Crosslinking of aminophospholipids in cellular membranes of lens by oxidative stress in vitro

Measurement of cellular MDA content through MTBE-extraction based TBA assay by eliminating cellular interferences

Malondialdehyde (MDA) has long been served as a crucial indicator for assessing cellular oxidative stress levels. In this study, we introduce a new approach to determine cellular MDA levels based on a methyl tert-butyl ether (MTBE) extraction, aimed at eliminating interferences from cellular components during thiobarbituric acid (TBA) derivatization of MDA. By leveraging the effective MTBE extraction, we identified that the determination of the MDA-TBA adduct formed from the MTBE extraction layer can effectively eliminate the interferences from cellular proteins and metabolites. This method demonstrated acceptable linearity and precision in cellular samples and showed significant differences in H2O2 treated cellular oxidative stress models. The MTBE extraction-based MDA-TBA approach provides a reliable, cost-effective, and feasible method to determine cellular MDA levels using batch microplate reader approach for the assessment of cellular oxidative stress.

The OSE complotype and its clinical potential

Cellular death, aging, and tissue damage trigger inflammation that leads to enzymatic and non-enzymatic lipid peroxidation of polyunsaturated fatty acids present on cellular membranes and lipoproteins. This results in the generation of highly reactive degradation products, such as malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE), that covalently modify free amino groups of proteins and lipids in their vicinity. These newly generated neoepitopes represent a unique set of damage-associated molecular patterns (DAMPs) associated with oxidative stress termed oxidation-specific epitopes (OSEs). OSEs are enriched on oxidized lipoproteins, microvesicles, and dying cells, and can trigger sterile inflammation. Therefore, prompt recognition and removal of OSEs is required to maintain the homeostatic balance. This is partially achieved by various humoral components of the innate immune system, such as natural IgM antibodies, pentraxins and complement components that not only bind OSEs but in some cases modulate their pro-inflammatory potential. Natural IgM antibodies are potent complement activators, and 30% of them recognize OSEs such as oxidized phosphocholine (OxPC-), 4-HNE-, and MDA-epitopes. Furthermore, OxPC-epitopes can bind the complement-activating pentraxin C-reactive protein, while MDA-epitopes are bound by C1q, C3a, complement factor H (CFH), and complement factor H-related proteins 1, 3, 5 (FHR-1, FHR-3, FHR-5). In addition, CFH and FHR-3 are recruited to 2-(ω-carboxyethyl)pyrrole (CEP), and full-length CFH also possesses the ability to attenuate 4-HNE-induced oxidative stress. Consequently, alterations in the innate humoral defense against OSEs predispose to the development of diseases associated with oxidative stress, as shown for the prototypical OSE, MDA-epitopes. In this mini-review, we focus on the mechanisms of the accumulation of OSEs, the pathophysiological consequences, and the interactions between different OSEs and complement components. Additionally, we will discuss the clinical potential of genetic variants in OSE-recognizing complement proteins – the OSE complotype - in the risk estimation of diseases associated with oxidative stress.

Oxidation of Membrane Curvature-Regulating Phosphatidylethanolamine Lipid Results in Formation of Bilayer and Cubic Structures

Oxidation is associated with conditions related to chronic inflammations and aging. Cubic structures have been observed in the smooth endoplasmic reticulum and mitochondrial membranes of cells under oxidative stress (e.g., tumor cells and virus-infected cells). It has been previously suspected that oxidation can result in the rearrangement of lipids from a fluid lamellar phase to a cubic structure in organelles containing membranes enriched with amphiphiles that have nonzero intrinsic curvature, such as phosphatidylethanolamine (PE) and cardiolipin. This study focuses on the oxidation of 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE), a lipid that natively forms an inverted hexagonal phase at physiological conditions. The oxidized samples contain an approximately 3:2 molar ratio of nonoxidized to oxidized DOPE. Optical microscopy images collected during the hydration of this mixture from a dried film suggest that the system evolves into a coexistence of a stable fluid lamellar phase and transient square lattice structures with unit cell sizes of 500-600 nm. Small-angle X-ray scattering of the same lipid mixture yielded a body-centered Im3m cubic phase with the lattice parameter of 14.04 nm. On average, the effective packing parameter of the oxidized DOPE species was estimated to be 0.657 ± 0.069 (standard deviation). This suggests that the oxidation of PE leads to a group of species with inverted molecular intrinsic curvature. Oxidation can create amphiphilic subpopulations that potently impact the integrity of the membrane, since negative Gaussian curvature intrinsic to cubic phases can enable membrane destabilization processes.

