Blood-brain barrier alteration after microwave-induced hyperthermia is purely a thermal effect: I. Temperature and power measurements

Strategies for enhanced gene delivery to the central nervous system

The delivery of genes to the central nervous system (CNS) has been a persistent challenge due to various biological barriers. The blood-brain barrier (BBB), in particular, hampers the access of systemically injected drugs to parenchymal cells, allowing only a minimal percentage (<1%) to pass through. Recent scientific insights highlight the crucial role of the extracellular space (ECS) in governing drug diffusion. Taking into account advancements in vectors, techniques, and knowledge, the discussion will center on the most notable vectors utilized for gene delivery to the CNS. This review will explore the influence of the ECS - a dynamically regulated barrier-on drug diffusion. Furthermore, we will underscore the significance of employing remote-control technologies to facilitate BBB traversal and modulate the ECS. Given the rapid progress in gene editing, our discussion will also encompass the latest advances focused on delivering therapeutic editing in vivo to the CNS tissue. In the end, a brief summary on the impact of Artificial Intelligence (AI)/Machine Learning (ML), ultrasmall, soft endovascular robots, and high-resolution endovascular cameras on improving the gene delivery to the CNS will be provided.

Large-Volume Focused-Ultrasound Mild Hyperthermia for Improving Blood-Brain Tumor Barrier Permeability Application

Mild hyperthermia can locally enhance permeability of the blood-tumor barrier in brain tumors, improving delivery of antitumor nanodrugs. However, a clinical transcranial focused ultrasound (FUS) system does not provide this modality yet. The study aimed at the development of the transcranial FUS technique dedicated for large-volume mild hyperthermia in the brain. Acoustic pressure, multiple-foci, temperature and thermal dose induced by FUS were simulated in the brain through the skull. A 1-MHz, 114-element, spherical helmet transducer was fabricated to verify large-volume hyperthermia in the phantom. The simulated results showed that two foci were simultaneously formed at (2, 0, 0) and (−2, 0, 0) and at (0, 2, 0) and (0, −2, 0), using the phases of focusing pattern 1 and the phases of focusing pattern 2, respectively. Switching two focusing patterns at 5 Hz produced a hyperthermic zone with an ellipsoid of 7 mm × 6 mm × 11 mm in the brain and the temperature was 41–45 °C in the ellipsoid as the maximum intensity was 150 W/cm² and sonication time was 3 min. The phased array driven by switching two mode phases generated a 41 °C-contour region of 10 ± 1 mm × 8 ± 2 mm × 13 ± 2 mm in the phantom after 3-min sonication. Therefore, we have demonstrated our developed FUS technique for large-volume mild hyperthermia.

Hyperthermia Treatment Planning Including Convective Flow in Cerebrospinal Fluid for Brain Tumour Hyperthermia Treatment Using a Novel Dedicated Paediatric Brain Applicator

Hyperthermia therapy (40-44 °C) is a promising option to increase efficacy of radiotherapy/chemotherapy for brain tumours, in particular paediatric brain tumours. The Chalmers Hyperthermia Helmet is developed for this purpose. Hyperthermia treatment planning is required for treatment optimisation, but current planning systems do not involve a physically correct model of cerebrospinal fluid (CSF). This study investigates the necessity of fluid modelling for treatment planning. We made treatments plans using the Helmet for both pre-operative and post-operative cases, comparing temperature distributions predicted with three CSF models: a convective "fluid" model, a non-convective "solid" CSF model, and CSF models with increased effective thermal conductivity ("high-k"). Treatment plans were evaluated by T90, T50 and T10 target temperatures and treatment-limiting hot spots. Adequate heating is possible with the helmet. In the pre-operative case, treatment plan quality was comparable for all three models. In the post-operative case, the high-k models were more accurate than the solid model. Predictions to within ±1 °C were obtained by a 10-20-fold increased effective thermal conductivity. Accurate modelling of the temperature in CSF requires fluid dynamics, but modelling CSF as a solid with enhanced effective thermal conductivity might be a practical alternative for a convective fluid model for many applications.

A Bioinspired Platform for Effective Delivery of Protein Therapeutics to the Central Nervous System

Central nervous system (CNS) diseases are the leading cause of morbidity and mortality; their treatment, however, remains constrained by the blood-brain barrier (BBB) that impedes the access of most therapeutics to the brain. A CNS delivery platform for protein therapeutics, which is achieved by encapsulating the proteins within nanocapsules that contain choline and acetylcholine analogues, is reported herein. Mediated by nicotinic acetylcholine receptors and choline transporters, such nanocapsules can effectively penetrate the BBB and deliver the therapeutics to the CNS, as demonstrated in mice and non-human primates. This universal platform, in general, enables the delivery of any protein therapeutics of interest to the brain, opening a new avenue for the treatment of CNS diseases.

Overcoming the Blood-Brain Barrier: The Role of Nanomaterials in Treating Neurological Diseases

Therapies directed toward the central nervous system remain difficult to translate into improved clinical outcomes. This is largely due to the blood-brain barrier (BBB), arguably the most tightly regulated interface in the human body, which routinely excludes most therapeutics. Advances in the engineering of nanomaterials and their application in biomedicine (i.e., nanomedicine) are enabling new strategies that have the potential to help improve our understanding and treatment of neurological diseases. Herein, the various mechanisms by which therapeutics can be delivered to the brain are examined and key challenges facing translation of this research from benchtop to bedside are highlighted. Following a contextual overview of the BBB anatomy and physiology in both healthy and diseased states, relevant therapeutic strategies for bypassing and crossing the BBB are discussed. The focus here is especially on nanomaterial-based drug delivery systems and the potential of these to overcome the biological challenges imposed by the BBB. Finally, disease-targeting strategies and clearance mechanisms are explored. The objective is to provide the diverse range of researchers active in the field (e.g., material scientists, chemists, engineers, neuroscientists, and clinicians) with an easily accessible guide to the key opportunities and challenges currently facing the nanomaterial-mediated treatment of neurological diseases.

