Copper transport from Cu(I)-thionein into apo-caeruloplasmin mediated by activated leucocytes

Copper-release from yeast Cu(I)-thionein by hypothiocyanite (OSCN-)

In the course of an oxidative burst oxygen free radicals and hypothiocyanite (OSCN-), a transiently abundant derivative of thiocyanate (SCN-), are formed in the presence of activated polymorphonuclear leukocytes (PMNs). At the same time Cu(I)-thionein is present and the question arose whether or not thiocyanate and its oxidized form may transiently release highly Fenton active copper to improve the efficacy of the above mentioned oxidative burst. Thus, the reaction of yeast Cu-thionein with OSCN- was examined. Indeed, a release of copper from the Cu(I)-thiolate clusters of the protein was observed ex vivo. Both the chiroptic and luminescence emission signals of Cu-thionein essentially levelled off in the presence of a 15-fold molar excess of OSCN- expressed per equivalent of thionein-copper. The effective copper-releasing activity of this reagent was confirmed by equilibrium dialysis. The demetallized protein could be reconstituted under reductive conditions. SCN- did not affect the copper-thiolate bonding. It rather acts as a potent metabolic source for the transient copper release from Cu-thionein in the presence of activated PMNs.

Antioxidant properties of omeprazole

Potential antioxidant properties of therapeutically achievable concentrations of the protonated, active form of omeprazole (OM) were investigated in vitro at specific acidic pH values to mimic intragastric conditions in the clinical setting. We found that OM is a powerful scavenger of hypochlorous acid (HOCl) even at a drug concentration of 10 microM at pH 5.3 or 3.5. This effect is also evident in the presence of the physiological HOCl scavenger ascorbate. Moreover, 10 and 50 microM OM inhibit significantly both iron- and copper-driven oxidant damage at pH 5.3 and 3.5, respectively. Since oxidative stress is involved the gastric injury of peptic ulcer and gastritis, it may be hypothesized that some therapeutical effects of OM could also be related to its antioxidant properties.

Reconstitution of ceruloplasmin by the Cu(I)-glutathione complex. Evidence for a role of Mg2+ and ATP

The copper-glutathione complex (Cu(I)-GSH) efficiently acted in vitro as the source of Cu(I) in the reconstitution of apoceruloplasmin. Copper was found to reinstate in the various sites in a multistep process, with metal entry into the protein in a first phase, and a second step involving conformational changes of the protein leading to the recovery of the native structural and functional properties. This latter phase was found to be strongly facilitated by Mg2+ or Ca2+ and by ATP. Both Mg2+ and ATP had to be present for optimal reconstitution. These results may shed some light on the mechanisms governing the biosynthesis of ceruloplasmin in vivo. Cu(I)-GSH was the only complex able to reconstitute ceruloplasmin at neutral pH. Glutathione may thus function to shuttle the metal from the membrane copper pump, as the Wilson disease ATPase, and ceruloplasmin in the secretory compartments of the cell. The finding that ceruloplasmin acquires the native conformation after metal entry through a complex pathway triggered by Mg2+ and ATP suggests that they may act as physiological modulators of this process in vivo.

Plasma copper and lipid peroxidation in cigarette smokers

Plasma levels of copper and lipid peroxidation were evaluated in 14 smokers as compared to 14 nonsmokers. Plasma copper concentrations were higher in smokers than in nonsmokers (122.5 +/- 19.15 vs. 101.5 +/- 16.2 micrograms/dl, P < .01). Plasma lipoperoxidation, evaluated as fluorescent damage products of lipid peroxidation (FDPL), also was higher in smokers than in nonsmokers (20.35 +/- 2.6 vs. 17.1 +/- 2.95 units of relative fluorescence/ml, P < .01). A significant and positive correlation between the number of cigarettes smoked, expressed as pack years, and the levels of either FDPL (r = .61, P < .025) or copper (r = .55, P < .05) was found. Moreover, a significant and positive relationship between copper and FDPL values was observed in smokers (r = .64; P < .025), but not in nonsmokers. These data indicate that cigarette smoke-related plasma oxidant load may be partly due to enhanced levels of the prooxidant metal cooper, potentially suggesting the supplementation of specific antioxidants (e.g., zinc) to counteract cigarette smoke-induced oxidative stress in smokers.

