The Amazon rain forest plant Uncaria tomentosa (cat's claw) and its specific proanthocyanidin constituents are potent inhibitors and reducers of both brain plaques and tangles.

Brain aging and Alzheimer's disease both demonstrate the accumulation of beta-amyloid protein containing "plaques" and tau protein containing "tangles" that contribute to accelerated memory loss and cognitive decline. In the present investigation we identified a specific plant extract and its constituents as a potential alternative natural solution for preventing and reducing both brain "plaques and tangles". PTI-00703 cat's claw (Uncaria tomentosa from a specific Peruvian source), a specific and natural plant extract from the Amazon rain forest, was identified as a potent inhibitor and reducer of both beta-amyloid fibrils (the main component of "plaques") and tau protein paired helical filaments/fibrils (the main component of "tangles"). PTI-00703 cat's claw demonstrated both the ability to prevent formation/aggregation and disaggregate preformed Aß fibrils (1-42 and 1-40) and tau protein tangles/filaments. The disaggregation/dissolution of Aß fibrils occurred nearly instantly when PTI-00703 cat's claw and Aß fibrils were mixed together as shown by a variety of methods including Thioflavin T fluorometry, Congo red staining, Thioflavin S fluorescence and electron microscopy. Sophisticated structural elucidation studies identified the major fractions and specific constituents within PTI-00703 cat's claw responsible for both the observed "plaque" and "tangle" inhibitory and reducing activity. Specific proanthocyanidins (i.e. epicatechin dimers and variants thereof) are newly identified polyphenolic components within Uncaria tomentosa that possess both "plaque and tangle" reducing and inhibitory activity. One major identified specific polyphenol within PTI-00703 cat's claw was epicatechin-4ß-8-epicatechin (i.e. an epicatechin dimer known as proanthocyanidin B2) that markedly reduced brain plaque load and improved short-term memory in younger and older APP "plaque-producing" (TASD-41) transgenic mice (bearing London and Swedish mutations). Proanthocyanidin B2 was also a potent inhibitor of brain inflammation as shown by reduction in astrocytosis and gliosis in TASD-41 transgenic mice. Blood-brain-barrier studies in Sprague-Dawley rats and CD-1 mice indicated that the major components of PTI-00703 cat's claw crossed the blood-brain-barrier and entered the brain parenchyma within 2 minutes of being in the blood. The discovery of a natural plant extract from the Amazon rain forest plant (i.e. Uncaria tomentosa or cat's claw) as both a potent "plaque and tangle" inhibitor and disaggregator is postulated to represent a potential breakthrough for the natural treatment of both normal brain aging and Alzheimer's disease.

Involvement of the Blood-Brain Barrier in Metabolic Regulation.

Pertinent to pandemic obesity, the discovery of endogenous peptides that affect the ingestion of food has led to the question of how these ingestive peptides exert their actions in the brain. Whereas peripheral sources provide a ready reserve, the availability of ingestive peptides to their central nervous system targets can be regulated by the blood-brain barrier (BBB). Some of the peptides/polypeptides are transported by saturable mechanisms from blood to brain. Examples include leptin, insulin, mahogany, and pancreatic polypeptide. Some enter the brain by passive diffusion, such as neuropeptide Y, orexin A, cocaine- and amphetamine-regulated transcript, cyclo His-Pro, and amylin. Some others may have essentially no penetration of the BBB; this class includes agouti-related protein, melanin-concentrating hormone, and urocortin. The regulatory function of the BBB can be seen in various physiological states. Hyperglycemia may upregulate transport systems for leptin, urocortin, and galanin-like peptide, whereas fasting can down-regulate those for leptin and galanin-like peptide. Thus, the BBB plays a dynamic role in modulating the passage of ingestive peptides from blood to brain.

Spinal Cord Injury Changes Cytokine Transport.

