Cellular oxidant stress and advanced glycation endproducts of albumin: caveats of the dichlorofluorescein assay

Improving the dichloro-dihydro-fluorescein (DCFH) assay for the assessment of intracellular reactive oxygen species formation by nanomaterials

To facilitate Safe and Sustainable by Design (SSbD) strategies during the development of nanomaterials (NMs), quick and easy in vitro assays to test for hazard potential at an early stage of NM development are essential. The formation of reactive oxygen species (ROS) and the induction of oxidative stress are considered important mechanisms that can lead to NM toxicity. In vitro assays measuring oxidative stress are therefore commonly included in NM hazard assessment strategies. The fluorescence-based dichloro-dihydro-fluorescein (DCFH) assay for cellular oxidative stress is a simple and cost-effective assay, making it a good candidate assay for SSbD hazard testing strategies. It is however subject to several pitfalls and caveats. Here, we provide further optimizations to the assay using 5-(6)-Chloromethyl-2',7'-dichlorodihydrofluorescein diacetate acetyl ester (CM-H2DCFDA-AE, referred to as DCFH probe), known for its improved cell retention. We measured the release of metabolic products of the DCFH probe from cells to supernatant, direct reactions of CM-H2DCFDA-AE with positive controls, and compared the commonly used plate reader-based DCFH assay protocol with fluorescence microscopy and flow cytometry-based protocols. After loading cells with DCFH probe, translocation of several metabolic products of the DCFH probe to the supernatant was observed in multiple cell types. Translocated DCFH products are then able to react with test substances including positive controls. Our results also indicate that intracellularly oxidized fluorescent DCF is able to translocate from cells to the supernatant. In either way, this will lead to a fluorescent supernatant, making it difficult to discriminate between intra- and extra-cellular ROS production, risking misinterpretation of possible oxidative stress when measuring fluorescence on a plate reader. The use of flow cytometry instead of plate reader-based measurements resolved these issues, and also improved assay sensitivity. Several optimizations of the flow cytometry-based DCFH ISO standard (ISO/TS 19006:2016) were suggested, including loading cells with DCFH probe before incubation with the test materials, and applying an appropriate gating strategy including live-death staining, which was not included in the ISO standard. In conclusion, flow cytometry- and fluorescence microscopy-based read-outs are preferred over the classical plate reader-based read-out to assess the level of intracellular oxidative stress using the cellular DCFH assay.

Cross-Talk Between Nitrosative Stress, Inflammation and Hypoxia-Inducible Factor in Patients with Adrenal Masses

Background

Adrenal masses are the most common of all human tumors. The role of nitrosative stress and inflammation in cancer development has already been demonstrated. However, it is not known whether they are involved in the pathogenesis of adrenal tumors. The aim of the study was to investigate a cross-talk between nitrosative stress, inflammation and hypoxia-inducible factor (HIF-1α) in 75 patients with different types of adrenal masses (non-functional incidentaloma, pheochromocytoma and Cushing's/Conn's adenoma).

Methods

The plasma concentrations of total nitric oxide (NO), S-nitrosothiols, peroxynitrite nitrotyrosine and the activity of serum myeloperoxidase (MPO) were measured spectrophotometrically, whereas concentrations of interleukin 1 beta (IL-1β), tumor necrosis factor α (TNF-α) and hypoxia-inducible factor 1 alpha (HIF-1α) were measured using commercial ELISA kits. The control group consisted of 50 healthy people matched by age and sex to the study group. The number of subjects was determined a priori based on our previous experiment (power of the test = 0.9; α = 0.05).

Results

We found significantly higher nitrosative stress (↑nitric oxide, ↑peroxynitrite, ↑S-nitrosothiols and ↑nitrotyrosine) in the plasma of patients with adrenal tumors, which was accompanied by increased inflammatory (↑myeloperoxidase, ↑interleukin 1 beta and ↑tumor necrosis factor α) and hypoxia (HIF-1α) biomarkers. Peroxynitrite and nitrotyrosine were positively correlated with aldosterone level. Nitrosative stress was also associated with inflammation and HIF-1α. Interestingly, plasma nitrotyrosine and serum MPO differentiated patients with adrenal tumor from healthy individuals with high sensitivity and specificity. Moreover, using multivariate regression analysis, we showed that ONOO^- and IL-1β depended on cortisol level, while ONOO^-, nitrotyrosine and HIF-1α were associated with aldosterone. Unfortunately, none of the assessed biomarkers differentiated between tumor types studied, suggesting that the severity of nitrosative damage and inflammation are similar in patients with incidentaloma, pheochromocytoma, and Cushing's or Conn's adenoma.

Conclusion

Adrenal tumors are associated with increased protein nitration/S-nitrosylation and inflammation.

Inhibitory Effect of Multimodal Nanoassemblies against Glycative and Oxidative Stress in Cancer and Glycation Animal Models

In recent years, there has been a progress in the study of glycation reaction which is one the possible reason for multiple metabolic disorders. Glycation is a nonenzymatic reaction between nucleic acids, lipids, and proteins resulting into the formation of early glycation products that may further lead to the accumulation of advanced glycation end products (AGEs). The precipitation of AGEs in various cells, tissues, and organs is one of the factors for the initiation and progression of various metabolic derangements including the cancer. The AGE interaction with its receptor "RAGE" activates the inflammatory pathway; yet, the downregulation of RAGE and its role in these pathways are not clear. We explore the effect of anticancer novel nanoassemblies on AGEs to determine its role in the regulation of the expression of RAGE, NFƙB, TNF-α, and IFN-γ. This paper is based on the in vivo and in vitro study in glycation and lung cancer model systems. Upon the treatment of nanoassemblies in both the model systems, we observed a protective effect of nanoassemblies over the inhibition of glycative and oxidative stress via mRNA expression analysis. The mRNA expression results corroborated with the reactive oxygen species (ROS), carboxy-methyl-lysine (CML), and fluorescence studies. In this study, we found that the presence of common factors for glycation and lung cancer is oxidative and glycative stress. This oxidation and glycation might be responsible for the initiation of inflammation which may further lead to uncontrolled growth of cells leading to cancer. This can be a strong association between lung cancer and glycation reaction. The intervention of the anticancer and antiglycation effects of multimodal nanoassemblies throughout the study promises a new pathway for cancer research.

