Opioid Peptides Determination by Tyrosinase-Modified Oxygen Electrode

Abstract

Opioid peptides morphiceptin (Tyr-Pro-Phe-Pro-NH₂), [D-Ala², D-Leu⁵]-enkephalin (Tyr-D-Ala-Gly-Phe-D-Leu, DADLE) and [D-Thr²]-Leu-enkephalin-Thr (Tyr-D-Thr-Gly-Phe-Leu-Thr, DTLET) containing tyrosine has been studied in the reaction with mushroom tyrosinase immobilized on Clark-type oxygen electrode. A 4–6-times higher response is observed for tyrosine compared to peptides. The detection limit of the tyrosinase-modified electrode for DADLE, morphiceptin and DTLET was 6 μM, 9 μM and 16 μM, respectively.     

Fluorescence Assay for Membrane Lytic Peptides

Abstract

Lytic peptides such as melittin and mastoparan are usually assayed by measuring the leakage of cell contents; e.g., hemolysis. When such peptides lyse liposomes containing concentration-quenched 6-carboxyfluorescein (6CF), the resulting fluorescence increase is proportional to the amount of lytic peptide added. Using this 6CF-liposome system, one can assay nanogram quantities of melittin. A protocol was developed to survey peptides for lytic activity and at the same time, to test for mast cell degranulating activity. Peptides possessed either, both, or neither of these activities. The dye-liposome system was used to assay HPLC fractions of bee venom. This fluorescence assay for lytic activity is more sensitive and convenient than the hemolysis method, does not require removal of unlysed structures, and does not require animal cells.     

Resonance Energy Transfer Relates the Gas‐Phase Structure and Pharmacological Activity of Opioid Peptides

Enkephalins are efficient pain‐relief drugs that bind to transmembrane opioid receptors. One key structural parameter that governs the pharmacological activity of these opioid peptides and is typically determined from condensed‐phase structures is the distance between the aromatic rings of their Tyr and Phe residues. We use resonance energy transfer, detected by a combination of cold ion spectroscopy and mass spectrometry, to estimate the Tyr–Phe spacing for enkephalins in the gas phase. In contrast to the condensed‐phase structures, these distances appear to differ substantially in enkephalins with different pharmacological efficiencies, suggesting that gas‐phase structures might be a better pharmacophoric metric for ligand peptides.     

Pre-Incubation and Low Temperatures in Quantitative Radioreceptor Assays

Abstract

The detection limits of drugs in quantitative RRA are primarily determined by their affinities towards the receptor. Yet, the concentration of radiolabeled ligand, necessary for quantification of receptor-bound drug, increases the theoretical detection limit. Therefore the influences of low temperatures and pre-incubation on the detection limit was studied.     

Near-Infrared Light Triggered-Release in Deep Brain Regions Using Ultra-photosensitive Nanovesicles

Remote and minimally-invasive modulation of biological systems with light has transformed modern biology and neuroscience. However, light absorption and scattering significantly prevents penetration to deep brain regions. Herein, we describe the use of gold-coated mechanoresponsive nanovesicles, which consist of liposomes made from the artificial phospholipid Rad-PC-Rad as a tool for the delivery of bioactive molecules into brain tissue. Near-infrared picosecond laser pulses activated the gold-coating on the surface of nanovesicles, creating nanomechanical stress and leading to near-complete vesicle cargo release in sub-seconds. Compared to natural phospholipid liposomes, the photo-release was possible at 40 times lower laser energy. This high photosensitivity enables photorelease of molecules down to a depth of 4 mm in mouse brain. This promising tool provides a versatile platform to optically release functional molecules to modulate brain circuits.     

Cross‐Reactive Sensor Arrays for the Detection of Peptides in Aqueous Solution by Fluorescence Spectroscopy

A simple but powerful method for the sensing of peptides in aqueous solution has been developed. The transition‐metal complexes [PdCl₂(en)], [{RhCl₂Cp*}₂], and [{RuCl₂(p‐cymene)}₂] were combined with six different fluorescent dyes to build a cross‐reactive sensor array. The fluorescence response of the individual sensor units was based on competitive complexation reactions between the peptide analytes and the fluorescent dyes. The collective response of the sensor array in a time‐resolved fashion was used as an input for multivariate analyses. A sensor array comprised of only six metal–dye combinations was able to differentiate ten different dipeptides in buffered aqueous solution at a concentration of 50 μM . Furthermore, the cross‐reactive sensor could be used to obtain information about the identity and the quantity of the pharmacologically interesting dipeptides carnosine and homocarnosine in a complex biological matrix, such as deproteinized human blood serum. The sensor array was also able to sense longer peptides, which was demonstrated by differentiating mixtures of the nonapeptide bradykinin and the decapeptide kallidin.     

