Free radicals and carcinogenesis. Some properties of the nitroxyl free radicals produced by covalent binding of 2-nitrosofluorene to unsaturated lipids of membranes

Rutin, a Flavonoid That Is a Main Component of Saussurea involucrata, Attenuates the Senescence Effect in D-Galactose Aging Mouse Model

Saussurea involucrata (Kar. et Kir.), known as the snow lotus, grows in the Tian Shan and A'er Tai areas of China. It has recently been reported that the ethyl acetate extract of S. involucrata (SI-2) can inhibit proliferation and induce apoptosis in PC-3 human prostate cancer cells. This study investigated the protective effect of ethyl acetate extract of S. involucrata (SI-2) or rutin, a flavonoid extracted from ethyl acetate extract of S. involucrata (SI-2), on D-galactose- (D-gal-) induced brain injury in mice. Administering SI-2 or rutin (30 mg/kg/d and 30 mg/kg/d) for 6 weeks, concomitant with D-gal injection, significantly increased superoxide dismutase and glutathione peroxidase activities and decreased the MDA level in plasma. Furthermore, the result showed that the percentages of cleaved caspase-3 and PARP in the D-gal-treated mice were much higher than those in the control. Pretreatment using SI-2 or rutin decreased the expression of cyclooxygenase-2 via downregulation of NF-kappaB, resulting in a decrease in lipid peroxidation. Furthermore, our results also showed that oral administration of rutin to these mice significantly improved behavioral performance in a step-through passive avoidance task and these results suggest that SI-2 or rutin exerts potent antiaging effects on D-gal in mice via antioxidative mechanisms.

Antioxidant effects of photodegradation product of nifedipine

Recently, increasing evidence suggests that the antihypertensive drug nifedipine acts as a protective agent for endothelial cells, and that the activity is unrelated to its calcium channel blocking. Nifedipine is unstable under light and reportedly decomposes to a stable nitrosonifedipine (NO-NIF). NO-NIF has no antihypertensive effect, and it has been recognized as a contaminant of nifedipine. The present study for the first time demonstrated that NO-NIF changed to a NO-NIF radical in a time-dependent manner when it interacted with human umbilical vein endothelial cells (HUVECs). The electron paramagnetic resonance (EPR) signal of NO-NIF radicals in HUVECs showed an asymmetric pattern suggesting that the radicals were located in the membrane. The NO-NIF radicals had radical scavenging activity for 1,1-diphenyl-2-picrylhydrazyl, whereas neither NO-NIF nor nifedipine did. In addition, the NO-NIF radical more effectively quenched lipid peroxides than NO-NIF or nifedipine. Furthermore, NO-NIF attenuated the superoxide-derived free radicals in HUVECs stimulated with LY83583, and suppressed iron-nitrilotriacetic acid (Fe-NTA)-induced cytotoxicity in rat pheochromocytoma (PC12) cells. Our findings suggest that NO-NIF is a candidate for a new class of antioxidative drugs that protect cells against oxidative stress.

Isochaihulactone protects PC12 cell against H(2)O(2) induced oxidative stress and exerts the potent anti-aging effects in D-galactose aging mouse model

AIM

to investigate the effect of isochaihulactone (also known as K8), a lignan compound of Bupleurum scorzonerifolium, on H(2)O(2)-induced cytotoxicity in neuronally differentiated PC12 cells (nPC12).

METHODS

viability of neuronal PC12 cells was measured using MTT assay. Protein expression was determined by Western blot. Apoptotic cells was determined using TUNEL assay. D-galactose aging mice were used as a model system to study the anti-oxidant effects of isochaihulactone in vivo.

RESULTS

pretreatment with isochaihulactone (5-10 micromol/L) increased cell viability and decreased membrane damage, generation of reactive oxygen species and degradation of poly (ADP-ribose) polymerase in H(2)O(2)-treated nPC12 cells and also decreased the expression of cyclooxygenase-2, via downregulation of NF-kappaB, resulting in a decrease in lipid peroxidation. The results suggest that isochaihulactone is a potential antioxidant agent. In a murine aging model, in which chronic systemic exposure to D-galactose (D-gal) causes the acceleration of senescence, administration of isochaihulactone (10 mgxkg(-1)xd(-1), sc) for 7 weeks concomitant with D-gal injection significantly increased superoxide dismutase and glutathione peroxidase activities and decreased the MDA level in plasma. Furthermore, H&E staining to quantify cell death within hippocampus showed that percentage of pyknotic nuclei in the D-gal-treated mice were much higher than in control.

CONCLUSION

the results suggest that isochaihulactone exerts potent anti-aging effects against D-gal in mice possibly via antioxidative mechanisms.

Light-induced oxidation of unsaturated lipids as sensitized by flavins

Triplet-excited riboflavin ((3)RF*) was found by laser flash photolysis to be quenched by polyunsaturated fatty acid methyl esters in tert-butanol/water (7:3, v/v) in a second-order reaction with k approximately 3.0 x 10(5) L mol(-1) s(-1) at 25 degrees C for methyl linoleate and 3.1 x 10(6) L mol(-1) s(-1), with DeltaH(double dagger) = 22.6 kJ mol(-1) and DeltaS(double dagger) = -62.3 J K(-1) mol(-1), for methyl linolenate in acetonitrile/water (8:2, v/v). For methyl oleate, k was <10(4) L mol(-1) s(-1). For comparison, beta-casein was found to have a rate constant k approximately 4.9 x 10(8) L mol(-1) s(-1). Singlet-excited flavin was not quenched by the esters as evidenced by insensitivity of steady-state fluorescence to their presence. Density functional theory (DFT) calculations showed that electron transfer from unsaturated fatty acid esters to triplet-excited flavins is endergonic, while a formal hydrogen atom transfer is exergonic (DeltaG(o)(HAT) = -114.3, -151.2, and -151.2 kJ mol(-1) for oleate, linoleate, and linolenate, respectively, in acetonitrile). The reaction is driven by acidity of the lipid cation radical for which a pK(a) approximately -0.12 was estimated by DFT calculations. Absence of electrochemical activity in acetonitrile during cyclic voltammetry up to 2.0 V versus NHE confirmed that DeltaG(o)(ET) > 0 for electron transfer. Interaction of methyl esters with (3)RF* is considered as initiation of the radical chain, which is subsequently propagated by combination reactions with residual oxygen. In this respect, carbon-centered and alkoxyl radicals were detected using the spin trapping technique in combination with electron paramagnetic resonance spectroscopy. Moreover, quenching of (3)RF* yields, directly or indirectly, radical species which are capable of initiating oxidation in unsaturated fatty acid methyl esters. Still, deactivation of triplet-excited flavins by lipid derivatives was slower than by proteins (factor up to 10(4)), which react preferentially by electron transfer. Depending on the reaction environment in biological systems (including food), protein radicals are expected to interfere in the mechanism of light-induced lipid oxidation.