The effect of systemic amantadine sulfate on malondialdehyde and total thiol levels in rat corneas

Purpose:

To evaluate the malondialdehyde (MDA) and total thiol (sulfhydryl, SH) levels in rat corneas after intraperitoneal injection of amantadine sulfate.

Methods:

A total of 12 Wistar albino rats were divided into two groups: control group (n = 6) and amantadine group (n = 6). Balanced salt solution (1 mL, 0.9% NaCl, twice/day) was injected into rats in control group. Amantadine sulfate (2 mg/1 mL, twice/day) was injected into rats in amantadine group. In each group, two rats were injected for 1 week, two received injections for 1 month, and two rats received injections for 3 months. The corneas were homogenized and MDA and SH levels were measured spectroflourometrically.

Results:

In control group, median MDA and SH levels were 2.37 (range, 0.92-3.60) and 25.35 (range, 6.30-54.0) nmol/mg, respectively. In amantadine group, median MDA and SH levels were 3.57 (range, 1.25-5.92) and 32.65 (range, 3.30-48.3) nmol/mg, respectively. The difference between this two groups regarding MDA (P = 0.14) and SH (P = 1.0) levels was statistically insignificant.

Conclusion:

Systemically administered amantadine sulfate seems not to cause MDA and SH imbalance in rat corneas.

Lipid peroxidation generates biologically active phospholipids including oxidatively N-modified phospholipids

Peroxidation of membranes and lipoproteins converts "inert" phospholipids into a plethora of oxidatively modified phospholipids (oxPL) that can act as signaling molecules. In this review, we will discuss four major classes of oxPL: mildly oxygenated phospholipids, phospholipids with oxidatively truncated acyl chains, phospholipids with cyclized acyl chains, and phospholipids that have been oxidatively N-modified on their headgroups by reactive lipid species. For each class of oxPL we will review the chemical mechanisms of their formation, the evidence for their formation in biological samples, the biological activities and signaling pathways associated with them, and the catabolic pathways for their elimination. We will end by briefly highlighting some of the critical questions that remain about the role of oxPL in physiology and disease.

Non-enzymatic modification of aminophospholipids by carbonyl-amine reactions

Non-enzymatic modification of aminophospholipids by lipid peroxidation-derived aldehydes and reducing sugars through carbonyl-amine reactions are thought to contribute to the age-related deterioration of cellular membranes and to the pathogenesis of diabetic complications. Much evidence demonstrates the modification of aminophospholipids by glycation, glycoxidation and lipoxidation reactions. Therefore, a number of early and advanced Maillard reaction-lipid products have been detected and quantified in different biological membranes. These modifications may be accumulated during aging and diabetes, introducing changes in cell membrane physico-chemical and biological properties.

Identification of novel bioactive aldehyde-modified phosphatidylethanolamines formed by lipid peroxidation

Lipid aldehydes generated by lipid peroxidation induce cell damage and inflammation. Recent evidence indicates that γ-ketoaldehydes (isolevuglandins, IsoLGs) form inflammatory mediators by modifying the ethanolamine headgroup of phosphatidylethanolamines (PEs). To determine if other species of aldehyde-modified PEs (al-PEs) with inflammatory bioactivity were generated by lipid peroxidation, we oxidized liposomes containing arachidonic acid and characterized the resulting products. We detected PE modified by IsoLGs, malondialdehyde (MDA), and 4-hydroxynonenal (HNE), as well as a novel series of N-acyl-PEs and N-carboxyacyl-PEs in these oxidized liposomes. These al-PEs were also detected in high-density lipoproteins exposed to myeloperoxidase. When we tested the ability of al-PEs to induce THP-1 monocyte adhesion to cultured endothelial cells, we found that PEs modified by MDA, HNE, and 4-oxononenal induced adhesion with potencies similar to those of PEs modified by IsoLGs (∼2μM). A commercially available medium-chain N-carboxyacyl-PE (C11:0CAPE) also stimulated adhesion, whereas C4:0CAPE and N-acyl-PEs did not. PEs modified by acrolein or by glucose were only partial agonists for adhesion. These studies indicate that lipid peroxidation generates a large family of al-PEs, many of which have the potential to drive inflammation.

