Biodegradable magnesium materials regulate ROS-RNS balance in pro-inflammatory macrophage environment

The relationship between reactive oxygen and nitrogen species (ROS-RNS) secretion and the concomitant biocorrosion of degradable magnesium (Mg) materials is poorly understood. We found that Mg foils implanted short term in vivo (24 h) displayed large amounts of proinflammatory F4/80+/iNOS + macrophages at the interface. We sought to investigate the interplay between biodegrading Mg materials (98.6% Mg, AZ31 & AZ61) and macrophages (RAW 264.7) stimulated with lipopolysaccharide (RAW 264.7 LPS ) to induce ROS-RNS secretion. To test how these proinflammatory ROS-RNS secreting cells interact with Mg corrosion in vitro, Mg and AZ61 discs were suspended approximately 2 mm above a monolayer of RAW 264.7 cells, either with or without LPS. The surfaces of both materials showed acute (24 h) changes when incubated in the proinflammatory RAW 264.7 LPS environment. Mg discs incubated with RAW 264.7 LPS macrophages showed greater corrosion pitting, while AZ61 showed morphological and elemental bulk product changes via scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX). X-ray photoelectron spectroscopy (XPS) analysis showed a reduction in the Ca/P ratio of the surface products for AZ61 disc incubated with RAW 264.7 LPS , but not the Mg discs. Moreover, RAW 264.7 LPS macrophages were found to be more viable in the acute biodegradative environment generated by Mg materials, as demonstrated by calcein-AM and cleaved (active) caspase-3 staining (CC3). LPS stimulation caused an increase in ROS-RNS, and a decrease in antioxidant peroxidase activity. Mg and AZ61 were found to change this ROS-RNS balance, independently of physiological antioxidant mechanisms. The findings highlight the complexity of the cellular driven acute inflammatory responses to different biodegradable Mg, and how it can potentially affect performance of these materials. • Proinflammatory iNOS and F4/80+ macrophages were present at 24hrs near the interface of Mg and AZ31 in vivo. • The corrosion products of magnesium (Mg) materials are modulated when exposed to inflammatory microenvironments. • RAW 264.7 LPS macrophages incubated with suspended AZ61 discs show a decreased surface Ca/P ratio and changes in bulk corrosion products. • RAW 264.7 LPS macrophages show increased viability when incubated with Mg materials, and the effect was spatially dependent. • Mg and AZ61 regulated ROS-RNS balance independent of physiological antioxidant mechanisms in pro-inflammatory RAW 264.7 LPS macrophages.