Direct Free Radical Scavenging Research Articles

Evaluation of antioxidant activity of epigallocatechin gallate in biphasic model systems in vitro.

The antioxidant activity of epigallocatechin gallate (EGCG) was studied in different in vitro model systems, which enabled evaluation of both chemical and physical factors involved in assessing the role of EGCG in oxidative reactions. EGCG suppressed the initiation rate and prolonged the lag phase duration of peroxyl radical-induced oxidation in a phospholipid liposome model to a greater extent (p < 0.01) compared to both Trolox and alpha-tocopherol. Effectiveness of these antioxidants to prolong the peroxyl radical-induced lag phase was inversely related to lipophilic character. EGCG also protected against both peroxyl radical and hydroxyl radical-induced supercoiled DNA nicking. The rate constant describing EGCG reaction against hydroxyl radical was 4.22+/-0.07 x 10(10) M(-1) x sec(-1), which was comparable to those of Trolox and alpha-tocopherol, respectively. EGCG exhibited a synergistic effect with alpha-tocopherol in scavenging 1,1-diphenyl-2-picylhydrazyl (DPPH) radical, thus displaying a direct free radical scavenging capacity. In vitro Cu2+-induced-human LDL oxidation was accelerated in the presence of EGCG and attributed to the conversion of Cu2+ to Cu+. We conclude that the particularly effective antioxidant properties of EGCG noted in both chemical and biological biphasic systems were related to a unique hydrophilic and lipophilic balance which enabled effective free radical scavenging. The same chemical-physical properties of EGCG also enabled prooxidant activity, only when in contact with unbound transition metal ions in a multiphasic system.

Actions of melatonin in the reduction of oxidative stress. A review.

Melatonin was discovered to be a direct free radical scavenger less than 10 years ago. Besides its ability to directly neutralize a number of free radicals and reactive oxygen and nitrogen species, it stimulates several antioxidative enzymes which increase its efficiency as an antioxidant. In terms of direct free radical scavenging, melatonin interacts with the highly toxic hydroxyl radical with a rate constant equivalent to that of other highly efficient hydroxyl radical scavengers. Additionally, melatonin reportedly neutralizes hydrogen peroxide, singlet oxygen, peroxynitrite anion, nitric oxide and hypochlorous acid. The following antioxidative enzymes are also stimulated by melatonin: superoxide dismutase, glutathione peroxidase and glutathione reductase. Melatonin has been widely used as a protective agent against a wide variety of processes and agents that damage tissues via free radical mechanisms.

Achyranthes aspera elevates thyroid hormone levels and decreases hepatic lipid peroxidation in male rats

A study was made to evaluate the role of Achyranthes aspera on the changes in serum thyroid hormone concentrations and glucose levels in male rats. An attempt was also made to establish the relationship between hepatic lipid peroxidation and extract induced changes in thyroid hormone concentration, if any. Adult male Wistar rats were orally administered with the aqueous leaf extract of Achyranthes aspera at a dose of 200 mg/kg b. wt./day for 7 days. The effects of the extract on body weight, hepatic protein content, lipid peroxidation (LPO), superoxide dismutase (SOD) and catalase (CAT) activities and on serum triiodothyronine (T 3), thyroxine (T 4) and glucose levels were evaluated. The extract exhibited significant prothyroidic activity as it enhanced the levels of both the thyroid hormones along with an increase in serum glucose concentration, body weight and hepatic protein content. On the other hand, it decreased hepatic LPO without altering the activities of the two antioxidant enzymes, SOD and CAT significantly, suggesting a direct free radical scavenging activity of the extract. It appears that the Achyranthes aspera leaf extract is both prothyroidic and antiperoxidative in nature.