2',7'-dichlorofluorescin-based analysis of Fenton chemistry reveals auto-amplification of probe fluorescence and albumin as catalyst for the detection of hydrogen peroxide

Fluorophore 2',7'-dichlorofluorescin (DCF) is the most frequently used probe for measuring oxidative stress in cells, but many aspects of DCF remain to be revealed. Here, DCF was used to study the Fenton reaction in detail, which confirmed that in a cell-free system, the hydroxyl radical was easily measured by DCF, accompanied by the consumption of H2O2 and the conversion of ferrous iron into ferric iron. DCF fluorescence was more specific for hydroxyl radicals than the measurement of thiobarbituric acid (TBA)-reactive 2-deoxy-D-ribose degradation products, which also detected H2O2. As expected, hydroxyl radical-induced DCF fluorescence was inhibited by iron chelation, anti-oxidants, and hydroxyl radical scavengers and enhanced by low concentrations of ascorbate. Remarkably, due to DCF fluorescence auto-amplification, Fenton reaction-induced DCF fluorescence steadily increased in time even when all ferrous iron was oxidized. Surprisingly, the addition of bovine serum albumin rendered DCF sensitive to H2O2 as well. Within cells, DCF appeared not to react directly with H2O2 but indirect via the formation of hydroxyl radicals, since H2O2-induced cellular DCF fluorescence was fully abolished by iron chelation and hydroxyl radical scavenging. Iron chelation in H2O2-stimulated cells in which DCF fluorescence was already increasing did not abrogate further increases in fluorescence, suggesting DCF fluorescence auto-amplification in cells. Collectively, these data demonstrate that DCF is a very useful probe to detect hydroxyl radicals and hydrogen peroxide and to study Fenton chemistry, both in test tubes as well as in intact cells, and that fluorescence auto-amplification is an intrinsic property of DCF.

The in vivo and in vitro approaches for establishing a link between advanced glycation end products and lung cancer

Advanced glycation end products (AGEs) are directly related to third aging-associated diseases, such as cardiovascular diseases, arteriosclerosis, and neurodegeneration. Likewise, these irreversible and nonenzymatic products have been reported to be involved in the progression of malignant cancers. In general, aging-associated diseases and the initiation of cancer have been subjects of interest for several years. Few studies on the role of AGEs in cancer have been performed on cell lines. Moreover, past investigations in the field of glycation biology still lack the knowledge of in vivo and in vitro approaches for cancer cells. Accordingly, we aimed to focus on and establish a link between cancer and glycation with respect to all the possible AGEs. In our study, the levels of carboxymethyllysine (CML) increased by 50.94% in an animal model of glycation, whereas in an animal model of cancer, the contents of CML increased by 45.94% compared with their negative controls. Similarly, fluorescent AGEs were also examined and were found to be increased by 65.3% and 58.63% in the animal models of glycation and cancer, respectively, compared with the control subjects. The protein carbonyl contents were also found to be enhanced in the animal models of glycation and cancer. In our study, the levels of reactive oxygen species were also found to be significantly increased in the in vitro model of cancer cells as compared with the controls. Such an initial breakthrough indicated that AGEs were present in the serum of the animal models of cancer and glycation.

Oxidative stress in acute pancreatitis: lost in translation?

Oxidative stress has been implicated in the pathogenesis of acute pancreatitis, a severe and debilitating inflammation of the pancreas that carries a significant mortality, and which imposes a considerable financial burden on the health system due to patient care. Although extensive efforts have been directed towards the elucidation of critical underlying mechanisms and the identification of novel therapeutic targets, the disease remains without a specific therapy. In experimental animal models of acute pancreatitis, increased oxidative stress and decreased antioxidant defences have been observed, changes also detected in patients clinically. However, despite the promise of studies evaluating the effects of antioxidants in these model systems, translation to the clinic has thus far been disappointing. This may reflect many factors involved in the design of both preclinical and clinical evaluations of antioxidant therapy, not least the fact that most experimental studies have focussed on pre-treatment rather than post-injury assessment. This review has examined evidence relating to the involvement of oxidative stress in the pathophysiology of acute pancreatitis, focussing on experimental models and the clinical experience, including the experimental techniques employed and potential of antioxidant therapy.

Troubleshooting the dichlorofluorescein assay to avoid artifacts in measurement of toxicant-stimulated cellular production of reactive oxidant species

INTRODUCTION

The dichlorofluorescein (DCF) assay is a popular method for measuring cellular reactive oxidant species (ROS). Although caveats have been reported with the DCF assay and other compounds, the potential for artifactual results due to cell-free interactions between the DCF compound and toxicants has hardly been explored. We evaluated the utility of the DCF assay for measuring ROS generation by the toxicants mono-(2-ethylhexyl) phthalate (MEHP), and tetrabromobisphenol A (TBBPA).

METHODS

DCF fluorescence was measured spectrofluorometrically after a 1-h incubation of toxicants with 6-carboxy-2',7'-dichlorodihydrofluorescein diacetate (carboxy-H2DCFDA). MEHP was incubated with carboxy-H2DCFDA in cell-free solutions of Hank's buffered salt solution (HBSS), or in Royal Park Memorial Institute (RPMI) medium with or without fetal bovine serum. TBBPA was incubated with carboxy-H2DCFDA in cell-free HBSS and with human trophoblast cells (HTR8/SVneo cells).

