Inactivation Of Catalase Research Articles

Glutathione peroxidase-catalase cooperativity is required for resistance to hydrogen peroxide by mature rat oligodendrocytes.

Oxidative mechanisms of injury are important in many neurological disorders, including hypoxic-ischemic brain damage. Cerebral palsy after preterm birth is hypothesized to be caused by hypoxic-ischemic injury of developing oligodendrocytes (OLs). Here we examined the developmental sensitivity of OLs to exogenous hydrogen peroxide (H2O2) with stage-specific rat oligodendrocyte cultures. We found that H2O2 itself or that generated by glucose oxidase was more toxic to developing than to mature OLs. Mature OLs were able to degrade H2O2 faster than developing OLs, suggesting that higher antioxidant enzyme activity might be the basis for their resistance. Catalase expression and activity were relatively constant during oligodendrocyte maturation, whereas glutathione peroxidase (GPx) was upregulated with a twofold to threefold increase in its expression and activity. Thus, it appeared that the developmental change in resistance to H2O2 was caused by modulation of GPx but not by catalase expression. To test the relative roles of catalase and GPx in the setting of oxidative stress, we measured enzyme activity in cells exposed to H2O2 and found that H2O2 induced a decrease in catalase activity in developing but not in mature OLs. Inhibition of GPx by mercaptosuccinate led to an increase in the vulnerability of mature OLs to H2O2 as well as a reduction in catalase activity. Finally, H2O2-dependent inactivation of catalase in developing OLs was prevented by the GPx mimic ebselen. These data provide evidence for a key role for GPx-catalase cooperativity in the resistance of mature OLs to H2O2-induced cell death.

Decreased chaperone activity of alpha-crystallin in selenite cataract may result from selenite-induced aggregation.

To investigate the role of chaperone activity of alpha-crystallin in selenite-induced cataract formation. Selenite cataract was induced in Sprague-Dawley rats by five subcutaneous injections of sodium selenite over a 20-day period starting at 8-10 days postpartum. alpha-Crystallin was separated from the rat lenses by size-exclusion chromatography. Bovine alpha(L)-crystallin and beta(L)-crystallin were isolated for studies in vitro, and for the chaperone assays. The protective effects of both alpha(H)- and alpha(L)-crystallin were measured spectrophotometrically in four different assay procedures including the thermally induced aggregation of catalase and beta(L)-crystallin, and the fructation- and heat-induced inactivation of catalase. The bovine alpha(L)-crystallin was incubated with different concentrations of sodium selenite for 72 h and then its chaperone activity against heat-induced beta(L)-crystallin aggregation was assayed. The aggregation of selenite-treated alpha(L)-crystallin was analysed by molecular sieve high-performance liquid chromatography (HPLC). The protection of alpha(H)-crystallin was less than that of alpha(L)-crystallin in both normal and cataractous lenses. The chaperone activities of both alpha(H)- and alpha(L)-crystallin in selenite cataract were decreased compared with normal lenses. The protection provided by both alpha(H)-crystallin and alpha(L)-crystallin against the thermal aggregation of catalase was much greater than their protection against thermally and chemically induced inactivation. HPLC analysis demonstrated aggregation of alpha-crystallin by sodium selenite after 24 h incubation in a dose-dependent fashion. The chaperone activity of alpha-crystallin presented parallel patterns of activity with different methods, further supporting the view that the different assays measure essentially the same property. The decreased chaperone activity of alpha-crystallin in selenite cataract may result from selenite-induced aggregation.

Effects of salicylic acid on paraquat tolerance inArabidopsis thaliana plants

Foliar spraying ofArabidopsis thaliana (Columbia ecotype) plants with a 1.0-mM salicylic acid (SA) solution significantly improved their tolerance to subsequent paraquat (PQ)-induced oxidative damage. Leaf injuries, including losses of chlorophyll, protein, and fresh weight, were reduced. Our analysis of antioxidant enzymes in the leaves showed that SA pre-treatment effectively retarded rapid decreases in the activities of Superoxide dismutase (SOD), catalase, and ascorbate peroxidase that are normally associated with PQ exposure. In addition, guaiacol peroxidase activity was remarkably increased. In a native gel assay of peroxidase (POD) isozymes, staining activity of the POD1 isozyme, which disappeared in plants exposed only to 10 µM PQ, was significantly recovered by the 1.0-mM SA pre-treatment POD2 isozyme activity was also pronounced in all SA-treated plants compared with the control. A 12-h SA pre-treatment, without subsequent PQ stress, also caused a small increase in the endogenous H2O2 content that accompanies the symptoms of mild leaf injuries. This enhanced level occurred in parallel with a slight SOD increase and a catalase decrease. From our results, it can be assumed that, due to the small increase in SOD as well as catalase inactivation via SA pre-treatment, a moderate increase in H2O2 levels may occur. In turn, a large induction of guaiacol peroxidase leads to enhanced PQ tolerance inA. thaliana plants.

