Alteration of the pro-oxidant xanthine oxidase (XO) in the thalamus and occipital cortex of patients with schizophrenia.

OBJECTIVES: Mounting evidence shows that oxidative stress (OS) and the purine/adenosine system play a key role in the pathophysiology of schizophrenia. Lately, our group pointed out that not only antioxidants, but also the prooxidant system plays an important role in neuro-psychiatric disorders. Xanthine oxidase (XO) is an enzyme of special interest in this context, since it acts as a prooxidant, but its main product is a vastly important antioxidant, uric acid (UA). Furthermore, XO plays major part in the purine/adenosine metabolism, which has been hypothesised to play a role in schizophrenia as well. METHODS: We examined the activity of XO in the striato-cortico-limbic system of schizophrenic patients (SP) and controls using a commercially available activity assay. RESULTS: We found decreased activity of XO in the occipital cortex and thalamus of patients with psychosis. Furthermore, XO shows a significant positive correlation with chlorpromazine equivalents in the putamen and the temporal cortex. CONCLUSIONS: Nevertheless, our results might suggest a downregulation of cellular defence mechanisms in schizophrenia in several brain regions, which could account for neuronal alterations which have been described before. This demonstrates that more research is needed to fully understand the role of the complex enzyme XO in the pathophysiology of schizophrenia.

Characterization of the enzymatic activity for biphasic competition by guanoxabenz (1-(2,6-dichlorobenzylidene-amino)-3-hydroxyguanidine) at alpha2-adrenoceptors. I. Description of an enzymatic activity in spleen membranes.

The mechanism for formation of high-affinity binding of 1-(2,6-dichlorobenzylidene-amino)-3-hydroxyguanidine (guanoxabenz) to alpha2-adrenoceptors was studied in particulate fractions from the rat spleen. The proportion of apparent high versus low-affinity alpha2-adrenoceptor binding sites increased with increasing incubation time and was also augmented by Mg2+ ions. The formation of high-affinity guanoxabenz binding seemed to be inhibited by a series of N-hydroxyguanidine analogs to guanoxabenz, as well as by a series of metabolic inhibitors that included allopurinol, 1-chloro-2,4-dinitrobenzene, 5,5'-dithiobis-(2-nitrobenzoic acid), cibacron blue, phenyl-p-benzoquinone, didox, and trimidox. The formation of guanoxabenz high-affinity binding was also inhibited in a time- and concentration-dependent fashion by preincubating the membranes with the LW03 N-hydroxyguanidine analogue of guanoxabenz. Moreover, when the spleen membranes were extensively washed for 30 min with buffers at 25 degrees, the guanoxabenz high-affinity binding disappeared. However, when these washed membranes were supplemented with xanthine, the apparent affinity of guanoxabenz increased four to five-fold. Taken together, all data were compatible with the theory that the formation of high-affinity binding was dependent on the generation of a guanoxabenz metabolite that showed an approximate 100-fold greater affinity for the alpha2-adrenoceptors than guanoxabenz itself. Because the most potent blocker of the formation of high-affinity binding was allopurinol (apart from some N-hydroxyguanidine analogs to guanoxabenz) and since the activity could be restored with xanthine, a likely candidate responsible for the metabolic activation is xanthine oxidase.

Dietary nicotinamide supplementation increases xanthine oxidoreductase activity in the kidney and heart but not liver of obese Zucker rats.

The conversion of xanthine dehydrogenase to xanthine oxidase that produces oxygen radicals has been implicated in the ischemic injury to the myocardium and to the kidney. Xanthine dehydrogenase uses NAD as the electron acceptor to catalyze a reaction which does not produce any oxygen free radicals and may depress the conversion of xanthine dehydrogenase to xanthine oxidase. Nicotinamide is the preferred precursor for NAD. This study was conducted to examine the effect of an 18% casein diet supplemented with 0.5% nicotinamide on the activity of oxidoreductase and its two enzyme forms, xanthine dehydrogenase and xanthine oxidase, in kidney, heart and liver of female obese Zucker rats that spontaneously develop glomerulosclerosis, cardiomegaly and fatty liver. Lean litter mates were used as controls. Nicotinamide supplementation had no effect on the activities of these enzyme forms in the liver of either obese rats or lean rats. Obese rats fed the nicotinamide supplemented diet had higher activities of these enzyme forms in kidneys and hearts than unsupplemented diet fed obese rats, but this difference was not observed in lean rats. In unsupplemented rats, xanthine oxidase activity in the kidney was greater in lean rats than obese rats. Thus, the abnormalities observed in obese rats are unlikely attributable to the xanthine oxidase-mediated oxidant stress.

