Banisteriopsis caapi, a unique combination of MAO inhibitory and antioxidative constituents for the activities relevant to neurodegenerative disorders and Parkinson’s disease

Banisteriopsis caapi is a South American vine traditionally used in ayahuasca preparations and has been shown in earlier chemical studies to contain β-carboline alkaloids such as harmine, harmaline and tetrahydroharmine (THH), which act as monoamine oxidase (MAO) inhibitors. Parkinson's disease (PD) involves loss of dopaminergic neurons and oxidative stress has been implicated in its pathogenesis; hence MAO inhibition and antioxidant activity are mechanisms of interest for neuroprotection and symptom management. Earlier clinical and preclinical observations have suggested B. caapi extracts, and harmine in particular, may improve motor function in PD and influence dopamine release, but detailed chemical characterisation linked to bioactivity across plant parts and cultivars remained incomplete. Samoylenko and colleagues set out to chemically profile an aqueous extract of a B. caapi cultivar called Da Vine, to isolate and elucidate bioactive constituents, and to evaluate those isolates and extracts for MAO-A and MAO-B inhibition, antioxidant activity (inhibition of cellular reactive oxygen species, ROS), and cytotoxicity. The study used bioassay-guided fractionation to link chemical markers to MAO inhibitory and antioxidant effects and compared the Da Vine cultivar to several regular/commercial B. caapi samples to assess variation in marker content and bioactivity.

Plant material comprised fresh leaves, stems and large branches of B. caapi cultivar Da Vine collected in Hawaii in 2007–2008; a voucher specimen was deposited at the Harold Lyon Arboretum. Regular/commercial B. caapi stem samples (labelled BCEx-1 to BCEx-4) were also analysed. Different plant parts were extracted with hot water by two methods: a ‘‘hot maceration’’ coffee-maker technique and an Accelerated Solvent Extractor (ASE) protocol; extracts were freeze-dried and stored for analysis. For chemical work, the freeze-dried aqueous extract of large-branch material was standardised and subjected to reversed-phase column chromatography (RP-CC) and centrifugal preparative thin-layer chromatography (CPTLC) to afford fractions and purified compounds. Structural elucidation used 1D and 2D NMR (1H, 13C, COSY, HMQC, HMBC, NOESY), high-resolution electrospray mass spectrometry (HRMS), infrared (IR) and circular dichroism (CD) spectroscopy, and chemical derivatisation (acetylation) where needed. Reverse-phase HPLC with a C18 column and photodiode array detection provided chemical profiling and quantification of marker compounds in extracts. Biological assays included recombinant human MAO-A and MAO-B inhibition measured by a kynuramine deamination fluorometric assay in 96-well plates. IC50 values for MAO-A were determined across five concentrations (1 to 0.0001 µg/mL) using 80 µM kynuramine as substrate (approximately 2×Km); MAO-B activity was probed at 1, 10 and 100 µg/mL with a modified emission wavelength to reduce fluorescence interference. Cellular antioxidant activity was measured as inhibition of PMA-induced ROS generation in HL-60 cells using the DCFH-DA probe; IC50 values were derived from dose–response curves. Cytotoxicity was assessed against several human cancer cell lines and mammalian cell lines using Neutral Red and XTT assays. Additional enzyme assays for acetylcholinesterase (AChE), butyrylcholinesterase (BuChE) and catechol-O-methyl transferase (COMT) were performed at 100 µg/mL according to published methods. Where the extracted text did not report sample sizes or numbers of biological replicates explicitly, those details are not stated here.

