Methods for determination of lipid peroxidation in biological samples

In Vivo Antioxidant Properties of Lotus Root and Cucumber: A Pilot Comparative Study in Aged Subjects

OBJECTIVES

To compare the effects of lotus root and cucumber on antioxidant function in aged subjects.

DESIGN

Pilot comparative study.

SETTING

Research setting with vegetable intervention.

PARTICIPANTS

Healthy aged subjects over the age of sixty.

INTERVENTION

30-day supplementation of lotus root or cucumber powder.

MEASUREMENTS

Plasma value of ferric reducing antioxidant power assay, activity of antioxidant enzymes, contents of some antioxidants, oxidation products, hemolysis, blood mononuclear cell DNA damage and urinary excretion of 8-hydroxy-2'-deoxyguanosine were measured before and after the intervention.

RESULTS

Plasma glutathione peroxidase activity, contents of vitamin C, total phenolics were significantly increased, while plasma uric acid content significantly decreased in both groups at the end of the intervention. Meanwhile, hemolysis was significantly reduced in both groups and DNA injury rate of blood mononuclear cells in lotus root group and the ratio of comet tail length to total length in cucumber group were also declined significantly post-intervention. However, plasma value of ferric reducing antioxidant power assay, contents of reduced glutathione, vitamin E, malondialdehyde, oxidized low density lipoprotein, carbonyls and activity of superoxide dismutase and catalase were not changed significantly in both group after the intervention.

CONCLUSION

These results suggest that lotus root and cucumber are not remarkably different in improving antioxidant function in aged subjects, though they are significantly different in antioxidant capacity in vitro. The benefits observed in this study may come from the additive or synergistic combinations of antioxidants contained in vegetables.

No correlation is found for vegetables between antioxidant capacity and potential benefits in improving antioxidant function in aged rats

Vegetables vary greatly in antioxidant capacity in vitro. This study was to investigate the actions of three vegetables different remarkably in antioxidant capacity in vitro on antioxidant function in aged rats. Sixty female aged Wistar rats were randomly assigned to the control, lotus root, rape and cucumber (high, moderate and low in antioxidant capacity, respectively) treated groups. After 6 weeks of feeding, there were no significant differences in plasma FRAP value and contents of vitamin C, vitamin E, uric acid and total phenolics among different groups, whereas the content of reduced glutathione was significantly higher in the rape and cucumber groups. Plasma superoxide dismutase activity also was significantly increased in the rape and cucumber groups. Plasma contents of malondialdehyde, carbonyls and hemolysis were decreased significantly in 3 vegetable-treated groups. Meanwhile, urinary 8-hydroxy-2'-deoxyguanosine excretion was lower significantly in the rape group and the ratio of comet tail length to total length of blood mononuclear cells was decreased significantly in 3 vegetables treated groups. These results suggest that 3 vegetables tested are effective in improving antioxidant function to some extent in aged rats and no correlation is found between antioxidant capacity in vitro and improvements of antioxidant function. The benefits observed in this study may come from additive or synergistic combinations of antioxidants contained in vegetables.

Determination of total plasma hydroperoxides using a diphenyl-1-pyrenylphosphine fluorescent probe

Plasma hydroperoxides (HPs) are widely accepted to be good indicators of oxidative stress. By means of the method proposed here, which uses diphenyl-1-pyrenylphosphine (DPPP) as a fluorescent probe, all types of plasma HP were determined. The limits of detection and quantification of the method were 0.08 and 0.25 nmol of cumene hydroperoxide (CHP) equivalents in 40 μl of plasma, respectively. The method is satisfactory in terms of precision (5.3% for 14.5 μM CHP eq., n=8), and the recoveries were 91% and 92% after standard additions of 26 and 52 μM CHP, respectively. The selectivity of the proposed method is higher than 96%. Moreover, optimization of the reaction conditions and the addition of ethylenediaminetetraacetic acid (EDTA) disodium salt and 2,6-di-tert-butyl-4-methylphenol (BHT) prevented the formation of HP artifacts during the analysis. Therefore, the proposed method is useful for simple and quantitative determination of total plasma HPs.

Estimation of Lipid Hydroperoxide Levels in Tropical Marine Macroalgae

The incipient levels of lipid hydroperoxides (LHPOs) were determined in selected green, brown, and red macroalgae by the FOX assay using hydroperoxy HPLC mix. The LHPOs contents varied between the investigated species and showed relatively low values in this study. Among the greens, it varied from 12 ± 6.2 μg · g(-1) (Codium sursum) to 31.5 ± 2.8 μg · g(-1) (Ulva lactuca), whereas in reds, from 5.7 ± 1.6 μg · g(-1) (Gracilaria corticata) to 46.2 ± 6 μg · g(-1) (Sarconema filiforme), and in browns, from 4.6 ± 4.4 μg · g(-1) (Dictyota bartayresiana) to 79 ± 5.0 μg · g(-1) (Sargassum tenerrimum), on fresh weight basis. These hydroperoxides represented a minor fraction of total lipids and ranged from 0.04% (S. swartzii) to 1.1% (S. tenerrimum) despite being a rich source of highly unsaturated fatty acids. The susceptibility of peroxidation was assessed by specific lipid peroxidazibility (SLP) values for macroalgal tissues. The LHPO values were found to be independent of both the PUFAs contents and their degree of unsaturation (DBI), as evident from the PCA analysis. SLP values were positively correlated with the LHPOs and negatively with DBI. The FOX assay gave ≥20-fold higher values for LHPOs as compared to the TBARS method for all the samples investigated in this study. Furthermore, U. lactuca cultured in artificial seawater (ASW) enriched with nutrients (N, P, and NP) showed a sharp decline in LHPOs contents relative to those cultured in ASW alone P ≤ 0.05. It is inferred from this study that the FOX assay is an efficient, rapid, sensitive, and inexpensive technique for detecting the incipient lipid peroxidation in macroalgal tissues.

