Effects Of Blood-brain Barrier Disruption Research Articles

Obstructive Sleep Apnea, Hypercoagulability, and the Blood-Brain Barrier.

Obstructive sleep apnea (OSA) is characterized by repeated episodes of intermittent hypoxia (IH) and is recognized as an independent risk factor for vascular diseases that are mediated by a multitude of mechanistic pathophysiological cascades including procoagulant factors. The pro-coagulant state contributes to the development of blood clots and to the increase in the permeability of the blood–brain barrier (BBB). Such alteration of BBB may alter brain function and increase the risk of neurodegenerative diseases. We aim to provide a narrative review of the relationship between the hypercoagulable state, observed in OSA and characterized by increased coagulation factor activity, as well as platelet activation, and the underlying neural dysfunction, as related to disruption of the BBB. We aim to provide a critical overview of the existing evidence about the effect of OSA on the coagulation balance (characterized by increased coagulation factor activity and platelet activation) as on the BBB. Then, we will present the emerging data on the effect of BBB disruption on the risk of underlying neural dysfunction. Finally, we will discuss the potential of OSA therapy on the coagulation balance and the improvement of BBB.

Biological effects of blood-brain barrier disruption using a focused ultrasound.

With focused ultrasound (FUS) and microbubbles, BBB can be transiently disrupted with a localized and non-invasive approach. BBB disruption induced by FUS has made progressions to move forward on delivery of therapeutic agents into a brain in a specific area of brain for better treatment of neurological diseases. In addition to be used as an improvement of drug delivery, BBB disruption has been found to induce biological effects such as a clearance of protein aggregation which cause Alzheimer's disease, regulation of proteins which facilitate drug uptake, and modulation of neuronal function and neurogenesis. In this review, we discuss overview about the principles of BBB opening with FUS and milestones in these biological effects of FUS-induced BBB disruption.

Boron neutron capture therapy of brain tumors: functional and neuropathologic effects of blood-brain barrier disruption and intracarotid injection of sodium borocaptate and boronophenylalanine.

Sodium borocaptate (BSH) and boronophenylalanine (BPA) are two drugs that have been used clinically for boron neutron capture therapy (BNCT) of brain tumors. We previously have reported that hyperosmotic mannitol-induced disruption of the blood-brain barrier (BBB-D), followed by intracarotid (i.c.) administration of BPA or BSH, either individually or in combination, significantly enhanced tumor boron delivery and the efficacy of BNCT in F98 glioma bearing rats. The purpose of the present study was to determine the short-term neuropathologic consequences of this treatment and the long-term effects on motor and cognitive function, as well as the neuropathologic sequelae 1 year following neutron capture irradiation. BBB-D was carried out in non-tumor bearing Fischer rats by infusing a 25% solution of mannitol i.c. followed by i.c. injection of BPA or BSH, either individually or in combination, immediately thereafter. Animals were euthanized 2 days after compound administration, and their brains were processed for neuropathologic examination, which revealed sporadic, mild, focal neuronal degeneration, hemorrhage, and necrosis. To assess the long-term effects of such treatment followed by neutron capture irradiation, non-tumor bearing rats were subjected to BBB-D after which they were injected i.c. with BPA (25 mg B/kg body weight (b.w)) or BSH (30 mg B/kg b.w.) either individually or in combination (BPA 12.5 mg and BSH 14 mg B/kg b.w.). Two and a half hours later they were irradiated at the Medical Research Reactor, Brookhaven National Laboratory, Upton, NY, with the same physical radiation doses (5.79, 8.10 or 10.06 Gy), delivered to the brain, as those that previously had been used for our therapy experiments. The animals tolerated this procedure well, after which they were returned to Columbus, Ohio where their clinical status was monitored weekly. After 1 year, motor function was assessed using a sensitive and reliable locomotor rating scale for open field testing in rats and cognitive function was evaluated by their performance in the Morris water maze, the results of which were similar to those obtained with age matched controls. After functional evaluation, the rats were euthanized, their brains were removed, and then processed for neuropathologic examination. Subtle histopathologic changes were seen in the choroid plexuses of irradiated animals that had received BPA, BSH or saline. Radiation related ocular changes consisting of keratitis, blepharitis, conjunctivitis and cataract formation were seen with similar frequency in most rats in each treatment group. Based on these observations, and the previously reported significant therapeutic gain associated with BBB-D and i.c. injection of BSH and BPA, the present observations establish its safety in rats and suggest that further studies in large animals and humans are warranted.

Effect of hyperosmotic solutions on human brain tumour vasculature.

