Blood-brain Barrier Passage Research Articles

13th Meeting of the Scientific Group on Methodologies for the Safety Evaluation of Chemicals (SGOMSEC): validation and acute toxicity testing.

Scientific principles demand that before newly developed alternative methods for safety testing are fully embraced by the industrial or regulatory community, they reliably and reproducibly predict the designated toxic end point. The process used to determine reliability and reproducibility is termed validation, and it generally culminates with a highly controlled, blinded study using multiple chemicals and laboratories. It is imperative that the validation study is designed to confirm the previously established reproducibility and predictive power of the assay. Much has been learned recently about the practical aspects of validation through investigation of alternative methods for acute toxicity testing, i.e., those methods that assess acute systemic toxicity, skin irritation, and eye irritation. Although considerable progress has been made--many alternative tests are now commonly used in various industrial settings--there have been few tests that have successfully passed a complete validation. Some of the barriers to successful validation have been a) lack of high-quality, reproducible animal data; b) insufficient knowledge of the fundamental biologic processes involved in acute toxicity; and c) the development of truly robust in vitro assays that can accurately respond to materials with a wide range of chemical and physical characteristics. It is recommended that to progress in the areas of eye and skin irritation we need to expand our knowledge of toxic markers in humans and the biochemical basis of irritation; progress in the area of acute systemic toxicity will require the development of in vitro models to determine gastrointestinal uptake, blood-brain barrier passage, and biotransformation.

Developmental changes in blood‐brain barrier potassium permeability in the rat: relation to brain growth.

1. The potassium permeability of the blood-brain barrier (BBB) was determined in anaesthetized rats aged between 21 days gestation and adult using 86Rb+ as a marker for potassium. 2. The brain influx rate constant for 86Rb+ was high in fetal cortex at 21 days gestation (42.5 +/- 4.3 microliters g-1 min-1) but had decreased markedly by just after birth (12.2 +/- 0.6 microliters g-1 min-1). There was a further, gradual, postnatal decline to 7.0 +/- 0.3 microliters g-1 min-1 by 50 days after birth. 3. Developmental changes in passive BBB permeability were examined over the same age range using 14[C]urea. These studies showed similar developmental changes in influx rate to those found for 86Rb+. Specifically, a marked perinatal decline followed by a more gradual postnatal fall. Thus, the changes in potassium permeability probably reflect a decrease in the BBB paracellular leak during development. 4. The changes in BBB permeability coincide with changes in the rate of brain growth and the associated rate of brain potassium accumulation. As the potassium permeability properties of the adult BBB would provide insufficient potassium influx to meet the requirement associated with fetal brain growth, it is suggested that need for potassium may be the reason for the greater BBB permeability early in development.

Passage of blood brain barrier by trandolapril and enalapril in SH rats after chronic treatment

Hemodynamic and autonomic evaluations were carried out after 2–3 weeks of treatment with placebo and at the end of 4 weeks of treatment with an anglotensin converting enzyme (ACE) inhibitor, trandolapril, 2 mg/day in 18 hypertensive patients (average age, 48 ± 2 years) of either sex. This treatment lowered the mean arterial pressure in the whole group from 112 to 105 mm Hg (p < 0.05) without significant changes in basal heart rate or norepinephrine (NE) and epinephrine plasma levels. Based on daytime ambulatory blood pressure monitoring, the patients were separated into 2 equal groups of 9 patients: the better responders (R), with an average decrease in mean arterial pressure of 12 mm Hg, and the lesser responders (NR), with an average fall of mean arterial pressure of 2 mm Hg. Before treatment, the R group had a higher resting heart rate, a lower cardiac output (−16%), and a higher peripheral resistance (+22%) than the NR group (difference not significant). Moreover, the R group was also observed to have a 33% higher plasma NE level (p < 0.05) In the supine position, associated with a 52% higher NE response to standing (p < 0.05), and a 40% lower number of β-adrenergic receptors on lymphocytes, suggesting a higher sympathetic tone and reactivity in that group. Following treatment with the ACE inhibitor, heart rate and plasma NE levels were not altered significantly in either group, suggesting a blunting of the baroreflex response concomitant with the lowered blood pressure, especially in the R group. The cardiac output was unchanged in both groups, but the peripheral resistance decreased by 10% only in the R group (difference not significant). The NE responses to standing and to isometric exercise were attenuated to a greater extent in the R group than In the NR group: −21% versus −14% and −43% versus −7%, respectively. The numbers of β adrenoceptors on lymphocytes were similarly increased by 100% in both groups following this therapy. It is concluded from these studies that patients presenting evidence of increased sympathetic tone and reactivity may be better responders to ACE inhibitor therapy. In fact, treatment with trandolapril was shown to reduce blood pressure and peripheral resistance, in part by attenuating the sympathetic reactivity to a greater extent in the subset of “responders,” presumably by interfering with the anglotensin II-medlated fadlitatory presynaptic mechanisms located on peripheral sympathetic fibers.

