Targeting Chronic Cerebral Toxoplasmosis in Immunocompromised Hosts: <i>In Vivo</i> Antiparasitic and Immuno-Apoptotic Effects of Phellandrene Combined with Pyrimethamine

Introduction: This investigation was conducted to assess the in vivo effects and potential mechanisms of action of phellandrene (PR) and pyrimethamine (PYM) combination therapy in the context of chronic cerebral toxoplasmosis in immunocompromised (ICM) murine models. Methods: BALB/c dexamethasone-induced ICM mice infected with the Toxoplasma gondii ME49 strain were treated with PR (10 and 20 mg/kg) alone or in combination with PYM for 2 weeks. The number and diameter of tissue cysts, oxidant/antioxidant markers, cell-mediated immunity indicators ( e.g., interferon‐gamma [ IFN‐γ ], interleukin-12 [ IL-12 ], IL-4 ), apoptosis-related genes ( e.g., Caspase-3, BAX, and Bcl-2 ), and pathogenesis-related genes (serine protease inhibitor [serpin A3k] and bradyzoite surface antigen 1 [BAG1]) were examined by qRT-PCR. Results: PR, principally in combination with PYM, reduced the load (26.6 cysts) and size (23.4 µm) of tissue cysts, modulated lipid peroxidation (2.36 nmol/mg tissue), glutathione peroxidase (5.31 U/mg tissue), and superoxide dismutase (47.4 U/mg tissue), and significantly elevated ( p &lt; 0.001) the expression levels of cytokines ( IFN‐γ = 4.12-fold change, IL-12 = 3.91-fold change, and IL-4 = 1.24-fold change) and apoptosis genes ( Caspase-3 = 3.1-fold change, BAX = 3.89-fold change, and Bcl-2 = 1.17-fold change), while altering the expression of BAG1 (1.28-fold change) and serpin A3k (3.46-fold change). Conclusion: In summary, PR, particularly in combination with PYM, demonstrated significant therapeutic efficacy against chronic toxoplasmosis in ICM mice. This effect appears to be mediated through modulation of oxidative stress, enhancement of antioxidant defenses, regulation of apoptosis, and improvement of host immune responses. Importantly, no significant toxicity was observed in vital organs. These findings highlight PR as a promising adjunct candidate; however, further pharmacokinetic and clinical investigations are required to confirm its translational potential.