Serendipitous findings while researching oxygen free radicals

This review is based on the honor of receiving the Discovery Award from the Society of Free Radical Biology and Medicine. The review is reflective and presents our thinking that led to experiments that yielded novel observations. Critical questioning of our understanding of oxygen free radicals in biomedical problems led us to use and develop more direct and extremely sensitive methods. This included nitrone free radical spin trapping and HPLC-electrochemical detection. This technology led to the pioneering use of salicylate to trap hydroxyl free radicals and show increased flux in ischemia/reperfused brain regions and also to first sensitively detect 8-hydroxyl-2-deoxyguanosine in oxidatively damaged DNA and help assess its role in cancer development. We demonstrated that methylene blue (MB) photoinduces formation of 8-hydroxyguanine in DNA and RNA and discovered that MB sensitively photoinactivates RNA viruses, including HIV and the West Nile virus. Studies in experimental stroke led us serendipitously to discover that alpha-phenyl-tert-butylnitrone (PBN) was neuroprotective if given after the stroke. This led to extensive commercial development of NXY-059, a PBN derivative, for the treatment of stroke. More recently we discovered that PBN nitrones have potent anti-cancer activity and are active in preventing hearing loss caused by acute acoustical trauma.

Human arylamine N-acetyltransferase 1: in vitro and intracellular inactivation by nitrosoarene metabolites of toxic and carcinogenic arylamines

Arylamines (ArNH 2) are common environmental contaminants, some of which are confirmed risk factors for cancer. Biotransformation of the amino group of arylamines involves competing pathways of oxidation and N-acetylation. Nitrosoarenes, which are products of the oxidation pathway, are electrophiles that react with cellular thiols to form sulfinamide adducts. The arylamine N-acetyltransferases, NAT1 and NAT2, catalyze N-acetylation of arylamines and play central roles in their detoxification. We hypothesized that 4-nitrosobiphenyl (4-NO-BP) and 2-nitrosofluorene (2-NO-F), which are nitroso metabolites of arylamines that are readily N-acetylated by NAT1, would be potent inactivators of NAT1 and that nitrosobenzene (NO-B) and 2-nitrosotoluene (2-NO-T), which are nitroso metabolites of arylamines that are less readily acetylated by NAT1, would be less effective inactivators. The second order rate constants for inactivation of NAT1 by 4-NO-BP and 2-NO-F were 59200 and 34500 M (-1) s (-1), respectively; the values for NO-B and 2-NO-T were 25 and 23 M (-1) s (-1). Densitometry quantification and comparisons of specific activities with those of homogeneous recombinant NAT1 showed that NAT1 constitutes approximately 0.002% of cytosolic protein in HeLa cells. Treatment of HeLa cells with 4-NO-BP (2.5 microM) for 1 h caused a 40% reduction in NAT1 activity, and 4-NO-BP (10 microM) caused a 50% loss of NAT1 activity within 30 min without affecting either glyceraldehyde 3-phosphate dehydrogenase (GAPDH) or glutathione reductase (GR) activities. 2-NO-F (1 microM) inhibited HeLa cell NAT1 activity by 36% in 1 h, and a 10 microM concentration of 2-NO-F reduced NAT1 activity by 70% in 30 min without inhibiting GAPDH or GR. Mass spectrometric analysis of NAT1 from HeLa cells in which NAT1 was overexpressed showed that treatment of the cells with 4-NO-BP resulted in sulfinamide adduct formation. These results indicated that exposure to low concentrations of nitrosoarenes may lead to a loss of NAT1 activity, thereby compromising a critical detoxification process.

Formation and reduction of aryl and heterocyclic nitroso compounds and significance in the flux of hydroxylamines

Cytochrome p450 (p450) 1A2 and NADPH-P450 reductase (NPR) catalyzed the oxidation of 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), with consumption of NADPH. The oxidation rate of NADPH by p450 1A2/NPR increased with time in the presence of IQ until depletion of NADPH. This unusual autocatalytic pattern of NADPH oxidation could be rationalized by formation of a nitroso derivative (IQ-N=O) and the subsequent reduction of the hydroxylamine (IQ-NHOH) and IQ-N=O, which would consume more NADPH. The formation of IQ-NHOH and IQ-N=O from IQ was confirmed using HPLC/MS. Reduction of IQ-NHOH and IQ-N=O was NPR-dependent but did not require p450. Autocatalytic NADPH oxidation was also observed in the oxidation of other heterocyclic and arylamines. However, the N-hydroxyl and nitroso oxidation products of 2-aminofluorene and 4-aminobiphenyl were reduced nonenzymatically by NADPH, and NPR did not catalyze the reactions. We simulated the enzymatic kinetic model for possible pathways for IQ metabolism, which included the formation of IQ-N=O, using some kinetic parameters obtained from the experimental results. In the kinetic model, we could reproduce the similar curvature for NADPH oxidation and the formation of IQ-N=O, and the reduction of IQ-NHOH and IQ-N=O is required to explain the observed results for NADPH oxidation. Our results support a role for nitroso derivatives of HAAs in the unusual autocatalytic NADPH oxidation and may have relevance in terms of possible toxicities of the nitroso derivatives. Both IQ-NHOH and IQ-N=O were mutagenic in a bacterial tester system devoid of p450 and NPR; the mutagenicity of both was decreased by expression of NPR, consistent with the reduction of these compounds observed with purified NPR.

Lung retrieval from non-heart beating cadavers with the use of a rat lung transplant model

BACKGROUND

Lungs retrieved from cadavers after death and circulatory arrest may alleviate the critical shortage of lungs for transplant. We report a rat lung transplantation model that allows serial measurement of arterial blood gases after left single lung transplantation from non-heart beating donors.

