Mechanisms by which cysteine can inhibit or promote the oxidation of low density lipoprotein by copper

Copper Speciation Evolution in Swine Manure Induced by Pyrolysis

Swine manures generally contain high levels of copper (Cu) resulting from its use as a growth promoter in feedstuff. Pyrolysis can further concentrate Cu whereas decrease its available fraction in swine manures. Here we investigated the speciation transformation of Cu and associated elements in swine manures induced by pyrolysis using multiple X-ray absorption spectroscopies. Results showed that over 82% of Cu existed as Cu(I)-S and Cu(I)-thiolate complexes in swine manures, which were transformed into stable Cu(I)₂S during pyrolysis at a low temperature of 300 °C and partially oxidized and desulfurized into Cu(II) compounds at a high temperature of 500 °C. The speciation evolution of Cu in swine manures was consistent with the speciation distribution of sulfur in feedstuff and its following changes in swine manures during pyrolysis. About 58% of phosphorus existed as CaHPO₄ and struvite in swine manures, which were gradually transformed into stable Ca-bound species such as hydroxyapatite during pyrolysis. The formation of stable phosphate, together with concentrated carbonates, significantly decreased the available Cu in pyrolyzed manures. These findings suggested that the high levels of S and P in feedstuff profoundly affected the speciation of Cu in the swine manures and derived biochars. This study has important implications to our understanding of the behaviors of heavy metals in manure-derived biochars once entering soil environments.

Plasma B-vitamins and one-carbon metabolites and the risk of breast cancer in younger women

PURPOSE

We examined the association of plasma B-vitamins and metabolites, and related genetic variants, with risk of breast cancer among predominantly premenopausal women.

METHODS

We conducted a nested case-control study within the Nurses' Health Study II. From blood samples collected in 1996-1999 and follow-up through 2007, plasma measures were available for 610 cases and 1207 controls. Unconditional multivariable logistic regression was used to estimate relative risks (RR) of breast cancer and 95% confidence intervals (CIs). We examined whether associations varied by methylenetetrahydrofolate reductase (MTHFR) and dihydrofolate reductase polymorphisms, breast cancer risk factors, or tumor characteristics.

RESULTS

Plasma vitamin B₁₂ was associated with a 64% higher risk of breast cancer comparing the highest versus lowest quintile (95% CI 1.17-2.29, p-trend = 0.02). Plasma folate (comparable RR = 1.18, 95% CI 0.84-1.66), pyridoxal 5'-phosphate (RR = 1.18, 95% CI 0.85-1.64), homocysteine (RR = 0.93, 95% CI 0.67-1.28), cysteine (RR = 1.14, 95% CI 0.81-1.62), and cysteinylglycine (RR = 0.93, 95% CI 0.66-1.31) were not associated with overall breast cancer risk. Folate was significantly positively associated with invasive and estrogen receptor-positive/progesterone receptor-positive breast cancer, and this association was suggestively stronger for bloods collected post-fortification. Several nutrient/breast cancer associations varied across subgroups defined by age, smoking, alcohol, multivitamin use, and MTHFR status (p-interaction < 0.05).

CONCLUSIONS

Overall, plasma B-vitamins and metabolites were not associated with lower breast cancer risk. Plasma vitamin B-12 was positively associated with higher risk of overall breast cancer, and plasma folate was positively associated with risk of invasive breast cancer. Additionally, there may be associations in subgroups defined by related genetic variants, breast cancer risk factors, and tumor factors. Further studies in younger women and in the post-fortification era are needed to confirm these findings.

Thiol oxidase ability of copper ion is specifically retained upon chelation by aldose reductase

Bovine lens aldose reductase is susceptible to a copper-mediated oxidation, leading to the generation of a disulfide bridge with the concomitant incorporation of two equivalents of the metal and inactivation of the enzyme. The metal complexed by the protein remains redox active, being able to catalyse the oxidation of different physiological thiol compounds. The thiol oxidase activity displayed by the enzymatic form carrying one equivalent of copper ion (Cu₁-AR) has been characterized. The efficacy of Cu₁-AR in catalysing thiol oxidation is essentially comparable to the free copper in terms of both thiol concentration and pH effect. On the contrary, the two catalysts are differently affected by temperature. The specificity of the AR-bound copper towards thiols is highlighted with Cu₁-AR being completely ineffective in promoting the oxidation of both low-density lipoprotein and ascorbic acid.

Homocysteine levels in Takayasu arteritis -- a risk factor for arterial ischemic events

OBJECTIVE

To evaluate homocysteine levels in patients with Takayasu arteritis (TA) and in controls, and to analyze associations between homocysteine levels and paraoxonase 1 (PON1) activity, cysteine levels, methotrexate use, disease activity, extent of arterial involvement, and ischemic events in patients with TA.

