Dr. Joseph Lorent
The activity of cold atmospheric plasma on biological membranes
Plasma is the fourth state of matter in which gas becomes ionized and strongly electrically conductive due to a supply of energy. It is composed of ions, electrons, UV and visible light, and reactive oxygen and nitrogen species (RONS). Non-equilibrium plasmas like cold atmospheric plasmas (CAP) can be generated by strong alternating electric fields and have the advantage that only electrons possess a very high temperature compared to the other composing species (Fig. 1). This reduces the heat impact on applied surfaces and makes CAP usable for biomedical applications.
In our group, we test the effects of CAP on bacteria, model membranes and eukaryotic cells with the aim to understand the mechanisms behind their activity. Recently, it was observed that CAP efficiently destroys multi-resistant bacteria, spores and biofilms. As an alternative to classic antibiotics and antiseptics, CAP has the advantage that it can flow into crevices of porous material (Fig. 2), and could therefore be used in complicated wounds or tooth infections. It can also be modulated by changing parameters such as the vector gas, the potential or the frequency of the alternating current. First clinical trials show encouraging results with minor side effects suggesting some selectivity of CAP towards bacteria. This bactericidal effect seems largely to arise from an activity on the cell membrane. Unfortunately, the details of this mechanisms are lacking, preventing hence a rationale modulation of CAPs which could potentially increase the selectivity towards bacteria (Fig. 3).
We especially focus on the effects on cellular membranes by using biophysical, biochemical, analytical and bioinformatic approaches (see below). By understanding the detailed mechanisms, we aim to increase the efficiency/selectivity of plasmas towards bacteria by varying different parameters such as the frequency, the potential or the vector gas. Our final goal is to make plasma a working alternative for antibiotic treatment. We are also interested in the general effects which RONS have on membranes. We therefore use CAP to create oxidative stress situations which are similar to physiological situations such as the respiratory burst in immune cells or aging. The current research should hence not only give information about CAP activity but also on how membranes are biophysically and physiologically affected by an oxidative environment.
To investigate different aspects of the effects of CAP on bacteria and eukaryotic cell membranes, we use different techniques/models (Fig. 4) such as:
- Liposomes (Small, Large and Giant Unilamellar Vesicles) as simple membrane models to investigate the effects of plasma on biophysical membrane properties like lipid membrane dynamics, permeability or diffusion of reactive molecules through the membrane.
- Proteoliposomes containing model peptides to investigate the effect of plasma on membrane inserted proteins
- Cell culture (Bacteria and Eukaryotic cells)
- High performance liquid chromatography (LC-MS), Gas Chromatography (GC) and High performance thin layer chromatography (HPTLC) to determine changes in the lipidomes and oxidation products in model or biological membranes
- Advanced microscopy (confocal microscopy, fluorescence lifetime imaging (FLIM), spectroscopic imaging, superresolution microscopy such as airyscan and STED) to investigate direct effects of plasma on cells or membranes
- Fluorescence spectroscopy
- Molecular biology (western blots, PCR) to pinpoint molecular targets of plasma in the cells
- Bioinformatic approaches (python, matlab, R) to establish oxidation sensitivity maps in cells
D. Yurtsever and J.H. Lorent.
Structural Modifications Controlling Membrane Raft Partitioning and Curvature in Human and Viral Proteins. J Phys Chem B. (2020) Sep 3; 124(35):7574–7585.
J.H. Lorent, E. Lyman, E. Sezgin, K.R. Levental, I. Levental
Plasma membranes are asymmetric in lipid unsaturation, packing and protein shape. Nature Chem. Biol. (2020) 16;644-652
J.H. Lorent, B.B. Diaz-Rohrer, X. Lin, K. Spring, A.A. Gorfe, K.R. Levental, I. Levental
Structural Determinants and Functional Consequences of Protein Affinity for Membrane Rafts. Nat Commun. (2019) 31;8(1):1219
X. Lin, J.H. Lorent, A.D. Skinkle, K.R. Levental K.R., Waxham M.N., Gorfe A.A., Levental I.
Domain Stability in Biomimetic Membranes Driven by Lipid Polyunsaturation. J Phys Chem B. (2016) 23;120(46):11930-11941
J.H. Lorent, C.S. Le Duff, J. Quetin-Leclercq, M.P. Mingeot-Leclercq
Induction of highly curved structures in relation to membrane permeabilization and budding by the triterpenoid saponins, alpha- and delta-Hederin. J Biol Chem (2013) 288(20): 14000-14017