Lipid peroxidation induced by an early inflammatory response in endotoxaemia

Exploring the role of antioxidants in sepsis-associated oxidative stress: a comprehensive review

Sepsis is a potentially fatal condition characterized by organ dysfunction caused by an imbalanced immune response to infection. Although an increased inflammatory response significantly contributes to the pathogenesis of sepsis, several molecular mechanisms underlying the progression of sepsis are associated with increased cellular reactive oxygen species (ROS) generation and exhausted antioxidant pathways. This review article provides a comprehensive overview of the involvement of ROS in the pathophysiology of sepsis and the potential application of antioxidants with antimicrobial properties as an adjunct to primary therapies (fluid and antibiotic therapies) against sepsis. This article delves into the advantages and disadvantages associated with the utilization of antioxidants in the therapeutic approach to sepsis, which has been explored in a variety of animal models and clinical trials. While the application of antioxidants has been suggested as a potential therapy to suppress the immune response in cases where an intensified inflammatory reaction occurs, the use of multiple antioxidant agents can be beneficial as they can act additively or synergistically on different pathways, thereby enhancing the antioxidant defense. Furthermore, the utilization of immunoadjuvant therapy, specifically in septic patients displaying immunosuppressive tendencies, represents a promising advancement in sepsis therapy.

Metabolomic Profiles Differentiate Scleroderma-PAH From Idiopathic PAH and Correspond With Worsened Functional Capacity

BACKGROUND

The prognosis and therapeutic responses are worse for pulmonary arterial hypertension associated with systemic sclerosis (SSc-PAH) compared with idiopathic pulmonary arterial hypertension (IPAH). This discrepancy could be driven by divergence in underlying metabolic determinants of disease.

RESEARCH QUESTION

Are circulating bioactive metabolites differentially altered in SSc-PAH vs IPAH, and can this alteration explain clinical disparity between these PAH subgroups?

STUDY DESIGN AND METHODS

Plasma biosamples from 400 patients with SSc-PAH and 1,082 patients with IPAH were included in the study. Another cohort of 100 patients with scleroderma with no PH and 44 patients with scleroderma with PH was included for external validation. More than 700 bioactive lipid metabolites, representing a range of vasoactive and immune-inflammatory pathways, were assayed in plasma samples from independent discovery and validation cohorts using liquid chromatography/high-resolution mass spectrometry-based approaches. Regression analyses were used to identify metabolites that exhibited differential levels between SSc-PAH and IPAH and associated with disease severity.

RESULTS

From hundreds of circulating bioactive lipid molecules, five metabolites were found to distinguish between SSc-PAH and IPAH, as well as associate with markers of disease severity. Relative to IPAH, patients with SSc-PAH carried increased levels of fatty acid metabolites, including lignoceric acid and nervonic acid, as well as eicosanoids/oxylipins and sex hormone metabolites.

INTERPRETATION

Patients with SSc-PAH are characterized by an unfavorable bioactive metabolic profile that may explain the poor and limited response to therapy. These data provide important metabolic insights into the molecular heterogeneity underlying differences between subgroups of PAH.

Changes in Biomarkers of Redox Status in Saliva of Pigs after an Experimental Sepsis Induction

Saliva from pigs is gaining attention as an easy sample to obtain, being a source of biomarkers that can provide information on animal health and welfare. This study aimed to evaluate the changes that can occur in salivary biomarkers of the redox status of pigs with an experimentally induced sepsis. For that, the cupric reducing antioxidant capacity (CUPRAC), ferric reducing ability of saliva (FRAS), Trolox equivalent antioxidant capacity (TEAC), advanced oxidation protein products (AOPP), ferrous oxidation-xylenol orange (FOX), peroxide activity (POX-Act), and reactive oxygen-derived compounds (d-ROMs) were measured in the saliva of pigs with experimentally induced sepsis by endotoxin lipopolysaccharide (LPS), non-septic inflammation induced by turpentine, and in healthy individuals before and after 3 h, 6 h, 24 h, and 48 h. AOPP, POX-Act, and d-ROMs in the sepsis group were higher than in the control from 3 h to 24 h after the inoculation. CUPRAC, FRAS, and TEAC were higher in sepsis than the control group at 24 h. These changes were of higher magnitude than those that occurred in the turpentine group. In conclusion, our findings reveal that sepsis produces changes in salivary biomarkers of redox status, which opens the possibility of using them as potential biomarkers in this species.