Reversible opening of the blood-brain barrier (BBB) has been used to increase delivery of chemotherapeutic agents into brain tumours, but it is complicated and requires general anaesthesia. Without affecting the normal BBB, and avoiding the complications of BBB modification by hyperosmotic solution, we tried an adequate minimal BBB disruption in brain tumours. Although the effect of BBB disruption on normal brain has been described, there are no reports of the effect of an impaired BBB on microcirculation. In this study, four patients underwent surgical resection of a glioblastoma multiforme (GM; n = 1), astrocytoma (n = 2), or metastatic brain tumour (n = 1). Epicerebral microcirculation was observed in the operative field. Serial fluorescein microangiograms of the tumour and peritumoural area were obtained before and after BBB disruption was introduced intra-operatively by retrograde infusion of mannitol introducing a catheter via the temporal superficial artery back to the carotid bifurcation. On the initial microangiogram, staining by the fluorescein dye was observed in the GM and metastatic tumour but not in the astrocytoma; no extravasation of fluorescein dye was observed in the peritumoural areas. After BBB disruption, fluorescein perfusion increased and extravasation of fluorescein dye from the venules was observed in the GM and the metastatic tumour and in the peritumoural area of both lesions; BBB disruption started from venules in the peritumoural area without affecting the normal brain. However, such effects were not observed in the astrocytomas after BBB disruption nor in normal brain tissue in any patient. It appears that the integrity of the BBB is less stable in the peritumoural area of GM and metastatic brain tumours than it is in astrocytomas or normal brain. Osmotic BBB disruption may offer a method for achieving global delivery of therapeutic agents to brain tumours and peritumoural areas.

Rationale for influx enhancement versus efflux blockade to increase drug exposure to the brain.

Various methods of optimizing brain exposure to polar compounds have been examined. However, direct comparisons of the potential efficacy of these methods have not been forthcoming. The present study utilized a mathematical approach to compare the efficacy of two pharmacologic methods of improving brain drug distribution: uptake enhancement and efflux blockade. In the present simulation study, the pharmacokinetics of a hypothetical marker and modifier were described by differential equations. The relationship between modifier effect on marker uptake into, or efflux from, the brain and modifier concentration in serum (uptake enhancement) or brain tissue (efflux blockade) was described by the Hill equation. Uptake enhancement increased both the rate and extent of marker penetration into the brain. Efflux blockade resulted in delayed attainment of maximum marker concentration, and prolonged marker residence, in brain tissue. Under all conditions and doses examined, uptake enhancement was more effective than efflux blockade in maximizing brain tissue exposure to the marker. Although development of agents that enhance uptake of polar compounds may be limited by the potential deleterious effects of blood-brain barrier disruption, use of this approach in theory could represent a significant advancement in the treatment of brain disorders.

Bilirubin-Induced Changes in Brain Energy Metabolism after Osmotic Opening of the Blood-Brain Barrier

Acute and residual effects of blood-brain barrier disruption and bilirubin on brain metabolism were studied in a rat model after osmotic opening of the blood-brain barrier under pentobarbital anesthesia. Arabinose (1.5 M) was infused via the right external carotid artery over 30 s, resulting in opening of the barrier within the right hemisphere. Two min later, bilirubin was infused i.v. over 3 min, raising the serum bilirubin concentration to 37-44 mg/dL (633-752 mumol/L). The animals were euthanized at 15 min or 4 h by freezing the brain in situ. Opening the blood-brain barrier produced small changes in cerebral energy metabolism in some animals at 15 min. Compared with saline-infused control animals, two out of nine rats had decreased brain phosphocreatine and three out of nine developed increased brain lactate levels. Infusion of bilirubin in rats with a disrupted blood-brain barrier produced profound decreases in brain energy metabolites, glucose, and glycogen and a markedly increased lactate/pyruvate ratio at 15 min. The markedly increased lactate in the presence of normal or low pyruvate in bilirubin-treated animals indicates accumulation of NADH and probably reflects severe mitochondrial dysfunction. Four h after the arabinose/bilirubin infusions, the barrier would be expected to be repaired and bilirubin levels were negligible, but two out of five arabinose and three out of six bilirubin rats continued to have severely altered brain metabolism indicating residual brain injury in some animals.

Distributed model for drug delivery to CSF and brain tissue.

Measurements of drug concentration in cerebrospinal fluid (CSF) provide the most accessible index of drug delivery to the brain. Our perception of the blood-brain barrier has been largely shaped by these measurements. A crucial question for the interpretation of these data is the nature of the relationships between drug concentration in CSF and the drug concentration profile in brain tissue. A distributed model for the delivery of drugs via plasma to brain tissue and CSF is presented, and the relationships between capillary exchange, tissue diffusion, and CSF turnover rate are explored. The effects of blood-brain barrier disruption on tissue and CSF concentrations are also simulated.