Here we summarize three aspects of our understanding of the interactions of cytokines and neurotrophic peptides/proteins with the blood-brain and bloodspinal cord barriers (BBB): (a) pharmacokinetic analysis that has been reported for native cytokines and neurotrophic peptides/proteins; (b) landmark work on conjugated proteins to enhance their delivery across the normal BBB; and (c) regulatory changes under pathophysiological conditions in rodents, particularly after spinal cord injury (SCI). First, though the BBB restricts the permeation of large proteins, some cytokines and neurotrophic peptides/proteins in the periphery can reach the central nervous system (CNS) by specific transport systems. Moreover, SCI and some other disease processes may regulate these transport systems. The significance of studies of the transport systems is obvious because of the biological impact of these molecules on the CNS in health and disease. We have characterized the pharmacokinetic characteristics of some stable cytokines and neurotrophic peptides/proteins in mice after intravenous administration and also in the setting of in situ brain perfusion. In the particular case of SCI, there are time- and regionspecific changes of BBB permeability and transport systems. Tumor necrosis factor-α, a cytokine with dual actions in regeneration of the spinal cord, has a slow basal influx into the brain and spinal cord. After SCI, the increase in the entry of tumor necrosis factor-α to the CNS differs from leakage after BBB disruption and is related to upregulation of the transport system in a unique temporal and regional pattern. Overall, the permeation of cytokines across the BBB can be mediated by specific transport systems. The regulation of transport in pathophysiological conditions affects the extent of neuroinflammation and is implicated in neuroregeneration.

TNF stimulates nuclear export and secretion of IL-15 by acting on CRM1 and ARF6.

Interleukin (IL)-15 is a ubiquitously expressed cytokine that in the basal state is mainly localized intracellularly, including the nucleus. Unexpectedly, tumor necrosis factor-α (TNF) time-dependently induced nuclear export of IL-15Rα and IL15. This process was inhibited by leptomycine B (LMB), a specific inhibitor of nuclear export receptor chromosomal region maintenance 1 (CRM1). In the presence of TNF, LMB co-treatment led to accumulation of both IL-15Rα and IL-15 in the nucleus of HeLa cells, suggesting that CRM1 facilitates nuclear export and that TNF enhances CRM1 activity. Once in the cytoplasm, IL-15 showed partial co-localization with late endosomes but very little with other organelles tested 4 h after TNF treatment. IL-15Rα showed co-localization with both early and late endosomes, and to a lesser extent with endoplasmic reticulum and Golgi. This indicates different kinetics and possibly different trafficking routes of IL-15 from its specific receptor. The TNF-induced secretion of IL-15 was attenuated by pretreatment of cells by brefeldin A that inhibits ER-to-Golgi transport, or by use of domain negative ADP-ribosylation factor 6 (ARF6) that interferes with exocytotic sorting. We conclude that TNF abolishes nuclear localization of IL-15 and IL-15Rα by acting on CRM1, and it facilitates exocytosis of IL-15 with the involvement of ARF6.

Loss of astrocytic leptin signaling worsens experimental autoimmune encephalomyelitis.

Leptin is commonly thought to play a detrimental role in exacerbating experimental autoimmune encephalomyelitis (EAE) and multiple sclerosis. Paradoxically, we show here that astrocytic leptin signaling has beneficial effects in reducing disease severity. In the astrocyte specific leptin receptor knockout (ALKO) mouse in which leptin signaling is absent in astrocytes, there were higher EAE scores (more locomotor deficits) than in the wildtype counterparts. The difference mainly occurred at a late stage of EAE when wildtype mice showed signs of recovery whereas ALKO mice continued to deteriorate. The more severe symptoms in ALKO mice coincided with more infiltrating cells in the spinal cord and perivascular brain parenchyma, more demyelination, more infiltrating CD4 cells, and a lower percent of neutrophils in the spinal cord 28 days after EAE induction. Cultured astrocytes from wildtype mice showed increased adenosine release in response to interleukin-6 and the hippocampus of wildtype mice had increased adenosine production 28 days after EAE induction, but the ALKO mutation abolished the increase in both conditions. This indicates a role of astrocytic leptin in normal gliotransmitter release and astrocyte functions. The worsening of EAE in the ALKO mice in the late stage suggests that astrocytic leptin signaling helps to clear infiltrating leukocytes and reduce autoimmune destruction of the CNS.