Changes in lipid peroxidation during pregnancy and after delivery in rats: effect of pinealectomy

Pregnancy is a physiological state accompanied by a high energy demand of many bodily functions and an increased oxygen requirement. Because of the increased intake and utilization of oxygen, increased levels of oxidative stress would be expected. In the present study, the degree of lipid peroxidation was examined in different tissues from non-pregnant and pregnant rats after the delivery of their young. Melatonin and other indole metabolites are known to be direct free radical scavengers and indirect antioxidants. Thus the effect of pinealectomy at 1 month before pregnancy on the accumulation of lipid damage was investigated in non-pregnant and pregnant rats after the delivery of their young. Malonaldehyde and 4-hydroxyalkenal concentrations were measured in the lung, uterus, liver, brain, kidney, thymus and spleen from intact and pinealectomized pregnant rats soon after birth of their young and at 14 and 21 days after delivery. The same parameters were also evaluated in intact and pinealectomized non-pregnant rats. Shortly after delivery, lipid oxidative damage was increased in lung, uterus, brain, kidney and thymus of the mothers. No differences were detected in liver and spleen. Pinealectomy enhanced this effect in the uterus and lung. It is concluded that during pregnancy high levels of oxidative stress induce an increase in oxidative damage to lipids, which in some cases is inhibited by the antioxidative actions of pineal indoles.

Allopurinol Does Not Increase Free Radical Scavenging Capacity During Reperfusion in Coronary Artery Bypass Graft Patients

Objectives: Allopurinol protects the heart against ischaemic events during coronary artery bypass grafting (CABG), possibly because of its antioxidant properties. This double-blind study was designed to investigate whether allopurinol (1 g), given before cardiopulmonary bypass and prior to the opening of cross-clamping, has an antioxidant effect in CABG patients by measuring plasma total peroxyl radical scavenging capacity. Design: Twenty-seven patients with stabile angina were randomized into allopurinol (n = 14) or placebo (n = 13) groups. Results: During 10 min reperfusion, plasma hypoxanthine and xanthine concentrations increased only in the allopurinol group, whereas uric acid concentrations decreased. Total peroxyl radical scavenging capacity (TRAP) decreased from the initial value at all measuring points in both groups. Conclusions: The reducing effect of allopurinol on free radical generation cannot be seen in TRAP values, obviously because the uric acid concentration of plasma decreases markedly. The positive clinical effects of allopurinol in CABG patients may arise from its direct oxygen free radical scavenging function.

Antioxidant activity of AO-8, a herbal formulation in vitro and in vivo experimental models.

The effect of AO-8, a herbal formulation was evaluated for free radical scavenging activity using in vitro and in vivo experimental models. AO-8 dose dependently inhibited ferric ion induced lipid peroxidation in vitro at 125-1000 micrograms. AO-8 was investigated at dose levels of 250, 500 and 750 mg/kg p.o. in isoproterenol-induced myocardial infarction and CCl4-induced hepatotoxicity in rats. The levels of serum GOT and LDH, cardiac glutathione, SOD and catalase were estimated following induction of myocardial infarction with isoproterenol. The estimation of parameters such as SGOT, SGPT, liver glycogen and lipid peroxidation were carried out in CCl4-induced hepatotoxicity. Treatment with AO-8 for 15 days at a dose of 500 and 750 mg/kg offered marked protection in both in vivo models. The reversal of increased serum enzymes in both the models may be due to the prevention of leakage of the intracellular enzymes by its membrane stabilizing activity. The inhibition of lipid peroxidation and enhancement of antioxidant enzymes by AO-8 may be due to the direct free radical scavenging activity which could be attributed to the antioxidant potential of various ingredients present in the formulation. Thus it can be concluded that AO-8 is an effective free radical scavenger and could prove beneficial in the treatment of various disorders associated with the involvement of free radicals.

Mechanism-based cancer prevention approaches: targets, examples, and the use of transgenic mice.

