay. Ethoxyresorufin deethylase activity (EROD), a measurement of CYP1A activity, was also inhibited by sulforaphane (100 M) but was not competitive, and a preincubation time-dependence was observed. In view of these results, the capacity of sulforaphane to inhibit N-nitrosodimethylamine (NDMA)-induced genotoxicity (CYP2E1-mediated) was studied using mouse liver activation systems. Sulforaphane (>0.8 M) inhibited the mutagenicity of NDMA (4.4 mg/plate) in Salmonella typhimurium strain TA100 after pre-incubation for 45 min with acetone-induced liver 9000 g supernatants from Balb/c mice. Unscheduled DNA synthesis induced by NDMA (33.5 M) in mouse hepatocytes was also reduced by sulforaphane in a concentration-dependent manner (0.064-20 M). Sulforaphane was not genotoxic itself in any of these systems and cytotoxic only at high concentrations (>0.5 mM and > 40 M respectively). The ability of sulforaphane to modulate the orthologous human enzymes was studied using a human epithelial liver cell line (THLE) expressing individual human CYP450 isoenzymes. Using the Comet assay (a measurement of DNA strand breakage under alkaline conditions), NDMA (0.01-1 g/ml) and IQ (0.1-10 g/ml) were used to produce strand breaks in T5-2E1 cells (expressing human CYP2E1) and T5-1A2 cells (expressing human CYP1A2) respectively, however no response was observed in T5-neo cells (without CYP450 cDNA transfection). Sulforaphane inhibited both NDMA and IQ-induced DNA strand breakage in a concentration-dependent manner (0.1-10 M). Inhibition of CYP2E1 and CYP1A by sulforaphane may contribute to its chemoprotective potential.
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