Chromate has been shown to dysregulate epigenetic mechanisms such as DNA methylation, leading to changes in gene expression and genomic instability. However, most in vitro studies are limited to short incubation periods, although chronic exposure may be more relevant for both environmental and occupational exposure. In this study, human adenocarcinoma A549 cells were treated with 1, 2 or 5 µM chromate for 24 h and compared with incubations with 0.2, 0.5 or 1 µM chromate for 1 to 5 weeks. Chromium accumulated in a pronounced time- and concentration-dependent manner after short-term treatment, whereas a plateau of intracellular chromium content was observed after long-term treatment. While short-term treatment induced a G2 arrest of the cell cycle, this effect was not observed after long-term treatment at lower concentrations. The opposite was observed for global DNA methylation: while short-term treatment showed no effect of chromate, significant dose-dependent hypomethylation was observed in the long-term experiments. Time-dependent effects were also observed in a high-throughput RT-qPCR gene expression analysis, particularly in genes related to the inflammatory response and DNA damage response. Taken together, the results suggest specific differences in toxicity profiles when comparing short-term and long-term exposure to chromate in A549 cells.

Although exposure to heavy metals such as cadmium and inorganic arsenic has declined in recent decades, they remain prevalent environmental contaminants in food, drinking water, and tobacco smoke. This study aimed to identify and compare molecular endpoints of arsenite and cadmium toxicity at the gene and protein expression levels, with a focus on metal homeostasis, the oxidative stress response and redox-regulated processes. Human bronchial epithelial cells (BEAS-2B) were used as an in vitro model. First, the appropriate exposure conditions were defined by assessing cytotoxicity and intracellular metal accumulation. The cells were then incubated with 1–10 µM NaAsO₂ or 1–5 µM CdCl₂ for 24 h, after which gene and protein expression were analyzed. When compared to arsenite, cadmium was a markedly stronger inducer of metallothionein (MT) expression, indicating distinct effects on metal homeostasis. Both metals induced a concentration-dependent upregulation of oxidative stress-related genes. Cadmium led to a stronger activation of NF-κB signaling, while arsenite decreased selenoprotein-associated gene expression and affected genes involved ferroptosis regulation. Differences in gene and protein expression patterns were also observed, suggesting that transcriptional responses do not necessarily translate into corresponding changes at the protein level after 24 h. These findings highlight shared and compound-specific mechanisms, as well as the importance of multi-level analyses.

The transition metal copper (Cu) is an essential trace element for humans and serves as a cofactor for numerous enzymes. Therefore, intracellular Cu homeostasis must be tightly regulated. Meanwhile, Cu is increasingly used in industrial and biomedical applications, particularly in nanoparticle (NP) form. However, studies have demonstrated that Cu(II) oxide (CuO) NPs are highly toxic. Therefore, understanding the underlying toxic effects of such compounds is of the utmost importance. In this context, transcriptomic profiling is regarded as a valuable tool. Nevertheless, comparative studies addressing organ-relevant models, such as the liver and lungs, are scarce. Furthermore, no transcriptomic studies have been conducted on human bronchial lung epithelial cells exposed to CuO NPs and Cu²⁺. In this study, we compared the cellular effects of human bronchial lung epithelial cells exposed to both CuO NPs and Cu²⁺ to the effects in human liver cells exposed to Cu²⁺ by applying RNA sequencing. Although cytotoxicity was comparable, we showed that Cu uptake was highly dependent on both the cell type and the form of Cu. The most pronounced concentration-dependent transcriptional changes were observed with CuO NP exposure in BEAS-2B cells. The only differentially expressed genes (DEGs) found by all exposures and treatments were metallothioneins (MTs). The most sensitive targets of Cu-induced toxicity were related to nuclear factor erythroid 2-related factor 2 (NRF2), nuclear factor kappa-light-chain-enhancer of activated B cells (NFkB), and mitogen-activated protein kinase (MAPK) signaling. Furthermore, the effects observed at the transcriptome level were studied at the functional level, such as cell cycle regulation and cytokine release. Thus, we demonstrated that the two cell types differ in susceptibility, and that complementing transcriptome profiling with functional studies provides important mechanistic insights.