METHODS

Twelve Sprague-Dawley rats underwent left lung transplantation with a vascular cuff technique. Donor rats were anesthetized with intraperitoneal injection of pentobarbital, heparinized, intubated via tracheotomy, and then killed with pentobarbital. Lungs were retrieved immediately or after 2 hours of oxygen ventilation after death (tidal volume 1 mL/100 g, rate 40/min FIO2 = 1.0, positive end-expiratory pressure 5 cm H2O). Recipient rats were anesthetized, intubated, and ventilated. The carotid artery and jugular vein were cannulated for arterial blood gases and infusion of Ringer's lactate (4 mL/h). Anesthesia was maintained with halothane 0.2%, and recipient arterial blood gases were measured at 4 and 6 hours after lung transplantation after snaring the right pulmonary artery for 5 minutes. Animals were put to death 6 hours after lung transplantation, and portions of transplanted lungs were frozen in liquid nitrogen and assayed for wet/dry ratio, myeloperoxidase as a measure of neutrophil infiltration, and conjugated dienes as a measure of free radical-mediated lipid peroxidation.

RESULTS

Arterial PO2 and wet/dry ratio were not significantly different in recipients of non-heart beating donor lungs retrieved immediately after death or after 2 hours of oxygen ventilation. Significant neutrophil infiltration was observed in recipients of non-heart beating donor lungs retrieved 2 hours after death from oxygen-ventilated donors.

CONCLUSIONS

Strategies to ameliorate reperfusion injury may allow for successful lung transplantation from non-heart beating donors.

A metabolite of carcinogenic 2-acetylaminofluorene, 2-nitrosofluorene, induces redox cycling in mitochondria

The present study was designed to confirm the recent proposal that 2-nitrosofluorene (2-NOF) as well as N-hydroxy-2-aminofluorene (N-OH-AF) induce a redox-cycle in rat liver mitochondria as part of the chronic toxic effects of the carcinogen 2-acetylaminofluorene (2-AAF). The formation of O2.- was demonstrated in submitochondrial particles by the formation of adrenochrome with NADH and succinate as respiratory substrates. 2-NOF was as effective as paraquat, a known redox-cycler, the lowest effective concentration being 0.4 nmol 2-NOF/mg protein. Experiments with isolated mitochondria showed that 2-NOF, in contrast to N-OH-AF, induces cyanide-resistant O2 consumption only in the presence of respiratory substrates, indicating that the reduction, but not the reoxidation, depends on a continuous flow of electrons through the respiratory chain of the mitochondrial membrane. Lipid peroxidation was estimated by the formation of thiobarbituric-acid-reactive substances. In comparison to the well-known prooxidant tert-butylhydroperoxide, 2-NOF was not significantly active. The results support the notion that 2-NOF induces oxidative stress by mitochondrial redox-cycling in vivo. Effects other than lipid peroxidation seem to be important for the chronic toxicity of 2-AAF.

Reactive radical intermediates formed from illuminated nifedipine

Nifedipine, (1,4-dihydro-2,6,dimethyl-4-(2-nitrophenyl)-3, 5-pyridinedicarboxylic acid dimethyl ester) a calcium channel blocker widely used in treatment of hypertension, is strongly photolabile. This may represent a problem in patients taking nifedipine and in handling of nifedipine samples. Reactive radical intermediates were determined and characterized in the process of nifedipine illumination using EPR spectroscopy. On illumination of nifedipine by daylight or by a mercury lamp, a nitroxide radical, RIIL-NIFNO.X was observed (in the first step), in various solvents like benzene, cyclohexane, methanol, acetonitrile, dimethylsulphoxide, or aqueous suspensions of liposomes. RIIL-NIF represents the nifedipine skeleton centered with phenyl group, and X is an EPR silent substituent. The generation of RIIL-NIFNO.X is coupled with the formation of nitroso compound, RIIL-NIFNO, as characterized by UV-visible spectroscopy. In a further step, RIIL-NIFNO abstracts hydrogen from nifedipine skeleton under the formation of RIIL-NIFNO.H radical. In addition to this, in system containing RIIL-NIFNO and unsaturated lipids, nitroxide radicals RIIL-NIFNO.RLIPIDS are formed probably via a pseudo Diels-Alder mechanism (RLIPIDS represents lipidic skeleton). The unusually easy photochemical activation of nifedipine is probably stimulated by photosensitization of its nitro group interacting with suitably positioned hydrogen or carboxylic methyl ester group from the pyridinyl ring.

Appearance of ESR signals by the reaction of 3,5-dibromo-4-nitrosobenzenesulfonate (DBNBS) and non-radical biological components

The reaction of 3,5-dibromo-4-nitrosobenzenesulfonate (DBNBS) with non-radical biological components produced spin adducts with ESR signals. The reactions of DBNBS with Trp, Gly-Trp, Trp-Gly, Pro, Cys and glutathione at pH 7.5 and room temperature for more than 1 hour gave the nitroxyl free radicals with ESR signals, whereas the reactions with other amino acids and bovine serum albumin did not. Among the amino acids and the peptides, Trp and Trp-containing peptides gave the most intense signals. The reactions of DBNBS with unsaturated fatty acids, i.e., linoleic acid and oleic acid, gave weak ESR signals, whereas the reaction with stearic acid did not. While DBNBS gave no ESR signals by the reactions with DNA, nucleosides and nucleobases, it caused strand breaking in supercoiled DNA. DBNBS also gave ESR signals by the reaction with human plasma similar to those from the reaction with Trp. It was suggested that the nitroxyl free radicals were produced by the addition of DBNBS to the amino acids and unsaturated fatty acids followed by oxidation in the presence of DBNBS. Hence, the use of DBNBS spin trap to detect free radicals in systems containing these biological components after long incubation may give misleading results.

Comparison of antioxidant properties of nifedipine and illuminated nifedipine with nitroso spin traps in low density lipoproteins and phosphatidylcholine liposomes

Illumination nifedipine, a calcium channel blocker, gives a nitroso-compound, 2,6-dimethyl-4-(2-nitrosophenyl)-3,5-pyridine-dicarboxylic acid dimethyl ester (NTP), which has spin trapping properties. The antioxidant ability of NTP was tested in a model of lipid peroxidation in low density lipoproteins (LDL) and phosphatidylcholine liposomes, and was compared with parent nifedipine and with other nitroso spin traps such as 3,5-dibromo-4-nitrosobenzene-sulfonic acid (BNTB), nitrosobenzene (NTB) and 2-methyl-2-nitrosopropane (MNP). Nifedipine (20-200 mumol/l) did not inhibit lipid peroxidation either in LDL on in liposomes, whereas its photolytical product NTP was found to be very effective at the same concentrations. The average antioxidant potencies of the nitroso spin traps were similar in both models and decreased in the order: NTP > or = BNTB > NTB > or = MNP. As detected by EPR spectroscopy, the studied nitroso compounds formed stable nitroxide radicals in a pseudo-Diels-Alder reaction, as a result of their interaction with unsaturated bonds of lipids in LDL and liposomes. The relative concentrations of thus formed radicals were in the order: NTP >> BNTB >> NTB approximately MNP and were related to their antioxidant properties. Thus it seems that the ability of the nitroso-compounds to form nitroxide radicals with unsaturated lipids may play a role in the antioxidant effect of these compounds.

