Isolation and Characterisation of Two Quercetin Glucosides with Potent Anti‐Reactive Oxygen Species (ROS) Activity and an Olean‐12‐en Triterpene Glucoside from the Fruit of Abelmoschus esculentus (L.) Moench

Abstract

Abelmoschus esculentus (Okra) is used in the traditional treatment of cancer, hyperlipidaemia and hyperglycaemia. We, therefore, investigated its composition and potential cytotoxic or antioxidant properties that might underlie its phytotherapeutic applications. Its methanolic fruit extract yielded compounds 1, 2 and 3, identified through NMR, UV and MS analyses as olean-12-en-3-O-β-D-glucopyranoside, isoquercitrin (quercetin glucoside) and 5,7,3',4'-tetrahydroxy-flavonol-3-O-[β-D-glucopyranosyl-(1!6)]-β-D-glucopyranoside (quercetin diglucoside), respectively. Following 48 h exposure, oleanene glucoside was mildly toxic to the HeLa and the MRC5-SV2 cancer cells, isoquercitrin was not toxic except at 100 μg/ml in HeLa, and quercetin diglucoside elicited no toxicity. In a 2',7'-dichlorofluorescein diacetate (DCFDA) assay of intracellular levels of reactive oxygen species (ROS), hydrogen peroxide increased ROS levels, an effect not affected by oleanene glucoside but protected against by isoquercitrin and quercetin diglucoside, with IC 50 values, respectively, of 2.7 � 0.5 μg/ml and 1.9 � 0.2 μg/ml (3 h post-treatment) and 2.0 � 0.8 μg/ml and 1.5 � 0.4 μg/ml (24 h post-treatment.) This is the first report of this oleanene skeleton triterpenoid in the plant. The work provides some insight into why the plant is included in remedies for cancers, cardiovascular complications and diabetes, and reveals it as a potential source of novel therapeutics.

Ethnomedicinal Uses, Phytochemistry, and Anticancer Potentials of African Medicinal Fruits: A Comprehensive Review

“…Okra has been used in folkloric medicine in many parts of East Africa to treat kidney stones, diabetes, jaundice, gastritis, gastric ulcers, and other infections or ailments. Phytochemical analysis has shown that okra is a rich source of several potent bioactive components, such as catechin; epigallocatechin; isoquercitrin; rhamnogalacturonan; quercetin -β-d-glucopyranoside14; and oligomeric proanthocyanidins [193][194][195]. Most of these bioactive compounds have been shown to induce potent anticancer effects in several studies [24,193,196].…”

“…Okra has been used in folkloric medicine in many parts of East Africa to treat kidney stones, diabetes, jaundice, gastritis, gastric ulcers, and other infections or ailments. Phytochemical analysis has shown that okra is a rich source of several potent bioactive components, such as catechin; epigallocatechin; isoquercitrin; rhamnogalacturonan; quercetin-3-O-sophoroside; quercetin-3-O-[glucosyl(1->6) glucoside]-7-O-rhamnoside; (3β,21β)-19,21-epoxylup-20(29)-en-3-yl acetate; (3β)-9,18-dihydroxyolean-12-en-3-yl acetate; polyphenolic groups of compounds like flavonoids; hydroxycinnamic derivatives; 5,7,3′,4′-tetrahydroxy flavonol-3-O-[β-d-rhamnopyranosyl-(1→2)]-β-d-glucopyranoside’ rutin; procyanidins B1 and B2; 5,7,3′,4′-tetrahydroxy-4″-O-methylflavonol-3-O-β-d-glucopyranoside; 5,7,3′,4′-tetrahydroxy flavonol-3-O-[β-d-glucopyranosyl-(1→6)]-β-d-glucopyranoside14; and oligomeric proanthocyanidins [ 193 , 194 , 195 ]. Most of these bioactive compounds have been shown to induce potent anticancer effects in several studies [ 24 , 193 , 196 ].…”

“…As an interesting finding, only oleanene glucoside showed mild toxicity towards cancer cells, followed by isoquercitrin which induced cytotoxicity only at a 100 μg/mL concentration, while quercetin diglucoside was completely nontoxic. However, when these compounds were tested for their ability to protect against ROS induction, isoquercitrin and quercetin diglucoside showed the most potent antioxidant property with IC 50 values of 2.0 ± 0.8 μg/mL and 1.5 ± 0.4 μg/mL, respectively, with no protective effect induced by oleanene glucoside [ 194 ]. In another study, the anticancer property of extracts of okra pods was reported due to the presence of phenolic and terpenoid compounds, as well as certain volatile compounds like β-caryophyllene, limonene, and eugenol [ 197 ].…”

The use of African medicinal plants in cancer management

“…Silver nanoparticles made using A. esculentus flower extracts showed antiproliferative, apoptotic and cytotoxic effects against A-549 and TERT-4 cancer cell lines. Quercetin diglucoside and isoquercitrin identified in A. esculentus were shown to be potently anti-ROS and thus could be used in cancer treatment ( Taiwo et al, 2021 ).…”