In Silico Identification of Tripeptides as Lead Compounds for the Design of KOR Ligands

Influence of extraction solvents on the chemical constituents and biological activities of Astragalus aduncus from Turkey flora: In vitro and in silico insights

The n-hexane, ethyl acetate, ethanol, ethanol/water (70% ethanol), and water extracts of Astragalus aduncus aerial parts were investigated for their antioxidant potential, enzyme inhibition activity (anti-acetylcholinesterase [AChE], anti-butyrylcholinesterase [BChE], antityrosinase, antiamylase, and antiglucosidase) and antiproliferative effect (against colon adenocarcinoma cell line [HT-29], gastric cancer cell line [HGC-27], prostate carcinoma cell line [DU-145], breast adenocarcinoma cell line [MDA-MB-231], and cervix adenocarcinoma cell line [HeLa]). In addition, the phytochemical profile of the extracts was evaluated using validated spectrophotometric and high-pressure liquid chromatography-electrospray ionization/tandem mass spectroscopy methods. Generally, the 70% ethanol extract demonstrated the strongest antioxidant properties, and it was the richest source of total phenolic constituents. Our findings indicated that the ethyl acetate extract was the most potent BChE inhibitor (11.44 mg galantamine equivalents [GALAE]/g) followed by the ethanol extract (8.51 mg GALAE/g), while the ethanol extract was the most promising AChE inhibitor (3.42 mg GALAE/g) followed by the ethanol/water extract (3.17 mg GALAE/g). Excellent tyrosinase inhibitory activity (66.25 mg kojic acid equivalent/g) was observed in ethanol/water extracts of the aerial part of A. aduncus. Тhese results showed that the most cytotoxic effects were exhibited by the ethyl acetate extract against HGC-27 cells (IC50: 36.76 µg/mL), the ethanol extract against HT-29 cells (IC50: 30.79 µg/mL), and the water extract against DU-145 cells (IC50: 37.01 µg/mL). A strong correlation was observed between the highest total flavonoid content and the highest content of individual compounds in the ethanol extract, including rutin, hyperoside, isoquercitrin, delphinidin-3,5-diglucoside (delphinidin-3,5-O-diglucoside), and kaempferol-3-glucoside (kaempferol-3-O-glucoside). In the present study, the A. aduncus plant was considered a new source of antioxidants, enzyme inhibitors, and anticancer agents and could be used as a future health-benefit natural product.

Analgesic Peptides: From Natural Diversity to Rational Design

Pain affects one-third of the global population and is a significant public health issue. The use of opioid drugs, which are the strongest painkillers, is associated with several side effects, such as tolerance, addiction, overdose, and even death. An increasing demand for novel, safer analgesic agents is a driving force for exploring natural sources of bioactive peptides with antinociceptive activity. Since the G protein-coupled receptors (GPCRs) play a crucial role in pain modulation, the discovery of new peptide ligands for GPCRs is a significant challenge for novel drug development. The aim of this review is to present peptides of human and animal origin with antinociceptive potential and to show the possibilities of their modification, as well as the design of novel structures. The study presents the current knowledge on structure-activity relationship in the design of peptide-based biomimetic compounds, the modification strategies directed at increasing the antinociceptive activity, and improvement of metabolic stability and pharmacodynamic profile. The procedures employed in prolonged drug delivery of emerging compounds are also discussed. The work summarizes the conditions leading to the development of potential morphine replacements.

Virtual Screening of Peptide Libraries: The Search for Peptide-Based Therapeutics Using Computational Tools

Over the last few decades, we have witnessed growing interest from both academic and industrial laboratories in peptides as possible therapeutics. Bioactive peptides have a high potential to treat various diseases with specificity and biological safety. Compared to small molecules, peptides represent better candidates as inhibitors (or general modulators) of key protein-protein interactions. In fact, undruggable proteins containing large and smooth surfaces can be more easily targeted with the conformational plasticity of peptides. The discovery of bioactive peptides, working against disease-relevant protein targets, generally requires the high-throughput screening of large libraries, and in silico approaches are highly exploited for their low-cost incidence and efficiency. The present review reports on the potential challenges linked to the employment of peptides as therapeutics and describes computational approaches, mainly structure-based virtual screening (SBVS), to support the identification of novel peptides for therapeutic implementations. Cutting-edge SBVS strategies are reviewed along with examples of applications focused on diverse classes of bioactive peptides (i.e., anticancer, antimicrobial/antiviral peptides, peptides blocking amyloid fiber formation).