Radiochemical quantitation of conjugated dienes in rat hepatocytes exposed to oxyradicals

Conjugated dienes are fingerprint signatures of oxidant damage in cells. We used a radiochemical method based on the Diels-Alder reaction of 14C-labeled tetracyanoethylene with conjugated dienes to delineate the changes of its levels in ischemia-reperfusion in the rat liver. To more directly illustrate the kinetics of diene appearance in hepatocytes, we have applied the same radiochemical assay to rat hepatocytes exposed to xanthine oxidase and hypoxanthine. We observed that the conjugated dienes rose to a maximum under our condition at approximately 10 min, while Trolox--an antioxidant derived from vitamin E found previously to protect rat hepatocytes from oxyradical damage (2)--markedly reduced the formation of conjugated dienes.

Formation of superoxide in the reaction of photolytically altered nifedipine--a nitroso compound--with unsaturated membrane lipids

Nifedipine, which is unstable at light, is photolytically converted to the corresponding 4-[2'-nitrosophenyl]-pyridine (NTP). We reported earlier that NTP react with unsaturated lipids in a pseudo Diels-Alder reaction, thus forming stable nitroxide radicals. In this paper we report that superoxide is being generated in the latter reaction. Superoxide formation was evidenced by SOD-inhibitable cytochrome c reduction in the reaction of NTP with egg phosphatidylcholine at molar ratio 1:1, and 1:3. In this reaction an ESR-observable nitroxide radical was formed. Maximum nitroxide formation was observed after 90 min; the addition of SOD (93 units/ml) increased the concentration of nitroxide. This effect of SOD was reversed by catalase, indicating involvement of hydrogen peroxide in this effect. The nitroxide radical formation appears to be metal-independent, since neither iron salts, nor an iron chelator, desferal, influenced the nitroxide formation. Although production of superoxide in our system was only observed at high concentrations of NTP and of unsaturated lipids, this reaction may be of potential cytotoxic significance due to redox cycling of the nitroxide/hydroxylamine couple in cellular systems.

Direct modification of low density lipoprotein by the spin trap 3,5-dibromo-4-nitrosobenzenesulfonic acid

We have previously reported that the spin trap alpha-phenyl-tert-butyl nitrone (PBN) inhibited the oxidative modification of low density lipoprotein (LDL) (Kalyanaraman, B., Antholine, W.E. and Parthasarathy, S. (1990) Biochim. Biophys. Acta 1035, 286-292). In the present study, we report that 3,5-dibromo-4-nitrosobenzenesulfonic acid (DBNBS), a water-soluble spin trap, also inhibited the oxidation of LDL as measured by the formation of thiobarbituric acid reactive substances (TBARS). However, when compared with LDL incubated without DBNBS, the DBNBS-incubated LDL showed increased negative charge on agarose gel electrophoresis and was avidly degraded by mouse peritoneal macrophages. Despite the suggestion of biological modification, there was no decrease in lysine-amino groups in DBNBS-incubated LDL. Furthermore, reductively methylated LDL in which more than 85% of the amino group of lysines was blocked, was also modified by DBNBS. A sulfonic acid analog of PBN failed to modify LDL in a similar manner, suggesting that the presence of sulfonic acid alone does not ensure modification. When LDL was incubated with DBNBS, radical adducts associated with both lipid and protein were detected by electron paramagnetic resonance (EPR) technique. It is suggested that DBNBS may bind to the apoprotein B100 and lipids of LDL by a lysine-independent mechanism resulting in increased recognition and degradation by macrophages. The present work offers a novel approach for rapid modification of LDL.

Interaction with microsomal lipid as a major factor responsible for S9-mediated inhibition of 1,8-dinitropyrene mutagenicity

1,8-Dinitropyrene (1,8-DNP), present in polluted air, is a rodent carcinogen and a potent, direct-acting mutagen in salmonella typhimurium TA98. This mutagenicity is markedly reduced in the presence of mammalian hepatic S9 or microsomes. We demonstrate that at least a substantial part of this effect is attributable to non-enzymatic processes. The microsomal-dependent inhibition was unaffected by omission of an NADPH-generating system or when the cytochrome P-450 inhibitor, SKF-525A, or the cytochrome P-448 inhibitor, ellipticine, was incorporated in the metabolic activation system, suggesting that mixed function oxidases are not involved. Heat inactivation partially decreased the ability of induced S9 to reduce DNP mutagenicity. Substitution of S9 with a similar concentration of bovine serum albumin did not affect DNP activity. Thus non-specific binding to microsomal protein is not involved. However, when lipids, derived from uninduced microsomes, were added to incubations of DNP and S. typhimurium TA98, mutagenicity was decreased. Furthermore, substitution of microsomal lipids with a suspension of phosphatidylcholine (PC), a major lipid constituent of microsomes, affected DNP mutagenicity similarly. An increase in PC concentration resulted in a greater inhibitory effect. The reduction in DNP mutagenicity observed with microsomal lipids or with PC was less than that detected with uninduced S9, whilst the mutagenicity of 2-nitrofluorene was reduced to an approximately equal extent by lipids and S9. This phenomenon may be responsible for the S9-mediated detoxification of other mutagenic nitroaromatic compounds and may have important implications for mutagenicity testing.

