The Distribution of Xanthine Oxidase I

The hypoxanthine-xanthine oxidase axis is not involved in the initial phase of clinical transplantation-related ischemia-reperfusion injury

The hypoxanthine-xanthine oxidase (XO) axis is considered to be a key driver of transplantation-related ischemia-reperfusion (I/R) injury. Whereas interference with this axis effectively quenches I/R injury in preclinical models, there is limited efficacy of XO inhibitors in clinical trials. In this context, we considered clinical evaluation of a role for the hypoxanthine-XO axis in human I/R to be relevant. Patients undergoing renal allograft transplantation were included (n = 40) and classified based on duration of ischemia (short, intermediate, and prolonged). Purine metabolites excreted by the reperfused kidney (arteriovenous differences) were analyzed by the ultra performance liquid chromatography-tandem mass spectrometer (UPLCMS/MS) method and tissue XO activity was assessed by in situ enzymography. We confirmed progressive hypoxanthine accumulation (P < 0.006) during ischemia, using kidney transplantation as a clinical model of I/R. Yet, arteriovenous concentration differences of uric acid and in situ enzymography of XO did not indicate significant XO activity in ischemic and reperfused kidney grafts. Furthermore, we tested a putative association between hypoxanthine accumulation and renal oxidative stress by assessing renal malondialdehyde and isoprostane levels and allantoin formation during the reperfusion period. Absent release of these markers is not consistent with an association between ischemic hypoxanthine accumulation and postreperfusion oxidative stress. On basis of these data for the human kidney we hypothesize that the role for the hypoxanthine-XO axis in clinical I/R injury is less than commonly thought, and as such the data provide an explanation for the apparent limited clinical efficacy of XO inhibitors.

Exploiting oxidative microenvironments in the body as triggers for drug delivery systems

SIGNIFICANCE

Reactive oxygen species and reactive nitrogen species (ROS/RNS) play an important role in cell signaling pathways. However, the increased production of these species may disrupt cellular homeostasis, giving rise to pathological conditions. Biomaterials that are responsive to ROS/RNS can be strategically used to specifically release therapeutics and diagnostic agents to regions undergoing oxidative stress.

RECENT ADVANCES

Many nanocarriers intended to exploit redox micro-environments as triggers for drug release, summarized and compared in this review, have recently been developed. We describe these carriers' chemical structures, strategies for payload protection and oxidation-selective release, and ROS/RNS sensitivity as tested in initial studies.

CRITICAL ISSUES

ROS/RNS are unstable, so reliable measures of their concentrations in various conditions are scarce. Combined with the dearth of materials shown to respond to physiologically relevant levels of ROS/RNS, evaluations of their true sensitivity are difficult.

FUTURE DIRECTIONS

Oxidation-responsive nanocarriers developed thus far show tremendous potential for applicability in vivo; however, the sensitivity of these chemistries needs to be fine tuned to enable responses to physiological levels of ROS and RNS.

New markers: urine xanthine oxidase and myeloperoxidase in the early detection of urinary tract infection

Objectives. The aim of this study was to evaluate if xanthine oxidase and myeloperoxidase levels quantitation method may alternate routine culture method, which takes more time in the diagnosis of urinary tract infections. Material and Methods. Five hundred and forty-nine outpatients who had admitted to Clinic Microbiology Laboratory were included in the study. The microorganisms were identified by using VITEK System. The urine specimens that were negative from the quantitative urine culture were used as controls. The activities of MPO and XO in spot urine were measured by spectrophotometric method. Results. Through the urine cultures, 167 bacteria were isolated from 163 urine specimens; 386 cultures yielded no bacterial growth. E. coli was the most frequent pathogen. In infection with E. coli both XO and MPO levels were increased the most. The sensitivity, specificity, positive predictive value, and negative predictive value for XO were 100%, 100%, 100%, and 100%, respectively. These values for MPO were 87%, 100%, 100%, and 94%, respectively. Conclusion. These data obtained suggest that urine XO and MPO levels may be new markers in the early detection of UTI.

