Comparative time-courses of copper-ion-mediated protein and lipid oxidation in low-density lipoprotein

Human papillomavirus infection, cervical cancer and the less explored role of trace elements

Cervical cancer is an aggressive type of cancer affecting women worldwide. Many affected individuals rely on smear tests for the diagnosis, surgery, chemotherapy, or radiation for their treatment. However, due to a broad set of undesired results and side-effects associated with the existing protocols, the search for better diagnostic and therapeutic interventions is a never-ending pursuit. In the purview, the bio-concentration of trace elements (copper, selenium, zinc, iron, arsenic, manganese, and cadmium) is seen to fluctuate during the occurrence of cervical cancer and its progression from pre-cancerous to metastatic nature. Thus, during the occurrence of cervical cancer, the detection of trace elements and their supplementation will prove to be highly advantageous in developing diagnostic tools and therapeutics, respectively. This review provides a detailed overview of cervical cancer, its encouragement by human papillomavirus infections, the mechanism of pathology, and resistance. Majorly, the review emphasizes the less explored role of trace elements, their contribution to the growth and inhibition of cervical cancer. Numerous clinical trials have been listed, thereby providing a comprehensive reference to the exploration of trace elements in the management of cervical cancer.

Reductions of copper ion-mediated low-density lipoprotein (LDL) oxidations of trypsin inhibitors, the sweet potato root major proteins, and LDL binding capacities

BACKGROUND

The root major proteins of sweet potato trypsin inhibitors (SPTIs) or named sporamin, estimated for 60 to 80% water-soluble proteins, exhibited many biological activities. The human low-density lipoprotein (LDL) showed to form in vivo complex with endogenous oxidized alpha-1-antitrypsin. Little is known concerning the interactions between SPTIs and LDL in vitro.

RESULTS

The thiobarbituric-acid-reactive-substance (TBARS) assays were used to monitor 0.1 mM Cu²⁺-mediated low-density lipoprotein (LDL) oxidations during 24-h reactions with or without SPTIs additions. The protein stains in native PAGE gels were used to identify the bindings between native or reduced forms of SPTIs or soybean TIs and LDL, or oxidized LDL (oxLDL). It was found that the SPTIs additions showed to reduce LDL oxidations in the first 6-h and then gradually decreased the capacities of anti-LDL oxidations. The protein stains in native PAGE gels showed more intense LDL bands in the presence of SPTIs, and 0.5-h and 1-h reached the highest one. The SPTIs also bound to the oxLDL, and low pH condition (pH 2.0) might break the interactions revealed by HPLC. The LDL or oxLDL adsorbed onto self-prepared SPTIs-affinity column and some components were eluted by 0.2 M KCl (pH 2.0). The native or reduced SPTIs or soybean TIs showed different binding capacities toward LDL and oxLDL in vitro.

CONCLUSION

The SPTIs might be useful in developing functional foods as antioxidant and nutrient supplements, and the physiological roles of SPTIs-LDL and SPTIs-oxLDL complex in vivo will investigate further using animal models.

Lipoproteins as targets and markers of lipoxidation

Lipoproteins are essential systemic lipid transport particles, composed of apolipoproteins embedded in a phospholipid and cholesterol monolayer surrounding a cargo of diverse lipid species. Many of the lipids present are susceptible to oxidative damage by lipid peroxidation, giving rise to the formation of reactive lipid peroxidation products (rLPPs). In view of the close proximity of the protein and lipid moieties within lipoproteins, the probability of adduct formation between rLPPs and amino acid residues of the proteins, a process called lipoxidation, is high. There has been interest for many years in the biological effects of such modifications, but the field has been limited to some extent by the availability of methods to determine the sites and exact nature of such modification. More recently, the availability of a wide range of antibodies to lipoxidation products, as well as advances in analytical techniques such as liquid chromatography tandem mass spectrometry (LC-MSMS), have increased our knowledge substantially. While most work has focused on LDL, oxidation of which has long been associated with pro-inflammatory responses and atherosclerosis, some studies on HDL, VLDL and Lipoprotein(a) have also been reported. As the broader topic of LDL oxidation has been reviewed previously, this review focuses on lipoxidative modifications of lipoproteins, from the historical background through to recent advances in the field. We consider the main methods of analysis for detecting rLPP adducts on apolipoproteins, including their advantages and disadvantages, as well as the biological effects of lipoxidized lipoproteins and their potential roles in diseases.

