Macrolides Inhibit Capsule Formation of Highly Virulent Cryptococcus gattii and Promote Innate Immune Susceptibility

Abstract

Cryptococcus gattii is a fungal pathogen, endemic in tropical and subtropical regions, the west coast of Canada, and the United States, that causes a potentially fatal infection in otherwise healthy individuals. Because the cryptococcal polysaccharide capsule is a leading virulence factor due to its resistance against innate immunity, the inhibition of capsule formation may be a promising new therapeutic strategy for C. gattii. Macrolides have numerous nonantibiotic effects, including immunomodulation of mammalian cells and suppression of bacterial (but not fungal) pathogenicity. Thus, we hypothesized that a macrolide would inhibit cryptococcal capsule formation and improve the host immune response. Coincubation with clarithromycin (CAM) and azithromycin significantly reduced the capsule thickness and the amount of capsular polysaccharide of both C. gattii and C. neoformans. CAM-treated C. gattii cells were significantly more susceptible to H 2 O 2 oxidative stress and opsonophagocytic killing by murine neutrophils. In addition, more C. gattii cells were phagocytosed by murine macrophages, resulting in increased production of tumor necrosis factor alpha (TNF-␣) by CAM exposure. After CAM exposure, dephosphorylation of Hog1, one of the mitogen-activated protein kinase (MAPK) signaling pathways of Cryptococcus, was observed in Western blot analysis. In addition, CAM exposure significantly reduced the mRNA expression of LAC1 and LAC2 (such mRNA expression is associated with cell wall integrity and melanin production). These results suggest that CAM may aid in inhibiting capsular formation via the MAPK signaling pathway and by suppressing virulent genes; thus, it may be a useful adjunctive agent for treatment of refractory C. gattii infection.

Versatile polymer-based strategies for antibacterial drug delivery systems and antibacterial coatings

“…Moreover, the anti-virulence factor methods can prevent the development of bacterial resistance, and do not have a negative impact on normal microorganisms and cells. [76][77][78] Virulence factors include hemolysin, 79,80 endotoxin, 81-83 adhesin, 84 capsular polysaccharide, 85,86 etc. Among them, a-hemolysin (Hla) is one of the important virulence factors and has been used as an important target of bacterial virulence in the development of drugs against bacterial infections.…”

Treatment strategies for cryptococcal infection: challenges, advances and future outlook

“…Deletion of CAP10 , CAP60 and PXB1 not only blocks capsule production but also leads to attenuated virulence 52 , 58 . Finally, the macrolides clarithromycin and azithromycin, as well as thiazole derivatives, disrupt the integrity and reduce the thickness of the capsule, resulting in enhanced phagocytosis of Cryptococcus by murine macrophages 59 , 60 , thus demonstrating the therapeutic potential of using small molecules to impair Cryptococcus spp. capsule formation.…”

“…The efficacy of fenbendazole was attributed to its growth-inhibitory properties, its inhibition of Cryptococcus virulence determinants and its inhibition of fungal proliferation inside macrophages 103 . Another example is the macrolides, commonly used antibiotics that target protein synthesis, which reduce capsule formation in C. gattii , impairing this key virulence trait and resulting in enhanced phagocytosis and inflammatory cytokine production by macrophages in culture 59 .…”

Combating increased antifungal drug resistance in <italic>Cryptococcus</italic>, what should we do in the future?

“…Therefore, it may be a useful adjunct drug for the treatment of refractory C . gattii infection [64] . In addition, immunomodulation with monoclonal antibodies against the capsular polysaccharides glucuronoxylomannan and melanin has also yielded promising results in animal models [65] .…”