Synthesis of CNS active thyrotropin-releasing hormone (TRH)-like peptides: Biological evaluation and effect on cognitive impairment induced by cerebral ischemia in mice

Nose-to-Brain (N2B) Delivery: An Alternative Route for the Delivery of Biologics in the Management and Treatment of Central Nervous System Disorders

In recent years, there have been a growing number of small and large molecules that could be used to treat diseases of the central nervous system (CNS). Nose-to-brain delivery can be a potential option for the direct transport of molecules from the nasal cavity to different brain areas. This review aims to provide a compilation of current approaches regarding drug delivery to the CNS via the nose, with a focus on biologics. The review also includes a discussion on the key benefits of nasal delivery as a promising alternative route for drug administration and the involved pathways or mechanisms. This article reviews how the application of various auxiliary agents, such as permeation enhancers, mucolytics, in situ gelling/mucoadhesive agents, enzyme inhibitors, and polymeric and lipid-based systems, can promote the delivery of large molecules in the CNS. The article also includes a discussion on the current state of intranasal formulation development and summarizes the biologics currently in clinical trials. It was noted that significant progress has been made in this field, and these are currently being applied to successfully transport large molecules to the CNS via the nose. However, a deep mechanistic understanding of this route, along with the intimate knowledge of various excipients and their interactions with the drug and nasal physiology, is still necessary to bring us one step closer to developing effective formulations for nasal-brain drug delivery.

Design, synthesis, and applications of ring-functionalized histidines in peptide-based medicinal chemistry and drug discovery

Modified and synthetic α-amino acids are known to show diverse applications. Histidine, which possesses numerous applications when subjected to synthetic modifications, is one such amino acid. The utility of modified histidines varies widely from remarkable biological activities to catalysis, and from nanotechnology to polymer chemistry. This renders histidine residue an important place in scientific research. Histidine is a well-studied scaffold and constitutes the active site of various enzymes catalyzing important reactions in the biological systems. A rational modification in histidine structure with a distinctly developed protocol extensively changes its physical and chemical properties. The utilization of modified histidines in search of potent, target selective and proteostable scaffolds is vital in the development of bioactive peptides with enhanced drug-likeliness. This review is a compilation and analysis of reported side-chain ring modifications at histidine followed by applications of ring-modified histidines in the synthesis of various categories of bioactive peptides and peptidomimetics.

Ring-Modified Histidine-Containing Cationic Short Peptides Exhibit Anticryptococcal Activity by Cellular Disruption

Delineation of clinical complications secondary to fungal infections, such as cryptococcal meningitis, and the concurrent emergence of multidrug resistance in large population subsets necessitates the need for the development of new classes of antifungals. Herein, we report a series of ring-modified histidine-containing short cationic peptides exhibiting anticryptococcal activity via membrane lysis. The N-1 position of histidine was benzylated, followed by iodination at the C-5 position via electrophilic iodination, and the dipeptides were obtained after coupling with tryptophan. In vitro analysis revealed that peptides Trp-His[1-(3,5-di-tert-butylbenzyl)-5-iodo]-OMe (10d, IC₅₀ = 2.20 μg/mL; MIC = 4.01 μg/mL) and Trp-His[1-(2-iodophenyl)-5-iodo)]-OMe (10o, IC₅₀ = 2.52 μg/mL; MIC = 4.59 μg/mL) exhibit promising antifungal activities against C. neoformans. When administered in combination with standard drug amphotericin B (Amp B), a significant synergism was observed, with 4- to 16-fold increase in the potencies of both peptides and Amp B. Electron microscopy analysis with SEM and TEM showed that the dipeptides primarily act via membrane disruption, leading to pore formation and causing cell lysis. After entering the cells, the peptides interact with the intracellular components as demonstrated by confocal laser scanning microscopy (CLSM).