Humans are exposed to a wide variety of carcinogenic insults, including endogenous and man-made chemicals, radiation, physical agents, and viruses. The ultimate goal of carcinogenesis research is to elucidate the processes involved in the induction of human cancer so that interventions may be developed to prevent the disease, either in the general population or in susceptible subpopulations. Progress to date in the carcinogenesis field, particularly regarding the mechanisms of chemically induced cancer, has revealed several points along the carcinogenesis pathway that may be amenable to mechanism-based prevention strategies. The purpose of this review is to examine the basic mechanisms and stages of chemical carcinogenesis, with an emphasis on ways in which preventive interventions can modify those processes. Possible ways of interfering with tumor initiation events include the following: i) modifying carcinogen activation by inhibiting enzymes responsible for that activation or by direct scavenging of DNA-reactive electrophiles and free radicals; ii) enhancing carcinogen detoxification processes by altering the activity of the detoxifying enzymes; and iii) modulating certain DNA repair processes. Possible ways of blocking the processes involved in the promotion and progression stages of carcinogenesis include the following: i) scavenging of reactive oxygen species; ii) altering the expression of genes involved in cell signaling, particularly those regulating cell proliferation, apoptosis, and differentiation; and iii) decreasing inflammation. In addition, the utility for mechanism-based cancer prevention research of new animal models that are based on the overexpression or inactivation of specific cancer-related genes is examined.

Reactive oxygen intermediates, molecular damage, and aging. Relation to melatonin.

Melatonin, the chief secretory product of the pineal gland, is a direct free radical scavenger and indirect antioxidant. In terms of its scavenging activity, melatonin has been shown to quench the hydroxyl radical, superoxide anion radical, singlet oxygen, peroxyl radical, and the peroxynitrite anion. Additionally, melatonin's antioxidant actions probably derive from its stimulatory effect on superoxide dismutase, glutathione peroxidase, glutathione reductase, and glucose-6-phosphate dehydrogenase and its inhibitory action on nitric oxide synthase. Finally, melatonin acts to stabilize cell membranes, thereby making them more resistant to oxidative attack. Melatonin is devoid of prooxidant actions. In models of oxidative stress, melatonin has been shown to resist lipid peroxidation induced by paraquat, lipopolysaccharide, ischemia-reperfusion, L-cysteine, potassium cyanide, cadmium chloride, glutathione depletion, alloxan, and alcohol ingestion. Likewise, free radical damage to DNA induced by ionizing radiation, the chemical carcinogen safrole, lipopolysaccharide, and kainic acid are inhibited by melatonin. These findings illustrate that melatonin, due to its high lipid solubility and modest aqueous solubility, is able to protect macromolecules in all parts of the cell from oxidative damage. Melatonin also prevents the inhibitory action of ruthenium red at the level of the mitochondria, thereby promoting ATP production. In humans, the total antioxidative capacity of serum is related to melatonin levels. Thus, the reduction in melatonin with age may be a factor in increased oxidative damage in the elderly.

Effect of HD-03, a herbal formulation, on the antioxidant defence system in rats

The effect of HD-03, a herbal formulation was investigated on the hepatocellular antioxidant defence system in CCl4 treated rats. Three doses of CCl4 were administered orally with liquid paraffin (1:1) to induce hepatic damage. Twenty four hours after the last dose, blood was collected by decapitation for the estimation of serum ALT and AST. The levels of antioxidant enzymes, lipid peroxidation and glycogen in the liver were estimated. Nineteen days pretreatment with HD-03 (750 mg/kg) significantly reversed CCl4-induced changes in serum ALT and AST levels. HD-03 pretreatment also significantly reversed the CCl4-induced changes in the different components of the cellular antioxidant system and lipid peroxidation. Pretreatment with HD-03 significantly restored the hepatic glycogen levels which were depleted in CCl4 intoxicated rats. The observed reversal produced by HD-03 in the serum AST and ALT may be due to the membrane stabilizing potential which helps in preventing the leakage of intracellular enzymes into the systemic circulation. The increase in the hepatic glycogen levels in HD-03 pretreated rats, indicates its preventive effect on subcellular injury caused by CCl4, which leads to glycogenolysis, as a result of disturbance in the intracellular Ca+2 pool. The inhibition of lipid peroxidation and enhancement in the activity of antioxidant enzymes by HD-03 may be due to the direct free radical scavenging activity and reactivation of these enzymes in the liver. Thus the antioxidant potential and inhibitory effect on­lipid peroxidation may play an important role in the antihepatotoxic activity of HD-03. © 1998 John Wiley & Sons, Ltd.