Maternal Urinary Metal and Metalloid Concentrations in Association with Oxidative Stress Biomarkers

Metal exposure has been associated with a wide range of adverse birth outcomes and oxidative stress is a leading hypothesis of the mechanism of action of metal toxicity. We assessed the relationship between maternal exposure to essential and non-essential metals and metalloids in pregnancy and oxidative stress markers, and sought to identify windows of vulnerability and effect modification by fetal sex. In our analysis of 215 women from the PROTECT birth cohort study, we measured 14 essential and non-essential metals in urine samples at three time points during pregnancy. The oxidative stress marker 8-iso-prostaglandin F2α (8-iso-PGF2α) and its metabolite 2,3-dinor-5,6-dihydro-15-15-F2t-IsoP, as well as prostaglandin F2α (PGF2α), were also measured in the same urine samples. Using linear mixed models, we examined the main effects of metals on markers of oxidative stress as well as the visit-specific and fetal sex-specific effects. After adjustment for covariates, we found that a few urinary metal concentrations, most notably cesium (Cs) and copper (Cu), were associated with higher 8-iso-PGF2α with effect estimates ranging from 7.3 to 14.9% for each interquartile range, increase in the metal concentration. The effect estimates were generally in the same direction at the three visits and a few were significant only among women carrying a male fetus. Our data show that higher urinary metal concentrations were associated with elevated biomarkers of oxidative stress. Our results also indicate a potential vulnerability of women carrying a male fetus.

Hemorrhage simulated by lower body negative pressure provokes an oxidative stress response in healthy young adults

IMPACT STATEMENT

We characterize the systemic oxidative stress response in young, healthy human subjects with exposure to simulated hemorrhage via application of lower body negative pressure (LBNP). Prior work has demonstrated that LBNP and actual blood loss evoke similar hemodynamic and immune responses (i.e. white blood cell count), but it is unknown whether LBNP elicits oxidative stress resembling that produced by blood loss. We show that LBNP induces a 29% increase in F₂-isoprostanes, a systemic marker of oxidative stress. The findings of this investigation may have important implications for the study of hemorrhage using LBNP, including future assessments of targeted interventions that may reduce oxidative stress, such as novel fluid resuscitation approaches.

Relation of blood cadmium, lead, and mercury levels to biomarkers of lipid peroxidation in premenopausal women

Exposures to cadmium, lead, and mercury are associated with adverse health effects, including cardiovascular disease, which may be promoted by lipid peroxidation. The authors examined cadmium, lead, and mercury in relation to plasma levels of F(2)-8α isoprostanes (isoprostane), 9-hydroperoxy-10,12-octadecadienoic acid (9-HODE), 13-hydroxy-9,11-octadecadienoic acid (13-HODE), and thiobarbituric acid reactive substances (TBARS) in 252 women from western New York State (2005-2007). Healthy premenopausal women were followed for ≤2 menstrual cycles, with biomarkers of lipid peroxidation being assessed ≤8 times per cycle. Metals were measured at baseline in whole blood. Linear mixed models were used to estimate the association between cadmium, lead, and mercury and lipid peroxidation biomarkers. Median cadmium, lead, and mercury levels were 0.30 μg/L, 0.86 μg/dL, and 1.10 μg/L, respectively. Blood cadmium, lead, and mercury were not associated with increases in isoprostane, TBARS, 9-HODE, or 13-HODE levels. Isoprostane levels decreased 6.80% (95% confidence interval: -10.40, -3.20) per 1% increase in mercury. However, after adjustment for a simulated strong confounding factor, such as precisely measured fish consumption, the observed association was attenuated, suggesting that this unexpected association could be attributable to unmeasured confounding. In this population of healthy premenopausal women with low exposure levels, cadmium, lead, and mercury were not associated with elevated lipid peroxidation biomarkers.

F2-isoprostanes in human health and diseases: from molecular mechanisms to clinical implications

Oxidative stress is implicated as one of the major underlying mechanisms behind many acute and chronic diseases, and involved in normal aging. However, the measurement of free radicals or their end products is complicated. Thus, proof of association of free radicals in pathologic conditions has been absent. Isoprostanes are prostaglandin-like bioactive compounds that are biosynthesized in vivo independent of cyclooxygenases, principally through free-radical catalyzation of arachidonic acid. Isoprostanes are now considered to be reliable biomarkers of oxidative stress, as evidenced by an autonomous study organized recently by the National Institutes of Health (NIH) in the United States. A number of these compounds have potent biologic activities such as vasoconstrictive and certain inflammatory properties. Isoprostanes are involved in many human diseases. Additionally, elevated levels of F(2)-isoprostanes have been seen in normal human pregnancy and after intake of some fatty acids, but their physiologic assignments have not yet been distinctive. This evidence indicates that measurement of bioactive F(2)-isoprostanes in body fluids offers a unique noninvasive analytic utensil to study the role of free radicals in physiology, oxidative stress-related diseases, experimental acute or chronic inflammatory conditions, and also in the assessment of various antioxidants, radical scavengers, and drugs.

