Spleen lipids

The red blood cell must be able to squeeze through some tight spots in the microcirculation during its numerous passages around the body the sinusoids of the spleen are of special importance in this regard. For the red cell to be easily and reversibly deformable, its membrane must be both fluid and flexible it should also preserve its biconcave shape, since this facilitates gas exchange. Membrane lipids help determine membrane fluidity. Attached to the inner aspect of the membrane of the red blood cell are a number of peripheral cytoskeletal proteins (Table 52-6) that play important roles in respect to preserving shape and flexibility these will now be described. 

The half-life of liposomes administered in the blood stream is affected by the composition, size, charge, and fluidity. Liposomes with a small size or with a rigid lipid bilayer have a longer half-life (38 9). Large liposomes administered iv tend to accumulate at a lymph node near the injected site. This tendency can be useful for preventing metastases. Liposomes which pass through the lymph node have a tendency to accumulate in the RES, such as the liver and spleen (40,41). The disposition of liposomes is altered by the dose of liposomes as well as size or lipid composition of liposomes. Cholesterol rich liposomes are cleared slower due to... 

Experiments with monkeys given intramuscular injections of a mineral oil emulsion with [l-14C] -hexa-decane tracer provide data illustrating that absorbed C-16 hydrocarbon (a major component of liquid petrolatum) is slowly metabolized to various classes of lipids (Bollinger 1970). Two days after injection, substantial portions of the radioactivity recovered in liver (30%), fat (42%), kidney (74%), spleen (81%), and ovary (90%) were unmetabolized -hexadecane. The remainder of the radioactivity was found as phospholipids, free fatty acids, triglycerides, and sterol esters. Essentially no radioactivity was found in the water-soluble or residue fractions. One or three months after injection, radioactivity still was detected only in the fat-soluble fractions of the various organs, but 80-98% of the detected radioactivity was found in non-hydrocarbon lipids. 

Distribution. Generally the highest concentration of PCB residues in fish are in tissues of high lipid content. In Table V juvenile coho salmon were fed equal amounts of three chlorobi-phenyls for 117 days. Fish were then killed and lipid content and PCB concentration of various tissues determined (33). Tissues are arranged from top to bottom in order of increasing PCB concentration. For most tissues, but not all, as lipid content increases so does PCB concentration. Lipid content and PCB concentration are low in liver and white muscle, intermediate in spinal column and lateral line muscle, and high in adipose tissue. Lipid content cannot be the sole determinant of PCB concentration in fish tissues because a discrepancy exists between lipid content of brain, heart and spleen and PCB concentration. 

The same liposomal preparation was used to investigate the effect of the administered dose on the biodistribution and pharmacokinetics (41). The effect of the lipid dose of Tc-HYNIC-PEG-liposomes was investigated in the low-dose range (0.02-1.0 pmol/kg), typically for noninvasive imaging applications. The biodistribution and pharmacokinetics of "Tc-HYNIC-PEG-liposomes at various dose levels were studied in rats and rabbits with a focal Escherichia coli infection. Moreover, the pharmacokinetics of Tc-HYNIC-PEG-liposomes at two lipid dose levels were studied in four patients. In rabbits, enhanced clearance was observed at a dose level of 0.02 pmol/kg. The circulatory half-life decreased from 10.4 to 3.5 hours (at 1.0 and 0.02 pmol/kg, respectively). At the lowest dose level, liposomes were mainly taken up by the liver and to a lesser extent by the spleen. Most importantly, the rapid clearance of low-dose PEG liposomes was also observed in humans when relatively low lipid doses were administered as is shown in Figure 4. This study showed that, at very low lipid doses, the biodistribution of PEG liposomes is dramatically altered. 

Heptachlor epoxide was measured in a strip of skin, fat, and subcutaneous tissue from 68 children who died in the perinatal period and ranged from not detected (nondetectable) to 0.563 ppm (mean 0.173) (Zavon et al. 1969). In 10 other stillborn infants, heptachlor epoxide levels measured in various tissues were as follows brain (nondetectable), lung (0.17 0.07 ppm), adipose (0.32 0.10 ppm), spleen (0.35 0.08 ppm), liver (0.68 0.50 ppm), kidney (0.70 0.28 ppm), adrenal (0.73 0.27 ppm), and heart (0.80 0.30 ppm) (Curley et al. 1969). In another study, the following heptachlor epoxide levels were measured in extracted lipids from mothers and newborn infants maternal adipose tissue (0.28 0.31 ppm), maternal blood (0.28 0.46 ppm), uterine muscle (0.49 0.51 ppm), fetal blood (1.00 0.95 ppm), placenta (0.50 0.40 ppm), and amniotic fluid (0.67 1.16 ppm) (Polishuk et al. 1977a). These data provide evidence of transplacental transfer to the fetus. 

Several glycoproteins, which are present in the lipid bilayer of the virus, are necessary for infection. One is known as GP120. It binds to the CD4 protein on the surface of the Th lymphocyte (i.e. the CD4-I- ceU). This initiates fusion with the plasma membrane of the CD4-I- cell so that the viral RNA and its proteins enter the cell (i.e. it infects the CD4-t cell). The original infection probably occurs in the peripheral circulation but the lymphocytes will be transported by the blood to the spleen, other lymph nodes and the brain, where the microglia become infected (Figure 17.46). 

The first extensively tested RES-specific contrast agent on the basis of iodinated lipids was EOE-13 with its precursors, AG 52-315 and AG 60-99. EOE-13 is an aqueous emulsion of the iodinated ester of poppy seed oil and is able to selectively enhance the normal liver and spleen parenchyma [10-12]. However, severe adverse events such as headache, fever and chills prevented further use of these contrast agents [13-15], although their extent could be decreased by hydrocortisone given prior to contrast injection. 

Lymphocytes from rat spleen synthesize cell-surface-bound, lipid-linked oligosaccharides,27 and, here, the presumed first step in the ca-... 

A few hours after its injection, circulating lipid A is found mainly in liver, lung as well as in the spleen, adrenals and kidneys [18]. In these... 

A well-known effect of LPS in mice is mitogenicity to B lymphocytes. Lipid A from P. gingivalis is shown to be mitogenic in vitro even to splenic B cells from LPS-unresponsive C3H/HeJ mice [31]. The lipid A ONO-4007 is mitogenic to spleen cells from BALB/c mice [135], The role of antibodies in tumor regression has solely been documented in the... 

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