Geissoschizine methyl ether, a corynanthean-type indole alkaloid fromUncaria rhynchophyllaas a potential acetylcholinesterase inhibitor

Advanced researches of traditional uses, phytochemistry, pharmacology, and toxicology of medical Uncariae Ramulus Cum Uncis

ETHNOPHARMACOLOGICAL RELEVANCE

Medical Uncariae Ramulus Cum Uncis consists of Uncaria rhynchophylla (Miq.) Miq. ex Havil, Uncaria macrophylla Wall, Uncaria sinensis (Oliv.) Havil, Uncaria hirsuta Havil, and Uncaria sessilifructus Roxb, which belongs to the species widely used in the genus Uncaria. These species resource widely distributed in China and abroad, and the hook-bearing stem is the primary constituent enrichment site. There are many different forms and architectures of chemicals, depending on the extraction site. Traditional remedies employing URCU had been used widely in antiquity and were first compiled in renowned ancient masterpiece 'Mingyi Bielu ()' written by Hongjing Tao. In modern pharmacological studies, both the total extracts and the phytoconstituents isolated from URCU have been shown to have neuroprotective, antioxidant, anti-inflammatory, anticancer, antibacterial, and autophagy-enhancer properties.

AIM OF THE STUDY

This review concentrates on the traditional uses, phytochemistry, pharmacology, toxicology, and nanomaterials studies of URCU, with a perspective to assist with further research and advance.

MATERIAL AND METHODS

The Chinese and English literature studies of this review are based on these database searches including Science Direct, CNKI, Wiley online library, Spring Link, Web of Science, PubMed, Medalink, Google scholar, Elsevier, ACS Publications, iPlant, Missouri Botanical Garden, Plant of the World Online. The pertinent data on URCU was gathered.

RESULTS

Based on the examination of the genus Uncaria, 107 newly marked chemical compositions have been identified from URCU from 2015 to present, including alkaloids, terpenoids, flavonoids, steroids, and others. Pharmacological studies have demonstrated that URCU has a variety of benefits in diseases such as neurodegenerative diseases, cancer, cardiovascular diseases, diabetes, and migraine, due to its neuroprotective, anti-inflammatory, antioxidant, anti-tumor, anti-bacterial and anti-viral properties. According to metabolic and toxicological studies, the dosage, frequency, and interactions of the drugs that occur in vivo are of great significance for determining whether the organic bodies can perform efficacy or produce toxicity. The research on URCU-mediated nanomaterials is expanding and increasing in order to address the inadequacies of conventional Chinese medicine. The alkaloids in URCU have the capability to self-assemble with other classes of components in addition to being biologically active.

CONCLUSION

URCU plants are widely distributed, abundant in chemical constituents, and widely used in both traditional and modern medicine for a variety of pharmacological effects. The utilization of herbal medicines can be raised by assessing the pharmacological distinctions among several species within the same genus and may accelerate the modernization of traditional Chinese medicine. Controlling the concentration of drug administration, monitoring metabolic markers, and inventing novel nanotechnologies are effective strategies for synergistic influence and detoxification to alleviate the main obstacles that toxicity, low bioavailability, and poor permeability. This review can assist further research and advances.

Phenolic Compounds and Antioxidant and Anti-Enzymatic Activities of Selected Adaptogenic Plants from South America, Asia, and Africa