Radical adducts of nitrosobenzene and 2-methyl-2-nitrosopropane with 12,13-epoxylinoleic acid radical, 12,13-epoxylinolenic acid radical and 14,15-epoxyarachidonic acid radical. Identification by h.p.l.c.-e.p.r. and liquid chromatography-thermospray-m.s

Linoleic acid-derived radicals, which are formed in the reaction of linoleic acid with soybean lipoxygenase, were trapped with nitrosobenzene and the resulting radical adducts were analysed by h.p.l.c.-e.p.r. and liquid chromatography-thermospray-m.s. Three nitrosobenzene radical adducts (peaks I, II and III) were detected; these gave the following parent ion masses: 402 for peak I, 402 for peak II, and 386 for peak III. The masses of peaks I and II correspond to the linoleic acid radicals with one more oxygen atom [L(O).]. The radicals are probably carbon-centred, because the use of 17O2 did not result in an additional hyperfine splitting. Computer simulation of the peak I radical adduct e.p.r. spectrum also suggested that the radical is carbon-centred. The peak I radical was also detected in the reaction of 13-hydroperoxylinoleic acid with FeSO4. From the above results, peak I is probably the 12,13-epoxylinoleic acid radical. An h.p.l.c.-e.p.r. experiment using [9,10,12,13-2H4]linoleic acid suggested that the 12,13-epoxylinoleic acid radical is a C-9-centred radical. Peak II is possibly an isomer of peak I. Peak III, which was observed in the reaction mixture without soybean lipoxygenase, corresponds to a linoleic acid radical (L.). The 12,13-epoxylinoleic acid radical, 12,13-epoxylinolenic acid radical and 14,15-epoxyarachidonic acid radical were also detected in the reactions of linoleic acid, linolenic acid and arachidonic acid respectively, with soybean lipoxygenase using nitrosobenzene and 2-methyl-2-nitrosopropane as spin-trapping agents.

Interaction of C-nitroso aromatics with polyunsaturated fatty acids: route to lipid peroxidation

The possibility that the interaction of C-nitroso aromatics with polyunsaturated fatty acids (PUFA) causes lipid peroxidation was investigated through determination of conjugated diene and malodialdehyde (MDA) formation after anaerobic/aerobic vs. aerobic incubations of nitrosobenzene (NOB) or 2-nitrosofluorene (2-NOF) with linoleic, linolenic or arachidonic acid or methyl linolenate. Anaerobic incubation of NOB or 2-NOF with linolenic acid at the molar ratio of 1:1 for 24 h yielded approximately 5.5-13% of the PUFA as conjugated diene which appeared stable upon exposure to air. Interaction of PUFA and 2-NOF or NOB yielded MDA, the amounts of which were significantly greater when 24-h anaerobic preceded 1-6-h aerobic incubation. Furthermore, the differences in the amounts of MDA resulting from 24- and 0-h anaerobic incubations were significantly greater when the molar ratio of 2-NOF (or NOB) to PUFA was increased (2.0 greater than 1.0 greater than 0.5). Superoxide dismutase or catalase had no effect on the yields of MDA following either anaerobic/aerobic or aerobic incubations of PUFA and 2-NOF. EDTA (1 or 10 microM) had no effect on the yields of MDA from aerobic incubations, but it decreased the amounts of MDA (by approximately 30 or 60%, respectively) from anaerobic/aerobic incubations. The data suggested that inhibition by EDTA was due to chelation of trace iron, which following anaerobic interaction of PUFA and 2-NOF might have been reduced to Fe2+ and contributed to the enhanced lipid peroxidation. Thus, adduction of C-nitroso aromatics to PUFA yields radical species which directly and/or via reaction with trace iron lead to lipid peroxidation. The lipophilicity of C-nitroso aromatics suggests that this process may be of consequence in their mutagenesis/carcinogenesis.

Covalent interaction of 3,3'-dichlorobenzidine with hepatic lipids. Enzymic basis and stability of the adducts

Administration of a single oral dose (20 mg/kg) of [U-14C]3,3'-dichlorobenzidine to rats resulted in the in vivo covalent binding of the compound to hepatic lipids. More than 70% of the lipid-3,3'-dichlorobenzidine adducts were accounted for in microsomes. Loss of the lipid-bound 3,3'-dichlorobenzidine residues from either total liver or endoplasmic reticulum occurred in at least two phases--an initial fast phase and a terminal slow phase. In vitro studies with hepatic microsomes in the presence of antibodies to specific P450 isozymes and chemical inhibitors to determine the enzymes that activate 3,3'-dichlorobenzidine to the lipid-binding derivative(s) implicated cytochrome P450d. The 3,3'-dichlorobenzidine-bound microsomal lipids were not mutagenic to Salmonella TA98 in the Ames test. The results suggest that adduct formation between 3,3'-dichlorobenzidine and membrane lipids may provide a measure of 3,3'-dichlorobenzidine activation. It is speculated that covalent interaction of the compound with membrane lipids may modify cellular processes, leading to either enhancement or attenuation of carcinogenesis by the chemical.

Spin trapping of lipid-derived radicals in liposomes

Electron-spin resonance-spin trapping has been used to detect lipid-derived radicals in liposomes. Using the lipid-soluble spin trap 2-methyl-nitrosopropane (MNP), we have detected both the lipid and hydrogen-atom spin adducts in liposomes composed of a fully saturated phospholipid (dimyristoylphosphatidylcholine, DMPC) with various mol fractions of unsaturated phospholipid (1-palmitoyl-2-arachidonoylphosphatidylcholine, PAPC) or fatty acid (arachidonic acid, AA). The lipid-derived spin adduct formed during autoxidation of liposomes was separated by thin-layer chromatography and found to co-migrate with the product(s) formed by direct addition of MNP to the corresponding unsaturated lipid or fatty acid. Both the MNP-PAPC and MNP-AA spin adducts showed some restriction of rotational motion when in the liposome bilayer (rotational correlation times 0.72 and 0.69.10(-9) s, respectively), and nitrogen hyperfine coupling constants (14.94-14.96 G) consistent with a hydrophobic localization. Radical versus non-radical mechanisms of spin adduct formation during liposome autoxidation were separated using alpha-tocopherol as a radical scavenger. The utility of nitroso spin traps in trapping of radicals in liposomes is discussed.

Possible role of certain antioxidant enzymes in dimethylnitrosamine-induced liver carcinogenesis

An investigation was carried out to establish whether the reduction in catalase, glutathione peroxidase and superoxide dismutase activity, normally observed in liver tumours, is an early event and therefore of pathogenetic importance, or whether it is a late occurrence. Experiments performed on dimethylnitrosamine-treated hepatectomized and non-hepatectomized rats show that the decrease in activity of these enzymes is entirely due to hepatectomy, since the tumour-inducing doses of dimethylnitrosamine failed to provoke variations in the activity of these enzymes, in either normal or regenerating liver.

