Detection of BBB disruption and hemorrhage by Gd-DTPA enhanced MRI after embolic stroke in rat

Applications and development of permeability imaging in ischemic stroke

Brain permeability imaging techniques are specific for the assessment of blood-brain barrier integrity. The present review article primarily focuses on the application of permeability imaging in cases of ischemic stroke. The permeability maps may be used to predict future hemorrhagic transformation in patients following acute ischemic stroke, that have been treated with tissue plasminogen activator (tPA) or recanalization therapy. The permeability imaging would help make the clinical decision to administer tPA following acute ischemic stroke or not, which is not only due to the current 3-4.5 h time window. Additionally, permeability imaging may also be used to evaluate the collateral circulation in the perfusion and permeability of the ischemic area of the brain.

Magnetic resonance imaging of blood-brain barrier permeability in ischemic stroke using diffusion-weighted arterial spin labeling in rats

Diffusion-weighted arterial spin labeling magnetic resonance imaging has recently been proposed to quantify the rate of water exchange (Kw) across the blood-brain barrier in humans. This study aimed to evaluate the blood-brain barrier disruption in transient (60 min) ischemic stroke using Kw magnetic resonance imaging with cross-validation by dynamic contrast-enhanced magnetic resonance imaging and Evans blue histology in the same rats. The major findings were: (i) at 90 min after stroke (30 min after reperfusion), group Kw magnetic resonance imaging data showed no significant blood-brain barrier permeability changes, although a few animals showed slightly abnormal Kw. Dynamic contrast-enhanced magnetic resonance imaging confirmed this finding in the same animals. (ii) At two days after stroke, Kw magnetic resonance imaging revealed significant blood-brain barrier disruption. Regions with abnormal Kw showed substantial overlap with regions of hyperintense T2 (vasogenic edema) and hyperperfusion. Dynamic contrast-enhanced magnetic resonance imaging and Evans blue histology confirmed these findings in the same animals. The Kw values in the normal contralesional hemisphere and the ipsilesional ischemic core two days after stroke were: 363 ± 17 and 261 ± 18 min-1, respectively (P < 0.05, n = 9). Kw magnetic resonance imaging is sensitive to blood-brain barrier permeability changes in stroke, consistent with dynamic contrast-enhanced magnetic resonance imaging and Evans blue extravasation. Kw magnetic resonance imaging offers advantages over existing techniques because contrast agent is not needed and repeated measurements can be made for longitudinal monitoring or averaging.

Advances in the development of biomarkers for epilepsy

Over 50 million people worldwide have epilepsy. In nearly 30% of these cases, epilepsy remains unsatisfactorily controlled despite the availability of over 20 antiepileptic drugs. Moreover, no treatments exist to prevent the development of epilepsy in those at risk, despite an increasing understanding of the underlying molecular and cellular pathways. One of the major factors that have impeded rapid progress in these areas is the complex and multifactorial nature of epilepsy, and its heterogeneity. Therefore, the vision of developing targeted treatments for epilepsy relies upon the development of biomarkers that allow individually tailored treatment. Biomarkers for epilepsy typically fall into two broad categories: diagnostic biomarkers, which provide information on the clinical status of, and potentially the sensitivity to, specific treatments, and prognostic biomarkers, which allow prediction of future clinical features, such as the speed of progression, severity of epilepsy, development of comorbidities, or prediction of remission or cure. Prognostic biomarkers are of particular importance because they could be used to identify which patients will develop epilepsy and which might benefit from preventive treatments. Biomarker research faces several challenges; however, biomarkers could substantially improve the management of people with epilepsy and could lead to prevention in the right person at the right time, rather than just symptomatic treatment.

Assessment of Blood-Brain Barrier Permeability by Dynamic Contrast-Enhanced MRI in Transient Middle Cerebral Artery Occlusion Model after Localized Brain Cooling in Rats

Objective

The purpose of this study was to evaluate the effects of localized brain cooling on blood-brain barrier (BBB) permeability following transient middle cerebral artery occlusion (tMCAO) in rats, by using dynamic contrast-enhanced (DCE)-MRI.