Bioactive aldehyde-modified phosphatidylethanolamines

Lipid peroxidation generates a variety of lipid aldehydes, which have been recognized to modify protein and DNA, causing inflammation and cancer. However, recent studies demonstrate that phosphatidylethanolamine (PE) is a major target for these aldehydes, forming aldehyde-modified PEs (al-PEs) as a novel family of mediators for inflammation. This review summarizes our current understanding of these al-PEs, including formation, detection, structural characterization, physiological relevance and mechanism of action.

A liquid chromatography-tandem mass spectrometry method for measurement of N-modified phosphatidylethanolamines

N-Acyl phosphatidylethanolamines (NAPEs) are synthesised in response to stress in a variety of organisms from bacteria to humans. More recently, nonenzymatic modification of the ethanolamine headgroup of phosphatidylethanolamine (PE) by various aldehydes, including levuglandins/isoketals (which are gamma-ketoaldehydes [gammaKAs] derived from arachidonic acid), has also been demonstrated. The levels of these various N-modified PEs formed during stress and their biological significance remain to be fully characterized. Such studies require an accurate, facile, and cost-effective method for quantifying N-modified PEs. Previously, NAPE and some of the nonenzymatically N-modified PE species have been quantified by mass spectrometry after hydrolysis to their constituent N-acylethanolamine by enzymatic hydrolysis, most typically with Streptomyces chromofuscus phospholipase D. However, enzymatic hydrolysis is not cost-effective for routine analysis of a large number of samples, and hydrolytic efficiency may vary for different N-modified PEs, making quantitation more difficult. Therefore, we sought a robust and inexpensive chemical hydrolysis approach. Methylamine (CH(3)NH(2))-mediated deacylation has previously been used in headgroup analysis of phosphatidylinositol phosphates. Therefore, we developed an accurate assay for NAPEs and gammaKA-PEs using CH(3)NH(2)-mediated deacylation and quantitation of the resulting glycerophospho-N-modified ethanolamines by liquid chromatography-tandem mass spectrometry.

Signaling actions of electrophiles: anti-inflammatory therapeutic candidates

Over the past several years, research on biologically relevant electrophiles has been replete with new insights, expanding our understanding of the roles electrophiles play in vivo. Importantly, many electrophiles can form reversible covalent adducts with both proteins and small-molecule thiols in cells. This post-translational protein modification has important ramifications, including changes in protein enzymatic activity, the transduction of signals within and between cells, and alterations in gene expression. Electrophiles modulate a variety of cellular signaling processes that are involved in several major diseases with inflammatory components. The electrophilic fatty-acid derivatives discussed in this work are naturally occurring products of redox reactions and enzymatic activity. Furthermore, several of these electrophilic species and their derivatives represent potential therapeutic candidates.

Role of lipid peroxidation in pathogenesis of senile cataract

Background /Aim. Cataract is a structural, biochemical and optical change in the eye lens, which changes transmission and refraction of light rays reducing keenness and clarity of a figure on the retina. Its occurrence is highest in older people, over the age of 65 (45.9%), thus a certain degree of opacification exists practically in all people over the 70. Our research was directed to measuring of lipid peroxidation products in cataract lenses involved in early stages of cataractogenesis through oxidative stress and in the development of mature cataract. Methods. Clinical and biochemical research was carried out in 101 patients with cataract, 46 women and 55 men. The average age of the group was 72.47 (? = 7.98). According to the cataract maturity degree the patients were classified into two groups as follows: cataracta senilis incipiens (n = 41) and cataracta senilis matura (n = 60). Measuring of diene conjugates was carried out by spectrophotometer. Fluorescent lipid peroxidation products were measured by a spectrofluorophotometer, and malondialdehyde (MDA) concentration was measured by colorimeter as a product of a reaction with thiobarbituric acid (TBA). Result. Significantly higher diene conjugated concentration in lenses was measured in the patients with the diagnosis cataracta senilis incipiens (p < 0.001) as well as the intensity of fluorescent iminopropens (p < 0.001). Significantly higher MDA concentration in lens (p < 0.001) was measured in the patients with cataracta senilis matura. Conclusion. The lens structure changes caused by lipid peroxidation can, with other risk factors present, influence the occurrence and development of mature cataract. Some cataract types show different lipid peroxidation intensity with the most distinct changes in cataract which started as corticonuclear.

