Exploring the in vivo and in vitro metabolism of glucosinolates by human gut microbiota

Abstract

Glucosinolates (GS), phytochemicals found in cruciferous vegetables (CRV) that may have anti‐carcinogenic effects, are metabolized to bioactive isothiocyanates (ITC) by certain bacteria in the human gut. We hypothesized that individual differences in gut microbiota contribute to the observed substantial individual variation in urinary ITC excretion after CRV feeding in previous studies. We recruited 23 individuals and fed them a standardized meal containing 200 g cooked broccoli. 24‐h urinary ITC excretion was measured after the meal. Study participants with the highest (n=5) and the lowest (n=5) ITC excretion provided fecal samples for in vitro cultivation with 50 μM glucoraphanin, a GS. Microbial fingerprints of fecal and in vitro culture microbiota were analyzed by terminal restriction fragment length polymorphism of the eubacterial 16S rRNA gene. There was no significant overall difference in fecal or in vitro culture microbiota between the high and low ITC excreters. However, when grown in vitro, fecal bacteria from the high ITC excreters degraded more GS than those from the low excreters (P=0.05). In conclusion, in vitro fecal bacterial GS degradation was associated with in vivo bacterial GS metabolism capacity but no direct link to specific bacterial species could be established, possibly due to the complexity and functional redundancy of the gut microbiota. Supported by NCI grant R01 CA070913.