Pea Ferritin Stability under Gastric pH Conditions Determines the Mechanism of Iron Uptake in Caco-2 Cells

Antonio Perfecto,Ildefonso Rodriguez-Ramiro,Jorge Rodriguez-Celma,Paul Sharp,Janneke Balk,Susan Fairweather-Tait

doi:10.1093/jn/nxy096

Antonio Perfecto, Ildefonso Rodriguez-Ramiro + Show 4 more

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https://doi.org/10.1093/jn/nxy096

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Abstract

BackgroundIron deficiency is an enduring global health problem that requires new remedial approaches. Iron absorption from soybean-derived ferritin, an ∼550-kDa iron storage protein, is comparable to bioavailable ferrous sulfate (FeSO4). However, the absorption of ferritin is reported to involve an endocytic mechanism, independent of divalent metal ion transporter 1 (DMT-1), the transporter for nonheme iron.ObjectiveOur overall aim was to examine the potential of purified ferritin from peas (Pisum sativum) as a food supplement by measuring its stability under gastric pH treatment and the mechanisms of iron uptake into Caco-2 cells.MethodsCaco-2 cells were treated with native or gastric pH–treated pea ferritin in combination with dietary modulators of nonheme iron uptake, small interfering RNA targeting DMT-1, or chemical inhibitors of endocytosis. Cellular ferritin formation, a surrogate measure of iron uptake, and internalization of pea ferritin with the use of specific antibodies were measured. The production of reactive oxygen species (ROS) in response to equimolar concentrations of native pea ferritin and FeSO4 was also compared.ResultsPea ferritin exposed to gastric pH treatment was degraded, and the released iron was transported into Caco-2 cells by DMT-1. Inhibitors of DMT-1 and nonheme iron absorption reduced iron uptake by 26–40%. Conversely, in the absence of gastric pH treatment, the iron uptake of native pea ferritin was unaffected by inhibitors of nonheme iron absorption, and the protein was observed to be internalized in Caco-2 cells. Chlorpromazine (clathrin-mediated endocytosis inhibitor) reduced the native pea ferritin content within cells by ∼30%, which confirmed that the native pea ferritin was transported into cells via a clathrin-mediated endocytic pathway. In addition, 60% less ROS production resulted from native pea ferritin in comparison to FeSO4.ConclusionWith consideration that nonheme dietary inhibitors display no effect on iron uptake and the low oxidative potential relative to FeSO4, intact pea ferritin appears to be a promising iron supplement.

Highlights

Iron deficiency is the most prevalent nutritional deficiency in the world, affecting 1–2 billion people worldwide [1, 2]
Pea ferritin exposed to gastric pH treatment was degraded, and the released iron was transported into Caco2 cells by divalent metal ion transporter 1 (DMT-1)
In the absence of gastric pH treatment, the iron uptake of native pea ferritin was unaffected by inhibitors of nonheme iron absorption, and the protein was observed to be internalized in Caco-2 cells

Summary

Introduction

Iron deficiency is the most prevalent nutritional deficiency in the world, affecting 1–2 billion people worldwide [1, 2]. The ratio of these 2 protein subunits is plant species dependent [8, 11] This may explain the variation in total iron bound to plant ferritin, which has been reported to vary considerably between different legumes, ranging from 18% in soybeans to 42% in dry peas [12]. Methods: Caco-2 cells were treated with native or gastric pH–treated pea ferritin in combination with dietary modulators of nonheme iron uptake, small interfering RNA targeting DMT-1, or chemical inhibitors of endocytosis. In the absence of gastric pH treatment, the iron uptake of native pea ferritin was unaffected by inhibitors of nonheme iron absorption, and the protein was observed to be internalized in Caco-2 cells. Conclusion: With consideration that nonheme dietary inhibitors display no effect on iron uptake and the low oxidative potential relative to FeSO4, intact pea ferritin appears to be a promising iron supplement.

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