Citrate-capped gold nanoparticles with a diameter of 14 nm alter the expression of genes associated with stress response, cytoprotection and lipid metabolism in CaCo-2 cells

The Cytotoxicity of Cotyledon orbiculata Aqueous Extract and the Biogenic Silver Nanoparticles Derived from the Extract

Green synthesized silver nanoparticles (AgNPs) have become popular because of their promising biological activities. However, for most of these nanoparticles, the cytotoxic effects have not been determined and their safety is not guaranteed. In a previous study, we successfully synthesized AgNPs (Cotyledon-AgNPs) using an extract of Cotyledon orbiculata, a medicinal plant traditionally used in South Africa to treat skin conditions. Cotyledon-AgNPs were shown to have significant antimicrobial and wound-healing activities. Fibroblast cells treated with extracts of C. orbiculata and Cotyledon-AgNPs demonstrated an enhanced growth rate, which is essential in wound healing. These nanoparticles therefore have promising wound-healing activities. However, the cytotoxicity of these nanoparticles is not known. In this study, the toxic effects of C. orbiculata extract and Cotyledon-AgNPs on the non-cancerous skin fibroblast (KMST-6) were determined using in vitro assays to assess oxidative stress and cell death. Both the C. orbiculata extract and the Cotyledon-AgNPs did not show any significant cytotoxic effects in these assays. Gene expression analysis was also used to assess the cytotoxic effects of Cotyledon-AgNPs at a molecular level. Of the eighty-four molecular toxicity genes analysed, only eight (FASN, SREBF1, CPT2, ASB1, HSPA1B, ABCC2, CASP9, and MKI67) were differentially expressed. These genes are mainly involved in fatty acid and mitochondrial energy metabolism. The results support the finding that Cotyledon-AgNPs have low cytotoxicity at the concentrations tested. The upregulation of genes such as FASN, SERBF1, and MKI-67 also support previous findings that Cotyledon-AgNPs can promote wound healing via cell growth and proliferation. It can therefore be concluded that Cotyledon-AgNPs are not toxic to skin fibroblast cells at the concentration that promotes wound healing. These nanoparticles could possibly be safely used for wound healing.

A Label-Free Gold Nanoparticles-Based Optical Aptasensor for the Detection of Retinol Binding Protein 4

Retinol-binding protein 4 (RBP4) has been implicated in insulin resistance in rodents and humans with obesity and T2DM, making it a potential biomarker for the early diagnosis of T2DM. However, diagnostic tools for low-level detection of RBP4 are still lagging behind. Therefore, there is an urgent need for the development of T2DM diagnostics that are rapid, cost-effective and that can be used at the point-of-care (POC). Recently, nano-enabled biosensors integrating highly selective optical detection techniques and specificity of aptamers have been widely developed for the rapid detection of various targets. This study reports on the development of a rapid gold nanoparticles (AuNPs)-based aptasensor for the detection of RBP4. The retinol-binding protein aptamer (RBP-A) is adsorbed on the surface of the AuNPs through van der Waals and hydrophobic interactions, stabilizing the AuNPs against sodium chloride (NaCl)-induced aggregation. Upon the addition of RBP4, the RBP-A binds to RBP4 and detaches from the surface of the AuNPs, leaving the AuNPs unprotected. Addition of NaCl causes aggregation of AuNPs, leading to a visible colour change of the AuNPs solution from ruby red to purple/blue. The test result was available within 5 min and the assay had a limit of detection of 90.76 ± 2.81 nM. This study demonstrates the successful development of a simple yet effective, specific, and colorimetric rapid assay for RBP4 detection.