Internal Carotid Artery Perfusion Research Articles

Evaluation of ocular blood flow in the assessment of symptomatic carotid stenosis.

The degree of internal carotid artery (ICA) stenosis determined by criteria from the North American Symptomatic Carotid Endarterectomy Trial (NASCET) is not the most accurate index to assess distal flow compromise. Distal ICA perfusion is also determined by factors such as tandem carotid stenosis and collateral circulation. Quantification of end-organ ocular perfusion using non-invasive laser speckle flowgraphy (LSFG) may provide insights into distal ICA flow. This study prospectively assessed the degree of ICA flow using LSFG. Eighteen patients with symptomatic carotid stenosis underwent LSFG evaluation. LSFG was used to extract ocular blood flow metrics recorded simultaneously in the retina, choroid, and optic nerve head. The following ocular flow parameters were measured with LSFG: mean blur rate (MBR), flow acceleration index (FAI), and rising rate (RR). Syngo iFlow perfusion imaging was used to objectively quantify contrast flow in the ICA and brain parenchyma during digital subtraction angiography. Time to peak (TTP) and contrast delay were extracted from seven different regions of interest (ROIs). MBR, FAI, and RR were correlated with NASCET degree of stenosis. FAI and RR also improved after stenting. TTP improved after stenting in three ROIs. A moderate negative correlation was observed between FAI and contrast delay. LSFG non-invasively quantifies end-organ blood flow distal to the ICA origin. LSFG metrics have the potential to quantify end-organ perfusion and determine if a proximal carotid stenosis is symptomatic.

Persistent Primitive Hypoglossal Artery with Ipsilateral Symptomatic Carotid Artery Stenosis and Cerebral Aneurysm

ObjectivePersistent primitive hypoglossal artery (PPHA) is a rare type of persistent carotid-basilar anastomosis sometimes associated with other vascular lesions. We treated an extremely rare case of PPHA with concomitant ipsilateral symptomatic cervical internal carotid artery (ICA) stenosis and unruptured aneurysm. Case presentationA 67-year-old woman visited our institution with acute onset of diplopia. Magnetic resonance imaging revealed multiple acute infarctions in the right anterior and posterior circulations. Digital subtraction angiography demonstrated the right PPHA concomitant with ipsilateral cervical ICA stenosis and an unruptured ICA aneurysm with maximum diameter of 8 mm. The multiple infarctions were considered to result from artery-to-artery embolism due to microthrombi from the ICA plaque passed along the PPHA, so carotid endarterectomy was performed as the first step with preoperative modified Rankin Scale (mRS) grade 1. During the operation, the patient had impaired ICA perfusion due to internal shunt catheter migration into the PPHA followed by acute infarction in the right hemisphere causing mild left hemiparesis. The patient was transferred to the rehabilitation hospital with mRS grade 3. After 3 months of rehabilitation, the patient recovered to mRS grade 1 and clipping surgery for the unruptured right ICA aneurysm was performed as the second step with uneventful postoperative course. ConclusionThe treatment strategy should be carefully considered depending on the specific blood circulation for such cases of PPHA with unique vasculature.

Involvement of a Novel Organic Cation Transporter in Paeonol Transport Across the Blood-Brain Barrier.

Paeonol has neuroprotective function, which could be useful for improving central nervous system disorder. The purpose of this study was to characterize the functional mechanism involved in brain transport of paeonol through blood-brain barrier (BBB). Brain transport of paeonol was characterized by internal carotid artery perfusion (ICAP), carotid artery single injection technique (brain uptake index, BUI) and intravenous (IV) injection technique in vivo. The transport mechanism of paeonol was examined using conditionally immortalized rat brain capillary endothelial cell line (TR-BBB) as an in vitro model of BBB. Brain volume of distribution (VD) of [3H]paeonol in rat brain was about 6-fold higher than that of [14C]sucrose, the vascular space marker of BBB. The uptake of [3H]paeonol was concentration-dependent. Brain volume of distribution of paeonol and BUI as in vivo and inhibition of analog as in vitro studies presented significant reduction effect in the presence of unlabeled lipophilic compounds such as paeonol, imperatorin, diphenhydramine, pyrilamine, tramadol and ALC during the uptake of [3H]paeonol. In addition, the uptake significantly decreased and increased at the acidic and alkaline pH in both extracellular and intracellular study, respectively. In the presence of metabolic inhibitor, the uptake reduced significantly but not affected by sodium free or membrane potential disruption. Similarly, paeonol uptake was not affected on OCTN2 or rPMAT siRNA transfection BBB cells. Interestingly. Paeonol is actively transported from the blood to brain across the BBB by a carrier mediated transporter system.

