Murine Model Of Systemic Candidiasis Research Articles

Low virulent strains of Candida albicans: unravelling the antigens for a future vaccine.

Several low virulent Candida albicans mutant strains: CM1613 (deleted in the Mitogen Activated Protein (MAP) Kinase MKC1), CNC13 (deleted in the MAP-kinase HOG1) and the morphological mutant 92' were used as vaccines employing a murine model of systemic candidiasis. In this vaccination trial, only the CNC13 strain was able to induce protection against a subsequent infection with a lethal dose of the wild-type strain. The protection induced by CNC13 vaccinated animals resulted in 60-70% percent of survival. These results demonstrate that collaboration between cellular and humoral responses, induced by the CNC13 mutant, elicited a long lasting and effective protection. Using a proteomic approach (two-dimensional gel electrophoresis followed by Western blotting), twenty-five C. albicans immunogenic proteins were detected and identified by matrix-assisted laser desorption/ionization and/or tandem mass spectrometry. We were able to define an antibody pattern in the sera from the nonvaccinating strains (92' and CM1613), which was different from the profile detected in the sera from surviving animals (vaccinated with the CNC13 mutant). The utility of this proteomic approach has allowed us to identify antigens that induce protective IgG2a antibody isotype in the sera from vaccinated animals: enolase (Eno1p), pyruvate kinase (Cdc19p), pyruvate decarboxylase (Pdc11p), a component from the 40S ribosomal subunit (Bel1p), triosephosphate isomerase (Tpi1p), DL-glycerol phosphatase (Rhr2p), fructose-bisphosphate aldolase (Fba1p) and two new protective antigens: IMP dehydrogenase (Imh3p), and acetyl-CoA synthetase (Acs2p). The antigenic proteins that promote protective antibodies described in this work are excellent candidates for a future fungal vaccine; their heterologous expression and vaccine design is currently underway.

Requirement of interleukin-17A for systemic anti-Candida albicans host defense in mice.

T cells are required for normal host defense against fungal infection, and individuals with T cell-deficiency syndromes are highly susceptible to fungal pathogens. Interleukin (IL)-17A is a proinflammatory cytokine that interconnects myeloid and lymphoid host defense. The role of murine (m) IL-17A/mIL-17A receptor (R) interactions was evaluated in a murine model of systemic candidiasis. In response to systemic challenge with Candida albicans, expression of mIL-17A was induced, and IL-17AR knockout (IL-17AR(-/-)) mice had dose-dependent, substantially reduced survival. Fungal burden in the kidneys of IL-17AR(-/-) mice was dramatically increased (25-fold at 96 h). In IL-17AR(-/-) mice, both mobilization of peripheral neutrophils and their influx to infected organs were significantly impaired and delayed. In vivo expression of mIL-17A protected normal mice from a lethal dose of C. albicans (100% at day 7 and 65% at day 42). The data suggest that the mIL-17A/mIL-17AR system is required for normal fungal host defense in vivo. IL-17A could have potential as a therapeutic cytokine for systemic C. albicans infections in immunocompromised patients with cancer or advanced acquired immunodeficiency syndrome.

Contribution of the antibodies response induced by a low virulent Candida albicans strain in protection against systemic candidiasis.

A low virulent Candida albicans mutant, CNC13, deleted in the Mitogen Activated Protein (MAP) kynase HOG1 was used to immunize BALB/c mice. Hog1p is essential for the oxidative stress and hyperosmolarity responses. Several doses and immunization procedures were employed. The protection capacity of the different sera generated was analyzed in a murine model of systemic candidiasis. Using a proteomic approach (two-dimensional gel electrophoresis followed by Western blotting), we were able to distinguish two categories of serum: protective and nonprotective, which showed different titres of total Immunoglobulins (Igs) and IgG2a (analyzed by enzyme-linked immunosorbent assay). The levels of Igs and IgG2a in protective sera were significantly higher compared to nonprotective sera. The pattern of a "nonprotective" profile was composed of enolase (Eno1p), transketolase, heat shock protein and methionine synthase. Only antibodies against enolase are the IgG2a isotype. The pattern of a "protective" sera, on the other hand, was composed of antibodies against the following antigens: several isoforms of Eno1p, pyruvate decarboxylase, pyruvate kynase, a protein of the 40S ribosomal subunit, triosephosphate isomerase, DL-glycerol phosphatase and fructose-bisphosphate aldolase. All these antibodies are the IgG2a isotype. The proteins described in the protective sera might be useful for future vaccine development.

