Cerebrovascular and metabolic effects on the rat brain of focal Nd:YAG laser irradiation

The blood-brain barrier: structure, regulation, and drug delivery

Blood-brain barrier (BBB) is a natural protective membrane that prevents central nervous system (CNS) from toxins and pathogens in blood. However, the presence of BBB complicates the pharmacotherapy for CNS disorders as the most chemical drugs and biopharmaceuticals have been impeded to enter the brain. Insufficient drug delivery into the brain leads to low therapeutic efficacy as well as aggravated side effects due to the accumulation in other organs and tissues. Recent breakthrough in materials science and nanotechnology provides a library of advanced materials with customized structure and property serving as a powerful toolkit for targeted drug delivery. In-depth research in the field of anatomical and pathological study on brain and BBB further facilitates the development of brain-targeted strategies for enhanced BBB crossing. In this review, the physiological structure and different cells contributing to this barrier are summarized. Various emerging strategies for permeability regulation and BBB crossing including passive transcytosis, intranasal administration, ligands conjugation, membrane coating, stimuli-triggered BBB disruption, and other strategies to overcome BBB obstacle are highlighted. Versatile drug delivery systems ranging from organic, inorganic, and biologics-derived materials with their synthesis procedures and unique physio-chemical properties are summarized and analyzed. This review aims to provide an up-to-date and comprehensive guideline for researchers in diverse fields, offering perspectives on further development of brain-targeted drug delivery system.

Current Update on Transcellular Brain Drug Delivery

It is well known that the presence of a blood-brain barrier (BBB) makes drug delivery to the brain more challenging. There are various mechanistic routes through which therapeutic molecules travel and deliver the drug across the BBB. Among all the routes, the transcellular route is widely explored to deliver therapeutics. Advances in nanotechnology have encouraged scientists to develop novel formulations for brain drug delivery. In this article, we have broadly discussed the BBB as a limitation for brain drug delivery and ways to solve it using novel techniques such as nanomedicine, nose-to-brain drug delivery, and peptide as a drug delivery carrier. In addition, the article will help to understand the different factors governing the permeability of the BBB, as well as various formulation-related factors and the body clearance of the drug delivered into the brain.

Laser Lesion in the Mouse Visual Cortex Induces a Stem Cell Niche-Like Extracellular Matrix, Produced by Immature Astrocytes

The mammalian central nervous system (CNS) is characterized by a severely limited regeneration capacity. Comparison with lower species like amphibians, which are able to restore even complex tissues after damage, indicates the presence of an inhibitory environment that restricts the cellular response in mammals. In this context, signals provided by the extracellular matrix (ECM) are important regulators of events like cell survival, proliferation, migration, differentiation or neurite outgrowth. Therefore, knowledge of the post-lesional ECM and of cells that produce these factors might support development of new treatment strategies for patients suffering from traumatic brain injury and other types of CNS damage. In the present study, we analyzed the surround of focal infrared laser lesions of the adult mouse visual cortex. This lesion paradigm avoids direct contact with the brain, as the laser beam passes the intact bone. Cell type-specific markers revealed a distinct spatial distribution of different astroglial subtypes in the penumbra after injury. Glial fibrillary acidic protein (GFAP) as marker for reactive astrocytes was found broadly up-regulated, whereas the more immature markers vimentin and nestin were only expressed by a subset of cells. Dividing astrocytes could be identified via the proliferation marker Ki-67. Different ECM molecules, among others the neural stem cell-associated glycoprotein tenascin-C and the DSD-1 chondroitin sulfate epitope, were found on astrocytes in the penumbra. Wisteria floribunda agglutinin (WFA) and aggrecan as markers for perineuronal nets, a specialized ECM limiting synaptic plasticity, appeared normal in the vicinity of the necrotic lesion core. In sum, expression of progenitor markers by astrocyte subpopulations and the identification of proliferating astrocytes in combination with an ECM that contains components typically associated with neural stem/progenitor cells suggest that an immature cell fate is facilitated as response to the injury.

Blood brain barrier: An overview on strategies in drug delivery, realistic in vitro modeling and in vivo live tracking

Blood brain barrier (BBB) is a group of astrocytes, neurons and endothelial cells, which makes restricted passage of various biological or chemical entities to the brain tissue. It gives protection to brain at one hand, but at the other hand it has very selective permeability for bio-actives and other foreign materials and is one of the major challenges for the drug delivery. Nanocarriers are promising to cross BBB utilizing alternative route of administration such as intranasal and intra-carotid drug delivery which bypasses BBB. In future more optimized drug delivery system can be achieved by compiling the best routes with the best carriers. Single photon emission tomography (SPECT) and different brain-on-a-chip in vitro models are being very reliable to study live in vivo tracking of BBB and its pathophysiology, respectively. In the current review we have tried to exploit mechanistically all these to understand and manage the various BBB disruptions in diseased condition along with crossing the hurdles occurring in drug or gene delivery across BBB.