Novel cyclooxygenase-catalyzed bioactive prostaglandin F2alpha from physiology to new principles in inflammation

Prostaglandin F2alpha (PGF2alpha), a foremost stable vasoactive cyclooxygenase (COX)-catalyzed prostaglandin, regulates a number of key physiological functions such as luteolysis, ovarian function, luteal maintenance of pregnancy, and parturition as a constitutive part of ongoing reproductive processes of the body. It has recently been implicated in the regulation of intricate pathophysiological processes, such as acute and chronic inflammation, cardiovascular and rheumatic diseases. Since the discovery of a second isoform of COXs, it has been shown that PGF2alpha can be formed in vivo from arachidonic acid through both isoforms of COXs, namely cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2). Being synthesized in various parts of the body, it metabolizes instantly to a number of rather inactive metabolites mainly in the lungs, liver, kidney, and efficiently excretes into the urine. 15-Keto-dihydro-PGF2alpha, a major stable metabolite of PGF2alpha that reflects in vivo PGF2alpha biosynthesis, is found in larger quantities than its parent compound in the circulation and urine in basal physiological conditions, with short-lived pulses during luteolysis, induced termination of pregnancy and parturition, and is increased in tissues and various body fluids during acute, sub-chronic, and severe chronic inflammation. Further, the close relationship of PGF2alpha with a number of risk factors for atherosclerosis indicates its major role in inflammation pathology. This review addresses multiple aspects of PGF2alpha in addition to its emerging role in physiology to inflammation.

Intra-day variation of in vivo prostaglandin F2α formation in healthy subjects

Prostaglandin F(2alpha) (PGF(2alpha)) is a major stable prostaglandin formed in vivo in physiological and pathophysiological situations and has mainly potent vasoconstrictive and pro-inflammatory properties. PGF(2alpha) is now used as an indicator of acute and chronic inflammation in human clinical settings but the extent of daily variation of PGF(2alpha)in vivo in healthy humans is unknown. We quantified levels of the PGF(2alpha) metabolite 15-keto-dihydro-PGF(2alpha) in 10 healthy males and females in spot urine samples during the day (including morning urine sample) and in 24-h urine during the same day. The intra-day coefficient of variation was 20.9%. However, the total mean value of 15-keto-dihydro-PGF(2alpha) in urine collected in the morning did not significantly differ from the mean level of 15-keto-dihydro-PGF(2alpha) in the 24-h urine samples in the 10 subjects. 15-Keto-dihydro-PGF(2alpha) levels in morning urine showed a positive linear correlation with levels of 15-keto-dihydro-PGF(2alpha) in 24-h urine (R=0.72, P<0.05). In conclusion, formation of PGF(2alpha) shows a biological variation within the day in healthy humans which should not be overlooked when planning a clinical study. Single morning urine samples can be used as an alternative to 24-h urine collections for quantification of PGF(2alpha) formation to simplify the sampling regime in larger clinical studies.

Factors regulating isoprostane formation in vivo

Discovery of the F2-isoprostanes, a group of prostaglandin F2-like compounds biosynthesized from arachidonic acid nonenzymatically, has uncovered a new and novel facet of free radical biology. Some of these compounds are bioactive and thus may mediate adverse effects associated with oxidant stress. F2-Isoprostanes have also been shown to be reliable biomarkers of lipid peroxidation. Factors influencing their formation and metabolism have been studied to some extent, although much remains to be determined. The purpose of this review is to summarize our current knowledge of conditions that modulate endogenous generation of these compounds. Isoprostanes have a wide daily variation in secretion in humans. Although normal levels can be defined, these compounds are found in increased concentrations in various pathophysiological states, including ischemia-reperfusion injury, atherosclerosis, and diabetes, and in experimental conditions of oxidative stress and inflammation. Alterations in isoprostane biosynthesis, secretion, and excretion in normal physiology and in pathophysiological states are due to the various types of endogenous and exogenous regulatory mechanisms that control the availability of precursors required for isoprostane synthesis, such as dietary and tissue arachidonic acid content, oxygen concentration, and the generation of various free radical species. Selected aspects of issues related to isoprostane formation and metabolism in vivo will be examined herein.

