Pilot study on in vitro silver nanoparticles permeation through meningeal membrane

Silver nanoparticles (AgNPs) are commonly used in antiseptic sprays and mist and can easily come in contact with the mucosa of the upper airways. The intranasal pathway represents the only direct connection between the external environment and the brain structures, which traditionally are considered well protected. Much is known regarding drugs absorption through this route, but toxicological knowledge is scant. The olfactory bundles are surrounded by meningeal sheets in their course from the nasal mucosa to the olfactory bulb. This study investigated in vitro the transmeningeal absorption of 19 nmAgNPs, using excised porcine meninges mounted on Franz diffusion cells. We used two donor solutions: the first containing AgNPs (0.5 g/L) and the second containing only the water-soluble silver species derived from the ultrafiltration of the first one. Each experiment was carried separately for 2 hours. Results showed silver flux permeation through the meninges, with similar values in both experiments (0.78 ± 0.71 ng cm-2 h-1 and 0.73 ± 0.43 ng cm-2 h-1, for AgNPs and Ag ions respectively, mean and SD). Our study demonstrate that the meningeal barrier is permeable to silver and silver ions, when is applied in the nanoparticles form. This could lead to neurotoxic and neurodegenerative effects, which are now emerging in the scientific literature. Metal nanoparticles are commonly encountered in working scenarios, but their behavior in physiological media is different. Therefore the toxicological potential of metal NPs is heterogeneous and requires further efforts to be assessed on a case by case basis.