Annona squamosa and Tetracapidium conophorum exhibited dose ratio dependent additive and synergic combination effects in in-vitro and in-vivo models of hyperthyroidism

Annona squamosa and Tetracapidium conophorum leaf extracts have been documented to possess anti-hyperthyroidal activity and are used together in ethnomedicine; however, their effective combination dose ratios have not been explored. This study investigated the combined therapeutic effects of Annona squamosa and Tetracapidium conophorum extracts in in vitro and in vivo models of hyperthyroidism. In vitro studies showed concentration-dependent inhibition of thyroid peroxidase (TPO) enzyme activity by both extracts, with Tetracapidium conophorum exhibiting a lower EC50 (224.05 μg/ml) than that of Annona squamosa (437.24 μg/ml). combination of half their EC₅₀ produced 51% TPO inhibition and a combination index (CI) of 1.0, indicating additivity, while 250 μg/ml Annona squamosa combined with 65 μg/ml Tetracapidium conophorum resulted in 57% inhibition and a CI of 0.8, suggesting synergism. In an in vivo hyperthyroidism model induced by L-thyroxine, both extracts dose-dependently increased thyroid-stimulating hormone (TSH) levels. The combination dose ratios of 30 mg/kg Annona squamosa + 90 mg/kg Tetracapidium conophorum and 25 mg/kg Annona squamosa + 105 mg/kg Tetracapidium conophorum produced a CI of 0.7, indicating synergism. The combination treatment also significantly reduced elevated T3 and T4 levels, liver enzymes, and lipid peroxidation while improving kidney function markers. Annona squamosa and Tetracapidium conophorum extracts exhibited both additive and synergistic effects at different dose ratios in hyperthyroidism models, highlighting their potential to enhance antithyroid efficacy through strategic combinations.