Dynamics of xanthine oxidase- and Fe(3+)-ADP-dependent lipid peroxidation in negatively charged phospholipid vesicles

Egg white hydrolysate inhibits oxidation in mayonnaise and a model system

The flavor deterioration of mayonnaise is induced by iron, which is released from egg yolk phosvitin under acidic conditions and promotes lipid oxidation. To prevent oxidative deterioration, natural components, rather than synthetic chemicals such as ethylenediaminetetraacetic acid have been required by consumers. In the present study, we evaluated the inhibitory effects of three egg white components with the same amino acid composition, namely egg white protein, hydrolysate, and the amino acid mixture, on lipid oxidation in mayonnaise and an acidic egg yolk solution as a model system. We found that the hydrolysate had the strongest inhibitory effect on lipid oxidation among the three components. The mechanism underlying the antioxidant effect was associated with Fe2+-chelating activity. Thus, egg white hydrolysate may have the potential as natural inhibitors of lipid oxidation in mayonnaise.

Dimyristoyl phosphatidylcholine: a remarkable exception to α-tocopherol's membrane presence

Using data obtained from different physical techniques (i.e., neutron diffraction, NMR and UV spectroscopy), we present evidence which explains some of the conflicting and inexplicable data found in the literature regarding α-tocopherol's (aToc's) behavior in dimyristoyl phosphatidylcholine (di-14:0PC) bilayers. Without exception, the data point to aToc's active chromanol moiety residing deep in the hydrophobic core of di-14:0PC bilayers, a location that is in stark contrast to aToc's location in other PC bilayers. Our result is a clear example of the importance of lipid species diversity in biological membranes and importantly, it suggests that measurements of aToc's oxidation kinetics, and its associated byproducts observed in di-14:0PC bilayers, should be reexamined, this time taking into account its noncanonical location in this bilayer.

Prooxidant mechanisms of free fatty acids in stripped soybean oil-in-water emulsions

The prooxidant role of free fatty acids was studied in soybean oil-in-water emulsions. Addition of oleic acid (0-5.0% of oil) to the emulsions increased lipid hydroperoxides and headspace hexanal formation and increased the negative charge of the emulsion droplet with increasing oleic acid concentration. Methyl oleate (1.0% of oil) did not increase oxidation rates. The ability of oleic acid to promote lipid oxidation in oil-in-water emulsions decreased with decreasing pH with dramatic reduction in oxidation observed when the pH was low enough so that the oleic acid was not able to increase the negative charge of the emulsion droplet. Ethylenediaminetetraacetic acid (EDTA, 200 microm) strongly inhibited lipid oxidation in emulsions with oleic acid, indicating that transition metals were responsible for accelerating oxidation. Oleic acid hydroperoxides did not increase oxidation rates, suggesting that hydroperoxides on free fatty acids are not strong prooxidants in oil-in-water emulsion. These results suggest that the prooxidant activity of free fatty acids in oil-in-water emulsions is due to their ability to attact prooxidant metals to the emulsion droplet surface.

Antioxidant properties of Krebs cycle intermediates against malonate pro-oxidant activity in vitro: A comparative study using the colorimetric method and HPLC analysis to determine malondialdehyde in rat brain homogenates

A variety of Krebs cycle intermediaries has been shown to possess antioxidant properties in different in vivo and in vitro systems. Here we examined whether citrate, succinate, malate, oxaloacetate, fumarate and alpha-ketoglutarate could modulate malonate-induced thiobarbituric acid-reactive species (TBARS) production in rat brain homogenate. The mechanisms involved in their antioxidant activity were also determined using two analytical methods: 1) a popular spectrophotometric method (Ohkawa, H., Ohishi, N., Yagi, K., 1979. Assay for lipid peroxides in animal tissues by thiobarbituric acid reaction. Analytical Biochemistry 95, 351-358.) and a high performance liquid chromatographic (HPLC) procedure (Grotto, D., Santa Maria, L. D., Boeira, S., Valentini, J., Charão, M. F., Moro, A. M., Nascimento, P. C., Pomblum, V. J., Garcia, S. C., 2006. Rapid quantification of malondialdehyde in plasma by high performance liquid chromatography-visible detection. Journal of Pharmaceutical and Biomedical Analysis 43, 619-624.). Citrate, malate, and oxaloacetate reduced both basal and malonate-induced TBARS production. Their effects were not changed by pre-treatment of rat brain homogenates at 100 degrees C for 10 min. alpha-Ketoglutarate increased basal TBARS without changing malonate-induced TBARS production in fresh and heat-treated homogenates. Succinate reduced basal--without altering malonate-induced TBARS production. Its antioxidant activity was abolished by KCN or heat treatment. Fumarate reduced malonate-induced TBARS production in fresh homogenates; however, its effect was completely abolished by heat treatment. There were minimal differences among the studied methods. Citrate, oxaloacetate, malate, alpha-ketoglutarate and malonate showed iron-chelating activity. We suggest that antioxidant properties of citrate, malate and oxaloacetate were due to their ability to cancel iron redox activity by forming inactive complexes, whereas alpha-ketoglutarate and malonate pro-oxidant activity can be due to formation of active complexes with iron. In contrast, succinate and fumarate antioxidant activity was probably due to some enzymatic system.

