Trapping of 4-hydroxynonenal by glutathione efficiently prevents formation of DNA adducts in human cells

Quantitative Analysis of Glutathione and Carnosine Adducts with 4-Hydroxy-2-nonenal in Muscle in a hSOD1G93A ALS Rat Model

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by the dysfunction and death of motor neurons through multifactorial mechanisms that remain unclear. ALS has been recognized as a multisystemic disease, and the potential role of skeletal muscle in disease progression has been investigated. Reactive aldehydes formed as secondary lipid peroxidation products in the redox processes react with biomolecules, such as DNA, proteins, and amino acids, resulting in cytotoxic effects. 4-Hydroxy-2-nonenal (HNE) levels are elevated in the spinal cord motor neurons of ALS patients, and HNE-modified proteins have been identified in the spinal cord tissue of an ALS transgenic mice model, suggesting that reactive aldehydes can contribute to motor neuron degeneration in ALS. One biological pathway of aldehyde detoxification involves conjugation with glutathione (GSH) or carnosine (Car). Here, the detection and quantification of Car, GSH, GSSG (glutathione disulfide), and the corresponding adducts with HNE, Car-HNE, and GS-HNE, were performed in muscle and liver tissues of a hSOD1G93A ALS rat model by reverse-phase high-performance liquid chromatography coupled to electrospray ion trap tandem mass spectrometry in the selected reaction monitoring mode. A significant increase in the levels of GS-HNE and Car-HNE was observed in the muscle tissue of the end-stage ALS animals. Therefore, analyzing variations in the levels of these adducts in ALS animal tissue is crucial from a toxicological perspective and can contribute to the development of new therapeutic strategies.

The Key Role of GSH in Keeping the Redox Balance in Mammalian Cells: Mechanisms and Significance of GSH in Detoxification via Formation of Conjugates

Glutathione (GSH) is a ubiquitous tripeptide that is biosynthesized in situ at high concentrations (1-5 mM) and involved in the regulation of cellular homeostasis via multiple mechanisms. The main known action of GSH is its antioxidant capacity, which aids in maintaining the redox cycle of cells. To this end, GSH peroxidases contribute to the scavenging of various forms of ROS and RNS. A generally underestimated mechanism of action of GSH is its direct nucleophilic interaction with electrophilic compounds yielding thioether GSH S-conjugates. Many compounds, including xenobiotics (such as NAPQI, simvastatin, cisplatin, and barbital) and intrinsic compounds (such as menadione, leukotrienes, prostaglandins, and dopamine), form covalent adducts with GSH leading mainly to their detoxification. In the present article, we wish to present the key role and significance of GSH in cellular redox biology. This includes an update on the formation of GSH-S conjugates or GSH adducts with emphasis given to the mechanism of reaction, the dependence on GST (GSH S-transferase), where this conjugation occurs in tissues, and its significance. The uncovering of the GSH adducts' formation enhances our knowledge of the human metabolome. GSH-hematin adducts were recently shown to have been formed spontaneously in multiples isomers at hemolysates, leading to structural destabilization of the endogenous toxin, hematin (free heme), which is derived from the released hemoglobin. Moreover, hemin (the form of oxidized heme) has been found to act through the Kelch-like ECH associated protein 1 (Keap1)-nuclear factor erythroid 2-related factor-2 (Nrf2) signaling pathway as an epigenetic modulator of GSH metabolism. Last but not least, the implications of the genetic defects in GSH metabolism, recorded in hemolytic syndromes, cancer and other pathologies, are presented and discussed under the framework of conceptualizing that GSH S-conjugates could be regarded as signatures of the cellular metabolism in the diseased state.

Detoxification of the Lipid Peroxidation Aldehyde, 4-Hydroxynonenal, by Apple Phloretin In Vitro and in Mice

4-Hydroxy-2-nonenal (4-HNE) is a secondary cytotoxic product generated from lipid peroxidation of polyunsaturated fatty acids (PUFAs). The accumulation of 4-HNE can covalently modify biomolecules, such as DNA and proteins, leading to various pathological conditions. Apple phloretin has been shown to be able to trap 4-HNE in vitro, but the trapping mechanisms of 4-HNE by phloretin are not fully understood. Moreover, whether the in vitro trapping efficacy of phloretin toward 4-HNE could be transferred into in vivo environments has never been investigated. In the present study, we observed the formation of 4-HNE conjugates of phloretin increased as phloretin decreased during the in vitro incubation. We then purified and characterized three mono-4-HNE-conjugates of phloretin using NMR and LC-MS/MS techniques. We thereafter demonstrated that apple phloretin could scavenge in vivo 4-HNE via the formation of at least three mono-4-HNE-conjugates of phloretin in a dose-dependent manner in mice after oral administration of three doses of phloretin (25, 100, and 400 mg/kg). The findings from this study pave the way to understanding how dihydrochalcones could act as effective scavengers of 4-HNE by working as sacrificial nucleophiles in vivo, thereby preventing or reducing the risk of 4-HNE-associated chronic diseases.

Discrete Correlation Summation Clustering Reveals Differential Regulation of Liver Metabolism by Thrombospondin-1 in Low-Fat and High-Fat Diet-Fed Mice

Thrombospondin-1 (TSP1) is a matricellular protein with many important roles in mediating carcinogenesis, fibrosis, leukocyte recruitment, and metabolism. We have previously shown a role of diet in the absence of TSP1 in liver metabolism in the context of a colorectal cancer model. However, the metabolic implications of TSP1 regulation by diet in the liver metabolism are currently understudied. Therefore Discrete correlation summation (DCS) was used to re-interrogate data and determine the metabolic alterations of TSP1 deficiency in the liver, providing new insights into the role of TSP1 in liver injury and the progression of liver pathologies such as nonalcoholic fatty liver disease (NAFLD). DCS analysis provides a straightforward approach to rank covariance and data clustering when analyzing complex data sets. Using this approach, our previous liver metabolite data was re-analyzed by comparing wild-type (WT) and Thrombospondin-1 null (Thbs1-/-) mice, identifying changes driven by genotype and diet. Principal component analysis showed clustering of animals by genotype regardless of diet, indicating that TSP1 deficiency alters metabolite handling in the liver. High-fat diet consumption significantly altered over 150 metabolites in the Thbs1-/- livers versus approximately 90 in the wild-type livers, most involved in amino acid metabolism. The absence of Thbs1 differentially regulated tryptophan and tricarboxylic acid cycle metabolites implicated in the progression of NAFLD. Overall, the lack of Thbs1 caused a significant shift in liver metabolism with potential implications for liver injury and the progression of NAFLD.

