Functional aspects of the superoxide dismutative action of Cu-penicillamine

Anti-inflammatory effects of tobramycin and a copper-tobramycin complex with superoxide dismutase-like activity

BACKGROUND AND PURPOSE

Airway inflammation in cystic fibrosis (CF) patients is characterized by accumulations of neutrophils in the airway and T cells in bronchial tissue, with activation of platelets in the circulation. CF patients are routinely treated with systemic or inhaled tobramycin for airway infection with Pseudomonas aeruginosa. Clinical trials have indicated an anti-inflammatory effect of tobramycin beyond its bactericidal activity. Here, we investigate the anti-inflammatory properties of tobramycin in vitro and consider if these relate to the ability of tobramycin to bind copper, which is elevated in blood and sputum in CF.

EXPERIMENTAL APPROACH

A copper-tobramycin complex was synthesized. The effect of tobramycin and copper-tobramycin on neutrophil activation and migration of T cells and neutrophils across human lung microvascular endothelial cells in response to thrombin-activated platelets were investigated in vitro. Tobramycin uptake was detected by immunocytochemistry. Intracellular reactive oxygen species were detected using the fluorescent indicator, 2',7'-dichlorofluorescein diacetate (DCFDA). Neutrophil superoxide, hydrogen peroxide and neutrophil elastase activity were measured using specific substrates. Copper was measured using atomic absorption spectroscopy.

KEY RESULTS

Tobramycin and copper-tobramycin were taken up by endothelial cells via a heparan sulphate-dependent mechanism and significantly inhibited T-cell and neutrophil transendothelial migration respectively. Copper-tobramycin has intracellular and extracellular superoxide dismutase-like activity. Neutrophil elastase inhibition by α1-antitrypsin is enhanced in the presence of copper-tobramycin. Tobramycin and copper-tobramycin are equally effective anti-pseudomonal antibiotics.

CONCLUSIONS AND IMPLICATIONS

Anti-inflammatory effects of tobramycin in vivo may relate to the spontaneous formation of a copper-tobramycin complex, implying that copper-tobramycin may be more effective therapy.

Inhibition of selenite-induced cytotoxicity and apoptosis in human colonic carcinoma (HT-29) cells by copper

Selenite catalytically oxidizes reduced glutathione (GSH) with subsequent generation of superoxide. Our laboratory has previously shown that this selenite-catalyzed generation of superoxide is strongly inhibited by copper [as copper(II) sulfate]. In the present study we have demonstrated that exposure of human colonic carcinoma cells (HT-29) to selenite resulted in the induction of apoptosis, DNA fragmentation, an increase in intracellular levels of the antioxidant GSH, and cytotoxicity. Selenite-induced apoptosis, DNA fragmentation, increases in GSH levels, and cytotoxicity were inhibited by copper(II) sulfate. Copper only protected cells from selenite cytotoxicity when cells were exposed to selenite and copper simultaneously, not when cells were pretreated with copper, then washed before selenite exposure. This suggests that copper elicits its protective effect extracellularly. Previous data reported by this laboratory clearly demonstrated that copper inhibited selenite-catalyzed superoxide generation. Collectively, these data suggest that reactive oxygen species may play a role in selenite-induced cytotoxicity, apoptosis, and DNA fragmentation.

Inhibition of selenite-catalyzed superoxide generation and formation of elemental selenium (Se(o)) by copper, zinc, and aurintricarboxylic acid (ATA)

Selenite catalyzes the oxidation of glutathione (GSH) with the subsequent generation of superoxide (O2.-). Copper, zinc, and aurintricarboxylic acid (ATA) were tested for their ability to inhibit both the selenite-catalyzed generation of superoxide and the conversion of selenite to elemental selenium (Se(o)). As measured by lucigenin-dependent chemiluminescence (CL), copper, zinc, and ATA were shown to inhibit significantly (P < 0.05) selenite-catalyzed CL in a concentration-dependent manner. The inhibition of the selenium-catalyzed generation of superoxide by copper(II) was greater than by either zinc or ATA. In addition, Copper, zinc, and ATA all inhibited the conversion of selenite to Se(o). Inhibition of selenite-catalyzed CL by copper, zinc, and ATA is believed to occur as the result of inhibition of Se2- and/or GSSe-, the catalytic selenopersulfide anion of GSH.

