Some neoplastic cell lines are readily killed when incubated in the presence of polyunsaturated fatty acids (PUFA). In an attempt to elucidate this phenomenon, we studied PUFA-driven superoxide (O2-) production by cultured NS-1 cells (murine lymphoid tumor cells). We find: (1) Even in the absence of added PUFA, NS-1 cells generate O2- (i.e., reduce nitroblue tetrazolium). (2) addition of PUFA increases O2- by greater than 50%. (3) Artificial loading of NS-1 cells with liposome encapsulated superoxide dismutase prevents the majority of spontaneous and PUFA-driven NBT reduction. We conclude that PUFA drives O2- generation by tumor cells, that this generation is largely intracellular, and that this phenomenon may help explain toxicity of PUFA for tumor cells.

Animals↗

PubMed1988

Oxidant defense enzymes of Plasmodium falciparum.

We have measured and characterized three oxidant defense enzymes in early and late intraerythrocytic stages of the human malarial parasite, Plasmodium falciparum. Isolated early intraerythrocytic stages contain catalase (24.1 mumol min-1 (mg protein)-1) and superoxide dismutase (SOD; 6.3 units (mg protein)-1) but little or no glutathione peroxidase (GPX; less than 2 mumol min-1 (mg protein)-1). Isolated late intraerythrocytic stages of P. falciparum contain slightly less catalase (17.0 mumol min-1 (mg protein)-1) but significantly more GPX (7.7 mumol min-1 (mg protein)-1) and SOD (25.1 units (mg protein)-1). P. falciparum, like P. berghei, probably acquires most of its SOD from its host, since parasite-associated SOD is predominantly cyanide-sensitive, and has the same pI as host SOD. Unlike P. berghei, however, late stages of P. falciparum contain an additional SOD isozyme which is not cyanide-sensitive and may represent an endogenous enzyme. Parasites grown in red cells that have been partially depleted of SOD are more sensitive to exogenously generated superoxide, suggesting some dependence of the parasite on host SOD.

Animals↗

PubMed1988

Oxidants, oxidant drugs, and malaria.

Explore the source record for details and available documents.

Animals↗

PubMed1988

Accelerated autoxidation and heme loss due to instability of sickle hemoglobin.

The pleiotropic effect of the sickle gene suggests that factors in addition to polymerization of the mutant gene product might be involved in sickle disease pathobiology. We have examined rates of heme transfer to hemopexin from hemoglobin in dilute aqueous solution (0.5 mg of Hb per ml) at 37 degrees C. HbO2 S loses heme 1.7 times faster than HbO2 A, with apparent rate constants of 0.024 hr-1 and 0.014 hr-1, respectively. In contrast, Hb A and Hb S behave identically in their MetHb forms (very rapid heme loss) and their HbCO forms (zero heme loss). This indicates that the faster heme loss from HbO2 S is due to accelerated autoxidation (HbO2----MetHb) rather than to some other type of instability inherent in the relationship of sickle heme to its pocket in globin. This interpretation is supported by spectrophotometric measurement of initial rates of MetHb formation during incubation at 37 degrees C. This directly shows 1.7 times faster autoxidation, with apparent rate constants of 0.050 hr-1 for HbO2 S and 0.029 hr-1 for HbO2 A. While the participation of this process in the cellular pathobiology of sickle erythrocytes remains unproven, the present data are consistent with, and perhaps help explain, two prior observations: the excessive spontaneous generation of superoxide by sickle erythrocytes; and the abnormal deposition of heme and heme proteins on membranes of sickle erythrocytes.

Anemia, Sickle Cell↗

PubMed1988

Hemoglobin-mediated oxidant damage to the central nervous system requires endogenous ascorbate.