Stimulation of the conjugation of lipid dienes in hepatic microsomes by 3,3'-dichlorobenzidine

Pretreatment of male rats with 3,3'-dichlorobenzidine (DCB) resulted in the accumulation of conjugated dienes in lipids from hepatic microsomes. In vitro, these microsomes had 2-fold the NADPH-dependent malondialdehyde (MDA)-forming capacity of microsomes from untreated rats. To determine the mechanisms of the DCB-induced accumulation of diene conjugation, the effects of added DCB on NADPH- or iron + ascorbic acid- (Fe2+-ascorbate-) dependent diene conjugation, oxygen uptake and MDA formation were examined in microsomes from untreated rats in vitro. In the presence of NADPH, added DCB stimulated diene conjugation in microsomal lipids as did in vivo DCB pretreatment but inhibited the uptake of oxygen and the formation of MDA. When Fe2+-ascorbate was substituted for NADPH, the formation of diene conjugation, oxygen uptake, and MDA formation were inhibited by added DCB. The DCB-induced stimulation of diene conjugation, in addition to being strictly NADPH dependent, was carbon monoxide sensitive and was concomitant with the binding of added DCB to microsomal lipids. It is postulated that a metabolite of DCB generated by cytochrome P-450 reacts with membrane lipids both in vivo and in vitro in a manner analogous to the initiation of lipid peroxidation but at the same time prevents the autocatalytic decomposition of the lipids. The DCB-induced diene conjugation is interpreted as predisposing to deleterious changes in microsomes.

Relationship between the covalent binding of N-acetoxy-2-acetylaminofluorene to DNA and a steroidal esterase activity in human mononuclear leukocytes

A method for the quantitative assessment of steroidal esterase activity in viable human mononuclear leukocytes (HML) has been developed. It is based on estimating the conversion of [3H]beclomethasone-17,21-dipropionate (BDP) to beclomethasone-17-monopropionate (BMP) using TLC on silica gel 60 F-254 plates developed in a solvent system of chloroform/methanol (97:3, v/v). The cell assay procedure was dependent on BDP concentration, incubation time and cell concentration. The steroidal esterase activity was completed for by N-acetoxy-N-acetyl-2-aminofluorene (NA-AAF) and completely inhibited by 100 microM paraoxon. When [3H]NA-AAF binding to DNA was used as an indicator of HML esterase (deacylase) activity, BDP functioned as a substrate inhibitor. Parallel estimations of BDP metabolism and NA-AAF binding to DNA indicated striking correlations in the interindividual variations (r = 0.62, P less than 0.001) and in relation to the menstrual cycle events of a healthy female. Hence, these data indicate that both BDP and NA-AAF are metabolized by the same non-specific steroidal esterase present in HML.

N-hydroxy-N-arylacetamides. II: Molecular aspects of ferrihaemoglobin formation by N-hydroxy-N-arylacetamides and arylhydroxylamines in the rat

Ferrihaemoglobin (HbFe3+) formation in rats after i.p. injection of 6 N-hydroxy-N-arylacetamides has shown that N-hydroxy-4-chloroacetanilide(N-hydroxy-4ClAA) was the most active and N-hydroxy-2-acetylaminofluorene(N-hydroxy-2AAF) the least active compound tested. As N-hydroxy-N-arylacetamides were thought to produce HbFe3+ only after enzymic N-deacetylation, the corresponding arylhydroxylamines were also tested for HbFe3+-forming activity and were found to be more active, N-hydroxy-4-chloroaniline(N-hydroxy-4ClA) being one of the most active and N-hydroxy-2-aminofluorene(N-hydroxy-2AF) the least active compound tested. N-Hydroxy-4-chloroacetanilide given i.p. to rats more rapidly invaded the blood and produced larger amounts of ferrihaemoglobin than did N-hydroxy-2-acetylaminofluorene, due to differences in their availability in plasma. Injection of 50 mg/kg of N-hydroxy-4-chloroacetanilide gave similar concn of HbFe3+ and 4-chloronitrosobenzene(4-CINOB) as injections of 8 mg/kg of N-hydroxy-4-chloroaniline, indicating that the arylhydroxylamine, after N-deacetylation, was the active molecule in vivo. The concn of 4-chloronitrosobenzene declined faster than HbFe3+ concn. 4-Chloronitrosobenzene therefore is a further example of a 'hit-and-run' chemical. Inhibition by the microsomal carboxylesterase inhibitor, bis(4-nitrophenyl)phosphate(BNPP), indicated that ferrihaemoglobin formation by 4-chloroacetanilide, but not by N-hydroxy-4-chloroacetanilide, depends on the enzymic activity of hepatic microsomal carboxylesterases.

N-Oxidation of 4-chloroaniline by prostaglandin synthase. Redox cycling of radical intermediate(s)

4-Chloroaniline undergoes N-oxidation in ram seminal-vesicle microsomal preparations supplemented with arachidonic acid to yield N-(4-chlorophenyl)-hydroxylamine and 1-chloro-4-nitrosobenzene. H2O2 also supports metabolism of the amine substrate to the same organic-solvent-extractable products, suggesting that the hydroperoxidase activity of prostaglandin synthase is responsible for the co-oxidation. Analysis of the reaction mixtures by e.s.r. spectrometry reveals the formation of a radical intermediate bearing the characteristics of a strongly immobilized nitroxide. Arylamine-stimulated O2.- release can be observed when the arachidonic acid-containing incubation media are supplemented with NADPH. Redox cycling of the nitroxide/hydroxylamine couple is presumed to represent the major source of O2.-, but additional mechanisms, such as redox changes of nitro anion radicals resulting from potential further metabolism of 1-chloro-4-nitrosobenzene, cannot be excluded. The concerted action of carrier-bound nitroxides and O2.- in initiating damage of cellular macromolecules is discussed.

Hydroxyl free radical reactions with amino acids and proteins studied by electron spin resonance spectroscopy and spin-trapping

It has recently been shown that Fe(I) complexes of ADP or ATP generate OH radicals with H2O2 in a Fenton-type reaction. The OH radicals can be detected by using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as a spin trap in electron spin resonance spectroscopy. All the biologically occurring amino acids, some related compounds and several proteins (histone, bovine serum albumin, collagen) were tested as OH radical scavengers against DMPO. The tested compounds competed with DMPO in trapping OH radicals to various extents as shown by the decrease of signal intensity of DMPO-OH spin-adduct. The tested compounds did not oxidize Fe(II) itself, with the only exception being tyrosine, as revealed by properly designed ferrozine reaction. Some of the amino acids reacted also with the DMPO-OH spin-adduct to a certain extent, whereas others did not. The formation of carbon centered organic radicals of the amino acids could be detected under the influence of OH radicals by using the spin traps phenyl-tert-butylnitrone (PBN) and alpha-pyridyl-1-oxide-N-tert-butylnitrone (4-POBN). The proteins, however, did not react with these spin traps. One can conclude that the amino acids and proteins can be targets of OH radical damage even in vivo, and such phenomena may be of importance in the deterioration of the conformation of proteins, e.g., during aging or in some pathological processes.