Inhibition of neutrophil oxidant secretion by D-penicillamine: scavenging of H2O2 and HOCl

D-Penicillamine inhibited oxidant secretion from human neutrophils after activation by the chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (fMet-Leu-Phe), as assessed by luminol dependent chemiluminescence. In contrast, this drug had little effect on either intracellular oxidant production or lucigenin dependent chemiluminescence activated by the same agonist. The drug was shown to scavenge both H2O2 and HOCl in a cell free luminol chemiluminescence system, though its ability to scavenge HOCl was greater than that for H2O2. Both these oxidants could oxidise the drug, but again HOCl was more potent than H2O2. When D-penicillamine was oxidised by exposure to H2O2 it could no longer serve as a scavenger of secreted oxidants from neutrophils. These data suggest that in vivo the preferential scavenging of HOCl may be important under pathological conditions where secreted myeloperoxidase may be functional.

Mn(III)-desferrioxamine superoxide dismutase-mimic: alternative modes of action

Various low-molecular-weight copper chelates have been synthesized to mimic superoxide dismutase (SOD) by catalyzing O2-. dismutation. However, in the presence of cellular proteins, such chelates dissociate and thereby lose their SOD-mimetic activity. In contrast, desferrioxamine-Mn(III) 1:1 chelate (DF-Mn), an SOD-mimic that affords protection from oxidative damage, reportedly is stable in the presence of serum albumin. DF-Mn, unlike SOD, is reported to permeate the membrane of at least one cell type and can protect cells by detoxifying intracellular O2-.. Recently DF-Mn was shown to protect hypoxic cells from H2O2-induced damage. Such results suggest that DF-Mn can protect cells from O2-.-independent damage by alternative mechanisms. This study examines such possibilities. To avoid O2-. participation in the damaging process, killing of monolayered V79 Chinese hamster cells was induced in a hypoxic environment by t-butyl hydroperoxide (t-BHP). Damage induced by t-BHP was inhibitable by DF-Mn. DF-Mn was also found to rapidly oxidize iron(II)-bound DNA. Additionally, once DF-Mn oxidizes Fe(II) or Cu(I), the DF moiety of DF-Mn dissociates and rapidly binds to Fe(III) or Cu(II). Without excluding the possibility that DF-Mn protects cells by facilitating the removal of O2-., the present results show that this SOD-mimic can confer protection from cytotoxic processes independent of O2-. or of O2-.-derived active species.

Nitroxide SOD-mimics: modes of action

Low molecular weight superoxide dismutase mimics have been shown to afford protection from oxidative damage. Such SOD-mimics can readily permeate cell membrane achieving sufficiently high levels both inside and outside the cell to effectively detoxify intracellular O2-.. Preliminary findings also indicated that metal-based and metal-free SOD-mimics can protect hypoxic cells from H2O2-induced damage. The present study explored the possibility that SOD-mimics such as desferrioxamine-Mn(III) chelate [DF-Mn] or cyclic nitroxide stable free radicals could protect from O2-.-independent damage. Killing of monolayered V79 Chinese hamster cells was induced by H2O2 or by t-butyl hydroperoxide (t-BHP) and assayed clonogenically. Neither catalase nor native SOD protected the cells from t-BHP. In contrast, both DF-Mn and cyclic nitroxides protected suggesting cytotoxic processes independent of O2-. or of O2-.-derived active species. The inhibition of the damage by both metal-free and metal-based SOD mimics is attributable to either SOD-mimic reacting with reduced transition metal to block the Fenton reaction and/or intercepting and detoxifying intracellular organic free radicals.

