Iron and a mixture of DHA and EPA supplementation, alone and in combination, affect bioactive lipid signalling and morbidity of iron deficient South African school children in a two-by-two randomised controlled trial

Abstract

We recently reported that iron supplementation increased respiratory morbidity in iron deficient South African children. This increase, however, was attenuated when iron was provided in combination with a mixture of DHA/EPA. To explore potential underlying mechanisms, we examined the effects of iron and DHA/EPA, alone and in combination, on plasma lipid-derived immune modulator concentrations and related gene expression in peripheral blood mononuclear cells (PBMC). DHA/EPA decreased inflammatory 12-hydroxyeicosatetraenoic acid and tended to increase anti-inflammatory and pro-resolving 17-hydroxydocosahexaenoic acid (17-HDHA), while iron decreased 17-HDHA. However, in combination with iron, the anti-inflammatory effect of DHA/EPA was maintained. These biochemical changes may explain the prevention of iron-induced respiratory morbidity that we observed when iron was supplemented in combination with DHA/EPA during the 8.5 month randomised controlled trial and might lead to a safer approach of delivering iron supplementation. The study was registered at clinicaltrials.gov as NCT01092377.

Introduction

Both iron and long-chain polyunsaturated fatty acids (LCPUFA) affect immune function [1], [2]. They act through multiple mechanisms to influence immune cell responses [1], [2], [3], [4]. N-6 and n-3 LCPUFA are the precursors of inflammatory and anti-inflammatory (pro-resolving) immune modulators, respectively. This appears to be a key mechanism by which LCPUFA affect immune responses and inflammatory processes [2], [5]. On the other hand, iron deficiency (ID) mostly impairs cell-mediated immunity [1], [3], by being structurally part of enzymes or involved in enzyme activation needed for cellular immune responses, such as myeloperoxidase [6] and phospholipase C [7]. As such, ID can increase susceptibility to infections, which might be overcome by iron supplementation [8]. In turn, it is known that iron supplementation can favour the growth of certain microorganisms [9] and this could be harmful in some settings [10]. We found, in a 8.5 mo randomised controlled trial (RCT), that supplementation of 50 mg iron per day increased respiratory morbidity in 6–11-y-old rural ID South African children. However, the combination of iron supplementation with 420 mg DHA and 80 mg EPA per day prevented this increase in respiratory morbidity [11]. This suggests a biologically important interaction between iron and n-3 LCPUFA.

There may be positive and negative interactions between iron and LCPUFA of relevance to immune function. The most obvious of these is that iron is a co-factor for the desaturase enzymes involved in LCPUFA synthesis [12], as well as of the catalytic sites of the cyclooxygenase (COX) and lipoxygenase (LOX) enzymes, which are involved in the production of lipid-derived immune modulators [13], [14]. Thus, ID may impair both LCPUFA synthesis and synthesis of modulatory lipid mediators. On the other hand, membrane n-3 LCPUFA composition influences membrane order (“fluidity”) and may affect cellular uptake of iron and the handling of intracellular iron [15], [16], [17]. Thus, n-3 LCPUFA deficiency may limit availablity of iron to immune cells. Through these interactions iron and n-3 LCPUFA may influence one another׳s effects and combined deficiency may have additive effects on functional outcomes, as was described recently for cognitive and infectious morbidity outcomes [11], [18], [19], [20].

This is a secondary study in children who were enroled in the randomized, placebo-controlled trial of iron and n-3 LCPUFA supplementation, alone and in combination, showing that iron supplementation increased respiratory infectious morbidity, whereas the supplementation of DHA and EPA in combination with iron prevented this increase [11]. The aim of this secondary study was therefore to examine the underlying biochemical effects of iron and a mixture of the two bioactive n-3 LCPUFA, DHA and EPA, alone and in combination, on plasma lipid-derived immune mediator concentrations and expression of genes involved in their synthesis, as well as on antioxidative and iron regulatory gene expression in peripheral blood mononuclear cells (PBMC).