Dietary n-3 polyunsaturated fatty acids increase oxidative stress in rats with intracerebral hemorrhagic stroke

Intake of n-3 polyunsaturated fatty acids such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) has been suggested to associate with an increased risk of hemorrhagic stroke. The present study was designed to investigate the hypothesis that EPA and DHA increase oxidative stress and hemorrhage volume in rats with intracerebral hemorrhagic (ICH) stroke. Thirty-five-week-old male rats were fed an American Institute of Nutrition-93M diet containing 0% (n = 27), 0.5% (n = 15), or 1% EPA + DHA of total energy for 5 weeks. Of 5 rats fed 1% EPA + DHA (41%), 5 died because of excessive bleeding within 12 hours after ICH surgery. Behavior test score and hemorrhage volume were significantly (P < .05) greater in the 1% EPA + DHA-fed rats than in other rats. Magnetic resonance imaging consistently showed that edema and bleeding were visible in only the rats fed 1% EPA + DHA. Levels of superoxide dismutase and glutathione were significantly (P < .05) lower in rats fed 0.5% and 1% EPA + DHA than those fed 0% EPA + DHA. Thiobarbituric acid-reactive substance content was significantly (P < .05) higher in 1% EPA + DHA-fed rats than in 0% and 0.5% EPA + DHA-fed rats. The level of 8-hydroxydeoxyguanosine was significantly (P < .05) higher in ICH rats with all diets than in sham surgery rats. Brain levels of EPA and DHA were highest in rats fed 1% EPA + DHA than in rats fed 0% and 0.5% EPA + DHA. These results suggested that intake of 1% EPA + DHA of total energy could lead to oxidative damage to the brain and thus increase the risk of intracerebral hemorrhagic stroke in this rat model.

Oxidative stress generated by diesel seawater contamination in the digestive gland of the Antarctic limpet Nacella concinna

The aim of this work was to investigate the activity of antioxidant enzymes and oxidative damage in the digestive gland of the limpet Nacella concinna, and their suitability as biomarkers for hydrocarbon pollution in Antarctic coasts. Three groups of 30 individuals each were kept in seawater containing 0%, 0.05% or 0.1% diesel. Superoxide dismutase, catalase, glutathione S transferase and glutathione peroxidase activities, as well as lipid peroxidation and protein oxidation were studied in 18 animals of each group after 24, 48 and 168 h of exposure. The activity levels of most enzymes were increased by diesel in a dose-dependent manner. Glutathione peroxidase showed the most clear effect; its activity significantly increased in the 0.1% diesel group respect to the control. Lipid peroxidation and protein oxidation were significantly increased by diesel after 168 h. Both variables were higher in the group exposed to the lowest dose.

Lipid peroxidation and antioxidant capacity in selected tissues of healthy black C57BL/6J mice and B16 melanoma-bearing mice

During the process of melanogenesis free radicals are generated. The aim of this study was to investigate the effects of melanogenesis in B16 melanoma on lipid peroxidation and antioxidant capacity in selected tissues of black C57BL/6J mice. The study was conducted on 24 mice: 12 healthy controls and 12 with a transplanted B16 melanoma. Two weeks after the melanoma transplant, when the average weight of the tumours was approximately 2.0 g, blood samples were taken from the orbital venous plexus. The mice were killed by dislocation of the spinal cord, and the brain, liver and lungs were removed for analysis. The level of thiobarbituric acid-reactive substances (TBARS) and of 1,1-diphenyl-2-picrylhydrazyl (DPPH) reactive substances were determined in full liver, lung and brain homogenates and in serum. The activity of superoxide dismutase (SOD) was determined only in homogenized tissue. The concentration of TBARS and the SOD activity were statistically significantly higher in all the studied tissues from mice with B16 melanoma than in tissues from healthy mice. The antioxidant capacity, however, was lower in the tissues of melanoma-bearing mice. The results obtained demonstrate an increase in oxidative stress in the tissues of mice bearing a transplanted B16 melanoma.

Do different dialytic techniques have different atherosclerotic and antioxidant activities?

