Covalent modification of cytochrome c exposed to trans,trans-2,4-decadienal

Impaired Detoxification of Trans, Trans-2,4-Decadienal, an Oxidation Product from Omega-6 Fatty Acids, Alters Insulin Signaling, Gluconeogenesis and Promotes Microvascular Disease

Omega-6 fatty acids are the primary polyunsaturated fatty acids in most Western diets, while their role in diabetes remains controversial. Exposure of omega-6 fatty acids to an oxidative environment results in the generation of a highly reactive carbonyl species known as trans, trans-2,4-decadienal (tt-DDE). The timely and efficient detoxification of this metabolite, which has actions comparable to other reactive carbonyl species, such as 4-hydroxynonenal, acrolein, acetaldehyde, and methylglyoxal, is essential for disease prevention. However, the detoxification mechanism for tt-DDE remains elusive. In this study, the enzyme Aldh9a1b is identified as having a key role in the detoxification of tt-DDE. Loss of Aldh9a1b increased tt-DDE levels and resulted in an abnormal retinal vasculature and glucose intolerance in aldh9a1b-/- zebrafish. Transcriptomic and metabolomic analyses revealed that tt-DDE and aldh9a1b deficiency in larval and adult zebrafish induced insulin resistance and impaired glucose homeostasis. Moreover, alterations in hyaloid vasculature is induced by aldh9a1b knockout or by tt-DDE treatment can be rescued by the insulin receptor sensitizers metformin and rosiglitazone. Collectively, these results demonstrated that tt-DDE is the substrate of Aldh9a1b which causes microvascular damage and impaired glucose metabolism through insulin resistance.

Antigiardial Activity of Foeniculum vulgare Hexane Extract and Some of Its Constituents

Foeniculum vulgare is used for the treatment of diarrhea in Mexican traditional medicine. Hexane extract showed 94 % inhibition of Giardia duodenalis trophozoites at 300 μg/mL. Therefore, 20 constituents of hexane extract were evaluated to determine their antigiardial activity. Interestingly, six compounds showed good activity toward the parasite. These compounds were (1R,4S) (+)-Camphene (61%), (R)(−)-Carvone (66%), estragole (49%), p-anisaldehyde (67%), 1,3-benzenediol (56%), and trans, trans-2,4-undecadienal (97%). The aldehyde trans, trans-2,4-undecadienal was the most active compound with an IC₅₀ value of 72.11 µg/mL against G. duodenalis trophozoites. This aldehyde was less toxic (IC₅₀ 588.8 µg/mL) than positive control metronidazole (IC₅₀ 83.5 µg/mL) against Vero cells. The above results could support the use of F. vulgare in Mexican traditional medicine.

trans,trans-2,4-Decadienal induces endothelial cell injury by impairing mitochondrial function and autophagic flux

This study investigated the toxic effects of trans,trans-2,4-decadienal (tt-DDE) on vascular endothelial cells as well as the underlying mechanisms involved. Human umbilical vascular endothelial cells (HUVECs) were treated with different concentrations of tt-DDE for 24 h, and cell viability, colony formation ability, apoptosis, mitochondrial function and autophagy pathway were determined. The results showed that tt-DDE dose-dependently inhibited cell viability and colony formation, and increased lactate dehydrogenase (LDH) release and apoptosis in HUVECs. Besides, tt-DDE exposure induced extensive mitochondrial damage, as evidenced by the decreased mitochondrial DNA copy number, ATP synthesis, and mitochondrial membrane potential, and increased mitochondrial reactive oxygen species (ROS) production and cytochrome c release from mitochondria. tt-DDE also induced mitochondrial fragmentation and fission by increasing DNM1L protein expression and DNM1L mitochondrial translocation. Additionally, tt-DDE treatment resulted in the blockage of autophagic flux and accumulation of autophagosomes in endothelial cells. Further investigation revealed that the inhibition of autophagy by 3-methyladenine aggravated tt-DDE-induced mitochondrial dysfunction and cell injury. However, scavenging of ROS by N-acetyl-l-cysteine (NAC) significantly prevented tt-DDE-induced mitochondrial damage, autophagy dysfunction, and cell injury. These data indicated that tt-DDE induced endothelial cell injury through impairing mitochondrial function and autophagic flux.