The interplay of the oral microbiome and alcohol consumption in oral squamous cell carcinomas

Oral cancer (OC) is among the top twenty occurring cancers in the world, with a mortality rate of 50%. A shift to a functionally inflammatory or a 'disease state' oral microbiome composition has been observed amongst patients with premalignant disorders and OC, with evidence suggesting alcohol could be exacerbating the inflammatory influence of the oral microorganisms. Alcohol dehydrogenase (ADH, EC 1.1.1.1) converts alcohol into a known carcinogenic metabolite, acetaldehyde and while ADH levels in oral mucosa are low, several oral commensal species possess ADH and could produce genotoxic levels of acetaldehyde. With a direct association between oral microbiome status, alcohol and poor oral health status combining to induce chronic inflammation with increased acetaldehyde levels - this leads to a tumour promoting environment. This new disease state increases the production of reactive oxygen species (ROS), while impairing anti-oxidant systems thus activating the redox signalling required for the promotion and survival of tumours. This review aims to highlight the evidence linking these processes in the progression of oral cancer.

The Disposal of Reactive Carbonyl Species through Carnosine Conjugation: What We Know Now

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Reactive Carbonyl Species are electrophiles generated by the oxidative cleavage of lipids and sugars. Such compounds have been described as important molecules for cellular signaling, whilst their accumulation has been found to be cytotoxic as they may trigger aberrant modifications of proteins (a process often referred to as carbonylation).

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A correlation between carbonylation of proteins and human disease progression has been shown in ageing, diabetes, obesity, chronic renal failure, neurodegeneration and cardiovascular disease. However, the fate of reactive carbonyl species is still far from being understood, especially concerning the mechanisms responsible for their disposal as well as the importance of this in disease progression.

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In this context, some data have been published on phase I and phase II deactivation of reactive carbonyl species. In the case of phase II mechanisms, the route involving glutathione conjugation and subsequent disposal of the adducts has been extensively studied both in vitro and in vivo for some of the more representative compounds, e.g. 4-hydroxynonenal.

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There is also emerging evidence of an involvement of carnosine as an endogenous alternative to glutathione for phase II conjugation. However, the fate of carnosine conjugates is still poorly investigated and, unlike glutathione, there is little evidence of the formation of carnosine adducts in vivo. The acquisition of such data could be of importance for the development of new drugs, since carnosine and its derivatives have been proposed as potential therapeutic agents for the mitigation of carbonylation associated with disease progression.

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Herein, we wish to review our current knowledge of the binding of reactive carbonyl species with carnosine together with the disposal of carnosine conjugates, emphasizing those aspects still requiring investigation such as conjugation reversibility and enzyme assisted catalysis of the reactions.

Generation and propagation of yeast prion [URE3] are elevated under electromagnetic field

In this study, we studied the effect of 2.0 GHz radio frequency electromagnetic field (RF-EMF) and 50 Hz extremely low frequency electromagnetic field (ELF-EMF) exposure on prion generation and propagation using two budding yeast strains, NT64C and SB34, as model organisms. Under exposure to RF-EMF or ELF-EMF, the de novo generation and propagation of yeast prions [URE3] were elevated in both strains. The elevation increased over time, and the effects of ELF-EMF occurred in a dose-dependent manner. The transcription and expression levels of the molecular chaperones Hsp104, Hsp70-Ssa1/2, and Hsp40-Ydj1 were not statistically significantly changed after exposure. Furthermore, the levels of ROS, as well as the activities of superoxide dismutase (SOD) and catalase (CAT), were significantly elevated after short-term, but not long-term exposure. This work demonstrated for the first time that EMF exposure could elevate the de novo generation and propagation of yeast prions and supports the hypothesis that ROS may play a role in the effects of EMF on protein misfolding. The effects of EMF on protein folding and ROS levels may mediate the broad effects of EMF on cell function.

Effects of Female Sex Steroids Administration on Pathophysiologic Mechanisms in Traumatic Brain Injury

Secondary brain damage following initial brain damage in traumatic brain injury (TBI) is a major cause of adverse outcomes. There are many gaps in TBI research and a lack of therapy to limit debilitating outcomes in TBI or enhance the neurogenesis, despite pre-clinical and clinical research performed in TBI. Females show harmful outcomes against brain damage including TBI less than males, independent of different TBI occurrence. A significant reduction in secondary brain damage and improvement in neurologic outcome post-TBI has been reported following the use of progesterone and estrogen in many experimental studies. Although useful features of sex steroids including progesterone have been identified in TBI clinical trials I and II, clinical trials III have been unsuccessful. This review article focuses on evidence of secondary injury mechanisms and neuroprotective effects of estrogen and progesterone in TBI. Understanding these mechanisms may enable researchers to achieve greater success in TBI clinical studies. It seems that the design of clinical studies should be revised due to translation loss of animal studies to clinical studies. The heterogeneous and complex nature of TBI, the endogenous levels of sex hormones at the time of taking these hormones, the therapeutic window of the drug, the dosage of the drug, the selection of appropriate targets in evaluation, the determination of responsive population, gender and age based on animal studies should be considered in the design of TBI human studies in future.

Catabolism of (2E)-4-hydroxy-2-nonenal via ω- and ω-1-oxidation stimulated by ketogenic diet

Oxidative stress triggers the peroxidation of ω-6-polyunsaturated fatty acids to reactive lipid fragments, including (2E)-4-hydroxy-2-nonenal (HNE). We previously reported two parallel catabolic pathways of HNE. In this study, we report a novel metabolite that accumulates in rat liver perfused with HNE or 4-hydroxynonanoic acid (HNA), identified as 3-(5-oxotetrahydro-2-furanyl)propanoyl-CoA. In experiments using a combination of isotopic analysis and metabolomics studies, three catabolic pathways of HNE were delineated following HNE conversion to HNA. (i) HNA is ω-hydroxylated to 4,9-dihydroxynonanoic acid, which is subsequently oxidized to 4-hydroxynonanedioic acid. This is followed by the degradation of 4-hydroxynonanedioic acid via β-oxidation originating from C-9 of HNA breaking down to 4-hydroxynonanedioyl-CoA, 4-hydroxyheptanedioyl-CoA, or its lactone, 2-hydroxyglutaryl-CoA, and 2-ketoglutaric acid entering the citric acid cycle. (ii) ω-1-hydroxylation of HNA leads to 4,8-dihydroxynonanoic acid (4,8-DHNA), which is subsequently catabolized via two parallel pathways we previously reported. In catabolic pathway A, 4,8-DHNA is catabolized to 4-phospho-8-hydroxynonanoyl-CoA, 3,8-dihydroxynonanoyl-CoA, 6-hydroxyheptanoyl-CoA, 4-hydroxypentanoyl-CoA, propionyl-CoA, and acetyl-CoA. (iii) The catabolic pathway B of 4,8-DHNA leads to 2,6-dihydroxyheptanoyl-CoA, 5-hydroxyhexanoyl-CoA, 3-hydroxybutyryl-CoA, and acetyl-CoA. Both in vivo and in vitro experiments showed that HNE can be catabolically disposed via ω- and ω-1-oxidation in rat liver and kidney, with little activity in brain and heart. Dietary experiments showed that ω- and ω-1-hydroxylation of HNA in rat liver were dramatically up-regulated by a ketogenic diet, which lowered HNE basal level. HET0016 inhibition and mRNA expression level suggested that the cytochrome P450 4A are main enzymes responsible for the NADPH-dependent ω- and ω-1-hydroxylation of HNA/HNE.