Cytochrome c/H2O2-mediated one electron oxidation of carcinogenic N-fluorenylacetohydroxamic acids to nitroxyl free radicals

The oxidation of carcinogenic hydroxamic acids, N-hydroxy-N-2-fluorenylacetamide (N-OH-2-FAA) and N-hydroxy-N-3-fluorenylacetamide (N-OH-3-FAA) catalyzed by horseradish peroxidase (HRP) or cytochrome c in the presence of H2O2 was investigated. HRP/H2O2 was a more efficient system in oxidation of both hydroxamic acids and the standard substrate, guaiacol, then cytochrome c/H2O2. Peroxidative activity of cytochrome c was shown after incubation with Triton X-100 and H2O2 for 20 min at room temperature in 0.05 M phosphate buffer (pH 7.5) or in 0.1 M sodium acetate (pH 6.0) without Triton X-100. Both hydroxamic acids were oxidized to nitroxyl free radicals as shown by electron spin resonance (ESR) spectroscopy. These radicals dismutated to equimolar amounts of 2- or 3-nitrosofluorene and acetate esters of the corresponding hydroxamic acids as shown by thin layer chromatography and spectrophotometric analysis of the products. In addition, large amounts of the N-fluorenylamides were generated in the reactions with cytochrome c/H2O2 system. Of the products, only 2- or 3-nitrosofluorene per se or when generated from the oxidation of the hydroxamic acids, interacted with lecithin (1 mg/ml) to yield ESR signals of the immobilized nitroxyl free radicals. In contrast to HRP/H2O2 system, in which the initial velocity of the radical formation was too fast to measure and the maximal concentrations of the nitroxyl free radicals of both hydroxamic acids were similar, in the cytochrome c/H2O2 system the nitroxyl free radical of N-OH-2-FAA formed at a 6-fold faster rate and accumulated at a 2-fold higher concentration than the radical of N-OH-3-FAA. In both enzyme systems, the persistence of the signal and the length of time before it had decreased to one half its maximum were several-fold longer for the nitroxyl free radical of N-OH-3-FAA than for that of N-OH-2-FAA. These data showed that these nitroxyl free radicals differed in their kinetic properties. One electron oxidation of N-OH-3-FAA by HRP/H2O2 system and of both isomeric hydroxamic acids by cytochrome c/H2O2 system are reported for the first time in this work and may be considered an activation reaction in carcinogenesis by these compounds.

Direct demonstration that ferrous ion complexes of di- and triphosphate nucleotides catalyze hydroxyl free radical formation from hydrogen peroxide

Utilizing an electron paramagnetic resonance (EPR) spin-trapping technique it was demonstrated that the di- and triphosphate nucleotides of adenosine, cytidine, thymidine, and guanosine in the presence of Fe(II) catalyze hydroxyl free radical formation from H2O2. The triphosphate nucleotides in general were about 20% more effective than the diphosphate nucleotides. The amount of OH produced from H2O2 as a function of nucleotide level tended to increase in a sigmoidal fashion beginning at a nucleotide/Fe(II) ratio of 2 but then rose rapidly up to a ratio of 5 at which point the increase became more gradual. The monophosphate nucleotides did not cause an increase in the amount of hydroxyl free radical produced from H2O2 over the low level obtained in the buffer system only. The cations, Mg2+ and Ca2+, even at much higher than physiological levels and much higher than the level of added Fe(II), did not cause a substantial diminution of the Fe(II)-nucleotide-catalyzed breakdown of H2O2 to yield OH. A study of the time course of the effectiveness of Fe(II)-nucleotide-mediated OH formation from H2O2 demonstrated that Fe(II) in the presence of nucleotides remained in an effective catalytic state with a halftime of about 160 s whereas in the absence of the nucleotides the halftime was 7.5 s. All observations indicate that Fe(II) ligates with di- and triphosphate nucleotides and remains in the ferrous state which is then capable of catalyzing OH formation from H2O2; but with time, oxidation of the metal ion to the ferric state occurs, which either ligated to the nucleotide or to buffer ions, is ineffective in H2O2 catalysis to yield OH. Iron-nucleotide complexes may be of importance in mediating oxygen free radical damage to biological systems. The observations presented here indicate that hydroxyl free radicals will be produced when H2O2 is present with ferrous-nucleotide complexes.

Interactions between the active metabolite of tryptophan pyrolysate mutagen, N-hydroxy-Trp-P-2, and lipids: the role of lipid peroxides in the conversion of N-hydroxy-Trp-P-2 to non-reactive forms

The interactions between lipids and the mutagenic active metabolite of 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2) and 3-hydroxyamino-1-methyl-5H-pyrido[4,3-b]indole (N-hydroxy-Trp-P-2), were studied. Oleic acid showed an inhibitory effect on the formation of this active metabolite mainly by inhibition of hepatic microsomal oxidation systems. On the other hand, microsomal lipids from rat liver and commercial pig liver lecithin diminished the amount of N-hydroxy-Trp-P-2 without inhibiting the metabolism of Trp-P-2. The direct reaction of these lipids with N-hydroxy-Trp-P-2 was disclosed by experiments using N-hydroxy-Trp-P-2 and lipids without microsomes. Furthermore, the participation of lipid peroxides in this reaction was suggested by a linear relationship between the concentrations of the conjugated diene of lipids and the disappearance of N-hydroxy-Trp-P-2. When [3H]N-hydroxy-Trp-P-2 was incubated in the presence of pig liver lecithin, the polar products which were not formed in the incubation without lipids were newly detected by thin-layer chromatography (TLC) analysis.

Effects of peroxides on rodent skin: epidermal hyperplasia and tumor promotion

Free radical generating peroxides are potent skin irritants. After a single topical application of either 10, 20, or 40 mg of lauroyl peroxides or benzoyl peroxide on the dorsal skin of Sencar mice, the epidermal thickness increased markedly. No major inflammatory or vascular alterations were noted. On the other hand, 15 or 30% hydrogen peroxide produced an extensive epidermolysis, as well as inflammation and vascular injury, followed by quick regeneration and epidermal hyperplasia. Both lauroyl peroxide- and benzoyl peroxide-induced hyperplasias were characterized by a sustained production of dark basal keratinocytes, which constituted approximately 10% of the basal cell population during the first week after single topical application. Hydrogen peroxide-induced epidermal hyperplasias also exhibited numerous dark cells, but their presence was less sustained. Although all these peroxides were inactive either as initiators or as complete carcinogens, lauroyl peroxide was as effective as benzoyl peroxide when used as a skin tumor promoter in a two-stage carcinogenesis protocol. In a similar experimental protocol, hydrogen peroxide proved to be a very weak skin tumor promoter.