Focused shockwave induced blood-brain barrier opening and transfection

Despite extensive efforts in recent years, the blood-brain barrier (BBB) remains a significant obstacle for drug delivery. This study proposes using a clinical extracorporeal shockwave instrument to open the BBB, combined with a laser assisted bi-axial locating platform to achieve non-invasive, controllable-focus and reversible BBB opening in the brains of rats. Under shockwave treatment with an intensity level of 5 (P^-9.79 MPa, energy flux density (EFD) 0.21 mJ/mm²) and a pulse repetition frequency of 5 Hz, the BBB could be opened after 50 shocks without the use of an ultrasound contrast agent. With the proposed method, the BBB opening can be precisely controlled in terms of depth, size and location. Moreover, a shockwave based gene transfection was demonstrated using a luciferase gene.

The effects of microwave radiation on rabbit's retina

Purpose

Mobile cell phones are used extensively these days, and their microwave (MW) radiation has been shown to affect the eye. The purpose of the present study was to evaluate the effects of MW radiation on rabbit retina.

Methods

This experimental study (concluded in 2015) was conducted on 40 adult white New Zealand rabbits. A Global System for Mobile Communications (GSM) cell phone simulator was used for MW irradiation. The rabbits were randomized into five groups (8 in each) and treated as follows: Group 1: no irradiation (sham); Group 2: irradiation at 10 cm for 1 day; Group 3: irradiation at 30 cm for 1 day; Group 4: irradiation at 10 cm for 3 days; and Group 5: irradiation at 30 cm for 3 days. Scotopic and photopic electroretinography (ERG) responses were obtained at baseline and 7 days after the last exposure. Then all the rabbits were euthanized, and their eyes were enucleated and sent for pathology examination. Kruskal–Wallis and Chi-Square tests were used to evaluate intergroup differences in ERG parameters and histological findings, respectively.

Results

ERG responses obtained 7 days after irradiation did not show any statistically significant difference between the groups (P > 0.1, for all tested parameters). There were statistically non-significant trends toward greater changes in the MW irradiated eyes. In pathological examination, retina was normal with no sign of degeneration or infiltration. Ciliary body congestion was observed in greater fraction of those who received higher MW doses. (P = 0.005).

Conclusions

Histopathologically, cell phone simulated MW irradiation had no significant detrimental effect on the retina. However, ciliary body congestion was observed in greater fraction of those who received higher MW doses. Although there was no significant difference between post-treatment mean ERG values, there were statistically non-significant trends toward greater changes in the MW irradiated eyes.

Noninvasive and targeted delivery of therapeutics to the brain using focused ultrasound

The range of therapeutic treatment options for central nervous system (CNS) diseases is greatly limited by the blood-brain barrier (BBB). While a variety of strategies to circumvent the blood-brain barrier for drug delivery have been investigated, little clinical success has been achieved. Focused ultrasound (FUS) is a unique approach whereby the transcranial application of acoustic energy to targeted brain areas causes a noninvasive, safe, transient, and targeted opening of the BBB, providing an avenue for the delivery of therapeutic agents from the systemic circulation into the brain. There is a great need for viable treatment strategies for CNS diseases, and we believe that the preclinical success of this technique should encourage a rapid movement towards clinical testing. In this review, we address the versatile applications of FUS-mediated BBB opening, the safety profile of the technique, and the physical and biological mechanisms that drive this process. This article is part of the Special Issue entitled "Beyond small molecules for neurological disorders".

Alternating magnetic field-induced hyperthermia increases iron oxide nanoparticle cell association/uptake and flux in blood-brain barrier models

PURPOSE

Superparamagnetic iron oxide nanoparticles (IONPs) are being investigated for brain cancer therapy because alternating magnetic field (AMF) activates them to produce hyperthermia. For central nervous system applications, brain entry of diagnostic and therapeutic agents is usually essential. We hypothesized that AMF-induced hyperthermia significantly increases IONP blood-brain barrier (BBB) association/uptake and flux.

METHODS

Cross-linked nanoassemblies loaded with IONPs (CNA-IONPs) and conventional citrate-coated IONPs (citrate-IONPs) were synthesized and characterized in house. CNA-IONP and citrate-IONP BBB cell association/uptake and flux were studied using two BBB Transwell(®) models (bEnd.3 and MDCKII cells) after conventional and AMF-induced hyperthermia exposure.

RESULTS

AMF-induced hyperthermia for 0.5 h did not alter CNA-IONP size but accelerated citrate-IONP agglomeration. AMF-induced hyperthermia for 0.5 h enhanced CNA-IONP and citrate-IONP BBB cell association/uptake. It also enhanced the flux of CNA-IONPs across the two in vitro BBB models compared to conventional hyperthermia and normothermia, in the absence of cell death. Citrate-IONP flux was not observed under these conditions. AMF-induced hyperthermia also significantly enhanced paracellular pathway flux. The mechanism appears to involve more than the increased temperature surrounding the CNA-IONPs.

CONCLUSIONS

Hyperthermia induced by AMF activation of CNA-IONPs has potential to increase the BBB permeability of therapeutics for the diagnosis and therapy of various brain diseases.