Advances in the Physicochemical Profiling of Opioid Compounds of Therapeutic Interest

This review focuses on recent developments in the physicochemical profiling of morphine and other opioids. The acid-base properties and lipophilicity of these compounds is discussed at the microscopic, species-specific level. Examples are provided where this type of information can reveal the mechanism of pharmacokinetic processes at the submolecular level. The role of lipophilicity in quantitative structure–activity relationship (QSAR) studies of opioids is reviewed. The physicochemical properties and pharmacology of the main metabolites of morphine are also discussed. Recent studies indicate that the active metabolite morphine-6-glucuronide (M6G) can contribute to the analgesic activity of systemically administered morphine. The unexpectedly high lipophilicity of M6G partly accounts for its analgesic activity. When administered parenterally, another suspected minor metabolite, morphine-6-sulfate (M6S) has superior antinociceptive effects to those of morphine. However, because sulfate esters of morphine derivatives cannot cross the blood-brain barrier these esters may be good candidates to develop peripheral analgesic drugs.     

利用棋盘格实验直接筛选酶免疫测定的最佳包被抗原和抗体浓度

以两个单克隆抗体及其相应的包被抗原为例,研究了棋盘格实验中包被抗原与抗体浓度组合对免疫检测中0孔吸光度值A0、IC50值和标准曲线斜率的影响.结果发现,A0和IC50值随包被抗原与抗体稀释倍数的增加而降低;斜率随抗体稀释倍数增加而降低,而随包被抗原的稀释倍数增加表现出先增加后降低的趋势.在同一抗体浓度和不同包被抗原浓度的组合中,斜率最大值出现在使板吸附达到饱和的最大稀释倍数的包被抗原浓度附近.综合实验结果确认从棋盘格实验中直接筛选最佳包被抗原、抗体浓度组合的标准是:选择使板吸附达到饱和的最大包被抗原稀释倍数为最佳包被抗原浓度,在不同抗体浓度与已选择的最佳包被抗原浓度组合中使0孔吸光度值达1.0左右的抗体稀释倍数为最佳抗体浓度.     

New Bioactive Peptides Identified from a Tilapia Byproduct Hydrolysate Exerting Effects on DPP-IV Activity and Intestinal Hormones Regulation after Canine Gastrointestinal Simulated Digestion

Like their owners, dogs and cats are more and more affected by overweight and obesity-related problems and interest in functional pet foods is growing sharply. Through numerous studies, fish protein hydrolysates have proved their worth to prevent and manage obesity-related comorbidities like diabetes. In this work, a human in vitro static simulated gastrointestinal digestion model was adapted to the dog which allowed us to demonstrate the promising effects of a tilapia byproduct hydrolysate on the regulation of food intake and glucose metabolism. Promising effects on intestinal hormones secretion and dipeptidyl peptidase IV (DPP-IV) inhibitory activity were evidenced. We identify new bioactive peptides able to stimulate cholecystokinin (CCK) and glucagon-like peptide 1 (GLP-1) secretions, and to inhibit the DPP-IV activity after a transport study through a Caco-2 cell monolayer.     

Light-Driven Diselenide Metathesis in Peptides

Peptides containing selenocysteine moieties are susceptible to non-catalytic reactions of diselenide bonds metathesis induced by visible light. In contrast to previously reported radical metathesis of disulfide bridges in cysteine derivatives, this newly developed reaction is fast and clean, and proceeds without decomposition of peptides and without formation of side products. The diselenide bond in peptides was reported in literature to be more stable than the disulfide one and also less susceptible to metathesis induced by thiols and reducing reagents. We demonstrated that visible light induces fast metathesis of Se−Se bonds in peptides. This reaction is important for the folding of peptides containing selenocysteine residues and may find application in designing dynamic combinatorial libraries of peptides responsive to external influence.     