Trans, trans-2,4-decadienal impairs vascular endothelial function by inducing oxidative/nitrative stress and apoptosis

Aldehydes are implicated in the development of hypertension. Trans, trans-2,4-decadienal (tt-DDE), a dietary α,β-unsaturated aldehyde, is widespread in many food products. However, the role of tt-DDE in the pathophysiology of hypertension remains unknown. This study was designed to investigate whether tt-DDE consumption evokes hypertension and to explore the mechanisms underlying such a role. Sprague-Dawley rats were administered different concentrations of tt-DDE. After 28 days, blood pressure and endothelial function of mesenteric arteries were measured. Results showed that tt-DDE treatment significantly increased blood pressure and impaired endothelial function based on endothelium-dependent vasorelaxation and p-VASP levels. Mechanistically, tt-DDE induced oxidative/nitrative stress in the arteries of rats as evidenced by overproductions of superoxide and peroxynitrite, accompanied with increased expressions of iNOS and gp91^phox. To further investigate the effects of tt-DDE on endothelial cells and underlying mechanisms, human umbilical vein endothelial cells (HUVECs) were treated with different concentrations of tt-DDE. tt-DDE induced oxidative/nitrative stress in HUVECs. Moreover, tt-DDE induced endothelial cells apoptosis through JNK-mediated signaling pathway. These results show, for the first time, that oral intake of tt-DDE elevates blood pressure and induces endothelial dysfunction in rats through oxidative/nitrative stress and JNK-mediated apoptosis signaling, indicating that excess ingestion of tt-DDE is a potential risk factor for endothelial dysfunction and hypertension.

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Trans, trans-2,4-decadienal (tt-DDE) is a dietary α,β-unsaturated aldehyde.

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tt-DDE raised blood pressure and impaired endothelial function in rats.

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Oxidative/nitrative stress was induced by tt-DDE in both rats and HUVECs.

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HUVEC apoptosis in response to tt-DDE exposure was mediated by JNK signaling.

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tt-DDE may be a risk factor for hypertension and associated cardiovascular disease.

Singlet oxygen-induced protein aggregation: Lysozyme crosslink formation and nLC-MS/MS characterization

Singlet molecular oxygen (¹ O₂ ) has been associated with a number of physiological processes. Despite the recognized importance of ¹ O₂ -mediated protein modifications, little is known about the role of this oxidant in crosslink formation and protein aggregation. Thus, using lysozyme as a model, the present study sought to investigate the involvement of ¹ O₂ in crosslink formation. Lysozyme was photochemically oxidized in the presence of rose bengal or chemically oxidized using [¹⁸ O]-labeled ¹ O₂ released from thermolabile endoperoxides. It was concluded that both ¹ O₂ generating systems induce lysozyme crosslinking and aggregation. Using SDS-PAGE and nano-scale liquid chromatography coupled to electrospray ionization mass spectrometry, the results clearly demonstrated that ¹ O₂ is directly involved in the formation of covalent crosslinks involving the amino acids histidine, lysine, and tryptophan.

A Metabolic Probe-Enabled Strategy Reveals Uptake and Protein Targets of Polyunsaturated Aldehydes in the Diatom Phaeodactylum tricornutum

Diatoms are unicellular algae of crucial importance as they belong to the main primary producers in aquatic ecosystems. Several diatom species produce polyunsaturated aldehydes (PUAs) that have been made responsible for chemically mediated interactions in the plankton. PUA-effects include chemical defense by reducing the reproductive success of grazing copepods, allelochemical activity by interfering with the growth of competing phytoplankton and cell to cell signaling. We applied a PUA-derived molecular probe, based on the biologically highly active 2,4-decadienal, with the aim to reveal protein targets of PUAs and affected metabolic pathways. By using fluorescence microscopy, we observed a substantial uptake of the PUA probe into cells of the diatom Phaeodactylum tricornutum in comparison to the uptake of a structurally closely related control probe based on a saturated aldehyde. The specific uptake motivated a chemoproteomic approach to generate a qualitative inventory of proteins covalently targeted by the α,β,γ,δ-unsaturated aldehyde structure element. Activity-based protein profiling revealed selective covalent modification of target proteins by the PUA probe. Analysis of the labeled proteins gave insights into putative affected molecular functions and biological processes such as photosynthesis including ATP generation and catalytic activity in the Calvin cycle or the pentose phosphate pathway. The mechanism of action of PUAs involves covalent reactions with proteins that may result in protein dysfunction and interference of involved pathways.

Accumulation of polyunsaturated aldehydes in the gonads of the copepod Acartia tonsa revealed by tailored fluorescent probes

Polyunsaturated aldehydes (PUAs) are released by several diatom species during predation. Besides other attributed activities, these oxylipins can interfere with the reproduction of copepods, important predators of diatoms. While intensive research has been carried out to document the effects of PUAs on copepod reproduction, little is known about the underlying mechanistic aspects of PUA action. Especially PUA uptake and accumulation in copepods has not been addressed to date. To investigate how PUAs are taken up and interfere with the reproduction in copepods we developed a fluorescent probe containing the α,β,γ,δ-unsaturated aldehyde structure element that is essential for the activity of PUAs as well as a set of control probes. We developed incubation and monitoring procedures for adult females of the calanoid copepod Acartia tonsa and show that the PUA derived fluorescent molecular probe selectively accumulates in the gonads of this copepod. In contrast, a saturated aldehyde derived probe of an inactive parent molecule was enriched in the lipid sac. This leads to a model for PUAs' teratogenic mode of action involving accumulation and covalent interaction with nucleophilic moieties in the copepod reproductive tissue. The teratogenic effect of PUAs can therefore be explained by a selective targeting of the molecules into the reproductive tissue of the herbivores, while more lipophilic but otherwise strongly related structures end up in lipid bodies.

