Lignans from silkworm droppings and their promotional activities on heme oxygenase-1 (HO-1)

Six lignans, (+)-pinoresinol (1), (+)-lariciresinol (2), (+)-syringaresinol (3), syringaresinol-4-O-β-Dglucopyranoside (4), (+)-lariciresinol-4-O-β-D-glucopyranoside (5), and dehydrodiconiferylalcohol- 9'-O-β-D-glucopyranoside (6), were isolated from silkworm droppings. The structures of six compounds were elucidated on the basis of 1D- and 2D-NMR spectroscopic analyses and optical rotational characteristics. The isolated compounds were evaluated for their effects on HO-1 activity. Compounds 2, 3, and 6 increased the expression of heme oxygenase-1 (HO-1) in HepG2 cells. HO-1 is an antioxidant enzyme that catabolizes heme to carbon monoxide, free iron, and biliverdin, all of which are involved in the suppression of inflammatory mediators.