Lipid Peroxidation In Homogenates Research Articles

Electrochemical transformations and photophysical, anti/prooxidant properties of triphenylantimony(V) complexes with tridentate redox-active Schiff bases

A number of novel triphenylantimony(V) complexes with O,N,O'- or O,N,S redox-active Schiff bases (Ph3Sb(Ln) were synthesized. Compounds 1–5 were characterized by 1H, 13C NMR, IR spectroscopy, and elemental analysis. The molecular structures of complexes 1 and 2 in crystal state were established by means of single-crystal X-ray analysis. Both complexes are mononuclear hexacoordinated triphenylantimony(V) compounds containing dianionic forms of O,N,O’-coordinated ligands. The electrochemical properties of complexes 1–5 were studied. In the cathode region, stable monoanionic forms were formed for all compounds, while the electrooxidation process is irreversible for most complexes. A quasi-reversible one-electron anode stage was observed only for complex 2 with donor tert‑butyl groups. Based on electrochemical data, the energy gap ΔEel between the boundary redox orbitals of complexes varies from 2.64 to 2.95 eV, while the optical ΔE has lower values (2.75 – 2.80 eV). Triphenylantimony(V) complexes possess luminescence in solutions. The maximum luminescence intensity and quantum yields change depending on the nature of the substituents in the coordinated Schiff bases. The radical scavenging activity of new complexes was estimated in the ABTS assay. It has been found that compounds 2 and 3 with tert‑butyl or chlorine substituents in ligand have IC50 values compared with Trolox. The anti/prooxidant effects of compounds 1–5 on the process of rat liver (Wistar) homogenate lipid peroxidation and the promoted oxidative damage of the DNA were determined.

The Synthesis and Biological Activity of Organotin Complexes with Thio-Schiff Bases Bearing Phenol Fragments.

A number of novel di- and triorganotin(IV) complexes 1-5 (Ph2SnL1, Ph2SnL2, Et2SnL2, Ph3SnL3, Ph3SnL4) with mono- or dianionic forms of thio-Schiff bases containing antioxidant sterically hindered phenol or catechol fragments were synthesized. Compounds 1-5 were characterized by 1H, 13C NMR, IR spectroscopy, and elemental analysis. The molecular structures of complexes 1 and 2 in the crystal state were established by single-crystal X-ray analysis. The antioxidant activity of new complexes as radical scavengers was estimated in DPPH and ABTS assays. It was found that compounds 4 and 5 with free phenol or catechol fragments are more active in these tests than complexes 1-3 with tridentate O,N,S-coordinated ligands. The effect of compounds 1-5 on the promoted oxidative damage of the DNA by 2,2'-azobis(2-amidinopropane) dihydrochloride and in the process of rat liver (Wistar) homogenate lipid peroxidation in vitro was determined. Complexes 4 and 5 were characterized by more pronounced antioxidant activity in the reaction of lipid peroxidation in vitro than compounds 1-3. The antiproliferative activity of compounds 1-5 was investigated against MCF-7, HTC-116, and A-549 cell lines by an MTT test. The values of IC50 are significantly affected by the presence of free antioxidant fragments and the coordination site for binding.

THE EFFECTS OF L-ORNITINE AND L-ARGININE ON THE PROCESSES OF LIPID PEROXIDATION IN THE FUNCTIONAL LAYERS OF KIDNEYS ON THE BACKGROUND OF ACUTE TOXIC HEPATITIS

