In vitro opioid receptor affinity and in vivo behavioral studies of Nelumbo nucifera flower

2023 Julius Axelrod Symposium: Plant-Derived Molecules Acting on G Protein-Coupled Receptors

Plant extracts have played a significant role in traditional medicine for centuries, contributing to improved health and the treatment of various human illnesses. G protein-coupled receptors (GPCRs) are crucial in numerous physiologic functions, and there is growing evidence suggesting their involvement in the therapeutic effects of many plant extracts. In recent years, scientists have identified an expanding number of isolated molecules responsible for the biologic activity of these extracts, with many believed to act on GPCRs. This article critically reviews the evidence supporting the modulation of GPCR function by these plant-derived molecules through direct binding. Structural information is now available for some of these molecules, allowing for a comparison of their binding mode with that of endogenous GPCR ligands. The final section explores future trends and challenges, focusing on the identification of new plant-derived molecules with both orthosteric and allosteric binding modes, as well as innovative strategies for designing GPCR ligands inspired by these plant-derived compounds. In conclusion, plant-derived molecules are anticipated to play an increasingly vital role as therapeutic drugs and serve as templates for drug design. SIGNIFICANCE STATEMENT: This minireview summarizes the most pertinent publications on isolated plant-derived molecules interacting with G protein-coupled receptors (GPCRs) and comments on available structural information on GPCR/plant-derived ligand pairs. Future challenges and trends for the isolation and characterization of plant-derived molecules and drug design are discussed.

Lotus (Nelumbo nucifera): a multidisciplinary review of its cultural, ecological, and nutraceutical significance

This comprehensive review systematically examines the multifarious aspects of Nelumbo nucifera, elucidating its ecological, nutritional, medicinal, and biomimetic significance. Renowned both culturally and scientifically, Nelumbo nucifera manifests remarkable adaptability, characterized by its extensive distribution across varied climatic regions, underpinned by its robust rhizome system and prolific reproductive strategies. Ecologically, this species plays a crucial role in aquatic ecosystems, primarily through biofiltration, thereby enhancing habitat biodiversity. The rhizomes and seeds of Nelumbo nucifera are nutritionally significant, being rich sources of dietary fiber, essential vitamins, and minerals, and have found extensive culinary applications. From a medicinal perspective, diverse constituents of Nelumbo nucifera exhibit therapeutic potential, including anti-inflammatory, antioxidant, and anti-cancer properties. Recent advancements in preservation technology and culinary innovation have further underscored its role in the food industry, highlighting its nutritional versatility. In biomimetics, the unique "lotus effect" is leveraged for the development of self-cleaning materials. Additionally, the transformation of Nelumbo nucifera into biochar is being explored for its potential in sustainable environmental practices. This review emphasizes the critical need for targeted conservation strategies to protect Nelumbo nucifera against the threats posed by climate change and habitat loss, advocating for its sustainable utilization as a species of significant value.

From Plant to Chemistry: Sources of Active Opioid Antinociceptive Principles for Medicinal Chemistry and Drug Design

Pain continues to be an enormous global health challenge, with millions of new untreated or inadequately treated patients reported annually. With respect to current clinical applications, opioids remain the mainstay for the treatment of pain, although they are often associated with serious side effects. To optimize their tolerability profiles, medicinal chemistry continues to study novel ligands and innovative approaches. Among them, natural products are known to be a rich source of lead compounds for drug discovery, and they hold potential for pain management. Traditional medicine has had a long history in clinical practice due to the fact that nature provides a rich source of active principles. For instance, opium had been used for pain management until the 19th century when its individual components, such as morphine, were purified and identified. In this review article, we conducted a literature survey aimed at identifying natural products interacting either directly with opioid receptors or indirectly through other mechanisms controlling opioid receptor signaling, whose structures could be interesting from a drug design perspective.

