Antifungal effect of voriconazole on intracellular Candida glabrata, Candida krusei and Candida parapsilosis in human monocyte-derived macrophages

A Histoplasma capsulatum Lipid Metabolic Map Identifies Antifungal Targets

Lipids play a fundamental role in fungal cell biology, being essential cell membrane components and major targets of antifungal drugs. A deeper knowledge of lipid metabolism is key for developing new drugs and a better understanding of fungal pathogenesis. Here, we built a comprehensive map of the Histoplasma capsulatum lipid metabolic pathway by incorporating proteomic and lipidomic analyses. We performed genetic complementation and overexpression of H. capsulatum genes in Saccharomyces cerevisiae to validate reactions identified in the map and to determine enzymes responsible for catalyzing orphan reactions. The map led to the identification of both the fatty acid desaturation and the sphingolipid biosynthesis pathways as targets for drug development. We found that the sphingolipid biosynthesis inhibitor myriocin, the fatty acid desaturase inhibitor thiocarlide, and the fatty acid analog 10-thiastearic acid inhibit H. capsulatum growth in nanomolar to low-micromolar concentrations. These compounds also reduced the intracellular infection in an alveolar macrophage cell line. Overall, this lipid metabolic map revealed pathways that can be targeted for drug development.

In vitro synergy of eugenol on the antifungal effects of voriconazole against Candida tropicalis and Candida krusei strains isolated from the genital tract of mares

BACKGROUND

Due to the limited range of antifungals available to treat genital Candida infections and the emergence of resistant isolates, attention has focused on the antifungal potency of natural compounds with promising biological properties.

OBJECTIVES

To examine whether eugenol synergises the in vitro efficacy of voriconazole against Candida strains isolated from the genital tract of mares.

STUDY DESIGN

In vitro experiment.

METHODS

The antifungal activity of eugenol and voriconazole was evaluated using the broth microdilution assay (CLSI- M27-A3). Synergism of eugenol and voriconazole against genital Candida isolates was evaluated by the microdilution checkerboard method.

RESULTS

Minimum inhibitory concentration (MIC) values for eugenol and voriconazole ranged from 400 to 800 µg/mL and 1 to 8 µg/mL, respectively, for C. tropicalis isolates, and from 200 to 400 µg/mL for eugenol and 2 to 16 µg/mL for voriconazole against C. krusei isolates. Eugenol decreased the arithmetic mean MIC for voriconazole against C. tropicalis and C. krusei isolates from 2.66 to 0.46 µg/mL and 7.77 to 0.41 µg/mL respectively. The fractional inhibitory concentration index (FICI) values for the eugenol-voriconazole combination ranged from 0.25 to 0.88 and 0.19 to 0.63 for C. tropicalis and C. krusei isolates respectively. A synergistic effect of eugenol in combination with voriconazole was observed for 83.3% of C. tropicalis and 77.7% of C. krusei isolates. Antagonistic activity was not seen in any of the isolates tested.

MAIN LIMITATIONS

Since in vitro antifungal susceptibility tests are not systematic analyses, any selection bias could influence the results. In addition, in vitro susceptibility does not uniformly predict clinical success in vivo.

CONCLUSIONS

Eugenol showed fungistatic and fungicidal effects against genital Candida isolates and, in combination, synergised the antifungal effects of voriconazole. The eugenol-voriconazole combination can lay the foundation for a therapeutic approach against isolates in which azole resistance has increased over time.

The potential impact of antifungal drug resistance mechanisms on the host immune response to Candida

A large number of studies have been published over the last two decades examining molecular mechanisms of antifungal resistance in Candida species. However, few of these studies have explored how such mechanisms influence the host immune response to this opportunistic pathogen. With recent advances in our understanding of host immunity to Candida, a body of emerging literature has begun to explore how intrinsic and adaptive resistance mechanisms in Candida alter host immune system evasion and detection, which could have important implications for understanding (1) why certain resistance mechanisms and Candida species predominate in certain patient populations, (2) the biological context for understanding why high in vitro levels of resistance in may not necessarily correlate with risk of drug failure in vivo and (3) insight into effective immunotherapeutic strategies for combatting Candida resistance. Although this area of research is still in its infancy, two themes are emerging: First, the immunoevasion and intracellular persistence of C. glabrata may be a key factor in the capability of this species to persist in the course of multiple antifungal treatments and develop multidrug resistance. Second, changes in the cell wall associated with antifungal resistance often favor evasion for the host immune response.

Immunomodulatory properties of antifungal agents on phagocytic cells

Phagocytic cells, particularly neutrophils and monocytes/macrophages, are the first line and the most effective form of innate host defence against pathogenic fungi. During antifungal therapy these phagocytic cells are also exposed to antifungal agents. In the phagocyte-fungus-antifungal agent interplay, drugs may directly interact with phagocytes through specific pattern recognition receptors, leading to altered antifungal activities. Antifungal agents, through modulation of fungal virulence, may initiate different immune response programs in the phagocytes, leading to antifungal synergism/antagonism or up-regulation of gene expression for a pro-inflammatory response. Additionally, indirect modulation of phagocyte behavior by pretreatment of neutrophils, monocytes, and macrophages with cytokines and exposure to antifungal agents have shown promising findings for combined drug-cytokine therapy that may improve treatment of life-threatening fungal diseases. In this review, we discuss the main in vitro and in vivo immunomodulatory effects of antifungal agents on phagocytes in response to pathogenic fungi, as well as we address underlying immunopharmacologic mechanisms and their potential impact on clinical outcome.

