Isolation, characterisation of Terpenoids and Biosynthesis of silver Nanoparticles of Acacia Mearnsii de Wild and Acacia Karroo Hayne and their Bioassays

Abstract

Great wealth of traditional knowledge about the use of plants had been transferred from generation to generations leading to the present day drug discovery and invention of new scientific methods of isolation, purification and identification. With the discovery of new diseases and drug-resistant organisms, there is no other source or deposit of lead compounds or drugs than the plant kingdom. As a result of this, about 25% of the current drug administered owe their origin to plant sources with the view to reduce the carcinogenic effect of synthetic drugs. Volatile terpenoids among other broad spectrum of natural product had been implicated to show high therapeutic properly. In the present study, selected locally-used medicinal plants were exploited for the presence of potent bioactive compounds and ability to form nanoparticles with distinctive property for use as chemoprotective agent against inflammation, tumors, cancer and other chronic diseases. Acacia mearnsii De Wild and Acacia karroo Hayne studied in this report are known to be invasive species with no proper regulation to conserve and preserve them. However, ethnopharmacology report of these plant species in the Southern Africa region reveals that they are good antiseptic, anti-diarrhea, anti-inflammation and a forage for livestock. These plants were subjected to volatile extraction protocol of some parts of the plants (stem and leaves) followed by examination of the anti-inflammation capacity of the extracts using an animal model. In addition, the bye-product (hydrosol) from the stem bark of each species possess a high reducing and stabilizing property leading to synthesis of silver nanoparticles, followed by investigation of the anti-inflammation potential of the synthesized silver nanoparticles using animal model. The volatile oils of the leaves and stem bark of Acacia mearnsii De Wild obtained by hydro-distillation were analyzed by Gas Chromatography-Mass Spectrometry (GC-MS). Twenty, Thirty-Eight, Twenty-nine and Thirty-Eight components accounting for 93.8%, 92.1%, 78.5% and 90.9% of the total oils of the fresh, dry leaves and fresh, dry stem bark respectively. The major components of the oil were octadecyl alcohol (25.5%) and phytol (10.5%); cis-verbenol (29.5%); phytol (10.1%) and phytol (23.4%) for the fresh leaves, dried leaves, and fresh stem, dry stem bark respectively. Oral administration of essential oils at the dose of 2% showed significant (p<0.05) anti-inflammatory properties in the albumin induced vi test model in rats. Oils from the fresh leaves and dry stems inhibited inflammation beyond 4 h post treatment. Furthermore, the chemical composition of the essential oils obtained by hydro-distillation from the leaves and stem bark (dry and fresh) of Acacia karroo Hayne, analysed by GC-MS, shows that hexanal (10.67%) and ß-ionone (9.74%) were dominant in the dried leaves, β-pinene (14.30%), and (Z)-2-Hexen-1-ol (10.21%) in the fresh leaves while Octacosane (10.59%) and phytol (23.38%) were dominant in the dry and fresh stem respectively. The anti-inflammation ability of these oils after an albumin-induced inflammation on wistar rats, shows a significant effect at the 1st h of treatment with a significance of P< 0.01 for all part plants, while the fresh leaves shows further inhibitory activities at the 2nd h of analysis. Silver nanoparticles (AgNPs) were successfully synthesized from AgNO3 through a green route using the aqueous extract (hydrosols) of Acacia mearnsii De Wild and Acacia karroo Hayne as reducing agent and as well as capping agent. The Acacia-mediated AgNPs were characterized with the use of UV-vis absorption spectroscopy, Fourier Transform Spectroscopy (FT-IR), Transmission electron microscope (TEM), Scanning Electron Microscope (SEM), Energy Dispersive Spectroscopy (EDX), and X-ray Diffractometry (XRD). A spherical, 10-40 nm diameter silver nanoparticles were synthesized with very low level of stability for the AMDS and the AKDS-AgNPs. In addition, nociceptive activity with a mice rat reveals higher inhibition at the neurogenic phase for the AKDS-AgNPs, while AMDS-AgNPs exhibited a high inhibition at the inflammatory phase. The potent anti-inflammatory activity of essential oils of A. mearnsii De Wild and A. karroo Hayne hereby confirmed its traditional use in treating various inflammatory diseases, while the inflammatory studies on the synthesized AgNPs reveals a very active compound which can be used as a potent opioid or non-steroidal anti-inflammatory drug (NSAID).