Lipids preservation

S. N. Dudd, R. P. Evershed and A. M. Gibson, Evidence for varying patterns of exploitation of animal products in different prehistoric pottery traditions based on lipids preserved in surface and absorbed residues, Journal of Archaeological Science, 26, 1473 1482 (1999). 

Entrapment in certain archaeological environments can enhance lipid preservation. For example, decomposition is slowed down by dry conditions such as arid or cold climates. In charred residues, the activity of micro-organisms present in organic tissues stops and the outer surfaces are fused, providing a barrier against microbial attack. This means that lipids are often encountered in many different environments associated with artworks and archaeological objects. They appear as constituents, decoration materials or residues of the materials originally contained in a vessel. 

Goldberg M and Septier D (1985) Improved lipid preservation by malachite green-glutaraldehyde fixation in rat incisor predentine and dentine. Arch Oral Biol 30, 717-726. 

The purpose of this review is to compare the various approaches used to improve cellular lipid preservation and discuss the results obtained in the study of different lipid compounds in several tissues. This review will be confined mostly to metabolic studies performed in mammals in vivo or in vitro and will encompass the following lipid classes triglycerides, free fatty acids, cholesterol (free and ester), and phospholipids. No attempt will be made to review histo-chemical approaches to localization of lipids or radioautographic localization of steroid hormones, as these subjects were dealt with recently in a detailed way by Adams (1969) and by Stumpf (1970). 

This outcome was consistent with a hypothesis that structural deterioration could have been a byproduct of microorganism activity. The higher lipid content in the poorly preserved tissue suggests that those lipids are primarily extrinsic, that is, that they were produced by bacteria and/or fungi. As the food source for such microorganisms, the protein within the bone may have been substantially altered in concert with the microstructure deterioration. The quantification of the changes to the organic fraction became our next focus of research. 

Ambrose (1990, 1993) found that for most samples well-preserved collagen had at least 3% carbon and 1% nitrogen. If this criterion is applied in this study, two of our 22 samples show aberrant values for carbon and one of 22 is aberrant for nitrogen, with three of the samples containing 1% nitrogen (Table 7.1). Of the three samples where we can compare bone with hpid-removed and lipids intact, both C and N concentrations are within acceptable limits in the lipid-removed sample, but substantially lower in most layers with lipid intact. The concentrations of both C and N are low, but within acceptable criteria, in the sample with well preserved histology (C = 5.11%, N= 1.77%). 

None of the elemental data show any correlation with collagen yield. When compared to yield, the correlation coefficients are non-significant for C N (r = 0.4), %C (r = 0.4) and %N (r = 0.2). All samples with low elemental values are from layers of bone that showed poor histological preservation. While low values tend to come from bone with poor histological preservation, many samples from bone of equally poor preservation produced acceptable values. Lipid removal generally improved both the yield characteristics and elemental values. 

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. 

Blocking the conversion to DA would appear stupid unless this could be restricted to the periphery. More dopa would then be preserved for entry into the brain, where it could be decarboxylated to DA as usual. Drugs like carbidopa and benserazide do precisely that and are used successfully with levodopa. They are known as extracerebral dopa decarboxylase inhibitors (ExCDDIs). Carbidopa (a-methyldopa hydrazine) is structurally similar to dopa but its hydrazine group (NHNH2) reduces lipid solubility and CNS penetration (Fig. 15.4). 

The permeabilities of the acid examples rise with increasing phospholipid content, up to 20% lipid, with rank ordering preserved. Naproxen and ketoprofen... 

Regert, M., N. Gamier, O. Decavallas, C. Cren-Olive, and Ch. Rolando (2003), Structural characterization of lipid constituents from natural substances preserved in archaeological environments, Meas. Sci. Technol. 14, 1620-1630. 

Stott, A. W., R. Berstan, R. P. Evershed, C. Bronk-Ramsey, M. Humm, and R. E. M. Hedges (2003), Direct dating of archaeological pottery by compound specific C-14 analysis of preserved lipids, Anal. Chem. 75(19), 5037-5045. 

Sample preparation used to extract proteins from cells prior to analysis is an important step that can have an effect on the accuracy and reproducibility of the results. Proteins isolated from bacterial cells will have co-extracted contaminants such as lipids, polysaccharides, and nucleic acids. In addition various organic salts, buffers, detergents, surfactants, and preservatives may have been added to aid in protein extraction or to retain enzymatic or biological activity of the proteins. The presence of these extraneous materials can significantly impede or affect the reproducibility of analysis if they are not removed prior to analysis. 

The permeabilities of the acid examples rise with increasing phospholipid content, up to 20% lipid, with rank ordering preserved (data not shown). Naproxen and ketoprofen show the most dramatic increases in going from 2% to 10% lipid membranes - somewhat higher in soy than in egg. Piroxicam shows less... 

These results show that, depending on the lipid substances present in a sample, direct mass spectrometry may allow the identification of all the lipid substances present in a material, in particular when their mass spectral fingerprints do not overlap, or to determine the main molecular constituents still preserved in the sample. 

Hence, direct mass spectrometry techniques, either using El or ESI, appear to be powerful and innovative analytical tools for elucidating the structure of the main biomarkers present in a wide range of waxes and lipids that may be preserved in archaeological objects and in museum works of art. In most cases, they have nevertheless to be cautiously exploited in combination with other complementary analytical techniques. 

The results are consistent with the beeswax that was used in the preparation of the cosmetics preserved in the unguentaria, while the other lipids are most likely the residue of... 

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