Inhibition of lipolysis: A novel explanation for the hypothermic actions of acetaminophen in non-febrile rodents.

Acetaminophen is both widely used to treat children with fever and is also responsible for thousands being hospitalised annually. Historically the antipyretic actions of acetaminophen were attributed to the inhibition of cyclooxygenase (COX-1/2) enzymes and more recently a novel COX-1 variant (COX-3) located in the brain. However, the evidence for acetaminophen-mediated COX inhibition remains contentious. This study assesses the impact of acetaminophen and other putative COX-3 inhibitors on the release of fatty acids during lipolysis as an alternative mechanism by which antipyretics can reduce body temperature during fever. 3T3-L1 adipocytes, primary brown adipocytes and isolated mitochondria were exposed to COX-3 inhibitors and lipolysis and mitochondrial electron transport chain function assessed. Acetaminophen, aminopyrine and antipyrine at 1-10 mM caused a significant decrease (up to 70%; P < 0.01, from control) in lipolysis within 1, 3 and 24 h without affecting cell viability. The inhibition was observed regardless of where along its signalling pathway lipolysis was stimulated. All three compounds were found to significantly attenuate mitochondrial function by up to 30% for complex I and 40% for complex II (P < 0.01, from control). These novel observations combined with the known limited inhibition of the COX enzymes by acetaminophen suggest both the antipyretic and hypothermia induced by acetaminophen and related compounds could be attributed to the direct inhibition of lipolysis and mitochondrial function, rather than cyclooxygenase inhibition centrally. Further these observations could provide new drug targets for reducing fever with the added bonus of fewer individuals being hospitalized by accidental acetaminophen overdose.

Acetaminophen and Metamizole Induce Apoptosis in HT 29 and SW 480 Colon Carcinoma Cell Lines In Vitro.

BACKGROUND/AIM: The perioperative phase is supposed to be a period with high vulnerability for cancer dissemination. Acetaminophen and metamizole are common analgesics administered during this phase. We investigated the effect of acetaminophen, metamizole and 4-methylaminoantipyrine (MAA) on proliferation and apoptosis of colon carcinoma cell lines (SW 480 and HT 29). MATERIALS AND METHODS: Proliferation was detected by cell proliferation ELISA BrdU, and apoptosis by Annexin V staining. Cytochrome c and caspase 3, 8 and 9 expression levels were detected by western blot. RESULTS: Acetaminophen, metamizole or MAA caused slight changes in proliferation. Acetaminophen, metamizole or the combination increased apoptosis in both cell lines. All agents decreased caspase 3 and 8 expression in SW480. Acetaminophen decreased caspase 9 expression in both cell lines. CONCLUSION: In clinically relevant doses, acetaminophen and/or metamizole induce apoptosis in both colon cancer cell lines. Both mitochondrial and death receptor pathways might be involved in acetaminophen-induced apoptosis.

Immobilized immune complexes induce neutrophil extracellular trap release by human neutrophil granulocytes via FcγRIIIB and Mac-1.

Canonical neutrophil antimicrobial effector mechanisms, such as degranulation, production of reactive oxygen species, and release of neutrophil extracellular traps (NETs), can result in severe pathology. Activation of neutrophils through immune complexes (ICs) plays a central role in the pathogenesis of many autoimmune inflammatory diseases. In this study, we report that immobilized ICs (iICs), which are hallmarks of several autoimmune diseases, induce the release of NETs from primary human neutrophils. The iIC-induced NET formation was found to require production of reactive oxygen species by NADPH oxidase and myeloperoxidase and to be mediated by FcγRIIIb. Blocking of the ß2 integrin macrophage-1 Ag but not lymphocyte function-associated Ag-1 abolished iIC-induced NET formation. This suggests that FcγRIIIb signals in association with macrophage-1 Ag. As intracellular signaling pathways involved in iIC-induced NET formation we identified the tyrosine kinase Src/Syk pathway, which downstream regulates the PI3K/Akt, p38 MAPK, and ERK1/2 pathways. To our knowledge, the present study shows for the first time that iICs induce NET formation. Thus, we conclude that NETs contribute to pathology in autoimmune inflammatory disorders associated with surface-bound ICs.

Efficacy of the non-adenosine analogue A1 adenosine receptor agonist (BR-4935) on cardiovascular function after cardiopulmonary bypass.

