Interestingly, however, is

our finding that long-term exposure (15–23 h in the medium used for cell growth) to 0.1–10 μM extracellular curcumin modulates IClswell in a dose-dependent manner in a human epithelial cell model. Particularly, 0.5–5.0 μM curcumin up-regulates IClswell, while 10 μM curcumin down-regulates IClswell current (Fig. 3 and Fig. 4). The current up-regulation reached its maximal extent with 1.0 μM curcumin. This effect could not be ascribed to a direct action of curcumin on the channel since short-term exposure with similar concentrations of curcumin applied Cyclopamine manufacturer to either the extracellular or intracellular side did not affect IClswell (Fig. 1 and Fig. 2). In agreement with previous reports, long-term exposure to curcumin induced apoptosis in the HEK293 Phoenix cells (Fig. 6 and Fig. 7). As it is known that IClswell activation is an early event in apoptosis and a key step in apoptotic volume decrease (Okada et al., 2006), we hypothesized that the observed IClswell up-regulation by curcumin is the consequence of the induction of apoptosis. Indeed, the swelling-activated chloride channel and the chloride channel triggering the apoptotic volume decrease are likely buy Inhibitor Library the same molecular entity (Okada et al., 2006 and Pasantes-Morales and Tuz, 2006). In agreement with this hypothesis, long-term exposure to curcumin also induces the activation of a chloride current resembling IClswell in the absence of hypotonic

shock (Fig. 5). Interestingly, we showed for the first time that a long-term exposure to 5.0–10 μM curcumin resulted in the appearance of a sub-population of cells with a volume nearly double that of the main cell population (Fig. 6a and c). In these “swollen” cells, volume regulation appears to be impaired and underscores the principle that basal cell volume is slightly smaller than the equilibrium would predict (Cao et al., 2011), most likely by active IClswell. We hypothesize that derangement of cell volume regulation is a possible consequence of the IClswell blockade that was observed

with higher curcumin concentrations (Fig. 3 and Fig. 4). Accordingly, Light et al. showed that 20 μM curcumin could inhibit cell volume regulation in mudpuppy red blood cells; although this effect was attributed to inhibition of the 5-lipoxygenase pathway (Light Niclosamide et al., 1997). The curcumin-induced derangement of cell viability and cell volume is not restricted to renal HEK293 Phoenix cells. Indeed, 5.0–50 μM curcumin induced apoptosis in intestinal HT-29 cells, evidenced as an increase of Annexin-V binding (Fig. 8b) and side scatter (Fig. 9a). Surprisingly, cell death in these cells was not accompanied by the typical apoptotic cell shrinkage. Indeed, the volume of necrotic (Fig. 9b) and late apoptotic (Fig. 9c) cells was significantly increased. Interestingly, a cell cycle arrest in G1 phase is often observed following exposure to a variety of substances (such as hydrogen peroxide, vitamin D and prostaglandin E2) (Artaza et al.