Recent developments in DNA adduct analysis by mass spectrometry: a tool for exposure biomonitoring and identification of hazard for environmental pollutants

DNA adducts represent an important category of biomarkers for detection and exposure surveillance of potential carcinogenic and genotoxic chemicals in the environment. Sensitive and specific analytical methods are required to detect and differentiate low levels of adducts from native DNA from in vivo exposure. In addition to biomonitoring of environmental pollutants, analytical methods have been developed for structural identification of adducts which provides fundamental information for determining the toxic pathway of hazardous chemicals. In order to achieve the required sensitivity, mass spectrometry has been increasingly utilized to quantify adducts at low levels as well as to obtain structural information. Furthermore, separation techniques such as chromatography and capillary electrophoresis can be coupled to mass spectrometry to increase the selectivity. This review will provide an overview of advances in detection of adducted and modified DNA by mass spectrometry with a focus on the analysis of nucleosides since 2007. Instrument advances, sample and instrument considerations, and recent applications will be summarized in the context of hazard assessment. Finally, advances in biomonitoring applying mass spectrometry will be highlighted. Most importantly, the usefulness of DNA adducts measurement and detection will be comprehensively discussed as a tool for assessment of in vitro and in vivo exposure to environmental pollutants.

4-Hydroxy-trans-2-nonenal (4-HNE) induces neuronal SH-SY5Y cell death via hampering ATP binding at kinase domain of Akt1

Inhibition mechanism(s) of protein kinase B/Akt1 and its consequences on related cell signaling were investigated in human neuroblastoma SH-SY5Y cells exposed to 4-hydroxy-trans-2-nonenal (4-HNE), one of the most reactive aldehyde by-products of lipid peroxidation. In silico data indicate that 4-HNE interacts with kinase domain of Akt1 with the total docking score of 6.0577 and also forms H-bond to Glu234 residue similar to highly potent Akt1 inhibitor imidazopiperidine analog 8b, in which the protonated imidazole nitrogen involves in two hydrogen bonds between Glu234 and Asp292. The strong hydrogen bonding with Glu234 and hydrophobic interactions with several residues, namely Leu156, Gly157, Val164, Ala177, Tyr229, Ala230, Met281 and Thr291, at the vicinity which is normally occupied by the ribose of ATP, appear to be the main causes of Akt1 inhibition and lead to the significant conformational change on this region of protein. Results of mutational docking prove that Glu234 plays a major role in 4-HNE-mediated Akt1 inhibition. In silico data on Akt inhibition were further validated by observing the down-regulated levels of phosphorylated (Thr308/Ser493) Akt1 as well as the altered levels of the downstream targets of pAkt, namely downregulated levels of pGSK3β (Ser9), β-catenin, Bcl2 and upregulated levels of pro-apoptotic markers, namely Bad, Bax, P(53) and caspase-9/3. The cellular fate of such pAkt inhibition was evidenced by increased reactive oxygen species, degraded nuclei, transferase dUTP nick end labeling positive cells and upregulated levels of pJNK1/2. We identified that 4-HNE-mediated Akt1 inhibition was due to the competitive inhibition of ATP by 4-HNE at the kinase domain of ATP binding sites.

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 (1mM 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.

Characterization of thiol-conjugated metabolites of ginger components shogaols in mouse and human urine and modulation of the glutathione levels in cancer cells by [6]-shogaol

SCOPE

Shogaols, a series of major constituents in dried ginger with the most abundant being [6]-, [8]-, and [10]-shogaols, show much higher anticancer potencies than gingerols. Previously, we reported the mercapturic acid pathway as a major metabolic route for [6]-shogaol in mice. However, it is still unclear how the side chain length affects the metabolism of shogaols and how shogaols are metabolized in humans.

METHODS AND RESULTS

We first investigate the metabolism of [10]-shogaol in mouse urine, and then investigate the biotransformation of shogaols in human urine. Our results show that eight major thiol-conjugated metabolites of [10]-shogaol were detected in mouse urine, while six major thiol-conjugated metabolites of [6]-shogaol, two thiol-conjugated metabolites of [8]-shogaol, and two thiol-conjugated metabolites of [10]-shogaol were detected in urine collected from human after drinking ginger tea, using LC/ESI-MS/MS. Our results clearly indicate the mercapturic acid pathway is a major metabolic route for [10]-shogaol in mice and for shogaols in human. Furthermore, we also investigated the regulation of glutathione (GSH) by [6]-shogaol in human colon cancer cells HCT-116. Our results show [6]-shogaol, after initially depleting glutathione levels, can subsequently restore and increase GSH levels over time.

CONCLUSION

Shogaols are metabolized extensively in mouse and human to form thiol-conjugated metabolites and GSH might play an important role in the cancer-preventive activity of ginger.

