Isolation of Megastigmane Sesquiterpenes from the Silkworm (Bombyx mori L.) Droppings and Their Promotion Activity on HO-1 and SIRT1

The silkworm (Bombyx mori L.) droppings were extracted with 80% aqueous MeOH, and the concentrated extract was partitioned in succession with EtOAc, n-BuOH, and H2O. From the EtOAc fraction, five megastigmane sesquiterpenes were isolated through repeated silica gel and ODS column chromatography. According to the results of spectroscopic data, such as NMR, MS, and IR, the chemical structures of the isolated compounds were determined as (3S,5R,8R)-3,5-dihydroxymegastigma-6,7-dien-9-one (1), (S)-dehydrovomifoliol (2), (6R,7E,9R) -9-hydroxy-4,7-megastigmadien-3-one (3), (3S,5R,6S,7E)-3,5,6-trihydroxy-7-megastigmen-9-one (4), (6R,9R)-9-hydroxy-4-megastigmen-3-one (5). Compounds 2 through 5 were isolated for the first time from silkworm droppings. GC/MS analysis indicated silkworm powder contained compound 3, and mulberry leaves contained compound 4. Compounds 1 and 5 increased the expression of heme oxygenase-1 and SIRT1 in HepG2 and HEK239 cells, respectively. Heme oxygenase-1 is considered to be an antioxidant enzyme that catabolizes heme to carbon monoxide, free iron and biliverdin, while SIRT1 is the mammalian homologue of the yeast silent information regulator (Sir)-2, which are involved in the suppression of inflammatory mediators or factors that may be used to improve atopy-related symptoms.