BACKGROUND: We tested the hypothesis that pharmacological preconditioning with a newly developed, potent non-adenosine analogue A1AdoR agonist (BR-4935) improves biventricular cardiac and endothelial function after cardiopulmonary bypass. METHODS: Twelve anesthetized dogs underwent cardiopulmonary bypass. Dogs were divided into two groups: group 1 (n = 6) received saline vehicle, group 2 (n = 6) received BR-4935 before cardiopulmonary bypass. Biventricular hemodynamic variables were measured using a combined pressure-volume conductance catheter. Coronary blood flow, ATP content, malondialdehyde and myeloperoxidase levels and vasodilatative responses to acetylcholine and sodium nitroprusside were also determined. RESULTS: Administration of the A1AdoR agonist led to a significantly better recovery of left and right ventricular systolic function after 60 minutes of reperfusion. Although the vasodilatative response to sodium nitroprusside was similar in both groups, acetylcholine resulted in a significantly greater increase in coronary blood flow in the BR-4935 group. In addition, the ATP content was significantly higher in the same group. Furthermore, malondialdehyde and myeloperoxidase levels significantly decreased in the A1AdoR group. CONCLUSION: Pharmacological preconditioning with a new, potent non-adenosine analogue A1AdoR agonist improves biventricular function recovery and endothelial function after hypothermic cardiac arrest.

Mediation of the behavioral, endocrine and thermoregulatory actions of ghrelin.

The action of ghrelin on telemetrically recorded motor activity and the transmission of the effects of this neuropeptide on spontaneous and exploratory motor activity and some related endocrine and homeostatic parameters were investigated. Different doses (0.5-5 microg) of ghrelin administered intracerebroventricularly caused significant increases in both square crossing and rearing activity in the "open-field" apparatus, while only the dose of 5 microg evoked a significant increase in the spontaneous locomotor activity recorded by telemetry. Ghrelin also induced significant increases in corticosterone release and core temperature. To determine the transmission of these neuroendocrine actions, the rats were pretreated with different antagonists, such as a corticotropin-releasing hormone (CRH) antagonist (alpha-helical CRH(9-41)), the nitric oxide synthase inhibitor Nomega-nitro-L-arginine-methyl ester (L-NAME), haloperidol, cyproheptadine or the cyclooxygenase inhibitor noraminophenazone (NAP). The open-field and biotelemetric observations revealed that the motor responses were diminished by pretreatment with the CRH antagonist and haloperidol. In the case of HPA (hypothalamic pituitary adrenal) activation, only cyproheptadine pretreatment proved effective; haloperidol and L-NAME did not modify the corticosterone response. NAP had only a transient, while cyproheptadine elicited a more permanent impact on the hyperthermic response evoked by ghrelin; the other antagonists proved to be ineffective. The present data suggest that both CRH release and dopaminergic transmission may be involved in the ghrelin-evoked behavioral responses. On the other hand, ghrelin appears to have an impact on the HPA response via a serotonergic pathway and on the hyperthermic response via a cyclooxygenase and a serotonergic pathway.

Acetaminophen-induced hypothermia in mice is mediated by a prostaglandin endoperoxide synthase 1 gene-derived protein.

Acetaminophen is a widely used antipyretic analgesic, reducing fever caused by bacterial and viral infections and by clinical trauma such as cancer or stroke. In rare cases in humans, e.g., in febrile children or HIV or stroke patients, acetaminophen causes hypothermia while therapeutic blood levels of the drug are maintained. In C57/BL6 mice, acetaminophen caused hypothermia that was dose related and maximum (>2 degrees C below normal) with a dose of 300 mg/kg. The reduction and recovery of body temperature was paralleled by a fall of >90% and a subsequent rise of prostaglandin (PG)E(2) concentrations in the brain. In cyclooxygenase (COX)-2(-/-) mice, acetaminophen (300 mg/kg) produced hypothermia accompanied by a reduction in brain PGE(2) levels, whereas in COX-1(-/-) mice, the hypothermia to this dose of acetaminophen was attenuated. The brains of COX-1(-/-) mice had approximately 70% lower levels of PGE(2) than those of WT animals, and these levels were not reduced further by acetaminophen. The putative selective COX-3 inhibitors antipyrine and aminopyrine also reduced basal body temperature and brain PGE(2) levels in normal mice. We propose that acetaminophen is a selective inhibitor of a COX-1 variant and this enzyme is involved in the continual synthesis of PGE(2) that maintains a normal body temperature. Thus, acetaminophen reduces basal body temperature below normal in mice most likely by inhibiting COX-3.

