Isoprostanes: novel bioactive products of lipid peroxidation

Neuroprotection of rat hippocampal slices exposed to oxygen–glucose deprivation by enrichment with docosahexaenoic acid and by inhibition of hydrolysis of docosahexaenoic acid-containing phospholipids by calcium independent phospholipase A2

Polyunsaturated fatty acids play an important role in the development of pathological states in brain after hypoxia/ischemia. Here, we investigated the role of docosahexaenoic acid (22:6n-3) in brain phospholipids for neuronal survival. We used organotypic cultures of rat brain hippocampal slices exposed to 40 min of oxygen-glucose deprivation, to study the consequences of experimental ischemia. In [14C]docosahexaenoic acid-labeled cultures, oxygen-glucose deprivation induced significant release of radioactive docosahexaenoic acid. This release could be blocked by the selective inhibitor of the Ca2+-independent phospholipase A2, 4-bromoenol lactone (10 microM), when it was added 30 min prior to oxygen-glucose deprivation. Addition of 4-bromoenol lactone at 30 min prior to oxygen-glucose deprivation markedly decreased the neuronal damage induced by oxygen-glucose deprivation. The protective effect was substantially higher in dentate gyrus than in CA1 and CA3 areas. Enrichment of the hippocampal tissue with docosahexaenoic acid by incubation with 10 microM docosahexaenoic acid for 24 h exerted the same neuroprotective effect, which was observed after treatment with 4-bromoenol lactone. In contrast to the 24 h-preincubation, simultaneous addition of docosahexaenoic acid with the onset of oxygen-glucose deprivation had no protective effect. This suggests that incorporation of docosahexaenoic acid into phospholipids is required for the protective effect observed. Then the possible involvement of arachidonic acid metabolism in docosahexaenoic acid-induced neuroprotection was tested. Inhibition of prostaglandin production by ibuprofen produced no change in neuroprotection after 24-h incubation of the hippocampal slices with docosahexaenoic acid. Simultaneous inhibition of Ca2+-independent and Ca2+-dependent phospholipases A2 by treatment with the general phospholipase A2 inhibitor methyl arachidonyl fluorophosphonate (3 microM, 30 min prior to oxygen-glucose deprivation) resulted in significant enhancement of the neuroprotective effect in the dentate gyrus, but not in the CA1 and CA3 areas. In summary, the results reported here indicate that docosahexaenoic acid and docosahexaenoic acid-containing phospholipids provide potent protection against neurodegeneration after hypoxia/hypoglycemia. Furthermore, our data suggest that Ca2+-independent phospholipase A2, the isoform, which has been largely ignored so far, is a possible target for treatment of ischemia-related pathologies in brain.

Tracing the origins of “fetal origins” of adult diseases: Programming by oxidative stress?

Too small size at birth (due to poor fetal growth and/or preterm delivery) has been associated with substantially elevated risks of the metabolic syndrome (dislipidemia, insulin resistance, hypertension), type 2 diabetes and cardiovascular disease in adulthood. The mechanisms of such "fetal origins" or "programming" of disease phenomenon remain unresolved. Too large size at birth seems also associated with an increased risk. Many known or suspected causes of or conditions associated with adverse (poor or excessive) fetal growth or preterm birth have been associated with oxidative stress. Plausibly, oxidative stress may be a common link underlying the superficial "programming" associations between adverse fetal growth or preterm birth and elevated risks of certain chronic diseases. The mechanisms of oxidative stress programming may be through directly modulating gene expression or indirectly through the effects of certain oxidized molecules. Experimental investigations have well demonstrated the role of redox balance in modulating gene expression, and recent studies indicate that both the insulin functional axis and blood pressure could be sensitive targets to oxidative stress programming. Adverse programming may occur without affecting fetal growth, but more frequently among low birth weight infants merely because they more frequently experienced known or unknown conditions with oxidative insults. As oxidative stress levels are easily modifiable during pregnancy and early postnatal periods (which are plausible critical windows), the hypothesis, if proved valid, will suggest new measures that could be very helpful on fighting the increasing epidemic of the metabolic syndrome, type 2 diabetes and cardiovascular disease. Currently, there are several ongoing large randomized trials of antioxidant supplementation to counter oxidative stress during pregnancy for the prevention of preeclampsia. It would be invaluable if long-term follow-ups of infants born to women in such trials could be realized to test the oxidative stress programming hypothesis in such experimental trial settings.

