The blood-brain barrier solute permeability and its regulation by chemical and physical stimuli.

摘要

The blood-brain barrier (BBB) is a unique barrier between the cerebral circulation and the brain tissue that maintains the delicate environment of the brain by limiting the entrance of molecules and ions from the blood stream. It also hinders drug delivery to the central nervous system (CNS) for the treatment of brain diseases. To search for strategies that improve drug delivery efficacy across the BBB, in the first part of the dissertation, a new method was developed to quantify the BBB solute permeability and solute diffusion coefficient in rat brain by using two-photon microscopy. Two-photon microscopy overcomes the limitations of fluorescent microscopy due to its much deeper penetration depth in the brain. It enabled us to determine the BBB permeability in rat brain parenchyma 100-250 microm below the pia mater. This minimally invasive technique also overcame the overestimation and uncertainties in determining solute diffusion coefficients in other invasive methods.;In cerebrovascular diseases, the BBB is compromised and its permeability is increased by various chemical stimuli, among which, vascular endothelial growth factor (VEGF) has been known to promote BBB leakage by disrupting endothelial tight junctions. However, it is unclear how quickly and how much VEGF can increase the BBB permeability in vivo. In the second part of the dissertation, the temporal effect of VEGF on BBB permeability was first determined by using two-photon microscopy. VEGF was found to transiently increase cerebral microvessel permeability in 15-30 seconds. Next, 3,5-cyclic monophosphate (cAMP) was applied to reinforce the BBB permeability, and it was found to completely abolished the VEGF-induced hyperpermeability in cerebral microvessels.;Although the chemical stimuli transiently increases BBB permeability and can be applied to brain drug delivery, it cannot be localized in the diseased region and may induce unwanted side effects. In the third part of the thesis, the optimized focused ultrasound (FUS) combined with microbubbles were employed to rat brain and the BBB permeability were examined in the FUS sonication region. This controlled physical stimulation transiently increased the BBB permeability to dextran 155k by ~14-fold 5 min post-FUS, while FUS or MBs alone did not change the BBB permeability.