The species distribution of xanthine oxidase

1. The distribution of xanthine oxidase in blood and tissues of various animals was studied by means of a radioactive assay capable of detecting 10(-7) unit of enzyme. The method was shown to be applicable to tissues with a high uricase content. 2. Of 16 mammalian species examined, six had low concentrations of xanthine oxidase in the serum. In six non-mammalian species, no activity was detected in the serum. 3. The enzyme was not found in the blood cells of any mammals, but was present in the nucleated red blood corpuscles of chicken, turtle and tortoise. 4. Studies of the tissue distribution in four species demonstrated high activities in the liver and intestinal mucosa and consistently low activities in skeletal muscle, heart and brain. 5. There is a rough correlation between the activity of enzyme in serum and its activity in lung tissue in 12 mammalian species. In the dog, left-atrial blood had higher concentrations of xanthine oxidase than right-atrial blood.

Antioxidant vitamins and enzymatic and synthetic oxygen-derived free radical scavengers in the prevention and treatment of cardiovascular disease

Oxygen-derived free radical formation can lead to cellular injury and death. Under normal situations, the human body has a free radical scavenger system (catalase, superoxide dismutase) that can detoxify free radicals. Antioxidant vitamins and enzymatic and synthetic oxygen-derived free radical scavengers have been used clinically to prevent the formation of oxidized LDL and to prevent reperfusion injury, which is often caused by free radicals. In this article, the pathogenesis of free radical production and cell injury are discussed, and therapeutic approaches for disease prevention are presented.

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.

Metabolism of 1-nitropyrene in mice: transport across the placenta and mammary tissues

The distribution and metabolism of the environmental pollutant 1-nitropyrene was studied in C57B1/6N mice following oral or intraperitoneal dosing. When administered by gavage, 1-nitropyrene and its metabolites demonstrated biphasic elimination kinetics from the blood, with half-lives of 0.3 and 1.8 days and a distribution volume of 74 ml. Intraperitoneal administration resulted in similar biphasic elimination, with half-lives of 0.5 and 3 days and a distribution volume of 98 ml. Treating pregnant C57B1/6N (C3H sire) mice by gavage resulted in similar absorption and elimination kinetics of 1-nitropyrene and metabolites, except that the distribution volume increased to 123 ml. 1-Nitropyrene and/or its metabolites (0.7% of the administered dose) crossed the placenta and accumulated in the fetuses and amniotic fluid, with both C-oxidized and nitroreduced metabolites being detected. Suckling neonates accumulated 1-nitropyrene and its metabolites when their dams were administered 1-nitropyrene by gavage. Each neonate received approximately 0.1% of the administered dose and demonstrated the presence of both C-oxidized and nitroreduced metabolites. These results demonstrate that this environmental pollutant is capable of crossing the placenta or mammary tissues to expose the offspring to a potentially genotoxic compound.

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.

Hepatocellular lipofuscin in pre-eclampsia

Thirty liver specimens from 30 pre-eclamptic women with and without liver dysfunction were examined for the amount of lipofuscin pigment deposited. The amount of hepatic lipofuscin correlated positively with plasma urate concentrations. This finding may indicate an involvement of oxygen-free radicals and xanthine oxidase in the pathophysiology of pre-eclampsia.

