Murine Candidiasis Model Research Articles

In Vitro Release—In Vivo Microbiological and Toxicological Studies on Ketoconazole Lipid Granules

In some multidrug therapy programs, ketoconazole (KTZ) may be administered with some antacids that could modify its dissolution rate and reduce its absorption, thus leading to therapeutic failures. The primary aim of this study was to evaluate the influence of Compritol HD5 ATO and Compritol 888 ATO on this interaction in comparison with commercial KTZ tablets. The second aim was to prepare lipid granules of KTZ that could be an alternative to the commercial formulation. Therefore, six KTZ sustained-release granules were prepared with different lipid concentrations, because they were found to be more suitable than tablets that are dissolved only in gastric medium. The results confirmed that the dissolution rate of KTZ granules was significantly reduced in the presence of antacids. The ideal formulation was selected as granules including 5% of Compritol lipids in relation to the suitability of the target profile. Therapeutic effects of orally administered, ideal KTZ granule formulations, and commercial tablets were evaluated in vivo by the experimental model of murine vulvo-vaginal candidiasis (VVC) with and without antacids. It was found that formulations were very effective on VVC, and the therapeutic effect decreased significantly in the presence of antacids. Histopathological studies were carried out for vagina, stomach, and liver tissues and hepatoxicity was also examined. The levels of reduced glutathione (GSH) were measured to assess the oxidative stress induced by KTZ and function of the liver. It was observed that orally administered formulations of KTZ were successful in treating candidiasis in mice without irritancy in stomach. However, liver tissues were damaged. The decreased GSH levels indicated toxicity in our study. This study suggested that in vitro release and in vivo microbiological-toxicological properties of KTZ were affected by antacids and drug-excipient interactions. Lipid granules of KTZ prepared with Compritol 888 ATO could be proposed as a new KTZ solid dosage form with optimum dissolution and therapeutic characteristics.

Local IL-23 expression in murine vaginal candidiasis and its relationship with infection and immune status

To investigate the expression of vaginal IL-23 and its role in experimental murine vaginal candidiasis and its relationship with infection and immune status, immuno-competent (group A) and immuno-suppressed (group B) murine models of vaginal candidiasis were established in estrogen-treated mice. Non-estrogen-treated mice were used as controls (group C). The level of IL-23 p19 mRNA in murine vaginal tissue was determined by RT-PCR. Significantly increased levels of IL-23p19mRNA were observed on the 4th, the 7th and 14th day after inoculation in immuno-competent group when compared with that in control group (P<0.01, P<0.05). However, significant increase of IL-23 p19mRNA were only observed on the 7th day and the 14th day after inoculatuon in immuno-suppressed groups (P<0.05). On the 4th and 7th day, the levels of IL-23 p19mRNA were significantly increased in immuno-competent group than those in immuno-suppressed group (P <0.05). Local IL-23 may play a role in the pathogenesis of murine vaginal candidiasis and has a protective function during infection. Low vaginal IL-23 level may correlate with the increased susceptibility to Candida albicans in immuno-suppressed group.

Surface Response Modeling to Examine the Combination of Amphotericin B Deoxycholate and 5‐Fluorocytosine for Treatment of Invasive Candidiasis

The strategy of combining antifungal drugs in a treatment regimen may improve the outcome of invasive candidiasis. Using a well-validated pharmacodynamic murine model of invasive candidiasis, we defined the effect of the combination of amphotericin B deoxycholate (AmB) and 5-fluorocytosine (5FC) by use of the Greco model of drug interaction. The combination was additive, meaning that the experimental effect did not deviate in a statistically significant manner from the null reference model (or additive surface) of the combined effect. From a clinical perspective, the addition of 5FC to a regimen of AmB may enable the near-maximum effect to be reached in circumstances in which the administration of a given dose of AmB alone produces a submaximum effect but an increase in the dose is not possible, because of dose-related toxicity. Our methods provide a way in which some of the complex issues surrounding antifungal combination treatment can be addressed.