Allergic cholestatic hepatitis and exanthema induced by metamizole: verification by lymphocyte transformation test.

We report about a 66-year-old-male patient who was hospitalized with generalized exanthema and increase of liver enzymes after intake of metamizole because of flue-like symptoms. Despite initial high dose steroids, disease activity persisted, and therefore liver biopsy was performed. Histology revealed acute hepatitis with perivenular non-bridging confluent necrosis and granuloma formation consistent with drug-induced hepatitis. A metamizole-induced process was suspected. Lymphocyte transformation test confirmed the sensitization of the patient's lymphocytes to metamizole and three of its four metabolites (4-methylaminoantipyrine, 4-acetylaminoantipyrine and 4-formylaminoantipyrine). Other drugs could be excluded with high probability. In the follow-up, the general condition of the patient improved, and liver enzymes decreased under treatment with steroids. Thus, we conclude that in this patient metamizole has induced an allergic reaction not only of the skin but also of the liver. To our knowledge, an allergic cholestatic hepatitis caused by metamizole has been reported only once in literature.

Pituitary adenylate cyclase-activating polypeptide induces hyperthermia in the rat.

The effects of centrally administered pituitary adenylate cyclase-activating polypeptide (PACAP-38) on body temperature were investigated in rats. Intracerebroventricular (i.c.v.) administration of PACAP-38 in doses of 500 and 1000 ng induced a dose-related elevation in colon temperature 2, 3, 4, 5 and 6 h after injection. The i.c.v. pretreatment of the animals with different dilutions of PACAP-38 antiserum prevented the development of hyperthermia in PACAP-38-treated animals, whereas PACAP-38 antiserum alone did not modify the colon temperature. An intramuscular injection of noraminophenazone (a cyclooxygenase inhibitor) abolished the PACAP-38-induced hyperthermia. Our data indicate that PACAP may induce hyperthermia via the central nervous system, and this hyperthermic effect may be mediated via a cyclooxygenase-involved pathway.

Effect of food products on endogenous generation of N-nitrosamines in rats.

An experiment was conducted to study the efficacy of two tomato pastes and aronia nectar (fruit juice + pulp from the black chokeberry, Aronia melanocarpa Elliot) as inhibitors of nitrosamine production in cancer prophylaxis programmes. White male rats of the Wistar strain were employed in an acute trial. Aminopyrin+sodium nitrite (APSN) were used as precursors for generation of endogenous nitrosamine. The animals were allocated to different dietary groups and fed by intubation with APSN or APSN + food products. Introduction of tomato paste (TP), high-beta-carotene tomato paste (HCTP) and aronia nectar (AN) as inhibitors of N-nitrosamine formation exerted a positive effect on blood and liver variables which was demonstrated by decreased concentrations of glutamic-oxaloacetic transaminase (EC 2.6.1.1), glutamic-pyruvic transaminase (EC 2.6.1.2) and uric acid in serum and lipid content in hepatocytes. Animals treated with APSN developed dystrophic changes in liver such as centrolobular necrosis, intense exangia, and enlarged cells with two, often large, pyknotic nuclei, while the structure of livers of rats fed with TP, HCTP or AN was well protected and almost normal. TP had a particularly beneficial effect on serum total protein and albumin concentrations as had AN on the urea value. The inhibitory effect of the food products used is explained by their chemical nature including pH, ascorbic index (ascorbate:nitrate), lycopene and beta-carotene contents.

Effect of Helicobacter pylori on dbc-AMP stimulated acid secretion by human parietal cells.

This study examines the effect of different H.p. strains (A-D) on dbc-AMP stimulated acid secretion by human parietal cells in vitro. H.p. strains A and D reduced acid secretion dose-dependently between 20 and 80%. In contrast, H.p. strains B and C had little or no effect. We conclude that H.p. strains vary in their ability to suppress acid secretion, and that the site of inhibition lies beyond the c-AMP level, possibly involving the K+H(+)-ATPase of the parietal cell. Interference with acid secretion may facilitate H.p. colonization of the stomach and may prove to be an important pathogenetic factor.

How the potency of the steroid RU486 is related to P450 activities induced by dexamethasone and phenobarbital in rat hepatoma cells.