METHODS

A cross-sectional study was performed with 29 patients with TA and 30 controls who underwent clinical evaluation and blood sample collection in the fasting state.

RESULTS

Among patients with TA, active disease was observed in 9 (31.0%) and previous arterial ischemic events in 10 (34.5%). Therapy with methotrexate was prescribed to 9 (31.0%) patients and it was associated with folic acid in 8 cases. Median homocysteine level was higher in patients with TA [10.9 μmol/l, interquartile range (IQR) 9.6-14.8] than in controls (6.9 μmol/l, IQR 5.1-11.9; p < 0.001). No difference was found regarding mean homocysteine levels between those using methotrexate and those under other therapies (12.8 ± 5.3 μmol/l vs 12.1 ± 3.2 μmol/l, respectively; p = 0.662). TA patients with active disease presented lower homocysteine levels (10.4 ± 2.1 μmol/l) compared to TA patients in remission (13.1 ± 4.2 μmol/l) (p = 0.034). A significant correlation was found between cysteine and homocysteine levels in patients with TA (ρ = 0.676, p < 0.0001), while there was no correlation between homocysteine and PON1 activity (ρ = 0.214, p = 0.265). Median homocysteine levels were higher in patients with ischemic events (13.2 μmol/l, IQR 10.9-17.5) compared to patients with no ischemic events (9.8 μmol/l, IQR 8.7-14.7; p = 0.027) and were associated with arterial ischemia in patients with TA (OR 1.31, 95% CI 1.01-1.71, p = 0.041).

CONCLUSION

Patients with TA presented higher homocysteine levels than controls and homocysteine was associated with an increased risk of arterial ischemic events in TA.

Plasma total cysteine and cardiovascular risk burden: action and interaction

We hypothesized that redox analysis could provide sensitive markers of the oxidative pathway associated to the presence of an increasing number of cardiovascular risk factors (RFs), independently of type. We classified 304 subjects without cardiovascular disease into 4 groups according to the total number of RFs (smoking, hypertension, hypercholesterolaemia, hyperhomocysteinaemia, diabetes, obesity, and their combination). Oxidative stress was evaluated by measuring plasma total and reduced homocysteine, cysteine (Cys), glutathione, cysteinylglycine, blood reduced glutathione, and malondialdehyde. Twenty-seven percent of subjects were in group 0 RF, 26% in 1 RF, 31% in 2 RF, and 16% in ≥3 RF. By multivariable ordinal regression analysis, plasma total Cys was associated to a higher number of RF (OR = 1.068; 95% CI = 1.027–1.110, P = 0.002). Total RF burden is associated with increased total Cys levels. These findings support a prooxidant effect of Cys in conjunction with RF burden, and shed light on the pathophysiologic role of redox state unbalance in preclinical atherosclerosis.

Dual role of selected antioxidants found in dietary supplements: crossover between anti- and pro-oxidant activities in the presence of copper

Overproduction of reactive oxygen species (ROS) in vivo can result in damage associated with many aging-associated diseases. Defenses against ROS that have evolved include antioxidant enzymes, such as superoxide dismutases, peroxidases, and catalases, which can scavenge ROS. In addition, endogenous and dietary antioxidants play an important role in moderating damage associated with ROS. In this study, we use four common dietary antioxidants to demonstrate that, in the presence of copper (cupric sulfate and cupric gluconate) and physiologically relevant levels of hydrogen peroxide, these antioxidants can also act as pro-oxidants by producing hydroxyl radicals. Using electron spin resonance (ESR) spin trapping techniques, we demonstrate that the level of hydroxyl radical formation is a function of the pH of the medium and the relative amounts of antioxidant and copper. On the basis of the level of hydroxyl radical formation, the relative pro-oxidant potential of these antioxidants is cysteine > ascorbate > EGCG > GSH. It has been reported that copper sequestered by protein ligands, as happens in vivo, loses its redox activity (diminishing/abolishing the formation of free radicals). However, in the presence of hydrogen peroxide, cysteine and GSH efficiently react with cupric sulfate sequestered with bovine serum albumin to generate hydroxyl radicals. Overall, the results demonstrate that in the presence of copper, endogenous and dietary antioxidants can also exhibit pro-oxidative activity.

