The In Vitro Immunomodulatory Effects Of Gold Nanoparticles Synthesized From Hypoxis hemerocallidea Aqueous Extract And Hypoxoside On Macrophage And Natural Killer Cells.

Macrophages and Natural Killer (NK) cells are an integral part of the innate immune system. These cells produce pro-inflammatory cytokines in response to bacterial infections. However, prolonged inflammation can be a contributing factor in the etiology of several diseases such as rheumatoid arthritis, inflammatory bowel disease, multiple sclerosis, psoriasis and eczema. Reducing the secretion of pro-inflammatory cytokines is an effective treatment strategy for these conditions. Gold nanoparticles (AuNPs) have been shown to have immunosuppressive effects. Extracts of the Hypoxis hemerocallidea plant have also been shown to have immunomodulatory effects. It has been demonstrated previously that extracts of the H. hemerocallidea can be used to synthesize AuNPs.

This study aimed to investigate whether AuNPs synthesized using H. hemerocallidea extract and its major secondary metabolite, hypoxoside, have any immunomodulatory effects in macrophages and NK cells.

AuNPs derived from the H. hemerocallidea extract were synthesized as previously described. Using similar methodologies, this study shows for the first time the synthesis of AuNPs from hypoxoside. The AuNPs were characterized using several optical and spectroscopic techniques. The immunomodulatory effects of the aqueous extract of H. hemerocallidea, hypoxoside, as well as the AuNPs produced from the extract and hypoxoside, were investigated by measuring the cytokine levels in macrophages (IL-1β, IL-6 and TNF-α) and NK cells (IFN-γ) using solid phase sandwich ELISA technique.

The results show that spherical AuNPs (average size 26 ± 2 nm) were synthesized from hypoxoside. The results also show that the four treatments (H. hemerocallidea extract, hypoxoside and their respective AuNPs can lower the pro-inflammatory cytokine levels in the macrophages cells, while only AuNPs produced from hypoxoside can reduce cytokine responses in NK cells.

This study shows that all four treatments investigated here could be further explored for the development of anti-inflammatory therapies.