Localization of 4-hydroxy-2-nonenal-modified proteins in kidney following iron overload.

Intraperitoneal (IP) injection of ferric nitrilotriacetate (Fe-NTA) to rats and mice results in iron-induced free radical injury and cancer in kidneys. We sought to clarify the exact localization of acute oxidative damage in Fe-NTA-induced nephrotoxicity by performing immunogold light and electron microscopic (EM) techniques using an antibody against 4-hydroxy-2-nonenal (HNE)-modified proteins. Biochemical assays were done to provide complementary quantitative data. Renal accumulation of lipid peroxidation-derived aldehydes, such as malondialdehyde (MDA) and 4-hydroxy-2-alkenals (4-HDA), increased in parallel with protein carbonyl content, an indicator of protein oxidation, 30 min after administration of Fe-NTA. Immunogold light microscopy showed that HNE-modified proteins increased at 30 min with positivity localized to proximal tubular cells. Immunogold EM demonstrated that HNE-modified proteins were mainly in the mitochondria and nuclei of the proximal tubular epithelium. The intensity of labeling at both the light and EM levels increased together with levels of biochemically measured lipid peroxidation products and protein carbonyl content. Our data suggest that the mechanism of acute nephrotoxicity of Fe-NTA involves mitochondrial and nuclear oxidative damage, findings that may help to define the mechanisms of iron-induced cell injury.     

Inactivation of the proteasome by 4-hydroxy-2-nonenal is site specific and dependant on 20S proteasome subtypes

The proteasome represents a major intracellular proteolytic system responsible for the degradation of oxidized and ubiquitinated proteins in both the nucleus and cytoplasm. We have previously reported that proteasome undergoes modification by the lipid peroxidation product 4-hydroxy-2-nonenal (HNE) and exhibits declines in peptidase activities during cardiac ischemia/reperfusion. This study was undertaken to characterize the effects of HNE on the structure and function of the 20S proteasome. To assess potential tissue-specific differences in the response to HNE, we utilized purified 20S proteasome from heart and liver, tissues that express different proteasome subtypes. Following incubation of heart and liver 20S proteasome with HNE, changes in the 2D gel electrophoresis patterns and peptidase activities of the proteasome were evaluated. Proteasome subunits were identified by mass spectrometry prior to and following treatment with HNE. Our results demonstrate that specific subunits of the 20S proteasome are targeted for modification by HNE and that modified proteasome exhibits selective alterations in peptidase activities. The results provide evidence for a likely mechanism of proteasome inactivation in response to oxidative stress particularly during cardiac ischemia/reperfusion.     

Proteomic analysis of 4-hydroxy-2-nonenal-modified proteins in G93A-SOD1 transgenic mice--a model of familial amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is an age-related, fatal motor neuron degenerative disease occurring both sporadically (sALS) and heritably (fALS), with inherited cases accounting for approximately 10% of diagnoses. Although multiple mechanisms likely contribute to the pathogenesis of motor neuron injury in ALS, recent advances suggest that oxidative stress may play a significant role in the amplification, and possibly the initiation, of the disease. Lipid peroxidation is one of the several outcomes of oxidative stress. Since the central nervous system (CNS) is enriched with polyunsaturated fatty acids, it is particularly vulnerable to membrane-associated oxidative stress. Peroxidation of cellular membrane lipids or circulating lipoprotein molecules generates highly reactive aldehydes, among which is 4-hydroxy-2-nonenal (HNE). HNE levels are increased in spinal cord motor neurons of ALS patients, indicating that lipid peroxidation is associated with the motor neuron degeneration in ALS. In the present study, we used a parallel proteomic approach to identify HNE-modified proteins in the spinal cord tissue of a model of fALS, G93A-SOD1 transgenic mice, in comparison to the nontransgenic mice. We found three significantly HNE-modified proteins in the spinal cord of G93A-SOD1 transgenic mice: dihydropyrimidinase-related protein 2 (DRP-2), heat-shock protein 70 (Hsp70), and possibly alpha-enolase. These results support the role of oxidative stress as a major mechanism in the pathogenesis of ALS. Structural alteration and activity decline of functional proteins may consistently contribute to the neurodegeneration process in ALS.     

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.     