Verminderung der Lipidperoxidation und der Apoptoserate in kornealen Endothelzellen durch Vitamin A

PURPOSE

The goal of this study was to determine the effects of lipid peroxidation-mediated toxicity of iron ions on corneal endothelial cells leading to apoptosis.

METHODS

Murine corneal endothelial cells were maintained in tissue culture medium supplemented with free iron ions, known to lead to increased lipid peroxidation. Retinoic acid in the cell supernatant and cytoplasm of these cells was determined using HPLC. The rate of apoptosis was assessed by quantification of caspase-3-like activity. The lipid peroxidation was measured using the malondialdehyde method. Supplementation of retinoic acid was tested in the setting of apoptosis.

RESULTS

Free iron ions led to a rapid loss of retinoic acid in the supernatant and the corneal endothelial cells. This was correlated with rising levels of malondialdehyde following oxidative stress and increased apoptosis. Supplementation of retinoic acid alone significantly reduced oxidative stress and apoptosis in the respective cells.

CONCLUSION

In this study the authors present a novel in vitro model to test the direct influence of pro-oxidative species on corneal endothelial cells. The authors also prove that supplementing corneal endothelial cells with retinoic acid sufficiently prevents free radical injury and apoptosis.

Anti-oxidative vitamins prevent lipid-peroxidation and apoptosis in corneal endothelial cells

To determine the effects of vitamin supplementation on the lipid-peroxidation-mediated toxicity of iron-ions on corneal endothelial cells (CECs) leading to apoptosis, murine CECs were maintained in tissue culture medium supplemented with increasing concentrations of free iron-ions, a treatment known to lead to increased lipid-peroxidation. The concentration of anti-oxidative vitamins (ascorbic acid, tocopherol and retinoic acid) in the cell supernatant and in the cells was determined by high-pressure liquid chromatography. Apoptosis was assessed by quantification of caspase-3-like activity and by using annexin-V/propidium iodide stains for flow cytometry. Lipid-peroxidation was measured by the malondialdehyde method. Supplementation with anti-oxidative vitamins was tested for the ability to counteract the induction of apoptosis. The production of nitric oxide was assessed spectrophotometrically and the expression levels of inducible and endothelial nitric oxide synthase were determined by Western blot. Increasing levels of free iron led to a rapid loss of anti-oxidative vitamins in the supernatant and in the CECs. This was correlated with rising levels of malondialdehyde and increased apoptosis. Supplementation with ascorbic acid or alpha-tocopherol alone did not prevent lipid-peroxidation in the cells. A combination of vitamins C and E (ascorbic acid, tocopherol) or solitary supplementation with vitamin A (retinoic acid) prevented lipid-peroxidation. We thus present a novel in vitro model for testing the direct influence of pro-oxidative species on CECs. We also show that supplementation with anti-oxidative vitamins to CECs significantly prevents the generation of free-radical-induced oxidative injury and apoptosis. These findings may have important implications for the storage of human corneae prior to transplantation and for the prolongation of corneal graft survival.

Sphingolipids in human lens membranes: an update on their composition and possible biological implications

The unique nature of the most abundant phospholipids in human lens membranes remained overlooked until the 1990s when it was possible to discern dihydrosphingomyelins (DHSMs) from the more common sphingomyelins (SMs). Unlike in other mammalian membranes, DHSMs comprise nearly half of the phospholipids in adult human lenses. Compared to SMs with a trans double bond between carbons 4 and 5 of the sphingoid backbone, the absence of this unsaturation site in DHSMs allows the participation of the OH group on C3 in intermolecular H-bonds and leads to stronger interlipid interactions with both neighboring DHSMs and cholesterol. Phospholipid compositional changes with age and lens region observed in mammals with various life spans and lens growth rates, suggest that the highest levels of DHSMs along with the lowest amounts of phosphatidylcholines and SMs are found in lenses with the lowest growth rate, namely human lenses. The participation of phospholipid metabolites in the control of mitosis and elongation of lens cells is plausible and deserves investigation.