Mechanisms whereby exogenous adenine nucleotides improve rabbit renal proximal function during and after anoxia

When a suspension of rabbit proximal tubules is subjected to anoxia, ATP falls by 80-90% during 40 min of anoxia, and upon reoxygenation (reox) the cells only recover 25-50% of their initial ATP. Addition of Mg-ATP (magnesium chloride-treated ATP), Mg-ADP, or Mg-AMP (five aliquots of 200 nmol/ml added 10 min apart) during anoxia causes complete recovery of ATP levels, and respiratory and transport function after 40 min of reox. Similar additions of adenosine (ADO), or inosine (INO), or Mg-ATP only during reox are less effective. Lactate dehydrogenase (LDH) release after 40 min of anoxia is 30-40% under control conditions, only 10-15% when adenine nucleotides or ADO are added during anoxia, and 20% when INO is added, suggesting that these additions may stabilize the plasma membrane during anoxia and help preserve cellular integrity. During reox, recovery may depend on the entry of ATP precursors and, therefore, we explored the mechanism whereby exogenous ATP increases the intracellular ATP content. Additions of Mg-ATP, Mg-ADP, or Mg-AMP to continuously oxygenated tubules increase cellular ATP content three- to fourfold in 1 h. The added ATP and ADP are rapidly degraded to AMP, and more slowly to ADO, INO, and hypoxanthine. Furthermore, the ATP-induced increase in cellular ATP is abolished by the exogenous addition of adenosine deaminase, which converts extracellular ADO to INO. These results suggest that the increase in cellular ATP requires extracellular ADO. The ADO obtained from the breakdown of AMP may be preferentially transported into the renal cells to be resynthesized into cellular AMP and ATP.

Renal metabolism and acute renal failure

We briefly review what appear to be the most important elements responsible for renal cell injury during and after oxygen deprivation. Recent studies in numerous laboratories have vastly improved our understanding of the changes in cell function that occur during ischemia and yet, the underlying mechanisms by which tubule damage and cell death occur remain elusive. We attempt to separate the effects that occur during ischemia or anoxia from those occurring during reperfusion (reoxygenation). These are not always separable, especially because it appears that ischemia initiates a series of complex events that may only become manifested during reperfusion. Ischemia-induced renal dysfunctions are clearly multifactorial events that will require major efforts to unravel.

Interorgan metabolism of amino acids, glucose, lactate, glycerol and uric acid in the domestic fowl (Gallus domesticus)

Arterial--venous differences for metabolites across liver, kidney and hindquarters were measured in fed or starved, artificially ventilated chickens. The results indicate that the liver takes up amino acids under both conditions. Urate and glucose are released by the liver in both the fed and the starved state. Lactate and amino acids are extracted from blood by the kidneys, and this increases in the starved chicken. Urate is removed from the circulation by the kidney in the fed and starved state and excreted. In the fed bird there is no significant arteriovenous difference of glucose across the kidney, but in the starved state the kidney releases glucose into the circulation. The hindquarters take up glucose in the fed but not in the starved state. The branched-chain amino acids valine and leucine were taken up by the hindquarters in the fed, but not the starved, chicken. Glycerol is released by the hindquarter of fed and starved chickens. In the starved state, alanine and glutamine represent 57% of the amino acids released by the hindquarter. Lactate is released by the hindquarter of starved chickens and represents the major gluconeogenic carbon source released by the hindquarter and taken up by kidney and liver. Although the liver is the major gluconeogenic organ in the starved chicken, the kidney accounts for approx. 30% of the glucose produced.

Enhancement of recovery of myocardial function by oxygen free-radical scavengers after reversible regional ischemia