Transient blood-brain barrier passage of polar compounds at low pH.

The brain uptake index (BUI) of polar 14C-labeled test compounds with molecular weights (MWs) of 79-70,000 was examined using the single-pass carotid injection technique in pentobarbital-anesthetized rats. Compounds were injected in 40 mM malonate, pH 2.5, and 10 mM N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid, pH 7.4. BUI is defined as (14C-labeled test compound/[3H]H2O in brain)/(14C-labeled test compound/[3H]H2O in injectate) x 100 at a 5-s decapitation time. Increased BUIs of compounds in pH 2.5 buffer were MW dependent with a threshold < 5,000. BUI, extraction, and permeability-surface area product (PS) were significantly greater at pH 2.5 compared with pH 7.4 (P < 0.05). Washouts of [14C]butanol and [3H]H2O at pH 2.5 and pH 7.4 were calculated. Cerebral blood flow and PS increased at low pH. Other buffers, oxalate, glycine, and lactate were used at low pH and also increased BUIs. The duration of the blood-brain barrier (BBB) opening at pH 2.5 was 60 s as estimated by penetrance of the normally excluded dye fluorescein. A plot of BUI or PS at pH 2.5 vs. (MW)1/2 suggests that transient BBB tight junction opening contributed to the passage of polar compounds at low pH.

Passage of amino acids and glucose across the blood-brain barrier in patients with hepatic encephalopathy

We repeatedly measured blood-brain barrier passage of phenylalanine, leucine, glucose and GABA in nine patients with hepatic encephalopathy using the intravenous double-indicator technique. Controls were four patients without liver disease and two of the patients who had recovered completely from their hepatic encephalopathy. The corrected cerebral venous output curves were fitted by use of a three-compartment model with four parameters. In the patients with hepatic encephalopathy, the permeability-surface area products for phenylalanine and leucine from the blood to the brain and from the brain interstitial fluid to the intracellular compartment, the unidirectional extraction and the brain amino acid influx were similar in the two groups. The permeability from the brain back to blood for phenylalanine was decreased by 72% in patients with hepatic encephalopathy compared with that in the control group (p < 0.05), whereas no difference was seen for leucine. The permeability from the brain back to the blood for phenylalanine decreased with coma grade and normalized in the two patients who recovered. Correspondingly, the calculated brain interstitial fluid concentration of phenylalanine was increased in the patients with hepatic encephalopathy. The transfer variables for blood-brain barrier passage of glucose were similar in the two groups. The permeability from the blood to the brain for GABA was very low in both the patients with hepatic encephalopathy and the control group. We conclude that in hepatic encephalopathy the permeability from brain to blood for phenylalanine decreases with coma grade. The decrease is caused by an increased interstitial fluid concentration of the amino acid. No evidence was found of general or selective blood-brain barrier disturbance in hepatic encephalopathy.

Passage of amino acids and glucose across the blood-brain barrier in patients with hepatic encephalopathy