Autoxidation of extracellular hydroquinones is a causative event for the cytotoxicity of menadione and DMNQ in A549-S cells

Cytotoxicity of 1,4-naphthoquinones has been attributed to intracellular reactive oxygen species (ROS) generation through one-electron-reductase-mediated redox cycling and to arylation of cellular nucleophiles. Here, however, we report that in a subclone of lung epithelial A549 cells (A549-S previously called A549-G4S (Watanabe, et al., Am. J. Physiol. 283 (2002) L726–736), the mechanism of ROS generation by menadione and by 2,3-dimethoxy-1,4-naphthoquinone (DMNQ), and therefore that of cytotoxicity, differs from the paradigm. Ninety percent of H 2O 2 generation by both the quinones can be prevented by dicumarol, an inhibitor of NAD(P)H quinone oxidoreductase (NQO1), at the submicromolar level, regardless of the quinone concentrations. Exogenous SOD also inhibits H 2O 2 production at low but not high concentrations of the quinones, especially DMNQ. Thus, at low quinone concentrations, superoxide-driven hydroquinone autoxidation accounts for more than half of H 2O 2 generation by both quinones, whereas at high quinone concentrations, especially for DMNQ, comproportionation-driven hydroquinone autoxidation becomes the predominant mechanism. Hydroquinone autoxidation appears to occur predominantly in the extracellular environment than in the cytosol as extracellular catalase can dramatically attenuate quinone-induced cytotoxicity throughout the range of quinone concentrations, whereas complete inactivation of endogenous catalase or complete depletion of intracellular glutathione has only a marginal effect on their cytotoxicity. Finally, we show evidence that ROS production is a consequence of the compensatory defensive role of NQO1 against quinone arylation.

Kinetics of catalase inactivation induced by ultrasonic cavitation

Kinetic patterns of sonication-induced inactivation of bovine liver catalase (CAT) were studied in buffer solutions (pH 4-11) within the temperature range from 36 to 55 degrees C. Solutions of CAT were exposed to low-frequency (20.8 kHz) ultrasound (specific power, 48-62 W/cm2). The kinetics of CAT inactivation was characterized by effective first-order rate constants (s-1) of total inactivation (kin), thermal inactivation (*kin), and ultrasonic inactivation (kin(us)). In all cases, the following inequality was valid: kin > *kin. The value of kin(us) increased with the ultrasound power (range, 48-62 W/cm2) and exhibited a strong dependence on pH of the medium. On increasing the initial concentration of CAT (0.4-4.0 nM), kin(us) decreased. The three rate constants were minimum within the range of pH 6.5-8; their values increased considerably at pH < 6 and pH > 9. At 36-55 degrees C, temperature dependence of kin(us) was characterized by an activation energy (Eact) of 19.7 kcal/mol, whereas the value of Eact for CAT thermoinactivation was equal to 44.2 kcal/mol. Bovine serum and human serum albumins (BSA and HSA, respectively) inhibited sonication-induced CAT inactivation; complete prevention was observed at concentrations above 2.5 micrograms/ml. Dimethyl formamide (DMFA), a scavenger of hydroxyl radicals (HO.), prevented sonication-induced CAT inactivation at 10% (kin and *kin increased with the content of DMFA at concentrations in excess of 3%). The results obtained indicate that free radicals generated in the field of ultrasonic cavitation play a decisive role in the inactivation of CAT, which takes place when its solutions are exposed to low-frequency ultrasound. However, the efficiency of CAT inactivation by the radicals is determined by (1) the degree of association between the enzyme molecules in the reaction medium and (2) the composition thereof.

Inhibition of oxygen radical formation by methylene blue, aspirin, or alpha-lipoic acid, prevents bacterial-lipopolysaccharide-induced fever.