Drug delivery strategies to enhance the permeability of the blood-brain barrier for treatment of glioma

Gliomas are amongst the most insidious and destructive types of brain cancer and are associated with a poor prognosis, frequent recurrences, and extremely high lethality despite combination treatment of surgery, radiotherapy, and chemotherapy. The existence of the blood–brain barrier (BBB) restricts the delivery of therapeutic molecules into the brain and offers the clinical efficacy of many pharmaceuticals that have been demonstrated to be effective for other kinds of tumors. This challenge emphasizes the need to be able to deliver drugs effectively across the BBB to reach the brain parenchyma. Enhancement of the permeability of the BBB and being able to transport drugs across it has been shown to be a promising strategy to improve drug absorption and treatment efficacy. This review highlights the innovative technologies that have been introduced to enhance the permeability of the BBB and to obtain an optimal distribution and concentration of drugs in the brain to treat gliomas, such as nanotechniques, hyperthermia techniques, receptor-mediated transport, cell-penetrating peptides, and cell-mediated delivery.

Methamphetamine effects on blood-brain barrier structure and function

Methamphetamine (Meth) is a widely abuse psychostimulant. Traditionally, studies have focused on the neurotoxic effects of Meth on monoaminergic neurotransmitter terminals. Recently, both in vitro and in vivo studies have investigated the effects of Meth on the BBB and found that Meth produces a decrease in BBB structural proteins and an increase in BBB permeability to various molecules. Moreover, preclinical studies are validated by clinical studies in which human Meth users have increased concentrations of toxins in the brain. Therefore, this review will focus on the structural and functional disruption of the BBB caused by Meth and the mechanisms that contribute to Meth-induced BBB disruption. The review will reveal that the mechanisms by which Meth damages dopamine and serotonin terminals are similar to the mechanisms by which the blood-brain barrier (BBB) is damaged. Furthermore, this review will cover the factors that are known to potentiate the effects of Meth (McCann et al., 1998) on the BBB, such as stress and HIV, both of which are co-morbid conditions associated with Meth abuse. Overall, the goal of this review is to demonstrate that the scope of damage produced by Meth goes beyond damage to monoaminergic neurotransmitter systems to include BBB disruption as well as provide a rationale for investigating therapeutics to treat Meth-induced BBB disruption. Since a breach of the BBB can have a multitude of consequences, therapies directed toward the treatment of BBB disruption may help to ameliorate the long-term neurodegeneration and cognitive deficits produced by Meth and possibly even Meth addiction.

Treatment of malignant glioma using hyperthermia

Thirty pathologically diagnosed patients with grade III–IV primary or recurrent malignant glioma (tumor diameter 3–7 cm) were randomly divided into two groups. The control group underwent conventional radiotherapy and chemotherapy. In the hyperthermia group, primary cases received hyperthermia treatment, and patients with recurrent tumors were treated with hyperthermia in com-bination with radiotherapy and chemotherapy. Hyperthermia treatment was administered using a 13.56-MHz radio frequency hyperthermia device. Electrodes were inserted into the tumor with the aid of a CT-guided stereotactic apparatus and heat was applied for 1 hour. During 3 months after hyperthermia, patients were evaluated with head CT or MRI every month. Gliomas in the hyper-thermia group exhibited growth retardation or growth termination. Necrosis was evident in 80% of the heated tumor tissue and there was a decrease in tumor diameter. Our findings indicate that ra-dio frequency hyperthermia has a beneficial effect in the treatment of malignant glioma.

Modern methods for delivery of drugs across the blood-brain barrier

The blood-brain barrier (BBB) is a highly regulated and efficient barrier that provides a sanctuary to the brain. It is designed to regulate brain homeostasis and to permit selective transport of molecules that are essential for brain function. Unfortunately, drug transport to the brain is hampered by this almost impermeable, highly selective and well coordinated barrier. With progress in molecular biology, the BBB is better understood, particularly under different pathological conditions. This review will discuss the barrier issue from a biological and pathological perspective to provide a better insight to the challenges and opportunities associated with the BBB. Modern methods which can take advantage of these opportunities will be reviewed. Applications of nanotechnology in drug transport, receptor-mediated targeting and transport, and finally cell-mediated drug transport will also be covered in the review. The challenge of delivering an effective therapy to the brain is formidable; solutions will likely involve concerted multidisciplinary approaches that take into account BBB biology as well as the unique features associated with the pathological condition to be treated.

Towards MR-navigable Nanorobotic Carriers for Drug Delivery into the Brain

Magnetic Resonance Navigation (MRN) relies on Magnetic Nanoparticles (MNPs) embedded in microcarriers or microrobots to allow the induction of a directional propelling force by 3-D magnetic gradients. These magnetic gradients are superposed on a sufficiently high homogeneous magnetic field (e.g. the Bo field of a MR scanner) to achieve maximum propelling force through magnetization saturation of the MNPs. As previously demonstrated by our group, such technique was successful at maintaining microcarriers along a planned trajectory in the blood vessels based on tracking information gathered using Magnetic Resonance Imaging (MRI) sequences from artifacts caused by the same MNPs. Besides propulsion and tracking, the same MNPs can be synthesized with characteristics that can allow for the diffusion of therapeutic cargo carried by these MR-navigable carriers through the Blood Brain Barrier (BBB) using localized hyperthermia without compromising the MRN capabilities. In the present study, localized hyperthermia induced by an alternating magnetic field (AC field) is investigated for the purpose of transient controlled disruption of the BBB and hence local delivery of therapeutic agents into the brain. Here, an external heating apparatus was used to impose a regional heat shock on the skull of a living mouse model. The effect of heat on the permeability of the BBB was assessed using histological observation and tissue staining by Evans blue dye. Results show direct correlation between hyperthermia and BBB leakage as well as its recovery from thermal damage. Therefore, in addition to on-command propulsion and remote tracking, the proposed navigable agents could be suitable for controlled opening of the BBB by hyperthermia and selective brain drug delivery.

