The Rabbit Model of Cryptococcal Meningitis.

Cryptococcal meningitis (CM) is a fungal disease caused by the invasion of Cryptococcus yeast cells into the central nervous system. The organism is thought to enter the body through the lungs and then escape due to dysregulation of the immune response. Multiple animal species have been used to model the infection and characterize CM including mice, rats, dogs, guinea pigs, and rabbits. The rabbit model has over 40 years of data and has been used to study host-pathogen interactions and the efficacy of antifungal therapeutics. The model begins with immune suppression to eliminate the lymphocytic cell population followed by direct infection of the central nervous system via an injection of a suspension of yeast cells into the cisterna magna. The organism remains in the CNS during the course of infection, and cerebrospinal fluid can be repeatedly sampled to quantify the burden of organism, measure drug levels in the CSF, profile the immune response in the CSF, and/or characterize the yeast cells. The rabbit model of infection is a robust experimental model for better understanding CM and Cryptococcus cellular behavior.

Cryptococcus neoformans trehalose-6-phosphate synthase (tps1) promotes organ-specific virulence and fungal protection against multiple lines of host defenses.

Trehalose-6-phosphate synthase (TPS1) was identified as a virulence factor for Cryptococcus neoformans and a promising therapeutic target. This study reveals previously unknown roles of TPS1 in evasion of host defenses during pulmonary and disseminated phases of infection. In the pulmonary infection model, TPS1-deleted (tps1Δ) Cryptococci are rapidly cleared by mouse lungs whereas TPS1-sufficent WT (H99) and revertant (tps1Δ:TPS1) strains expand in the lungs and disseminate, causing 100% mortality. Rapid pulmonary clearance of tps1Δ mutant is T-cell independent and relies on its susceptibility to lung resident factors and innate immune factors, exemplified by tps1Δ but not H99 inhibition in a coculture with dispersed lung cells and its rapid clearance coinciding with innate leukocyte infiltration. In the disseminated model of infection, which bypasses initial lung-fungus interactions, tps1Δ strain remains highly attenuated. Specifically, tps1Δ mutant is unable to colonize the lungs from the bloodstream or expand in spleens but is capable of crossing into the brain, where it remains controlled even in the absence of T cells. In contrast, strains H99 and tps1Δ:TPS1 rapidly expand in all studied organs, leading to rapid death of the infected mice. Since the rapid pulmonary clearance of tps1Δ mutant resembles a response to acapsular strains, the effect of tps1 deletion on capsule formation in vitro and in vivo was examined. Tps1Δ cryptococci form capsules but with a substantially reduced size. In conclusion, TPS1 is an important virulence factor, allowing C. neoformans evasion of resident pulmonary and innate defense mechanisms, most likely via its role in cryptococcal capsule formation.

A ketogenic diet enhances fluconazole efficacy in murine models of systemic fungal infection.

Invasive fungal infections are a significant public health concern, with mortality rates ranging from 20% to 85% despite current treatments. Therefore, we examined whether a ketogenic diet could serve as a successful treatment intervention in murine models of Cryptococcus neoformans and Candida albicans infection in combination with fluconazole-a low-cost, readily available antifungal therapy. The ketogenic diet is a high-fat, low-carbohydrate diet that promotes fatty acid oxidation as an alternative to glycolysis through the production of ketone bodies. In this series of experiments, mice fed a ketogenic diet prior to infection with C. neoformans and treated with fluconazole had a significant decrease in fungal burden in both the brain (mean 2.66 ± 0.289 log10 reduction) and lung (mean 1.72 ± 0.399 log10 reduction) compared to fluconazole treatment on a conventional diet. During C. albicans infection, kidney fungal burden of mice in the keto-fluconazole combination group was significantly decreased compared to fluconazole alone (2.37 ± 0.770 log10-reduction). Along with higher concentrations of fluconazole in the plasma and brain tissue, fluconazole efficacy was maximized at a significantly lower concentration on a keto diet compared to a conventional diet, indicating a dramatic effect on fluconazole pharmacodynamics. Our findings indicate that a ketogenic diet potentiates the effect of fluconazole at multiple body sites during both C. neoformans and C. albicans infection and could have practical and promising treatment implications.IMPORTANCEInvasive fungal infections cause over 2.5 million deaths per year around the world. Treatments for fungal infections are limited, and there is a significant need to develop strategies to enhance antifungal efficacy, combat antifungal resistance, and mitigate treatment side effects. We determined that a high-fat, low-carbohydrate ketogenic diet significantly potentiated the therapeutic effect of fluconazole, which resulted in a substantial decrease in tissue fungal burden of both C. neoformans and C. albicans in experimental animal models. We believe this work is the first of its kind to demonstrate that diet can dramatically influence the treatment of fungal infections. These results highlight a novel strategy of antifungal drug enhancement and emphasize the need for future investigation into dietary effects on antifungal drug activity.