Alkaline phosphatase in the lactating bovine mammary gland and the milk fat globule membrane. Release by phosphatidylinositol-specific phospholipase C

Milk Fat Globule Membrane Proteome and Micronutrients in the Milk Lipid Fraction: Insights into Milk Bioactive Compounds

Milk lipids are composed of milk fat globules (MFGs) surrounded by the milk fat globule membrane (MFGM). MFGM protects MFGs from coalescence and enzymatic degradation. The milk lipid fraction is a “natural solvent” for macronutrients such as phospholipids, proteins and cholesterol, and micronutrients such as minerals and vitamins. The research focused largely on the polar lipids of MFGM, given their wide bioactive properties. In this review we discussed (i) the composition of MFGM proteome and its variations among species and phases of lactation and (ii) the micronutrient content of human and cow’s milk lipid fraction. The major MFGM proteins are shared among species, but the molecular function and protein expression of MFGM proteins vary among species and phases of lactation. The main minerals in the milk lipid fraction are iron, zinc, copper and calcium, whereas the major vitamins are vitamin A, β-carotene, riboflavin and α-tocopherol. The update and the combination of this knowledge could lead to the exploitation of the MFGM proteome and the milk lipid fraction at nutritional, biological or technological levels. An example is the design of innovative and value-added products, such as MFGM-supplemented infant formulas.

Milk fat: opportunities, challenges and innovation

Milk fat is a high-value milk component that is processed mainly as butter, cheese, cream and whole milk powder. It is projected that approximately 35 million tonnes of milk fat will be produced globally by 2025. This surplus, enhances the need for diversification of milk fat products and the milk pool in general. Infant milk formula producers, for instance, have incorporated enzyme modified ("humanised") milk fat and fat globule phospholipids to better mimic human milk fat structures. Minor components like mono- and di-glycerides from milk fat are increasingly utilized as emulsifiers, replacing palm esters in premium-priced food products. This review examines the chemistry of milk fat and the technologies employed for its modification, fractionation and enrichment. Emerging processing technologies such as ultrasound, high pressure processing, supercritical fluid extraction and fractionation, can be employed to improve the nutritional and functional attributes of milk fat. The potential of recent developments in biological intervention, through dietary manipulation of milk fatty acid profiles in cattle also offers significant promise. Finally, this review provides evidence to help redress the imbalance in reported associations between milk fat consumption and human health, and elucidates the health benefits associated with consumption of milk fat and dairy products.

Compositional Dynamics of the Milk Fat Globule and Its Role in Infant Development

Human milk is uniquely optimized for the needs of the developing infant. Its composition is complex and dynamic, driven primarily by maternal genetics, and to a lesser extent by diet and environment. One important component that is gaining attention is the milk fat globule (MFG). The MFG is composed of a triglyceride-rich core surrounded by a tri-layer membrane, also known as the milk fat globule membrane (MFGM) that originates from mammary gland epithelia. The MFGM is enriched with glycerophospholipids, sphingolipids, cholesterol, and proteins, some of which are glycosylated, and are known to exert numerous biological roles. Mounting evidence suggests that the structure of the MFG and bioactive components of the MFGM may benefit the infant by aiding in the structural and functional maturation of the gut through the provision of essential nutrients and/or regulating various cellular events during infant growth and immune education. Further, antimicrobial peptides and surface carbohydrate moieties surrounding the MFG might have a pivotal role in shaping gut microbial populations, which in turn may promote protection against immune and inflammatory diseases early in life. This review seeks to: (1) understand the components of the MFG, as well as maternal factors including genetic and lifestyle factors that influence its characteristics; (2) examine the potential role of this milk component on the intestinal immune system; and (3) delineate the mechanistic roles of the MFG in infant intestinal maturation and establishment of the microbiota in the alimentary canal.

The role of alkaline phosphatase in intracellular lipid accumulation in the human hepatocarcinoma cell line, HepG2

Inhibition of tissue non-specific alkaline phosphatase (TNALP) decreases intracellular lipid accumulation in human preadipocytes and the murine preadipocyte cell line, 3T3-L1. Therefore, the current study was performed to determine if TNALP is required for intracellular lipid deposition in the human hepatocyte cell line, HepG2. Intracellular lipid accumulation, TNALP activity and peroxisome proliferator activated receptor (PPAR) γ gene expression were measured in HepG2 and 3T3-L1 cells in the presence and absence of the TNALP inhibitors levamisole and histidine. Sub-cellular TNALP activity was localized using cytochemical analysis. Both PPARγ gene expression and TNALP activity increased during intracellular lipid accumulation in HepG2 and 3T3-L1 cells. Inhibition of TNALP blocked intracellular lipid accumulation but did not alter expression of the PPARγ gene. In HepG2 cells, TNALP co-localized with adipophilin on the lipid droplet membrane. These data suggest a role for TNALP in lipid droplet formation, possibly downstream from PPARγ, within HepG2 and 3T3-L1 cells.

Milk lipoprotein membranes and their imperative enzymes

There are two main sources of lipoprotein membranes in milk: the relatively well-defined milk fat globule membrane (MFGM) that covers the milk fat globules, and the much less attended lipoprotein source, in the form of vesicles floating in the milk serum. We challenge the common view that the milk serum lipoprotein membrane (MSLM) is secondly derived from the MFGM and present a different view suggesting that it represents Golgi-derived vesicles that are released intact to milk. The potential role of enzymes attached to the MSLM and MFGM is considered in detail for select ubiquitously expressed enzymes.

FMRFamide-related peptides in the sex segmental ganglia of the Pharyngobdellid leech Erpobdella octoculata. Identification and involvement in the control of hydric balance

Using enzyme-linked immunosorbent assays, a dot-immunobinding assay and a three-step reverse-phase HPLC separation, four Arg-Phe-amide (RFamide) peptides were purified from sex segmental ganglia extracts of the leech Erpobdella octoculata; FMRFamide, FM(O)RFamide, FLRFamide and GDPFLRFamide. Their amino acid sequences were elucidated by means of a combined approach using antiserum specificity, synthetic-peptide coelution, automated Edman degradation and electrospray mass spectrometry. One of these peptides, GDPFLRFamide, is a novel leech RFamide neuropeptide. Two of the above RFamide peptides are involved in the control of leech hydric balance; one (GDPFLRFamide) is diuretic, the other (FMRFamide) is anti-diuretic. Titration of each purified RFamide peptide indicated a similar amount of each tetrapeptide and of tetrapeptides and heptapeptides. A comparison between RFamide peptides of E. octoculata and molluscs reveals structural similarities supporting the hypothesis for the existence of an ancestral RFamide peptide gene common to leeches and molluscs.

Purification and properties of alkaline phosphatase in the lactating bovine mammary gland

Alkaline phosphatase has been purified 1400-fold from homogenates of lactating bovine mammary tissue. The purification procedure included subcellular fractionation, solubilization with butanol, fractionation with acetone, chromatography on concanavalin A-Sepharose, DEAE cellulose, DEAE-Sephadex, and gel filtration on Sephadex G-200. The enzyme activity was measured with the substrate p-nitrophenylphosphate in three buffers, and the maximum rate occurred at pH 10. For maximum activity, Mg2+ was required. Substrate specificity studies at three pH values indicated that the enzyme had broad specificity. It catalyzed the hydrolysis of aliphatic and aromatic phosphates and pyrophosphates, but the phosphoprotein beta-casein was a poor substrate. Potent inhibitors of the enzyme were levamisole and sulfhydryl reagents (2-mercaptoethanol, dithiothreitol, and cysteine).