Effects of fatty acids and fatty acyl CoA esters on Cu(2+)-induced conversion of xanthine dehydrogenase to oxidase in rabbit liver

Effects of various fatty acids and fatty acyl CoA esters on Cu(2+)-induced conversion of xanthine dehydrogenase to oxidase in rabbit liver were examined. Cu2+ (2-10 microM) brought about the conversion of xanthine dehydrogenase to oxidase in a dose-dependent manner. Oleic, arachidonic, eicosapentaenoic, and docosahexaenoic acids (50-200 microM) prevented the conversion of xanthine dehydrogenase to oxidase catalyzed by 6 microM-Cu2+. The effect of these four fatty acids was concentration-dependent, whereas palmitic, stearic, and linoleic acids had no effect on the conversion of xanthine dehydrogenase to oxidase at the same concentration range. On the other hand, palmitoyl, linoleoyl, and arachidonoyl CoAs elicited the inhibition of 6 microM-Cu(2+)-induced conversion of xanthine dehydrogenase to oxidase at concentrations of 50, 100, and 200 microM. These results suggest that oleic, arachidonic, eicosapentaenoic and docosahexaenoic acids, and fatty acyl CoAs have the potential to inhibit the conversion of xanthine dehydrogenase to oxidase in rabbit liver.

Studies of diagnosis and pathogenesis of Wilson's disease

We have studied the copper and metallothionein (MT) in culture skin fibroblasts of patients and heterozygotes with Wilson's disease (WD) and controls (5 cases each) after incubation in mediums containing various concentrations of copper (C1: 15.74 mumol/L, C2: 78.70 mumol/L, C3: 157.38 mumol/L, C4: 314.76 mumol/L). The results are as follows: 1. In each of the three groups, the copper/protein ratio (Cu/P) in cytosols of 1-5 passages is significantly higher than that of 6-10, 11-15, 16-20 passages. There are no significant differences among 6-10, 11-15 and 16-20 passages. 2. In standard medium, Cu/P in cytosols of three groups are not significantly different, but Cu/P of patients is significantly higher than that of the other two groups after incubation in C4 medium for 12 or 24 hours. 3. After incubation in C1, C2, C3 and C4 mediums respectively, the Cu/P in cytosols of the three groups only increased in C4 medium with time (within 72 hours). It is higher in the patient group than the other two groups. 4. In the three groups, cytosol copper distributed similarly in two peaks after Sephadex G-75 chromatography, which are on high molecular weight (HMW) proteins and MT fractions respectively. It remained the same after incubation in various concentrations of copper. The copper content found in MT fractions in WD patients is much higher than that of controls and heterozygotes. It is even higher after incubation in various concentrations of copper but no changes was found in controls and heterozygotes.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypochlorous acid-induced zinc release from thiolate bonds: a potential protective mechanism towards biomolecules oxidant damage during inflammation

It has been proposed that metalloprotein zinc mobilization mediated by hypochlorous acid (HOCl) may induce cell injury (see H. Fliss and M. Ménard (1991), Archives of Biochemistry and Biophysics, 287, 175-179). In the present paper, we have demonstrated using a dimercaptopropanol-zinc complex that, once released from thiolate bonds by HOCl, zinc can exert a significant antioxidant effect on both linolenic acid and deoxyribose oxidation induced by iron. In these experimental conditions, however, the antagonism towards deoxyribose oxidation is notably less than that towards linolenic acid peroxidation, thus suggesting a more specific inhibitory effect of zinc on iron-mediated oxidant damage when polyunsaturated fatty acids represent the oxidizable substrate. The antioxidant effects of zinc are strictly related to the "free" form; indeed, the dimercaptopropanol-zinc complex per se is stimulatory even on biomolecules oxidant damage, apparently as a result of the prooxidant prooxidant interaction of the thiol compound with iron. In light of these results, it may be proposed that the zinc released from thiolate bonds by HOCl could specifically limit tissue oxidative burden in pathological conditions involving neutrophil accumulation and activation, such as inflammation and ischemia-reperfusion.

An X-ray absorption study of the reconstitution process of bovine Cu,Zn superoxide dismutase by Cu(I)-glutathione complex

The Cu(I)GSH complex has recently been shown to be a good candidate for delivering copper to the active site of Cu-free Cu,Zn superoxide dismutase both in vivo and in vitro. In this work X-ray absorption spectroscopy has been used to characterize the Cu(I)GSH complex and to follow in vitro the reconstitution of Cu,Zn superoxide dismutase from the copper-free protein and this complex. The results obtained indicate that the copper is directly transferred as Cu(I) from the GSH complex into the empty copper binding site. No evidence has been obtained for a ternary complex in which the metal is bound to both GSH and the protein.

