A Comparison of Marine and Non-Marine Magnesium Sources for Bioavailability and Modulation of TRPM6/TRPM7 Gene Expression in a Caco-2 Epithelial Cell Model

Background/Objectives: Magnesium (Mg2+) supplements can contain different types of Mg2+ salts, which influence their bioavailability. A highly bioavailable and bioaccessible Mg2+ source is essential to meet requirements for many physiological processes that are fundamental to human health. The objective of this study was to compare the bioavailability of Mg2+ from different sources, with different composition and chemical structure, namely, Aquamin Mg Soluble (seawater), magnesium oxide, commercial magnesium bisglycinate 1, and analytical grade magnesium bisglycinate 2. In addition, the influence of the different Mg2+ sources on transported Mg2+ and expression of TRPM6 and TRPM7 genes in Caco-2 cell monolayers was also evaluated to estimate bioavailability. TRPM6 and TRPM7 are members of the transient receptor potential melastatin subfamily characterized as Mg2+ permeable channels. Method: The study involved analyzing bioavailability of the Mg2+ sources predigested with and without food using the Infogest model prior to application to a Caco-2 cell monolayer in transwells for assessing transport. Mg2+ concentration on the basolateral side was analyzed by ICP-MS, and expression of TRPM6 and TRPM7 genes in the monolayer was analyzed using real-time qPCR. Results: Aquamin Mg Soluble showed significantly higher bioavailability compared to magnesium bisglycinate 2 (p = 0.016) when digested with food prior to application to the Caco-2 monolayer. In the digestion without food prior to the Caco-2 monolayer, there was no significant difference between Mg2+ bioavailability among the tested supplements. The TRPM6 gene was significantly downregulated in Caco-2 monolayers exposed to Aquamin Mg Soluble compared to untreated Caco-2 cells (p < 0.001). Conclusions: The INFOGEST digestion model showed that Aquamin Mg Soluble provides a highly bioavailable form of Mg2+, while the Caco-2 monolayer model also demonstrated its increased bioavailability by the modulation of TRPM6 gene expression.