To compare the chronic effect of several dialytic techniques (bicarbonate dialysis, BHD; acetate free biofiltration, AFB; hemodiafiltration, HDF; paired filtration dialysis, PFD) on atherosclerosis and antioxidant activity, three different indices were created. The first (atherosclerotic index = AI) is formed using the sum of three plasma substances: MDA, Hcy, and Cys (malondialdehyde, homocysteine, cysteine). The second (antioxidant activity index = AOAI) is the sum of five erythrocyte (E) parameters: E-GSH, GPx, CAT, SOD, GR (E-glutathione, E-glutathione peroxidase, E-catalase, E-superoxide dismutase, E-glutathione reductase). The third (defense index = DI) is derived from the previous two: (AOAI - AI). The indices were so expressed as AI in mmol/L, AOAI in U/g hemoglobin (Hb), and DI in arbitrary units. These indices were calculated in 20 controls and 51 chronic HD patients (26 female, 25 male) before, during, and after the first session of the week. HD patients were divided according to their dialytic technique: BHD, n = 35; AFB, n = 5 patients; HDF, n = 7 patients; or PFD = 4 patients. All patients had been treated with a given technique for at least 12 months, before entering the study. As expected, HD patients had AI values higher than controls, both before and after the session, with a mean value of 541 (before) and 331 (after), whereas controls had a mean value of 205. The AOAI was lower than controls, both before and after the session, the mean value being 1,122 (before) and 1,582 (after), that of controls being 2,424. In all cases, PFD gave the best "acute" results; at the end of a PFD session, near normal values of AI, AOAI, and DI (defensive index = AOAI - AI) were obtained.

Total plasma malondialdehyde levels in 16 Taiwanese college students determined by various thiobarbituric acid tests and an improved high-performance liquid chromatography-based method

OBJECTIVES

In determining the plasma malondialdehyde MDA levels in some Taiwanese college students, we found rather different results by using different thiobarbituric acid TBA tests, even by the high-performance liquid chromatography HPLC-based methods. Here, we re-evaluated four commonly used TBA tests and improved the HPLC-based test.

DESIGN AND METHODS

We used the blood plasma of 16 college volunteers to determine plasma MDA by using four methods: a spectrophotometric measurement of thiobarbituric acid-reactive substances (TBARS) in the TCA-supernatant of plasma (Method A); a fluorescence measurement of plasma lipid peroxides (Method B); and two different HPLC-based measurements of MDA with either 532-nm measurement (Method C, HPLC/532 nm) or fluorescence measurement (Method D, HPLC/fluor.).

RESULTS

The levels of MDA or TBA reactive substances obtained from the four methods differed substantially (0.39 +/- 0.15; 2.14 +/- 0.73; 0.75 +/- 0.22; and 0.38 +/- 0.15 microM for Methods A, B, C, and D, respectively). The results were positively correlated between Methods A and B (r = 0.740, p < 0.02) and between Methods C and D (r = 0.516, p < 0.05). However, results were negatively correlated between Methods B and D (r = -0.548, p < 0.05). Because most plasma MDA is bound to proteins, we modified the HPLC-based methods (C and D) by adding an alkaline hydrolysis step, and the plasma TBA-MDA adduct detected by HPLC/532 nm was referred to as total MDA. RESULTS show that alkaline hydrolysis was a critical step for measurement of total MDA in plasma because this treatment led to release of MDA from plasma proteins. We also adapted the potassium iodide (KI) treatment of plasma from Method D to reduce lipid hydroperoxides. Our modified method gave a total MDA level in the 16 volunteers of approximately 1.5 microM, which was equal to protein-bound MDA plus free MDA. This total MDA level was positively (p < 0.05) correlated with the level of TBA reactive substances obtained from Methods C (r = 0.63, p < 0.05) and D (r = 0.48, p < 0.07), but was not correlated with those from Methods A and B. The recovery (84 approximately 105%), precision (within-assay coefficient of variation: 2.4%, between-assay coefficient of variation: 4 approximately 8%) and sensitivity of the modified procedure were comparable to other HPLC-based methods.

CONCLUSION

By using a validated modification of HPLC-based TBA method, the total plasma MDA in 16 Taiwanese college students was found to be 1.54 microM, which was relatively high compared to those obtained by other HPLC-based method, primarily due to the release of protein-bound MDA by alkaline hydrolysis. This level equaled the sum of protein-bound MDA and free MDA in plasma, confirming that this level represents total plasma MDA.

Role of cellulosic and noncellulosic membranes in hyperhomocysteinemia and oxidative stress

Hyperhomocysteinemia is an independent risk factor for cardiovascular morbidity and mortality in end-stage renal disease (ESRD) with an increased relative risk (RR) of 1% per micromol/L in total homocysteine concentration. In ESRD patients who undergo hemodialysis (HD), the antioxidant system is largely inadequate in correcting the imbalance between generation and scavenging of reactive oxygen species (ROS). To clarify the role of several cellulosic (CMs) and noncellulosic of synthetic membranes (NCMs) upon hyperhomocysteinemia and the oxidative stress, we measured plasma (P) homocysteine (t-HCY), plasma lipid peroxidation (LPO), and erythrocyte (E) concentration of several antioxidant enzymes in 20 normal subjects, in 35 HD patients treated with CMs, and in 29 patients treated with NCMs. Before, during, and after the first session of the week (at times 0', 120', end, 30' after HD end), blood samples were drawn. Plasma (P) homocysteine (t-HCY), cysteine (CYS), malondialdehyde (MDA), erythrocyte (E)-glutathione (GSH), glucose-6-phosphodehydrogenase (G6PD), glutathione reductase (GR), glutathione peroxidase (GPx), catalase (CAT), and superoxide-dismutase (SOD) were determined. The dialytic procedure significantly decreased the three plasma parameters, but none normalized (as a mean). The E-enzymes scavenging ROS (lower than normal before session) increased throughout the session, but the normal range of activity was never reached. Different membranes have shown different effects. When these effects on P and E spaces were pooled, we were able to classify the membranes as follows. In a general sense, cellulosic membranes are less effective than synthetic membranes both on lipoperoxides (LPO) and antioxidant activity (AOA). Among synthetic membranes, PMMA is the best membrane both for plasma values and lesser enzymatic derangement during the session. A practical system for classifying the anti-atherosclerotic action and antioxidant activity of dialytic membranes is proposed.

