Growth-inhibitory effects of a mineralized extract from the red marine algae, Lithothamnion calcareum, on Ca(2+)-sensitive and Ca(2+)-resistant human colon carcinoma cells

Abstract

Proliferation and differentiation were assessed in a series of human colon carcinoma cell lines in response to a mineral-rich extract derived from the red marine algae, Lithothamnion calcareum. The extract contains 12% Ca2+, 1% Mg2+, and detectable amounts of 72 trace elements, but essentially no organic material. The red algae extract was as effective as inorganic Ca2+ alone in suppressing growth and inducing differentiation of colon carcinoma cells that are responsive to a physiological level of extracellular Ca2+ (1.4mM). However, with cells that are resistant to Ca2+ alone, the extract was still able to reduce proliferation and stimulate differentiation.

Fig. 1

Effects of a red algae extract on proliferation and differentiation of parental human colon carcinoma (CBS) cells and Ca²⁺-resistant (NR-1) variant cells. Upper-left panel: Cells were treated with the mineral-rich red algae extract (2.5 mg/ml) or with calcium chloride (1.4mM) and cell numbers were determined after 72 hours of incubation. Values represent means and standard errors based on nine independent experiments with both cell types. Statistical significance of the differences was determined by ANOVA followed by paired group comparisons. *Indicates difference from control at p <0.05. **Indicates difference from calcium chloride alone at p <0.05. Upper right-hand panel: Morphology: Cells were stained with hematoxylin and eosin after 72 hours of incubation. Lower left-hand panel: Confocal immunofluorescence microscopy: E-cadherin was assessed after two days of treatment. Lower right-hand panel: Western blot for E-cadherin: Whole cell extracts made after 3 days of treatment with either the red algae extract or calcium chloride (1.4mM) were assessed.

Fig. 2

Dose-responsive suppression of NR-1 proliferation with the red algae extract. Cell counts were made after 72 hours of incubation under the indicated conditions. Values represent means and standard errors based on six independent experiments. Statistical significance of the differences was determined by ANOVA followed by paired group comparisons. *Indicates difference from the control at p <0.05. **Indicates difference from the equivalent concentration of calcium chloride at p <0.05.

Fig. 3

Effects of a red algae extract on growth of four different human colon carcinoma cell lines. Cell counts were made after 72 hours of incubation under the indicated conditions. Values represent means and standard errors based on 3 –6 independent experiments with each cell line. Statistical significance of the differences was determined by ANOVA followed by paired group comparisons. *Indicates difference from the respective control at p <0.05. **Indicates difference from 5.6 mM calcium chloride alone at p <0.05.