Suppressive properties of extracts from Japanese edible plants regarding nitric oxide generation

Acetone extracts from a total of 30 species (197 samples) of plants commonly eaten in Japan were tested for their in vitro inhibitory properties against nitric oxide (NO) generation in a murine macrophage cell line, RAW 264.7, that had been stimulated with lipopolysaccharide in combination with interferon-g. Evaluation of the effects of treatment with 100 mg/mL revealed that 6 extracts (3.1%) exerted a strong inhibitory effect (inhibition rate (IR) > or = 70%) with strong cell viability (CV> or = 70%). However, nine extracts that exhibited an IR of greater than 70% were not considered to exert a significant effect at 100 microg/mL due to their low CV (<70%). Of the 14 plant families evaluated, Cucurbitaceae (extracts of watermelon 1 and melon 2), Liliaceae (extracts of garlic 1 and 2) and Solanaceae (extracts of tomato 3 and eggplant 5) were shown to be promising candidates for the inhibition of NO generation at the tested concentration. When tested at 20 microg/mL, 6 extracts, one of garland-chrysamthemums (sample 5), one of lettuce (sample 2), one of tomatoes (sample 3), two of Japanese hornworts (Mitsuba 1 and 2), and one of carrots (sample 4) showed strong inhibition of NO generation (IR> or = 70%). Even though one of the test samples (sample 2) of Japanese hornwort had a CV of less than 70% (67.8%), Japanese hornwort was still considered to be a highly promising species for the inhibition of NO generation. Furthermore, the activity varied significantly among samples from the same species for several plants. This variation may have been due to differences between cultivars and/or growing districts, or to differences in post-harvesting treatment. Taken together, the results of the present study may provide an experimental basis for new strategies for the production of highly functional dietary plants and food items.