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.

Locoregional opening of the rodent blood-brain barrier for paclitaxel using Nd:YAG laser-induced thermo therapy: a new concept of adjuvant glioma therapy?

BACKGROUND AND OBJECTIVES

Nd:YAG laser-induced thermo therapy (LITT) of rat brains is associated with blood-brain barrier (BBB) permeability changes. We address the question of whether LITT-induced locoregional disruption of the BBB could possibly allow a locoregional passage of chemotherapeutic agents into brain tissue to treat malignant glioma.

STUDY DESIGN/MATERIALS AND METHODS

CD Fischer rats were subject to LITT of the left forebrain. Disruption of the BBB was analyzed using Evans blue and immunohistochemistry (IH). Animals were perfused with paclitaxel, and high-pressure liquid chromatography (HPLC) was employed to analyze the content of paclitaxel in brain and plasma samples.

RESULTS

LITT induces an opening of the BBB as demonstrated by locoregional extravasation of Evans blue, C3C, fibrinogen, and IgM. HPLC proved the passage of paclitaxel across the disrupted BBB.

CONCLUSIONS

LITT induces a locoregional passage of chemotherapeutic agents into the brain tissue. This is of potential interest for the treatment of brain tumors.

Intracranial pressure waves generated by high-energy short laser pulses can cause morphological damage in remote areas: comparison of the effects of 2.1-micron Ho:YAG and 1.06-micron Nd:YAG laser irradiations in the rat brain

BACKGROUND AND OBJECTIVE

Histological effects of 2.1-micron Ho:YAG and 1.06-micron Nd:YAG laser pulses were compared in the rat brain, with special regard to areas remote from the irradiated site.

STUDY DESIGN/MATERIALS AND METHODS

Laser pulses were delivered through a 0.6-mm glass fiber, the tip of which was either introduced into the caudate nucleus (application mode I), or held at a 2-mm distance above the exposed intact dura. In the latter case, the space between the dura and the fiber tip was filled either with physiological saline (application mode II) or with air (application mode III).

RESULTS

In application modes I and II, but not in application mode III, Ho:YAG laser pulses of 1.5 J and 200 microseconds, but not Nd:YAG laser pulses with the same parameters, immediately caused morphological damage to a considerable number of neurons and axons randomly distributed among apparently normal ones in certain areas remote from the irradiated site. A decrease in the energy and an increase in the length of the pulses lowered the incidence of the remote morphological damage.

CONCLUSION

This novel finding may impose limits on the application of Ho:YAG lasers in human endoscopic neurosurgery.

Laser-induced thermal lesions in the human brain: short- and long-term appearance on MRI

PURPOSE

The purpose of our study was to investigate with MRI the development of thermal lesions in the human brain up to almost 4 years after laser-induced interstitial thermotherapy (LITT).

METHOD

Eighteen patients with brain tumors who underwent LITT entered the study.

RESULTS

In all patients the acute lesion comprised five concentric zones that showed reverse signal intensities on T1- versus T2-weighted images. Lesion development over time was uniform in 89% of the lesions. In two cases variations were observed.

CONCLUSION

The results of our MR follow-up studies showed that post-LITT, laser-induced lesions will shrink exponentially after an initial expansion without any pseudocystic effects.

Somatosensory evoked potentials modified by laser-induced lesions of the rat cortex

The effect of focal application of laser energy on the modification of somatosensory evoked potentials (SEPs) was studied in sensory cortical fields of the rat. This article describes the methodological set-up for recording of SEPs and for determining location and size of the laser-induced lesion. The results show that both the size of the lesion of the somatosensory cortex, and the suppression and time of recovery of cortical SEPs varied depending on the laser energy dose. It remains to be analyzed by further experiments if the recovery of SEPs is due to a transient dysfunction of the somatosensory cortex or if it reflects cortical plasticity.