白苔をともなう新規マウス食道カンジダ症モデルの作製と経口イトラコナゾールシクロデキストリン包接可溶化製剤 (ITZ-OS) の有効性の検討

白苔をともなう新規マウス食道カンジダ症モデルの作製と経口イトラコナゾールシクロデキストリン包接可溶化製剤 (ITZ-OS) の有効性の検討

Role of the fungal Ras-protein kinase A pathway in governing epithelial cell interactions during oropharyngeal candidiasis

Tpk1p, Tpk2p and Efg1p are members of the Ras-protein kinase A pathway that governs the yeast-to-hyphal transition in Candida albicans. We used tpk1Delta/tpk1Delta, tpk2Delta/tpk2Delta and efg1Delta/efg1Delta mutants to investigate the role of these proteins in regulating the interactions of C. albicans with oral epithelial cell lines in vitro and virulence in murine models of oropharyngeal candidiasis (OPC) and haematogenously disseminated candidiasis (HDC). The tpk1Delta/tpk1Delta strain adhered to, invaded and damaged oral epithelial cells in vitro similarly to the wild-type strain. In contrast, both the tpk2Delta/tpk2Delta and efg1Delta/efg1Delta strains had reduced capacity to invade and damage oral epithelial cells, and the efg1Delta/efg1Delta strain also exhibited decreased adherence to these cells. Consistent with these in vitro findings, the tpk2Delta/tpk2Delta and efg1Delta/efg1Delta strains also had significantly attenuated virulence during OPC. Therefore, Tpk2p and Efg1p both govern factors that enable C. albicans to invade and damage oral epithelial cells in vitro and cause OPC. These results also suggest that hyphal formation mediated by the Ras-protein kinase A pathway is a key virulence mechanism during OPC. Interestingly, the efg1Delta/efg1Delta strain, but not the tpk2Delta/tpk2Delta had reduced virulence during HDC. Thus, Tpk2p may be more important for governing virulence during OPC than HDC.

The expression of toll-like receptor 2 and 4 mRNA in local tissues of model of oropharyngeal candidiasis in mice.

To investigate the expression of Toll-like receptor (TLR) 2 and 4 mRNA in local tissues of model of oropharyngeal candidiasis in mice and to explore the potential role of TLR2 and TLR4 in earlier period of immune response, a murine model of oropharyngeal candidiasis inoculated by cotton wool balls saturated with Candida albicans was established. Mice were sacrificed at the indicated time points and the oropharyngeal tissues were excised. The expression of TLR2 and TLR4 mRNA was detected by RT-PCR. The results showed that low level of TLR2/4 mRNA could be detected in oropharyngeal tissues, but they were markedly up-regulated 6 h after inoculation, peaking after 12-24 h. Tissue TLR4 mRNA was gradually down-regulated 24-48 h, while TLR2 mRNA levels remained high up to the 72nd h. These data suggested that oropharyngeal infection of Candida albicans could result in up-regulation of TLR2/4 mRNA expression in local tissues, which might play important roles in earlier period of immune response.

Tolerance to amphotericin B in clinical isolates of Candida tropicalis

A broth microdilution method was used for testing amphotericin B against 33 clinical isolates of Candida tropicalis. All isolates were in vitro susceptible to the polyene (MIC [minimal inhibitory concentration] ≤1.0 μg/mL). However, when the isolates were cultured in a medium containing amphotericin B at a concentration of 1.5 μg/mL, a wide interstrain variation of growth rate was observed. Five isolates (15%) proved to be highly tolerant to the drug and grew at a frequency ranging from 1 × 10 −1 to 2 × 10 −2. Twenty-three isolates (70%) grew at a frequency ranging from 1 × 10 −5 to 1 × 10 −8. The remaining five isolates (15%) failed to grow in drug-containing medium. In general, this growth variation was not associated with amphotericin B MICs displayed by the single isolates. In addition, the strains grown in drug-containing medium did not represent amphotericin B–resistant mutants, as shown by the maintenance of MICs similar to those of their respective parent isolates. Killing experiments conducted in selected isolates confirmed a variation of fungicidal activity of amphotericin B. To see whether this phenomenon was associated with a variation of amphotericin B response in vivo, we established an experimental model of systemic murine candidiasis in CD1 mice by intravenous injection of cells belonging to Candida tropicalis 3147 (growth rate at a frequency of 1 × 10 −1 in amphotericin B medium) and Candida tropicalis 4055 (no growth). Low (0.3 mg/kg/day) and high (1 mg/kg/day) doses of amphotericin B were both effective at reducing the fungal burdens in the kidneys of mice infected with either strain ( p, 0.01 to 0.02). However, whereas the burden of mice infected with isolate 3147 and treated with the polyene at 0.3 mg/kg/day was reduced by 1.2 ± 0.25 (mean ± standard deviation) log 10 cfu/g compared to untreated mice, the same dosing regimen yielded a burden reduction of 2.6 ± 0.07 log 10 cfu/g in mice infected with isolate 4055 ( p < 0.001). Similarly, amphotericin B at 1 mg/kg/day yielded a burden reduction of 1.8 ± 0.20 vs. 2.5 ± 0.30 log 10 cfu/g in mice infected with isolates 3147 and 4055, respectively ( p < 0.001). Our data revealed a variable pattern of tolerance to amphotericin B among isolates of Candida tropicalis and showed that this phenomenon might influence the rate of organ clearance during therapy.