Free-radical degradation of high-molecular-weight hyaluronan induced by ascorbate plus cupric ions. Testing of bucillamine and its SA981-metabolite as antioxidants

High-molecular-weight hyaluronan (HA) samples were exposed to free-radical chain-degradation reactions induced by ascorbate in the presence of Cu(II) ions - the so-called Weissberger's oxidative system. The concentrations of both reactants [ascorbate, Cu(II)] were comparable to those that may occur during an early stage of the acute phase of joint inflammation. The time-dependent changes of the viscosity of the HA solution in the absence of the substance tested were monitored by rotational viscometry. However, when the anti- or pro-oxidative effects of the antioxidants/drugs were investigated, their dose-dependency was also examined. Additionally, the anti-oxidative activities of these substances were screened by the well-established ABTS and DPPH decolorization assays. The actions of the disease-modifying anti-rheumatic drugs, namely bucillamine and D-penicillamine, were compared to those of L-cysteine and of SA981, the oxidized metabolite of bucillamine. The results indicated that bucillamine was the most efficient scavenger of hydroxyl- and/or peroxyl-type radicals, even at the lowest drug concentration. In contrast, SA981 demonstrated no scavenging activity against the aforementioned free radicals. D-Penicillamine and L-cysteine showed a dual effect, i.e. a pronounced anti-oxidative effect was, after a given time period, followed by a significant pro-oxidative effect.

Combination therapy with andrographolide and d-penicillamine enhanced therapeutic advantage over monotherapy with d-penicillamine in attenuating fibrogenic response and cell death in the periportal zone of liver in rats during copper toxicosis

Long treatment regime with d-penicillamine is needed before it can exert clinically meaningful benefits in the treatment of copper toxicosis. The consequence of long-term d-penicillamine treatment is associated with numerous side effects. The limitations of d-penicillamine monotherapy prompted us to search for more effective treatment strategies that could decrease the duration of d-penicillamine therapy. The present study was designed to evaluate the therapeutic potential of d-penicillamine in combination with another hepatoprotective drug, andrographolide in treatment of copper toxicosis in rats. d-penicillamine treatment led to the excretion of copper through urine. Addition of andrographolide to d-penicillamine regime appeared to increase protection of liver by increasing the biliary excretion of copper and reduction in cholestatic injury. The early removal of the causative agent copper during combination treatment was the most effective therapeutic intervention that contributed to the early rectification of fibrosis in liver. Combination treatment reduced Kupffer cells accumulation and TNFα production in liver of copper exposed rats. In particular, andrographolide mediated the anti-inflammatory effect by inhibiting the cytokine production. However, another possible mechanism of cytoprotection of andrographolide was decreasing mitochondrial production of superoxide anions that resulted in better restoration of mitochondrial dysfunction during combination therapy than monotherapy. Furthermore, ROS inhibition by combination regimen resulted in significant decline in activation of caspase cascade. Inhibition of caspases attenuated apoptosis of hepatocytes, induced by chronic copper exposure. In summary, this study suggested that added benefit of combination treatment over use of either agent alone in alleviating the hepatotoxicity and fibrosis associated with copper toxicosis.

Double edge redox-implications for the interaction between endogenous thiols and copper ions: In vitro studies

The present study investigated the redox-consequences of the interaction between various endogenous thiols (RSH)-glutathione, cysteine, homocysteine, gamma-glutamyl-cysteine, and cysteinyl-glycine- and Cu(2+) ions, in terms of their free radical-scavenging, ascorbate-oxidizing and O2(*-)-generating properties of the resulting mixtures. Upon a brief incubation (3-30 min) with Cu(2+), the free radical-scavenging properties (towards ABTS(*)(+) and DPPH(*)) and thiol-titratable groups of the RSH added to the mixtures decreased significantly. Remarkably, both effects were only partial, even in the presence of a large molar Cu(2+)-excess, and were unaffected despite increasing the incubation time. At equimolar concentrations, the RSH/Cu(2+) mixtures led to the formation of (EPR paramagnetic) Cu(II)-complexes that were time-stable and ascorbate-reducible, but redox-inactive towards oxygen. In turn, at a slight molar thiol-excess (3:1), the mixtures resulted in the formation of time-stable Cu(I)-complexes (EPR silent) that were unreactive towards ascorbate and oxygen. The only exception was seen for the thiol, glutathione, whose mixture with Cu(2+) mixture displayed a O2(*-)-generating capacity (cytochrome c- and lucigenin-reduction). The data indicate that, depending on their molar ratio, the interaction between Cu(2+) and the tested thiols would give place to mixtures containing either: (i) time-stable and ascorbate-reducible Cu(II)-complexes which display free radical-scavenging properties, or (ii) time-stable but redox-inactive towards oxygen Cu(I)-complexes. Among the latter, the only exception was that of glutathione.