Protective role of astrocytic leptin signaling against excitotoxicity.

Both proconvulsive and anticonvulsive roles of leptin have been reported, suggesting cell-specific actions of leptin in different models of seizure and epilepsy. The goal of our study was to determine the regulation and function of astrocytic leptin receptors in a mouse model of epilepsy and glutamate-induced cytotoxicity. We show that in pilocarpine-challenged mice developing epilepsy with recurrent seizures after a latent period of 2 weeks, hippocampal leptin receptor (ObR) immunofluorescence was increased at 6 weeks. This was more pronounced in astrocytes than in neurons. In cultured astrocytes, glutamate increased ObRa and ObRb expression, whereas leptin pretreatment attenuated glial cytotoxicity by excess glutamate, reflected by better preserved adenosine triphosphate production. The protective role of astrocytic leptin signaling is further supported by the higher lethality of the astrocyte-specific leptin receptor knockout mice in the initial phase of seizure production. Thus, leptin signaling in astrocytes plays a protective role against seizure, and the effects are at least partially mediated by attenuation of glutamate toxicity. Astrocytic leptin signaling, therefore, may be a novel therapeutic target.

Brain interleukin-15 in neuroinflammation and behavior.

Interleukin (IL)-15 is a ubiquitously expressed cytokine existing in both intracellular and secretory forms. Here we review the expression, regulation, and functions of IL15 and its receptors in the brain. IL15 receptors show robust upregulation after neuroinflammation, suggesting a major role of IL15 signaling in cerebral function. Involvement of the IL15 system in neuropsychiatric behavior is reflected by the effects of IL15, IL15Rα, and IL2Rγ deletions on neurobehavior and neurotransmitters, the effects of IL15 treatment on neuronal activity, and the potential role of IL15 in neuroplasticity/neurogenesis. The results show that IL15 modulates GABA and serotonin transmission. This may underlie deficits in mood (depressive-like behavior and decreased normal anxiety) and memory, as well as activity level, sleep, and thermoregulation. Although IL15 has only a low level of permeation across the blood-brain barrier, peripheral IL15 is able to activate multiple signaling pathways in neurons widely distributed in CNS regions. The effects of IL15 in "preventing" neuropsychiatric symptoms in normal mice implicate a potential therapeutic role of this polypeptide cytokine.

Endothelial leptin receptor mutation provides partial resistance to diet-induced obesity.

Leptin, a polypeptide hormone produced mainly by adipocytes, has diverse effects in both the brain and peripheral organs, including suppression of feeding. Other than mediating leptin transport across the blood-brain barrier, the role of the endothelial leptin receptor remains unclear. We recently generated a mutant mouse strain lacking endothelial leptin receptor signaling, and showed that there is an increased uptake of leptin by brain parenchyma after its delivery by in situ brain perfusion. Here, we tested the hypothesis that endothelial leptin receptor mutation confers partial resistance to diet-induced obesity. These ELKO mice had similar body weight and percent fat as their wild-type littermates when fed with rodent chow, but blood concentrations of leptin were significantly elevated. In response to a high-fat diet, wild-type mice had a greater gain of body weight and fat than ELKO mice. As shown by metabolic chamber measurement, the ELKO mice had higher oxygen consumption, carbon dioxide production, and heat dissipation, although food intake was similar to that of the wild-type mice and locomotor activity was even reduced. This indicates that the partial resistance to diet-induced obesity was mediated by higher metabolic activity in the ELKO mice. Since neuronal leptin receptor knockout mice show obesity and diabetes, the results suggest that endothelial leptin signaling shows opposite effects from that of neuronal leptin signaling, with a facilitatory role in diet-induced obesity.