Design and synthesis of novel benzofurans as a new class of antifungal agents targeting fungal N-myristoyltransferase. Part 3

A new series of acid-stable antifungal agents having strong inhibitory activity against Candida albicans N-myristoyltransferase (CaNmt) has been developed starting from acid-unstable benzofuranylmethyl aryl ether 2. The inhibitor design is based on X-ray crystallographic analysis of a CaNmt complex with aryl ether 3. Among the new inhibitors, pyridine derivative 8b and benzimidazole derivative 8k showed clear antifungal activity in a murine systemic candidiasis model.

Design and synthesis of novel benzofurans as a new class of antifungal agents targeting fungal N-myristoyltransferase. Part 2

Modification of the C-2 position of a benzofuran derivative 6 (RO-09-4609), an N-myristoyltransferase (Nmt) inhibitor, has led us to discover antifungal agents that are active in a murine systemic candidiasis model. The drug design is based on the analysis of a crystal structure of a Candida Nmt complex with 2. The optimization has been guided by various biological evaluations including a quasi in vivo assay and pharmacokinetic analysis.

Attenuation of Virulence and Changes in Morphology in Candida albicans by Disruption of the N -Acetylglucosamine Catabolic Pathway

A Candida albicans mutant with mutations in the N-acetylglucosamine (GlcNAc) catabolic pathway gene cluster, including the GlcNAc-6-phosphate deacetylase (DAC1), glucosamine-6-phosphate deaminase (NAG1), and GlcNAc kinase (HXK1) genes, was not able to grow on amino sugars, exhibited highly attenuated virulence in a murine systemic candidiasis model, and was less adherent to human buccal epithelial cells in vitro. No germ tubes were formed by the mutant after induction with GlcNAc, but the mutant exhibited hyperfilamentation under stress-induced filamentation conditions. In addition, the GlcNAc catabolic pathway played a vital role in determining the colony phenotype. Our results imply that this pathway is very important because of its diverse links with pathways involved in virulence and morphogenesis of the organism.

Antifungal activities of origanum oil against Candida albicans.

The antimicrobial properties of volatile aromatic oils from medicinal as well as other edible plants has been recognized since antiquity. Origanum oil, which is used as a food flavoring agent, possesses a broad spectrum of in vitro antimicrobial activities attributed to the high content of phenolic derivatives such as carvacrol and thymol. In the present study, antifungal properties of origanum oil were examined both in vitro and in vivo. Using Candida albicans in broth cultures and a micro dilution method, comparative efficacy of origanum oil, carvacrol, nystatin and amphotericin B were examined in vitro. Origanum oil at 0.25 mg/ml was found to completely inhibit the growth of C. albicans in culture. Growth inhibitions of 75% and >50% were observed at 0.125 mg/ml and 0.0625 mg/ml level, respectively. In addition, both the germination and the mycelial growth of C. albicans were found to be inhibited by origanum oil and carvacrol in a dose-dependent manner. Furthermore, the therapeutic efficacy of origanum oil was examined in an experimental murine systemic candidiasis model. Groups of mice (n = 6) infected with C. albicans (5 x LD50) were fed varying amounts of origanum oil in a final vol. of 0.1 ml of olive oil (vehicle). The daily administration of 8.6 mg of origanum oil in 100 microl of olive oil/kg body weight for 30 days resulted in 80% survivability, with no renal burden of C. albicans as opposed to the group of mice fed olive oil alone, who died within 10 days. Similar results were obtained with carvacrol. However, mice fed origanum oil exhibited cosmetically better clinical appearance compared to those cured with carvacrol. The results from our study encourage examination of the efficacy of origanum oil in other forms of systemic and superficial fungal infections and exploration of its broad spectrum effect against other pathogenic manifestations including malignancy.

