Size-Dependent Effects of Gold Nanoparticles on the Left Ventricular Myocardium in Adult Male Albino Rats: A Histological and Immunohistochemical Study

Background: The increasing use of gold nanoparticles (GNPs) in biomedical applications necessitates a thorough assessment of their potential cardiotoxicity. This study aimed to assess the size-dependent effects of 10- and 40-nm diameter GNPs on the left ventricular myocardium. Materials and Methods: Thirty-two adult male albino rats were randomly allocated into four groups (8 rats/group). The Untreated Control (Group A) received no treatment, while the Vehicle Control (Group B) received a daily intraperitoneal injection of trisodium citrate solution for 14 days. The GNP10-treated (Group C) and GNP40-treated (Group D) received a daily intraperitoneal injection of 400 μg/kg b.w. of 10 nm and 40 nm GNPs, dispersed in the vehicle solution, respectively, for 14 days. Left ventricular myocardial specimens were collected following anesthesia and processed for histological, Caspase-3 immunohistochemistry, and morphometric studies. Results: The GNP10-treated group exhibited pronounced structural alterations, including myofibrillar fragmentation, nuclear pyknosis, and disrupted intercalated discs. Morphometric analysis revealed a significant increase (p < 0.001) in both the area percentage of collagen fibers (fibrosis marker) and Caspase-3 immunoreactivity (apoptosis marker) compared to the control groups. In contrast, the GNP40-treated group showed largely preserved myocardial architecture, with no significant difference in fibrosis or apoptosis markers relative to the control groups. Conclusion: Gold nanoparticle cardiotoxicity is size-dependent. Smaller particles (10 nm) induce severe myocardial injury, characterized by apoptosis and fibrosis, likely driven by cellular penetration and oxidative stress. Conversely, larger particles (40 nm) appear safer. These findings underscore the necessity of nanoparticle size optimization to minimize toxicity in biomedical applications.