Absence of alkaloids in Psychotria carthagenensis Jacq. (Rubiaceae)

Toxicological profile and acetylcholinesterase inhibitory potential of Palicourea deflexa, a source of β-carboline alkaloids

Palicourea genus is chemically and taxonomically close to Psychotria genus, a well-known source of neuroactive alkaloids. It has been previously reported the pharmacological potential of these alkaloids in some targets related to the neurodegenerative process. In this context, this study was carried out in order to evaluate the toxic effects and acetylcholinesterase (AChE) inhibitory potential of Palicourea deflexa fraction of total alkaloids (FTA). P. deflexa FTA was analyzed by means of HPLC-DAD and HRMS-ESI. We performed toxicological screening through Fish Embryo Toxicity (FET) test using zebrafish embryo and abnormal developmental phenotypes were recorded daily. For AChE inhibition, zebrafish brains were used as enzymatic source and formation of thiolate dianion of 5,5'-Dithiobis(2-nitrobenzoic acid) (DTNB) was used to monitor acetylthiocholine hydrolysis. Lineaweaver-Burk double reciprocal plots were used to indicate mode of inhibition. Chemical analysis of the P. deflexa FTA allowed the identification of the main compound as harman-3-carboxylic acid. This fraction was evaluated in vivo for its toxicological effect. The zebrafish embryo test indicated that the FTA has a lethal concentration of 50% (LC₅₀)=72.18μg/mL. Further, the FTA was evaluated for its AChE inhibitory profile, demonstrating an inhibitory concentration of 50% (IC₅₀) of 50.65μg/mL. Lineaweaver-Burk double reciprocal plots indicated a mixed mode of inhibition. It is reported for the first time the toxicological and pharmacological profile of the alkaloid fraction of Palicourea deflexa in zebrafish models.

Isolation and Characterization of Cyclotides from Brazilian Psychotria: Significance in Plant Defense and Co-occurrence with Antioxidant Alkaloids

Plants from the genus Psychotria include species bearing cyclotides and/or alkaloids. The elucidation of factors affecting the metabolism of these molecules as well as their activities may help to understand their ecological function. In the present study, high concentrations of antioxidant indole alkaloids were found to co-occur with cyclotides in Psychotria leiocarpa and P. brachyceras. The concentrations of the major cyclotides and alkaloids in P. leiocarpa and P. brachyceras were monitored following herbivore- and pathogen-associated challenges, revealing a constitutive, phytoanticipin-like accumulation pattern. Psyleio A, the most abundant cyclotide found in the leaves of P. leiocarpa, and also found in P. brachyceras leaves, exhibited insecticidal activity against Helicoverpa armigera larvae. Addition of ethanol in the vehicle for peptide solubilization in larval feeding trials proved deleterious to insecticidal activity and resulted in increased rates of larval survival in treatments containing indole alkaloids. This suggests that plant alkaloids ingested by larvae might contribute to herbivore oxidative stress detoxification, corroborating, in a heterologous system with artificial oxidative stress stimulation, the antioxidant efficiency of Psychotria alkaloids previously observed in planta. Overall, the present study reports data for eight novel cyclotides, the identification of P. leiocarpa as a cyclotide-bearing species, and the absence of these peptides in P. umbellata.

Shoot Accumulation Kinetics and Effects on Herbivores of the Wound-Induced Antioxidant Indole Alkaloid Brachycerine of Psychotria brachyceras

A major shoot-specific monoterpene indole alkaloid produced by Psychotria brachyceras, brachycerine, is regulated by either wounding or jasmonate application. Highest concentrations of the alkaloid are found in inflorescences, suggesting a defence role. Brachycerine has antimutagenic and antioxidant properties, capable of quenching singlet oxygen, hydroxyl radical, and superoxide. This study aimed at characterizing the putative role of brachycerine in P. brachyceras responses to wounding and herbivory. Damage to leaves increased the content of brachycerine locally. Wounding did not affect phenolics content in P. brachyceras leaves, and no tannins were detected in the species. In generalist herbivore bioassays, neither brachycerine nor P. brachyceras extracts showed toxic effects. In vivo hydrogen peroxide staining assay showed less wound-generated peroxide accumulation in alkaloid treated tissues. This pattern was confirmed in quantitative assays measuring tissue hydrogen peroxide concentrations. Data indicate that brachycerine is not a herbivore deterrent, but rather an indirect chemical defence, modulating oxidative stress caused by mechanical damage.

