Kristina L. Wade

Safety, tolerance, and metabolism of broccoli sprout glucosinolates and isothiocyanates: a clinical phase I study.

Abstract: 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 μmol of glucosinolate (cohort A), 100 μmol of glucosinolate (cohort B), or 25 μmol 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.

Induction of the Phase 2 Response in Mouse and Human Skin by Sulforaphane-containing Broccoli Sprout Extracts

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)

Separation and purification of glucosinolates from crude plant homogenates by high-speed counter-current chromatography

Glucosinolates are anionic, hydrophilic plant secondary metabolites which are of particular interest due to their role in the prevention of cancer and other chronic and degenerative diseases. The separation and purification of glucosinolates from a variety of plant sources (e.g. seeds of broccoli, arugula and the horseradish tree), was achieved using high-speed counter-current chromatography (HSCCC). A high-salt, highly polar system containing 1-propanol-acetonitrile-saturated aqueous ammonium sulfate-water (1:0.5:1.2:1), was run on a semi-preparative scale and then transferred directly to preparative scale. Up to 7 g of a concentrated methanolic syrup containing about 10% glucosinolates was loaded on an 850-ml HSCCC column, and good separation and recovery were demonstrated for 4-methylsulfinylbutyl, 3-methylsulfinylpropyl, 4-methylthiobutyl, 2-propenyl and 4-(rhamnopyranosyloxy)benzyl glucosinolates. Multiple injections (5 to 6 times) were performed with well-preserved liquid stationary phase under centrifugal force. Pooled sequential runs with broccoli seed extract yielded about 20 g of its predominant glucosinolate, glucoraphanin, which was produced at > 95% purity and reduced to powdered form.

Potent activation of mitochondria-mediated apoptosis and arrest in S and M phases of cancer cells by a broccoli sprout extract

We have previously shown that broccoli sprouts are a rich source of chemopreventive isothiocyanates, which potently induce carcinogen-detoxifying enzymes and inhibit the development of mammary and skin tumors in rodents. However, the principal isothiocyanate present in broccoli sprout extracts, sulforaphane, not only induces carcinogen-detoxifying enzymes but also activates apoptosis and blocks cell cycle progression. In this article, we show that an aqueous extract of broccoli sprouts potently inhibits the growth of human bladder carcinoma cells in culture and that this inhibition is almost exclusively due to the isothiocyanates. Isothiocyanates are present in broccoli sprouts as their glucosinolate precursors and blocking their conversion to isothiocyanates abolishes the antiproliferative activity of the extract. Moreover, the potency of isothiocyanates in the extract in inhibiting cancer cell growth was almost identical to that of synthetic sulforaphane, as judged by their IC50 values (6.6 versus 6.8 μmol/L), suggesting that other isothiocyanates in the extract may be biologically similar to sulforaphane and that nonisothiocyanate substances in the extract may not interfere with the antiproliferative activity of the isothiocyanates. Further study showed that the isothiocyanate extract of broccoli sprouts activated the mitochondria-mediated apoptosis pathway and halted cells in S and M phases. Cell cycle arrest was associated with down-regulation of Cdc25C and disruption of mitotic spindles. These data show that broccoli sprout isothiocyanate extract is a highly promising substance for cancer prevention/treatment and that its antiproliferative activity is exclusively derived from isothiocyanates. [Mol Cancer Ther 2006;5(4):935–44]

Cultivar Effect on Moringa oleifera Glucosinolate Content and Taste: A Pilot Study

Leaves of the tropical tree Moringa oleifera are widely promoted in areas of chronic malnutrition as nutritional supplements for weaning infants and nursing mothers. Adoption, in these circumstances may hinge upon taste, which can vary greatly amongst cultivars. It is widely assumed that this taste variation is primarily germplasm-dependent, and results from the breakdown of glucosinolates to isothiocyanates. Leaves of 30 accessions, grown at a single field plot, were sampled 3 times over the course of a year. Taste, assessed in a masked protocol, was not related to glucosinolate content of the leaves.