Phagocytic cells contain NADPH oxidase that they use for host defense by catalyzing the production of superoxide. Bacterial lipopolysaccharide (LPS) has been found to stimulate NADPH oxidase in mobile and sessile macrophages and microglia. It also evokes fever in homeothermic animals and men, a reaction mediated by central nervous system (CNS) activities. The purpose of the present study was to determine whether reactive oxygen species are involved in LPS-induced fever. In rabbits we found that plasma hydroperoxide levels increased and catalase activity decreased 15 min after LPS injection and that fever started with a similar latency, while plasma levels of tumor necrosis factor-alpha (TNFalpha) increased 30 min after the injection. Treating rabbits with methylene blue or aspirin did not affect TNFalpha secretion but prevented the LPS-induced rise of hydroperoxides and the inactivation of catalase, abolishing fever. Incubation of human blood with nitroblue tetrazolium and LPS increased the number of formazan-positive neutrophils from 10 +/- 5 to 52 +/- 9%. Adding LPS to blood preincubated with either methylene blue, alpha-lipoic acid, or aspirin respectively decreased the number of formazan-positive neutrophils to 0.9 +/- 0.8, 0.8 +/- 0.9, or 2.0 +/- 0.9%, disclosing the antioxidant capacity of these drugs. Systemic application of 80 mg/kg alpha-lipoic acid elicited heat-loss reactions within 15 min and decreased core temperature by 2.2 +/- 0.3 degrees C within 2 h. Alpha-lipoic acid applied 45 min after LPS induced antipyresis within 15 min, and this antipyresis was associated with a decrease of elevated hydroperoxide levels and restoration of catalase activity. Our results show that fever is prevented when the production of reactive oxygen species is blocked and that an elevated body temperature returns to normal when oxygen radical production decreases. Estimation of plasma dihydrolipoic acid (DHLA) levels following injection of 80 mg/kg alpha-lipoic acid in afebrile and febrile rabbits revealed that this acid is converted into DHLA, which in afebrile rabbits increased the plasma DHLA concentration from 2.22 +/- 0.26 microg/ml to peak values of 8.60 +/- 2.28 microg/ml DHLA within 30 min and which in febrile rabbits increased it from 0.84 +/- 0.22 microg/ml to peak values of 3.90 +/- 0.94 microg/ml within 15 min. Methylene blue, aspirin, and alpha-lipoic acid, which all cross the blood-brain barrier, seem to act not only on peripheral tissues but also on the CNS. Brain structures that have been shown to sense oxidative stress are vicinal thiol groups attached to the NMDA subtype of glutamate receptor. Their reduction by thiol-reducing drugs like dithiothreitol or DHLA has been found to increase glutamate-mediated neuronal excitability, while the opposite effect has been observed after their oxidation. Because we found that systemic application of alpha-lipoic acid in the afebrile state elicits hypothermia and in the febrile state is antipyretic, we think this type of NMDA receptor is involved in thermoregulation and that oxidation of its thiol groups induces fever. It appears that temperature homeostasis can be maintained only if the redox homeostasis of the brain is guaranteed.

Oxidative Damage to Catalase Induced by Peroxyl Radicals: Functional Protection by Melatonin and Other Antioxidants

Thermal decomposition by the azo initiator 2,2' azobis-(2-amidinopropane) dihydrochloride (AAPH) has been widely used as a water-soluble source of free radical initiators capable of inducing lipid peroxidation and protein damage. Here, in a lipid-free system, AAPH alone (40 mM) rapidly induced protein modification and inactivation of the enzyme catalase (EC 1.11.1.6). Using SDS-PAGE, it was shown that protein band intensity is dramatically reduced after 4 h of incubation with AAPH, leading to protein aggregation. Several antioxidants including melatonin, glutathione (GSH) and trolox prevented catalase modification when used at a 250 w M concentration whereas ascorbate was only effective at 1 mM concentration. All the antioxidants tested reduced carbonyl formation although melatonin was the most effective in this regard. Enzyme inactivation caused by AAPH was also significantly reduced by the antioxidants and again melatonin was more efficient than the other antioxidants used in this study. Results shown here demonstrate that alkyl peroxyl radicals inactivate catalase and reduce the effectiveness of cells to defend against free radical damage; the damage to catalase can be prevented by antioxidants, especially melatonin.

