Balancing efficacy and safety: Inorganic and organic Fe-Ca Co-interventions reduce oral Cd bioavailability from rice and their impacts on gut health.

Dietary iron (Fe) and calcium (Ca) intervention can reduce rice cadmium (Cd) bioavailability, however, the efficacy of various Fe-Ca combinations and impacts on gut health remain poorly understood. By exposing mice to Cd-containing rice alongside with Fe (100 mg Fe L⁻1 in drinking water) and Ca supplementation (4000 mg Ca kg-1 in diet), we investigated the effects of different forms of Fe-Ca co-intervention on Cd bioavailability, nutrition status, gut microbiota, and gut health. Results showed that Fe-Ca co-intervention reduced mouse liver and kidney Cd concentrations synergistically due to downregulation of both Fe and Ca intestinal transporters, with ferrous gluconate combined with Ca gluconate (Fe-Glu+Ca-Glu) being most efficient. Fe-Ca combination also avoided the nutritional imbalance effects of Fe and Ca alone. However, gut microbiota and gut health analyses, including 16S rRNA sequencing, mRNA expression of intestinal tight junctions and pro-inflammatory cytokines, and ileal tissue section staining, demonstrated that Fe-Glu+Ca-Glu remarkably decreased relative abundance of beneficial bacteria in the gut, damaged intestinal morphology, enhanced intestinal permeability, and elevated intestinal inflammatory responses. Assessment effects of gluconic acid intake in mice confirmed the gut health side effects of Fe-Glu+Ca-Glu were caused by high intake of gluconate ligand. In comparison, the combination of ferrous sulfate (FeSO4) with Ca hydrogen phosphate (CaHPO4) demonstrated limited effects on gut microbiota and gut health while being efficient in reducing rice Cd bioavailability. Collectively, our findings identify inorganic rather than organic Fe-Ca combinations may be safe, efficient, and gut-friendly strategy to address dietary Cd exposure risk and nutrient deficiency.