Materials and Methods

Thirty rats were divided into 3 groups of 10 rats each: control group, localized cold-saline (20℃) infusion group, and localized warm-saline (37℃) infusion group. The left middle cerebral artery (MCA) was occluded for 1 hour in anesthetized rats, followed by 3 hours of reperfusion. In the localized saline infusion group, 6 mL of cold or warm saline was infused through the hollow filament for 10 minutes after MCA occlusion. DCE-MRI investigations were performed after 3 hours and 24 hours of reperfusion. Pharmacokinetic parameters of the extended Tofts-Kety model were calculated for each DCE-MRI. In addition, rotarod testing was performed before tMCAO, and on days 1-9 after tMCAO. Myeloperoxidase (MPO) immunohisto-chemistry was performed to identify infiltrating neutrophils associated with the inflammatory response in the rat brain.

Results

Permeability parameters showed no statistical significance between cold and warm saline infusion groups after 3-hour reperfusion 0.09 ± 0.01 min^-1 vs. 0.07 ± 0.02 min^-1, p = 0.661 for K^trans; 0.30 ± 0.05 min^-1 vs. 0.37 ± 0.11 min^-1, p = 0.394 for kep, respectively. Behavioral testing revealed no significant difference among the three groups. However, the percentage of MPO-positive cells in the cold-saline group was significantly lower than those in the control and warm-saline groups (p < 0.05).

Conclusion

Localized brain cooling (20℃) does not confer a benefit to inhibit the increase in BBB permeability that follows transient cerebral ischemia and reperfusion in an animal model, as compared with localized warm-saline (37℃) infusion group.

Permeability Parameters Measured with Dynamic Contrast-Enhanced MRI: Correlation with the Extravasation of Evans Blue in a Rat Model of Transient Cerebral Ischemia

OBJECTIVE

The purpose of this study was to correlate permeability parameters measured with dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) using a clinical 3-tesla scanner with extravasation of Evans blue in a rat model with transient cerebral ischemia.

MATERIALS AND METHODS

Sprague-Dawley rats (n = 13) with transient middle cerebral artery occlusion were imaged using a 3-tesla MRI with an 8-channel wrist coil. DCE-MRI was performed 12 hours, 18 hours, and 36 hours after reperfusion. Permeability parameters (K(trans), ve, and vp) from DCE-MRI were calculated. Evans blue was injected after DCE-MRI and extravasation of Evans blue was correlated as a reference with the integrity of the blood-brain barrier. Correlation analysis was performed between permeability parameters and the extravasation of Evans blue.

RESULTS

All permeability parameters (K(trans), ve, and vp) showed a linear correlation with extravasation of Evans blue. Among them, K(trans) showed highest values of both the correlation coefficient and the coefficient of determination (0.687 and 0.473 respectively, p < 0.001).

CONCLUSION

Permeability parameters obtained by DCE-MRI at 3-T are well-correlated with Evans blue extravasation, and K(trans) shows the strongest correlation among the tested parameters.

Losartan prevents acquired epilepsy via TGF-β signaling suppression

OBJECTIVE

Acquired epilepsy is frequently associated with structural lesions after trauma, stroke, and infections. Although seizures are often difficult to treat, there is no clinically applicable strategy to prevent the development of epilepsy in patients at risk. We have recently shown that vascular injury is associated with activation of albumin-mediated transforming growth factor β (TGF-β) signaling, and followed by local inflammatory response and epileptiform activity ex vivo. Here we investigated albumin-mediated TGF-β signaling and tested the efficacy of blocking the TGF-β pathway in preventing epilepsy.

METHODS

We addressed the role of TGF-β signaling in epileptogenesis in 2 different rat models of vascular injury, combining in vitro and in vivo biochemical assays, gene expression, and magnetic resonance and direct optical imaging for blood-brain barrier permeability and vascular reactivity. Long-term electrocorticographic recordings were acquired in freely behaving animals.

RESULTS

We demonstrate that serum-derived albumin preferentially induces activation of the activin receptor-like kinase 5 pathway of TGF-β receptor I in astrocytes. We further show that the angiotensin II type 1 receptor antagonist, losartan, previously identified as a blocker of peripheral TGF-β signaling, effectively blocks albumin-induced TGF-β activation in the brain. Most importantly, losartan prevents the development of delayed recurrent spontaneous seizures, an effect that persists weeks after drug withdrawal.

INTERPRETATION

TGF-β signaling, activated in astrocytes by serum-derived albumin, is involved in epileptogenesis. We propose losartan, a drug approved by the US Food and Drug Administration, as an efficient antiepileptogenic therapy for epilepsy associated with vascular injury.

