Limitations to effect of alpha-MSH on permeability of blood-brain barrier to IV 99mTc-pertechnetate

Protection of cultured brain endothelial cells from cytokine-induced damage by α-melanocyte stimulating hormone

The blood–brain barrier (BBB), an interface between the systemic circulation and the nervous system, can be a target of cytokines in inflammatory conditions. Pro-inflammatory cytokines tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) induce damage in brain endothelial cells and BBB dysfunction which contribute to neuronal injury. The neuroprotective effects of α-melanocyte stimulating hormone (α-MSH) were investigated in experimental models, but there are no data related to the BBB. Based on our recent study, in which α-MSH reduced barrier dysfunction in human intestinal epithelial cells induced by TNF-α and IL-1β, we hypothesized a protective effect of α-MSH on brain endothelial cells. We examined the effect of these two pro-inflammatory cytokines, and the neuropeptide α-MSH on a culture model of the BBB, primary rat brain endothelial cells co-cultured with rat brain pericytes and glial cells. We demonstrated the expression of melanocortin-1 receptor in isolated rat brain microvessels and cultured brain endothelial cells by RT-PCR and immunohistochemistry. TNF-α and IL-1β induced cell damage, measured by impedance and MTT assay, which was attenuated by α-MSH (1 and 10 pM). The peptide inhibited the cytokine-induced increase in brain endothelial permeability, and restored the morphological changes in cellular junctions visualized by immunostaining for claudin-5 and β-catenin. Elevated production of reactive oxygen species and the nuclear translocation of NF-κB were also reduced by α-MSH in brain endothelial cells stimulated by cytokines. We demonstrated for the first time the direct beneficial effect of α-MSH on cultured brain endothelial cells, indicating that this neurohormone may be protective at the BBB.

The Blood-Brain Barrier: Regulatory Roles in Wakefulness and Sleep

Sleep and its disorders are known to affect the functions of essential organs and systems in the body. However, very little is known about how the blood-brain barrier (BBB) is regulated. A few years ago, we launched a project to determine the impact of sleep fragmentation and chronic sleep restriction on BBB functions, including permeability to fluorescent tracers, tight junction protein expression and distribution, glucose and other solute transporter activities, and mediation of cellular mechanisms. Recent publications and relevant literature allow us to summarize here the sleep-BBB interactions in five sections: (1) the structural basis enabling the BBB to serve as a huge regulatory interface; (2) BBB transport and permeation of substances participating in sleep-wake regulation; (3) the circadian rhythm of BBB function; (4) the effect of experimental sleep disruption maneuvers on BBB activities, including regional heterogeneity, possible threshold effect, and reversibility; and (5) implications of sleep disruption-induced BBB dysfunction in neurodegeneration and CNS autoimmune diseases. After reading the review, the general audience should be convinced that the BBB is an important mediating interface for sleep-wake regulation and a crucial relay station of mind-body crosstalk. The pharmaceutical industry should take into consideration that sleep disruption alters the pharmacokinetics of BBB permeation and CNS drug delivery, being attentive to the chrono timing and activation of co-transporters in subjects with sleep disorders.

Passage of peptides across the blood-brain barrier: pathophysiological perspectives

Blood-borne peptides are capable of affecting the central nervous system (CNS) despite being separated from the CNS by the blood-brain barrier (BBB), a monolayer comprised of brain endothelial and ependymal cells. Blood-borne peptides can directly affect the CNS after they cross the BBB by nonsaturable and saturable transport mechanisms. The ability of peptides to cross the BBB to a meaningful degree suggests that the BBB may act as a modulatory pathway in the exchange of informational molecules between the brain and the peripheral circulation. The permeability of the BBB to peptides is a regulatory process affected by developmental, physiological, and pathological events. This regulation sets the stage for the relation between peptides and the BBB to be involved in pathophysiological events. For example, some of the classic actions of melanocortins on the CNS are explained by their abilities to cross the BBB, whereas aspects of feeding and alcohol-related behaviors are associated with the passage of other specific peptides across the BBB. The BBB should no longer be considered a static barrier but should be recognized as a regulatory interface controlling the exchange of informational molecules, such as peptides, between the blood and CNS.