To tag or not to tag: a comparative evaluation of immunoaffinity-labeling and tandem mass spectrometry for the identification and localization of posttranslational protein carbonylation by 4-hydroxy-2-nonenal, an end-product of lipid peroxidation

Posttranslational carbonylation of proteins by the covalent attachment of the lipid peroxidation product 4-hydroxy-2-nonenal (HNE) is a biomarker of oxidative stress. Tandem mass spectrometry (MS/MS) has become an essential tool for characterization of this modification. Chemical tagging methods have been used to facilitate the immunoaffinity-based enrichment or even quantification of HNE-modified peptides and proteins. With MS/MS spectra of the untagged modified peptides considered as references, a comparative evaluation is presented focusing on the impact of affinity-tagging with four carbonyl-specific reagents (2,4-dinitrophenyl hydrazine, biotin hydrazide, biotinamidohexanoic acid hydrazide and N'-aminooxymethylcarbonyl-hydrazino D-biotin) on collision-induced dissociation of the tagged HNE-carbonylated peptides. Our study has shown that chemical labeling may not be carried out successfully for all the peptides and with all the reagents. The attachment of a tag usually cannot circumvent the occurrence of strong neutral losses observed with untagged species and, in addition, fragmentation of the introduced tag may also happen. Chemical tagging of certain peptides may, nevertheless, afford more sequence ions upon MS/MS than the untagged carbonylated peptide, especially when Michael addition of the lipid peroxidation product occurs on cysteine residues. Therefore, tagging may increase the confidence of identifications of HNE-modified peptides by database searches.     

The effect of high-density lipoproteins on the formation of lipid/protein conjugates during in vitro oxidation of low-density lipoprotein

High-density lipoprotein (HDL) incubated with low-density lipoprotein (LDL) under oxidising conditions has previously been reported to decrease the accumulation of lipid peroxides on LDL and to diminish the biological effects of LDL, which would have been present had it been oxidatively modified in the absence of HDL. Thus far direct evidence that oxidative modification of LDL is diminished by HDL has, however, been lacking. We used electrospray ionisation mass spectrometry (ESI-MS) to detect 4-hydroxy-2-nonenal (HNE)-modified histidine residues of tryptic fragments of LDL which had been subject to Cu(2+) induced oxidation both in the presence and absence of human or avian HDL. HNE-modified angiotensin II was introduced into the incubation mixture as an internal standard and to check that HDL did not interfere in the detection of HNE-modified peptides non-specifically. Our results confirmed earlier reports that HNE modification of histidine occurs during the oxidation of LDL and for the first time revealed a marked attenuation of the process in the presence of human HDL with no effect on the detection of HNE-modified angiotensin II by ESI-MS. Avian HDL, which lacks the anti-oxidative enzyme paraoxonase, did not affect the formation of apo B adducts. Our findings therefore suggest that covalent linkage of lipid peroxidation products to LDL protein as well as the accumulation of lipid peroxides on LDL is diminished in the presence of HDL containing paraoxonase.     

Proteasome inactivation upon aging and on oxidation-effect of HSP 90

Increases of oxidatively modified protein in the cell have been associated with the aging process. Such an accumulation of damaged protein may be the result of increase in the rate of protein oxidation and/or decrease in the rate of degradation of oxidized protein. The multicatalytic proteinase or proteasome is known to be the major proteolytic system involved in the removal of oxidized protein. We have reported that, after isolation of the 20S proteasome from the liver of young and old male Fischer 344 rat, out of the three peptidase activities (chymotrypsin-like, trypsin-like and peptidyl-glutamyl peptide hydrolase) we assayed with fluorogenic peptides, the peptidyl-glutamyl peptide hydrolase activity was declining with age to a value approximately 50% of that observed for protease purified from young rats. The proteasome was subjected to metal catalyzed oxidation to determine the susceptibility of the different peptidase activities to oxidative inactivation. Both trypsin-like and peptidyl-glutamyl peptide hydrolase activities were found sensitive to oxidation. Treatment of the proteasome with 4-hydroxy-2-nonenal, a major lipid peroxidation product, was also found to inactivate the trypsin-like activity. However, the trypsin-like activity was protected from inactivation by metal catalyzed oxidation in proteasome preparations contaminated with HSP 90, a protein that often copurifies with the proteasome. Upon addition of HSP 90 to pure 20S active proteasome, the trypsin-like activity was protected from inactivation by metal catalyzed oxidation and from inactivation by treatment with 4-hydroxy-2-nonenal. These results suggest a possible intervention of HSP 90 in response to oxidative stress in preventing the inactivation of the proteasome by oxidative damage. Abbreviations: AAF-amc – Ala-Ala-Phe-7-amido-4-methylcoumarin; LSTR-amc – N-t-Boc-Leu-Ser-Thr-Arg-7-amido-4-methylcoumarin; LLE-na – Leu-Leu-Glu-b-naphthylamide; HSP 90: heat shock protein 90, MCP – multicatalytic proteinase or 20S proteasome.     

