Quantification of malondialdehyde and 4-hydroxynonenal adducts to lysine residues in native and oxidized human low-density lipoprotein

Modification of casein by the lipid oxidation product malondialdehyde

The reaction of malondialdehyde with casein was studied in aqueous solution to evaluate the impact of this lipid oxidation product on food protein modification. By using multiresponse modeling, a kinetic model was developed for this reaction. The influence of temperature and pH on protein browning and malondialdehyde degradation was evaluated. The hypothesis that one malondialdehyde unit leads to the cross-linking of two casein-bound lysine residues was in accordance with the data. At higher malondialdehyde concentrations, a different reaction mechanism was operative, probably involving a dihydropyridine cross-link. The results obtained were compared with the reaction of casein with 2-oxopropanal, a well-studied alpha-dicarbonyl compound. The reaction of casein with 2-oxopropanal followed a different reaction pathway. Comparison of the degree of browning of casein by reaction with malondialdehyde and 2-oxopropanal showed a considerably higher degree of browning induced by malondialdehyde. This research has shown that kinetic modeling is a useful tool to unravel reaction mechanisms. Clearly, the contribution of lipid oxidation products, such as malondialdehyde, to protein modification (both in food and in vivo) can be substantial and needs to be taken into account in future studies.

Mechanisms of oxidative modification of low density lipoproteins under conditions of oxidative and carbonyl stress

Low-molecular-weight aldehydes (glyoxal, methylglyoxal, 3-deoxyglucosone) generated on autooxidation of glucose under conditions of carbonyl stress react much more actively with amino groups of L-lysine and epsilon-amino groups of lysine residues of apoprotein B-100 in human blood plasma low density lipoproteins (LDL) than their structural analogs (malonic dialdehyde (MDA), 4-hydroxynonenal) resulting on free radical oxidation of lipids under conditions of oxidative stress. Glyoxal-modified LDL aggregate in the incubation medium with a significantly higher rate than LDL modified by MDA, and MDA-modified LDL are markedly more poorly absorbed by cultured human macrophages and significantly more slowly eliminated from the rat bloodstream upon intravenous injection. Studies on kinetics of free radical oxidation of rat liver membrane phospholipids have shown that ubiquinol Q(10) is the most active lipid-soluble natural antioxidant, and suppression of ubiquinol Q(10) biosynthesis by beta-hydroxy-beta-methylglutaryl coenzyme A reductase inhibitors (statins) is accompanied by intensification of lipid peroxidation in rat liver biomembranes and in LDL of human blood plasma. Injection of ubiquinone Q(10) protects the human blood plasma LDL against oxidation and prevents oxidative stress-induced damages to rat myocardium. A unified molecular mechanism of atherogenic action of carbonyl-modified LDL in disorders of lipid and carbohydrate metabolism is discussed.

Glycated LDL increases monocyte CC chemokine receptor 2 expression and monocyte chemoattractant protein-1-mediated chemotaxis

BACKGROUND

Previous reports have suggested that levels of advanced glycation end product-modified LDL (AGE-LDL) increase in patients with diabetes due to elevated plasma glucose. However, understanding of the mechanisms by which AGE-LDL may accelerate atherogenesis remains incomplete.

METHODS AND RESULTS

Microarray and reverse transcription real-time PCR (RT-PCR) analyses revealed that AGE-LDL significantly increased levels of CC chemokine receptor 2 (CCR2) mRNA in human macrophages compared with LDL, an effect accompanied by increased levels of CCR2 protein. Flow cytometry also showed that AGE-LDL increases CCR2 expression on the cell surface following stimulation (48h) (P<0.05). This effect appeared to depend on the receptor for AGE (RAGE), since an anti-RAGE antibody significantly blocked increased CCR2 mRNA. Functional studies demonstrated that exposure of THP-1 monocytoid cells to AGE-LDL increases chemotaxis mediated by monocyte chemoattractant protein-1 (MCP-1) up to 3-fold compared to LDL treatment (P<0.05).

CONCLUSIONS

These data show that AGE-LDL can increase CCR2 expression in macrophages and stimulate the chemotactic response elicited by MCP-1. This novel mechanism may contribute to accelerated atherogenesis in diabetic patients.

Site-specific Effects of Peptide Lipidation on β-Amyloid Aggregation and Cytotoxicity

Beta-amyloid (Abeta) aggregates at low concentrations in vivo, and this may involve covalently modified forms of these peptides. Modification of Abeta by 4-hydroxynonenal (4-HNE) initially increases the hydrophobicity of these peptides and subsequently leads to additional reactions, such as peptide cross-linking. To model these initial events, without confounding effects of subsequent reactions, we modified Abeta at each of its amino groups using a chemically simpler, close analogue of 4-HNE, the octanoyl group: K16-octanoic acid (OA)-Abeta, K28-OA-Abeta, and Nalpha-OA-Abeta. Octanoylation of these sites on Abeta-(1-40) had strikingly different effects on fibril formation. K16-OA-Abeta and K28-OA-Abeta, but not Nalpha-OA-Abeta, had increased propensity to aggregate. The type of aggregate (electron microscopic appearance) differed with the site of modification. The ability of octanoyl-Abeta peptides to cross-seed solutions of Abeta was the inverse of their ability to form fibrils on their own (i.e. Abeta approximately Nalpha-OA-Abeta>>K16-OA-Abeta>>K28-OA-Abeta). By CD spectroscopy, K16-OA-Abeta and K28-OA-Abeta had increased beta-sheet propensity compared with Abeta-(1-40) or Nalpha-OA-Abeta. K16-OA-Abeta and K28-OA-Abeta were more amphiphilic than Abeta-(1-40) or Nalpha-OA-Abeta, as shown by lower "critical micelle concentrations" and higher monolayer collapse pressures. Finally, K16-OA-Abeta and K28-OA-Abeta are much more cytotoxic to N2A cells than Abeta-(1-40) or Nalpha-OA-Abeta. The greater cytotoxicity of K16-OA-Abeta and K28-OA-Abeta may reflect their greater amphiphilicity. We conclude that lipidation can make Abeta more prone to aggregation and more cytotoxic, but these effects are highly site-specific.

HNE Michael adducts to histidine and histidine-containing peptides as biomarkers of lipid-derived carbonyl stress in urines: LC-MS/MS profiling in Zucker obese rats

A new liquid chromatography-tandem mass spectrometric (LC-MS/MS) approach, based on the precursor ion scanning technique using a triple-stage quadrupole, has been developed to detect free and protein-bound histidine (His) residues modified by reactive carbonyl species (RCS) generated by lipid peroxidation. This approach has been applied to urines from Zucker obese rats, a nondiabetic animal model characterized by obesity and hyperlipidemia, where RCS formation plays a key role in the development of renal and cardiac dysfunction. The immonium ion of His at m/z 110 was used as a specific product ion of His-containing peptides to generate precursor ion spectra, followed by MS2 acquisitions of each precursor ion of interest for structural characterization. By this approach, three novel adducts, which are excreted in free form only, have been identified, two of them originating from the conjugation of 4-hydroxy-trans-2-nonenal (HNE) to His, followed by reduction/oxidation of the aldehyde: His-1,4-dihydroxynonane (His-DHN), His-4-hydroxynonanoic acid (His-HNA), and carnosine-HNE, this last recognized in previous in vitro studies as a new potential biomarker of carbonyl stress. No free His-HNE was found in urines, which was detected only in protein hydrolysates. The same LC-MS/MS method, working in multiple reaction monitoring (MRM) mode, has been developed, validated, and applied to quantitatively profile in Zucker urines both conventional (1,4-dihydroxynonane mercapturic acid, DHN-MA) and the newly identified adducts, except His-HNA. The analytes were separated on a C12 reversed-phase column by gradient elution from 100% A (water containing 5 mM nonafluoropentanoic acid) to 80% B (acetonitrile) in 24 min at a flow rate of 0.2 mL/min and analyzed for quantification in MRM mode by applying the following precursor-to-product ion transitions m/z 322.2 --> 164.1 + 130.1 (DHN-MA), m/z 314.7 --> 268.2 + 110.1 (His-DHN), m/z 312.2 --> 110.1 + 156.0 (His-HNE), m/z 383.1 --> 266.2 + 110.1 (CAR-HNE), m/z 319.2 --> 301.6 + 156.5 (H-Tyr-His-OH, internal standard). Precision and accuracy data, as well as the lower limits of quantification in urine, were highly satisfactory (from 0.01 nmol/mL for CAR-HNE, His-DHN, His-HNE, to 0.075 nmol/mL for DHN-MA). The method, applied to evaluate for the first time the advanced lipoxidation end products profile in urine from obese Zucker rats, an animal model for the metabolic syndrome, has proved to be suitable and sensitive enough for testing in vivo the carbonyl quenching ability of newly developed RCS sequestering agents.

