Lipidome analysis of milk composition in humans, monkeys, bovids, and pigs

Abstract

Background: Lipids contained in milk are an essential source of energy and structural materials for a growing neonate. Furthermore, lipids' long-chain unsaturated fatty acid residues can directly participate in neonatal tissue formation. Here, we used untargeted mass spectrometric measurements to assess milk lipid composition in seven mammalian species: humans, two macaque species, cows, goats, yaks, and pigs.

Results: Analysis of the main milk lipid class, triacylglycerides (TAGs), revealed species-specific quantitative differences in the composition of fatty acid residues for each of seven species. Overall, differences in milk lipid composition reflect evolutionary distances among species, with each species group demonstrating specific lipidome features. Among them, human milk contained more medium and long-chain unsaturated fatty acids compared to other species, while pig milk was the most distinct, featuring the highest proportion of long-chain polyunsaturated fatty acids.

Conclusions: We show that milk lipidome composition is dynamic across mammalian species, changed extensively in pigs, and contains features particular to humans.

Keywords: Evolution; Fatty acids; Human; Lipidome; Milk.

Fig. 1

Milk lipidome evolution. a Dendrogram showing the phylogenetic relationship among seven mammalian species used in the study. Colored dots indicate species, with colors used consistently throughout figures. Colored frames indicate three groups: primate (red), artiodactyla (blue), and bovidae (green). b The relationship among milk samples based on the signal intensities of 472 detected lipid features plotted in two dimensions using a multidimensional scaling algorithm. Colors represent species. Small dots represent individual milk samples. Large dots represent pools of samples from one species. c The relationship between lipid-intensity-based distances between species pairs and phylogenetic distances

Fig. 2

Patterns of lipid composition differences among species. a Unsupervised hierarchical clustering dendrogram and heatmap based on pairwise correlation-based distances between lipid intensity vectors. Color bar indicates four major lipid clusters: cluster 1 – yellow, cluster 2 – pink, cluster 3 – brown, cluster 4 – gray. b Distribution of centered lipid intensities in each cluster. Each box represents the interquartile distribution of lipid intensities in a sample. The number of lipids contained in a cluster is shown at the top of the panels. Samples colored and ordered by species. c Mass spectrometry output showing 76 computationally annotated TAGs colored by clusters. The x-axis shows the compounds’ mass-by-charge ratio (m/z). The y-axis shows retention time (RT) of the compound on the liquid chromatography preceding mass spectrometry

Fig. 3

Milk TAG repertoire in each species. a Distribution of milk TAGs in each species and two human populations. The x-axis represents the total chain length of three TAG fatty acid residues. The y-axis represents the number of double bonds in TAG fatty acid residues. The size of the circles represents TAG intensity calculated as the mean intensity of the TAG in a species divided by the sum of the mean intensities of all TAGs in this species. Colors represent the number of double bonds with a gradient from orange – zero double bonds to purple – seven double bonds. b Cumulative distribution of species-specific TAGs features. The axes as in panel A. Size of the circles represents the maximum intensity of a TAG across species. Colors indicate species with the maximum intensity of a TAG

Fig. 4

Comparison of milk TAG profiles between humans and other species. a Left: Distribution of centered intensities of 94 lipids showing differences between humans and two macaque species separated into two clusters. Each box represents the interquartile distribution of lipid intensities in a sample. The number of lipids contained in a cluster is shown at the top of the panels. Samples colored and ordered by species. Right: Mass spectrometry output with 76 computationally annotated TAGs showing the difference between humans and two macaque species colored by clusters. b As panel A, for 76 lipids showing intensity differences between humans and three bovidae species. c As panel A, for 76 lipids showing intensity differences between humans and pigs