Reperfusion after reversible regional ischemia has been shown to result in delayed recovery of myocardial function, but the mechanism responsible for this phenomenon remains unknown. We explored the potential role of oxygen-free radicals as mediators of postischemic dysfunction in open-chest dogs undergoing a 15 min occlusion of the left anterior descending coronary artery (LAD) followed by 2 hr of reperfusion. Treated animals (n = 19) received an infusion of the oxygen free-radical scavengers superoxide dismutase (SOD; 15,000 U/kg) and catalase (CAT; 55,000 U/kg) for 1 hr starting 15 min before LAD occlusion, while control animals (n = 20) received an equal volume of saline. SOD and CAT produced no discernible effect on heart rate, aortic pressure, or left atrial pressure. Collateral flow to the ischemic zone (radioactive microspheres) was 0.07 +/- 0.01 ml/min/g in both groups. The size of the occluded bed as determined by postmortem perfusion was 26.1 +/- 1.2% of the left ventricle in the control group and 26.5 +/- 0.9% in the treated group. Systolic wall thickening (an index of regional function) was assessed with an epicardial pulsed-Doppler probe. The two groups exhibited comparable systolic thickening under baseline conditions and similar degrees of dyskinesia during ischemia. Nevertheless, recovery of function (expressed as percent of baseline) was considerably greater in the treated dogs, both at 1 hr (43.8 +/- 14.3 vs 12.8 +/- 11.6) and 2 hr of reperfusion (74.2 +/- 8.4 vs 31.6 +/- 9.8, p less than .005). This improved recovery of function obtained with SOD and CAT suggests that oxygen-free radicals play an important role in the genesis of myocardial dysfunction after a brief episode of regional ischemia.

Failure of the xanthine oxidase inhibitor allopurinol to limit infarct size after ischemia and reperfusion in dogs

During the acute phase of myocardial ischemia, adenine nucleotides are degraded to nucleosides and bases, especially inosine and hypoxanthine. Simultaneously, xanthine dehydrogenase is converted to xanthine oxidase, an enzyme that converts hypoxanthine to xanthine, and xanthine to uric acid, producing a superoxide anion for each molecule of hypoxanthine or xanthine oxidized. To determine if free radicals via this enzymatic source contribute to cell death in myocardial ischemia, we determined whether allopurinol, an inhibitor of xanthine oxidase, could limit infarct size in a reperfusion preparation of myocardial infarction. The circumflex coronary artery of each of 34 dogs was occluded for 40 min, followed by reperfusion for 4 days. Infarct size then was measured by histologic methods and was related to major baseline predictors of infarct size, including anatomic area at risk and collateral blood flow. Infarct size was larger (NS) in the allopurinol (n = 8) than in the control (n = 11) group, a trend that was related to slightly higher (NS) collateral blood flow in the control group. We conclude that allopurinol has no beneficial effect in this preparation of experimental myocardial infarction. The results oppose the hypothesis that free radicals, produced via the xanthine oxidase reaction, are an important contributing factor in myocardial ischemic cell death.

Azathioprine metabolism in kidney transplant recipients

Azathioprine metabolite concentrations were studied in 54 kidney transplant recipients. Thirty-seven of these patients were studied over a 6 month period to investigate the intrapatient variation in metabolite concentrations. All patients had stable functioning grafts and normal peripheral white blood cell counts. The metabolites measured were plasma 6-mercaptopurine and red blood cell 6-thioguanine nucleotide. There was no correlation between azathioprine dose and plasma 6-mercaptopurine concentration but there was a significant correlation between dose and red blood cell 6-thioguanine nucleotide concentration (rs = 0.41, P less than 0.005). The individual transplant recipient showed little variation in metabolite concentrations over several months. Using this group as a control we studied metabolite concentrations in patients with kidney transplants who developed leucopenia. Our preliminary findings indicate that elevated red cell 6-thioguanine nucleotide concentrations, above the control range, can be associated with bone marrow depression.

The predictive value of 5'-adenine nucleotide depletion and replenishment in ischaemic rabbit kidney tissue

Renal ischaemia produced by clamping of the blood vessels in situ for periods of 10 to 150 minutes resulted in a progressive depletion of the total content of adenylates in the kidney tissue (sigma ATP, ADP, AMP). Initial dephosphorylation of ATP and ADP, resulting in further catabolism of AMP to hypoxanthine and xanthine, accumulated in the ischaemic tissue. The postischaemic ability of the kidney tissue to functional regeneration was in correlation with the ischaemic adenylate loss (r = +0.94, P less than 0.001) as well as the accumulation of hypoxanthine and xanthine (r = -0.90, P less than 0.001). The initial adenylate resynthesis rate was constant during recovery (0.5--0.8 mumol/g . h-1), independent of the duration of the preceding ischaemia. Determination of the postischaemic adenylate regeneration thus gave no additional prediction of the reversibility of the ischaemic parenchymal damages.