Metabolism of [6]-shogaol in mice and in cancer cells

Ginger has received extensive attention because of its antioxidant, anti-inflammatory, and antitumor activities. However, the metabolic fate of its major components is still unclear. In the present study, the metabolism of [6]-shogaol, one of the major active components in ginger, was examined for the first time in mice and in cancer cells. Thirteen metabolites were detected and identified, seven of which were purified from fecal samples collected from [6]-shogaol-treated mice. Their structures were elucidated as 1-(4'-hydroxy-3'-methoxyphenyl)-4-decen-3-ol (M6), 5-methoxy-1-(4'-hydroxy-3'-methoxyphenyl)-decan-3-one (M7), 3',4'-dihydroxyphenyl-decan-3-one (M8), 1-(4'-hydroxy-3'-methoxyphenyl)-decan-3-ol (M9), 5-methylthio-1-(4'-hydroxy-3'-methoxyphenyl)-decan-3-one (M10), 1-(4'-hydroxy-3'-methoxyphenyl)-decan-3-one (M11), and 5-methylthio-1-(4'-hydroxy-3'-methoxyphenyl)-decan-3-ol (M12) on the basis of detailed analysis of their (1)H, (13)C, and two-dimensional NMR data. The rest of the metabolites were identified as 5-cysteinyl-M6 (M1), 5-cysteinyl-[6]-shogaol (M2), 5-cysteinylglycinyl-M6 (M3), 5-N-acetylcysteinyl-M6 (M4), 5-N-acetylcysteinyl-[6]-shogaol (M5), and 5-glutathiol-[6]-shogaol (M13) by analysis of the MS(n) (n = 1-3) spectra and comparison to authentic standards. Among the metabolites, M1 through M5, M10, M12, and M13 were identified as the thiol conjugates of [6]-shogaol and its metabolite M6. M9 and M11 were identified as the major metabolites in four different cancer cell lines (HCT-116, HT-29, H-1299, and CL-13), and M13 was detected as a major metabolite in HCT-116 human colon cancer cells. We further showed that M9 and M11 are bioactive compounds that can inhibit cancer cell growth and induce apoptosis in human cancer cells. Our results suggest that 1) [6]-shogaol is extensively metabolized in these two models, 2) its metabolites are bioactive compounds, and 3) the mercapturic acid pathway is one of the major biotransformation pathways of [6]-shogaol.

Replication bypass of the trans-4-Hydroxynonenal-derived (6S,8R,11S)-1,N(2)-deoxyguanosine DNA adduct by the sulfolobus solfataricus DNA polymerase IV

trans-4-Hydroxynonenal (HNE) is the major peroxidation product of ω-6 polyunsaturated fatty acids in vivo. Michael addition of the N(2)-amino group of dGuo to HNE followed by ring closure of N1 onto the aldehyde results in four diastereomeric 1,N(2)-dGuo (1,N(2)-HNE-dGuo) adducts. The (6S,8R,11S)-HNE-1,N(2)-dGuo adduct was incorporated into the 18-mer templates 5'-d(TCATXGAATCCTTCCCCC)-3' and d(TCACXGAATCCTTCCCCC)-3', where X = (6S,8R,11S)-HNE-1,N(2)-dGuo adduct. These differed in the identity of the template 5'-neighbor base, which was either Thy or Cyt, respectively. Each of these templates was annealed with either a 13-mer primer 5'-d(GGGGGAAGGATTC)-3' or a 14-mer primer 5'-d(GGGGGAAGGATTCC)-3'. The addition of dNTPs to the 13-mer primer allowed analysis of dNTP insertion opposite to the (6S,8R,11S)-HNE-1,N(2)-dGuo adduct, whereas the 14-mer primer allowed analysis of dNTP extension past a primed (6S,8R,11S)-HNE-1,N(2)-dGuo:dCyd pair. The Sulfolobus solfataricus P2 DNA polymerase IV (Dpo4) belongs to the Y-family of error-prone polymerases. Replication bypass studies in vitro reveal that this polymerase inserted dNTPs opposite the (6S,8R,11S)-HNE-1,N(2)-dGuo adduct in a sequence-specific manner. If the template 5'-neighbor base was dCyt, the polymerase inserted primarily dGTP, whereas if the template 5'-neighbor base was dThy, the polymerase inserted primarily dATP. The latter event would predict low levels of Gua → Thy mutations during replication bypass when the template 5'-neighbor base is dThy. When presented with a primed (6S,8R,11S)-HNE-1,N(2)-dGuo:dCyd pair, the polymerase conducted full-length primer extension. Structures for ternary (Dpo4-DNA-dNTP) complexes with all four template-primers were obtained. For the 18-mer:13-mer template-primers in which the polymerase was confronted with the (6S,8R,11S)-HNE-1,N(2)-dGuo adduct, the (6S,8R,11S)-1,N(2)-dGuo lesion remained in the ring-closed conformation at the active site. The incoming dNTP, either dGTP or dATP, was positioned with Watson-Crick pairing opposite the template 5'-neighbor base, dCyt or dThy, respectively. In contrast, for the 18-mer:14-mer template-primers with a primed (6S,8R,11S)-HNE-1,N(2)-dGuo:dCyd pair, ring opening of the adduct to the corresponding N(2)-dGuo aldehyde species occurred. This allowed Watson-Crick base pairing at the (6S,8R,11S)-HNE-1,N(2)-dGuo:dCyd pair.

Formation of a N2-dG:N2-dG carbinolamine DNA cross-link by the trans-4-hydroxynonenal-derived (6S,8R,11S) 1,N2-dG adduct

Michael addition of trans-4-hydroxynonenal (HNE) to deoxyguanosine yields diastereomeric 1,N²-dG adducts in DNA. When placed opposite dC in the 5′-CpG-3′ sequence, the (6S,8R,11S) diastereomer forms a N²-dG:N²-dG interstrand cross-link [Wang, H.; Kozekov, I. D.; Harris, T. M.; Rizzo, C. J. J. Am. Chem. Soc.2003, 125, 5687–5700]. We refined its structure in 5′-d(G¹C²T³A⁴G⁵C⁶X⁷A⁸G⁹T¹⁰C¹¹C¹²)-3′·5′-d(G¹³G¹⁴A¹⁵C¹⁶T¹⁷C¹⁸Y¹⁹C²⁰T²¹A²²G²³C²⁴)-3′ [X⁷ is the dG adjacent to the C6 carbon of the cross-link or the α-carbon of the (6S,8R,11S) 1,N²-dG adduct, and Y¹⁹ is the dG adjacent to the C8 carbon of the cross-link or the γ-carbon of the HNE-derived (6S,8R,11S) 1,N²-dG adduct; the cross-link is in the 5′-CpG-3′ sequence]. Introduction of ¹³C at the C8 carbon of the cross-link revealed one ¹³C8→H8 correlation, indicating that the cross-link existed predominantly as a carbinolamine linkage. The H8 proton exhibited NOEs to Y¹⁹ H1′, C²⁰ H1′, and C²⁰ H4′, orienting it toward the complementary strand, consistent with the (6S,8R,11S) configuration. An NOE was also observed between the HNE H11 proton and Y¹⁹ H1′, orienting the former toward the complementary strand. Imine and pyrimidopurinone linkages were excluded by observation of the Y¹⁹N²H and X⁷ N1H protons, respectively. A strong H8→H11 NOE and no ³J(¹³C→H) coupling for the ¹³C8–O–C11–H11 eliminated the tetrahydrofuran species derived from the (6S,8R,11S) 1,N²-dG adduct. The (6S,8R,11S) carbinolamine linkage and the HNE side chain were located in the minor groove. The X⁷N² and Y¹⁹N² atoms were in the gauche conformation with respect to the linkage, maintaining Watson–Crick hydrogen bonds at the cross-linked base pairs. A solvated molecular dynamics simulation indicated that the anti conformation of the hydroxyl group with respect to C6 of the tether minimized steric interaction and predicted hydrogen bonds involving O8H with C²⁰O² of the 5′-neighbor base pair G⁵·C²⁰ and O11H with C¹⁸O² of X⁷·C¹⁸. These may, in part, explain the stability of this cross-link and the stereochemical preference for the (6S,8R,11S) configuration.