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Lipoproteins can be modified by reactive Lipid Peroxidation Products (rLPPs).

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Lipoprotein lipoxidation is known to occur in several inflammatory diseases.

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Biochemical, immunochemical and mass spectrometry methods can detect rLPP adducts.

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Due to higher information output, MS can facilitate localization of modifications.

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Antibodies against some rLPPs have been used to identify lipoxidation in vivo.

Oxidation of myofibrillar proteins and impaired functionality: underlying mechanisms of the carbonylation pathway

The potential impact of protein oxidation on the functional properties of myofibrillar proteins (MP) was investigated in the present study. To accomplish this purpose, myofibrillar proteins were oxidized in vitro for 12 days at 37 °C in the presence of Cu(2+), Fe(3+), and Mb in combination with H(2)O(2) and analyzed at sampling times for chemical changes induced by oxidative reactions and functional properties. The oxidation measurements included specific protein carbonyls (α-aminoadipic semialdehyde, AAS), advanced lysine oxidation products (α-aminoadipic acid, AAA, and Schiff bases), and thiobarbituric acid-reactive substances (TBARS). The factors and mechanisms involved in the oxidative degradation of lysine residues through the carbonylation pathway are precisely described. According to the present results, intense lipid and protein carbonylation, principally induced by Cu(2+)/systems, leads to a fast and severe loss of MP functionality, including impaired water-holding, foaming, and gelling capacities. The implication of Mb in the oxidation events enhances the production of AAA and Schiff bases, compromising to a larger extent the solubility of MP and worsening the aggregation and the gelling capacity. The connection between the oxidation-induced chemical changes and the loss of protein functionality is thoroughly discussed.

Free and Peptide-bound DOPA Can Inhibit Initiation of Low Density Lipoprotein Oxidation

Hydroxyl radicals have been shown to convert free tyrosine to 3,4-dihydroxyphenyl-alanine (DOPA) which has reducing properties. During protein or peptide oxidation such reducing species are also formed from tyrosine residues. Free DOPA or peptide-bound DOPA (PB-DOPA) is able to promote radical-generating events, facilitating the damage of biomolecules such as nucleic acids. Radical induced lipid oxidation in low density lipoprotein (LDL) transforms the lipoprotein into an atherogenic particle. As PB-DOPA has been found in atherosclerotic plaques, we tested the ability of free and PB-DOPA to influence LDL oxidation. Free DOPA, in contrast to tyrosine had strong inhibitory action on both, the copper-ion initiated and metal ion independent (AAPH-induced) lipid oxidation. Free DOPA also inhibited LDL oxidation induced by the copper transport protein ceruloplasmin. To test if PB-DOPA was also able to inhibit LDL oxidation, DOPA residues were generated enzymatically in the model peptides insulin and tyr-tyr-tyr, respectively. PB-DOPA formation substantially increased the ability of both molecules to inhibit LDL oxidation by copper or AAPH. We hypothesize that DOPA-peptides and -proteins may have the potential to act as efficacious antioxidants in the atherosclerotic plaque.