Peptide Hormones in Medicine: A 100-Year History

Abstract

This review is devoted to the 100-year history of the investigation of peptide hormones and the creation of drugs on their basis, starting from the insulin discovery and its introduction into a medical practice in 1921. The basic groups of the peptide hormones are discussed: neurohypophyseal hormones, hypothalamic releasing hormones, incretins, insulin, adrenocorticotropic hormone (ACTH), and calcitonin. The first therapeutic agents based on the peptide hormones were created by a traditional approach that involved the isolation of peptides from animal tissues, their purification to individual compounds, determination of their primary structure, their chemical synthesis or their deep purification, and the creation of a pharmaceutical substance. A modern approach to creation of peptide hormone drugs is based on their consideration as ligands of the corresponding cellular receptors and the use of computer modeling, efficient synthesis methods, and high-throughput screening. The combination of these methods enabled the development of analogs which would be more active than the corresponding natural compounds, exhibit other activities in addition to the hormonal regulation, and be resistant to biodegradation. Such therapeutic agents have been designed on the basis of agonistic and antagonistic analogs of somatostatin and luliberin, and have found wide application in hormonal regulation and cancer treatment. Over the past two decades, the glucagon-like peptide (GLP-1) has been intensively investigated as a potential therapeutic agent. In our review, we describe modifications which resulted in the most highly effective long-acting drugs. Now, natural hormones and their analogs are widely present in the pharmaceutical market.

Modulatory Role of Quercetin in Mitochondrial Dysfunction in Titanium Dioxide Nanoparticle-Induced Hepatotoxicity

Background : Titanium dioxide (TiO₂) nanoparticles are among the largely manmade nanomaterials worldwide and are broadly used as both industrial and user products. The primary target site for several nanoparticles is the liver, including TiO₂ nanoparticles (TNPs), exposed directly or indirectly through ingestion of contaminated water, food, or animals and elevated environmental contamination. Oxidative stress is a known facet of nanoparticle-induced toxicity, including TNPs. Mitochondria are potential targets for nanoparticles in several types of toxicity, such as hepatotoxicity. Nevertheless, its causal mechanism is still controversial due to scarcity of literature linking the role of mitochondria-mediated TNP-induced hepatotoxicity. Aim : The objective of the current study was to evaluate the relation of mitochondrial oxidative stress and respiratory chain mechanisms with TNP-induced mitochondrial dysfunction in vitro, and explore the hepatoprotective effect of quercetin (QR), which is a polyphenolic flavonoid abundant in fruits and vegetables with known antioxidant properties, on TNP-induced mitochondrial oxidative stress and disturbance in respiratory chain complex enzymes in the liver of rats. Results: Enzymatic and non-enzymatic antioxidant levels, oxidative stress markers, and mitochondrial complexes were assessed with regard to TNP-induced hepatotoxicity. The depleted lipid peroxidation levels and protein carbonyl content, in mitochondria, induced by TNPs were restored significantly by pretreatment with QR. QR modulated the altered non-enzymatic and enzymatic antioxidants and mitochondrial complex enzymes. Conclusion : Based on the findings, we conclude that QR, which mitigates oxidative stress caused by mitochondrial dysfunction, holds promising capability to potentially diminish TNP-induced adverse effects in the liver.

Synthesis and Evaluation of in Vivo Anti-hypothermic Effect of the N- and C-Terminus Modified Thyrotropin-Releasing Hormone Mimetic: [(4S,5S)-(5-Methyl-2-oxooxazolidine-4-yl)carbonyl]-[3-(thiazol-4-yl)-L-alanyl]-L-prolinamide

We explored orally effective thyrotropin-releasing hormone (TRH) mimetics, which show high central nervous system effects in structure-activity relationship studies based on in vivo antagonistic activity on reserpine-induced hypothermia (anti-hypothermic effect) in mice starting from TRH. This led us to the TRH mimetic: [(4S,5S)-(5-methyl-2-oxooxazolidine-4-yl)carbonyl]-[3-(thiazol-4-yl)-L-alanyl]-L-prolinamide 1, which shows a higher anti-hypothermic effect compared with that of TRH after oral administration. We next attempted further chemical modification of the N- and C-terminus of 1 to find more orally effective TRH mimetics. As a result, we obtained several N- and C-terminus modified TRH mimetics which showed high anti-hypothermic effects.