The toxicity redox mechanisms of cadmium alone or together with copper and zinc homeostasis alteration: its redox biomarkers

Cadmium (Cd) is a toxic metal and can induce and/or promote diseases in humans (cancer, aging diseases, kidney and bone diseases, etc.). Its toxicity involves many mechanisms including the alteration of copper (Cu) and zinc (Zn) homeostasis leading to reactive oxygen species (ROS) production, either directly or through the inhibition of antioxidant activities. Importantly, ROS can induce oxidative damages in cells. Cadmium, Cu and Zn are also able to induce glutathione (GSH) and metallothioneins (MT) synthesis in a cell-type-dependent manner. As a consequence, the effects induced by these three metals result simultaneously from the inhibition of antioxidant activities and the induction of other factors such as GSH and MT synthesis. MT levels are regulated not only by the p53 protein in a cell-type-dependent manner, or by transcription factors such as metal-responsive transcription factor 1 (MTF-1) and cellular Zn levels but also by cellular GSH level. As described in the literature, DNA damage, GSH and MT levels are sensitive biomarkers used to identify Cd-induced toxicity alone or together with Cu and Zn homeostasis alteration.

[Nuclear glutathione and its functions]

During recent years the nuclear localization of glutathione has been confirmed and this fraction has been quantitatively determined. The nuclear GSH and the enzymes of its metabolism realize independent and important functions. They considerably differ from functions of hyaloplasmic and mitochondrial GSH. Glutathione interacts with regulatory pathways, involved into signal transmission into the nucleus.

Induction of cell cycle arrest and DNA damage by the HDAC inhibitor panobinostat (LBH589) and the lipid peroxidation end product 4-hydroxynonenal in prostate cancer cells

Histone deacetylase inhibitors (HDACIs) are promising antineoplastic agents for the treatment of cancer. Here we report that the lipid peroxidation end product 4-hydroxynonenal (HNE) significantly potentiates the anti-tumor effects of the HDAC inhibitor panobinostat (LBH589) in the PC3 prostate cancer cell model. Panobinostat and HNE inhibited proliferation of PC3 cells and the combination of the two agents resulted in a significant combined effect. Cell cycle analysis revealed that both single agents and, to a greater extent, their combined treatment induced G2/M arrest, but cell death occurred in the combined treatment only. Furthermore, HNE and, to a greater extent, the combined treatment induced dephosphorylation of Cdc2 leading to progression into mitosis as confirmed by α-tubulin/DAPI staining and phospho-histone H3 (Ser10) analysis. To evaluate possible induction of DNA damage we utilized the marker phosphorylated histone H2A.X. Results showed that the combination of panobinostat and HNE induced significant DNA damage concomitant with the mitotic arrest. Then, by using androgen receptor (AR)-expressing PC3 cells we observed that the responsiveness to HNE and panobinostat was independent of the expression of functional AR. Taken together, our data suggest that HNE potentiates the antitumoral effect of the HDACI panobinostat in prostate cancer cells.

Cadmium chloride-induced oxidative stress and DNA damage in the human Jurkat T cell line is not linked to intracellular trace elements depletion

Cadmium (Cd) is a widespread environmental contaminant. Cd affects the cellular homeostasis and generates damage via complex mechanisms involving interactions with other metals, induction of oxidative stress and apoptotic or necrotic cell death, depending on the cell type and the concentration. The goal of the present study was to investigate the effect of exposure to CdCl(2) on the intracellular trace elements levels, the antioxidant enzyme activities and on DNA damage in the Jurkat T cell line. Cells were exposed to 5, 25 and 50 μM of CdCl(2) for 24 h. Cd significantly reduced the viability of Jurkat T cells and induced a dose-dependent increase in DNA damage with statistically significant differences relative to controls (p<0.001); the superoxide dismutase and glutathione peroxidase activities were significantly decreased. Lipid peroxidation and protein carbonyl levels were significantly increased while glutathione and the total intracellular sulfhydryl groups were decreased showing clearly that an oxidative stress was generated by Cd. Surprisingly the treatment with Cd induced a significant increase in the intracellular levels of all the trace elements measured. The results indicate that cellular pro-oxidative stress induced by Cd is most likely mediated by disruption of redox homeostasis associated to a mishandling of redox-active transition metals and causes lipid and protein oxidation and oxidative DNA damage in Jurkat T cells.

Oxidatively generated base damage to cellular DNA

Search for the formation of oxidatively base damage in cellular DNA has been a matter of debate for more than 40 years due to the lack of accurate methods for the measurement of the lesions. HPLC associated with either tandem mass spectrometry (MS/MS) or electrochemical detector (ECD) together with optimized DNA extraction conditions constitutes a relevant analytical approach. This has allowed the accurate measurement of oxidatively generated single and clustered base damage in cellular DNA following exposure to acute oxidative stress conditions mediated by ionizing radiation, UVA light and one-electron oxidants. In this review the formation of 11 single base lesions that is accounted for by reactions of singlet oxygen, hydroxyl radical or high intensity UVC laser pulses with nucleobases is discussed on the basis of the mechanisms available from model studies. In addition several clustered lesions were found to be generated in cellular DNA as the result of one initial radical hit on either a vicinal base or the 2-deoxyribose. Information on nucleobase modifications that are formed upon addition of reactive aldehydes arising from the breakdown of lipid hydroperoxides is also provided.