Study on selective cerebral hypothermia protection by carotid perfusion

Therapeutic hypothermia is known as an effective method for cerebral protection. However, its application is limited due to the complications of whole body hypothermia and low effectiveness of ice blankets and caps. Recently, internal carotid artery perfusion has drawn considerable attentions with the advantages of high effectiveness, long maintenance time, blood dilution and fleshing of inflammatory mediators. This article reviewed the principle, methods and advantages of carotid selective brain cooling, discuss carotid infusion for selective brain cooling in recent study, so as to provide more safely and reliable methods for cerebral protection and improve long-term quality of life. Key words: Intracarotid perfusion; Hypothermia; Cerebral protection

Reduced arterial vasodilatation in response to hypoxia impairs cerebral and peripheral oxygen delivery in hypertensive men

Hypoxaemia evokes a repertoire of homeostatic adjustments that maintain oxygen supply to organs and tissues including the brain and skeletal muscles. Because hypertensive patients have impaired endothelial-dependent vasodilatation and an increased sympathetic response to arterial oxygen desaturation, we investigated whether hypertension impairs isocapnic hypoxia-induced cerebral and skeletal muscle hyperaemia to an extent that limits oxygen supply. In middle-aged hypertensive men, vertebral and femoral artery blood flow do not increase in response to isocapnic hypoxia, limiting brain and peripheral hyperaemia and oxygen supply. Increased chemoreflex-induced sympathetic activation impairs skeletal muscle perfusion and oxygen supply, whereas an attenuation of local vasodilatory signalling in the posterior cerebrovasculature reduced brain hyperperfusion of hypertensive middle-aged men in response to isocapnic hypoxia. The present study investigated whether hypertension impairs isocapnic hypoxia (IH)-induced cerebral and skeletal muscle hyperaemia to an extent that limits oxygen supply. Oxygen saturation (oxymetry), mean arterial pressure (photoplethysmography) and muscle sympathetic nerve activity (MSNA; microneugraphy), as well as femoral artery (FA), internal carotid artery and vertebral artery (VA) blood flow (BF; Doppler ultrasound), were quantified in nine normotensive (NT) (aged 40±11years, systolic pressure 119±7mmHg and diastolic pressure 73±6mmHg) and nine hypertensive men (HT) (aged 44±12years, systolic pressure 152±11mmHg and diastolic pressure 90±9mmHg) during 5min of normoxia (21% O2 ) and IH (10% O2 ). Total cerebral blood flow (tCBF), brain (CDO2 ) and leg (LDO2 ) oxygen delivery were estimated. IH provoked similar oxygen desaturation without changing mean arterial pressure. Internal carotid artery perfusion increased in both groups during IH. However, VA and FA BF only increased in NT. Thus, IH-induced increase in tCBF was smaller in HT. CDO2 only increased in NT and LDO2 decreased in HT. Furthermore, IH evoked a greater increase in HT MSNA. Changes in MSNA were inversely related to FA BF, LDO2 and end-tidal oxygen tension. In conclusion, hypertension disturbs regional and total cerebrovascular and peripheral responses to IH and consequently limits oxygen supply to the brain and skeletal muscle. Although increased chemoreflex-induced sympathetic activation may explain impaired peripheral perfusion, attenuated vasodilatory signalling in the posterior cerebrovasculature appears to be responsible for the small increase in tCBF when HT were exposed to IH.

Increase in extraction of I-123 iomazenil in patients with chronic cerebral ischemia.

