Antifungal activity of Allamanda polyantha seed extract and its iridoids promote morphological alterations in Cryptococcus spp.

Abstract

Cryptococcosis, caused by Cryptococcus spp., is an invasive fungal infection of the central nervous system, associated with high mortality, affecting mainly immunocompromised patients. Due to the development of resistance to the current therapy, there is an urgent need for less toxic and more effective antifungal agents. In this study, we describe the antifungal activity against Cryptococcus spp. of an aqueous seed extract from Allamanda polyantha (ASEAP) and two iridoids, plumieride and plumieridine, isolated from this extract with an antifungal activity. The capsule formation and the morphological alterations were evaluated using fluorescent microscopy. The cytotoxic activity was also investigated. The minimal inhibitory concentration (MIC) values of ASEAP for Cryptococcus gattii were 70 and 36 µg/ml (for the R265 and R272 strains, respectively) and 563 µg/ml for Cryptococcus neoformans H99. ASEAP inhibited C. neoformans H99 capsule formation, an important virulence factor, and decreased the cell body size for both the C. gattii strains. H99 cells also presented morphological alterations, with defects in bud detachment and nuclear fragmentation. Plumieride and plumieridine presented higher MIC values than ASEAP, indicating that other compounds might contribute to antifungal activity and/or that combination of the compounds results in a higher antifungal activity.

A Plumieridine-Rich Fraction From Allamanda polyantha Inhibits Chitinolytic Activity and Exhibits Antifungal Properties Against Cryptococcus neoformans

“…Through NMR spectra, plumieridine was identified as the main compound present in the chromatographic fraction obtained from the seed extract of A. polyantha with anti-cryptococcal activity ( Bresciani et al, 2020 ). To obtain enough plumieridine for all experiments, several batches of purification were needed.…”

“…To obtain enough plumieridine for all experiments, several batches of purification were needed. To ensure reproducibility, every new batch of the plumieridine-rich fraction was assayed against C. neoformans , aiming for MIC concentrations close to the one obtained previously ( Bresciani et al, 2020 ). The MIC values for each batch varies between 125 and 312 μg/mL, but all batches used in this work had a MIC of 312 μg/mL ( Supplementary Table S4 ).…”

“…Plumieridine isolation was performed as recently published ( Bresciani et al, 2020 ). Briefly, A. polyantha seeds were crushed in a kitchen blender.…”

“…Plumieridine was serially diluted, starting with 1 or 1.25 mg/mL, in RPMI 1640 (pH 7; Gibco® Life Technologies, Waltham, MA, United States) buffered with MOPS (Acros Organics, Geel, Belgium). Plates were incubated at 37°C for 72 h. To ensure reproducibility, MIC assays were performed with every new batch of the plumieridine-rich fraction and the obtained values were compared with previous results ( Bresciani et al, 2020 ).…”

“…Arg. This antifungal activity was attributed to a fraction rich in plumieridine ( Bresciani et al, 2020 ). However, the target and mode of action of this potential antifungal agent are still unknown.…”