Composition, Standardization and Chemical Profiling of Banisteriopsis caapi, a Plant for the Treatment of Neurodegenerative Disorders Relevant to Parkinson’s Disease

Banisteriopsis caapi, a woody vine from the Amazon used traditionally as an ingredient of the psychoactive brew ayahuasca, contains β-carboline alkaloids that act as monoamine oxidase (MAO) inhibitors and has been reported to alleviate symptoms in neurological disorders including Parkinson’s disease. Earlier phytochemical studies identified harmine, harmaline and tetrahydroharmine (THH) among other β-carbolines, as well as various terpenoids. Recent work by the study team on a cultivated Hawaiian plant material named Da Vine additionally isolated two tetrahydro-β-carboline glycosides (banistenoside A and B), a new tetrahydronorharmine analogue, and antioxidant flavan-3-ols (epicatechin and procyanidin B2). Wang and colleagues set out to develop standardised aqueous extracts of B. caapi with high potency for inhibition of human MAOs and antioxidant activity, and to perform chemical profiling across plant parts, seasons and sources. The study aimed to quantify marker compounds (including β-carbolines and proanthocyanidins), formulate standardised pharmaceutical compositions from isolated markers, and test those preparations in vitro for MAO inhibition and antioxidant effects to explore correlations between phytochemistry and bioactivity.

The researchers analysed material from B. caapi cultivar Da Vine grown in Hawaii and from commercially sourced matured stems. Fresh leaves, stems and large branches were collected from Oahu and Hilo between 2007 and 2008; a voucher specimen was deposited at the Harold Lyon Arboretum. Plant extracts were prepared using either water maceration (coffee-maker style) or an accelerated solvent extractor (ASE) with water as solvent; extracts were freeze-dried for analysis. Phytochemical profiling used reversed-phase HPLC with photodiode array detection on a Gemini C18 column. Separate chromatographic methods were employed for alkaloids and catechins, with detection wavelengths chosen to optimise sensitivity for particular β-carbolines and proanthocyanidins. Calibration curves were prepared for markers 1–9 across defined concentration ranges; isolated markers and reference standards (harmol, harmine, harmaline, epicatechin) were used for peak assignment and quantification. Peak purity was evaluated from PDA data and samples were injected in triplicate to assess precision. Standardised pharmaceutical compositions were prepared by combining stock DMSO solutions of key active constituents: tetrahydroharmine (THH, 5), harmaline (6), harmine (7), epicatechin (8) and procyanidin B2 (9) in three different ratios (compositions 1–3) intended to simulate the range observed in natural extracts. B. caapi extract DMSO solutions (10 mg/mL) were used as references. Bioactivity assays comprised in vitro inhibition kinetics against recombinant human MAO-A and MAO-B and a cell-based assay of antioxidant activity. MAO-A IC50 values were determined from five concentrations ranging from 0.0001 to 1 μg/mL; MAO-B inhibitory effects of crude extracts were screened at 100, 10 and 1 μg/mL. Intracellular reactive oxygen species (ROS) generation was measured in HL-60 cells using the DCFH-DA method across multiple concentrations. Most experiments were performed in duplicate (bioassays) or triplicate (HPLC injections) as reported.

HPLC profiling consistently assigned nine marker compounds (banistenoside A and B [1,2], THNH [3], harmol [4], THH [5], harmaline [6], harmine [7], epicatechin [8] and procyanidin B2 [9]) across fresh and dried samples of leaves, stems, bark and large branches. Alkaloid chromatograms showed approximately 10 dominant signals and catechin analysis revealed two main peaks; three additional, not fully characterised peaks with UV spectra consistent with THH analogs were also observed. Peak purity checks showed no gross impurities for the majority of markers. Marker contents were higher in dried material than fresh. Using ASE, leaves and young stems yielded higher marker contents, whereas maceration was more efficient for mature plant material. The dried bark of matured stem/large branch contained the highest concentrations of dominant β-carboline markers and proanthocyanidins: for example, ranges reported included banistenoside A (1) 0.31–0.71%, banistenoside B (2) 0.81–1.93%, harmine (7) 0.28–0.67%, THH (5) 0.04–0.1%, epicatechin (8) 0.43–0.67% and procyanidin B2 (9) 0.16–0.49% in some samples. Whole dried matured stems and debarked stems showed lower but still notable amounts. Harmaline (6) was consistently present only in small amounts (≈0.02–0.05%), and THNH (4) and harmol (3) were minor markers. Commercial stem extracts (BCEx-1 to BCEx-4) displayed assignable peaks for 1–9 but generally contained lower amounts of major markers compared with Da Vine dried materials; epicatechin was an exception in one commercial sample (BCEx-4) which showed higher epicatechin content. In vitro MAO-A inhibition assays showed that pharmaceutical compositions 2 and 3 were the most potent, with IC50 values of 0.027 μg/mL and 0.024 μg/mL respectively. These potencies were comparable to two Da Vine standardised extracts (IC50 0.029 μg/mL and 0.032 μg/mL). Composition 1, containing lower amounts of harmaline and harmine, had weaker MAO-A inhibition (IC50 ≈0.047 μg/mL) similar to a commercial dried stem extract (BCEx-4, IC50 ≈0.059 μg/mL) that had comparable 6 and 7 contents. Antioxidant activity measured in the HL-60 cell assay tracked with amounts of epicatechin and procyanidin B2: compositions 2 and 3 had antioxidant potency similar to a commercial extract containing comparable 8 and 9 levels, whereas whole dried matured stem material and composition 1 exhibited weaker antioxidant effects. Notably, the large branch extract (BCdBS) displayed stronger antioxidant activity than compositions 2 and 3 and BCEx-4 despite having lower measured 8 and 9, suggesting additional antioxidant constituents in that extract.

Wang and colleagues prepared and chemically profiled multiple standardised aqueous extracts of B. caapi using maceration and ASE methods, identifying β-carboline alkaloids and proanthocyanidins as principal bioactive markers. Marker concentrations were highest in dried bark of matured stem/large branch, followed by whole dried stem and debarked stem; dried material generally contained more markers than fresh. The study found that variation in MAO-A inhibitory and antioxidant activities across extracts and prepared compositions correlated with differing phytochemical compositions, particularly levels of THH (5), harmaline (6), harmine (7), epicatechin (8) and procyanidin B2 (9). Pharmaceutical compositions assembled from these active constituents (compositions 2 and 3) produced in vitro MAO-A inhibitory and antioxidant activity comparable to that of Da Vine stem extracts. The authors propose an optimal marker composition for a standardised B. caapi phytopharmaceutical preparation (reported ranges: 1 0.81–3.93%, 2 0.50–10.72%, 5 0.29–3.48%, 6 0.12–0.59%, 7 1.26–3.71%, 8 0.6–5.4% and 9 0.9–7.2%). They note that the two glycosides 1 and 2, though major markers, appeared inactive and warrant further study of their aglycones. Finally, the authors link the observed MAO inhibition and antioxidant properties to traditional uses of B. caapi in ayahuasca preparations and suggest potential relevance for neurodegenerative conditions such as Parkinson’s disease, given the roles of MAO inhibition and oxidative stress in neurodegeneration.