The effects of prolonged endurance exercise on the neurological system in horses

Horses compete routinely in endurance-type activities. Many of the various pathophysiological mechanisms which arise during endurance exercise have implications for the health and function of the neurological system. The development of centrally-mediated fatigue is a normal homeostatic physiological event with several possible mechanisms. Development of pathophysiological phenomena such as cerebral oedema may be near-terminal events during or after endurance exhaustion. Cellular damage resulting in cytotoxic cerebral oedema may result from decreases in circulating blood volume (dehydration), blood pressure, oxygen, and glucose, or increases in brain temperature. Vasogenic cerebral oedema arises from changes in cerebral vascular perfusion, tone, and permeability. Increased vascular permeability results from increased brain temperature, poor vascular integrity due to severe dehydration, disseminated intravascular coagulation due to hemoconcentration or endotoxemia, and iatrogenic overhydration during therapy. Clinical signs of intracranial disease after endurance exercise include staggering, shaking, ataxia, paresis, poor tongue tone, facial twitching, collapse, recumbency, seizures, and death. Treatment should include active and aggressive cooling, intravenous polyionic fluids, acid-base imbalance correction, intravenous glucose and calcium supplementation, non-steroidal anti-inflammatory agents once the patient is better hydrated, intra-nasal oxygen therapy if practicable, and achievement of a non-dependent head posture to prevent jugular venous hypertension and further increases in intracranial pressure. The prognosis for central fatigue is good with appropriate supportive care, but the prognosis for successful treatment of cerebral oedema must be considered guarded at best. Prevention is critical and must be through incorporation of mandatory rest stops with sufficient length and veterinary monitoring to allow prevention and detection of exhaustion, excessive dehydration, and neurological signs. Management flexibility in shortening or postponing rides in hot and humid conditions, mandated use of aggressive cooling techniques, and more restrictive entry criteria for upper level Fédération Equestre Internationale races should all be considered as viable options for optimising the safety of endurance horses.

Contrast-enhanced in vivo magnetic resonance microscopy of the mouse brain enabled by noninvasive opening of the blood-brain barrier with ultrasound

The use of contrast agents for neuroimaging is limited by the blood-brain barrier (BBB), which restricts entry into the brain. To administer imaging agents to the brain of rats, intracarotid infusions of hypertonic mannitol have been used to open the BBB. However, this technically challenging approach is invasive, opens only a limited region of the BBB, and is difficult to extend to mice. In this work, the BBB was opened in mice, using unfocused ultrasound combined with an injection of microbubbles. This technique has several notable features: it (a) can be performed transcranially in mice; (b) takes only 3 min and uses only commercially available components; (c) opens the BBB throughout the brain; (d) causes no observed histologic damage or changes in behavior (with peak-negative acoustic pressures of 0.36 MPa); and (e) allows recovery of the BBB within 4 h. Using this technique, Gadopentetate Dimeglumine (Gd-DTPA) was administered to the mouse brain parenchyma, thereby shortening T(1) and enabling the acquisition of high-resolution (52 × 52 × 100 micrometers(3)) images in 51 min in vivo. By enabling the administration of both existing anatomic contrast agents and the newer molecular/sensing contrast agents, this technique may be useful for the study of mouse models of neurologic function and pathology with MRI.

Local exposure of the rat cortex to radiofrequency electromagnetic fields increases local cerebral blood flow along with temperature

Few studies have shown that local exposure to radiofrequency electromagnetic fields (RF) induces intensity-dependent physiological changes, especially in the brain. The aim of the present study was to detect reproducible responses to local RF exposure in the parietal cortex of anesthetized rats and to determine their dependence on RF intensity. The target cortex tissue was locally exposed to 2-GHz RF using a figure-eight loop antenna within a range of averaged specific absorption rates (10.5, 40.3, 130, and 263 W/kg averaged over 4.04 mg) in the target area. Local cerebral blood flow (CBF) and temperatures in three regions (target area, rectum, and calf hypodermis) were measured using optical fiber blood flow meters and thermometers during RF exposure. All parameters except for the calf hypodermis temperature increased significantly in exposed animals compared with sham-exposed ones during 18-min exposures. Dependence of parameter values on exposure intensity was analyzed using linear regression models. The elevation of local CBF was correlated with temperature rise in both target and rectum at the end of RF exposure. However, the local CBF elevation seemed to be elevated by the rise in target temperature, but not by that of the rectal temperature, in the early part of RF exposure or at low-intensity RF exposure. These findings suggest that local RF exposure of the rat cortex drives a regulation of CBF accompanied by a local temperature rise, and our findings may be helpful for discussing physiological changes in the local cortex region, which is locally exposed to RF.

Effects of 915 MHz electromagnetic-field radiation in TEM cell on the blood-brain barrier and neurons in the rat brain

The aim of this study was to determine whether albumin leakage and dark neurons were present in rat brains 14 and 50 days after a single 2-h exposure to a 915 MHz electromagnetic field, as reported by Salford et al. (Environ. Health Perspect. 111, 881-883, 203). Sixty-four male F344 rats (12 weeks old) were exposed to a 915 MHz electromagnetic field at whole-body average specific absorption rates of 0, 0.02, 0.2 and 2.0 W/kg in TEM cells for 2 h, following the protocol reported by Salford et al. The brains were examined histologically and immunohistochemically. No albumin immunoreactivity was observed in the exposed groups. In addition, dark neurons, assessed using hematoxylin and eosin staining, were rarely present, with no statistically significant difference between exposed and sham-exposed animals. This study thus failed to confirm the results of Salford et al.