Interaction between fluconazole and amphotericin B in mice with systemic infection due to fluconazole-susceptible or -resistant strains of Candida albicans.

The interaction between fluconazole (Flu) and amphotericin B (AmB) was evaluated in a murine model of systemic candidiasis for one Flu-susceptible strain (MIC, 0.5 microg/ml), two strains with intermediate Flu resistance (Flu mid-resistant strains) (MIC, 64 and 128 microg/ml), and one highly Flu-resistant strain (MIC, 512 microg/ml) of Candida albicans. Differences in fungal densities in kidneys of infected mice after 24 h of therapy and in survival rates at 62 days of mice treated with an antifungal drug or a combination of antifungal drugs for 4 days were compared. For the Flu-susceptible and Flu mid-resistant strains, the combination of Flu and AmB was antagonistic, as shown by both quantitative culture results and survival. The interaction was additive for the highly Flu-resistant strain. These results suggest that the combination of Flu and AmB should be used with caution in infections due to fungi that are usually susceptible to both antifungal agents and as empirical antifungal drug therapy.

Fluconazole versus Candida albicans: a complex relationship.

A murine model of systemic candidiasis was used to assess the virulence of serial Candida albicans strains for which fluconazole MICs were increasing. Serial isolates from five patients with 17 episodes of oropharyngeal candidiasis were evaluated. The MICs for these isolates exhibited at least an eightfold progressive increase from susceptible (MIC < 8 microg/ml; range, 0.25 to 4 microg/ml) to resistant (MIC >/= 16 microg/ml; range, 16 to >/=128 microg/ml). Virulence of the serial isolates from three of five patients showed a more than fivefold progressive decrease in the dose accounting for 50% mortality and was associated with development of fluconazole resistance. Low doses of fluconazole prolonged survival of mice infected with susceptible yeasts but failed to prolong survival following challenge with a resistant strain. In addition, a decreased burden of renal infection was noted in mice challenged with two of the three resistant strains. This was consistent with reduced virulence. Fluconazole did not further decrease the level of infection. In the isolates with a decrease in virulence, two exhibited overexpression of CDR, which encodes an ABC drug efflux pump. In contrast, serial isolates from the remaining two patients with the development of resistance did not demonstrate a change in virulence and fluconazole remained effective in prolonging survival, although significantly higher doses of fluconazole were required for efficacy. Resistant isolates from both of these patients exhibited overexpression of MDR. This study demonstrates that decreased virulence of serial C. albicans isolates is associated with increasing fluconazole MICs in some cases but not in others and shows that these low-virulence strains may not consistently cause infection.

Pharmacodynamics of fluconazole in a murine model of systemic candidiasis.

In this study we defined the pharmacodynamic parameter that optimizes outcome in deep-seated Candida albicans infections treated with fluconazole. Using a murine model of systemic candidiasis, we conducted single-dose dose-ranging studies with fluconazole to determine the dosage of this drug that resulted in a 50% reduction in fungal densities (50% effective dose [ED50]) in kidneys versus the fungal densities in the kidneys of untreated controls. We found that the ED50 of fluconazole given intraperitoneally was 4.56 mg/kg of body weight/day (95% confidence interval, 3.60 to 5.53 mg/kg/day), and the dose-response relationship was best described by an inhibitory sigmoid maximal effect (Emax) curve. To define the pharmacodynamics of fluconazole, we gave dosages lower than, approximating, and higher than the ED50 of fluconazole (range, 3.5 to 5.5 mg/kg/day, equivalent to the ED16 to the ED75) to various groups of infected animals using three dose-fractionation schedules. For each total dose of fluconazole examined, the dose-fractionation schedules optimized the ratio of the area under the concentration-time curve (AUC) to the MIC (the AUC/MIC ratio), the ratio of the maximum concentration of drug in serum (Cmax) to the MIC, and the time that the drug remained above the MIC for the infecting C. albicans isolate. Similar reductions in fungal densities in kidneys were seen between groups that received the same total dose of fluconazole in one, two, or four equally divided doses. Thus, dose-fractionation studies demonstrated that the pharmacodynamic parameter of fluconazole that best predicted outcome was the AUC/MIC ratio.

