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Exposure to airborne fine particles (PM2.5) is implicated in excess of 50 000 yearly deaths in the USA as well as a number of chronic respiratory illnesses. Despite intense interest in the toxicity of PM2.5, the mechanisms by which it causes illnesses are poorly understood. Since the principal source of airborne fine particles is combustion and combustion sources generate free radicals, we suspected that PM2.5 may contain radicals. Using electron paramagnetic resonance (EPR), we examined samples of PM2.5 and found large quantities of radicals with characteristics similar to semiquinone radicals. Semiquinone radicals are known to undergo redox cycling and ultimately produce biologically damaging hydroxyl radicals. Aqueous extracts of PM2.5 samples induced damage to DNA in human cells and supercoiled phage DNA. PM2.5-mediated DNA damage was abolished by superoxide dismutase, catalase, and deferoxamine, implicating superoxide radical, hydrogen peroxide, and the hydroxyl radical in the reactions inducing DNA damage.

Peroxynitrite reacts with morpholine (MorH) to give both N-nitromorpholine (Mor-NO2) and N-nitrosomorpholine (Mor-NO). The pH profile of Mor-NO2 formation shows a bell-shaped curve with a maximum yield of 1.6 mol % (relative to peroxynitrite) centered around pH 9.0. Yields of Mor-NO, on the other hand, increase until the pH reaches 10.0 and then reach a plateau; the maximum yield of Mor-NO is 12 mol % relative to peroxynitrite. Both the nitration and nitrosation of MorH are catalyzed by low levels of CO2; however, excess CO2 dramatically reduces the yields of Mor-NO but not Mor-NO2, and the combined yields of Mor-NO and Mor-NO2 are about the same under conditions of high and low concentrations of CO2. These data indicate that both nitration and nitrosation by peroxynitrite are free radical processes. The morpholine radical (Mor•), formed from the reactions of carbonate and/or hydroxyl radicals with MorH, reacts with either •NO or •NO2 and serves as a common precursor for Mor-NO and Mor-NO2.

The pH profile of the peroxynitrite/melatonin reaction suggests that both peroxynitrous acid (ONOOH) and its anion (ONOO-) are reactive toward melatonin, but at physiological pH most of the reaction with melatonin involves ONOOH and the activated form of peroxynitrous acid (ONOOH). The formation of hydroxylated products (mainly 6-hydroxymelatonin) suggests that melatonin also reacts with ONOOH. The overall peroxynitrite/melatonin reaction is first-order in melatonin and first-order in peroxynitrite, but the hydroxylation of melatonin is presumed to be zero-order in melatonin. Melatonin is metabolized in the liver, mainly to 6-hydroxymelatonin, so we do not think this metabolite is a useful biomarker for melatonin's antioxidant activity; however, 6-hydroxymelatonin is a better chain-breaking antioxidant than melatonin and may contribute to the beneficial effects of melatonin in vivo. As is now well-known, CO2 modulates the reactions of peroxynitrite. The reaction of peroxynitrite with melatonin in the absence of added bicarbonate produces mainly 6-hydroxymelatonin and 1,2,3,3a,8, 8a-hexahydro-1-acetyl-5-methoxy-8a-hydroxypyrrolo[2,3-b]indole, with some isomeric 1,2,3,3a,8, 8a-hexahydro-1-acetyl-5-methoxy-3a-hydroxypyrrolo[2,3-b]indole. In the presence of added bicarbonate, product yields decrease and 6-hydroxymelatonin is not formed. These facts suggest that melatonin scavenges reactive species (such as CO3*- and *NO2) that are produced from the peroxynitrite/CO2 reaction. The spectrum of the melatoninyl radical cation is observed both in the absence and in the presence of added bicarbonate, suggesting that the melatoninyl radical cation is the initial product and the hydroxypyrrolo[2, 3-b]indole products are derived from it. Unlike tyrosine, where both nitrated and hydroxylated products can be isolated, nitromelatonin is not found in the final products from the melatonin/peroxynitrite reaction in either the absence or presence of added bicarbonate. However, we suggest that 2-hydroxy-3-nitro- and/or 2-hydroxy-3-peroxynitro-2,3-dihydromelatonin are formed as intermediates and subsequently decompose to give 1,2,3,3a,8, 8a-hexahydro-1-acetyl-5-methoxy-8a-hydroxypyrrolo[2,3-b]indole. Since peroxynitrite/CO2 governs the reactions of peroxynitrite in vivo, we suggest that the hydroxypyrrolo[2,3-b]indole products are the main products from the oxidation of melatonin by peroxynitrite-derived species in vivo, and that these products may serve as indexes for melatonin's antioxidant activity.

The activation of phospholipase A{sub 2} (PLA{sub 2}) by lipid ozonation products is reported. The principal products from the ozonation of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) are 1-palmitoyl-2-[8-3(5-octyl-1,2,4-trioxolan-3-yl)octanoyl]--sn-glycero-3-phosphocholine (PC-Criegee ozonide) and 1-palmitoyl-2-(9-oxononanoyl)-sn-glycero-3-phosphocholine (PC-aldehyde). Here we test the hypothesis that these two compounds are mediators of ozone toxicity. Using POPC vesicles, we find that PLA{sub 2} recognizes and hydrolyzes PC-Criegee ozonide at the same rate as that of arachidonic acid. Although the PC-aldehyde is not a substrate for PLA{sub 2}, the enzymatic rate of hydrolysis by PLA{sub 2} of unaltered fatty acids incorporated into POPC is enhanced when PC-aldehyde is present in the bilayer. Thus, both PC-Criegee ozonide and PC-aldehyde alter the activity of PLA{sub 2}, perhaps via an effect on membrane packing order. The capacity of PLA{sub 2} to recognize the PC-Criegee, and therefore ozone-induced damage, suggests a detoxification property of the enzyme and also a role in maintaining the structural properties of bilayer membranes that have been altered by exposure to ozone. 29 refs., 3 figs., 1 tab.

We report herein a high-yield, one-pot method for the synthesis of the isomers of DDA. We also report the assignment of stereochemistry, 'H and '3c NMR resonances in solution, and the single-crystal X-ray analysis for cisand trans-DDA. The reaction of AN with NO2 in CC14, CHCl,, and CH2C12 is discussed in terms of a radical reaction. Stopped-flow kinetics evidence for a first intermediate of the charge-transfer type has been obtained; a charge-transfer intermediate is consistent with the linear relationship previously found between the logarithm of relative rates of reaction of several PAH and their halfwave oxidation p0tentia1s.l~

The 1H NMR spectra of the nitrofluoranthene isomers are presented to allow gas chromatographic analysis of environmental samples suspected of containing nitrofluoranthenes. The mutagenic isomers 1-, 2-, 3-, 7-, and 8-nitrofluoranthene and 1,2- and 1,3-dinitrofluoranthene and a nonmutagenic analogue, 1-phenyl-4-nitronaphthalene, have been studied by using nuclear Overhauser effects and 2D shift-correlated 1H NMR spectroscopy. The X-ray crystal structure of 1-phenyl-4-nitronaphthalene is also reported. Reduction potentials and coplanarity of the nitro group have been used to correlate the mutagenicity of nitrated polycyclic aromatic hydrocarbons (nitro-PAH) measured by the Ames assay, but our data suggest that these parameters are not sufficient for the prediction of mutagenic potency in the nitrofluoranthene series.