Penetration of interleukin-6 across the murine blood-brain barrier

Interleukin-6 (IL-6) can alter brain function after peripheral administration, suggesting that it, like IL-1 alpha, IL-1 beta and TNF-alpha, might be able to cross the blood-brain barrier (BBB). We used multiple-time regression analysis to measure the unidirectional influx constant (Ki) into brain of radioactively labeled murine and human IL-6 given i.v. Ki values ranged from 3.05 to 4.54 (10(-4)) ml/g/min and were inhibited by unlabeled IL-6 but not IL-1 alpha or TNF-alpha, showing that the transport system for IL-6 is distinct from those for IL-1 alpha and TNF-alpha. Approximately 0.2% of the dose injected i.v. entered each gram of brain. The capillary depletion method showed that most of the IL-6 taken up by brain entered the parenchyma. However, only approximately 16% of the radioactivity recovered eluted as intact I-IL-6 in brain and approximately 50% in CSF after chromatographic separation by HPLC/Sephadex. The efflux rate for IL-6 injected into the lateral ventricle of the brain suggests that it enters the blood with the reabsorption of CSF. These results suggest that blood-borne IL-6 can reach sites behind the BBB, but that susceptibility to enzymatic degradation may limit contact time within the CNS.

Blood-borne interleukin-1 alpha is transported across the endothelial blood-spinal cord barrier of mice

1. Previous work has shown that one mechanism by which blood-borne interleukin-1 alpha (IL-1) may be able to affect the central nervous system (CNS) is by direct transport into the brain across the blood-brain barrier (BBB). The BBB of the brain consists of endothelial (between blood and interstitial fluid) and ependymal (between blood and cerebrospinal fluid) barriers. Which of these barriers IL-1 can cross has not previously been investigated. At the spinal cord, which could be the site of action for some of the effects of IL-1 such as analgesia, the BBB consists only of the endothelial barrier. 2. We show here that IL-1 labelled with 125I (I-IL) is transported across the BBB of the spinal cord by a saturable system similar to the one previously described for the brain. High performance liquid chromatography (HPLC) showed that most of the material entering the spinal cord represented intact I-IL. The BBB of the spinal cord was no more leaky to radioactively labelled albumin than the BBB of the brain and was not disrupted by 50 micrograms kg-1 of IL-1. 3. Capillary depletion showed that most of the I-IL entered the parenchymal-interstitial fluid space of the spinal cord with only a modest amount being sequestered by the endothelial cells of its BBB. 4. I-IL entered the cervical, thoracic and lumbar regions of the spinal cord equally well. I-IL entering at the brain and diffusing caudally was estimated only to account for about 1% of the total radioactivity found in the spinal cord after i.v. injection.(ABSTRACT TRUNCATED AT 250 WORDS)

Extreme stability of Tyr-MIF-1 in CSF

Tyr-MIF-1 (Tyr-Pro-Leu-Gly-NH2), an endogenous brain peptide, was incubated at 37 degrees C in cerebrospinal fluid (CSF) from rats and the amount remaining in intact from determined by high performance liquid chromatography (HPLC). By 3 min, a time at which Tyr-MIF-1 had been considerably degraded by rat plasma, essentially no degradation of the tetrapeptide had occurred in CSF. Tyr-MIF-1 persisted in mainly intact form for the 8 days tested, with a calculated half-time degradation of 11.4 days. The simultaneous addition to CSF of equal amounts of Tyr-MIF-1 tritiated on the Tyr and Tyr-MIF-1 tritiated on the Pro facilitated determination of whether Tyr-MIF-1 serves as a precursor of MIF-1 (Pro-Leu-Gly-NH2) in CSF. This possibility was excluded by the findings that the primary metabolite was Tyr-Pro, with minimal and equal amounts of the free amino acids Pro and Tyr being formed, but no MIF-1. The results show the extreme stability of Tyr-MIF-1 in CSF and are consistent with a role for this peptide in the CNS.

Blood to brain and brain to blood passage of native horseradish peroxidase, wheat germ agglutinin, and albumin: pharmacokinetic and morphological assessments

Native horseradish peroxidase (HRP) and the lectin wheat germ agglutinin (WGA) conjugated to HRP are protein probes represented in the blood-brain barrier (BBB) literature for elucidating morphological routes of passage between blood and brain. We report the application of established pharmacokinetic methods, e.g., multiple-time regression analysis and capillary depletion technique, to measure and compare bidirectional rates of passage between blood and brain for radioactive iodine-labeled HRP (I-HRP), WGA-HRP (I-WGA-HRP), and the serum protein albumin (I-ALB) following administration of the probes intravenously (i.v.) or by intracerebroventricular (i.c.v.) injection in mice. The pharmacokinetic data are supplemented with light and electron microscopic analyses of HRP and WGA-HRP delivered i.v. or by i.c.v. injection. The rates of bidirectional movement between blood and brain are the same for coinjected I-HRP and I-ALB. Blood-borne HRP, unlike WGA-HRP, has unimpeded access to the CNS extracellularly through sites deficient in a BBB, such as the circumventricular organs and subarachnoid space/pial surface. Nevertheless, blood-borne I-WGA-HRP enters the brain approximately 10 times more rapidly than I-HRP and I-ALB. Separation of blood vessels from the neocortical parenchyma confirms the entry of blood-borne I-WGA-HRP to the brain and sequestration of I-WGA-HRP by cerebral endothelial cells. Nearly half the I-WGA-HRP radioactivity associated with cortical vessels is judged to be subcellular. Light microscopic results suggest the extracellular pathways into the brain available to blood-borne native HRP do not represent predominant routes of entry for blood-borne WGA-HRP. Ultrastructural analysis further suggests WGA-HRP is likely to undergo adsorptive transcytosis through cerebral endothelia from blood to brain via specific subcellular compartments within the endothelium. Entry of blood-borne I-WGA-HRP, but not of I-ALB, is stimulated with coinjected unlabeled WGA-HRP, suggesting the latter may enhance the adsorptive endocytosis of blood-borne I-WGA-HRP. With i.c.v. coinjection of I-WGA-HRP and I-ALB, I-WGA-HRP exists the brain more slowly than I-ALB. The brain to blood passage of I-WGA-HRP is nil with inclusion of unlabeled WGA-HRP, which does not alter the exist of I-ALB. Adsorptive endocytosis of i.c.v. injected WGA-HRP appears restricted largely to cells lining the ventricular cavities, e.g., ependymal and choroid plexus epithelia. In summary, the data suggest that the bidirectional rates of passage between brain and blood for native HRP are comparable to those for albumin.

Medical consequences of multiple fire ant stings occurring indoors

Stings by the imported fire ant almost always lead to dermal wheal and flare reactions followed by sterile pustules at sting sites. Less commonly, large local dermal reactions, pyoderma, anaphylaxis, or neuropathy may occur. Such reactions have previously been associated with contact with the insects out of doors. We present two previously unreported cases of indoor attacks on individuals by imported fire ants. One patient experienced a cerebrovascular accident in association with the attack, whereas the second patient had no obvious sequelae. With those two reports, a total of four such indoor massive sting episodes have appeared in the recent medical literature. Physicians and other individuals living in areas indigenous to the fire ant should be aware that infestation of buildings with fire ants may be associated with attacks on human beings indoors. Individuals with cognitive dysfunction seem to be especially at risk for attacks by fire ants.

