Abstract
The treatment of CNS disorders suffers from the inability to deliver large therapeutic agents to the brain parenchyma due to protection from the blood-brain barrier (BBB). Herein, we investigated high-frequency pulsed electric field (HF-PEF) therapy of various pulse widths and interphase delays for BBB disruption while selectively minimizing cell ablation. Eighteen male Fisher rats underwent craniectomy procedures and two blunt-tipped electrodes were advanced into the brain for pulsing. BBB disruption was verified with contrast T1W MRI and pathologically with Evans blue dye. High-frequency irreversible electroporation cell death of healthy rodent astrocytes was investigated in vitro using a collagen hydrogel tissue mimic. Numerical analysis was conducted to determine the electric fields in which BBB disruption and cell ablation occur. Differences between the BBB disruption and ablation thresholds for each waveform are as follows: 2-2-2 s (1028 V/cm), 5-2-5 s (721 V/cm), 10-1-10 s (547 V/cm), 2-5-2 s (1043 V/cm), and 5-5-5 s (751 V/cm). These data suggest that HF-PEFs can be fine-tuned to modulate the extent of cell death while maximizing peri-ablative BBB disruption. Furthermore, numerical modeling elucidated the diffuse field gradients of a single-needle grounding pad configuration to favor large-volume BBB disruption, while the monopolar probe configuration is more amenable to ablation and reversible electroporation effects.
Highlights
The blood-brain barrier (BBB) is primarily composed of tight junction proteins and central nervous system (CNS) endothelial cells which form a protective barrier isolating systemic neurotoxins, macromolecules, and infectious particles from the brain parenchyma [1]
In the 2-2-2 μs (n = 2), 5-2-5 μs (n = 2), 2-5-2 μs (n = 2), and 5-5-5 μs (n = 2), the intracranial Evans blue dye (EBD) was 14.1 ± 0.2 μg/g, 15.2 ± 0.1 μg/g, 16.9 ± 0.1 μg/g, and 18.5 ± 0.3 μg/g, respectively. These results indicate high-frequency pulsed electric field (HF-pulsed electric fields (PEFs)) are required for a significant diffusion of EBD from systemic circulation in the brain (Figure 1b), though these measurements do not provide spatial information of the BBB disruption (BBBd) relative to the applied electric field
The effects of HF-PEF waveforms were modeled in two ways: (1) the electrical conductivity sigmoid was specific for each waveform (Table 3), and (2) the electric field threshold for BBBd, ablation, reversible electroporation, and nerve excitation were specific for each waveform and are those determined in Section 2.4 (Table 2)
Summary
The blood-brain barrier (BBB) is primarily composed of tight junction proteins (occludin and claudins) and central nervous system (CNS) endothelial cells which form a protective barrier isolating systemic neurotoxins, macromolecules, and infectious particles from the brain parenchyma [1] While this structure is critical for maintaining brain homeostasis, the BBB poses a challenge for intracranial drug delivery [2]. Passive diffusion across the BBB favors small lipid-soluble molecules, while large molecular weight solutes are transported via highly selective active transport mechanisms [3] This selectivity often leads essential drug molecules designed to target malignant cells in the brain to be screened out, presenting an obstacle for the treatment of intracranial diseases including brain cancers, Alzheimer’s disease, Parkinson’s disease, and targeting drug-resistant epileptic foci [4,5,6].
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