The possible physiological function of thioltransferase in cells

We sought to study the possible physiological function of thioltransferase (TTase) in combating oxidative damage in the lens epithelial cells. The cells transfected with either TTase-containing plasmid or vector only were compared for their resistance to oxidative stress in the presence of a bolus of H2O2 (0.1 mM) for 3 h. Cells depleted of TTase activity upon cadmium treatment were also examined for the resistance to oxidative stress under the same conditions. TTase activity assay, Western blot, and Northern blot analyses confirmed that hTTase gene was successfully transfected into the HLE B3 cells and was overexpressed. The TTase-transfected cells detoxified H2O2 as efficiently as the control cells but displayed a faster and more complete recovery of oxidatively inactivated glyceraldehyde 3-phosphate dehydrogenase (GAPDH) and glutathione peroxidase (GPx) activities and suppressed protein thiolation (PSSG formation). With TTase activity being inhibited by cadmium, the spontaneous reactivation of GAPDH under bolus H2O2 treatment was not accomplished in cadmium-pretreated cells. These data indicate a new physiological function of TTase, which involves in the reactivation of the oxidatively inactivated enzymes through dethiolation; thus this redox-regulating enzyme can protect the human lens epithelial cells and maybe other cell types by preventing them from permanent oxidative damage.

The effect of H2O2 and tertiary butyl hydroperoxide upon a murine immortal lens epithelial cell line, alphaTN4-1

The effect of comparable concentrations of H(2)O(2) and tertiary butyl hydroperoxide (TBHP) upon an immortal murine lens epithelial cell line was examined as part of an ongoing effort to delineate differences in the mechanism by which these peroxides cause cell death. Both compounds result in cell death of normal, unconditioned cells within 24hr. It was found that with similar conditions, TBHP conditioned alphaTN4-1 cells survive H(2)O(2) stress while H(2)O(2) conditioned cells are killed by TBHP. To better understand how these peroxides act, their effect upon unconditioned cells has been investigated. Both peroxides cause a rapid loss of GSH and disruption of pump activity as illustrated by (14)C-choline transport and (86)Rb uptake. While H(2)O(2) exposure resulted in extensive DNA damage, TBHP had a minimal effect. DNA damage caused by H(2)O(2) was shown to activate polyADP-ribosyl polymerase (PARP), leading to depletion of NAD and ATP. H(2)O(2) induced cell death could be delayed by addition of 3-aminobenzamide (3AB), an inhibitor of PARP. ATP levels in cells subjected to H(2)O(2) were also maintained by the presence of 3AB. H(2)O(2) stress also disrupted glycolysis and mitochondrial activity but these parameters were not affected by TBHP. TBHP induced cell death, under the relatively mild conditions used in this work, appears to be caused by membrane disruption and loss of a reducing environment.

Evidence of oxidative stress in human corneal diseases

This study localized malondialdehyde (MDA, a toxic byproduct of lipid peroxidation), nitrotyrosine [NT, a cytotoxic byproduct of nitric oxide (NO)], and nitric oxide synthase isomers (NOS) in normal and diseased human corneas. Normal corneas (n=11) and those with clinical and histopathological diagnoses of keratoconus (n=26), bullous keratopathy (n=17), and Fuchs' endothelial dystrophy (n=12) were examined with antibodies specific for MDA, NT, eNOS (constitutive NOS), and iNOS (inducible NOS). Normal corneas showed little or no staining for MDA, NT, or iNOS, whereas eNOS was detected in the epithelium and endothelium. MDA was present in all disease groups, with each group displaying a distinct pattern of staining. NT was detected in all keratoconus and approximately one half of Fuchs' dystrophy corneas. iNOS and eNOS were evident in all the diseased corneas. Keratoconus corneas showed evidence of oxidative damage from cytotoxic byproducts generated by lipid peroxidation and the NO pathway. Bullous keratopathy corneas displayed byproducts of lipid peroxidation but not peroxynitrite (MDA but not NT). Conversely, Fuchs' dystrophy corneas displayed byproducts of peroxynitrite with little lipid peroxidation (NT >> MDA). These data suggest that oxidative damage occurs within each group of diseased corneas. However, each disease exhibits a distinctive profile, with only keratoconus showing prominent staining for both nitrotyrosine and MDA. These results suggest that keratoconus corneas do not process reactive oxygen species in a normal manner, which may play a major role in the pathogenesis of this disease.