Wild and domesticated Moringa oleifera differ in taste, glucosinolate composition, and antioxidant potential, but not myrosinase activity or protein content

Taste drives consumption of foods. The tropical tree Moringa oleifera is grown worldwide as a protein-rich leafy vegetable and for the medicinal value of its phytochemicals, in particular its glucosinolates, which can lead to a pronounced harsh taste. All studies to date have examined only cultivated, domestic variants, meaning that potentially useful variation in wild type plants has been overlooked. We examine whether domesticated and wild type M. oleifera differ in myrosinase or glucosinolate levels, and whether these different levels impact taste in ways that could affect consumption. We assessed taste and measured levels of protein, glucosinolate, myrosinase content, and direct antioxidant activity of the leaves of 36 M. oleifera accessions grown in a common garden. Taste tests readily highlighted differences between wild type and domesticated M. oleifera. There were differences in direct antioxidant potential, but not in myrosinase activity or protein quantity. However, these two populations were readily separated based solely upon their proportions of the two predominant glucosinolates (glucomoringin and glucosoonjnain). This study demonstrates substantial variation in glucosinolate composition within M. oleifera. The domestication of M. oleifera appears to have involved increases in levels of glucomoringin and substantial reduction of glucosoonjnain, with marked changes in taste.

Abstract A38: Structure-activity relationship of closely-related flavonoids with possible chemopreventive qualities

A38 Dietary flavonoids are now widely presumed to have human health benefits, and increased intake is epidemiologically correlated with decreased risk of cardiovascular disease and cancer. The general mechanisms thought to be involved in chemoprevention through dietary compounds include the inhibition of the carcinogen-bioactivating phase I enzymes and/or induction of carcinogen-bioinactivating phase II enzymes. Methoxylated flavonoids have been shown to have chemopreventive activity in a number of in vitro assays, and we have selected 27 of them as the objects of this work. Furthermore, these flavonoids were analyzed to investigate possible structure-activity relationships for effective, non-toxic agents with chemopreventive potential. The flavonoids are a structurally diverse class of low molecular weight polyphenolic benzo-c-pyrone derivatives. The basic structure is composed of two benzene rings (A and B) separated by an oxygen-containing heterocyclic ring. Substituent groups can attach on each of the molecule’s rings, with hydroxyl, methoxy groups or sugar moieties being present most frequently. Neither hydroxylation nor methoxylation solely on the B-ring had a strong inducing effect on the phase II enzyme NAD(P)H:quinone-reductase (NQO1) in murine hepatoma cells. However, flavonoids with a methoxy-group substitution at the 5-position of the A-ring were the most potent inducers of NQO1. Other flavonoids were equally potent inducers, but exhibited much higher toxicity in at least one of the cell lines tested. Certain methoxylated flavonoids that are found in dietary fruits and vegetables have significant potential for prevention of chemically-induced carcinogenesis and should be investigated further in animal models of cancer prevention. Citation Information: Cancer Prev Res 2008;1(7 Suppl):A38.

The Diversity of Chemoprotective Glucosinolates in Moringaceae ( Moringa spp.)

Glucosinolates (GS) are metabolized to isothiocyanates that may enhance human healthspan by protecting against a variety of chronic diseases. Moringa oleifera, the drumstick tree, produces unique GS but little is known about GS variation within M. oleifera, and even less in the 12 other Moringa species, some of which are very rare. We assess leaf, seed, stem, and leaf gland exudate GS content of 12 of the 13 known Moringa species. We describe 2 previously unidentified GS as major components of 6 species, reporting on the presence of simple alkyl GS in 4 species, which are dominant in M. longituba. We document potent chemoprotective potential in 11 of 12 species, and measure the cytoprotective activity of 6 purified GS in several cell lines. Some of the unique GS rank with the most powerful known inducers of the phase 2 cytoprotective response. Although extracts of most species induced a robust phase 2 cytoprotective response in cultured cells, one was very low (M. longituba), and by far the highest was M. arborea, a very rare and poorly known species. Our results underscore the importance of Moringa as a chemoprotective resource and the need to survey and conserve its interspecific diversity.