The
limonoids,
limonin and
nomilin, are bitter principles found in common edible citrus fruits.
Nomilin, when given three times (at 5 and 10 mg per animal) every two days, induced increased
glutathione S-transferase activity 2.48 and 3.44 times over the control, respectively, in the liver of female ICR/Ha mice. The increases of GST activity in the small intestinal mucosa were 3.00 and 4.17, respectively, over the control.
Limonin, when given at the same dose levels, was not active in the liver. However, marginal activity was obtained in the small intestinal mucosa.
Nomilin, which is the more active
enzyme inducer, was found to inhibit
benzo[a]pyrene (BP)-induced
neoplasia in the forestomach of ICR/Ha mice. The number of mice with
tumors was reduced from 100 to 72%, and the number of
tumors per mouse was significantly decreased as a result of
nomilin treatment.
Limonin, which is a weak
enzyme inducer, was less potent as an inhibitor of BP-induced
neoplasia. These findings suggest
limonoids as a class of regularly consumed natural products may be effective chemopreventive agents.