Liver xanthine oxidase increase in mice in three patholgoical models. A possible defence mechanism

Oxidative Stress and Pathogenesis in Malaria

Malaria is a highly inflammatory and oxidative disease. The production of reactive oxygen species by host phagocytes is an essential component of the host response to Plasmodium infection. Moreover, host oxidative enzymes, such as xanthine oxidase, are upregulated in malaria patients. Although increased production of reactive oxygen species contributes to the clearance of the parasite, excessive amounts of these free radicals can mediate inflammation and cause extensive damage to host cells and tissues, probably contributing to severe pathologies. Plasmodium has a variety of antioxidant enzymes that allow it to survive amidst this oxidative onslaught. However, parasitic degradation of hemoglobin within the infected red blood cell generates free heme, which is released at the end of the replication cycle, further aggravating the oxidative burden on the host and possibly contributing to the severity of life-threatening malarial complications. Additionally, the highly inflammatory response to malaria contributes to exacerbate the oxidative response. In this review, we discuss host and parasite-derived sources of oxidative stress that may promote severe disease in P. falciparum infection. Therapeutics that restore and maintain oxidative balance in malaria patients may be useful in preventing lethal complications of this disease.

Malaria inflammation by xanthine oxidase-produced reactive oxygen species

Malaria is a highly inflammatory disease caused by Plasmodium infection of host erythrocytes. However, the parasite does not induce inflammatory cytokine responses in macrophages in vitro and the source of inflammation in patients remains unclear. Here, we identify oxidative stress, which is common in malaria, as an effective trigger of the inflammatory activation of macrophages. We observed that extracellular reactive oxygen species (ROS) produced by xanthine oxidase (XO), an enzyme upregulated during malaria, induce a strong inflammatory cytokine response in primary human monocyte-derived macrophages. In malaria patients, elevated plasma XO activity correlates with high levels of inflammatory cytokines and with the development of cerebral malaria. We found that incubation of macrophages with plasma from these patients can induce a XO-dependent inflammatory cytokine response, identifying a host factor as a trigger for inflammation in malaria. XO-produced ROS also increase the synthesis of pro-IL-1β, while the parasite activates caspase-1, providing the two necessary signals for the activation of the NLRP3 inflammasome. We propose that XO-produced ROS are a key factor for the trigger of inflammation during malaria.

Uric acid and xanthine oxidase in heart failure - Emerging data and therapeutic implications

The role of hyperuricaemia as cardiovascular risk factor has exhaustingly been debated for decades. While the association of elevated uric acid (UA) levels with increased mortality risk as convincingly been shown, the question whether UA is independently predictive of just a related effect within a more complex risk factor profile (including metabolic, inflammatory and haemodynamic risk factors) is still a matter of dispute. In heart failure the independent prognostic and functional impact of elevated UA has not only been shown but also the pathophysiologic mechanism(s) and the potential of targeted therapeutic interventions have been investigated in some detail. The emerging picture suggests the increased activity of the enzyme xanthine oxidase (XO) with corresponding increased production of free oxygen radical (ROS) as a main underlying principle with the resulting increase in UA levels being mostly a marker of this up-regulated pathway. While this concept will not diminish the value of UA as a prognostic marker, it provides the basis for a novel metabolic treatment option and the means to identify those patients most eligible for this tailored therapy. This review will summarize the recent evidence on XO as a novel and promising therapeutic target in heart failure.

Significance of hepatic xanthine oxidase and uric acid in aged and dietary restricted rats

Xanthine oxidase (XOD), one of the major intracellular sources of superoxide production, is well characterized as a causative factor in ischemia/reperfusion related damage. In the present study, we investigated age-effect on the status of XOD, an enzyme interconvertible with xanthine dehydrogenase (XDH) under oxidative stress. We also examined the modulation of the enzyme using the anti-oxidative action of dietary restriction (DR). We obtained evidence showing XOD activity to be significantly increased by DR, peaking at 24 months, although no progressive, age-related changes were noticed. On the other hand, while XDH activity decreased in ad libitum fed rats with age, DR maintained higher activity levels at 18 and 24 months of age. During aging, the conversion of XDH to XOD was slightly increased, as indicated by the XOD/XDH ratio. One novel finding of the present study is DR's ability to elevate the uric acid level, which likely augments the anti-oxidative defense system, thereby buffering against oxidatively stressed conditions during aging. Based on what is known about the antioxidative abilities of DR and uric acid, we propose that the high uric acid levels we observed in DR rats may well serve as part of a defense strategy to protect redox balance.

