Abstract
Plants have a rich history in folk medicine for treating many diseases, mainly attributed to their phytochemicals. Therefore, the research in this study was aimed at extracting, isolating, and characterizing active phytochemicals and studying the most bioactive compounds found in the three traditional medicinal plants against cancer and bacterial cells. The hypothesis of the study was then to extract compounds that have effect on cancer cell growth and bacteria inhibition. The three plants of interest were Tabernaemontana contorta stapf (Cameroon), Sclerocarya birrea (Limpopo Province-South Africa) and Senna italica (Limpopo Province-South Africa). These three African plants were chosen because of their use in ethnopharmacology for symptoms associated with cancer and bacterial infections.
The fine powder of these plants’ materials (fruits, leaves, stem bark, and roots) were soaked in various organic solvents for 7 days, filtered, and concentrated and then the crude extracts were collected. These extracts were then subjected to successive column chromatography. The collected isolates or pure compounds were studied using 1D and 2D NMR to elucidate their structures. The crude, fractions and isolates were evaluated for their cytotoxicity against bacteria cell strains, and cell cancer lines to determine their potency.
The raw materials of the three plants were soaked for seven days separately in a 1:1 mixture of DCM: MeOH. This mixture was then filtered and concentrated on a Rotary evaporator to collect the crude extracts. The crude extracts were then tested for their antibacterial activity against twelve bacteria strains, thus five Gram-positive (Bacillus subtilis, Enterococcus faecalis, Mycobacterium smegmatis, Staphylococcus epidermidis, Staphylococcus aureus) and seven Gram-negative (Escherichia coli, Enterobacter cloacae, Proteus vulgaris, Pseudomonas aeruginosa, Proteus mirabilis, Klebsiella pneumoniae, Klebsiella oxytoca) bacteria by MIC method. The MIC values of the extracts ranged from 15.625 μg/mL to 500 μg/mL with S. italica being the most potent followed by T. contorta Stapf and S. birrea.
The crude extracts were subjected to column chromatography where the volatile oil fractions were collected, which were then analysed by GC-MS to study the secondary metabolites present in the oils. On GC-MS spectra different classes of compounds were identified from the crude extracts,
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and their volatile oil fractions. The pure compounds isolated from column chromatography were analyzed on 1D- and 2D-NMR analysis, including COSY, DEPT, HSQC, and HMBC, and by comparison with those in the literature to elucidate their structures. From the fruits of T. contorta Stapf, two compounds we’ve isolated: apparicin-21-one, and ursolic acid. From the leaves, we isolated three compounds, α-amyrin propanoate, α-amyrin acetate, and oleanolic acid. Finally, from the stem bark of T. contorta Stapf, a mixture of ursolic and oleanolic acid were isolated. Three compounds; retusasterol, β-sitosterol-D-glycoside, and glycoside alcohol, were isolated from the inner bark of S. birrea. From the S. italica roots extract we’ve isolated two compounds: chrysophanol and β-stigmasterol β-sitosterol.
The isolated compounds were further assayed for their in-vitro cytotoxicity against cancer cells.
T. contorta Stapf (α-amyrin propanoate) and S. birrea (retusasterol and glycoside alcohol) compounds were tested against breast cancer cell line MCF7. S. birrea compound, glycoside alcohol, showed better results even though all compounds were not cytotoxic. In another study, S. birrea (retusasterol) and S. italica (chrysophanol and β-stigmasterol β-sitosterol) compounds were tested against human androgens-independent prostate carcinoma (DU145, PC3, and LNCaP) cell lines. Retusasterol isolated from S. birrea was the most active with CC50 values of 38 μg/mL, 40 μg/mL, and 32 μg/mL, in DU145, PC3, and LNCaP cells, respectively. To our disappointment retusasterol was found to accelerates tumor growth.
In conclusion the crude extracts were able to inhibit pathogenic bacteria strains because of their synergetic effect, and some of the isolated compounds were also found to be cytotoxic to the MCF7, DU145, PC3, and LNCaP cancer cells.