Curcumin affects cell survival and cell volume regulation in human renal and intestinal cells

Curcumin (1,7-bis(4-hydroxy-3-methoxyphenyl)-1E,6E-heptadiene-3,5-dione or diferuloyl methane) is a polyphenol derived from the Curcuma longa plant, commonly known as turmeric. This substance has been used extensively in Ayurvedic medicine for centuries for its anti-oxidant, analgesic, anti-inflammatory and antiseptic activity. More recently curcumin has been found to possess anti-cancer properties linked to its pro-apoptotic and anti-proliferative actions. The underlying mechanisms of these diverse effects are complex, not fully elucidated and subject of intense scientific debate. Despite increasing evidence indicating that different cation channels can be a molecular target for curcumin, very little is known about the effect of curcumin on chloride channels. Since, (i) the molecular structure of curcumin indicates that the substance could potentially interact with chloride channels, (ii) chloride channels play a role during the apoptotic process and regulation of the cell volume, and (iii) apoptosis is a well known effect of curcumin, we set out to investigate whether or not curcumin could (i) exert a modulatory effect (direct or indirect) on the swelling activated chloride current IClswell in a human cell system, therefore (ii) affect cell volume regulation and (iii) ultimately modulate cell survival. The IClswell channels, which are essential for regulating the cell volume after swelling, are also known to be activated under isotonic conditions as an early event in the apoptotic process. Here we show that long-term exposure of a human kidney cell line to extracellular 0.1-10 μM curcumin modulates IClswell in a dose-dependent manner (0.1 μM curcumin is ineffective, 0.5-5.0 μM curcumin increase, while 10 μM curcumin decrease the current), and short-term exposure to micromolar concentrations of curcumin does not affect IClswell neither if applied from the extracellular nor from the intracellular side - therefore, a direct effect of curcumin on IClswell can be ruled out. Furthermore, we show that curcumin exposure induces apoptosis in human kidney cells, and at a concentration of 5.0-10 μM induces the appearance of a sub-population of cells with a dramatically increased volume. In these cells the regulation of the cell volume seems to be impaired, most likely as a consequence of the IClswell blockade. Similarly, 50 μM curcumin induced apoptosis, caused cell cycle arrest in G1-phase and increased the volume of human colorectal adenocarcinoma HT-29 cells. The cell cycle arrest in G1 phase may be the mechanism underlying the volume increase observed in this cell line after exposure to curcumin.