Preventive effect of Shigyaku-san on progression of acute gastric mucosal lesions induced by compound 48/80, a mast cell degranulator, in rats

The study examined whether Shigyaku-san (Si-Ni-San) extract (TJ-35), a traditional Kampo medicine, prevents acute gastric mucosal lesion progression in rats treated once with compound 48/80 (C48/80). Rats treated with C48/80 (0.75 mg/kg body weight, i.p.) received TJ-35 (0.15, 0.35 or 0.75 g/kg body weight, p.o.) 0.5 h after the treatment at which time gastric mucosal lesions appeared. At 0.5 h after C48/80 treatment, the gastric mucosa of the treated rats had increased myeloperoxidase (an index of neutrophil infiltration) and xanthine oxidase activities and thiobarbituric acid reactive substances (an index of lipid peroxidation) content. At 3 h after C48/80 treatment, the gastric mucosa of the treated rats showed progressive lesions and further increases in myeloperoxidase and xanthine oxidase activities and thiobarbituric acid reactive substances content and decreases in vitamin E, ascorbic acid and adherent mucus contents and Se-glutathione peroxidase activity. Post-administered TJ-35 attenuated all these changes found at 3 h after C48/80 treatment dose-dependently. These results indicate that TJ-35 prevents the progression of C48/80-induced acute gastric mucosal lesions in rats possibly by attenuating enhanced neutrophil infiltration, enhanced lipid peroxidation associated with decreased vitamin E and ascorbic acid contents and Se-glutathione peroxidase activity, and destruction of the defensive barrier in the gastric mucosa.

Role of gastric mucosal ascorbic acid in gastric mucosal lesion development in rats with water immersion restraint stress

We examined the role of gastric mucosal ascorbic acid (AA) in gastric mucosal lesion development in rats with water immersion restraint stress (WIRS). When fasted rats were subjected to WIRS for 1, 3 or 6 h, gastric mucosal lesions developed at 3 and 6 h. Gastric mucosal AA concentration decreased at 3 and 6 h after the onset of WIRS, while gastric mucosal non-protein SH concentration decreased at 1, 3, and 6 h and gastric mucosal vitamin E concentration decreased at 6 h. Gastric mucosal lipid peroxide concentration and myeloperoxidase activity increased at 3 and 6 h of WIRS. Pre-administration of AA (250 mg/kg) prevented gastric mucosal development with attenuation of the decreased gastric mucosal AA, non-protein SH and vitamin E concentrations, and the increased gastric mucosal lipid peroxide concentration and myeloperoxidase activity. These results suggest that gastric mucosal AA plays an important role in WIRS-induced gastric mucosal lesion development.

Antioxidant effect of bovine serum albumin on membrane lipid peroxidation induced by iron chelate and superoxide

Albumin is supposed to be the major antioxidant circulating in blood. This study examined the prevention of membrane lipid peroxidation by bovine serum albumin (BSA). Lipid peroxidation was induced by the exposing of enzymatically generated superoxide radicals to egg yolk phosphatidylcholine liposomes incorporating lipids with different charges in the presence of chelated iron catalysts. We used three kinds of Fe3+-chelates, which initiated reactions that were dependent on membrane charge: Fe3+-EDTA and Fe3+-EGTA catalyzed peroxidation in positively and negatively charged liposomes, respectively, and Fe3+-NTA, a renal carcinogen, catalyzed the reaction in liposomes of either charge. Fe3+-chelates initiated more lipid peroxidation in liposomes with increased zeta potentials, followed by an increase of their availability for the initiation of the reaction at the membrane surface. BSA inhibits lipid peroxidation by preventing the interaction of iron chelate with membranes, followed by a decrease of its availability in a charge-dependent manner depending on the iron-chelate concentration: one is accompanied and the other is unaccompanied by a change in the membrane charge. The inhibitory effect of BSA in the former at high concentrations of iron chelate would be attributed to its electrostatic binding with oppositely charged membranes. The inhibitory effect in the latter at low concentrations of iron chelate would be caused by BSA binding with iron chelates and keeping them away from membrane surface where lipid peroxidation is initiated. Although these results warrant further in vivo investigation, it was concluded that BSA inhibits membrane lipid peroxidation by decreasing the availability of iron for the initiation of membrane lipid peroxidation, in addition to trapping active oxygens and free radicals.