Post-antifungal effects and time-kill studies of anidulafungin, caspofungin, and micafungin against Candida glabrata and Candida parapsilosis

Candida glabrata (Cgl) and Candida parapsilosis (Cpa) can cause serious infections and can be resistant to some antifungal drugs. In treating infections caused by these organisms, killing rates and post-antifungal effects (PAFE) are important factors in both dose interval choice and outcome. Two strains each of Cgl and Cpa were studied. For PAFE studies, each organism was exposed to micafungin (MCF), anidulafungin (ANF), or caspofungin (CAS) for 1 h at concentrations ranging from 0.25 to 16×MIC. Cell suspensions were then washed 3 times and resuspended in fresh broth. Time 0 was immediately after resuspension of the yeast. Time-kill experiments were done using similar drug concentrations. Samples were removed at each time point (0-120 h) and viable counts determined. PAFE of ANF and CAS were generally very long, were markedly longer than those of MCF, and increased with increased drug concentration. For ANF and CAS, PAFE for Cgl were greater than those for Cpa only at 0.5 to 2 × MIC. Time-kill experiments showed that ANF, CAS, and MCF were fungicidal at 8 to 16 × MIC up to 120 h. CAS had the greatest activity against Cgl, while ANF and MCF were more active than CAS against Cpa. Because of the prolonged PAFE of these echinocandins, especially ANF and CAS, less frequent dosing during therapy of Cpa and Cgl infections could be considered. Further studies are needed to determine the clinical efficacy of longer dosing intervals.

Intracellular concentrations of posaconazole in different compartments of peripheral blood

Therapeutic drug monitoring (TDM) of antifungal plasma concentrations is increasingly recommended. However, data on antifungal concentrations in the other compartments of the peripheral blood are limited. Hence, we collected 23 blood samples from 14 patients receiving posaconazole for prophylaxis of fungal infections. These samples were separated by double-discontinuous Ficoll-Hypaque density gradient centrifugation. The intracellular posaconazole concentrations of the obtained cells, i.e., the peripheral blood mononuclear cells (PBMCs), polymorphonuclear leukocytes (PMNs), and red blood cells (RBCs), were determined by liquid chromatography-tandem mass spectrometry. The intracellular concentrations of the PBMCs and PMNs were significantly higher than those of surrounding media (P < 0.001). The ratios between the intracellular and extracellular concentrations (C/E) were 22.5 +/- 21.2, 7.66 +/- 6.50, and 0.09 +/- 0.05 for the PBMCs, PMNs, and RBCs, respectively. Posaconazole reaches high concentrations within human PBMCs and PMNs and is, to a lesser extent, present in RBCs. The high intracellular concentrations might contribute to posaconazole efficacy and distribution.

Quantitation of azoles and echinocandins in compartments of peripheral blood by liquid chromatography-tandem mass spectrometry

A rapid turnaround is a prerequisite of therapeutic drug monitoring (TDM). For antifungals, this need is still unmet, since hardly any method has been established to simultaneously quantitate concentrations of different antifungal classes. A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed allowing quantitation of anidulafungin (ANF), caspofungin (CSF), isavuconazole (ISC), micafungin (MCF), posaconazole (PSC), and voriconazole (VRC). Quantitation was successful with diluted plasma samples, peripheral blood mononuclear cells (PBMC), polymorphonuclear leukocytes (PMN), and erythrocytes (RBC). A triple quadrupole mass spectrometer in selected reaction monitoring mode was used with positive electrospray ionization. Cells and calibration standards were extracted with acetonitrile containing internal standard. Internal standards were a CSF derivate for echinocandins and itraconazole for triazoles. Chromatographic separation of the supernatant was achieved by a gradient method facilitating a BetaBasic C4 column. Analytes were quantified in a single 8-min run. Calibration curves were linear and fitted using least squares with a weighting factor of the reciprocal concentration. Limits of detection (ng/ml) were ANF, 8.3; CSF, 31.5; ISC, 1.5; MCF, 97.7; PSC, 3.3; and VRC, 1.4. The lower limits of quantitation (ng/ml) were ANF, 64; CSF, 108; ISC, 4.5; MCF, 160; PSC, 10; and VRC, 4.2. Intraday precisions ranged from 6.3% to 8.8% for azoles and 8.8% to 15.4% for echinocandins. Intraday and interday accuracies (percent bias) of all analytes were within 13.8%. The method was established as standard practice for the quantitation of intracellular antifungal concentrations and optimizes TDM by applying a rapid single method for 6 antifungals.

Escherichia coli and TNF-alpha modulate macrophage phagocytosis of Candida glabrata

BACKGROUND

The incidence of systemic nonalbicans Candida (especially C. glabrata) infections is increasing dramatically in intensive care units, but relatively little is known about the pathogenesis or host defenses associated with these life threatening infections.

