The impact of loss of myrosinase on the bioactivity of broccoli products in F344 rats

Abstract

In vitro, animal, and epidemiological studies all show that broccoli products containing sulforaphane, the bioactive hydrolysis product of glucoraphanin (GRP), lower risk for cancer. As a result, GRP-rich extracts are appearing on the market as dietary supplements. However, these products typically have no hydrolyzing enzyme for sulforaphane (SF) formation. We evaluated safety and compared efficacy to other broccoli preparations. Four daily doses of 0.5 mmol GRP/kg BW, given by gavage to adult male F344 rats, caused temporary cecal inflammation that was essentially resolved four days later. A similar dose dispersed in the diet caused no inflammation. To compare efficacy, we fed rats 20% freeze-dried broccoli (heated or unheated), 3.5% broccoli seed meal, or 4.3% semipurified GRP, each balanced within an AIN93G semipurified diet, for 4 days. Diets lacking myrosinase (semipurified GRP and heated broccoli florets) caused upregulation of NAD(P)H-quinone oxidoreductase 1 (NQO1) in colon but not liver. Surprisingly, broccoli seed, rich in myrosinase and GRP, also caused NQO1 upregulation in colon but not liver. In contrast, unheated broccoli florets caused upregulation in both colon and liver. These data suggest that GRP supplements may not exert systemic effects. We hypothesize that within whole broccoli additional components enhanced sulforaphane-dependent upregulation of NQO1 in liver.