Evaluation of activity of selected antioxidants on proteins in solution and in emulsions

Protection against protein oxidation by lipophilic and hydrophilic antioxidants in model systems using bovine serum albumin (BSA) in solution alone, or in an emulsion with linolenic acid methyl ester (LnMe) was found to be strongly dependent on the oxidation initiator. Tocopherol, Trolox, or the carotenoids astaxanthin and canthaxanthin were incubated with BSA or BSA/LnMe and oxidation was initiated either with the water-soluble azo-initiator 2,2' azo-bis-(2-amidinopropane) hydrochloride (AAPH), or FeCl3 and ascorbate, or the Fenton system using FeCl2/EDTA/H2O2, or with the singlet oxygen generating species anthracene-9,10-dipropionic acid disodium 1,4 endoperoxide (NDPO2). The results show that all the antioxidants tested were inefficient in the system with FeCl3/ascorbate. However, with the other initiating agents, the hydrophilic antioxidant, Trolox, was the most effective in preventing both protein and lipid oxidation. In contrast the lipophilic antioxidants were ineffective in preventing oxidation of BSA in aqueous solution, but did show some moderate antioxidative activity on protein and lipid in the BSA/LnMe system. Using the singlet oxygen generating system it was also demonstrated that Trolox always provided better protection of the protein than tocopherol and the carotenoids in both the BSA and the BSA/LnMe systems. In conclusion, prevention of protein oxidation using a water-soluble antioxidant has a protective effect on the lipid fraction and this approach deserves further attention in complex biological systems.

Modified Low-Density Lipoproteins and High-Density Lipoproteins

It has long been known that the oxidative state of the various plasma lipoproteins modulates platelet aggregability, thereby contributing to atherogenesis. Low-density lipoprotein (LDL), occurring in vivo both in the native and oxidised forms, interacts directly with platelets, by binding to specific receptors. While the identity of the receptors for native LDL and some subfractions of high-density lipoproteins (HDL) remains disputed, apoE-containing HDL(2) binds to LRP8. The nature of these interactions as well as the distinction between candidate receptor proteins was elucidated using covalently modified apolipoproteins, which pointed to the participation of apolipoproteins in high affinity binding. However, the platelet effects initiated by binding of native lipoproteins remain controversial. Some of this ambiguity can be traced to the fact that native LDL inevitably undergoes substantial oxidisation upon modification, including by radiolabelling. The platelet-activating effects provoked by oxidised LDL are irrefutable, but many details remain unknown. The role of CD36 in platelet binding by oxidised LDL is well established, although additional receptors may exist. Much less is known about the interaction of oxidised HDL with platelets, since platelet activation was observed in some, but not all studies. Various frequently applied in vitro oxidation methods produce modified lipoprotein species that may not be relevant in vivo. Based on the reported modifications obtained by in vitro oxidation of LDL, early investigations focused mainly on the formation and the eventual effects of oxidised lipids. More recently, alterations to lipoproteins performed using hypochloric acid and myeloperoxidase redirected the attention to the role of modified apoproteins in triggering platelet responses.

Concentrations of iron correlate with the extent of protein, but not lipid, oxidation in advanced human atherosclerotic lesions

Previous studies have provided compelling evidence for the presence of oxidized proteins and lipids in advanced human atherosclerotic lesions. The catalyst responsible for such oxidation is unknown and controversial. We have previously provided evidence for elevated levels of iron in lesions. In this study we hypothesized that if iron ions catalyzed protein and lipid oxidation in the artery wall, then there should be a positive correlation between these parameters. Iron concentrations in ex vivo healthy human arteries and advanced carotid lesions were quantified by electron paramagnetic resonance spectroscopy. Four specific side-chain oxidation products of proteins, and the lipid oxidation products 7-ketocholesterol and cholesterol ester alcohols and hydroperoxides, were quantified by HPLC in the same samples used for the iron measurements. Parent amino acids, cholesterol, and cholesterol esters were also quantified. Statistically elevated levels of iron, cholesterol, cholesterol esters, 7-ketocholesterol, and cholesterol ester alcohols and hydroperoxides were detected in advanced lesions compared with healthy control tissue. Iron levels correlated positively and strongly with all four markers of protein oxidation, but not with either marker of lipid oxidation. These data support the hypothesis that elevated levels of iron contribute to the extent of protein, but not lipid, oxidation in advanced human lesions.