The aim is to evaluate the effects of L-arginine and L-ornithine on the processes of lipid peroxidation in homogenates of renal cortex, renal medulla and renal papilla under conditions of acute toxic hepatitis. Materials and methods: The study was performed on 40 outbred white male rats with experimental hepatitis, caused by carbon tetrachloride. The animals were divided into five groups: control group (the rats were simulated carbon tetrachloride poisoning and its correction by administering of olive oil and normal saline in equivalent doses), acute carbon tetrachloride hepatitis (single intraperitoneal injection of 50% carbon tetrachloride oil solution at the dose of 2 mlxkg-1 of body weight and simulation of treatment by administration of normal saline in equivalent doses), acute carbon tetrachloride hepatitis + L-ornithine (1000 mgxkg-1), acute carbon tetrachloride hepatitis + L-arginine (500 mgxkg-1) and acute carbon tetrachloride hepatitis + combination of substances. Results: On the background of acute carbon tetrachloride intoxication it was observed the development of renal failure in experimental animals, manifested by activation of lipid peroxidation processes in homogenates of renal cortex, renal medulla and renal papilla. The administration of L-ornithine and L-arginine demonstrates positive impact on renal function and hepato-renal syndrome by stabilization of cell membranes and regeneration of functional capacity of injured renal cells. Conclusions: The results of our study confirm both the presence of unidirectional effects and absence of toxic influences of L-ornithine and L-arginine on renal cells under the conditions of acute carbon tetrachloride intoxication, which are the most important requirements for modern drugs for the treatment of hepato-renal syndrome.

A new antioxidant flavone glycoside from Scutellaria baicalensis Georgi

A new flavone glycoside, wogonin 7-O-β-d-ethylglucuronide (1), together with a new natural flavone glycoside baicalein 7-O-β-d-ethylglucuronide (2) and four known analogues, wogonoside (3), wogonin (4), oroxylin A 7-O-β-d-methylglucuronide (5) and oroxylin A (6), was isolated from the roots of Scutellaria baicalensis Georgi. The structure elucidation of the new compound was primarily based on HR-ESI-MS, 1D and 2D NMR analyses. Compounds 1 and 3 inhibited FeSO4–Cys-induced liver homogenate lipid peroxidation with IC50 at 18.2 μM and 24.9 μM, respectively, and exhibited strong cytoprotective effects against H2O2-induced oxidative damage in human umbilical vein endothelial cells at low concentrations of 10.0 μM and 3.0 μM.

Antioxidant activity of catecholamines as a chane of them antistress effect

The antioxidant activity of some native catecholamines (adrenaline, noradrenaline, dopamine), water-soluble antioxidant emoxipine, agonist (apomorphine) and antagonist (haloperidol) of dopamine receptors was assessed as their influence on malonic dialdehyde content and products of lipid peroxidation in homogenates and suspension of the rat cortical brain cells. All catecholamines (adrenaline, noradrenaline, dopamine in concentrations of 10-4 M and 10-5 M) possessed a high (compartable with emoxipine) antioxidant activity. The most antioxidant effect was registered in apomorphine. The inhibitory action of apomorphine on lipid peroxidation in the brain cortex can be a result from both dopamine receptor activation and “direct” antioxidant mechanism.

Comparison of potential protective effects of melatonin and propylthiouracil against lipid peroxidation caused by nitrobenzene in the thyroid gland

Nitrobenzene is a carcinogen, which induces-among others-thyroid tumors. Melatonin is an effective antioxidant, whereas some antioxidative effects of propylthiouracil (PTU; an antithyroid medication used for the treatment of thyrotoxicosis) were also found. The aim of the study was to compare protective effects of melatonin and PTU against lipid peroxidation in homogenates of porcine thyroids, incubated in the presence of nitrobenzene. Homogenates of porcine thyroids were incubated for 30 min in the presence of nitrobenzene (0.001, 0.01, 0.1, 0.25, 0.5, 1.0, 2.5, 5.0, 7.5, and 10.0 mM). The level of lipid peroxidation products (malondialdehyde + 4-hydroxyalkenals) was measured spectrophotometrically. Nitrobenzene (7.5 and 10.0 mM) increased lipid peroxidation in the homogenates of porcine thyroids. Subsequently, homogenates of porcine thyroids were incubated for 30 min in the presence of nitrobenzene (7.5 mM) plus one of the antioxidants: melatonin (0.000001, 0.00001, 0.0001, 0.001, 0.01, 0.1, 0.25, 0.5, 1.0, 2.5, 5.0, and 7.5 mM) or PTU (0.01, 0.1, 0.25, 0.5, 1.0, 2.5, 5.0, and 7.5 mM). Lipid peroxidation caused by nitrobenzene was effectively prevented by melatonin, with the lowest effective concentration of 0.0001 mM, being only two orders of magnitude higher than physiological blood concentration in humans. At the same time, PTU revealed protective effects only in the highest used concentration (7.5 mM), which is practically never reached during pharmacological treatment in patients with thyrotoxicosis. Melatonin can serve as an effective agent in protection against nitrobenzene-induced lipid peroxidation in porcine thyroid.