MRI evaluation of BBB disruption after adjuvant AcSDKP treatment of stroke with tPA in rat

The primary limitation of thrombolytic treatment of ischemic stroke with tissue plasminogen activator (tPA) is the hemorrhagic risk. We tested AcSDKP (N-acetyl-seryl-aspartyl-lysyl-proline), as an auxiliary therapeutic agent, to reduce blood-brain barrier (BBB) disruption in a combination tPA thrombolytic treatment of stroke. Wistar rats subjected to embolic stroke were randomly assigned to either the tPA monotherapy group (n=9) or combination of tPA and AcSDKP treatment group (n=9) initiated at 4 h after ischemia. Magnetic resonance imaging (MRI) measurements were performed before and after the treatments. Immunohistochemical staining and measurements were performed to confirm MRI findings. Longitudinal MRI permeability measurements with gadolinium-diethylenetriamine penta-acetic acid (Gd-DTPA) demonstrated that combination treatment of acute embolic stroke with AcSDKP and tPA significantly reduced BBB leakage, compared to tPA monotherapy, at 3 and 6 days (18.3±9.8 mm3 vs. 65.0±21.0 mm3, p<0.001) after the onset of stroke, although BBB leakage was comparable between the two groups prior to the treatments (6.8±4.4 mm3 vs. 4.3±3.3 mm3, p>0.18). The substantial reduction of BBB leakage observed in the combination treatment group was closely associated with reduced ischemic lesions measured by T2 maps (113.6±24.9 mm3 vs. 188.1±60.8 mm3, p<0.04 at 6 days). Histopathological analysis of the same population of rats showed that the combination treatment significantly reduced parenchymal fibrin deposition (0.063±0.059 mm2 vs. 0.172±0.103 mm2, p<0.03) and infarct volume (146.7±35.9 mm3 vs. 199.3±60.4 mm3, p<0.05) compared to the tPA monotherapy at 6days after stroke. MRI provides biological insight into the therapeutic benefit of combination treatment of stroke with tPA and AcSDKP 4h after onset, and demonstrates significantly improved cerebrovascular integrity with neuroprotective effects compared with tPA monotherapy.

MRI of blood-brain barrier permeability in cerebral ischemia

Quantitative measurement of blood-brain barrier (BBB) permeability using MRI and its application to cerebral ischemia are reviewed. Measurement of BBB permeability using MRI has been employed to evaluate ischemic damage during acute and subacute phases of stroke and to predict hemorrhagic transformation. There is also an emerging interest on the development and use of MRI to monitor vascular structural changes and angiogenesis during stroke recovery. In this review, we describe MRI BBB permeability and susceptibility-weighted MRI measurements and its applications to evaluate ischemic damage during the acute and subacute phases of stroke and vascular remodeling during stroke recovery.

A review of current imaging methods used in stroke research

Stroke is a serious healthcare problem with high mortality and long-term disability. However, to date, our ability to prevent and cure stroke remains limited. One important goal in stroke research is to identify the extent and location of lesion for treatment. In addition, accurately differentiating salvageable tissue from infarct and evaluating therapeutic efficacies are indispensible. These objectives could potentially be met with the assistance of modern neuroimaging techniques. This paper reviews current imaging methods commonly used in ischemic stroke research. These methods include positron emission tomography, computed tomography, T1 MRI, T2 MRI, diffusion and perfusion MRI, diffusion tensor imaging, blood-brain barrier permeability MRI, pH-weighted MRI, and functional MRI.

MRI blood-brain barrier permeability measurements to predict hemorrhagic transformation in a rat model of ischemic stroke