A critical role of gastric mucosal ascorbic acid in the progression of acute gastric mucosal lesions induced by compound 48/80 in rats

AIM: To study the role of gastric mucosal ascorbic acid (AA) in the progression of acute gastric mucosal lesions induced by compound 48/80 (C48/80), a mast cell degranulator, in rats.

METHODS: C48/80 (0.75 mg/kg) was intraperitoneally injected to fasted Wistar rats. Oral administration of AA (10, 50 or 100 mg/kg) was performed 0.5 h after C48/80 treatment. Determinations for gastric mucosal lesion severity and blood flow, and assays for gastric mucosal total AA, reduced AA, oxidized AA, vitamin E, thiobarbituric acid reactive substances (TBARS), adherent mucus, nitrite/nitrate (NO_x), non-protein SH (NPSH), and myeloperoxidase (MPO), and serum total AA, reduced AA, oxidized AA, and NO_x were conducted 0.5 and 3 h after C48/80 treatment.

RESULTS: Gastric mucosal lesions occurred 0.5 h after C48/80 treatment and progressed at 3 h. Gastric mucosal blood flow decreased 0.5 h after C48/80 treatment but the decrease was recovered at 3 h. Gastric mucosal total AA, reduced AA, vitamin E, and adherent mucus concentrations decreased 3 h after C48/80 treatment. Gastric mucosal oxidized AA concentration remained unchanged after C48/80 treatment. Gastric mucosal NPSH concentration decreased 0.5 h after C48/80 treatment, but the decrease was recovered at 3 h. Gastric mucosal TBARS concentration and MPO activity increased 0.5 h after C48/80 treatment and further increased at 3 h. Serum total AA and reduced AA concentrations increased 0.5 h after C48/80 treatment and further increased at 3 h, while serum oxidized AA concentration increased at 0.5 h. Serum and gastric mucosal NOx concentrations increased 3 h after C48/80 treatment. AA administration to C48/80-treated rats at 0.5 h after the treatment prevented the gastric mucosal lesion progression and the changes in gastric mucosal total AA, reduced AA, vitamin E, adherent mucus, NOx, and TBARS concentrations and MPO activity and serum NOx concentration found at 3 h after the treatment dose-dependently. The AA administration to C48/80-treated rats caused further increases in serum total AA and reduced AA concentrations at 3 h after the treatment dose-dependently.

CONCLUSION: Gastric mucosal AA plays a critical role in the progression of C48/80-induced acute gastric mucosal lesions in rats.

Effect of Gefarnate on Acute Gastric Mucosal Lesion Progression in Rats Treated with Compound 48/80, a Mast Cell Degranulator, in Comparison with That of Teprenone

We have reported that teprenone (geranylgeranylacetone), an anti-ulcer drug, prevents acute gastric mucosal lesion progression in rats treated once with compound 48/80 (C48/80), a mast cell degranulator, possibly by suppressing mucus depletion, neutrophil infiltration, and oxidative stress in the gastric mucosa. Herein, we examined the preventive effect of gefarnate (geranyl farnesylacetate), an anti-ulcer drug, on acute gastric mucosal lesion progression in rats treated once with C48/80 (0.75 mg/kg, i.p.) in comparison with that of teprenone, because the chemical structure and anti-ulcer action of gefarnate are similar to those of teprenone. Gefarnate (50, 100 or 200 mg/kg) administered orally at 0.5 h after C48/80 treatment, at which time gastric mucosal lesions appeared, reduced progressive gastric mucosal lesions at 3 h dose-dependently. At 3 h after C48/80 treatment, the gastric mucosa had decreased adherent mucus and hexosamine contents and increased myeloperoxdiase (an index of neutrophil infiltration) and xanthine oxidase activities and thiobarbituric acid reactive substances (an index of lipid peroxidation) content. Post-administered gefarnate attenuated all these changes dose-dependently. These preventive effects of gefarnate were similar to those of teprenone at a dose of 200 mg/kg. Post-administered gefarnate did not affect the increases in serum serotonin and histamine concentrations and the decrease in gastric mucosal blood flow at 3 h after C48/80 treatment like teprenone. These results indicate that orally administered gefarnate prevents acute gastric mucosal lesion progression in C48/80-treated rats possibly by suppressing mucus depletion, neutrophil infiltration, and oxidative stress in the gastric mucosa like teprenone.