DNA cross-link induced by trans-4-hydroxynonenal

Trans-4-Hydroxynonenal (HNE) is a peroxidation product of omega-6 polyunsaturated fatty acids. Michael addition of HNE to deoxyguanosine yields four diastereomeric 1,N(2)-dG adducts. The adduct of (6S,8R,11S) stereochemistry forms interstrand N(2)-dG:N(2)-dG cross-links in the 5'-CpG-3' sequence. It has been compared with the (6R,8S,11R) adduct, incorporated into 5'-d(GCTAGCXAGTCC)-3' . 5'-d(GGACTCGCTAGC)-3', containing the 5'-CpG-3' sequence (X = HNE-dG). Both adducts rearrange in DNA to N(2)-dG aldehydes. These aldehydes exist in equilibrium with diastereomeric cyclic hemiacetals, in which the latter predominate at equilibrium. These cyclic hemiacetals mask the aldehydes, explaining why DNA cross-linking is slow compared to related 1,N(2)-dG adducts formed by acrolein and crotonaldehyde. Both the (6S,8R,11S) and (6R,8S,11R) cyclic hemiacetals are located within the minor groove. However, the (6S,8R,11S) cyclic hemiacetal orients in the 5'-direction, while the (6R,8S,11R) cyclic hemiacetal orients in the 3'-direction. The conformations of the diastereomeric N(2)-dG aldehydes, which are the reactive species involved in DNA cross-link formation, have been calculated using molecular mechanics methods. The (6S,8R,11S) aldehyde orients in the 5'-direction, while the (6R,8S,11R) aldehyde orients in the 3'-direction. This suggests a kinetic basis to explain, in part, why the (6S,8R,11S) HNE adduct forms interchain cross-links in the 5'-CpG-3' sequence, whereas (6R,8S,11R) HNE adduct does not. The presence of these cross-links in vivo is anticipated to interfere with DNA replication and transcription, thereby contributing to the etiology of human disease.

Mutagenicity of acrolein and acrolein-induced DNA adducts

Acrolein mutagenicity relies on DNA adduct formation. Reaction of acrolein with deoxyguanosine generates alpha-hydroxy-1, N(2)-propano-2'-deoxyguanosine (alpha-HOPdG) and gamma-hydroxy-1, N(2)-propano-2'-deoxyguanosine (gamma-HOPdG) adducts. These two DNA adducts behave differently in mutagenicity. gamma-HOPdG is the major DNA adduct and it can lead to interstrand DNA-DNA and DNA-peptide/protein cross-links, which may induce strong mutagenicity; however, gamma-HOPdG can be repaired by some DNA polymerases complex and lessen its mutagenic effects. alpha-HOPdG is formed much less than gamma-HOPdG, but difficult to be repaired, which contributes to accumulation in vivo. Results of acrolein mutagenicity studies haven't been confirmed, which is mainly due to the conflicting mutagenicity data of the major acrolein adduct (gamma-HOPdG). The minor alpha-HOPdG is mutagenic in both in vitro and in vivo test systems. The role of alpha-HOPdG in acrolein mutagenicity needs further investigation. The inconsistent result of acrolein mutagenicity can be attributed, at least partially, to a variety of acrolein-DNA adducts formation and their repair in diverse detection systems. Recent results of detection of acrolein-DNA adduct in human lung tissues and analysis of P53 mutation spectra in acrolein-treated cells may shed some light on mechanisms of acrolein mutagenicity. These aspects are covered in this mini review.

Exposure to chrysotile asbestos causes carbonylation of glucose 6-phosphate dehydrogenase through a reaction with lipid peroxidation products in human lung epithelial cells

Exposure to asbestos is known to lead to a reduction in glucose 6-phosphate dehydrogenase (G6PDH) activity and to cause oxidative damage to cells. In the present study, we exposed the human lung carcinoma cell line A549 to chrysotile. We observed an increase in the production of thiobarbituric acid-reactive substances (TBARS, the breakdown products of lipid peroxide) along with a significant decrease in G6PDH activity. Alternatively, when chrysotile was added directly to the cell extract obtained by removing the cell membrane, no loss of G6PDH activity was observed. To elucidate the mechanism of G6PDH inactivation due to exposure to chrysotile, we focused on the TBARS responsible for protein modification via carbonylation. When malondialdehyde or 4-hydroxy-2-nonenal was added to a membrane-free A549 cell extract, G6PDH activity was reduced markedly. However, when t-butylhydroperoxide was added to the extract, there was no significant decrease in G6PDH activity. Western blot analysis and immunoprecipitation of the carbonylated proteins in the A549 cell lysate that was prepared after exposure to chrysotile demonstrated that G6PDH had been carbonylated. Our findings indicate that the decrease in G6PDH activity that occurs after exposure of the cultured cells to chrysotile results from the carbonylation of G6PDH by TBARS.

Lipid mediator interplay: resolvin D1 attenuates inflammation evoked by glutathione-conjugated lipid peroxidation products

Non-enzymatic oxidation of cellular lipids, one of the characteristic features of inflammation, leads to formation of highly reactive and toxic alpha,beta-unsaturated aldehydes, such as 4-hydroxy-trans-2-nonenal (HNE). Conjugation of HNE with reduced glutathione (GS-HNE) is widely believed to represent a form of detoxification. The study by Spite et al. in the current issue of the British Journal of Pharmacology shows that glutathiolation of HNE confers potent pro-inflammatory properties on this alpha,beta-unsaturated aldehyde. They find that GS-HNE directly activates human neutrophil granulocytes in vitro and evokes peritonitis in mice. Pre-treatment with resolvin D1, which is derived from omega-3 fatty acids, markedly attenuated the peritoneal leukocyte accumulation and production of prostaglandins and leukotrienes induced by GS-HNE. Their findings have profound implications for the analysis of inflammation in describing the generation of a novel class of pro-inflammatory mediators, through glutathione-dependent metabolism of lipid-peroxidation products, and emphasize the therapeutic potential of resolvin D1 in inflammatory diseases.

