The translation of lipid profiles to nutritional biomarkers in the study of infant metabolism

Introduction

Links between early life exposures and later health outcomes may, in part, be due to nutritional programming in infancy. This hypothesis is supported by observed long-term benefits associated with breastfeeding, such as better cognitive development in childhood, and lower risks of obesity and high blood pressure in later life. However, the possible underlying mechanisms are expected to be complex and may be difficult to disentangle due to the lack of understanding of the metabolic processes that differentiate breastfed infants compared to those receiving just formula feed.

Objective

Our aim was to investigate the relationships between infant feeding and the lipid profiles and to validate specific lipids in separate datasets so that a small set of lipids can be used as nutritional biomarkers.

Method

We utilized a direct infusion high-resolution mass spectrometry method to analyse the lipid profiles of 3.2 mm dried blood spot samples collected at age 3 months from the Cambridge Baby Growth Study (CBGS-1), which formed the discovery cohort. For validation two sample sets were profiled: Cambridge Baby Growth Study (CBGS-2) and Pregnancy Outcome Prediction Study (POPS). Lipidomic profiles were compared between infant groups who were either exclusively breastfed, exclusively formula-fed or mixed-fed at various levels. Data analysis included supervised Random Forest method with combined classification and regression mode. Selection of lipids was based on an iterative backward elimination procedure without compromising the class error in the classification mode.

Conclusion

From this study, we were able to identify and validate three lipids: PC(35:2), SM(36:2) and SM(39:1) that can be used collectively as biomarkers for infant nutrition during early development. These biomarkers can be used to determine whether young infants (3–6 months) are breast-fed or receive formula milk.

     

The use of mutants and transgenic plants to study amino acid metabolism

Mutants of higher plants with alterations in amino acid metabolism have now been available for 20 years. Following the realization that at least four distinct classes of herbicides (phosphinothricins, glyphosates, imidazolinones and sulphonylureas) act by the inhibition of amino acid biosynthesis, mutants resistant to the herbicides have also been obtained. More recently, transgenic plants containing altered levels of enzymes of amino acid biosynthesis have been constructed. In this article, we have attempted to review several areas of amino acid biosynthesis including ammonia assimilation, the aspartate pathway, branched chain amino acids, aromatic amino acids and proline.     

Luminescence in the study of lipid metabolism

Using bioluminescence assays for glycerol, free fatty acids, β-hydroxybutyrate and lactate, we were able to perform complex studies of human energy and lipid metabolism both in serum samples in vivo and in isolated fat cells in vitro. These studies would have been impossible without reliable, specific and highly sensitive luminescence methods. Oxidatively modified low density lipoprotein (LDL) has been implicated in the pathogenesis of atherosclerosis. Adaptation of a chemiluminescence assay for lipid hydroperoxides to LDL isolated by specific precipitation from serum makes it possible to measure LDL oxidation in vivo. Cell dependent chemiluminescence was used to investigate whether receptor mediated endocytosis of LDL by macrophages leads to oxygen radical production in these cells. No activation of the membrane NAD(P)H oxidase was observed.     

The use of computers in molecular biology studies

The paper contains a brief review of the studies involving application of computers, carried out at the Institute of Molecular Biology (investigation of the structure and dynamics of nucleic acids; modelling of the DNA-ligand interactions; analysis of the spectral data of different types: electron paramagnetic resonance, magnetic circular dichroism, absorption and fluorescence spectra; analysis of the thin-layer samples labelled by radioactive elements; chromosome analysis).     