BackgroundCerebral extraction of diffusively distributed substances like oxygen has been suggested to change according to the cerebral blood flow (CBF) and status of the microvasculature. The relationships between the cerebral extraction of diffusively distributed lipophilic tracers and the severity of cerebral ischemia has not yet been clarified. In the present study, we attempted to elucidate the association between the extraction fraction of the lipophilic tracer I-123 iomazenil (IMZ) (IMZ-EF) and the oxygen extraction fraction (OEF) derived from O-15 PET in patients with chronic steno-occlusive disease of internal carotid artery (ICA) or middle cerebral artery (MCA).MethodsSeven patients with unilateral chronic severe stenosis or occlusion of the middle cerebral/internal cerebral artery were prospectively recruited for this study. All the patients underwent both O-15 PET and quantitative I-123 IMZ SPECT. Parametric images derived from the PET and SPECT scans were anatomically normalized and evaluated by automated image analysis based on the volume-of-interest template.ResultsThe asymmetry index (AI) of IMZ-EF was shown to be significantly correlated with the AI of OEF (r = 0.562, P < 0.001) in the internal carotid artery perfusion area. Strong and significant correlation between the AI of the influx rate constant K1 of IMZ and the AI of the cerebral metabolic rate of oxygen (r = 0.552, P = 0.001) was clarified.ConclusionsOur results suggested that the transportation efficiency of I-123 IMZ into the brain tissue was an indicator for evaluating severity of cerebral ischemia in patients with chronic steno-occlusive disease of ICA or MCA. Cerebral metabolic state can possibly be estimated by I-123 IMZ SPECT without cyclotron.

Perioperative Changes in Cerebral Perfusion Territories Assessed by Arterial Spin Labeling Magnetic Resonance Imaging Are Associated with Postoperative Increases in Cerebral Blood Flow in Patients with Carotid Stenosis

The magnetic resonance imaging technique known as territorial arterial spin labeling (TASL) allows for noninvasive visualization of perfusion territories. The objective of this study was to use TASL to assess the relationship between perioperative changes in the perfusion territories of the internal carotid artery (ICA) and cerebral blood flow (CBF) after carotid revascularization. In 32 patients, ICA perfusion volume (PV) and CBF were measured before and after carotid endarterectomy/carotid artery stenting using TASL and single-photon emission computed tomography, respectively. ICA flow was measured during carotid endarterectomy before and after reconstruction, using an electromagnetic flowmeter. Eleven healthy volunteers, as the normal control group, underwent TASL evaluation. We classified patients into 2 groups: the normal PV group (ICA PV ≥ mean-2 standard deviation of healthy volunteers; n= 13) and the reduced PV group (ICA PV < mean-2 standard deviation; n= 19). The postoperative increase in the ICA PV and CBF were significantly greater in the reduced PV group than in the normal group (90.4% ± 131.8% vs. 10.5 ± 9.8%, P= 0.017, 32.0±25.7% vs. 10.5% ± 10.7%, P= 0.0032, respectively). ICA flow increased significantly after reconstruction in both the normal PV group (115.1 ± 48.1 mL/minute to 159.1± 53 mL/minute; P= 0.016) and reduced PV group (57.8 ± 38.3 mL/minute to 182.3 ± 52.6 mL/minute; P<0.0001). However, in some patients in the reduced PV group, the PV increased only slightly, whereas the ICA flow markedly increased, which resulted in a large CBF increase, such as hyperperfusion. The TASL study suggested that an imbalance between increases in the PV and ICA flow could play an important role in the pathophysiology underlying postoperative abnormal increases in CBF.

In Vivo and In Vitro Evidence for Brain Uptake of 4-Phenylbutyrate by the Monocarboxylate Transporter 1 (MCT1).

4-Phenylbutyrate (4-PBA) is expected to be a potential therapeutic for several neurodegenerative diseases. These activities require 4-PBA transport into the brain across the blood-brain barrier (BBB). The objective of the present study was to characterize the brain transport mechanism of 4-PBA through the BBB. The brain transport of 4-PBA across the BBB was investigated following intravenous (IV) injection and internal carotid artery perfusion (ICAP) in vivo. The mechanism of transport was examined using TR-BBB cells, an in vitro model of the BBB. The volume of distribution (VD) of 4-PBA by rat brain was about 7-fold greater than that of sucrose, a BBB impermeable vascular space marker, suggesting the blood-to-brain transport of 4-PBA through the BBB in the physiological state. [(14)C]4-PBA uptake by TR-BBB cells showed time-, pH- and concentration-dependence with a K m of 13.4mM at pH7.4 and 3.22mM at pH6.0. The uptake was Na(+) independent, and was significantly inhibited by alpha-cyano-4-hydroxycinnamate (a typical inhibitor for monocarboxylate transport), endogenous monocarboxylate compounds and monocarboxylic drugs. Lactate and valproate competitively inhibited [(14)C]4-PBA uptake with K i value of 13.5mM and 7.47mM, respectively. These results indicate the role of monocarboxylate transporters (MCTs) in 4-PBA transport into the brain at the BBB. TR-BBB cells expressed mRNA of rMCT1, 2, and 4, especially, rMCT1 showed high mRNA expression level. In addition, [(14)C]4-PBA uptake was inhibited by rMCT1 specific small interfering RNA. The transport mechanism of 4-PBA from blood to brain across the BBB likely involves MCT1.

