Surface carboxylation or PEGylation decreases CuO nanoparticles’ cytotoxicity to human cells in vitro without compromising their antibacterial properties

Abstract

Clinical use of CuO nanoparticles (NPs) as antibacterials can be hampered by their toxicity to human cells. We hypothesized that certain surface functionalizations of CuO NPs may render NPs toxic to bacteria, but still be relatively harmless to human cells. To control this hypothesis, the toxicity of differently functionalized CuO NPs to bacteria Escherichia coli vs human cells (THP-1 macrophages and HACAT keratinocytes) was compared using similar conditions and end points. CuO NPs functionalized with polyethylene glycol (CuO-PEG), carboxyl (CuO-COOH, anionic), ammonium (CuO-NH 4 + , cationic) and unfunctionalized CuO NPs and CuSO 4 (controls) were tested. In general, the toxicity of Cu compounds decreased in the following order: CuO-NH 4 + > unfunctionalized CuO > CuSO 4 > CuO-COOH > CuO-PEG. Positively charged unfunctionalized CuO and especially CuO-NH 4 + proved most toxic (24-h EC 50 = 21.7-47 mg/l) and had comparable toxicity to bacterial and mammalian cells. The multivariate analysis revealed that toxicity of these NPs was mostly attributed to their positive zeta potential, small hydrodynamic size, high Cu dissolution, and induction of reactive oxygen species (ROS) and TNF-α. In contrast, CuO-COOH and CuO-PEG NPs had lower toxicity to human cells compared to bacteria despite efficient uptake of these NPs by human cells. In addition, these NPs did not induce TNF-α and ROS. Thus, by varying the NP functionalization and Cu form (soluble salt vs NPs), it was possible to "target" the toxicity of Cu compounds, whereas carboxylation and PEGylation rendered CuO NPs that were more toxic to bacteria than to human cells envisaging their use in medical antibacterial products.

Copper Oxide Nanoparticles Stimulate the Immune Response and Decrease Antioxidant Defense in Mice After Six-Week Inhalation

“…Already available in vitro studies have indicated possible immunotoxicity of CuO NPs mediated by cytotoxicity towards immune cells (human blood lymphocytes) ( 16 ), RAW264.7 (murine macrophage cell line) ( 19 ), or potent induction of proinflammatory cytokine TNF-α in differentiated human THP-1 cells (human monocytic leukemia cell line) ( 17 ).…”

Inorganic Nanoparticles Applied as Functional Therapeutics

“…, Staphylococcus aureus ) bacteria. [ 152 ] Cu NPs affect the protein structure in the bacterial membrane through denaturation of the intracellular proteins and interaction with phosphorus‐ and sulfur‐containing compounds such as DNA. In addition, increased ROS levels by Cu NPs lead to noticeable lipid peroxidation, protein oxidation, and DNA degradation, finally inducing bacterial death.…”

“…[ 153 ] The antibacterial characteristic of CuO NPs against gram‐negative bacterium E. coli is prolonged even after surface modification and shows significant potential for future application. [ 152a ] It has been shown that negatively charged NPs, that is, CuOCOOH and CuOPEG, are more cytotoxic to bacteria than human cells. Because wound healing can be delayed through bacterial infection, the antibacterial effect of Cu‐substituted mesoporous bioactive glasses improved chronic wound healing.…”

Copper oxide nanoparticles trigger macrophage cell death with misfolding of Cu/Zn superoxide dismutase 1 (SOD1)

“…In a previous study, we found that CuO NPs elicited significantly more cytotoxicity than CuCl 2 and we also noted an interplay between the NPs and their surface coating with respect to cytotoxicity [ 7 ]. In fact, it is possible to “passivate” CuO NPs through surface modification, and poly(ethylene) glycol (PEG) functionalization has been shown to mitigate the toxicity of CuO NPs both in vitro and in vivo [ 8 , 9 ].…”