Cytotoxic, cytoprotective and antioxidant effects of isolated phenolic compounds from fresh ginger

Twenty-nine phenolic compounds were isolated from the root bark of fresh (Yunnan) ginger and their structures fully characterized. Selected compounds were divided into structural categories and twelve compounds subjected to in-vitro assays including DPPH radical scavenging, xanthine-oxidase inhibition, monoamine oxidase inhibition, rat-brain homogenate lipid peroxidation, and rat pheochromocytoma PC12 cell and primary liver cell viability to determine their antioxidant and cytoprotective properties. Isolated compounds were also tested against nine human tumor cell lines to characterize anticancer potency. Several diarylheptanoids and epoxidic diarylheptanoids were effective DPPH radical scavengers and moderately effective at inhibiting xanthine oxidase. An enone–dione analog of 6-shogaol (compound 2) was isolated and identified to be most effective at protecting PC12 cells from H2O2-induced damage. Almost all tested compounds inhibited lipid peroxidation. Three compounds, 6-shogaol, 10-gingerol and an enone-diarylheptanoid analog of curcumin (compound 6) were identified to be cytotoxic in cell lines tested, with KB and HL60 cells most susceptible to 6-shogaol and the curcumin analog with IC50<10μM. QSAR analysis revealed cytotoxicity was related to compound lipophilicity and chemical reactivity. In conclusion, we observed distinct compounds in fresh ginger to have biological activities relevant in diseases associated with reactive oxygen species.

Preparation of C-23 esterified silybin derivatives and evaluation of their lipid peroxidation inhibitory and DNA protective properties

A diverse series of C-23 esterified silybin derivatives ( 1a– n) were designed and synthesized. The antioxidative properties of these compounds were evaluated by 1,1-diphenyl-2-picrylhydrazyl (DPPH) and superoxide anion radical scavenging, ferrous ion chelation, and inhibition of rat liver homogenate lipid peroxidation. Their protective effects on the prevention of hydrogen peroxide induced DNA damage were also investigated. Most of the synthesized compounds exhibited more effective antioxidant activities than silybin. The esterified silybin analogues displayed satisfactory performance especially on iron chelation and antiperoxidative activity. Compound 1n in particular exhibited remarkable antiperoxidative effect with an IC 50 value of 0.2 ± 0.1 μM, which was stronger than that of quercetin (IC 50 = 1.8 ± 0.6 μM). Compounds 1c, 1e, 1g, 1h and 1k displayed potent, dose-dependent protective properties against DNA cleavage. The results of the bioassays support the antioxidative and DNA protective effects of these synthesized silybin derivatives.

Preparation of silybin 23-esters and evaluation of their inhibitory ability against LPO and DNA protective properties

Twelve 23-esterified silybin derivatives with different patterns of substituents such as aromatic and aliphatic groups ( 1– 12) were designed and synthesized. The antioxidative properties of these compounds were evaluated. The modified silybin analogues exhibited improved inhibitory effects against rat liver homogenate lipid peroxidation compared to silybin, with exception of the trimethoxylated ester ( 5) and the aliphatic one ( 9). Compounds 3, 5, 7, 8 and 11 displayed their protective properties on DNA cleavage in a dose-dependent manner.