Despite the fact that there are many studies related to the adaptogenic and pro-healthy activities of plant-based compounds, there are some adaptogenic plants whose activities are not fully known, especially those coming from the wild regions of Asia, Africa, and South America. The aim of these studies was to examine the contents of non-nutritional compounds, such as polyphenols, flavonoids, and phenolic acids in ten adaptogenic species (Astragalus membranaceus (AM), Uncaria rhynchophylla (UR), Polygonum multiflorum (PM), Angelica sinensis (AS), Andrographis paniculatea (AP), Tinospora cordifolia (TC), Uncaria tomentosa (UT), Pfaffia paniculate (PP), Sutherlandia frutescens (SF), and Rhaponticum carthamoides (RC)). Considering biological activity, their antioxidant (DPPH, ABTS, FRAP, and ferrous-ion-chelating ability assays), anti-acetylcholinesterase, anti-hyaluronidase, and anti-tyrosinase activities were evaluated. The richest in polyphenols, flavonoids, and phenolic acids was UR (327.78 mg GAE/g, 230.13 mg QE/g, and 81.03 mg CA/g, respectively). The highest inhibitions of acetylcholinesterase, hyaluronidase, and tyrosinase were observed for TC, UR, and PM, respectively. In the case of antioxidant properties, extract from PM appeared to most strongly reduce DPPH, extract from UR inhibited ABTS, and extract from SF showed the best chelating properties. It should be noted that a particularly interesting plant was Ulcaria rhynchophylla. The results mean that there were compounds in UR with broad biological activities, and this species should be explored in more detail. Additionally, our results justify the traditional use of these species in the nutripharmacological or ethnopharmacological care systems of different regions.

Structurally diverse lignans from Solanum lyratum: chemical evidence for their acetylcholinease inhibitory activity

A chemical investigation of Solanum lyratum Thumb. (Solanace) afforded two new lignans (1b and 3) and eleven known lignan analogues (1a, 2a/2b and 4-11). Compounds 1a/1b and 2a/2b were separated as two pairs of enantiomers by chiral high-performance liquid chromatography (HPLC). Their structures were elucidated by detailed spectroscopic and comparative literature data analysis. The absolute configurations of compounds 1a/1b and 2a/2b were determined by comparing the experimental ECD data with the calculated values. All compounds were evaluated for their acetylcholinesterase (AChE) inhibitory activity. Notably, compared to the positive control, compounds 4 and 9 showed obvious AChE inhibition with their IC50 values of 1.30 ± 0.25 and 0.89 ± 0.04 μM, respectively. In addition, the possible interaction between acetylcholinesterase and the active compounds was also investigated by molecular docking.

Natural Corynanthe-Type Cholinesterase Inhibitors from Malaysian Uncaria attenuata Korth.: Isolation, Characterization, In Vitro and In Silico Studies

The Uncaria genus is notable for its therapeutic potential in treating age-related dementia, such as Alzheimer’s disease. A phytochemical study of the leaves of Malaysian Uncaria attenuata Korth., afforded an undescribed natural corynanthe-type oxindole alkaloid, isovillocarine D (1) together with two known indole alkaloids, villocarine A (2) and geissoschizine methyl ether (3), and their structural identification was performed with extensive mono- and bidimensional NMR and MS spectroscopic methods. The isolated alkaloids were evaluated for their acetylcholinesterase (AChE)- and butyrylcholinesterase (BChE)-inhibitory activity. The results indicated that compound (2) was the most potent inhibitor against both AChE and BChE, with IC50 values of 14.45 and 13.95 µM, respectively, whereas compounds (1) and (3) were selective BChE inhibitors with IC50 values of 35.28 and 17.65 µM, respectively. In addition, molecular docking studies revealed that compound (2) interacts with the five main regions of AChE via both hydrogen and hydrophobic bonding. In contrast to AChE, the interactions of (2) with the enzymatic site of BChE are established only through hydrophobic bonding. The current finding suggests that U. attenuata could be a good source of bioactive alkaloids for treating age-related dementia.

Protection against H2O2-evoked toxicity in HT22 hippocampal neuronal cells by geissoschizine methyl ether via inhibiting ERK pathway

