Normal Lipid Concentrations

Normal values for the various lipid classes are derived from determinations in populations composed of normal subjects. In doing so it is essential to define normality by careful medical examination, and to include a sufficient number of subjects for statistical evaluation. 

Cumulative distribution curves may be used for defining normal ranges if the values do not correspond to a normal distribution. 

In determination of tissue concentrations values can be related to various factors, e.g. wet weight, dry weight, total protein etc. Sometimes simultaneous estimation of deoxyribonucleic acid is used for comparison as a measure of total cell number. Nevertheless care should be taken to receive material for control examinations in each case. Plasma lipids are generally related to 100 ml of plasma. 

An additional difficulty in defining normal plasma lipid values results from the influence of various factors on plasma lipid concentrations. Cholesterol and phospholipid concentrations vary with age and show an increase from the third to the sixth decade followed by a slight decrease thereafter (Adlersberg et al. 1956, Lewis et al. 1957, Schaefer et al. 1958). In higher decades values may be influenced by the inclusion of persons with clinically silent disease. Furthermore, alimentary influences result from the total amount of ingested fat and the composition of dietary fatty acids. Therefore, blood samples should not only be taken in the fasting state, but in many instances after a period of controlled dietary intake. 

The following tables give normal ranges for plasma lipids expressed as mean values 2 standard deviations. 

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In summary, results from several studies in to the effects of impaired insulin action can now be linked to CVD. Because of the numbers of people exhibiting sings of insulin resistance, there has been a lot of research effort has gone in to finding suitable therapeutic interventions. One group of drugs in particular, the thiazolidinediones (also known as glitazones) has attracted attention because they both increase insulin sensitivity and help to normalize plasma lipid concentrations. 

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. 

Fig. 14 Lipid-normalized PCB concentrations in the Lake Michigan food web, showing 95th, 90th, 75th, 50th, 25th, 10th, and 5th percentiles (data from the Lake Michigan Mass Balance study)...

V pg-kg-1 lipid lipid-normalized chemical concentration in phytoplankton... 

In Taiwan, Huang et al. investigated the correlation between serum lipid, lipoprotein concentrations and major depressive disorder in patients admitted for general health screening [33]. They found that the ratios of TC/HDL and LDL/HDL showed significant differences between patients with major depressive disorder and normal controls in women. Huang and Chen also pointed out that no significant differences were found in lipid concentrations of TC, TG, HDL, VLDL, LDL, TC/HDL, and LDL/HDL between patients with dysthymia and normal controls [41],... 

Dl. Dasgupta, A., Malhotra, D., Levy, H., Marcadis, D., Blackwell, W., and Johnston, D., Decreased total antioxidant capacity but normal lipid hydroperoxide concentrations in sera of critically ill patients. Life Sci. 60,335-340 (1997). 

In many cases, sample preparation is mandatory prior to lipid extraction. This crucial process might include tissue homogenization, determination of dry weights, cell numbers, protein content, or DNA content for normalization purposes. The addition of internal standards is not only used to control extraction efficiency, but also is required for lipid quantification by mass spectrometric analysis, in which an ion current is translated into a lipid concentration. Many standard lipids that can be distinguished from endogenously occurring lipids by using rare... 

In any study, it is important that researchers first establish whether or not their data demonstrate a relationship between POP tissue concentration and tissue lipid levels. This is seldom done, as it is typically assumed that such a relationship must exist for lipophilic contaminants. As is compellingly demonstrated by Hebert and Keenley-side47 in their paper To normalize or not to normalize Fat is the question , such assumptions can lead to lipid normalized POP concentrations that are completely at odds with measured wet weight POP values. Further, since factors other than total lipid (such as differences in lipid class, for example) can affect POP levels in organisms, simple ratios (e.g. ng POP/ng lipid) are often inadequate and may actually increase data variability. In many cases, analysis of covariance (ANCOVA) may prove to be a more appropriate method for lipid normalization of POP concentrations47. 

A number of studies have concluded that anionic surfactants are very effective at cleaning sebum at normal shampoo concentrations [2,3,151-155], Shaw [152], for example, on the basis of SEM results, concluded that almost complete removal of surface lipid could be effected by anionic surfactants in a single application. Experiments involving extraction of wool swatches and hair clippings led Robbins [2] to reach the same conclusion for two surfactant applications. 

For transfection, H9C2 cells (5 x 10s) are placed in six-well culture plates together with fetal calf serum in DMEM at 37°C, 5% C02, and incubated overnight. Then the cells are washed with PBS and recultured in 1 mL of serum-free medium (SFM)/liposome mixture (0.5 mL SFM + 0.5 mL PL or IL in PBS at lipid concentration of 7-10 mg/mL). Nitrogen gas is passed through the medium for 1 min, and wells are covered tightly with Parafilm and incubated for 6 h (these conditions result in mild hypoxia). Normoxic cells are kept under normal conditions for 6 h. 

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