| Abstract |
Objectives
C. parapsilosis is one of the most common causes of invasive candidiasis. The echinocandins, including caspofungin (CAS) , micafungin (MICA) and anidulafungin (ANF), possess broad spectrum fungicidal activity and are currently considered the treatment of choice for many forms of invasive candidiasis. Importantly, these agents retain their activity against azole-resistant Candida spp. Nonthelless, the echinocandins demonstrate reduced in vitro activity against C. parapsilosis, whereas clinical failure due to CAS-resistant (CAS-R) C. parapsilosis isolates have been recently reported in patients receiving CAS, causing breakthrough infections to echinocandins. Overall, this recent shift in the epidemiology of Candida infections raises concerns about the optimal regiment for empirical treatment of invasive candidasis.
However, the clinical implications of the differencial activity of echinocandins against C. parapsilosis remain currently unknown, as comparative in vivo studies are completely lacking. Furthermore, because the echnocandins possess significant immunomodulatory properties that are mediated via beta-glucan unmasking, it is plausible that differences in the in vitro activity of echinocandins against Candida spp. may also result in significant quantitative and qualititive changes in antifungal host immune response in vivo.
The purpose of the present study was to establish a clinically relevant mouse model of invasive C. parapsilosis infection in immunocompetent mice, and to compare the in vivo activity of ANF and CAS in experimental candidemia caused by C. parapsilosis isolates that are sensitive in vitro to ANF but are resistant to CAS. The
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degree of the in vivo cross-resistance among echinocandins and the fitness loss associated with caspofungin (CAS) non-susceptibility of C. parapsilosis are not well studied. Overall, we anticipate that the results of our in vivo studies in murine model of invasive candidiasis should provide important information on the optimal management of infections caused by this emerging Candida spp.
Materials and Methods
Female BALB/c mice were infected with three different ANF-susceptible isolates of C. parapsilosis with different degrees of non-susceptibility to CAS via injection of blastospores dissolved in 200 μL of phosphate-buffered saline into the lateral tail veins. Initial experiments were performed to define the optimal C. parapsilosis inoculum (LD50) for studying antifungal activity (inoculum range 10^5-10^7 blastospores). It will be established a mouse model of invasive candidiasis for evaluation of survival, assessment of fungal burden in organs and measurement of weight loss.
The efficacy of respective echinocandin regimens (CAS, ANF) against 3 C. parapsilosis isolates was analyzed. Starting 6 hours after infection with each of C. parapsilosis isolate, intraperitoneal administration of each echinocandin (CAS, ANF), in two doses (1 mg/kg and 10 mg/kg) corresponding to that used for treatment of invasive candidiasis in humans, or DMSO (control group) was administered once daily for 7 days or until the death of the animal. Fungal burden was measured in kidney, spleen and liver in selected mice (n=6) euthanized on day 2 after infection.
In addition, measurement of weight loss of infected mice, an established marker of disease severity, distributed to the evaluation of comparative efficacy of
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echinocandins against invasive candidiasis of C. parapsilosis. To further evaluate differences in fungal burden of the organs in mice infected with CAS-S, CAS-I or CAS-R C. parapsilosis isolates, histopathological examination of the kidneys was performed in selected mice (n=3) euthanized on day 2 after infection and treated, as described above.
Results
Increasing CAS resistance was associated with reduced virulence of C. parapsilosis isolates (mortality rates CAS-S 100% vs CAS-I 11.1% vs CAS-R 0% P = 0.001). The CAS-S isolate was more virulent in comparison to the other two isolates, while there was a trend towards reduced mortality following infection with CAS-R isolate when compared to the CAS-I isolate.
High doses of either echinocandin were active against infection with CAS-I isolate when assessed by fungal burden reduction and weight gain. However, no reduction in fungal burden in mice infected with the CAS-R isolate following treatment with either echinocandin in both doses. Nevetherless, mice infected with the CAS-R isolate had reduced disease severity following echinocandin treatment, suggesting that echinocandins have activity in vivo, even against echinocandin-resistant strains. In animals infected with the CAS-S strain, high and low dose doses of CAS or low dose of ANF treatment resulted in lower organ fungal burdens versus controls. Weight loss was less in mice infected by the CAS-S C. parapsilosis following high dose CAS or ANF treatment, while all mice of the control group lost substantial weight and died on day 5 after infection.
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Conclusions
A reproducible model of C. parapsilosis IC in immunocompetent mice was established that mimics the pathobiology of hematogenous infection in humans and allows comparisons of antifungal drug activity based on differences in fungal burden and weight loss of infected mice. It is suggested that echinocandins are effective antifungal agents against C. parapsilosis infections and concurrently, they possess significant immunomodulatory properties. There is no straightforward in vitro/in vivo correlation of echinocandin activity against C. parapsilosis displaying non-susceptibility to CAS. A complex interplay of residual echinocandin activity, decreased virulence and/or fitness of isolates with altered cell wall, and possible immunomodulatory effects, can be encountered in vivo during infection with CAS-non-susceptible C. parapsilosis isolates.
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