Heat-shock protein and C-fos expression in focal microvascular brain damage

Cortical brain damage was produced in rats by a focal pulse from a Nd-YAG laser, and evolution of the lesion was evaluated at 30 min, and 2, 8, and 24 h with respect to microvascular perfusion, blood-brain barrier (BBB) permeability, and expression of both the heat-shock/stress protein, hsp72, and the c-fos proto-oncogene transcription factor. A double-labeling fluorescence technique employing intravenously injected Evans blue albumin (EBA) and fluorescein-labeled dextran was used to map and measure BBB damage and microvascular perfusion in fresh frozen brain sections. Hsp72 and c-fos mRNAs were localized by in situ hybridization, and the respective proteins were identified by immunocytochemistry. Parallel sections were stained for glial fibrillary acidic protein and for routine histologic examination. Striking hsp72 mRNA expression was evident by 2 h in an approximately 300 microns wide rim surrounding an area of expanding BBB damage. Increased hsp72 mRNA was observed only in regions of preserved microcirculation, where the hsp72 protein was subsequently localized exclusively in the vasculature at 24 h after the insult. Hsp72-positive endothelial cells spanned the narrow margin between the lesion and histologically normal, glial fibrillary acidic protein (GFAP)-positive cortical tissue. There was no hsp72 expression in the area of subcortically migrating edema fluid. Inductions of c-fos mRNA and Fos protein were not strikingly evident around the focal brain lesion, but were observed transiently throughout the injured hemisphere at 30 min and 2.5 h, respectively, indicating that spreading depression was triggered by the focal injury. These results are in striking contrast to those previously obtained from studies of models of focal ischemic or traumatic brain injury, which are characterized by a complex pattern of glial and neuronal hsp72 expression in the periphery of an infarct, and which suggest that the tightly demarcated lesion produced by the Nd-YAG laser lacks these components of graded injury that are evident following other types of focal brain damage.

Efficacy of high dose amino acid solution on spinal cord injury induced by focal Nd:YAG laser irradiation

In this experimental study, a neodymium:yttrium-aluminium-garnet (Nd:YAG) laser was used to induce highly reproducible focal spinal cord lesions in anaesthetized guinea pigs. The efficacy of high dose amino acid solution (HDAAS) on this injury is investigated. Experiments were performed on 36 animals divided into three groups; sham operated controls, laser irradiated surgical controls, and amino acid groups. Acute responses to injury were evaluated with somatosensory (SSEP) and motor evoked potentials (MEP) and functional recovery was assessed for 8 weeks using the inclined plane technique. In the laser irradiated surgical control group, MEP disappeared one hour after the laser injury, but SSEP revealed changes of amplitude and latency. In this group, the average value of the inclined plane at 24 hours after the laser application was 45.3 +/- 1.4 degrees. In the amino acid group, at the sixth hour of injury, MEP and SSEP changes improved with infusion of HDAAS for 4 hours. This improvement was statistically significant (for latency of SSEP U = 140 p < 0.05). Inclined plane value at 24 hours after the laser application was 65.5 +/- 1.2 degrees in this group. This study showed that application of Nd:YAG laser irradiation on the spinal cord induced spinal cord injury which presented as paraparesis, HDAAS may provide significant therapeutic protection in secondary damage following this injury and may have a potential role in the treatment of acute spinal cord injury.

The heat shock/stress response in focal cerebral ischemia

Focal ischemia results in striking changes in gene expression. Induction of hsp72, a member of the family of 70 kDa heat shock/stress proteins is a widely studied component of the generalized cellular response to injury known as the 'stress response' that is detected in brain after ischemia and other insults. This overview summarizes observations on hsp72 expression in models of focal cerebral ischemia, considering its cellular distribution, factors affecting its transcriptional and translational expression, and its potential relevance to post-ischemic pathophysiology. Hsp72 expression is essentially limited to regions in which cerebral blood flow falls below 50% of control levels, provided that residual perfusion allows synthesis of the induced mRNA and protein. The cellular distribution of hsp72 depends on the nature of the ischemic insult, with preferential vascular expression in severely ischemic territory that is destined to necrose, pronounced neuronal expression throughout the ischemic 'penumbra', and limited glial involvement in a narrow zone immediately surrounding the infarct. Together with results in other injury models, these observations indicate that hsp72 induction identifies discrete populations of surviving cells that are metabolically compromised, but not irreversibly damaged after focal ischemia. Available evidence suggests that the stress response is an important component of cellular defense mechanisms, and that successful accumulation of hsp72 is critical to survival following ischemia. Its expression may also contribute to mechanisms of induced ischemic tolerance. Future studies may be expected to more fully characterize the range of altered gene expression in response to focal ischemic injury and to establish specific roles for hsp72 and other induced proteins in the progression of injury and recovery following such insults.