Specificity of a phenobarbital-induced cytochrome P-450 for metabolism of carbon tetrachloride to the trichloromethyl radical

Evidence is presented which demonstrates that the first polypeptide to disappear in liver microsomes of phenobarbital-induced rats treated with CC14 was the 52,000 dalton p-450 cytochrome. Data are also presented which show that this form of cytochrome P-450 was capable of generating the trichloromethyl radical from CCl4 in a reconstituted system containing the purified cytochrome, NADPH-cytochrome P-450 reductase, NADPH, CCl4, and the spin-trapping agent, phenyl-t-butyl nitrone. Other cytochrome P-450 fractions not containing the 52,000 dalton form did not produce this radical. The formation of this highly reactive radical may have resulted in localized damage to the cytochrome, causing the cytochrome either to be released from the microsomal membrane or to form large aggregates which did not migrate in the gel electrophoretic procedures employed.

A new technique of depositing phospholipid bilayers on quartz surfaces: its use in membrane spin-label studies

We have developed a new improved technique termed the parallel-beam spattering (PBS) method for depositing phospholipid bilayers on quartz surfaces. This technique involves atomizing the phospholipid mixture with a stream of nitrogen gas and passing this atomized mixture through two orifices separated by a distance to achieve a parallel beam of atomized particles before deposition on the quartz plate. A static electric field can easily be applied to the quartz surface. Also a goniometer of new design has been constructed to allow precise positioning of the deposited phospholipid bilayers with reference to the magnetic field. We have utilized the PBS method to deposit phosphatidylcholine/nitroxyl labeled cholestane mixtures on quartz plates and have found that hydrated bilayers of these mixtures yield ESR spectra with essentially the same characteristics as those obtained using more conventional techniques. The distinct advantage of the new technique for depositing bilayers is that there is no spectral anomaly present which usually is present when the more conventional method of depositing bilayers is used. The spectral anomaly is apparently caused by a portion of the bilayers aligned in directions not directly parallel to the quartz surface. For precision work the spectral anomaly is unacceptable. It is not observed with the new PBS method which has yielded highly reproducible results.

The role of lipophilicity in the extrahepatic disposition of aminostilbene derivatives following administration to rat

1. Carcinogenic trans-4-dimethylaminostilbene and its unbound metabolites in rat tissues are highly lipophilic with partition coefficients of 10 000 to 80 000. The values for bibenzyl derivatives are somewhat lower. 2. Sulphates and glucuronic acid conjugates are present in liver, kidney, blood and bile, but not to any extent in other extrahepatic tissues. 3. The patterns of unbound metabolites in lung, spleen, adrenals, brain and fat after oral administration of 3H-labelled trans-4-dimethylaminostilbene, cis-4-dimethylaminostilbene and 4-dimethylaminobibenzyl have been determined. The concn. of tissue metabolites do not parallel plasma concn. of metabolites and do not correlate with lipophilicity. 4. Binding of trans-4-aminostilbene metabolites to tissue proteins is 3--5 times greater than that of cis-4-aminostilbene metabolites and more than 10 times higher than that of aminobibenzyl metabolites. In Zymbal gland, the target tissue for trans-4-dimethylaminostilbene carcinogenicity, the tissue concn. of reactive metabolites is insufficiently high to account for the specific effect. 5. The analysis of fat tissue provided circumstantial evidence that reactive metabolites bind covalently to fatty acids.

Studies of the fatty acid composition and membrane microviscosity in Salmonella typhimurium TA98

When the mutagen tester bacterial strain Salmonella typhimurium TA 98 was grown at different temperatures, we found that the unsaturated fatty acid composition increased at the lower growth temperatures. Membrane microviscosity, as assessed with spin-probe fatty acids using electron spin resonance, decreased as the unsaturated fatty acid content increased. These findings are of importance in understanding our recent observation that the mutagenic response of these bacteria was increased when they were grown at 27 degrees C vs. 37 degrees C, and indicate that membrane properties may play an important role in the sequence of events leading to mutagenesis.

Redox cycle of stable mixed nitroxides formed from carcinogenic aromatic amines

1. Of the carcinogenic aromatic nitrogenous compounds investigated, 10 out of 11 were found to be biotransformed in rabbit liver microsomal preparations to nitroxide radicals, as detected by ESR spectroscopy; with non-carcinogenic nitrogenous compounds only 2 out of 8 formed nitroxide radicals. 2. The radicals are stable mixed nitroxides formed by covalent binding of the aromatic nitroxide to endogenous constituents of the microsomal membrane with preservation of the nitroxide radical group (spin-trapping). 3. From the high chemical stability and the observed ESR spectra, spin-label-like structures can be deduced. 4. From this and the known one-electron redox properties of spin-labels, a redox cycle catalysing the production of reactive oxygen species and involved in tumour initiation and/or promotion by aromatic nitrogenous compounds is proposed.

Binding and mutagenicity studies with 2-nitrosofluorene on Salmonella typhimurium TA98 grown at different temperatures

The growth temperature of the histidine auxotroph Salmonella typhimurium TA98 influences the extent of binding of 2-nitrosofluorene (NOF) to this bacterium as well as the mutagenicity of this chemical carcinogen. Gas-liquid chromatography (GLC) of bacteria grown at 37, 27 and 17 degrees C revealed that the unsaturated (hexadecenoic plus octadecenoic) fatty-acid content increased from 15.0% at 37 degrees C to 20.5% at 27 degrees C and to 22.2% at 17 degrees C. It has been shown using both artificial and natural mammalian membranes that NOF adds to carbon-carbon double bonds in unsaturated fatty acids via an "Alder-ene" type reaction to produce a nitroxyl free radical adduct (N-O-LAF). The same adduct was formed when NOF was incubated with Salmonella typhimurium TA98. There was an increase in N-O-LAF formed in bacteria grown at 27 degrees C as compared to those grown at 37 degrees C, but very little formed in bacteria grown at 17 degrees C. Therefore the amount of N-O-LAF formed did not correlate with unsaturated fatty-acid content. 14C-labeled NOF uptake in bacteria grown at different temperatures showed a good correlation with mutagenicity data.