The neurotrophins and their receptors: structure, function, and neuropathology

The neurotrophins are a family of polypeptides that promote differentiation and survival of select peripheral and central neurons. Nerve growth factor, brain-derived neurotrophic factor, neurotrophin-3, neurotrophin-4, and neurotrophin-5 are included in this group. In recent years, tremendous advances have been made in the study of these factors. This has stimulated our review of the field, characterizing the neurotrophins from initial isolation to molecular analysis. The review also discusses their synthesis, localization, and responsive tissues, in both the periphery and CNS. The complex receptor interactions of the neurotrophins are also analyzed, as are putative signal transduction mechanisms. Discussion of the observed and postulated involvement in neuropathological disorders leads to the conclusion that the neurotrophins are involved in the function and dysfunction of the nervous system.

Differential metabolism of Tyr-MIF-1 and MIF-1 in rat and human plasma

The metabolism of the endogenous brain peptides Tyr-MIF-1 (Tyr-Pro-Leu-Gly-NH2) and MIF-1 (Pro-Leu-Gly-NH2) was determined by HPLC after incubation of the tritiated peptides in human and rat plasma. Degradation of Tyr-MIF-1 was rapid in the plasma from both species, in contrast to the slightly delayed degradation of MIF-1 in rat plasma and the extremely prolonged persistence of MIF-1 in human plasma. In rat plasma, more than half of the intact Tyr-MIF-1 and MIF-1 was degraded within 5 min, in contrast to the 5 days required for 50% degradation of MIF-1 in human plasma at 37 degrees. To slow the rapid rate of metabolism, studies were then performed at 0 degree. Incubation of Tyr-MIF-1 in human plasma at 0 degree for 2 hr resulted in HPLC identification of more Tyr-Pro than Tyr at all times. At 0 degree in rat plasma, however, more Tyr than Tyr-Pro was formed after the first 5 min of incubation of the Tyr-MIF-1 that was labeled on the Tyr. This raised the possibility that the tetrapeptide Tyr-MIF-1 might be serving as a precursor of the tripeptide MIF-1. Incubation of Tyr-MIF-1 tritiated at the Pro under the same conditions with and without Tyr-MIF-1 tritiated at the Tyr showed that Tyr-Pro, not MIF-1, was the predominant degradation product of Tyr-MIF-1. In addition to the metabolism of Tyr-MIF-1 being slower at lower temperatures, it was also slowed by some enzyme inhibitors. After 10 min of incubation at 37 degrees, EDTA appeared to be more effective than bestatin, p-chloromercuribenzoic acid (PCMB), pepstatin, or aprotinin, but after 30 min, bestatin was more effective. Intravenous injection of the tritiated peptides into rats showed short half-time disappearances; again, MIF-1 persisted in blood longer than Tyr-MIF-1. Thus, the results show the rapid metabolism of Tyr-MIF-1 in human and rat plasma, the slightly slower metabolism of MIF-1 in rat plasma, the predominant formation of Tyr-Pro rather than MIF-1 from Tyr-MIF-1, and the markedly delayed metabolism of MIF-1 in human plasma.

Opposite direction of transport across the blood-brain barrier for Tyr-MIF-1 and MIF-1: comparison with morphine

Tyr-MIF-1 (Tyr-Pro-Leu-Gly-NH2) and MIF-1 (Pro-Leu-Gly-NH2) are endogenous peptides that can exert opiate-related actions on the CNS after peripheral administration. We found that Tyr-MIF-1 radioactively labeled at the tyrosine was transported across the blood-brain barrier (BBB) in the direction of brain to blood by a saturable system. Transport occurred equally well when the tetrapeptide was labeled with 125I or when it was labeled with 3H. [3H]MIF-1 and [3H]morphine were not transported out of the CNS but were retained by the brain after intracerebroventricular injection. Both [3H]MIF-1 and [3H]morphine entered the brain after i.v. injection, with [3H]MIF-1 crossing the BBB by a mechanism that was partially saturable. The entry rate and accumulation of radioactivity by the brain was 50-100 times greater after the i.v. injection of [3H]MIF-1 than after [3H]morphine. The results show that Tyr-MIF-1 labeled with either 3H or 125I can serve equally well for the measurement of transport across the BBB, that MIF-1 has relatively substantial and rapid access from the blood to the CNS by directly crossing the BBB, and that the BBB can differentially regulate the exchange of related substances between the CNS and blood.

The opiate system in invertebrates

The presence in diverse species of a similar mode of communication, that of a soluble messenger binding to a receptor, raises the question as to whether the specific components of this system are equally widespread. Do invertebrates use the same hormones and receptors as vertebrates do? Invertebrates ranging from unicellular organisms to insects have been shown to contain opiate-like peptides and binding sites, and they exhibit biological responses to opiates. However, critical genetic data are lacking. It is not known how signal systems arise phylogenetically, but it is conceivable that signal molecules that are already present cause the formation of their own receptors from membrane proteins.

Delayed degradation of Tyr-MIF-1 in neonatal rat plasma

Peptides like Tyr-MIF-1 (Tyr-Pro-Leu-Gly-NH2) that are administered during the neonatal period can result in biological effects persisting into the adult period. The possibility that Tyr-MIF-1 might have a prolonged half-life in neonatal blood was investigated by HPLC of plasma obtained from 4-day-old rat pups. More than half (65%) of the tritiated Tyr-MIF-1 incubated with neonatal rat plasma at 37 degrees C remained in intact form at 30 min compared with less than a quarter of the Tyr-MIF-1 incubated with adult rat plasma. The calculated half-life of the tetrapeptide incubated in neonatal plasma was 50.2 min, compared with 13.8 min for adult plasma (p < 0.01). The simultaneous addition of Tyr-MIF-1 tritiated on the Tyr and Tyr-MIF-1 tritiated on the Pro showed the formation of equal amounts of the free amino acids Tyr and Pro; this indicates that Tyr-MIF-1 is not a precursor of MIF-1 in neonatal rat plasma. The results show that the degradation of Tyr-MIF-1 is significantly delayed in plasma from neonatal rats, suggesting the possibility that the metabolism of other peptides and different types of compounds also may be delayed during the perinatal period.

Passage of human amyloid beta-protein 1-40 across the murine blood-brain barrier

Previous studies have suggested that the amyloid beta-protein present in the brains of patients with Alzheimer's disease may be derived in part from peripheral blood. We determined that after IV injection of synthetic amyloid beta-protein 1-40 (A beta), labeled with radioactive 125I (I-A beta), radioactivity accumulated in the brains of mice by a nonsaturable mechanism. Radioactivity also accumulated in the brain after the i.v. injection of radioiodinated reverse amyloid beta-protein 40-1 (I-rA beta). Capillary depletion techniques, however, showed I-A beta to have a much greater degree of association with brain capillaries than I-rA beta. Acid precipitation of radioactivity in CSF samples and recovery from cortical homogenates suggested the presence of intact I-A beta within the CNS after peripheral administration. HPLC analysis of cortical homogenates confirmed the presence of intact I-A beta. Gel electrophoresis of the CSF acid precipitates and of the HPLC fractions further verified the presence of intact blood-derived I-A beta peptide in CNS. These results suggest that endogenous bloodborne A beta can enter the CNS after associating with the capillary endothelium to accumulate intact within the parenchymal and CSF spaces of the brain.

