Atherosclerotic Oxidized Lipids Affect Formation and Biophysical Properties of Supported Lipid Bilayers and Simulated Membranes

Oxidized lipids arising from oxidative stress are associated with many serious health conditions, including cardiovascular diseases. For example, KDdiA-PC and KOdiA-PC are two oxidized phosphatidylcholines (oxPC) directly linked to atherosclerosis, which precipitate heart failure, stroke, aneurysms, and chronic kidney disease. These oxPCs are well-characterized in small particles such as low-density lipoprotein, but how their presence affects the biophysical properties of larger bilayer membranes is unclear. It is also unclear how membrane mediators, such as cholesterol, affect lipid bilayers containing these oxPCs. Here, we characterize supported lipid bilayers (SLBs) containing POPC, KDdiA-PC, or KOdiA-PC, and cholesterol. We used a quartz crystal microbalance with dissipation monitoring (QCM-D), fluorescence microscopy, and all-atom molecular dynamics (MD) to examine the formation process, biophysical properties, and specific lipid conformations in simulated bilayers. Experimentally, we show that liposomes containing either oxPC form SLBs by rupturing on contact with SiO2 substrates, which differs from the typical adsorption-rupture pathway observed with nonoxidized liposomes. We also show that increasing the oxPC concentration in SLBs results in thinner bilayers that contain defects. Simulations reveal that the oxidized sn-2 tails of KDdiA-PC and KOdiA-PC bend out of the hydrophobic membrane core into the hydrophilic headgroup region and beyond. The altered conformations of these oxPC, which are affected by cholesterol content and protonation state of the oxidized functional groups, contribute to trends of decreasing membrane thickness and increasing membrane area with increasing oxPC concentration. This combined approach provides a comprehensive view of the biophysical properties of membranes containing KDdiA-PC and KOdiA-PC at the molecular level, which is crucial to understanding the role of lipid oxidation in cardiovascular disease and related immune responses.

Odorant-responsive biological receptors and electronic noses for volatile organic compounds with aldehyde for human health and diseases: A perspective review

Volatile organic compounds (VOCs) are gaseous chemicals found in ambient air and exhaled breath. In particular, highly reactive aldehydes are frequently found in polluted air and have been linked to various diseases. Thus, extensive studies have been carried out to elucidate disease-specific aldehydes released from the body to develop potential biomarkers for diagnostic purposes. Mammals possess innate sensory systems, such as receptors and ion channels, to detect these VOCs and maintain physiological homeostasis. Recently, electronic biosensors such as the electronic nose have been developed for disease diagnosis. This review aims to present an overview of natural sensory receptors that can detect reactive aldehydes, as well as electronic noses that have the potential to diagnose certain diseases. In this regard, this review focuses on eight aldehydes that are well-defined as biomarkers in human health and disease. It offers insights into the biological aspects and technological advances in detecting aldehyde-containing VOCs. Therefore, this review will aid in understanding the role of aldehyde-containing VOCs in human health and disease and the technological advances for improved diagnosis.

Quartz crystal microbalance-based method to study adsorption of endocrine disruptor compounds on zeolite

Endocrine disrupting chemicals (EDCs) can be present as trace-level organic pollutants in aquatic environments and are difficult to measure and remove. In this study, a method was developed using a modified quartz crystal microbalance (QCM) to investigate the adsorption of EDCs by zeolite filter. Bisphenol A (BPA), oestrone (E1), oestradiol (E2), and sulfamethoxazole (SMZ) were selected as four representative endocrine disruptors in a water environment and their adsorption on zeolite was measured by QCM in real-time. The adsorption results were well described by a pseudo-first-order kinetic model and by a Sips isotherms model. The adsorption of the four adsorbents is related to their molecular structure, molecular polarity, and chargeability. The removal rate of EDCs by zeolite for different initial concentrations appeared to plateau, with the removal rates of the four selected EDCs all above 80% except for the maximum initial concentration. Changes of pH and ionic strength had no effect on the adsorption capacity of the four EDCs, with a removal rate of about 90%. However, the response time at pH 5.50 was about 300 s faster than that at pH 8.50 and the addition of electrolyte shortened the mass response time of several organic compounds on QCM.

Frequency Shift of a SH-SAW Biosensor with Glutaraldehyde and 3-Aminopropyltriethoxysilane Functionalized Films for Detection of Epidermal Growth Factor

The frequency shift of a shear-horizontal surface-acoustic-wave (SH-SAW) biosensor in which the concentration of biomolecule is determined by the amount of its adsorption on the sensing film was studied. Simulation results were compared with experimental results to investigate its sensitivity and to develop a model to estimate the concentration of a cancer-related biomarker antigen epidermal growth factor (EGF) in the sample, with two types of sensing films, 3-aminopropyltriethoxysilane (APTES) and glutaraldehyde. With the concentration of the targeted biomarker varying from 0.2 to 5 ng/mL, a typical exponential relationship was found between the concentration and the frequency shift of the SH-SAW sensor. Measurement results showed a clear response of this immunosensor to the mass-loading effects of the antibody–antigen. The sensitivity of the glutaraldehyde film is greater than that of the APTES film owing to the chemisorption of the antibody. In the simulation, a shift of the SH-SAW resonant frequency due to added mass occurred on applying an incremental surface mass density on the sensing film, while in real applications, the concentration of the targeted biomarker to be absorbed in the sensing film is demanded. An empirical model was proposed to calculate the frequency shift in the simulation of the SH-SAW biosensor, corresponding to the concentration of specific biomolecules absorbed on a specific film. From the semi-empirical model, the sensitivity level is found to be 0.641 and 1.709 kHz/(ng/mL) for APTES and glutaraldehyde sensing films, respectively, at a biomarker concentration of less than 1 ng/mL. The developed method is useful for quickly estimating the frequency shift with respect to the concentration of the target molecules in the simulation for SH-SAW sensors.