Permeability imaging might add valuable information in the risk assessment of hemorrhagic transformation. This study evaluates the predictive value of blood-brain barrier permeability (BBBP) measurements extracted from dynamic contrast-enhanced MRI for hemorrhagic transformation in ischemic stroke. Spontaneously hypertensive and Wistar rats with 2 h filament occlusion of the right MCA underwent MRI during occlusion, at 4 and 24 h post reperfusion. BBBP was imaged by DCE imaging and quantified by Patlak analysis. Cresyl-violet staining was used to characterize hemorrhage in sacrificed rats at 24 h, immediately following the last imaging study. BBBP changes were evaluated at baseline, 4 and 24 h after reperfusion. Receiver-operating characteristic (ROC) analysis was performed to determine the most accurate BBBP threshold to predict hemorrhagic transformation. In animals showing macroscopic hemorrhage at 24 h, 95th BBBP percentile values ipsilateral were 0.323 [0.260, 0.387], 0.685 [0.385, 0.985], and 0.412 [0.210, 0.613] ml/min·100 g (marginal mean [95%CI]) during occlusion, at 4 and 24 h post reperfusion, respectively. The BBBP values on the infarcted and contralateral side were significantly different at 4 (p = 0.034) and 24 h post reperfusion (p = 0.031). The predictive value of BBBP in terms of macroscopic hemorrhage was highest 4 h after reperfusion (ROC area under the curve = 84 %) with a high negative predictive value (98.3 %) and limited positive predictive value (14.9 %) for a threshold of 0.35 ml/min·100g. Altered BBBP is a necessary but not sufficient condition to cause hemorrhagic transformation in rats with an infarct. Further research is needed to identify those additional risk factors that are required for hemorrhagic transformation to develop in the setting of ischemic stroke.

THE IMPACT OF FACTOR TE ON THE MEASUREMENT OF T1 RELAXIVITY

Relaxivity is a very important indicator to evaluate the signal enhancement caused by MRI contrast agents. Many factors can affect the relaxivity values. The aim of this study is to investigate the influence of factor TE in the curve-fitting equation for T1 measurements. A spin echo pulse sequence was used as the scanning method. The relaxivity of Gd -DTPA doped saline at a 1.5 T MR scanner was under investigation. Gd -DTPA is the most widely used MRI contrast agent nowadays. In this study, both computer simulations and phantom studies were performed. T1 values were calculated by using both spin echo MR signal equations: one with the TE factor included and the other with the TE factor omitted. Then, the relaxivity values obtained from these two sets of T1 values would be compiled and compared. The results show that the T1 values are longer and the relaxivity is smaller when the factor TE is omitted from the curve-fitting equation. Therefore, it is more desirable to keep the factor TE in the curve-fitting equation to obtain more accurate relaxivity values.

In vivo MR quantification of superparamagnetic iron oxide nanoparticle leakage during low-frequency-ultrasound-induced blood-brain barrier opening in swine

PURPOSE

To verify that low-frequency planar ultrasound can be used to disrupt the BBB in large animals, and the usefulness of MRI to quantitatively monitor the delivery of superparamagnetic iron oxide (SPIO) nanoparticles into the disrupted regions.

MATERIALS AND METHODS

Two groups of swine subjected to craniotomy were sonicated with burst lengths of 30 or 100 ms, and one group of experiment was also performed to confirm the ability of 28-kHz sonication to open the BBB transcranially. SPIO nanoparticles were administered to the animals after BBB disruption. Procedures were monitored by MRI; SPIO concentrations were estimated by relaxivity mapping.

RESULTS

Sonication for 30 ms created shallow disruptions near the probe tip; 100-ms sonications after craniotomy can create larger and more penetrating openings, increasing SPIO leakage ∼3.6-fold than 30-ms sonications. However, this was accompanied by off-target effects possibly caused by ultrasonic wave reflection. SPIO concentrations estimated from transverse relaxation rate maps correlated well with direct measurements of SPIO concentration by optical emission spectrometry. We have also shown that transcranial low-frequency 28-kHz sonication can induce secure BBB opening from longitudinal MR image follow up to 7 days.

CONCLUSION

This study provides valuable information regarding the use low-frequency ultrasound for BBB disruption and suggest that SPIO nanoparticles has the potential to serve as a thernostic agent in MRI-guided ultrasound-enhanced brain drug delivery.

The application of MRI for depiction of subtle blood brain barrier disruption in stroke

The development of imaging methodologies for detecting blood-brain-barrier (BBB) disruption may help predict stroke patient's propensity to develop hemorrhagic complications following reperfusion. We have developed a delayed contrast extravasation MRI-based methodology enabling real-time depiction of subtle BBB abnormalities in humans with high sensitivity to BBB disruption and high spatial resolution. The increased sensitivity to subtle BBB disruption is obtained by acquiring T1-weighted MRI at relatively long delays (~15 minutes) after contrast injection and subtracting from them images acquired immediately after contrast administration. In addition, the relatively long delays allow for acquisition of high resolution images resulting in high resolution BBB disruption maps. The sensitivity is further increased by image preprocessing with corrections for intensity variations and with whole body (rigid+elastic) registration. Since only two separate time points are required, the time between the two acquisitions can be used for acquiring routine clinical data, keeping the total imaging time to a minimum.

