Gadolinium-Based Contrast Agents Stimulate Adaptive Immune Response through Release of DAMP Signals in Neuronal SH-SY5Y Cells

Abstract

The use of gadolinium-based compounds as contrast agents in magnetic resonance imaging scans has been popularized owing to the superior anatomical images they produce and tracking of a broad spectrum of clinical conditions. While these compounds are considered safe when administered at appropriate dose levels, toxicity has been reported for patients with impaired renal functions. Toxicogenomic and intracellular accumulation studies have also implicated genes relevant to lipid synthesis, disruption of cytoplasmic membrane integrity, and accumulation in the neuronal interstitium, kidney, liver, and skin. These findings have prompted widespread studies into the mechanism of intracellular accumulation and cytotoxicity of gadolinium-based contrast agents (GBCAs). In the present work, neuroblastoma SH-SY5Y cells were treated with macrocyclic Gd chelate gadoterate meglumine, linear Gd chelate gadopentetic acid, and GdCl3 salt to decipher their ability to activate the release of danger-associated molecular pattern signals (DAMPs), key steps in the induction of immunologic cell death (ICD). Furthermore, intracellular accumulation and localization of the GBCAs in SH-SY5Y cells were studied using inductively coupled plasma optical emission spectroscopy (ICP-OES) and transmission electron microscopy (TEM). Our results showed no significant cytotoxicity to SH-SY5Y cells until 5 mM for all compounds tested except gadopentetic acid. Cells undergoing early apoptosis were observed with both gadoterate meglumine and gadopentetic acid at 1 and 10 mM compared to nontreated control samples. Evidence for mild induction of immunogenic cell death was observed for both linear and macrocyclic GBCAs but not in GdCl3-treated SH-SY5Y cells, with a concentration-dependent increase in extracellular adenosine triphosphate (ATP) level, high mobility group box 1 (HMGB1) protein, and relocation of calreticulin. Furthermore, uptake inhibition studies suggest clathrin-dependent endocytosis by blocking GTPase activity of dynamin proteins in linear gadopentetic acid and accumulation along the cell membrane as seen in TEM images.