4-Hydroxynonenal, an Aldehydic Product of Lipid Peroxidation, Impairs Signal Transduction Associated with Muscarinic Acetylcholine and Metabotropic Glutamate Receptors: Possible Action on Gαq/11

Abstract: Considerable data indicate that oxidative stress and membrane lipid peroxidation contribute to neuronal degeneration in an array of age-related neurodegenerative disorders. In contrast, the impact of subtoxic levels of membrane lipid peroxidation on neuronal function is largely unknown. We now report that 4-hydroxy-nonenal (HNE), an aldehydic product of lipid peroxidation, disrupts coupling of muscarinic cholinergic receptors and metabotropic glutamate receptors to phospholipase C-linked GTP-binding proteins in cultured rat cerebrocortical neurons. At subtoxic concentrations, HNE markedly inhibited GTPase activity, inositol phosphate release, and elevation of intracellular calcium levels induced by carbachol (muscarinic agonist) and ( RS )-3,5-dihydroxyphenyl glycine (metabotropic glutamate receptor agonist). Maximal impairment of agonist-induced responses occurred within 30 min of exposure to HNE. Other aldehydes, including malondialdehyde, had little effect on agonist-induced responses. Antioxidants that suppress lipid peroxidation did not prevent impairment of agonist-induced responses by HNE, whereas glutathione, which is known to bind and detoxify HNE, did prevent impairment of agonist-induced responses. HNE itself did not induce oxidative stress. Immunoprecipitation-western blot analysis using an antibody to HNE-protein conjugates showed that HNE can bind to Gα_q/11. HNE also significantly suppressed inositol phosphate release induced by aluminum fluoride. Collectively, our data suggest that HNE plays a role in altering receptor-G protein coupling in neurons under conditions of oxidative stress that may occur both normally, and before cell degeneration and death in pathological settings.     

Modifications of proteins by 4-hydroxy-2-nonenal in the ventilatory muscles of rats

Although 4-hydroxy-2-nonenal (HNE, a product of lipid peroxidation) is a major cause of oxidative damage inside skeletal muscles, the exact proteins modified by HNE are unknown. We used two-dimensional electrophoresis, immunoblotting, and mass spectrometry to identify selective proteins targeted by HNE inside the diaphragm of rats under two conditions: severe sepsis [induced by E. coli lipopolysaccharides (LPS)] and during strenuous muscle contractions elicited by severe inspiratory resistive loading (IRL). Diaphragm HNE-protein adduct formation (detected with a polyclonal antibody) increased significantly after 1 and 3 h of LPS injection with a return to baseline values thereafter. Similarly, HNE-protein adduct formation inside the diaphragm rose significantly after 6 but not 3 h of IRL. Mass spectrometry analysis of HNE-modified proteins revealed enolase 3b, aldolase and triosephosphate isomerase 1, creatine kinase, carbonic anyhdrase III, aconitase 2, dihydrolipoamide dehydrogenase, and electron transfer flavoprotein-beta. Measurements of in vitro enolase activity in the presence of pure HNE revealed that HNE significantly attenuated enolase activity in a dose-dependent fashion, suggesting that HNE-derived modifications have inhibitory effects on enzyme activity. We conclude that lipid peroxidation products may inhibit muscle contractile performance through selective targeting of enzymes involved in glycolysis, energy production as well as CO(2) hydration.     

Degradation of HNE-modified proteins--possible role of ubiquitin

4-Hydroxynonenal (HNE) is a lipid peroxidation product that is able to modify proteins. HNE-modified proteins are degraded to a considerable extend by the proteasomal system. It is unclear whether the recognition of HNE-modified proteins is mediated by ubiquitin, or whether the ubiquitin-independent proteasomal pathway is involved. In this study we demonstrate that HNE-modified GAPDH is preferentially ubiquitinated in vitro. In an attempt to demonstrate the formation of poly-ubiquitinated HNE-modified proteins in living cells we explored E36 fibroblasts. A clear rise in HNE-protein modification could be demonstrated after HNE treatment of the cells. Using inhibitors, we could show that the ubiquitin-dependent, ubiquitin-independent, and the lysosomal pathways affect the presence of HNE-modified proteins. We conclude that, although several proteolytic pathways exist for the degradation of HNE-modified proteins, there is the possibility of involvement of ubiquitin-dependent degradation.     