Characterization of a lipopeptide-resistant strain ofCandida albicans

Lipopeptides are antifungal agents that inhibit cell wall beta-(1,3)-glucan biosynthesis in fungal organisms. A mutant resistant to lipopeptides was generated by UV mutagenesis and characterized. The Candida albicans mutant (LP3-1) was stable and showed resistance specificity to a broad range of lipopeptides and certain glycolipid inhibitors. Other antifungal agents with diverse modes of action had a normal minimum inhibitory concentration profile for LP3-1 compared with the wild-type strain (CCH 442). In the in vitro beta-(1,3)-glucan synthase assay, both the lipopeptides and papulacandin-related agents had considerably higher 50% inhibitory concentration values in the LP3-1 strain than in the wild-type strain. In reconstitution assays, the resistance factor was associated with the integral membrane pellet rather than the peripheral GTP-binding protein. The LP3-1 strain had a membrane lipid profile similar to that of the parent strain and was virulent in a murine model of systemic candidiasis. Taken together, these results indicate that the resistance factor is associated with the integral membrane component of beta-(1,3)-glucan synthase. Lipopeptides are common antifungal agents encountered during screening of natural products. The LP3-1 strain was resistant to natural product extracts known to contain various lipopeptides. Thus, LP3-1 can be used in a dereplication assay.

Avirulence of Candida albicans FAS2 mutants in a mouse model of systemic candidiasis.

Disruption of both alleles of the Candida albicans FAS2 gene abolishes the ability of the organism to establish infection in a murine model of systemic candidiasis. Within 72 h all mice inoculated with 10(6) CFU of the parental C. albicans strain had died. In contrast, all animals inoculated with the mutant strain CFD2 survived for the course of the experiment (21 days). Animals infected with either mutant strain CFD1 or CFD3, in which only one FAS2 allele was disrupted, also succumbed to infection, but mortality was not observed until 4 days postinfection and survivors remained for up to 20 days postinfection. The results demonstrate that FAS2 is required for successful C. albicans infection.

IL-12 is both required and prognostic in vivo for T helper type 1 differentiation in murine candidiasis.

In murine models of systemic candidiasis, healing and nonhealing patterns of disease are associated with preferential expansion of Th1 and Th2 cells, respectively. As previous studies have shown IL-12 to be expressed transcriptionally in healer mice and to be required for Th1 development in vitro, this cytokine might play a role in Candida-driven Th1 cell differentiation in vivo. In the present study, IL-12-neutralizing Abs or recombinant IL-12 were administered to mice with healing or progressive candidiasis, respectively, and the animals were monitored for mortality, resistance to reinfection, serum levels of specific Abs, and IFN-gamma, IL-4, and IL-10 message/protein expression by CD4+ cells. In self-limiting infection by a yeast vaccine strain, neutralization of IL-12 ablated development of acquired anticandidal resistance and led to appearance of Candida-specific IgE and IL-4-producing cells. In mice with progressive systemic disease as well as in a mucosal infection model, administration of IL-12 did not result in therapeutic activity under conditions of yeast infection that would instead be resolved by serologic ablation of IL-4 or IL-10. Yet, in systemically infected mice cured by anti-IL-4 or anti-IL-10 therapy, the emergence of a Th1 response correlated with the detection of high levels of circulating IL-12 and splenic IL-12 transcripts. Although exogenous IL-12 may not be sufficient for Th conversion in the presence of an overwhelming IL-4/IL-10 response, endogenous production of IL-12 may be both required and prognostic for Th1 differentiation in vivo.