RESULTS

MEHP did not increase fluorescence in solutions of carboxy-H2DCFDA in HBSS or RPMI medium without serum. However, MEHP (90 and 180μM) increased DCF fluorescence in cell-free RPMI medium containing serum. Furthermore, serum-free and cell-free HBSS containing 25μM TBBPA exhibited concentration-dependent increased fluorescence with 5-100μM carboxy-H2DCFDA (p<0.05), but not 1μM carboxy-H2DCFDA. In addition, we observed increased fluorescence in HTR8/SVneo cell cultures exposed to TBBPA (0.5-25μM) (p<0.05), as we had observed in cell-free buffer.

DISCUSSION

MEHP demonstrated an interaction with serum in cell-free generation of DCF fluorescence, whereas TBBPA facilitated conversion of carboxy-H2DCFDA to the fluorescent DCF moiety in the absence of serum. Because TBBPA increased fluorescence in the absence of cells, the increased DCF fluorescence observed with TBBPA in the presence of cells cannot be attributed to cellular ROS and may, instead, be the result of chemical activation of carboxy-H2DCFDA to the fluorescent DCF moiety. These data illustrate the importance of including cell-free controls when using the DCF assay to study toxicant-stimulated cellular production of ROS.

Effect of exercise training on nitric oxide and superoxide/H₂O₂ signaling pathways in collateral-dependent porcine coronary arterioles

Endothelial nitric oxide (NO) synthase (NOS) has been shown to contribute to enhanced vascular function after exercise training. Recent studies have revealed that relatively low concentrations of reactive oxygen species can contribute to endothelium-dependent vasodilation under physiological conditions. We tested the hypothesis that exercise training enhances endothelial function via endothelium-derived vasodilators, NO and superoxide/H(2)O(2), in the underlying setting of chronic coronary artery occlusion. An ameroid constrictor was placed around the proximal left circumflex coronary artery to induce gradual occlusion in Yucatan miniature swine. At 8 wk postoperatively, pigs were randomly assigned to sedentary (pen-confined) or exercise-training (treadmill-run: 5 days/wk for 14 wk) regimens. Exercise training significantly enhanced concentration-dependent, bradykinin-mediated dilation in cannulated collateral-dependent arterioles (∼130 μm diameter) compared with sedentary pigs. NOS inhibition reversed training-enhanced dilation at low bradykinin concentrations in collateral-dependent arterioles, although increased dilation persisted at higher bradykinin concentrations. Total and phosphorylated (Ser(1179)) endothelial NOS protein levels were significantly increased in arterioles from collateral-dependent compared with the nonoccluded region, independent of exercise. The H(2)O(2) scavenger polyethylene glycol-catalase abolished the training-enhanced bradykinin-mediated dilation in collateral-dependent arterioles; similar results were observed with the SOD inhibitor diethyldithiocarbamate. Fluorescence measures of bradykinin-stimulated H(2)O(2) levels were significantly increased by exercise training, independent of occlusion. The NADPH inhibitor apocynin significantly attenuated bradykinin-mediated dilation in arterioles of exercise-trained, but not sedentary, pigs and was associated with significantly increased protein levels of the NADPH subunit p67phox. These data provide evidence that, in addition to NO, the superoxide/H(2)O(2) signaling pathway significantly contributes to exercise training-enhanced endothelium-mediated dilation in collateral-dependent coronary arterioles.

Truncated human serum albumin retains general anaesthetic binding activity

Multiple binding sites for anaesthetics in HSA (human serum albumin) make solution studies difficult to interpret. In the present study, we expressed the wild-type HSA domain 3 (wtHSAd3), a peptide with two known anaesthetic binding sites in a yeast expression system. We also expressed a site-directed mutant of domain 3 (Y411Wd3). The stability and secondary structure of the constructed fragments were determined by HX (hydrogen-tritium exchange) and CD spectroscopy. The binding of two general anaesthetics, 2-bromo-2-chloro-1,1,1-trifluoroethane and propofol, to wtHSAd3 and Y411Wd3 was determined using isothermal titration calorimetry, HX and intrinsic tryptophan fluorescence quenching. Although the expressed fragments are less stable than intact wtHSA as indicated by both CD and HX, they retain the secondary structure and anaesthetic-binding characteristics of an intact HSA molecule, but with fewer binding sites. Y411Wd3 had decreased affinity for propofol but not for 2-bromo-2-chloro-1,1,1-trifluoroethane, consistent with steric hindrance. Retention of structural features and anaesthetic binding properties with fewer binding sites in this truncated protein provide feasibility for using scaled-down models of otherwise intractable systems to gain an understanding of anaesthetic binding requirements and binding-stability relationships.

Aging impairs flow-induced dilation in coronary arterioles: role of NO and H(2)O(2)

Aging contributes significantly to the development of cardiovascular disease and is associated with elevated production of reactive oxygen species (ROS). The beneficial effects of nitric oxide (NO)-mediated vasodilation are quickly abolished in the presence of ROS, and this effect may be augmented with aging. We previously demonstrated an age-induced impairment of flow-induced dilation in rat coronary arterioles. Therefore, the purpose of this study was to determine the effects of O(2)(-) scavenging, as well as removal of H(2)O(2), the byproduct of O(2)(-) scavenging, on flow-mediated dilation in coronary resistance arterioles of young (4 mo) and old (24 mo) male Fischer 344 rats. Flow increased NO and H(2)O(2) production as evidenced by enhanced diaminofluorescein and dichlorodihydrofluorescein fluorescence, respectively, whereas aging reduced flow-induced NO and H(2)O(2) production. Endothelium-dependent vasodilation was evaluated by increasing intraluminal flow (5-60 nl/s) before and after treatment with the superoxide dismutase mimetic Tempol (100 muM), the H(2)O(2) scavenger catalase (100 U/ml), or Tempol plus catalase. Catalase reduced flow-induced dilation in both groups, whereas Tempol and Tempol plus catalase diminished vasodilation in young but not old rats. Tempol plus deferoxamine (100 muM), an inhibitor of hydroxyl radical formation, reversed Tempol-mediated impairment of flow-induced vasodilation in young rats and improved flow-induced vasodilation in old rats compared with control. Immunoblot analysis revealed increases in endogenous superoxide dismutase, catalase, and nitrotyrosine protein levels with aging. Collectively, these data indicate that NO- and H(2)O(2)-mediated flow-induced signaling decline with age in coronary arterioles and that elevated hydroxyl radical formation contributes to the age-related impairment of flow-induced vasodilation.