Oxidative stress is considered as an important mechanism underlying the pathology of neurodegenerative disorders. In this study, we utilized an in vitro model where oxidative stress process was evoked by exogenous hydrogen peroxide (H₂O₂) in HT22 murine hippocampal neurons and evaluated the neuroprotective effects of geissoschizine methyl ether (GME), a naturally occurring alkaloid from the hooks of Uncaria rhynchophylla (Miq.) Jacks. After a 24 h H₂O₂ (350 μM) insult, a significant decrease in cell survival and a sharp increase in intracellular reactive oxygen species were observed in HT22 cells. Encouragingly, GME (10-200 μM) effectively reversed these abnormal cellular changes induced by H₂O₂. Moreover, mechanistic studies using Western blot revealed that GME inhibited the increase of phospho-ERK protein expression, but not phospho-p38, caused by H₂O₂. Molecular docking simulation further revealed a possible binding mode that GME inhibited ERK protein, showing that GME favorably bound to ERK via multiple hydrophobic and hydrogen bond interactions. These findings indicate that GME provide effective neuroprotection via inhibiting ERK pathway and also encourage further ex vivo and in vivo pharmacological investigations of GME in treating oxidative stress-mediated neurological disorders.

Uncaria rhynchophylla mediated Ag/NiO nanocomposites: A new insight for the evaluation of cytotoxicity, antibacterial and photocatalytic applications

The increase of microbial resistance poses threat to the human health. Therefore, the efficient treatment of the microbial resistance is a global challenge and highly desired to explore it. During this study, the Ag/NiO nanocomposite was fabricated via simple and ecofriendly method, using Uncaria rhynchophylla extract as a reducing and capping agent to avoid the aggregation of as synthesized nanomaterials. Here, a range of characterization techniques were employed to characterize the sample which includes UV-vis spectroscopy, X-ray diffraction, FTIR spectroscopy, electron diffraction spectroscopy (EDX), scanning electron microscopy (SEM). Furthermore, the resultant nanocomposite demonstrated an efficient ability for the inhibition of both gram-positive and gram negative pathogenic multidrug resistant bacteria. Additionally, the Ag/NiO nanocomposite showed a durable antioxidant effect against DPPH that could still reach 63% at very low concentration, i.e. 0.5 mg/mL. Interestingly, the synthesized nanocomposite is efficient for the production of reactive oxygen species (ROS) and shows no hemolytic activity. Likewise, the Ag/NiO nanocomposite displayed excellent photocatalytic activity to degrade 85% methylene blue (MB) by 4 mg/25 mL and could be used for waste water treatment. It is believed that synthesized nanostructure with desirable morphology and preparation simplicity can be promising material for the antimicrobial, antioxidant and catalytic applications.

Natural spirocyclic alkaloids and polyphenols as multi target dementia leads

The U rhynchophylla, U tomentosa, Isatis indigotica Fortune, Voacanga Africana, herbal constituents, fungal extracts from Aspergillus duricaulis culture media, include spirooxindoles, polyphenols or bridged spirocyclic alkaloids. Their constituents exhibit specific and synergistic multiple neuroprotective properties including inhibiting of Aβ fibril induced cytotoxicity, NMDA receptor inhibition in mice models of Alzheimer's disease (AD). The pioneering research from Woodward to Waldmann has advanced the synthesis of spirocyclic alkaloids. Furthermore, the elucidation of the genetic analysis, biochemical pathways that links strictosidine to the alkaloids akuammicine, stemmadenine, tabersonine, catharanthine, will now enable the biotechnological generation, also stimulate synthesis of related bridged spirocyclic alkaloids for medicinal investigations. From the value of spirocyclic structures as multi target dementia leads, we hypothesise that simpler Lipinski-like natural/synthetic alkaloid analogues may likewise be discovered that provide neurocognitive enhancing activities against dementia and AD.

Uncaria rhynchophylla and its Major Constituents on Central Nervous System: A Review on Their Pharmacological Actions

BACKGROUND

Uncaria rhynchophylla (Miq.) Jacks (Rubinaceae), a common herbal medicine known as Gou-teng in Chinese, is commonly used in Chinese medicine practice for the treatment of convulsions, hypertension, epilepsy, eclampsia and other cerebral diseases. The major active components of U. rhynchophylla are alkaloids, terpenoids and flavonoids. The protective effects of U. rhynchophylla and its major components on central nervous system (CNS) have become a focus of research in recent decades.