Radiofrequency-radiation exposure does not induce detectable leakage of albumin across the blood-brain barrier

The blood-brain barrier (BBB) consists of tight junctions between the endothelial cells that line the capillaries in the central nervous system. This structure protects the brain, and neurological damage could occur if it is compromised. Several publications by researchers at Lund University have reported alterations in the BBB after exposure to low-power 915 MHz energy. These publications increased the level of concern regarding the safety of wireless communication devices such as mobile phones. We performed a confirmation study designed to determine whether the BBB is altered in rats exposed in a transverse electromagnetic (TEM) transmission line cell to 915 MHz energy at parameters similar to those in the Lund University studies. Unanesthetized rats were exposed for 30 min to either continuous-wave or modulated (16 or 217 Hz) 915 MHz energy at power levels resulting in whole-body specific absorption rates (SARs) of 0.0018-20 W/kg. Albumin immunohistochemistry was performed on perfused brain tissue sections to determine the integrity of the BBB. Chi-square analysis revealed no significant increase in albumin extravasation in any of the exposed animals compared to the sham-exposed or home cage control animals.

Radiofrequency and extremely low-frequency electromagnetic field effects on the blood-brain barrier

During the last century, mankind has introduced electricity and during the very last decades, the microwaves of the modern communication society have spread a totally new entity--the radiofrequency fields--around the world. How does this affect biology on Earth? The mammalian brain is protected by the blood-brain barrier, which prevents harmful substances from reaching the brain tissue. There is evidence that exposure to electromagnetic fields at non thermal levels disrupts this barrier. In this review, the scientific findings in this field are presented. The result is a complex picture, where some studies show effects on the blood-brain barrier, whereas others do not. Possible mechanisms for the interactions between electromagnetic fields and the living organisms are discussed. Demonstrated effects on the blood-brain barrier, as well as a series of other effects upon biology, have caused societal anxiety. Continued research is needed to come to an understanding of how these possible effects can be neutralized, or at least reduced. Furthermore, it should be kept in mind that proven effects on biology also should have positive potentials, e.g., for medical use.

Brief heat shock affects the permeability and thermotolerance of an in vitro blood-brain barrier model of porcine brain microvascular endothelial cells

Heat shock was imposed on an in vitro model of the blood-brain barrier (BBB) by submersion into prewarmed growth medium. Transendothelial electrical resistance (TEER) was used to assess the functional integrity of the endothelial barrier. Consequences of the heat shock were highly dependent upon the temperature and duration of exposure. Temperatures below 47 degrees C required more than 30 s of exposure to significantly impair barrier function, but full recovery occurred within 1 h. When the temperature was 50-54 degrees C, an exposure of only 10 s significantly diminished barrier function. Ten seconds of 51 degrees C or 54 degrees C caused a significant loss of barrier function (45% and 80%, respectively). Full recovery from the 51 degrees C shock occurred within 5 min, while recovery from the 54 degrees C shock required more than 10 h. When the temperature was 57 degrees C or greater, a 3-s duration diminished barrier function by 80%. In response to heat shock, the brain microvascular endothelial cells developed thermotolerance and over-compensated in their ability to form a physiological barrier. The BBB models lost more than 60% of barrier function when initially exposed to 53 degrees C for 5 s but lost only 30% of function when exposed to the same treatment 24 h later. The BBB models over-compensated to produce a reinforced barrier with double the original TEER following repeated application of heat treatment (57 degrees C for 3 s). In vivo experiments will require exquisite manipulation of the temperature and duration in order to achieve the desired opening of the BBB in therapeutic applications.

Interstitial Hyperthermia With Intra-arterial Injection of Adriamycin for Malignant Glioma

A new method for treating malignant glioma by concurrent intra-arterial injection of adriamycin during thermotherapy was performed in seven patients with malignant glioma, four males and three females, with five cases of glioblastoma and two of anaplastic oligodendroglioma. Adriamycin was intra-arterially injected at a dose of 20 mg via the common carotid artery during thermotherapy. The heating procedure was repeated three times combined with chemotherapy in one therapy course, and a total of nine therapy courses were performed in the seven patients. All patients tolerated the protocol well. Based on post-therapy computed tomography, five of the therapy courses achieved partial response, one course resulted in disease progression, and the remaining three courses showed no change. The median time to progression was 3.4 months and the overall median length of survival following stereotactic biopsy was 13.2 months. Facial flushing was observed during eight therapy courses, and extensive alopecia in six therapy courses. Intracystic concentrations of adriamycin were determined in three patients, and marked increases were observed. Intra-arterial injection chemotherapy during hyperthermia is a promising therapeutic method for treatment of malignant glioma with few adverse effects.

Blood–brain barrier and electromagnetic fields: Effects of scopolamine methylbromide on working memory after whole-body exposure to 2.45GHz microwaves in rats

We first verified that our 12-arm radial maze test enabled demonstration of memory deficits in rats treated with the muscarinic antagonist scopolamine hydrobromide (0.5mg/kg, i.p.). We then investigated whether a systemically-injected quaternary-ammonium derivate of this antagonist (scopolamine methylbromide; MBR), which poorly crosses the blood-brain barrier (BBB), altered maze performance after a 45-min exposure to 2.45 GHz electromagnetic field (EMF; 2 micros pulse width, 500 pps, whole-body specific energy absorption rate [SAR] of 2.0 W/kg, +/-2dB and brain averaged SAR of 3.0 W/kg, +/-3 dB); if observed, such an alteration would reflect changes in BBB permeability. The drug was injected before or after exposure. Controls were naive rats (no experience of the exposure device) and sham-exposed rats (experience of the exposure device without microwaves). In a final approach, rats were subjected to i.v. injections of Evans blue, a dye binding serum albumin, before or after EMF exposure. Whether scopolamine MBR was injected before or after exposure, the exposed rats did not perform differently from their naive or sham-exposed counterparts. Thus, EMFs most probably failed to disrupt the BBB. This conclusion was further supported by the absence of Evans blue extravasation into the brain parenchyma of our exposed rats.