Preventive effect of teprenone on acute gastric mucosal lesion progression in compound 48/80-treated rats

The preventive effect of teprenone (6,10,14,18-teramethyl-5,9,13,17-nonadecatetaene-2-one), an anti-ulcer drug, on acute gastric mucosal lesion progression was examined in rats with a single intraperitoneal (i.p.) injection of compound 48/80 (0.75 mg/kg). Teprenone (20, 100 or 200 mg/kg), which was orally administered 0.5 h after compound 48/80 treatment at which time gastric mucosal lesions appeared, prevented gastric mucosal lesion development at 3 h after the treatment dose-dependently. Gastric mucosal tissues of compound 48/80-treated rats showed increases in myeloperoxidase (an index of neutrophil infiltration) and xanthine oxidase activities and thiobarbituric acid reactive substances (an index of lipid peroxidation) content and decreases in Se-glutathione peroxidase activity and hexosamine and vitamin E contents at 3 h after the treatment. Post-administered teprenone attenuated all these changes dose-dependently. These results indicate that teprenone prevents acute gastric mucosal lesion progression in compound 48/80-treated rats possibly by suppressing gastric mucus depletion, neutrophil infiltration and oxidative stress in the gastric mucosal tissue.

Novel antioxidants isolated from plants of the genera Ferula, Inula, Prangos and Rheum collected in Uzbekistan

We examined the effects of 48 compounds isolated from Ferula pallida, F. penninervis, Inula macrophylla, Prangos pabularia, P. tschimganica and Rheum maximowiczii collected in Uzbekistan on ADP/Fe2+-induced lipid peroxidation of egg yolk phosphatidylcholine liposomes. Of those compounds, 23 inhibited ADP/Fe2+-induced lipid peroxidation and nine showed especially strong inhibition of lipid peroxidation. Most compounds that inhibited peroxidation scavenged the 1,1'-diphenyl-2-picrylhydrazyl (DPPH) radical, indicating that the inhibition was due to radical scavenging. However, some compounds did not scavenge DPPH but inhibited lipid peroxidation significantly, suggesting that their inhibitory effect was not due to radical scavenging but to some other mechanism, such as prevention of Fe2+ function. Thus, we found various new antioxidants, some of which had a unique mechanism of action, in Ferula, Inula, Prangos and Rheum plants collected in Uzbekistan as seeds used in medicine.

Protective effect of teprenone against acute gastric mucosal lesions induced by compound 48/80, a mast cell degranulator, in rats

The protective effect of teprenone, an anti-ulcer drug, against acute gastric mucosal lesions was examined in rats with a single intraperitoneal injection of compound 48/80 (0.75 mg/kg). Teprenone (50, 100, or 200 mg/kg) was orally administered 0.5 h before compound 48/80 treatment. Administered teprenone prevented gastric mucosal lesion development found at 3 h after compound 48/80 treatment dose-dependently, although no dose of teprenone affected the decreased gastric mucosal blood flow and increased serum serotonin and histamine concentrations found at 3 h after the treatment. Increases in the activities of myeloperoxdiase (an index of neutrophil infiltration) and xanthine oxidase and the content of thiobarbituric acid reactive substances (an index of lipid peroxidation) and decreases in the contents of hexosamine (a marker of gastric mucus) and adherent mucus occurred in gastric mucosal tissues at 3 h after compound 48/80 treatment. Administered teprenone dose-dependently attenuated all these changes found at 3 h after compound 48/80 treatment. These results indicate that orally administered teprenone protects against compound 48/80-induced acute gastric mucosal lesions in rats possibly through its stimulatory action on gastric mucus synthesis and secretion and its inhibitory action on neutrophil infiltration and enhanced lipid peroxidation in the gastric mucosal tissue.