Measures of Oxidized Low-Density Lipoprotein and Oxidative Stress Are Not Related and Not Elevated in Otherwise Healthy Men With the Metabolic Syndrome

OBJECTIVE

The metabolic syndrome predisposes to the development of cardiovascular diseases. Oxidative stress and elevated circulating oxidized low-density lipoprotein (LDL) concentrations are related to cardiovascular disease and proposed to be features of the metabolic syndrome. F2-isoprostanes are lipid peroxidation products and considered the most reliable biomarkers of oxidative stress.

METHODS AND RESULTS

Plasma oxidized LDL (oxLDL) and urinary 8-iso-prostaglandin F2alpha (8-iso-PGF2alpha; the major F2-isoprostane) were analyzed in a cross-sectional study of 289 healthy men (62 to 64 years of age). Individuals completed a 7-day dietary record, and fasting plasma insulin, lipid, and lipoprotein concentrations, LDL particle size, and inflammatory markers were determined. National Cholesterol Education Program/Adult Treatment Panel III (NCEP/ATPIII) criteria were used to define the metabolic syndrome and individuals were grouped according to the number of risk factors for the metabolic syndrome (0, [n=88; 30%]; > or =1, [n=179; 62%], metabolic syndrome [n=22; 8%]). Group comparisons revealed no differences for oxLDL, 8-iso-PGF2alpha, or reported intake of macronutrients, whereas C-reactive protein and interleukin-6 were increased in the metabolic syndrome. LDL cholesterol strongly determined oxLDL in univariate and multivariate analysis, but no relationship to 8-iso-PGF2alpha was found. In turn, 8-iso-PGF2alpha was related to reported intake of fat, fatty acids, and dietary antioxidants.

CONCLUSIONS

There were no increases in plasma oxLDL or measures of oxidative stress (urinary 8-iso-PGF2alpha) in these otherwise healthy 63-year-old men with the metabolic syndrome. Furthermore, no relationship between oxLDL and 8-iso-PGF2alpha was found, but our results suggest a role for dietary factors in oxidative stress.

Lipid peroxidation induced by carbon tetrachloride and its inhibition by antioxidant as evaluated by an oxidative stress marker, HODE

We have recently proposed total hydroxyoctadecadienoic acid (HODE) as a biomarker for oxidative stress in vivo. The biological samples such as plasma, urine, and tissues were first reduced and then saponified to convert the oxidation products of linoleate to HODE. In the present study, this method was applied to measure the oxidative damage induced by the administration of carbon tetrachloride to mice and also to evaluate the capacity of antioxidant to inhibit the above damage. alpha-Tocopherol transfer protein knock out (alpha-TTP-/-) mice were used to evaluate antioxidant effect in the absence of alpha-tocopherol. The intraperitoneal administration of carbon tetrachloride to mice induced the increase in HODE in liver and plasma, which was followed by an increase in plasma glutamic-oxaloacetic transaminase (GOT) and glutamic-pyruvic transaminase (GPT). F2-isoprostanes, another prevailing biomarker, were also increased similarly, but their concentration was approximately two to three orders of magnitude smaller than that of HODE. The lipophilic antioxidants such as gamma-tocopherol, gamma-tocotrienol and 2,3-dihydro-5-hydroxy-4,6-di-tert-butyl-2,2-dipentylbenzofuran (BO-653) were effective in suppressing the formation of HODE.

Isoprostanes, prostaglandins and tocopherols in pre-eclampsia, normal pregnancy and non-pregnancy

This study is designed to evaluate whether oxidative stress and inflammation are involved in severe pre-eclampsia compared to normal pregnancy and non-pregnancy. We have measured plasma and urinary levels of 8-iso-PGF2alpha, a major isoprostane as an indicator of oxidative stress; plasma and urinary 15-keto-dihydro-PGF2alpha, a major metabolite of cyclooxygenase-catalysed PGF2alpha as an indicator of inflammatory response, and plasma -alpha-and -gamma-tocopherol in 18 pre-eclamptic, 19 normal pregnancy and 20 non-pregnant women. Pregnant women had significantly higher levels of 8-iso-PGF2alpha and PGF2alpha metabolite as compared to the non-pregnancy. Levels of 8-iso-PGF2alpha in the pre-eclamptic women did not differ from the normal pregnancy but PGF2alpha metabolite levels were significantly higher in normal pregnancy. On the other hand, gamma-tocopherol levels were significantly lower in pre-eclampsia than normal pregnancy. In contrast, the concentration of alpha-tocopherol was very similar between the groups. alpha-and gamma-tocopherol levels were significantly lower in pregnancy compared to non-pregnancy. Although no direct evidence of oxidative stress and inflammatory response was observed in severe pre-eclampsia, a reduction of gamma-tocopherol suggests the possible precedence of oxidative stress in this condition. Higher levels of isoprostanes and prostaglandin metabolite in late pregnancy suggest the importance of both free radicals and cyclooxygenase-catalysed oxidation products in normal biological processes of pregnancy.

