Kirenol is a diterpenoid that has been found in S. orientalis and has diverse biological activities, including anti-arthritic and anti-inflammatory properties. It inhibits Gram-positive and Gram-negative bacterial growth in disc diffusion assays with MICs ranging from 39 to 156 and 312.5 to 625 μg/ml, respectively. Kirenol also reduces K652 chronic myeloid leukemia cell viability with a 48 hour IC50 value of 18.19 μg/ml and induces apoptosis. In vivo, kirenol (2 mg/kg, p.o.) reduces motor deficit, delays disease onset by approximately five days, and downregulates inflammatory CD4+IFN-γ+ Th1 cells and CD4+IL-17A+ Th17 cells in a mouse model of experimental autoimmune encephalomyelitis (EAE). Intragastric administration of kirenol (1-4 mg/kg) reduces the arthritis index, NF-kB activity, and paw swelling and increases annexin-1 expression without affecting glucocorticoid receptor α (GRα) expression in the synovium in a rat model of collagen-induced arthritis. Topical administration of kirenol (0.3-0.5% w/w) reduces edema induced by carrageenan, complete Freund''s adjuvant (CFA), and formalin in rats up to 44, 67, and 65%, respectively.