Interaction of tocopherols and phenolic compounds with membrane lipid components: evaluation of their antioxidant activity in a liposomal model system

This paper describes the use of complex liposomes as real membrane models to evaluate the potential benefits of several antioxidants in relation to lipid peroxidation. The xanthine oxidase/Fe(3+)-ADP-EDTA and the Fe(2+)/H2O2 systems have been used to generate hydroxyl radicals and the water soluble azo-compound 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH) to generate carbon centered radicals (A*) by thermal decomposition. The antioxidant behavior of the rosemary and citrus plant extracts and vitamin-E and vitamin-E acetate alpha-tocopherols have been analyzed. The order of effectiveness in avoiding radical chain reactions has been established by using the colorimetric thiobarbituric acid reaction and the fluorescent probe DPH-PA. ESR spectroscopy has been used to carry out the pursuit of the oxidation processes on the basis of the identification of the radical species resulting from the oxidant system and the ability of the antioxidants to act as scavengers for hydroxyl and AAPH-derived radicals. The modification of the main transition temperature for the lipid mixture and the splitting of the calorimetric peak in the presence of the antioxidants were demonstrated by differential scanning calorimetry. The results obtained showed that the phenols-containing plant extracts and alpha-tocopherols perturb the phase behavior of the BBE lipid bilayer and have a fluidifying effect that could favor the known antioxidant capability and scavenging characteristics of these compounds. 31P-NMR results could be interpreted as, after the incorporation of these antioxidants, those lipid molecules interacting with antioxidants give rise to lamellar phase spectral components with resonance position at lower fields or to isotropic signals in accordance with a higher motion of their phosphate groups.

A unique antioxidant activity of phosphatidylserine on iron-induced lipid peroxidation of phospholipid bilayers

The relationship between the antioxidant effect of acidic phospholipids, phosphatidic acid (PA), phosphatidylglycerol (PG) and phosphatidylserine (PS), on iron-induced lipid peroxidation of phospholipid bilayers and their abilities to bind iron ion was examined in egg yolk phosphatidylcholine large unilamellar vesicles (EYPC LUV). The effect of each acidic phospholipid added to the vesicles at 10 mol% was assessed by measuring phosphatidylcholine hydroperoxides (PC-OOH) and thiobarbituric acid-reactive substances. The addition of dipalmitoyl PS (DPPS) showed a significant inhibitory effect, although the other two acidic phospholipids, dipalmitoyl PA (DPPA) and dipalmitoyl PG (DPPG), did not exert the inhibition. Neither dipalmitoyl PC (DPPC) nor dipalmitoyl phophatidylethanolamine (DPPE) showed any remarkable inhibition on this system. None of the tested phospholipids affected the lipid peroxidation rate remarkably when the vesicles were exposed to a water-soluble radical generator. The iron-binding ability of each phospholipid was estimated on the basis of the amounts of iron recovered in the chloroform/methanol phase after separation of the vesicle solution to water/methanol and chloroform/methanol phases. EYPC LUV containing DPPS, DPPA, and DPPG had higher amounts of bound iron than those containing DPPC and DPPE, indicating that these three acidic phospholipids possess an iron-binding ability at a similar level. Nevertheless, only DPPS suppressed iron-dependent decomposition of PC-OOH significantly. Therefore, it is likely that these three acidic phospholipids possess a significant iron-binding ability, although this ability per se does not warrant them antioxidative activities. The ability to suppress the iron-dependent decomposition of PC-OOH may explain the unique antioxidant activity of PS.

A comparative study of the ability of ferric nitrilotriacetate [correction of nitriloacetate] and other iron chelators to assist membrane lipid peroxidation by superoxide radicals

This study examined some of the variables determining the efficiency of lipid peroxidation in egg yolk phosphatidylcholine liposomes and in microsomes exposed to enzymatically-generated superoxide radicals. The initiation of peroxidation required the presence of preformed lipid peroxides and a chelated metal catalyst. Comparison of the relative effectiveness of four iron chelating agents showed that the chelate must bind to the membrane by coulombic attraction between the charged membrane and a chelate carrying an opposite net charge. Of the chelates tested, only the carcinogenic ferric nitrilotriacetate [corrected] (Fe(3+)-NTA) was an effective catalyst of oxidation of all membranes, whether carrying a net charge, or not. We postulate that the unique catalytic capacity of the ferric nitrilotriacetate [corrected] (Fe(3+)-NTA) can be explained by its existence in two forms at neutral pH, each binding to oppositely charged membranes and initiating their peroxidation. This gives the complex the unique ability to bind to any membrane, which may be a factor in its carcinogenicity.