We repeatedly measured blood-brain barrier passage of phenylalanine, leucine, glucose and GABA in nine patients with hepatic encephalopathy using the intravenous double-indicator technique. Controls were four patients without liver disease and two of the patients who had recovered completely from their hepatic encephalopathy. The corrected cerebral venous output curves were fitted by use of a three-compartment model with four parameters. In the patients with hepatic encephalopathy, the permeability-surface area products for phenylalanine and leucine from the blood to the brain and from the brain interstitial fluid to the intracellular compartment, the unidirectional extraction and the brain amino acid influx were similar in the two groups. The permeability from the brain back to blood for phenylalanine was decreased by 72% in patients with hepatic encephalopathy compared with that in the control group (p < 0.05), whereas no difference was seen for leucine. The permeability from the brain back to the blood for phenylalanine decreased with coma grade and normalized in the two patients who recovered. Correspondingly, the calculated brain interstitial fluid concentration of phenylalanine was increased in the patients with hepatic encephalopathy. The transfer variables for bloodbrain barrier passage of glucose were similar in the two groups. The permeability from the blood to the brain for GABA was very low in both the patients with hepatic encephalopathy and the control group. We conclude that in hepatic encephalopathy the permeability from brain to blood for phenylalanine decreases with coma grade. The decrease is caused by an increased interstitial fluid concentration of the amino acid. No evidence was found of general or selective blood-brain barrier disturbance in hepatic encephalopathy. (HEPATOLOGY 1993;17:987–992.)

Blood-brain barrier permeability to sodium. Modification by glucose or insulin?

In order to explore the pathogenetic mechanism underlying the changes in blood-brain barrier sodium transport in experimental diabetes, the effects of hyperglycemia and of hypoinsulinemia were studied in nondiabetic rats. In untreated diabetes, the neocortical blood-brain barrier permeability for sodium decreased by 20% (5.6 +/- 0.7 versus 7.0 +/- 0.8 X 10(5) ml/g/s) as compared to controls. Intravenous infusion of 50% glucose for 2 h was associated with a decrease in the blood-brain barrier permeability to sodium (5.4 +/- 1.2 X 10(5) ml/g/s), whereas rats treated with an inhibitor of insulin-secretion (SMS 201-995, a somatostatin-analogue) had normal sodium permeability (7.3 +/- 2.0 X 10(5) ml/g/s). Acute insulin treatment of diabetic rats normalized the sodium permeability within a few hours as compared to a separate control group (7.7 +/- 1.1 versus 6.9 +/- 1.4 X 10(5) ml/g/s). To elucidate whether the abnormal blood-brain barrier passage is caused by a metabolic effect of glucose or by the concomitant hyperosmolality, rats were made hyperosmolar by intravenous injection of 50% mannitol. Although not statistically significant, blood-brain barrier sodium permeability increased in hyperosmolar rats as compared to the control rats (8.3 +/- 1.0 and 7.0 +/- 1.9 X 10(5) ml/g/s, respectively). It is concluded that either hyperglycemia per se or a glucose metabolite is responsible for the blood-brain barrier abnormality which occurs in diabetes. Further, we suggest that the specific decrease of sodium permeability could be the result of glucose-mediated inhibition of the Na+K+-ATPase localized at the blood-brain barrier.

Role of the binding of neuropeptides to blood plasma proteins in the control of their blood-brain barrier passage.

Annals of the New York Academy of SciencesVolume 496, Issue 1 p. 278-291 Role of the Binding of Neuropeptides to Blood Plasma Proteins in the Control of Their Blood-Brain Barrier Passage V. B. VINNITSKY, V. B. VINNITSKY Institute for Oncology Problems Academy of Sciences of the Ukrainian SSR Kiev, USSRSearch for more papers by this authorG. V. GLINSKY, G. V. GLINSKY Institute for Oncology Problems Academy of Sciences of the Ukrainian SSR Kiev, USSRSearch for more papers by this author V. B. VINNITSKY, V. B. VINNITSKY Institute for Oncology Problems Academy of Sciences of the Ukrainian SSR Kiev, USSRSearch for more papers by this authorG. V. GLINSKY, G. V. GLINSKY Institute for Oncology Problems Academy of Sciences of the Ukrainian SSR Kiev, USSRSearch for more papers by this author First published: May 1987 https://doi.org/10.1111/j.1749-6632.1987.tb35776.xCitations: 3AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume496, Issue1Neuroimmune InteractionsMay 1987Pages 278-291 RelatedInformation

Capillary junctions of the rat are not affected by osmotic opening of the blood-brain barrier.