Isoprostanes: novel bioactive products of lipid peroxidation

Isoprostanes, are a novel group of prostaglandin-like compounds that are biosynthesised from esterified polyunsaturated fatty acid (PUFA) through a non-enzymatic free radical-catalysed reaction. Several of these compounds possess potent biological activity, as evidenced mainly through their pulmonary and renal vasoconstrictive effects, and have short half-lives. It has been shown that isoprostanes act as full or partial agonists through thromboxane receptors. Both human and experimental studies have indicated associations of isoprostanes and severe inflammatory conditions, ischemia-reperfusion, diabetes and atherosclerosis. Reports have shown that F2-isoprostanes are authentic biomarkers of lipid peroxidation and can be used as potential in vivo indicators of oxidant stress in various clinical conditions, as well as in evaluations of antioxidants or drugs for their free radical-scavenging properties. Higher levels of F2-isoprostanes have been found in the normal human pregnancy compared to non-pregnancy, but their physiological role has not been well studied so far. Since bioactive F2-isoprostanes are continuously formed in various tissues and large amounts of these potent compounds are found unmetabolised in their free acid form in the urine in normal basal conditions with a wide inter-individual variation, their role in the regulation of normal physiological functions could be of further biological interest, but has yet to be disclosed. Their potent biological activity has attracted great attention among scientists, since these compounds are found in humans and animals in both physiological and pathological conditions and can be used as reliable biomarkers of lipid peroxidation.

Microdialysis-evaluated myocardial cyclooxygenase-mediated inflammation and early circulatory depression in porcine endotoxemia

OBJECTIVE

To evaluate the early myocardial biochemical inflammatory response with the microdialysis technique during porcine endotoxemia and to simultaneously monitor systemic hemodynamics.

DESIGN

Prospective, randomized, placebo-controlled trial with parallel groups.

SETTING

Animal research laboratory at the University Hospital of Uppsala, Sweden.

SUBJECTS

Thirteen piglets aged 12-14 wks receiving general anesthesia.

INTERVENTIONS

After thoracotomy and the insertion of microdialysis probes in standardized locations in the left ventricle of the heart and in the quadriceps muscle, seven pigs received a continuous infusion of endotoxin, initiating a severe endotoxemic shock. Six pigs received saline instead of endotoxin.

MEASUREMENTS AND MAIN RESULTS

Endotoxemia caused a rapid and pronounced elevation of a metabolite obtained from prostaglandin degradation, 15-keto-dihydro-PGF(2alpha), in myocardial microdialysate fluid being specific of cyclooxygenase (COX)-mediated inflammation (p <.001 vs. saline-infused controls). Simultaneously, we observed a decrease in left ventricular stroke work index in the endotoxemic pigs (p <.01 vs. saline-infused controls). Endotoxemia did not alter 15-keto-dihydro-PGF(2alpha) levels in quadriceps muscle. Endotoxemia caused increases in taurine, hypoxanthine, and magnesium in myocardial microdialysate (p <.05 vs. saline-infused controls), whereas the contents of pyruvate, lactate, inosine, adenosine, and calcium were not significantly changed.

CONCLUSION

Endotoxemia induced a myocardial COX-mediated inflammation without signs of ischemia. In parallel, a depletion of myocardial energy substrates and a deterioration in myocardial performance were seen.

Biomarkers of free radical injury during spinal cord ischemia

Plasma and urinary levels of 8-iso-PGF(2alpha) and 15-keto-dihydro-PGF(2alpha) were analysed at baseline and during the ischemia-reperfusion period in experimental spinal cord ischemia. A significant and immediate increase of 8-iso-PGF(2alpha) in plasma at the start and up to 60 min, and in the urine at 90-150 min following ischemia indicate an association of oxidative injury. The inflammatory response indicator 15-keto-dihydro-PGF(2alpha) in plasma increased significantly at the start and up to 60 min after ischemia. No such increase was seen in animals with no spinal cord ischemia. Thus, free radical mediated and cyclooxygenase catalysed products of arachidonic acid are increased during spinal cord ischemia as a consequence of oxidative injury and inflammation.