Synthesis and evaluation of in vivo anti-hypothermic effect of all stereoisomers of the thyrotropin-releasing hormone mimetic: Rovatirelin Hydrate

We discovered the orally active thyrotropin-releasing hormone (TRH) mimetic: (4S,5S)-5-methyl-N-{(2S)-1-[(2R)-2-methylpyrrolidin-1-yl]-1-oxo-3-(1,3-thiazol-4-yl)propan-2-yl}-2-oxo-1,3-oxazolidine-4-carboxamide 1 (rovatirelin). The central nervous system (CNS) effect of rovatirelin after intravenous (iv) administration is 100-fold higher than that of TRH. As 1 has four asymmetric carbons in its molecule, there are 16 stereoisomers. We synthesized and evaluated the anti-hypothermic effect of all stereoisomers of 1, which has the (4S),(5S),(2S),(2R) configuration from the N-terminus to the C-terminus, in order to clarify the structure-activity relationship (SAR) of stereoisomers. The (4R),(5R),(2R),(2S)-isomer 16 did not show any anti-hypothermic effect. Only the (4S),(5S),(2S),(2S)-isomer 10, which has the (2S)-2-methylpyrrolidine moiety at the C-terminus showed the anti-hypothermic effect similar to 1. Stereoisomers, which have the (5R) configuration of the oxazolidinone at the N-terminus and the (2R) configuration at the middle-part, showed a much lower anti-hypothermic effect than that of 1. On the other hand, stereoisomers, which have the (4R) configuration of the oxazolidinone at the N-terminus or the (2S) configuration of the C-terminus, have little influence on the anti-hypothermic effect.

Discovery of the Orally Effective Thyrotropin-Releasing Hormone Mimetic: 1-{N-[(4S,5S)-(5-Methyl-2-oxooxazolidine-4-yl)carbonyl]-3-(thiazol-4-yl)-l-alanyl}-(2R)-2-methylpyrrolidine Trihydrate (Rovatirelin Hydrate)

We have explored orally effective thyrotropin-releasing hormone (TRH) mimetics, showing oral bioavailability and brain penetration by structure-activity relationship (SAR) study on the basis of in vivo antagonistic activity on reserpine-induced hypothermia in mice. By primary screening of the synthesized TRH mimetics, we found a novel TRH mimetic: l-pyroglutamyl-[3-(thiazol-4-yl)-l-alanyl]-l-prolinamide with a high central nervous system effect compared with TRH as a lead compound. Further SAR optimization studies of this lead compound led to discovery of a novel orally effective TRH mimetic: 1-{N-[(4S,5S)-(5-methyl-2-oxooxazolidine-4-yl)carbonyl]-3-(thiazol-4-yl)-l-alanyl}-(2R)-2-methylpyrrolidine trihydrate (rovatirelin hydrate), which was selected as a candidate for clinical trials.

Synthesis and biology of ring-modified l-Histidine containing thyrotropin-releasing hormone (TRH) analogues

Thyrotropin-releasing hormone (TRH) analogues bearing halogen groups (Cl, Br and I) at the C-2 and/or C-5 position, and the alkyl group (CH3, C2H5, C3H7, CH2C6H5) at the N-1 position of the imidazole ring of the central histidine residue were synthesized and evaluated for the receptor binding, calcium mobilization (FLIPR), and IP-1 assay at the HEK mTRHR1 and HEK mTRHR2 expressing cell lines. The most promising analogue 7k showed 925-fold selectivity for HEK mTRH-R2 receptor subtype in the IP-1 assay, 272-fold selectivity for HEK mTRH-R2 receptor subtype in the FLIPR assay, and 21-fold receptor binding specificity at HEK TRH-R2 receptor subtype. The peptide 7k was evaluated in vitro in a brain membrane competitive binding assay, and for stability analysis in the presence of TRH-DE, in vivo. The analogue 7k showed decrease in the sleeping time by more than 76% in a pentobarbital-induced sleeping assay, and showed comparatively less elevation in the TSH level in the blood, in vivo. The computational homology modeling of TRH-R1 and TRH-R2 and docking study with the most potent peptide 7k provide impetus to design CNS specific TRH analogues.

Regioselective copper-catalyzed N(1)-(hetero)arylation of protected histidine

We report regioselective N(1)-arylation of protected histidine using copper(i) iodide as a catalyst, trans-N,N′-dimethylcyclohexane-1,2-diamine as a ligand and readily available aryl iodides as coupling partners under microwave irradiation at 130 °C for 40 min.