Characterising the post-antifungal effects of micafungin against Candida albicans, Candida glabrata, Candida parapsilosis and Candida krusei isolates

Postantifungal Effect of Antifungal Drugs against Candida: What Do We Know and How Can We Apply This Knowledge in the Clinical Setting?

The study of the pharmacological properties of an antifungal agent integrates the drug pharmacokinetics, the fungal growth inhibition, the fungicidal effect and the postantifungal activity, laying the basis to guide optimal dosing regimen selection. The current manuscript reviews concepts regarding the postantifungal effect (PAFE) of the main classes of drugs used to treat Candida infections or candidiasis. The existence of PAFE and its magnitude are highly dependent on both the fungal species and the class of the antifungal agent. Therefore, the aim of this article was to compile the information described in the literature concerning the PAFE of polyenes, azoles and echinocandins against the Candida species of medical interest. In addition, the mechanisms involved in these phenomena, methods of study, and finally, the clinical applicability of these studies relating to the design of dosing regimens were reviewed and discussed. Additionally, different factors that could determine the variability in the PAFE were described. Most PAFE studies were conducted in vitro, and a scarcity of PAFE studies in animal models was observed. It can be stated that the echinocandins cause the most prolonged PAFE, followed by polyenes and azoles. In the case of the triazoles, it is worth noting the inconsistency found between in vitro and in vivo studies.

Evaluation of the Post-Antifungal Effect of Rezafungin and Micafungin against Candida albicans, Candida parapsilosis, and Candida glabrata

BACKGROUND

Rezafungin, a new echinocandin with an extended half-life, exhibits potent activity against Candida spp. Aside from the MIC, specific interactions between antifungal and isolate, including the duration of anti-infective activity, may impact dose interval choices and infection outcome.

OBJECTIVES

We evaluated rezafungin and micafungin post-antifungal effect (PAFE) against C. albicans, C. parapsilosis, and C. glabrata.

METHODS

Six Candida spp. isolates were tested, including 2 of each species, C. albicans, C. parapsilosis, and C. glabrata. Antifungal susceptibility testing was performed using the CLSI reference broth microdilution method. Antifungal concentrations of 1X, 4X, and 16X the baseline MIC were used for PAFE determinations. Colony counts were performed at T0 (pre-exposure), after the 1-h drug exposure, after the cell wash (T1), and at T2, T4, T8, T12, T24, and T48 hours.

RESULTS

Rezafungin PAFE results were equivalent to micafungin PAFE values for one C. albicans (>14.9 h and both C. glabrata (>40 h) isolates for all concentrations tested. The rezafungin and micafungin PAFEs could not be determined against one C. albicans isolate. Prolonged PAFE results were also noted for rezafungin (range, 18.4 h to >40 h) against both C. parapsilosis isolates at all concentrations, while no micafungin PAFE or a short PAFE (range, 1.8 h to 7.4 h) was observed against these organisms, except at 16X bMIC.

CONCLUSIONS

Rezafungin showed sustained growth inhibition following drug removal and displayed equivalent or longer PAFE values than micafungin against all tested Candida spp.

Micafungin-Induced Hypoglycemia in a Patient With Type 1 Diabetes: A Case Report and Review of Literature

OBJECTIVE

Patients with type 1 diabetes mellitus (T1DM) are insulin dependent. Infection increases insulin resistance and subsequently increases insulin needs. We are reporting a case of a patient with T1DM and severe infection who has reduced insulin needs after starting micafungin therapy.

PARTICIPANT

A 29-year-old Hispanic woman with known history of long-standing, uncontrolled T1DM presented for evaluation of worsening dysphagia and dyspnea. She was found to have cervical necrotizing fasciitis extending into the mediastinum and required several debridement surgeries along with broad-spectrum antibiotics and antifungal therapy. She had uncontrolled diabetes with a glycosylated hemoglobin of 13.4% (18.8 mM) on admission. Her insulin requirements progressively increased as a result of worsening infection, continuous tube feeds, and multiple debridement surgeries. She was started on micafungin, a potent 1,3-β-D glucan synthase inhibitor, to broaden antimicrobial coverage when her insulin requirement decreased to zero for >48 hours. Right after discontinuation of micafungin and her switch to a different antifungal, insulin requirements increased back to her baseline needs.

RESULTS

This is a report of decreased insulin requirements in a patient with T1DM correlating with micafungin administration. The mechanism of micafungin-induced hypoglycemia is not yet established. Oral administration of linear 1,3-β-D glucan has been documented to decrease blood glucose levels significantly by inhibition of expression of sodium-glucose transporter 1 (SGLT1) in intestinal mucosa.

CONCLUSION

We hypothesize that micafungin may inhibit SGLT-1 function and decrease insulin requirements in patient with T1DM.

