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Bhatia T, Cornelius F, Ipsen JH. Capturing suboptical dynamic structures in lipid bilayer patches formed from free-standing giant unilamellar vesicles. Nat Protoc 2017; 12:1563-1575. [DOI: 10.1038/nprot.2017.047] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
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Abstract
Technical improvements in electron microscopy, both instrumental and preparative, permit increasingly accurate analyses. Digital images for transmission electron microscopy (TEM) can be processed by software programs that automate tasks and create custom tools that allow for image enhancement for brightness, contrast and coloration; for creation of rectangular, ellipsoidal or irregular area selections; and for measurement of mean area and standard deviation. Sample preparation remains a source of error since organelles and spatial arrangements of macromolecules rapidly change after anoxia. Guidelines for maintaining consistency in preparation, examination and interpretation are presented for different electron microscopy (EM) modalities.
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Affiliation(s)
- N. F. Cheville
- Department of Veterinary Pathology, Iowa State University, Ames, IA, USA
| | - J. Stasko
- Microscopy Services, National Animal Disease Center, Ames, IA, USA
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Rodríguez G, Cócera M, Rubio L, Alonso C, Pons R, Sandt C, Dumas P, López-Iglesias C, de la Maza A, López O. Bicellar systems to modify the phase behaviour of skin stratum corneum lipids. Phys Chem Chem Phys 2012; 14:14523-33. [DOI: 10.1039/c2cp42421e] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
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Samoshina NM, Liu X, Brazdova B, Franz AH, Samoshin VV, Guo X. Fliposomes: pH-Sensitive Liposomes Containing a trans-2-morpholinocyclohexanol-Based Lipid That Performs a Conformational Flip and Triggers an Instant Cargo Release in Acidic Medium. Pharmaceutics 2011; 3:379-405. [PMID: 24310586 PMCID: PMC3857072 DOI: 10.3390/pharmaceutics3030379] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2011] [Revised: 06/07/2011] [Accepted: 06/30/2011] [Indexed: 02/02/2023] Open
Abstract
Incorporation of a pH-sensitive conformational switch into a lipid structure enables a drastic conformational flip upon protonation that disrupts the liposome membrane and causes rapid release of cargo specifically in areas of increased acidity. pH-sensitive liposomes containing the amphiphile (1) with trans-2-morpholinocyclohexanol conformational switch, a phospholipid, and a PEG-lipid conjugate were constructed and characterized. The optimized composition—1/POPC/PEG-ceramide (50/4/5)—could be stored at 4 °C and pH 7.4 for up to 1.5 years, and was stable in blood serum in vitro after 48 h at 37 °C. Liposomes loaded with ANTS/DPX or methotrexate demonstrated an unusually quick content release (in a few seconds) at pH below 5.5, which was independent of inter-liposome contact. The pH-titration curve for the liposome leakage paralleled the curve for the acid-induced conformational flip of 1 studied by 1H-NMR. Freeze-fracture electron microscopy images showed budding and division of the bilayer at pH 5.5. A plausible mechanism of pH-sensitivity involves an acid-triggered conformational flip of 1, shortening of lipid tails, and membrane perturbations, which cause the content leakage. The methotrexate-loaded liposomes demonstrated much higher cytotoxicity in HeLa cells than the free drug indicating that they can serve as viable drug delivery systems.
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Affiliation(s)
- Nataliya M. Samoshina
- Department of Pharmaceutics and Medicinal Chemistry, University of the Pacific, 751 Brookside Road, Stockton, CA 95211, USA
- Department of Chemistry, University of the Pacific, 3601 Pacific Ave., Stockton, CA 95211, USA
| | - Xin Liu
- Department of Chemistry, University of the Pacific, 3601 Pacific Ave., Stockton, CA 95211, USA
| | - Barbora Brazdova
- Department of Chemistry, University of the Pacific, 3601 Pacific Ave., Stockton, CA 95211, USA
| | - Andreas H. Franz
- Department of Chemistry, University of the Pacific, 3601 Pacific Ave., Stockton, CA 95211, USA
| | - Vyacheslav V. Samoshin
- Department of Chemistry, University of the Pacific, 3601 Pacific Ave., Stockton, CA 95211, USA
- Authors to whom correspondence should be addressed; E-Mails: (V.V.S.); (X.G.); Tel.: +1-209-946-2921 (V.V.S.); +1-209-946-2321 (X.G.); Fax: +1-209-946-2607 (V.V.S.)
| | - Xin Guo
- Department of Pharmaceutics and Medicinal Chemistry, University of the Pacific, 751 Brookside Road, Stockton, CA 95211, USA
- Authors to whom correspondence should be addressed; E-Mails: (V.V.S.); (X.G.); Tel.: +1-209-946-2921 (V.V.S.); +1-209-946-2321 (X.G.); Fax: +1-209-946-2607 (V.V.S.)
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Lipid clustering by three homologous arginine-rich antimicrobial peptides is insensitive to amino acid arrangement and induced secondary structure. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2010; 1798:1272-80. [PMID: 20302840 DOI: 10.1016/j.bbamem.2010.03.012] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/21/2010] [Revised: 03/04/2010] [Accepted: 03/05/2010] [Indexed: 11/22/2022]
Abstract
Three Arg-rich nonapeptides, containing the same amino acid composition but different sequences, PFWRIRIRR-amide (PR-9), RRPFWIIRR-amide (RR-9) and PRFRWRIRI-amide (PI-9), are able to induce segregation of anionic lipids from zwitterionic lipids, as shown by changes in the phase transition properties of lipid mixtures detected by differential scanning calorimetry and freeze fracture electron microscopy. The relative Minimal Inhibitory Concentration (MIC) of these three peptides against several strains of Gram positive bacteria correlated well with the extent to which the lipid composition of the bacterial membrane facilitated peptide-induced clustering of anionic lipids. The lower activity of these three peptides against Gram negative bacteria could be explained by the retention of these peptides in the LPS layer. The membrane morphologies produced by PR-9 as well as by a cathelicidin fragment, KR-12 that had previously been shown to induce anionic lipid clustering, was directly visualized using freeze fracture electron microscopy. This work shows the insensitivity of phase segregation to the specific arrangement of the cationic charges in the peptide sequence as well as to their tendency to form different secondary structures. It also establishes the role of anionic lipid clustering in the presence of zwitterionic lipids in determining antimicrobial selectivity.
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