Novel iron complexes behave like superoxide dismutase in vivo

Novel iron and copper complexes having tris[N-(5-methyl-2-pyridylmethyl)-2-aminoethyl]amine (5MeT-PAA), tris[N-(3-methyl-2-pyridylmethyl)-2-aminoethyl]amine (3MeTPAA), tris[N-(5-methoxycarbonyl-2-pyridylmethyl)-2-aminoethyl]amine (TNAA), tris[(2-thienylmethyl)-2-aminoethyl]amine (TTAA), tris[(2-furylmethyl)-2-aminoethyl]amine (TFAA) or tris[(2-imidazoyl)-2-aminoethyl]amine (TIAA) as ligand, were synthesized to examine the superoxide dismutase (SOD) activity. The concentrations of Fe-3MeTPAA and Fe-TIAA equivalent to 1 unit of SOD (IC50) were 0.5 microM and 1.0 microM, respectively. Fe-3MeTPAA and Fe-TIAA had higher SOD activity than other Fe and Cu complexes and protected Escherichia coli cells from paraquat toxicity. In case of using tris[N-(6-methyl-2-pyridylmethyl)-2-aminoethyl]amine (6MeTPAA) as ligand, the Fe complex could not be obtained, which may be due to the steric hindrance of 6-methyl substituent. Generally, Cu complexes had low SOD activity, compared with Fe complexes, and could not suppress paraquat toxicity.

Copper salicylate and copper phenylbutazone as topically applied anti-inflammatory agents in the rat and horse

Topically applied copper phenylbutazone, phenylbutazone, copper salicylate, salicylate and dimethylsulfoxide glycerol (80:20) were investigated as anti-inflammatory agents in rats and horses. Dimethylsulfoxide and glycerol (80:20) or dimethylsulfoxide, ethanol and glycerol (60:20:20) were used as the drug solvents. Subcutaneously administered carrageenin was used to induce inflammatory oedema, either in the paws of rats or the alar fold of the horse. The severity of the oedema and the anti-inflammatory effect of the drugs were assessed by measuring changes in the paw or alar-fold diameters. Copper salicylate and copper phenylbutazone were effective inhibitors of the inflammatory oedema in both species, but dimethylsulfoxide:glycerol (80:20) was not. In the rat, copper salicylate and copper phenylbutazone were superior anti-inflammatory agents compared to either salicylate or phenylbutazone, respectively. Following the topical application of four times the recommended daily dose of copper phenylbutazone to the horse for 5 days, minor skin irritation occurred and trace concentrations of phenylbutazone (maximum 0.6 microgram/ml) and negligible concentrations of oxyphenbutazone and gamma-hydroxyphenylbutazone were detected in the plasma.

Free radicals, immunoglobulins and complement as mediators of inflammation

There is evidence for both oxygen-centred free radicals and products of complement activation acting as mediators of inflammation. Evidence for the generation and reaction of free radicals at sites of inflammation can only be indirect and circumstantial due to their very transient nature. Evidence for complement activation in several inflammatory conditions, including rheumatoid arthritis is strong. These mediator classes individually possess a range of potential proinflammatory activities. Their effects may be linked through the formation of immune complexes and the activation of polymorphonuclear leukocytes. Their actions will also be linked with and modulated by the activities of other mediators mentioned only briefly in this chapter. The relative importance of the different mediators in any particular inflammatory condition is difficult to ascertain. The importance of free radicals and complement will be better understood when drugs specifically and unequivocally aimed at their control are identified. This potential for therapeutic advances in the treatment of inflammatory disorders has yet to be realized.

Clinical trials of penicillamine in Indian childhood cirrhosis

The outcome in 15 children with advanced Indian childhood cirrhosis (ICC) treated with penicillamine 20 mg/kg/day was not significantly different from that in untreated children. Among children admitted to a further double blind trial who had ICC but who had not yet developed jaundice or ascites 10 treated with penicillamine and 10 treated with penicillamine plus prednisolone had a significantly improved survival. Fourteen of 29 treated cases made a clinical recovery and were alive 489 to 1460 days from the start of treatment. Biopsy specimens in survivors showed a return to normal liver histology in three, residual fibrosis in six, and inactive micronodular cirrhosis in five. Thus penicillamine, while not shown to be beneficial in advanced ICC, lowered mortality from 93% to 52% in preicteric cases of ICC.