A proof of concept study was performed in 34 patients with ischemic stroke and 2 patients with brain metastases undergoing high resolution T1-weighted MRI acquired at 3 time points after contrast injection. The MR images were pre-processed and subtracted to produce BBB disruption maps. BBB maps of patients with brain metastases and ischemic stroke presented different patterns of BBB opening. The significant advantage of the long extravasation time was demonstrated by a dynamic-contrast-enhancement study performed continuously for 18 min. The high sensitivity of our methodology enabled depiction of clear BBB disruption in 27% of the stroke patients who did not have abnormalities on conventional contrast-enhanced MRI. In 36% of the patients, who had abnormalities detectable by conventional MRI, the BBB disruption volumes were significantly larger in the maps than in conventional MRI.

These results demonstrate the advantages of delayed contrast extravasation in increasing the sensitivity to subtle BBB disruption in ischemic stroke patients. The calculated disruption maps provide clear depiction of significant volumes of BBB disruption unattainable by conventional contrast-enhanced MRI.

Thymosin beta4 improves functional neurological outcome in a rat model of embolic stroke

Thymosin beta4 (Tbeta4) is a developmentally expressed 43-amino acid peptide that inhibits organization of the actin-cytoskeleton by sequestration of G-actin monomers. Tbeta4 improves cardiac function after myocardial infarction in adult mice and promotes healing properties in both dermal and corneal wounds. We tested the hypothesis that Tbeta4 improves functional neurological outcome in a rat model of embolic stroke.

EXPERIMENTAL PROCEDURES

Male Wistar rats (n=18) were subjected to embolic middle cerebral artery occlusion (MCAo). Tbeta4 (6 mg/kg, IP) was administered 24 h after MCAo and then every 3 days for four additional doses (n=9). Rats treated with saline were used as a control (n=9). The adhesive-removal test (ART) and modified Neurological Severity Score (mNSS) were performed to measure functional outcome. Rats were sacrificed 56 days after MCAo. Immunostaining was performed with antibodies against NG-2 (chondroitin sulfate proteoglycan), CNPase (2", 3"-cyclic nucleotide 3'-phosphodiesterase) to detect immature and mature oligodendrocytes. Neurofilament-H (NF-H) antibodies were used to detect axons while myelinated axons were identified with Bielschowsky/Luxol (B/L) Blue staining. EBA (endothelial barrier antigen) was used for detection of mature vessels.

RESULTS

Ischemic rats treated with Tbeta4 demonstrated a significant overall improvement (P<0.01) in the ART and the mNSS when compared to controls. Significant improvement was observed beginning at 14 and 35 days, respectively. Lesion volumes showed no significant differences between the two groups. Treatment with Tbeta4 increased myelinated axons and increased vessel density in the ischemic boundary (P<0.05) and augmented remyelination which was associated with an increase of oligodendrocyte progenitor cells (OPCs) and myelinating oligodendrocytes (P<0.05).

CONCLUSIONS

The present study suggests that Tbeta4 improves neurological functional outcome after embolic stroke in rats. Axonal remodeling from mobilization of OPCs is proposed as contributing to Tbeta4 induced functional improvement.

A translationally relevant thromboembolic stroke model for the study of secondary hemorrhage after thrombolysis in rats

Secondary hemorrhage after thrombolysis in ischemic stroke is an important complication, which has been difficult to study in preclinical disease models. We have established and characterized a model of thromboembolic middle cerebral artery occlusion in rats. Advantages of this model include a very low rate of spontaneous recanalization and good reperfusion after intravenous thrombolysis with recombinant tissue plasminogen activator (rt-PA). In vivo T2* MR imaging and postmortem assays were used for quantification of secondary brain hemorrhage. In our protocol, 12 thrombin-induced autologous blood clots are injected into the internal carotid artery. No spontaneous reperfusion occurs in the first 24h. However, injection of rt-PA 2 or 4h thereafter leads to reperfusion of the MCA territory consistent infarcts, increased blood-brain barrier permeability, and secondary hemorrhage. Remarkably, clinically important factors known to affect the extent and likelihood of secondary hemorrhage such as hypertension and delayed onset of thrombolysis also increase hematoma size in the model. Thus, the model may serve to investigate the pathophysiology of thrombolysis-induced hemorrhage in thromboembolic ischemia as well as potential adjunctive therapies to prevent this complication.