Oxidant-induced mobilization of zinc from metallothionein

Neutrophils which accumulate at sites of inflammation secrete a number of injurious oxidants which are highly reactive with protein sulfhydryls. The present study examined the possibility that this reactivity with thiols may cause protein damage by mobilizing zinc from cellular metalloproteins in which the metal is bound to cysteine. The ability of the three principal neutrophil oxidants, hypochlorous acid (HOCl), superoxide (.O2-), and hydrogen peroxide (H2O2), to cleave thiolate bonds and mobilize complexed zinc was compared using two model compounds (2,3-dimercaptopropanol and metallothionein peptide fragment 56-61), as well as metallothionein. With all compounds, 50 microM HOCl caused high rates of Zn2+ mobilization as measured spectrophotometrically with the metallochromic indicator 4-(2-pyridylazo)resorcinol. Xanthine (500 microM) plus xanthine oxidase (30 mU), which produced a similar concentration of .O2-, also effected a rapid rate of Zn2+ mobilization which was inhibited by superoxide dismutase but not catalase, indicating that .O2- is also highly reactive with thiolate bonds. In contrast, H2O2 alone was much less reactive at comparable concentrations. These data suggest that HOCl and .O2- can cause damage to cellular metalloproteins through the mobilization of complexed zinc. In view of the essential role played by zinc in numerous cellular processes, Zn2+ mobilization by neutrophil oxidants may cause significant cellular injury at sites of inflammation.

Hypochlorous acid-induced mobilization of zinc from metalloproteins

Hypochlorous acid (HOCl), a neutrophil oxidant, can contribute to tissue injury at sites of inflammation by its reactivity with protein sulfhydryls. The present study shows that physiological concentrations (50-200 microM) of HOCl can displace Zn2+ from metalloproteins, such as metallothionein and alcohol dehydrogenase, in which the metal is bound to sulfhydryls by means of thiolate (S-Zn) bonds. No mobilization of Zn2+ was observed from superoxide dismutase in which the metal is not bound to cysteine, suggesting that HOCl reacts selectively with thiolate bonds. Zn2+ mobilization, measured spectrophotometrically with the metallochromic indicator 4-(2-pyridylazo)resorcinol, was also observed from complexes of this metal with other thiol-containing compounds such as 2,3-dimercaptopropanol and metallothionein fragment 56-61. HOCl cleavage of the thiolate bonds was confirmed by the decrease in absorbance at 250 nm. This study shows for the first time that HOCl can mobilize protein-bound Zn2+ and suggests that neutrophil oxidant injury may be partially mediated by the mobilization of cellular Zn2+.

Hereditary low level of plasma ceruloplasmin in LEC rats associated with spontaneous development of hepatitis and liver cancer

Both young (5 weeks old) and old (61-100 weeks old) hereditary hepatitis LEC rats showed a markedly low level of plasma ceruloplasmin (Cp) ferroxidase activity as compared with that of age-matched LEA and BN strain rats. This trait was genetically examined by the use of (BN x LEC) F1 hybrid and (F1 x LEC) backcross rats. The F1 hybrids never developed hepatitis and showed a similar level of Cp to that found in the parental BN rats. Among the backcross rats with about 1:1 segregation rate for hepatitis, affected rats had a remarkably decreased level of Cp, as found in LEC rats, whereas unaffected rats exhibited a similar level of Cp to that of BN, F1 and LEA rats. These results indicate that the low level of Cp is heritable in a single autosomal recessive mode in LEC rats. The observed tight link between the low Cp level and the hepatitis in LEC rats suggests that defective copper metabolism may be associated with the occurrence of hepatitis in LEC rats, since Cp is a copper-binding protein primarily involved in copper transport from the liver.