Urid acid accumulated in isolated kidney grafts: an assessment of agonal ischaemia

Hypoxanthine-xanthine washed out from kidney tissue during preservation has previously been found to be a reliable measure of the in vitro assessment of the deleterious effect of ischaemia on the functional regenerative ability of the graft. We have now studied the question: can uric acid accumulation in the isolated kidney graft be employed as a retrospective measure of the agonal ischaemia? We have found that uric acid alone accumulates in renal tissue during the agonal phase, in an amount that remains unchanged during the subsequent in vitro ischaemia. The determination of hypoxanthine-xanthine and uric acid in kidney perfusate samples during preservation must thus be presumed to be an optimal clinical-chemical method of assessing the graft ischaemia.

Urine xanthine oxidase activity in urinary tract infection

Xanthine oxidase (XO) activity was found to be negligible in sterile human urines (less than 480 units, as presently defined, per litre). Significant XO activity was found in all urines containing more than 10(5) bacteria/ml, except for urines infected with Staphylococcus aureus, in which XO activity ranged from 347 to 714 units per litre. Plasma XO is not transferred to the urine, as demonstrated by the negligible XO activity found in sterile urines from patients with raised plasma XO activity. Determination of urinary XO activity is a suitable procedure for the detection of urinary tract infection.

Transport of bovine milk xanthine oxidase into mammary glands of the rat

This research investigated transport of bovine milk xanthine oxidase into mammary glands of the lactating rat. Transport capability suggested an exogenous, nonmammary, source for the enzyme. Five lactating rats were injected intracardially with 100 microgram of purified iodine-125 labeled xanthine oxidase and five were injected with 100 microgram of the enzyme unpurified. Four hours later the rodents were hand-milked, and radiation was confirmed in all samples by liquid scintillation counting. Counts were recorded per volume of milk and the percentage radiation was computed. Autoradiographs of the rats indicated radiation almost exclusively associated with the mammary glands. Greatest concentration of radioactivity was in the micellar casein fraction of milk, and a compound of high molecular weight, presumably [iodine-125]xanthine oxidase, was confirmed by gel filtration of the casein. Results suggest that the compound was transported into the mammary glands. The degree of transport was dependent upon the stage of lactation.

Elevation of serum xanthine oxidase activity following halothane anesthesia in man

Halothane, but not methoxyflurane, was found to cause specific hepatocellular damage, the hepatotoxicity being prompt but transient. The hepatotoxicity was demonstrated by the elevation in the serum activity of xanthine oxidase, a highly sensitive marker for acute liver damage.

Antigenicity of bovine milk xanthine oxidase in guinea pigs

Six female and four male albino guinea pigs were immunized with active purified xanthine oxidase of bovine milk mixed with equal volume of Freund's complete adjuvant. One male and one female were immunized with heat-inactivated xanthine oxidase mixed with equal volume of adjuvant. Two males and four females were controls and received a phosphate buffer mixed with equal volume of adjuvant. The mixtures were administered intradermally and subcutaneously at weekly intervals for 6 consecutive wk and blood samples collected weekly. The enzyme was antigenic by the coated tanned red blood cell method. After the third weekly immunization, precipitating antibodies were in the sera of animals that received the active enzyme. Hemagglutination titers increased during subsequent weeks and reached a maximum after the sixth weekly immunization. Antisera from animals immunized with heat-inactivated xanthine oxidase gave a positive response similar to that with animals immunized with the active enzyme. However, when the same antisera were tested with sheep red blood cells coated with heat-inactivated enzyme, no hemagglutination was observed. Ouchterlony double gel-diffusion tests showed that it may be possible to differentiate between antibodies elicited to active and heat-inactivated xanthine oxidase.