UVA Light In vivo Reaches the Nucleus of the Guinea Pig Lens and Produces Deleterious, Oxidative Effects

The possible role of ultraviolet light in the formation of cataract is not well understood. In this study, guinea pigs were exposed to a chronic, low level of UVA light (0.5mWcm−2, 340–410nm wavelength, peak at 365nm) for 4–5 months. It is known that the lens of the guinea pig possesses unusually high levels of the UVA chromophore NADPH. In a preliminary analysis, it was found that isolated guinea pig corneas transmitted 70–90% of 340–400nm light, and that UVA radiation was able to penetrate deep into the nucleus of the guinea pig lens, where it was absorbed. Exposure of guinea pigs to UVA in vivo produced a 60% inactivation of lens epithelial catalase; however, analysis by transmission electron microscopy (TEM) showed no apparent morphological effects on either the lens epithelium or the cortex. A number of UVA-induced effects were found in the nucleus of the guinea pig lens, but were observed either not at all or to a lesser extent in the cortex. The effects included an increase in light scattering (two-fold; slit-lamp examination), distention of intercellular spaces (TEM), an increase in lipid peroxidation (30–35%; infrared spectroscopy), a decrease in GSH level (30%), an increase in protein–thiol mixed disulfide levels (80%), loss of water-soluble protein (20%), an increase in the amount of protein disulfide (two-fold; two-dimensional diagonal electrophoresis), degradation of MIP26 (15%) and loss of cytoskeletal proteins including actin, α- and β- tubulin, vimentin and α-actinin (60–100%). The results indicate that a 4–5 month exposure of guinea pigs to a biologically relevant level of UVA light produces deleterious effects on the central region of the lenses of the animals. UVA radiation, coupled presumably with the photoreactive UVA chromophore NADPH and trace amounts of O2 present in the lens nucleus, produced significant levels of oxidized products in the nuclear region over a five month period. The data demonstrate the potentially harmful nature of UVA light with respect to the lens, and highlight the importance of investigating a possible role for this type of radiation in the formation of human cataract.

Enhancement of glutathione-dependent haemin degradation by ascorbic acid

In the current work, we investigated the effect of ascorbic acid on GSH-mediated haemin degradation. GSH-mediated haemin degradation in the presence of ascorbic acid in phosphate-buffered saline and in erythrocyte ghosts was determined by recording absorbance at 365 and 399 nm, respectively. Generation of intracellular H 2O 2 was measured indirectly in terms of the inactivation of endogenous catalase in erythrocytes in the presence of 3-amino-1,2,4-triazole. Although ascorbic acid itself did not induce haemin degradation, it enhanced GSH-mediated haemin degradation. Experiments with catalase showed that H 2O 2 was essential in this process. The oxidation of ascorbic acid in the presence of haemin was stimulated by GSH, suggesting that ascorbic acid can alter the mechanism of H 2O 2 generation observed with GSH and haemin alone. These results suggest that enhancement of GSH-mediated haemin degradation by ascorbic acid may be due to an increase in the production of H 2O 2 generated by GSH and haemin in the absence of ascorbic acid.

Inhibition of experimental pulmonary metastasis by controlling biodistribution of catalase in mice.

In a previous study, we showed that targeted delivery of bovine liver catalase to hepatocytes by direct galactosylation augmented the inhibitory effect of the enzyme on experimental hepatic metastasis of colon carcinoma cells (unpublished data). Here, we examined the ability of catalase to inhibit tumor metastasis to the lung by controlling its biodistribution. Four types of catalase derivative, Gal-CAT, Man-CAT, Suc-CAT and PEG-CAT, were synthesized. Experimental pulmonary metastasis was induced in mice by i.v. injection of 1 x 10(5) colon 26 tumor cells. An i.v. injection of catalase (35,000 units/kg) partially, but significantly, decreased the number of colonies in the lung 2 weeks after tumor injection, from 93 +/- 29 (saline injection) to 63 +/- 23 (p < 0.01). Suc-CAT, Man-CAT and Gal-CAT showed effects similar to those of catalase on the number of colonies. However, PEG-CAT greatly inhibited pulmonary metastasis to 22 +/- 11 (p < 0.001). Furthermore, s.c. injection of catalase also greatly inhibited metastasis (11 +/- 6, p < 0.001). Neither inactivated catalase nor BSA showed any effects on the number of metastatic colonies, indicating that the enzymatic activity of catalase to detoxify H(2)O(2) is the critical factor inhibiting metastasis. (111)In-PEG-CAT showed a sustained concentration in plasma, whereas s.c.-injected (111)In-catalase was slowly absorbed from the injection site. These results suggest that retention of catalase activity in the circulation is a promising approach to inhibit pulmonary metastasis.