Inactivation of transcription factor gene ACE2 in the fungal pathogen Candida glabrata results in hypervirulence.

During an infection, the coordinated orchestration of many factors by the invading organism is required for disease to be initiated and to progress. The elucidation of the processes involved is critical to the development of a clear understanding of host-pathogen interactions. For Candida species, the inactivation of many fungal attributes has been shown to result in attenuation. Here we demonstrate that the Candida glabrata homolog of the Saccharomyces cerevisiae transcription factor gene ACE2 encodes a function that mediates virulence in a novel way. Inactivation of C. glabrata ACE2 does not result in attenuation but, conversely, in a strain that is hypervirulent in a murine model of invasive candidiasis. C. glabrata ace2 null mutants cause systemic infections characterized by fungal escape from the vasculature, tissue penetration, proliferation in vivo, and considerable overstimulation of the proinflammatory arm of the innate immune response. Compared to the case with wild-type fungi, mortality occurs much earlier in mice infected with C. glabrata ace2 cells, and furthermore, 200-fold lower doses are required to induce uniformly fatal infections. These data demonstrate that C. glabrata ACE2 encodes a function that plays a critical role in mediating the host-Candida interaction. It is the first virulence-moderating gene to be described for a Candida species.

Immunogenicity and protective effect of recombinant enolase of Candida albicans in a murine model of systemic candidiasis.

Enolase, a 46-kDa glycolytic enzyme, is an immunodominant antigen of the opportunistic pathogen Candida albicans. A recombinant 6 x His-tagged enolase was studied, in conjunction with interleukin-12 (IL-12), as an adjuvant for cytokine induction favouring protection in a murine model of haematogenous candidiasis. Mice immunized with enolase plus IL-12 showed increased antibody titres against enolase, as well as increased median survival time and decreased fungal burden in kidneys, in comparison to non-immunized or IL-12-treated mice. This increased survival was attributable to enolase-induced cell-mediated immunity as it also occurred in B-cell-deficient mice. Enolase immunization stimulated a predominant T-helper-1 (Th1) cytokine pattern in splenic cells and induced production of interferon-gamma (IFN-gamma) and interleukin-2 (IL-2) by purified CD4+ T cells. However, despite the elevation of immunogenicity, recombinant enolase induced only a modest protection against disseminated candidiasis, suggesting a form of protection likely attributable to the induction of a Th1 cell-mediated immune response.

Efficacy of human salivary mucin MUC7-derived peptide and histatin 5 in a murine model of candidiasis

MUC7 16-mer (residues 36–51 of human salivary mucin, MUC7) and histatin 5 possess potent in vitro antifungal activity. In the present study, we have evaluated the efficacy of these peptides in vivo using the experimental model of murine vulvo-vaginal candidiasis. The treatment groups included MUC7 16-mer, histatin 5, clotrimazole (all in pluronic F127 gel), and placebo (gel alone). Mice were treated intravaginally for 7 consecutive days. At the end of the treatment, anticandidal activities were assessed by colony counts and by histological examination. All groups except clotrimazole presented positive cultures; no statistically significant differences were found in fungal burden amongst placebo and any treatment group except clotrimazole. Histopathological findings confirmed the microbiological results; all groups with the exception of clotrimazole showed variable signs of infection.

In vivo pharmacokinetics and pharmacodynamics of a new triazole, voriconazole, in a murine candidiasis model.