Rapid complexing of oxoacylglycerols with amino acids, peptides and aminophospholipids

We prepared model Schiff bases from 2-[9-oxo]nonanoyl glycerol (2-MAG-ALD) and various amino compounds. 2-MAG-ALD was obtained by pancreatic lipase hydrolysis of trioleoyl glycerol and reductive ozonolysis of the resulting 2-monooleoyl glycerol. The reaction products were purified by thin-layer chromatography. Schiff bases were synthesized in greater than 50% yield by reacting 2-MAG-ALD with twofold molar excess of valine, Nalpha-acetyl-L-lysine methyl ester and the tripeptides glycyl-glycyl-glycine, glycyl-glycyl-histidine, and glycyl-histidyl-lysine in aqueous methanol and with 1-palmitoyl-2-stearoyl glycerophosphoethanolamine (PE) in chloroform/methanol for 16 h at room temperature. Prior to analysis the bases were reduced with sodium cyanoborohydride in methanol for 30 min at 4 degrees C. Reaction products were analyzed by high-performance liquid chromatography/electrospray ionization/mass spectrometry (HPLC/ESI/MS). Reduced Schiff bases of 2-MAG-ALD with PE and amino acids were analyzed by normal-phase HPLC/ESI/MS and those with peptides by reversed-phase HPLC/ESI/MS. Single adducts were obtained in all cases and both the alpha-amino group of valine and the epsilon-amino group of Nalpha-acetyl-L-lysine methyl ester were reactive. Molecular ions of reaction products were the only detected ions in the negative ionization mode, whereas in the positive ion mode sodiated molecular ions were also detected. The present study suggests that 2-MAG-ALD may form Schiff base adducts with amino compounds in other aqueous media, such as the intestinal lumen and in the hydrophobic environment of cell membranes.

Detection of oxidized phospholipid-protein adducts using anti-15-hydroperoxyeicosatetraenoic acid-modified protein antibody: contribution of esterified fatty acid-protein adduct to oxidative modification of LDL

The reaction of lipid hydroperoxide with protein was investigated using an antibody, which was prepared using 15-hydroperoxyeicosatetraenoic acid (15-HPETE)-modified keyhole limpet hemocyanin as an immunogen. The obtained antibody recognized not only 15-HPETE-modified bovine serum albumin (BSA) but also 13-hydroperoxyoctadecadienoic acid (13-HPODE)-modified BSA. Glutaroyl-BSA adduct, which was prepared by the reaction of glutaric anhydride with protein, was also recognized by the antibody. The results revealed that the carboxyl terminus of lipid moiety in adducts was required for an appearance of the antigenicity. The cross-reactivity of phosphatidylcholine hydroperoxide-modified BSA (PCAOOH-BSA) with the antibody was examined. The antibody could not recognize the intact PCAOOH-BSA, whereas alkaline-treated modified BSA revealed the antigenicity. Furthermore, stearic acid at the 1 position in the phospholipid was liberated from the PCAOOH-BSA following treatment with 0.25 N NaOH. The result showed that the phospholipid moiety could be covalently bound to the protein molecule. The formation of esterified fatty acid-protein adduct during oxidation was confirmed using low-density lipoprotein (LDL). During oxidation of LDL by copper ion or 2,2'-azo-bis(2-amidinopropane)dihydrochloride, the formation of antigenic materials was observed in a time- or dose-dependent fashion. The antigenicity was significantly enhanced by the alkaline treatment on the oxidized LDL, suggesting that considerable amounts of oxidized esterified fatty acids can covalently react with apoprotein B-100 in oxidatively modified LDL.