Mechanisms of heme iron absorption: Current questions and controversies

Abstract

THE IMPORTANCE OF DIETARY IRON AND HEMEIron is a vitally important element in biological terms (for review see [1] ). Iron is a transition metal with the ability to readily accept and donate electrons, allowing it to function as an oxidant or reductant in a large number of biochemical reactions. In mammals, iron is notably required for oxygen transport as a component of hemoglobin, DNA synthesis as a component of ribonucleotide reductase, and as an electron acceptor/ donor in the cytochromes that are essential for energy transduction. Currently, iron deficiency is the most common diet related health problem in the world [2] , and the effects on human health are wide ranging. Iron deficiency manifests as anaemia in up to 2 billion people, impairs physical and mental development in children, and can exacerbate many other health problems.Heme is a biologically important iron containing compound and a key source of dietary iron. Historically, it was doubted that heme iron could be absorbed by the enterocyte and it was not until 1955 that the absorption of heme-derived iron was demonstrated for the first time [3] . Currently, the importance of heme iron in the diet cannot be underestimated. Studies estimate that in Western societies, iron derived from heme sources such as myoglobin and hemoglobin make up twothirds of the average person's total iron stores despite only constituting one-third of the iron that is actually ingested [4][5][6] . This likely explains why vegetarians are more prone to iron deficiency than those who regularly consume red meat [7] . T h e r e l a t ive i m p o r t a n c e o f d i e t a r y h e m e i s attributable to its high bioavailability compared with AbstractIron is a critical micronutrient, and iron derived from heme contributes a large proportion of the total iron absorbed in a typical Western diet. Heme iron is absorbed by different mechanisms than non-heme iron, but despite considerable study over many years these mechanisms remain poorly understood. This review provides an overview of the importance of heme iron in the diet and discusses the two prevailing hypotheses of heme absorption; namely receptor mediated endocytosis of heme, and direct transport into the intestinal enterocyte by recently discovered heme transporters. A specific emphasis is placed on the questions surrounding the site of heme catabolism and the identity of the enzyme that performs this task. Additionally, we present the hypothesis that a nonheme iron transport protein may be required for heme iron absorption and discuss the experiences of our laboratory in examining this hypothesis.

Genetic parameters for concentrations of minerals in longissimus muscle and their associations with palatability traits in Angus cattle1

“…In this context, a 100 g serving of beef would provide between 8% and 18% of the recommended daily allowance. The amount of iron absorbed compared with the amount ingested is typically low, and the source of iron is an important factor determining the effi ciency of absorption (Kapsokefalou and Miller, 1993;Andrews, 2005;West and Oates, 2008;Han, 2011). Iron in animal and some plant products is mostly in the form of heme iron, which is more effi ciently absorbed.…”

Proteínas relacionadas con el metabolismo del hierro corporal

“…La hemo oxigenasa (HO): existen dos isoformas la HO1 con 288 aa (21), cuya expresión se induce por situaciones de trauma, hemorragia, estrés o por aumento de la concentración de hierro hemo; se ubica en el interior de la células y su principal función es protegerlas del estrés oxidativo por medio de la degradación limitada del hierro hemo (20); en tanto que la HO2 con 316 aa (22), es una proteína de expresión constante y por aná-lisis in vitro, con microscopía confocal, parece ubicarse de manera exclusiva en la región subapical de las células, donde es colocalizada con endosomas (23). Ambas isoformas catalizan la misma reacción con el hierro hemo, así en la absorción de esta forma de hierro, la HO se encarga de continuar con el proceso de absorción que inició la proteína HCP1; una vez en el enterocito, el hierro hemo ingresa en una vesícula citoplasmática, donde la HO hidroliza el hierro hemo dejando hierro ferroso y protoporfirina (18,20).…”

Advantages and disadvantages of the animal models v. in vitro studies in iron metabolism: a review

“…The mechanism and control of iron uptake by the gut has puzzled investigators in both in vivo and in vitro studies (LatundeDada et al, 1998;Morgan and Oates, 2002;Latunde-Dada, 2009). Studies about the effect of iron are focused mainly in two ways; basic studies to elucidate iron metabolism, and nutritional studies to evaluate the efficacy of iron supplementation to prevent or treat iron deficiency and anemia (Lynch and Stoltzfus, 2003;Nadadur et al, 2008;Theurl et al, 2008;West and Oates, 2008;Lö nnerdal, 2009). There are many studies available in the scientific literature about iron absorption and regulation.…”