Mediterranean vegetable soup consumption increases plasma vitamin C and decreases F2-isoprostanes, prostaglandin E2 and monocyte chemotactic protein-1 in healthy humans

Consumption of fruits and vegetables is associated with a reduced risk of death from all causes including heart disease and stroke. In this work, the bioavailability of vitamin C from a Mediterranean vegetable soup (gazpacho) constituted mainly of tomato, pepper and cucumber, and its influence on plasma vitamin C, 8-epi-prostaglandin F(2alpha) (8-epi-PGF2alpha), prostaglandin E2 (PGE2), monocyte chemotactic protein-1 (MCP-1), and the cytokines/tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), and IL-6 concentrations in a healthy human population were assessed. Six men and six women consumed 500 ml of commercial gazpacho per day for 14 days, corresponding to an intake of 78 mg of ascorbic acid per day. There were no differences (P = .22) in baseline plasma vitamin C concentrations between the men and women. The maximum increase (P < .05) in plasma vitamin C occurred 4 h postdose in both men and women. Vitamin C concentrations were significantly higher (P < .03) on Days 7 and 14 of the intervention. Baseline concentrations of uric acid and 8-epi-PGF2alpha were significantly higher (P < or = .032) in men than in women. Baseline concentrations of 8-epi-PGF2alpha decreased significantly (P < or = .05) by Day 14 of the intervention. A significant inverse correlation was observed between vitamin C and 8-epi-PGF2alpha (r = -.415, P = .049). Baseline concentrations of PGF2 and MCP-1 were significantly higher (P< or = .025) in men than in women but decreased significantly (P< or = .05) by Day 14 of the intervention. No effect on TNF-alpha, IL-1beta and IL-6 was observed at Day 14 of the intervention. Drinking gazpacho (500 ml/day) significantly increases plasma concentrations of vitamin C and significantly decreases 8-epi-PGF2alpha, PGE2 and MCP-1 concentrations in healthy humans.

Pulmonary oxidant stress in murine sepsis is due to inflammatory cell nitric oxide

OBJECTIVE

Pulmonary oxidant stress is an important pathophysiologic feature of acute lung injury. It is unclear whether nitric oxide contributes to this oxidant stress. Thus, we examined the role of inducible nitric oxide synthase (iNOS) in pulmonary oxidant stress in murine sepsis and the differential contribution of different cellular sources of iNOS.

DESIGN

Randomized, controlled animal study.

SETTING

Research laboratory of an academic institution.

SUBJECTS

Male iNOS+/+, iNOS-/- C57Bl/6 mice, and bone-marrow transplanted iNOS chimeric mice: +to- (wild-type iNOS+/+ donor bone-marrow transplanted into iNOS-/- recipient mice) and the reciprocal -to+ chimeras.

INTERVENTIONS

Animals were randomized to sepsis (n = 264), induced by cecal ligation and perforation, vs. naive groups (n = 138).

MEASUREMENTS AND MAIN RESULTS

In septic iNOS-/- vs. wild-type iNOS+/+ mice, sepsis-induced pulmonary oxidant stress (33 +/- 11 [mean +/- sem] vs. 365 +/- 48 pg 8-isoprostane/mg protein, p < .01) and nitrosative stress (0.0 +/- 0.0 vs. 0.9 +/- 0.4 micromol 3-nitrotyrosine/mmol para-tyrosine, p < .05) were abolished, despite similar septic increases in pulmonary myeloperoxidase activity in both (86 +/- 20 vs. 83 +/- 12 mU/mg protein, p = .78). In +to- iNOS chimeric mice (iNOS localized only to donor bone-marrow-derived inflammatory cells), cecal ligation and perforation resulted in significant pulmonary oxidant stress (368 +/- 81 pg 8-isoprostane/mg protein) and nitrosative stress (0.6 +/- 0.2 micromol 3-nitrotyrosine/mmol para-tyrosine), similar in degree to septic wild-type mice. In contrast, pulmonary oxidant and nitrosative stresses were absent in septic -to+ iNOS chimeras (iNOS localized only to recipient parenchymal cells), similar to iNOS-/- mice.