Methylglyoxal induces advanced glycation end product (AGEs) formation and dysfunction of PDGF receptor‐β: implications for diabetic atherosclerosis

PURPOSE

Low molecular weight carbonyl compounds, such as the alpha-ketoaldehydes methylglyoxal (MGO) and glyoxal (GO), are formed under hyperglycemic conditions and behave as advanced glycation end product (AGE) precursors. They form adducts on proteins, thereby inducing cellular dysfunctions involved in chronic complications of diabetes.

METHODS AND MAIN FINDINGS

Nontoxic concentrations of GO or MGO altered the PDGF-induced PDGFRbeta-phosphorylation, ERK1/2-activation, and nuclear translocation, and the subsequent proliferation of mesenchymal cells (smooth muscle cells and skin fibroblasts). This resulted mainly from inhibition of the intrinsic tyrosine kinase of PDGFRbeta and in part from altered PDGF-BB binding to PDGFRbeta. Concomitantly, the formation of AGE adducts (N(epsilon)carboxymethyl-lysine and N(epsilon)carboxyethyl-lysine) was observed on immunoprecipitated PDGFRbeta. Arginine and aminoguanidine, used as carbonyl scavengers, reversed the inhibitory effect and the formation of AGE adducts on PDGFRbeta. AGE-PDGFRbeta adducts were also detected by anti-AGE antibodies in PDGFRbeta immunopurified from aortas of diabetic (streptozotocin-treated) compared to nondiabetic apolipoprotein E-null mice. Mass spectrometry analysis of aortas demonstrated increased AGE formation in diabetic specimens.

CONCLUSIONS

These data indicate that MGO and GO induce desensitization of PDGFRbeta that helps to reduce mesenchymal cell proliferation.

New functions of glucosamine as a scavenger of the lipid peroxidation product malondialdehyde

Direct reaction between malondialdehyde (MDA) and glucosamine (GlcN) was studied using high-performance liquid chromatography, liquid chromatography/mass spectrometry, spectrophotometry, and spectrofluorometry. The results indicated that GlcN reacted readily with MDA at supraphysiological conditions to form different products, such as a nonfluorescent enamine with an absorption peak at 281 nm (product 1) and a lipofuscin-like fluorescent (Ex. 392 nm/Em. 454 nm) 1,4-dihydropyridine (product 2). GlcN also greatly inhibited the formation of lipofuscin-like fluorescence induced by MDA reacted with bovine serum albumin. The reaction of GlcN with MDA suggested a novel anticarbonylation function of GlcN in pathophysiological situations related to aging-related diseases and provided insight into the reaction mechanism of GlcN in protecting proteins against carbonyl stress.

Membrane-mediated amyloidogenesis and the promotion of oxidative lipid damage by amyloid beta proteins

Evidence of oxidative stress and the accumulation of fibrillar amyloid beta proteins (Abeta) in senile plaques throughout the cerebral cortex are consistent features in the pathology of Alzheimer disease. To define a mechanistic link between these two processes, various aspects of the relationship between oxidative lipid membrane damage and amyloidogenesis were characterized by chemical and physical techniques. Earlier studies of this relationship demonstrated that oxidatively damaged synthetic lipid membranes promoted amyloidogenesis. The studies reported herein specify that 4-hydroxy-2-nonenal (HNE) is produced in both synthetic lipids and human brain lipid extracts by oxidative lipid damage and that it can account for accelerated amyloidogenesis. Abeta promotes the copper-mediated generation of HNE from polyunsaturated lipids, and in turn, HNE covalently modifies the histidine side chains of Abeta. HNE-modified Abeta have an increased affinity for lipid membranes and an increased tendency to aggregate into amyloid fibrils. Thus, the prooxidant activity of Abeta leads to its own covalent modification and to accelerated amyloidogenesis. These results illustrate how lipid membranes may be involved in templating the pathological misfolding of Abeta, and they suggest a possible chemical mechanism linking oxidative stress with amyloid formation.

Lipofuscin-like fluorophores originated from malondialdehyde

The accumulation of fluorescent age pigment or lipofuscin is a frequently observed age-associated cellular alteration in a variety of post-mitotic cells of many species. These pigments are observed within granules composed, in part, of damaged protein and lipid. In the present mini-review, I provide a comprehensive summary of fluorescent adducts originated from malondialdehyde (MDA).

Enzyme-linked immunosorbent assay for 4-hydroxynonenal-histidine conjugates

Highly reactive aldehyde 4-hydroxynonenal (HNE) is the final product of lipid peroxidation, known as a second messenger of free radicals and a signaling molecule. It forms protein conjugates involved in pathology of various diseases. To determine cellular HNE-protein conjugates we developed indirect ELISA based on well-known, monoclonal antibody against HNE-histidine (HNE-His) adducts. The method was calibrated using HNE-albumin conjugates as standards (R(2) = 0.999) and validated on human osteosarcoma cell cultures (HOS). The ELISA showed good sensitivity (8.1 pmol HNE-His/mg of protein), precision ( +/- 8% intra-assay and +/- 12% inter-assay) and spiking recovery ( +/- 9%). The assay revealed 60-fold increase of cellular HNE-His adducts upon copper-induced lipid peroxidation of HOS. The ELISA matched HNE-immunocytochemistry of HNE-treated HOS cells and quantified the increase of cellular HNE-His conjugates in parallel to the decrease of free HNE in culture medium. The ELISA was developed as ELISA Stress for severe lipid peroxidation and ELISA Fine for studies on HNE physiology.

Lipid nitration and formation of lipid-protein adducts: biological insights

Lipid-protein adducts are formed during oxidative and nitrative stress conditions associated with increasing lipid and protein oxidation and nitration. The focus of this review is the analysis of interactions between oxidative-modified lipids and proteins and how lipid nitration can modulate lipid-protein adducts formation. For this, two biologically-relevant models will be analysed: a) human low density lipoprotein, whose oxidation is involved in the early steps of atherogenesis, and b) alpha-synuclein/lipid membranes system, where lipid-protein adducts are being associated with the develop of Parkinson disease and other synucleinopathies.

Oxidized proteins and their contribution to redox homeostasis

Proteins are major target for radicals and other oxidants when these are formed in both intra- and extracellular environments in vivo. Formation of lesions on proteins may be highly sensitive protein-based biomarkers for oxidative damage in mammalian systems. Oxidized proteins are often functionally inactive and their unfolding is associated with enhanced susceptibility to proteinases. ROS scavenging activities of intact proteins are weaker than those of misfolded proteins or equivalent concentrations of their constituent amino acids. Protein oxidation and enhanced proteolytic degradation, therefore, have been suggested to cause a net increase in ROS scavenging capacity. However, certain oxidized proteins are poorly handled by cells, and together with possible alterations in the rate of production of oxidized proteins, may contribute to the observed accumulation and damaging actions of oxidized proteins during ageing and in pathologies such as diabetes, arteriosclerosis and neurodegenerative diseases. Protein oxidation may play a controlling role in cellular remodelling and cell growth. There is some evidence that antioxidant supplementation may protect against protein oxidation, but additional controlled studies of antioxidant intake to evaluate the significance of dietary/pharmacological antioxidants in preventing physiological/pathological oxidative changes are needed.