Preparation of two sets of 5,6,7-trioxygenated dihydroflavonol derivatives as free radical scavengers and neuronal cell protectors to oxidative damage

An unusual class of 5,6,7-trioxygenated dihydroflavonols ( 3a– e and 4a– j) were designed and prepared. Their antioxidative properties were assessed by examining their capacities in several in vitro models, including superoxide anion and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging, rat liver homogenate lipid peroxidation inhibition, PC12 cells protection from oxidative damage, and xanthine oxidase inhibition. These dihydroflavonols displayed positive quenching abilities towards O 2 - and DPPH free radicals, in which the majority exhibited superior antioxidant properties to Vitamin C. cis-Configurated compound (±)- 3e demonstrated remarkable inhibition to LPO with an IC 50 value of 1.9 ± 0.3 μM, which was apparently stronger than that of quercetin (IC 50 = 6.0 ± 0.4 μM). trans-Configurated dihydroflavonol (±)- 4h exhibited significant protective effect on PC12 cells against oxidative damage with an EC 50 value of 41.5 ± 5.3 μM, more effective compared to that of quercetin (EC 50 = 81.8 ± 8.7 μM). The 6-OH-5,7-dimethoxy analogue (±)- 3d showed significant inhibition of xanthine oxidase with an IC 50 value of 16.0 ± 0.8 μM, which is superior to that of allopurinol (IC 50 = 23.5 ± 2.0 μM). In addition to the hypothesized action mechanism of the bio-active compounds, 3D modeling was used to analyze the relationship between the minimized-energy structures and antioxidant activities.

Increased Lipid Peroxidation and Ascorbic Acid Utilization in Testis and Epididymis of Rats Chronically Exposed to Lead

The hypothesis has been recently presented that lead may exert its negative effect at least partially through the increase of reactive oxygen species (ROS) level in tissues. However, little is known about the influence of lead intoxication on equilibrium between generation and elimination of ROS in the male reproductive system. Sexually mature male Wistar rats were given ad libitum 1% of aqueous solution of lead acetate (PbAc) for 9 months. Significantly higher lead concentrations were found in blood [median 7.03 (Q25-Q75: 2.99-7.65) versus 0.18 (0.12-0.99) microg dl-1, P < 0.01], caput epididymis [median 5.51 (Q25-Q75: 4.31-7.83) versus 0.51 (0.11-0.80) microg g-1 d.m., P < 0.001], cauda epididymis [median 5.88 (Q25-Q75: 4.06-8.37) versus 0.61 (0.2 - 1.08) microg g-1 d.m., P < 0.001] and testis [median 1.81 (Q25-Q75: 0.94-2.31) versus 0.17 (0.03-0.3) microg g-1 d.m., P < 0.01] of lead-intoxicated rats when compared to the control. The concentration of ascorbyl radical, generated in vitro from L: -ascorbic acid (present in tissues in vivo) was measured by means of Electron Paramagnetic Resonance (EPR) spectroscopy. The EPR signal of ascorbyl radical in caput epididymis, cauda epididymis, testis and liver of lead acetate-treated animals revealed a significant decrease by 53%, 45%, 40% and 69% versus control tissues, respectively. Plasma L: -ascorbic acid content measured by high performance liquid chromatography (HPLC) method and total antioxidant status (TAS) measured by means of spectrophotometry were also significantly lower in the intoxicated versus control animals (28% and 21%, respectively). In the group exposed to lead the concentration of lipid peroxide in homogenates of the reproductive system organs was significantly elevated versus control group. It can be assumed that the lower EPR signal was caused by decreased tissue concentrations of L: -ascorbic acid. The latter may have resulted from consumption of ascorbic acid for scavenging of ROS excess in tissues of animals chronically exposed to lead.

Antioxidant properties of minocycline: neuroprotection in an oxidative stress assay and direct radical‐scavenging activity

Minocycline is neuroprotective in animal models of a number of acute CNS injuries and neurodegenerative diseases. While anti-inflammatory and anti-apoptotic effects of minocycline have been characterized, the molecular basis for the neuroprotective effects of minocycline remains unclear. We report here that minocycline and a number of antioxidant compounds protect mixed neuronal cultures in an oxidative stress assay. To evaluate the role of minocycline's direct antioxidant properties in neuroprotection, we determined potencies for minocycline, other tetracycline antibiotics, and reference antioxidant compounds using a panel of in vitro radical scavenging assays. Data from in vitro rat brain homogenate lipid peroxidation and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assays show that minocycline, in contrast to tetracycline, is an effective antioxidant with radical scavenging potency similar to vitamin E. Our findings suggest that the direct antioxidant activity of minocycline may contribute to its neuroprotective effects in some cell-based assays and animal models of neuronal injury.