Interleukin-2 does not cross the blood-brain barrier by a saturable transport system

Blood-borne interleukin-2 (IL-2), like other cytokines, is known to affect the central nervous system (CNS). One mechanism by which circulating substances can alter brain function is to directly cross the blood-brain barrier (BBB). We investigated the ability of IL-2 to cross the BBB, the interface between the periphery and the CNS. IL-2 labeled with 125I (I-IL-2) was injected into mice intravenously and its rate of entry into the brain determined by multiple-time regression analysis. I-IL-2 was found to enter the brain about 10 times faster than albumin. Neither morphine nor antibodies to IL-2, IL-1 alpha, or the IL-1 receptor affected the entry of I-IL-2. High performance liquid chromatography (HPLC) confirmed that the radioactivity entering the brain represented intact cytokine. However, excess unlabeled IL-2 was unable to impede the entry of I-IL-2, indicating that this transport is nonsaturable. This contrasts with saturable transport systems found for the cytokines IL-1 alpha and TNF-alpha, but still may explain how IL-2 can exert central effects.

CNS effects of peptides: a cross-listing of peptides and their central actions published in the journal Peptides, 1986-1993

The centrally mediated effects of peptides as published in the journal Peptides from 1986 to 1993 are tabulated in two ways. In one table, the peptides are listed alphabetically. In another table, the effects are arranged alphabetically. Most of the effects observed after administration of peptides are grouped, wherever possible, into categories such as cardiovascular and gastrointestinal. The species used in most cases has been rats; where other animals were used, the species is noted. The route of administration of peptides and source of information also are included in the tables, with a complete listing provided at the end. Many peptides have been shown to exert a large number of centrally mediated effects.

Saturable efflux of the peptides RC-160 and Tyr-MIF-1 by different parts of the blood-brain barrier

Peptides have been shown to be transported in the direction of both blood to brain and brain to blood. Although blood to brain transport is known to occur at both the choroid plexus and the capillary bed of the brain, comprising the two major components of the blood-brain barrier, the location of efflux systems for peptides remains largely unstudied. We adapted established methodologies to study this question for two peptides known to be transported out of the brain after injection into the cerebrospinal fluid (CSF): Tyr-MIF-1, transported by peptide transport system (PTS)-1 and RC-160, a somatostatin analog transported by PTS-5. Radioactive iodide, known to be transported out of the brain primarily by the capillaries, also was studied. We found that after injection into brain tissue, RC-160 and iodide were rapidly transported out of the brain by saturable mechanisms. By contrast, efflux of Tyr-MIF-1 was slow and nonsaturable after injection into brain tissue, but rapid and saturable after injection into the lateral ventricle of the brain. Autoradiography confirmed that peptide injected into brain tissue did not diffuse far from the site of injection during the study period. The results indicate that the efflux system for RC-160 is located at least partly at the capillaries and suggest that the major location for the efflux system of Tyr-MIF-1 is at the choroid plexus.

Interleukin-1 alpha in blood has direct access to cortical brain cells

Interleukin-1 alpha (IL-1 alpha), an immunoregulatory protein secreted by the peripheral immune system, affects the central nervous system (CNS). IL-1 alpha could directly enter the parenchyma of the brain in intact form to alter brain function, or it could be blocked or sequestered by the capillary bed comprising the blood-brain barrier (BBB) that normally retards entry of circulating proteins to the brain and cerebrospinal fluid (CSF). We show here by use of the selective interleukin receptor antagonist (IL-1ra), capillary depletion method, high performance liquid chromatography (HPLC) and saturation with unlabeled IL-1 alpha that radioactively labeled IL-1 alpha injected iv directly enters the CNS in intact form. This also occurs in the brain cortex, an area devoid of circumventricular organs (CVOs), and in the CSF, an area devoid of capillaries. Capillaries can also sequester IL-1 alpha in a saturable manner, suggesting that they may be the site for the carrier-mediated entry of IL-1 alpha into the CNS. Thus, the results show that circulating IL-1 alpha has direct access to cortical brain cells behind the BBB through a saturable transport system that provides a major pathway by which the brain and immune system interact.

Passage of pituitary adenylate cyclase activating polypeptide1-27 and pituitary adenylate cyclase activating polypeptide1-38 across the blood-brain barrier

Pituitary adenylate cyclase activating polypeptide (PACAP) is a newly discovered regulatory peptide related to vasoactive intestinal peptide and is found widely distributed throughout peripheral tissues and the central nervous system. We examined the ability of its two major forms of 38 (P38) and 27 (P27) amino acid residues to cross the murine blood-brain barrier. After i.v. injection, [125I]P27 had a unidirectional influx constant (Ki) into the brain of 2.13 (10(-3)) ml/g/min with no saturable component to entry. Despite being larger and less lipophilic, [125I]P38 entered the brain more than 30% faster by a saturable transport system. A peptide-T analog related to PACAP that has its own saturable transport system did not inhibit the entry of [125I]P38, but did alter its binding to vascular receptors. Despite the greater Ki of [125I]P38, a larger percentage of the i.v. dose of [125I]P27 entered the brain due to favorable pharmacokinetics. However, [125I]P38 was more resistant to degradation within the brain and, after correction for degradation, its Ki increased to 16.5 (10(-3)) ml/g/min. The influences of peripheral degradation and sequestration by capillaries were negated by use of the brain perfusion and capillary depletion methods. These showed that the Ki into the brain interstitial fluid/parenchymal space for [125I]P38 was 15.3 (10(-3)) ml/g/min and was again inhibited with unlabeled P38. Both PACAPs were transported out of the central nervous system and inhibited the efflux of the other, but there was a [125I]P38 preferring subcomponent to the transport system.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of neonatal treatment with Tyr-MIF-1, morphiceptin, and morphine on development, tail flick, and blood-brain barrier transport

Morphine and endogenous peptides can alter developmental processes, inducing changes that can endure into adulthood. Morphiceptin binds to mu opiate receptors and to non-opiate sites labeled by Tyr-MIF-1 (Tyr-Pro-Leu-Gly-NH2), an endogenous brain peptide known to modulate opiate effects. Morphine, morphiceptin, Tyr-MIF-1, morphine + Tyr-MIF-1, and morphiceptin+Tyr-MIF-1 (50 micrograms, s.c.) were given to rats during their first week of life. Animals given morphine alone or in combination with Tyr-MIF-1 had significantly lower body weights for the first 3 weeks of life and delayed eye opening on day 16. Rats given morphine had hypersensitive tail flick responses on day 9 while those given morphine + Tyr-MIF-1 were hypersensitive on days 3, 8, and 9. Locomotor, passive avoidance, and rotorod behaviors were not altered by the neonatal treatments. Transport of [125I]Tyr-MIF-1 out of the brain was tested on day 23 and found to be increased by neonatal morphine, an effect that was significantly potentiated by neonatal Tyr-MIF-1. The results indicate that neonatal administration of peptides and opiates can affect later peptide transport across the blood-brain barrier as well as selected developmental characteristics.

