Carbon tetrachloride (CCl4) has been demonstrated to induce testicular damage via oxidative stress. Bromelain (Br), a proteolytic enzyme known for its biological activities and pharmacological properties, exhibits limited absorption owing to its low solubility and bioavailability. The present study aimed to investigate the histological and immunohistochemical effects of bromelain conjugated with gold nanoparticles (AuNPs) on the testis histology of albino mice treated with CCl4. Thirty-five male albino mice (Mus musculus), with an average age of 9 weeks, were randomly divided into five groups, each containing seven mice. The experiment was prolonged for four weeks. The first group (G1) was the control group, the second group (G2) received weekly sub-peritoneal injections of CCl4 until the end of the experiment, and the third group (G3) received an oral dose of Au-NPs solution. The fourth group (G4) received injections of CCl4; one hour later, the mice were given an oral dose of 300 mg/kg bromelain. The fifth group (G5) received an injection of CCl4; subsequently, the mice received the same oral dosage of 300 mg/kg Au-NPs-bromelain after 60 minutes. The mice's testes were sampled to evaluate histopathological alterations and immunohistochemical markers, particularly Ki-67 and caspase-9. The present results indicated that mice treated with CCl4 displayed a range of histological alterations, including testicular damage, degeneration in seminiferous tubules, vacuolation, and loss of germ cells. Furthermore, the immunohistochemistry study demonstrated that Ki-67 intensity decreased while caspase-9 intensity increased in groups G2 and G4 compared to the control group. Bromelain loaded with gold nanoparticles at a dosage of 300 mg/kg exhibited a notable reduction in the harmful effects of CCl4 on the testicular tissue of mice by restoring the histological structure, enhancing the Ki-67 proliferation protein, and suppressing the apoptotic cascade protein indicated by caspase 9. Keywords: Bromelain, Carbon tetrachloride, Caspase, Gold nanoparticle