Free radical processes in the liver of adult and old rats during stress.

We measured the content of free radical lipid peroxidation products, intensity of induced lipid peroxidation, and concentration of carbonylated proteins in the liver of adult (10-12 months) and old rats (22-25 months) subjected to 30-min immobilization. Changes in the intensity of induced lipid peroxidation in homogenates and accumulation of carbonylated proteins in subcellular liver fractions indicate that immobilization stimulates free radical generation in the liver of both adult and old rats. The intensity of this process in old rats surpassed that in adult animals.

Melatonin reduces Fenton reaction-induced lipid peroxidation in porcine thyroid tissue.

Free radicals and reactive oxygen species (ROS) participate in physiological and pathological processes in the thyroid gland. Bivalent iron cation (ferrous, Fe(2+)), which initiates the Fenton reaction (Fe(2+) + H2O2 --> Fe(3+) + *OH + OH(-)) is frequently used to experimentally induce oxidative damage, including that caused by lipid peroxidation. Lipid peroxidation is involved in DNA damage, thus indirectly participating in the early steps of carcinogenesis. In turn, melatonin is a well-known antioxidant and free radical scavenger. The aim of the study was to estimate the effect of melatonin on basal and iron-induced lipid peroxidation in homogenates of the porcine thyroid gland. In order to determine the effect of melatonin on the auto-oxidation of lipids, thyroid homogenates were incubated in the presence of that indoleamine in concentrations of 0.0, 0.00001, 0.0001, 0.001, 0.01, 0.1, 0.25, 0.5, 1.0, 2.5, or 5.0 mM. To study melatonin effects on iron-induced lipid peroxidation, the homogenates were incubated in the presence of FeSO(4) (40 microM) plus H2O2 (0.5 mM), and, additionally, in the presence of melatonin in the same concentrations as above. The degree of lipid peroxidation was expressed as the concentration of malondialdehyde + 4-hydroxyalkenals (MDA + 4-HDA) per mg protein. Melatonin, in a concentration-dependent manner, decreased lipid peroxidation induced by Fenton reaction, without affecting the basal MDA + 4-HDA levels. In conclusion, melatonin protects against iron + H2O2-induced peroxidation of lipids in the porcine thyroid. Thus, the indoleamine would be expected to prevent pathological processes related to oxidative damage in the thyroid, cancer initiation included.

Relative efficacies of indole antioxidants in reducing autoxidation and iron-induced lipid peroxidation in hamster testes.

Increased iron stores are associated with free radical generation and carcinogenesis. Lipid peroxidation is involved in DNA damage, thus indirectly participating in the early steps of tumor initiation. Melatonin and structurally related indoles are effective in protecting against oxidative stress. The aim of the study was to compare the relative efficacies of melatonin, N-acetylserotonin (NAS), indole-3-propionic acid (IPA), and 5-hydroxy-indole-3-acetic acid (5HIAA) in altering basal and iron-induced lipid peroxidation in homogenates of hamster testes. To determine the effect of the indoles on the autoxidation of lipids, homogenates were incubated in the presence of each agent in concentrations of 0.0, 0.01, 0.05, 0.1, 0.25, 0.5, 0.75, 1.0, 2.0, 2.5, or 5.0 mM. To study their effects on induced lipid peroxidation, homogenates were incubated with FeSO(4) (30 microM + H(2)O(2) (0.1 mM) + each of the indoles in the same concentrations as above. The degree of lipid peroxidation was expressed as concentrations of malondialdehyde + 4-hydroxyalkenals (MDA + 4-HDA) per mg protein. The indoles decreased both basal and iron-related lipid peroxidation in a concentration-dependent manner. Melatonin reduced basal MDA + 4-HDA levels when used at the concentrations of 0.25 mM or higher, and prevented iron-induced lipid peroxidation at concentrations of 1.0, 2.0, 2.5, or 5.0 mM. The lowest effective concentrations of NAS required to lower basal and iron-related lipid peroxidation were 0.05 mM and 0.25 mM, respectively. IPA, only when used in the highest concentrations of 2.5 mM or 5 mM inhibited basal lipid peroxidation levels and it was ineffective on the levels of MDA + 4-HDA due to iron damage. 5HIAA reduced basal lipid peroxidation when used at concentrations of 0.25 mM or higher, and it prevented iron-induced lipid peroxidation only at the highest applied concentration (5 mM). In conclusion, melatonin and related indoles at pharmacological concentrations protect against both the autoxidation of lipids as well as induced peroxidation of lipids in testes. In doing so, these agents would be expected to reduce testicular cancer that is initiated by products of lipid peroxidation.