Physiological consequences of the passage of peptides across the blood-brain barrier

Peptides given peripherally have been shown to affect the central nervous system (CNS). Peptides are also capable of crossing the blood-brain barrier (BBB). It is unclear, however, whether such crossing underlies the ability of peptides to affect the CNS. We review specific examples in which a peptide must cross the BBB to produce its effect. The effect elicited by passage often duplicates the effect elicited at peripheral sites of action. Other examples, however, are reviewed in which peptides have opposite effects after central and peripheral administration. Such paradoxical effects suggest that passage of peptides may be involved in feedback or counter-regulatory loops.

Murine tumor necrosis factor alpha is transported from blood to brain in the mouse

The cytokines are important components of the brain-immune axis. Recent work has shown that [125I]IL-1 alpha and [125I]IL-1 beta are transported from the blood into the brain by a saturable system. Here we show that murine tumor necrosis factor alpha (mTNF alpha) labeled with 125I (I-mTNF alpha) crosses the blood-brain barrier (BBB) after i.v. injection by a transport system different from that for the interleukins. Self inhibition with mTNF alpha showed that this transport system was saturable, and lack of inhibition by IL-1 alpha, IL-1 beta, IL-6, or MIP-1 alpha showed selectivity of the system. High performance liquid chromatography (HPLC) of the radioactivity recovered from brain and from cerebrospinal fluid after the i.v. injection of I-mTNF alpha showed that the cytokine crossed the BBB largely in intact form. Capillary depletion showed that the accumulation of I-mTNF alpha in the cerebral cortex was due to passage across the BBB rather than to sequestration by capillaries. Transport rate was not changed by acute treatment with the neurotoxin aluminium or by acute and chronic treatment with the cationic chelator deferoxamine, but it was more than three times faster in neonatal rats. Efflux of I-mTNF alpha from the brain was slower than would have been predicted based on reabsorption of cerebrospinal fluid, suggesting that TNF alpha is sequestered by the brain. The BBB was not disrupted by up to 50 micrograms kg-1 of mTNF alpha i.v. in either adult mice or neonatal rats as assessed by the BBB's impermeability to radioactively labeled albumin.(ABSTRACT TRUNCATED AT 250 WORDS)

Endogenous peptide Tyr-Pro-Trp-Gly-NH2 (Tyr-W-MIF-1) is transported from the brain to the blood by peptide transport system-1

Tyr-W-MIF-1 (Tyr-Pro-Trp-Gly-NH2) is a recently isolated peptide that belongs to a larger family that includes Tyr-MIF-1 (Tyr-Pro-Leu-Gly-NH2) and MIF-1 (Pro-Leu-Gly-NH2). Despite similarities in structure, Tyr-MIF-1 and MIF-1 can act differently in behavioral, blood-brain barrier (BBB) transport, and receptor binding systems. Tyr-W-MIF-1, like Tyr-MIF-1, has both opiate and antiopiate activity, but may be more opiate-like than Tyr-MIF-1. Tyr-MIF-1, but not MIF-1, is transported from brain to blood by peptide transport system (PTS)-1. PTS-1 transports mainly Tyr-MIF-1 and methionine enkephalin, but does not transport amino acids, peptide fragments of Tyr-MIF-1, D-Tyr-MIF-1, or unrelated peptides and proteins. We tested whether Tyr-W-MIF-1 also was transported across the BBB and, if so, whether PTS-1 was involved. 125I-Tyr-W-MIF-1 had a half-time disappearance from the brain of 22.4 min. This is faster than the efflux occurring with non-saturable reabsorption of the cerebrospinal fluid and, therefore, is consistent with saturable transport, but it is slower than the efflux rate of Tyr-MIF-1, suggesting a less robust transport than for Tyr-MIF-1 Self-inhibition with excess unlabeled Tyr-W-MIF-1 confirmed a saturable component, with a dose of 4.2 nmol producing 50% inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)

Pituitary adenylate cyclase activating polypeptide (PACAP) can cross the vascular component of the blood-testis barrier in the mouse

Pituitary adenylate cyclase activating polypeptide (PACAP), present in highest concentrations in the hypothalamus and testes, affects the release of LH, FSH, and prolactin, as well as Sertoli cell function. We examined the ability of the 38-amino acid form of PACAP labeled with 125I (I-P38) to cross the vascular component of the blood-testis barrier. The unidirectional influx constant (Ki) was 4.23 x 10(-3) ml/g-minute, which is about 5 times faster than the entry of LH and about 17 times faster than that of serum albumin. Entry occurred in part by a saturable transport system, with 20 micrograms/mouse of unlabeled P38 inhibiting transport by 40%. An analog of peptide T, which like PACAP is related to vasoactive intestinal polypeptide and has been found to have its own saturable transport system into the brain, did not alter the uptake of I-P38 by the testes. A dose of 10 micrograms/mouse, but not of 20 micrograms/mouse, was associated with a contraction of the vascular space of the testes. HPLC confirmed that a small but persistent percentage of the radioactivity recovered from the testes represented intact I-P38. These results suggest that circulating P38 may contribute to the testicular pool of PACAP, which may play an active role in the function of the testes.

Radioactively iodinated cyclo(His-Pro) crosses the blood-brain barrier and reverses ethanol-induced narcosis

Cyclo(His-Pro) (cHP) is a peptide widely distributed in the central nervous system (CNS) and peripheral tissues that can affect brain function after either peripheral or CNS administration. This suggests that cHP may be a neuromodulator capable of crossing the blood-brain barrier (BBB). We, therefore, studied the ability of radioactively labeled cHP (I-cHP) to cross the BBB. We found that I-cHP can cross the BBB in either the direction of blood to brain or brain to blood by nonsaturable mechanisms. The rate of entry of I-cHP into the CNS was low in comparison with other peptides, especially considering its relatively low molecular weight and high lipid solubility. However, this slow entry was offset by a long half-life in blood and extreme enzymatic resistance, allowing cHP to accumulate in the CNS. This accumulation was sufficient to allow intravenous cHP to reverse ethanol-induced narcosis, an effect mediated through the CNS. The rate of entry of I-cHP was resistant to conditions that alter the passage of some other substances across the BBB or that have been shown to affect cHP metabolism such as aging, diabetes, and pretreatment with aluminum. Entry of cHP into the brain was not retarded by binding to serum proteins. Significant amounts of I-cHP entered the serum, brain, and other tissues after intraperitoneal administration, the route used in many studies of cHP. Taken together, these results show that cHP is a highly stable peptide that, after intravenous injection, slowly enters the brain by a nonsaturable mechanism in amounts large enough to affect such aspects of the CNS as ethanol-induced narcosis.

