An Immunomodulatory Peptide Confers Protection in an Experimental Candidemia Murine Model

Abstract

Fungal Candida species are commensals present in the mammalian skin and mucous membranes. Candida spp. are capable of breaching the epithelial barrier of immunocompromised patients with neutrophil and cell-mediated immune dysfunctions and can also disseminate to multiple organs through the bloodstream. Here we examined the action of innate defense regulator 1018 (IDR-1018), a 12-amino-acid-residue peptide derived from bovine bactenecin (Bac2A): IDR-1018 showed weak antifungal and antibiofilm activity against a Candida albicans laboratory strain (ATCC 10231) and a clinical isolate (CI) (MICs of 32 and 64 μg · ml^-1, respectively), while 8-fold lower concentrations led to dissolution of the fungal cells from preformed biofilms. IDR-1018 at 128 μg · ml^-1 was not hemolytic when tested against murine red blood cells and also has not shown a cytotoxic effect on murine monocyte RAW 264.7 and primary murine macrophage cells at the tested concentrations. IDR-1018 modulated the cytokine profile during challenge of murine bone marrow-derived macrophages with heat-killed C. albicans (HKCA) antigens by increasing monocyte chemoattractant protein 1 (MCP-1) and interleukin-10 (IL-10) levels, while suppressing tumor necrosis factor alpha (TNF-α), IL-1β, IL-6, and IL-12 levels. Mice treated with IDR-1018 at 10 mg · kg^-1 of body weight had an increased survival rate in the candidemia model compared with phosphate-buffered saline (PBS)-treated mice, together with a diminished kidney fungal burden. Thus, IDR-1018 was able to protect against murine experimental candidemia and has the potential as an adjunctive therapy.

Keywords: Candida albicans; IDR-1018 peptide; antifungals; host-directed therapy; immunomodulatory effects; murine experimental candidemia.

FIG 1

Effects of IDR-1018 against preformed biofilm of C. albicans CI strain. (A) Untreated C. albicans 2-day-old biofilm (control). (B) Two-day-old biofilm after treatment with IDR-1018 at 8 μg · ml⁻¹. Each panel shows reconstructions from the top in the large panel and sides in the right and bottom panels (x-y, y-z, and x-z dimensions, respectively).

FIG 2

Effects of IDR-1018 on the viability of a 2-day-old biofilm of C. albicans strains assessed by XTT assay. (A) C. albicans ATCC 10231 and (B) C. albicans clinical isolate (CI) untreated biofilms and biofilms treated with amphotericin B (16 μg · ml⁻¹), fluconazole (64 μg · ml⁻¹), and IDR-1018 (2 to 256 μg · ml⁻¹). Results are expressed as mean biofilm inhibition percentages ± standard errors of the mean (SEM).

FIG 3

Influence of IDR-1018 on cytokine production by bone marrow-derived macrophages stimulated or not with heat-killed C. albicans (HKCA). (A) MCP-1. (B) TNF-α. (C) IL-1β. (D) IL-6. (E) IL-12. (F) IL-10. Results are expressed as means ± SEM. Statistical comparisons were made using ANOVA with Tukey's correction for multiple testing. IFN-γ, gamma interferon; IDR, innate defense regulator; MCP-1, macrophage chemoattractant protein I; TNF-α, tumor necrosis factor-α; IL, interleukin; *, P < 0.05; **, P < 0.005; ***, P < 0.0005; ****, P < 0.00005.

FIG 4

Protection by IDR-1018 in a murine candidemia model. Mice treated with 10 mg · kg⁻¹ IDR-1018 had an increased survival rate compared with those infected and phosphate-buffered saline (PBS) treated. Statistical comparisons were made using log rank (Mantel-Cox) correction for multiple testing. *, P < 0.05.

FIG 5

Influence of IDR-1018 treatment on the viable C. albicans kidney burden. Shown are results prior to treatment (24 h postinfection) and at days 4 and 7 of treatment. Noninfected mice treated with PBS showed no C. albicans. Only after 7 days of treatment were the kidney burdens significantly different for both the amphotericin B and IDR-1018 treatments compared with the PBS-treated group. Statistical comparisons were made using ANOVA with Tukey's correction for multiple testing. *, P < 0.05; ****, P < 0.0005.