Involvements of the lipid peroxidation product,HNE, in the pathogenesis and progression of Alzheimer's disease

Alzheimer's disease (AD) is an age-related neurodegenerative disorder. A number of hypotheses have been proposed to explain AD pathogenesis. One such hypothesis proposed to explain AD pathogenesis is the oxidative stress hypothesis. Increased levels of oxidative stress markers including the markers of lipid peroxidation such as acrolein, 4-hydroxy-2-trans-nonenal (HNE), malondialdehyde, etc. are found in brains of AD subjects. In this review, we focus principally on research conducted in the area of HNE in the central nervous system (CNS) of AD and mild cognitive impairment (MCI), and further, we discuss likely consequences of lipid peroxidation with respect to AD pathogenesis and progression. Based on the research conducted so far in the area of lipid peroxidation, it is suggested that lipid accessible antioxidant molecules could be a promising therapeutic approach to treat or slow progression of MCI and AD.     

The proteasomal system and HNE-modified proteins

Metabolic processes and environmental conditions cause the constant formation of oxidizing species over the lifetime of cells and organisms. This leads to a continuous oxidation of intracellular components, including lipids, DNA and proteins. During the extensively studied process of lipid peroxidation, several reactive low-molecular weight products are formed, including reactive aldehydes as 4-hydroxynonenal (HNE). These aldehydic lipid peroxidation products in turn are able to modify proteins. The degradation of oxidized and oxidatively modified proteins is an essential part of the oxidant defenses of cells. The major proteolytic system responsible for the removal of oxidized cytosolic and nuclear proteins is the proteasomal system. The proteasomal system by itself is a multicomponent system responsible for the degradation of the majority of intracellular proteins. It has been shown that some, mildly cross-linked, HNE-modified proteins are preferentially degraded by the proteasome, but extensive modification with this cross-linking aldehyde leads to the formation of protein aggregates, that can actually inhibit the proteasome. This review summarizes our knowledge of the interactions between lipid peroxidation products, proteins, and the proteasomal system.     

Degradation of glyceraldehyde-3-phosphate dehydrogenase triggered by 4-hydroxy-2-nonenal and 4-hydroxy-2-hexenal

Lipid peroxidation products such as 4-hydroxy-2-nonenal (HNE) may be responsible for various pathophysiological events under oxidative stress, since they injure cellular components such as proteins and DNA. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH), which is a key enzyme of glycolysis and has been reported to be a multifunctional enzyme, is one of the enzymes inhibited by HNE. Previous studies showed that GAPDH is degraded when incubated with acetylleucine chloromethyl ketone (ALCK), resulting in the liberation of a 23-kDa fragment. In this study, we examined whether GAPDH incubated with HNE or other aldehydes of lipid peroxidation products are degraded similarly to that with ALCK. The U937 cell extract was incubated with these aldehydes at 37 degrees C and analyzed by Western blotting using anti-GAPDH antibodies. Incubation with HNE or 4-hydroxy-2-hexenal (HHE) decreased GAPDH activity and GAPDH protein level, and increased the 23-kDa fragment, in time- and dose-dependent manners, but that with other aldehydes did not. Gel filtration using the Superose 6 showed that the GAPDH-degrading activity was eluted in higher molecular fractions than proteasome activity. The enzyme activity was detected at the basic range of pH and inhibited by serine protease inhibitors, diisopropyl fluorophosphate and phenylmethylsulfonyl fluoride, but not by other protease inhibitors including a proteasome inhibitor, MG-132, and a tripeptidyl peptidase II (TPP II) inhibitor, AAF-CMK. These results suggest that GAPDH modified by HNE and HHE is degraded by a giant serine protease, releasing the 23-kDa fragment, not by proteasome or TPP II.     