OBJECTIVE

The study aimed to systematically summarize the pharmacological activities of U. rhynchophylla and its major components on the CNS.

METHODS

This review summarized the experimental findings from our laboratories, together with other literature data obtained through a comprehensive search of databases including the Pubmed and the Web of Science.

RESULTS

U. rhynchophylla and its major components such as rhynchophylline and isorhynchophylline have been shown to have neuroprotective effects on Alzheimer's disease, Parkinson's disease, depression, cerebral ischaemia through a number of mechanisms including anti-oxidant, anti-inflammatory actions and regulation on neurotransmitters.

CONCLUSION

U. rhynchophylla and its major components have multiple beneficial pharmacological effects on CNS. Further studies on U. rhynchophylla and its major components are warranted to fully illustrate the underlying molecular mechanisms, pharmacokinetics, and toxicological profiles of these naturally occurring compounds and their potential for clinical application.

Recent research progress of Uncaria spp. based on alkaloids: phytochemistry, pharmacology and structural chemistry

Medicinal plants are well-known in affording clinically useful agents, with rich medicinal values by combining with disease targets through various mechanisms. Plant secondary metabolites as lead compounds lay the foundation for the discovery and development of new drugs in disease treatment. Genus Uncaria from Rubiaceae family is a significant plant source of active alkaloids, with anti-hypertensive, sedative, anti-Alzheimer's disease, anti-drug addiction and anti-inflammatory effects. This review summarizes and discuss the research progress of Uncaria based on alkaloids in the past 15 years, mainly in the past 5 years, including biosynthesis, phytochemistry, pharmacology and structural chemistry. Among, focusing on representative compounds rhynchophylline and isorhynchophylline, the pharmacological activities surrounding the central nervous system and cardiovascular system are described in detail. On the basis of case studies, this article provides a brief overview of the synthesis and analogues of representative compounds types. In summary, this review provides an early basis for further searching for new targets and activities, discussing the mechanisms of pharmacological activity and studying the structure-activity relationships of active molecules.

High-performance liquid chromatographic profile and 1H quantitative nuclear magnetic resonance analyses for quality control of a Xinjiang licorice extract

Various pharmacological properties of Xinjiang licorice flavonoids have been reported recently. We have investigated constituents corresponding to distinct peaks on the high-performance liquid chromatography (HPLC) profile of a flavonoid-rich extract from licorice, and identified 13 flavonoids, including licochalcone A (1), licochalcone B (3), glabrone (4), and echinatin (5), by isolating them and then performing high-resolution electrospray ionization mass spectrometry and 1H nuclear magnetic resonance (NMR) spectral analyses. We then applied the 1H quantitative NMR (qNMR) method for analysis of major flavonoids, 1 and 3–5 in the extract. The 1H qNMR results were supported by 13C NMR analysis. The results demonstrated the utility of the combination of HPLC profiling and qNMR analyses for quality control of Xinjiang licorice. Additionally, we observed a moderate inhibitory effect of the most abundant constituent, licochalcone A (1), on acetylcholine esterase activity, suggesting utility as a seed for drug development.

Antiepileptic geissoschizine methyl ether is an inhibitor of multiple neuronal channels

