Oxidatively modified plasma phospholipids containing reactive carbonyl functions measured by HPLC: evidence for phosphatidylcholine-bound aldehydes in plasma of burn patients

Generation and biological activities of oxidized phospholipids

Glycerophospholipids represent a common class of lipids critically important for integrity of cellular membranes. Oxidation of esterified unsaturated fatty acids dramatically changes biological activities of phospholipids. Apart from impairment of their structural function, oxidation makes oxidized phospholipids (OxPLs) markers of "modified-self" type that are recognized by soluble and cell-associated receptors of innate immunity, including scavenger receptors, natural (germ line-encoded) antibodies, and C-reactive protein, thus directing removal of senescent and apoptotic cells or oxidized lipoproteins. In addition, OxPLs acquire novel biological activities not characteristic of their unoxidized precursors, including the ability to regulate innate and adaptive immune responses. Effects of OxPLs described in vitro and in vivo suggest their potential relevance in different pathologies, including atherosclerosis, acute inflammation, lung injury, and many other conditions. This review summarizes current knowledge on the mechanisms of formation, structures, and biological activities of OxPLs. Furthermore, potential applications of OxPLs as disease biomarkers, as well as experimental therapies targeting OxPLs, are described, providing a broad overview of an emerging class of lipid mediators.

Oxidation of carotenoids by heat and tobacco smoke

The stability to autoxidation of the polar carotenoids, lutein and zeaxanthin, was compared to that of the less polar carotenoids, beta-carotene and lycopene at physiologically or pathophysiologically relevant concentrations of 2 and 6 microM, after exposure to heat or cigarette smoke. Three methodological approaches were used: 1) Carotenoids dissolved in solvents with different polarities were incubated at 37 and 80 degrees C for different times. 2) Human plasma samples were subjected to the same temperature conditions. 3) Methanolic carotenoid solutions and plasma were also exposed to whole tobacco smoke from 1-5 unfiltered cigarettes. The concentrations of individual carotenoids in different solvents were determined spectrophotometrically. Carotenoids from plasma were extracted and analyzed using high performance liquid chromatography. Carotenoids were generally more stable at 37 than at 80 degrees C. In methanol and dichloromethane the thermal degradation of beta-carotene and lycopene was faster than that of lutein and zeaxanthin. However, in tetrahydrofuran beta-carotene and zeaxanthin degraded faster than lycopene and lutein. Plasma carotenoid levels at 37 degrees C did not change, but decreased at 80 degrees C. The decrease of beta-carotene and lycopene levels was higher than those for lutein and zeaxanthin. Also in the tobacco smoke experiments the highest autoxidation rates were found for beta-carotene and lycopene at 2 microM, but at 6 microM lutein and zeaxanthin depleted to the same extent as beta-carotene. These data support our previous studies suggesting that oxidative stress degrade beta-carotene and lycopene faster than lutein and zeaxanthin. The only exception was the thermal degradation of carotenoids solubilized in tetrahydrofuran, which favors faster breakdown of beta-carotene and zeaxanthin.

Oxidative damage to protein and alterations to antioxidant levels in human cutaneous thermal injury

Evidence that oxygen free radicals may be contributory to further tissue damage in the events following cutaneous thermal injury supports a role for interventional therapy using antioxidants. However, previous work has relied almost entirely on animal-based models with little clinical information available. Also, methods used to support an oxidative role in thermal injury have relied almost exclusively upon the use of lipid peroxidation studies. Further work substantiating a contributory role of free radicals is therefore required using additional methodology before considering antioxidant therapy aimed at retarding tissue damage. We investigated general oxidative damage to protein in burn blister fluid by quantifying the protein carbonyl levels from 11 patients admitted with superficial or partial thickness burns. Total antioxidant capacity was also assessed, together with measurement of protein and the antioxidants uric acid and bilirubin. Data were compared with values obtained for serum in healthy volunteers. Following thermal injury, burn blister fluid protein carbonyl level was increased by almost 50 per cent (P = 0.005) compared with normal serum. Antioxidant scavenging capacity, protein and bilirubin were all significantly reduced, but uric acid unaltered compared with control values. The present data support a role for oxidative damage in cutaneous thermal injury.