In a previous work on rat liver microsomes, we demonstrated that cytochrome P450 isozymes (P450) are engaged in the metabolism of RU486. In order to study the underlying mechanism at the molecular level, our investigations were shifted to a simplified system of cultured hepatoma cells which present a dissociation in the expression of distinct P450 coding genes. Our results show that Fao cells represent a convenient model to study both: (i) the degradation of RU486. Forms IIB1,2 and IIC7, which are present in Fao cells, may contribute to the demethylation of the molecule. Form IIIA, which has not been detected in Fao cells, is probably responsible for its oxidation in the liver; (ii) the effect of RU486 on the expression of P450 enzymes. Unlike other steroids (dexamethasone and pregnenolone 16 alpha-carbonitrile), RU486 does not induce P450 activity but inhibits the inducing activity of other agents such as dexamethasone and also phenobarbital. These findings may be important for the therapeutic use of RU486 since its inhibitory effect on P450 activity may be at the origin of drug interactions by modifying the endogenous hormonal status.

[Glucocorticoid receptor mechanism of regulation of the activity of angiotensin-converting enzyme and new prospects in the treatment of cardiovascular diseases]. / Gliukokortikoid-retseptornyi mekhanizm reguliatsii aktivnosti angiotenzinprevrashchaiushchego fermenta i novye perspektivy lecheniia serdechno-sosudistykh zabolevanii.

Based on the concept of glucocorticoid-receptor induction of angiotensin-converting enzyme (ACE), approaches to inhibiting enzyme induction with drugs that suppress the function of type II cytoplasmic glucocorticoid receptors, (genuine glucocorticoid receptors), are suggested. Three types of inhibiting the function of type II glucocorticoid receptors by drugs were distinguished. Type I is characterized by competition of the drugs with natural and synthetic glucocorticoids for interaction with glucocorticoid receptors (cortexolone, progesterone); type II is determined by irreversible inactivation of type II glucocorticoid receptors (aminazine, tisercin); type III is related to an increase of interaction of transcorticoid receptors with natural glucocorticoids which is accompanied by a reduction of the interaction of natural glucocorticoids with genuine glucocorticoid receptors (analgin, amidopyrine). It has been established that the drugs that provoke irreversible inactivation of the function of type II glucocorticoid receptors decrease ACE activity in blood plasma and in the lungs, that may serve the main reason for their high hypotensive effect in arterial hypertension. A concept is advanced, providing evidence for the use of the classical ACE inhibitors and of type II glucocorticoid receptor inhibitors.

The effect of substrates and inhibitors of cytochrome P-450 on the NADPH inhibition of the ATP-dependent, hepatic, microsomal calcium pump.

In hepatic microsomes one or more isozymes of cytochrome P-450 inhibits the ATP-dependent Ca2+ pump. This inhibition is reversible by GSH and appears to be due to a direct oxidation of the pump proteins by the oxygenated cytochrome. To determine which isozyme mediates this inhibition, we have examined the effect of various substrates and inhibitors on the NADPH inhibition of Ca2+ uptake. We find that aminopyrine, benzphetamine and SKF-525A reverse this inhibition while a number of other substrates do not. This pattern suggests that a previously unreported isozyme of cytochrome P-450 mediates the Ca2+ pump inhibition.

A micromethod for the assay of cellular secretory physiology: application to rabbit parietal cells.

A micromethod for investigating secretory physiology in isolated cells was evaluated. The method utilized a specially designed polycarbonate incubation chamber to provide constant oxygenation to cells incubating in a 96-well microtiter plate. Cells were rapidly separated from media by vacuum filtration. Isolated parietal cells were utilized to demonstrate the versatility of the method for assay of intracellular accumulation of [14C]-aminopyrine, secretion of intrinsic factor into the medium, and assay of intracellular cAMP. Histamine stimulated the uptake of [14C]aminopyrine and intrinsic factor secretion in a sustained and linear fashion. At the end of the 2-h period uptake of aminopyrine and secretion of intrinsic factor were increased 17- and 5-fold, respectively. This response to histamine was accompanied by a rapid and sustained 3-fold rise in intracellular cyclic AMP. In contrast, carbamylcholine caused a transient increase in [14C]aminopyrine accumulation and intrinsic factor secretion which was most pronounced during the first 10 min and had almost ceased by 30 min. Carbamylcholine had no effect on intracellular cAMP levels. This new method, which can handle 400 replicates using parietal cells from the fundic mucosa of a single rabbit, is suitable for studying the time course of intracellular events which accompany general secretory processes.