Effect of supplementation of vitamin E, vitamin C and reduced glutathione on copper ion induced lipoprotein oxidation in renal diseased patients-Anin vitro study

The oxidative modification of lipoprotein especially low density lipoprotein (LDL) plays a key role in the initiation and progression of atherosclerosis. Serum apolipoproteinB (apoB) level is found to be an important marker for atherosclerosis. The present paper focuses on the measurement of serum apoB levels and the effect of Vitamin E, Vitamin C and reduced glutathione on the copper ion induced oxidation of LDL + VLDL (VLDL-Very Low Density Lipoprotein) lipoprotein fraction isolated from the serum of chronic renal failure (CRF) and renal transplanted patients. The level of apoB is significantly higher in the serum of transplanted patients when compared to CRF patients and normal subjects. The level of TBARS formed in oxidized LDL + VLDL lipoprotein fraction of CRF and renal transplanted patients are significantly increased than normal even in the presence of antioxidants but the level of TBARS produced, with antioxidants is comparatively lesser than that produced by oxidized lipoprotein fraction without antioxidants. It may be concluded than that produced by oxidized lipoprotein fraction without antioxidants. It may be concluded that oxidation of LDL can be prevented at an earlier stage by Vitamin E supplementation. The supplementation with Glutathione serves as the best method of preventing the lipoprotein oxidation among the renal diseased patients.

Progressive dopamine neuron loss following supra-nigral lipopolysaccharide (LPS) infusion into rats exposed to LPS prenatally

Toxin-induced animal models of Parkinson's disease (PD) exhibit many of the same neuroinflammatory changes seen in patients suggesting a role for inflammation in DA neuron loss. Yet, despite this inflammation, the progressive loss of DA neurons that characterizes PD is rarely seen in animals. We infused lipopolysaccharide (LPS) or saline into 7-month-old rats that had been exposed to LPS or saline prenatally and assessed them for DA neuron loss and inflammatory measures (interleukin 1 beta, tumor necrosis factor-alpha, glutathione, and activated microglia) over a period of 84 days to examine the role of pre-existing inflammation in progressive DA neuron loss. LPS infusion into both prenatal treatment groups produced neuroinflammation during the 14 days of LPS infusion that subsequently reverted toward normal over the next 70 days. In animals with pre-existing inflammation (i.e., prenatal LPS), however, the acute changes seen were attenuated, but took much longer to return to normal suggesting a prolonged inflammatory response. These inflammatory changes were consistent with the greater acute DA neuron loss seen in the prenatal saline controls and the progressive DA neuron loss seen only in the animals exposed to LPS prenatally. Interestingly, both prenatal treatment groups exhibited increases in microglia over the entire 84-day course of the study. These data suggest that pre-existing neuroinflammation prolongs the inflammatory response that occurs with a second toxic exposure, which may be responsible for progressive DA neuron loss. This provides further support for the "multiple hit" hypothesis of PD.

Increased plasma concentrations of Palmitoylethanolamide, an endogenous fatty acid amide, affect oxidative damage of human low-density lipoproteins: An in vitro study

Fatty acid ethanolamides (NAEs) are naturally occurring hydrophobic molecules usually present in a very small amount in many mammalian tissues and cells. Moreover, these compounds have been isolated in mammalian biological fluids, such as blood. Palmitoylethanolamide (C16:0) (PEA) is a fully saturated NAE, which presents some possible pharmaceutical activities, such as anti-inflammatory and antinociceptive effects. PEA is physiologically present in the mammalian blood at concentrations ranging from 9.4 to 16.7 pmol/ml. Since increasing evidence indicates that oxidative modification of low-density lipoproteins (LDL) is an important determinant in atherogenesis, the aim of this study was to evaluate the effect of physiologically relevant concentrations of PEA on Cu2+-induced LDL oxidation (measured as conjugated dienes formation). Our experiments indicate both anti-oxidative and slightly pro-oxidative effects of PEA. The anti-oxidative effect is obtained at low PEA concentrations (0.01 and 0.1 microM), while the pro-oxidative effect is obtained at a higher PEA concentration (1 microM). Fluorescence and circular dichroism data indicate that the effect of PEA occurs mainly by affecting the conformational features of ApoB-100.