In vivo studies have described the pharmacodynamic (PD) characteristics of several triazoles. These investigations have demonstrated that the 24-h area under the concentration-time curve (AUC)/MIC ratio is the critical pharmacokinetic (PK)-PD parameter associated with treatment efficacy. Further analyses from these in vivo studies have demonstrated that a triazole free drug 24-h AUC/MIC of 20 to 25 is predictive of treatment success. We used a neutropenic murine model of disseminated Candida albicans infection to similarly characterize the PK-PD of the new triazole voriconazole. PK and PD parameters (percentage of time that the concentration remains above the MIC [T > MIC], AUC/MIC ratio, and peak level in serum/MIC ratio) were correlated with in vivo efficacy, as measured by the organism number in kidney cultures after 24 h of therapy. Voriconazole kinetics and protein binding were studied in infected neutropenic mice. Peak level/dose and AUC/dose values ranged from 0.1 to 0.2 and 0.1 to 0.7, respectively. The serum elimination half-life ranged from 0.7 to 2.9 h. The level of protein binding in mouse serum was 78%. Treatment efficacy with the four dosing intervals studied was similar, supporting the AUC/MIC ratio as the PK-PD parameter predictive of efficacy. Nonlinear regression analysis also suggested that the AUC/MIC ratio was strongly predictive of treatment outcomes (R(2) for AUC/MIC ratio = 82%, R(2) for peak level/MIC ratio = 63%, R(2) for T > MIC = 75%). Similar studies were conducted with nine additional C. albicans isolates with various voriconazole susceptibilities (MICs, 0.007 to 0.25 micro g/ml) to determine if a similar 24-h AUC/MIC ratio was associated with efficacy. The voriconazole free drug AUC/MIC ratios were similar for all of the organisms studied (range, 11 to 58; mean +/- standard deviation, 24 +/- 17 [P = 0.45]). These AUC/MIC ratios observed for free drug are similar to those observed for other triazoles in this model.

In vivo pharmacodynamics of a new triazole, ravuconazole, in a murine candidiasis model.

In vivo studies have characterized the pharmacodynamic characteristics of the triazole fluconazole. These investigations demonstrated that the ratio of the area under the concentration-time curve from 0 to 24 h to the MIC (24-h AUC/MIC ratio) is the critical pharmacokinetic/pharmacodynamic (PK/PD) parameter associated with treatment efficacy. Further analysis demonstrated that a fluconazole 24-h AUC/MIC ratio of 20 to 25 was predictive of treatment success in both experimental models and clinical trials. We used a neutropenic murine model of disseminated Candida albicans infection to similarly characterize the time course activity of the new triazole ravuconazole. The PK/PD parameters (percent time above the MIC, AUC/MIC ratio, and peak level in serum/MIC ratio) were correlated with in vivo efficacy, as measured by organism number in kidney cultures after 24 and 72 h of therapy. Ravuconazole kinetics and protein binding were performed in neutropenic infected mice. Peak/dose and AUC/dose values ranged from 0.03 to 0.04 and 0.30 to 0.34, respectively. Serum elimination half-life ranged from 3.9 to 4.8 h. Protein binding was 95.8%. Single-dose postantifungal effect studies demonstrated prolonged suppression of organism regrowth after serum ravuconazole levels had fallen below the MIC. Treatment efficacies with the five dosing intervals studied were similar, supporting the argument for the AUC/MIC ratio as the PK/PD parameter predictive of efficacy. Nonlinear regression analysis also suggested that the AUC/MIC ratio was strongly predictive of treatment outcomes (AUC/MIC ratio, R(2) = 91%; peak/MIC ratio, R(2) = 85%; percent time above the MIC, R(2) = 47 to 65%). Similar studies were conducted with seven additional C. albicans isolates with various ravuconazole susceptibilities (MIC, 0.016 to 0.12 micro g/ml) to determine if a similar 24-h AUC/MIC ratio was associated with efficacy. The ravuconazole free-drug AUC/MIC ratios were similar for all of the organisms studied (10 to 36; mean +/- SD = 20.3 +/- 8.2; P = 0.43). These free-drug AUC/MIC ratios are similar to those observed for fluconazole in this model.

Experimental keratomycosis in a mouse model.