NFĸB is an unexpected major mediator of interleukin-15 signaling in cerebral endothelia.

Interleukin (IL)-15 and its receptors are induced by tumor necrosis factor α (TNF) in the cerebral endothelial cells composing the blood-brain barrier, but it is not yet clear how IL-15 modulates endothelial function. Contrary to the known induction of JAK/STAT3 signaling, here we found that nuclear factor (NF)- κB is mainly responsible for IL-15 actions on primary brain microvessel endothelial cells and cerebral endothelial cell lines. IL-15-induced transactivation of an NFκB luciferase reporter resulted in phosphorylation and degradation of the inhibitory subunit IκB that was followed by phosphorylation and nuclear translocation of the p65 subunit of NFκB. An IκB kinase inhibitor Bay 11-7082 only partially inhibited IL-15-induced NFκB luciferase activity. The effect of IL-15 was mediated by its specific receptor IL-15Rα, since endothelia from IL-15Rα knockout mice showed delayed nuclear translocation of p65, whereas those from knockout mice lacking a co-receptor IL-2Rγ did not show such changes. At the mRNA level, IL-15 and TNF showed similar effects in decreasing the tight junction protein claudin-2 and increasing the p65 subunit of NFκB but exerted different regulation on caveolin-1 and vimentin. Taken together, NFκB is a major signal transducer by which IL-15 affects cellular permeability, endocytosis, and intracellular trafficking at the level of the blood-brain barrier.

Role of astrocytic leptin receptor subtypes on leptin permeation across hCMEC/D3 human brain endothelial cells.

Astrocytic leptin receptors (ObR) can be up-regulated in conditions such as adult-onset obesity. To determine whether the levels and subtypes of astrocytic ObR modulate leptin transport, we co-cultured hCMEC/D3 human brain endothelial cells and C6 astrocytoma cells in the Transwell system, and tested leptin permeation from apical to basolateral chambers. In comparison with hCMEC alone, co-culture of C6 cells reduced the permeability of paracellular markers and leptin. Unexpectedly, ObRb over-expression in C6 cells increased leptin permeation whereas ObRa over-expression showed no effect when compared with the control group of pcDNA-transfected C6 cells. By contrast, the paracellular permeability to the sodium fluorescein control was unchanged by over-expression of ObR subtypes. Leptin remained intact after crossing the monolayer as shown by HPLC and acid precipitation, and this was not affected by C6 cell co-culture or the over-expression of different ObR subtypes. Thus, increased expression of ObRb (and to a lesser extent ObRe) in C6 cells specifically increased the permeation of leptin across the hCMEC monolayer. Consistent with the evidence that the most apparent regulatory changes of ObR during obesity and inflammation occur in astrocytes, the results indicate that astrocytes actively regulate leptin transport across the blood-brain barrier, a mechanism independent of reduction of paracellular permeability.

Concepts for biologically active peptides.

Here we review a unique aspect of CNS research on biologically active peptides that started against a background of prevalent dogmas but ended by exerting considerable influence on the field. During the course of refuting some doctrines, we introduced several concepts that were unconventional and paradigm-shifting at the time. We showed that (1) hypothalamic peptides can act 'up' on the brain as well as 'down' on the pituitary, (2) peripheral peptides can affect the brain, (3) peptides can cross the blood-brain barrier, (4) the actions of peptides can persist longer than their half-lives in blood, (5) perinatal administration of peptides can exert actions persisting into adulthood, (6) a single peptide can have more than one action, (7) dose-response relationships of peptides need not be linear, (8) the brain produces antiopiate as well as opiate peptides, (9) there is a selective high affinity endogenous peptide ligand for the mu-opiate receptor, (10) a peptide's name does not restrict its effects, and (11) astrocytes assume an active role in response to metabolic disturbance and hyperleptinemia. The evolving questions in our laboratories reflect the diligent effort of the neuropeptide community to identify the roles of peptides in the CNS. The next decade is expected to see greater progress in the following areas: (a) interactions of peptides with other molecules in the CNS; (b) peptide involvement in cell-cell interactions; and (c) peptides in neuropsychiatric, autoimmune, and neurodegenerative diseases. The development of peptidomics and gene silencing approaches will expedite the formation of many new concepts in a new era.

