Title

 

Authors

S. Melega

Doctorate School in Pharmacology and Toxicology
Dept. of Pharmacology, Molecular Toxicology Unit, Alma Mater Studiorum - University of Bologna, Via Irnerio 48 - 40126 Bologna, Italy.

 

Abstract

A plethora of epidemiological and experimental studies suggests an inverse association between regular fruit and vegetable consumption and cancer risk. In recent years, cruciferous vegetables (genus Brassica) such as Brussels sprouts, broccoli and cabbage, have been regarded as potential cancer chemopreventive functional foods. This protective property has been mostly attributed to the high glucosinolate (GL) content, and in particular to the isythiocyanates (ITCs), their bioactive hydrolysis (myrosinase-mediated) products. The anti-carcinogenic properties of these phythochemicals are assumed to be primarily due to their abilty to inactivate phase-I (carcinogen-bioactivating) and/or induce phase-II (detoxifying) xenobiotic metabolizing enzymes (XMEs); an indirect antioxidant effect is also thought [1]. The currently accepted view is that the beneficial activity of Cruciferae is exclusively the result of exposure to ITCs (e.g. sulforaphane, the hydrolysis metabolite of glucoraphanin), and that the precursors GLs make no contribution. Brassicaceae are generally consumed cooked, a process which inactivates the myrosinase (Myr), exposing people to intact GLs rather than their degradation products. Intestinal microflora, can only partially metabolize GLs [2]. Cruciferous vegetables are also eaten raw, or assumed as extracts. We believe that the addition of exogenous Myr to cruciferous extracts, might be an innovative stratagem to improve their effectiveness.
It is challenging therefore to discern whether the health effects of cruciferous intake are caused by GLs per se, by ITCs after enteric or exogenous Myr hydrolysis, or both, together with the other phytochemicals and matrix components of the vegetable itself. To address this issue, the effects of Brassica oleracea L. var. acephala sabellica (Cavolo nero di Toscana)sprout extract (CSE) on XMEs were examined. Male Sprague-Dawley rats were administered either orally or intraperitoneally (ip), daily for 21 consecutive days, with CSE (rich in glucoraphanin but lacking ITCs and Myr) dissolved in saline at 15 mg/kg body weight, according to the human daily GLs intake for human. Rats were randomized into four groups (n=6): CSE (with the addition of Myr) per os; CSE (no Myr) per os; CSE (with the addition of Myr) ip; CSE (no Myr) ip. Six rats were given an equal volume of vehicle (saline) as control group.
After the sacrifice, hepatic microsomes were prepared and tested for various cytochrome P450 (CYP) linked-monooxygenases, via specific substrates as probes: aminopyrine N-demethylase (CYP3A1/2), ethoxyresorufin O-deethylase (CYP1A1), methoxyresorufin O-demethylase (CYP1A2), pentoxyresorufin O-dealkylase (CYP2B1/2), ethoxycoumarin O-deethylase (CYP1A1, 2A, 2B, 2E1) and NADPH cytochrome c-reductase (P450-reductase). UDP-glucuronosyl transferase (UDP-GT) was studied as phase-II marker.
From this preliminary investigation, no significant modulation of the aforementioned CYP isoforms has emerged, except for a trend towards an up-regulation for the CYP3A1/2 and the CYP1A2, in the orally administered group with CSE plus Myr (containing ITCs but not GLs), and towards a down-regulation for the CYP1A1 and CYP1A2, in the ip treated group with CSE lacking Myr (containing GLs but not ITCs). A generalized induction of phase-II UDP-GT was also recorded, up to 100% for the orally treated group without Myr.
Although the exact mechanism of chemoprevention of cruciferous vegetables is not yet completely known, a moderate intake of derived nutraceuticals seems to affect XMEs. Experiments to investigate the possible antioxidant property of CSE are in progress.
 
1)     Paolini M et al. (2003) - Mutat Res vol 543: 181-9.
2)     Herr I et al. (2010) - Cancer Treat Rev vol 36: 377-83.