Abstract
In the eye lens cell membrane, the lipid composition changes during the aging process: the proportion of sphingomyelins (SM) increases, that of phosphatidylcholines decreases. To investigate the protective role of the SMs in the lens cell membrane against oxidative damage, analytical techniques such as electrochemistry, high-resolution mass spectrometry (HR-MS), and atomic force microscopy (AFM) were applied. Supported lipid bilayers (SLB) were prepared to mimic the lens cell membrane with different fractions of PLPC/SM (PLPC: 1-palmitoyl-2-linoleoyl-sn-glycero-3-phosphocholine). The SLBs were treated with cold physical plasma. A protective effect of 30% and 44% in the presence of 25%, and 75% SM in the bilayer was observed, respectively. PLPC and SM oxidation products were determined via HR-MS for SLBs after plasma treatment. The yield of fragments gradually decreased as the SM ratio increased. Topographic images obtained by AFM of PLPC-bilayers showed SLB degradation and pore formation after plasma treatment, no degradation was observed in PLPC/SM bilayers. The results of all techniques confirm the protective role of SM in the membrane against oxidative damage and support the idea that the SM content in lens cell membrane is increased during aging in the absence of effective antioxidant systems to protect the eye from oxidative damage and to prolong lens transparency.
Highlights
The oxidation of cellular components such as lipids, DNA and proteins occurs when the level of reactive species is higher than the level of antioxidants in the cells and eventually leads to the loss of cell function [1]
Liposomes were prepared by sonication and their sizes were determined by dynamic light scattering (DLS) confirming the formation of small unilamellar vesicles (SUV) with an average radius of 76.3 ± 1.2 nm, 75.8 ± 0.7 nm and 96.1 ± 1.2 nm for PLPC, PLPC:SM (3:1)
The results indicated that at a lower fraction of SM, the size of liposomes is almost similar to PLPC but there is an increase in radius of liposomes with 75% SM
Summary
The oxidation of cellular components such as lipids, DNA and proteins occurs when the level of reactive species is higher than the level of antioxidants in the cells and eventually leads to the loss of cell function [1]. AFM complemented the approach, allowing the correlation of functional, chemical, and structural changes It shows how degradation of amphiphilic molecules alters lipid self-assembly within a membrane, provides a topographic image of the supported lipid bilayer (SLB), and information on oxidative damage in PLPC/SM membranes. 1-palmitoyl-2-linoleoyl-sn-glycero-3phosphocholine (PLPC (16:0/18:2)) and n-oleoyl-d-erythro sphingosylphosphorylcholine (SM (d18:1/18:1)) were selected because such phospholipids with unsaturated alkyl chains have been reported in mammalian eye lens membrane [72,73] and they are preferred targets of lipid peroxidation during oxidative stress [74]. We could show that a higher fraction of SM resulted in a decrease in lipid oxidation products during CPP treatment; and the SLB was more stable and did not show pores
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