Nanoparticle-mediated delivery of oligonucleotides to the blood–brain barrier: in vitro and in situ brain perfusion studies on the uptake mechanisms

Except for the few exceptions where topical administration is feasible, progress towards broad clinical application of nucleic acid therapeutics requires development of effective systemic delivery strategies. The central nervous system represents a particularly difficult organ for systemic delivery due to the blood–brain barrier. We previously reported a nanoparticulate delivery system for targeted brain delivery of oligonucleotides upon systemic administration, i.e. liposome-encapsulated polyethylenimine/oligonucleotides polyplexes. In this study, cellular uptake and intracellular trafficking of the nanoparticles were further investigated using in situ brain perfusion technique followed by colocalization and fluorescence resonance energy transfer techniques. The brain endothelial uptake and possibly parenchymal accumulation were readily visualized upon administration via internal carotid artery perfusion. The nanoparticles were colocalized with early-endosome antigen, which confirms the brain endothelial uptake through transferrin receptor-mediated endocytosis. Fluorescence resonance energy transfer analysis also suggested the nanoparticles entered the brain endothelial cells while maintaining their integrity. Together, the enhanced brain uptake, as claimed previously, of the antibody-targeted nanoparticles was clearly confirmed with more convincing evidences. In addition, the experimental techniques described here should be applicable to the studies involving nanoparticle-mediated brain delivery of nucleic acid therapeutics.

Methods to assess drug permeability across the blood-brain barrier

Much research has focussed on the development of novel therapeutic agents to target various central nervous system disorders, however less attention has been given to determining the potential of such agents to permeate the blood-brain barrier (BBB), a factor that will ultimately govern the effectiveness of these agents in man. In order to assess the potential for novel compounds to permeate the BBB, various in-vitro, in-vivo and in-silico methods may be employed. Although in-vitro models (such as primary cell culture and immortalized cell lines) are useful as a screening method and can appropriately rank compounds in order of BBB permeability, they often correlate poorly to in-vivo brain uptake due to down-regulation of some BBB-specific transporters. In-vivo models (such as the internal carotid artery single injection or perfusion, intravenous bolus injection, brain efflux index and intracerebral microdialysis) provide more accurate information regarding brain uptake, and these can be complemented with novel imaging techniques (such as magnetic resonance imaging and positron emission tomography), although such methods are not suited to high-throughput permeability assessment. This paper reviews current methods used for assessing BBB permeability and highlights the particular advantages and disadvantages associated with each method, with a particular focus on methods suitable for moderate- to high-throughput screening.

The Haemodynamic Effect of Carotid Endarterectomy

Objectives: to assess the haemodynamic effect of carotid artery surgery, and to relate postoperative changes to the state of cerebral circulation before revascularisation.Materials and methods: using transcranial Doppler we studied bilateral middle cerebral artery (MCA) flow velocities before and on 1st day, 2nd or 3rd day and 4th or 5th day and 3 months after carotid surgery in 61 patients. In addition, ipsilateral MCA flow velocity was monitored continuously during surgery. Data were related to the internal carotid artery (ICA) perfusion pressure (cerebral perfusion pressure index, CPPI), measured directly before ICA clamping.Results: postoperatively, MCA flow velocities increased significantly overall (p<0.01), mainly due to pronounced and longer lasting flow velocities in the group of 18 patients with CPPI<0.7 (p<0.05). Flow velocities peaked – absolute as well as relative – on the first postoperative day and then gradually levelled off to reach preoperative values after 4–5 days in patients with high CPPI, whereas MCA flow velocities remained increased in the group of patients with low CPPI. At 3 months flow velocities in both groups were normalised. New neurological symptoms occurred in four patients, who all had low CPPI preoperatively (22% (4/18) vs 0%; Fisher's exact test: p=0.006).Conclusion: some degree of hyperperfusion was seen in most patients, but the changes were significantly more pronounced in patients with preoperative hypoperfusion, who also suffered significantly more neurological complications.