Chromium(V) Peptide Complexes: Synthesis and Spectroscopic Characterization

A series of stable Cr(V) model complexes that mimic the binding of Cr(V) to peptide backbones at the C-terminus of proteins have been prepared for N,N-dimethylurea derivatives of the tripeptides Aib3-DMF, AibLAlaAib-DMF, and AibDAlaAib-DMF (Aib = 2-amino-2-methylpropanoic acid, DMF = N,N-dimethylformamide). The Cr(ll) precursor complexes were synthesized by the initial deprotonation of the amide and acid groups of the peptide ligands in DMF with potassium tert-butoxide in the presence of CrCl2. The Cr(II) intermediates thus formed were then immediately oxidized to Cr(V) using tert-butyl hydroperoxide. Spectroscopic and mass-spectrometric analyses of the Cr(V) complexes showed that a new metal-directed organic transformation of the ligand had occurred. This involved a DMF solvent molecule becoming covalently bound to the amine group of the peptide ligand, yielding a urea group, and a third coordinated deprotonated urea nitrogen donor. A metal-directed oxidative coupling has been proposed as a possible mechanism for the organic transformation. The Cr(V/IV) reduction potential was determined for the three Cr(V) complexes using cyclic voltammetry, and in all cases it was quasi-reversible. These are the first isolated and fully characterized Cr(V) complexes with non-sulfur-containing peptide ligands.

Analysis of β-carotene absorbance for studying structural properties of human plasma low-density lipoproteins

A novel spectrophotometric assay for monitoring structural rearrangements of native low-density lipoproteins (LDL) is proposed. The approach is based on the analysis of the visible light absorbance maximum of lipoproteins at approximately 461 nm assigned to beta-carotene situated in the hydrophobic parts of LDL. It offers a direct method to study the surface-interior coupling of the lipoprotein particle under physiological conditions. The detected signal is intrinsic to LDL and responsible for the most of the beta-carotene signal from the whole plasma. The negligible interference of beta-carotene absorbance due to the high-density lipoproteins is experimentally verified. Since beta-carotene absorbance belongs to the visible spectral region, no spectral overlapping/artifacts in plasma are expected. The signal sensitivity has been studied through conformational changes of LDL induced by ionic strength, by temperature, and by ligand binding. The results of caffeine binding to LDL indicate that there could be only one dominant type of binding site for caffeine on LDL particles. It can be concluded that visible spectrum characteristics of beta-carotene molecules offer advantages in LDL ligand binding studies which can possibly be extended to monitor the interactions of LDL directly in plasma.

Protein hydroperoxides are a major product of low density lipoprotein oxidation during copper, peroxyl radical and macrophage-mediated oxidation

Damage to apoB100 on low density lipoprotein (LDL) has usually been described in terms of lipid aldehyde derivatisation or fragmentation. Using a modified FOX assay, protein hydroperoxides were found to form at relatively high concentrations on apoB100 during copper, 2,2'-azobis(amidinopropane) dihydrochloride (AAPH) generated peroxyl radical and cell-mediated LDL oxidation. Protein hydroperoxide formation was tightly coupled to lipid oxidation during both copper and AAPH-mediated oxidation. The protein hydroperoxide formation was inhibited by lipid soluble alpha-tocopherol and the water soluble antioxidant, 7,8-dihydroneopterin. Kinetic analysis of the inhibition strongly suggests protein hydroperoxides are formed by a lipid-derived radical generated in the lipid phase of the LDL particle during both copper and AAPH mediated oxidation. Macrophage-like THP-1 cells were found to generate significant protein hydroperoxides during cell-mediated LDL oxidation, suggesting protein hydroperoxides may form in vivo within atherosclerotic plaques. In contrast to protein hydroperoxide formation, the oxidation of tyrosine to protein bound 3,4-dihydroxyphenylalanine (PB-DOPA) or dityrosine was found to be a relatively minor reaction. Dityrosine formation was only observed on LDL in the presence of both copper and hydrogen peroxide. The PB-DOPA formation appeared to be independent of lipid peroxidation during copper oxidation but tightly associated during AAPH-mediated LDL oxidation.