Calorie restriction delays lipid oxidative damage in Drosophila melanogaster

The oxidative stress hypothesis predicts that the accumulation of oxidative damage to a variety of macromolecules is the molecular trigger driving the process of aging. Although an inverse relationship between oxidative damage and lifespan has been established in several different species, the precise relationship between oxidative damage and aging is not fully understood. Drosophila melanogaster is a favored model organism for aging research. Environmental interventions such as ambient temperature and calorie restriction can alter adult lifespan to provide an excellent system to examine the relationship between oxidative damage, aging and lifespan. We have developed an enzyme-linked immunosorbent assay (ELISA) using commercially available reagents for measuring 4-hydroxy-2-nonenal (HNE) in proteins, a marker for oxidative damage to lipids, and present data in flies to show that HNE adducts accumulate in an age-dependent manner. With immunohistology, we also find the primary site of HNE accumulation is the pericerebral fat body, where induction of dFOXO was recently shown to retard aging. When subjected to environmental interventions that shorten lifespan, such as elevated ambient temperature, the chronological accumulation of HNE adduct is accelerated. Conversely, interventions that extend lifespan, such as lower ambient temperature or low calorie diets, slow the accumulation of HNE adduct. These studies associate damage from lipid peroxidation with aging and lifespan in Drosophila and show that calorie restriction in flies, as in mammals, slows the accumulation of lipid related oxidative damage.     

4-Hydroxy-2(E)-nonenal (HNE) catabolism and formation of HNE adducts are modulated by β oxidation of fatty acids in the isolated rat heart

We previously reported that a novel metabolic pathway functionally catabolizes 4-hydroxy-2(E)-nonenal (HNE) via two parallel pathways, which rely heavily on β-oxidation pathways. The hypothesis driving this report is that perturbations of β oxidation will alter the catabolic disposal of HNE, favoring an increase in the concentrations of HNE and HNE-modified proteins that may further exacerbate pathology. This study employed Langendorff perfused hearts to investigate the impact of cardiac injury modeled by ischemia/reperfusion and, in a separate set of perfusions, the effects of elevated lipid (typically observed in obesity and type II diabetes) by perfusing with increased fatty acid concentrations (1 mM octanoate). During ischemia, HNE concentrations doubled and the glutathione–HNE adduct and 4-hydroxynonanoyl-CoA were increased by 7- and 10-fold, respectively. Under conditions of increased fatty acid, oxidation to 4-hydroxynonenoic acid was sustained; however, further catabolism through β oxidation was nearly abolished. The inhibition of HNE catabolism was not compensated for by other disposal pathways of HNE, rather an increase in HNE-modified proteins was observed. Taken together, this study presents a mechanistic rationale for the accumulation of HNE and HNE-modified proteins in pathological conditions that involve alterations to β oxidation, such as myocardial ischemia, obesity, and high-fat diet-induced diseases.     

Identification of an unstable 4-hydroxynoneal modification on the 20S proteasome subunit α7 by recombinant antibody technology.

Numerous cellular functions rely on an active proteasome allowing degradation of damaged or misfolded proteins. Therefore changes in the proteasomal activity have important physiological consequences. During oxidative stress the production of free radicals can result in the formation of 4-hydroxynonenal (HNE) following lipid peroxidiation. The HNE moiety is highly reactive and via a nucleophilic attack readily forms covalent links to cysteine, histidine and lysine side chains. However, as the chemical properties of these amino acids differ, so does the kinetics of the reactions. While covalent linkage through Michael addition is well established, reversible and unstable associations have only been indicated in a few cases. In the present study we have identified an unstable HNE adduct on the α7 subunit of the 20S proteasome using phage display of recombinant antibodies. This recombinant antibody fragment recognized HNE modified proteasomes in vitro and showed that this epitope was easily HNE modified, yet unstable, and influenced by experimental procedures. Hence unstable HNE-adducts could be overlooked as a regulatory mechanism of proteasomal activity and a participating factor in the decreased proteasomal activity associated with oxidative stress.     

Oxidatively Modified GST and MRP1 in Alzheimer’s Disease Brain: Implications for Accumulation of Reactive Lipid Peroxidation Products

Alzheimer disease (AD) is a neurodegenerative disorder characterized pathologically by intracellular inclusions including neurofibrillary tangles (NFT) and senile plaques. Several lines of evidence implicate oxidative stress with the progression of AD. 4-hydroxy-2-trans-nonenal (HNE), an aldehydic product of membrane lipid peroxidation, is increased in AD brain. The alpha class of glutathione S-transferase (GST) can detoxify HNE and plays an important role in cellular protection against oxidative stress. The export of the glutathione conjugate of HNE is required to fully potentiate the GST-mediated protection. The multidrug resistance protein-1 (MRP1) and GST proteins may act in synergy to confer cellular protection. In the present study, we studied oxidative modification of GST and MRP1 in AD brain by immunoprecipitation of GST and MRP1 proteins followed by Western blot analysis using anti-HNE antibody. The results suggested that HNE is covalently bound to GST and MRP1 proteins in excess in AD brain. Collectively, the data suggest that HNE may be an important mediator of oxidative stress-induced impairment of this detoxifying system and may thereby play a role in promoting neuronal cell death. The results from this study also imply that augmenting endogenous oxidative defense capacity through dietary or pharmacological intake of antioxidants may slow down the progression of neurodegenerative processes in AD.     

