Mesoporous Aerogel Microparticles Injected into the Abdominal Cavity of Mice Accumulate in Parathymic Lymph Nodes.

Mesoporous aerogel microparticles are promising drug delivery systems. However, their in vivo biodistribution pathways and health effects are unknown. Suspensions of fluorescein-labeled silica-gelatin hybrid aerogel microparticles were injected into the peritoneum (abdominal cavity) of healthy mice in concentrations of 52 and 104 mg kg-1 in a 3-week-long acute toxicity experiment. No physiological dysfunctions were detected, and all mice were healthy. An autopsy revealed that the aerogel microparticles were not present at the site of injection in the abdominal cavity at the end of the experiment. The histological study of the liver, spleen, kidneys, thymus and lymphatic tissues showed no signs of toxicity. The localization of the aerogel microparticles in the organs was studied by fluorescence microscopy. Aerogel microparticles were not detected in any of the abdominal organs, but they were clearly visible in the cortical part of the parathymic lymph nodes, where they accumulated. The accumulation of aerogel microparticles in parathymic lymph nodes in combination with their absence in the reticuloendothelial system organs, such as the liver or spleen, suggests that the microparticles entered the lymphatic circulation. This biodistribution pathway could be exploited to design passive targeting drug delivery systems for flooding metastatic pathways of abdominal cancers that spread via the lymphatic circulation.