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- Broccoli (Brassica oleracea var. italica, Brassicaceae)
- Sulforaphane Bioavailability
- Myrosinase
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Date:
07-15-2016 | HC# 121513-548
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Re: Increased Sulforaphane Bioavailability from Broccoli Preparations with Myrosinase
Fahey JW, Holtzclaw WD, Wehage SL, Wade KL,
Stephenson KK, Talalay P. Sulforaphane bioavailability from glucoraphanin-rich
broccoli: control by active endogenous myrosinase. PLoS One. 2015;10(11):e0140963. doi: 10.1371/journal.pone.0140963.
Many of the health benefits associated with
cruciferous vegetables are attributed to glucosinolates. Although the glucosinolate glucoraphanin (GR), found in broccoli (Brassica oleracea var. italica,
Brassicaceae), is inert, this compound can be converted into the bioactive
compound sulforaphane by the microflora of the gastrointestinal tract or the endogenous
plant enzyme myrosinase. The aim of this clinical study was to evaluate if the addition of myrosinase to different broccoli
preparations containing GR increased the bioavailability of sulforaphane.
GR and active myrosinase are found in both
broccoli seeds and sprouts. The broccoli products
used in this study included broccoli sprout extracts (BSE) and broccoli seed powder (BSdP) (prepared
by Johns Hopkins University; Baltimore, Maryland); broccoli seed extracts
(BSdE) (Brassica Protection Products LLC; Baltimore,
Maryland); and freeze-dried broccoli sprouts (FDBS) (grown under contract by Hanover
Foods Corp.; Sunsprout; Ridgely, Maryland). The GR content of the broccoli
products was determined using high-performance liquid chromatography (HPLC).
Myrosinase activity was determined spectrophotometrically.
Subjects were instructed not to consume any
cruciferous vegetables or products 3 days prior to the study and 24 hours after
dosing. After an overnight fast, baseline urine samples were collected and then
the broccoli preparations were consumed. Afterwards, the subjects collected
their urine for 24 hours.
Subjects consumed BSE either mixed with
water (≤1 g; 50 mL x 2), in clear capsules without excipients (50 μmol GR), or in
opaque green gel-caps with inert excipients (69 or 230 μmol of GR)
(encapsulated by Xymogen; Orlando, Florida). Similarly, BSdE and BSdP were consumed
in gel-caps (69 or 230 μmol of GR and 100 μmol of GR, respectively). FDBS were consumed
as standard capsules; acid-resistant gel-caps (100 μmol GR); or prehydrolyzed
in 50% water, 46.5% pineapple (Ananas comosus,
Bromeliaceae) juice (Dole; Westlake Village, California), and 3.5% lime (Citrus × aurantifolia, Rutaceae) juice (Safeway; Pleasanton,
California) (50, 100, and 200 μmol of GR). All subjects (17 females and 5 males;
mean age, 51.3 years; 9 African-American and 13 white) included in the study
were healthy. Only 5 of these subjects (4 females and 1 male; mean age, 53.8 years;
1 African-American and 4 white) were included for extended studies.
Urinary dithiocarbamate (DTC) excretion
levels were used to measure sulforaphane bioavailability from the broccoli
preparations. DTC was quantified from all the urine samples. Compliance also was
assessed.
The bioavailability of GR varied among and
within the subjects. Baseline conversion efficiency of a 50-μmol dose of
GR-rich BSE, lacking myrosinase, had DTC levels ranging
from 3.7 to 6.9 μmol (mean, 4.7 μmol or 9.4% of dose). Comparison of the
bioavailability of BSE to that of a commercially prepared GR-rich supplement
indicated they were equally bioavailable (10.4% and 10.3%, respectively;
P=0.2340). It was also found that higher doses were slightly, but not
significantly, higher in bioavailability than the lower doses for the
commercial BSdE (9.7% and 11.2%, P=0.412) and non-commercial BSE (8.2% and
12.5%, P=0.0956) supplements.
FDBS, in which the glucosinolates had been
hydrolyzed to isothiocyanates by myrosinase (50, 100, and 200 μmol of GR),
resulted in urinary DTCs that ranged from 13.8 to 30.1 μmol (mean, 20.5 μmol or
41.0% of dose). FDBS in gel-cap form produced similar results. The amount of
24-hr urine DTC was also similar for FDBS consumed in standard capsules with
myrosinase that dissolved in the stomach (range, 31.3 to 42.8 μmol; mean, 35.1%
of dose), compared to acid-resistant capsules that dissolved in the gastrointestinal
tract (range, 21.7 to 37.7 μmol; mean, 32.7% of dose). Evaluation of the
bioavailability of BSdP, which had active myrosinase, indicated the mean
conversion to DTC urinary metabolites was 36.1% of the dose. Compliance was
considered 100% for the dosing studies and overall considered good.
The authors found that regardless of the
matrix used, the presence of active myrosinase led to the greatest enhancement
of sulforaphane bioavailability from the broccoli preparations. These results
are consistent with the results of a previous study.1 FDBS mixed
with a diluted juice mixture that had endogenous myrosinase was found to be the
most effective at increasing sulforaphane bioavailability. The authors indicate
this is over 4-fold greater than the DTC recovery found for BSE without
myrosinase, but only marginally better than other preparations with myrosinase.
Future studies may want to focus on optimizing broccoli preparations that
produce less variability among subjects in order to obtain predictable results.
This study was partially funded by Brassica Protection Products LLC, and the
supplements were provided free of charge by the manufacturer, Xymogen.
—Laura
M. Bystrom, PhD
Reference
1Shapiro TA, Fahey JW,
Dinkova-Kostova AT, et al. Safety, tolerance, and metabolism of broccoli sprout
glucosinolates and isothiocyanates: a clinical phase I study. Nutr Cancer. 2006;55(1):53-62.
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