Lipids and Related Compounds

The MS analysis of Upids and related compounds has been frequently reviewed. An elaborate review of the MS and MS-MS analysis of lipids, bile acids, and steroids, covering a range of analyte ionization techniques, has been compiled by Griffiths [190]. The MS analysis of long-chain hpids, especially focusing on 

Using soft-ionization techniques, fatty acids, including prostaglandins and related acidic compounds, are analyzed mostly as deprotonated molecules [M-H] in negative-ion mode, although the formation of lithiated lithium salts [(M-H+Li)+Li]+, to be analyzed in positive-ion mode, can have certain advantages for structure elucidation (see below). 

FDI-MS has been applied to the characterization of natural waxes and other types of lipid-related compounds [195,196], For components extracted from waxes, such as fatty alcohols and diols, fatty acids, and fatty acid esters, M and [M+H]+ were observed. The same holds for free fatty acids, cholesterol and its esters, and triglycerides extracted from human plasma, whereas [M+H] , [M+Na] , and/or [M+K] were observed for GPCho from human plasma. FDI-MS proofs to be a versatile technique for lipid profiling [196]. Cs -cationization has been applied in the FDI-MS analysis of glycolipids such as P-hydroxyacyltrehaloses [197]. 

After its introduction in 1981, FAB-MS has also been widely applied in the characterization of lipids and related compounds. Both [M+H] and [M+Na] are generally observed in the positive-ion FAB-MS analysis of phospholipids [198, 199]. This was applied in, for instance, phospholipid profiling in extracts from the archae-hacianumHalobacterium cutivubrum [199]. 

Phospholipids have been studied by means of maity condensed-phase ionization techniques. In the FAB-MS mass spectra of GPCho, the three most abundant ions were [M+H]+, [M+Na]+, and a fragment ion [M+Na-59]+ due to the loss of trimethylamine. CID mass spectra with [M+Na]+ as precursor ion resulted in the loss of the fatty acids and the loss of choline phosphate, thus [M+Na-183]+, 

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Hajra, A. K., Fisher, S. K. and Agranoff, B. W. Isolation, separation and analysis of phosphoinositides from biological sources. In A. A. Boulton, G. B. Baker and L. A. Horrocks (eds), Neuromethods (Neurochemistry). Lipids and Related Compounds, vol. 8. Clifton, NJ Humana Press, 1987. 

Thin-layer chromatography (TLC) on silica gel is well known for its separation power for lipids and related compounds. The flame ionization detector (FID) is a universal analytical instrument that offers high sensitivity and linearity for carbon-containing organic compounds. The combination of TLC and FID led to the wide use of the Iatroscan TLC-FID for the analysis of lipid classes. The adoption of the Iatroscan TLC-FID in both academia and industry has generated sufficient data to indicate that TLC-FID is currently one of the most efficient tools for the quantitation of lipids classes (Ackman et al., 1990 Hammond, 1993). 

Reversed-phase chromatography is the term commonly applied to a system where a nonpolar liquid phase is coated on the solid support and elution carried out with an immiscible polar phase. Such systems are often necessary for separations which cannot be carried out by normal partition or adsorption chromatography. For TLC, the stationary phase is normally a liquid of high boiling point which does not readily evaporate from the adsorbent. Paraffin oil, silicone oil or n-tetradecane coated on silica gel or Kieselguhr are frequently used with water-based mobile phases such as acetone—water (3 2) or acetic acid-water (3 1). Reversed-phase chromatography is very useful for the TLC analysis of lipids and related compounds. 

Bonded diol Si-O-Si-C OH OH 1 1 -c—c-1 Polar bonded phase A polar phase that has a hydrogen bonding capability similar to that of unbonded silica useful in size-exclusion chromatography and in the analysis of glycols and glycerol, oils, lipids, and related compounds... 

An alternative candidate for a cell membrane is one composed of mostly hydrophobic molecules that would spontaneously aggregate if suspended in water. It is important that the molecule is not entirely hydrophobic, like hexane or benzene, as some part of it must be solvated if it is to aggregate with others to form a structure capable of encapsulating other species. Candidates for this type of molecule are the lipids and related compounds. The formation of protocells by lipids has been discussed previously as part of the Lipid World hypothesis. In the context of compartmentalization it is important to consider how such an aggregate could evolve. 

