Inhibition of melanin synthesis pathway by tricyclazole increases susceptibility ofFonsecaea pedrosoi against mouse macrophages

Abstract

Fonsecaea pedrosoi produces melanin, a pigment related to virulence in pathogenic fungi. To understand the involvement of melanin in the protection of fungi, the authors used tricyclazole to inhibit the melanin pathway in F. pedrosoi. Experiments of pigmentation suggested that F. pedrosoi uniquely produces dihydroxynaphthalene-melanin. Pigments produced on cultures modified or not with tricyclazole were extracted by an alkali-acid method and submitted to infrared and ion exchange chromatography analysis; also cytochemistry analysis for cationized ferritin of whole cells was carried out. This group of experiments showed that the tricyclazole treatment on F. pedrosoi produced a melanin-like pigment, but less negatively charged and with less affinity for iron ions than that without the tricyclazole treatment, and this in turn lead to a less negatively charge cell wall surface. Scanning electron microscopy of such pigments showed that the melanin from control cultures maintained their hyphae-like structures, which have been described as "melanin-ghosts," whereas the tricyclazole pigment showed an amorphous surface. Interaction of conidia from cultures of F. pedrosoi, modified by tricyclazole or not, with peritoneal activated macrophages suggested that tricyclazole causes higher association of fungus with macrophages, weakens the fungus capacity to destroy the macrophages, and diminishes the resistance to dry fracture procedures on samples prepared for high resolution scanning electron microscopy.

New Biosynthetic Step in the Melanin Pathway ofWangiella(Exophiala)dermatitidis: Evidence for 2-Acetyl-1,3,6,8-Tetrahydroxynaphthalene as a Novel Precursor

“…Although we presently know that a large number of other plant-and human-pathogenic fungi make melanin from D2HN via T4HN, we do not know which of the three pathways they use. Additional studies with important plant pathogens, such as V. dahliae and Magnaporthe grisea, and melanized human pathogens, such as Sporothrix schenckii (31), Fonsecaea pedrosoi (11,15), and Hortaea werneckii (25,36), need to be carried out to determine how they make T4HN. Specifically, it would be helpful to know if they make AT4HN by PKS in a manner similar to that for WdPks1p in W. dermatitidis (14), YWA1 via a PKS in a manner similar to that for Alb1p in A. fumigatus (38), or T4HN directly by an enzyme, as reported for PKS in C. lagenarium (16).…”

Chromoblastomycosis

“…Melanin derived from DHN is synthesized by the polyketide path, a route starting with acetyl coenzyme A (acetyl-CoA) (199). Interestingly, the inhibition of this specific biochemical process with tricyclazole may be used to induce morphological changes in the cellular wall of F. pedrosoi leading to diminished resistance of the fungus to mechanical lysis and macrophage killing (200,201). Melanin is mainly stored, as revealed by transmission electron microscopy, in concentric layers in intracellular vesicles, known as melanosomes, similarly to mammalian cells (201).…”

Melanin as a virulence factor of Paracoccidioides brasiliensis and other dimorphic pathogenic fungi: a minireview

“…In addition to reducing ingestion, melanization protects P. brasiliensis against killing by macrophages [14]. Similarly, melanin production in C. neoformans [45], F. pedrosoi [46], S. schenckii [5] and Exophiala spp. [47] enhances resistance to killing by phagocytic cells.…”