Methods to assess free radicals and oxidative stress in biological systems

Oxidative stress results from a disruption of the prooxidant/antioxidant cellular balance and monitoring free radical status becomes an interesting challenge in animal and human nutrition. In the present work, merits and limitations of different analytical techniques (HPLC, GC-MS, fluorometric and colourometric assays, ELISA, gel electrophoresis) for the measurement of radical mediated alterations in the cellular integrity of lipids (malondialdehyde, hydrocarbon gases, F2-isoprostanes) proteins (protein carbonyls, 3-nitrotyrosine) and DNA (8-hydroxy-2'-deoxyguanosine) are discussed. Besides these indirect methods, owing to the fact that free radicals are paramagnetic, electron paramagnetic resonance spectroscopy combined with spin trapping has become a valuable tool to directly assess and to better understand the mechanisms of free radical reactions. With this approach a radical that is too short-lived to be detected, adds to a spin-trapping agent to form a relatively long-lived radical adduct. Information obtained from the hyperfine splitting of the spin-trapped adduct can provide identification and quantification of the originally generated free radicals.

Alcohol-induced generation of lipid peroxidation products in humans

To address the hypothesis that elevated blood alcohol increases systemic oxidant stress, we measured urinary excretion of isoprostanes (iPs), free radical-catalyzed products of arachidonic acid. Ten healthy volunteers received acute doses of alcohol (Everclear-R) or placebo under randomized, controlled, double-blind conditions. Urinary iPF2a-III increased in a time- and dosage-dependent manner after dosing with alcohol, with the peak urinary iPF2a-III excretion correlating with the rise in blood alcohol. To determine whether oxidant stress was associated with alcohol-induced liver disease (ALD), we then studied the excretion of iP in individuals with a documented history of alcohol-induced hepatitis or alcohol-induced chronic liver disease (AC). Both urinary iPF2a-III and urinary iPF2a-VI were markedly increased in patients with acute alcoholic hepatitis. In general, urinary iPF2a-III was significantly elevated in cirrhotic patients, relative to controls, but excretion was more pronounced when cirrhosis was induced by alcohol than by hepatitis C. Excretion of iPF2a-VI, as well as 4-hydroxynonenal and the iPF2a-III metabolite, 2,3-dinor-5, 6-dihydro-iPF2a-III, was also increased in AC. Vitamin C, but not aspirin, reduced urinary iPs in AC. Thus, vasoactive iPs, which serve as indices of oxidant stress, are elevated in the urine in both acute and chronic ALD. Increased generation of iPs by alcohol in healthy volunteers is consistent with the hypothesis that oxidant stress precedes and contributes to the evolution of ALD.

The role of oxygen free radicals in cisplatin-induced acute renal failure in rats

We examined the role of oxygen free radicals in cisplatin-induced acute renal failure (ARF). The intravenous injection of cisplatin (5 mg/kg body weight) induced an increase in serum creatinine and tubular damage in the outer stripe of the outer medulla in rats. The renal content of malondialdehyde (MDA) transiently increased. Treatment with the free radical scavengers dimethylthiourea (DMTU) or lecithinized superoxide dismutase (L-SOD) attenuated the increase in serum creatinine. The beneficial effect of DMTU, a hydroxyl radical scavenger, was associated with less accumulation of MDA, less tubular damage, and enhanced expression of proliferating cell nuclear antigen (PCNA) in the damaged tubular cells, but not with improvement of reduced renal blood flow (RBF). On the other hand, the beneficial effect of L-SOD, a superoxide anion scavenger, was associated with preservation of RBF and increased urinary guanosine 3',5'-cyclic monophosphate excretion but not with modification of tubular damage or PCNA expression. These results suggest that (1) cisplatin-induced nephrotoxicity was associated with lipid peroxidation, (2) the hydroxyl radical scavenger prevented ARF through both attenuation of tubular damage and enhanced regenerative response of the damaged tubular cells, and (3) the superoxide anion scavenger did the same through preservation of RBF. It follows that oxygen free radicals may play an important role in cisplatin-induced ARF by reducing RBF and inducing tubular damage.

