Study of biological activities of extracts from Thymelaea microphylla Coss. and Dur

Abstract

Thymelaea microphylla Coss. and Dur. (Methnane) is a medicinal plant with Saharan affinity, belonging to the Mediterranean genus Thymelaea. Leaves decoction is used in traditional medicine for anticancer, anti-inflammatory, and anti-diabetic properties. Herein, the antioxidant and antiinflammatory activities of five extracts prepared using solvents with different polarities from leaves and flowers of Algerian T. microphylla, collected from the region of Draa El- were evaluated. In addition, preliminary studies on phytochemical composition and toxicity estimation were realized. Extracts were first characterized for their content in some secondary metabolites, where acetone extract contained the highest amounts of flavonoids (137.56 μg Cat eq/mg) and flavonols (94.13 μg Que eq/mg), and ethyl acetate extract was the richest in tannins (29.23 μg Cat eq/mg). HPLC analysis revealed the presence of phenolic acids (gallic, caffeic, ferulic and p-coumaric acids) especially in aqueous extract, and flavonoids (luteolin and kaempferol) in organic extracts. Furthermore, antioxidant/free radical scavenging activity which was carried out by in vitro cell-free assays, showed that aqueous and acetone extracts exhibited the best potential in Folin, DPPH , FRAP, ABTS and ORAC assays, while in BCB, acetone and hexane extracts were very likely richer in antioxidants able to reach the lipophilic phase. In the same way, acetone extract was the most potent in SOD mimetic assay; with IC50 of 1.81mg/ml. Extracts were also tested for their inhibitory activity on in vitro AGEs formation, where aqueous extract was the most potent (IC50 = 33.24 μg/ml). The antiinflammatory activity, which was first evaluated using albumin heat-induced denaturation assay, revealed that acetone extract was the most active with IC50 of 0.15 mg/ml, and it was further tested in ex vivo experiments, to estimate its inhibitory potential on prostaglandin E2 and thromboxane B2 release in human whole blood, where it showed excellent anti-inflammatory and cyclooxygenaseinhibitory activity, together with lack of toxicity on normal human blood cells; furthermore, it was able to protect human endothelial cells against dysfunction induced by TNF- , as shown by decrease in cell death, E-selectin expression, leukocyte adhesion and prevention of depletion in GSH cell content. Moreover, ethanol and aqueous extracts had a significant cytotoxicity on peripheral blood mononuclear cells; however, aqueous extract did not cause mortality or any serious toxicity signs when tested in vivo. This experimental study support the use of this plant in phytotherapy and prevention of diseases related to oxidative stress and inflammation.