Osmotic opening of the blood-brain barrier had no effect on the structure of the interendothelial tight junctions located within approximately 9 micron 2 of brain capillary endothelial plasma membrane (junction-containing) examined in this study. These tight junctions restrict the passive diffusion between the blood and the brain and constitute the anatomic basis of the blood-brain barrier. Increased permeability of the blood-brain barrier in the cerebral cortex of the right hemisphere of rats, induced by an infusion of a hypertonic solution of arabinose and monitored with the protein tracer horseradish peroxidase (HRP), was evidenced by the extravasation of the tracer into the extracellular compartment of the brain. Freeze-fracture analysis of the capillaries from the same tissue revealed no alterations in the intramembrane components of the endothelial tight junctions. The junctions, which consist of 8-12 highly anastomosed parallel ridges situated on the PF fracture face of the endothelial plasmalemma, showed no loss of ridge continuity or intra-ridge connections, and were identical to zonulae occludentes from control capillaries. Consistent labeling of numerous vesiculo-tubular elements by HRP in the endothelia of experimental tissue and the three-dimensional nature of these elements observed in platinum replicas support the interpretation that these structures represent transendothelial conduits which are continuous with the luminal and abluminal surfaces of the endothelial cells. Absence of similar structures in control endothelia is taken as evidence that their presence in experimental tissues is a direct response to the osmotic insult. It was concluded, therefore, that during osmotic opening of the blood-brain barrier passage of HRP across the endothelium of brain capillaries is not by an inter-endothelial route due to disruption of tight junctions but rather by a transendothelial route due to amplified vesicular activity.

Chemistry and pharmacology of nootropics

AbstractNicolaus, B.J.R.: Chemistry and pharmacology of nootropics. Drug Dev. Res. 2: 463–474, 1982.The paper discusses the chemistry and pharmacology of the nootropics, reviewing the new chemical entities to recently emerge and in particular the five‐membered heterocyclic lactams belonging to the pyrrolidinone class, such as piracetam and oxiracetam. These gammalactams are related to the folded conformation of GABA, which seems to play a role in the uptake mechanisms—that is, in the transport of GABA across the membrances into differnt nervous tissue elements. The classification of nootropics is discussed, taking into consideration the six main criteria recently suggested, which are: no direct vasoactivity, no change in basic rhythm of EEG activity, blood brain barrier passage, positive metabolic activity in humans and animals, low incidence of side‐effects, and objective demonstration of clinivicacy. A critical analysis is made of the various pharmacological and biochemical models employed to screen the nootropics, including a new approach based on the impaired learning rate of spontaneously hypertensive rats with cerebrovascular lesions. The activity of the new GABA‐derivative nootropic called oxiracetam is also described and compared with the forerunner of the class, piracetam.

The application of brain capillary permeability coefficient measurements to pathological conditions and the selection of agents which cross the blood-brain barrier.

Capillary permeability was analyzed in both normal rat brain and intracerebral 9L gliosarcoma tumor and in rhesus monkey brain using a newly derived formula for the capillary permeability coefficient (P).The Pvalue for isotopic urea and sodium was less in monkey brain than in rat brain. The Pvalue for tumor was 1 log unit higher in tumor for all but the most rapidly transported drugs. Amphotericin B increased the normal brain Pvalue for galactitol but not for urea. Glucocorticoids did not alter brain Pvalues for sucrose or urea. Using P,drugs can be categorized in terms of blood-brain barrier (BBB) exclusion, slow BBB passage, moderate BBB passage, and rapid BBB passage. The technique described in this article is applicable to the study of regional differences in brain capillary permeability associated with disease states.

Brain uptake of selenomethionine Se 75. I. Effects of elevated blood levels of methionine and phenylalanine.

Uptake of selenomethionine Se 75 after intravenous injection in rat was studied in brain, pancreas, plasma, muscle, scalp, and skull. Selenomethionine Se 75 enters rat brain by a rate-limited process with a free exchange at low blood concentrations. Acute preloading with intravenously administered nonradioactive L-methionine or L-phenylalanine results in a reduction of brain uptake of selenomethionine Se 75. Phenylalanine is a more effective inhibitor than methionine. Measurable inhibition of brain uptake of selenomethionine Se 75 is demonstrated at lower plasma levels of phenylalanine than commonly found in clinical phenylketonuria. Bidirectionality of carrier mediated exchange of selenomethionine Se 75 between blood and brain was demonstrated by ventriculocisternal perfusion studies in rabbits. The gamma emissions of selenomethionine Se 75 may be useful in clinical studies of blood brain barrier (BBB) penetration by amino acids which share the same carrier mechanism facilitating BBB passage of selenomethionine Se 75.