Methionine restriction decreases mitochondrial oxygen radical generation and leak as well as oxidative damage to mitochondrial DNA and proteins

Previous studies have consistently shown that caloric restriction (CR) decreases mitochondrial reactive oxygen species (ROS) (mitROS) generation and oxidative damage to mtDNA and mitochondrial proteins, and increases maximum longevity, although the mechanisms responsible for this are unknown. We recently found that protein restriction (PR) also produces these changes independent of energy restriction. Various facts link methionine to aging, and methionine restriction (MetR) without energy restriction increases, like CR, maximum longevity. We have thus hypothesized that MetR is responsible for the decrease in mitROS generation and oxidative stress in PR and CR. In this investigation we subjected male rats to exactly the same dietary protocol of MetR that is known to increase their longevity. We have found, for the first time, that MetR profoundly decreases mitROS production, decreases oxidative damage to mtDNA, lowers membrane unsaturation, and decreases all five markers of protein oxidation measured in rat heart and liver mitochondria. The concentration of complexes I and IV also decreases in MetR. The decrease in mitROS generation occurs in complexes I and III in liver and in complex I in heart mitochondria, and is due to an increase in efficiency of the respiratory chain in avoiding electron leak to oxygen. These changes are strikingly similar to those observed in CR and PR, suggesting that the decrease in methionine ingestion is responsible for the decrease in mitochondrial ROS production and oxidative stress, and possibly part of the decrease in aging rate, occurring during caloric restriction.

Effect of graded corticosterone treatment on aging-related markers of oxidative stress in rat liver mitochondria

Caloric restriction (CR) decreases aging rate and lowers the rate of reactive oxygen species (ROS) production at mitochondria in different organs, but the signal responsible for this last change is unknown. Glucocorticoids could constitute such a signal since it is well known that their levels increase during CR, and available studies failed to find consistent effects of insulin, the other better described hormone that varies during CR, on mitochondrial oxidative stress. In addition, there is almost no information on the possible in vivo effects of glucocorticoids on specific markers of mitochondrial and tissue oxidative stress. In this investigation, male Wistar rats were treated with corticosterone at doses of 150 and 400 mg/kg of diet during 4 weeks. After that time, oxidative stress-related parameters were measured in the liver. The corticosterone treatments did not change the rate of ROS production or the rate of oxygen consumption of rat liver mitochondria. The two lipoxidation protein markers measured (malondialdehyde-lysine and carboxymethyllysine) were decreased by both corticosterone treatments. These changes were associated with decreases in fatty acid unsaturation, especially with lowered levels of the highly unsaturated araquidonic and docosahexaenoic acids, which decrease the sensitivity to lipid peroxidation processes. The specific protein carbonyl glutamic semialdehyde, a marker of protein oxidation, was also lowered at 400 mg/kg corticosterone. The protein glycoxydation marker carboxyethyllysine and the level of oxidative damage to mtDNA (8-oxo-7,8-dihydro-2 9-deoxyguanosine) were increased by corticosterone. The results do not support the idea that corticosterone is the signal responsible for the decrease in mitochondrial ROS generation during CR. However, they show that this hormone modulates the level of oxidative stress both in proteins and in mtDNA. Some of these changes can contribute to the chronic effects of the hormone at tissue level.

Effects of fasting on oxidative stress in rat liver mitochondria

While moderate caloric restriction has beneficial effects on animal health state, fasting may be harmful. The present investigation was designed to test how fasting affects oxidative stress, and to find out whether the effects are opposite to those previously found in caloric restriction studies. We have focused on one of the main determinants of aging rate: the rate of mitochondrial free radical generation. Different parameters related to lipid and protein oxidative damage were also analyzed. Liver mitochondria from rats subjected to 72 h of fasting leaked more electrons per unit of O(2) consumed at complex III, than mitochondria from ad libitum fed rats. This increased leak led to a higher free radical generation under state 3 respiration using succinate as substrate. Regarding lipids, fasting altered fatty acid composition of hepatic membranes, increasing the double bond and the peroxidizability indexes. In accordance with this, we observed that hepatic membranes from the fasted animals were more sensitive to lipid peroxidation. Hepatic protein oxidative damage was also increased in fasted rats. Thus, the levels of oxidative modifications, produced either indirectly by reactive carbonyl compounds (N(epsilon)-malondialdehyde-lysine), or directly through amino acid oxidation (glutamic and aminoadipic semialdehydes) were elevated due to the fasting treatment in both liver tissue and liver mitochondria. The current study shows that severe food deprivation increases oxidative stress in rat liver, at least in part, by increasing mitochondrial free radical generation during state 3 respiration and by increasing the sensitivity of hepatic membranes to oxidative damage, suggesting that fasting and caloric restriction have different effects on liver mitochondrial oxidative stress.

Contribution of mass spectrometry to assess quality of milk-based products

The vast knowledge of milk chemistry has been extensively used by the dairy manufacturing industry to develop and optimize the modern technology required to produce high-quality milk products to which we are accustomed. A thorough understanding of the chemistry of milk and its numerous components is essential for designing processing equipment and conditions needed for the manufacture and distribution of high-quality dairy products. Knowledge and application of milk chemistry is also indispensable for fractionating milk into its principal components for use as functional and nutritional ingredients by the food industry. For all these reasons, powerful analytical methods are required. Because of the complexity of the milk matrix, mass spectrometry, coupled or not to separation techniques, constitutes a key tool in this area. In the present manuscript, we review the contribution and potentialities of mass spectrometry-based techniques to assess quality of milk-based products.

Cysteine modification by lipid peroxidation products inhibits protein disulfide isomerase

A proteomic approach was applied to mitochondrial protein isolated from the livers of rats fed a combination high-fat and ethanol diet to identify proteins modified by 4-hydroxynonenal (4-HNE). Using this approach, the endoplasmic reticulum chaperone, protein disulfide isomerase (PDI), which participates in the maturation of newly synthesized proteins through promoting correct disulfide formation, was consistently found to be modified by 4-HNE. Further mass spectral analysis of PDI isolated from the animals revealed modification of an active site Cys residue thought to be involved in client protein binding. To test the hypothesis that 4-HNE inhibits the chaperone, purified bovine PDI was treated with concentrations of 4-HNE ranging from 20 to 200 microM (10-100-fold molar excess aldehyde), resulting in 14-56% inhibition, respectively. Similar treatments with the lipid peroxidation products acrolein (ACR) and 4-oxononenal (4-ONE) resulted in 60 and 100% inhibition, respectively, suggesting inactivation of the chaperone via Cys modification. Thiol sensitivity was confirmed through concentration-dependent inhibition of PDI by the Cys modifier N-ethylmaleimide (NEM). While some degree of sensitivity to these lipid aldehydes is suggested by the data, when compared to inactivation of other proteins by 4-HNE, PDI has demonstrated a relative resistance. It was also observed that physiologic (e.g., 4 mM) concentrations of GSH were capable of removing the 4-HNE adducts, likely serving as a protective mechanism against inactivation by 4-HNE and other lipid peroxidation products. However, because an active site Cys was found to be modified by 4-HNE on PDI in vivo, it is possible that the protective effect of GSH on the chaperone decreases under conditions of sustained oxidative stress, such as during chronic alcohol consumption, as GSH is depleted. The data presented here thus suggest potential impairment of an important molecular chaperone during oxidative stress.

Protein and lipid oxidative damage and complex I content are lower in the brain of budgerigar and canaries than in mice. Relation to aging rate

What are the mechanisms determining the rate of animal aging? Of the two major classes of endothermic animals, bird species are strikingly long-lived compared to mammals of similar body size and metabolic rate. Thus, they are ideal models to identify longevity-related characteristics not linked to body size or low metabolic rates. Since oxidative stress seems to be related to the basic aging process, we measured specific markers of different kinds of oxidative damage to proteins, like glutamic and aminoadipic semialdehydes (GSA and AASA, specific protein carbonyls), Nɛ-(carboxyethyl)lysine (CEL), Nɛ-(carboxymethyl)lysine (CML), and Nɛ-(malondialdehyde)lysine (MDAL), as well as mitochondrial Complex I content and amino acid and membrane fatty acyl composition, in the brain of short-lived mice (maximum life span [MLSP] 3.5 years) compared with those of long-lived budgerigar 'parakeets' (MLSP, 21 years) and canaries (MLSP, 24 years). The brains of both bird species had significantly lower levels of compounds formed as a result of oxidative (GSA and AASA), glycoxidative (CEL and CML), and lipoxidative (CML and MDAL) protein modifications, as well as a lower levels of mitochondrial complex I protein. Although it is known that fatty acid unsaturation is lower in many tissues of long-lived compared to short-lived mammals, this is not true in the particular case of brain. In agreement with this, we also found that the brain tissue of bugerigars and canaries contains no fewer double bonds than that of mice. Amino acid composition analyses revealed that bird proteins have a significantly lower content of His, Leu and Phe, as well as, interestingly, of methionine, whereas Asp, Glu, Ala, Val, and Lys contents were higher than in the mammals. These results, together with those previously described in other tissues of pigeons (MLSP, 35 years) compared to rats (MLSP, 4 years), indicate that oxidative damage to proteins, lipids and mitochondrial DNA are lower in birds (very long-lived species) than in short-lived mammals of similar body size. The lower degree of oxidative modification of bird brain proteins was not due to decreases in the target amino acids (lysine for CEL, CML, MDAL, and AASA; and arg and pro for GSA), since these were present in bird brain proteins at higher or similar levels than in those of mice. These results are consistent with the possibility that decreases in oxidative protein modification are caused at least in part by the low rate of mitochondrial oxygen radical generation in these birds, as in all long-lived homeothermic vertebrates investigated so far.

