Selective GLP-1 secretagogues represent a novel potential therapy for type 2 diabetes mellitus. This study examined the GLP-1 secretory activity of the ethnomedicinal plant, Fagonia cretica, which is postulated to possess anti-diabetic activity. After extraction and fractionation extracts and purified compounds were tested for GLP-1 and GIP secretory activity in pGIP/neo STC-1 cells. Intracellular levels of incretin hormones and their gene expression were also determined. Crude F. cretica extracts stimulated both GLP-1 and GIP secretion, increased cellular hormone content, and upregulated gene expression of proglucagon, GIP and prohormone convertase. However, ethyl acetate partitioning significantly enriched GLP-1 secretory activity and this fraction underwent bioactivity-guided fractionation. Three isolated compounds were potent and selective GLP-1 secretagogues: quinovic acid (QA) and two QA derivatives, QA-3β-O-β-D-glycopyranoside and QA-3β-O-β-D-glucopyranosyl-(28→1)-β-D-glucopyranosyl ester. All QA compounds activated the TGR5 receptor and increased intracellular incretin levels and gene expression. QA derivatives were more potent GLP-1 secretagogues than QA. This is the first time that QA and its naturally-occurring derivatives have been shown to activate TGR5 and stimulate GLP-1 secretion. These data provide a plausible mechanism for the ethnomedicinal use of F. cretica and may assist in the ongoing development of selective GLP-1 agonists.

Secondary metabolites present in medicinal plants offer a golden opportunity to fight different ailments, such as cancer, infections, diabetes, neurodegenerative and cardiovascular diseases, etc. The traditional use of various parts of Fraxinus xanthoxyloides is known to serve as a cure for pneumonia, pain, jaundice, malaria, fracturing of bones, and internal wounds. The aim of this research was to validate the antioxidant and cardio-protective properties of F. xanthoxyloides leaves. The antioxidant potential was evaluated by employing different assays on the crude methanol extract, as well as its derived fractions. The extract/fraction that showed significant activity was further investigated for the presence of phytochemicals using high performance liquid chromatography-diode array detector (HPLC-DAD) analysis and also for cardio-protective potential. In the case of the antioxidant potential, the ethyl acetate fraction (FXE) was demonstrated to have the most potent total antioxidant (26.3 ± 2.4 AAE μg mg⁻¹), hydroxyl ion scavenging (IC₅₀ = 7.9 ± 0.9 μg mg⁻¹), ferrous ion chelating (IC₅₀ = 28.2 ± 2.7 μg mg⁻¹) and nitric oxide scavenging (IC₅₀ = 32.5 ± 2.9 μg mg⁻¹) effects among all of the extract/fractions, whereas in the case of DPPH (IC₅₀ = 17.5 ± 2.7 μg mg⁻¹) and the reducing power assay (16.7 ± 2.8 GAE μg mg⁻¹), promising antioxidant potential was shown by the n-butanol fraction. The presence of different concentrations of rutin, caffeic acid, catechin, and gallic acid was observed in the high performance liquid chromatography (HPLC) profile of FXE. Furthermore, in in vivo experimentation, the oral administration of FXE and silymarin significantly restored the CCl₄-induced increase in the levels of creatine kinase, creatine kinase-MB, cholesterol and triacylglycerides when compared with the untreated group. FXE and silymarin treatment also restored the levels of the tissue antioxidant enzymes, for example glutathione-S-transferase, glutathione reductase, catalase, peroxidase and superoxide dismutase. Furthermore, significantly lower levels of reduced glutathione and enhanced levels of lipid peroxides, hydrogen peroxide, comet length and DNA damages were observed after CCl₄ administration in the cardiac tissue of rats. FXE was able to restore these biochemical parameters, as well as the histological status of heart tissue. Based upon the present investigation, we concluded that F. xanthoxyloides leaves may have cardio-protective potential similar to silymarin against CCl₄ induced injuries owing to its antioxidant constituents.