The role of cerebral vascular NFkappaB in LPS-induced inflammation: differential regulation of efflux transporter and transporting cytokine receptors.

BACKGROUND/AIMS: The transcription factor NFkappaB is a major mediator of lipopolysaccharide (LPS) signaling. We determined the role of NFkappaB activation in regulatory changes of the P-glycoprotein (Pgp) drug efflux transporter at the blood-brain barrier (BBB) and proinflammatory cytokine receptors. METHODS: We treated NFkappaB knockout and wildtype mice with LPS or vehicle, obtained enriched cerebral microvessels, and determined target mRNA by qPCR for MDR1a/b, IL15Ralpha, IL2 Ralpha, IL2Rgamma, LIFR, gp130, and TNFR1/2, and protein expression by western blotting for P-gp, IL15Ralpha, IL2Rgamma, LIFR, and gp130. RESULTS: The effects of LPS on the transporters and cytokine receptors showed differences between wildtype and NFkappaB knockout mice, and between mRNA and protein changes. NFkappaB not only mediated the LPS-induced increase of MDR1b, IL2Rgamma, and TNFR2 mRNA in the wildtype mice, but it showed opposite effects by elevating IL15Ralpha and TNFR1 mRNA and decreasing IL2Ralpha in the knockout mice. Although basal vinblastine uptake was unchanged in the NFkappaB knockout mice, LPS induced an increase of the uptake (depressed efflux transport) greater than that seen in the wildtype mice, indicating that NFkappaB helps to maintain Pgp efflux transporter function. CONCLUSION: The results show differential involvement of NFkappaB signaling in response to LPS at the BBB.

Expression and signaling of novel IL15Ralpha splicing variants in cerebral endothelial cells of the blood-brain barrier.

Interleukin (IL)-15 and its receptors in cerebral microvascular endothelial cells play an important role in mediating neuroinflammatory signaling across the blood-brain barrier. Although alternative splice variants of IL15Ralpha (the specific receptor) are seen in immune cells, the presence and functions of splice variants have not been studied in the cerebral endothelia that compose the blood-brain barrier. In this study, we identified five splice variants from mouse cerebral capillaries by RT-PCR, cloning, and DNA sequencing, and performed domain analysis. Four of these isoforms have never been described in any tissue. All isoforms were detected by qPCR in enriched mouse cerebral microvessels and their expression was increased by tumor necrosis factor treatment in vivo. To determine their functions, plasmids encoding individual isoforms were transfected into RBE4 cerebral endothelial cells. All of these predicted alkalinic proteins were expressed and most showed post-translational modifications. There were variations in their subcellular distribution. Only the full length IL15Ralpha and to a lesser degree isoform alpha1 were trafficked to the cell surface 24 h after over-expression. As shown by a luciferase reporter for signal transducer and activator of transcription (STAT)-3, over-expression of isoforms alpha2 and alpha4 reduced basal STAT3 activation. In comparison with the control, over-expression of the full length IL15Ralpha had a greater effect in increasing IL15-induced STAT3 transactivation than other isoforms. The results show that IL15 signaling in cerebral endothelia is probably an orchestrated effect of all IL15Ralpha splice variants that determine the eventual outcome by differential regulation.

IL-15 receptor deletion results in circadian changes of locomotor and metabolic activity.

