Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2005
Publication Date: 6/18/2005
Citation: Hintze, K.J., Wald, K., Finley, J.W. 2005. Phytochemicals in broccoli transcriptionally induce thioredoxin reductase. Journal of Agricultural and Food Chemistry. 53:5535-40. Interpretive Summary: Thioredoxin reductase, glutathione peroxidase and quinone reductase are enzymes that may protect the body against oxidative damage. This study has examined how chemicals found in broccoli regulate these enzymes. Thioredoxin reductase was found to be regulated by many substances through a variety of mechanisms. However glutathione peroxidase was regulated almost exclusively by the selenium content and quinone reductase was unaffected by selenium, but regulated by an important phytochemical - sulforaphane. Results of this study serve to demonstrate that the chemical composition of different versions of the same food may have great effects on how the body uses that food. Plant breeders and food manufacturers should keep this in mind when altering plants or preparing "functional foods".
Technical Abstract: Previous studies have demonstrated transcriptional induction of thioredoxin reductase (TR) by sulforaphane (SF) purified from broccoli; the mechanism of induction is via an antioxidant response element (ARE) in the promoter region of the gene. The purpose of the present study was to further characterize the induction of TR by compounds in broccoli, and determine if SF is the primary compound responsible for this induction. Aqueous extracts were made from broccoli with low (0 µg/g) or high (1000 µg/g) concentrations of selenium (Se) and tested in a TR/luciferase reporter gene system in cultured cells. Phenolic acids commonly found in broccoli (sinapic, caffeic, ferulic and protocatechuic) and ascorbic acid were also tested. At SF concentrations of 2 uM or less, broccoli extracts and purified SF activated transcription equally well, but 4 µM SF in broccoli extracts resulted in almost twice as much induction as 4 uM purified SF (P < 0.05). No phenolic acids tested induced transcription, but ascorbic acid resulted in modest dose dependent induction between 0 and 120 uM (P < 0.001). These data suggest that SF accounts for most of the ARE-activated transcriptional induction of antioxidant genes by broccoli.