The morphological characterization, chemical composition and biological activity of barleria albostellata (Acanthaceae).

Abstract

Herbal preparations of plants continue to present mankind with novel remedies as many of these plants contain important secondary metabolites. Medicines manufactured by pharmaceutical companies are largely synthetic. The fear for ineffectiveness, adverse side-effects and toxicity, has brought about further scientific investigations on the potential usage of medicinal plants. Plants of the family Acanthaceae are rich in bioactive phytochemicals. Several plant species are being utilized for their ethnomedicinal properties based on their phytocompounds they acquire, with Barleria (Acanthaceae) being one of such genera. Barleria albostellata C.B. Clarke (Acanthaceae) is a shrub indigenous to South Africa. Herbal use of this plant has not been fully documented, however, several species of Barleria are used in traditional medicine. Little or no investigations have been undertaken to evaluate the micromorphology secretory mechanisms, through which such phytochemicals are synthesized and secreted; floral biology; phytochemical profile; antibacterial and antioxidant activity, cytotoxicity and synthesis of nanoparticles using the leaf and stem extracts of B. albostellata. Therefore, this study aimed at bridging these gaps by first characterizing the morphology, chemical composition and biological activity of leaves and stems of B. albostellata, using various microscopy techniques and biological assays. Floral biology of the plant was conducted using stereo- and scanning electron microscopic (SEM) techniques. ImageJ was used to measure the length and diameter of the different trichome types and pollen structures. Histo-phytochemical, thin-layer chromatography (TLC), fluorescence microscopy and gas-chromatography mass spectrometry (GC-MS) analysis were performed on crude extracts (hexane, chloroform and methanol) to determine the composition of the compounds that may be of medicinal importance. Biological (antibacterial and antioxidant) analyses were also conducted on the crude extracts. Cytotoxicity of the crude extracts were evaluated established using 3-[(4,5- dimethylthiazol- 2-yl)-2,5-diphenyl tetrazolium bromide] (MTT) assay in the human embryonic kidney (HEK293), cervical cancer (HeLa), and breast adenocarcinoma (MCF-7) cell lines. Silver nanoparticles (AgNPs) were synthesized using methanolic, aqueous- powdered and -fresh leaf and stem extracts. These AgNPs were characterized using UV–visible spectroscopy, high resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray (EDX), Fourier transform infrared (FTIR) spectral analysis and nanoparticle tracking analysis (NTA). Antibacterial analysis of the synthesized AgNPs was assessed using the disk diffusion method. Cytotoxicity of the synthesized nanoparticles were investigated using the MTT assay on the three cell lines. Histochemically stained sections, stereo, SEM and TEM micrographs revealed a dense indumentum with the presence of five morphologically distinct glandular capitate trichome types, multangulate-dendritic branched (MDB) non-glandular trichomes and a glandular head attached to a branched non-glandular trichome. Both glandular and non-glandular trichomes in the leaves and stems of B. albostellata are important diagnostic features of this species. The secretory head of glandular typed trichomes varied from 20.72 ± 1.36 µm to 54.23 ± 2.08 µm. Additionally, the length of these stalks varied from 15.11 ± 3.89 µm to 101.92 ± 1.78 µm, and the width ii from 11.62 ± 1.03 µm to 35.32 ± 3.87 µm. Multangulate-dendritic branched trichomes had a stalk length of 554.10 ± 92.27 µm and width of 28.55 ± 2.48 µm. Stained sections and crude extracts indicated the presence of important medicinal compounds such as alkaloids and phenolics. The histochemical tests indicated the presence of various phytocompounds that have medicinal importance and aid in defense against pathogens and herbivores. Pollen grains of B. albostellata are complex, intricate and display reticulate sculpturing, with a diameter of 77.53 ± 5.63 μm and aperture of 14.31 ± 0.59 µm. This will contribute significantly to our growing understanding on the floral and pollen biology of this species. Qualitative phytochemical screening, GC-MS and florescence microscopy of the leaf and stem extracts revealed various biologically active compounds and the presence of different colours in the leaf and stem powder. Different colour intensities obtained from TLC suggested concentrations of the separated compounds were varied. Additionally, the phyto-constituents found in the leaf and stem crude extracts of could inhibit the growth of various pathogenic strains. Results from this study revealed the medicinal potential of B. albostellata in the treatment of various bacterial diseases Ultraviolet spectra, NTA and EDX, revealed varying absorption peaks, size distribution, and elemental Ag in all extracts. Crude extracts and synthesized AgNPs displayed varying degrees of antioxidant, antibacterial and cytotoxic activities. Significance was established at P 63 µg/mL and >9 µg/mL, respectively) may be due to the presence of flavonoids, phenols, and antioxidant activity in the different parts of this species. Synthesized AgNPs showed possible bacteriostatic effects against Gram-positive and -negative human pathogenic bacteria. Their broad spectrum of bioactivity suggested that they may be as promising agents in fighting infections. This study ultimately proved that leaf and stem extracts of B. albostellata contained numerous biologically active compounds such as alkaloids and phenolics. These results are suggestive that the leaves and stems of B. albostellata are rich in bioactive compounds which, could be a possible source of antibacterial agents in treating several diseases .There is a great potential for B. albostellata as this plant displays valuable biological activities. Future studies on this plant are recommended, as this could advance the use of indigenous herbal medicine or product novel drug leads.