The potential of the hydrocarbon breath test as a measure of lipid peroxidation

Isoleukotrienes are biologically active free radical products of lipid peroxidation

The free radical oxidation of arachidonic acid esterified to glycerophospholipids is known to generate complex metabolites, termed isoprostanes, that share structural features of prostaglandins derived from prostaglandin H2 synthase. Furthermore, certain isoprostanes have been found to exert biological activity through endogenous receptors on cell surfaces. Using mass spectrometry and ancillary techniques, the free radical oxidation of 1-hexadecanoyl-2-arachidonoyl-glycerophosphocholine was studied in the search for products of arachidonic acid isomeric to the leukotrienes that are derived from 5-lipoxygenase-catalyzed metabolism of arachidonic acid. Several conjugated triene metabolites were chromatographically separated from known 5-lipoxygenase products and structures characterized as 5,12-dihydroxy-6,8,10,14-eicosatetraenoic acid esterified to the glycerophosphocholine backbone. We have termed these products as B4-isoleukotrienes. Following saponification some, but not all, B4-isoleukotrienes were found to exert biological activity in elevating intracellular calcium in Indo-1-loaded human polymorphonuclear leukocytes. This activity could be blocked by a leukotriene B4 receptor antagonist. An EC50 of approximately 30 nM was determined for one unique B4-isoleukotriene with a relative retention index of 2.54. We have shown that free radical processes can lead to the formation of biologically active isoleukotrienes in glycerophosphocholine liposomes, and we propose that B4-isoleukotrienes may also be formed in membrane glycerophospholipids as a result of lipid peroxidation during tissue injury. Such B4-isoleukotrienes could then mediate events of tissue damage through activation of leukotriene B4 receptors on target cells.

Oxidative stress during exercise: implication of antioxidant nutrients

Research evidence has accumulated in the past decade that strenuous aerobic exercise is associated with oxidative stress and tissue damage in the body. There is indication that generation of oxygen free radicals and other reactive oxygen species may be the underlying mechanism for exercise-induced oxidative damage, but a causal relationship remains to be established. Enzymatic and nonenzymatic antioxidants play a vital role in protecting tissues from excessive oxidative damage during exercise. Depletion of each of the antioxidant systems increases the vulnerability of various tissues and cellular components to reactive oxygen species. Because acute strenuous exercise and chronic exercise training increase the consumption of various antioxidants, it is conceivable that dietary supplementation of specific antioxidants would be beneficial.

Breath ethane generation during clinical total body irradiation as a marker of oxygen-free-radical-mediated lipid peroxidation: a case study

Total body irradiation (TBI) is used therapeutically for treatment of leukemias and other malignancies of the hemopoietic system. Ionizing radiation produces oxygen free radicals that contribute to cytotoxicity. Breath collected from one patient undergoing therapeutic TBI showed measurable changes in levels of ethane during treatment. Breath ethane is a marker of lipid peroxidation of n-3 fatty acids. The TBI treatment involved 4 days of irradiation. The largest changes in breath ethane occurred on Day 2. The increased levels of breath ethane on Day 2 were correlated to clinical manifestations of toxicity. The correlation of the onset of gastrointestinal side effects with higher levels of breath ethane suggests that breath ethane may be a clinically useful measure of the toxicity of various TBI fractionation treatment protocols currently in use at different medical centers. The levels of breath ethane on the other days of treatment were lower, suggesting that the oxidative-antioxidative balance of the patient may be important in protection against free radical mediated injury. These results for a single patient suggest that breath ethane may be a promising approach to elucidate the role of antioxidants in clinical TBI and should be extended for verification to a larger volunteer patient population.

One- and two-electron oxidations of methionine by peroxynitrite

Peroxynitrite is stable, but its acid, HOONO, either rearranges to form nitrate or oxidizes nearby biomolecules. We report here the reactions of HOONO with methionine and the methionine analog 2-keto-4-thiomethylbutanoic acid (KTBA). These oxidations proceed by two competing mechanisms. The first yields the sulfoxide; the second-order rate constants, k2, for this process for methionine and KTBA are 181 +/- 8 and 277 +/- 11 M-1.s-1, respectively, at pH 7.4 and 25 degrees C. In the second mechanism, methionine or KTBA undergoes a one-electron oxidation that ultimately gives ethylene. We propose that the one-electron oxidant is an activated form of peroxynitrous acid, HOONO*, that is formed in a steady state mechanism. The ratios of the second-order rate constants for the ethylene-producing reaction (k*2) and the first-order rate constant to produce nitric acid (kN) for methionine and KTBA, k*2/kN, are 1250 +/- 290 and 6230 +/- 1390 M-1, respectively. Both ceric and peroxydisulfate ions also oxidize KTBA to ethylene, confirming a one-electron transfer mechanism. The yields of neither MetSO nor ethylene are affected by several hydroxyl radical scavengers, suggesting that a unimolecular homolysis of HOONO to HO. and .NO2 is not involved in these reactions. HOONO* gives hydroxyl radical-like products from various substrates but displays more selectivity than does the hydroxyl radical; thus, HOONO* is incompletely trapped by typical HO. scavengers. However, a mechanism involving dissociation of HOONO* to caged radicals cannot be ruled out at this time.