Protective effects of ibuprofen and its major metabolites against in vitro inactivation of catalase and fumarase: relevance to cataract

Ibuprofen and its major metabolites were incubated with catalase and fumarase, in the presence of protein-modifying biomolecules, to explore the mode of action of ibuprofen in protection against cataract. Both 2 and 10 mM ibuprofen/metabolites protected catalase against fructose-, cyanate- and prednisolone-induced inactivation; the carboxy-metabolite gave the highest protection (31%). The 2 mM ibuprofen/metabolites protected fumarase against fructose- and cyanate-induced inactivation by up to 26%, but had no effect on prednisolone-induced inactivation. Ibuprofen/metabolites did not bind to catalase or fumarase. They penetrated into the lens in vitro. When in the lens, the metabolites may reduce the risk of cataract by protecting lenticular enzymes.

Kinetic Characterization of Extracellular Catalases fromPenicillium piceum F-648 and Its Hydrogen Peroxide-Adapted Variants

A comparative kinetic study of extracellular catalases produced by Penicillium piceum F-648 and their variants adapted to H2O2 was performed in culture liquid filtrates. The specific activity of catalase, the maximum rate of catalase-induced H2O2 degradation (Vmax), Vmax/KM ratio, and the catalase inactivation rate constant in the enzymatic reaction (kin, s–1) were estimated in phosphate buffer (pH 7.4) at 30°C. The effective constant representing the rate of catalase thermal inactivation (kin*, s–1) was determined at 45°C. In all samples, the specific activity and KM for catalase were maximum at a protein concentration in culture liquid filtrates of (2.5–3.5) × 10–4 mg/ml. The effective constants describing the rate of H2O2 degradation (k, s–1) were similar to that observed in the initial culture. These values reflected a twofold decrease in catalase activity in culture liquid filtrates. We hypothesized that culture liquid filtrates contain two isoforms of extracellular catalase characterized by different activities and affinities for H2O2. Catalases from variants 5 and 3 with high and low affinities for H2O2, respectively, had a greater operational stability than the enzyme from the initial culture. The method of adaptive selection for H2O2 can be used to obtain fungal variants producing extracellular catalases with improved properties.

Inactivation of catalase and superoxide dismutase by singlet oxygen derived from photoactivated dye

Both superoxide dismutase (SOD) and catalase are key enzymes in the antioxidant system of the cells that work to maintain low steady-state concentrations of the reactive oxygen species. When exposed to a singlet oxygen-producing system composed of dye, such as methylene blue or rose bengal, and visible light both SOD and catalase were susceptible to oxidative modification and damage as indicated by the loss of activity, fragmentation and aggregation of peptide as well as by the formation of carbonyl groups. Histidine, a powerful quenching agent for singlet oxygen, and the polyamines, such as spermine and spermidine, were effective at protecting the activity loss mediated by illuminated dye, whereas spin traps were only mildly effective. The structural alterations of modified enzymes were indicated by the increase in susceptibility to proteases, the change in absorption spectra and in fluorescence spectra. The singlet oxygen-mediated damage to SOD and catalase may result in the perturbation of cellular antioxidant defense mechanisms and subsequently lead to a pro-oxidant condition.

Comparative kinetic characterization of catalases of the genusPenicillum

Extracellular catalases produced by fungi of the genusPenicillium, i.e.,P. piceum, P. varians, andP. kapuscinskii, were purified by consecutive filtration of culture liquids. The maximum reaction rate of H2O2 decomposition, the Michaelis constants, and specific catalytic activities of isolated catalases were determined. The operational stability was characterized by the effective rate of catalase inactivation during enzymatic reaction (k in at 30°C). The thermal stability was determined by the rate of enzyme thermal inactivation at 45°C (k in * , s-1). Catalase fromP. piceum displayed the maximum activity, which was higher than the activity of catalase from bovine liver. The operational stability of catalase fromP. piceum was twofold to threefold higher than the stability of catalase from bovine liver. The physicochemical characteristics of catalases of fungi are better than the characteristics of catalase from bovine liver and intracellular catalase of yeastC. boidinii.