Harborne, J. B. (1984) Organic acids, lipids and related compounds, in Phytochemical Methods, 2nd ed., Chapman and Hall, London, pp 142-175. 

Thermal analyses have been used for over 20 years to characterise heart-valve poppets (silicone elastomer) implanted into humans [29] and to evaluate the in vivo absorption of lipids and related compounds fix)m the body. Important deleterious effects on the implants, observed under in vivo conditions include changes in the hardness and mechanical properties, which appear to be associated with colour changes from white to yellow then brown. Because the thermal curves of the samples extracted from new and unused implants were almost identical, the differences were attributed to materials absorbed into the polymer matrix. Thermal analyses may therefore be useful in understanding the behaviour of these poppets in vivo. Table 1 shows the thermoanalytical data for new and used poppets, with those used poppets differing in terms of the extent extracted materials in vivo. 

A good experimental model for biomembranes should possess a lipid bilayer structure, onto as well as into which functional entities can be embedded. Thus, since the 1960s, the two most widely used model membranes have been BLMs, also referred to as planar lipid bilayers and spherical liposomes. Planar BLMs and spherical liposomes are complementary to each other, since both types are derived from common amphipathic lipids and related compounds. Both are excellent model membrane systems, and have been extensively employed for investigations into a variety of physical, chemical, and biological functions. In the remainder of this chapter on membrane electrochemistry, the focus will be mainly on planar BLMs, because they are easily and have been investigated electrochemically (for K-posomes, see Refs. [3, 12, 34]). As a result... 

The antioxidant property of ferulic acid and related compounds from rice bran was reported by Kikuzaki et al, (2002). Their results indicated that these compounds elicit their antioxidant function through radical scavenging activity and their affinity with lipid substrates. Another recent study reported by Butterfield et al, (2002) demonstrated that ferulic acid offers antioxidant protection against hydroxyl and peroxyl radical oxidation in synaptosomal and neuronal cell culture systems in vitro. The effect of ferulic acid on blood pressure (BP) was investigated in spontaneously hypertensive rats (SHR). After oral administration of ferulic acid the systolic blood pressure (SBP) decreased in a dose-dependent manner. There was a significant correlation between plasma ferulic acid and changes in the SBP of the tail artery, suggesting... 

Schweizer E (1989) Biosynthesis of fatty acids and related compounds. In Ratledge C, Wilkinson SG (eds), Microbial lipids, vol. 2. Academic Press, London, p 3 -50... 

Plant metabolism can be separated into primary pathways that are found in all cells and deal with manipulating a uniform group of basic compounds, and secondary pathways that occur in specialized cells and produce a wide variety of unique compounds. The primary pathways deal with the metabolism of carbohydrates, lipids, proteins, and nucleic acids and act through the many-step reactions of glycolysis, the tricarboxylic acid cycle, the pentose phosphate shunt, and lipid, protein, and nucleic acid biosynthesis. In contrast, the secondary metabolites (e.g., terpenes, alkaloids, phenylpropanoids, lignin, flavonoids, coumarins, and related compounds) are produced by the shikimic, malonic, and mevalonic acid pathways, and the methylerythritol phosphate pathway (Fig. 3.1). This chapter concentrates on the synthesis and metabolism of phenolic compounds and on how the activities of these pathways and the compounds produced affect product quality. 

A wide variety of other biochemical effects has been reported to be associated with treatment of cells with vinblastine, vincristine, and related compounds (S). These effects include inhibition of the biosynthesis of proteins and nucleic acids and of aspects of lipid metabolism it is not clear whether such effects contribute to the therapeutic or toxic actions of vincristine and vinblastine. Vinblastine and vincristine inhibit protein kinase C, an enzyme system that modulates cell growth and differentiation (9). The pharmacological significance of such inhibition has not been established, however, and it must be emphasized that the concentrations of the drugs required to inhibit protein kinase C are several orders of magnitude higher than those required to alter tubulin polymerization phenomena (10). 

Vitamin E (tocopherol) and related compounds only occur in plants (e.g., wheat germ). They contain what is known as a chro-man ring. In the lipid phase, vitamin E is mainly located in biological membranes, where as an antioxidant it protects unsaturated lipids against ROS (see p. 284) and other radicals. 

Setchell KDR, Lawson AM, Tanida N, Sjovall J (1983) General methods for the analysis of metabolic profiles of bile acids and related compounds in faeces. J Lipid Res 24 1085-1100... 