Permeability of the blood-brain barrier to melanocortins

Adrenocorticotropin (ACTH)-related compounds, termed melanocortins, produce a large number of effects on the central nervous system (CNS) after their peripheral administration. Some of the CNS effects of ACTH are mediated through the release of glucocorticoids from the adrenal gland, but there are fragments and analogues of ACTH that do not act on the adrenals. This raises the possibility that some blood-borne melanocortins may be acting directly on the brain, which would necessitate their crossing the blood-brain barrier (BBB). We review here the literature showing that melanocortins can affect the BBB in several ways, including an alteration of the permeability of the BBB to other substances.

Modulation of immunoactive levels of DSIP and blood-brain permeability by lighting and diurnal rhythm

The brain and plasma levels of immunoactive delta sleep-inducing peptide (DSIP) as well as the permeability of the blood-brain barrier (BBB) to radioiodinated N-Tyr-DSIP (125I-DSIP) were measured at 0400, 0800, 1200, 1600, 2000, and 2400 hr in rats in a normal 12-hr-light/12-hr-dark cycle and at 0800 in rats in constant light or constant dark. Both brain and blood levels of immunoactivity showed statistically significant diurnal changes, whereas the measurement of BBB permeability varied in a regular fashion over time without the changes reaching statistical significance. Immunoactive levels of DSIP in both the plasma and the brain were higher and permeability of the BBB to 125I-DSIP increased in both the constant light and especially the constant dark groups in comparison with the cycled 0800 group. Diurnal variations continued to occur in the blood levels of immunoactive DSIP in the constant dark animals. Studies with radioiodinated serum albumin (RISA) showed that these findings did not result from a change in brain hemodynamics. Immunoactive levels of DSIP in the plasma correlated with brain immunoactive levels and with BBB permeability to 125I-DSIP. The increase in penetration of 125I-DSIP into the brain that occurred with changes in the lighting cycle appeared to be magnified by pre-treatment with aluminum. The results show interrelationships among various aspects of the neuroendocrine axis for DSIP and their modulation by physiological factors.

Permeability of the blood-brain barrier to neuropeptides: the case for penetration

Evidence that peptides can cross the blood-brain barrier (BBB) is reviewed. Penetration is suggested by the observations that blood levels correlate with cerebrospinal fluid levels for many peptides and that peripheral administration of peptides results in effects on the CNS. Passage is confirmed by experiments involving administration of a peptide (immunoactive or radioactive) in one compartment and identification of its appearance in the other, supported by such methods as selective labeling, cross-reactivity with highly specific antibodies, and chromatography. The degree of passage varies among peptides and their analogs. The major route of passage is probably by a non-competitive, non-saturable mechanism, wih the physicochemical characteristics of the peptide (e.g. lipophilicity, charge, molecular weight, and protein binding) determining the degree of passage. A competitive transport mechanism also exists for some peptides. Penetration of the BBB via large pores or by pinocytosis does not appear to be of major importance for peptides. Permeability of the BBB to peptides, but not to the larger iodinated albumin, is affected by intraperitoneal administration of aluminum, apparently by an increase in the permeability of the membrane to lipophilic materials.

Quantification of the permeability of the blood-CSF barrier to alpha-MSH in the rat

The ability of alpha-MSH to cross the blood-CSF barrier of the rat was assessed by measurement of the rate of appearance of immunoreactive alpha-MSH in a cerebrospinal fluid (CSF) perfusate following intravenous injection of peptide. Comparisons were made with the rate of appearance of a simultaneously administered dose of 14C-inulin which is poorly permeable at the blood-CSF barrier. Concentrations of drugs measured in plasma were fitted to two-compartment pharmacokinetic models, and those measured in the CSF perfusate to one-compartment open systems receiving an input from the plasma compartment. The rate constant for entry of alpha-MSH into CSF was 0.00087 min-1, which was not significantly different from that for inulin of 0.00055 min-1. As alpha-MSH penetrated into CSF at a rate comparable to inulin, it was concluded that the limited entry of peptide was by aqueous diffusion along with other water-soluble macromolecules.