Chronic intraperitoneal injection of polyethylene glycol 200 in mice induces hippocampal neuroinflammation

In vivo treatment of hydrophobic substances requires the use of organic solvents, which are often toxic. Consequently, polyethylene glycols (PEGs), which are considered as nontoxic, have been widely used for many years in chemistry and biology. We used PEG 200, which was administrated by intraperitoneal (i.p.) injection once a week to mice. After 4 months of injections, at the dose of 1.67 mL/kg, a surprising increase in expression of GFAP (glial fibrillary acidic protein) and IBA1 (ionized calcium binding adaptor molecule 1), glial markers of astrocytes and microglia respectively, was observed in the mice's hippocampus. These results were associated with a dramatic increase in pro-inflammatory cytokine interleukin-1β (IL-1β) expression, all together suggesting an inflammatory process. It is important to communicate these results to the scientific community to provide awareness of this potential effect when PEG 200 is used under similar conditions as a vehicle in mice.