Micafungin Enhances the Human Macrophage Response to Candida albicans through β-Glucan Exposure

Micafungin belongs to the antifungal family of echinocandins, which act as noncompetitive inhibitors of the fungal cell wall β-1,3-d-glucan synthase. Since Candida albicans is the most prevalent pathogenic fungus in humans, we study the involvement of micafungin in the modulation of the inflammatory response developed by human tissue macrophages against C. albicans The MIC for micafungin was 0.016 μg/ml on the C. albicans SC5314 standard strain. Micafungin induced a drastic reduction in the number of exponential SC5314 viable cells, with the fungicidal effect being dependent on the cellular metabolic activity. Notably, micafungin also caused a structural remodelling of the cell wall, leading to exposure of the β-glucan and chitin content on the external surface. At the higher doses used (0.05 μg/ml), the antifungal also induced the blowing up of budding yeasts. In addition, preincubation with micafungin before exposure to human tissue macrophages enhanced the secretion of tumor necrosis factor alpha (TNF-α), interleukin-17A (IL-17A), and IL-10 cytokines. Our results strongly suggest that in C. albicans treatment with micafungin, in addition to having the expected toxic antifungal effect, it potentiates the immune response, improving the interaction and activation of human macrophages, probably through the unmasking of β-glucans on the cell wall surface.

Fungicidal efficacy of various honeys against fluconazole-resistant Candida species isolated from HIV+ patients with candidiasis

OBJECTIVE

Honey is well known to possess a broad spectrum of activity against medically important organisms. The purpose of this study was to assess the antifungal activity of different honeys against 40 fluconazole (FLU) resistant Candida species, including Candida albicans (C. albicans), Candida glabrata, Candida krusei and Candida tropicalis.

MATERIALS AND METHODS

Three honey samples were collected from northern (Mazandaran, A), southern (Hormozgan, B) and central (Lorestan, C) regions of Iran. A microdilution technique based on the CLSI, M27-A2 protocol was employed to compare the susceptibility of honeys "A", "B" and "C" against different pathogenic Candida isolates.

RESULTS

The results showed that different Candida isolates were resistant to FLU, ranging from 64μg/mL to 512μg/mL. All of the honeys tested had antifungal activities against FLU-resistant Candida species, ranging from 20% to 56.25% (v/v) and 25% to 56.25% (v/v) for minimum inhibitory concentrations (MICs) and minimum fungicidal concentrations (MFCs), respectively. Honey "A" (MIC: 31.59%, v/v) showed higher anti-Candida activity than honey "B" (MIC: 35.99%, v/v) and honey "C" (MIC: 39.2%, v/v). No statistically significant differences were observed among the mean MIC values of the honey samples (P>0.05). The order of overall susceptibility of Candida species to honey samples were; C. krusei>C. glabrata>C. tropicalis>C. albicans (P>0.05). In addition, the mean MICs of Candida strains isolated from the nail, vagina and oral cavity were 33.68%, 36.44% and 39.89%, respectively, and were not significantly different (P>0.05).

CONCLUSION

Overall, varying susceptibilities to the anti-Candida properties of different honeys were observed with four FLU-resistant species of Candida. Further research is needed to assess the efficacy of honey as an inhibitor of candidal growth in clinical trials.

Highly Dynamic and Specific Phosphatidylinositol 4,5-Bisphosphate, Septin, and Cell Wall Integrity Pathway Responses Correlate with Caspofungin Activity against Candida albicans

Phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2] activates the yeast cell wall integrity pathway. Candida albicans exposure to caspofungin results in the rapid redistribution of PI(4,5)P2 and septins to plasma membrane foci and subsequent fungicidal effects. We studied C. albicans PI(4,5)P2 and septin dynamics and protein kinase C (PKC)-Mkc1 cell wall integrity pathway activation following exposure to caspofungin and other drugs. PI(4,5)P2 and septins were visualized by live imaging of C. albicans cells coexpressing green fluorescent protein (GFP)-pleckstrin homology (PH) domain and red fluorescent protein-Cdc10p, respectively. PI(4,5)P2 was also visualized in GFP-PH domain-expressing C. albicans mkc1 mutants. Mkc1p phosphorylation was measured as a marker of PKC-Mkc1 pathway activation. Fungicidal activity was assessed using 20-h time-kill assays. Caspofungin immediately induced PI(4,5)P2 and Cdc10p colocalization to aberrant foci, a process that was highly dynamic over 3 h. PI(4,5)P2 levels increased in a dose-response manner at caspofungin concentrations of ≤4× MIC and progressively decreased at concentrations of ≥8× MIC. Caspofungin exposure resulted in broad-based mother-daughter bud necks and arrested septum-like structures, in which PI(4,5)P2 and Cdc10 colocalized. PKC-Mkc1 pathway activation was maximal within 10 min, peaked in response to caspofungin at 4× MIC, and declined at higher concentrations. The caspofungin-induced PI(4,5)P2 redistribution remained apparent in mkc1 mutants. Caspofungin exerted dose-dependent killing and paradoxical effects at ≤4× and ≥8× MIC, respectively. Fluconazole, amphotericin B, calcofluor white, and H2O2 did not impact the PI(4,5)P2 or Cdc10p distribution like caspofungin did. Caspofungin exerts rapid PI(4,5)P2-septin and PKC-Mkc1 responses that correlate with the extent of C. albicans killing, and the responses are not induced by other antifungal agents. PI(4,5)P2-septin regulation is crucial in early caspofungin responses and PKC-Mkc1 activation.