Microwave effects on the nervous system

Studies have evaluated the electroencephalography (EEG) of humans and laboratory animals during and after Radiofrequency (RF) exposures. Effects of RF exposure on the blood-brain barrier (BBB) have been generally accepted for exposures that are thermalizing. Low level exposures that report alterations of the BBB remain controversial. Exposure to high levels of RF energy can damage the structure and function of the nervous system. Much research has focused on the neurochemistry of the brain and the reported effects of RF exposure. Research with isolated brain tissue has provided new results that do not seem to rely on thermal mechanisms. Studies of individuals who are reported to be sensitive to electric and magnetic fields are discussed. In this review of the literature, it is difficult to draw conclusions concerning hazards to human health. The many exposure parameters such as frequency, orientation, modulation, power density, and duration of exposure make direct comparison of many experiments difficult. At high exposure power densities, thermal effects are prevalent and can lead to adverse consequences. At lower levels of exposure biological effects may still occur but thermal mechanisms are not ruled out. It is concluded that the diverse methods and experimental designs as well as lack of replication of many seemingly important studies prevents formation of definite conclusions concerning hazardous nervous system health effects from RF exposure. The only firm conclusion that may be drawn is the potential for hazardous thermal consequences of high power RF exposure.

Effects of electromagnetic radiation of mobile phones on the central nervous system

With the increasing use of mobile communication, concerns have been expressed about the possible interactions of electromagnetic radiation with the human organism and, in particular, the brain. The effects on neuronal electrical activity, energy metabolism, genomic responses, neurotransmitter balance, blood-brain barrier permeability, cognitive function, sleep, and various brain diseases including brain tumors are reviewed. Most of the reported effects are small as long as the radiation intensity remains in the nonthermal range, and none of the research reviewed gives an indication of the mechanisms involved at this range. However, health risks may evolve from indirect consequences of mobile telephony, such as the sharply increased incidence rate of traffic accidents caused by telephony during driving, and possibly also by stress reactions which annoyed bystanders may experience when cellular phones are used in public places. These indirect health effects presumably outweigh the direct biological perturbations and should be investigated in more detail in the future.

Temperature dependence of synaptic responses in guinea pig hippocampal CA1 neurons in vitro

1. Temperature-dependent properties of synaptic transmission were studied by recording orthodromic responses of the population spike and excitatory postsynaptic potential in CA1 pyramidal neurons of guinea pig hippocampal slices. 2. Increasing the temperature of the perfusing medium from 30 to 43 degrees C resulted in a decrease in the amplitude of the population spike (A-PS) and a reduced slope of the excitatory postsynaptic potential (S-EPSP). Bath application of the gamma-aminobutyric acid receptor antagonist, picrotoxin, or a change in the calcium concentration of the perfusate did not affect the A-PS during heating. 3. Increasing the strength of the synaptic input to that eliciting a PS with an amplitude 50, 75, or 100% of maximal at 30 degrees C resulted in a significant increase in the A-PS during the middle phase of hyperthermia (35-39 degrees C). 4. The long-term potentiation (LTP) induced at either 30 or 37 degrees C showed the same percentage increase in both the amplitude of the population spike and the S-EPSP after delivery of a tetanus (100 Hz. 100 pulses) to CA1 synapses. 5. The results of the present study, therefore, indicate that the decrease in CA1 field potential was linearly related to the temperature of the slice preparation, while LTP was induced in these responses during heating from 30 to 37 degrees C.

Effect of long-term mobile communication microwave exposure on vascular permeability in mouse brain

AIMS

To study the effect of long-term exposure to global system for mobile communication (GSM) radiofrequency fields on vascular permeability in murine brains.

METHODS

Using a purpose-designed exposure system at 900 MHz, mice were given a 60-minute far-field, whole body exposure on each of 5 days per week for 104 weeks at specific absorption rates (SAR) of 0.25, 1.0,2.0 and 4.0 W/kg. Control mice were sham-exposed or permitted free movement in a cage to evaluate any stress-related effects. Albumin immunohistochemistry was used to detect increased vascular permeability and the efficacy of the vascular tracer was confirmed with a positive control group exposed to a clostridial toxin known to increase vascular permeability in the brain.

RESULTS

In all exposed and control groups, albumin extravasation was minimal, often leptomeningeal, and was deemed insignificant as a maximum of three capillaries or venules in a given brain showed leakage from the very many blood vessels present in the three coronal brain sections.

CONCLUSIONS

These results suggest that prolonged exposure to mobile telephone-type radiation produces negligible disruption to blood-brain barrier integrity at the light microscope level using endogenous albumin as a vascular tracer.

Induction of micronuclei in human lymphocytes exposed in vitro to microwave radiation

Increasing applications of electromagnetic fields are of great concern with regard to public health. Several in vitro studies have been conducted to detect effects of microwave exposure on the genetic material leading to negative or questionable results. The micronucleus (MN) assay which is proved to be a useful tool for the detection of radiation exposure-induced cytogenetic damage was used in the present study to investigate the genotoxic effect of microwaves in human peripheral blood lymphocytes in vitro exposed in G(0) to electromagnetic fields with different frequencies (2.45 and 7.7GHz) and power density (10, 20 and 30mW/cm(2)) for three times (15, 30 and 60min). The results showed for both radiation frequencies an induction of micronuclei as compared to the control cultures at a power density of 30mW/cm(2) and after an exposure of 30 and 60min. Our study would indicate that microwaves are able to cause cytogenetic damage in human lymphocytes mainly for both high power density and long exposure time.