Raised levels of F(2)-isoprostanes and prostaglandin F(2alpha) in different rheumatic diseases

OBJECTIVE

To evaluate oxidative injury and inflammatory status in various rheumatic diseases by measuring the levels of isoprostanes and prostaglandins in serum and synovial fluid.

METHODS

The concentrations of 8-iso-PGF(2alpha) (F(2)-isoprostane indicating oxidative injury) and 15-keto-dihydro-PGF(2alpha) (a major metabolite of prostaglandin F(2alpha)) were measured in both serum and synovial fluid aspirated from 26 patients with various arthritic diseases, including rheumatoid arthritis (RA), reactive arthritis (ReA), psoriatic arthritis (PsA), and osteoarthritis (OA). These prostaglandin derivatives were also measured in serum samples collected from 42 healthy control subjects.

RESULTS

Overall, serum levels of 8-iso-PGF(2alpha) and 15-keto-dihydro-PGF(2alpha) were much higher in patients with arthritic diseases than in the healthy control subjects. The levels of 8-iso-PGF(2alpha) and 15-keto-dihydro-PGF(2alpha) in synovial fluid aspirated from knee joints were also high and varied among various types of arthritic patients. Although the synovial fluid level of these prostaglandin derivatives was sometimes higher than in the corresponding serum sample, this was not a consistent finding. Overall, there was no correlation between serum and synovial fluid levels of 8-iso-PGF(2alpha), or between serum and synovial fluid levels of 15-keto-dihydro-PGF(2alpha). However, a strong relation was found between the levels of 8-iso-PGF(2alpha) and 15-keto-dihydro-PGF(2alpha,) in both serum (r(s)=0.53, p<0.001) and synovial fluid (r(s)=0.62, p<0.001).

CONCLUSIONS

These data suggest that both free radical mediated oxidative injury and cyclo-oxygenase dependent inflammatory responses are closely correlated in various types of arthritis.

Radioimmunological measurement of F(2)-isoprostanes after hydrolysis of lipids in tissues

8-Iso-prostaglandin F(2 alpha)(8-iso-PGF(2 alpha)) is a major isoprostane formed in vivo mainly by non-enzymatic peroxidation of arachidonic acid and a potential biomarker of oxidative injury. We have recently reported development of a specific radioimmunoassay for the measurement of free 8-iso-PGF(2 alpha)in plasma and urine. The aim of this study was to employ this radioimmunoassay to analyze the total amount of 8-iso-PGF(2 alpha)(sum of free and esterified) in liver tissues by using alkaline hydrolysis, and to apply it in an experimental model of carbon tetrachloride-induced lipid peroxidation in rats. Basal levels of total 8-iso-PGF(2 alpha)in hydrolyzed liver tissues of control rats were 6.5 times higher than the levels of free 8-iso-PGF(2 alpha). At maximum formation of total 8-iso-PGF(2 alpha)in the livers of carbon tetrachloride-treated rats, total levels of 8-iso-PGF(2 alpha)were almost 13 times higher than the levels of free 8-iso-PGF(2 alpha). In conclusion, high levels of 8-iso-PGF(2 alpha)in tissues can be quantified after hydrolysis both at basal conditions and in a model of increased lipid peroxidation. The methodology for measurement of total levels of 8-iso-PGF(2 alpha)in tissues may be suitable for future investigations of the location of oxidative injury in the body.

Effects of melagatran, a novel direct thrombin inhibitor, during experimental septic shock

Sepsis and endotoxaemia initiate the generation of thrombin, which is responsible for the conversion of fibrinogen to fibrin, platelet aggregation and acts as an inflammatory mediator affecting numerous types of cells, including myocardial, smooth muscle and endothelial cells. Human Gram-negative septic shock, frequently seen in intensive care units, is a condition with high mortality. This condition can be replicated in the endotoxaemic pig. As many of the toxic effects of sepsis are due to thrombin generation, it was of interest to study, using this porcine experimental septic shock model, whether inhibition of thrombin could alleviate the effects of endotoxaemia. For this purpose melagatran, a direct synthetic thrombin inhibitor with a molecular weight of 429 Da, was employed. Melagatran does not significantly interact with any other enzymes in the coagulation cascade or fibrinolytic enzymes aside from thrombin. Furthermore, melagatran does not require endogenous co-factors such as antithrombin or heparin co-Factor II for its antithrombin effect, which is important, as these inhibitors are often consumed in septic patients. We have shown that melagatran exerts a beneficial effect on renal function, as evaluated by plasma creatinine and urinary output, during experimental septic shock. These effects were most pronounced during the later phase of the experimental period, after the infusion of melagatran had been discontinued. Prevention of intrarenal coagulation may be attributable to this finding. In addition, melagatran had beneficial effects on systemic haemodynamics (left ventricular stroke work index, pulmonary capillary wedge pressure and systemic vascular resistance index) in endotoxaemic pigs. This result may be explained by the ability of melagatran to inhibit thrombin, thereby counteracting thrombin's cellular effects. Thus, it can be seen, using this experimental model of septic shock, that melagatran may help to alleviate some of the damaging effects of endotoxaemia, although more research is required to test this further.