Endogenous opiates and behavior: 2021

This paper is the forty-fourth consecutive installment of the annual anthological review of research concerning the endogenous opioid system, summarizing articles published during 2021 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides and receptors as well as effects of opioid/opiate agonizts and antagonists. The review is subdivided into the following specific topics: molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (1), the roles of these opioid peptides and receptors in pain and analgesia in animals (2) and humans (3), opioid-sensitive and opioid-insensitive effects of nonopioid analgesics (4), opioid peptide and receptor involvement in tolerance and dependence (5), stress and social status (6), learning and memory (7), eating and drinking (8), drug abuse and alcohol (9), sexual activity and hormones, pregnancy, development and endocrinology (10), mental illness and mood (11), seizures and neurologic disorders (12), electrical-related activity and neurophysiology (13), general activity and locomotion (14), gastrointestinal, renal and hepatic functions (15), cardiovascular responses (16), respiration and thermoregulation (17), and immunological responses (18).

Kappa Opioid Receptors Reduce Serotonin Uptake and Escitalopram Efficacy in the Mouse Substantia Nigra Pars Reticulata

The serotonin and kappa opioid receptor (KOR) systems are strongly implicated in disorders of negative affect, such as anxiety and depression. KORs expressed on axon terminals inhibit the release of neurotransmitters, including serotonin. The substantia nigra pars reticulata (SNr) is involved in regulating affective behaviors. It receives the densest serotonergic innervation in the brain and has high KOR expression; however, the influence of KORs on serotonin transmission in this region is yet to be explored. Here, we used ex vivo fast-scan cyclic voltammetry (FSCV) to investigate the effects of a KOR agonist, U50, 488 (U50), and a selective serotonin reuptake inhibitor, escitalopram, on serotonin release and reuptake in the SNr. U50 alone reduced serotonin release and uptake, and escitalopram alone augmented serotonin release and slowed reuptake, while pretreatment with U50 blunted both the release and uptake effects of escitalopram. Here, we show that the KOR influences serotonin signaling in the SNr in multiple ways and short-term activation of the KOR alters serotonin responses to escitalopram. These interactions between KORs and serotonin may contribute to the complexity in the responses to treatments for disorders of negative affect. Ultimately, the KOR system may prove to be a promising pharmacological target, alongside traditional antidepressant treatments.

Design of κ-Opioid Receptor Agonists for the Development of Potential Treatments of Pain with Reduced Side Effects

The κ-opioid receptor (KOR) has recently emerged as an alternative therapeutic target for the development of pain medications, without deleterious side effects associated with the μ-opioid receptor (MOR). However, modulation of KOR is currently under investigation for the treatment of depression, mood disorders, psychiatric comorbidity, and specific drug addictions. However, KOR agonists also trigger adverse effects including sedation, dysphoria, and hallucinations. In this respect, there is currently much debate on alternative paradigms. Recent effort has been devoted in search of biased ligands capable of selectively activating favorable signaling over signaling associated with unwanted side effects. On the other hand, the use of partial agonists is expected to allow the analgesia to be produced at dosages lower than those required to produce the adverse effects. More empirically, the unwanted central effects can be also avoided by using peripherally restricted agonists. In this review, we discuss the more recent trends in the design of KOR-selective, biased or partial, and finally, peripherally acting agonists. Special emphasis is given on the discussion of the most recent approaches for controlling functional selectivity of KOR-specific ligands.

Discovery of κ Opioid Receptor (KOR)-Selective d-Tetrapeptides with Improved In Vivo Antinociceptive Effect after Peripheral Administration

Peripherally active tetrapeptides as selective κ opioid receptor (KOR) agonists have been prepared in good overall yields and high purity following solid-phase peptide synthesis via Fmoc protection strategy. Structural modifications at the first and second position of the lead compound FF(d-Nle)R-NH2 (FE200041) were contemplated with aromatic side chains containing d-amino acids, such as (d)-pF-Phe, (d)-mF-Phe, (d)-oF-Phe, which led to highly selective and efficacious KOR agonists endowed with strong antinociceptive activity in vivo following intravenous (i.v.) and subcutaneous (s.c.) administration in the tail flick and formalin tests. These results suggest potential clinical applications in the treatment of neuropathic and inflammatory pain.

Targeting the HIV-1 Tat and Human Tat Protein Complex through Natural Products: An In Silico Docking and Molecular Dynamics Simulation Approach

Background:

Tat protein is considered essential for substantial HIV-1 replication, and is also required to break HIV-1 latency, resulting in productive HIV replication. The multifaceted regulatory role of HIV Tat and the fact that it is expressed in the early stages of HIV infection justify its potential as an anti-HIV drug target.