MATERIALS AND METHODS

The course of systemic C. glabrata infection was assessed as the fungal burden in the kidneys and livers of mice sacrificed 1, 8, and 15 d after intravenous C. glabrata. Sixteen hours before each sacrifice, half of the mice were injected intraperitoneally with intact viable or nonviable E. coli cells, or with E. coli lipopolysaccharide (LPS), or with tumor necrosis factor (TNF)-alpha. To clarify the effect of LPS and TNF-alpha on phagocytosis, resident (unstimulated) mouse peritoneal macrophages were harvested, cultivated ex vivo, and some cultures were treated with LPS or TNF-alpha prior to 30 min incubation with C. glabrata.

RESULTS

Compared with mice injected with vehicle, each agent (intact E. coli cells or E. coli LPS or TNF-alpha) was consistently associated with decreased numbers of tissue C. glabrata, and some of these decreases were significant (P < 0.05). Compared with untreated macrophages, phagocytosis of C. glabrata was increased with LPS-treated macrophages (P < 0.01), and phagocytosis was also increased in the presence of TNF-alpha (P < 0.01).

CONCLUSION

E. coli LPS and TNF-alpha may participate in host defense against C. glabrata by a mechanism involving increased macrophage phagocytosis, suggesting that stimulation of inflammatory cytokines may facilitate host clearance of C. glabrata.

Immunomodulatory effects of voriconazole on monocytes challenged with Aspergillus fumigatus: differential role of Toll-like receptors

Voriconazole (VRC) has activity against Aspergillus fumigatus, the most frequent cause of invasive aspergillosis in immunocompromised patients. The combination of VRC and A. fumigatus hyphae induced a more pronounced profile of expression of genes encoding inflammatory molecules in human monocytes than Aspergillus alone did. Herein, we provide further evidence of the potential mechanism underlying this immunomodulatory effect of VRC on human monocytes in response to A. fumigatus hyphae. A significant additive antifungal effect was shown when VRC was combined with monocytes against A. fumigatus hyphae. Both A. fumigatus hyphae and VRC induced pronounced profiles of mRNA and protein expression of Toll-like receptor 2 (TLR2) as well as tumor necrosis factor alpha (TNF-alpha) in THP-1 monocytic cells compared to untreated cells. The VRC-induced increase was greater than that induced by hyphae. The combination of VRC and hyphae increased mRNA and protein expression of TLR2 and TNF-alpha to even higher levels than did either VRC or hyphae alone. In contrast, TLR4 expression, both at the mRNA and protein levels, was not increased by either VRC or hyphae or their combination. In addition, significantly more NF-kappaB was translocated to the nuclei of THP-1 cells treated with VRC than untreated cells. While VRC induced more NF-kappaB than hyphae did, treatment with the combination of the two factors induced the greatest NF-kappaB expression. The pronounced profile of TLR2 signaling, TNF-alpha expression, and NF-kappaB activation in the presence of VRC suggests an immunomodulatory effect leading to a more efficient response to A. fumigatus.

Expression of immunomodulatory genes in human monocytes induced by voriconazole in the presence of Aspergillus fumigatus

We assessed the effect of voriconazole (VRC) on the expression and release of selected cytokines and chemokines in the THP-1 human monocytic cell line in response to Aspergillus fumigatus hyphal fragments (HF) by cDNA microarray analysis, reverse transcriptase (RT) PCR, and enzyme-linked immunosorbent assay. Stimulation of THP-1 cells by HF alone caused a significant up-regulation of CCL4 (MIP1B) and CCL16, while CCL2 (MCP1) was down-regulated. By comparison, in the presence of VRC, a large number of genes such as CCL3 (MIP1A), CCL4 (MIP1B), CCL5 (RANTES), CCL7 (MCP3), CCL11 (EOTAXIN), CCL15 (MIP1Delta), CXCL6, and CXCL13 were strongly up-regulated in THP-1 cells challenged by HF, whereas CCL20 (MIP3A) and CCL21 (MIP2) were down-regulated. Among five genes differentially expressed in THP-1 cells, IL12A, IL12B, and IL-16 were down-regulated whereas IL-11 and TGFB1 were significantly up-regulated in the presence of VRC. The inflammation-related genes IFNgamma, IL1R1, and TNFA were also up-regulated in THP-1 cells exposed to HF only in the presence of VRC. RT-PCR of four selected genes validated the results of microarrays. The release of interleukin 1beta (IL-1beta) and IL-12 was significantly increased from monocytes stimulated either by HF alone (P < 0.05) or in the presence of VRC (P < 0.01 and P < 0.05, respectively). In contrast, tumor necrosis factor alpha release from monocytes was enhanced only in the presence of VRC (P < 0.01). The chemokines monocyte chemoattractant protein 1 and macrophage inflammatory protein 1beta were decreased under both conditions (P < 0.01). These results demonstrate that in the presence of VRC, HF induces a more pronounced profile of gene expression in THP-1 cells than HF alone, potentially leading to more-efficient host resistance to A. fumigatus.