Enhancement of Lipid Peroxidation by Chromium(IV) and Chromium(V) is Remarkable Compared to That by Chromium(VI) and is Effectively Suppressed by Scavengers of Reactive Oxygen Species

It is assumed that oxidative stress due to reactive oxygen species (ROS) such as superoxide anion (·O2 -), hydrogen peroxide (H2O2) and hydroxyl radical (·OH) may result in oxidative damage to lipids and DNA. On the other hand, chromium(VI) compounds, potent carcinogens, are known to induce lipid peroxidation. However, it is not clear how Cr(VI) induces lipid peroxidation and DNA damage. In this article, in order to clarify the mechanism by which Cr(VI) enhances lipid peroxidation, the lipid-peroxidizing activity of Cr(IV) and Cr(V), Cr intermediates possibly produced in the reductive metabolism of Cr(VI), were compared with that of Cr(VI) and Cr(III), and the inhibitory effects of ROS scavengers on lipid peroxidation induced by Cr(IV) and Cr(V) were examined by incubating mouse liver homogenate with Cr and scavenger compounds. Cr(IV), Cr(V) and Cr(VI) compounds effectively enhanced lipid peroxidation of homogenate in this order. The lipid-peroxidizing effect of Cr(IV) was suppressed more remarkably by superoxide dismutase, catalase and formate, specific scavengers of ·O2 -, H2O2 and ·OH, respectively, than that of Cr(V), which is indicative of the involvement of ·O2 -, H2O2 and ·OH in lipid peroxidation stimulated by these Cr species. These results suggest the possible participation of Cr(IV), Cr(V), ·O2 -, H2O2 and ·OH in Cr(VI)-enhanced lipid peroxidation.

SYNTHESIS AND ANTIOXIDATIVE ACTIVITY OF N-[(BENZOYLAMINO) THIOXOMETHYL]-GLYCINE COMPLEXES WITH RARE EARTH METALS

Nine new solid complexes of N-[(benzoylamino) thioxomethyl]-glycine with rare earth metals (M) have been synthesized. Elemental analysis, IR, molar conductance, TG-DTA and 1H NMR spectra have been used to characterize the complexes. The general formula of the complexes is ML3 1.5CH3OH(M = La, Ce, Nd, Sm, Gd, Dy, Er, Yb and Y). The antioxidative activity of La, Gd and Yb complexes was tested. The results obtained showed that the complexes possess scavenging effects on O2- radicals. It was also found that some complexes inhibit lipid peroxidation of homogenate of mouse liver.

