Broccoli sprouts are widely consumed in many parts of the world. There have been no reported concerns with respect to their tolerance and safety in humans. A formal phase I study of safety, tolerance, and pharmacokinetics appeared justified because these sprouts are being used as vehicles for the delivery of the glucosinolate glucoraphanin and its cognate isothiocyanate sulforaphane [1-isothiocyanato-(4R)-(methylsulfinyl)butane] in clinical trials. Such trials have been designed to evaluate protective efficacy against development of neoplastic and other diseases. A placebo-controlled, double-blind, randomized clinical study of sprout extracts containing either glucosinolates (principally glucoraphanin, the precursor of sulforaphane) or isothiocyanates (principally sulforaphane) was conducted on healthy volunteers who were in-patients on our clinical research unit. The subjects were studied in three cohorts, each comprising three treated individuals and one placebo recipient. Following a 5-day acclimatization period on a crucifer-free diet, the broccoli sprout extracts were administered orally at 8-h intervals for 7 days (21 doses), and the subjects were monitored during this period and for 3 days after the last treatment. Doses were 25 micromol of glucosinolate (cohort A), 100 micromol of glucosinolate (cohort B), or 25 micromol of isothiocyanate (cohort C). The mean cumulative excretion of dithiocarbamates as a fraction of dose was very similar in cohorts A and B (17.8 +/- 8.6% and 19.6 +/- 11.7% of dose, respectively) and very much higher and more consistent in cohort C (70.6 +/- 2.0% of dose). Thirty-two types of hematology or chemistry tests were done before, during, and after the treatment period. Indicators of liver (transaminases) and thyroid [thyroid-stimulating hormone, total triiodothyronine (T3), and free thyroxine (T4)] function were examined in detail. No significant or consistent subjective or objective abnormal events (toxicities) associated with any of the sprout extract ingestions were observed.

Glucoraphanin from broccoli and its sprouts and seeds is a water soluble and relatively inert precursor of sulforaphane, the reactive isothiocyanate that potently inhibits neoplastic cellular processes and prevents a number of disease states. Sulforaphane is difficult to deliver in an enriched and stable form for purposes of direct human consumption. We have focused upon evaluating the bioavailability of sulforaphane, either by direct administration of glucoraphanin (a glucosinolate, or β-thioglucoside-N-hydroxysulfate), or by co-administering glucoraphanin and the enzyme myrosinase to catalyze its conversion to sulforaphane at economic, reproducible and sustainable yields. We show that following administration of glucoraphanin in a commercially prepared dietary supplement to a small number of human volunteers, the volunteers had equivalent output of sulforaphane metabolites in their urine to that which they produced when given an equimolar dose of glucoraphanin in a simple boiled and lyophilized extract of broccoli sprouts. Furthermore, when either broccoli sprouts or seeds are administered directly to subjects without prior extraction and consequent inactivation of endogenous myrosinase, regardless of the delivery matrix or dose, the sulforaphane in those preparations is 3- to 4-fold more bioavailable than sulforaphane from glucoraphanin delivered without active plant myrosinase. These data expand upon earlier reports of inter- and intra-individual variability, when glucoraphanin was delivered in either teas, juices, or gelatin capsules, and they confirm that a variety of delivery matrices may be equally suitable for glucoraphanin supplementation (e.g. fruit juices, water, or various types of capsules and tablets).

A recently developed UV spectroscopic method for quantitating isothiocyanates (R-N=C=S) at the nanomole level is based on the observation that the highly electrophilic central carbon atom of the -N=C=S group can undergo successive nucleophilic additions with reagents containing two sulfhydryl groups on adjacent carbon atoms to form a cyclic thiocarbonyl product and release the nitrogen atom as a primary amine (Y. Zhang, C.-G. Cho, G. H. Posner, and P. Talalay, Anal. Biochem. 205, 100-107, 1992). The assay utilizes 1, 2-benzenedithiol as the vicinal dithiol reagent and measures the reaction product, 1,3-benzodithiole-2-thione, spectroscopically (am of 23,000 M-1 cm-1 at lambdamax = 365 nm). This paper reports a dramatic improvement in the analytical sensitivity of this method. By separating the cyclocondensation product by a simple isocratic HPLC method and using an automatic integrator, the sensitivity of detection has been lowered to a few picomoles of isothiocyanate. Furthermore, we now find that the chemical specificity of the cyclocondensation reaction is not restricted to isothiocyanates, but includes dithiocarbamates, and related thiocarbonyl compounds such as carbon disulfide, certain substituted thiourea derivatives, and xanthates. The availability of such analytical methods is important not only because isothiocyanates (and their glucosinolate precursors) are present in edible plants and are consumed by humans in substantial quantities, but also because some dithiocarbamates are toxic, and are widely used in the rubber industry as vulcanization accelerators and in agriculture as fungicides, insecticides, and herbicides. The analysis of many isothiocyanates is complicated by their extreme volatility. This difficulty can be circumvented by converting isothiocyanates quantitatively into dithiocarbamates (by facile addition of a mercaptan such as N-acetylcysteine) and quantitating the nonvolatile dithiocarbamate by the cyclocondensation reaction.

The isothiocyanate sulforaphane was isolated from broccoli extracts in a bioactivity-guided fractionation as the principal and very potent inducer of cytoprotective phase 2 enzymes and subsequently shown to inhibit tumor development in animal models that involve various carcinogens and target organs. Because broccoli and broccoli sprouts are widely consumed, extracts obtained from them are viewed as convenient vehicles for sulforaphane delivery to humans. In relation to our current interest in devising strategies for protection against UV light–induced skin cancer, it was necessary to examine the safety and efficacy of topical application of sulforaphane-containing broccoli sprout extracts as single and multiple doses in both mice and humans. Topical application of an extract delivering 100 nmol sulforaphane/cm² increased the protein levels of NAD(P)H:quinone oxidoreductase 1 (NQO1), glutathione S-transferase A1, and heme oxygenase 1, three representative phase 2 enzymes, in mouse skin epidermis. Quantitative assessment of the activity of NQO1 24 h after dosing showed increases of 1.5- and 2.7-fold after application of single and multiple (thrice, every 24 h) doses, respectively. A dose-escalation safety study in healthy human subjects revealed no adverse reactions when doses as high as 340 nmol of sulforaphane in the form of broccoli sprout extracts were applied topically to the center of a 1-cm-diameter circle drawn on the volar forearm. A subsequent efficacy study showed that despite the interindividual differences in basal levels, the enzyme activity of NQO1 in homogenates of 3-mm full thickness skin punch biopsies increased in a dose-dependent manner, with maximum increases of 1.5- and 4.5-fold after application of 150 nmol doses, once or three times (at 24 h-intervals), respectively, thus providing direct evidence for induction of the phase 2 response in humans. (Cancer Epidemiol Biomarkers Prev 2007;16(4):847–51)