Assay of protein and peptide adducts of cholesterol ozonolysis products by hydrophobic and click enrichment methods

Cholesterol undergoes ozonolysis to afford a variety of oxysterol products, including cholesterol-5,6-epoxide (CholEp) and the isomeric aldehydes secosterol A (seco A) and secosterol B (seco B). These oxysterols display numerous important biological activities, including protein adduction; however, much remains to be learned about the identity of the reactive species and the range of proteins modified by these oxysterols. Here, we synthesized alkynyl derivatives of cholesterol-derived oxysterols and employed a straightforward detection method to establish secosterols A and B as the most protein-reactive of the oxysterols tested. Model adduction studies with an amino acid, peptides, and proteins provide evidence for the potential role of secosterol dehydration products in protein adduction. Hydrophobic separation methods—Folch extraction and solid phase extraction (SPE)—were successfully applied to enrich oxysterol-adducted peptide species, and LC-MS/MS analysis of a model peptide–seco adduct revealed a unique fragmentation pattern (neutral loss of 390 Da) for that species. Coupling a hydrophobic enrichment method with proteomic analysis utilizing characteristic fragmentation patterns facilitates the identification of secosterol-modified peptides and proteins in an adducted protein. More broadly, these improved enrichment methods may give insight into the role of oxysterols and ozone exposure in the pathogenesis of a variety of diseases, including atherosclerosis, Alzheimer’s disease, Parkinson’s disease, and asthma.

Covalent modification of cytochrome c by reactive metabolites of furan

Metabolism of the hepatotoxicant furan leads to protein adduct formation in the target organ. The initial bioactivation step involves cytochrome P450-catalyzed oxidation of furan, generating cis-2-butene-1,4-dial (BDA). BDA reacts with lysine to form pyrrolin-2-one adducts. Metabolic studies indicate that BDA also reacts with glutathione (GSH) to generate 2-(S-glutathionyl)butanedial (GSH-BDA), which then reacts with lysine to form GSH-BDA-lysine cross-links. To explore the relative reactivity of these two reactive intermediates, cytochrome c was reacted with BDA in the presence and absence of GSH. As judged by MALDI-TOF mass spectrometry, BDA reacts extensively with cytochrome c to form adducts that add 66 Da to the protein, consistent with the formation of pyrrolinone adducts. Addition of GSH to the reaction mixture reduced the overall extent of adduct formation. The mass of the adducted protein was shifted by 355 Da as expected for GSH-BDA-protein cross-link formation. LC-MS/MS analysis of the tryptic digests of the alkylated protein indicated that the majority of adducts occurred on lysine residues, with BDA reacting less selectively than GSH-BDA. Both types of adducts may contribute to the toxic effects of furan.

Covalent binding and anchoring of cytochrome c to mitochondrial mimetic membranes promoted by cholesterol carboxyaldehyde

Mitochondrial cholesterol has been reported to be increased under specific pathological conditions associated with enhanced oxidative stress parameters. In this scenario, cholesterol oxidation would be increased, leading to the production of reactive aldehydes, including cholesterol carboxyaldehyde (ChAld). By using SDS micelles as a mitochondrial mimetic model, we have demonstrated that ChAld covalently modifies cytochrome c (cytc), a protein known to participate in electron transport and apoptosis signaling. This mimetic model induces changes in cytc structure in the same way as mitochondrial membranes do. Tryptic digestion of the cytc-ChAld adduct followed by MALDI-TOF/TOF analyses revealed that modifications occur at Lys residues (K22) localized at cytc site L, a site involved in protein-protein and protein-membrane interactions. Interestingly, ChAld ligation prevented cytc detachment from liposomes even under high ionic strength conditions. Overall, it can be concluded that ChAld ligation to Lys residues at site L creates a hydrophobic tail at cytc, which promotes cytc anchoring to the membrane. Although not investigated in detail in this study, cytc adduction to cholesterol derived aldehydes could have implications in cytc release from mitochondria under apoptotic stimuli.

Mass spectrometric evidence for the existence of distinct modifications of different proteins by 2(E),4(E)-decadienal

2(E),4(E)-Decadienal (DDE), a lipid peroxidation product, was found to covalently modify Lys residues of different proteins by different reactions using mass spectrometry (MALDI-TOF-MS and LC-ESI-MS). DDE mainly formed Lys Schiff base adducts with cytochrome c and ribonuclease A at 10 min, but these reversibly formed adducts almost disappeared after 24 h. In contrast, beta-lactoglobulin (beta-LG) was highly modified by DDE after 24 h. In addition to the Lys Schiff base adducts, DDE formed novel Lys pyridinium adducts as well as Cys Michael adducts with beta-LG.