Intranasal delivery of a thyrotropin-releasing hormone analog attenuates seizures in the amygdala-kindled rat

The Thyrotropin-Releasing Hormone-Degrading Ectoenzyme, a Therapeutic Target?

Thyrotropin releasing hormone (TRH: Glp-His-Pro-NH2) is a peptide mainly produced by brain neurons. In mammals, hypophysiotropic TRH neurons of the paraventricular nucleus of the hypothalamus integrate metabolic information and drive the secretion of thyrotropin from the anterior pituitary, and thus the activity of the thyroid axis. Other hypothalamic or extrahypothalamic TRH neurons have less understood functions although pharmacological studies have shown that TRH has multiple central effects, such as promoting arousal, anorexia and anxiolysis, as well as controlling gastric, cardiac and respiratory autonomic functions. Two G-protein-coupled TRH receptors (TRH-R1 and TRH-R2) transduce TRH effects in some mammals although humans lack TRH-R2. TRH effects are of short duration, in part because the peptide is hydrolyzed in blood and extracellular space by a M1 family metallopeptidase, the TRH-degrading ectoenzyme (TRH-DE), also called pyroglutamyl peptidase II. TRH-DE is enriched in various brain regions but is also expressed in peripheral tissues including the anterior pituitary and the liver, which secretes a soluble form into blood. Among the M1 metallopeptidases, TRH-DE is the only member with a very narrow specificity; its best characterized biological substrate is TRH, making it a target for the specific manipulation of TRH activity. Two other substrates of TRH-DE, Glp-Phe-Pro-NH2 and Glp-Tyr-Pro-NH2, are also present in many tissues. Analogs of TRH resistant to hydrolysis by TRH-DE have prolonged central efficiency. Structure-activity studies allowed the identification of residues critical for activity and specificity. Research with specific inhibitors has confirmed that TRH-DE controls TRH actions. TRH-DE expression by β2-tanycytes of the median eminence of the hypothalamus allows the control of TRH flux into the hypothalamus-pituitary portal vessels and may regulate serum thyrotropin secretion. In this review we describe the critical evidences that suggest that modification of TRH-DE activity in tanycytes, and/or in other brain regions, may generate beneficial consequences in some central and metabolic disorders and identify potential drawbacks and missing information needed to test these hypotheses.

Epilepsy Disease and Nose-to-Brain Delivery of Polymeric Nanoparticles: An Overview

Epilepsy is the fourth most common global neurological problem, which can be considered a spectrum disorder because of its various causes, seizure types, its ability to vary in severity and the impact from person to person, as well as its range of co-existing conditions. The approaches to drug therapy of epilepsy are directed at the control of symptoms by chronic administration of antiepileptic drugs (AEDs). These AEDs are administered orally or intravenously but alternative routes of administration are needed to overcome some important limits. Intranasal (IN) administration represents an attractive route because it is possible to reach the brain bypassing the blood brain barrier while the drug avoids first-pass metabolism. It is possible to obtain an increase in patient compliance for the easy and non-invasive route of administration. This route, however, has some drawbacks such as mucociliary clearance and the small volume that can be administered, in fact, only drugs that are efficacious at low doses can be considered. The drug also needs excellent aqueous solubility or must be able to be formulated using solubilizing agents. The use of nanomedicine formulations able to encapsulate active molecules represents a good strategy to overcome several limitations of this route and of conventional drugs. The aim of this review is to discuss the innovative application of nanomedicine for epilepsy treatment using nose-to-brain delivery with particular attention focused on polymeric nanoparticles to load drugs.

Mottled Mice and Non-Mammalian Models of Menkes Disease

Menkes disease is a multi-systemic copper metabolism disorder caused by mutations in the X-linked ATP7A gene and characterized by progressive neurodegeneration and severe connective tissue defects. The ATP7A protein is a copper (Cu)-transporting ATPase expressed in all tissues and plays a critical role in the maintenance of copper homeostasis in cells of the whole body. ATP7A participates in copper absorption in the small intestine and in copper transport to the central nervous system (CNS) across the blood-brain-barrier (BBB) and blood–cerebrospinal fluid barrier (BCSFB). Cu is essential for synaptogenesis and axonal development. In cells, ATP7A participates in the incorporation of copper into Cu-dependent enzymes during the course of its maturation in the secretory pathway. There is a high degree of homology (>80%) between the human ATP7A and murine Atp7a genes. Mice with mutations in the Atp7a gene, called mottled mutants, are well-established and excellent models of Menkes disease. Mottled mutants closely recapitulate the Menkes phenotype and are invaluable for studying Cu-metabolism. They provide useful models for exploring and testing new forms of therapy in Menkes disease. Recently, non-mammalian models of Menkes disease, Drosophila melanogaster and Danio rerio mutants were used in experiments which would be technically difficult to carry out in mammals.