Neferine alleviates chronic stress-induced depression by regulating monoamine neurotransmitter secretion and gut microbiota structure

Neferine (Nef) might possess anti-depressive properties; however, its therapeutic effects are yet to be elucidated. Therefore, in this study, we aimed to explore the anti-depressant property of Nef using a mouse model of chronic stress-induced depression. Fifteen depression-prone mice were randomly selected and divided into three groups, namely, the model, Nef, and fluoxetine (Flu) groups. We observed that in tail suspension and forced swimming tests, the Nef and Flu treatments significantly decreased the immobility time of the depressed mice, and increased their sucrose preference indices. Moreover, both Nef and Flu treatments induced significant increases in the levels of anti-depressant neurotransmitters, including dopamine (DA), serotonin (5-HT), and norepinephrine (NE), and also reduced pathological damage to the hippocampus of the depressed mice. Incidentally, Illumina MiSeq sequencing analysis demonstrated that the relative abundance of Lactobacillus in the intestinal microbiota of depressed mice was restored after Nef/Flu treatment. Moreover, colonic Lactobacillus abundance was positively correlated with the levels of DA, 5-HT, and NE in the hippocampus of the mice. In conclusion, Nef improved monoamine neurotransmitter secretion and modulated the intestinal flora structure, particularly the abundance of Lactobacillus. Hence, it showed considerable anti-depressant potential, and might be a prospective anti-depressant therapeutic agent.

Discovery of eight alkaloids with D1 and D2 antagonist activity in leaves of Nelumbo nucifera Gaertn. Using FLIPR assays

ETHNOPHARMACOLOGICAL RELEVANCE

Dopamine receptors are long-standing primary targets in the treatment of mental diseases and there is growing evidence that suggests relationships between obesity and the dopamine system, especially dopamine D1 and D2 receptors. Leaves of Nelumbo nucifera Gaertn. (lotus leaves) have been medically used for helping long-term maintenance of weight loss. Whether and how components of lotus leaves function through the dopamine receptors remains unclear.

AIM OF THE STUDY

This work aimed to discover dopamine receptor-active alkaloids isolated from the lotus leaves, to evaluate their potencies and to analyze their structure activity relationship.

MATERIALS AND METHODS

Dried lotus leaves were prepared and total extract was divided into alkaloids and flavones. Eight alkaloids were separated and characterized by a combination of high-performance liquid chromatography, quadrupole time-of-flight mass spectrometry and nuclear magnetic resonance, and assayed by a fluorometric imaging plate reader platform. Human embryonic kidney 239 cell lines expressing dopamine D1, D2 and serotonin 2A (5-HT2A) receptors, respectively, were cultured and used in the assay.

RESULTS

Alkaloids in the lotus leaves were the bioactive phytochemicals and inhibited dopamine from accessing the D1 and D2 receptors. All eight compounds functioned as D1-receptor antagonists and except N-nornuciferine, seven alkaloids functioned as D2-receptor antagonists. (S)-coclaurine and (R)-coclaurine are optical isomers and antagonized both D1 and D2 with equivalent potencies, suggesting that the optical rotation of the methylene linker in the monobenzyl isoquinoline backbone did not influence their activity. Among the eight alkaloids, O-nornuciferine was the potent antagonist to both receptors (the lowest IC₅₀ values, D1: 2.09 ± 0.65 μM and D2: 1.14 ± 0.10 μM) while N-nornuciferine was found to be the least potent as it moderately antagonized D1 and was inactive on D2. O-nornuciferine was also a 5-HT2A antagonist (IC₅₀~20 μM) while N-nornuciferine had no activity. These hinted the importance of a methyl group attached to the nitrogen atom in the aporphine backbone. Armepavine showed a nearly 10-fold selectivity to D2.

CONCLUSIONS

In this work, eight alkaloids were isolated from the leaves of Nelumbo nucifera Gaertn. and assayed on the D1 and D2 receptors. They were D1/D2 antagonists with IC₅₀ values in the mid- to low-micromolar range and O-nornuciferine was the most potent alkaloid among the eight. This family of alkaloids was biochemically evaluated on the dopamine receptors by the same platform for the first time.

