Bioavailability of Sulforaphane from two broccoli sprout beverages: results of a short-term, cross-over clinical trial in Qidong, China

Abstract

One of several challenges in design of clinical chemoprevention trials is the selection of the dose, formulation, and dose schedule of the intervention agent. Therefore, a cross-over clinical trial was undertaken to compare the bioavailability and tolerability of sulforaphane from two of broccoli sprout-derived beverages: one glucoraphanin-rich (GRR) and the other sulforaphane-rich (SFR). Sulforaphane was generated from glucoraphanin contained in GRR by gut microflora or formed by treatment of GRR with myrosinase from daikon (Raphanus sativus) sprouts to provide SFR. Fifty healthy, eligible participants were requested to refrain from crucifer consumption and randomized into two treatment arms. The study design was as follows: 5-day run-in period, 7-day administration of beverages, 5-day washout period, and 7-day administration of the opposite intervention. Isotope dilution mass spectrometry was used to measure levels of glucoraphanin, sulforaphane, and sulforaphane thiol conjugates in urine samples collected daily throughout the study. Bioavailability, as measured by urinary excretion of sulforaphane and its metabolites (in approximately 12-hour collections after dosing), was substantially greater with the SFR (mean = 70%) than with GRR (mean = 5%) beverages. Interindividual variability in excretion was considerably lower with SFR than with GRR beverage. Elimination rates were considerably slower with GRR, allowing for achievement of steady-state dosing as opposed to bolus dosing with SFR. Optimal dosing formulations in future studies should consider blends of sulforaphane and glucoraphanin as SFR and GRR mixtures to achieve peak concentrations for activation of some targets and prolonged inhibition of others implicated in the protective actions of sulforaphane. Cancer Prev Res; 4(3); 384-95. ©2011 AACR.

Fig 1

Outline of the intervention protocol, schedule, and timeline. Placebo beverages were administered daily, shortly before dinner, for 5 consecutive days (“run-in”). Participants were randomized to receive either the GRR beverage containing 800 μmole glucoraphanin or the SFR beverage containing 150 μmole sulforaphane for 7 consecutive days. The placebo beverage was then administered for 5 consecutive days (“wash-out”), at which time cross-over assignments of the study beverages were consumed nightly for an additional 7 days. Overnight voids (0–12 h) were collected each morning on days 1 through 24. In addition, follow-up daytime voids (12–24 h) were collected on days 6, 12, 18, 24.

Fig. 2

Glucoraphanin in broccoli is converted to sulforaphane either by plant myrosinases, or if the plant myrosinases have been denatured by cooking, by bacterial myrosinases in the human colon. Sulforaphane is passively absorbed and rapidly conjugated with glutathione by glutathione S-transferases (GSTs), then metabolized sequentially by γ-glutamyl-transpeptidase (GTP), cysteinyl-glycinease (GCase) and N-acetyltransferase (NAT). The conjugates are actively transported into the systemic circulation where the merapturic acid (SF-NAC) and its precursors are urinary excretion products.. Deconjugation may also occur to yield the parent isothiocyanate, sulforaphane. For the beverages used in the intervention, sulforaphane metabolites were generated enterically from glucoraphanin through the action of thioglucosidases in the gut microflora (GRR); or pre-released by treatment of aqueous broccoli sprout extract with myrosinase from the daikon plant Raphanus sativus (SFR).

Fig.3

Urinary levels of sulforaphane and conjugates (log scale) as determined by HPLC/isotope-dilution mass spectrometry. Lines represent excretion amounts for individual study participants with green indicating the period an individual was on SFR treatment and blue when the individual was on GRR treatment. The black portion of the lines corresponds to the pre-treatment and wash-out periods. The dots represent the medians on each day and correspond to the data presented in Supplemental Table 1 for the total sulforaphane amounts (SF_T). A. GRR → SFR. B. SFR → GRR.

Fig. 4

Modeled urinary elimination kinetics (arithmetic scale) for sulforaphane and conjugates. ●, median. A. GRR → SFR. B. SFR → GRR. See text for detailed description.