Whole body lipid

Using PCB levels in five species of freshwater finfish, collected over a course of 20 years. Stow (1995) failed to find a significant relationship between residue concentrations and percent lipid. The finding of Randall et al. (1991) may explain part of the problem. They found that using different extraction solvents for tissues, lipid concentrations can vary by 3.5 fold and that laboratories vary widely in the type of solvents used for the extraction of HOC residues in tissues. Whole body lipid levels across BMO species typically vary from about 1 to 15% (based on wet tissue weights). Thus, the lipid mediated differences in BMO tissue concentrations may be as high as 15 fold. Unlike BMOs, Standard SPMDs have a uniform lipid content, which precludes any need for lipid normalization, and the extraction or dialysis solvent is standardized. 

Table 7.3 gives SPMD FswS (Eq. 7.10), lipid-normalized BCFs (Eqs. 7.7 and 7.8), and BCF/Fgw ratios for model compounds with log Fow values ranging from 3.0 to 6.0. In this comparison, a lipid content of 5% was adopted for lipid normalization of whole body fish concentrations (note that the whole body lipid content... 

One approach to determination of whole-body lipid peroxidation has been measurement of exhaled hydrocarbons by GLC, especially ethane. Hydrocarbon gases are, however, minor end-products of peroxidation and their formation depends on the decomposition of peroxide. Recent studies have demonstrated that isoprostane is a good biomarker of lipid peroxidation in the human body. Isoprostanes are specific products arising from the peroxidation of unsaturated fatty acid residues in lipids and detection of them and their metabolites in urine is a useful assay of whole-body lipid peroxidation. Isoprostanes can be accurately and sensitively measured by mass spec-trometric techniques. 

Because so many factors in addition to lipid composition can affect POP accumulation (discussed above), some researchers currently favor using whole body lipid and POP measurements to estimate risk of effects from POP exposure. This is essentially a lipid-adjusted CBR. A recent example of this approach is shown in detail by Meador et al.122. These authors used a number of studies from the literature on appropriate life stages of salmon to determine a lipid-adjusted threshold for effects for a wide range of endpoints after PCB exposure. This threshold number was then compared to levels of PCBs measured in wild juvenile salmon from a contaminated estuary, and many of the fish, on the lipid-adjusted basis, were determined to be at risk of effects from environmental exposure to PCBs. 

Rustan AC, Hustvedt BE, Drevon CA. Dietary supplementation of very long-chain n-3 fatty acids decreases whole body lipid utilization in the rat. J Lipid Res 1993 34 1299-1309. 

Members of the Nuclear Receptor Superfamily Contribute to Cellular and Whole-Body Lipid Regulation... 

In addition to SREBPs, several members of the nuclear receptor superfamily regulate lipid metabolism. Nuclear receptors are transcription factors that are generally activated when bound to specific small-molecule ligands (Chapter 11). Certain nuclear receptors influence whole-body lipid metabolism by regulating the absorption of dietary lipids, cellular synthesis of lipids, transport protein-mediated import and export of lipids, levels of lipoproteins and their receptors, and catabolism of lipids (e.g., fatty acid oxidation in the peroxisome) and their secretion from the body. 

Two key transcription-control pathways are employed to regulate the expression of enzymes, transporters, receptors, and other proteins taking part in cellular and whole-body lipid metabolism. 

The fourth class of lipoproteins is HDL, which plays several roles in whole body lipid metabolism. 

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