Hemorrhage within the central nervous system (CNS) may be associated with subsequent development of seizure states or paralysis. Prior investigations indicate that hemoglobin, released from extravasated erythrocytes, may be toxic to the CNS by promoting peroxidation of lipids and inhibition of Na,K-ATPase. These deleterious effects are blocked both in vitro and in vivo by the Fe3+ chelator, desferrioxamine, indicating the involvement of free iron derived from hemoglobin. We now report that the Fe2+ chelator, ferene, also inhibits methemoglobin- and ferric iron-mediated CNS lipid oxidation, reflecting the reduction of Fe3+ by some component of the CNS. This reduction is apparent in the accumulation of the highly chromophoric ferene: Fe2+ chelate after the addition of Fe3+ salts to supernatants of murine brain homogenates. Because large amounts of ascorbic acid occur in mammalian CNS, we suspected that this reducing substance might be responsible. Indeed, the peroxidative effects of hemoglobin and iron on murine brain are blocked by washing of CNS membranes or by preincubation of crude homogenates with ascorbate oxidase. Furthermore, the addition of ascorbate to washed CNS membranes fully restores hemoglobin/iron-driven peroxidation. We conclude that posthemorrhagic CNS dysfunction may stem from damaging redox reactions between hemoglobin iron, ascorbic acid, and oxidizable components of the nervous system.

Animals↗

PubMed1988

Antimalarial properties of orally active iron chelators.

The appearance of widespread multiple drug resistance in human malaria has intensified the search for new antimalarial compounds. Metal chelators, especially those with high affinity for iron, represent one presently unexploited class of antimalarials. Unfortunately the use of previously identified chelators as antimalarials has been precluded by their toxicity and, in the case of desferrioxamine, the necessity for parenteral administration. The investigators now report that a new class of orally active iron chelators, namely the derivatives of alpha-ketohydroxypyridines (KHPs), are potent antimalarials against cultured Plasmodium falciparum. The KHPs evidently exert this effect by sequestering iron because a preformed chelator:iron complex has no antimalarial action. The pool(s) of iron being sequestered by the chelators have not been identified but may not include serum transferrin. Preincubation of human serum with KHPs followed by removal of the drug results in the removal of greater than 97% of total serum iron. Nonetheless, this serum effectively supports the growth of P falciparum cultures. Therefore the KHPs may exert antimalarial effect through chelation of erythrocytic rather than serum iron pool(s). The investigators conclude that these powerful, orally active iron chelators may form the basis of a new class of antimalarial drugs.

Administration, Oral↗

PubMed1987

Phytic acid. A natural antioxidant.

The catalysis by iron of radical formation and subsequent oxidative damage has been well documented. Although many iron-chelating agents potentiate reactive oxygen formation and lipid peroxidation, phytic acid (abundant in edible legumes, cereals, and seeds) forms an iron chelate which greatly accelerates Fe2+-mediated oxygen reduction yet blocks iron-driven hydroxyl radical generation and suppresses lipid peroxidation. Furthermore, high concentrations of phytic acid prevent browning and putrefaction of various fruits and vegetables by inhibiting polyphenol oxidase. These observations indicate an important antioxidant function for phytate in seeds during dormancy and suggest that phytate may be a substitute for presently employed preservatives, many of which pose potential health hazards.

Adenosine Diphosphate↗

PubMed1987

Superoxide dismutase-rich bacteria. Paradoxical increase in oxidant toxicity.