In vitro and in vivo antifungal activity of liposomal and free itraconazole against Candida albicans

Killing curves for both free and liposomal itraconazole were measured against Candida albicans. The in vivo efficacy of both itraconazole formulations was assessed in a murine model of systemic candidiasis. There was no fungicidal effect in vitro, and the in vitro time-kill curves were not predictive of the in vivo efficacy of both formulations of itraconazole. In vivo, treated mice survived longer than the control mice, but there were no significant differences between the two treated groups.

Tumor necrosis factor alpha has a protective role in a murine model of systemic candidiasis.

The role of tumor necrosis factor alpha (TNF-alpha) in host defense against systemic Candida albicans infection was evaluated in a murine model of systemic candidiasis in which uniform death occurred between 5 and 6 days after infection. TNF-alpha was first detected at 16 h postinfection and progressively increased thereafter. Peak levels (700 to 900 pg/ml) were measured in mice near death. Administration of 0.5 to 1.0 mg of polyclonal immunoglobulin G (IgG) TNF-alpha antibody (TNF-alpha Ab) to mice 2 h preinfection neutralized serum TNF-alpha for up to 30 h. However, this regimen shortened survival from a mean of 5.5 days for IgG controls to 3.4 days (P = 1.9 x 10(-12)). Semiquantitative cultures of spleen, lung, liver, and kidney conducted at 1, 2, and 3 days postinfection found colony counts of spleen and kidney to be significantly higher for TNF-alpha Ab recipients but only for the first 48 h. Administration of 1.5 and 1.0 mg of TNF-alpha Ab at 2 h before and 48 h after fungal injection, respectively, shortened the mean survival from 4.9 to 2.3 days (P = 5.2 x 10(-8)). This regimen neutralized serum TNF-alpha throughout infection. With this regimen, colony counts of all organs were significantly higher in TNF-alpha Ab recipients at 1, 2, and 3 days postinfection. Histopathologic studies showed an increase in the number and size of C. albicans foci in tissues. Peripheral leukocyte counts and inflammatory response in tissue were similar for TNF-alpha Ab and IgG sham recipients. In vitro, incubation of C. albicans with four to eight times the peak serum levels of TNF-alpha for up to 24 h did not inhibit the rate of germ tube or pseudohypha formation. Thus, TNF-alpha that was produced during infection with C. albicans augmented host resistance against this organism and prolonged survival. The protective effect of TNF-alpha was not mediated by increased leukocytes in blood or tissues nor by a direct anticandidal effect of TNF-alpha. This study suggests that the administration of exogenous TNF-alpha may enhance host resistance against systemic C. albicans infection and may improve host survival.

Cure of murine candidiasis by recombinant soluble interleukin-4 receptor.

Neutralization of interleukin (IL)-4 by specific antibody exerts therapeutic activity in a murine model of systemic candidiasis characterized by strong T helper type 2 (Th2) responses. To investigate whether recombinant soluble IL-4 receptor (sIL-4R) could be used to block IL-4 action in vivo, mice treated with pharmacologic doses of sIL-4R at the time of infection were examined for progression of disease, development of footpad responses, serum IgE levels, and cytokine production in vitro by CD4+ lymphocytes. Following sIL-4R treatment, persistent ablation of circulating IL-4 detected by ELISA was associated with a cure rate of > 90% in otherwise lethally infected mice, onset of durable protection, and a shift from a predominant Th2 to a Th1 pattern of reactivity. In addition, when administered to genetically susceptible adult mice with gastrointestinal yeast colonization, the sIL-4R stimulated Th1-associated anticandidal resistance.

Antifungal properties in a novel series of triazino[5,6-b]indoles.