Inconsistent suppression of nocturnal pineal melatonin synthesis and serum melatonin levels in rats exposed to pulsed DC magnetic fields.

The purpose of these experiments was to determine whether the exposure of rats at night to pulsed DC magnetic fields (MF) would influence the nocturnal production and secretion of melatonin, as indicated by pineal N-acetyltransferase (NAT) activity (the rate limiting enzyme in melatonin production) and pineal and serum melatonin levels. By using a computer-driven exposure system, 15 experiments were conducted. MF exposure onset was always during the night, with the duration of exposure varying from 15 to 120 min. A variety of field strengths, ranging from 50 to 500 microT (0.5 to 5.0 G) were used with the bulk of the studies being conducted using a 100 microT (1.0 G) field. During the interval of DC MF exposure, the field was turned on and off at 1-s intervals with a rise/fall time constant of 5 ms. Because the studies were performed during the night, all procedures were carried out under weak red light (intensity of <5 microW/cm2). At the conclusion of each study, a blood sample and the pineal gland were collected for analysis of serum melatonin titers and pineal NAT and melatonin levels. The outcome of individual studies varied. Of the 23 cases in which pineal NAT activity, pineal melatonin, and serum melatonin levels were measured, the following results were obtained; in 5 cases (21.7%) pineal NAT activity was depressed, in 2 cases (8.7%) studies pineal melatonin levels were lowered, and in 10 cases (43.5%) serum melatonin concentrations were reduced. Never was there a measured rise in any of the end points that were considered in this study. The magnitudes of the reductions were not correlated with field strength (i.e., no dose-response relationships were apparent), and likewise the reductions could not be correlated with the season of the year (experiments conducted at 12-month intervals under identical exposure conditions yielded different results). Duration of exposure also seemed not to be a factor in the degree of melatonin suppression. The inconsistency of the results does not permit the conclusion that pineal melatonin production or release are routinely influenced by pulsed DC MF exposure. In the current series of studies, a suppression of serum melatonin sometimes occurred in the absence of any apparent change in the synthesis of this indoleamine within the pineal gland (no alteration in either pineal NAT activity or pineal melatonin levels). Because melatonin is a direct free radical scavenger, the drop in serum melatonin could theoretically be explained by an increased uptake of melatonin by tissues that were experiencing augmented levels of free radicals as a consequence of MF exposure. This hypothetical possibly requires additional experimental documentation.

Melatonin reduces the increase in 8-hydroxy-deoxyguanosine levels in the brain and liver of kainic acid-treated rats.

In the present study, the effect of melatonin on oxidative DNA damage induced by kainic acid (KA) treatment was investigated. 8-hydroxy-deoxyguanosine (8-OH-dG) is a main product of oxidatively damaged DNA and was used as the endpoint in these studies. The levels of 8-OH-dG were found to be elevated in the hippocampus and frontal cortex of rats treated with KA. These elevated levels were significantly reduced in animals that were co-treated with melatonin. Thus, there was no difference in 8-OH-dG levels in the brain of control rats compared to those treated with KA (10 mg/kg) plus melatonin (10 mg/kg). The levels of 8-OH-dG also increased in the liver of rats treated with KA. This rise in oxidatively damaged DNA was also prevented by melatonin administration. Melatonin's ability to reduce KA-induced increases in neural and hepatic 8-OH-dG levels presumably relates to its direct free radical scavenging ability and possibly to other antioxidative actions of melatonin.