The use of hyperbaric oxygen for preservation of free flaps.

The effects of hyperbaric oxygen (HBO) during tissue preservation on flap survival have been investigated in free flaps in rats. Groin skin flaps were harvested, stored in either room air or HBO (100% oxygen at 2.9 atm absolute) at 23 degrees C for 18 hours, and transplanted to the contralateral groin. Free flaps exhibit a high incidence of complete necrosis in the room air control. The survival of free flaps stored under HBO increased from 10% to 60% (p less than 0.05) after 18 hours of preservation. Skin flaps exhibited an increase in tissue hypoxanthine by 3.6-fold normal after 18 hours of storage in room air. HBO preservation prevented the accumulation of hypoxanthine and inhibited xanthine oxidase. Inhibition of the xanthine oxidase system may be one of the mechanisms of improved success of skin flap transplantation.

Activated neutrophils increase microvascular permeability in skeletal muscle: role of xanthine oxidase.

To determine the role of xanthine oxidase in the microvascular dysfunction produced by activated granulocytes, we examined the effect of xanthine oxidase depletion or inhibition on the increase in microvascular permeability produced by infusion of the neutrophil activator phorbol myristate acetate (PMA). Changes in vascular permeability were assessed by measurement of the solvent drag reflection coefficient for total plasma proteins (sigma) in rat hindquarters subjected to PMA infusion in xanthine oxidase-replete and -depleted animals, in animals pretreated with the xanthine oxidase inhibitor oxypurinol, and in animals depleted of circulating neutrophils by pretreatment with antineutrophil serum (ANS). Xanthine oxidase depletion was accomplished by administration of a tungsten-supplemented (0.7 g/kg diet) molybdenum-deficient diet. In animals fed the tungsten diet, muscle total xanthine dehydrogenase plus xanthine oxidase activity was decreased to less than 10% of control values. Estimates of sigma averaged 0.84 +/- 0.04 in control hindquarters, whereas PMA infusion was associated with a marked increase in microvascular permeability (decrease in sigma to 0.68 +/- 0.03). PMA infusion also caused an increase in the amount of the radical-producing oxidase form of xanthine oxidase (from 3.9 +/- 0.05 to 5.6 +/- 0.4 mU/g wet wt). ANS pretreatment attenuated this permeability increase (sigma = 0.77 +/- 0.04) and diminished the rise in xanthine oxidase activity (4.9 +/- 0.5 mU/g wet wt). Xanthine oxidase depletion with the tungsten diet or pretreatment with oxypurinol had no effect on this neutrophil-mediated microvascular injury (sigma = 0.69 +/- 0.06 and 0.67 +/- 0.03, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Role of xanthine oxidase and neutrophils in ischemia-reperfusion injury in rabbit lung.

This study evaluated the effect of ischemia-reperfusion (I-R) on pulmonary capillary permeability in isolated rabbit lungs and the roles of xanthine oxidase (XO), aldehyde oxidase (AO), and neutrophils (PMN) in producing this lung injury. Effects of XO and AO were studied by inactivation with a tungsten-enriched diet (0.7 g/kg) and inhibition of XO by allopurinol (100 microM) or AO by menadione (3.5 microM). PMN effects were studied by preventing endothelial adhesion with the monoclonal antibody IB4 (10 microM). Vascular permeability was evaluated by determining the capillary filtration coefficient (Kf,c) measured before and after I-R in all experimental conditions. Reperfusion after 2 h of ischemia significantly increased pulmonary capillary permeability (Kf,c changed from 0.096 +/- 0.014 to 0.213 +/- 0.025 ml.min-1. cmH2O-1.100 g-1), and this increase was blocked by the addition of catalase (50,000 U) at reperfusion (baseline Kf,c was 0.125 +/- 0.023 and 0.116 +/- 0.014 ml.min-1.cmH2O-1.100 g-1). XO inactivation with the tungsten-supplemented diet and XO inhibition with allopurinol prevented the Kf,c increase observed after I-R (0.183 +/- 0.030 to 0.185 +/- 0.033 and 0.126 +/- 0.018 to 0.103 +/- 0.005 ml.min-1.cmH2O-1.100 g-1). Inhibition of AO had no effect on I-R injury (Kf,c 0.108 +/- 0.011 to 0.167 +/- 0.014 ml.min-1.cmH2O-1.100 g-1). Preventing PMN adhesion resulted in significant attenuation of the change in Kf,c associated with I-R (0.112 +/- 0.032 to 0.090 +/- 0.065 ml.min-1.cmH2O-1.100 g-1). We conclude that XO and PMN adherence, but not AO, are involved in the increased capillary permeability associated with I-R.