Neferine improves oxidative stress and apoptosis in benign prostate hyperplasia via Nrf2-ARE pathway

BACKGROUND

Progression of Benign Prostate hyperplasia (BPH) is vulnerable to oxidative stress (OS) and prostatic enlargement among the aging males through apoptosis deregulation. Our present study aimed to investigate the effect of neferine (NF) in the regulation of oxidative stress and apoptosis in human BPH-1 cells.

METHODS

BPH epithelial cell line BPH-1 was treated with NF for 24 and 48 h. To measure oxidative stress (OS) we investigated MDA, SOD, and GST expression along with Nrf2 and its downstream gene and protein expression. Cell proliferation and apoptosis regulation was assayed with respective methods.

RESULTS

Investigation revealed NF remarkably activate Nrf2 and its downstream proteins HO-1 and NQO1 at 48 h more substantially. Nrf2/Keap1 relative gene and protein expression indicated that NF might trigger Nrf2 upregulation by decreasing Keap1 expression. Both NF concentrations (3 µM and 9 µM) were able to deplete ROS and lipid peroxidation, concurrently, up-regulated SOD and GST. NF reduced cell proliferation significantly along with the regulation of apoptotic proteins Bax, Bcl2, Cyt-C, Caspase 9, and Caspase 3 at the same time (48 h).

CONCLUSION

This study is the first to manifest that NF may potentially regulate BPH by counterbalancing between OS and apoptosis through the activation of Nrf2-ARE pathway.

Salvindolin elicits opioid system-mediated antinociceptive and antidepressant-like activities

BACKGROUND

Salvinorin A is known as a highly selective kappa opioid receptor agonist with antinociceptive but mostly pro-depressive effects.

AIMS

In this article, we present its new semisynthetic analog with preferential mu opioid affinity, and promising antinociceptive, as well as antidepressant-like activities.

METHODS

Competitive binding studies were performed for salvindolin with kappa opioid and mu opioid. The mouse model of nociception (acetic-acid-induced writhing, formalin, and hot plate tests), depression (forced swim and tail suspension tests), and the open field test, were used to evaluate antinociceptive, antidepressant-like, and locomotion effects, respectively, of salvindolin. We built a 3-D molecular model of the kappa opioid receptor, using a mu opioid X-ray crystal structure as a template, and docked salvindolin into the two proteins.

RESULTS/OUTCOMES

Salvindolin showed affinity towards kappa opioid and mu opioid receptors but with 100-fold mu opioid preference. Tests of salvindolin in mice revealed good oral bioavailability, antinociceptive, and antidepressive-like effects, without locomotor incoordination. Docking of salvindolin showed strong interactions with the mu opioid receptor which matched well with experimental binding data. Salvindolin-induced behavioral changes in the hot plate and forced swim tests were attenuated by naloxone (nonselective opioid receptor antagonist) and/or naloxonazine (selective mu opioid receptor antagonist) but not by nor-binaltorphimine (selective kappa opioid receptor antagonist). In addition, WAY100635 (a selective serotonin 1A receptor antagonist) blocked the antidepressant-like effect of salvindolin.

CONCLUSIONS/INTERPRETATION

By simple chemical modification, we were able to modulate the pharmacological profile of salvinorin A, a highly selective kappa opioid receptor agonist, to salvindolin, a ligand with preferential mu opioid receptor affinity and activity on the serotonin 1A receptor. With its significant antinociceptive and antidepressive-like activities, salvindolin has the potential to be an analgesic and/or antidepressant drug candidate.

One-step, stereoselective synthesis of octahydrochromanes via the Prins reaction and their cannabinoid activities

Novel, functionalized octahydrochromene derivatives were synthesized in a single step via the Prins reaction. Enantiomerically pure (+)-isopulegol was reacted with benzaldehyde to stereoselectively yield the corresponding octahydro-2H-chromen-4-ol derivative containing five stereocenters. A total of 10 compounds were synthesized by altering the enantiomer of isopulegol and the substituted benzaldehyde, and the resulting enantiopure octahydrochromenes were screened in vitro against the cannabinoid receptor isoforms CB1 and CB2. Compounds containing an olefin at the C4 position [(+)-3c, (-)-3c, (-)-7c, (-)-9c and (-)-11c] of the octahydrochromene scaffold were found to exhibit reasonable displacement of [3H] CP55,940 from the CB receptors, whereas the corresponding hydroxy analogs [(+)-3a, (+)-3b, (-)-3a, (-)-3b and (+)-5a] had very little or no effect.

