Growth control in colon epithelial cells: gadolinium enhances calcium-mediated growth regulation

Abstract

Gadolinium, a member of the lanthanoid family of transition metals, interacts with calcium-binding sites on proteins and other biological molecules. The overall goal of the present investigation was to determine if gadolinium could enhance calcium-induced epithelial cell growth inhibition in the colon. Gadolinium at concentrations as low as 1-5 μM combined with calcium inhibits proliferation of human colonic epithelial cells more effectively than calcium alone. Gadolinium had no detectable effect on calcium-induced differentiation in the same cells based on change in cell morphology, induction of E-cadherin synthesis, and translocation of E-cadherin from the cytosol to the cell surface. When the colon epithelial cells were treated with gadolinium and then exposed to increased calcium concentrations, movement of extracellular calcium into the cell was suppressed. In contrast, gadolinium treatment had no effect on ionomycin-induced release of stored intracellular calcium into the cytoplasm. Whether these in vitro observations can be translated into an approach for reducing abnormal proliferation in the colonic mucosa (including polyp formation) is not known. These results do, however, provide an explanation for our recent findings that a multi-mineral supplement containing all of the naturally occurring lanthanoid metals including gadolinium are more effective than calcium alone in preventing colon polyp formation in mice on a high-fat diet.

Fig. 1

Effects of calcium and gadolinium on growth of human colon epithelial cells. Values shown are means and standard errors based on triplicate experiments with each line. *p<0.05, compared to calcium alone at the same concentration

Fig. 2

Effects of calcium and Magnevist on growth of human colon epithelial cells. Values shown are means and standard errors based on triplicate experiments with each line. *p<0.05, compared to calcium alone at the same concentration

Fig. 3

E-cadherin expression in colon epithelial cells. a Lysates were prepared from HCT-116 cells and assessed by Western blotting for E-cadherin expression 48 h after exposure to the indicated conditions. b β-catenin served as a control. Lysates from three different HCT-116 preparations were assessed with virtually identical results

Fig. 4

E-cadherin expression in colon epithelial cells. HCT-116 cells were stained 48 h after exposure to the indicated conditions and examined by fluorescence confocal microscopy. a SMEM-dFBS, b SMEM-dFBS plus 50 µM gadolinium, c SMEM-dFBS plus 1.5 mM calcium, d SMEM-dFBS plus 1.5 mM calcium and 50 µM gadolinium, e SMEM-dFBS plus 3.0 mM calcium, and f SMEM-dFBS plus 3.0 mM calcium and 50 µM gadolinium

Fig. 5

Intracellular calcium changes in response to calcium and gadolinium. Fluo-3 fluorescence was used to estimate intracellular calcium concentrations ([Ca²⁺]_i) in HCT-116 cells. Values shown represent mean [Ca²⁺]_i along with standard errors based on three to five separate experiments for each data point. Values with 5-h gadolinium pretreatment were statistically significant at p<0.05 relative to control. Inset: Histogram from a study showing the fluorescence values in HCT-116 cells under basal conditions versus 3.0 mM calcium and with a 5-h pretreatment with gadolinium