Role of 8-epi PGF2alpha, 8-isoprostane, in H2O2-induced derangements of pulmonary artery endothelial cell barrier function

The non-enzymatic peroxidation product of arachidonic acid, 8-epi-PGF2alpha or 8-isoprostane (8-IP) was measured in H2O2-exposed cultured pulmonary artery endothelial cell (PAEC) monolayers using a commercially-available enzyme immunoassay kit. H2O2 (50 microM for 1-30 min) significantly increased 8-IP production in a time-dependent fashion. Treatment with higher H2O2 concentrations (100 or 250 microM) failed to further increase 8-IP generation. Determinations of thiobarbituric acid reactive substances (TBARS) and lipid hydroperoxides (LOOH) were not sufficiently sensitive to detect lipid peroxidation in PAEC exposed to 50 microM H2O2 for 15 min. 8-IP (100 pM-500 nM for 2 h) caused PAEC monolayer barrier dysfunction measured as the transmonolayer clearance of albumin without causing significant PAEC cytotoxicity (measured as intracellular lactate dehydrogenase release). This is the first report to provide evidence that 8-IP generated in H2O2-exposed PAEC contributes to oxidant-mediated alterations in monolayer barrier function at non-cytotoxic concentrations.

Oxidative stress and erythrocyte membrane fluidity in patients undergoing regular dialysis

Oxidative damage due to free radical production is increased in uraemic patients and has been suggested as a possible factor contributing to the anaemia of chronic renal failure (CRF) and the pathogenesis of atherosclerosis. Oxidative stress was assessed in 40 patients with CRF maintained by either haemodialysis (HD) or continuous ambulatory peritoneal dialysis (CAPD) and in 18 healthy controls. Lipid peroxidation (assessed as malondialdehyde, MDA), total glutathione (TG), antioxidant enzyme (glutathione reductase (GSHRx), glutathione peroxidase (GSHPx) and superoxide dismutase (SOD)) activity and antioxidant associated trace metal (selenium, copper, zinc) levels were studied. Erythrocyte membrane fluidity was examined using the fluorescent probe 1,6 diphenyl-1,3,5-hexatriene (DPH). The results indicate increased levels of oxidative stress and altered erythrocyte membrane fluidity in patients treated with CAPD compared with controls and patients treated with HD. Only minor changes were observed in patients treated with HD. Altered free radical activity, oxidative stress and altered erythrocyte membrane fluidity observed in patients with CRF may contribute to the increase in vascular disease in such patients and to the anaemia of CRF.

Lipoperoxides as an index of free radical activity in bone marrow transplant recipients. Preliminary observations

It has been previously demonstrated that the conditioning therapy given to bone marrow transplant (BMT) recipients creates a high oxidant stress, resulting in a measured reduction in antioxidants, such as glutathione peroxidase (GSH-Px), vitamin E, and cell peroxide fragilities. As part of a current intervention trial of antioxidant therapy in BMT recipients, plasma thiobarbituric acid reactive substances (TBARS) were measured to assess peroxidation and free radical activity. Measurements were performed before and after conditioning therapy, and then at weekly intervals for a period of 6 wk after transplantation in 20 patients (10 controls and 10 antioxidant therapy [AOT] recipients). The TBARS results were compared with concurrent measurements of more specific elements of the antioxidant pathways, such as red blood cell glutathione peroxidase (RBC-GSH-Px), plasma vitamin C, and serum vitamin E. In all cases, TBARS concentration was significantly increased after conditioning compared with baseline levels (p < 0.001), an increase that correlated inversely with RBC-GSH-Px (r = -0.81; p < 0.01). The TBARS concentration fell gradually after conditioning in all patients. The fall in the AOT group was more rapid than in the control group, and it paralleled the gradual return toward normal levels of the other antioxidants. The change in TBARS concentration occurred faster than changes in other indices, suggesting that TBARS might be a better index of overall free radical activity. Although the patient numbers are small, there is some evidence to suggest that MDA may act as a prognostic marker.(ABSTRACT TRUNCATED AT 250 WORDS)

Heightened free radical activity in blacks with chronic pancreatitis at Johannesburg, South Africa

Four indices of free radical activity were measured in fasting serum/plasma samples from 14 consecutive blacks with clinically quiescent chronic pancreatitis and 15 outwardly healthy hospital personnel at Soweto, the township near Johannesburg in South Africa. The patients had higher serum levels than did controls of lipid isomerisation (P < 0.002) and peroxidation (P < 0.05) markers, with lower plasma levels of glutathione (P < 0.0001) and bioactive fraction of vitamin C (P < 0.002). Lipid peroxide and non-bioavailable vitamin C concentrations in Sowetan patients were significantly higher than in their counterparts from Manchester, UK (P < 0.0001, P < 0.0005, respectively). These differences mirrored those in controls in that outwardly healthy Sowetans had much higher serum lipid peroxide levels than Manchester controls (P < 0.001) and much lower plasma concentration of vitamin C (P < 0.001) and hence of the bioavailable fraction ascorbate (P < 0.0002). Heightened free radical activity is thus a common denominator in chronic pancreatitis irrespective of geography, or putative aetiological factors whether alcoholism or idiopathic, since that ratio was approximately 95:5 at Johannesburg and 50:50 at Manchester. The further finding of subclinical oxidative stress in Sowetan controls and the endemic nature of chronic pancreatitis in that area supports the hypothesis that oxidative stress may be involved in its pathogenesis.