Studies on plantacyanin. IV. Reconstitution with Cu-thionein, oxidation by cytochrome oxidase and autooxidation in the presence of cardiolipin

Cu-thionein isolated from cucumber roots was used for reconstitution of plantacyanin from cucumber. The rate of the copper transfer from Cu-thionein to apoplantacyanin was found to depend on pH, ionic strength and concentrations of the proteins. The rate of reconstitution with Cu-thionein was 10-times higher than with copper ions. No intermediate was observed during reconstitution with Cu-thionein. The incubation of oxidized holoplantacyanin with Cu-thionein or apothionein brings about the reduction of plantacyanin copper. This process, however, was found to be slow as compared to the rate of copper transfer from Cu-thionein to apoplantacyanin. Cytochrome oxidase from heart mitochondria was detected to possess some plantacyanin oxidase activity with the turnover number 5 min-1. The activity of the enzyme towards plantacyanin as well as with cytochrome c as a substrate was established to be lipid and ionic strength-dependent, and it was inhibited by CN- and N3-. Lineweaver-Burk plots show that the inhibitory effect of ionic strength on plantacyanin oxidase activity is connected with changes of Michaelis constant rather than of the maximal rate. Plantacyanin which is known to be very resistant towards many cationic, anionic and nonionic detergents, becomes, as well as cytochrome c, autooxidable in the presence of cardiolipin.

Reconstitution of neurocupreins by Cu-thioneins

Cu-thioneins isolated from liver and brains are able to transfer their copper atoms to apoforms of neurocuprein 1 and 2. At the same time, the apoform of Cu-thionein is unable to accept copper from holoforms of both neurocupreins.

Cu(I)-thionein release from copper-loaded yeast cells

The release of intact Cu(I)8-thionein from copper-resistant copper-loaded yeast cells, strain X2180-1Aa, has been shown. This copper(I)-thiolate-rich protein was characterized and compared with the chemical and physiocochemical properties of intracellular yeast Cu-thionein. The same molecular mass and stoichiometry of 8 mol copper atoms/mol protein was found. No detectable difference between the Cu-thioneins was seen in luminescence emission, electronic absorption in the ultraviolet region, chiroptical data or amino acid composition. The importance of stable Cu(I)-thiolates in Cu-thionein as a safe vehicle for transporting copper in a non-reactive manner is confirmed.

Copper-thionein in leucocytes

Upon incubation of peripheral leucocytes with copper sulphate a dramatic cellular copper uptake reaching levels of 25-50-fold compared to that of the natural copper content was measured. The orange-red fluorescence of the copper-treated white blood cells was assigned to the formation of Cu(I)-thiolate clusters in Cu(I)-thionein. A protein of 6-8 kDa was isolated from homogenized bovine leucocytes and characterized by its electronic absorption and amino acid composition to be identical to the above Cu(I)-thionein. More than 70% of the intracellular copper was attributed to this protein in its monomeric and polymeric form. Cu-thionein formation was more pronounced in monocytes than in granulocytes. As most intriguing phenomenon, the release of this Cu-thionein from leucocytes, was also noticed. The occurrence of Cu-thionein in leucocytes and the excretion of the intact Cu(I)-thiolate protein is of considerable interest with respect to the observed elevated copper levels in white blood cells and plasma during tumor malignancies and inflammatory processes.

On the copper transfer between dopamine beta-monooxygenase and Cu-thionein

Metallothionein saturated with copper is able to donate copper to apodopamine beta-monooxygenase. The complete recovery of dopamine beta-monooxygenase activity is observed at the molar ratio Cu-thionein/apoenzyme of 25. On the other hand, apothionein accepts copper easily from the holoenzyme.

Release of copper from yeast copper-thionein after S-alkylation of copper-thiolate clusters

Our knowledge on the release of copper from Cu-thionein in biological systems is limited. Other than oxidative cleavage or direct transfer, the possibility of an alkylation mechanism seemed attractive. Iodoacetamide and methyl methanesulphonate were successfully employed to alkylate the Cu-thiolate sulphur atom of homogeneous Cu(I)-thionein from yeast. The alkylation caused a weakening of the Cu-S bonding, which led to the release of copper. After equilibrium dialysis a proportion of the released copper was found in the dialysis buffer. When iodoacetamide was used carboxymethylcysteine was detected in the protein hydrolysate. A 10-fold molar excess over cysteine was sufficient for complete alkylation, which could be conveniently monitored by c.d. at 328 and 359 nm. The reaction proceeded under both aerobic and anaerobic conditions. E.p.r. measurements of Cu2+ revealed unequivocally the complete cleavage of the Cu-thiolate bonding in less than 5 h. It is possible that this mode of copper release might be of relevance to the molecular transport of this biochemically important transition metal.