Xanthine oxidase and uric acid in cardiovascular disease: clinical impact and therapeutic options

The association between increased uric acid (UA) levels and cardiovascular disease (CVD) has been observed and studied for many decades. The value of UA as an independent factor within the metabolic risk profile for prediction of CVD in the normal population remains an issue of ongoing discussion. In turn, increasing evidence suggests that among patients with established CVD such as heart failure UA is an independent marker of disease state and prognosis. Increased UA levels may be an indicator of up-regulated activity of xanthine oxidase, a powerful oxygen radical-generating system in human physiology. Increased reactive oxygen species (ROS) accumulation contributes to endothelial dysfunction, metabolic and functional impairment, inflammatory activation, and other features of cardiovascular pathophysiology. Accordingly, inhibition of xanthine oxidase activity has been shown to improve a range of surrogate markers in patients with CVD, but this effect seems to be confined to hyperuricemic patients because disappointing results were reported in studies with normouricemic patients. In this review we summarize current evidence on hyperuricemia in CVD. The value of UA as a biomarker and as a potential therapeutic target for tailored metabolic treatment in CVD is discussed.

Levels and interactions of plasma xanthine oxidase, catalase and liver function parameters in Nigerian children with Plasmodium falciparum infection

Elevated plasma levels of xanthine oxidase and liver function parameters have been associated with inflammatory events in several human diseases. While xanthine oxidase provides in vitro protection against malaria, its pathophysiological functions in vivo and interactions with liver function parameters remain unclear. This study examined the interactions and plasma levels of xanthine oxidase (XO) and uric acid (UA), catalase (CAT) and liver function parameters GOT, GPT and bilirubin in asymptomatic (n=20), uncomplicated (n=32), and severe (n=18) falciparum malaria children aged 3-13 years. Compared to age-matched control (n=16), significant (p<0.05) elevation in xanthine oxidase by 100-550%, uric acid by 15.4-153.8%, GOT and GPT by 22.1-102.2%, and total bilirubin by 2.3-86% according to parasitaemia (geometric mean parasite density (GMPD)=850-87100 parasites/microL) was observed in the malarial children. Further comparison with control revealed higher CAT level (16.2+/-0.5 vs 14.6+/-0.4 U/L; p<0.05) lacking significant (p>0.05) correlation with XO, but lower CAT level (13.4-5.4 U/L) with improved correlations (r=-0.53 to -0.91; p<0.05) with XO among the asymptomatic and symptomatic malaria children studied. 75% of control, 45% of asymptomatic, 21.9% of uncomplicated, and none of severe malaria children had Hb level>11.0 g/dL. Multivariate analyses further revealed significant (p<0.05) correlations between liver function parameters and xanthine oxidase (r=0.57-0.64) only in the severe malaria group. We conclude that elevated levels of XO and liver enzymes are biochemical features of Plasmodium falciparum parasitaemia in Nigerian children, with both parameters interacting differently to modulate the catalase response in asymptomatic and symptomatic falciparum malaria.

Uric acid in chronic heart failure

The pathophysiologic understanding of chronic heart failure (CHF) has shifted from a mere hemodynamic disorder to a much more complex approach including changes and imbalances in neurohormonal, immune, and metabolic functions. Among metabolic abnormalities, hyperuricemia is a constant finding in CHF. The xanthine oxidase metabolic pathway increasingly is appreciated as an important contributor to both symptoms of CHF as well as progression of the disease. Recent data suggest hyperuricemia to be an independent marker of impaired prognosis in CHF. In this article, the significance of the xanthine oxidase metabolic pathway in CHF is discussed. Data on xanthine oxidase inhibition are reviewed, which suggest a beneficial effect of therapeutically targeting this enzymatic pathway.