Fructose induced deactivation of antioxidant enzymes: Preventive effect of pyruvate

Glycation initiated changes in tissue proteins, which are triggered by the Schiff base formation between the sugar carbonyl and the protein -NH2, have been suggested to play an important role in the development of diabetes-related pathological changes such as the formation of cataracts. While the initial reaction takes place by the interaction of >C=O of the parent sugars with the -NH2 of proteins, reactive oxygen species (ROS) dependent generation of more reactive dicarbonyl derivatives from the oxidation of sugars also plays a significant role in these changes, altering the structural as well as functional properties of proteins. The purpose of this study was to examine whether the activities of glyceraldehyde-3-phosphate dehydrogenase (GAPDH), catalase and superoxide dismutase (SOD) could be affected by the high levels of fructose prevalent in diabetic lenses. Incubation of the enzymes with this sugar led to a significant loss of their activities. GAPDH was inactivated within a day. This was followed by the inactivation of catalase (3–4 days) and SOD (6 days). The loss of the activities was prevented significantly by incorporation of pyruvate in the incubation mixture. The protective effect is ascribable to its ability to competitively inhibit glycation as well as to its ROS scavenging activity. Hence, it could play a significant role in the maintenance of lens physiology and cataract prevention.

Amyloid-β binds catalase with high affinity and inhibits hydrogen peroxide breakdown

Amyloid-beta (Abeta) specifically bound purified catalase with high affinity and inhibited catalase breakdown of H(2)O(2). The Abeta-induced catalase inhibition involved formation of the inactive catalase Compound II and was reversible. Catalase<-->Abeta interactions provide rapid functional assays for the cytotoxic domain of Abeta and suggest a mechanism for some of the observed actions of Abeta plus catalase in vitro.

Resistance of cold‐hardened winter rye leaves (Secale cereale L.) to photo‐oxidative stress

ABSTRACTCatalase and photosystem II (PSII) were strongly inactivated during exposure to 4 °C and moderate light in 22 °C‐grown non‐hardened leaves (NHL) of winter rye (Secale cereale L.), but highly resistant to photo‐inactivation at low temperature in 4 °C‐grown cold‐hardened leaves (CHL). Resistance of CHL to chilling‐induced photo‐inactivation of catalase and PSII depended partially on more efficient de novo synthesis at 4 °C and partially on improved protection. Lower rates of chloroplast‐mediated inactivation of catalase in vitro indicated that less reactive oxygen was released by chloroplasts from CHL than by chloroplasts from NHL. The contents of xanthophyll cycle carotenoids, α‐tocopherol, ascorbate, glutathione, the activities of superoxide dismutase and glutathione reductase, and the tolerance against paraquat‐induced photo‐oxidative damage were greatly increased in CHL, relative to NHL. Zeaxanthin‐related thermal energy dissipation was only of minor importance for paraquat‐tolerance and protection of catalase in CHL. When CHL were transferred to a higher temperature of 22 °C the increased resistance to photo‐inactivation of catalase and PSII and the increased paraquat‐tolerance were largely lost within 3 d, whereas most non‐enzymic and enzymic antioxidants retained higher levels than in NHL. The decline of resistance to photodamage during dehardening was not related to concomitant changes of antioxidants or antioxidative enzymes.

Significance of antioxidants and electron sinks for the cold‐hardening‐induced resistance of winter rye leaves to photo‐oxidative stress

ABSTRACTThe contents of ascorbate and glutathione and the activities of superoxide dismutase and glutathione reductase were increased to levels as high as those in cold‐hardened leaves (CHL) by incubating non‐hardened leaves (NHL) of winter rye (Secale cereale L.) with the precursor substrates L‐galactonic acid‐γ‐lactone and 2‐oxothiazolidine‐4‐carboxylate. Reduced glutathione was rapidly depleted from NHL after application of D, L‐buthionine sulfoximine, an inhibitor of its biosynthesis. In spite of greatly divergent antioxidant contents the rates of photo‐inactivation of photosystem II (PSII) and catalase observed in the presence of translation inhibitors did not differ greatly. The paraquat‐induced catalase inactivation and chlorophyll degradation in light were reduced in NHL with increased antioxidant levels. Paraquat‐induced photo‐inactivation of PSII was, however, not mitigated. The CHL had a higher capacity to prevent paraquat‐induced oxidation of ascorbate and glutathione than NHL with increased antioxidant contents. Increased antioxidant contents did not establish resistance to low temperature‐induced photo‐inactivation of PSII and catalase in NHL. The resistance of CHL to low temperature‐induced photo‐inactivation of PSII and catalase required repair at low temperature and active carbon assimilation but was only little affected when photorespiration was suppressed by phosphinothricin. Protection of PSII depended also on non‐photochemical quenching of excitation energy.