Uptake, content, regulation of plasma concentrations, and binding of Tyr-MIF-1 by the adrenals

The known occurrence of opiates in the adrenals stimulated us to determine whether Tyr-MIF-1 (Tyr-Pro-Leu-Gly-NH2), an endogenous peptide that can act as an antiopiate, is present in these glands and whether adrenalectomy affects its concentrations in plasma. The presence of Tyr-MIF-1 in the adrenals of the rat was shown by radioimmunoassay (RIA) and high performance liquid chromatography (HPLC). Binding sites for the tetrapeptide also were found in the adrenal. The concentrations and binding of Tyr-MIF-1 were higher in the adrenal medulla than in the adrenal cortex. The adrenals preferentially trapped 125I-Tyr-MIF-1 as compared with 99mTc-albumin after intravenous administration. However, after correction for tissue weight and vascular space, accumulation of 125I-Tyr-MIF-1 by the adrenals was in the general range seen for several other tissues. The concentrations of Tyr-MIF-1-like immunoreactivity determined by RIA in the plasma of adrenalectomized rats were increased in comparison with sham operated or unoperated controls. This approximate doubling was unchanged by the site of sampling: hepatic portal vein, renal vein, inferior vena cava, jugular vein, or truncal blood. Hypophysectomy, removal of the adrenal medulla, or treatment with corticosterone also did not block this increase. Tyr-MIF-1-like immunoreactivity in the plasma of adrenalectomized rats eluted at the same position by HPLC as did the synthetic Tyr-MIF-1 standard. Thus, the adrenal gland contains Tyr-MIF-1 and can affect its concentrations in plasma.

Orally administered cyclo(His-Pro) reduces ethanol-induced narcosis in mice

Cyclo(His-Pro) (cHP) is an endogenous, enzymatically resistant, biologically active peptide. We examined its ability to be absorbed after oral administration. cHP radioactively labeled with 125I (I-cHP) was fed to adult mice, and blood and tissue samples were taken 15-90 min later. Radioactivity quickly appeared in blood at levels about one half to one fourth those previously found after IV injection. The highest concentrations were in the kidney and liver, but the testes, muscle, lung, and brain also contained more radioactivity than was accounted for by their vascular spaces. Between 25-32% of the radioactivity recovered from blood 30 min after feeding eluted on high-performance liquid chromatography in the position of intact peptide. Oral cHP reversed ethanol-induced narcosis, an effect previously found to occur within the brain. These results show that cHP can be absorbed orally in amounts sufficient to affect the CNS.

Permeability of the blood-brain barrier to peptides: an approach to the development of therapeutically useful analogs

Peptides have been shown in both in vivo and in vitro systems to cross the blood-brain barrier (BBB) and so affect function on the side contralateral to their origin. Some peptides cross primarily by transmembrane diffusion, a nonsaturable mechanism largely dependent on the lipid solubility of the peptide. Other peptides are transported by saturable systems across the BBB. These transport systems can be in the CNS to blood direction, as in the cases of Tyr-MIF-1 and methionine enkephalin, in the blood to CNS direction, as in the case of peptide T, or bidirectional, as in the case of LHRH. Other factors that also affect the amount of peptide crossing the BBB include binding in blood, volume of distribution, enzymatic resistance, and half-time disappearance from the blood. An in vitro model of the BBB has been characterized and used to confirm that peptides can cross the BBB. Results with the model agree with those obtained in vivo and have been used to study the permeability of the BBB to peptides, the effect of peptides on BBB integrity, the cellular pathway peptides and proteins use to cross the BBB, and the ability of the BBB to degrade peptides. The in vivo and in vitro methods have been used together to develop halogenated enkephalin analogs that are enzymatically resistant, cross the BBB readily to accumulate in areas of the brain rich in opiate receptors, and are powerful analgesics.(ABSTRACT TRUNCATED AT 250 WORDS)

Selective uptake of the somatostatin analog RC-160 across the blood-brain tumor barrier of mice with KHT sarcomas

The development of somatostatin analogs with anti-tumor effects has raised hopes for their use in various cancers and tumors of the central nervous system. However, for many therapeutic agents, access to normal brain is retarded by the blood-brain barrier (BBB) and to tumor tissues by a blood-brain tumor barrier (BBTB). We examined the ability of RC-160, a somatostatin analog with known anti-tumor activity, to cross the normal BBB and the BBTB in mice with brain sarcomas. In comparison with the normal BBB, the BBTB was about 10 times more permeable to the vascular marker albumin (radioactively labeled with 99mTc), but the BBTB still represents a substantial barrier. By contrast, the entry rate of RC-160, radioactively labeled with 125I, into brain sarcomas was 60 times higher than into normal brain tissue; more than 1% of the RC-160 injected i.v. was taken up by each gram of brain tumor. These results show that a brain tumor can selectively accumulate the potentially therapeutic agent RC-160.

Transport, uptake, and metabolism of blood-borne vasopressin by the blood-brain barrier

Transport, binding, and metabolism of [phenylalanyl-3,4,5,-3H(N)]arginine vasopressin (AVP) by the blood-brain barrier (BBB) was studied in adult guinea-pigs by means of a novel vascular brain perfusion (VBP)/capillary depletion technique and HPLC. A time-dependent, progressive brain uptake of 3H-radioactivity was measured over the 10 min period of VBP both in brain homogenates and in brain tissue depleted of cerebral microvessels. The unidirectional blood-to-brain transport constant, K(IN), estimated by multiple-time tissue uptake analysis of the homogenate and postcapillary supernatant, indicated that the BBB transfer rate for [3H]AVP (K(IN) = 2.37 +/- 0.25 microliters min-1 per gram brain homogenate) was almost 10 times higher than for simultaneously perfused [14C]sucrose, a cerebrovascular space marker. In contrast to homogenate and postcapillary supernatant, the [3H]radioactivity determined in the vascular pellet after dextran density centrifugation of the brain homogenate was very low and only somewhat higher than for [14C]sucrose. HPLC analysis of the perfused brain tissue revealed time-dependent degradation of the blood-borne neuropeptide. The percentage of intact [3H]AVP as determined in the postcapillary supernatant progressively declined during brain perfusion, from 49% at 1 min to 11.9% at 10 min. The major detectable labeled metabolite was [3H]phenylalanine, the labeled amino acid residue of [3H]AVP. The aminopeptidase inhibitor bestatin (0.5 mM), perfused simultaneously with [3H]AVP by the VBP technique, did not alter tissue uptake of [3H]AVP, indicating that there was no significant hydrolysis of peptide by the luminal BBB surface.(ABSTRACT TRUNCATED AT 250 WORDS)

The interleukins-1 alpha, -1 beta, and -2 do not acutely disrupt the murine blood-brain barrier