Geissoschizine methyl ether (GM) is an indole alkaloid isolated from Uncaria rhynchophyll (UR) that has been used for the treatment of epilepsy in traditional Chinese medicine. An early study in a glutamate-induced mouse seizure model demonstrated that GM was one of the active ingredients of UR. In this study, electrophysiological technique was used to explore the mechanism underlying the antiepileptic activity of GM. We first showed that GM (1−30 μmol/L) dose-dependently suppressed the spontaneous firing and prolonged the action potential duration in cultured mouse and rat hippocampal neurons. Given the pivotal roles of ion channels in regulating neuronal excitability, we then examined the effects of GM on both voltage-gated and ligand-gated channels in rat hippocampal neurons. We found that GM is an inhibitor of multiple neuronal channels: GM potently inhibited the voltage-gated sodium (Na_V), calcium (Ca_V), and delayed rectifier potassium (I_K) currents, and the ligand-gated nicotinic acetylcholine (nACh) currents with IC₅₀ values in the range of 1.3−13.3 μmol/L. In contrast, GM had little effect on the voltage-gated transient outward potassium currents (I_A) and four types of ligand-gated channels (γ-amino butyric acid (GABA), N-methyl-D-aspartate (NMDA), α-amino-3-hydroxy-5-methylisoxazole-4-propionate/kainite (AMPA/KA receptors)). The in vivo antiepileptic activity of GM was validated in two electricity-induced seizure models. In the maximal electroshock (MES)-induced mouse seizure model, oral administration of GM (50−100 mg/kg) dose-dependently suppressed generalized tonic-clonic seizures. In 6-Hz-induced mouse seizure model, oral administration of GM (100 mg/kg) reduced treatment-resistant seizures. Thus, we conclude that GM is a promising antiepileptic candidate that inhibits multiple neuronal channels.

Glucoconjugated Monoterpene Indole Alkaloids from Uncaria rhynchophylla

Twenty-six glucoconjugated monoterpene indole alkaloids, including 12 new compounds, rhynchophyllosides A-L (1-12), and 14 known ones, 13-26, were obtained from the hook-bearing stems of Uncaria rhynchophylla (Miq.) Miq. ex Havil. Their structures were unambiguously elucidated by analyses of UV, MS, NMR, ECD, and single-crystal X-ray diffraction data. The ESI-MSⁿ behavior of the new glucoalkaloids was also elucidated. Although comprising the same glucosyl moiety, the aglycone skeletons and glucosidic numbers and linkage varied greatly, implying the diversity in biosynthetic pathways. This is the first report of such structurally diverse glucoconjugated monoterpene indole alkaloids from U. rhynchophylla. Compound 1 represents a new subtype of oxindole alkaloid with a seven-membered D-ring, 10 is a rare monoterpene indole alkaloid with the glucosyl moiety located at C-9, 4 and 5 are the first two oxindole alkaloid diglycosides, and 11 and 12 represent the first two examples of alkaloids with a quinolone nucleus from the genus Uncaria. Compound 10 exhibited moderate acetylcholinesterase (AChE) inhibitory activity with an IC₅₀ value of 10.5 μM. Molecular docking was performed to explore the binding mode of inhibitor 10 at the active site of AChE.

Traditional Oriental Medicines and Alzheimer's Disease

Alzheimer’s disease (AD), which is the most major cause of dementia, is a progressive neurodegenerative disease that affects cognitive functions. Even though the prevalence of AD is continuously increasing, few drugs including cholinesterase inhibitors and N-methyl D-aspartate-receptor antagonists were approved to treat AD. Because the clinical trials of AD drugs with single targets, such as β-amyloid and tau, have failed, the development of multi-target drugs that ameliorate many of the symptoms of AD is needed. Thus, recent studies have investigated the effects and underlying mechanisms of herbal formulae consisting of various herb combinations used to treat AD. This review discusses the results of clinical and nonclinical studies of the therapeutic efficacy in AD and underlying mechanisms of the herbal formulae of traditional Oriental medicines and bioactive compounds of medicinal plants.

Retro-biosynthetic construction of corynanthe alkaloid skeletons from rhynchophylline alkaloids

Corynanthe alkaloids could be generated from rhynchophylline alkaloids in a retro-biosynthetic manner via a Wagner–Meerwein rearrangement.

