Dose-Response Effect of Various Concentrations of Cl-Containing Water-Soluble Derivatives of C60 Fullerenes on a Selective Regulation of Gene Expression in Human Embryonic Lung Fibroblasts (HELF).

Background: The new synthesized water-soluble derivatives of C₆₀ fullerenes are of a great interest to researchers since they can potentially be promising materials for drug delivery, bioimaging, biosonding, and tissue engineering. Surface functionalization of fullerene derivatives changes their chemical and physical characteristics, increasing their solubility and suitability for different biological systems applications, however, any changes in functionalized fullerenes can modulate their cytotoxicity and antioxidant properties. The toxic or protective effect of fullerene derivatives on cells is realized through the activation or inhibition of genes and proteins of key signaling pathways in cells responsible for regulation of cellular reactive oxygen species (ROS) level, proliferation, and apoptosis.

Methods: The 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide (MTT) assay was used to assess cells viability. Flow cytometry analyses was applied to measure proteins levels in human embryonic lung fibroblasts (HELF) cells. HELF is a standard, stable and well described human cell line that can be passaged many times. Quantitation of ROS was assessed using H2DCFH-DA. Fluorescence images were obtained using microscopy. Expression of BCL2, CCND1, CDKN2A, BRCA1, BAX, NFKB1, NOX4, NRF2, TBP (reference gene) was analyzed using real-time Polymerase chain reaction (PCR).

Results: We found that high and low concentrations of fullerene C₆₀ derivatives with the five residues of potassium salt of 6-(3-phenylpropanamido)hexanoic (F1) or 6-(2-(thiophen-2-yl)acetamido)hexanoic (F2) acid and a chlorine atom attached directly to the cage cause diametrically opposite activation of genes and proteins of key signaling pathways regulating the level of oxidative stress and apoptosis in HELF. High concentrations of F1 and F2 have a genotoxic effect, causing NADPH oxidase 4 (NOX4) expression activation in 24-72 hours (2-4 fold increase), ROS synthesis induction (increase by 30-40%), DNA damage and breaks (2-2.5 fold 8-oxodG level increases), and activation of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) (by 40-80%) against the background of reduced NF-E2-related factor 2 (NRF2) expression (by 20-45%). Low concentrations of F1 and F2 produced a cytoprotective effect: in 24-72 hours they reduce the oxidative DNA damage (by 20-40%), decrease the number of double-strand DNA breaks (by 20-30%), increase the level of anti-apoptotic proteins and enhance the antioxidant response activating the NRF2 expression (NRF2 gene expression increases 1.5-2.3 fold, phosphorylated form of the NRF2 protein increases 2-3 fold).

Conclusions: Obtained results show that in low doses studied fullrens may serve as perspective DNA protectors against the damaging genotoxic factors.