Hormesis-associated mechanisms underlying stress-resistant effects of allyl isothiocyanate

Background and objectives: Most, if not all, previous studies on phytochemicals have so far evaluated their effects with a single treatment of cultured cells. In general, however, we ingest them multiple times or continuously in daily life. On the other hand, phytochemicals may exhibit hormetic effects since they are substantially xenobiotics to humans. This study aimed to evaluate the stress-resistant effects of multiple treatments with allyl isothiocyanate (AITC), a pungent in wasabi, by focusing on hormesis. Methods and Results: RGM1 rat gastric mucosa cells were pretreated on four different schedules, in which treatment times and the concentrations of AITC are as follows, group (1) 0 and 24 hr: 0 μM (2) 0 hr: 10-30 μM, 24 hr: 0 μM (3) 0 hr: 0 μM, 24 hr: 10-30 μM (4) 0 and 24 hr: 10-30 μM. Then all four groups were treated with AITC (20 μM), then cell viability was measured. Pretreatment with AITC (10-30 μM) significantly decreased AITC (20 μM)-induced cytotoxicity in group (2)-(4). In group (3), the protective effect was highest at the concentration of 15 μM, then decreased and almost disappeared at 20 and 30 μM, respectively. Group (4) also exhibited a similar trend. In addition, the mRNA expression levels of catalase and HSP27 were higher in the cells exposed to double treatments with AITC (15 and 20 μM, 24 and 6 hr) than those by its single treatment (20 μM, 6 hr). Interestingly, pretreatment with AITC (2.5-15 μM, 1 hr) showed the cytoprotective effects in RGM1 cells, which were incubated in a low pH medium (pH 4.6, 1 hr). Conclusions: We found that pretreatment with AITC enhances the resistance to cytotoxicity induced by a high concentration of AITC, suggesting that multiple treatments with AITC may increase its adaptation capacity against AITC exposures. Mechanisms underlying stress resistance to AITC, together with that to a low pH condition, are currently under investigation.