Minimally invasive molecular delivery into the brain using optical modulation of vascular permeability

Abstract

Systemic delivery of bioactive molecules in the CNS is hampered by the blood-brain barrier, which has bottlenecked noninvasive physiological study of the brain and the development of CNS drugs. Here we report that irradiation with an ultrashort pulsed laser to the blood vessel wall induces transient leakage of blood plasma without compromising vascular integrity. By combining this method with a systemic injection, we delivered target molecules in various tissues, including the brain cortex. This tool allows minimally invasive local delivery of chemical probes, nanoparticles, and viral vectors into the brain cortex. Furthermore, we demonstrated astrocyte-mediated vasodilation in vivo without opening the skull, using this method to load a calcium indicator in conjunction with label-free photoactivation of astrocytes.femtosecond pulsed laser | laser tissue interaction | molecular delivery | permeability M icrovascular endothelial cells in the brain are interconnected through complex tight junctions, forming a physiological barrier against endogenous and exogenous molecules (1). Becauee of this blood-brain barrier (BBB), nearly 100% of macromolecules and more than 98% of small molecules do not cross the blood vessel wall. Thus, exogenously introduced molecular probes are widely used in vivo to study the molecular physiology of the brain. Systemic delivery through the blood circulation would be a safe, effective, and desirable method of distributing molecular probes or drugs into the brain.Various strategies have been proposed to circumvent the BBB. A transcranial approach invasively bypasses the BBB by drilling a hole in the head and injecting probes or drugs intracerebrally or intracerebroventricularly (2). At present, intracerebral injection is the gold standard for in vivo brain experiments; however, the invasiveness of opening the skull and inserting a pipette remains controversial (3, 4). A transnasal approach can noninvasively deliver molecular probes or drugs across the nasal mucosal barrier, but is limited to lipid-soluble small molecules (5). Another approach is to chemically modify therapeutic agents so that they can traverse the BBB effectively by enhancing lipid solubility, lowering molecular weight, or taking advantage of an endogenous transporter-mediated process. Various BBB disruption methods also have been proposed, including intracarotid arterial infusion of vasoactive agents and local ultrasonic irradiation with i.v. microbubble injection (6). However, no method allows the noninvasive and spatially specific delivery of large molecules into the brain.Near-infrared femtosecond pulsed lasers have been widely used for in vivo imaging because of their deep tissue penetration, reduced scattering, and localized nonlinear absorption. These properties also have enabled noninvasive optical modulation of live cells and tissues with subcellular resolution, including the generation of intracellular calcium, dissection of intracellular organelles, transient plasma membrane permeabilization, induction of arteria...

In vivo femtosecond endosurgery: an intestinal epithelial regeneration-after-injury model

“…In this study, the femtosecond endosurgery enabled regeneration-after-injury assay of the colonic epithelium in response to the genetic intervention on Card9 gene. The endosurgery technique can be extended to other tissues in various parts in the body [16] to generate photo-induced perturbations such as tissue injury, enhanced permeability, and cell activation [12][13][14]. Image-guided femtosecond laser endosurgery is expected to be useful in a wide range of applications.…”

“…This technique has been used to ablate individual intracellular compartments, such as plasma membrane [10], chromosome, and mitochondrion in cultured mammalian cells [11]. In experimental animals, femtosecond laser surgery has been used to create micro-thrombi [12], deliver drugs [13], and control vascular tones [14]. Femtosecond laser is widely used in precision refractive surgery in the clinic [15].…”

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“…Existing treatments, such as the administration of hyperosmotic agents (e.g., mannitol) or blood vessel dilators (e.g., bradykinin), have been shown to increase BBB permeability, providing an enhanced therapeutic window lasting several hours 42,43 . On top of that, direct targeting methods using lasers, focused ultrasound, or hyperthermia have also been evaluated as an alternative way to create a transient opening in the BBB 44,45 .…”

Optical modulation of astrocyte network using ultrashort pulsed laser

“…This phenomenon allowed biological function modulation such as intracellular calcium altering in cultured cells, artery contraction in mice brain in vivo [6], and drug delivery to mice brain through blood-brain barrier opening in vivo. [7] High laser power, however, could damage to biological sample. The effect of femtosecond pulsed laser induced damage and its applications are still unclear.…”