Modulation of cellular reducing equivalent homeostasis by α-lipoic acid: Mechanisms and implications for diabetes and ischemic injury

The therapeutic potential of α-lipoic acid (thioctic acid) was evaluated with respect to its influence on cellular reducing equivalent homeostasis. The requirement of NADH and NADPH as cofactors in the cellular reduction of α-lipoic acid to dihydrolipoate has been reported in various cells and tissues. However, there is no direct evidence describing the influence of such reduction of α-lipoate on the levels of cellular reducing equivalents and homeostasis of the NAD(P)H NAD(P) ratio. Treatment of the human Wurzburg T-cell line with 0.5 mM α-lipoate for 24 hr resulted in a 30% decrease in cellular NADH levels. α-Lipoate treatment also decreased cellular NADPH, but this effect was relatively less and slower compared with that of NADH. A concentration-dependent increase in glucose uptake was observed in Wurzburg cells treated with α-lipoate. Parallel decreases (30%) in cellular NADH NAD + and in lactate/pyruvate ratios were observed in α-lipoate-treated cells. Such a decrease in the NADH NAD + ratio following treatment with α-lipoate may have direct implications in diabetes, ischemia-reperfusion injury, and other pathologies where reductive (high NADH NAD + ratio) and oxidant (excess reactive oxygen species) imbalances are considered as major factors contributing to metabolic disorders. Under conditions of reductive stress, α-lipoate decreases high NADH levels in the cell by utilizing it as a co-factor for its own reduction process, whereas in oxidative stress both α-lipoate and its reduced form, dihydrolipoate, may protect by direct scavenging of free radicals and recycling other antioxidants from their oxidized forms.

Cardioprotective and Anti-oxidant Effects of the Terpenoid Constituents ofGinkgo bilobaExtract (EGb 761)

Hemodynamic and electron spin resonance analyses were used to assess thein vivoandin vitrocardioprotective and antioxidant effects of therapeutically relevant doses ofGinkgo bilobaextract (EGb 761) and its terpenoid constituents (ginkgolides A and B, bilobalide) in the rat. Significant anti-ischemic effects, indicating improved myocardial functional recovery, were observed after repeated (15-day) oral treatments with both EGb 761 (60 mg/kg/day) and ginkgolide A (4 mg/kg/day), as compared to placebo.In vitropre- and post-ischemic perfusion of hearts in the presence of the ginkgolides A and B (both at 0.05μg/ml) or bilobalide (0.15μg/ml), but not EGb 761 (5μg/ml), significantly improved all hemodynamic parameters. Post-ischemic levels of the 5,5-dimethyl-1-pyrrolineN-oxide (DMPO)/hydroxyl radical spin-adduct (DMPO-OH) in coronary effluents were significantly decreased afterin vivooral treatments or afterin vitroperfusion with EGb 761 or the terpenes, the most effective compound being ginkgolide A. As the presence of the terpenes did not influence the formation of the superoxide/DMPO adduct or DMPO-OH in acellular tests with superoxide and hydroxyl radical generators, their cardioprotective effects appear to involve an inhibition of free radical formation rather than direct free radical scavenging.

Free radical reactions involving the angiotensin converting enzyme inhibitor captopril.

Using the pulse radiolysis technique, absolute rate constants have been obtained for the reaction of captopril with several free radicals. The results demonstrate that although captopril reacts rapidly with a number of free radicals, such as the hydroxyl radical (k = 5.1 × 10(9) dm(-3)mol(-1)s(-1)) and the thiocyanate radical anion (k = 1.3 × 10(7) dm(-3)mol(-1)s(-1)), it is not exceptional in this ability. Similarly, the reactions with carbon centred radicals although rapid are an order of magnitude slower than those observed with glutathione. Additional lipid peroxidation studies further demonstrate that captopril is a much less effective antioxidant than glutathione. The data go some way to supporting the view that any attenuation of reperfusion injury by captopril is not through a direct free radical scavenging mechanism but may be afforded by other, non-radical-mediated mechanisms.