Postantifungal Effect of Micafungin against the Species Complexes of Candida albicans and Candida parapsilosis

Micafungin is an effective antifungal agent useful for the therapy of invasive candidiasis. Candida albicans is the most common cause of invasive candidiasis; however, infections due to non-C. albicans species, such as Candida parapsilosis, are rising. Killing and postantifungal effects (PAFE) are important factors in both dose interval choice and infection outcome. The aim of this study was to determinate the micafungin PAFE against 7 C. albicans strains, 5 Candida dubliniensis, 2 Candida Africana, 3 C. parapsilosis, 2 Candida metapsilosis and 2 Candida orthopsilosis. For PAFE studies, cells were exposed to micafungin for 1 h at concentrations ranging from 0.12 to 8 μg/ml. Time-kill experiments (TK) were conducted at the same concentrations. Samples were removed at each time point (0-48 h) and viable counts determined. Micafungin (2 μg/ml) was fungicidal (≥ 3 log₁₀ reduction) in TK against 5 out of 14 (36%) strains of C. albicans complex. In PAFE experiments, fungicidal endpoint was achieved against 2 out of 14 strains (14%). In TK against C. parapsilosis, 8 μg/ml of micafungin turned out to be fungicidal against 4 out 7 (57%) strains. Conversely, fungicidal endpoint was not achieved in PAFE studies. PAFE results for C. albicans complex (41.83 ± 2.18 h) differed from C. parapsilosis complex (8.07 ± 4.2 h) at the highest tested concentration of micafungin. In conclusion, micafungin showed significant differences in PAFE against C. albicans and C. parapsilosis complexes, being PAFE for the C. albicans complex longer than for the C. parapsilosis complex.

In vitro fungicidal activities of anidulafungin, caspofungin, and micafungin against Candida glabrata, Candida bracarensis, and Candida nivariensis evaluated by time-kill studies

Anidulafungin, caspofungin, and micafungin killing activities against Candida glabrata, Candida bracarensis, and Candida nivariensis were evaluated by the time-kill methodology. The concentrations assayed were 0.06, 0.125, and 0.5 μg/ml, which are achieved in serum. Anidulafungin and micafungin required between 13 and 26 h to reach the fungicidal endpoint (99.9% killing) against C. glabrata and C. bracarensis. All echinocandins were less active against C. nivariensis.

Efficacy of micafungin in pediatric immunocompromised patients with invasive fungal infection

BACKGROUND

Micafungin, an antifungal echinocandin, has been indicated for pediatric patients with invasive fungal infection (IFI) in Japan and Europe. Its efficacy in immunocompromised pediatric patients with IFI, however, has not been fully investigated.

METHODS

The safety and efficacy of micafungin as an antifungal therapy were analyzed in nine consecutive severe immunocompromised patients with IFI.

RESULTS

Three patients with proven or probable Candida infections had complete response to micafungin therapy. Of the other six patients with proven, probable or possible Aspergillus infection, four had complete response and one had partial response to micafungin treatment. No severe adverse events were observed.

CONCLUSIONS

In this small series, micafungin was effective for IFI caused by both Candida and Aspergillus species and no severe adverse events were observed in these immunocompromised patients.

Echinocandins: are they all the same?

The discovery of echinocandins, and their development and approval, was hailed as a significant addition to our antifungal armamentarium, previously predominated by polyenes and azoles. To date, three echinocandins (anidulafungin, caspofungin, and micafungin) have been approved by the U.S. Food and Drug Administration for the treatment of fungal infections. Since all three echinocandins target the fungal cell wall and share a similar structural chemical backbone, they are perceived to be identical. However, a scientific literature review shows distinct differences among the echinocandins in terms of in vitro activity, fungicidal activity, post-antifungal effect, paradoxical effect, and activity on biofilms. More investigation is warranted to determine if the observed differences among the echinocandins can translate to clinical advantages.