Biological activities of extracts from Aspidosperma subincanum Mart. and in silico prediction for inhibition of acetylcholinesterase

Species of Aspidosperma are traditionally used to treat malaria, leishmaniasis, microbial, and inflammatory diseases. Aspidosperma subincanum Mart. known as "guatambu" is used in Brazilian traditional medicine to treat diabetes, hypercholesterolemia, and digestive diseases. Its tonic properties have been employed by the indigenous populations to stimulate the circulatory and genitourinary tracts and to improve respiratory function as well as to relieve spasms and to reduce fever. The species is known to contain antitumoural and antimalarial indole alkaloids. In the present study, various less explored biological activities of extracts from leaves and branches of A. subincanum were investigated, that is, inhibition of acetylcholinesterase as well as antioxidant and antibacterial activity. Twenty-one known indole alkaloids from this species were targeted for predicting the inhibition of acetylcholinesterase, and their biological activities were collected from the literature. Through in silico the prediction, the indole alkaloids uleine and derivatives demonstrated a strong probability of being able to inhibit the acetylcholinesterase enzyme, as well as the olivacine derivatives 3,4-dihydroolivacine and N-methyl-tetrahydro-olivacine (guatambuine), and the subincanadines C and E. Indeed, the extracts of A. subincanum showed acetylcholinesterase inhibitory activity, antioxidant activity in the lipid peroxidation assay, and antimicrobial activity against Staphylococcus aureus ATCC 25923, and their pharmacological properties should be explored further.

Sarpagan bridge enzyme has substrate-controlled cyclization and aromatization modes

Cyclization reactions that create complex polycyclic scaffolds are hallmarks of alkaloid biosynthetic pathways. We present the discovery of three homologous cytochromes P450 from three monoterpene indole alkaloid-producing plants (Rauwolfia serpentina, Gelsemium sempervirens and Catharanthus roseus) that provide entry into two distinct alkaloid classes, the sarpagans and the β-carbolines. Our results highlight how a common enzymatic mechanism, guided by related but structurally distinct substrates, leads to either cyclization or aromatization.

Metabolic Profile of Isocorynoxeine in Rats Obtained by Ultra-High Performance Liquid Chromatography/Quadrupole Time-of-Flight Mass Spectrometry

BACKGROUND AND OBJECTIVE

Isocorynoxeine (IC), a major alkaloid found in Uncaria rhynchophylla, exhibits wide beneficial effects on the cardiovascular and cardiocerebral vascular systems. Its metabolic pathway, however, has not been well studied yet. In this study, an ultra-high-performance liquid chromatography/quadrupole time-of-flight mass spectrometry (U-HPLC/Q-TOFMS) method was developed to investigate IC metabolism in plasma, urine and bile in rats given IC orally at 40 mg/kg.

METHODS

Nine male Wistar rats were given IC 40 mg/kg orally. Blood, urine and bile samples were collected at pre-specified times to measure the concentration of IC.

RESULTS

A total of 35 metabolites were tentatively identified by the co-chromatography of biosamples and comparison of the retention time, characteristic molecular ions and fragment ions with those of the authentic standards or tentatively identified by MS/MS determination along with MassFragment software. Among them, 18, 33 and 18 metabolites were found in plasma, urine and bile samples, respectively. The relative percentage area of each metabolite was also determined to better understand the major metabolic pathways of IC in rats.

CONCLUSIONS

The result indicates that IC undergoes extensive metabolism in vivo, mainly including hydrolysis, oxidation, isomerization, demethylation, epoxidation, reduction, glucuronidation, hydroxylation and N-oxidation, which is helpful for the further pharmacokinetic study of IC in vivo.

Natural AChE Inhibitors from Plants and their Contribution to Alzheimer's Disease Therapy

As acetylcholinesterase (AChE) inhibitors are an important therapeutic strategy in Alzheimer's disease, efforts are being made in search of new molecules with anti-AChE activity. The fact that naturally-occurring compounds from plants are considered to be a potential source of new inhibitors has led to the discovery of an important number of secondary metabolites and plant extracts with the ability of inhibiting the enzyme AChE, which, according to the cholinergic hypothesis, increases the levels of the neurotransmitter acetylcholine in the brain, thus improving cholinergic functions in patients with Alzheimer's disease and alleviating the symptoms of this neurological disorder. This review summarizes a total of 128 studies which correspond to the most relevant research work published during 2006-2012 (1st semester) on plant-derived compounds, plant extracts and essential oils found to elicit AChE inhibition.