Phytochemical, biological, and molecular docking studies on Fraxinus excelsior, Stachys arabica, Pelargonium sidoides, and Pelargonium reniforme

Rights statement
Awarding institution
  • University of Strathclyde
Date of award
  • 2021
Thesis identifier
  • T16097
Person Identifier (Local)
  • 201772112
Qualification Level
Qualification Name
Department, School or Faculty
  • Plants have a long history of use in traditional medicine and several plant species are natural cures for tuberculosis (TB) or TB-related symptoms. Such natural sources can be a worthy starting point in the search for new drugs since they are rich in diverse phytochemicals which may possess antimicrobial and/or immunomodulatory activity. TB is still a growing public health concern worldwide, especially with the emerging challenge of drug resistance to current anti-TB drugs. There is an urgent need for effective and safe therapeutic interventions to tackle TB globally. One approach to achieve this goal is to combine host directed therapies (HDT) with current anti-TB therapies. Pro-inflammatory cytokines (TNF-α and IL-12) are essential for an effective immune response against bacterial infections and play a crucial role in controlling TB. Another promising approach is to identify compounds that could target key virulence enzymes of Mtb such as protein kinase G (MtPKnG). This study describes the phytochemical investigation of two medicinal plants (Fraxinus excelsior and Stachys arabica) selected based on their traditional and/or chemo-taxonomical use in the treatment for TB or TB-related symptoms. The work also focused on the evaluation of these plant extracts and selected isolated phytochemicals for their potential immunomodulatory effect in LPS-stimulated THP-1 cells. A total of 28 phytochemicals were isolated and characterised from both plants. The phytochemical investigation of the n-hexane and ethyl acetate extracts of F. excelsior leaves revealed the presence of 20 phytochemicals. The isolated phytochemicals included two pentacyclic triterpenoids (oleanolic acid and ursolic acid), squalene, one flavonoid (pinocembrin), five phenylethanoid esters (4-hydroxyphenethyl dotriacontanoate, 4-hydroxyphenethyl triacontanoate, 4-hydroxyphenethyl octacosanoate, 4-hydroxyphenethyl hexacosanoate, and 4-hydroxyphenethyl tetracosanoate), steryl fatty acid esters (β-sitosterol oleate), phytyl fatty acid esters (phytyl palmitate, phytyl oleate, and phytyl linolenate), and a mixture of acyclic alkanes (heptacosane, octacosane, nonacosane, triacontane, hentriacontane, dotriacontane and tritriacontane). Although ursolic acid, phytyl linolenate, nonacosane, and hentriacontane have already been reported in F. excelsior leaves, all other phytochemicals are reported here for the first time A total of 17 phytochemicals were isolated from the n-hexane and ethyl acetate extracts of S. arabica leaves. This included pheophytins (pheophytin a, 132 (R,S)-hydroxy pheophytin a, and pheophytin b), a mixture of phytosterols (stigmasterol, β-sitosterol and campesterol), a mixture of steryl fatty acid esters (β-sitosterol oleate & campesterol oleate), a mixture of phytyl fatty acid esters (phytyl palmitate, phytyl oleate), and a mixture of acyclic alkanes (heptacosane, octacosane, nonacosane, triacontane, hentriacontane and tritriacontane). Although all are known compounds, they are reported from S. arabica for the first time. When screened for potential Immunomodulatory effect in LPS-stimulated THP-1 cells, all the plant extracts and selected purified phytochemicals (oleanolic acid, ursolic acid, pinocembrin, and pheophytins) were able to reduce the production of the pro-inflammatory cytokines (TNF- α and IL-12). The mixture of phenylethanoid esters did not appear to influence the production of either of the cytokines studied. Our results indicate that the two plant extracts and their selected phytochemicals (oleanolic acid, ursolic acid, pinocembrin, and pheophytins) exhibited anti-inflammatory effect that could validate to a certain extent their potential use for complications associated with inflammation including TB as adjunct host therapy. Molecular docking using AutoDock Vina was conducted to predict the interactions between MtPknG and eighty-four phytochemicals from Pelargonium sidoides and Pelargonium reniforme as well as six selected phytochemicals identified through the phytochemical work. The flavonoids present in the aerial parts of Pelargonium plants displayed the best predicted binding energy towards MtPknG. The highest binding affinity towards MtPknG was recorded for isoorientin 2”-O-gallate (79), isovitexin 2”-O-gallate (77), nicotiflorin (61), orientin (74) and populnin (60) (−13.2, −12.6, −12.2, −11.8, and −11.6 kcal/mol, respectively) accompanied with SILE values (4.27, 4.11, 3.98, 4.17 and 4.10, respectively) that were superior to the control inhibitor AX20017 (−7.9 kcal/mol and SILE value of 3.32, respectively). Medicinal plants and their phytochemicals, owing to their abundance and diversity, could provide valuable alternatives for design of new generation of anti-TB drugs by serving as adjunct host-directed therapy and/or pathogen-directed therapy.
Advisor / supervisor
  • Seidel, Veronique
  • Rotondo, Dino
Resource Type