Xanthine oxidase inhibition for chronic heart failure: is allopurinol the next therapeutic advance in heart failure?

A substantial body of evidence has accumulated to suggest a role for the xanthine oxidase metabolic pathway in the pathophysiology of chronic heart failure and other cardiovascular diseases.

Xanthine oxidoreductase is present in bile ducts of normal and cirrhotic liver

Xanthine oxidoreductase (XOR) is a widely distributed enzyme, involved in the metabolism of purines, which generates superoxide and is thought to be involved in free radical-generated tissue injury. It is present at high concentrations in the liver, from where it may be released during liver injury into the circulation, binding to vascular endothelium and causing vascular dysfunction. The cellular localization of the enzyme, essential to understanding its function, is, however, still debated. The present study has used a highly specific mouse monoclonal antibody to define the cellular distribution of XOR in normal and cirrhotic human liver. As shown previously, XOR is present in hepatocytes. However, the novel finding of this study is that XOR is present in bile duct epithelial cells, where it is concentrated toward the luminal surface. Moreover, in liver disease, proliferating bile ducts are also strongly positive for XOR. These findings suggest that the enzyme is secreted into bile, and this was confirmed by analysis of human and rat bile. Xanthine oxidase activity was 10 to 20-fold higher in liver tissue obtained from patients with liver disease, than in healthy liver. We conclude that XOR is expressed primarily in hepatocytes, but is also present in bile duct epithelial cells and is secreted into bile. Its role in bile is unknown but it may be involved in innate immunity of the bowel muscosa.

Endotoxin challenge increases xanthine oxidase activity in cattle: effect of growth hormone and vitamin E treatment

In addition to its basic role in the metabolism of purine nucleotides, xanthine oxidoreductase (XOR) is involved in the generation of oxygen-derived free radicals and production and metabolic fate of nitric oxide (NO). Growth hormone (GH) and Vitamin E (E) have been shown previously to modify immune response to infection. Our objective was to determine in heifers the effect of endotoxin challenge (LPS; 3.0 microg/kg BW, i.v. bolus, Escherichia coli 055:B5) on xanthine oxidase (XO) activity in plasma and liver and the modification of this response by daily treatment with recombinant GH (0.1 mg/kg BW, i.m., for 12 days) or GH+E (E: mixed tocopherol, 1000 IU/heifer, i.m., for 5 days). In experiment 1, 16 heifers ( 348.7 +/- 6.1 kg) were assigned to control (C, daily placebo injections), GH, or GH+E treatments and were challenged with two consecutive LPS injections (LPS1 and LPS2, 48 h apart). After LPS1, plasma XO activity increased 290% (P < 0.001) at 3 h, reached peak (430%) at 24 h and returned to basal level by 48 h after LPS2. XO responses (area under the time x activity curve, AUC) were greater after LPS1 than LPS2 (P< 0.001). Total plasma XO responses to LPS (AUC, LPS1+LPS2) were augmented 55% (P < 0.05) over C with GH treatment but diminished to C responses in GH+E. There was a linear relationship (r2 = 0.605, P < 0.001) between total response in plasma XO activity and plasma nitrate + nitrate concentration. In experiment 2, 24 heifers ( 346 +/- 6 kg) were assigned to C or GH treatments and liver biopsy samples were obtained at 0, 3, 6, and 24h after a single LPS challenge. Hepatic XO activities increased 63.3% (P < 0.05) 6 h after single LPS challenge and remained elevated at 24 h (100.1%, P < 0.01) but were not affected by GH treatment. Results indicate that LPS-induced increases in plasma XO activity could be amplified by previous GH treatment but attenuated by E administration. The data also suggest that E may be effective in controlling some mediators of immune response associated with increased production of NO via the effect on XO activity and its production of superoxide anion as well as uric acid.

