The Effect of Calcium on Non-heme Iron Uptake, Efflux, and Transport in Intestinal-like Epithelial Cells (Caco-2 Cells)

Abstract

It has been suggested that calcium inhibits the absorption of dietary iron by directly affecting enterocytes. However, it is not clear if this effect is due to a decreased uptake of iron or its efflux from enterocytes. We studied the effect of calcium on the uptake, efflux, and net absorption of non-heme iron using the intestinal-like epithelial cell line Caco-2 as an in vitro model. Caco-2 cells were incubated for 60 min in a buffer supplemented with non-heme iron (as sulfate) and calcium to achieve calcium to iron molar ratios ranging from 50:1 to 1,000:1. The uptake, efflux, and net absorption of non-heme iron were calculated by following a radioisotope tracer of (55)Fe that had been added to the buffer. Administration of calcium and iron at molar ratios between 500 and 1,000:1 increased the uptake of non-heme iron and decreased efflux. Calcium did not have an effect on the net absorption of non-heme iron. At typical supplementary doses for calcium and non-heme iron, calcium may not have an effect on the absorption of non-heme iron. The effect of higher calcium to iron molar ratios on the efflux of non-heme iron may be large enough to explain results from human studies.

Knockdown of copper-transporting ATPase 1 (Atp7a) impairs iron flux in fully-differentiated rat (IEC-6) and human (Caco-2) intestinal epithelial cells

“…To ensure that the monolayers were intact with fully-formed tight junctions, trans -epithelial electrical resistance (TEER) and phenol red flux were routinely assessed, as we described previously 15, 16 . For IEC-6 cells, TEER values were routinely 36 – 40 Ω/cm 2 and >250 Ω/cm 2 for Caco-2 cells.…”

Effect of phytic acid, tannic acid and pectin on fasting iron bioavailability both in the presence and absence of calcium

“…In agreement with these results, a previous study performed by us, and recently published by Gaitan et al [15] found that doses ≤800 mg of Ca (CaCl 2 ) did not decrease the bioavailability of 5 mg of Fe (FeSO 4 ) in subjects with similar characteristics. Also, a study focused on the effect of calcium on uptake, efflux, and net absorption of non-heme iron using the intestinal-like epithelial Caco-2 cell found that calcium did not have an effect on the net absorption of non-heme iron [39].…”

Calcium as a nutrient involved in the synthesis and localization of proteins that facilitate iron uptake and efflux in enterocytes

“…The author reported that there were no signifi cant differences in the DMT1 mRNA expression between the cells incubated in the absence or presence of calcium for 1.5 h (p=0.06). However, the cells cultured for 4 hours with 100μM calcium demonstrated a signifi cant increase in DMT1 expression (p-value not reported), which may explain the fi ndings obtained by Gaitan et al (37), who observed that calcium signifi cantly increases iron uptake in Caco-2 cells. Regarding Fpn mRNA expression, Lönnerdal (36) found no signifi cant differences between the cells incubated with and without calcium for 1.5 or 4 hours.…”

“…Conversely, in a review on this subject, Lönnerdal (36) reported that there is a decrease in basolateral iron transport in Caco-2 cells incubated in the presence of 1 μM Fe (FeSO4) and 100 μM calcium chloride compared with cells cultured in the absence of calcium; the culture times were 1.5 and 4 hours (the Ca:Fe molar ratios were 0:1 and 100:1, respectively). Moreover, Gaitan et al (37) evaluated, the effect of calcium (in the form of calcium chloride) on the uptake, effl ux, and net absorption of a 2 μM iron solution (FeSO4) in Caco-2 cells; the calcium was administered at Ca:Fe molar ratios of 50:1 -1000:1. In this study, calcium did not affect the net absorption of iron; however, iron uptake by the cells was signifi cantly higher than uptake by the control group at molar ratios of 500:1 and 1000:1(ANOVA p<0.009), while the effl ux of iron decreased signifi cantly at a molar ratio of 1000:1 (ANOVA p<0.002).…”