Previous studies have suggested that some of the central nervous system (CNS) effects of interleukin-2 (IL-2) and perhaps other cytokines might be mediated through disruption of the blood-brain barrier (BBB). We investigated the ability of human IL-2 and, in selected studies, human IL-1 alpha and human IL-1 beta to disrupt the BBB to radioiodinated bovine serum albumin (RISA) after intravenous (i.v.) and intracerebroventricular (i.c.v.) injection. No disruption of the BBB occurred for up to 2 h after the i.v. injection of 2 micrograms/mouse of IL-2 (10(5) U/kg of body weight), 2 micrograms of IL-1 alpha (10(7) U/kg), or 2 micrograms of IL-1 beta (10(7) U/kg). This dose of i.v. IL-2 also did not affect BBB permeability to RISA in the brain to blood direction. Damage to the BBB induced by hypertension elicited by i.v. epinephrine was not enhanced or prolonged by IL-2. When given directly into the CNS by the i.c.v. route, 100 ng of IL-2 (2.2 x 10(5) U/kg of brain), 100 ng of IL-1 alpha (2.2 x 10(7) U/kg of brain), or 100 ng of IL-1 beta (2.2 x 10(7) U/kg of brain) had no effect on BBB integrity in either the blood to brain or the brain to blood direction. We conclude that the effects of IL-1 alpha, IL-1 beta, and IL-2 on the CNS, as studied under these conditions, are not due to disruption of the BBB but are mediated by other mechanisms including the ability of some interleukins to cross the BBB by a saturable transport system described previously.

Human interleukin-1 alpha crosses the blood-testis barriers of the mouse

Interleukin-1 alpha (IL-1 alpha) has been shown to have direct effects on the gonads, affecting steroidal secretion, DNA synthesis by spermatogonia, and the immune function of the testes. It is unclear, however, how IL-1 alpha exerts these effects because the testis is partitioned into basal and adluminal compartments by both a vascular and a Sertoli cell barrier. The authors used a highly sensitive method to quantify the unidirectional flux rates (Ki) into the testis of technetium pertechnetate-labeled human albumin (T-alb), a compound that does not readily cross the vascular barrier, and human IL-1 alpha radioactively labeled with 125I (I-IL). The entry rate (Ki) was almost six times greater for I-IL than for T-alb. Part of the enhanced entry of I-IL was due to a saturable transport system. Nearly 0.2% of the total injection had entered the testes 60 minutes after intravenous administration, and more than 75% of that amount was not accounted for by the albumin space. Collection of testicular interstitial fluid from the basal compartment and seminiferous tubule fluid from the adluminal compartment showed preferential entry of I-IL into these compartments. Analysis by high-pressure liquid chromatography or radioactivity recovered from the testis showed that intact I-IL was entering the testis. The leakiness of the blood-testis barrier was measured by the rate of entry for T-alb, which was not altered by injection of unlabeled human IL-1 alpha in doses of up to 50 micrograms/kg (5 x 10(6) U/kg), and by the wet weight of the testes. The results show that circulating IL-1 alpha can have direct access to the testis, supporting previous studies suggesting a direct effect of IL-1 alpha on gonadal function.

Effects of various reproductive hormones on the penetration of LHRH across the blood-brain barrier

A previous study has shown bidirectional saturable transport of LHRH across the blood-brain barrier. Here, the effects of the steroids progesterone and beta-estradiol and the pituitary glycoproteins luteinizing hormone (LH) and follicle stimulating hormone (FSH) on the bidirectional transport rate were determined. No statistically significant difference in brain to blood transport of 125I-LHRH was found in mice given ICV progesterone (1 and 100 pmol/mouse), beta-estradiol (1 and 100 pmol/mouse), FSH (10 and 1000 pmol/mouse) or LH (100 and 1000 pmol/mouse). Blood to brain transport of 125I-LHRH, tested in rats with a carotid artery perfusion method, was not affected by inclusion of progesterone (100 nmol/ml), beta-estradiol (100 nmol/ml), LH (2 and 10 nmol/ml), or FSH (10 nmol/ml) in the perfusate. We conclude, therefore, that unlike its release from the hypothalamus, the exchange of LHRH between the CNS and blood is unlikely to be influenced by reproductive hormones.

Lack of saturable transport across the blood-brain barrier in either direction for beta-amyloid1-28 (Alzheimer's disease protein)

beta-Amyloid and related peptides are components of the neurofibrillary tangles found in the brains of patients with Alzheimer's disease and have been suggested to be directly involved in the pathophysiology of that condition. It is unclear whether the amyloid deposited in the brain arises from the peripheral circulation, which would require passage across the blood-brain barrier (BBB), or whether it is produced within the brain itself. We examined the ability of beta-amyloid1-28 (beta Am), a commercially available, biologically active fragment, radioactively labeled with 125I (I-beta Am), to cross the BBB. After IV injection of I-beta Am, radioactivity entered the brain slowly, but to a greater extent than could be attributed to its being trapped in the vascular space of the brain. Entry was not inhibited by an excess of unlabeled beta Am or by pretreatment with aluminum, indicating that entry was by the nonsaturable mechanism of transmembrane diffusion. After intraventricular injection of I-beta Am, radioactivity was cleared slowly from the brain and was not affected by excess unlabeled beta Am or by pretreatment with aluminum, indicating that clearance probably occurred with reabsorption of cerebrospinal fluid. The excess beta Am did not alter the brain/blood ratio or the clearance rate of radioactively labeled albumin, indicating that under the conditions of this experiment beta Am did not have measurable effects on BBB integrity or on the rate of reabsorption of cerebrospinal fluid. High performance liquid chromatography (HPLC) showed that I-beta Am was rapidly degraded, especially by the brain, to smaller peptide fragments.(ABSTRACT TRUNCATED AT 250 WORDS)

EEG evidence that morphine and an enkephalin analog cross the blood-brain barrier

The ability of naltrexone but not methyl naltrexone to cross the blood-brain barrier (BBB) was used to provide a different approach for the demonstration that opiates can enter the brain. Cortical electroencephalographic (EEG) measurements were made in rats receiving peripheral (IP) injections of naltrexone or methyl naltrexone and morphine or an enkephalin analog [Tyr-D-Ala-Gly-MePhe-Met(O)-ol]. Naltrexone significantly blocked the EEG effects of morphine and the enkephalin analog, but methyl naltrexone failed to do so. The results provide biological evidence that an opiate peptide can cross the BBB to affect the activity of the brain.

Human interleukin (IL) 1 alpha, murine IL-1 alpha and murine IL-1 beta are transported from blood to brain in the mouse by a shared saturable mechanism

Interleukins (ILs) 1 alpha and 1 beta are important components of the neuroimmune axis. Recent work has shown that human 125I-IL-1 alpha can enter the brain from the blood by a saturable system, suggesting a mechanism that may directly link the immune and nervous systems. Here, it is shown that radioiodinated murine IL-1 beta and especially murine IL-1 alpha are even more rapidly transported into the brain of the mouse than is radioiodinated human IL-1 alpha after i.v. injection. All three cytokines exhibited self-inhibition, thus demonstrating saturable transport. Also, they all cross-inhibited the transport of each other. This shows that there are not three separate transport systems, but that they either share transport systems with overlapping affinities or share a single system. It was calculated that 0.06% to 0.08% of the dose of human 125I-IL-1 alpha injected i.v. was present in the brain during the first 60 min. By contrast, no saturable component could be detected in the brain to blood passage of the three ILs. No disruption of the blood-brain barrier to radioactively labeled albumin was found with i.v. doses of up to 50 micrograms/kg of human IL-1 alpha. Additional studies on the blood to brain transport of human 125I-IL-1 alpha showed no modification by dexamethasone, morphine, indomethacin or alpha-melanocyte stimulating hormone. Studies with antibodies directed toward the binding or nonbinding sites of IL or its receptor on the murine T lymphocyte suggest similar, but not identical, structural requirements for transport and for receptor binding.(ABSTRACT TRUNCATED AT 250 WORDS)

