Phospholipids and membranes

Prostaglandins are a group of lipid autacoids known as eicosanoids. They are produced from membrane phospholipids and found in almost every tissue and body fluid. They are involved in a number of physiological processes including inflammation, smooth muscle tone and gastrointestinal secretion. In the central nervous system they have been reported to produce both excitation and inhibition of neuronal activity. 

With respect to vasodilation, niacin-elicited vasodilation requires the activation of GPR109A in skin Langerhans cells [34,35], which then triggers the release of arachidonic acid from membrane phospholipids and its subsequent metabolism to PGD2. The production of PGD2 then activates DPI receptors in dermal blood vessels to cause vasodilation [36]. 

A chronic change in the diet can influence the composition of membrane phospholipids and such a change can be important in health. The ratio of the amount of these two fatty acids consumed (i.e. omega-6/omega-3) in a typical... 

The eicosanoids, so called because of their derivation from a 20-carbon unsaturated fatty acid, arachidonic acid (eicosatetraenoic acid), are obtained from membrane phospholipids and synthesized de novo at the time of cellular stimulation. Arachidonic acid is cleaved from membrane-bound phosphatidylcholine by the enzyme phospholipase A2. Alternatively, arachidonic acid may be derived by the sequential actions of phospholipase C and diacylglyceryl lipase. Arachidonic acid can then follow either of two enzymatic pathways that result in the production of inflammatory mediators. The pathway initiated by cyclooxygenase (COX) produces prostaglandins the lipoxygenase pathway generates leukotrienes (Fig. 36.2). 

The polymyxins are polypeptide antibiotics that contain both hydrophilic and lipophilic regions. These antibiotics accumulate in the cell membrane and probably interact with membrane phospholipids. Most likely the fatty acid portion of the antibiotic penetrates the hydrophobic portion of the membrane phospholipid and the polypeptide ring binds to the exposed phosphate... 

Two main types of lipids occur in biological membranes phospholipids and sterols. The predominant phospholipids in most membranes are phosphoglycerides, which are phosphate esters of the three-carbon alcohol, glycerol. A typical structure is that of phosphatidylcholine (lecithin) ... 

Fig. 4.4 Hypothetical model showing the modulation of glutamate transporter by arachidonic acid. Interactions of glutamate with its receptor result in depolarization and Ca2+ entry into the cell. Ca2+-mediated stimulation of PLA2 results in breakdown of neural membrane phospholipids and the release of arachidonic acid. Arachidonic acid not only modulates proton conductance associated with neuronal excitability, but also provides eicosanoids, which may control the glutamate transporter (modified from Fairman and Amara, 1999)...

Farooqui A. A., Ong W. Y., and Horrocks L. A. (2004). Biochemical aspects of neurodegeneration in human brain involvement of neural membrane phospholipids and phospholipases A2. Neurochem. Res. 29 1961-1977. 

Pettegrew J. W., Klunk W. E., Kanal E., Panchalingam K., and McClure R. J. (1995). Changes in brain membrane phospholipid and high-energy phosphate metabolism precede dementia. Neurobiol. Aging 16 973-975. 

The larger biomolecules that have potential Al3+ binding sites are phosphate-bearing biomolecules such as ATP, membrane phospholipids and nucleic acids. It is important to recognize that the metal coordination of these biomolecules might lead to serious disgorges in central biological processes necessary to cell homeostasis and consequently for its overall healthy condition [21]. 

Apart from the hydrophobic interactions provided by the alkyl part of the molecule, octanol has also hydrogen-bond acceptor and donor functions like lipid membranes have. This property of n-octanol made the octanol-water distribution coefficient that widely used. However, n-octanol or reversed phase materials cannot mimic the interfacial character of the bilayer structure. The ionic interactions between membrane phospholipids and solute are also not represented in the properties of octanol or reversed phase materials. To overcome this issue, alternative stationary phases... 

Triacylglycerol has no polar interaction with the membrane phospholipids and is either released into the cytosol as tiny lipid droplets or into the lumen of the ER. In fat cells, oil droplets in the cytosol coalesce, migrate toward and fuse with the large central oil droplets. In the liver and intestine, triacylglycerol is packaged into lipoproteins (VLDL and chylomicrons, respectively), which then are secreted into the circulation (see Fig. 13-11). 

These results suggest that a GSH deficit significantly contributes to the oxidative stress-induced impairment of membrane phospholipid and mitochondrial function proposed to be involved in the pathophysiology of schizophrenia (Mahadik and Mukherjee, 1996 Mahadik et al., 1998 Yao et al., 1999 Herken et al., 2001 Evans et al., 2003 Marchbanks et al., 2003 Prabakaran et al., 2004). 

Calcitriol modulates the maturation of chondrocytes via a cell surface receptor linked to phospholipase and protein kinase C in response to calcitriol, there are rapid changes in arachidonic acid release from, and reincorporation into, membrane phospholipids, and increased synthesis of prostaglandins Ei and E2 (Boyan et al., 1999). 24-Hydroxycalcidiol also modulates the maturation of chondrocytes, acting via cell surface receptors linked to phospholipase D, causing inactivation of both protein kinase C and MAP kinases, thus... 

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