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Cytotoxicity and metabolism of 4-hydroxy-2-nonenal and 2-nonenal in H2O2-resistant cell lines. Do aldehydic by-products of lipid peroxidation contribute to oxidative stress?

ABSTRACT: Toxic aldehydes, such as 4-hydroxy-2-nonenal (4HNE) and 2-nonenal (2NE), formed during lipid peroxidation have been isolated and implicated in the cytotoxic effects of oxidative stress. We have investigated the cytotoxicity and metabolism of 4HNE and 2NE in control (HA-1) cells and in two H2O2-resistant Chinese hamster fibroblast cell lines. The H2O2-resistant cells were found to be significantly more resistant than HA-1 cells to the cytotoxicity of 4HNE, as determined by clonogenic cell survival (dose-modifying factors at 10% isosurvival of 2.0-3.0). The H2O2-resistant cells demonstrated a significant 2-3-fold increase in the amount of 4HNE removed (mol/cell) from culture media containing 72 microM-4HNE when compared with HA-1 cells. The enhanced ability of H2O2-resistant cells to metabolize 4HNE was abolished by heating the cells at 100 degrees C for 45 min. Similar results were obtained with 2NE. Total glutathione and glutathione transferase activity, believed to be involved in cellular detoxification of 4HNE, were found to be significantly increased (2-3-fold) in the resistant cells when compared with the HA-1 cells. These results show that cell lines adapted and/or selected in a highly peroxidative environment are also resistant to the cytotoxicity of aldehydes formed during lipid peroxidation. This resistance appears to be related to increased cellular metabolism of these aldehydes, possibly through the glutathione transferase system. These findings suggest that the formation of aldehydes due to lipid peroxidation may contribute significantly to the mechanisms of oxidant-induced injury and the selective pressure exerted by H2O2-mediated cytotoxicity in culture.

SUBMITTER: Spitz DR

PROVIDER: S-EPMC1131310 | biostudies-other | 1990 Apr

REPOSITORIES: biostudies-other

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Project description:Reactive oxygen species (ROS) are elevated in the heart in response to hemodynamic and metabolic stress and promote hypertrophic signaling. ROS also mediate the formation of lipid peroxidation-derived aldehydes that may promote myocardial hypertrophy. One lipid peroxidation by-product, 4-hydroxy-trans-2-nonenal (HNE), is a reactive aldehyde that covalently modifies proteins thereby altering their function. HNE adducts directly inhibit the activity of LKB1, a serine/threonine kinase involved in regulating cellular growth in part through its interaction with the AMP-activated protein kinase (AMPK), but whether this drives myocardial growth is unclear. We tested the hypothesis that HNE promotes myocardial protein synthesis and if this effect is associated with impaired LKB1-AMPK signaling. In adult rat ventricular cardiomyocytes, exposure to HNE (10 μM for 1h) caused HNE-LKB1 adduct formation and inhibited LKB1 activity. HNE inhibited the downstream kinase AMPK, increased hypertrophic mTOR-p70S6K-RPS6 signaling, and stimulated protein synthesis by 27.1 ± 3.5%. HNE also stimulated Erk1/2 signaling, which contributed to RPS6 activation but was not required for HNE-stimulated protein synthesis. HNE-stimulated RPS6 phosphorylation was completely blocked using the mTOR inhibitor rapamycin. To evaluate if LKB1 inhibition by itself could promote the hypertrophic signaling changes observed with HNE, LKB1 was depleted in adult rat ventricular myocytes using siRNA. LKB1 knockdown did not replicate the effect of HNE on hypertrophic signaling or affect HNE-stimulated RPS6 phosphorylation. Thus, in adult cardiac myocytes HNE stimulates protein synthesis by activation of mTORC1-p70S6K-RPS6 signaling most likely mediated by direct inhibition of AMPK. Because HNE in the myocardium is commonly increased by stimuli that cause pathologic hypertrophy, these findings suggest that therapies that prevent activation of mTORC1-p70S6K-RPS6 signaling may be of therapeutic value.