A marked stimulation of Fe(3+)-dependent lipid peroxidation in phospholipid liposomes under acidic conditions

Lipid peroxidation in phosphatidylcholine liposomes induced by Fe(3+) alone, assessed by thiobarbituric acid-reactive substances (TBARS) production, was markedly enhanced as the solution pH was lowered from 7.4 to 5.5. On the other hand, at physiological pH, TBARS production by Fe(3+) was almost negligible. Results of the radical scavenger experiments with superoxide dismutase, catalase and hydroxyl radical ((&z.rad;)OH) scavengers (sodium benzoate, mannitol and dimethylthiourea), deoxyribose degradation and ESR spectrometry suggest that the stimulation of Fe(3+)-dependent lipid peroxidation under acidic conditions is involved in generation of superoxide anion (O(2)(&z.rad;-)), hydrogen peroxide (H(2)O(2)) and (&z.rad;)OH during the reaction. The stimulation of Fe(3+)-dependent TBARS production by increasing the [H(+)] completely disappeared by triphenylphosphine (TPP) treatment of the liposomes, but the reaction was reversible with either incorporation of cumen hydroperoxide (CumOOH) into the TPP-treated liposomes or the addition of CumOOH to the treated liposomes. Incubation of the CumOOH-incorporated TPP-treated liposomes with Fe(3+) at pH 5.5 also resulted in (&z.rad;)OH generation. Based on these results, a possible mechanism of stimulatory effect of Fe(3+) on lipid peroxidation under acidic conditions is discussed.

The antioxidative effect of ganhuangenin against lipid peroxidation

The antioxidative effect of ganhuangenin (GHG), isolated from Scutellaria baicalensis Georgi, was examined by measuring its ability to suppress the formation of phospatidylcholine hydroperoxide (PCOOH). The results show that a pretreatment with GHG effectively suppressed PCOOH formation, which was initiated by the peroxyl-generating oxidant, AAPH (2,2'-azobis-2-aminopropane hydrochloride). The protective action of GHG against the formation of the PCOOH was observed in liver, lung, and kidney. When compared with other known antioxidants, we found the antioxidative potency of GHG to be greater than that of alpha-tocopherol. Our data strongly indicate that GHG is a powerful antioxidant against lipid peroxidation and is, therefore, responsible for this prophylactic effect.

Comparison between in vitro lipid peroxidation in fresh sheep platelets and peroxidative processes during sheep platelet ageing under storage at 4 degrees C

Incubation of sheep platelet crude membranes with xanthine oxidase (XO)/hypoxanthine/Fe(2+)-ADP revealed: (i) a fast peroxidative response - with a maximal linear rate of 14 nmol malondialdehyde (MDA) equivalents/mg protein, as evidenced by the thiobarbituric acid test - and a decrease in the polyunsaturated fatty acid (PUFA) content of the platelet crude membranes; (ii) a decrease in the lipid fluidity in the deep lipid core of the membranes but not at the membrane surface; (iii) a dramatic inhibitory effect on glucose 6-phosphatase (Glc-6-Pase) but not on acetylcholinesterase activity. Platelets were also aged by storage at 4 degrees C in their own plasma or in Seto additive solution. In these media, platelet aggregates were visible and the effects on platelet phospholipids, PUFA, lipid extract fluorescence, crude membrane fluidity and membrane-bound enzyme activities were assessed for comparison with those observed in in vitro lipid peroxidation. The sensitivity of membranes from stored platelets to lipid peroxidation was also assessed. Storage of platelets in plasma for 5 days was associated with different changes in their crude membranes such as decreases in arachidonic acid contents, the decrease not being avoided by the presence of phospholipase A(2) inhibitors, increases in MDA equivalents, conjugated dienes and lipid extract fluorescence, decreases in the amounts of MDA equivalents formed by platelet crude membranes treated with the oxidizing agents, changes in membrane fluidity and inhibition of Glc-6-Pase. All these alterations were less pronounced or even abolished after platelet storage in Seto. These findings suggest that platelet lipid peroxidation due to XO/hypoxanthine/Fe(2+)-ADP and platelet membrane alterations observed after platelet ageing under storage at 4 degrees C share common features. Also, as regards the prevention of peroxidative processes, Seto solution permits better storage of sheep platelets than plasma.

Oxidative inactivation of human and sheep platelet membrane-associated phosphotyrosine phosphatase activity

