Lipids, biomarker molecules

Results obtained in in vivo and ex vivo experiments are of various types. Some studies have found positive effects of the consumption of carotenoids or foods containing carotenoids on the markers of in vivo oxidative stress, even in smokers. Other studies demonstrated no effects of carotenoid ingestion on oxidative stress biomarkers of lipid peroxidation. " It should be noted that for studies using food, the activity observed may also be partly due to other antioxidant molecules in the food (phenols, antioxidant vitamins) or to the combination of actions of all the antioxidants in the food. 

Anaerobic CH4 oxidation, now referred to as anaerobic oxidation of methane (AOM), has received renewed attention with introduction of new organic geochemical and molecular techniques. Hinrichs et al. (1999) applied compound-specific isotope analyses of lipid biomarker molecules associated with specific archea and culture-independent techniques involving 16S rRNA identification studies to samples collected from an Eel River Basin seep. This work showed that the biomarker compounds were so strongly depleted in that CH4 must be the source rather... 

Compound-specific A C values for 31 different lipid biomarker molecules are shown in Figure 8 for sedimentary horizons corresponding to pre-bomb (before ad 1950) and post-bomb (1950-1996) eras. These organic compounds represent phytoplank-tonic, zooplanktonic, bacterial, archaeal, terrestrial higher plant, and fossil carbon sources. The lipid classes include long-chain n-alkanes, alkanoic (fatty) acids, -alcohols, C30 mid-chain ketols and diols, sterols, hopanols, and C40 isoprenoid side chains of the ether-linked glycerols of the Archaea. 

Biological marker (biomarker) molecules are compounds that have distinctive biotic sources and that retain their identity after burial in sediments, even after partial alteration. Most biomarkers are lipids, which are hydrocarbons and hydrocarbon-like molecules. Because of their low susceptibility to microbial degradation compared to other types of organic matter, saturated hydrocarbons — those having only carbon-carbon single bonds — can record many aspects of the depositional history of organic matter sources in lake sediments. A number of detailed reviews of the biomarker contents of lake sediments exist (e.g., Barnes Barnes, 1978 Cranwell, 1982 Johns, 1986 Muller, 1987 Meyers Ishiwatari, 1993). 

The isoprostanes are a unique series of prostaglandin-like compounds formed in vivo via a nonenzymatic mechanism involving the free radical-initiated peroxidation of arachidonic acid. This article summarizes our current knowledge of these compounds. Herein, a historical account of their discovery and the mechanism of their formation are described. Methods by which these compounds can be analyzed and quantified are also discussed, and the use of these molecules as biomarkers of in vivo oxidant stress is summarized. In addition to being accurate indices of lipid peroxidation, some isoprostanes possess potent biological activity. This activity will be discussed in detail. Finally, in more recent years, isoprostane-like compounds have been shown to be formed from polyunsaturated fatty acids, including eicosapentaenoic acid and docosahexaenoic acid. These findings will be summarized as well. 

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