The immunogenicity of modified lipoproteins

The immunogenicity of modified low-density lipoprotein (mLDL) has been demonstrated both in laboratory animals and humans. Circulating human mLDL antibodies, purified by affinity chromatography, are predominantly of the IgG isotype, subclasses 1 and 3. The purified antibodies react with malondialdehyde-lysine and carboxymethyl-lysine epitopes, but also recognize minimally modified forms of LDL that do not contain significant amounts of those two epitopes. The quantitative assays of mLDL and mLDL antibodies in serum samples by enzymoimmunoassay (EIA) are unreliable owing to the interference of preformed circulating immune complexes (CICs). Isolation of CICs by precipitation with low concentrations of polyethylene glycol followed by analysis of antigens and antibodies contained in the precipitates is a technically complex approach, but one that yields valuable data. With this approach we have confirmed that the IgG antibodies involved in IC formation belong to the proinflammatory IgG1 and IgG3 isotypes, have a higher avidity than those that remain unbound in the supernatant after CIC precipitation, and are of higher avidity in diabetic patients with macroalbuminuria than in those with normal albuminuria. We have also developed capture assays for different forms of mLDL. These assays have shown a significant enrichment in mLDL of the precipitated ICs. The enrichment is also more pronounced in the CICs obtained from diabetic patients with macroalbuminuria. In conclusion, isolation and characterization of LDL-ICs appears to yield information of significant value that is not derived from other approaches to measure LDL modifications and their corresponding antibodies in humans.

Protective role of antioxidative food factors in oxidative stress caused by hyperglycemia

Hyperglycemia causes the autoxidation of glucose, glycation of proteins, and the activation of polyol metabolism. These changes accelerate generation of reactive oxygen species (ROS) and increases in oxidative chemical modification of lipids, DNA, and proteins in various tissues. Oxidative stress may play an important role in the development of complications in diabetes such as lens cataracts, nephropathy, and neuropathy. Glycation reactions, especially Maillard reactions, occur in vivo as well as in vitro and are associated with the chronic complications of diabetes mellitus and aging and age-related diseases by increases in oxidative chemical modification of lipids, DNA, and proteins. In particular, long-lived proteins such as lens crystallines, collagens, and hemoglobin may react with reducing sugars to form advanced glycation end products (AGEs). Recently, we found a novel type of AGE, named MRX, and we found that MRX is a good biomarker for detecting oxidative stress produced during Maillard reaction. We also examined in detail the role of lipid peroxidation reaction in hyperglycemia and found that hexanoyl modification formed by the reaction of oxidized lipids and proteins must be important for oxidative stress. Detailed analyses of the formation mechanism of hexanoyl lysine (HEL) moiety in proteins were conducted, and excretion of HEL into urine was quantified by using LC/MS/MS. Macrophages and neutrophils play an important role in oxidative stress during hyperglycemia, and we determined that oxidatively modified tyrosines are a good biomarker for formation of oxidative stress at an early stage. Immunochemical analyses by application of monoclonal antibodies specific to lipid hydroperoxide-modified proteins produced by polyunsaturated fatty acids including docosahexaenoic acid (DHA) in oxidative stress caused by hyperglycemia were conducted, and the relationship between glycation and lipid peroxidation reactions both by chemical and immunochemical approaches are discussed. Recently, we put much more focus on dietary antioxidants for prevention of diabetic complications. Curcuminoids, the main yellow pigments in Curcuma longa (turmeric), have been used widely and for a long time in the treatment of sprain and inflammation in indigenous medicine. Curcumin is the main component of turmeric, and two minor components are also present as the curcuminoids. Curcuminoids possess antioxidant activity. Protective effects of curcumin (U1) and one of its major metabolites, tetrahydrocurcumin (THU1), have been examined for development of diabetic cataract in 25% galactose-fed SD rats. Through detailed examination of protective mechanisms of THU1, it was found that THU1 showed that scavenger ROS not only formed during hyperglycemia, but also induced antioxidative enzymes including detoxification enzymes such as glutathine S-transferase. THU1 also showed significant increase of glutathione concentration in the cultured rat lens. Glutathione (gamma-glutamylcysteinyl glycine [GSH]) is thought to be an important factor in cellular function and defense against oxidative stress, and we found that dietary GSH suppresses oxidative stress in vivo in prevention of diabetic complications such as diabetic nephropathy and neuropathy.

From molecular footprints of disease to new therapeutic interventions in diabetic nephropathy

Proteins are particularly attractive targets for product analysis, which is used to understand pathology. Protein modifications, such as advanced glycation end products (AGEs), serve as footprints of biochemical processes and also help in the search for novel agents that efficiently inhibit protein damage. Interestingly, several medical agents that are used clinically interfere with oxidative protein damage through different mechanisms characteristic of their chemical structures. We recently found that angiotensin II receptor blockers (ARBs) and angiotensin converting enzyme inhibitors (ACEIs) lower the in vitro formation of the AGEs pentosidine and carboxymethyllysine. Their inhibition for AGE formation is more striking than aminoguanidine. Unlike aminoguanidine, ARBs and ACEIs do not trap reactive carbonyl precursors of AGEs. Rather, they inhibit AGE formation, possibly as a result of their potent ability to scavenge hydroxyl radicals and to chelate the transition metals necessary for the Fenton reaction. We tested their AGE-lowering ability in vivo in a unique type-2 diabetic model with nephropathic SHR/NDmcr-cp rats, which exhibits the metabolic syndrome (obesity, hyperglycemia, hyperlipidemia, hyperinsulinemia) in addition to hypertension. Obesity and associated metabolic derangements, in addition to hypertension, markedly accelerate renal injury. Expectedly, correction of hyperglycemia and hyperinsulinemia partially but significantly improves renal injury. A low-calorie diet greatly improves renal injury despite persistent hypertension. Among antihypertensive agents, ARBs, unlike nifedipine and atenolol, are renoprotective despite persistent metabolic syndrome, but their action is independent of blood pressure lowering and is observed in a dose-dependent manner despite the complete blockade of angiotensin II receptor. Interestingly, the improvement of renal injury by ARBs as well as a low-calorie diet is associated with a significant reduction in local oxidative stress and AGE formation in the kidney. During the characterization of the AGE-lowering profile of our chemical compound libraries ( approximately 2000), we identified several inhibitors of oxidative stress and advanced glycation. They are indeed renoprotective, independently of correction of hypertension and metabolic syndrome, in experimental diabetic nephropathy and other nephritis models. Altogether, our data are in good agreement with the recent therapeutic concept for diabetic nephropathy that multiple risk factor interventions are critical in the treatment of diabetic renal injury, and further implicate a therapeutic potential of inhibition of oxidative stress and advanced glycation.