Interleukin-15 (IL-15) is a cytokine produced in the normal brain that acts on its specific receptor IL-15Ralpha and co-receptors IL-2Rbeta and IL-2Rgamma in neuronal cells. The functions of the cerebral IL-15 system, however, are not yet clear. To test the hypothesis that IL-15Ralpha regulates metabolic activity and body temperature, we quantified the specific metabolic phenotype of IL-15Ralpha knockout mice. These normal-appearing mice were leaner with lower fat composition. During the entire circadian cycle, the knockout mice had a significantly higher acrophase in locomotor activity and heat dissipation. During the light phase, there was significantly greater food intake, oxygen consumption, and carbon dioxide production. The difference in the dark and light phases suggests that IL-15Ralpha participates in circadian rhythm regulation. The higher oxygen consumption in the light phase indicates adaptive thermogenesis in the knockout mice. The body temperature of the receptor knockout mice was significantly higher than the control in the light phase, and this was mainly caused by a large difference occurring between 0600 and 0900 h. In addition to the metabolic chamber studies and circadian rhythm analyses, qPCR of hypothalamic homogenates indicated higher mRNA expression of orexin and transient receptor potential vanilloid 4 cation channels. Consistent with a direct role of IL-15Ralpha in the hypothalamus, IL-15 treatment of the wild-type mice induced c-Fos expression in the preoptic area. We conclude that activation of hypothalamic neurons by IL-15 in mice contributes to thermoregulation and modifies the metabolic phenotype.

Cerebral microvascular IL15 is a novel mediator of TNF action.

The blood-brain barrier is a gatekeeper and modulatory interface for the CNS. Cerebral endothelial cells are the major component of the blood-brain barrier, and they modify inflammatory signals from the circulation to the CNS by production and secretion of secondary substances. The inflammatory mediators induced by tumor necrosis factor alpha (TNF) were determined by microarray analysis of RBE4 cerebral endothelial cells, at 0, 6, 12, or 24 h after TNF treatment. Interleukin (IL)-15 and its receptors were among the most robustly up-regulated genes. This was confirmed by real-time RT-PCR and western blotting. The three subunits of the IL15 receptor complex (IL15Ralpha, IL2Rbeta, and IL2Rgamma) showed differential regulation by TNF in their time course and amplitude of increased expression. Consistent with increased expression of the specific high affinity receptor IL15Ralpha, TNF increased cellular uptake of (125)I-IL15 and enhanced the fluorescent intensity of Alexa568-IL15 in RBE4 cells. TNF treatment in mice also increased the level of expression of IL15 receptors in enriched cerebral microvessels. We conclude that the cerebral microvascular IL15 system is a novel inflammatory mediator that transduces the actions of TNF.

Leptin receptor mRNA in rat brain astrocytes.

We recently reported that mouse astrocytes express leptin receptors (ObR), and that obesity induces upregulation of astrocytic ObR. To provide further evidence of the importance of astrocytic ObR expression, we performed double-labeling fluorescent in situ hybridization (FISH) and immunohistochemistry in the rat hypothalamus. Laser confocal microscopic image analysis showed that ObR mRNA was present in glial fibrillary acidic protein (+) cells that show distinctive astrocytic morphology as well as in neurons. In addition to the presence of ObR mRNA, ObR protein was shown in both astrocytes and neurons in the rat hypothalamus by double-labeling immunohistochemistry. In cultured rat C6 astrocytoma cells treated with different doses of lipopolysaccharide for 6h, the mRNA for ObRa or ObRb did not show significant changes, as measured by quantitative RT-PCR. However, the protein expression of both ObRa and ObRb, determined by Western blotting, was increased after the C6 cells were treated with either lipopolysaccharide or tumor necrosis factor-alpha. The results indicate that astrocytic ObR expression is present in rats as well as mice, and that it probably plays a role in the neuroinflammatory response.

Melanocortin potentiates leptin-induced STAT3 signaling via MAPK pathway.

