Anti-Inflammatory, Antidiabetic Properties and In Silico Modeling of Cucurbitane-Type Triterpene Glycosides from Fruits of an Indian Cultivar of Momordica charantia L

Abstract

Diabetes mellitus is a chronic disease and one of the fastest-growing health challenges of the last decades. Studies have shown that chronic low-grade inflammation and activation of the innate immune system are intimately involved in type 2 diabetes pathogenesis. Momordica charantia L. fruits are used in traditional medicine to manage diabetes. Herein, we report the purification of a new 23-O-β-d-allopyranosyl-5β,19-epoxycucurbitane-6,24-diene triterpene (charantoside XV, 6) along with 25ξ-isopropenylchole-5(6)-ene-3-O-β-d-glucopyranoside (1), karaviloside VI (2), karaviloside VIII (3), momordicoside L (4), momordicoside A (5) and kuguaglycoside C (7) from an Indian cultivar of Momordica charantia. At 50 µM compounds, 2-6 differentially affected the expression of pro-inflammatory markers IL-6, TNF-α, and iNOS, and mitochondrial marker COX-2. Compounds tested for the inhibition of α-amylase and α-glucosidase enzymes at 0.87 mM and 1.33 mM, respectively. Compounds showed similar α-amylase inhibitory activity than acarbose (0.13 mM) of control (68.0-76.6%). Karaviloside VIII (56.5%) was the most active compound in the α-glucosidase assay, followed by karaviloside VI (40.3%), while momordicoside L (23.7%), A (33.5%), and charantoside XV (23.9%) were the least active compounds. To better understand the mode of binding of cucurbitane-triterpenes to these enzymes, in silico docking of the isolated compounds was evaluated with α-amylase and α-glucosidase.

Keywords: Momordica charantia; anti-inflammatory activity; charantoside XV; cucurbitane-type triterpene glycosides; in silico study; α-amylase; α-glucosidase.

Figure 1

Crucial HMBC, ¹H-¹H COSY (A) and NOESY correlations (B) for compound 6.

Figure 2

Chemical structures of compounds isolated and identified in the present study. (1) 25ξ-isopropenylchole-5(6)-ene-3-O-β-d-glucopyranoside, (2) karaviloside VI, (3) karaviloside VIII, (4) momordicoside L, (5) momordicoside A, (6) charantoside XV, and (7) kuguaglycoside C.

Figure 3

Effect of purified compounds on mRNA expression of IL-6, TNF-α, iNOS, and COX-2 in LPS-induced murine macrophage RAW 264.7 cells. The cells were pretreated with 50 µM karaviloside VI (2), karaviloside VIII (3), momordicoside L (4), momordicoside A (5), and charantoside XV (6) followed by LPS (1 μg/mL) stimulation. Data are expressed as mean ± SD (n = 9) and analyzed by one-way ANOVA with a Tukey post hoc test. Different letters within the same plot indicate the significant differences at p < 0.05.

Figure 4

α-Amylase (A) and α-glucosidase (B) inhibitory effects of purified compounds: karaviloside VI (2), karaviloside VIII (3), momordicoside L (4), momordicoside A (5) and charantoside XV (6). Compounds were assayed at 0.67 mM and data are expressed as mean ± SD (n = 3), and analyzed by one-way ANOVA with a Tukey post hoc test. Different letters within the same plot indicate there were significant differences at p < 0.05.

Figure 5

The 3D protein-ligand interactions for (A) karaviloside VI (2), (B) karaviloside VIII (3), (C) momordicoside L (4), (D) momordicoside A (5), (E) Charantoside XV (6), and (F) kuguaglycoside C (7) in the binding sites of α-amylase. Black dotted lines indicate hydrogen bonds between compounds and amino acid residues. Ligands in the active sites are denoted in green color. Active site residues are shown in cyans color.

Figure 6

The 3D protein-ligand interactions for (A) karaviloside VI (2), (B) karaviloside VIII (3), (C) momordicoside L (4), (D) momordicoside A (5), (E) charantoside XV (6), and (F) kuguaglycoside C (7) in the binding sites of isomaltase. Black dotted lines indicate hydrogen bonds between compounds and amino acid residues. Ligands in the active sites are denoted in green color. Active site residues are shown in white color.