Effects of Astragaloside IV Combined With Metronidazole on Cyst Shedding and Mucosal Immune and Inflammatory Responses in a Murine Model of Giardiasis.

BACKGROUND: Giardiasis continues to be a significant intestinal parasitic infection, with instances of treatment failure and recurrence underscoring the necessity for supplementary therapeutic approaches. Astragaloside (AGS), a bioactive compound known for its anti-inflammatory and immunomodulatory effects, may serve as a promising adjunctive treatment; however, its efficacy against Giardia infection has not been thoroughly examined. Accordingly, this study aimed to assess the antigiardial efficacy of AGS both as a monotherapy and in combination with metronidazole (METR), focusing specifically on parameters such as parasite cyst burden and viability, intestinal mucosal immune responses, inflammatory markers, and hepatic safety associated with treatment. METHODS: The MTT colorimetric assay was used to evaluate the in vitro antigiardial effects of AGS against Giardia trophozoites. Mice infected with Giardia were treated with AGS (10 and 15 mg/kg/day) and METR (7.5 and 15 mg/kg/day), both individually and in combination, over a 7-day period. Subsequently, stool samples were collected and analyzed to assess the presence and viability of Giardia cysts. The levels of secretory IgA (sIgA) in intestinal tissue, as well as the expression of tumor necrosis factor-alpha (TNF-α), nuclear factor kappa B (NF-κB), and interleukin-1 beta (IL-1β), were quantified using commercial ELISA kits and real-time polymerase chain reaction (PCR), respectively. RESULTS: AGS exhibited a clear concentration-dependent inhibitory effect on the viability of Giardia trophozoites, with a calculated half-maximal inhibitory concentration (IC50) value of 30.24 ± 2.43 μg/mL. The administration of either METR or AGS (10 and 15 mg/kg) individually resulted in a partial reduction in both cyst quantity and viability. Notably, combined treatment with AGS and METR resulted in no detectable cysts in fecal samples collected 24 h after the final treatment dose, within the detection limits of microscopy-based analysis (p < 0.001). Secretory IgA concentrations showed modest improvement following monotherapy but increased substantially after combination therapy (4.36 ng/mL, p < 0.001). Correspondingly, elevated levels of pro-inflammatory markers TNF-α, NF-κB, and IL-1β observed in untreated mice (5.3-, 4.29-, and 5.16-fold, respectively) were nearly restored to baseline values by the co-administration regimen of AGS 15 mg/kg + METR 7.5 mg/kg (1.11-, 0.86-, and 0.91-fold change, p < 0.001). These findings indicate that AGS not only lacks hepatotoxicity but may also exert protective effects against infection-associated hepatic dysfunction. CONCLUSION: AGS administration was associated with a reduced Giardia cyst burden at the prespecified 24-h post-treatment endpoint, restoration of mucosal immune responses, attenuation of inflammatory signaling, and improved biochemical profiles in experimentally infected mice. These findings suggest that AGS may function as an immunomodulatory and anti-inflammatory adjunct, potentially contributing to host-mediated parasite load reduction and improved treatment outcomes when combined with METR. However, additional antiparasitic mechanisms and formal pharmacodynamic synergistic interactions were not demonstrated in this study and require further investigation through dedicated in vitro and mechanistic analyses.