Evaluation of Cell‐Penetrating Peptides Using Microfluidic In Vitro 3D Brain Endothelial Barrier

In drug delivery to the human brain, blood vessels are a significant hurdle because they restrict the entry of most solutes to protect brain. To overcome this hurdle, an in vitro 3D model for brain endothelial barrier is developed using a microfluidic device with hydrogel providing a 3D extracellular matrix scaffold. Using the model, peptides known to utilize receptor‐mediated transcytosis are verified, which has been one of the most promising mechanisms for brain‐specific penetration. The cytotoxicity and cellular damage to the peptide are investigated and the receptor‐mediated transcytosis and brain endothelial specific penetrating abilities of the peptides in a quantitative manner are demonstrated. As a preclinical test, applying the quantification assays conducted in this study are suggested, including the penetrating ability, cytotoxicity, endothelial damage, and receptor specificity. Using this microfluidic device as an in vitro platform for evaluating various brain targeting drugs and drug carrier candidates is also proposed.     

Osmometric Molecular Weight Determinations of Peptides Using o-Chlorophenol

Abstract

Osmometric molecular weight determinations of peptides carried out at 37° using o-chlorophenol as solvent have been found to be precise with the exception of determinations involving peptides containing free carboxyl groups.     

Optimizing Charge Switching in Membrane Lytic Peptides for Endosomal Release of Biomacromolecules

Endocytic pathways are practical routes for the intracellular delivery of biomacromolecules. Along with this, effective strategies for endosomal cargo release into the cytosol are desired to achieve successful delivery. Focusing on compositional differences between the cell and endosomal membranes and the pH decrease within endosomes, we designed the lipid-sensitive and pH-responsive endosome-lytic peptide HAad. This peptide contains aminoadipic acid (Aad) residues, which serve as a safety catch for preferential permeabilization of endosomal membranes over cell membranes, and His-to-Ala substitutions enhance the endosomolytic activity. The ability of HAad to destabilize endosomal membranes was supported by model studies using large unilamellar vesicles (LUVs) and by increased intracellular delivery of biomacromolecules (including antibodies) into live cells. Cerebral ventricle injection of Cre recombinase with HAad led to Cre/loxP recombination in a mouse model, thus demonstrating potential applicability of HAad in vivo.     

Lights and Shadows on the Therapeutic Use of Antimicrobial Peptides

The emergence of antimicrobial-resistant infections is still a major concern for public health worldwide. The number of pathogenic microorganisms capable of resisting common therapeutic treatments are constantly increasing, highlighting the need of innovative and more effective drugs. This phenomenon is strictly connected to the rapid metabolism of microorganisms: due to the huge number of mutations that can occur in a relatively short time, a colony can “adapt” to the pharmacological treatment with the evolution of new resistant species. However, the shortage of available antimicrobial drugs in clinical use is also caused by the high costs involved in developing and marketing new drugs without an adequate guarantee of an economic return; therefore, the pharmaceutical companies have reduced their investments in this area. The use of antimicrobial peptides (AMPs) represents a promising strategy for the design of new therapeutic agents. AMPs act as immune defense mediators of the host organism and show a poor ability to induce antimicrobial resistance, coupled with other advantages such as a broad spectrum of activity, not excessive synthetic costs and low toxicity of both the peptide itself and its own metabolites. It is also important to underline that many antimicrobial peptides, due to their inclination to attack cell membranes, have additional biological activities, such as, for example, as anti-cancer drugs. Unfortunately, they usually undergo rapid degradation by proteolytic enzymes and are characterized by poor bioavailability, preventing their extensive clinical use and landing on the pharmaceutical market. This review is focused on the strength and weak points of antimicrobial peptides as therapeutic agents. We give an overview on the AMPs already employed in clinical practice, which are examples of successful strategies aimed at overcoming the main drawbacks of peptide-based drugs. The review deepens the most promising strategies to design modified antimicrobial peptides with higher proteolytic stability with the purpose of giving a comprehensive summary of the commonly employed approaches to evaluate and optimize the peptide potentialities.