Delivering peptides to the central nervous system: dilemmas and strategies

Peptides have been shown to cross the blood-brain barrier (BBB) as intact molecules so that they can influence the central nervous system. Peptides cross by saturable and nonsaturable mechanisms in the direction of both brain to blood and blood to brain. Passage of peptides, especially by saturable transport, has been shown to be influenced by pharmacological agents and physiological events. These findings support the view that peptides or their analogues could be useful as therapeutic agents for disorders of the central nervous system. They also suggest strategies in approaching therapeutic goals, including manipulating transport rates, targeting diseases due to altered BBB-peptide interactions, and designing analogues capable of taking advantage of such mechanisms of passage as paracellular transmembrane diffusion and brain-to-blood transport.

Bidirectional saturable transport of LHRH across the blood-brain barrier

Systemic administration of luteinizing hormone-releasing hormone (LHRH) in rats has been found to influence behavior independently of pituitary or ovarian function. A previous study has shown that LHRH can cross the blood-brain barrier in one direction, but it was not known whether this was due to a saturable transport system. The rate of entry of 125I-labeled LHRH from blood to brain was determined by two different single-pass methods of carotid perfusion. The first, a multiple time point method, measures Ki from the slope of the linear regression when brain-to-blood ratios of radioiodinated LHRH are plotted against time. Saturable transport was determined by the difference between the Ki of rats perfused with 125I-LHRH (12.51 X 10(-3) mg.g-1.min-1) vs. rats perfused with 125I-LHRH and unlabeled LHRH (10 nmol/ml; 2.20 X 10(-3) ml.g-1.min-1). The inhibition by the unlabeled peptide was statistically significant (P less than 0.001). The second method, a single time point technique, measures the cerebrovascular permeability-surface area coefficient (PA). Saturable transport was determined in rats by the competition of unlabeled LHRH with 125I-LHRH. The PA value for 125I-LHRH (20.00 X 10(-3) ml.g-1.min-1) was significantly greater (P less than 0.05) than for 125I-LHRH with the addition of 10 nmol/ml unlabeled LHRH (4.14 X 10(-3) ml.g-1.min-1). Saturable transport of LHRH from brain to blood in mice was also determined.(ABSTRACT TRUNCATED AT 250 WORDS)

Carrier-mediated transport of labeled oxytocin from brain to blood

The transport of 125I-oxytocin from brain to blood was investigated in mice after intraventricular injection of radioactively labeled oxytocin with or without unlabeled candidate inhibitors. Residual radioactivity in the brain detected after decapitation was the principal determinant of transport activity. The half-time disappearance from the central nervous system of labeled oxytocin was 19.1 min. Inhibition by 10 nmol/mouse of oxytocin showed a saturable component to transport. A 10-nmol dose of tyrosine-melanocyte-stimulating hormone release inhibiting factor (Tyr-MIF-1) and pressinamide also significantly inhibited transport of labeled oxytocin (p less than 0.05). There was no inhibition of the system by a 10-nmol dose of tyrosine, iodotyrosine, MIF-1, or arginine vasopressin. Studies performed with 125I-oxytocin injected simultaneously with 131I-Tyr-MIF-1 with or without unlabeled oxytocin or Tyr-MIF-1 were consistent with both peptides being transported by the previously described peptide transport system-1 (PTS-1). Pretreatment with aluminum (100 mg/kg of elemental aluminum given 60-90 min before intraventricular injection), previously shown to inhibit PTS-1 and some other transport systems, inhibited the transport of labeled oxytocin. Radioactivity collected from the blood after intraventricular injection of 125I-oxytocin eluted on HPLC at the same position as the labeled oxytocin standard and differently from tyrosine, Tyr-MIF-1, MIF-1 and tocinamide. It is concluded that a saturable system exists for the transport of intact oxytocin from brain to blood which appears to be the previously described PTS-1.

Leucine modulates peptide transport system-1 across the blood-brain barrier at the stereospecific site within the central nervous system

Previous results have shown that leucine injected into a cerebral ventricle (i.c.v.) can act as an allosteric regulator of peptide transport system-1 (PTS-1), the system that transports Tyr-Pro-Leu-Gly-NH2 (Tyr-MIF-1) and the enkephalins out of the central nervous system (CNS). D-Leucine appeared more potent than L-leucine. In the current study, dose-response curves were constructed for each compound after both intravenous (i.v.) and i.c.v. injection. Based on ED50 values after i.c.v. injection, D-leucine was about 200 times more potent than L-leucine in its inhibition of PTS-1, thereby confirming stereospecificity of the allosteric site. D- and L-Leucine were also more potent when given i.c.v. than when given i.v., suggesting that the site is located on the CNS side of the blood-brain barrier (BBB). The finding that D-leucine was less potent than L-leucine when given i.v. is also consistent with a CNS site of action because the L-isomer of leucine has been shown to be preferentially transported into the brain. These findings agree with the previous suggestion that some of the neurotoxic effects of leucine may be mediated through PTS-1 and could help explain how D-amino acids can exert opiate-related effects on the CNS.

Blood to brain transport of interleukin links the immune and central nervous systems

Interleukins (IL) are naturally occurring proteins that regulate, and thus link, both the immune system and the central nervous system (CNS). Since proteins are assumed not to be able to cross the blood-brain barrier (BBB), it is controversial how this linkage could occur. We show here that after iv injection of 125I-hIL-1 alpha, radioactivity in the brain eluted on HPLC in the position of the labeled cytokine. In addition, entry was inhibited by unlabeled hIL-1 alpha. Our demonstration of a saturable, carrier-mediated system that transports recombinant human IL-1 alpha in intact form from the blood into the CNS indicates a direct immune-CNS connection.