Project description:Peroxidation of cellular membrane lipids, rich in polyunsaturated fatty acids, generates electrophilic, α, β-unsaturated aldehydes such as 4-hydroxy-2-nonenal (HNE). HNE is a highly reactive and cytotoxic molecule that can react with the nucleophilic sites in proteins causing posttranslational modification. The identification of protein targets is an important first step; however, quantitative profiling of site-specific modifications is necessary to understand the biological impact of HNE-induced carbonylation. We report a method that uses light (H(12)CHO) and heavy (D(13)CDO) isotopic variant of formaldehyde to differentially label primary amines (N-termini and ε-amino group of lysines) in peptides through reductive methylation and, combined with selective enrichment of modified peptides, permits comparison of the extent of carbonylation in two samples after mixing for simultaneous liquid chromatography-mass spectrometry. Specifically, dimethyl-labeled peptide carbonyls were fractionated from unmodified peptides using solid-phase hydrazide chemistry to immobilize them to porous glass beads and, after removing the unmodified peptides by thoroughly washing the beads, subsequently recover them by acid-catalyzed hydrolysis. The method was developed using HNE-modified synthetic peptides and also showing enrichment from a complex matrix of digested human plasma proteins. Applicability was confirmed using apomyoglobin as an analyte, implicating thereby its potential value to proteome-wide identification and relative quantification of posttranslational protein carbonylation with residue-specific information. Because HNE attachment may not necessarily cause change in protein abundance, this modification-focused quantification should facilitate the characterization of accompanied changes in protein function and, also, provide important insights into molecular signaling mechanisms and a better understanding of cellular processes associated with oxidative stress.

Project description:Elevated cellular oxidative stress and oxidative DNA damage are key contributors to impaired cardiac function in diabetes. During chronic inflammation, reactive oxygen species (ROS)-induced lipid peroxidation results in the formation of reactive aldehydes, foremost of which is 4-hydroxy-2-nonenal (4HNE). 4HNE forms covalent adducts with proteins, negatively impacting cellular protein function. During conditions of elevated oxidative stress, oxidative DNA damage such as modification by 8-hydroxydeoxyguanosine (8OHdG) is repaired by 8-oxoguanine glycosylase-1 (OGG-1). Based on these facts, we hypothesized that 4HNE forms adducts with OGG-1 inhibiting its activity, and thus, increases the levels of 8OHG in diabetic heart tissues. To test our hypothesis, we evaluated OGG-1 activity, 8OHG and 4HNE in the hearts of leptin receptor deficient db/db mice, a type-2 diabetic model. We also treated the recombinant OGG-1 with 4HNE to measure direct adduction. We found decreased OGG-1 activity (P > .05), increased 8OHG (P > .05) and increased 4HNE adducts (P > .05) along with low aldehyde dehydrogenase-2 activity (P > .05). The increased colocalization of OGG-1 and 4HNE in cardiomyocytes suggest 4HNE adduction on OGG-1. Furthermore, colocalization of 8OHG and OGG-1 with mitochondrial markers TOM 20 and aconitase, respectively, indicated significant levels of oxidatively-induced mtDNA damage and implicated a role for mitochondrial OGG-1 function. In vitro exposure of recombinant OGG-1 (rOGG-1) with increasing concentrations of 4HNE resulted in a concentration-dependent decrease in OGG-1 activity. Mass spectral analysis of trypsin digests of 4HNE-treated rOGG-1 identified 4HNE adducts on C28, C75, C163, H179, H237, C241, K249, H270, and H282. In silico molecular modeling of 4HNE-K249 OGG-1 and 4HNE-H270 OGG-1 mechanistically supported 4HNE-mediated enzymatic inhibition of OGG-1. In conclusion, these data support the hypothesis that inhibition of OGG-1 by direct modification by 4HNE contributes to decreased OGG-1 activity and increased 8OHG-modified DNA that are present in the diabetic heart.

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Cytotoxicity and metabolism of 4-hydroxy-2-nonenal and 2-nonenal in H2O2-resistant cell lines. Do aldehydic by-products of lipid peroxidation contribute to oxidative stress?

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