In Silico Evaluation of Pharmacokinetics and Toxicity Profile of AlkaloidsPresent in Leaves of Catharanthus roseus L.

Introduction

For centuries, medicinal plants have played a significant role in traditional medicine. Such remedies remain accessible to millions worldwide, especially in regions including India, China, Africa, Pakistan, America and Korea. The effective utilization and understanding of these plants are key to unlocking their natural potential.¹

Catharanthus roseus L, commonly referred as Madagascar periwinkle, is a medicinal plant with abundant bioactive alkaloids and it belongs to Apocynaceae family.^2-4 In Northern India, C. roseus is cultivated on a large scale to fulfill the increasing commercial needs, as well as the requirements of indigenous medicine and the pharmaceutical industry.⁵ It possesses antibacterial, anticancer, antidiabetic, antifungal and antiviral activities. Phytoconstituents of this plant have demonstrated significant anticancer efficacy against multiple cell types.⁴ C. roseus contains a variety of compounds including carbohydrates, flavonoids, saponins, and alkaloids. Among these, alkaloids are the plant's most active chemical constituents. With over 400 different alkaloids identified, these compounds are utilized in pharmaceuticals, agrochemicals, flavors, fragrances, ingredients, food additives, and pesticides. Alkaloids such as Vinblastine, Vincristine, Vindesine, Vindeline, and Tabersonine are predominantly found in the aerial parts of C. roseus. In contrast, compounds like Ajmalicine, Vinceine, Vineamine, Raubasin, Reserpine, and Catharanthine are concentrated in the roots and basal stem. Additionally, Rosindin, an anthocyanin pigment, is present in the flowers of C. roseus.^6-8

According to published research, among all the plant components, the leaves of C. roseus was most frequently used in traditional medicine to treat diabetes, cancer, hypertension, Alzheimer’s, herpes simplex virus and also as an antimicrobial agent.² The leaves of this plant contain over 70 different chemical constituents,including indole-type alkaloids such as ajmalicine, serpentine, and reserpine.

Based on the author’s understanding, no prior literature exists on computer-based screening studies that analyze the leaves of C. roseus L for ADME (Absorption, Distribution, Metabolism, and Excretion) and toxicity profiles. Therefore, this study employed computational tools and servers to evaluate the drug-like properties, ADME characteristics, and toxicity profiles of selected phytochemicals from C. roseus L.

Materials and Methods

Server used: ChemDraw Professional 16.0 from CambridgeSoft was used for sketching molecular structures.⁹

Phytoconstituents: The study focused on the following phytoconstituents - Vincristine, Vinblastine, Catharanthine, Vindoline, Ajmalicine, Vindolidine, Lochnericine, Serpentine and Tabersonine.

Evaluation of Drug-Likeness and Physicochemical Properties: In the present study, we identified and selected phytoconstituents to determine their drug-likeness scores based on Lipinski's Rule of Five (Ro5). Lipinski’s rule of five was followed so as to determine the drug likeness property of each of the selected constituents. The canonical SMILES (Simplified Molecular Line Entry System) were obtained from PubChem and applied in Molsoft software, which is available online. This software was used to collect the data and to calculate the descriptions (www://molsoft.com/mprop/).¹⁰

Computational and Server Based Prediction of Pharmacokinetic and Toxicological Properties: The pharmacokinetic characteristics of phytoconstituents, such as ADME, play a critical role in the drug development process. To predict various pharmaco-kinetic parameters, we used the online server admetSAR. This tool evaluated essential ADME aspects, including plasma protein binding (PPB), skin permeability, blood-brain barrier (BBB) penetration, and interactions with P-glycoprotein, among other key pharmacokinetic features.^11,12

Results

C. roseus contains a diverse array of phytoconstituents and has demonstrated a wide range of pharmacological and biological effects. Out of the nine alkaloids listed in Table 1, seven did not violate Lipinski’s rule of five for oral availability, demonstrating that the compounds have drug-like molecular nature, except Vinblastine and Vincristine having molecular weight >500g and holding more than 10 number of hydrogen bond acceptor (>10). It is important to note that Lipinski’s rule of five is essential for rational drug design and it has been suggested that the low permeability or poor absorption for a given compound results when it violates one of Lipinski’s rule of five.

Pharmacokinetic Properties

Absorption

To evaluate the absorption property of the alkaloids present in the leaves of C. roseus, we predicted Caco-2-Permeability (Papp), P-glycoprotein (P-gp) inhibitor and substrate, Human intestinal absorption (HIA) as presented in Table 2. It was found that the values of Caco-2-Permeability were in the range of -4.674 to -5.70 cm/s. The high negative permeability (cm/s) of Vinblastine (-5.615 cm/s) and Vincristine (-5.70 cm/s) is mainly due to the presence of large number of nHBDs and nHBAs in their structures which have the potential to rendere their permeability. The predicted HIA data of the nine flavonoids are presented as + and - symbol which showed that Vinblastine (1), Vincristine (2), and Vindoline (4) have high HIA, whereas Vindolidine (6) has moderate HIA and the rest five alkaloids are predicted to have low HIA permeability. Vinblastine (1), Catharanthine (3), Vindoline (4), Vindolidine (6) and Tabersonine (9) are predicted to act as Pgp inhibitor, while all the remaining alkaloids except 5 alkaloid are predicted to act as Pgp substrate.