Use of plant cell cultures to study graminicide effects on lipid metabolism

Graminicides belonging to the cyclohexanedione and aryloxyphenoxypropionate classes are well established to act by disrupting acyl lipid biosynthesis via specific inhibition of acetyl-CoA carboxylase. Species of grass inherently resistant to such herbicides, or biotypes of grassy weed species which display acquired resistance to recommended rates of graminicide application, are known to possess an altered plastidic multifunctional acetyl-CoA carboxylase showing reduced sensitivity to these herbicides in vitro. Studies reported here demonstrate that cell suspension cultures of maize, a graminicide-sensitive species and Poa annua, a graminicide-insensitive species, display a similar differential sensitivity of acyl lipid biosynthesis as tissue from corresponding intact plants. Acyl lipid biosynthesis in P. annua can be inhibited if sufficiently high concentrations of graminicide are used. The major plastidic form and the minor cytosolic forms of acetyl-CoA carboxylase were successfully purified from maize cell suspensions, were compared to those from leaf tissue and were shown to be differentially inhibited by graminicides in a similar manner to their counterparts from leaf tissue. These studies demonstrate that cell suspensions are useful for studying the mode of action of graminicides, especially in view of the limited amount of material obtainable from many grassy species which are very fine-growing.     

The chemical biology of branched-chain lipid metabolism

Mammalian metabolism of some lipids including 3-methyl and 2-methyl branched-chain fatty acids occurs within peroxisomes. Such lipids, including phytanic and pristanic acids, are commonly found within the human diet and may be derived from chlorophyll in plant extracts. Due to the presence of a methyl group at its beta-carbon, the well-characterised beta-oxidation pathway cannot degrade phytanic acid. Instead its alpha-methylene group is oxidatively excised to give pristanic acid, which can be metabolised by the beta-oxidation pathway. Many defects in the alpha-oxidation pathway result in an accumulation of phytanic acid, leading to neurological distress, deterioration of vision, deafness, loss of coordination and eventual death. Details of the alpha-oxidation pathway have only recently been elucidated, and considerable progress has been made in understanding the detailed enzymology of one of the oxidative steps within this pathway. This review summarises these recent advances and considers the roles and likely mechanisms of the enzymes within the alpha-oxidation pathway.     

Perfused heart studies to investigate lipid metabolism

The isolated perfused heart preparation is an invaluable model for investigating metabolism in a variety of physiological and pathological states. It avoids confounding systemic factors (e.g. endocrine, metabolic and work load changes) and permits simultaneous measurement of mechanical function. The ability to measure arteriovenous concentration differences across the myocardium and the coronary flow rate, together with the use of radiolabelled substrates, permits assessment of substrate assimilation and disposition of most potential energetic substrates. In the case of lipids, metabolism of non-esterified fatty acids has been extensively investigated in the perfused rat heart, but fatty acids may also be derived from circulating triacylglycerols (TAG) in lipoproteins [chylomicrons, very-low-density-lipoprotein (VLDL)]. TAG requires initial hydrolysis by the endothelial enzyme lipoprotein lipase and hence an intact heart preparation is vital to maintain tissue structural integrity. Chylomicron-TAG utilization and fate (oxidation, tissue-lipid deposition) in isolated working hearts has been studied using chylomicrons obtained from thoracic-duct catheters. However, lack of availability of sufficient quantities of VLDL has hindered examination of their cardiac utilization; the recent development of a technique to produce large quantities of radio-labelled rat VLDL has facilitated these studies and established that VLDL-TAG is an important metabolic substrate for working heart. Results relating to myocardial utilization of VLDL-TAG under varying physiological (lactation) and pathological (endotoxinaemia) conditions will be presented. The putative role of VLDL as a regulator of cardiac lipid metabolism will also be discussed.     

The use of telemetry to study light synchronization with feeding and gill ventilation rates in Salmo trutta

A technique is described whereby the electromyogram of the m. adductor mandibulae of brown trout is detected by implanted extracellular electrodes and used as the input signal for an ultrasonic transmitter attached externally to the fish. The periodic electrical activity of the muscle during ventilation is relayed by the transmitter using an analogue pulse system.
As the ventilatory electromyogram occurs in discrete rhythmic trains, it follows that alterations to this rhythm can be used to telemeter, instantaneously, single feeding events from a free swimming fish. Laboratory tests have shown that the feeding act is unequivocally distinct electromyographically from other manoeuvres such as 'coughing'.
Four adult brown trout have been equipped with this transmitter system and released in Airthrey Loch, Stirling. Using a tracking facility, feeding activity and ventilatory rhythms have been recorded for extended periods.
The results indicate the presence of three daily peaks of feeding activity, which is discussed in relation to changes in light levels. The telemetry records indicate that night feeding is a common occurrence in brown trout. In addition, ventilatory rates were found to be at or near resting levels.     