Comparative histochemical and immunohistochemical study on xanthine oxidoreductase/xanthine oxidase in mammalian corneal epithelium

We have previously found that xanthine oxidase (one form of xanthine oxidoreductase that generates reactive oxygen species, such as superoxide radicals and hydrogen peroxide) is present in corneal epithelium of normal rabbit eye. It was suggested that the reactive oxygen species contribute to additional eye damage related to prolonged continuous contact lens wear and irradiation of the eye with UV-B light. To further explore the potential danger of xanthine oxidase as a source of reactive oxygen species, we have examined in the present paper whether xanthine oxidoreductase and xanthine oxidase are present in corneal epithelium of other mammalian species, employing immunohistochemical and enzyme histochemical methods. In corneal epithelium of normal eyes of ox, pig, guinea-pig, and rat xanthine oxidoreductase activity was detected by the tetrazolium salt reduction method and xanthine oxidase activity was localized by a method based on cerium ions capturing hydrogen peroxide. For the immunohistochemical demonstration of the enzymes, rabbit anti-bovine xanthine oxidase antibody, rabbit anti-human xanthine oxidase antibody and monoclonal mouse anti-human xanthine oxidase/xanthine dehydrogenase/aldehyde oxidase antibody were used. The immunohistochemical and enzyme histochemical results show that xanthine oxidoreductase and xanthine oxidase are present both as proteins and as active enzymes in the corneal epithelium of all animals studied. It is hypothesized that under various pathological states, xanthine oxidase-generated reactive oxygen species might contribute to eye damage.

Kalopanaxsaponin A from Kalopanax pictus, a potent antioxidant in the rheumatoidal rat treated with Freund's complete adjuvant reagent

The stem bark of Kalopanax pictus is an anti-rheumatoidal arthritis drug in Oriental medicine. In the rheumatoidal rat, induced by Freund's complete adjuvant (FCA) reagent, we investigated the effects of hederagenin monodesmosides of K. pictus on oxidative stress and hepatic drug-metabolizing enzymes. Kalopanaxsaponin-A (KPS-A) significantly decreased malondialdehyde formation and the activities of xanthine oxidase and aldehyde oxidase of hepatic non-microsomal systems in FCA reagent-treated rats. In addition, increased activity levels of superoxide dismutase, catalase and glutathione peroxidase were also observed. The effects of KPS-A were more potent than the effects of KPS-I. These results suggested that KPS-A, extracted from K. pictus, could reduce rheumatoidal syndromes through antioxidative mechanisms.

Marked elevation in cortical urate and xanthine oxidoreductase activity in experimental bacterial meningitis

Experimental bacterial meningitis due to Streptococcus pneumoniae in infant rats was associated with a time-dependent increase in CSF and cortical urate that was approximately 30-fold elevated at 22 h after infection compared to baseline. This increase was mirrored by a 20-fold rise in cortical xanthine oxidoreductase activity. The relative proportion of the oxidant-producing xanthine oxidase to total activity did not increase, however. Blood plasma levels of urate also increased during infection, but part of this was as a consequence of dehydration, as reflected by elevated ascorbate concentrations in the plasma. Administration of the radical scavenger alpha-phenyl-tert-butyl nitrone, previously shown to be neuroprotective in the present model, did not significantly affect either xanthine dehydrogenase or xanthine oxidase activity, and increased even further cortical accumulation of urate. Treatment with the xanthine oxidoreductase inhibitor allopurinol inhibited CSF urate levels earlier than those in blood plasma, supporting the notion that urate was produced within the brain. However, this treatment did not prevent the loss of ascorbate and reduced glutathione in the cortex and CSF. Together with data from the literature, the results strongly suggest that xanthine oxidase is not a major cause of oxidative stress in bacterial meningitis and that urate formation due to induction of xanthine oxidoreductase in the brain may in fact represent a protective response.