Different factors govern the formation of these molecular compounds. Where lipids and related substances are concerned the governing factor is the realization of the best hydrophilic-lipophilic balance producing hydration or dispersion. The case of lecithin and sodium cholate associated in the presence of water may be used to illustrate the conditions of association and formation of different types of structure and of micelles. 

The number of fatty acids and related compounds in milk lipids grew from 16 in 1959 (Jenness and Patton, 1959) to 142 in 1967 (Jensen et al. 1967) to over 400 in 1983. However, there are only 10 fatty acids of quantitative importance. The amounts (weight percent) as butyl esters prepared by three methods of esterification were determined by Iverson and Sheppard (1977). Because of the widely differing molecular weights of the fatty acids (4 0-18 0), fatty acid compositions of ruminant milk fats are often presented as a mole percent. The nutritionist needs the data calculated in yet another manner weight of fatty acid/100 g or 100 ml of edible portion. Analyses of food fatty acids should always be accompanied by the fat content so that the actual weights of the fatty acids and be calculated. A compilation of this type was made by Posati et al. (1975). Since these analyses were done with methyl esters, the contents of 4 0 are low. Data from Feeley et al. (1975), obtained from careful analyses, are more reliable, and USDA Handbook 8-1 (Posati and Orr 1976) has data for many milk and dairy products. 

CHAPTER TWENTY-SIX Lipids Much of the fundamental work on prostaglandins and related compounds was carried out by Sune Bergstrom and Bengt Samuelsson of the Karolinska Institute (Sweden) and by Sir John Vane of the Wellcome Foundation (Great Britain). These three shared the Nobel Prize for physiology or medicine in 1982. 

Recently, Maruta et al. [112] have found that methanol extracts of roots of burdock show a significant antioxidant activity in an in vitro lipid peroxidation assay, and have isolated five caffeoylquinic acid derivatives (CQAs) from the roots of burdock (Arctium lappa L ), an edible plant in Japan. Antioxidant activities of DCQAs and related compounds have been investigated by measuring the hydroperoxidation of methyl linolate via radical chain reaction. This study indicates that in this particular system caffeic acid and CQAs are more effective than a-tocopherol. These results approximately agree with our findings [38], Additionally, CQAs as the principle antioxidative substance in burdock root have been characterized. 

The activation of silica gel, alumina or similar adsorbents is often necessary for the chromatography of many types of compound, especially lipids and related materials. It involves heating of the TLC plate at 110- 130°C for > 2 h in order to remove all of the water that is not strongly chemically bound to the adsorbent. Such plates must be cooled and stored in desiccators and should be covered when taken out for spotting. The elution solvents should also be free from water or preferably should contain a well defined content of water which might permit a reproducible equilibrium. Chromatography is often difficult to reproduce from day to day, since the highly activated layer rapidly adsorbs water and... 

In vitro, allicin and related compounds inhibit HMG-CoA reductase, which is involved in cholesterol biosynthesis (see Chapter 35 Agents Used in Hyperlipidemia). Several clinical trials have investigated the lipid-lowering potential of garlic. Some have shown significant reductions in cholesterol and others no effect. The most recent meta-analysis suggested a minor (5%) reduction of total cholesterol that was insignificant when dietary controls were in place. 

Apart from classical organochlorines, not much literature is available on the occurrence of other PTS compounds like butyltins, polybromin-ated diphenyl ethers, etc. in Indian human breast milk. Indian Council of Medical Research (ICMR) in their news bulletin of the year 2004 has indicated that they could detect PCDDs and PCDFs in the human milk samples collected from Ahmedabad, Vadodara and Surat cities (http //icmr.nic.in). They have found that the TEQs of dioxins and related compounds in their samples ranged from about 2 to 16 pg g 1 lipid weight of human milk. 

Arachidonic acid, a 20-carbon fatty acid, is the primary precursor of the prostaglandins and related compounds (see Figure 39.3). Arachidonic acid is present as a component of the phospholipids of cell membranes, primarily phosphatidyl inositol and other complex lipids.1 Free arachidonic acid is released from tissue phospholipids by the action of phospholipase A2 and other acyl hydrolases, via a process controlled by hormones and other stimuli (see Figure 39.3). There are two major pathways in the synthesis of the eicosanoids from arachidonic acid (see Figure 39.3). 

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