Objective:

The present study was undertaken with the aim to target HIV-1 Tat protein with natural compounds which could help in identifying potential inhibitors against HIV-1 Tat.

Methods:

In this study, we compared the binding of Tat protein and Human P-TEFb Tat protein complex (TPC) with phyto-steroids and terpenes to evaluate their potential for HIV-1 treatment. The docking ability of plant products with HIV-1 Tat and TPC was studied with respect to dissociation constant, geometric shape complementary score, approximate interface area, and binding energy using Patch dock and YASARA. Molecular dynamics simulation was set up to investigate the interactions of the natural compounds with Tat protein and human tat protein complex (TPC).

Results:

The binding energy and dissociation constant of Diosgenin, Catharanthine and Ginkgolide A with Tat and TPC were comparable to antiretroviral drugs, Maraviroc and Emtricitabine. The natural products, Diosgenin, Ginkgolide A and Catharanthine, showed the highest binding energy and were stable with Tat protein and TPC in the entire MD simulation run.

Conclusion:

The natural products, Diosgenin, Ginkgolide A and Catharanthine, showed highest binding energy and were stable with Tat protein and TPC in the entire MD simulation run. The binding energy and dissociation constant of Diosgenin, Catharanthine and Ginkgolide A with Tat and TPC were comparable to antiretroviral drugs, Maraviroc and Emtricitabine.

An updated assessment of the translational promise of G-protein-biased kappa opioid receptor agonists to treat pain and other indications without debilitating adverse effects

Kappa opioid receptor (κOR) agonists lack the abuse liability and respiratory depression effects of clinically used mu opioid receptor (μOR) analgesics and are hypothesized to be safer alternatives. However, κOR agonists have limiting adverse effects of their own, including aversion, sedation, and mood effects, that have hampered their clinical translation. Studies performed over the last 15 years have suggested that these adverse effects could result from activation of distinct intracellular signaling pathways that are dependent on β-arrestin, whereas signaling downstream of G protein activation produces antinociception. This led to the hypothesis that agonists biased away from β-arrestin signaling would have improved therapeutic windows over traditional unbiased agonists and allow for clinical development of analgesic G-protein-biased κOR agonists. Given a recent controversy regarding the benefits of G-protein-biased μOR agonists, it is timely to reassess the therapeutic promise of G-protein-biased κOR agonists. Here we review recent discoveries from preclinical κOR studies and critically evaluate the therapeutic windows of G-protein-biased κOR agonists in each of the adverse effects above. Overall, we find that G-protein-biased κOR agonists generally have improved therapeutic window relative to unbiased agonists, although frequently study design limits strong conclusions in this regard. However, a steady flow of newly developed biased κOR agonists paired with recently engineered behavioral and molecular tools puts the κOR field in a prime position to make major advances in our understanding of κOR function and fulfill the promise of translating a new generation of biased κOR agonists to the clinic.

Repurposing Novel Antagonists to p7 Viroporin of HCV Using in silico Approach

Abstract:

Background: P7 viroporin in HCV is a cation-selective ion channel-forming protein, functional in the oligomeric form. It is considered to be a potential target for anti-HCV compounds due to its crucial role in viral entry, assembly and release.

Method:

Conserved crucial residues present in HCV p7 protein were delineated with a specific focus on the genotypes 3a &1b prevalent in India from the available literature. Using the Flex-X docking tool, a library of FDA-approved drugs was docked on the receptor sites prepared around crucial residues. In the present study, we propose drug repurposing to target viroporin p7, which may help in the rapid development of effective anti-HCV therapies.

Results:

With our approach of poly-pharmacology, a variety of drugs currently identified classified as antibiotics, anti-parasitic, antiemetic, anti-retroviral, and anti-neoplastic were found to dock successfully with the p7 viroporin. Noteworthy among these are general-purpose cephalosporin antibiotics, leucal, phthalylsulfathiazole, and granisetron, which may be useful in acute HCV infection and anti-neoplastic sorafenib and nilotinib, which may be valuable in advanced HCV-HCC cases.

Conclusion:

This study could pave the way for quick repurposing of these compounds as anti-HCV therapeutics.

New insights on Phyllanthus reticulatus Poir. leaves and stem bark extracts: UPLC-ESI-TOF-MS profiles, and biopharmaceutical and in silico analysis

Our results could provide a great scientific starting point on the way from the bench to functional applications through the use of P. reticulatus, namely novel nutraceuticals, pharmaceuticals and cosmeceuticals.