Appraisal of potential therapeutic index of antioxidants on the basis of their in vitro effects on HIV replication in monocytes and interleukin 2-induced lymphocyte proliferation.

Antioxidant molecules have been suggested to be of therapeutic value in the treatment of HIV-infected patients. To evaluate this possibility, we examined in vitro the effects of two types of antioxidant molecules in terms of inhibition of HIV replication in monocytes, one of the main reservoirs of HIV, and also in terms of modulation of the immune competence as measured by PBMC proliferation. We tested the effects of BHA, a phenolic, lipid-soluble, chain-breaking antioxidant, and NAC, a known glutathione precursor with some direct free-radical scavenging properties as well, on the regulation of HIV-1 expression in latently infected U1 cells and in productively and chronically infected U937 cells. Both antioxidants inhibited TNF- or PMA-induced NF-kappa B activity in U1 cells, as well as the sustained NF-kappa B activity permanently induced by the virus itself in chronically HIV-infected U937 cells. This resulted in only a partial inhibition of TNF- or PMA-induced HIV replication in U1 cells, and no detectable effect on HIV replication in chronically infected U937 cells. This may be the first limitation to potential antiviral effects of antioxidant therapies. Another limitation is that antioxidant concentrations high enough to block NK-kappa B activation were shown to have a suppressive effect on immune functions in vitro, because NAC and BHA blocked IL-2-induced PBMC proliferation. These data warrant prudence in the design of antioxidant-based therapies aimed at suppressing HIV replication.

Attenuation of myocardial reperfusion injury by reducing intracellular calcium overloading with dihydropyridines

The effects of three different dihydropyridine (DHP) calcium channel antagonists, nisoldipine, nimodipine, and nifedipine, on myocardial ischemie and reperfusion injury were studied using isolated rat hearts subjected to ischemia and reperfusion. Hearts were perfused with Krebs-Henseleit bicarbonate buffer containing 0, 4,16, 64 and 100 nM concentrations of the above dihydropyridines for 15 min. Global ischemia was then induced by terminating the aortic flow for 30 min at 37°, followed by 30 min of reperfusion. Left ventricular (LV) functional (LV developed pressure, its first derivative and coronary flow) and biochemical parameters (creatine kinase release) were monitored prior to ischemia and during reperfusion. In separate group of hearts, intracellular free Ca 2+ ([Ca 2+] i) was monitored with an intracellular calcium analyzer using a fluorescent Ca 2+ indicator (Fura-2 AM). Tissue Ca 2+ was also measured by atomic absorption spectroscopy after perfusing the hearts with ion-free cold buffer to wash out extracellular Ca 2+ Significant recovery of the coronary flow was observed in all hearts treated with a high concentration (100 nM) of DHPs compared with the control group (P < 0.05), while a lower dose of nisoldipine (16 nM) and nifedipine (64 nM) also improved the coronary flow effectively. Reduction of myocardial creatine kinase release and improvement of the recovery of LV developed pressure, dp/dt max, were achieved by DHPs in a concentration-dependent manner. A higher concentration of DHPs also decreased the formation of myocardial thiobarbituric acid reactive substances, although these compounds did not possess direct free radical scavenging effects in vitro. Tissue Ca 2+ content was reduced significantly in treated groups. The rise of [Ca 2+] i during ischemia and reperfusion appeared to be attenuated by these DHPs. The concentration-response study of the three DHPs showed the effective concentrations for reducing [Ca 2+] i to be 16, 64 and 100 nM nisoldipine, nifedipine and nimodipine, respectively, in this experimental setting. The above results indicate that pretreatment with DHPs can attenuate the myocardial reperfusion injury by modulating Ca 2+ overloading and decreasing the susceptibility of the membrane to free radical attack.

