Lipids morphology

Proteins and lipids interact cooperatively in the membrane. The type(s) and state(s) of lipids influence the mobility and conformation of the proteins in the membrane matrix. This, in turn, may well alter the properties of the membrane proteins. Similarly, proteins affect the phase behavior of the lipids and/or promote domain formation in membranes containing mixtures of lipids. Morphological alteration of the lipid architecture leads to changes in the membrane permeability. 

Denda, M. et al. Stratum comeum lipid morphology and transepidermal water loss in normal skin and surfactant-induced scaly skin. Archives of Dermatological Research 256 41-46, 1994. 

Deme, B., Dubois, M., Gulik-Krzywicki, T. and Zemb, Th. (2002) Giant collective fluctuations of charged membranes at the lamellar-to-vesicle unbinding transition. 1. Characterisation of a new lipid morphology by SANS, SAXS, and electron microscopy. Fangmuir, 18, 997-1004. 

For books and reviews see Berge, 1995 Blomberg et aL, 1994 Charpentier and Sevenants, 1988 Dean, 1993 Jinno, 1992 Lee and Markides, 1989 Luque de Castro, Valcarcel and Tena, 1994 McHugh and Krukonis, 1994 Saito, Yamauchi and Okuyama, 1994 Smith, 1988 Taylor, 1995, 1996 Wenclawiak, 1992 Westwood, 1993 for publications dedicated to lipid morphology, see King, 1995 King and List, 1996 Laakso, 1992. 

The relation between the architecture of the molecules and the spatial morphology into which they assemble has attracted longstanding interest because of their importance in daily life. Lipid molecules are important constituents of the cell membrane. Amphiphilic molecules are of major importance for teclmological applications (e.g., in detergents and the food industry). 

Volume feed rate Lipid Cell morphology... 

The ER has a reticular morphology which provides a large surface area, which presumably is required for the synthesis and transport of proteins and lipids and for the storage of calcium. The ER is associated with microtubules, and the two are highly interdependent structures. Terasaki et al. (1986) found that when microtubules in the cell are depolymerized by colchicine, the ER network slowly retracts toward the center of the cell. If the microtubules are repolymerized, the ER network is restored to its original morphology, thereby suggesting that the MTs participate in the formation and maintenance of the ER. 

The earliest morphological change in the sebaceous follicle is an abnormal follicular epithelial differentiation, which results in ductal hypercornification. Cornified cells in the upper section of the follicular canal become abnormally adherent. Comedones represent the retention of hyperproliferating ductal keratinoc-ytes in the duct. Several factors have been implicated in the induction of hyperproliferation sebaceous lipid composition, androgens, local cytokine production (IL-i, EGF) and bacteria (P. acnes). 

Several of these morphological factors are illustrated in Figure 1. Figure lA is of the fat portion of bacon and has been stained for connective tissue. It is noted that fat tissue is not all lipid but has an extensive connective tissue component ranging from fairly thick layers to delicate layers defining each adipose cell. Figure IB is from a finely chopped emulsion. Connective tissue pieces are stained dark, the protein matrix is gray and the... 

We have already stressed the potential importance of lipid-rich membranes in the skin as potential targets for ROS-induced damage and ageing of human skin is morphologically identical to changes found by peroxidative processes (Serri et al., 1977). The involvement of AA metabolites in skin disease, and in particular psoriasis, has been the subject of much recent interest. Studies have included topical and intradermal administrations of AA metabolites, and assay of such products in clinical specimens. Results show that concentration of AA, 12-hydroxy-eicosatetraenoic acid (12-HETE), PG and leu-kotrienes are increased in psoriatic lesions (Hammarstrom etal., 1975 Camp etal., 1983 Brain etal., 1984 Duell et al., 1988) and also that full-thickness epidermis from normal and diseased skin has the enzymatic capacity to convert AA to some of the same metabolites (Hammarstrom etal., 1975, 1979 Camp etal., 1983 Brain etal., 1984 Ziboh et al., 1984 DueU et al., 1988). The biological effect of both 12-HETE and leukotrienes was confirmed by both topical application and intradermal injection, which caused epidermal inflammation and... 

Liposomes are formed due to the amphiphilic character of lipids which assemble into bilayers by the force of hydrophobic interaction. Similar assemblies of lipids form microspheres when neutral lipids, such as triglycerides, are dispersed with phospholipids. Liposomes are conventionally classified into three groups by their morphology, i.e., multilamellar vesicle (MLV), small unilamellar vesicle (SUV), and large unilamellar vesicle (LUV). This classification of liposomes is useful when liposomes are used as models for biomembranes. However, when liposomes are used as capsules for drugs, size and homogeneity of the liposomes are more important than the number of lamellars in a liposome. Therefore, "sized" liposomes are preferred. These are prepared by extrusion through a polycarbonate... 

In addition, the physical dimensions of the cells making up the monolayer should be considered. Cell shape can influence the relative contributions of the paracellular and transcellular pathways. For example, junctional density is greater in cells that are narrow or of small diameter than in cells that are wide or spread out on the substrate. The height of the cells can impact the path length traveled by a permeant, as will the morphology of the junctional complex and lateral space (Section m.B.2). It is unknown how the mass of lipid or membrane within a cell influences transcellular flux of a lipophilic permeant. 

Westesen and Siekmann [11] used suspensions of colloidal solid lipid particles as well as lyophilizates as delivery systems for the parenteral administration of the drug for its particle morphology determination. 

Fig. 11 Islets with immobilized urokinase (UK-islets) were tested for the ability to dissolve fibrin, (a) Fibrin in the plate gel medium was dissolved by UK-islets (clear areas). Fifty islets were applied to each spot, and the plate was observed after incubation at 37 °C for 14 h. (1) untreated islets (2) UK-islets treated with oligo(dT)2o-PEG-lipid (C16), just after preparation (3) UK-islets treated with oligo(dT)2o-PEG-lipid (C16) lost activity after 2 days in culture (4) UK-islets treated with oligo(dT)20-PEG-lipid (C18), just after preparation and (5) UK-islets treated with oligo (dT)20-PEG-lipid (C16) lost activity after 2 days in culture, (b) Morphology of UK-islets after 1 and 7 days of culture...

Liposomes are artificial structures composed of phospholipid bilayers exhibiting amphiphilic properties (Chapter 22). In complex liposome morphologies, concentric spheres or sheets of lipid bilayers are usually separated by aqueous regions that are sequestered or compartmentalized... 

Figure 22.1 The amphiphilic nature of phospholipids in solution drives the formation of complex structures. Spherical micelles may form in aqueous solution, wherein the hydrophilic head groups all point out toward the surrounding water environment and the hydrophobic tails point inward to the exclusion of water. Larger lipid bilayers may form by similar forces, creating sheets, spheres, and other highly complex morphologies. In non-aqueous solution, inverted micelles may form, wherein the tails all point toward the outer hydrophobic region and the heads point inward forming hexagonal shapes.

Figure 22.2 The highly varied morphologies of lipid bilayer construction.

Mixtures of phospholipids in aqueous solution will spontaneously associate to form liposomal structures. To prepare liposomes having morphologies useful for bioconjugate or delivery techniques, it is necessary to control this assemblage to create vesicles of the proper size and shape. Many methods are available to accomplish this goal, however all of them have at least several steps in common (1) dissolving the lipid mixture in organic solvent, (2) dispersion in an aqueous phase, and (3) fractionation to isolate the correct liposomal population. 

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