Conjugated linoleic acid and atherosclerosis in rabbits

Conjugated linoleic acid (CLA) consists of a series of positional and geometric dienoic isomers of linoleic acid that occur naturally in foods. CLA exhibits antioxidant activity in vitro and in vivo. To assess the effect of CLA on atherosclerosis, 12 rabbits were fed a semi-synthetic diet containing 14% fat and 0.1% cholesterol for 22 weeks. For 6 of these rabbits, the diet was augmented with CLA (0.5 g CLA/rabbit per day). Blood samples were taken monthly for lipid analysis. By 12 weeks total and LDL cholesterol and triglycerides were markedly lower in the CLA-fed group. Interestingly, the LDL cholesterol to HDL cholesterol ratio and total cholesterol to HDL cholesterol ratio were significantly reduced in CLA-fed rabbits. Examination of the aortas of CLA-fed rabbits showed less atherosclerosis.

Dietary fat effects on hepatic lipid peroxidation and enzymes of H2O2 metabolism and NADPH generation

The purpose of this study was to determine the effects of dietary fat quantity and fatty acid composition on hepatic H2O2-metabolizing systems, activities of NADPH-generating enzymes and lipid peroxidation. One-month-old male C57BL/6J mice were fed one of six diets: (i) 5% fat, rich in 18:2n-6 fatty acid (5% N-6); (ii) 20% fat, rich in 18:3n-3 (N-3); (iii) 20% fat, rich in 18:2n-6 (N-6); (iv) 20% fat, rich in 18:1n-9 (N-9); (v) 20% fat, rich in saturated fatty acids (SAT); and (vi) 20% fat, deficient in essential fatty acids (EFAD); for 11 wk. Comparisons between animal groups receiving different fat quantities showed that activities of glucose-6-phosphate dehydrogenase (G6PDH, EC 1.1.1.49) and malic enzyme (ME, EC 1.1.1.40) and the levels of conjugated dienes were significantly lower in the N-6 than in 5% N-6 group. Conversely, activities of catalase (CAT, EC 1.11.1.6) and selenium-glutathione peroxidase (SeGSHPx, EC 1.11.1.9) were higher in the N-6 than in 5% N-6 group. Among the five dietary groups receiving 20% fat but differing in fatty acid composition, CAT activity was lower in the N-9 group, SeGSHPx activity was lower in the EFAD group, and glutathione reductase (GSSGR, EC 1.6.4.2) activity was higher in the N-6 than in the N-3, N-9, SAT and EFAD group. The EFAD group had much higher levels of total lipids and conjugated dienes, as well as activities of NADPH-generating enzymes, including G6PDH, ME and isocitrate dehydrogenase (EC 1.1.1.42), than the other four high-fat groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Monitoring of oxidative free radical damage in vivo: analytical aspects

Free radical damage is an important factor in many pathological and toxicological processes. During the last decade a wide range of methods has been developed to determine free radical damage in various biological fluids and at various stages of development. This review offers an overview of the state of the art of monitoring free radical damage in vivo, with special emphasis on the analytical aspects of non-invasive methods.

Reduced activity of antioxidant enzymes underlies contrast media-induced renal injury in volume depletion

Oxidant-mediated renal injury has been suggested as an important mechanism of acute renal failure induced by contrast media. Since volume depletion has been recognized as a predisposing factor for contrast media nephropathy, the present study was designed to characterize host-defense mechanisms against oxidant-mediated renal injury during volume depletion. Antioxidant enzyme activities in renal cortex were compared between acutely water deprived (WD, 72 hours) and non-WD rats. WD rats had reduced activities of catalase and superoxide dismutase activities (on average, 48% and 60% of values in non-WD, respectively). In separate groups of WD rats, saline or one of three different contrast media, namely diatrizoate meglumine/diatrizoate sodium (DTZ), ioxaglate meglumine/ioxaglate sodium (IXG), and iohexol (IHX) was injected. Both GFR and renal plasma flow rate, measured 24 hours later, was some 50% less in DTZ-injected than saline-injected WD rats. WD rats treated with IXG and IHX had similar GFR to saline-treated rats. In DTZ-treated WD rats, specific products of membrane lipid peroxidation, phosphatidylcholine and phosphatidylethanolamine hydroperoxide, determined by chemiluminescent HPLC, were more than two-fold higher than saline, IXG, or IHX-treated WD rats. DTZ did not induce renal dysfunction and enhance lipid peroxidation in non-WD rats. Therefore, DTZ appeared to induce oxidant-mediated injury only in WD rats. When WD rats were pretreated with polyethylene glycol-coupled catalase (1.4 mg x 2 days), renal cortical catalase activity remained at a level similar to that of non-WD rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Oxygen-dependent lipid peroxidation during lung ischemia

The effect of alveolar oxygen tension on lung lipid peroxidation during lung ischemia was evaluated by using isolated rat lungs perfused with synthetic medium. After a 5-min equilibration period, global ischemia was produced by discontinuing perfusion while ventilation continued with gas mixtures containing 5% CO2 and a fixed oxygen concentration between 0 and 95%. Lipid peroxidation was assessed by measurement of tissue thiobarbituric acid-reactive products and conjugated dienes. Control studies (no ischemia) showed no change in parameters of lipid peroxidation during 1 h of perfusion and ventilation with 20% or 95% O2. With 60 min of ischemia, there was increased lipid peroxidation which varied with oxygen content of the ventilating gas and was markedly inhibited by ventilation with N2. Perfusion with 5-, 8-, 11-, 14-eicosatetraynoic acid indicated that generation of eicosanoids during ischemia accounted for approximately 40-50% of lung lipid peroxide production. Changes of CO2 content of the ventilating gas (to alter tissue pH) or of perfusate glucose concentration had no effect on lipid peroxidation during ischemia, but perfusion at 8% of the normal flow rate prevented lipid peroxidation. Lung dry/wet weight measured after 3 min of reperfusion showed good correlation between lung fluid accumulation and lipid peroxidation. These results indicate that reperfusion is not necessary for lipid peroxidation with ischemic insult of the lung and provide evidence that elevated PO2 during ischemia accelerates the rate of tissue injury.

