The methanol extract of the roots and stems of Daphne genkwa and its constituents yuanhuacin (1) and genkwanine N were previously reported to have Nurr1 activating effects and neuroprotective effects in an animal model of Parkinson's disease (PD). In this study, four more daphnane-type diterpenes (acutilonine F (2), wikstroemia factor M1 (3), yuanhuadine (5), and yuanhuatine (6)) and two phorbol-type diterpenes (prostratin Q (4) and 12-O-n-deca-2,4,6-trienoyl-phorbol-(13)-acetate (7)) were isolated as Nurr1 activating compounds from the D. genkwa extract. Consistent with their higher Nurr1 activating activity, compounds 1, 4, 5, and 7 exhibited higher inhibitory activity on lipopolysaccharide (LPS)-induced nitric oxide (NO) production in murine microglial BV-2 cells with an IC50 (µM) of 1-2, which was 15-30 times more potent than that of minocycline (29.9 µM), a well-known anti-neuroinflammatory agent. Additionally, these diterpenes reduced expression and transcription of LPS-induced pro-inflammatory cytokines in BV-2 cells. Thus, the daphnane-type and phorbol-type diterpenes had anti-neuroinflammatory activity with Nurr1 activation and could be responsible for the anti-PD effect of the roots and stems of D. genkwa.
Keywords: Daphne genkwa; Nurr1; anti-neuroinflammatory; daphnane-type diterpene; phorbol-type diterpene.