A mimic of superoxide dismutase activity based upon desferrioxamine B and manganese(IV)

MnO2 reacted with desferrioxamine B yielding a green, water-soluble complex, with absorption maxima at 315 and 635 nm whose extinction coefficients were 925 and 60 M-1 cm-1, respectively. Increasing the proportion of ligand to metal increased both color yield and ability to scavenge O2-, with maximal color yield and activity being achieved at a 1:1 ratio. The complex catalyzed the dismutation of O2- and 1 microM was equivalent to 1 unit of superoxide dismutase activity in the xanthine oxidase-cytochrome c assay. The complex thus exhibited approximately 0.1% as much activity as did the manganese-containing superoxide dismutase, on the basis of manganese content. The activity of the complex was not suppressed by bovine serum albumin or by the soluble proteins extracted from Lactobacillus plantarum. In contrast, the activities of Cu(II) complexes of salicylate or Gly-His-Lys were suppressed by these proteins.

D-penicillamine therapy and interstitial lung disease in scleroderma. A long-term followup study

Sequential lung function tests were performed on 17 scleroderma patients who were treated with D-penicillamine (DP) (total of 66 treatment years) and on 10 control scleroderma patients who were not treated or were treated with low-dose prednisone (total of 25 treatment years). Cusum plots showed significant differences between the 2 groups in their cumulative changes in carbon monoxide diffusing capacity (DLCO) (P less than 0.005) and in DLCO/lung volume (P less than 0.02). The end value of the DLCO was greater than 10% lower than the initial value in 3 of the 17 DP-treated patients versus 5 of the 10 control patients (P less than 0.01, Fisher's exact probability test); in 3 DP-treated patients and 8 control patients (P less than 0.003, Fisher's exact probability test), the end value of the DLCO/lung volume was greater than 10% lower than the initial value. We conclude that DP has a beneficial effect on interstitial lung disease in patients with scleroderma.

Effects of hyperthermic conditions on the reactivity of oxygen radicals

Generation and reactivity of superoxide (O2.-) and hydroxyl (OH.) radicals in enzymatic and radiolytic systems were investigated over the temperature range from 20 degrees-50 degrees C. The generation rate and reaction kinetics of both enzymatically and radiolytically produced superoxide radicals were determined by a cytochrome c reduction assay. For OH. radical reaction studies the degradation of hyaluronic acid was assayed. An increase in temperature leads to a greater reactivity of both radicals, but in the case of an enzymatic source a disproportionate increase in the rate of generation is observed. In the pulse radiolysis system, the reactivity of superoxide radicals was found to be stimulated 15-fold over the temperature range from 20 degrees C to 60 degrees C, although the activity of superoxide dismutase was only minimally increased (about 1.6-fold). The results are discussed with respect to the possible importance of active oxygen species to the biological effects of hyperthermia.

D-penicillamine in patients with rheumatoid arthritis. Serum levels, pharmacokinetic aspects, and correlation with clinical course and side effects

After administration of D-penicillamine to patients with rheumatoid arthritis, measurements of serum level and urinary excretion showed half-life times of 1.6 hours in the rapid phase and 4-6 days in the slow phase. The latter evidence suggests that tissue pooling occurs. With a dosage of 750 mg/day, basic serum levels of 100 microM are gradually reached. Serum D-penicillamine levels were shown to be the same for patients who responded well to treatment, those who did not respond, and for patients who had adverse side effects as well as those who had none. Intestinal resorption decreased when D-penicillamine was taken close to meals and was greatly reduced by iron preparations.

Radical formation during autoxidation of 4-dimethylaminophenol and some properties of the reaction products