Development of a novel biomarker of free radical damage in reperfusion injury after cardiac arrest

In a porcine model of cardiopulmonary resuscitation (CPR), we investigated changes in the plasma levels of 8-iso-PGF(2alpha), a marker for oxidative injury, and 15-keto-dihydro-PGF(2alpha), an inflammatory response indicator during the post-resuscitation period after cardiac arrest. Twelve piglets were subjected to either 2 or 5 min (VF2 and VF5 group) of ventricular fibrillation (VF) followed by 5 min of closed-chest CPR. Six piglets without cardiac arrest were used as controls. In VF5 group, 8-iso-PGF(2alpha) in the jugular bulb plasma (draining the brain) increased four-fold. Jugular bulb 8-iso-PGF(2alpha) in the control group remained unchanged. The 15-keto-dihydro-PGF(2alpha) also increased four-fold in the VF5 group. Thus, 8-iso-PGF(2alpha) and 15-keto-dihydro-PGF(2alpha) measurements in jugular bulb plasma may be used as biomarkers for quantification of free radical catalyzed oxidative brain injury and inflammatory response in reperfusion injury.

Vitamin E in relation to lipid peroxidation in experimental septic shock

Lipid peroxidation and antioxidant balance in the body is a crucial factor in the pathophysiology of various diseases. This study investigates the circulatory alpha-tocopherol levels and its relationship with 8-iso-prostaglandin F2alpha (8-iso-PGF2alpha), a non-enzymatic and, 15-keto-13,14-dihydro-PGF2alpha (15-K-DH-PGF2alpha), a cyclooxygenase catalysed oxidation product of arachidonic acid in experimental septic shock in pigs. A steady decrease in alpha-tocopherol levels in plasma was observed in both survivor and non-survivor animals. A simultaneous increase of oxidative injury indicator, plasma 8-iso-PGF2alpha was seen in both groups but with a different fashion. 8-Iso-PGF2alpha levels increased steadily in the animals that died during the experiment. An early and rapid increase of plasma 15-K-DH-PGF2alpha, an inflammatory response indicator, was also observed in all animals. There was a significant difference in the kinetics of decrement of alpha-tocopherol levels and a concomitant increase in 15-K-DH-PGF2alpha levels among the non-survivors. Thus, a successive disappearance of circulatory vitamin E in conjunction with the surge of plasma isoprostanes and prostaglandins impairs the oxidant-antioxidant balance in favour of the former and may possibly have an effect on the survivality during experimental porcine septicaemia.

Conjugated linoleic acid induces lipid peroxidation in humans

Conjugated linoleic acid (CLA) is shown to have chemoprotective properties in various experimental cancer models. CLA is easily oxidised and it has been suggested that an increased lipid oxidation may contribute to the antitumorigenic effects. This report investigates the urinary levels of 8-iso-PGF(2alpha), a major isoprostane and 15-keto-dihydro-PGF(2alpha), a major metabolite of PGF(2alpha), as indicators of non-enzymatic and enzymatic lipid peroxidation after dietary supplementation of CLA in healthy human subjects for 3 months. A significant increase of both 8-iso-PGF(2alpha) and 15-keto-dihydro-PGF(2alpha) in urine was observed after 3 months of daily CLA intake (4.2 g/day) as compared to the control group (P<0.0001). Conjugated linoleic acid had no effect on the serum alpha-tocopherol levels. However, gamma-tocopherol levels in the serum increased significantly (P=0. 015) in the CLA-treated group. Thus, CLA may induce both non-enzymatic and enzymatic lipid peroxidation in vivo. Further studies of the mechanism behind, and the possible consequences of, the increased lipid peroxidation after CLA supplementation are urgently needed.