Tolerance of guinea pig hippocampal slice CA1 neurons to hyperthermia evaluated by orthodromic and antidromic responses

The tolerance of electrical responses in the CA1 neurons of guinea pig hippocampal slices to elevated temperatures was studied by recording orthodromic and antidromic responses of the population spike (PS). Increasing the temperature of the perfusing medium from 30 degrees C to 49 degrees C resulted in a decreased amplitude of both the orthodromic and antidromic PS, the former disappearing at 42.0 +/- 1.8 degrees C and the latter at 46.2 +/- 1.3 degrees C (n = 8 for both). When the temperature was increased to 44 degrees C, maintained at this level for less than 27 min, then lowered to 30 degrees C, both the orthodromic and antidromic PS recovered within 60 min. When the temperature was increased to 45-49 degrees C, marked irreversible effects were seen with the orthodromic PS, recovery being dependent on the maximum temperature and duration of exposure, the change becoming irreversible after 13 min at 45 degrees C, 6 min at 46 degrees C, 4 min at 47 degrees C or 2.5 min at 48 degrees C. In contrast, the antidromic PS, recorded simultaneously, recovered on lowering the temperature to 30 degrees C in all cases tested, except when the temperature was increased to 46 degrees C and maintained at this level for 25-27 min. These results indicate that, in CA1 neurons, temperatures above 44 degrees C have more potent irreversible effects on synaptic transmission than on axonal or somal function.

Neurological effects of microwave exposure related to mobile communication

Due to the wide and growing use of mobile communication, there is increasing concern about the interactions of electromagnetic radiation with the human organism, and, in particular, with the brain. In the present report, experimental studies on putative electrophysiological, biochemical and morphological effects of continuous or pulsed microwave radiation are briefly reviewed. Such effects have been described in vitro and in vivo using animals and humans. Particularly, effects on neuronal electrical activity, cellular calcium homeostasis, energy metabolism, genomic responses, neurotransmitter balance and blood-brain barrier permeability have been reported. However, some results have either been disputed, since experimental replication led to contradictory findings, or been related to procedural side effects. Since neurological disturbances induced by mobile telephone devices would be of considerable interest for public health, the authors recognize that further experimental studies, involving strict positive and negative control conditions, will be required in the future. At the present state of knowledge there is no positive evidence that pulsed or continuous microwave exposure in the non-thermal range confers elevated risk to the health of the brain.

Sequential changes in cerebral blood flow, early neuropathological consequences and blood-brain barrier disruption following radiofrequency-induced localized hyperthermia in the rat

We investigated the temperature distribution, early histological changes, blood brain barrier (BBB) disruption and sequential changes in cerebral blood flow (CBF) following hyperthermia ranging from 37 to 45 degrees C in a new rat model of radiofrequency-induced localized cerebral hyperthermia. Significant histological changes and BBB disruption were observed in brain regions heated to 43 degrees C and above. In the cortex heated to 41 degrees C, the CBF doubled 20 min after hyperthermia induction, and then returned gradually to the pre-hyperthermic level. In the cortex heated to 43 degrees C, the CBF increased to 134% of the baseline level 10 min after hyperthermia induction, and then fell gradually to reach its minimum level (31% of the baseline level). In the cortex heated to 45 degrees C, the CBF decreased immediately after hyperthermia induction to reach 10% of the baseline level. The results indicate that hyperthermia-induced cellular injury in the central nervous system is associated with cerebral ischaemia and the threshold temperature for such injury is 43 degrees C. This model is useful for investigating the effects of hyperthermia on various cerebral functions and the CBF changes demonstrated in the present study may provide key information for the analysis of other cerebral functions.

Conductive interstitial hyperthermia in the treatment of intracranial metastatic disease

BACKGROUND

Intracranial metastases commonly complicate oncologic care affecting 140,000 patients per year in the United States. Treatment of these tumors is difficult and often unsuccessful. Hyperthermia is a treatment alternative that has shown promise in treating cancer in other areas. Therefore it was employed in an attempt to provide increased tumor control in CNS metastases.

METHODS

This Phase I and Phase II clinical trial of interstitial hyperthermia with recurrent or progressive intracranial metastatic disease was undertaken to evaluate complications, delivery of heat and patient outcome.

RESULTS

Feared complications of clinically significant bleeding, increased mass, or infection from the interstitial implant and treatment did not occur. The seizures which occurred in 4 patients were controlled with additional anticonvulsants. Three venous thromboembolic events were treated medically and with percutaneously placed inferior vena cava filters. The KPS of the majority of patients declined slightly with treatment but rebounded to near baseline within several months. CT scans demonstrated decrease or stabilization of tumor volumes in 7 of the 13 patients. In 4 of these patients, regression or stabilization persisted until death from nonCNS disease.

CONCLUSIONS

Interstitial hyperthermia therapy for intracranial metastases is technically feasible and may provide increased tumor control. In this small series, it did not cause unreasonable complications. This therapy has some positive effect, but requires study of more patients before its role is definitively known. Combining hyperthermia with brachytherapy and/or chemotherapy is being evaluated.

Blood-brain barrier disturbance following localized hyperthermia in rats

We investigated the morphological effect of hyperthermia on the blood-brain barrier (BBB). The heads of rats were heated locally using flood-lamps. BBB changes were assessed morphologically with horseradish peroxidase (HRP). Histological examinations were carried out 2 and 6 h, 1 and 3 days, and 1 week after the hyperthermia. The acute thermal lesions had three zones, i.e. a necrotic zone, a reactive zone and a permeable zone of viable brain tissue. HRP extravasation was seen in the necrotic zone and the permeable zone. Electron micrographic observation revealed HRP had entered the CNS through damaged endothelial cells and disruption of the tight junctions in the necrotic zone, and through numerous pinocytotic vesicles in the permeable zone. BBB opening to HRP was observed from 6 h to 3 days after hyperthermia.