Distribution

To study the distribution of drug candidates, parameters such as Blood-Brain Barrier (BBB) permeability, Plasma Protein Binding (PPB), and Volume of Distribution (VD) were considered. The PPB of all alkaloids was predicted to be below 90%, indicating a significant binding to common blood proteins. Catharanthine (3), Vindoline (4), Ajmalicine (5), Vindolidine (6), Lochnericine (7), Serpentine (8) and Tabersonine (9) were predicted to permeate BBB using ADMETLab. However, our prediction using SwissADME webtool showed that Vindolidine (6) too cannot penetrate BBB. All nine alkoaloids showed optimal volume of distribution i.e., between 0.04 - 20 L/Kg.

Metabolism and Excretion

Metabolism parameter is important from the drug plasmaconcentration perspective. All nine phyto-constituents were predicted as CYP3A4 substrate and inhibitor. All nine phytoconstituents were predicted as CYP1A2 substrate. Catharanthine (3), Ajmalicine (5) and Serpentine (8) showed CYP1A2 inhibition. Whereas all phytoconstituents, except Lochnericine (7) act as CYP2C19 substrate. The clearance (CL) for all nine constituents were predicted using ADMETlab server.

A drug is classified as having a high clearance rate if its score exceeds 15 mL/min/kg, a moderate clearance rate if it falls between 5 and 15 mL/min/kg, and a low clearance rate if it is below 5 mL/min/kg. Vinblastine (1), vincristine (2), Catharanthine (3), Vindolidine (6) and Serpentine (8) showed low clearance rates, while the remaining constituents showed moderate clearance rate. The database output value for plasma t1/2 may be from category 1 (long half-life, >3 h) or category 0 (short half-life). The output value is the probability of having long half-life. Compared to all the constituents, Serpentine (8) showed high probability of having long half-life.

Toxicity Profile

The toxicity parameters verified by ADMETlab include AMES toxicity, eye corrosion, eye irritation, skin sensitization, carcinogenicity, acute dermal toxicity and rat oral acute toxicity. The results showed that all of the compounds were not prone to cause eye corrosion and eye irritation. Catharanthine (3), Ajmalicine (5) and Serpentine (8) were predicted to show AMES toxicity and carcinogenicity, while Ajmalicine (5) and Serpentine (8) showed skin sensitization. Except Vindoline (4) and Vindolidine (6), all constituents are predicted to show rat oral acute toxicity.

All the pharmacokinetic (absorption, distribution, metabolism, and excretion) and toxicity parameters are summarized in Table 2.

Discussion

The study provides valuable insights into the pharmacokinetic and toxicological profiles of C. roseus leaf alkaloids, highlighting their potential for further drug development. We selected Vincristine, Vinblastine, Catharanthine, Vindoline, Ajmalicine, Vindolidine, Lochnericine, Serpentine and Tabersonine to predict pharmacokinetic and toxicological profiles. The selected alkaloids, Vincristine, Vinblastine, Catharanthine, Vindoline, Ajmalicine, Vindolidine, Lochnericine, Serpentine, and Tabersonine were chosen for their significant pharmacological relevance, particularly in cancer and cardiovascular treatments. Vincristine and Vinblastine are well-known anticancer agents, while Ajmalicine and Serpentine have cardiovascular benefits. Catharanthine, Vindoline, and Tabersonine are key biosynthetic precursors for these therapeutic compounds.

Additionally, their varied pharmacokinetic and toxicological profiles offer valuable insights for drug development. This selection allows for a comprehensive assessment of both pharmacological potential and safety. ChemDraw software was employed to draw molecular structures and generate canonical SMILES. The Molsoft server was used to assess the drug-likeness of the selected alkaloids, while the admetSAR (Structure Activity Relationship) server was utilized to evaluate their pharmacokinetic properties and toxicity profiles.

The findings demonstrate that most alkaloids exhibit favorable drug-like properties according to Lipinski's rule of five, suggesting good oral bioavailability. However, Vinblastine and Vincristine, despite their therapeutic efficacy, may face challenges related to absorption due to their molecular size and hydrogen bonding characteristics.

The pharmacokinetic data suggest that certain alkaloids, like Vindoline and Catharanthine, may have desirable properties for central nervous system (CNS) drug development due to their ability to cross the BBB. However, the metabolic interactions involving CYP450 enzymes, particularly CYP3A4, may affect their bioavailability and safety. Thus, careful consideration must be given to potential drug-drug interactions in future therapeutic applications. From a toxicity perspective, the presence of AMES toxicity, carcinogenicity, and skin sensitization in certain alkaloids warrant caution. Compounds like Ajmalicine and Serpentine, which exhibited multiple toxicological risks, may require structural modification or further investigation to mitigate these effects.

Overall, this study underscores the utility of computational tools in the early screening of natural compounds, providing a foundation for further experimental validation. The promising pharmacokinetic profiles and the limited toxicity of certain alkaloids indicate their potential as drug candidates, especially in anticancer and CNS-targeted therapies. Further experimental studies are essential to confirm these findings and explore the therapeutic potential of these compounds in detail.

Conclusion

This study provides a computational analysis of nine alkaloids from Catharanthus roseus leaves, revealing their potential as drug candidates based on their pharmacokinetic and toxicological properties. While most alkaloids showed favorable drug-like characteristics and ADME profiles, a few demonstrated potential toxicity concerns, such as mutagenicity and skin sensitization. Vindoline and Vindolidine emerged as particularly promising due to their minimal toxicity risks. These findings underscore the value of computational tools in early drug discovery, guiding experimental validation and development of these natural compounds for therapeutic use, particularly in cancer treatment.

 Conflict of Interest

The authors have declared that no conflict of interest is linked with this work.