Incubation of human or sheep platelet crude membranes with xanthine oxidase/hypoxanthine in the presence of Fe2+/ADP inactivated phosphotyrosine phosphatase (PTPase, protein-tyrosine-phosphate-phosphohydrolase, EC 3.1.3.48) activity in a time-dependent manner, this inhibition being significant within 5 min of treatment. The dynamics of protein thiols differed depending on the platelet species, but in any case decreases in protein thiols were only visible 20-45 min after the start of the treatment. The inhibition of PTPase activity in general showed good a correlation with the production of thiobarbituric acid-reactive substances (TBARS). The results with several antioxidants suggest that the inhibition of PTPase activity is related to the generation of alkoxyl and/or peroxyl radicals. Furthermore, the formation of fluorescent products and changes in amino groups were observed only after long incubation times with the oxidizing agents, these fluorescent products and the residual enzyme activity remaining in the membrane fraction. Treatment of platelet membranes with trans-2-nonenal and n-heptaldehyde, but not with acetaldehyde, also inhibited membrane-associated PTPase activity. However, the amount of protein thiols was reduced only by treatment with trans-2-nonenal. Fluorescence product formation was always higher with trans-2-nonenal, these products being mainly located in the protein fraction. The results with aldehydes suggest that secondary degraded products of lipid hydroperoxides affect PTPase activity. Kinetic studies of PTPase activity indicated that with all treatments enzyme inhibition is mainly due to a decrease in the Vmax value. The results of fluorescence anisotropy measurements of labeled platelet membranes did not support the notion of a contribution of the lipid organization to peroxidation-mediated PTPase inhibition. All the above results indicate that platelet membrane-associated PTPase inhibition due to treatment with xanthine oxidase/ hypoxanthine in the presence of Fe2+/ADP is a very complex, time-dependent process, and that it is probably related, at least after long periods of peroxidation, to changes in protein thiols and amino groups. We predict that the sensitivity of PTPase to lipid peroxidation must be physiologically relevant because of the increasing importance of tyrosine phosphorylation in signal transduction, in general, and in platelet activation and aggregation in particular.

Inhibition of xanthine oxidase by pterins

The effect of a panel of pterins on xanthine oxidase was investigated by measuring formation of urate from xanthine as well as formazan production from nitroblue tetrazolium. The pterin derivatives, depending on their chemical structure, decreased urate as well as formazan generation: 200 microM neopterin and biopterin suppressed urate formation (90% from baseline) and formazan production (80% from baseline) as well. Their reduced forms, 7,8-dihydroneopterin and 5,6,7,8-tetrahydrobiopterin, showed a lesser but still strongly diminishing influence (40% from baseline). Another oxidized pterin namely leukopterin showed only a weak inhibitory effect. Xanthopterin, a known substrate of xanthine oxidase, had a strong effect on urate formation (80% inhibition), but a lesser effect on formazan production (30% reduction). When iron-(III)-EDTA complex was added to the reaction mixture all the effects were more pronounced. Superoxide dismutase, which removes superoxide anion by dismutation into oxygen, decreased formazan production in addition to pterin derivatives and had a small but enhancing effect on urate formation. Also the reductant N-acetylcysteine had an additive effect to pterins to diminish formazan production in a dose-dependent way. The results of our study suggest that depending on their chemical structure pterins reduce superoxide anion generation by xanthine oxidase.

Preparation and characterization of 8a-(phosphatidylcholine-dioxy)-alpha-tocopherones and their formation during the peroxidation of phosphatidylcholine in liposomes

alpha-Tocopherol was reacted with the phosphatidylcholines (PCs), 1-palmitoyl-2-linoleoyl-3-sn-PC (PLPC), 1-palmitoyl-2-linolenoyl-3-sn-PC, 1-palmitoyl-2-arachidonoyl-3-sn-PC (PAPC) and 1-stearoyl-2-arachidonoyl-3-sn-PC, in the presence of the free radical initiator, 2,2'-azobis (2,4-dimethylvaleronitrile), at 37 degrees C. The addition products of alpha-tocopherol with the PC peroxyl radicals were isolated and identified as 8a-(PC-dioxy)-alpha-tocopherones, in which the peroxyl radicals derived from each PC molecule attacked the 8a-position of the alpha-tocopheroxyl radical. The antioxidative efficiency of alpha-tocopherol against the peroxidation of PLPC and PAPC in liposomes was assessed by the formation of the reaction products of alpha-tocopherol. When alpha-tocopherol was oxidized in the presence of the water-soluble free radical initiator, 2,2'-azobis (2-amidinopropane) dihydrochloride, epoxy-alpha-tocopherylquinones were mainly produced together with 8a-(PC-dioxy)-alpha-tocopherones and alpha-tocopherylquinone. The yield of alpha-tocopherylquinone was increased by treating each sample with dilute acid which indicates the presence of tocopherone precursors other than the 8a-(PC-dioxy)-alpha-tocopherones. The same products were also detected from iron-dependent peroxidation, although the yields were very low.