Direct detection and quantification of transition metal ions in human atherosclerotic plaques: evidence for the presence of elevated levels of iron and copper

OBJECTIVE

The involvement of transition metals in atherosclerosis is controversial. Some epidemiological studies have reported a relationship between iron (Fe) and cardiovascular disease, whereas others have not. Experimental studies have reported elevated levels of iron and copper (Cu) in diseased human arteries but have often used methods that release metal ions from proteins.

METHODS AND RESULTS

In this study, we have used the minimally invasive technique of electron paramagnetic resonance (EPR) spectroscopy and inductively coupled plasma mass spectroscopy (ICPMS) to quantify iron and copper in ex vivo healthy human arteries and carotid lesions. The EPR spectra detected are characteristic of nonheme Fe(III) complexes. Statistically elevated levels of iron were detected in the intima of lesions compared with healthy controls (0.370 versus 0.022 nmol/mg tissue for EPR, 0.525 versus 0.168 nmol/mg tissue by ICPMS, P<0.05 in each cases). Elevated levels of copper were also detected (7.51 versus 2.01 pmol/mg tissue, lesion versus healthy control, respectively, P<0.05). Iron levels did not correlate with the gender or age of the donor, or tissue protein or calcium levels, but cholesterol levels correlated positively with iron accumulation, as measured by EPR.

CONCLUSIONS

These data support the hypothesis that iron accumulates in human lesions and may contribute to disease progression.

Glycation and glycoxidation of low-density lipoproteins by glucose and low-molecular mass aldehydes. Formation of modified and oxidized particles

Patients with diabetes mellitus suffer from an increased incidence of complications including cardiovascular disease and cataracts; the mechanisms responsible for this are not fully understood. One characteristic of such complications is an accumulation of advanced glycation end-products formed by the adduction of glucose or species derived from glucose, such as low-molecular mass aldehydes, to proteins. These reactions can be nonoxidative (glycation) or oxidative (glycoxidation) and result in the conversion of low-density lipoproteins (LDL) to a form that is recognized by the scavenger receptors of macrophages. This results in the accumulation of cholesterol and cholesteryl esters within macrophages and the formation of foam cells, a hallmark of atherosclerosis. The nature of the LDL modifications required for cellular recognition and unregulated uptake are poorly understood. We have therefore examined the nature, time course, and extent of LDL modifications induced by glucose and two aldehydes, methylglyoxal and glycolaldehyde. It has been shown that these agents modify Arg, Lys and Trp residues of the apoB protein of LDL, with the extent of modification induced by the two aldehydes being more rapid than with glucose. These processes are rapid and unaffected by low concentrations of copper ions. In contrast, lipid and protein oxidation are slow processes and occur to a limited extent in the absence of added copper ions. No evidence was obtained for the stimulation of lipid or protein oxidation by glucose or methylglyoxal in the presence of copper ions, whereas glycolaldehyde stimulated such reactions to a modest extent. These results suggest that the earliest significant events in this system are metal ion-independent glycation (modification) of the protein component of LDL, whilst oxidative events (glycoxidation or direct oxidation of lipid or proteins) only occur to any significant extent at later time points. This 'carbonyl-stress' may facilitate the formation of foam cells and the vascular complications of diabetes.