Gadolinium toxicity: mechanisms, clinical manifestations, and nanoparticle role.

Gadolinium-based contrast agents (GBCAs), essential for MRI, are facing renewed scrutiny due to gadolinium (Gd) retention and emerging toxicity profiles. While the link between less stable agents and Nephrogenic Systemic Fibrosis (NSF) in renal impairment is established, gadolinium (Gd) deposition is also observed in the brain, bone, and skin across all GBCA classes, even in patients with normal renal function. This finding has raised concerns and led to a concept of Gadolinium Deposition Disease (GDD). The present review synthesizes current evidence on clinical manifestations and underlying mechanisms. It highlights pathways beyond traditional transmetallation, particularly endogenous nanoparticle formation as a key mechanism for Gd release and retention, potentially challenging the stability assumptions for even macrocyclic agents. Structural factors (linear/macrocyclic; ionic/non-ionic) and stability parameters (thermodynamic log K; kinetic kobs) influencing risk are evaluated alongside regulatory responses. GBCAs should be viewed not as inert diagnostics but as agents with complex, cumulative biological interactions. Future research should focus on developing non-gadolinium alternatives, validating biomarkers for early detection of Gd retention, and conducting controlled trials on chelation therapy efficacy. Clinicians must balance the diagnostic benefits of GBCAs with potential long-term risks, ensuring informed patient consent and judicious use. Innovative approaches, such as Gd-grafted nanodiamonds with high relaxivity and enhanced safety via polyvinylpyrrolidone (PVP) coating, may offer alternatives to traditional GBCAs by reducing toxicity risks. Manganese-based contrast agents, such as Mn-PyC3A, show promise as safer alternatives due to efficient renal and hepatobiliary elimination, even in renal impairment, as demonstrated in rat models.