Interaction of Plant Extracts with Central Nervous System Receptors

Background: Plant extracts have been used in traditional medicine for the treatment of various maladies including neurological diseases. Several central nervous system receptors have been demonstrated to interact with plant extracts and components affecting the pharmacology and thereby potentially playing a role in human disease and treatment. For instance, extracts from Hypericum perforatum (St. John’s wort) targeted several CNS receptors. Similarly, extracts from Piper nigrum, Stephania cambodica, and Styphnolobium japonicum exerted inhibition of agonist-induced activity of the human neurokinin-1 receptor. Methods: Different methods have been established for receptor binding and functional assays based on radioactive and fluorescence-labeled ligands in cell lines and primary cell cultures. Behavioral studies of the effect of plant extracts have been conducted in rodents. Plant extracts have further been subjected to mood and cognition studies in humans. Results: Mechanisms of action at molecular and cellular levels have been elucidated for medicinal plants in support of standardization of herbal products and identification of active extract compounds. In several studies, plant extracts demonstrated affinity to a number of CNS receptors in parallel indicating the complexity of this interaction. In vivo studies showed modifications of CNS receptor affinity and behavioral responses in animal models after treatment with medicinal herbs. Certain plant extracts demonstrated neuroprotection and enhanced cognitive performance, respectively, when evaluated in humans. Noteworthy, the penetration of plant extracts and their protective effect on the blood-brain-barrier are discussed. Conclusion: The affinity of plant extracts and their isolated compounds for CNS receptors indicates an important role for medicinal plants in the treatment of neurological disorders. Moreover, studies in animal and human models have confirmed a scientific basis for the application of medicinal herbs. However, additional investigations related to plant extracts and their isolated compounds, as well as their application in animal models and the conducting of clinical trials, are required.

Endogenous Opiates and Behavior: 2015

This paper is the thirty-eighth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2015 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia, stress and social status, tolerance and dependence, learning and memory, eating and drinking, drug abuse and alcohol, sexual activity and hormones, pregnancy, development and endocrinology, mental illness and mood, seizures and neurologic disorders, electrical-related activity and neurophysiology, general activity and locomotion, gastrointestinal, renal and hepatic functions, cardiovascular responses, respiration and thermoregulation, and immunological responses.

Quantitative Determination of Betaine, Choline, Acetylcholine, and 20-Hydroxyecdysone Simultaneously from Atriplex Species by UHPLC-UV-MS

A simple, rapid, and sensitive UHPLC-UV-MS method was developed for the quantitative determination of betaine (1), choline (2), acetylcholine (3), and 20-hydroxyecdysone (4) from various species of Atriplex. The baseline separation of the four analytes was achieved on a reversed phase C18 column within nine minutes. The mobile phase was composed of 50 mM ammonium formate in 2% methanol-water containing 5 mM sodium dodecyl sulfate (pH = 8.2) and methanol with 0.01% ammonium hydroxide. The analytical method was validated for recovery, precision, limits of detection (LOD), and limits of quantification (LOQ). The developed method was applied for the characterization and quantitation of analytes from plant parts of different Atriplex species, including A. canescens, A. fruticulosa, A. fasciculata, A. semibaccata, and A. lentiformis. Compounds 1–4 were found in a range of 0.53–1.61%, detection under limit of quantification (DUL)-0.74, DUL-0.0038, and 0-0.10% ( w/w, mg in 100 mg plant material), respectively, in test samples. In leaf and fruit of A. canescens, a high content of 1, 2, and 4 were identified. The content of 1, 2, and 4 in A. canescens explains the potential implications of this native US plant for human health and nutrition. The result of this study provides a new method to analyze these phytoconstituents simultaneously in a mixture.