Singlet oxygen scavenging by alpha-tocopherol and beta-carotene: kinetic studies in phospholipid membranes and ethanol solution

The rate constants (ks) of 1O2 scavenging for alpha-tocopherol (alpha-Toc) and beta-carotene (beta-Car) were measured in liposome membranes, and compared with those in EtOH solution. 1O2 was site-specifically generated by photoirradiation using two photosensitizers, water-soluble Rose bengal (RB) and lipid-soluble 12-(1-pyrene)-dodecanoic acid (PDA). The ks value for beta-Car in EtOH solution was 1.3 x 10(10) M-1 s-1, which was 36 times that for alpha-Toc (3.6 x 10(8) M-1 s-1), but there was no difference between their ks values in liposomes (1.8 x 10(7) M-1 s-1 for beta-Car and 1.2 x 10(7) M-1 s-1 for alpha-Toc). In the liposomes, the ks value for alpha-Toc was affected by the membrane site where 1O2 was generated, which depended on the localization of the photosensitizer, being high at the membrane surface in the RB-system and low in the inner region of the membrane in the PDA-system. In contrast, the ks value for beta-Car was not affected by the 1O2-generating site. These differences were supposed to be caused by differences in the relative concentrations of 1O2 and active sites of alpha-Toc and beta-Car in the membranes. alpha-Toc and beta-Car inhibited 1O2-dependent peroxidation of egg yolk phosphatidylcholine (egg PC). The concentrations of alpha-Toc required for 50% inhibition of lipid peroxidation (IC50) were higher than those of beta-Car, being more than 6 times higher in EtOH solution and less than 2 times higher in liposomes. The ratio of the antioxidant activity of beta-Car to that of alpha-Toc was more in EtOH solution than in liposomes, and was well correlated with the ratio of their 1O2 scavenging rate constants.

Kinetics and dynamics of singlet oxygen scavenging by alpha-tocopherol in phospholipid model membranes

Scavenging of singlet oxygen (1O2) by alpha-tocopherol (alpha-Toc) was investigated in liposomes. 1O2 was generated by photoirradiation in the presence of two photosensitizers, water-soluble methylene blue (MB) and lipid-soluble 12-(1-pyrene)dodecanoic acid (PDA). The rates of oxidation of alpha-Toc differed depending on the photosensitizing dye and the membrane charge: in the MB-system, alpha-Toc was oxidized fast in negatively charged dimyristoylphosphatidylcholine (DMPC) liposomes containing dicetylphosphate (DCP) and slowly in neutrally charged DMPC liposomes and positively charged DMPC liposomes containing stearylamine (SA), but in the PDA-system, the oxidation rate was independent of the membrane charge. The charge-dependent difference in the MB-system would be due to the site of 1O2 generation depending on the charge-dependent distribution of MB, because positively charged MB increased the zeta-potential of DCP-DMPC liposomes by its interaction with DCP at the membrane surface, but changed the zeta-potentials of DMPC and SA-DMPC liposomes less because of its location in the bulk water phase. The oxidation rate of alpha-Toc in liposomes was different from that in EtOH solution: in the MB system, the oxidation rate was faster in EtOH solution than in DMPC or SA-DMPC liposomes but the same as that in DCP-DMPC liposomes. However, in the PDA system, the oxidation rate was slower in EtOH solution than in DMPC liposomes with or without a charge. Membrane fluidity changed the rate of alpha-Toc oxidation in liposomes, the rate being higher in the liquid crystalline phase than the gel phase, as judged by the higher rate in DMPC liposomes than in dipalmitoylphosphatidylcholine (DPPC) liposomes at 30 degrees C. The rate constants of alpha-Toc for scavenging, the chemical reaction and physical quenching of 1O2 were determined in membranes using DCP-DMPC liposomes labeled with 1,3-diphenyl-isobenzofuran (DPBF), which traps 1O2. These constants differed in the two photosensitizing systems, being higher in the MB-system than in the PDA-system, and were lower than those in EtOH solution.

Vincristine resistant HL-60 cells show cross-resistance to hypoxanthine-xanthine oxidase

This is the first observation that active an oxygen-producing system showed cross-resistance to vincristine (VCR) resistant cells or other anticancer agent-resistant cells. The extent of cross-resistance against oxygen radicals and anticancer agents in wild type and VCR resistant human promyelocytic leukemia cell line, HL-60 and HL-60/VCR, is compared. Superoxide was generated by reaction with hypoxanthine(HX)-xanthine oxidase(XO). HL-60/VCR was 81-fold resistant to VCR, 11.8-fold resistant to adriamycin, and 8.5-fold resistant to the XO concentration required for 50% growth inhibition compared with HL-60. Because oxygen radicals injure the cell membrane, the results indicate an increased resistance to membrane damage by oxygen radicals in drug resistant cells.