Effect of tumor necrosis factor on hepatic oxidative stress and antioxidant defense indices in normal and Plasmodium yeolii nigeriensis infected mice

BACKGROUND

Plasmodium yoelii nigeriensis (P. y. nigeriensis) produces lethal malaria infection in Swiss albino mice. Reactive oxygen species (ROS) such as superoxide anion, hydrogen peroxide along with endogenously produced tumor necrosis factor (TNF) have been implicated in the pathogenesis of malaria.

OBJECTIVE

Study the effect of TNF on hepatic oxidative stress and antioxidant defense indices in normal and P. y. nigeriensis infected mice.

METHODS

Mice were divided into four groups. Normal group, TNF treated group, P. y. nigeriensis infected group, and P. y. nigeriensis infected mice treated with TNF group (250 microg/kg body weight, i.p.).

RESULTS

TNF treatment of normal mice caused a highly significant decrease in hepatic superoxide dismutase (SOD) while changes in other oxidative stress and antioxidant defense indices were nonsignificant. On the other hand, TNF treatment of P. y. nigeriensis infected mice caused a highly significant increase in hepatic xanthine oxidase, lipid peroxidation and a significant decrease in hepatic SOD with respect to infected mice.

CONCLUSION

These results suggest that exogenous TNF acts synergistically with P. y. nigeriensis infection to generate oxidative stress in the host and also causes an impairment of antioxidant defense enzyme such as superoxide dismutase.

Studies on hepatic oxidative stress and antioxidant defence system during chloroquine/poly ICLC treatment of Plasmodium yoelii nigeriensis infected mice

Reactive oxygen species are important mediators of tissue injury during malaria infection. The status of hepatic oxidative stress and antioxidant defence indices were studied during Plasmodium yoelii nigeriensis (P. y. nigeriensis) infection and chloroquine/ polyinosinic-polycytidylic acid stabilized with polylysine and carboxymethylcellulose (poly ICLC) treatment of infected mice. P. y. nigeriensis infection resulted in a significant increase in oxidative stress indices viz., xanthine oxidase and rate of lipid peroxidation (LPO). This was accompanied by a highly significant increase in antioxidant defence indices viz., reduced glutathione (GSH) and glutathione reductase while superoxide dismutase (SOD) and catalase showed a highly significant decrease with respect to normal mice. Chloroquine treatment of infected mice caused a decrease in parasitaemia which was associated with restoration of indices altered during infection towards normalization. Poly ICLC treatment of infected mice caused no change in blood parasitaemia but resulted in a significant increase in GSH, glutathione reductase, SOD and catalase with respect to infected mice. Combination therapy of chloroquine and poly ICLC resulted in clearance of parasitaemia and restoration of all oxidative stress and antioxidant defence indices to normal levels.

Induction of nitric oxide synthesis and xanthine oxidase and their roles in the antimicrobial mechanism against Salmonella typhimurium infection in mice

The role of superoxide anion (O2-) and nitric oxide (NO) in the host defense mechanism against Salmonella typhimurium (LT-2) was examined by focusing on xanthine oxidase (XO) as an O2(-)-generating system and on inducible NO synthase (iNOS). When ICR mice were infected with a 0.1 50% lethal dose (2 x 10(5) CFU) of S. typhimurium, bacterial growth in the liver reached a peak value 3 days after infection (10(4.32) CFU/g of liver) and decreased thereafter. XO activity in the liver became maximum at 7 days after infection; the value was 34.6 +/- 1.4 mU/g of liver at 7 days (compared with 11.0 +/- 1.3 mU/g of liver before infection). The time profile of NO production in the liver as determined by electron spin resonance spectroscopy was consistent with that of XO activity. Histological examination of infected liver showed the formation of multiple microabscesses with granulomatous lesions consisting of polymorphonuclear cells and mononuclear cells, and iNOS-expressing cells were localized in the confined areas of the microabscesses. When XO inhibitors such as allopurinol and 4-amino-6-hydroxypyrazolo[3,4-d]pyrimidine (AHPP) were administered to the infected mice, the mortality of the mice was significantly increased (10 of 21 and 11 of 20 for the allopurinol- and AHPP-treated groups, respectively, versus 2 of 20 for control mice), and bacterial growth was significantly enhanced. A similar exacerbation of the infection was obtained with N(omega)-monomethyl-L-arginine (L-NMMA) treatment of the mice. Of considerable importance is that granuloma formation in the liver was poorly developed by treatment with either XO inhibitors or L-NMMA. These results suggest that XO and NO play an important role in the antimicrobial mechanism against S. typhimurium in mice.