Cross-linking of the extracellular matrix by the maillard reaction in aging and diabetes: an update on "a puzzle nearing resolution"

The aging extracellular matrix is characterized by an age-related increase in insolubilization, yellowing, and stiffening, all of which can be mimicked by the Maillard reaction in vitro. These phenomena are accelerated in metabolic diseases such as diabetes and end-stage renal disease, which have in common with physiological aging the accumulation of various glycation products and cross-links. Eight years ago we concluded that the evidence favored oxidative cross-linking in experimental diabetes [Monnier, V.M. et al. 1996. The mechanism of collagen cross-linking in diabetes: a puzzle nearing completion. Diabetes 45(Suppl. 3): 67-72] and proposed a major role for a putative non-UV active cross-link derived from glucose. Below, we provide an update of the field that leads to the conclusion that, while oxidation might be important for Maillard reaction-mediated cross-linking via Strecker degradation and allysine formation, the single most important collagen cross-link known to date in diabetes and aging is glucosepane, a lysyl-arginine cross-link that forms under nonoxidative conditions.

Protein methionine content and MDA-lysine adducts are inversely related to maximum life span in the heart of mammals

Aging affects all organisms and its basic mechanisms are expected to be conserved across species. Oxidation of proteins has been proposed to be one of the basic mechanisms linking oxygen radicals with the basic aging process. If oxidative damage to proteins is involved in aging, long-lived animals (which age slowly) should show lower levels of markers of this kind of damage than short-lived ones. However, this possibility has not been investigated yet. In this study, steady-state levels of markers of different kinds of protein damage--oxidation (glutamic and aminoadipic semialdehydes), mixed glyco- and lipoxidation (carboxymethyl- and carboxyethyllysine), lipoxidation (malondialdehydelysine) and amino acid composition--were measured in the heart of eight mammalian species ranging in maximum life span (MLSP) from 3.5 to 46 years. Oxidation markers were directly correlated with MLSP across species. Mixed glyco- and lipoxidation markers did not correlate with MLSP. However, the lipoxidation marker malondialdehydelysine was inversely correlated with MLSP (r2=0.85; P<0.001). The amino acid compositional analysis revealed that methionine is the only amino acid strongly correlated MLSP and that such correlation is negative (r2=0.93; P<0.001). This trait may contribute to lower steady-state levels of oxidized methionine residues in cellular proteins. These results reinforce the notion that high longevity in homeothermic vertebrates is achieved in part by constitutively decreasing the sensitivity of both tissue proteins and lipids to oxidative damage. This is obtained by modifying the constituent structural components of proteins and lipids, selecting those less sensitive to oxidative modifications.

Geometrical trans Lipid Isomers: A New Target for Lipidomics

Evidence that lipids play different roles in the biological environment, particularly in dealing with metabolic regulation and cell signaling, has led to a growing interest in these molecules, and nowadays the research field of lipid structures and functions is called lipidomics. The term describes diverse research areas, from mapping the entire spectrum of lipids in organisms to describing the function and metabolism of individual lipids. Recent investigations on geometrical trans isomers of fatty acid derivatives, which have the double bonds in the same position as the natural compounds but with the trans instead of the naturally occurring cis geometry, highlighted these compounds as a new target for lipidomics. In addition to the identification of their structures and functions, research in a multidisciplinary context aims at understanding the biochemical significance of cis and trans lipid geometry, and a chemical biology approach can be envisaged to explore the role of the geometry change as either an alteration or a signal that can perturb a biological system and induce a cellular response.

Chemical modification of proteins during peroxidation of phospholipids

Chemical modification of proteins by advanced glycation and lipoxidation end products is implicated in the pathogenesis of macrovascular disease in aging and diabetes. To identify biomarkers of the lipoxidative modification of protein, we studied the oxidation of phospholipids in the presence of the model protein RNase A and compared protein-bound products formed in these reactions with those formed during oxidation of plasma proteins. Metal-catalyzed oxidation of 1-palmitoyl-2-arachidonoyl-phosphatidylcholine or 1-palmitoyl-2-linoleoyl-phosphatidylcholine in the presence of RNase led to the loss of amino groups in RNase and the incorporation of phosphate, hexanoate, pentanedioate, nonanedioate, and palmitate into protein. Protein-bound palmitate and phosphate correlated strongly with one another, and protein-bound pentanedioate and nonanedioate, derived from arachidonate and linoleate, respectively, accounted for approximately 20% of the cross-linking of lipid phosphorus to protein. Similar results were obtained on oxidation of total plasma or isolated LDL. We conclude that alkanedioic acids are quantitatively important linkers of oxidized phospholipids to proteins and that measurement of protein-bound phosphate and long-chain fatty acids may be useful for assessing long-term lipid peroxidative damage to proteins in vivo. Analyses of plasma proteins from control and diabetic patients indicated significant increases in lipoxidative modification of protein in diabetic compared with control subjects.

Inhibition of Glycosylation Processes: the Reaction between Pyridoxamine and Glucose

Glycosylation of proteins by glucose produces toxic and immunogenic compounds called 'advanced glycosylation end products' (AGEs), which are the origin of pathological symptoms in various chronic diseases. In this work, a kinetic study of the reaction between glucose (2) and pyridoxamine (1)--a potent inhibitor of AGEs formation both in vivo and in vitro--was conducted. The NH2 group of pyridoxamine was found to react with the C=O group of glucose to form the Schiff base 9 (Scheme 2). Subsequently, the Schiff base gives rise to other products, including compound 3, pyridoxal, pyridoxine, and 4-pyridoxic acid. Compound 3 inhibits the Amadori rearrangement, and prevents the formation of other C=O groups capable of triggering glycosylation processes. Pyridoxal and pyridoxine can also inhibit protein glycosylation via other previously reported mechanisms.

Development of capture assays for different modifications of human low-density lipoprotein

Antibodies to malondialdehyde (MDA)-modified low-density lipoprotein (LDL), copper-oxidized LDL (oxLDL), Nepsilon(carboxymethyl) lysine (CML)-modified LDL, and advanced glycosylation end product (AGE)-modified LDL were obtained by immunization of rabbits with in vitro-modified human LDL preparations. After absorption of apolipoprotein B (ApoB) antibodies, we obtained antibodies specific for each modified lipoprotein with unique patterns of reactivity. MDA-LDL antibodies reacted strongly with MDA-LDL and also with oxLDL. CML-LDL antibodies reacted strongly with CML-LDL and also AGE-LDL. oxLDL antibodies reacted with oxLDL but not with MDA-LDL, and AGE-LDL antibodies reacted with AGE-LDL but not with CML-LDL. Capture assays were set with each antiserum, and we tested their ability to capture ApoB-containing lipoproteins isolated from precipitated immune complexes (IC) and from the supernatants remaining after IC precipitation (free lipoproteins). All antibodies captured lipoproteins contained in IC more effectively than free lipoproteins. Analysis of lipoproteins in IC by gas chromatography-mass spectrometry showed that they contained MDA-LDL and CML-LDL in significantly higher concentrations than free lipoproteins. A significant correlation (r=0.706, P<0.019) was obtained between the MDA concentrations determined by chemical analysis and by the capture assay of lipoproteins present in IC. In conclusion, we have developed capture assays for different LDL modifications in human ApoB/E lipoprotein-rich fractions isolated from precipitated IC. This approach obviates the interference of IC in previously reported modified LDL assays and allows determination of the degree of modification of LDL with greater accuracy.

Inhibition of Hsp72-mediated protein refolding by 4-hydroxy-2-nonenal

A proteomic approach was applied to liver cytosol from rats fed a diet consisting of high fat and ethanol to identify 4-hydroxy-2-nonenal (4-HNE)-modified proteins in vivo. Cytosolic Hsp72, the inducible variant of the Hsp70 heat shock protein family, was consistently among the proteins modified by 4-HNE. Despite 1.3-fold induction of Hsp72 in the livers of ethanol-fed animals, no increase in Hsp70-mediated luciferase refolding in isolated heptocytes was observed, suggesting inhibition of this process by 4-HNE. A 50% and 75% reduction in luciferase refolding efficiency was observed in rabbit reticulocyte lysate (RRL) supplemented with recombinant Hsp72 which had been modified in vitro with 10 and 100 microM 4-HNE, respectively. This observation was accompanied by a 25% and 50% decrease in substrate binding by the chaperone following the same treatment; however, no effect on complex formation between Hsp72 and its co-chaperone Hsp40 was observed. Trypsin digest and mass spectral analysis of Hsp72 treated with 10 and 100 microM 4-HNE consistently identified adduct formation at Cys267 in the ATPase domain of the chaperone. The role of this residue in the observed inhibition was demonstrated through the use of DnaK, a bacterial Hsp70 variant lacking Cys267. DnaK was resistant to 4-HNE inactivation. Additionally, Hsp72 was resistant to inactivation by the thiol-unreactive aldehyde malondialdehyde (MDA), further supporting a role for Cys in Hsp72 inhibition by 4-HNE. Finally, the affinity of Hsp72 for ATP was decreased 32% and 72% following treatment of the chaperone with 10 and 100 microM 4-HNE, respectively. In a model of chronic alcoholic liver injury, induction of Hsp72 was not accompanied by an increase in protein refolding ability. This is likely the result of 4-HNE modification of the Hsp72 ATPase domain.