Noninvasive measures of oxidative stress status in humans

Although oxidative stress is thought to be involved in the pathophysiology of several diseases and aging, it is not routinely measured in clinical diagnosis. This is at least partly because accepted and standardized methods for measuring oxidative stress in humans are not yet established. One of the greatest needs in the field of free radical biology is the development of reliable methods for measuring oxidative stress status (OSS) in humans. A listing of some analytical approaches to measuring oxidative stress is provided as well as a listing of some noninvasive techniques that have been used in humans.

Reactive oxygen and ischemia/reperfusion injury of the liver

Pharmacological experiments suggested that reactive oxygen species contribute to ischemia-reperfusion injury of the liver. Since there is no evidence that quantitatively sufficient amounts of reactive oxygen are generated intracellularly to overwhelm the strong antioxidant defense mechanisms in the liver and cause parenchymal cell injury, the role of reactive oxygen in the pathogenesis remains controversial. This paper reviews the data and conclusions obtained with pharmacological intervention studies in vivo, the sources of reactive oxygen in the liver as well as the growing evidence for the importance of liver macrophages (Kupffer cells) and infiltrating neutrophils in the pathogenesis. A comprehensive hypothesis is presented that focuses on the extracellular generation of reactive oxygen in the hepatic sinusoids, where Kupffer cell-derived reactive oxygen species seem to be involved in the initial vascular and parenchymal cell injury and indirectly also in the recruitment of neutrophils into the liver. Reactive oxygen species may also contribute to the subsequent neutrophil-dependent injury phase as one of the toxic mediators released by these inflammatory cells.

Determination of picomole quantities of hydroperoxides by a coupled glutathione peroxidase and glutathione disulfide specific glutathione reductase assay

A procedure to quantitate picomole amounts of hydroperoxides based on GSSG formation is described. Hydroperoxides are incubated with GSH and glutathione peroxidase, and the GSSG formed is measured by a GSSG-specific glutathione reductase recycling assay. Prior to analysis the remaining GSH is removed with N-ethylmaleimide. N-Ethylmaleimide inhibition of the recycling assay is prevented by alkaline hydrolysis of the N-ethylmaleimide, without GSSG hydrolysis, at pH 11. The method is rapid, 30 min, with a limit of detection of 142 pmol calculated by linear regression analysis. Stoichiometric amounts of GSSG are produced in response to hydroperoxides. An application of the method is shown with air oxidation of arachidonic acid solutions over 4 h at room temperature. The method is sufficiently sensitive to quantitate the low amounts of hydroperoxides present in fresh arachidonic acid samples.

Histamine release from rat mast cells induced by metabolic activation of polyunsaturated fatty acids into free radicals

Polyunsaturated fatty acids (PUFA: arachidonic and linoleic acid) release histamine from isolated purified rat serosal mast cells only in the presence of oxidizing systems such as phenobarbital-induced rat liver microsomes, prostaglandin-H-synthetase (PHS) or soybean lipoxygenase. The release of mast cell histamine by activated PUFA has a long time-course and the electron microscopical features are consistent with an exocytotic secretion in the case of arachidonic acid and cell lysis in the case of linoleic acid. The phenomenon is associated with a significant increase in malonyldialdehyde (MDA) and conjugated diene generation, suggesting a relationship between histamine release and membrane lipid peroxidation. The secretion of histamine was inhibited by anti-free radical interventions such as D-mannitol, reduced glutathione and alpha-tocopherol. Some cyclooxygenase and lipoxygenase inhibitors, cimetidine and carnitine derivatives, are differentially active in the inhibition of mast cell histamine release by activated arachidonic acid. These results suggest that free radical derivatives of PUFA, generated by metabolic activation, trigger mast cell histamine release.

Rationale for antioxidant therapy in pancreatitis and cystic fibrosis

The overlapping features of the acquired diseases acute pancreatitis and chronic pancreatitis on the one hand, and of chronic pancreatitis and pancreatic involvement in the congenital condition cystic fibrosis on the other, suggest that the basic mechanism of pancreatic injury may be the same in each illness. We propose that pancreatic oxidant stress is the common denominator and, furthermore, that this is facilitated by a shortfall of micronutrient antioxidants in the face of heightened free radical activity through different sources. If so antioxidant supplements should alleviate symptoms. This deduction was supported by an exploratory dose-seeking study that spanned five years in 20 patients with recurrent (non-gall stone) acute or chronic pancreatitis and confirmed by a 20-week double-blind placebo-controlled crossover trial of the successful combination (daily doses of 600 micrograms organic selenium, 0.54 g vitamin C, 9000 IU B-carotene, 270 IU vitamin E and 2 g methionine) in a further 20 cases. A randomised trial of glutathione precursors, given intravenously for 24 hours after admission in patients with a first attack of acute pancreatitis, is in progress. Long-term trials of oral antioxidant formulas are planned in patients with cystic fibrosis.