Mechanisms involved in the modulation of astroglial resistance to oxidative stress induced by activated microglia: antioxidative systems, peroxide elimination, radical generation, lipid peroxidation

Microglia and astrocytes are the cellular key players in many neurological disorders associated with oxidative stress and neuroinflammation. Previously, we have shown that microglia activated by lipopolysaccharides (LPS) induce the expression of antioxidative enzymes in astrocytes and render them more resistant to hydrogen peroxide (H2O2). In this study, we examined the mechanisms involved with respect to the cellular action of different peroxides, the ability to detoxify peroxides, and the status of further antioxidative systems. Astrocytes were treated for 3 days with medium conditioned by purified quiescent (microglia-conditioned medium, MCM[-]) or LPS-activated (MCM[+]) microglia. MCM[+] reduced the cytotoxicity of the organic cumene hydroperoxide in addition to that of H2O2. Increased peroxide resistance was not accompanied by an improved ability of astrocytes to remove H2O2 or an increased expression/activity of peroxide eliminating antioxidative enzymes. Neither peroxide-induced radical generation nor lipid peroxidation were selectively affected in MCM[+] treated astrocytes. The glutathione content of peroxide resistant astrocytes, however, was increased and superoxide dismutase and heme oxygenase were found to be upregulated. These changes are likely to contribute to the higher peroxide resistance of MCM[+] treated astrocytes by improving their ability to detoxify reactive oxygen radicals and oxidation products. For C6 astroglioma cells a protective effect of microglia-derived factors could not be observed, underlining the difference of primary cells and cell lines concerning their mechanisms of oxidative stress resistance. Our results indicate the importance of microglial-astroglial cell interactions during neuroinflammatory processes.

Resolvin D1 controls inflammation initiated by glutathione-lipid conjugates formed during oxidative stress

BACKGROUND AND PURPOSE

Inflammation is associated with oxidative stress and local generation of lipid peroxidation-derived aldehydes, such as 4-hydroxy-trans-2-nonenal (HNE). In most tissues, HNE is readily conjugated with glutathione and presently it is unknown whether glutathionyl-HNE (GS-HNE) plays a functional role in inflammation. Here, we sought to determine whether GS-HNE is a mediator of oxidative stress-initiated inflammation and if its actions can be regulated by the anti-inflammatory and pro-resolving lipid mediator, resolvin D1 (RvD1).

EXPERIMENTAL APPROACH

GS-HNE was administered intraperitoneally to mice and peritoneal lavages were assessed for leukocyte infiltration and lipid mediators were targeted by mediator-lipidomics. RvD1 was administered to mice treated with GS-HNE and leukocyte infiltration was assessed in the peritoneum. Superoxide production and CD11b modulation were measured in isolated human polymorphonuclear leukocytes incubated with GS-HNE.

KEY RESULTS

GS-HNE (1-10 microg) evoked infiltration of Gr-1(+) leukocytes into the peritoneum to form an inflammatory exudate. With isolated human polymorphonuclear leukocytes, GS-HNE stimulated both superoxide generation and CD11b expression. Among the lipid mediators, both cyclooxygenase- and lipoxygenase-derived pro-inflammatory eicosanoids, including prostaglandin E(2), leukotriene B(4) and cysteinyl leukotrienes, were generated in exudates of mice injected intraperitoneally with GS-HNE. RvD1, given i.v. in doses as low as 0.01-10.0 ng, sharply reduced GS-HNE-stimulated leukocyte infiltration ( approximately 30-70%).

CONCLUSIONS AND IMPLICATIONS

Glutathione conjugates of HNE, derived during oxidative stress, are pro-inflammatory in vivo. RvD1 protects against this oxidative stress-initiated inflammation.

Conformational interconversion of the trans-4-hydroxynonenal-derived (6S,8R,11S) 1,N(2)-deoxyguanosine adduct when mismatched with deoxyadenosine in DNA

The (6S,8R,11S) 1,N(2)-HNE-dGuo adduct of trans-4-hydroxynonenal (HNE) was incorporated into the duplex 5'-d(GCTAGCXAGTCC)-3'.5'-d(GGACTAGCTAGC)-3' [X = (6S,8R,11S) HNE-dG], in which the lesion was mismatched opposite dAdo. The (6S,8R,11S) adduct maintained the ring-closed 1,N(2)-HNE-dG structure. This was in contrast to when this adduct was correctly paired with dCyd, conditions under which it underwent ring opening and rearrangement to diastereomeric minor groove cyclic hemiacetals [ Huang , H. , Wang , H. , Qi , N. , Lloyd , R. S. , Harris , T. M. , Rizzo , C. J. , and Stone , M. P. ( 2008 ) J. Am. Chem. Soc. 130 , 10898 - 10906 ]. The (6S,8R,11S) adduct exhibited a syn/anti conformational equilibrium about the glycosyl bond. The syn conformation was predominant in acidic solution. Structural analysis of the syn conformation revealed that X(7) formed a distorted base pair with the complementary protonated A(18). The HNE moiety was located in the major groove. Structural perturbations were observed at the neighbor C(6).G(19) and A(8).T(17) base pairs. At basic pH, the anti conformation of X(7) was the major species. The 1,N(2)-HNE-dG intercalated and displaced the complementary A(18) in the 5'-direction, resulting in a bulge at the X(7).A(18) base pair. The HNE aliphatic chain was oriented toward the minor groove. The Watson-Crick hydrogen bonding of the neighboring A(8).T(17) base pair was also disrupted.

Activated microglia modulate astroglial enzymes involved in oxidative and inflammatory stress and increase the resistance of astrocytes to oxidative stress in vitro

Neuropathological processes in the central nervous system are commonly accompanied by an activation of microglia and astrocytes. The involvement of both cell populations in the onset and progress of neurological disorders has been widely documented, implicating both beneficial and detrimental influences on the neural tissue. Nevertheless, little is known about the interplay of these glial cell populations, especially under diseased conditions. To examine the effects of activated microglia on astrocytes purified rat astroglial cell cultures were treated with medium conditioned by purified quiescent (MCM[-]) or lipopolysaccharide (LPS)-activated rat microglia (MCM[+]) and subjected to a comparative proteome analysis based on two-dimensional gel electrophoresis. No significant down regulation of proteins was observed. The majority of the 19 proteins identified by means of nano HPLC/ESI-MS/MS in the 12 most prominent protein spots significantly overexpressed (> or =2-fold) in MCM[+] treated astrocytes are involved in inflammatory processes and oxidative stress response: superoxide dismutases (Sod), peroxiredoxins, glutathione S-transferases (Gst), nucleoside diphosphate kinase B, argininosuccinate synthase (Ass), and cellular retinol-binding protein I (Rbp1). Sod2, Rbp1, Gstp1, and Ass were also significantly increased on the mRNA level determined by quantitative RT-PCR. The upregulation of antioxidative enzymes in astrocytes was accompanied by a higher resistance to oxidative stress induced by H2O2. These results show that activated microglia change the expression of antioxidative proteins in astrocytes and protect them against oxidative stress, which might be an effective way to increase the neuroprotective potential of astrocytes under pathological conditions associated with oxidative stress and inflammation.