Tobacco smoke: a critical etiological factor for vascular impairment at the blood-brain barrier

Active and passive tobacco smoke are associated with the dysfunction of endothelial physiology and vascular impairment. Studies correlating the effects of smoking and the brain microvasculature at the blood-brain barrier (BBB) level have been largely limited to few selective compounds that are present in the tobacco smoke (TS) yet the pathophysiology of smoking has not been unveiled. For this purpose, we characterized the physiological response of isolated human brain microvascular endothelial cells (HBMEC) and monocytes to the exposure of whole soluble TS extract. With the use of a well established humanized flow-based in vitro blood-brain barrier model (DIV-BBB) we have also investigated the BBB physiological response to TS under both normal and impaired hemodynamic conditions simulating ischemia. Our results showed that TS selectively decreased endothelial viability only at very high concentrations while not significantly affecting that of astrocytes and monocytes. At lower concentrations, despite the absence of cytotoxicity, TS induced a strong vascular pro-inflammatory response. This included the upregulation of endothelial pro-inflammatory genes, a significant increase of the levels of pro-inflammatory cytokines, activated matrix metalloproteinase, and the differentiation of monocytes into macrophages. When flow-cessation/reperfusion was paired with TS exposure, the inflammatory response and the loss of BBB viability were significantly increased in comparison to sham-smoke condition. In conclusion, TS is a strong vascular inflammatory primer that can facilitate the loss of BBB function and viability in pathological settings involving a local transient loss of cerebral blood flow such as during ischemic insults.

In vivo quantification of transvascular water exchange during the acute phase of permanent stroke

Mechanisms that underlie early ischemic damages to the blood-brain-barrier (BBB) are not well understood. This study presents a novel magnetic resonance imaging (MRI) technique using a widely available pulse sequence and a long-circulating intravascular contrast agent to quantify water movements across the BBB at early stages of stroke progression. We characterized the integrity of the BBB by measuring the flip angle dependence of the water exchange-affected MRI signal intensity, to generate an efficient quantitative index of vascular permeability (WEI, or water exchange index). We performed in vivo MRI experiments to measure the transvascular WEI immediately after the permanent filament occlusion of the middle cerebral artery of mice (n = 5), in which we monitored changes in blood volume (V(b)), apparent diffusion coefficient (ADC), and intra-/extravascular WEI for 4 hours. Statistically significant elevations (P < 0.05) of WEI in the ischemic tissue were observed as early as 1 hour after ischemic onset. Initial reduction of the apparent blood volume (V(app)) in the infarct cortex was followed by a continuous increase of V(app) over time. Although the measured ADC in the ipsilesional cortex continuously decreased, the abnormally high intra-/extravascular WEI remained constant at a significantly elevated level, indicating apparent BBB injury at this early stage of stroke.

Structural determination of Zn and Cd-DTPA complexes: MS, infrared, (13)C NMR and theoretical investigation

The joint application of MS, infrared and (13)C NMR techniques for the determination of metal-DTPA structures (metal=Zn and Cd; DTPA=diethylenetriaminepentacetic acid) is reported. Mass spectrometry allowed determining the 1:1 stoichiometry of the complexes, while infrared analysis suggested that both nitrogen and carboxyl groups are sites for complexation. The (13)C NMR spectrum for the cadmium-containing complex evidenced the existence of free and complexed carboxyl groups, due to a straight singlet at 179.0 ppm (free carboxylic (13)C) and to two broad singlets or a broad doublet at 178.3 ppm (complexed carboxylic (13)C, (2)J(Cd-C(=O))=45.2 Hz). A similar interpretation might be given for the zinc derivative and, with the aid of DFT calculations, structures for both complexes were then proposed.

Targeting the brain: rationalizing the novel methods of drug delivery to the central nervous system

Drug delivery to the brain has remained one of the most vexing problems in translational neuroscience research. This review rationalizes the strategies to target drugs to the brain. Factors such as the speed of intervention, the scale of intervention, the state of BBB, and the permissible risks, will all be critical in deciding how best to deliver drugs to a target site in the brain for a specific clinical situation.