Detection of glutathione thiyl free radical catalyzed by prostaglandin H synthase present in keratinocytes. Study of co-oxidation in a cellular system.

We report here the application of the electron spin resonance technique to detect free radicals formed by the hydroperoxidase activity of prostaglandin H synthase in cells. Studies were done using keratinocytes obtained from hairless mice. These cells can be prepared in large number and possess significant prostaglandin H synthase activity. Initial attempts to directly detect free radical metabolites of several amines in cells were unsuccessful. A technique was developed based on the ability of some free radicals formed by prostaglandin hydroperoxidase to oxidize reduced glutathione (GSH) to a thiyl radical, which was trapped by 5,5-dimethyl-1-pyrroline N-oxide (DMPO). Phenol and aminopyrine are excellent hydroperoxidase substrates for this purpose and thus were used for all further experiments. Using this approach we detected the DMPO/GS.thiyl radical adduct catalyzed by cellular prostaglandin hydroperoxidase. The formation of the radical was dependent on the addition of substrate, inhibited by indomethacin, and supported by either exogenous arachidonic acid or endogenous arachidonic acid released from phospholipid stores by Ca2+ ionophore A-23187. The addition of GSH significantly increased the intracellular GSH concentration and concomitantly stimulated the formation of the DMPO/GS.thiyl radical adduct. Phenol, but not aminopyrine, enhanced thiyl radical adduct formation and prostaglandin formation with keratinocytes while both cofactors were equally effective in incubations containing microsomes prepared from keratinocytes. These results suggest that prostaglandin hydroperoxidase-dependent co-oxidation of chemicals can result in the intracellular formation of free radical metabolites.

Relation between biliary glutathione excretion and bile acid-independent bile flow.

Glutathione efflux into bile of the fluorocarbon-perfused isolated rat liver was altered with eight different agents (L-buthionine-[S,R]-sulfoximine, cefamandole, sodium arsenite, phenobarbital, furosemide, nitrofurantoin, aminopyrine, and benzylamine), and correlations were established between bile flow and biliary excretion of 1) glutathione, 2) endogenous bile acids, and 3) glutathione plus bile acids. Biliary efflux of endogenous bile acids was relatively low (0.5-5 nmol.min-1.g liver-1) and was minimally affected by these agents. Biliary glutathione excretion in control livers was between 4 and 9 nmol.min-1.g-1 and in treated livers ranged from 1 to 21 nmol.min-1.g-1. For each of the various interventions, an increase or decrease in glutathione excretion was always accompanied by a change in bile flow in the same direction; however, these changes were not always directly proportional when comparisons were made between treatment groups. Nevertheless, when bile flow (microliter.min-1.g-1; ordinate) was plotted against glutathione excretion into bile for the pooled data, a significant correlation was observed that was adequately described by a straight line: y = 0.071 chi + 0.72 (r2 = 0.62, P less than 0.001). A similar function described the relation between bile flow and the sum of bile acids and glutathione in bile: y = 0.077 chi + 0.55 (r2 = 0.62, P less than 0.001). In contrast, the taurocholate- or glycocholate-induced choleresis had only minimal effects on glutathione efflux. These findings support the hypothesis that glutathione is one of the osmotic driving forces in bile acid-independent bile formation.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of nonvolatile agents on oxygen demand and energy status in isolated hepatocytes.

The role of hepatic energy deficits in the pathogenesis of anesthetic hepatotoxicity is suggested by the involvement of hypoxia in various animal models and by the ability of anesthetics to inhibit mitochondrial oxidations. We have been studying anesthetic effects on hepatocellular energy metabolism using suspensions of intact hepatocytes freshly isolated from phenobarbital-treated or untreated rats (+PB or -PB cells, respectively), an experimental system that is metabolically complete yet also biochemically homogeneous and accessible. In the present work, diazepam, lidocaine, thiopental, and enflurane, as well as the combination of thiopental and enflurane, were studied at concentrations similar to those achieved in vivo. Thiopental increased cellular oxygen consumption rate (VO2) in both +PB and -PB cells significantly, as did aminopyrine, a test substrate for PB-inducible cytochrome P450 activity. Diazepam increased VO2 only in +PB cells, as did enflurane, whereas lidocaine did not increase VO2 in either +PB or -PB cells. The combination of thiopental and enflurane significantly decreased VO2 in -PB cells but increased it in +PB cells. The higher VO2 in +PB cells compared to -PB cells, seen with all drugs tested (except lidocaine), was eliminated by prior addition of the P450 inhibitor metyrapone. Starting from steady states of oxygen metabolism, with VO2 offset by O2 supply from an overlying gas phase and PO2 stabilized at 24 mm Hg, aminopyrine significantly lowered extracellular PO2, increased lactate production, and decreased high energy phosphate levels within 10 minutes.(ABSTRACT TRUNCATED AT 250 WORDS)

