High Hydrostatic Pressure Induces a Lipid Phase Transition and Molecular Rearrangements in Low-Density Lipoprotein Nanoparticles

Effect of high-hydrostatic pressure on the digestibility of egg yolk and granule

The impact of high hydrostatic pressure (HHP) on protein digestibility of egg yolk and egg yolk granule was evaluated by static in vitro digestion using the standardized INFOGEST 2.0 method. The degree of hydrolysis (DH) and the phospholipid content were determined during digestion, and the protein and peptide profiles were characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and reverse phase-high pressure liquid chromatography (RP-HPLC). The results showed that HHP induced protein aggregation in egg yolk and granule, mainly by disulfide bridges, which were not disrupted in the oral phase. Proteolysis during the gastric phase improved egg yolk and granule protein solubility, regardless of whether HHP was applied. However, the extent of the samples' digestibility was not affected, with DH values ranging from 15% to 20%. During the intestinal phase, the DH of egg yolk protein (∼40%) was higher than that of the granule (∼25%), probably due to the denser structure of the granule reducing the accessibility of intestinal enzymes. The DH, peptide, and protein profiles of control and HHP-treated egg yolk showed similar protein digestion behaviors for both gastric and intestinal phases. Among the different proteins, only the digestibility of β-phosvitin in HHP-treated granule was enhanced. Consequently, applying HHP to granules represents an interesting process that improves the digestibility of phosvitin with the potential to generate bioactive phosvitin-derived phosphopeptides. PRACTICAL APPLICATION: High hydrostatic pressure, mainly used as a preservation process, did not impair the nutritional quality of the egg yolk and granule proteins but improved the susceptibility of phosvitin (protein contained in egg yolk) proteolysis to produce bioactive phosphopeptides. Consequently, applying HHP to granules represents an interesting process that improves the digestibility of phosvitin.

Cellular transfection using rapid decrease in hydrostatic pressure

Of all methods exercised in modern molecular biology, modification of cellular properties through the introduction or removal of nucleic acids is one of the most fundamental. As such, several methods have arisen to promote this process; these include the condensation of nucleic acids with calcium, polyethylenimine or modified lipids, electroporation, viral production, biolistics, and microinjection. An ideal transfection method would be (1) low cost, (2) exhibit high levels of biological safety, (3) offer improved efficacy over existing methods, (4) lack requirements for ongoing consumables, (5) work efficiently at any scale, (6) work efficiently on cells that are difficult to transfect by other methods, and (7) be capable of utilizing the widest array of existing genetic resources to facilitate its utility in research, biotechnical and clinical settings. To address such issues, we describe here Pressure-jump-poration (PJP), a method using rapid depressurization to transfect even difficult to modify primary cell types such as embryonic stem cells. The results demonstrate that PJP can be used to introduce an array of genetic modifiers in a safe, sterile manner. Finally, PJP-induced transfection in primary versus transformed cells reveals a surprising dichotomy between these classes which may provide further insight into the process of cellular transformation.

Squeezing lipids: NMR characterization of lipoprotein particles under pressure

Determining the particle size and number of lipoprotein components found in blood plasma (HDL, LDL and VLDL) has become an important clinical tool in diagnosing risk of cardiovascular disease. Proton (1H) NMR spectroscopy methods to quantify lipoprotein particle subclasses have been advancing since NMR lineshape analysis of plasma samples was first proposed in the 1990's. NMR methods, including a more recent DOSY-based diffusion spectroscopy test, provide the foundation for the advanced lipoprotein tests, including Lipoprotein® and Liposcale® analyses available for clinical use to determine particle size and number. At the time of this submission, no NMR studies exist which explore physical parameters of individual lipoprotein fractions when they are deformed by pressure. This study reports 1H NMR frequency shifts and T2* measurements for the broad methyl peak attributed to terminal methyls (cholesteryl positions 26, 27 and terminal acyl methyl groups) in three primary lipoprotein fractions as a function of hydraulic pressure. This terminal CH3 resonance shifted linearly upfield as a function of pressure for HDL and VLDL (observed slopes of -0.014 Hz/bar). The LDL terminal CH3 resonance shows segmented behavior, with a shallow slope between 0-900 bar (-0.008 hz/bar) and a slope similar to HDL and VDL across the range from 1000 to 2400 bar (slope -0.016 Hz/bar). 1H T2* values measured for VLDL and HDL dropped linearly with increasing pressure. 1H T2* values for LDL demonstrated segmented behavior as a function of pressure. The unique behavior observed for LDL terminal CH3 frequency and 1H T2* trends suggests an approximate pressure at which phase transition occurs.