The cell and tissues
Peate Ian, Dutton Helen in Acute Nursing Care, 2020
The molecules that make up the lipid bilayer are phospholipids. Phospholipids are neutral fats that have had one of the three fatty acids replaced by phosphate (PO43−), which is anionic and is therefore compatible with water. The consequence of this is that the molecules have a hydrophilic (water-attracting phosphate) end and a hydrophobic (water-repelling fatty acid) end. On both layers, the hydrophilic end is on the outer face, with the hydrophobic, fatty acid end on the inside of the layer. This means that the outside of the membrane is compatible with the aqueous medium, both inside and outside the cell, but, because of the hydrophobic nature of the interior of the bilayer, water and electrolytes cannot cross the lipid sections of the membrane. The movement of electrolytes through the membrane is facilitated by protein channels.
Structures and Properties of Self-Assembled Phospholipids in Excess Water
E. Nigel Harris, Thomas Exner, Graham R. V. Hughes, Ronald A. Asherson in Phospholipid-Binding Antibodies, 2020
The integral membrane proteins or glycoproteins usually have one or more segments of hydrophobic amino acid residues penetrating the lipid bilayer.6 Within the lipid bilayer, these residues are almost exclusively arranged as a-helices with an orientation nearly perpendicular to the bilayer surface. The dynamics and mobility of these bilayer-spanning proteins or glycoproteins must, therefore, be subject to modulation by the organization and polymorphism of the lipid bilayer. Consequently, the functional states of bilayer-spanning proteins or glycoproteins in biological membranes may be correlated with the physical state of the lipid bilayer. The function of lipid bilayers should, therefore, be considered not only to serve as a barrier separating two aqueous compartments, but also to modulate the activity of membrane proteins. Hence, studies of phospholipids and other membrane lipids in the form of a bilayer are of great importance in understanding the functional control of bilayer-spanning proteins in biological membranes and for providing basic information explaining the dynamic regulation of membrane activities in general.
The cell and tissues
Ian Peate, Helen Dutton in Acute Nursing Care, 2014
The molecules that make up the lipid bilayer are phospholipids. Phospholipids are neutral fats that have had one of the three fatty acids replaced by a phosphate molecule (PO−4) which is anionic and therefore is compatible with water. The consequence of this is that the molecules have a hydrophilic (water-attracting phosphate) end and a hydrophobic (water-repelling fatty acid) end. On both layers; the hydrophilic end is on the outer face with the fatty acid, hydrophobic end on the inside of the layer. This means that the outside of the membrane is compatible with the aqueous medium both inside and outside the cell but because of the hydrophobic nature of the interior of the bilayer water and electrolytes cannot cross the lipid sections of the membrane. The movement of electrolytes is facilitated by protein channels.
Systematic review on activity of liposomal encapsulated antioxidant, antibiotics, and antiviral agents
Published in Journal of Liposome Research, 2022
Reshna K. R, Preetha Balakrishnan, Sreerag Gopi
Essentially, a liposome is an area of aqueous solution enclosed inside a hydrophobic membrane. Chemicals that are hydrophobic may be dissolved into lipid membranes, allowing liposomes to transport both hydrophilic and hydrophobic molecules at the same time. While the extent to which the drug is distributed will be determined by its physiochemical features and lipid composition, the extent to which the drug is distributed will be determined by its physiochemical qualities. The fusion of lipid bilayers with other bilayers of the cell (cell membrane) allows the release of the liposomal content, which is important for the delivery of necessary drug molecules to the site of action. The adsorption of liposomes to cell membranes results in the formation of a contact between the liposome and the cell membrane. After adhesion of liposomes to cell surface membranes, followed by engulfment and internalization into liposomes, and fusion of lipoidal cell membranes with liposome lipid bilayers through the process of laminar diffusion and lipid intermingling, the liposomal contents are delivered directly to the cytoplasm. Because the liposomal lipid membrane is identical to the phospholipids found in the cell membrane, lipid transfer proteins found in the cell membrane have an easy time recognizing liposomes and causing lipid exchange. Liposomes containing antioxidants, antibiotics, or antiviral medicines are released from their capsular shells when the gut pH is raised. It will enhance in the absorption of antioxidants, antivirals, and antibiotics to their greatest potential (Torres et al.2012). The mechanism shown in Figure 9.
Chimeric liposomes incorporating functional copolymers: preparation and pH/thermo-responsive behaviour in aqueous solutions
Published in Journal of Liposome Research, 2021
Theodore Sentoukas, Costas Demetzos, Stergios Pispas
Stimuli-responsive chimeric liposomes are a special category of hybrid nanosystems that are comprised of liposomes with docked stimuli-responsive amphiphilic polymeric chains, forming a co-assembled vesicular structure. The hydrophobic part of the polymeric chain will be docked inside the lipophilic tails of the lipid bilayer, while the hydrophilic part of the polymeric chain will extend beyond the polar phospholipid heads. The main idea behind this concept is to provide the liposomes with extra stability, ‘stealth’ properties, and functionality, such as pH- and thermo-responsiveness, for active targeting and controlled drug release (Lee and Nguyen 2013, Pippa et al.2013, Demetzos and Pippa 2014, Naziris et al. 2017a, 2017b, Yamazaki et al.2017, Naziris et al.2018).
Brain-targeted delivery of PEGylated nano-bacitracin A against Penicillin-sensitive and -resistant Pneumococcal meningitis: formulated with RVG29 and Pluronic® P85 unimers
Published in Drug Delivery, 2018
Wei Hong, Zehui Zhang, Lipeng Liu, Yining Zhao, Dexian Zhang, Mingchun Liu
Another emerging strategy to enhance drug delivery to the central nervous system is the co-administration of a pharmacological modulator or a formulation component that blocks P-gp-mediated drug efflux. Both in vitro and in vivo studies have demonstrated that Pluronic block copolymers, such as P85, can inhibit the P-gp drug efflux system and increase the permeability of a broad spectrum of drugs across the BBB (Miller et al., 1997). Pluronics can influence mitochondria function and energy conservation, resulting in depletion of the intracellular ATP. Since the drug efflux transporters require an expenditure of cellular energy, the effects of Pluronics on intracellular ATP levels can reduce the drug efflux. In addition to energy depletion, Pluronics can also decrease membrane fluidization contributing to the inhibition of P-gp efflux function. Thus, Pluronic block copolymers have a ‘double-punch’ effect in BBB: (i) effect on the energy conservation and (ii) effect on membrane fluidization, both of which have a combined potent inhibition of P-gp function. Remarkably, these effects are most apparent at the copolymer concentrations below their critical micellization concentration (CMC), suggesting that the Pluronics unimers are responsible for the BBB permeabilization. This is attributed to the alternatives in the structure of the lipid bilayers as a result of immersion of hydrophobic PPO chains into the biomembrane hydrophobic areas (Regev et al., 1999).
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