Bioassay-guided fractionation of the aqueous extract of B. caapi Da Vine yielded two previously undescribed alkaloidal glycosides, named banistenoside A (1) and banistenoside B (2), both featuring an azepino[1,2-a]tetrahydro-β-carboline framework, plus a new tetrahydronorharmine (4), known β-carbolines harmol (3), tetrahydroharmine (5), harmaline (6) and harmine (7), two proanthocyanidins (-)-epicatechin (8) and (-)-procyanidin B2 (9), and a new disaccharide β-D-fructofuranosyl-(2→5)-fructopyranose (14). Structural assignments were supported by comprehensive NMR, HRMS, CD and derivatisation data; stereochemical configurations of the glycosides were inferred from CD and NOESY correlations. In enzyme assays, hot aqueous extracts of fresh and dried large branches showed strong MAO-A inhibition with IC50 values in the range ∼0.01–0.4 µg/mL for crude extracts, and weak MAO-B inhibition (for many extracts only about 25% inhibition at 5 µg/mL was observed, with MAO-B percent inhibitions later measured at 1, 10 and 100 µg/mL to mitigate fluorescence interference). Specifically, extracts of bark/debarked large branch demonstrated potent MAO-A inhibition (IC50 0.02–0.05 µg/mL) and modest MAO-B inhibitory activity (approximate IC50 ≈100 µg/mL), indicating roughly 2,500-fold greater potency at MAO-A than MAO-B in these extracts. Pure compounds harmine (7) and harmaline (6) were highly selective MAO-A inhibitors (IC50 2.0 nM and 2.5 nM, respectively) and showed much weaker MAO-B inhibition (IC50 about 20 µM and 25 µM, respectively). Compounds 3 and 5 had weaker MAO-A activity than 6 or 7, and compounds 1, 2 and 4 were inactive in the MAO assays reported. Antioxidant activity measuring inhibition of cellular ROS generation showed that large-branch extracts had IC50 values in the range 0.4–3.0 µg/mL. The flavan-3-ol markers were potent antioxidants: (-)-epicatechin (8) and (-)-procyanidin B2 (9) had IC50 values <0.13 µg/mL and 0.57 µg/mL, respectively, which the authors state were more potent than vitamin C (IC50 1.34 µg/mL); 8 was also more effective than trolox (IC50 0.14 µg/mL). Both 8 and 9 exhibited MAO-B inhibitory activity (IC50 65 µM and 35 µM, respectively) and weak MAO-A inhibition (IC50 51.7 µM for 8 and 8.5 µM for 9). HPLC quantification of markers in dried bark of the large branch of the Da Vine cultivar showed substantial marker levels: compound 1 at 0.71%, 2 at 1.93%, 5 at 0.10%, 7 at 0.67%, 8 at 0.43% and 9 at 0.16% (w/w in extract). Regular/commercial dried stem samples BCEx-1 and BCEx-4 displayed a similar profile qualitatively but with lower contents of key markers (for example, 1 at 0.15% and 0.17%, 2 at 0.07% and 0.15%, 7 at 0.04% and 0.13%, and 9 at 0.03% and 0.38%, respectively), correlating with reduced MAO and antioxidant potency in those samples; two other commercial samples (BCEx-2 and BCEx-3) lacked detectable markers 1–9 and were inactive in the assays reported. Extracts and isolated compounds were inactive in assays for AChE, BuChE and COMT at 100 µg/mL, and showed no cytotoxic activity against the tested human cancer and mammalian cell lines at the concentrations evaluated.

Samoylenko and colleagues interpret their findings as the identification of a distinctive chemical profile in the Da Vine cultivar of B. caapi, wherein potent MAO-A inhibitory β-carbolines and strong antioxidant proanthocyanidins coexist. The discovery of two novel azepino-tetrahydro-β-carboline glycosides (banistenosides A and B) and a new tetrahydronorharmine broadens the known chemistry of the species. Structural elucidation, including stereochemical assignments, was achieved through combined NMR, MS, CD and derivatisation studies. The authors emphasise the pharmacological relevance: highly selective MAO-A inhibitors harmine and harmaline may contribute to antidepressant activity and could have neuroprotective implications, while the antioxidant activity of (-)-epicatechin and procyanidin B2 could mitigate oxidative stress implicated in neurodegenerative disorders such as Parkinson's and Alzheimer's disease. They note that the selective MAO-B inhibition observed for 8 and 9 further supports potential neuroprotective benefits. Samoylenko and colleagues also highlight that a related synthetic azepinotetrahydro-β-carboline has shown α2-adrenoceptor activity, suggesting the newly identified glycosides merit additional biological investigation. Several sources of variability and limitations are acknowledged in the text: taxonomic uncertainty across Banisteriopsis collections and cultivar differences led to marked variation in marker content and bioactivity among commercial samples; the study did not detect certain methoxy-THH derivatives of potential psychoactive concern in the Da Vine cultivar or the commercial samples analysed. Finally, the authors propose that the combined MAO inhibitory and antioxidant activities found in this cultivar provide additional pharmacological rationale for the traditional and experimental use of B. caapi extracts in contexts related to Parkinsonism and other neurodegenerative conditions, while recommending further biological work on the new constituents.

This study reports, for the first time, the isolation and structural characterisation of two novel azepino[1,2-a]tetrahydro-β-carboline glycosides (banistenosides A and B), a new tetrahydronorharmine, and a new fructose disaccharide from B. caapi cultivar Da Vine, together with known β-carbolines and proanthocyanidins. The chemical profile of this cultivar combines potent MAO-A inhibitory β-carbolines with strong antioxidant proanthocyanidins, which the authors argue supports potential therapeutic relevance for Parkinson's disease and other neurodegenerative disorders. Given the structural novelty and the bioactivity profile, the authors recommend further biological characterisation of the new compounds.