Function and structure of parietal cells after H+-K+-ATPase blockade.

Omeprazole was administered to rabbits as a single dose or daily for 1 wk. H+-K+-ATPase and isolated gastric glands were prepared from the oxyntic corpus mucosa and used for functional and quantitative morphological studies. Both 10 and 100 mumol omeprazole/kg increased the pH of the gastric content when measured at death. The stimulated oxygen uptake and the rate of aminopyrine (AP) uptake were both inhibited in the isolated gastric gland preparations. Morphometric studies of biopsy specimens taken from the corpus mucosa and isolated gastric glands showed that omeprazole treatment increased the volume density of the acid compartments. This expansion provides an increased accumulation space for AP. Therefore, an increased AP uptake might be seen in glands isolated from omeprazole-treated animals. Blockade of the H2-receptor by ranitidine transformed the morphology of the cell into a more resting type and, furthermore, reduced the omeprazole-induced increase in the volume density of the acid compartments in the parietal cell. The H+-K+-ATPase activity measured in membrane fractions from the omeprazole-treated animals was decreased dose dependently and inhibited by 95% after 100 mumol omeprazole/kg. However, the concentration of the enzyme in these fractions did not change. These results indicate a specific inhibitory action of omeprazole on the H+-K+-ATPase.

Estudio histopatológico del hígado de ratas tratadas con aminopirina y nitrito de sodio / Histopathologic study of the liver of rat treated with aminopyrine and sodium nitrite

Se informa que entre los productos que contienen aminas terciarias se encuentra la aminopirina, conocida como el analgésico piramidón, la cual es fácilmente nitrosable en condiciones de pH moderadamente ácido. Se expresa que el compuesto resultante de la nitrosación es la dimetilnitrosamina (DMN), un agente altamente hepatotóxido y carcinogénico, especialmente al nivel del hígado, donde es metabolizado. Se señala que el modelo experimental, mediante la utilización de ratas albinas hembras con un peso de 100 a 140 g, a las cuales les fue administrada diariamente la aminopirina y el nitrito de sodio aisladamente y en combinación, durante 35 días, confirma la hepatotoxicidad de la combinación, de acuerdo con los cambios hísticos observados que corresponden a alteraciones del tipo cirrótico

Evidence for a free radical mechanism of styrene-glutathione conjugate formation catalyzed by prostaglandin H synthase and horseradish peroxidase.

We have proposed, using styrene as a model, a new mechanism for the formation of glutathione conjugates that is independent of epoxide formation but dependent on the oxidation of glutathione to a thiyl radical by peroxidases such as prostaglandin H synthase or horseradish peroxidase. The thiyl radical reacts with styrene to yield a carbon-centered radical which subsequently reacts with molecular oxygen to give the styrene-glutathione conjugate. We have used electron spin resonance spin trapping techniques to detect the proposed free radical intermediates. A styrene carbon-centered radical was trapped using the spin traps 5,5-dimethyl-1-pyrroline N-oxide (DMPO) and t-nitrosobutane. The position of the carbon-centered radical was confirmed to be at carbon 7 by the use of specific 2H-labeled styrenes. The addition of the spin trap DMPO inhibited both the utilization of molecular oxygen and the formation of styrene-glutathione conjugates. Under anaerobic conditions additional styrene-glutathione conjugates were formed, one of which was identified by fast atom bombardment mass spectrometry as S-(2-phenyl)ethylglutathione. The glutathione thiyl radical intermediate was observed by spin trapping with DMPO. These results support the proposed free radical-mediated formation of styrene-glutathione conjugates by peroxidase enzymes.