Purified Glycosaminoglycans from Cooked Haddock May Enhance Fe Uptake Via Endocytosis in a Caco-2 Cell Culture Model

This study aims to understand the enhancing effect of glycosaminoglycans (GAGs), such as chondroitin/dermatan structures, on Fe uptake to Caco-2 cells. High-sulfated GAGs were selectively purified from cooked haddock. An in vitro digestion/Caco-2 cell culture model was used to evaluate Fe uptake (cell ferritin formation) from a Fe+3-containing solution, and Fe+3/ascorbic acid (AA) and Fe+3/GAGs mixtures. Mitochondria (MTT test) and endosomal/lysosomal activities (neutral red uptake, NR), intracellular accumulation of reactive oxygen species, and GSH concentration were monitored as biomarkers of the changes of cellular metabolism. Changes in mRNA expression of Fe transporters, divalent metal transporter-1 (DMT1), and duodenal cytochrome-b (DcytB) were also evaluated. The Fe uptake from Fe+3/GAGs mixture was up to 1.8-fold higher than from Fe+3 alone. Both Fe+3 alone and Fe+3/AA mixture produced highest increase in MTT conversion. In contrast, cell cultures exposed to the Fe+3/GAGs mixture exhibited highest NR uptake values. All Fe-containing solutions tested caused a sharp in-tramitochondrial accumulation of reactive oxygen species. Cell cultures exposed to the Fe+3/GAGs mixture exhibited a more preserved (by 8%) intracellular GSH concentration compared to cultures exposed to Fe+3 or Fe+3/AA mixture. In addition to cell responses, the mRNA expression of Fe transporters may suggest that Fe could also be internalized into cells by endocytosis in addition to via DMT1 in Fe+3/GAGs mixtures. These aspects need to be confirmed in in vivo experiments to better establish nutritional interventional strategies.