Anti-inflammatory and diuretic effects of the diterpene ent-dihydrotucumanoic acid

Gymnosperma glutinosum (Spreng) Less (Asteraceae) is a shrub used in traditional medicine for the treatment of inflammatory and renal diseases. The ent-dihydrotucumanoic acid (DTA) is a diterpene obtained from G. glutinosum. This study evaluated the antioxidant, genotoxic, and diuretic properties of DTA, as well as its in vitro and in vivo anti-inflammatory actions. The antioxidant actions of DTA were assessed with the 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) (ABTS), ferric reducing antioxidant power (FRAP), and 2,2'-diphenyl-1-picrylhydrazyl (DPPH) assays, the genotoxic action was assessed with the comet assay, and the diuretic effects of DTA were assessed using metabolic cages. The anti-inflammatory actions were evaluated using primary murine peritoneal macrophages stimulated with LPS and the λ-carrageenan-induced hind paw edema test. DTA lacked antioxidant (IC₅₀  > 25,000 μg/mL) activity in the ABTS, FRAP, and DPPH assays. DTA at 500-1,000 μg/mL showed moderate genotoxicity. In LPS-stimulated macrophages, DTA showed IC₅₀ values of 74.85 μg/mL (TNF-α) and 58.12 μg/mL (NO), whereas the maximum inhibition of IL-6 (24%) and IL-1β (36%) was recorded at 200 μg/mL. DTA induced in vivo anti-inflammatory effects with ED₅₀ = 124.3 mg/kg. The in vitro anti-inflammatory activity of DTA seems to be associated with the decrease in the release of TNF-α and NO. DTA promoted the excretion of urine (ED₅₀ = 86.9 mg/kg), Na⁺ (ED₅₀ = 66.7 mg/kg), and K⁺ (ED₅₀ = 8.6 mg/kg). The coadministration of DTA with L-NAME decreased the urinary excretion shown by DTA alone. Therefore, the diuretic activity is probably associated with the participation of nitric oxide synthase. In conclusion, DTA exerted anti-inflammatory and diuretic effects, but lacked antioxidant effects.