Immunohistochemical localization of aldehyde and xanthine oxidase in rat tissues using polyclonal antibodies

Tissues from male Wistar rats, fixed with 4% paraformaldehyde and embedded in paraffin, were studied with immunoperoxidase techniques using polyclonal antibodies raised against aldehyde oxidase or xanthine oxidase purified from rat liver. Immunohistochemical studies demonstrated that aldehyde oxidase-bearing cells were strongly stained in renal tubules, esophageal, gastric, intestinal and bronchial epithelium as well as liver cytoplasm. Weak but positive immunoreactivity was observed on the pulmonary alveolar epithelial cells, gastric glands and intestinal goblet cells. In contrast, it was demonstrated that cells with xanthine oxidase were strongly stained in renal tubules, esophageal, gastric, and small and large intestinal and bronchial epithelia etc. Positive immunostaining was also found in adrenal gland, skeletal muscle, spleen and cerebral hippocampus. Immunoreactivity againt aldehyde oxidase was not found in adrenal gland, spleen, mesentery or aorta, while immunoreactivity against xanthine oxidase was not found in mesentery or aorta. Although the significance of this ubiquitous and similar localization of aldehyde and xanthine oxidase seems unclear at present, these results may provide a clue as to the full understanding of the pathophysiological role of these oxidases in tissues.

A re-evaluation of the tissue distribution and physiology of xanthine oxidoreductase

Xanthine oxidoreductase is an enzyme which has the unusual property that it can exist in a dehydrogenase form which uses NAD+ and an oxidase form which uses oxygen as electron acceptor. Both forms have a high affinity for hypoxanthine and xanthine as substrates. In addition, conversion of one form to the other may occur under different conditions. The exact function of the enzyme is still unknown but it seems to play a role in purine catabolism, detoxification of xenobiotics and antioxidant capacity by producing urate. The oxidase form produces reactive oxygen species and, therefore, the enzyme is thought to be involved in various pathological processes such as tissue injury due to ischaemia followed by reperfusion, but its role is still a matter of debate. The present review summarizes information that has become available about the enzyme. Interpretations of contradictory findings are presented in order to reduce confusion that still exists with respect to the role of this enzyme in physiology and pathology.

High levels of xanthine oxidoreductase in rat endothelial, epithelial and connective tissue cells

The localization of xanthine oxidoreductase activity was investigated in unfixed cryostat sections of various rat tissues by an enzyme histochemical method which specifically demonstrates both the dehydrogenase and oxidase forms of xanthine oxidoreductase. High activity was found in epithelial cells from skin, vagina, uterus, penis, liver, oral and nasal cavities, tongue, esophagus, fore-stomach and small intestine. In addition activity was demonstrated in sinusoidal cells of liver and adrenal cortex, endothelial cells in various organs and connective tissue fibroblasts. Xanthine oxidoreductase produces urate which is a scavenger of oxygen-derived radicals. Because the enzyme is found in epithelial and endothelial cells which are subject to relatively high oxidant stress, it is postulated that in these cells xanthine oxidoreductase is involved in the antioxidant enzyme defense system. In addition, a possible role for the enzyme in proliferation and differentiation processes is discussed.