Articular chondrocytes and synoviocytes in culture: influence of antioxidants on lipid peroxidation and proliferation

Chondrocytes and synoviocytes are the main cell types in articular joints. Articular cartilage is fed by synoviocytes via synovial fluid and has a low partial oxygen pressure. Thus, chondrocytes show oxygen radical protective mechanisms in vivo and are unprotected against these factors under common culture conditions. We investigated the influence of ascorbic acid, Fe2+, glutathione and alpha-tocopherol on lipid peroxidation and proliferation of rat articular chondrocytes and rabbit synoviocytes (HIG-82) in vitro. A combination of ascorbic acid and Fe2+ induced the production of thiobarbituric acid-reactive material as a marker of radical-mediated lipid peroxidation in homogenates and/or supernatants of cultured chondrocytes and synoviocytes. The amount of lipid peroxidation of chondrocytes was about 3-fold higher than that of synoviocytes. Ascorbic acid or Fe2+ alone had no significant influence on the production of thiobarbituric acid-reactive material. Lipid peroxidation could be abolished by addition of the radical scavenger alpha-tocopherol, whereas glutathione had no effect. 25-50 microM alpha-tocopherol decreased the ascorbic acid-(100 micrograms/ml) and Fe(2+)-(3 microM) induced lipid peroxidation to a basal level. Moreover, ascorbic acid inhibited the proliferation of rat chondrocytes and rabbit synoviocytes measured by [3H]-thymidine incorporation. Alpha-tocopherol and glutathione had no influence on the proliferation of chondrocytes but alpha-tocopherol decreased the growth of synoviocytes and increased the anti-proliferative effect of ascorbic acid on these cells. The importance of these findings for the use of ascorbic acid, glutathione and alpha-tocopherol in chondrocyte and synoviocyte cultures, or the influence of these molecules on the etiology and treatment of articular diseases will be discussed.

The effect of quinolinate on rat brain lipid peroxidation is dependent on iron

Quinolinate, an endogenous excitotoxic metabolite of tryptophan with affinity to the N-methyl- d-aspartate type of glutamate receptor, is known as a stimulator of lipid peroxidation in vitro [Neurochem. Res. (1991) 16, 1139–1143]. To analyse the mechanism of this quinolinate toxicity we used the thiobarbituric acid test to measure malondialdehyde in homogenates of rat cerebral hemispheres incubated in air at 37°C for 30 min in the presence of 0.015–15.0 mM quinolinate, endogenous iron or 0.5–2.0 μM FeSO 4 and with or without 250 μM ascorbate. Quinolinate in the concentrations of 0.15–2.5 mM stimulated lipid peroxidation in the homogenates in the presence of 0.5–2.0 μM Fe 2+. However, quinolinate concentrations higher than 3.0 mM inhibited the lipid peroxidation at all the tested concentrations of iron. In the presence of a potent iron chelator (10 μM deferoxamine) quinolinate completely failed to induce lipid peroxidation in rat brain homogenates. Spectral analysis revealed that quinolinate is able to form a complex with Fe 2+. The results suggest that quinolinate does not have a direct peroxidative effect, but that it modulates lipid peroxidation via its interaction with iron.

SUPEROXIDE DISMUTASE ACTIVITY AND REDUCED GLUTATHIONE LEVELS IN Cu-OVERLOAD LIVER FROM SHEEP

To explain the cytotoxicity of excessive copper accumulation in the liver of sheep, we measured Cu-Zn superoxide dismutase (SOD) activity, reduced glutathione (GSH) levels and lipid peroxidation in homogenates and subcellular fractions of hepatocytes. Sheep were dosed orally with a 2 per cent solution of CuSO4 on 5 days of the week at the rate of 10 ml per kg body weight, to induce the Cu toxicity. Serum copper levels and acid phosphatase (AP) activity were determined at frequent intervals. At time of the first increase of serum AP activity, three treated sheep (group 2A) were euthanased, and at the first day of hemolysis the others treated sheep (group 2B) also were euthanased. We found high liver Cu content and evidence of lipid peroxidation. In whole homogenate, mitochondrial and microsomal fractions, the thiobarbituric acid reacting substances were increased. This was correlated with an increase in the SOD activity and with decrease of the GSH levels. It could be argued that high copper status might have increased the SOD activity and induced lowest levels of GSH. Additionally, lipid peroxidation was induced by Cu-overload.Copyright © 1996 Elsevier Science Inc.