In vivo and in vitro evidence for hydrogen peroxide (H2O2) accumulation in the epidermis of patients with vitiligo and its successful removal by a UVB-activated pseudocatalase.

To date there is compelling in vitro and in vivo evidence for epidermal H2O2 accumulation in vitiligo. This paper reviews the literature and presents new data on oxidative stress in the epidermal compartment of this disorder. Elevated H2O2 levels can be demonstrated in vivo in patients compared with healthy controls by utilizing Fourier-Transform Raman spectroscopy. H2O2 accumulation is associated with low epidermal catalase levels. So far, four potential sources for epidermal H2O2 generation in vitiligo have been identified: (i) perturbed (6R)-L-erythro 5,6,7,8 tetrahydrobiopterin (6BH4) de novo synthesis/recycling/regulation; (ii) impaired catecholamine synthesis with increased monoamine oxidase A activities; (iii) low glutathione peroxidase activities; and (iv) "oxygen burst" via NADPH oxidase from a cellular infiltrate. H2O2 overproduction can cause inactivation of catalase as well as vacuolation in epidermal melanocytes and keratinocytes. Vacuolation was also observed in vitro in melanocytes established from lesional and nonlesional epidermis of patients (n = 10) but was reversible upon addition of catalase. H2O2 can directly oxidize 6BH4 to 6-biopterin, which is cytotoxic to melanocytes in vitro. Therefore, we substituted the impaired catalase with a "pseudocatalase". Pseudocatalase is a bis-manganese III-EDTA-(HCO3-)2 complex activated by UVB or natural sun. This complex has been used in a pilot study on 33 patients, showing remarkable repigmentation even in long lasting disease. Currently this approach is under worldwide clinical investigation in an open trial. In conclusion, there are several lines of evidence that the entire epidermis of patients with vitiligo is involved in the disease process and that correction of the epidermal redox status is mandatory for repigmentation.

Immunotargeting of glucose oxidase: intracellular production of H(2)O(2) and endothelial oxidative stress.

Extracellular and intracellular reactive oxygen species attack different targets and may, therefore, result in different forms of oxidative stress. To specifically study an oxidative stress induced by a regulated intracellular flux of a defined reactive oxygen species in endothelium, we used immunotargeting of the H(2)O(2)-generating enzyme glucose oxidase (GOX) conjugated with an antibody to platelet-endothelial cell adhesion molecule (PECAM)-1, an endothelial surface antigen. Anti-PECAM-(125)I-GOX conjugates specifically bind to both endothelial and PECAM-transfected cells. Approximately 70% of cell-bound anti-PECAM-(125)I-GOX was internalized. The cell-bound conjugate was enzymatically active and generated H(2)O(2) from glucose. Use of the fluorescent dye dihydrorhodamine 123 revealed that 70% of H(2)O(2) was generated intracellularly, whereas 30% of H(2)O(2) was detected in the cell medium. Catalase added to the cells eliminated H(2)O(2) in the medium but had little effect on the intracellular generation of H(2)O(2) by anti-PECAM-GOX. Both H(2)O(2) added exogenously to the cell medium (extracellular H(2)O(2)) and that generated by anti-PECAM-GOX caused oxidative stress manifested by time- and dose-dependent irreversible plasma membrane damage. Inactivation of cellular catalase by aminotriazole treatment augmented damage caused by either extracellular H(2)O(2) or anti-PECAM-GOX. Catalase added to the medium protected either normal or aminotriazole-treated cells against extracellular H(2)O(2), yet failed to protect cells against injury induced by anti-PECAM-GOX. Therefore, treatment of PECAM-positive cells with anti-PECAM-GOX leads to conjugate internalization, predominantly intracellular H(2)O(2) generation and intracellular oxidative stress. These results indicate that anti-PECAM-GOX 1) provides cell-specific intracellular delivery of an active enzyme and 2) causes intracellular oxidative stress in PECAM-positive cells.