Absorption and chemopreventive targets of sulforaphane in humans following consumption of broccoli sprouts or a myrosinase-treated broccoli sprout extract

Abstract

Scope: Sulforaphane (SFN), an isothiocyanate derived from crucifers, has numerous health benefits. SFN bioavailability from dietary sources is a critical determinant of its efficacy in humans. A key factor in SFN absorption is the release of SFN from its glucosinolate precursor, glucoraphanin, by myrosinase. Dietary supplements are used in clinical trials to deliver consistent SFN doses, but myrosinase is often inactivated in available supplements. We evaluated SFN absorption from a myrosinase-treated broccoli sprout extract (BSE) and are the first to report effects of twice daily, oral dosing on SFN exposure in healthy adults.

Methods and results: Subjects consumed fresh broccoli sprouts or the BSE, each providing 200 μmol SFN daily, as a single dose and as two 100-μmol doses taken 12 h apart. Using HPLC-MS/MS, we detected ∼3 x higher SFN metabolite levels in plasma and urine of sprout consumers, indicating enhanced SFN absorption from sprouts. Twelve-hour dosing retained higher plasma SFN metabolite levels at later time points than 24-hour dosing. No dose responses were observed for molecular targets of SFN (i.e. heme oxygenase-1, histone deacetylase activity, p21).

Conclusion: We conclude that the dietary form and dosing schedule of SFN may impact SFN absorption and efficacy in human trials.

Keywords: Absorption; Broccoli sprout; Chemoprevention; Excretion; Sulforaphane.

Figure 1

Human feeding study design. Subjects consumed single and divided doses of 200 μmol SFN equivalents from either fresh broccoli sprouts or myrosinase-treated broccoli sprout extract (BSE) supplements (n = 10). Divided doses were consumed 12 h apart within a single day.

Figure 2

Sulforaphane (SFN) metabolite levels in plasma and urine following consumption of fresh broccoli sprouts and the broccoli sprout extract (BSE). Total levels (mean ± SEM) of SFN metabolites in plasma (A and C) and urine (B and D) of subjects at time 0 and at 3, 6, 12, 24, and 48 h after consuming broccoli sprouts (closed) or the BSE (open). (A and B) SFN metabolite levels detected following the single dose of 200 μmol SFN equivalents. (C and D) SFN metabolite levels following two 100-μmol SFN doses consumed within a single day. Insets: Close-up of SFN metabolite levels at 12 and 24 h in (A and C) plasma and (B and D) urine. Arrows indicate times of SFN consumption. Free SFN was only detected in four subjects at 3 h following the single dose and comprised < 2% of total SFN metabolites (data not included). *p < 0.05, **p < 0.01, ***p < 0.001.

Figure 3

HDAC activity in PBMCs following consumption of broccoli sprouts or the broccoli sprout extract (BSE). (A) Average fold changes (mean ± SEM) in PBMC HDAC activity after consuming a single dose of 200 μmol SFN equivalents from broccoli sprouts (solid, n = 9) or BSEs (open, n = 10). (B) Individual fold changes in HDAC activity from time 0–3 h. Note: Offsets for the BSE group are for visualization purposes only. **p < 0.01. HDAC, histone deacetylase; PBMC, peripheral blood mononuclear cells.

Figure 4

p21 and HO-1 expression following consumption of broccoli sprouts or the broccoli sprout extract (BSE). Changes in (A) whole blood p21 mRNA levels, (B) plasma HO-1 protein levels, and (C) whole blood HO-1 mRNA after consuming a single dose of 200 μmol SFN equivalents from broccoli sprouts (solid) or BSEs (open). The sprout subject excluded from analyses is shown separately in the figure (-x-). Values represent mean ± SEM (A and B) and geometric mean ± SD (C). Note: Offsets for the BSE group are for visualization purposes only. HO-1, heme oxygenase-1.