Proteins in human brain cortex are modified by oxidation, glycoxidation, and lipoxidation. Effects of Alzheimer disease and identification of lipoxidation targets

Diverse oxidative pathways, such as direct oxidation of amino acids, glycoxidation, and lipoxidation could contribute to Alzheimer disease pathogenesis. A global survey for the amount of structurally characterized probes for these reactions is lacking and could overcome the lack of specificity derived from measurement of 2,4-dinitrophenylhydrazine reactive carbonyls. Consequently we analyzed (i) the presence and concentrations of glutamic and aminoadipic semialdehydes, N(epsilon)-(carboxymethyl)-lysine, N(epsilon)-(carboxyethyl)-lysine, and N(epsilon)-(malondialdehyde)-lysine by means of gas chromatography/mass spectrometry, (ii) the biological response through expression of the receptor for advanced glycation end products, (iii) the fatty acid composition in brain samples from Alzheimer disease patients and age-matched controls, and (iv) the targets of N(epsilon)-(malondialdehyde)-lysine formation in brain cortex by proteomic techniques. Alzheimer disease was associated with significant, although heterogeneous, increases in the concentrations of all evaluated markers. Alzheimer disease samples presented increases in expression of the receptor for advanced glycation end products with high molecular heterogeneity. Samples from Alzheimer disease patients also showed content of docosahexaenoic acid, which increased lipid peroxidizability. In accordance, N(epsilon)-(malondialdehyde)-lysine formation targeted important proteins for both glial and neuronal homeostasis such as neurofilament L, alpha-tubulin, glial fibrillary acidic protein, ubiquinol-cytochrome c reductase complex protein I, and the beta chain of ATP synthase. These data support an important role for lipid peroxidation-derived protein modifications in Alzheimer disease pathogenesis.

HNE-dependent molecular damage in diabetic nephropathy and its possible prevention by N-acetyl-cysteine and oxerutin

Accumulation of Advanced Lipoxidation End-products (ALE), such as MDA- and HNE-protein adducts, and Advanced Glycation End-products, such as carboxymethyl-lysine (CML), are probably involved in the development of diabetic nephropathy. In this study the effect of some antioxidant treatments (oxerutin, N-acetylcysteine, taurine and N-acetylcysteine+taurine) on kidney lipoxidative damage has been evaluated by immunohistochemistry in streptozotocined rats. Diabetic rats showed marked glomerular positivity for ALE, while the samples from Control rats were negative. All treatments except taurine were able to protect the glomeruli from ALE accumulation; the failure of taurine may be due to residual oxidative properties of its derivatives. These data are consistent with those of our previous study, which showed that all the antioxidants used except taurine protected the glomeruli from diabetes-induced enlargement, increased apoptotic rate, decreased cell density and CML accumulation. These data attest to a role of glycoxidative and lipoxidative damage in diabetes-dependent damage of the kidney, and indicate that specific antioxidants can prevent or attenuate diabetic nephropathy.

Proteins as biomarkers of oxidative/nitrosative stress in diseases: the contribution of redox proteomics

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) contribute to the pathogenesis and/or progression of several human diseases. Proteins are important molecular signposts of oxidative/nitrosative damage. However, it is generally unresolved whether the presence of oxidatively/nitrosatively modified proteins has a causal role or simply reflects secondary epiphenomena. Only direct identification and characterization of the modified protein(s) in a given pathophysiological condition can decipher the potential roles played by ROS/RNS-induced protein modifications. During the last few years, mass spectrometry (MS)-based technologies have contributed in a significant way to foster a better understanding of disease processes. The study of oxidative/nitrosative modifications, investigated by redox proteomics, is contributing to establish a relationship between pathological hallmarks of disease and protein structural and functional abnormalities. MS-based technologies promise a contribution in a new era of molecular medicine, especially in the discovery of diagnostic biomarkers of oxidative/nitrosative stress, enabling early detection of diseases. Indeed, identification and characterization of oxidatively/nitrosatively modified proteins in human diseases has just begun.

Identification and quantification of N(epsilon)-(Hexanoyl)lysine in human urine by liquid chromatography/tandem mass spectrometry

The identification and quantification of N(epsilon)-(hexanoyl)lysine (N(epsilon)-HEL), which was found from the reactions between lipid hydroperoxide and lysine, from human urine was examined using liquid chromatography/tandem mass spectrometry (LC/MS/MS). The N(epsilon)-HEL in the partially purified urine fraction was identified using LC/MS/MS by several approaches including precursor/product ion scans. The peak found by the multiple-reaction monitoring (MRM) of the collision-induced fragmentation of N(epsilon)-HEL was clearly observed in urine, and the elution position coincided with the synthetic standard N(epsilon)-HEL. The product, estimated N(epsilon)-HEL, was absorbed by a specific antibody to N(epsilon)-HEL. Moreover, N(alpha)-HEL, one of the plausible hexanoyl adducts from the reaction between the N(alpha) moiety of L-lysine and the peroxidized lipid, was hardly detected in urine samples, suggesting that the origin of the N(epsilon)-HEL is the peroxidized lipid-modified proteins but not artificial hexanoylated L-lysine. Using the MRM technique, the amount of urinary N(epsilon)-HEL from the control subjects (observed healthy) was estimated to be 1.58 +/- 0.23 mumol/mol of creatinine. A comparative study of the urinary N(epsilon)-HEL with an oxidative stress marker, 8-oxo-7,8-dihydro-2'-deoxyguanosine, showed a high correlation (r = 0.844) between the two biomarkers. Furthermore, the quantification of N(epsilon)-HEL in the control and diabetic urines revealed that the urinary N(epsilon)-HEL from diabetic subjects (3.21 +/- 0.65 mumol/mol of creatinine) was significantly higher than that from the control subjects.

Malondialdehyde, a lipoperoxidation-derived aldehyde, can bring about secondary oxidative damage to proteins

Lipoperoxidation-derived aldehydes, for example malondialdehyde (MDA), can damage proteins by generating covalent adducts whose accumulation probably participates in tissue damage during aging. However, the mechanisms of adduct formation and their stability are scarcely known. This article investigates whether oxidative steps are involved in the process. As a model of the process, the interaction between MDA and bovine serum albumin (BSA) was analyzed. Incubation of BSA with MDA resulted in rapid quenching of tryptophan fluorescence and appearance of MDA protein adduct fluorescence; transition metal ion traces interfered with the latter process. MDA induced generation of peroxides in BSA, which was preventable with the antioxidant 2,6,-di-tert-butyl-4-methylphenol (BHT). MDA-exposed BSA underwent aggregation, degradation, and BHT-sensitive "gel retardation" effects. Phycoerythrin fluorescence disappearance, a marker of damage mediated by reactive oxygen species, indicated synergism between MDA and metal ions. The interaction between reactive aldehydes and proteins is likely to occur in several steps, some of them oxidative in nature, giving rise to advanced lipoperoxidation end-products, which could participate, with advanced glycation end-products, in the generation of tissue damage during aging.

