Supported Lipid Bilayer Platform for Characterizing the Membrane-Disruptive Behaviors of Triton X-100 and Potential Detergent Replacements

Mechanisms of Triton X-100 reducing the Ag+-resistance of Enterococcus faecalis

To investigate the mechanism of Triton X-100 (TX-100) reducing the Ag+-resistance of Enterococcus faecalis (E. faecalis), and evaluate the antibacterial effect of TX-100 + Ag+ against the induced Ag+-resistant E. faecalis (AREf). The minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of AgNO3 against E. faecalis with/without TX-100 were determined to verify the enhanced antibacterial activity. Transmission electron microscopy (TEM) was used to observe the morphological changes of E. faecalis after treatment. The intra- and extracellular concentration of Ag+ in treated E. faecalis was evaluated using inductively coupled plasma mass spectrometer (ICP-MS). The changes in cell membrane potential and integrity of treated E. faecalis were also observed using the flow cytometer. Moreover, AREf was induced through continuous exposure to sub-MIC of Ag+ and the antibacterial effect of TX-100 + Ag+ on AREf was further evaluated. The addition of 0.04% TX-100 showed maximal enhanced antibacterial effect of Ag+ against E. faecalis. The TEM and ICP-MS results demonstrated that TX-100 could facilitate Ag+ to enter E. faecalis through changing the membrane structure and integrity. Flow cytometry further showed the effect of TX-100 on membrane potential and permeability of E. faecalis. In addition, the enhanced antibacterial effect of TX-100 + Ag+ was also confirmed on induced AREf. TX-100 can facilitate Ag+ to enter E. faecalis through disrupting the membrane structure and changing the membrane potential and permeability, thus reducing the Ag+-resistance of E. faecalis and enhancing the antibacterial effect against either normal E. faecalis or induced AREf.

Lipase-catalyzed solvent-free synthesis of monoglycerides from biodiesel-derived crude glycerol: Optimized using response surface methodology

The growth of the biodiesel industry has resulted in significant quantity of crude glycerol. It is necessary to explore the synthesis of high-value-added products from crude glycerol. In this study, the enzymatic synthesis of monoglycerides under solvent-free conditions, employing crude glycerol as the primary feedstock, had been investigated. The analysis showed that the highest yield of monoglycerides was obtained after 12 h, and Novozym 435 showed the highest monoglyceride yield of 18.41 % among the three lipases tested, followed by Lipozyme TL IM and Lipozyme RM IM. Monoglycerides were synthesized from biodiesel-derived crude glycerol using Novozym 435 as the catalyst under solvent-free conditions at different parameters, which were catalyst concentration, substrate molar ratio, and temperature. The yield of monoglycerides was examined in single-factor experiments. Response surface methodology (RSM) was subsequently employed to optimize the synthesis conditions based on the single-factor experimental results. The optimal conditions were at an enzyme concentration of 12.7 wt% and a molar ratio of crude glycerol:oil of 5.7:1 at a reaction temperature of 65.2 °C. The experimental yield of monoglycerides under the optimal conditions was 28.93 %, which is close to the value predicted from the RSM model (29.02 %).

Unraveling the Biophysical Mechanisms of How Antiviral Detergents Disrupt Supported Lipid Membranes: Toward Replacing Triton X-100

Triton X-100 (TX-100) is a membrane-disrupting detergent that is widely used to inactivate membrane-enveloped viral pathogens, yet is being phased out due to environmental safety concerns. Intense efforts are underway to discover regulatory acceptable detergents to replace TX-100, but there is scarce mechanistic understanding about how these other detergents disrupt phospholipid membranes and hence which ones are suitable to replace TX-100 from a biophysical interaction perspective. Herein, using the quartz crystal microbalance-dissipation (QCM-D) and electrochemical impedance spectroscopy (EIS) techniques in combination with supported lipid membrane platforms, we characterized the membrane-disruptive properties of a panel of TX-100 replacement candidates with varying antiviral activities and identified two distinct classes of membrane-interacting detergents with different critical micelle concentration (CMC) dependencies and biophysical mechanisms. While all tested detergents formed micelles, only a subset of the detergents caused CMC-dependent membrane solubilization similarly to that of TX-100, whereas other detergents adsorbed irreversibly to lipid membrane interfaces in a CMC-independent manner. We compared these biophysical results to virus inactivation data, which led us to identify that certain membrane-interaction profiles contribute to greater antiviral activity and such insights can help with the discovery and validation of antiviral detergents to replace TX-100.

Unraveling Membrane-Disruptive Properties of Sodium Lauroyl Lactylate and Its Hydrolytic Products: A QCM-D and EIS Study