Blood-Brain Barrier Disruption Following the Internal Carotid Arterial Perfusion of Alkyl Glycerols

Non ionic, amphipathic molecules form vesicles and this property correlates with the disruption of membranes. In the present studies, high mM concentrations of aliphatic alcohols, 1- O -hexyldiglycerol (HDG) and 1- O -heptyltriglycerol (HTG), are shown to cause enhanced drug transport into brain via disruption of the blood-brain barrier (BBB) in vivo, as determined with an internal carotid artery perfusion method. The intravenous administration of comparable concentrations of HDG or HTG caused no increase in BBB transport of drug. The enhanced transport of drug showed a dependency on molecular weight as 45 mM HTG increased the transport of sucrose, 360 Da, but did not increase the transport of arginine vasopressin (AVP), 1084 Da, although AVP transport across the BBB was increased by 80 mM HDG or HTG. Quasielastic light scattering measurements provided evidence for the formation of vesicular structures in aqueous solutions containing high mM concentrations of the HDG or HTG. In summary, these studies demonstrate BBB disruption following the internal carotid arterial infusion of high mM concentrations of membrane active alkyl glycerols.

Position dependent changes of cerebral blood flow velocities in premature infants.

The supine or prone positioning of infants has been a cause of much controversy. Recently it has been postulated that the position dependent hypoperfusion of the brainstem represents a possible cause of sudden infant death. To demonstrate position dependency and maturational changes of cerebral perfusion in premature newborn infants we investigated cerebral blood flow velocities (CBFV) in the main supratentorial and brainstem cerebral arteries. Measurements of CBFV were done with transfontanellar colour-coded Doppler sonography in the internal carotid artery (ICA), basilar artery (BA), and vertebral artery (VA) in the prone (head centered-baseline) and supine positions (maximal rotation to both sides) in 23 premature infants aged between 3-5 days of life. We performed follow-up measurements in 17 infants 7-10 days later and in 16 infants at the corrected age of 1 month. There was no difference in mean CBFVs between the prone and supine position at the first investigation. At the third investigation, CBFVs were significantly higher in the supine compared to the prone position. The CBFVs of the ICA were higher than in the BA and VA. This difference was not influenced by the body position but increased with post-natal age more in the VA (159%) than in the BA (129%) and ICA (128%). Position dependency was not seen in the ICA perfusion. In the prone position, five infants showed an incomplete steal effect in the contralateral VA. There was no significant side difference in the CBFVs of the ICA and VA, but in the resistance indices in the VA (left > right). in premature newborns, position dependent changes of cerebral blood flow velocity develop with maturation and are most pronounced in the vertebrobasilar system. These changes are possibly due to compression of the vertebral artery by neck movement and suggest an individual risk of brainstem perfusion deficits that may be aggravated with age and head rotation in a prone position.

Acute upregulation of blood-brain barrier glucose transporter activity in seizures.

Brain extraction of (18)F-labeled 2-fluoro-2-deoxy-D-glucose (FDG) was significantly higher in pentylene tetrazole (PTZ)-treated rats (32 +/- 4%) than controls (25 +/- 4%). The FDG permeability-surface area product (PS) was also significantly higher with PTZ treatment (0.36 +/- 0.05 ml. min(-1). g(-1)) than in controls (0.20 +/- 0.06 ml. min(-1). g(-1)). Cerebral blood flow rates were also elevated by 50% in seizures. The internal carotid artery perfusion technique indicated mean [(14)C]glucose clearance (and extraction) was increased with PTZ treatment, and seizures increased the PS by 37 +/- 16% (P < 0.05) in cortical regions. Because kinetic analyses suggested the glucose transporter half-saturation constant (K(m)) was unchanged by PTZ, we derived estimates of 1) treated and 2) control maximal transporter velocities (V(max)) and 3) a single K(m). In cortex, the glucose transporter V(max) was 42 +/- 11% higher (P < 0.05) in PTZ-treated animals (2.46 +/- 0.34 micromol. min(-1). g(-1)) than in control animals (1.74 +/- 0.26 micromol. min(-1). g(-1)), and the K(m) = 9.5 +/- 1.6 mM. Blood-brain barrier (BBB) V(max) was 31 +/- 10% greater (P < 0.05) in PTZ-treated (2.36 +/- 0. 30 micromol. min(-1). g(-1)) than control subcortex (1.80 +/- 0.25 micromol. min(-1). g(-1)). We conclude acute upregulation of BBB glucose transport occurs within 3 min of an initial seizure. Transporter V(max) and BBB glucose permeability increase by 30-40%.