The influence of total body hyperthermia on brain haemodynamics and blood-brain barrier in dogs

This study was designed to examine the influence of total body hyperthermia (TBHT) using an extracorporeal circuit with a heat exchanger on the cerebral blood flow (CBF), intracranial pressure (ICP), brain tissue pH, cerebral autoregulation and blood-brain barrier (BBB) permeability in dogs. The rectal temperature of the dow was raised to 41.5 degrees C, maintained at 41.5-42.0 degrees C for 2 hours (HT period) and then reduced to normothermia by cooling. Regional CBF was measured by the hydrogen clearance method before heating, during the HT period and after cooling. ICP and brain tissue pH were monitored during the TBHT treatment. Autoregulation of the CBF during the HT period was assessed by measuring the regional CBF and the ICP in a state of induced hypo- or hypertension. The influence of TBHT on BBB permeability was examined using an immunohistochemical technique. The regional CBF increased from 38.1 +/- 6.5 (mean +/- SD) to 49.1 +/- 9.8 ml/100 g/min and the ICP from 10.3 +/- 4.2 to 16.8 +/- 3.4 mmHg when TBHT was raised. These returned to normal values after cooling. The regional CBF and the ICP changed in parallel with drug-induced changes of mean arterial blood pressure during the HT period. These changes suggest that autoregulation of the CBF is paralysed during the HT period. Brain tissue pH decreased rapidly when the rectal temperature exceeded 41.0 degrees C. The pH was 7.18 +/- 0.05 during the HT period and was relatively stable. The pH returned to a normal value after cooling. Immunopositive stain for albumin was not observed in heated brain tissue except for the normally leaky pineal gland and the choroid plexus, indicating preservation of BBB during TBHT. These results suggest that brain oedema may occur easily due to paralysed cerebral autoregulation when the arterial blood pressure fluctuates excessively, so arterial blood pressure must be controlled strictly during TBHT.

Experimental study on thermal damage to dog normal brain

We investigated the temperature changes and their distribution in agar phantoms and dog normal brains induced by 8 MHz radiofrequency interstitial hyperthermia and observed the histological changes, with respect to the neurons and myelinated nerve fibres, induced by the same heat source in dog normal brains. We also examined the change of blood-brain barrier permeability using Evans blue solution. The heating limits of dog normal brain were 42 degrees C for 45 min or 43 degrees C for 15 min and the breakdown of the BBB was observed at 43 degrees C for 60 min.

Permeability of the blood-brain barrier induced by 915 MHz electromagnetic radiation, continuous wave and modulated at 8, 16, 50, and 200 Hz

Biological effects of electromagnetic fields (EMF) on the blood-brain barrier (BBB) can be studied in sensitive and specific models. In a previous investigation of the permeability of the blood-brain barrier after exposure to the various EMF-components of proton magnetic resonance imaging (MRI), we found that the exposure to MRI induced leakage of Evans Blue labeled proteins normally not passing the BBB of rats [Salford et al. (1992), in: Resonance Phenomena in Biology, Oxford University Press, pp. 87-91]. In the present investigation we exposed male and female Fischer 344 rats in a transverse electromagnetic transmission line chamber to microwaves of 915 MHz as continuous wave (CW) and pulse-modulated with repetition rates of 8, 16, 50, and 200 s-1. The specific energy absorption rate (SAR) varied between 0.016 and 5 W/kg. The rats were not anesthetized during the 2-hour exposure. All animals were sacrificed by perfusion-fixation of the brains under chloral hydrate anesthesia about 1 hour after the exposure. The brains were perfused with saline for 3-4 minutes, and thereafter fixed in 4% formaldehyde for 5-6 minutes. Central coronal sections of the brains were dehydrated and embedded in paraffin and sectioned at 5 microns. Albumin and fibrinogen were demonstrated immunohistochemically. The results show albumin leakage in 5 of 62 of the controls and in 56 of 184 of the animals exposed to 915 MHz microwaves. Continuous wave resulted in 14 positive findings of 35, which differ significantly from the controls (P = 0.002).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of hyperthermia on the central nervous system: a review

Experimental data show that nervous tissue is sensitive to heat. Animal data indicate that the maximum tolerated heat dose after local hyperthermia of the central nervous system (CNS) lies in the range of 40-60 min at 42-42 x 5 degrees C or 10-30 min at 43 degrees C. No conclusions concerning the heat sensitivity of nervous tissue can be derived from clinical studies using localized hyperthermia. The choice whether or not to exceed the critical heat dose, as derived from laboratory studies, in clinical practice is very much dependent on the clinical situation such as the anatomical site and volume of the tissue involved, and prior therapy. Data on clinical application of whole body hyperthermia (WBH) show that nervous tissue can withstand a slightly higher heat dose than after localized heating, which might be the result of developing thermal resistance during treatment. Expression of thermotolerance was observed in the spinal cord of laboratory animals. After WBH in man at a maximum between 40 and 43 degrees C for 6 h-30 min CNS complications were reported, but other complications seemed to be more life-threatening. Most studies indicate that impairment of the CNS after WBH was not due to direct heat injury to the brain or spinal cord, but was secondary as a result of physiological changes. Heat, at least if applied shortly after X-rays, enhances the response of nervous tissue to radiation. Neurotoxicity of chemotherapeutic drugs does not seem to be a limiting complication in hyperthermia if combined with chemotherapy, but only few data are available. The limited clinical experience shows that safe hyperthermic treatment of CNS malignancies or tumours located close to the CNS seems feasible under appropriate technical conditions with adequate thermometry and taking the sensitivity of the surrounding normal nervous tissue into account.