Superoxide dismutase is considered important in protection of aerobes against oxidant damage, and increased tolerance to oxidant stress is associated with induction of this enzyme. However, the importance of superoxide dismutase in this tolerance is not clear because conditions which promote the synthesis of superoxide dismutase likewise affect other antioxidant enzymes and substances. To clarify the role of superoxide dismutase per se in organismal defense against oxidant-generating drugs, we employed Escherichia coli transformed with multiple copies of the gene for bacterial iron superoxide dismutase. These bacteria have greater than ten times the superoxide dismutase activity of wild-type E. coli but, importantly, are normal in other oxidant defense parameters including catalase, peroxidases, glutathione, and glutathione reductase. High superoxide dismutase and control bacteria were exposed to the O2- -generating drug paraquat and to elevated pO2. We find; high superoxide dismutase E. coli are more readily killed by paraquat under aerobic, but not anaerobic, conditions. During exposure to paraquat, high superoxide dismutase E. coli accumulate more H2O2. Coincidentally, the reduced glutathione content of high superoxide dismutase E. coli declines more than in control E. coli. E. coli with high superoxide dismutase activity are also more readily killed by hyperoxia. Interestingly, the susceptibility of the parental and high superoxide dismutase E. coli to killing by exogenous H2O2 is not significantly different. Thus, under these experimental conditions, greatly enhanced superoxide dismutase activity accelerates H2O2 formation. The increased H2O2 probably accounts for the exaggerated sensitivity of high superoxide dismutase bacteria to oxidant-generating drugs. These results support the concept that the product of superoxide dismutase, H2O2, is at least as hazardous as the substrate, O2-. We conclude that effective organismal defense against reactive oxygen species may require balanced increments in antioxidant enzymes and cannot necessarily be improved by increases in the activity of single enzymes.

Aerobiosis↗

PubMed1987

Natural variation in passive sodium permeability in human erythrocytes.

The rate of influx of 22Na+ into human erythrocytes (RBC) varies greatly depending upon the donor. A high rate of influx may be related to a congenital predisposition to essential hypertension. In Northern Europeans, we find a threefold difference in the rate of 22Na+ influx between those with the least (LP) and most highly permeable (HP) RBC (from less than 0.15 to greater than 0.60 mmol Na+/liter RBC/hr). In order to further define determinants of these apparently hereditary differences in passive membrane Na+ transport, we identified two groups of normal laboratory and hospital personnel differing markedly (greater than twofold) in RBC 22Na+ influx rate. We find that the loop diuretics furosemide and bumetanide decrease by about 50% the influx of 22Na+ into HP RBC, but have a lesser influence on LP RBC. Impermeant polyanions such as citrate and pyrophosphate also specifically diminish 22Na+ influx into HP, but not LP, RBC. Therefore, the exaggerated 22Na+ influx into HP RBC probably occurs through a discrete pathway (perhaps via "Na/K/Cl cotransport"), which appears to be almost absent in LP RBC. The differences between HP and LP RBC most likely do not involve polymorphisms of RBC anion transport per se. The rate of RBC anion (35SO4(2-)) transport is the same in HP and LP RBC and is equally inhibited by furosemide and (to a lesser extent) bumetanide. Furthermore, the potent inhibitor of RBC anion transport, DIDS (diisothiocyanostilbene disulfonate) does not affect RBC Na+ permeability in either group. Nonetheless, the preferential reduction of Na+ permeation of HP RBC by loop diuretics may be of help in experimentally distinguishing HP from LP phenotypes. This information may be crucial in unraveling the structural basis of intrinsic differences in cell membrane Na+ permeability and their possible relationship to essential hypertension.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗

PubMed1987

Hemoglobin potentiates central nervous system damage.

Iron and iron compounds--including mammalian hemoglobins--catalyze hydroxyl radical production and lipid peroxidation. To determine whether hemoglobin-mediated lipid peroxidation might be important in hemorrhagic injuries to the central nervous system (CNS), we studied the effects of purified hemoglobin on CNS homogenates and injected hemoglobin into the spinal cords of anesthetized cats. Hemoglobin markedly inhibits Na/K ATPase activity in CNS homogenates and spinal cords of living cats. Hemoglobin also catalyzes substantial peroxidation of CNS lipids. Importantly, the potent iron chelator, desferrioxamine, blocks these adverse effects of hemoglobin, both in vitro and in vivo. Because desferrioxamine is not known to interact with heme iron, these results indicate that free iron, derived from hemoglobin, is the proximate toxic species. Overall, our data suggest that hemoglobin, released from red cells after trauma, can promote tissue injury through iron-dependent mechanisms. Suppression of this damage by desferrioxamine suggests a rational therapeutic approach to management of trauma-induced CNS injury.