Protein nonenzymatic modifications and proteasome activity in skeletal muscle from the short-lived rat and long-lived pigeon

What are the mechanisms determining the rate of animal aging? Of the two major classes of endothermic animals, bird species are strikingly long-lived compared to similar size mammalian counterparts. Since oxidative stress is causally related to the basic aging process, markers of different kinds of oxidative damage to proteins (glutamic semialdehyde, aminoadipic semialdehyde, N(epsilon)-(carboxyethyl)lysine; N(epsilon)-(carboxymethyl)lysine, N(epsilon)-(malondialdehyde)lysine and dinitrophenylhydrazyne-reactive protein carbonyls, peptidase activities of the proteasome, and amino acid and membrane fatty acyl composition were identified and measured in skeletal muscle from the short-lived rat (maximum life span, 4 years) and compared with the long-lived pigeon (maximum life span, 35 years). Skeletal muscle from pigeon showed significantly higher levels of glutamic semialdehyde, protein carbonyls (by western blot), N(epsilon)-(carboxyethyl)lysine and N(epsilon)-(carboxymethyl)lysine. No differences were observed for aminoadipic semialdehyde, whereas the lipoxidation marker N(epsilon)-(malondialdehyde)lysine displayed a significant low steady-state level, probably related with their significantly lower membrane unsaturation. The amino acid compositional analysis revealed that arginine, serine, threonine and methionine showed significantly lower levels in pigeon. Finally, pigeon samples showed also significantly lower levels of the peptidase activities of the proteasome. These results reinforces the role of structural components such as membrane unsaturation and protein composition in determining the longer maximum life span showed by birds compared with mammals of similar body size.

Green tea extract suppresses the age-related increase in collagen crosslinking and fluorescent products in C57BL/6 mice

Collagen crosslinking during aging in part results from Maillard reaction endproducts of glucose and oxoaldehydes. Because of the tight link between oxidative and carbonyl stress, we hypothesized that natural antioxidants and "nutriceuticals" could block collagen aging in C57BL/6 mice. Six groups of young and adult mice received vitamin C, vitamin E, vitamin C&E, blueberry, green tea extract (GTE), or no treatment for a period of 14 weeks. Body weights and collagen glycation were unaltered by the treatment. However, GTE or vitamin C&E combined blocked tendon crosslinking at 10 months of age (p < 0.05, adult group). GTE also blocked fluorescent products at 385 and 440 nm (p = 0.052 and < 0.05, respectively) and tended to decrease skin pentosidine levels. These results suggest that green tea is able to delay collagen aging by an antioxidant mechanism that is in part duplicated by the combination of vitamin C and E.

Effect of antioxidants and ACE inhibition on chemical modification of proteins and progression of nephropathy in the streptozotocin diabetic rat

AIMS/HYPOTHESIS

This study was designed to determine whether inhibition of formation of AGE and advanced lipoxidation end-products (ALE) is a mechanism of action common to a diverse group of therapeutic agents that limit the progress of diabetic nephropathy. We compared the effects of the ACE inhibitor enalapril, the antioxidant vitamin E, the thiol compound lipoic acid, and the AGE/ALE inhibitor pyridoxamine on the formation of AGE/ALE and protection against nephropathy in streptozotocin diabetic rats.

METHODS

Renal function and AGE/ALE formation were evaluated in rats treated with the agents listed above. Plasma was monitored monthly for triglycerides, cholesterol, creatinine and TNF-alpha, and 24-h urine samples were collected for measurement of albumin and total protein excretion. After 29 weeks, renal expression of mRNA for extracellular matrix proteins was measured, and AGE/ALE were quantified in skin and glomerular and tubular collagen.

RESULTS

Diabetic animals were both hyperglycaemic and dyslipidaemic, and showed evidence of early nephropathy (albuminuria, creatinaemia). All interventions limited the progression of nephropathy, without affecting glycaemia. The order of efficacy was: pyridoxamine (650 mg.kg(-1).day(-1)) > vitamin E (200 mg.kg(-1).day(-1)) > lipoic acid (93 mg.kg(-1).day(-1)) approximately enalapril (35 mg.kg(-1).day(-1)). Pyridoxamine also significantly inhibited AGE/ALE accumulation in tissues; effects of other agents were mixed, but the degree of renoprotection was consistent with their effects on AGE/ALE formation.

CONCLUSIONS/INTERPRETATION

All interventions inhibited the progression of nephropathy at the doses studied, but the maximal benefit was achieved with pyridoxamine, which also limited dyslipidaemia and AGE/ALE formation. These experiments indicate that the more effective the renoprotection, the greater the inhibition of AGE/ALE formation. For optimal protection of renal function, it would be beneficial to select drugs whose mechanism of action includes inhibition of AGE/ALE formation.

In vivo glycated low-density lipoprotein is not more susceptible to oxidation than nonglycated low-density lipoprotein in type 1 diabetes

It has been suggested that low-density lipoprotein (LDL) modified by glycation may be more susceptible to oxidation and thus, enhance its atherogenicity. Using affinity chromatography, LDL glycated in vivo (G-LDL) and relatively nonglycated. (N-LDL) subfractions can be isolated from the same individual. The extent of and susceptibility to oxidation of N-LDL compared with G-LDL was determined in 15 type 1 diabetic patients. Total LDL was isolated and separated by boronate affinity chromatography into relatively glycated (G-) and nonglycated (N-) subfractions. The extent of glycation, glycoxidation, and lipoxidation, lipid soluble antioxidant content, susceptibility to in vitro oxidation, and nuclear magnetic resonance (NMR)-determined particle size and subclass distribution were determined for each subfraction. Glycation, (fructose-lysine) was higher in G-LDL versus N-LDL, (0.28 +/- 0.08 v 0.13 +/- 0.04 mmol/mol lysine, P < .0001). However, levels of glycoxidation/lipoxidation products and of antioxidants were similar or lower in G-LDL compared with N-LDL and were inversely correlated with fructose-lysine (FL) concentrations in G-LDL, but positively correlated in N-LDL. In vitro LDL (CuCl2) oxidation demonstrated a longer lag time for oxidation of G-LDL than N-LDL (50 +/- 0.16 v 37 +/- 0.15 min, P < .01), but there was no difference in the rate or extent of lipid oxidation, nor in any aspect of protein oxidation. Mean LDL particle size and subclass distribution did not differ between G-LDL and N-LDL. Thus, G-LDL from well-controlled type 1 diabetic patients is not more modified by oxidation, more susceptible to oxidation, or smaller than relatively N-LDL, suggesting alternative factors may contribute to the atherogenicity of LDL from type 1 diabetic patients.

Effect of ageing and caloric restriction on specific markers of protein oxidative damage and membrane peroxidizability in rat liver mitochondria

To gain insight into the anti-ageing mechanisms of caloric restriction (CR), liver mitochondria were isolated from male Brown-Norway rats of different ages (fully fed control and CR) and various specific markers of non-enzymatic protein modification (by oxidative, glyco- and lipoxidative-reactions) were measured by GC/MS and Western blotting. A membrane peroxidizability index (PI) was calculated from the fatty acid profiles. Between 6 and 18 months of age, there were significant decreases in the concentration of all markers of damage in mitochondria from both the fully fed and CR groups. In contrast, between the ages of 18 and 28 months, there were significant increases in the concentrations of all markers of damage. In mitochondria from both fully fed and CR groups, there were significant increases in N-epsilon (Nepsilon)-(carboxymethyl)lysine (CML) and N-epsilon-(malondialdehyde)lysine (MDAL) between 6 and 28 months of age. In general, damage tended to be lower in mitochondria from CR animals, but the effects were not significant, except for the concentration of N-epsilon-(carboxymethyl)lysine at 28 months of age. PI increased steadily and significantly with age in fully fed animals, whilst CR induced a significant decrease in this index at 28 months of age. It is concluded that for male rats of the Brown-Norway strain, and mitochondria from liver (i) old (but not mature) age is associated with an increased membrane PI and protein oxidative damage and (ii) CR does not lead to a general reversion in age-related protein damage, but it does prevent the age-induced increase in PI very late in life.

Oxidative fragmentation of hydroxy octadecadienoates generates biologically active gamma-hydroxyalkenals

Oxidative fragmentation of polyunsaturated fatty acids (PUFAs) in vivo generates cytotoxic aldehydes. Among these, 4-hydroxynon-2-enal and analogous gamma-hydroxyalkenal phosphatidylcholines (PCs) have attracted attention because these oxidatively truncated lipids are biologically active and have been implicated in diseases. A previous study showed that hydroxydienes, generated by allylic oxygenation of linoleic acid, are unreactive toward oxidative fragmentation. We now show that, in the presence of hydroperoxides, hydroxydienes fragment as readily as the corresponding hydroperoxydienes, generating gamma-hydroxyalkenals. In a physiomimetic model study, myeloperoxidase-promoted free radical-induced fragmentation of either hydroperoxy- or hydroxyoctecadienoate esters of 2-lyso-PC in small unilamellar vesicles produced the 9-hydroxy-12-oxododec-10-enoic acid (HODA) ester HODA-PC. Therefore, hydroxydienes, that are generally more abundant in vivo than hydroperoxydienes, are plausible intermediates in the production of oxidatively truncated lipids in vivo where a constant flux of radicals and hydroperoxides is present. Our findings also show that the formation of dioxetane intermediates through peroxyradical cyclization is not required to achieve oxidative fragmentation of PUFAs.