The integral role of mTOR in lipid metabolism

Comment on: Soliman GA, et al. Lipids 2010; 45:1089-100.     

The human hepatocyte cell lines IHH and HepaRG: models to study glucose, lipid and lipoprotein metabolism

Metabolic diseases reach epidemic proportions. A better knowledge of the associated alterations in the metabolic pathways in the liver is necessary. These studies need in vitro human cell models. Several human hepatoma models are used, but the response of many metabolic pathways to physiological stimuli is often lost. Here, we characterize two human hepatocyte cell lines, IHH and HepaRG, by analysing the expression and regulation of genes involved in glucose and lipid metabolism. Our results show that the glycolysis pathway is activated by glucose and insulin in both lines. Gluconeogenesis gene expression is induced by forskolin in IHH cells and inhibited by insulin in both cell lines. The lipogenic pathway is regulated by insulin in IHH cells. Finally, both cell lines secrete apolipoprotein B-containing lipoproteins, an effect promoted by increasing glucose concentrations. These two human cell lines are thus interesting models to study the regulation of glucose and lipid metabolism.     

The flexibility of Apicomplexa parasites in lipid metabolism

Apicomplexa are obligate intracellular parasites responsible for major human infectious diseases such as toxoplasmosis and malaria, which pose social and economic burdens around the world. To survive and propagate, these parasites need to acquire a significant number of essential biomolecules from their hosts. Among these biomolecules, lipids are a key metabolite required for parasite membrane biogenesis, signaling events, and energy storage. Parasites can either scavenge lipids from their host or synthesize them de novo in a relict plastid, the apicoplast. During their complex life cycle (sexual/asexual/dormant), Apicomplexa infect a large variety of cells and their metabolic flexibility allows them to adapt to different host environments such as low/high fat content or low/high sugar levels. In this review, we discuss the role of lipids in Apicomplexa parasites and summarize recent findings on the metabolic mechanisms in host nutrient adaptation.     

The role of the kidney in lipid metabolism

PURPOSE OF REVIEW: Cellular uptake of plasma lipids is to a large extent mediated by specific membrane-associated proteins that recognize lipid-protein complexes. In the kidney, the apical surface of proximal tubules has a high capacity for receptor-mediated uptake of filtered lipid-binding plasma proteins. We describe the renal receptor system and its role in lipid metabolism in health and disease, and discuss the general effect of the diseased kidney on lipid metabolism. RECENT FINDINGS: Megalin and cubilin are receptors in the proximal tubules. An accumulating number of lipid-binding and regulating proteins (e.g. albumin, apolipoprotein A-I and leptin) have been identified as ligands, suggesting that their receptors may directly take up lipids in the proximal tubules and indirectly affect plasma and tissue lipid metabolism. Recently, the amnionless protein was shown to be essential for the membrane association and trafficking of cubilin. SUMMARY: The kidney has a high capacity for uptake of lipid-binding proteins and lipid-regulating hormones via the megalin and cubilin/amnionless protein receptors. Although the glomerular filtration barrier prevents access of the large lipoprotein particles to the proximal tubules, the receptors may be exposed to lipids bound to filtered lipid-binding proteins not associated to lipoprotein particles. Renal filtration and receptor-mediated uptake of lipid-binding and lipid-regulating proteins may therefore influence overall lipid metabolism. The pathological mechanisms causing the pronounced atherosclerosis-promoting effect of uremia may involve impairment of this clearance pathway.     

The versatility of algae and their lipid metabolism

Eukaryotic algae are a very diverse group of organisms that are key components of ecosystems ranging from deserts to the Antarctic. They account for over half of the primary production at the base of food chains. The lipids of different classes are varied and contain unusual compounds not found in other phyla. In this short review, we introduce the major cellular lipids and their fatty acids and then describe how the latter (particularly the polyunsaturated fatty acids, PUFAs) are synthesised. The discovery of different elongases and desaturases important for PUFA production is detailed and their application for biotechnology described. Finally, the potential for algae in commercial applications is discussed, particularly in relation to the production of very long chain PUFAs and biofuel.