Composition, standardization and chemical profiling of Banisteriopsis caapi, a plant for the treatment of neurodegenerative disorders relevant to Parkinson's disease

ETHNOPHARMACOLOGICAL RELEVANCE

Banisteriopsis caapi, a woody vine from the Amazonian basin, is popularly known as an ingredient of a sacred drink ayahuasca, widely used throughout the Amazon as a medicinal tea for healing and spiritual exploration. The usefulness of Banisteriopsis caapi has been established for alleviating symptoms of neurological disorders including Parkinson's disease.

AIM OF THE STUDY

Primary objective of this study was to develop the process for preparing standardized extracts of Banisteriopsis caapi to achieve high potency for inhibition of human monoamine oxidases (MAO) and antioxidant properties. The aqueous extracts prepared from different parts of the plant collected from different geographical locations and seasons were analyzed by HPLC for principal bioactive markers. The extracts were simultaneously tested in vitro for inhibition of human MAOs and antioxidant activity for analysis of correlation between phytochemical composition of the extracts and bioactivities.

MATERIALS AND METHODS

Reversed-phase HPLC with photodiode array detection was employed to profile the alkaloidal and non-alkaloidal components of the aqueous extract of Banisteriopsis caapi. The Banisteriopsis caapi extracts and standardized compositions were tested in vitro for inhibition of recombinant preparations of human MAO-A and MAO-B. In vitro cell-based assays were employed for evaluation of antioxidant property and mammalian cell cytotoxicity of these preparations.

RESULTS

Among the different aerial parts, leaves, stems/large branches and stem bark of Banisteriopsis caapi, HPLC analysis revealed that most of the dominant chemical and bioactive markers (1, 2, 5, 7-9) were present in high concentrations in dried bark of large branch. A library of HPLC chromatograms has also been generated as a tool for fingerprinting and authentication of the studied Banisteriopsis caapi species. The correlation between potency of MAO inhibition and antioxidant activity with the content of the main active constituents of the aqueous Banisteriopsis caapi extracts and standardized compositions was established. Phytochemical analysis of regular/commercial Banisteriopsis caapi dried stems, obtained from different sources, showed a similar qualitative HPLC profile, but relatively low content of dominant markers 1, 2, 7, and 9, which led to decreased MAO inhibitory and antioxidant potency compared to Banisteriopsis caapi Da Vine.

CONCLUSION

The ethnopharmacological use of bark of matured stem/large branch of Banisteriopsis caapi as well as whole matured stem is supported by the results obtained in this investigation. Among various constituents of Banisteriopsis caapi, harmine (7), harmaline (6) and tetrahydroharmine (5) are responsible for MAO-A inhibition, while two major proanthocyanidines, epicatechin (8) and procyanidine B2 (9) produce antioxidant effects. The compounds 1-9 can serve as reliable markers for identification and standardization of Banisteriopsis caapi aerial parts, collected in different seasons and/or from different geographical regions.

Bioactive Alkaloids from South American Psychotria and Related Species

Many important molecules have been discovered from tropical and sub-tropical plant biodiversity. However, the largest part of the chemical profile of such biodiversity remains unknown. Combining ethnopharmacological and chemotaxonomical investigation can be a good strategy in bioactive compound discovery. South American Psychotria species studied by this approach proved to be a rich source of new bioactive alkaloids, some of which bear unique chemical skeletons.

Growth characteristics and chemical analysis of Psychotria carthagenensis cell suspension cultures

Callus and cell suspension cultures of Psychotria carthagenensis have been established in Gamborg's B5 medium supplemented, respectively, with 3% sucrose, 0.2 mg/l kinetin, and 1.0 mg/l 2,4-D and 2% sucrose, 2.0 mg/l 2,4-D, 0.2 mg/l kinetin, and 50 mg/l cysteine. Suspension culture presented a typical growth curve with the complete cycle of ca. 18 days and the maximum specific growth rate (µ) was 0.0099 day. The presence of different secondary metabolite pathways was determined by measuring the enzyme activity of phenylalanine ammonia lyase (PAL), tryptophan decarboxylase (TDC), strictosidine synthase (STR), strictosidine-beta-glucosidase (SG), and geraniol-10-hydroxylase (G10H). Activity could only be measured for SG (14.55 pkatal/mg protein) and G10H (0.3 pkatal/mg protein). Analysis of extracts from leaves, callus and cell suspension cultures demonstrated the presence of two major triterpenes: beta-sitosterol and ursolic acid.(2)