GR99060 and GR99062 are representatives of a series of 1,2,4-triazino[5,6-b]indole compounds. This series possessed broad-spectrum antifungal activity in vitro. The MIC ranges of the two compounds were as follows: 0.25 to 4 micrograms/ml for Candida albicans, 0.25 to 16 micrograms/ml for Candida sp., 1 to 8 micrograms/ml for Aspergillus spp., and 0.25 to 16 micrograms/ml for Cryptococcus neoformans. GR99062 was metabolized in vitro by a mouse liver microsomal preparation, while GR99060 was stable. GR99060 was efficacious in a murine model of systemic candidiasis by oral or parenteral administration, although no clear dose-response was achieved, suggesting that other factors adversely affected the compound's in vivo activity.

Antigen detection in the murine models of systemic candidiasis

We compared two latex agglutination tests for serum candidal antigen in murine models of systemic infection and gastrointestinal colonization. In the intravascular-infection model, mannan detection test was positive at 2 hours after inoculation, but Cand-Tec was less sensitive than mannan detection test in this model. In the gastrointestinal colonization model followed by systemic infection in neutropenic mice, the mannan antigen test became positive after 3 weeks of colonization with increased number of Candida of the stool, and Cand-Tec became positive after 5 weeks in neutropenic mice.

Comparison of immunosuppressive effects of cyclosporine A in a murine model of systemic candidiasis and of localized thrushlike lesions.

Candida albicans is an opportunistic human pathogen preferentially causing invasive and disseminated infection in patients with defective phagocytic defenses and serious mucocutaneous infection in patients with deficient T-cell function. Phagocytes appear to protect the host from fungal invasion even in the absence of adaptive immune mechanisms, while as-yet-undefined T-cell-dependent factors seem necessary for control of C. albicans on body surfaces. To study host defense mechanisms on body surfaces, we developed a new model of thrush in artificial pneumatized cysts in mice. Cyclosporine A, a relative selective suppressor of T-cell-mediated immunity and natural killer cell activity, promoted the formation of thrushlike lesions on cyst surfaces and impeded elimination of C. albicans from such lesions. As expected from the absence of an impairment of antimicrobial phagocytic activity, cyclosporine A had no effect on systemic candidiasis induced by intravenous inoculation. Surprisingly, athymic nude mice were not more susceptible to superficial candidiasis than control mice and were comparably affected by cyclosporine A. In contrast, beige mice, which in addition to phagocytic dysfunction have reduced natural killer cell activity, were more susceptible to thrushlike lesions, and cyclosporine A was correspondingly less active in this mouse strain. Immunosuppression with cyclosporine A affects host defense mechanisms which are operative against superficial candidiasis but appear superfluous in resistance to the invasive form of this mycosis, an indication for the divergent nature of host defense against the two forms of candidiasis.

Studies on detection of Candida antigen in the sera of mice inoculated orally with Candida albicans.

The authors succeeded in establishing a murine model of systemic candidiasis being disseminated from the primary gastrointestinal lesions caused by oral inoculation of Candida albicans. Using this model, an attempt was made for detecting the Candida antigen by enzyme-linked immunosorbent assay using avidin-biotin (AB-ELISA) from the serum of infected mice. Gastrointestinal candidiasis was formed in all of the 20 mice treated with the drugs (antibiotics, antineoplastic agents, hydrocortisone, etc.) and inoculated orally with C. albicans. Fourteen of these mice suffered from submucosal candidiasis, and C. albicans was cultured from the visceral organs in 12 of them. The assay by AB-ELISA was able to detect 1.0 ng/ml Candida mannan in the mouse serum. The Candida antigen was detected in the sera of 11 of the 14 mice with submucosal candidiasis. However, the antigen could not be detected in the sera of the 6 mice with intramucosal candidiasis. The assay by AB-ELISA is more sensitive and specific for the diagnosis of systemic candidiasis than other serological assays.