Identification of preferential protein targets for carbonylation in human mature adipocytes treated with native or glycated albumin

Oxidative modifications in proteins can participate in the regulation of cellular functions and are frequently observed in numerous states of diseases. Albumin can undergo increased glycation during diabetes. An accumulation of oxidatively modified proteins in human mature adipocytes incubated with glycated albumin has previously been described. This study herein reports the identification of specifically carbonylated targets following separation of the cell proteins by 2D gels, Western blotting and mass spectrometry analyses. It identified eight oxidatively modified proteins, two of which (ACTB and Annexin A2) appeared as significantly more carbonylated in adipocytes treated with glycated albumin than with native albumin. Intracellular stress, evaluated in SW872 cell line, showed an impairment in the protective antioxidant action exerted by native BSA after the glycation of the protein. Decreased proteasome peptidase activities were found in glycated BSA-treated mature adipocytes. The data suggest an association of oxidative damage with the progression of diabetes disorders at the adipocytes level.

Cytotoxicity of advanced glycation endproducts in human micro- and astroglial cell lines depends on the degree of protein glycation

Advanced glycation endproducts (AGEs) arise from the reaction of sugars with side chains and the N-terminus of proteins and are thought to be involved in the pathogenesis of several diseases by inducing oxidative stress, inflammation and cell death presumably mediated through activation of the receptor of AGE (RAGE). To address the question whether the cell damaging effect of AGE depends on the degree of its protein glycation, differential modified AGEs derived from incubating human serum albumin with increasing concentrations of methyl glyoxal were tested on cell viability, reactive oxygen species (ROS) formation, intracellular ATP levels, and activation of caspases 3/7 in two human glial cell lines, which were used as a model for human glia cells. All AGEs tested, regardless of their degree of modification, were found to induce ROS formation in both microglial (CHME-5) and astroglial cells (U373 MG), while only highly modified AGEs were able to decrease the cell viability and to induce apoptosis. This indicates that apoptotic events may be involved in the change of physiological parameters.

Oxidative stresses induced by glycoxidized human or bovine serum albumin on human monocytes

Oxidative stress and protein modifications are frequently observed in numerous disease states. Albumin, the major circulating protein in blood, can undergo increased glycoxidation in diabetes. Protein glycoxidation can lead to the formation of advanced glycoxidation end products, which induce various deleterious effects on cells. Herein, we report the effect of glucose or methylglyoxal-induced oxidative modifications on BSA or HSA protein structures and on THP1 monocyte physiology. The occurrence of oxidative modifications was found to be enhanced in glycoxidized BSA and HSA, after determination of their free thiol group content, relative electrophoretic migration, carbonyl content, and antioxidant activities. Cells treated with glycoxidized albumin exhibited an overgeneration of intracellular reactive oxygen species, impairments in proteasomal activities, enhancements in RAGE expression, and an accumulation of carbonylated proteins. These novel observations made in the presence of a range of modified BSA and HSA facilitate the comparison of the glycoxidation extent of albumin with the oxidative stress induced in cultured monocytes. Finally, this study reconfirms the influence of experimental conditions in which AGEs are generated and the concentration levels in experiments designed to mimic pathological conditions.

Cell lysis with dimethyl sulphoxide produces stable homogeneous solutions in the dichlorofluorescein oxidative stress assay

The oxidation of 2',7'-dichlorodihydrofluorescein (2',7'-dichlorofluorescin, DCFH) to a fluorescent product, 2',7'-dichlorofluorescein (DCF), is commonly used to quantitatively measure oxidative stress in cells using a fluorescence microplate reader. However, many cell lines tend to grow non-uniformly in the wells. This non-uniform distribution results in a high degree of variability in the fluorescence signal and decreases the precision of the method. Also, samples treated in large culture plates, dishes or flasks cannot be assayed directly in fluorescence microplate readers. This study reports an improved DCF assay method that lyses cells with DMSO/PBS (90% dimethyl sulphoxide/10% phosphate buffered saline). Oxidative stress was induced with either hydrogen peroxide or an hypoxia-reoxygenation treatment. Cell lysis with DMSO/PBS resulted in highly stable fluorescence signals in comparison to Triton X-100/PBS lysed cells. The precision of DCF fluorescence measurements of DMSO/PBS lysed cells was much better than for attached cells measured directly in 96-well plates. While DCF fluorescence in PBS was strongly quenched by albumin, no quenching occurred in DMSO/PBS. In conclusion this study describes a more convenient and accurate method for measuring cellular oxidative stress that also makes it possible to assay cells treated in large culture plates.

Molecular action mechanism against apoptosis by aqueous extract from guava budding leaves elucidated with human umbilical vein endothelial cell (HUVEC) model

Chronic cardiovascular and neurodegenerative complications induced by hyperglycemia have been considered to be associated most relevantly with endothelial cell damages (ECD). The protective effects of the aqueous extract of Psidium guajava L. budding leaves (PE) on the ECD in human umbilical vein endothelial cell (HUVEC) model were investigated. Results revealed that glyoxal (GO) and methylglyoxal (MGO) resulting from the glycative and autoxidative reactions of the high blood sugar glucose (G) evoked a huge production of ROS and NO, which in turn increased the production of peroxynitrite, combined with the activation of the nuclear factor kappaB (NFkappaB), leading to cell apoptosis. High plasma glucose activated p38-MAPK, and high GO increased the expressions of p38-MAPK and JNK-MAPK, whereas high MGO levels induced the activity of ERK-MAPK. Glucose and dicarbonyl compounds were all found to be good inducers of intracellular PKCs, which together with MAPK acted as the upstream triggering factor to activate NFkappaB. Conclusively, high plasma glucose together with dicarbonyl compounds can trigger the signaling pathways of MAPK and PKC and induce cell apoptosis through ROS and peroxynitrite stimulation and finally by NFkappaB activation. Such effects of PE were ascribed to its high plant polyphenolic (PPP) contents, the latter being potent ROS inhibitors capable of blocking the glycation of proteins, which otherwise could have brought forth severe detrimental effects to the cells.