Stimulus-transcription coupling in focal cerebral ischemia

Glutamate-mediated spreading depression is currently thought to be a key event in the pathogenesis of potential neuronal degeneration in the ischemic 'penumbra'. Glutamate receptor stimulation causes induction of transcription factors that belong to the class of immediate early genes (IEGs), thought to be involved in coupling neuronal excitation to target gene expression. Focal cerebral ischemia elicits a homogeneous expression of several IEGs, prominently in cortex. In the ischemic core, discrepancies are observed between mRNA and protein levels, due to a severe, persistent protein synthesis deficit, preventing the translation of IEG encoded mRNAs. Outside the ischemic core, widespread IEG expression occurs in the entire ipsilateral cortex at mRNA as well as at protein level. This homogeneous expression of transcription factors can be pinpointed to at least two different pathogenetic mechanisms by means of appropriate pharmacological antagonists. Prolonged IEG induction in the 'penumbra', an area in which neurons are metabolically compromised but not yet energy-depleted, cannot be suppressed by the administration of N-methyl-D-aspartate (NMDA) receptor antagonists. In contrast, short-lasting IEG induction in undamaged neurons remote from the ischemic territory, though also caused by ischemia-elicited spreading depression, can be blocked by NMDA receptor antagonists. In both areas, IEG expression identifies neurons destined to survive but is likely to be mediated by different signal transduction pathways, at the receptor, second messenger and/or the DNA level.

Fine structure of zonal changes in experimental Nd:YAG laser-induced interstitial hyperthermia

Interstitial thermotherapy using Nd:YAG-laser induced hyperthermia is a new stereotactic method for the treatment of brain tumors in poorly accessible regions. To provide a basis for the underlying tissue alterations, we have analyzed the spatial and temporal pattern of interstitial laser hyperthermia lesions in the normal rat brain by histological, immunohistochemical, and electron microscopical methods. The acute changes corresponded to the temperature gradient surrounding the laser probe and showed a distinct zonal architecture. Membrane destruction on a cellular and subcellular level appears to be of major significance in the pathogenesis of the laser lesion. The tissue reaction followed the course known for coagulation necrosis and resulted in a well-defined defect. These results, although limited by the choice of the experimental model, may be helpful in the interpretation of images obtained in future applications of interstitial thermotherapy.

In situ photocoagulation of spinal dural arteriovenous malformations using the Nd:YAG laser

Spinal dural arteriovenous malformations (AVM's) are the most common type of AVM involving the spinal cord in adults. Direct obliteration of the fistula nidus located in the dura is the preferred method of treatment. Five cases of spinal dural AVM were treated by open surgical exposure, microsurgical disconnection of the dural nidus from the coronal venous plexus, and in situ obliteration of the nidus using the Nd:YAG laser. Use of the Nd:YAG laser reduced nidus obliteration to a simple 10-minute technical exercise. All patients improved neurologically following surgery, and complete obliteration of all lesions was verified by delayed angiography. There were no permanent complications related to either the surgical exposure or the use of the Nd:YAG laser. Open surgical treatment of spinal dural AVM's using the Nd:YAG laser appears to be a safe, effective, and durable method of treating these lesions. Photocoagulation is discussed in the context of the other treatment modalities available.

Induction of FOS and JUN proteins after focal ischemia in the rat: differential effect of the N-methyl-D-aspartate receptor antagonist MK-801

FOS and JUN proteins are transcription factors thought to be involved in coupling neuronal excitation to target gene expression. Cortical infarction of consistent size and location was produced by irradiating the rat brain with Xenon light through the intact skull for 20 min following systemic injection of the photo-sensitizing dye, rose bengal. To investigate the time course and distribution pattern of five cellular immediate early gene (IEG)-encoded proteins after focal ischemia, the expression of c-FOS, FOS B, c-JUN, JUN B and JUN D was studied immunocytochemically in sham-operated control animals and at different postischemic time intervals up to 24 h. A separate group of animals was pretreated with the non-competitive N-methyl-D-aspartate (NMDA) antagonist MK-801. Photochemically induced focal ischemia caused a rapid induction of FOS and JUN proteins in the entire ipsilateral cortex apart from the ischemic focus. Immunoreactivity in the ipsilateral subcortical gray and white matter and in the entire contralateral hemisphere was indistinguishable from control animals. Individual IEG-encoded proteins were sequentially induced with increased levels of immunoreactivity persisting for different time periods up to 24 h. c-FOS, FOS B, c-JUN and JUN B exhibited a characteristic distribution pattern as reflected by different staining intensities in individual cortical layers. The rapid IEG induction in the entire ipsilateral sensorimotor and limbic structure-associated cortices after photochemically induced infarction most likely reflects spreading depression caused by ischemia and mediated by NMDA receptors.(ABSTRACT TRUNCATED AT 250 WORDS)