TRANSPORT MECHANISM OF BASIC FIBROBLAST GROWTH FACTOR (bFGF) THROUGH THE BLOOD-BRAIN BARRIER

The purpose of the present study was to characterize the transport mechanism of basic fibroblast growth factor (bFGF) through the blood-brain barrier (BBB). Following internal carotid artery perfusion, 125I-bFGF was transcytosed through the BBB from blood into brain parenchyma. The binding of 125I-bFGF to the isolated bovine brain capillaries was saturated with a dissociation constant of 40 nM. This binding was significantly inhibited by unlabeled peptide, poly-L-lysine, heparin and glycosaminoglycans with a sulfate residue. RT -PCR analysis revealed mRNA of perlecan, FGF receptors (FGFR1 and FGFR2) in the conditionally immortalized mouse brain capillary endothelial cell lines (TM-BBB). The internalization of 125I-bFGF in TM-BBB was temperature-dependent and concentration-dependent, and showed a dependence on medium osmolarity. This internalization was significantly inhibited by the treatment of heparinase, sodium chlorate and antibody specific to mouse perlecan, a heparan sulfate proteoglycan. These results are consistent with the conclusion, 1) 125I-bFGF is transcytosed through the BBB, 2) internalization of 125I-bFGF into brain capillary endothelial cells is, in part, brought about by an endocytosis mechanism that is triggered by binding to HSPG.

Blood-brain barrier transport of 125I-labeled basic fibroblast growth factor.

This study was carried out to examine the blood-brain barrier (BBB) transport of human basic fibroblast growth factor (bFGF) and investigate its mechanism. The BBB transport of 125I-bFGF was measured by several in vivo methods including intravenous administration, in situ internal carotid artery perfusion, and intracerebral microinjection. The in vitro binding of 125I-bFGF was characterized using freshly prepared bovine brain capillaries. The distribution volume of 125I-bFGF in the postvascular supernatant increased with the perfusion time, and exceeded the space occupied by the brain microvasculature and its trichloroacetic acid (TCA) precipitability was more than 90%. 125I-bFGF avidly bound to isolated bovine brain capillaries with a Bmax of 206 +/- 48 pmol/mg protein, and a Kd of 36.5 +/- 15.7 nM. This binding was significantly inhibited by unlabeled bFGF and heparin in a concentration-dependent manner. The cationic peptides, protamine and poly-L-lysine (each 300 microM), produced over 85% inhibition of 125I-bFGF binding to brain capillaries. Furthermore, glycosaminoglycans with a sulfate residue, chondroitin sulfate B and C (each 10 microg/mL) also inhibited the binding of 125I-bFGF The in vivo transcytosis of 125I-bFGF from the luminal side to the brain was also inhibited by the presence of heparin (10 microg/mL) and poly-L-lysine (300 microM), whereas neither hyaruronic acid (10 microg/mL) nor insulin (10 microM) had any effect. In addition to these results, the brain efflux index method was used to confirm that the transcytosis of 125I-bFGF from brain to blood across the BBB was negligible. These results suggest that 125I-bFGF is transported across the BBB, possibly by an adsorptive-mediated transcytosis mechanism that is triggered by binding to negatively charged species on the luminal membrane surface of the brain microvasculature, such as heparan sulfate proteoglycans.

Permeability of a capsaicin derivative, [14C]DA-5018 to blood-brain barrier corrected with HPLC method.

In the present work, the transport mechanism of a capsaicin derivative, DA-5018, through blood-brain barrier (BBB) has been investigated to evaluate the feasibility of potential drug development. The result of pharmacokinetic parameters obtained from the intravenous injection of plasma volume marker, [3H]RSA and [14C]DA-5018, indicated that both AUC, area under the plasma concentration curve and VD, volume of distribution in brain of [3H]RSA agreed with those reported (1620 +/- 10 percentage injected dose minute per milliliter (%IDmin/ml) and 12.0 +/- 0.1 microliters/g, respectively). Elimination half-life and AUC of [14C]DA-5018 is corrected by the HPLC analysis, 19.6 +/- 1.2 min and 7.69 +/- 0.85% IDmin/ml, respectively. The metabolic rate of [14C] DA-5018 was very rapid. The blood-brain barrier permeability surface area (PS) product of [14C]DA-5018 was calculated to be 0.24 +/- 0.05 microliter/min/g. The result of internal carotid artery perfusion and capillary depletion suggested that [14C]DA-5018 pass through BBB with the time increasingly. Investigation of transport mechanism of [14C]DA-5018 using agonist and antagonist suggested that vanilloid (capsaicin) receptor did not exist in the BBB, and nutrient carrier system in the BBB has no effect on the transport of DA-5018. In conclusion, despite the fact that penetration of DA-5018 through BBB is significant, the intact drug found in the brain tissue is small because of a rapid metabolism. Therefore, for the central analgesic effect of DA-5018, the method to increase the metabolic stability in plasma and the brain permeability should be considered.