Animals↗

PubMed1986

Superoxide dismutase and catalase in the murine malaria, Plasmodium berghei: content and subcellular distribution.

Plasmodium berghei, a murine malaria, lacks endogenous superoxide dismutase (SOD). Instead it appears to take up and concentrate SOD from its host cell, the erythrocyte. We now demonstrate that the adopted host enzyme is localized in granules which are probably lysosomes. In addition, isolated P. berghei parasites contain only low levels of catalase, probably as a result of contamination of the preparation with host cell material. Thus, the cytosol of this organism appears to be deficient in enzymes which protect against damage by activated oxygen.

Animals↗

PubMed1986

Reduced plasma haptoglobin and urinary taurine in familial seizures identified through the multisib strategy.

The multisib (MS) sampling strategy was used for detecting possible genetic influences on a complex and heterogeneous disorder. The MS strategy increases the likelihood of selecting pedigrees for single genetic factors and allows the efficient analysis of data. The collection of complete pedigrees will procure additional data, but at a large marginal expense. The MS ascertainment procedure was applied to seizure disorders by examination of taurine excretion levels and by conducting two-dimensional gel electrophoresis of plasma proteins. Reduced taurine excretion (proposed to be genetically controlled) was found to associate with seizures, particularly in those individuals with a generalized spike and wave (GSW) EEg, or in families with a GSW-seizure history. Examination of two-dimensional gels showed hypohaptoglobinemia in several seizure patients [Panter et al, 1984]. The frequency of hypohaptoglobinemia is greatly increased in familial seizure cases, and may also be genetically controlled. Thus the MS strategy has proven successful in identifying kindreds in which specific physiological alterations may contribute toward the complex phenotype of seizures.

Adult↗

PubMed1986

Erythrocyte catalase. A somatic oxidant defense?

Mammalian erythrocytes have large amounts of catalase, an enzyme which catabolizes hydrogen peroxide (H2O2). Because catalase has a low affinity for H2O2, others have suggested that glutathione peroxidase clears most H2O2 within the erythrocyte and that catalase is of little import. We hypothesized that erythrocyte catalase might function to protect heterologous somatic cells against challenge by high levels of exogenous H2O2 (e.g., in areas of inflammation). We find that, whereas nucleated cells (L1210 murine leukemia) are readily killed by an enzymatically generated flux of superoxide (and, therefore, H2O2), the addition of human and murine erythrocytes blocks lethal damage to the target cells. Inhibition of erythrocyte superoxide dismutase, depletion of glutathione, and lysis of the erythrocytes do not diminish this protection. However, inhibition of erythrocyte catalase abrogates the protective effect and the addition of purified catalase (but not superoxide dismutase) restores it. Furthermore, erythrocytes derived from congenitally hypocatalasemic mice (in which other antioxidant systems are intact) do not protect L1210 cells. Our results raise the possibility that the erythrocyte may serve as protection against by-products of its own cargo, oxygen.

Animals↗

PubMed1985

Dietary suppression of colonic cancer. Fiber or phytate?

The incidence of colonic cancer differs widely between various human populations. It has been suggested that dietary fiber content is of utmost importance and is inversely related to the occurrence of colonic cancer. However, high-fiber diets are not always correlated with low frequency of colonic cancer, suggesting the involvement of additional dietary constituents. Inositol hexaphosphate (phytic acid) is an abundant plant seed component present in many, but not all, fiber-rich diets. The authors have found that phytic acid is a potent inhibitor of iron-mediated generation of the hazardous oxidant, hydroxyl radical. Herein, the authors propose that inhibition of intracolonic hydroxyl radical generation, via the chelation of reactive iron by phytic acid, may help explain the suppression of colonic carcinogenesis and other inflammatory bowel diseases by diets rich in phytic acid.

Colonic Neoplasms↗