Dietary broccoli alters rat cecal microbiota to improve glucoraphanin hydrolysis to bioactive isothiocyanates
Citation
Liu, X., Wang, Y., Hoeflinger, J.L., Neme, B.P., Jeffery, E.H., Miller, M.J. (2017). Dietary broccoli alters rat cecal microbiota to improve glucoraphanin hydrolysis to bioactive isothiocyanates, 9(3), http://dx.doi.org/10.3390/nu9030262
Plain language summary
Broccoli belongs to the glucosinolate (GSL)-containing family of brassica vegetables. The major GSL in broccoli is glucoraphanin (GRP) which, upon hydrolysis, produces the bioactive isothiocyanate (ITC) sulforaphane (SFN), shown to slow or prevent cancer in humans. Previous research suggested microorganisms isolated from the mammalian gut, including lactic acid bacteria, Enterobacteriaceae, Bifidobaicterium spp. , and Bacteroides spp. , appear to have myrosinase-like activity that hydrolases GSL. Yet GSL can be hydrolyzed into multiple products and only ITC have confirmed bioactivity to the best of our knowledge. It is not yet clear which such gut commensal microorganism(s) are responsible for GSL conversion to ITC rather than non-bioactives.
In this study, we examined the effect of broccoli/GRP feeding on the composition of rat cecal microbiota by Illumina 16S rRNA sequencing. We also determined changes in GRP hydrolytic activity ex vivo by measuring the ITC (SFN) formation by incubation with cecal microbiota. We also measured the host (rat) NAD(P)H: quinone oxidoreductase 1 (NQO1) activity in rat colonic mucosa and liver as a measure of broccoli-induced bioactivity. We found that feeding raw or cooked broccoli for four days or longer both changed the cecal microbiota composition and caused a greater production of ITC ex vivo. A more than two-fold increase in NQO1 activity of the host colon mucosa after feeding cooked broccoli for seven days confirmed the positive health benefits. Further studies revealed that dietary GRP was specifically responsible for the increased microbial GRP hydrolysis ex vivo, whereas changes in the cecal microbial communities were attributed to other broccoli components. Interestingly, a three-day withdrawal from a raw broccoli diet reversed the increased microbial GRP hydrolysis ex vivo. Findings suggest that enhanced conversion of GRP to bioactive isothiocyanates by the cecal microbiota requires four or more days of broccoli consumption and is reversible.
Abstract
© 2017 by the authors. Licensee MDPI, Basel, Switzerland.Broccoli consumption brings many health benefits, including reducing the risk of cancer and inflammatory diseases. The objectives of this study were to identify global alterations in the cecal microbiota composition using 16S rRNA sequencing analysis and glucoraphanin (GRP) hydrolysis to isothiocyanates ex vivo by the cecal microbiota, following different broccoli diets. Rats were randomized to consume AIN93G (control) or different broccoli diets; AIN93G plus cooked broccoli, a GRP-rich powder, raw broccoli, or myrosinase-treated cooked broccoli. Feeding raw or cooked broccoli for four days or longer both changed the cecal microbiota composition and caused a greater production of isothiocyanates ex vivo. A more than two-fold increase in NAD(P)H: quinone oxidoreductase 1 activity of the host colon mucosa after feeding cooked broccoli for seven days confirmed the positive health benefits. Further studies revealed that dietary GRP was specifically responsible for the increased microbial GRP hydrolysis ex vivo, whereas changes in the cecal microbial communities were attributed to other broccoli components. Interestingly, a three-day withdrawal from a raw broccoli diet reversed the increased microbial GRP hydrolysis ex vivo. Findings suggest that enhanced conversion of GRP to bioactive isothiocyanates by the cecal microbiota requires four or more days of broccoli consumption and is reversible.