An in-vitro evaluation of the wound healing properties of cotyledon orbiculata extracts and its silver nanoparticles

Abstract

Chronic wounds are a silent epidemic affecting a large segment of the world’s population. They are associated with severe healthcare and socio-economic burdens, and are a great financial burden on healthcare institutions worldwide. Medicinal plants have been used traditionally as a source of medicine. To date, medicinal plants continue to play a significant role in the treatment of wounds. The synthesis of silver nanoparticles using chemicals derived from biological systems, particularly plants led to the discovery of nanoparticles with useful bioactivities. In many instances, plant derived silver nanoparticles have been shown to have higher activity than the plant extract itself. The plant, Cotyledon orbiculata, a medicinal plant from South Africa has been used traditionally for the treatment of skin wounds. Solvent extracts of the plant have been shown to have good antimicrobial, antioxidant and anti-inflammatory activities. Silver nanoparticles (Cotyledon-AgNPs) synthesized from the water extract of C. orbiculata were also reported to exhibit good antimicrobial and anti-inflammatory activities however, their antioxidant and wound healing properties, as well as the cytotoxicity have not been determined. This study therefore aimed to investigate these properties of C. orbiculata extract and Cotyledon-AgNPs. The antioxidant activity of C. orbiculata extract and Cotyledon-AgNPs was determined using the Ferric Reducing Antioxidant Power and the 2’-Azino-Bis-3-Ethylbenzotiazolin-6- Sulfonic Acid assays. The wound healing activity of C. orbiculata extract and Cotyledon-AgNPs was investigated using the cell growth and the wound healing scratch assay. Gene expression studies using real time qPCR were also performed to underpin the molecular mechanisms of wound healing exerted by C. orbiculata extract and Cotyledon-AgNPs treatments. The cytotoxic effects of the Cotyledon-AgNPs on non-cancerous skin fibroblast cells (KMST-6) were also investigated using in vitro bioassays and real time qPCR. Several in vitro assays, specifically the Mitochondrial Membrane Potential assay, APOPercentageTM assay, and the oxidative stress assay were used to study the cytotoxicity of the treatments. Both the C. orbiculata extract and Cotyledon-AgNPs showed the presence of polyphenols, flavanols, tannins and flavonols. They also exhibited some antioxidant activity however the extract showed more reducing activity than the Cotyledon-AgNPs. Some of these phytochemicals have been shown to possess antimicrobial and anti-inflammatory activities. At low concentrations, Cotyledon-AgNPs promoted cell growth and cell migration. Gene expression studies showed that the Cotyledon-AgNPs promoted wound healing by upregulating genes involved in cell proliferation, migration and growth while downregulating pro-inflammatory genes. This confirmed that C. orbiculata and Cotyledon-AgNPs are potentially good wound healing agents. The toxic effects of the Cotyledon-AgNPs to non-cancerous skin fibroblasts were determined using in vitro assays. The Cotyledon-AgNPs did not show any significant mitochondrial or cellular damage; instead it exhibited signs of cell proliferation. Gene expression studies showed the upregulation of genes involved in fatty acid and mitochondrial energy metabolism, steatosis, cholestasis, and apoptosis. The study shows that Cotyledon-AgNPs are not toxic to skin fibroblasts at the concentration that promote cell growth and wound healing. This study provides scientific evidence which lends credibility to the traditional use of C. orbiculata for the treatment of skin wounds. It also shows that C. orbiculata derived silver nanoparticles are non-toxic potent wound healing agents. In the future these nanoparticles for can be used in the development of novel wound healing treatments.