Rapid redistribution of phosphatidylinositol-(4,5)-bisphosphate and septins during the Candida albicans response to caspofungin

We previously showed that phosphatidylinositol-(4,5)-bisphosphate [PI(4,5)P2] and septin regulation play major roles in maintaining Candida albicans cell wall integrity in response to caspofungin and other stressors. Here, we establish a link between PI(4,5)P2 signaling and septin localization and demonstrate that rapid redistribution of PI(4,5)P2 and septins is part of the natural response of C. albicans to caspofungin. First, we studied caspofungin-hypersusceptible C. albicans irs4 and inp51 mutants, which have elevated PI(4,5)P2 levels due to loss of PI(4,5)P2-specific 5'-phosphatase activity. PI(4,5)P2 accumulated in discrete patches, rather than uniformly, along surfaces of mutants in yeast and filamentous morphologies, as visualized with a green fluorescent protein (GFP)-pleckstrin homology domain. The patches also contained chitin (calcofluor white staining) and cell wall protein Rbt5 (Rbt5-GFP). By transmission electron microscopy, patches corresponded to plasma membrane invaginations that incorporated cell wall material. Fluorescently tagged septins Cdc10 and Sep7 colocalized to these sites, consistent with well-described PI(4,5)P2-septin physical interactions. Based on expression patterns of cell wall damage response genes, irs4 and inp51 mutants were firmly positioned within a group of caspofungin-hypersusceptible, septin-regulatory protein kinase mutants. irs4 and inp51 were linked most closely to the gin4 mutant by expression profiling, PI(4,5)P2-septin-chitin redistribution and other phenotypes. Finally, sublethal 5-min exposure of wild-type C. albicans to caspofungin resulted in redistribution of PI(4,5)P2 and septins in a manner similar to those of irs4, inp51, and gin4 mutants. Taken together, our data suggest that the C. albicans Irs4-Inp51 5'-phosphatase complex and Gin4 function upstream of PI(4,5)P2 and septins in a pathway that helps govern responses to caspofungin.

Miconazole induces fungistasis and increases killing of Candida albicans subjected to photodynamic therapy

Cutaneous and mucocutaneous Candida infections are considered to be important targets for antimicrobial photodynamic therapy (PDT). Clinical application of antimicrobial PDT will require strategies that enhance microbial killing while minimizing damage to host tissue. Increasing the sensitivity of infectious agents to PDT will help achieve this goal. Our previous studies demonstrated that raising the level of oxidative stress in Candida by interfering with fungal respiration increased the efficiency of PDT. Therefore, we sought to identify compounds in clinical use that would augment the oxidative stress caused by PDT by contributing to reactive oxygen species (ROS) formation themselves. Based on the ability of the antifungal miconazole to induce ROS in Candida, we tested several azole antifungals for their ability to augment PDT in vitro. Although miconazole and ketoconazole both stimulated ROS production in Candida albicans, only miconazole enhanced the killing of C. albicans and induced prolonged fungistasis in organisms that survived PDT using the porphyrin TMP-1363 and the phenothiazine methylene blue as photosensitizers. The data suggest that miconazole could be used to increase the efficacy of PDT against C. albicans, and its mechanism of action is likely to be multifactorial.

Five-minute exposure to caspofungin results in prolonged postantifungal effects and eliminates the paradoxical growth of Candida albicans

We studied the impact of brief caspofungin exposures on postantifungal effects (PAFEs) and paradoxical effects for five Candida albicans isolates. In time-kill studies, caspofungin at 4× and 16× the MIC resulted in significant killing of all isolates. Caspofungin at 8 μg/ml resulted in lower levels of killing, and paradoxical effects were evident with 4 isolates. Caspofungin exposures of 5 to 60 min caused prolonged, concentration-dependent killing that approached or exceeded the results seen with time-kill experiments and eliminated paradoxical growth.

Antifungal effect of lavender honey against Candida albicans , Candida krusei and Cryptococcus neoformans

Monofloral lavender honey samples (n = 30), were analyzed to test antifungal effect against Candida albicans, Candida krusei, and Cryptococcus neoformans. The specific growth rates (μ) showed that all the yeast growths were reduced in the presence of honey. The honey concentration (% w/v) that inhibited 10% of the yeasts growth (X min) ranged from 31.0% (C. albicans), 16.8% (C. krusei) and 23.0% (C. neoformans). A synthetic honey solution was also tested to determine antifungal activity attributable to sugars. The presence of synthetic honey in the C. krusei culture medium at concentrations above 58.0% (w/v) was established as X min, while C. albicans and C. neoformans were more resistant, since X min values were not reached over the ranged tested (10-60%, w/v). What the data suggests is that the component in the lavender honey responsible for the observed antifungal in vitro properties is not sugar based. Honey might be tapped as a natural resource to look for new medicines for the treatment of mycotic infections. This could be very useful, onsidering the increasing resistance of antifungals. It should be noticed that this is the first study concerning the effect of lavender honey on the growth of pathogenic yeasts.