To establish a murine model of corneal candidiasis that permits molecular evaluation of fungal adherence and invasion. Corneas of immunocompetent, methylprednisolone-treated, and cyclophosphamide-treated adult NIH Swiss and BALB/c mice were topically mock inoculated or inoculated with 10-fold increasing amounts between 100 and 100 million colony-forming units (CFU) of Candida albicans after unilateral corneal scarification. Mock-inoculated eyes served as the control. Eyes were scored daily on a 12-point scale to categorize corneal inflammation and were enucleated for quantitative fungal cultures, analysis by polymerase chain reaction (PCR), and histopathologic examination. At least 100 CFU of C. albicans initiated measurable corneal infection, but 1 million or more colony-forming units were needed to induce consistent keratitis. Treatment with methylprednisolone increased disease severity in infected BALB/c mice and fungal persistence in both BALB/c and NIH Swiss mice. Treatment with cyclophosphamide increased disease severity and fungal persistence in both strains of mice. Infectious organisms were recovered by quantitative culture, and candidal DNA was detectable by PCR. C. albicans, inflammatory cells, and stromal necrosis were histologically evident within ocular tissue. Although mice are innately resistant to Candida infection after corneal inoculation, moderate to severe keratomycosis can be established in immunocompromised mice by the route of corneal scarification. Although differences between mouse strains and among immunosuppressive regimens remain to be explored, this murine model provides the basis for understanding the pathogenesis of fungal infections of the cornea.

1,4-Benzothiazine and 1,4-Benzoxazine imidazole derivatives with antifungal activity: A docking study

We have recently described the synthesis and antifungal activity of a series of 1,4-benzothiazine and 1,4-benzoxazine imidazole derivatives that mainly showed in vivo activity against a murine experimental model of candidiasis but that very often lacked in vitro activity. Here, we report a docking study of a representative set of our molecules in a 3D model of CYP51 of Candida albicans (CA-CYP51). The model was constructed on the basis of the sequence homology relationship with the recently reported crystal structure of the CYP51 of Mycobacterium tuberculosis (MT- CYP51).

Deletion of the two-component histidine kinase gene (CHK1) of Candida albicans contributes to enhanced growth inhibition and killing by human neutrophils in vitro.

We have observed that human neutrophils (polymorphonuclear leukocytes [PMNs]) have an increased growth-inhibitory and killing effect on a strain of Candida albicans with a deletion of CHK1, a gene encoding a putative histidine kinase. The PMN effect was not due to increased phagocytosis of the null strain. This observation may partially explain the reduced virulence in a hematogenously disseminated murine model of candidiasis.

New model of oropharyngeal candidiasis in mice.

We established a straightforward murine model of oropharyngeal candidiasis. Mice were immunosuppressed with cortisone acetate, anesthetized, and then inoculated by placing cotton wool balls saturated with Candida albicans sublingually for 2 h. A prolonged, reproducible infection was induced. This model may be useful for antifungal screening or pathogenesis studies.

Cell adhesion molecule and lymphocyte activation marker expression during experimental vaginal candidiasis.

Cell-mediated immunity by Th1-type CD4(+) T cells is the predominant host defense mechanism against mucosal candidiasis. However, studies using an estrogen-dependent murine model of vaginal candidiasis have demonstrated little to no change in resident vaginal T cells during infection and no systemic T-cell infiltration despite the presence of Candida-specific systemic Th1-type responses in infected mice. The present study was designed to further investigate these observations by characterizing T-cell activation and cell adhesion molecule expression during primary and secondary C. albicans vaginal infections. While flow cytometry analysis of activation markers showed some evidence for activation of CD3(+) draining lymph node and/or vaginal lymphocytes during both primary and secondary vaginal Candida infection, CD3(+) cells expressing the homing receptors and integrins alpha(4)beta(7), alpha(M290)beta(7), and alpha(4)beta(1) in draining lymph nodes of mice with primary and secondary infections were reduced compared to results for uninfected mice. At the local level, few vaginal lymphocytes expressed integrins, with only minor changes observed during both primary and secondary infections. On the other hand, immunohistochemical analysis of vaginal cell adhesion molecule expression showed increases in mucosal addressin cell adhesion molecule 1 and vascular cell adhesion molecule 1 expression during both primary and secondary infections. Altogether, these data suggest that although the vaginal tissue is permissive to cellular infiltration during a vaginal Candida infection, the reduced numbers of systemic cells expressing the reciprocal cellular adhesion molecules may preempt cellular infiltration, thereby limiting Candida-specific T-cell responses against infection.

