Copper-induced non-monotonic dose response in Caco-2 cells

Copper is an essential dietary micronutrient in humans for proper cell function; however, in excess, it is toxic. The human cell line Caco-2 is popular as an in vitro model for intestinal absorption and toxicology. This study investigated the response of exponentially growing Caco-2 cells to prolonged copper exposure (120 h). An unexpected non-monotonic dose-response profile was observed in Caco-2 cells. Exposure to media supplemented with 3.125 μM CuSO₄ resulted in decreased cell yield vs. untreated. However, toxicity was progressively reduced from 90% at 3.125 μM to 60% at 25 μM. This effect was documented between 48 and 120 h continuous exposure (p < 0.05). This triphasic toxicity curve was observed to be specific to copper in Caco-2 cells, as iron, manganese and zinc displayed monotonic dose-response profiles. Two inorganic copper forms, copper sulphate and copper chloride, were shown to conserve the non-monotonic dose-response curve. The triphasic effect was shown to be specific to Caco-2 cells. These results have implications for research investigating the effect of copper and other micronutrients using Caco-2 cells.