Effects of advanced glycation end product modification on proximal tubule epithelial cell processing of albumin

AIM

The goal of this work is to understand the cellular effects of advanced glycation end product (AGE)-modified protein on renal proximal tubule cells.

BACKGROUND

A major function of the proximal tubule is to reabsorb and process filtered proteins. Diabetes is characterized by increased quantities of tissue and circulating proteins modified by AGEs. Therefore in diabetes, plasma proteins filtered at the glomerulus and presented to the renal proximal tubule are likely to be highly modified by AGEs.

METHODS

The model system was electrically resistant polarized renal proximal tubular epithelial cells in monolayer culture. The model proteins comprise a well-characterized AGE, methylglyoxal-modified bovine serum albumin (MGO-BSA), and unmodified BSA.

RESULTS

Renal proximal tubular cells handle MGO-BSA and native BSA in markedly disparate ways, including differences in: (1) kinetics of binding, uptake, and intracellular accumulation, (2) processing and fragmentation, and (3) patterns of electrical conductance paralleling temporal changes in binding, uptake and processing.

CONCLUSION

These differences support the idea that abnormal protein processing by the renal tubule can be caused by abnormal proteins, thereby forging a conceptual link between the pathogenic role of AGEs and early changes in tubular function that can lead to hypertrophy and nephropathy in diabetes.

The binding of advanced glycation end products to cell surfaces can be measured using bead-reconstituted cellular membrane proteins

Advanced glycation end products (AGEs) that arise from the reaction of sugars with protein side chains are supposed to be involved in the pathogenesis of several diseases and therefore the effects of AGEs on cells are the objective of numerous investigations. Although different cellular responses to AGEs can be measured in cell culture studies, knowledge about the nature of AGE-binding and the involved cell surface receptors is poor. The measurement of AGE-binding to cell surfaces bears the potential to gain a deeper understanding about the nature of AGE-binding to cell surface proteins and could be applied as a preliminary test before performing cell culture studies on AGE effects. Herein, a new material and method for the detection of AGE-binding to cell surfaces is introduced, which has the potential to facilitate the detection of binding. In the present paper, the detection of AGE-binding to cell surface proteins using an artificial system of cellular membrane proteins reconstituted on beads (TRANSIL CaCo-2) is described. The binding of a BSA-AGE derived from a 37 degrees C incubation with 500 mM Glc (BSA-Glc 500) and the corresponding control to this artificial system was compared with the binding to intact cells and was found to be in good agreement. Additionally, the K(d) for the binding of the BSA-Glc 500 used in the study to CaCo-2 surfaces was determined using FITC-labelled samples in a flow cytometric approach. Competitive binding studies were performed using a set of non-labelled BSA-AGEs to compete with FITC-labelled BSA-Glc 500 for the cell surface binding sites. The binding was found to be inhibited to different extends, virtually depending on the degree of arginine modifications within the modified protein used for competition. Additionally, the effects of all AGEs used in the study on CaCo-2 cells was measured using the detection of reactive oxygen species (ROS), which are known to be induced as a primary result of AGE-receptor binding. The induction of ROS was found to linearly correlate to the capacity of the individual AGE to displace FITC-labelled BSA-Glc 500 in competitive binding studies. Therefore, the data indicate, that at least in case of CaCo-2 cells the detection of cell surface binding can serve as a reliable preliminary test for a potential cell-damaging effect of AGEs.

Induction of reactive oxygen species and cell survival in the presence of advanced glycation end products and similar structures

Advanced glycation end products (AGEs) that arise from the reaction of sugars with protein side chains and the terminal amino group are supposed to be involved in the pathogenesis of several diseases and therefore the effects of AGEs on cells are the objective of numerous investigations. The effects of AGEs on cells are commonly assumed to be transduced via the receptor for AGEs (RAGE) but there are also other receptors known to interact with AGEs and they are likely to be involved in signal transduction. The primary cellular effect of AGEs on cultured cells was found to be the formation of reactive oxygen species (ROS). For the present study one murine and three human cell lines were used. The effects of a set of different highly modified AGEs and AGE-like compounds derived from the incubation of different modifiers with BSA were tested for their effects on these cells. Almost all AGEs tested induced the production of reactive oxygen species (ROS) in the different cell lines although the intensity of the detected signals varied considerably between the cell lines and are strongly dependent on the AGE used for cell activation. The most highly modified BSA-species were shown to inhibit cell growth in all cell lines, whereas a moderately modified glucose derived BSA-AGE and BSA-GA(red) did not show any inhibitory effect on cell growth even when a high ROS formation was detected.