Membrane-disrupting lactylates are an important class of surfactant molecules that are esterified adducts of fatty acid and lactic acid and possess industrially attractive properties, such as high antimicrobial potency and hydrophilicity. Compared with antimicrobial lipids such as free fatty acids and monoglycerides, the membrane-disruptive properties of lactylates have been scarcely investigated from a biophysical perspective, and addressing this gap is important to build a molecular-level understanding of how lactylates work. Herein, using the quartz crystal microbalance-dissipation (QCM-D) and electrochemical impedance spectroscopy (EIS) techniques, we investigated the real-time, membrane-disruptive interactions between sodium lauroyl lactylate (SLL)-a promising lactylate with a 12-carbon-long, saturated hydrocarbon chain-and supported lipid bilayer (SLB) and tethered bilayer lipid membrane (tBLM) platforms. For comparison, hydrolytic products of SLL that may be generated in biological environments, i.e., lauric acid (LA) and lactic acid (LacA), were also tested individually and as a mixture, along with a structurally related surfactant (sodium dodecyl sulfate, SDS). While SLL, LA, and SDS all had equivalent chain properties and critical micelle concentration (CMC) values, our findings reveal that SLL exhibits distinct membrane-disruptive properties that lie in between the rapid, complete solubilizing activity of SDS and the more modest disruptive properties of LA. Interestingly, the hydrolytic products of SLL, i.e., the LA + LacA mixture, induced a greater degree of transient, reversible membrane morphological changes but ultimately less permanent membrane disruption than SLL. These molecular-level insights support that careful tuning of antimicrobial lipid headgroup properties can modulate the spectrum of membrane-disruptive interactions, offering a pathway to design surfactants with tailored biodegradation profiles and reinforcing that SLL has attractive biophysical merits as a membrane-disrupting antimicrobial drug candidate.

Detergent-Mediated Virus Inactivation in Biotechnological Matrices: More than Just CMC

For decades, the ability of detergents to solubilize biological membranes has been utilized in biotechnological manufacturing to disrupt the lipid envelope of potentially contaminating viruses and thus enhance the safety margins of plasma- and cell-derived drugs. This ability has been linked to detergent micelles, which are formed if the concentration of detergent molecules exceeds the critical micelle concentration (CMC). Traditionally, the CMC of detergents is determined in deionized water (ddH₂O), i.e., a situation considerably different from the actual situation of biotechnological manufacturing. This study compared, for five distinct detergents, the CMC in ddH₂O side-by-side with two biopharmaceutical process intermediates relevant to plasma-derived (Immunoglobulin) and cell-derived (monoclonal antibody) products, respectively. Depending on the matrix, the CMC of detergents changed by a factor of up to ~4-fold. Further, the CMC in biotechnological matrices did not correlate with antiviral potency, as Triton X-100 (TX-100) and similar detergents had comparatively higher CMCs than polysorbate-based detergents, which are known to be less potent in terms of virus inactivation. Finally, it was demonstrated that TX-100 and similar detergents also have virus-inactivating properties if applied below the CMC. Thus, the presence of detergent micelles might not be an absolute prerequisite for the disruption of virus envelopes.

Tethered Bilayer Lipid Membrane Platform for Screening Triton X-100 Detergent Replacements by Electrochemical Impedance Spectroscopy

In light of regulatory considerations, there are ongoing efforts to identify Triton X-100 (TX-100) detergent alternatives for use in the biological manufacturing industry to mitigate membrane-enveloped pathogen contamination. Until now, the efficacy of antimicrobial detergent candidates to replace TX-100 has been tested regarding pathogen inhibition in endpoint biological assays or probing lipid membrane disruption in real-time biophysical testing platforms. The latter approach has proven especially useful to test compound potency and mechanism of action, however, existing analytical approaches have been limited to studying indirect effects of lipid membrane disruption such as membrane morphological changes. A direct readout of lipid membrane disruption by TX-100 detergent alternatives would be more practical to obtain biologically relevant information to guide compound discovery and optimization. Herein, we report the use of electrochemical impedance spectroscopy (EIS) to investigate how TX-100 and selected replacement candidates-Simulsol SL 11W (Simulsol) and cetyltrimethyl ammonium bromide (CTAB)-affect the ionic permeability of tethered bilayer lipid membrane (tBLM) platforms. The EIS results revealed that all three detergents exhibited dose-dependent effects mainly above their respective critical micelle concentration (CMC) values while displaying distinct membrane-disruptive behaviors. TX-100 caused irreversible membrane disruption leading to complete solubilization, whereas Simulsol caused reversible membrane disruption and CTAB induced irreversible, partial membrane defect formation. These findings establish that the EIS technique is useful for screening the membrane-disruptive behaviors of TX-100 detergent alternatives with multiplex formatting possibilities, rapid response, and quantitative readouts relevant to antimicrobial functions.

Facile and scalable fabrication of exosome-mimicking nanovesicles through PEGylated lipid detergent-aided cell extrusion

We report a scalable fabrication method to generate exosome-mimicking nanovesicles (ENVs) by using a biocompatible, cell-binding lipid detergent during cell extrusion. A PEGylated mannosylerythritol lipid (MEL_PEG) detergent was rationally engineered to strongly associate with phospholipid membranes to increase cell membrane deformability and the corresponding friction force during extrusion and to enhance the dispersibility of ENVs. Compared to cell extrusion without detergent, cell extrusion in the presence of MEL_PEG increased the ENV production yield by approximately 20 times and cellular protein content per MEL_PEG-functionalized ENV by approximately 2-fold relative to that of unmodified ENVs. We verified that MEL_PEG strongly binds to ENV membranes and increases membrane deformability via expansion/swelling while preserving the integrity of the phospholipid bilayer structure. The results highlight that the MEL_PEG-aided cell extrusion process broadly applies to various cell lines; hence, it could be helpful in the production of ENVs for tissue regeneration, drug delivery, and cancer nanomedicine.