Elevation of serum xanthine oxidase following halothane anesthesia in the rat

Halothan anesthesia was found to be hapatotoxic in the rat, as demonstrated by a significant elevation of serum xanthine oxidase (SXO) level. SXO appeared to be more sensitive marker of liver damage than serum glutamic oxalacetic transaminase. SXO was found to be elevated also following exposure to relative hypoxia.

Serum xanthine oxidase in jaundice

Serum xanthine oxidase activity was measured by a radiochemical method in 137 consecutive patients with jaundice of varying etiology and in 40 non-jaundiced patients with liver or other disease. Serum xanthine oxidase was markedly increased, up to 50 times the upper normal limit (mean + 2 S.D.), in 32 out of 34 patients with infectious hepatitis. A slight elevation of serum xanthine oxidase, up to twice the upper normal limit, was found in 2 out of 49 patients with extrahepatic obstructive jaundice and in 4 out of 20 patients with chronic renal failure. In comparison to serum glutamic-oxaloacetic transaminase and lactate dehydrogenase serum xanthine oxidase appeared to be the more sensitive and specific indicator of acute hepatocellular damage.

Polarographic assay and intracellular distribution of superoxide dismutase in rat liver

1. A polarographic assay of superoxide (O2--) dismutase (EC 1.15.1.1) activity is described, in which the ability of the enzyme to inhibit O2---dependent sulphite oxidation, initiated by xanthine oxidase activity, is measured. The assay was used in a study of the intracellular distribution of superoxide dismutase in rat liver. Both cyanide-sensitive cupro-zinc dismutase (92% of the total activity) and cyanide-insensitive mangano-dismutase (8%) were measured. 2. Rat liver homogenates contained both particulate (16%y and soluble (84%) dismutase activity. The particulate activity contained both types of dismutase, whereas nearly all the soluble dismutase was a cupro-zinc enzymes. The distribution pattern of mangano-dismutase was similar to that of cytochrome oxidase and glutamate dehydrogenase, indicating that the enzyme was probably present exclusively in the mitochondria. 3. Superoxide dismutase activity in the heavy-mitochondrial (M) fraction was latent and was activated severalfold and largely solubilized by sonication. Treatment of the M fraction with digitonin or a hypo-osmotic suspending medium indicated that most of the cupro-zinc dismutase was located in the mitochondrial intermembrane space, whereas the mangano-enzyme was located in the inner-membrane and matrix space. 4. A small amount of dismutase activity appeared to be present in the nuclei and microsomal fraction, but little or no activity in the lysosomes or peroxisomes. 5. The results are discussed in relation to the intracellular location of known O2---generating enzymes, the possible role of superoxide dismutase activity in intracellular H2O2 formation, and to current views on the physiological function of the enzyme.

Breakdown of 5'-adenine nucleotides in ischaemic renal cortex estimated by oxypurine excretion during perfusion

The catabolism of 5'-adenine nucleotides in the cortex of the rabbit kidney was studied during normothermic and hypothermic ischaemia. Changes were found in the cortical content of ATP, ADP, AMP, and SAN (the sum of 5'-adenine nucleotides) during ischaemia; those changes were delayed by hypothermia. The loss of SAN was found to be significantly correlated to the duration of normothermic as well as hypothermic ischaemia. The oxypurines hypoxanthine and xanthine and the nucleoside inosine were shown to be the final products of the catabolism of 5'-adenine nucleotides. An accumulation of hypoxanthine-xanthine and inosine in the tissue and a corresponding excretion in the perfusion fluid occurred simultaneously with the catabolism of 5'-adenine nucleotides, in equivalent amounts. It is concluded that determination of the amount of oxypurines excreted during kidney preservation is an indirect measure of the loss of SAN in the tissue, and a reflection of the changes in the metabolic state.