Definition of the immunogenic forms of modified human LDL recognized by human autoantibodies and by rabbit hyperimmune antibodies

Humans and laboratory animals recognize human modified LDL as immunogenic. Immune complexes (ICs) isolated from human sera contain malondialdehyde-modified LDL (MDA-LDL) and N (epsilon)(carboxymethyl)lysine-modified LDL (CML-LDL) as well as antibodies reacting with MDA-LDL, copper-oxidized LDL (OxLDL), CML-LDL, and advanced glycosylation end product (AGE)-modified LDL. OxLDL and AGE-LDL antibodies isolated from human sera recognize the same LDL modifications and do not react with modified non-LDL proteins. Rabbit antibodies have different reactivity patterns: MDA-LDL antibodies react strongly with MDA-LDL and MDA-BSA but weakly with OxLDL; OxLDL antibodies react strongly with OxLDL and weakly with MDA-LDL; CML-LDL antibodies react with CML-LDL > CML-BSA > AGE-LDL > OxLDL; AGE-LDL antibodies react strongly with AGE-LDL, react weakly with OxLDL, and do not react with CML-LDL. Thus, human and rabbit antibodies seem to recognize different epitopes. Capture assays carried out with all rabbit antibodies showed binding of apolipoprotein B-rich lipoproteins isolated from ICs, suggesting that laboratory-generated epitopes are expressed by in vivo-modified LDL, although they are not necessarily recognized by the human immune system. Thus, the definition of immunogenic forms of modified LDL eliciting human autoimmune responses requires the isolation and characterization of autoantibodies and modified LDL from human samples, whereas rabbit antibodies can be used to detect in vivo-modified human LDL.

Mass spectrometry for detection of 4-hydroxy-trans-2-nonenal (HNE) adducts with peptides and proteins

Despite the great technical advancement of mass spectrometry, this technique has contributed in a limited way to the discovery and quantitation of specific/precocious markers linked to free radical-mediated diseases. Unsaturated aldehydes generated by free radical-induced lipid peroxidation of polyunsaturated fatty acids, and in particular 4-hydroxy-trans-2 nonenal (HNE), are involved in the onset and progression of many pathologies such as cardiovascular (atherosclerosis, long-term complications of diabetes) and neurodegenerative diseases (Alzheimer's disease, Parkinson's disease, and cerebral ischemia). Most of the biological effects of HNE are attributed to the capacity of HNE to react with the nucleophilic sites of proteins and peptides (other than nucleic acids), to form covalently modified biomolecules that can disrupt important cellular functions and induce mutations. By considering the emerging role of HNE in several human diseases, an unequivocal analytical approach as mass spectrometry to detect/elucidate the structure of protein-HNE adducts in biological matrices is strictly needed not only to understand the reaction mechanism of HNE, but also to gain a deeper insight into the pathological role of HNE. This with the aim to provide intermediate diagnostic biomarkers for human diseases. This review sheds focus on the "state-of-the-art" of mass spectrometric applications in the field of HNE-protein adducts characterization, starting from the fundamental early studies and discussing the different MS-based approaches that can provide detailed information on the mechanistic aspects of HNE-protein interaction. In the last decade, the increases in the accessible mass ranges of modern instruments and advances in ionization methods have made possible a fundamental improvement in the analysis of protein-HNE adducts by mass spectrometry, and in particular by matrix-assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI) tandem mass spectrometry. The recent developments and uses of combined analytical approaches to detect and characterize the type/site of interaction have been highlighted, and several other aspects, including sample preparation methodologies, structure elucidation, and data analysis have also been considered.

Chemical modification of muscle protein in diabetes

Levels of glycation (fructose-lysine, FL) and advanced glycoxidation and lipoxidation end-products (AGE/ALEs) were measured in total skeletal (gastrocnemius) muscle and myofibril protein and compared to levels of the same compounds in insoluble skin collagen of control and diabetic rats. Levels of FL in total muscle and myofibril protein were 3-5% the level of FL in skin collagen. The AGE/ALEs, N(epsilon)-(carboxymethyl)lysine (CML) and N(epsilon)-(carboxyethyl)lysine, were also significantly lower in total muscle and myofibril protein, approximately 25% of levels in skin collagen. The newly described sulfhydryl AGE/ALE, S-(carboxymethyl)cysteine (CMC), was also measured in muscle; levels of CMC were comparable to those of CML and increased similarly in response to diabetes. Although FL and AGE/ALEs increased in muscle protein in diabetes, the relative increase was less than that seen in skin collagen. These data indicate that muscle protein is partially protected against the increase in both glycation and AGE/ALE formation in diabetes.

Modification of the longevity-related degree of fatty acid unsaturation modulates oxidative damage to proteins and mitochondrial DNA in liver and brain

Previous studies have shown that tissue fatty acid unsaturation correlates inversely with maximum longevity. However, it is unclear if this is related to the effects of fatty acid unsaturation only on lipids, or also on proteins and DNA, specially on mitochondrial DNA (mtDNA) oxidative damage. In this investigation the degree of fatty acid unsaturation of liver and brain was successfully manipulated in Wistar rats by chronic feeding with specially designed semipurified diets rich in saturated or unsaturated fats. The brain, an organ of special relevance for aging, was most profoundly affected by the increase in fatty acid unsaturation, and showed significant increases in malondialdehyde (MDA)-lysine, aminoadipic semialdehyde (a protein carbonyl), N(epsilon)-(carboxymethyl)lysine, and N(epsilon)-(carboxyethyl)lysine in proteins, as well as in 8-oxo,7,8-dihydro-2'-deoxyguanosine (8-oxodG) in mtDNA without changes in nuclear DNA (nDNA). In the liver 8-oxodG was also increased in mtDNA and not in nDNA. These DNA results are consistent with the presence of a high density of mitochondrial inner membranes (rich in lipids and in reactive oxygen species generation capacity) near mtDNA but not near nDNA. Among the protein markers analyzed, MDA-lysine was most consistent and responsive to fatty acid unsaturation, since it increased in both organs and showed the highest increase. These results, together with previous data from our laboratories, show that increasing the degree of fatty unsaturation of postmitotic tissues in vivo can raise not only lipid but also protein and mtDNA oxidative damage. This is mechanistically relevant in relation to the constitutively low tissue fatty acid unsaturation of long-lived animals.

Polyunsaturated fatty acids acutely suppress antibodies to malondialdehyde-modified lipoproteins in patients with vascular disease

Antibodies to malondialdehyde (MDA)-modified low-density lipoprotein (LDL) are transiently reduced during the postprandial period in patients with atherosclerotic heart disease. Previous experiments using mixed meals high in fat have found reductions of approximately 20% within 2 hours. This study was designed to reveal if this phenomenon was due uniquely to saturated fats. Using a standardized immunoassay for the detection of circulating levels of autoantibodies (AAbs) against MDA-modified LDL, we examined the acute changes in AAb levels during 6 hours of postprandial lipemia in 10 men with known atherosclerotic heart disease. Each subject was given 4 meals 1 week apart. Three of the meals differed in content of saturated fat, monounsaturated fat, and polyunsaturated fat. A fat-free meal with equivalent carbohydrate and equivalent protein was also administered. The study was double blinded and the meals were administered in random order. Only the meal enriched with polyunsaturated fatty acids caused the reduction in antibodies to MDA-LDL. This decrease was statistically significant from baseline at 1 hour (p <0.05), 2 hours (p <0.004), and 3 hours (p <0.02), with the nadir occurring at 2 hours. Polyunsaturated fatty acids are the major stimulus for causing a reduction in the AAbs to MDA-LDL during postprandial lipemia. These results strongly suggest that fat in chylomicrons may be a major source of oxidized lipids in the blood of patients with arteriosclerosis.