CONCLUSIONS

In murine sepsis-induced acute lung injury, pulmonary oxidant stress is completely iNOS dependent and is associated with tyrosine nitration. Moreover, pulmonary oxidant stress and nitrosative stress were uniquely dependent on the presence of iNOS in inflammatory cells (e.g., macrophages and neutrophils), with no apparent contribution of iNOS in pulmonary parenchymal cells. iNOS inhibition targeted specifically to inflammatory cells may be an effective therapeutic approach in sepsis and acute lung injury.

Urinary 8-epi-PGF2α and its endogenous β-oxidation products (2,3-dinor and 2,3-dinor-5,6-dihydro) as biomarkers of total body oxidative stress

Although measurements of plasma F2-isoprostanes are established markers of oxidative stress, their quantification only reflects acute non-enzymatic lipid peroxidation. In this study, a new approach is described for the rapid isolation and measurement of urinary 8-epi-PGF2alpha and its endogenous beta-oxidation metabolites (2,3-dinor-8-epi-PGF2alpha and 2,3-dinor-5,6-dihydro-PGF2alpha) for use as index of total body oxidative stress. Isoprostanes were partitioned with ethyl acetate and subsequently purified by chromatography on an aminopropyl (NH2) and silica (Si) cartridge. Final analysis of F2-isoprostanes as trimethylsilyl-ester/pentafluorobenzyl ester derivatives was carried out by stable isotope dilution mass spectrometry. Overall recovery of F2-isoprostanes was 80+/-4%. Inter- and intra-assay coefficients of variation were 5% and 7%, respectively. In a group of healthy humans, the mean excretion rates expressed as nmol/mmol creatinine for 2,3-dinor-8-epi-PGF2alpha, 2,3-dinor-5,6-dihydro-8-epi-PGF2alpha, and 8-epi-PGF2alpha were 5.43+/-1.93, 2.16+/-0.71, and 0.36+/-0.16, respectively. Correlations were obtained between 8-epi-PGF2alpha and 2,3-dinor-8-epi-PGF2alpha or 2,3-dinor-5,6-dihydro-8-epi-PGF2alpha (r=0.998 and r=0.937, respectively). A strong relationship was also seen between 2,3-dinor-8-epi-PGF2 and 2,3-dinor-5,6-dihydro-8-epi-PGF2alpha (r=0.949). The new technique allows for high sample throughput and avoids the need for HPLC and/or other expensive equipment required for the initial sample preparation. Simultaneous analysis of urinary 8-epi-PGF2alpha and its metabolites should provide unique tool in clinical trials exploring the role of oxidant injury in human disease.

Health promotion by flavonoids, tocopherols, tocotrienols, and other phenols: direct or indirect effects? Antioxidant or not?

Foods and beverages rich in phenolic compounds, especially flavonoids, have often been associated with decreased risk of developing several diseases. However, it remains unclear whether this protective effect is attributable to the phenols or to other agents in the diet. Alleged health-promoting effects of flavonoids are usually attributed to their powerful antioxidant activities, but evidence for in vivo antioxidant effects of flavonoids is confusing and equivocal. This may be because maximal plasma concentrations, even after extensive flavonoid intake, may be low (insufficient to exert significant systemic antioxidant effects) and because flavonoid metabolites tend to have decreased antioxidant activity. Reports of substantial increases in plasma total antioxidant activity after flavonoid intake must be interpreted with caution; findings may be attributable to changes in urate concentrations. However, phenols might exert direct effects within the gastrointestinal tract, because of the high concentrations present. These effects could include binding of prooxidant iron, scavenging of reactive nitrogen, chlorine, and oxygen species, and perhaps inhibition of cyclooxygenases and lipoxygenases. Our measurements of flavonoids and other phenols in human fecal water are consistent with this concept. We argue that tocopherols and tocotrienols may also exert direct beneficial effects in the gastrointestinal tract and that their return to the gastrointestinal tract by the liver through the bile may be physiologically advantageous.

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.

