A high intake of glucosinolate-containing cruciferous vegetables, such as Brussels
sprouts (Brassica oleraceae), has been linked to a decreased cancer risk, but the
underlying mechanism is still unclear. The aim of this study was to reveal possible
modulating effects of consumption of Brussels sprouts on duodenal, rectal and lymphocytic
(i) glutathione S-transferase (GST) enzyme activity, (ii) GST isozyme levels and (iii)
glutathione (GSH) content. Ten healthy non-smoking volunteers were randomly assigned
to two groups in a cross-over design. Five persons started on a glucosinolate-free
diet (control period), while the other five consumed 300 g/day cooked Brussels sprouts,
at the expense of 300 g glucosinolate-free vegetables (sprouts period). After 7 days
the regimen was changed for a further week. At the end of both periods blood samples
and duodenal and rectal biopsies were taken. Mean GST activity showed marked differences
between duodenal, rectal and lymphocytic cytosols (737 +/- 54, 321 +/- 29 and 154
+/- 14 nmol/min/mg protein respectively), but was uninfluenced by the dietary regimen.
Isozyme distribution varied greatly between the tissues. In duodenum GST-alpha, -pi,
and -mu isozymes were expressed in considerable amounts (8441 +/- 1365, 3002 +/- 223
and 536 +/- 248 ng/mg protein respectively). Rectal biopsies also contained above
three GST classes, but here GST-pi was the most pronounced expressed isozyme (2849
+/- 246) followed by GST-mu (495 +/- 242), while GST-alpha was only present in minor
quantities (149 +/- 31). In lymphocytes only GST-pi (755 +/- 96) and GST-mu (83 +/-
54) could be detected. As a result of the dietary regimen rectal GST-alpha and -pi
levels were slightly increased at the end of the sprouts period, by 30 and 15% respectively.
GSH contents were uninfluenced by the dietary regimen. In conclusion, consumption
of glucosinolate-containing Brussels sprouts for 1 week results in increased rectal
GST-alpha and -pi isozyme levels. We hypothesize that these enhanced detoxification
enzyme levels may partly explain the epidemiological association between a high intake
of glucosinolates (cruciferous vegetables) and a decreased risk of colorectal cancer.