Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2008
Publication Date: 11/13/2008
Citation: Laparra, J.M., Tako, E., Glahn, R.P., Miller, D. 2008. Isolated Glycosaminoglycans from Cooked Haddock Enhance Nonheme Iron Uptake by Caco-2 cells. Journal of Agricultural and Food Chemistry. 56(21):10346-10351.
Interpretive Summary: An in vitro model has been developed in our laboratory to evaluate iron bioavailability from foods. This model has demonstrated strong correlations with human studies in predicting the intestinal response of enhancers of iron absorption. Previous studies demonstrated that consumption of animal muscle tissues enhance non heme iron absorption, however, no specific compound has been isolated that clearly enhance iron absorption. Some of our previous studies suggested that specific glycosaminoglycans (GAGs) may enhance iron absorption from non heme iron foods as part of the so called “meat factor”. Proteoglycans are one of the major components of the extracellular matrix in connective tissues. In this study, by using a selective extraction procedure GAGs were purified from cooked haddock. The nature and identity of specific chemical structures present in the obtained fractions was evaluated. Once confirmed the presence and identity of specific GAGs, the isolated compounds were tested in our model and their positive effect on enhancing non heme iron uptake was confirmed. This study could be the basis for further experiments to optimize the isolation of GAGs, which could be used as specific dietary supplements in preventing iron deficiency.
Technical Abstract: This study presents new evidence and continues previous research to confirm that glycosaminoglycans (GAGs) exert a positive effect on promoting iron uptake by Caco-2 cells. After being cooked and lyophilized, fish muscle tissue was digested with papain, a cysteine protease that cleaves peptide bonds of basic amino acids, leucine, or glycine. Then, GAGs were further purified based on low and high sulfur content. Enzymatic digestion with chondroitinase ABC (50 mU/mg, 1h, 37ºC) and reverse phase chromatography (RP-HPLC) were used to identify the GAGs structures. Nonheme Fe was then mixed with aliquots of high-sulfur isolated fractions and iron uptake was measured by ferritin formation using an in vitro digestion/Caco-2 cell model. RP-HPLC analyses showed that chondroitin/dermatan sulfate-related structures were present in the active fractions isolated. The high-sulfur fraction increased ferritin formation up to 185% relative to the independent addition of nonheme iron and 60% with respect to uptake values obtained when non-heme iron was mixed with cooked fish. Treatment of the high-sulfur isolated fraction with chondroitinase ABC eliminated the enhancing effect on iron uptake. These results, in conjunction with RP-HPLC analysis, indicate that specific GAGs contribute to the enhancing effect on iron uptake by Caco-2 cells. These results indicate that the GAGs may contribute to the “meat factor” effect on Fe absorption. Further in vivo studies addressing this aspect of the meat factor are needed.