Photodynamic opening of the blood-brain barrier to high weight molecules and liposomes through an optical clearing skull window.

The photodynamic (PD) effect has been reported to be efficient for the opening of the blood-brain barrier (BBB), which provides a new informative platform for developing perspective strategies towards brain disease therapy and drug delivery. However, this method is usually performed via craniotomy due to high scattering of the turbid skull. In this work, we employed a newly-developed optical clearing skull window for investigating non-invasive PD-induced BBB opening to high weight molecules and 100-nm fluid-phase liposomes containing ganglioside GM1. The results demonstrated that the BBB permeability to the Evans blue albumin complex is related to laser doses. By in vivo two-photon imaging and ex vivo confocal imaging with specific markers of the BBB, we noticed PD-related extravasation of rhodamine-dextran and liposomes from the vessels into the brain parenchyma. The PD induced an increase in oxidative stress associated with mild hypoxia and changes in the expression of tight junction (CLND-5 and ZO-1) and adherens junction (VE-cadherin) proteins, which might be one of the mechanisms underlying the PD-related BBB opening for liposomes. Our experiments indicate that optical clearing skull window will be a promising tool for non-invasive PD-related BBB opening for high weight molecules and liposomes that provides a novel useful tool for brain drug delivery and treatment of brain diseases.