Dose-Dependent Hepatotoxicity of Zinc Oxide Nanoparticles in Rats: Oxidative Stress, Apoptosis, and Dysregulation of Hepatic miR-122, miR-34a, and miR-21

Zinc oxide nanoparticles (ZnO NPs) are widely used in biomedical, agricultural, and industrial applications, raising concerns about their potential hepatotoxicity. This study investigated the effects of 28-day oral ZnO NP exposure on hepatic function, oxidative stress, apoptosis, inflammatory signaling, and microRNA expression in rats. Sixty male Wistar albino rats were allocated to three groups (n = 20 each),control, low dose (30 mg/kg), and high dose (100 mg/kg), and treated by oral gavage. The administered material had a nominal particle size of 50 nm and a supplier-stated purity of 99.9%. Serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST), hepatic malondialdehyde (MDA) and reduced glutathione (GSH), histopathology, immunohistochemistry, mRNA expression, and hepatic microRNAs were assessed. ZnO NPs induced dose-related liver injury: ALT increased from 31.26 ± 2.5 to 75.48 ± 12.3 IU/L, while AST increased from 32.47 ± 4.1 to 85.57 ± 18.9 IU/L. Hepatic MDA increased, whereas GSH increased at the low dose but was depleted at the high dose. Histopathology demonstrated sinusoidal congestion, hepatocellular necrosis, and inflammatory infiltration. Immunohistochemistry indicated reduced B-cell lymphoma 2 (Bcl-2) and increased caspase-3 and tumor necrosis factor-alpha (TNF-α) immunoreactivity. Interleukin-6 (IL-6) and heme oxygenase-1 (HO-1) were upregulated, whereas superoxide dismutase 2 (SOD2) was downregulated. At the high dose, miR-122-5p, miR-34a-5p, and miR-21-5p increased by 8.74-, 6.53-, and 4.38-fold, respectively (all p< 0.05). Their expression levels were also strongly and positively correlated with biochemical, oxidative, and histopathological indicators of liver injury. These findings indicate that ZnO NP exposure is associated with oxidative, inflammatory, apoptotic, and microRNA responses; the altered hepatic microRNAs may represent candidate tissue indicators of ZnO NP-induced liver injury.