Virulence of a phosphoribosylaminoimidazole carboxylase-deficient Candida albicans strain in an immunosuppressed murine model of systemic candidiasis.

The relative pathogenicities of three Candida albicans strains differing in the function of ADE2 (the gene encoding phosphoribosylaminoimidazole carboxylase) were evaluated in a murine candidiasis model. C. albicans strain CAI7 (ade2/ade2), previously constructed by site-specific recombination, was avirulent in immunosuppressed mice compared to the parent strain, CAF2-1, and a heterozygous ADE2/ade2 strain obtained by transforming CAI7 with a wild-type allele. The reduced virulence of CAI7 was correlated with the inability to proliferate in either synthetic medium or serum without the exogenous addition of >10 microg of adenine/ml. The loss of virulence upon site-specific disruption of the ade2 locus, and the restoration of wild-type virulence with the repair of just one ade2 allele, confirmed that the ADE2 gene and de novo purine biosynthesis were required for Candida pathogenicity. The potential of the phosphoribosylaminoimidazole carboxylase enzyme as a novel target for antifungal drug discovery is discussed.

Phenotypic analysis and virulence of Candida albicans LIG4 mutants.

In previous studies, we reported the isolation and preliminary characterization of a DNA ligase-encoding gene of Candida albicans. This gene (LIG4) is the structural and functional homologue of both yeast and human ligase IV, which is involved in nonhomologous end joining (NHEJ) of DNA double-strand breaks. In the present study, we have shown that there are no other LIG4 homologues in C. albicans. In order to study the function of LIG4 in morphogenesis and virulence, we constructed gene deletions. LIG4 transcript levels were reduced in the heterozygote and were completely absent in null strains. Concomitantly, the heterozygote showed a pronounced defect in myceliation, which was slightly greater in the null strain. This was true with several solid and liquid media, such as Spider medium, medium 199, and 2% glucose-1% yeast extract-2% Bacto Peptone, at several pHs. Reintroduction of the wild-type allele into the null mutant partially restored the ability of cells to form hyphae. In agreement with the positive role of LIG4 in morphogenesis, we detected a significant rise in mRNA levels during the morphological transition. LIG4 is not essential for DNA replication or for the repair of DNA damage induced by ionizing radiation or UV light, indicating that these lesions are repaired primarily by homologous recombination. However, our data show that the NHEJ apparatus of C. albicans may control morphogenesis in this diploid organism. In addition, deletion of one or both copies of LIG4 resulted in attenuation of virulence in a murine model of candidiasis.

The TEA/ATTS transcription factor CaTec1p regulates hyphal development and virulence in Candida albicans.

The temporal and spatial expression of stage-specific genes during morphological development of fungi and higher eukaryotes is controlled by transcription factors. In this study, we report the cloning and functional analysis of the Candida albicans TEC1 (CaTEC1) gene, a new member of the TEA/ATTS family of transcription factors that regulates C. albicans virulence. The promoters of the type 4, 5 and 6 proteinase isogenes (SAP4-6) contain repetitive TEA/ATTS consensus sequence motifs. This finding suggests a possible role for a homologue of Saccharomyces cerevisiae TEC1 during the activation of proteinase gene expression in C. albicans. CaTEC1 is predominantly expressed in the hyphal form of C. albicans. In vitro, serum-induced hyphal formation as well as evasion from MPhi after phagocytosis is suppressed in catec1/catec1 mutant cells. Furthermore, expression of the proteinase isogenes SAP4-6 is no longer inducible in these mutant cells. The deletion of the CaTEC1 gene attenuates virulence of C. albicans in a systemic model of murine candidiasis, although both mutant and revertant cells that were prepared from infected tissues or the vaginal mucosa grew in a hyphal morphology in vivo. CaTEC1 complements the pseudohyphal and invasive growth defect of haploid and diploid S. cerevisiae tec1/tec1 mutant cells and strongly activates the promoter of FLO11, a gene required for pseudohyphal growth. This study provides the first evidence pointing to an essential role for a member of the TEA/ATTS transcription factor family that had so far only been ascribed to function during development as a virulence regulator in microbial pathogenesis.