Low blood–brain barrier permeability to azidothymidine (AZT), 3TC™, and thymidine in the rat

The blood–brain barrier (BBB) permeability to [ 3H]-azidodeoxythymidine (AZT), deoxythiacytidine (3TC™), and thymidine was studied using both an intravenous injection/external organ (IV/EO) method and an internal carotid artery perfusion (ICAP) technique in parallel with [ 14C]-sucrose as a plasma volume marker. The brain volumes of distribution ( V D) of the three compounds approximated that of sucrose with either method. Although the lipid solubility of AZT, as determined by the 1-octanol/buffer partition coefficient ( P), was 16-fold higher than that of thymidine, the BBB permeability-surface area (PS) products were almost identical, consistent with preferential efflux of AZT from brain to blood.

Blood-brain barrier carrier-mediated transport and brain metabolism of amino acids.

The transport of neutral amino acids through the brain capillary endothelial wall, which makes up the blood-brain barrier (BBB) in vivo, is an important control point for the overall regulation of cerebral metabolism, including protein synthesis and neurotransmitter production. The Michaelis-Menten kinetics of BBB amino acid transport have been investigated in vivo with the brain uptake index (BUI) technique, and in vitro with the isolated human brain capillary preparation. The only amino acid that is albumin-bound is tryptophan, and the majority of albumin-bound tryptophan in the plasma is available for transport through the BBB via an enhanced dissociation mechanism that operates at the surface of the brain capillary endothelium. The availability in brain of amino acids is predicted from the BBB Km values to be sharply influenced by supra-physiological concentrations of phenyalanine in the 200-500 microM range. Moreover, the measurement of cerebral protein synthesis with an internal carotid artery perfusion technique and HPLC-based measurements of aminoacyl-transfer RNA specific activities shows an inverse relationship between cerebral protein synthesis and plasma phenyalanine concentrations in the 200-500 microM range. These findings indicate the neurotoxicity of hyperphenylalninemia is not restricted to the phenylketonuria range of approximately 2000 microM, but is exerted in the supra-physiological range of 200-500 microM.

Upregulation of Blood-Brain Barrier GLUT1 Glucose Transporter Protein and mRNA in Experimental Chronic Hypoglycemia

An in vivo model of chronic hypoglycemia was used to investigate changes in blood-brain barrier (BBB) glucose transport activity and changes in the expression of GLUT1 mRNA and protein in brain microvasculature occurring as an adaptive response to low circulating glucose levels. Chronic hypoglycemia was induced in rats by constant infusion of insulin via osmotic minipumps; control animals received infusions of saline. The criterion for chronic hypoglycemia was an average blood glucose concentration of < 2.3 mmol/l (42 mg/dl) after 5 days. The average blood glucose concentration at the end of the experimental period in the rats selected for study was 2.0 +/- 0.1 mmol/l (36 +/- 1 mg/dl) vs. 4.9 +/- 0.1 mmol/l (88 +/- 1 mg/dl) in the controls. Internal carotid artery perfusion studies demonstrated an increase in the BBB permeability-surface area (PS) product of 40% (P < 0.0005) in the chronically hypoglycemic animals as compared with controls. Western blotting of solubilized isolated brain capillaries demonstrated a 51% increase (P < 0.05) in immunoreactive BBB GLUT1 in the chronically hypoglycemic rats, and Northern blotting of whole-brain poly(A+) mRNA revealed a 50% increase in the GLUT1-to-actin ratio in the insulin-treated group (P < 0.05). Northern blotting analysis of microvessel-depleted total brain poly(A+) showed that the increase in GLUT1 mRNA in the chronically hypoglycemic rats was restricted to the BBB. The present study demonstrates increased expression of GLUT1 mRNA and protein at the BBB in chronic hypoglycemia and suggests that this increase is responsible for the compensatory increase in BBB glucose transport activity that occurs with chronically low circulating blood glucose levels.