Role of cytosolic liver fatty acid binding protein in hepatocellular oxidative stress: effect of dexamethasone and clofibrate treatment

The presence of cysteine and methionine groups together with an ability to bind long-chain fatty acid (LCFA) oxidation products makes liver fatty acid binding protein (L-FABP) an attractive candidate against hepatocellular oxidative stress. In this report, we show that pharmacological treatment directed at modulating L-FABP level affected hepatocellular oxidant status. L-FABP expressing 1548-hepatoma cells, treated with dexamethasone or clofibrate, decreased and increased intracellular L-FABP levels, respectively. Oxidative stress was induced by H2O2 incubation or hypoxia-reoxygenation. The fluorescent marker, dichlorofluorescein (DCF), was employed to measure intracellular reactive oxygen species (ROS). Hepatocellular damage was assessed by lactate dehydrogenase (LDH) level. Dexamethasone treatment resulted in a significant increase in DCF fluorescence with higher LDH release compared to control cells. Clofibrate treatment, however, resulted in a significant decrease in both parameters (p<0.05). Drug treatments did not affect cytosolic activities of glutathione peroxidase (GPx), superoxide dismutase (SOD), or catalase suggesting that the differences between treated and control cells may likely be associated with varying L-FABP levels. We conclude that L-FABP may act as an effective endogenous cytoprotectant against hepatocellular oxidative stress.

Use of spectroscopic probes for detection of reactive oxygen species

The detection and quantitation of reactive oxygen species (ROS) receives a great deal of interest because of their importance in a wide range of physiological and pathogenic events. Probe-assisted spectroscopy (electron spin resonance, spectrophotometry, fluorescence and luminescence) is the main tool for this application. This review discusses the properties of spectroscopic probes most commonly used for ROS detection and highlights their limitations in cellular systems. These include poor stability of some probes and/or products that may be subjected to cellular metabolism and lack of specificity in their reactions with oxidants or reductants. Additional problems often arise from undesired reactions of the probes and from their non-homogeneous distribution in the studied system, production of ROS by the probes themselves, perturbation of the systems under investigation by the probes, and artifacts due to the presence of ROS in the reaction medium. The limits imposed by these difficulties on the precise evaluation of the amounts and rates of formation of ROS are discussed critically.

Tankyrase-1 overexpression reduces genotoxin-induced cell death by inhibiting PARP1

Poly(ADP-ribose) polymerases or PARPs are a family of NAD(+)-dependent enzymes that modify themselves and other substrate proteins with ADP-ribose polymers. The founding member PARP 1 is localized predominantly in the nucleus and is activated by binding to DNA lesions. Excessive PARP 1 activation following genotoxin treatment causes NAD(+) depletion and cell death, whereas pharmacological PARP 1 inhibition protects cells from genotoxicity. This study investigates whether cellular viability and NAD(+) metabolism are regulated by tankyrase-1, a PARP member localized predominantly in the cytosol. Using a tetracycline-sensitive promoter to regulate tankyrase-1 expression in Madin-Darby canine kidney (MDCK) cells, we found that a 40-fold induction of tankyrase-1 (from 1,500 to 60,000 copies per cell) lowers steady-state NAD(+) levels but does not affect basal cellular viability. Moreover, the induction confers protection against the oxidative agent H(2)O(2) and the alkylating agent MNNG, genotoxins that kill cells by activating PARP 1. The cytoprotective effect of tankyrase-1 is not due to enhanced scavenging of oxidants or altered expression of Mcl-1, an anti-apoptotic molecule previously shown to be down-regulated by tankyrase-1 in CHO cells. Instead, tankyrase-1 appears to protect cells by preventing genotoxins from activating PARP 1-mediated reactions such as PARP 1 automodification and NAD(+) consumption. Our findings therefore indicate a cytoprotective function of tankyrase-1 mediated through altered NAD(+) homeostasis and inhibition of PARP 1 function.

Processing Advanced Glycation End Product-Modified Albumin by the Renal Proximal Tubule and the Early Pathogenesis of Diabetic Nephropathy

Diabetes is characterized by increased quantities of circulating proteins modified by advanced glycation end products (AGEs). Proteins filtered at the glomerulus and presented to the renal proximal tubule are likely to be highly modified by AGEs. The proximal tubule binds, takes up, and catabolizes AGE-modified albumin by pathways different from those of unmodified albumin. These differences were examined in polarized, electrically resistant proximal tubular cells grown in monolayer culture. In patients with type 1 diabetes, urinary excretion of a lysosomal enzyme predicted the development of nephropathy.

Aminoguanidine and metformin prevent the reduced rate of HDL-mediated cell cholesterol efflux induced by formation of advanced glycation end products

OBJECTIVE

The mechanisms whereby advanced glycation end products (AGE) contribute to atherogenesis in diabetes mellitus are not fully understood. In this study we analyzed in vitro the influence of advanced glycated albumin (AGE-albumin) as well as the role of the AGE inhibitors--aminoguanidine (AMG) and metformin (MF)--on the cell cholesterol efflux.

METHODS

HDL3 and albumin-mediated cholesterol efflux was measured in mouse peritoneal macrophages and in SR-BI transfected cells that had been treated along time with dicarbonyl sugars or AGE-albumin, both in the presence or in the absence of AMG and MF. 125I-HDL3 cell binding and 125I-AGE-albumin cell degradation were measured. Carboxymethyllysine (CML) formation and SR-BI expressions were determined by immunoblot.

RESULTS

AGE-albumin efficiently trapped cell cholesterol but impaired the HDL-mediated cell cholesterol efflux by decreasing HDL binding to the cell surface and inducing intracellular glycoxidation, without interfering with the SR-BI expression. Cell treatment with dicarbonyl sugars also disrupted the HDL-mediated cell cholesterol efflux, but this was prevented by AMG and MF that reduced CML formation.

CONCLUSIONS

By adversely impairing the HDL-mediated cell cholesterol removal rate, AGE-albumin and cell glycoxidation could facilitate the development of premature atherosclerosis in diabetes mellitus (DM) and in other diseases associated with carbonyl and oxidative stress like in chronic uremia. Thus, drugs that prevent AGE formation may be useful to correct disturbances in cell cholesterol transport.