Proteasome activity in experimental diabetes

Numerous studies have indicated that oxidative stress contributes to the development and progression of diabetes and other related complications. Since the ubiquitin-proteasome pathway is involved in degradation of oxidized proteins, it is to be expected that alterations in proteasome-dependent proteolysis accompany diabetes. This paper focuses on the role of the proteasome in alloxan-induced experimental diabetes. The changes in proteasomal activity and oxidative stress indices (protein oxidation and lipid peroxidation) were evaluated. The obtained results revealed increased protein oxidation and lipid peroxidation, as well as alterations in proteasomal activities in diabetic rats. Our data indicates a significant decrease in chymotryptic-like activity; increased tryptic-like activity; and unchanged post-glutamyl peptide hydrolytic-like activity. These findings suggest the presence of oxidative stress in diabetes that appears to result in changes to the ubiquitin-proteasome pathway.     

Caloric restriction of rhesus monkeys lowers oxidative damage in skeletal muscle.

In laboratory rodents, caloric restriction (CR) retards several age-dependent physiological and biochemical changes in skeletal muscle, including increased steady-state levels of oxidative damage to lipids, DNA, and proteins. We used immunogold electron microscopic (EM) techniques with antibodies raised against 4-hydroxy-2-nonenal (HNE) -modified proteins, dinitrophenol, and nitrotyrosine to quantify and localize the age-dependent accrual of oxidative damage in rhesus monkey vastus lateralis skeletal muscle. Using immunogold EM analysis of muscle from rhesus monkeys ranging in age from 2 to 34 years old, a fourfold maximal increase in levels of HNE-modified proteins was observed. Likewise, carbonyl levels increased approximately twofold with aging. Comparing 17- to 23-year-old normally fed to age-matched monkeys subjected to CR for 10 years, levels of HNE-modified proteins, carbonyls, and nitrotyrosine in skeletal muscle from the CR group were significantly less than control group values. Oxidative damage largely localized to myofibrils, with lesser labeling in other subcellular compartments. Accumulation of lipid peroxidation-derived aldehydes, such as malondialdehyde and 4-hydroxy-2-alkenals, and protein carbonyls were measured biochemically and confirmed the morphological data. Our study is the first to quantify morphologically and localize the age-dependent accrual of oxidative damage in mammalian skeletal muscle and to demonstrate that oxidative damage in primates is lowered by CR.     

Proteasomal dysfunction induced by 4‐hydroxy‐2,3‐trans‐nonenal,an end‐product of lipid peroxidation: a mechanism contributing to neurodegeneration?

4-Hydroxy-2,3-trans-nonenal (HNE) is a neurotoxic unsaturated aldehyde end-product of lipid peroxidation. The addition of HNE to NT-2 and SK-N-MC cell lines induces apoptosis and we now investigated the time-course of events occurring prior to apoptosis. Treatment of both NT-2 and SK-N-MC cell lines with HNE led to HNE association with the proteasome, increased levels of protein carbonyls and ubiquitinated proteins, and decreased proteasomal function. There was also decreased metabolic activity, cytochrome c release and activation of caspase 3, followed by apoptotic changes including chromatin condensation, cell shrinkage and DNA fragmentation and laddering. Overexpression of mutant superoxide dismutase 1 proteins associated with amyotrophic lateral sclerosis decreased proteasomal activities in the absence of HNE and accelerated the apoptosis induced by HNE. By contrast, overexpression of wild-type superoxide dismutase 1 did not affect basal levels of proteasomal activity. The data suggest that accumulation of ubiquitinated proteins and impairment of proteasomal function are important events in HNE toxicity. We propose that the proteasomal system is a significant target of HNE neurotoxicity in a wide range of neurodegenerative diseases, especially if abnormal proteins are being expressed.