Mechanism of the antioxidant to pro-oxidant switch in the behavior of dehydroascorbate during LDL oxidation by copper(II) ions

Oxidised low density lipoprotein (LDL) may be involved in the pathogenesis of atherosclerosis. We have therefore investigated the mechanisms underlying the antioxidant/pro-oxidant behavior of dehydroascorbate, the oxidation product of ascorbic acid, toward LDL incubated with Cu(2+) ions. By monitoring lipid peroxidation through the formation of conjugated dienes and lipid hydroperoxides, we show that the pro-oxidant activity of dehydroascorbate is critically dependent on the presence of lipid hydroperoxides, which accumulate during the early stages of oxidation. Using electron paramagnetic resonance spectroscopy, we show that dehydroascorbate amplifies the generation of alkoxyl radicals during the interaction of copper ions with the model alkyl hydroperoxide, tert-butylhydroperoxide. Under continuous-flow conditions, a prominent doublet signal was detected, which we attribute to both the erythroascorbate and ascorbate free radicals. On this basis, we propose that the pro-oxidant activity of dehydroascorbate toward LDL is due to its known spontaneous interconversion to erythroascorbate and ascorbate, which reduce Cu(2+) to Cu(+) and thereby promote the decomposition of lipid hydroperoxides. Various mechanisms, including copper chelation and Cu(+) oxidation, are suggested to underlie the antioxidant behavior of dehydroascorbate in LDL that is essentially free of lipid hydroperoxides.

Protective effects of endomorphins, endogenous opioid peptides in the brain, on human low density lipoprotein oxidation

Neurodegenerative disorders are associated with oxidative stress. Low density lipoprotein (LDL) exists in the brain and is especially sensitive to oxidative damage. Oxidative modification of LDL has been implicated in the pathogenesis of neurodegenerative diseases. Therefore, protecting LDL from oxidation may be essential in the brain. The antioxidative effects of endomorphin 1 (EM1) and endomorphin 2 (EM2), endogenous opioid peptides in the brain, on LDL oxidation has been investigated in vitro. The peroxidation was initiated by either copper ions or a water-soluble initiator 2,2'-azobis(2-amidinopropane hydrochloride) (AAPH). Oxidation of the LDL lipid moiety was monitored by measuring conjugated dienes, thiobarbituric acid reactive substances, and the relative electrophoretic mobility. Low density lipoprotein oxidative modifications were assessed by evaluating apoB carbonylation and fragmentation. Endomorphins markedly and in a concentration-dependent manner inhibited Cu2+ and AAPH induced the oxidation of LDL, due to the free radical scavenging effects of endomorphins. In all assay systems, EM1 was more potent than EM2 and l-glutathione, a major intracellular water-soluble antioxidant. We propose that endomorphins provide protection against free radical-induced neurodegenerative disorders.

Evidence of a distinct lipid fraction in historical parchments: a potential role in degradation?

Parchment, a biologically based material obtained from the processed hides of animals such as cattle and sheep, has been used for millennia as a writing medium. Although numerous studies have concentrated on the structure and degradation of collagen within parchment, little attention has been paid to noncollagenous components, such as lipids. In this study, we present the results of biochemical and structural analyses of historical and newly manufactured parchment to examine the potential role that lipid plays in parchment stability. The lipid fraction extracted from the parchments displayed different fatty acid compositions between historical and reference materials. Gas chromatography, small-angle X-ray scattering, and solid-state NMR were used to identify and investigate the lipid fraction from parchment samples and to study its contribution to collagen structure and degradation. We hypothesize that the origin of this lipid fraction is either intrinsic, attributable to incomplete fat removal in the manufacturing process, or extrinsic, attributable to microbiological attack on the proteinaceous component of parchments. Furthermore, we consider that the possible formation of protein-lipid complexes in parchment over the course of oxidative degradation may be mediated by reactive oxygen species formed by lipid peroxidation.

Antioxidant action of eugenol compounds: role of metal ion in the inhibition of lipid peroxidation

Antioxidant action of eugenol compounds was analyzed in relation to the role of transition metal. Iron-mediated lipid peroxidation and autooxidation of Fe2+ ion were inhibited markedly by isoeugenol, and less effectively by eugenol. Copper-dependent oxidation of low density lipoprotein (LDL) was potently inhibited by eugenol and isoeugenol to the same extent: eugenol compounds showed protective effects by prolonging lag phase and by suppressing propagation rate in the absence and presence of alpha-tocopherol. Inhibition of LDL oxidation by eugenol compounds was closely related to activities reducing copper and scavenging a stable radical, 1,1'-diphenyl-2-picrylhydrazyl (DPPH). Antioxidant properties of eugenol compounds can be explained by forming complexes with reduced metals. Potent inhibitory effect of isoeugenol on lipid peroxidation may be related to the decreased formation of perferryl ion or the iron-oxygen chelate complex as the initiating factor of lipid peroxidation by keeping iron at a reduced state. Inhibition of LDL oxidation by eugenol compounds is due to the suppression of free radical cascade of lipid peroxidation in LDL by reducing copper ion.