The stereochemistry of trans-4-hydroxynonenal-derived exocyclic 1,N2-2'-deoxyguanosine adducts modulates formation of interstrand cross-links in the 5'-CpG-3' sequence

The trans-4-hydroxynonenal (HNE)-derived exocyclic 1, N(2)-dG adduct with (6S,8R,11S) stereochemistry forms interstrand N(2)-dG-N(2)-dG cross-links in the 5'-CpG-3' DNA sequence context, but the corresponding adduct possessing (6R,8S,11R) stereochemistry does not. Both exist primarily as diastereomeric cyclic hemiacetals when placed into duplex DNA [Huang, H., Wang, H., Qi, N., Kozekova, A., Rizzo, C. J., and Stone, M. P. (2008) J. Am. Chem. Soc. 130, 10898-10906]. To explore the structural basis for this difference, the HNE-derived diastereomeric (6S,8R,11S) and (6R,8S,11R) cyclic hemiacetals were examined with respect to conformation when incorporated into 5'-d(GCTAGC XAGTCC)-3' x 5'-d(GGACTCGCTAGC)-3', containing the 5'-CpX-3' sequence [X = (6S,8R,11S)- or (6R,8S,11R)-HNE-dG]. At neutral pH, both adducts exhibited minimal structural perturbations to the DNA duplex that were localized to the site of the adduction at X(7) x C(18) and its neighboring base pair, A(8) x T(17). Both the (6S,8R,11S) and (6R,8S,11R) cyclic hemiacetals were located within the minor groove of the duplex. However, the respective orientations of the two cyclic hemiacetals within the minor groove were dependent upon (6S) versus (6R) stereochemistry. The (6S,8R,11S) cyclic hemiacetal was oriented in the 5'-direction, while the (6R,8S,11R) cyclic hemiacetal was oriented in the 3'-direction. These cyclic hemiacetals effectively mask the reactive aldehydes necessary for initiation of interstrand cross-link formation. From the refined structures of the two cyclic hemiacetals, the conformations of the corresponding diastereomeric aldehydes were predicted, using molecular mechanics calculations. Potential energy minimizations of the duplexes containing the two diastereomeric aldehydes predicted that the (6S,8R,11S) aldehyde was oriented in the 5'-direction while the (6R,8S,11R) aldehyde was oriented in the 3'-direction. These stereochemical differences in orientation suggest a kinetic basis that explains, in part, why the (6S,8R,11S) stereoisomer forms interchain cross-links in the 5'-CpG-3' sequence whereas the (6R,8S,11R) stereoisomer does not.

Rearrangement of the (6S,8R,11S) and (6R,8S,11R) exocyclic 1,N2-deoxyguanosine adducts of trans-4-hydroxynonenal to N2-deoxyguanosine cyclic hemiacetal adducts when placed complementary to cytosine in duplex DNA

trans-4-Hydroxynonenal (HNE) is a peroxidation product of omega-6 polyunsaturated fatty acids. The Michael addition of deoxyguanosine to HNE yields four diastereomeric exocyclic 1,N(2)-dG adducts. The corresponding acrolein- and crotonaldehyde-derived exocyclic 1,N(2)-dG adducts undergo ring-opening to N(2)-dG aldehydes, placing the aldehyde functionalities into the minor groove of DNA. The acrolein- and the 6R-crotonaldehyde-derived exocyclic 1,N(2)-dG adducts form interstrand N(2)-dG:N(2)-dG cross-links in the 5'-CpG-3' sequence context. Only the HNE-derived exocyclic 1,N(2)-dG adduct of (6S,8R,11S) stereochemistry forms interstrand N(2)-dG:N(2)-dG cross-links in the 5'-CpG-3' sequence context. Moreover, as compared to the exocyclic 1,N(2)-dG adducts of acrolein and crotonaldehyde, the cross-linking reaction is slow (Wang, H.; Kozekov, I. D.; Harris, T. M.; Rizzo, C. J. J. Am. Chem. Soc. 2003, 125, 5687-5700). Accordingly, the chemistry of the HNE-derived exocyclic 1,N(2)-dG adduct of (6S,8R,11S) stereochemistry has been compared with that of the (6R,8S,11R) adduct, when incorporated into 5'-d(GCTAGCXAGTCC)-3'.5'-d(GGACTCGCTAGC)-3', containing the 5'-CpG-3' sequence (X = HNE-dG). When placed complementary to dC in this duplex, both adducts open to the corresponding N(2)-dG aldehydic rearrangement products, suggesting that the formation of the interstrand cross-link by the exocyclic 1,N(2)-dG adduct of (6S,8R,11S) stereochemistry, and the lack of cross-link formation by the exocyclic 1,N(2)-dG adduct of (6R,8S,11R) stereochemistry, is not attributable to inability to undergo ring-opening to the aldehydes in duplex DNA. Instead, these aldehydic rearrangement products exist in equilibrium with stereoisomeric cyclic hemiacetals. The latter are the predominant species present at equilibrium. The trans configuration of the HNE H6 and H8 protons is preferred. The presence of these cyclic hemiacetals in duplex DNA is significant as they mask the aldehyde species necessary for interstrand cross-link formation.

Autoantibodies to the C-terminal subunit of RLIP76 induce oxidative stress and endothelial cell apoptosis in immune-mediated vascular diseases and atherosclerosis

Although detection of autoantibodies in the peripheral blood from patients with immune-mediated endothelial dysfunctions has so far failed to provide tools of diagnostic or pathogenetic value, putative bioindicators include anti-endothelial cell antibodies, a heterogeneous family of antibodies that react with autoantigens expressed by endothelial cells. In this study, to identify endothelial autoantigens involved in the autoimmune processes causing endothelial damage, we screened a human microvascular endothelial cell cDNA library with sera from patients with Behçet's disease. We identified antibodies to the C-terminus of Ral binding protein1 (RLIP76), a protein that catalyzes the ATP-dependent transport of glutathione (GSH) conjugates including GSH-4-hydroxy-t-2,3-nonenal, in the serum of a significant percentage of patients with various diseases characterized by immune-mediated endothelial dysfunction, including Behçet disease, systemic sclerosis, systemic lupus erythematosus and carotid atherosclerosis. These autoantibodies increased intracellular levels of 4-hydroxy-t-2,3-nonenal, decreased levels of GSH and activated C-Jun NH2 Kinase signaling (JNK), thus inducing oxidative stress-mediated endothelial cell apoptosis. The dietary antioxidant alpha-tocopherol counteracted endothelial cell demise. These findings suggest that autoantibodies to RLIP76 play a pathogenetic role in immune-mediated vascular diseases and represent a valuable peripheral blood bioindicator of atherosclerosis and immune-mediated vascular diseases.