Formation of Activated States of Indoleacetic Acid and Cytokinins: An Experimental Approach to a Hypothesis Concerning Signal Transduction

Heterocyclic compounds such as IAA or cytokinins are involved in plant regulation. Some of the effects of these hormones are related with H 2 O 2 or the promotion of the formation of free radicals. Cytokinins also play an active role in preventing aging and senescence in plant cells. They seem to act either by means of direct scavenging of free radicals or preventing their formation. Recently peroxides have been found to transduce messages, but both peroxides and free radicals have a short half-life which makes it difficult for them to act as a messengers between the primary production sites and the responding sites such as DNA. They may, however, secondarily oxidize key molecules such as ACC producing ethylene, which in turn can act as a secondary messenger. In this paper we show that IAA and cytokinins are able to form excited states either in the dark in the presence of pyridoxal phosphate, H 2 O 2 and linolenic acid or in the light in the presence of riboflavin. These systems are also able to promote ethylene formation from ACC. We also show that different substituents in the hormone molecules can significantly modify their reactivity, thus suggesting a possibility for hormone regulation.

Direct scavenging of free radicals by captopril, an angiotensin converting enzyme inhibitor: Randall Jones, M. Renuka Prasad, Richard M. Engelman and Dipak K. Das. Cardiovascular Division, Department of Surgery, University of Connecticut School of Medicine, Farmington, CT and Department of Surgery, Baystate Medical Center, Springfield, MA

Direct scavenging of free radicals by captopril, an angiotensin converting enzyme inhibitor: Randall Jones, M. Renuka Prasad, Richard M. Engelman and Dipak K. Das. Cardiovascular Division, Department of Surgery, University of Connecticut School of Medicine, Farmington, CT and Department of Surgery, Baystate Medical Center, Springfield, MA

Direct scavenging of free radicals by captopril, an angiotensin converting enzyme inhibitor

Captopril, an angiotensin converting enzyme (ACE) inhibitor, was hypothesized to be a potential scavenger of free radicals because of the presence of a thiol group. The scavenging action of captopril was examined against superoxide anion (O2-), hydroxyl radical (OH.), hypohalite radical (HOCL) either generated biochemically, or derived from activated polymorphonuclear leukocytes (PMN). Our results indicate that captopril is an extremely potent free radical scavenger, scavenging power being as effective as superoxide dismutase (SOD) against O2-, or dimethylthiourea against OH., but better than allopurinol against OCL. plus HOCL. Free radical scavenging action of captopril against PMN-derived free radical is equivalent to the combined effects of SOD, catalase and allopurinol.

Allopurinol does not enhance antioxidant properties of extracellular fluid.

Allopurinol has been shown to provide significant protection against ischemia/reperfusion-induced microvascular and parenchymal cell injury. It has been hypothesized that the protection seen with allopurinol after ischemia/reperfusion (I/R) is caused by inhibition of xanthine oxidase. However, recent reports suggest that the beneficial effects of allopurinol in I/R may be caused by direct free radical scavenging. The objective of this study was to determine whether the regimen of allopurinol administration used in most I/R studies leads to a significant modification of the free radical scavenging properties of extracellular fluid (ECF), i.e., plasma and lymph. Plasma and intestinal lymph samples obtained from both control and allopurinol-treated cats were used to assess the following: 1) allopurinol and oxypurinol concentrations, 2) xanthine oxidase inhibition, 3) myoglobin-catalyzed linolenic acid peroxidation, 4) hypochlorous acid scavenging, and 5) protein and nonprotein sulfhydryl content. ECF from allopurinol-treated animals contained approximately 10 microM each of allopurinol and oxypurinol. Ten percent ECF resulted in 80% inhibition of xanthine oxidase activity. Comparable volumes of control ECF did not inhibit xanthine oxidase. Furthermore, allopurinol treatment did not enhance the antioxidant properties of ECF. The results of this study do not support the contention that the beneficial effects of allopurinol in I/R injury are caused by the scavenging of oxidants produced in ECF by activated granulocytes.