4-Dimethylaminophenol (DMAP), after intravenous injection, rapidly forms ferrihaemoglobin and has been successfully used in the treatment of cyanide poisoning. Since DMAP produces many equivalents of ferrihaemoglobin, it was of interest to obtain further insight into this catalytic process. DMAP autoxidizes readily at pH regions above neutrality, a process which is markedly accelerated by oxyhaemoglobin. The resulting red-coloured product was identified as the 4-(N,N-dimethylamino) phenoxyl radical by EPR spectroscopy. The same radical was also produced by pulse radiolysis and oxidation with ferricyanide. The 4-(N,N-dimethylamino)phenoxyl radical is quite unstable and decays in a pseudo-first order reaction (k = 0.4 sec-1 at pH 8.5, 22 degrees) with the formation of p-benzoquinone and dimethylamine. This observed decay rate is identical with the rate of hydrolysis of N,N-dimethylquinonimine. When a solution containing the phenoxyl radical was extracted with ether, half the stoichiometric amount of DMAP was recovered. Hence it is apparent that the phenoxyl radical decays by disproportionation yielding DMAP and N,N-dimethylquinonimine. The latter product then quickly hydrolyses. The equilibrium of this disproportionation reaction is far towards the radical side, and the pseudo-first order hydrolysis controls the radical decay rate. p-Benzoquinone rapidly reacts with DMAP (k2 = 2 X 10(4) M-1 sec-1) with the formation of the 4-(N,N-dimethylamino)phenoxyl and the semiquinone radicals. This reaction explains the autocatalytic phenoxyl radical formation during autoxidation of DMAP. DMAP is not oxidized by H2O2 or O-.2 but the 4-(N,N-dimethylamino)phenoxyl radical is very rapidly reduced by O-.2 (k2 = 2 X 10(8) M-1 sec-1). In addition, the phenoxyl radical is quickly reduced by NAD(P)H or GSH with the formation of NAD(P)+ or GSSG. Since DMAP is also able to reduce two equivalents of ferrihaemoglobin (provided that the ferrohaemoglobin produced is trapped by carbon monoxide), electrophilic addition reactions of the phenoxyl radical seem unimportant in contrast to N,N-dimethylquinonimine. Hence, during the catalytic ferrihaemoglobin formation, DMAP is oxidized by oxygen which is activated by haemoglobin, and the phenoxyl radical oxidizes ferrohaemoglobin. This catalytic process is terminated by covalent binding of N,N-dimethylquinonimine to SH groups of haemoglobin (and GSH in red cells).

The effect of D-penicillamine on human myeloperoxidase, a mechanism for the efficacy of the drug in rheumatoid arthritis

We investigated the effect of D-penicillamine on the ability of myeloperoxidase, purified from human leukocytes, to catalyse the oxidation of chloride ions to hypochlorite (HOCl) in the presence of H2O2. It is shown that, due to the interaction of D-penicillamine with both myeloperoxidase itself and HOCl, the chlorinating activity of myeloperoxidase in the presence of H2O2 and chloride ions is prevented. A concentration of 100 microM D-penicillamine inhibits the chlorinating activity of myeloperoxidase completely, which Is due to the stabilization of Compound II, an inactive form of the enzyme. In addition, HOCl reacts directly with D-penicillamine. Analysis of the reaction products of D-penicillamine and HOCl showed that D-penicillamine was oxidized to penicillamine disulphide and penicillamine sulphinic acid, and eventually deaminated (indicated by the release of ammonia). Lower concentrations of D-penicillamine (10 microM) inhibited myeloperoxidase less, but still acted as effective scavengers of HOCl. In very low concentrations (1 microM), D-penicillamine did not scavenge HOCl effectively, but rather stimulated the chlorinating activity of myeloperoxidase. However, when instead of D-penicillamine a comparable amount of ascorbate was added, a similar but even larger stimulation was observed. Since the concentration of free D-penicillamine in serum from rheumatoid patients treated with this drug is about 20 microM (Saetre, R. and Rabenstein, D.L. (1978) Anal. Chem. 50, 276-280), the therapeutic effect of D-penicillamine may be due to the protection of tissues against the reactive HOCl released by activated granulocytes at inflammation sites.

Further studies on superoxide dismutase activities of macrocyclic polyamine complexes of copper(II)

The superoxide dismutase (EC 1.15.1.1) activities of new series of macrocyclic complexes with copper(II) have been measured. Chemical modifications in macrocyclic ring size, donor atom, donor atom number, substituents on the macrocyclic skeletons, and length of bridges linking two macrocycles are shown to have profound effects on the superoxide dismutase activities of the metal complexes. The quantitative measurement by the standard xanthine-xanthine oxidase assay, which depends on the conversion of nitroblue tetrazolium to formazan, has been corroborated by a direct assay method using an oxygen electrode.

