Inhibition copper

Tea extracts and tea polyphenols inhibit copper- and peroxide-induced oxidation of LDL in vitro (116,123,124). The inhibitory concentration for 50% reduction (IC q) values for inhibition of copper-induced oxidation of LDL by some phenoHc antioxidants are Hsted in Table 7. The IC q for epigaHocatechin gaHate was found to be 0.075 p.mM, which was the most potent of all the phenoHc antioxidants tested (123,124). Similar results have been reported elsewhere (115,116,125,126). 

Dissimilar metals in the same system Because of the specific action of many inhibitors towards particular metals, problems arise in systems containing more than one metal. In the majority of cases these problems can be overcome by the choice of a formulation incorporating inhibitors for the protection of each of the metals involved. With this procedure it is necessary not only to maintain an adequate concentration of each of the inhibitors but also to ensure that they are present in the correct proportion. This is because of two effects firstly, failure to inhibit the corrosion of one metal may intensify the attack on the other metal the best example of this is with aluminium and copper in the same system, and failure to inhibit copper corrosion — usually achieved with sodium mercaptobenzothiazole or benzotriazole—can lead to increased corrosion of the aluminium as a result of deposition of copper from copper ions in solution on to the aluminium surface. Secondly, an inhibitor of the corrosion of one metal may actually intensify the corrosion of another metal. Thus, benzoate is usually used to prevent the corrosion of soldered joints by nitrite inhibitor added to protect cast iron in the same system. A benzoate nitrite ratio of greater than 7 1 is necessary in these cases. 

KERRY N and ABBEY M (1998) The isoflavone genistein inhibits copper and peroxyl radical mediated low density lipoprotein oxidation in vitro. Atherosclerosis. 140 (2) 341-7. 

Red wine contains quercetin, rutin, catechin, and epicatechin, among other flavonoids (Frankel and others 1993). Quercetin and other phenolic compounds isolated from wines were found to be more effective than a-tocopherol in inhibiting copper-catalyzed LDL oxidation. It has been determined that quercetin has also several anti-inflammatory effects it inhibits inflammatory cytokine production (Boots and others 2008), inducible NO synthase expression and activation of inflammatory transcription factors (Hamalainen and others 2007), and activity of cyclooxygenase and lipooxygenase (Issa 2006), among others. 

Contrary to LDL, high-density lipoproteins (HDL) prevent atherosclerosis, and therefore, their plasma levels inversely correlate with the risk of developing coronary artery disease. HDL antiatherogenic activity is apparently due to the removal of cholesterol from peripheral tissues and its transport to the liver for excretion. In addition, HDL acts as antioxidants, inhibiting copper- or endothelial cell-induced LDL oxidation [180], It was found that HDL lipids are oxidized easier than LDL lipids by peroxyl radicals [181]. HDL also protects LDL by the reduction of cholesteryl ester hydroperoxides to corresponding hydroperoxides. During this process, HDL specific methionine residues in apolipoproteins AI and All are oxidized [182]. 

Thomas and Jackson [329] have shown that ebselen inhibited copper-initiated LDL oxidation in the presence of glutathione. Noguchi et al. [330] showed that the inhibitory effect of ebselen on copper-initiated LDL was also observed without glutathione, while in the case of radical-initiated LDL oxidation ebselen was inactive. However, it is possible that ebselen may inhibit both copper- and peroxyl radical-initiated LDL oxidation although in the latter case the inhibitory effect of ebselen depends on the size of peroxyl radical flux [331]. The inhibitory effect of ebselen on LDL oxidation also depends on its ability to reduce LDL hydroperoxides. 

Thus, the mechanism of MT antioxidant activity might be connected with the possible antioxidant effect of zinc. Zinc is a nontransition metal and therefore, its participation in redox processes is not really expected. The simplest mechanism of zinc antioxidant activity is the competition with transition metal ions capable of initiating free radical-mediated processes. For example, it has recently been shown [342] that zinc inhibited copper- and iron-initiated liposomal peroxidation but had no effect on peroxidative processes initiated by free radicals and peroxynitrite. These findings contradict the earlier results obtained by Coassin et al. [343] who found no inhibitory effects of zinc on microsomal lipid peroxidation in contrast to the inhibitory effects of manganese and cobalt. Yeomans et al. [344] showed that the zinc-histidine complex is able to inhibit copper-induced LDL oxidation, but the antioxidant effect of this complex obviously depended on histidine and not zinc because zinc sulfate was ineffective. We proposed another mode of possible antioxidant effect of zinc [345], It has been found that Zn and Mg aspartates inhibited oxygen radical production by xanthine oxidase, NADPH oxidase, and human blood leukocytes. The antioxidant effect of these salts supposedly was a consequence of the acceleration of spontaneous superoxide dismutation due to increasing medium acidity. 