The co-existence of receptors for leptin and melanocortin in cerebral microvessels suggests possible interactions between leptin and alpha-melanocyte stimulating hormone (MSH) signaling. In this study, we showed that ObRb and melanocortin receptor MC3R and MC4R were present in enriched cerebral microvessels. To test the interactions between ObRb and MC3R or MC4R-mediated cellular signaling, we over-expressed these plasmids in RBE4 cerebral microvascular endothelial cells and HEK293 cells in culture. Activation of signal transducers and activators of transcription-3 (STAT3) in response to leptin was determined by western blotting and luciferase reporter assays. Production of cAMP downstream to melanocortin receptors was determined with a chemiluminescent ELISA kit. alphaMSH, which increased intracellular cAMP, also potentiated leptin-induced STAT3 activation. This potentiation was abolished by a specific MEK inhibitor, indicating the involvement of the mitogen-activated kinase pathway. Reversely, the effect of leptin on alphaMSH-induced cAMP production was minimal. Thus, melanocortin specifically potentiated STAT3 signaling downstream to ObRb by cross-talk with mitogen-activated kinase. The cooperation of ObRb and G protein-coupled receptors in cellular signaling may have considerable biological implications not restricted to feeding and obesity.

Neuroinflammation activates Mdr1b efflux transport through NFkappaB: promoter analysis in BBB endothelia.

BACKGROUND/AIMS: Although it is known that drug delivery across the blood-brain barrier (BBB) may be hampered by efflux transport activity of the multidrug resistance (mdr) gene product P-glycoprotein, it is not clear how inflammation regulates efflux transporters. In rat brain endothelial (RBE4) cells of BBB origin, the proinflammatory cytokine TNF mainly induced transcriptional upregulation of mdr1b, and to a lesser extent mdr1a, resulting in greater efflux of the substrates. This study further determines the mechanisms by which TNF activates mdr1b promoter activity. METHODS/RESULTS: Luciferase reporter assays and DNA binding studies show that (1) maximal basal promoter activity was conferred by a 476 bp sequence upstream to the mdr1b transcriptional initiation site; (2) TNF induced upregulation of promoter activity by NFkappaB nuclear translocation; and (3) the NFkappaB binding site of the mdr1b promoter was solely responsible for basal and TNF-activated gene transcription, whereas the p53 binding site was not involved. Binding of the p65 subunit of NFkappaB to nuclear DNA from RBE4 cells was shown by electrophoretic mobility shift assay and chromatin immunoprecipitation assays. CONCLUSION: NFkappaB mediates TNF-induced upregulation of mdr1b promoter activity, illustrating how inflammation activates BBB efflux transport.

Peptides and hormesis.

Biology is replete with examples of hormesis, the term introduced and developed by Calabrese. The corresponding concept in the field of peptide research has been characterized as the inverted U-shaped dose-response relationship. The articles by Calabrese in this issue summarize the notable progress occurring in the past three decades. In contrast to the skepticism encountered when we introduced this concept for peptides in the early 1970s, hormesis is now becoming recognized as characteristic of many actions of these small proteins. Calabrese is performing a considerable service by his strong advocacy and promotion of the concept to a more general readership. Hopefully, hormesis will be routinely considered in the design of research projects and the discovery of pharmaceutical agents.

Blood-brain barrier and feeding: regulatory roles of saturable transport systems for ingestive peptides.

The two main ways for peptides in the peripheral body to enter the brain are by either saturable transport or passive diffusion across the blood-brain barrier (BBB). Saturable transport systems have the advantage of being responsive to physiological and pathological stimuli. Since saturable systems can regulate peptide entry into the brain, they have the potential to play controlling roles in feeding behavior. For therapeutic applications, however, saturable systems have the disadvantage of functioning as a threshold to limit access of large amounts of peptides into the brain. This pharmacological problem presumably would not be encountered for peptides crossing the BBB by passive diffusion, a process dependent on physicochemical properties. Thus, the gatekeeper function of the BBB can be expanded to a primary governing role, especially for entry of ingestive peptides subject to their respective saturable transport systems.