Selective inhibition of Rhizopus eumelanin biosynthesis by novel natural product scaffold-based designs caused significant inhibition of fungal pathogenesis

Abstract

<jats:p>Melanin is a dark color pigment biosynthesized naturally in most living organisms. Fungal melanin is a major putative virulence factor of Mucorales fungi that allows intracellular persistence by inducing phagosome maturation arrest. Recently, it has been shown that the black pigments of Rhizopus delemar is of eumelanin type, that requires the involvement of tyrosinase (a copper-dependent enzyme) in its biosynthesis. Herein, we have developed a series of compounds (UOSC-1–14) to selectively target Rhizopus melanin and explored this mechanism therapeutically. The compounds were designed based on the scaffold of the natural product, cuminaldehyde, identified from plant sources and has been shown to develop non-selective inhibition of melanin production. While all synthesized compounds showed significant inhibition of Rhizopus melanin production and limited toxicity to mammalian cells, only four compounds (UOSC-1, 2, 13, and 14) were selected as promising candidates based on their selective inhibition to fungal melanin. The activity of compound UOSC-2 was comparable to the positive control kojic acid. The selected candidates showed significant inhibition of Rhizopus melanin but not human melanin by targeting the fungal tyrosinase, and with an IC50 that are 9 times lower than the reference standard, kojic acid. Furthermore, the produced white spores were phagocytized easily and cleared faster from the lungs of infected immunocompetent mice and from the human macrophages when compared with wild-type spores. Collectively, the results suggested that the newly designed derivatives, particularly UOSC-2 can serve as promising candidate to overcome persistence mechanisms of fungal melanin production and hence make them accessible to host defenses.</jats:p>

Stable and reproducible homologous recombination enables CRISPR-based engineering in the fungus Rhizopus microsporus

“…Despite the pleiotropic effect provoked by disruption of crgA in R. microsporus, the virulence of the crgA mutant suggests that none of the regulatory pathways controlled by this gene are involved in the pathogenic potential of Mucorales. The lack of melanin correlates with a decreased virulence in other Mucorales ( Soliman et al., 2020 ), but its overaccumulation has not been analyzed. Full virulence of the crgA mutant suggests that melanin overaccumulation does not increase virulence, although we cannot discard a compensatory effect on virulence by the diverse pathways altered in the crgA mutant.…”

Cellular Cytotoxicity and Oxidative Potential of Recurrent Molds of the Genus Aspergillus Series Versicolores

“…Pigments and exudates contain secondary metabolites with various activities: antifungal and antibacterial agents (asperversin, averufins, aspergillomarasmine A) [46,47] or cytotoxic agents (versixanthones) [27]. One of the molecules found in the pigments of Aspergillus of the series Versicolores is melanin, which, although historically known for its antioxidant properties, in fact has a duality of functional activity through eumelanin (photoprotective and antioxidant) and pheomelanin (phototoxic and prooxidant) [48][49][50]. A variable production of pheomelanin and/or eumelanin or other unidentified compounds from one isolate to another could explain this variability in the oxidative potential measured for the extract from isolates belonging to the same species of the series Versicolores.…”

SARS-CoV-2-induced hypomethylation of the ferritin heavy chain (FTH1) gene underlies serum hyperferritinemia in severe COVID-19 patients

“…Blood samples were collected from 5 healthy adults who never tested positive for COVID-19 and received their last vaccine shot at least three months prior to donating the sample; blood samples were then pooled and processed. Freshly-isolated peripheral blood monocytes (PBMCs) were enriched following a previously published protocol [ 33 ]. Blood samples were collected in EDTA tubes and pooled in 50 ml falcon tubes.…”