Rapid headspace gas chromatography of hexanal as a measure of lipid peroxidation in biological samples

A rapid, sensitive and convenient capillary gas chromatographic-headspace method was developed to determine hexanal as an important volatile decomposition product of hydroperoxides formed from n-6 polyunsaturated fatty acids in rat liver samples. Total volatiles were also determined as a measure of overall lipid peroxidation. Samples of headspace taken from sealed serum bottles incubated at 37 degrees C were injected into a gas chromatograph. It was possible to make 15 determinations per hour. This method is convenient because no special sample manipulations are necessary. The addition of 0.5 mM ascorbic acid prior to gas chromatographic analysis significantly increased hexanal production. The applicability of the method was demonstrated in studies of the effect of iron in the presence or absence of hydroperoxides of methyl linoleate and methyl linolenate and tert-butyl hydroperoxide on rat liver homogenates, slices and microsomes. A rapid silica cartridge chromatographic procedure was used to purify hydroperoxides from autoxidized methyl linoleate and methyl linolenate, and hydroperoxy epidioxides (cyclic peroxides) from autoxidized methyl linolenate in 20-40 mg quantities. The hydroperoxides and hydroperoxy epidioxides of methyl linolenate were effective inducers of n-6 polyunsaturated fatty acid peroxidation in liver homogenates. Hexanal and thiobarbituric acid-reacting substances were significantly correlated in liver homogenates and microsomes but not in slices. This specific method for hexanal, a known product of peroxidation of n-6 polyunsaturated fatty acids, can be used as a good measure of lipid peroxidation.

Gas chromatographic determination of malonaldehyde formed by lipid peroxidation

Gas chromatographic (GC) methods for the determination of malonaldehyde (MA) all require formation of a stable derivative of MA since free MA is not suitable for direct GC analysis. Most reported GC methods give a total measure of free MA and its bound forms because their assay conditions are sufficient to hydrolyze or decompose bound MA during sample preparation. In this paper, GC methods that provide a measure of total MA (free plus bound) are reviewed. A recently developed capillary GC method that allows determination of free MA apart from other forms is also discussed. The method involves derivatization of MA to N-methylpyrazole under milder reaction conditions than with other GC methods. The method represents an advantage over existing techniques for free MA determination because capillary GC offers the highest efficiency of separation among chromatographic methods thus allowing a more specific and accurate measure of MA.

Systematic isolation and identification of membrane lipid oxidation products

This report discusses the analytical procedure by which it is possible to isolate and identify the oxidation products of cellular and subcellular membrane lipids. The key point of this procedure is the method used for the transmethylation of the lipid material isolated from the tissues. In effect, both the conversion of the glycerides into methyl esters and the reduction of the hydroperoxyl groups into the corresponding hydroxyl groups is performed in one step, without breaking any oxirane rings that may be present. The methyl esters containing functional groups introduced by oxidative processes are separated from the non-modified ones by preparative TLC and are identified by GLC and GC-MS.

Evaluation of an isoluminol chemiluminescence assay for the detection of hydroperoxides in human blood plasma

An assay for the separation and detection of lipid hydroperoxides and hydrogen peroxide in biological samples using HPLC and isoluminol chemiluminescence was recently described (Y. Yamamoto, M. H. Brodsky, J. C. Baker, and B. N. Ames (1987) Anal. Biochem. 160, 7-13; Y. Yamamoto and B. N. Ames (1987) Free Rad. Biol. Med. 3, 359-361). In this paper the application of this assay to the analysis of human blood plasma is described in detail, and three compounds producing chemiluminescence that were observed in the initial studies in plasma extracted with methanol and hexane are further characterized. It is shown that various lipid hydroperoxides added to plasma are detected by the assay. In contrast, hydrogen peroxide added to plasma is rapidly degraded by endogenous catalase. Hydrogen peroxide and a second, minor compound producing chemiluminescence, which appear in the assay of the methanol and the hexane extract of plasma, respectively, appear to be generated during analysis and are not likely to be present in plasma. The third compound yielding a chemiluminescence peak, which is extracted into the hexane phase of plasma and was earlier assigned to cholesterol ester hydroperoxide, is shown to be neither a cholesterol ester nor a hydroperoxide, but the hydroquinone ubiquinol-10. As the chemiluminescence response of hydroperoxides, but not of hydroquinones, is eliminated by reducing reagents such as sodium borohydride or triphenylphosphine, such reduction should be used to confirm that any chemiluminescence producing lipid observed in the assay is a hydroperoxide, not a hydroquinone. We conclude that isolated human plasma from healthy subjects is very unlikely to contain hydrogen peroxide in concentrations greater than about 0.25 microM and does not contain lipid hydroperoxides in concentrations greater than 0.03 microM. The method described, when used with appropriate precautions, is a convenient and very sensitive assay for lipid hydroperoxides in biological tissues.