In mammals, cadmium inhibits copper absorption across the intestinal mucosa (Aaseth and Norseth 1986). Intercorrelations of copper with cadmium and zinc in livers of polar bears (Ursus maritimus) are probably mediated by metallothioneins, which may contain all three metals (Braune etal. 1991). In rats, copper protects against nephrotoxicity induced by cadmium, provided that copper is administered 24 h prior to cadmium insult. Specifically, rats given 12.5 mg Cu/kg BW by way of subcutaneous injection 24 h before receiving 0.4 mg Cd/kg BW — when compared to a group receiving Cd alone — did not have excessive calcium in urine and renal cortex or excessive protein in urine. Thus, 2.8 mg Cu/kg BW protects against 0.25 mg Cd/kg BW (Liu et al. 1992). 

Dopastin is an experimental antihypertensive agent which has been noted to potently inhibit copper-dependent dopamine p hydroxylase [100]. The pharmacological... 

As described earlier, the native copper oxide structures formed in the presence of an oxidizer under certain pH conditions can prevent the free dissolution of copper into copper ions. In addition to such oxide structures, there are at least three other types of layers that can accumulate on the oxidized copper surface to inhibit copper corrosion ... 

Figure 7.15 also demonstrates the importance of the NH3 complexing agent in the Cu(N03)2 slurry. Recall from Section 4.6.5 that the copper polish rate decreases when Cu(N03)2 is added to the H2O only slurry. In the H20-only slurry, the increase in Cu ions inhibits dissolution of the abraded material. However, when the Cu(N03)2 is added to the 1 vol% NH4OH slurry, NH3 complexes the Cu " ions from the Cu(N03)2 salt so that the Cu ions do not inhibit copper dissolution. In addition, by complexing the Cu ions, the NH3 drives reaction (7.10) further to the right, increasing the supply of N03 . 

In products with complex combinations of various types of flavonoids and other phenolic compounds, effort has been made to ascribe the antioxidant activity of the product to different classes of polyphenols. Frankel et al. (1995) studied 20 selected California wines and related the antioxidant activity to the polyphenolic components of the wines, rather than to resveratrol. Antioxidant activity was measured by the ability of the wines to inhibit copper-catalyzed oxidation of human LDL. The correlation coefficient between antioxidant activity and total phenolic components of the wines was r = 0.94. Individual phenolic compounds (gallic acid, catechin, myricetin, quercetin, caffeic acid, rutin, epicatechin, cyanidin, malvidin-3-glucoside) contributed to the antioxidant activity. The correlation coefficient for the compounds ranged from r = 0.92 to r = 0.38 in descending order. 

Ide, N., Nelson, A.B. and Lau, B.H. (1996) Aged garlic extract and its consituents inhibit copper-induced oxidative modification of low density lipoprotein. Planta Med. 63 263. 

Treatment of active, symptomatic Wilson s disease is aimed at increasing urine copper excretion to eliminate excess copper from tissue. The primary therapy for Wilson s disease involves chelating agents such as o-penicillamine and trientine, which is now more widely used because of its lower rate of side effects. In patients with minimal symptoms or in asymptomatic family members, zinc is used to competitively inhibit copper absorption from the intestinal tract. Lifelong therapy with one of these types of treatment is required and is usually successful in limiting further damage. 

Figure 2.19 Rising chronoamperometric transients characterizing the activation of PEG-CI inhibited copper electrodes induced by gradual accumulation of SPS adsorbate at —0.25 V [12].

Other investigators have examined the potential antioxidant properties of habenariol [251] particularly to inhibit copper-induced lipid peroxidationof human low density lipoprotein (LDL). However, in both kinetic and end-point spectrophotometric assays, it was found to be less effective than a-tocopherol. 

There has been an increased interest in natural antioxidants from plant-derived foods and then-by-products for their role in preventing oxidation of human LDL cholesterol. Table 13.8 shows the inhibition of copper-induced human LDL oxidation by hazelnut extracts. Hazelnut skin and hazelnut green leafy cover extracts at 50 ppm concentration effectively inhibited copper-induced oxidation of... 

Respiration and Photosynthesis in Chlorella pyrenoidosa by Organic Compounds that Inhibit Copper Catalysis," J. Biol. Chem. 128 447 (1939). 

Marchantin H is a natural compound isolated from Marchantia diptera (Wu 1990). Marchantins are naturally phenolic structures isolated from different species of liverwort (Tori et al. 1985, Asakawa et al. 1987). Marchantin H could scavenge the stable free radical l,l-diphenyl-2-picrylhydrazyl and per-oxyl radical derived from 2,2 -azobis(2-amidino-propane) dihydrochloride in aqueous phase, but not the peroxyl radical derived from 2,2 -azobis (2,4-dimethylvaleronitrile) in hexane (Hsiao et al. 1996). It was reactive toward superoxide anion generated by the xanthine/xanthine oxidase system. Marchantin H inhibited copper-catalysed oxidation of human low-density lipoprotein, as measured by... 

---