# Oral L-Arginine treatment attenuates Cryptococcus neoformans extrapulmonary dissemination and disease progression

## TL;DR

Oral L-arginine reduces the spread of Cryptococcus neoformans in mice by boosting brain immunity and improving survival.

## Contribution

This study reveals that L-arginine supplementation mitigates cryptococcal dissemination by enhancing brain immune responses.

## Key findings

- Oral L-arginine reduces fungal burdens in the brain and spleen of infected mice.
- L-arginine supplementation improves survival and reduces brain cryptococcoma in murine models.
- L-arginine enhances protective immune responses and microglial clearance of Cryptococcus in the brain.

## Abstract

Cryptococcus neoformans is an opportunistic fungal pathogen causing severe infections in immunocompromised individuals. Arginine metabolism is critical for immune regulation, but its precise role in cryptococcal pathogenesis is not well understood. In this study, we investigated systemic and tissue-specific alterations in L-arginine metabolism during pulmonary C. neoformans infection and evaluated L-arginine supplementation as a potential therapy using a murine model. Key assessments included fungal burden quantification, inflammatory cell and cytokine characterization, brain gene expression analysis, histological examinations, and survival studies. We found significant depletion of serum L-arginine and its downstream metabolites, accompanied by increased arginase activity in infected tissues, indicating a disrupted metabolic balance. Gene expression analysis showed distinct metabolic shifts, including upregulation of arginase-1 (Arg1) and proline metabolism genes, with concurrent suppression of nitric oxide synthase 2 (Nos2) in the brain during the late infection phase. Oral L-arginine supplementation significantly reduced fungal burdens in the brain and spleen, suggesting its effectiveness in controlling cryptococcal dissemination from the lungs. Consequently, L-arginine administration improved survival and clinical scores while also reducing brain cryptococcoma in infected mice. Mechanistically, L-arginine enhanced protective immune responses within the mouse brain, facilitated microglial-mediated clearance of Cryptococcus, and reduced cryptococcal invasion across brain endothelial cells in vitro. In summary, oral administration of L-arginine mitigates C. neoformans dissemination by augmenting brain’s immune response. This study provides crucial insights into arginine metabolism in cryptococcal disease progression, supporting L-arginine as a promising immunomodulatory therapy.