J Ethnopharmacol. 2013 Jun 3;147(3):645-52. doi: 10.1016/j.jep.2013.03.062. Epub 2013 Mar 30.
Nrf2-dependent neuroprotective activity of diterpenoids isolated from Sideritis spp.
González-Burgos E, Carretero ME, Gómez-Serranillos MP.

ETHNOPHARMACOLOGICAL RELEVANCE:
The species of the genus Sideritis are extensively used in the Mediterranean area in folk medicine for their digestive, antimicrobial, anti-inflammatory and antioxidant properties, among others. Moreover, Sideritis species as tea infusions are popularly known for improving memory function and cognitive ability. Diterpenoids are one of the most abundant and important pharmacological interest of the classes of natural products presented in these medicinal plants.

AIM OF THE STUDY:
To determine for the first time the neuroprotective effects, based on their antioxidant properties, of the three isolated major diterpenoids andalusol, conchitriol and lagascatriol in an oxidative stress model.

MATERIALS AND METHODS:
H2O2 was used as oxidant inductor and rat adrenal pheochromocytoma PC12 cells as cellular model. Cell viability was measured using MTT and LDH assays, lipid peroxidation was determined by HPLC, GSH and GSSG levels assessed by fluorometric techniques, enzymatic activity and protein expression were determined by spectrofometric techniques and Western blot, respectively.

RESULTS:
Pretreatments with the three diterpenoids significantly attenuated H2O2-induced changes in mitochondrial integrity and activity (MTT assay), in cell membrane integrity (LDH assay) and in cell morphology. Moreover, these diterpenoids inhibited intracellular ROS production H2O2-induced, reduced lipid peroxidation and counteracted GSH/GSSG changes. Furthermore, both activities and protein expression of the endogenous antioxidant enzymes (CAT, SOD, GR, GPx and HO-1) were increased. The Nrf2 pathway was involved, at least in part, in the protective effects of these diterpenoids.

CONCLUSION:
These findings suggest that these natural compounds provide significant antioxidant effects in PC12 under for counteracting the oxidative damage H2O2-induced and their potential role as useful agents for the prevention of those oxidative stress-mediated dementia disorders. Andalusol was the most active compound among the studied diterpenoids.