Antioxidative function of L-FABP in L-FABP stably transfected Chang liver cells

Liver fatty acid binding protein (L-FABP) contains amino acids that are known to possess antioxidant function. In this study, we tested the hypothesis that L-FABP may serve as an effective endogenous cytoprotectant against oxidative stress. Chang liver cells were selected as the experimental model because of their undetectable L-FABP mRNA level. Full-length L-FABP cDNA was subcloned into the mammalian expression vector pcDNA3.1 (pcDNA-FABP). Chang cells were stably transfected with pc-DNA-FABP or vector (pcDNA3.1) alone. Oxidative stress was induced by incubating cells with 400 micromol/L H2O2 or by subjecting cells to hypoxia/reoxygenation. Total cellular reactive oxygen species (ROS) was determined using the fluorescent probe DCF. Cellular damage induced by hypoxia/reoxygenation was assayed by lactate dehydrogenase (LDH) release. Expression of L-FABP was documented by regular reverse transcription polymerase chain reaction (RT-PCR), real-time RT-PCR, and Western blot. The pcDNA-FABP-transfected cells expressed full-length L-FABP mRNA, which was absent from vector-transfected control cells. Western blot showed expression of 14-kd L-FABP protein in pcDNA-FABP-transfected cells, but not in vector-transfected cells. Transfected cells showed decreased DCF fluorescence intensity under oxidative stress (H2O2 and hypoxia/reoxygenation) conditions versus control in inverse proportion to the level of L-FABP expression. Lower LDH release was observed in the higher L-FABP-expressed cells in hypoxia/reoxygenation experiments. In conclusion, we successfully transfected and cloned a Chang liver cell line that expressed the L-FABP gene. The L-FABP-expressing cell line had a reduced intracellular ROS level versus control. This finding implies that L-FABP has a significant role in oxidative stress.

Receptor for advanced glycation end product (RAGE) upregulation in human gingival fibroblasts incubated with nornicotine

BACKGROUND

Clinical and epidemiological data strongly support a link between smoking and periodontal disease. The mechanism by which smoking contributes to the destruction of periodontal tissue is not clear and cannot be attributed solely to the vasoconstrictive effects of nicotine. Our hypothesis is that nornicotine, a metabolite of nicotine, upregulates the expression of the receptor for the advanced glycation end products (RAGE) in the gingiva of smokers and triggers the proinflammatory effects of AGE by stimulating the secretion of cytokines and reactive oxygen species which directly cause destruction of the periodontal apparatus.

METHODS

Human gingival cells grown in tissue culture were exposed to 1 microM nornicotine for 72 hours. Following the nornicotine pretreatment, some of the cells were also treated with AGE that was generated with nornicotine for 48 hours and another group was continued on nornicotine only for 48 hours. Control cells that were not exposed to either nornicotine or AGE were also cultured. The cells were harvested and RNA was extracted for reverse transcription-polymerase chain reaction (RT-PCR) and RAGE mRNA was amplified.

RESULTS

The nornicotine-treated cells increased their expression of RAGE by approximately 4-fold (P <0.05, Student t test). These data suggest that nornicotine, a byproduct of cigarette smoke, can induce RAGE expression in gingival tissues. Therefore, our data support the hypothesis that RAGE potentially plays a significant role in the progression of periodontal disease exacerbated by smoking.

CONCLUSION

Nornicotine, AGE, and upregulation of RAGE may be involved in the pathogenesis of periodontal disease associated with smoking.

Albumin antioxidant capacity is modified by methylglyoxal

OBJECTIVE

Oxidative stress seems to play a major role in diabetic vascular complication development. Plasma albumin, via its thiol groups, is the main extracellular antioxidant molecule. Methylglyoxal (MG) is a very reactive dicarbonyl compound increased in diabetes which strongly modifies proteins by non-enzymatic glycosylation. The aim of this work was to study if MG could modify albumin antioxidant capacity.

METHODS

Bovine serum albumin was incubated with 1 mM MG at 37 degrees C for 7 days (MG-BSA). Albumin physico-chemical changes were evaluated by tryptophan autofluorescence measurement in the presence or in the absence of a quencher (acrylamide). Albumin antioxidant capacity was determined by thiol measurement using Ellman's reagent as well as in a cellular system (HeLa cells stressed by H2O2).

RESULTS

MG-BSA exhibited important modifications as shown by conformational changes, decreased tryptophan autofluorescence (30%) and significant thiol loss (40%). MG-BSA led to important modifications resulting in oxidation and loss of albumin antioxidant capacity. MG-BSA modifications were close to the one observed in albumin isolated from diabetic patients.

CONCLUSION

Our results suggest that deleterious effects induced by carbonyl stress in diabetes could also originate from a loss of albumin antioxidant capacity by dicarbonyl compound attack. The biological consequences of these findings have now to be investigated.

Comparative binding character of two general anaesthetics for sites on human serum albumin

Propofol and halothane are clinically used general anaesthetics, which are transported primarily by HSA (human serum albumin) in the blood. Binding characteristics are therefore of interest for both the pharmacokinetics and pharmacodynamics of these drugs. We characterized anaesthetic-HSA interactions in solution using elution chromatography, ITC (isothermal titration calorimetry), hydrogen-exchange experiments and geometric analyses of high-resolution structures. Binding affinity of propofol to HSA was determined to have a K(d) of 65 microM and a stoichiometry of approx. 2, whereas the binding of halothane to HSA showed a K(d) of 1.6 mM and a stoichiometry of approx. 7. Anaesthetic-HSA interactions are exothermic, with propofol having a larger negative enthalpy change relative to halothane. Hydrogen-exchange studies in isolated recombinant domains of HSA showed that propofol-binding sites are primarily found in domain III, whereas halothane sites are more widely distributed. Both location and stoichiometry from these solution studies agree with data derived from X-ray crystal-structure studies, and further analyses of the architecture of sites from these structures suggested that greater hydrophobic contacts, van der Waals interactions and hydrogen-bond formation account for the stronger binding of propofol as compared with the less potent anaesthetic, halothane.

Measuring reactive species and oxidative damage in vivo and in cell culture: how should you do it and what do the results mean?