Neuropeptides as targets for the development of anticonvulsant drugs

Epilepsy is a common neurological disorder characterized by recurrent seizures. These seizures are due to abnormal excessive and synchronous neuronal activity in the brain caused by a disruption of the delicate balance between excitation and inhibition. Neuropeptides can contribute to such misbalance by modulating the effect of classical excitatory and inhibitory neurotransmitters. In this review, we discuss 21 different neuropeptides that have been linked to seizure disorders. These neuropeptides show an aberrant expression and/or release in animal seizure models and/or epilepsy patients. Many of these endogenous peptides, like adrenocorticotropic hormone, angiotensin, cholecystokinin, cortistatin, dynorphin, galanin, ghrelin, neuropeptide Y, neurotensin, somatostatin, and thyrotropin-releasing hormone, are able to suppress seizures in the brain. Other neuropeptides, such as arginine-vasopressine peptide, corticotropin-releasing hormone, enkephalin, β-endorphin, pituitary adenylate cyclase-activating polypeptide, and tachykinins have proconvulsive properties. For oxytocin and melanin-concentrating hormone both pro- and anticonvulsive effects have been reported, and this seems to be dose or time dependent. All these neuropeptides and their receptors are interesting targets for the development of new antiepileptic drugs. Other neuropeptides such as nesfatin-1 and vasoactive intestinal peptide have been less studied in this field; however, as nesfatin-1 levels change over the course of epilepsy, this can be considered as an interesting marker to diagnose patients who have suffered a recent epileptic seizure.

Peptidylgycine α-amidating monooxygenase and copper: a gene-nutrient interaction critical to nervous system function

Peptidylgycine alpha-amidating monooxygenase (PAM), a highly conserved copper-dependent enzyme, is essential for the synthesis of all amidated neuropeptides. Biophysical studies revealed that the binding of copper to PAM affects its structure, and cell biological studies demonstrated that the endocytic trafficking of PAM was sensitive to copper. We review data indicating that genetic reduction of PAM expression and mild copper deficiency in mice cause similar alterations in several physiological functions known to be regulated by neuropeptides: thermal regulation, seizure sensitivity, and anxiety-like behavior.

A new minimal-stress freely-moving rat model for preclinical studies on intranasal administration of CNS drugs

Purpose

To develop a new minimal-stress model for intranasal administration in freely moving rats and to evaluate in this model the brain distribution of acetaminophen following intranasal versus intravenous administration.

Methods

Male Wistar rats received one intranasal cannula, an intra-cerebral microdialysis probe, and two blood cannulas for drug administration and serial blood sampling respectively. To evaluate this novel model, the following experiments were conducted. 1) Evans Blue was administered to verify the selectivity of intranasal exposure. 2) During a 1 min infusion 10, 20, or 40 μl saline was administered intranasally or 250 µl intravenously. Corticosterone plasma concentrations over time were compared as biomarkers for stress. 3) 200 µg of the model drug acetaminophen was given in identical setup and plasma, and brain pharmacokinetics were determined.

Results

In 96% of the rats, only the targeted nasal cavity was deeply colored. Corticosterone plasma concentrations were not influenced, neither by route nor volume of administration. Pharmacokinetics of acetaminophen were identical after intravenous and intranasal administration, although the Cmax in microdialysates was reached a little earlier following intravenous administration.

Conclusion

A new minimal-stress model for intranasal administration in freely moving rats has been successfully developed and allows direct comparison with intravenous administration.

Attenuation of kindled seizures by intranasal delivery of neuropeptide-loaded nanoparticles

Thyrotropin-releasing hormone (TRH; Protirelin), an endogenous neuropeptide, is known to have anticonvulsant effects in animal seizure models and certain intractable epileptic patients. Its duration of action, however, is limited by rapid tissue metabolism and the blood-brain barrier. Direct nose-to-brain delivery of neuropeptides in sustained-release biodegradable nanoparticles (NPs) is a promising mode of therapy for enhancing CNS neuropeptide bioavailability. To provide proof of principle for this delivery approach, we used the kindling model of temporal lobe epilepsy to show that 1) TRH-loaded copolymer microdisks implanted in a seizure focus can attenuate kindling development in terms of behavioral stage, afterdischarge duration (ADD), and clonus duration; 2) intranasal administration of an unprotected TRH analog can acutely suppress fully kindled seizures in a concentration-dependent manner in terms of ADD and seizure stage; and 3) intranasal administration of polylactide nanoparticles (PLA-NPs) containing TRH (TRH-NPs) can impede kindling development in terms of behavioral stage, ADD, and clonus duration. Additionally, we used intranasal delivery of fluorescent dye-loaded PLA-NPs in rats and application of dye-loaded or dye-attached NPs to cortical neurons in culture to demonstrate NP uptake and distribution over time in vivo and in vitro respectively. Also, a nanoparticle immunostaining method was developed as a procedure for directly visualizing the tissue level and distribution of neuropeptide-loaded nanoparticles. Collectively, the data provide proof of concept for intranasal delivery of TRH-NPs as a viable means to 1) suppress seizures and perhaps epileptogenesis and 2) become the lead compound for intranasal anticonvulsant nanoparticle therapeutics.