Malabaricones from the fruit of Myristica cinnamomea King as potential agents against Acanthamoeba castellanii

Acanthamoeba castellanii is an opportunistic free-living amoeba (FLA) pathogen which can cause fatal central nervous system (CNS) infection, granulomatous amoebic encephalitis (GAE) and potentially blinding ocular infection, Acanthamoeba keratitis (AK). Acanthamoeba species remain a challenging protist to treat due to the unavailability of safe and effective therapeutic drugs and their ability to protect themselves in the cyst stage. Natural products and their secondary metabolites play a pivotal role in drug discovery against various pathogenic microorganisms. In the present study, the ethyl acetate extract of Myristica cinnamomea King fruit was evaluated against A. castellanii (ATCC 50492), showing an IC50 of 45.102 ± 4.62 µg/mL. Previously, the bio-guided fractionation of the extract resulted in the identification of three active compounds, namely Malabaricones (A-C). The isolated and thoroughly characterized acylphenols were evaluated for their anti-amoebic activity against A. castellanii for the first time. Among tested compounds, Malabaricone B (IC50 of 101.31 ± 17.41 µM) and Malabaricone C (IC50 of 49.95 ± 6.33 µM) showed potent anti-amoebic activity against A. castellanii trophozoites and reduced their viability up-to 75 and 80 %, respectively. Moreover, both extract and Malabaricones also significantly (p < 0.05) inhibit the encystation and excystation of A. castellanii, while showed minimal toxicity against human keratinocyte cells (HaCaT cells) at lower tested concentrations. Following that, the explanation of the possible mechanism of action of purified compounds were assessed by detection of the state of chromatin. Hoechst/PI 33342 double staining showed that necrotic cell death occurred in A. castellanii trophozoites after 8 h treatment of Malabaricones (A-C). These findings demonstrate that Malabaricones B and C could serve as promising therapeutic options against A. castellanii infections.

Giganteone A and malabaricone C as potential pharmacotherapy for diabetes mellitus

The use of antidiabetic agents which control glycemic levels in the blood and simultaneously inhibit oxidative stress is an important strategy in the prevention of Diabetes Mellitus and its complications. In our previous study, malabaricone C (3) and its dimer, giganteone A (5) exhibited significant DPPH free radical scavenging activities which were lower than the activity of the positive control, ascorbic acid. These compounds were evaluated for their α-glucosidase inhibitory activities at different concentrations (0.02-2.5 mM) in the present study. Compounds 3 (IC₅₀ 59.61 µM) and 5 (IC₅₀ 39.52 µM) were identified as active alpha-glucosidase inhibitors, each respectively being 24 and 37 folds more potent than the standard inhibitor, acarbose. Based on the molecular docking studies, compounds 3 and 5 docked into the active site of the α-glucosidase enzyme, forming mainly hydrogen bonds in the active site.

Quorum Sensing Inhibitory Activity of Giganteone A from Myristica cinnamomea King against Escherichia coli Biosensors

Malabaricones A-C (1-3) and giganteone A (4) were isolated from the bark of Myristica cinnamomea King. Their structures were elucidated and characterized by means of NMR and MS spectral analyses. These isolates were evaluated for their anti-quorum sensing activity using quorum sensing biosensors, namely Escherichia coli [pSB401] and Escherichia coli [pSB1075], whereby the potential of giganteone A (4) as a suitable anti-quorum sensing agent was demonstrated.

A potent alpha-glucosidase inhibitor from Myristica cinnamomea King

A dimeric acylphenol and a potent α-glucosidase inhibitor, giganteone D (IC50 5.05μM), was isolated and characterized from the bark of Myristica cinnamomea King. The bark also yielded an acylphenol with an unprecedented skeleton for which the name cinnamomeone A (IC50 358.80μM) was proposed. Their structures were established by means of NMR and MS spectrometric analyses. The Lineweaver-Burk plot of giganteone D indicated that it was a mixed-type inhibitor. This is the first report on the α-glucosidase inhibiting potential of acylphenols.