Free radicals and other reactive species (RS) are thought to play an important role in many human diseases. Establishing their precise role requires the ability to measure them and the oxidative damage that they cause. This article first reviews what is meant by the terms free radical, RS, antioxidant, oxidative damage and oxidative stress. It then critically examines methods used to trap RS, including spin trapping and aromatic hydroxylation, with a particular emphasis on those methods applicable to human studies. Methods used to measure oxidative damage to DNA, lipids and proteins and methods used to detect RS in cell culture, especially the various fluorescent "probes" of RS, are also critically reviewed. The emphasis throughout is on the caution that is needed in applying these methods in view of possible errors and artifacts in interpreting the results.

Scavenging system efficiency is crucial for cell resistance to ROS-mediated methylglyoxal injury

Methylglyoxal is a reactive dicarbonyl compound endogenously produced mainly from glycolytic intermediates. Recent research indicates that methylglyoxal is a potent growth inhibitor and genotoxic agent. The antiproliferative activity of methylglyoxal has been investigated for pharmacological application in cancer chemotherapy. However, various cells are not equally sensitive to methylglyoxal toxicity. Therefore, it would be important to establish the cellular factors responsible for the different cell-type specific response to methylglyoxal injury, in order to avoid the risk of failure of a therapy based on increasing the intracellular level of methylglyoxal. To this purpose, we comparatively evaluated the signaling transduction pathway elicited by methylglyoxal in human glioblastoma (ADF) and neuroblastoma (SH-SY 5Y) cells. Results show that methylglyoxal causes early and extensive reactive oxygen species generation in both cell lines. However, SH-SY 5Y cells show higher sensitivity to methylglyoxal challenge due to a defective antioxidant and detoxifying ability that, preventing these cells from an efficient scavenging action, elicits extensive caspase-9 dependent apoptosis. These data emphasize the pivotal role of antioxidant and detoxifying systems in determining the grade of sensitivity of cells to methylglyoxal.

Methylglyoxal-bovine serum albumin stimulates tumor necrosis factor alpha secretion in RAW 264.7 cells through activation of mitogen-activating protein kinase, nuclear factor kappaB and intracellular reactive oxygen species formation

Accumulating evidence suggests that the pathophysiology of diabetes is analogous to chronic inflammatory states. Circulating levels of inflammatory cytokines such as IL-6 and tumor necrosis factor alpha (TNFalpha) are increased in both type 1 and type 2 diabetes. TNFalpha plays an important role in the pathogenesis of insulin resistance in type 2 diabetes. However, the reason for this increase remains unclear. Levels of the dicarbonyl methylglyoxal (MGO) are elevated in diabetic plasma and MGO-modified bovine serum albumin (MGO-BSA) can trigger cellular uptake of TNF. Therefore we tested the hypothesis that MGO-modified proteins may cause TNFalpha secretion in macrophage-like RAW 264.7 cells. Treatment of cells with MGO-BSA induced TNFalpha release in a dose-dependent manner. MGO-modified ribonuclease A and chicken egg ovalbumin had similar effects. Cotreatment of cells with antioxidant reagent N-acetylcysteine (NAC) inhibited MGO-BSA-induced TNFalpha secretion. MGO-BSA stimulated the simultaneous activation of p44/42 and p38 mitogen-activated protein kinase. PD98059, a selective MEK inhibitor, inhibited MGO-BSA-induced TNFalpha release as well as ERK phosphorylation. Pretreatment of cells with NAC also resulted in inhibition of MGO-BSA-induced ERK phosphorylation. MGO-BSA induced dose-dependent NFkappaB activation as shown by electrophoresis mobility shift assay. The MGO-BSA-induced NFkappaB activation was prevented in the presence of PD98059, NAC, and parthenolide, a selective inhibitor of NFkappaB. Furthermore, the NFkappaB inhibitor parthenolide suppressed MGO-BSA-induced TNFalpha secretion. Confocal microscopy using dichlorofluorescein to demonstrate intracellular reactive oxygen species (ROS) showed that MGO-BSA produced more ROS compared with native BSA. MGO-BSA could also stimulate protein kinase C (PKC) translocation to the cell membrane, considered a key signaling pathway in diabetes. However, there was no evidence that PKC was involved in TNFalpha release based on inhibition by calphostin C and staurosporine. Our findings suggest that the presence of chronically elevated levels of MGO-modified bovine serum albumin may contribute to elevated levels of TNFalpha in diabetes.

Hyperglycemic switch from mitochondrial nitric oxide to superoxide production in endothelial cells

The accumulated ultrastructural and biochemical evidence is highly suggestive of the existence of mitochondrial nitric oxide (NO) synthase (mtNOS), where local production of NO regulates the electron transport along the respiratory chain. Here, the functional competence of mtNOS in situ in a living cell was examined using an intravital fluorescent NO indicator, 4,5-diaminofluorescein, employing a new procedure for loading it into the mitochondria to demonstrate local NO generation in undisrupted endothelial cells and in isolated mitochondria as well as in human embryonic kidney cells stably expressing endothelial NOS. With the use of this approach, we showed that endothelial cells incubated in the presence of high concentration of D-glucose (but not L-glucose) are characterized by the reduced NO synthetic function of mitochondria despite the unaltered abundance of the enzyme. In parallel, mitochondrial generation of superoxide was augmented in endothelial cells incubated in the presence of a high concentration of D-glucose. Both the NO generation and superoxide production in hyperglycemic environment could be restored to control levels by treating cells with a cell-permeable superoxide dismutase mimetic. In addition, enhanced mitochondrial superoxide production could be suppressed with an inhibitor of NOS in stimulated endothelial cells. In conclusion, the data 1) provide direct evidence of mitochondrial NO production in endothelial cells, 2) demonstrate its suppression and enhanced superoxide generation in hyperglycemic environment, and 3) provide evidence that "uncoupled" mtNOS represents an important source of superoxide anions in endothelial cells incubated in high glucose-containing medium.