Circumstantial evidence link the high levels of environmental pollutants to increased incidence of different chronic-degenerative diseases. Among these, the levels of heavy metals (HM) can certainly play a key role. On the other hand, a qualified literature highlights how different phytochemicals, normally present in the diet are able to interfere with HM metabolism helping to reduce tissue concentrations and their negative effects on health. Curcumin appears of particular interest for its protective properties against cadmium (Cd) toxicity.
HL-60 cells, undifferentiated and differentiated by vitamin D analogue EB1089, were pre-incubated with low doses of curcumin (1 microM) and treated for 24 h with different concentrations of Cd. Cell viability was measured using CyQuant fluorescent dye. Autophagy was detected by Cyto-ID assay and measuring the expression of specific markers (LC3-II; p62). ROS (reactive oxygen species) variation was assayed by dichlorofluorescein- diacetate method. The bioavailability of curcumin in HL-60 cells was successfully performed using RP-HPLC coupled with UV-Vis, MS/MS or MS/MSn.
In both differentiated and undifferentiated HL-60 cells, the pre-incubation with 1 microM curcumin determined a significant 20% protection towards the cytotoxicity induced by Cd. The investigation of the mechanism of action evidenced that curcumin lowered ROS increase caused by Cd. The antioxidant activity of curcumin was strengthened by the detection of free curcumin inside the cells after 5 min of treatment. In parallel, we measured the ability of both curcumin and Cd to activate autophagy, as a stress response.
The antioxidant effect induced by curcumin, possibly through Keap1/Nrf2 system and GSH synthesis, is capable to re-modulate the autophagic flux converting the lethal autophagy triggered by Cd to a protective form. Overall, these preclinical results substantiate the design of nutritional interventional studies to investigate the capacity of curcumin to lower the concentration of HM in subjects exposed to environmental pollutants.
