Abstract
Zinc absorption in the small intestine is one of the main mechanisms regulating the systemic homeostasis of this essential trace element. This review summarizes the key aspects of human zinc homeostasis and distribution. In particular, current knowledge on human intestinal zinc absorption and the influence of diet-derived factors on bioaccessibility and bioavailability as well as intrinsic luminal and basolateral factors with an impact on zinc uptake are discussed. Their investigation is increasingly performed using in vitro cellular intestinal models, which are continually being refined and keep gaining importance for studying zinc uptake and transport via the human intestinal epithelium. The vast majority of these models is based on the human intestinal cell line Caco-2 in combination with other relevant components of the intestinal epithelium, such as mucin-secreting goblet cells and in vitro digestion models, and applying improved compositions of apical and basolateral media to mimic the in vivo situation as closely as possible. Particular emphasis is placed on summarizing previous applications as well as key results of these models, comparing their results to data obtained in humans, and discussing their advantages and limitations.
Highlights
The essential trace element zinc plays a key role for several important biological processes in the human body [1]
Human body zinc homeostasis is predominantly regulated by its intestinal absorption [3]
This review aims to provide an overview of the current knowledge on human intestinal zinc absorption, including the major cellular processes and nutritional aspects
Summary
The essential trace element zinc plays a key role for several important biological processes in the human body [1]. Human body zinc homeostasis is predominantly regulated by its intestinal absorption [3] In this process, zinc transporters on the apical and basolateral membrane of enterocytes are engaged and regulate cellular and body zinc homeostasis together with the cellular zinc-binding protein metallothionein [4,5]. Zinc transporters on the apical and basolateral membrane of enterocytes are engaged and regulate cellular and body zinc homeostasis together with the cellular zinc-binding protein metallothionein [4,5] Despite this knowledge and ongoing research, a deeper understanding of the molecular processes regulating zinc absorption via the intestinal epithelium is still scarce. This is mainly due to high costs and ethical standards of animal studies and the benefits of in vitro models providing a microenvironment that advances studies of cellular processes on a molecular level [9,10]
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