Xanthine oxidase activity and immunologically detectable protein in the C57B1/6 mouse

1. Xanthine oxidase (XO) was purified from livers of C57B1/6 mice. Antibodies generated against the purified protein were used in an immunoassay to measure total XO protein. 2. Both the specific activity and amount of XO protein were greater in the proximal small intestine than in the liver. A pool of inactive enzyme was present in the small intestine which developed after weaning. 3. Male C57B1/6 mice had the same XO specific activity as females and neither the hepatic nor the intestinal XO activity were affected by the level of dietary protein. 4. When mice were fed diets with tungsten, XO activity was lost and the amount of XO protein in the small intestine was decreased.

Elevation of molybdenum hydroxylase levels in rabbit liver after ingestion of phthalazine or its hydroxylated metabolite

Oral administration of phthalazine (50 mg/kg/day) or 1-hydroxyphthalazine (10 mg/kg/day) to female rabbits caused an increase in the specific activity of the hepatic molybdenum hydroxylases aldehyde oxidase and xanthine oxidase, whereas no effect on microsomal cytochrome P-450 activity was observed. The rise in the specific activity of purified aldehyde oxidase fractions was accompanied by a similar increase in molybdenum content. A significant lowering of the Km value for phthalazine was demonstrated with enzyme from treated rabbits whereas Km values for structurally similar substrates such as isoquinoline were unchanged from control values. Iso-electric focusing of DEAE-cellulose fractions showed the presence of an additional band of activity indicating that genuine induction of aldehyde oxidase had occurred in rabbits treated with phthalazine or 1-hydroxyphthalazine.

Enhanced xanthine oxidase activity in mice treated with interferon and interferon inducers

Administration to mice of either interferon (IFN) or IFN inducers resulted in a marked increase of xanthine oxidase (XO) activity in different organs. Dose response studies revealed that serum XO was increased by administration of polyinosylic-polycyticylic acid (poly I-C) at doses as low as 0.1 mg/kg. In view of the well known ability of XO to generate superoxide radicals it is suggested that its induction might play a role in several biological effects of IFN.

Killing of Plasmodium yoelii by enzyme-induced products of the oxidative burst

The murine malaria parasite Plasmodium yoelii was killed in vitro when incubated with glucose and glucose oxidase, a system generating hydrogen peroxide, or with xanthine and xanthine oxidase, a system which produces the superoxide anion and subsequently other products of the oxidative burst. Catalase blocked the killing in both cases; superoxide dismutase and scavengers of hydroxyl radicals or singlet oxygen were ineffective in the xanthine oxidase system. Thus, hydrogen peroxide appears to be the main reactive oxygen species killing P. yoelii.

Superoxide dismutase activity, caeruloplasmin activity and lipoperoxide levels in tumour and host tissues of mice bearing the Lewis lung carcinoma

Superoxide dismutase (SOD) activity, plasma caeruloplasmin activity and the level of whole tissue and subcellular lipoperoxides have been determined in normal and neoplastic tissues from control and tumour-bearing mice, measurements being made nine, twelve and fifteen days after the inoculation of Lewis lung carcinoma cells. SOD activity of host liver and lung tissues did not vary significantly from those of the control animals. Blood SOD activity of the tumoured animals was markedly elevated on the ninth and twelfth days after inoculation, decreasing to control levels on the fifteenth day. Tumor SOD diminished from activity on the ninth day which was greater than that for control lung to a level significantly lower than that for control lung on the twelfth and fifteenth days after inoculation. The presence of a tumor did not appear to affect plasma caeruloplasmin oxidase levels. The lipoperoxide level of hepatic tissue rose significantly as the tumour progressed. In the lung tissue the lipoperoxides decreased from a level four times higher on the ninth day to one not significantly different from that of the controls. Tumour lipoperoxides were about twice the level of hepatic tissue and of the order of ten-fold greater than those of lung. The level of lipoperoxide in the plasma of tumoured mice did not differ markedly from that of control mice. Assays of lipoperoxide in subcellular fractions of liver, lung and tumour tissue revealed that the elevated lipoperoxide was principally synthesized in the endoplasmic reticulum.