A giant prolactinoma and the effect of chronic bromocriptine therapy on basal and TRH-stimulated serum prolactin levels

The role of bromocriptine as primary therapy for prolactin-producing tumors is currently well accepted in the literature. Bromocriptine decreases the concentration of serum prolactin and this decrease precludes tumor shrinkage, despite the lack of correlation between amount of decrease in tumor size and baseline serum prolactin. We submit the case of a patient on chronic bromocriptine therapy followed by measuring baseline and thyrotropin-releasing hormone (TRH)-stimulated serum prolactins. Bromocriptine affects both release and storage of prolactin. The literature has suggested that the effects of bromocriptine on storage and synthesis may be responsible for its effects on tumor size. It was felt that TRH stimulation would more accurately reflect storage and synthesis, and thus correlate better with tumor size. The pituitary was initially debulked via a right frontal approach; then the patient was placed on bromocriptine therapy and postoperatively followed with baseline and TRH-stimulated serum prolactins. The size of the pituitary was measured by computed tomography. Baseline serum prolactin levels rapidly decreased, but despite the slow decrease in TRH-stimulated prolactins no change was noted in tumor size. Because of the time difference between the baseline and TRH-stimulated prolactin levels, we conclude that clinically bromocriptine affects primarily secretion of prolactin and secondarily storage and synthesis. We also show that TRH-stimulated prolactin does not correlate with size of prolactin-secreting pituitary tumors and therefore tumor size should be independently measured. The literature has shown that prolactinomas do not respond well to TRH stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Stereospecific transport of Tyr-MIF-1 across the blood-brain barrier by peptide transport system-1

Previous studies have suggested that peptide transport system-1 (PTS-1), the saturable system that transports Tyr-MIF-1, the enkephalins, and related peptides out of the central nervous system (CNS), exhibits stereospecificity. In the present studies, we showed that 125I-L-Tyr-MIF-1, but not 131I-D-Tyr-MIF-1, was cleared from the CNS more rapidly than could be accounted for by nonspecific mechanisms. Such clearance was inhibited by a 1.0 nmol dose of L-Tyr-MIF-1, but not by D-Tyr-MIF-1. Neither L- nor D-Tyr-MIF-1 altered the much lower clearance of I-D-Tyr-MIF-1 from the brain. Radioactivity recovered from the vascular space after the injection of 125I-Tyr-MIF-1 into the lateral ventricle of the brain eluted by HPLC primarily as intact peptide, demonstrating that most of the Tyr-MIF-1 was not degraded during transport. By contrast, the nonsaturable unidirectional influx of Tyr-MIF-1 into the CNS did not distinguish between the isomers. These studies confirm and extend the observations that Tyr-MIF-1 is transported out of the CNS by a saturable, stereospecific transport system as an intact peptide while the influx into the CNS is by a nonsaturable mechanism that does not distinguish between the isomers.

Uptake of peptides containing Tyr-Pro by human and mouse erythrocytes

Red blood cells (RBCs) harvested from mice were used to investigate the possible existence of an uptake system for peptides in these cells. The radioactively iodinated tetrapeptide Tyr-MIF-1 (Tyr-Pro-Leu-Gly-amide) was incubated with RBCs for varying lengths of time with or without inhibitors. The RBCs showed saturable uptake that could be inhibited by Tyr-Pro containing peptides. Uptake was also found in human RBCs, but was more robust in the mouse. Uptake by mouse RBCs was temperature dependent and magnesium sensitive but did not require sodium, potassium, or glucose. With the exception of some enkephalin- and dynorphin-related peptides that partially inhibited uptake, most substances tested were without effect. The results of HPLC showed internalization of the N-Tyr-Pro containing peptides, with accumulation of degradation products over time. The degradation products, however, did not inhibit transport, suggesting that peptides were transported intact into the RBCs with degradation occurring after internalization. This suggestion was strengthened by the finding that only the cytosol of the RBC, not its membranes, rapidly degraded Tyr-MIF-1 to free iodine and iodotyrosine. Nevertheless, the cytosol contained a large amount of immunoreactive material that eluted at the position of intact Tyr-MIF-1 on HPLC. These findings show that RBCs can take up, store, and degrade Tyr-Pro containing peptides.

Peptide transport systems for opiates across the blood-brain barrier

Opiate peptides administered on one side of the blood-brain barrier can exert powerful effects on processes occurring on the other side. There is evidence for direct passage of opiate peptides and their analogues across this barrier. Beta-Endorphin can enter the cerebrospinal fluid after systemic administration, but its entry into brain tissue has been more difficult to demonstrate, even though analogues enter at a modest rate. Enkephalins enter and exit the central nervous system as intact molecules by a combination of saturable and nonsaturable mechanisms. A family of transport systems may exist with varying affinities for the opiate enkephalins, antiopiates like tyrosine melanocyte-stimulating hormone inhibitory factor 1 (Tyr-MIF-1), and related peptides. The major system transporting these peptides, termed Peptide transport system 1, can be influenced by several factors with entry and exit rates affected by aging, drugs, amino acids, monoamines, aluminum, stress, and ethanol addiction and withdrawal. The homeostatic role of the blood-brain barrier thus extends to the regulation of the bidirectional transport of informational peptides such as the opiates.

Hypoxia and hypercarbia of chronic lung disease: minimal effects on anterior pituitary function

Previous studies have suggested that the hypoxia and/or hypercapnia associated with chronic lung diseases may lead to pituitary and gonadal dysfunction, with destruction of the sella turcica. It is unclear, however, whether these abnormalities were due to lung disease or to confounding factors. We studied the relationships between hormonal levels (triiodothyronine, thyroxine, T3 resin uptake, thyrotropin, prolactin, cortisol, and testosterone) and PaO2, PaCO2, pH, and alveolar-arterial gradient in 25 patients with chronic lung disease. These patients were highly homogeneous for diagnosis, age, sex, ambulatory status, lack of other illnesses, and minimal use of medications unrelated to lung disease, but did have various degrees of hypoxia and hypercarbia at the time of study. We found no relationship between hormonal levels and lung function, or evidence of major pituitary involvement on lateral roentgenograms of the skull, CT of the sella turcica, or stimulation of the pituitary. An inverse correlation did occur between serum levels of thyroxine and the daily dose of oral prednisone. We conclude that most of the endocrine dysfunction ascribed to chronic lung diseases is probably due to factors other than hypoxia or hypercarbia.

A decade of changing perceptions about neuropeptides

The last decade has seen rapid growth in research with neuropeptides. During this time, we have been actively developing several concepts including the highly controversial one that peptides can cross the blood-brain barrier in intact form. One of the endogenous brain peptides used as a prototype for that concept, Tyr-MIF-1, also was used for the concept of the existence of endogenous antiopiate neuropeptides. As has been true for most novel developments in science, these concepts, as well as some older ones, were met with a great deal of skepticism when first suggested. Eventually, however, amnesia concerning the difficulties initially encountered with the introduction of new concepts occurs, with their subsequent "rediscovery" made easier.

Bidirectional transport of interleukin-1 alpha across the blood-brain barrier

Circulating interleukin-1 alpha (IL-1 alpha) has multiple effects on the central nervous system. We investigated the ability of radioiodinated IL-1 alpha (rIL-1 alpha) to cross the rodent blood-brain barrier and found its entry rate to be 43.9 times greater than that predicted by leakage alone. The rIL-1 alpha entered multiple regions of the brain, with over 40% entering at the cortex. The hypothalamus had the highest entry rate on a weight basis but only accounted for 2% of total entry. In all experiments, the entry rate of rIL-1 alpha greatly exceeded that of simultaneously injected radiolabeled albumin. The half-time disappearance of rIL-1 alpha from the brain after central injection was 21.9 min, a time that exceeds the reabsorption rate of cerebrospinal fluid. Pretreatment of animals with aluminum decreased both entry and exit rates, which is compatible with a saturable component of transport. Thus, rIL-1 alpha has access to many regions of the brain with bidirectional transport rates across the blood-brain barrier exceeding those predicted by nonspecific mechanisms.