Total hydroxyoctadecadienoic acid as a marker for lipid peroxidation in vivo

An improved method for the measurement of lipid peroxidation in vivo has been recently developed, where total hydroxyoctadecadienoic acid (HODE) and 7-hydroxycholesterol (FCOH) were determined by GC/MS analysis from physiological samples after reduction with sodium borohydride and saponification by potassium hydroxide. In this method, both free and ester forms of hydroperoxides and ketones as well as hydroxides of linoleic acid and cholesterol are measured as HODE and FCOH, respectively. The ratio of stereo-isomer, (Z, E)-HODE/(E, E)-HODE, could be also measured. In the present study, in order to examine the effect of continuous, slow flux of free radicals in vivo, a water-soluble radical generator was administered to rats and mice and the amounts of HODE and 8-isoprostane in plasma and liver were measured. It was found that the administration of free radical-generating azo compound increased the level of HODE and decreased the (Z, E)-HODE/(E, E)-HODE ratio in both plasma and liver. The level of HODE was much higher than 8-isoprostane.

Flavanol-rich cocoa drink lowers plasma F(2)-isoprostane concentrations in humans

Flavan-3-ols are potent antioxidants in vitro, but convincing evidence for antioxidant action in vivo is lacking. We examined whether an oxidative stress-mediated increase in plasma F(2)-isoprostanes is counteracted by a flavanol-rich cocoa beverage. Twenty volunteers were examined in a comparative randomized double-blind crossover design with respect to ingestion of high-flavanol cocoa drink (HFCD; 187 mg flavan-3-ols/100 ml) vs. low-flavanol cocoa drink (LFCD; 14 mg/100 ml). With 10 individuals, the treatment was combined with strenuous physical exercise. Total (esterified plus nonesterified) F(2)-isoprostanes were analyzed by GC/MS. LFCD caused a slight increase in the mean (+/- SEM) plasma concentrations of F(2)-isoprostanes 2 and 4 h after intake (2.16 +/- 0.19 nM at 4 h vs. 1.76 +/- 0.11 nM at 0 h, n = 10), which may be attributable to postprandial oxidative stress. This increase did not occur with HFCD (1.57 +/- 0.06 nM at 4 h vs. 1.65 +/- 0.10 nM at 0 h, n = 10). The difference in F(2)-isoprostanes 2 and 4 h after intake of HFCD vs. LFCD became statistically significant when the intake was combined with physical exercise (P < 0.01, ANOVA). We conclude that dietary flavanols, using cocoa drink as example, can lower the plasma level of F(2)-isoprostanes, indicators of in vivo lipid peroxidation.

Rapid preparation of human urine and plasma samples for analysis of F2-isoprostanes by gas chromatography-mass spectrometry

Reliable MS-based methods have been developed for the measurement of free and esterified F2-isoprostanes. However, prior to sample analysis several steps of purification, including solid-phase extraction followed by TLC or HPLC, are usually required, making it tedious to analyze large sample numbers, e.g., for population studies. We report a quick sample purification method using anion exchange solid phase extraction (SPE), which is highly selective for acidic compounds. Urine and hydrolyzed plasma of healthy individuals were acidified before SPE extraction, washed with 4 different solvent mixtures and finally eluted with ethyl acetate. The eluted samples were first derivatized with pentafluorobenzyl bromide followed by a second derivatization with bis-(trimethylsilyl)trifluoroacetamide. F2-isoprostanes were analyzed by GC-MS-NCI. The method was highly sensitive; the limit of detection at 5:1 signal-to-noise ratio was 0.037 ng/ml and 0.007 ng/mg creatinine for plasma and urine, respectively. Anion exchange SPE extraction for F2-isoprostane showed recovery of 55-65% and high linearity for concentration 0-1.0 ng/ml for urine (CV=4.08%, r2=0.990) and 0-0.5 ng/ml for plasma (CV=4.07%, r2=0.998). Fasting for 6h significantly increased plasma F2-isoprostanes levels, which has implications for the design of intervention studies using this biomarker.

Measuring reactive species and oxidative damage in vivo and in cell culture: how should you do it and what do the results mean?

Free radicals and other reactive species (RS) are thought to play an important role in many human diseases. Establishing their precise role requires the ability to measure them and the oxidative damage that they cause. This article first reviews what is meant by the terms free radical, RS, antioxidant, oxidative damage and oxidative stress. It then critically examines methods used to trap RS, including spin trapping and aromatic hydroxylation, with a particular emphasis on those methods applicable to human studies. Methods used to measure oxidative damage to DNA, lipids and proteins and methods used to detect RS in cell culture, especially the various fluorescent "probes" of RS, are also critically reviewed. The emphasis throughout is on the caution that is needed in applying these methods in view of possible errors and artifacts in interpreting the results.