Mechanistic aspects of enhanced lipid peroxidation following glutathione depletion in vivo

Several agents known to conjugate with glutathione (GSH) were administered to phenobarbital-induced rats resulting in a more or less pronounced depletion of hepatic GSH. In vitro incubations showed that a large enhancement of spontaneous lipid peroxidation was observed when the GSH content was below 1 mumol/g liver. This effect was inhibited by addition of exogenous GSH in a concentration-dependent manner, the GSH-concentration yielding 50% inhibition (I50) being 1 microM. Using phorone (diisopropylidene acetone), which proved to be the most potent GSH-depletor, the time- and dose-dependence of the GSH-depletion and the consequent lipid peroxidation was studied. Again it was assured that the GSH concentration must reach a critical value of about 20% of the initial hepatic GSH content, before an enhanced lipid peroxidation is seen. Employing scavengers of excited oxygen species no evidence was found for the involvement of free oxygen radicals. Hepatoprotective agents and inhibitors of mixed-function oxidases exerted a more or less pronounced inhibitory action. Our findings are further support of our previous postulate that GSH depletion per se might lead to an increased lipid peroxidation, possibly due to its lack as a part of the cellular defence system against endogenous toxic intermediates.

Structure of Cu2(indomethacin)4 and the reaction with superoxide in aprotic systems

The copper complex of indomethacin (1-(p-chlorobenzoyl)-5-methoxy-2-methyl-indole acetate), a common anti-inflammatory drug, was prepared and characterized. Crystal structure determination revealed the dimeric form of the 1 : 2 complex, namely Cu2(indomethacin)4 x L2, in the unit cell. Surprisingly, the copper-copper distance (263 pm) was very close to metallic copper (256 pm). The two coordination sites in the copper-copper axis can be readily replaced by superoxide. An intriguing similarity to Cu2(acetate)4 was seen. Due to the lipophilic nature of the indomethacin ligand, this copper complex reacted with superoxide in aprotic solvents. the superoxide dismutating activity was successfully demonstrated in Me2SO/water and acetonitrile/water mixtures using the nitro-blue tetrazolium assay and pulse radiolysis. The second-order rate constant of 6 x 10(9) M-1 x s-1 in strictly aqueous systems dropped only slightly to 1.1 x 10(9) M-1 x s-1 when aprotic solvents were used. This is the fastest rate constant ever observed for a copper-dependent dismutation of superoxide. The KO2-induced lipid peroxidation in both erythrocytes and liver microsomes was suppressed by 70% in the presence of 1 x 10(-10) mol x ml-1 of Cu2(indomethacin)4. The inhibitory action dropped to 25% when Cu2Zn2superoxide dismutase was employed. The formation of copper x indomethacin in rat serum after administration of indomethacin was shown in vitro and vivo.

Oxygen utilization by Lactobacillus plantarum. II. Superoxide and superoxide dismutation

Cell-free extracts of Lactobacillus plantarum contain non-proteinaceous compounds which mimic superoxide dismutase activity. Using the test system in which O-2 is generated by xanthine oxidase, superoxide dismutase activity is found in cell-free extracts, where proteins are removed by precipitation. This activity is strongly decreased after dialysis of cell-free extracts. Superoxide dismutase activity was also investigated by means of pulse radiolysis. Cell-free extracts of Escherichia coli were also investigated as a comparison, which were known to contain superoxide dismutase. With cell-free extracts of both L. plantarum and E. coli the decay of O-2 was markedly increased. However, the type of reaction of the O-2 decay was of first order in the presence of E. coli extracts due to superoxide dismutase(s), and of second order in the presence of L. plantarum extracts, indicating that O-2 elimination is not an enzymic reaction. Mn2+ phosphate(s) might be responsible for the observed elimination of O-2. The production of O-2 is not detectable during NADH-, lactate- or pyruvate oxidase reactions in L. plantarum extracts.

Effect of oxygen-derived free radicals on hyaluronic acid

To investigate possible mechanisms of hyaluronic acid depolymerization, superoxide anion and other secondary oxygen-derived free radicals were generated in vitro and allowed to act upon a hyaluronate substrate. Superoxide, generated either enzymatically with xanthine oxidase or by stimulation of polymorphonuclear leukocytes, reduced the viscosity of hyaluronate solutions dramatically while the chromatographic profiles of the glycosaminoglycan shifted toward lower molecular weights. Superoxide-treated hyaluronate also became susceptible to further degradation by beta-N-acetylglucosaminidase A. Experiments with scavengers of various toxic oxygen-derived free radicals clearly implicated these reactants as mediators of hyaluronate depolymerization. Generation of superoxide by leukocytes in vivo may account for the loss of synovial fluid viscosity that accompanies inflammatory joint disease.