BIOACTIVITY-GUIDED ISOLATION OF ANTIULCER CONSTITUENTS OF Securidaca longepedunculata FRES. ANDLuffa cylindrica (L.) ROEM. LEAF EXTRACTS

Abstract

Gastric ulcer results from persistent erosions and damage of the stomach wall. Ethnomedicinalsurvey revealed two plants, Securidaca longepedunculata(Polygalaceae, SL) and Luffa cylindrica (Cucurbitaceae, LC) among others used for the treatment of gastric ulcer in southwestern Nigeria. However, there is no reported scientific evidence to justify this claim. This study was designed to investigate antiulcer activity of selected plants, isolate and characterise the bioactive constituents.

Plant samples were macerated for 72 h in n-hexane, ethyl acetate (EtOAc) and methanol successively. Phytochemical screening of SL (FHI 109974) and LC (FHI 109973) leaves was carried out using standard methods. Antiulcer effect was assessed using ethanol-induced gastric ulcer in Wistar rats (n=5, 140-160 g) at varying doses. Crude extracts (150 and 300 mg/kg b.w.) and cimetidine (50 and 100 mg/kg b.w.) were administered 50 min prior to ulcerogenic procedure. Ulcer index was determined in excised stomach by scoring severity of ulceration. In vitro antioxidant activities of the crude extracts were evaluated by 2, 2-Di-Phenyl-1-PicrylHydrazyl (DPPH) Radical Scavenging Activity (RSA) using Quercetin Equivalent (QE), metal chelation and inhibition of Nitric Oxide (NO). Total Phenolic and Flavonoid Contents (TPC, TFC) were determined spectrophotometrically. Superoxide dismutase (SOD), Catalase (CAT) and reduced Glutathione (GSH) activities were also determined in gastric tissues. The EtOAc extract having the highest antiulcer effect was subjected to Vacuum Liquid Chromatography (VLC), VLC fractions A, B, C, D (50 and 100 mg/kg b.w.) were evaluated for antiulcer activity. Compounds were isolated using chromatographic techniques (Column, TLC, Prep. TLC). Structures of bioactivity-guided isolated compounds were elucidated using various spectroscopic techniques (IR,1-D NMR, and 2-D NMR). Cytotoxicity test of compounds (12.5-50.0 µg/mL) was conducted using liver epithelial cell lines (C3A) with melphalan as standard. Data were analysed using student t-test and one-way ANOVA at p=0.05.

Alkaloids, steroids and flavonoids were present in the leaves. The EtOAcextractsof SL and LC (150 and 300 mg/kg b.w.)gave 91.3%, 97.8% and 97.8%, 100.0% ulcer inhibition, respectively. Cimetidine had 91.3% inhibition. EtOAc extracts of SL and LC gave TFC of 340.68 ± 30.94 and 678.41 ± 76.30 mgQE/g extract, respectively, while DPPH RSA of methanol extract of SL and EtOAc extract of LC had IC50 of 0.47 ± 0.01 and 1.04 ± 0.02, respectively. The high TFC and DPPH RSA showed the antioxidant capacity of the plants. Ethanol treated group revealed elevated levels of SOD, CAT and GSH activities compared to the extracts and cimetidine that showed reduced levels thereby suggesting gastroprotective activity of the plants. The VLC fraction D of SL (100 mg/kg) had 92.3%, while fraction B of LC (100 mg/kg) gave 94.9% compared to cimetidine, which had 71.8% ulcer inhibition. Sitosterol and stigmasterolwere identified from EtOAc fractions of SL and citronellol from LC. Phytosterols showed cell proliferative activity (1900-2750) compared to melphalan (650-950) and anti-apoptotic activity (5.0-6.0) compared to melphalan (12.5-16.5).

Securidaca longepedunculata and Luffa cylindricahadantiulcer and gastroprotectiveactivities.Sitosterol, stigmasterol and citronellol exhibited cell proliferative and anti-apoptotic activities, which could contribute to their antiulcerogenic property.