In vitro study of the cytotoxicity of isolated oxidized lipid low-density lipoproteins fractions in human endothelial cells: relationship with the glutathione status and cell morphology

Lycium barbarum polysaccharide's protective effects against PM2.5-induced cellular senescence in HUVECs

Fine particulate matter (PM2.5) exposure is strongly associated with vascular endothelial senescence, a process implicated in cardiovascular diseases. While there is existing knowledge on the impact of Lycium barbarum polysaccharide (LBP) on vascular endothelial damage, the protective mechanism of LBP against PM2.5-induced vascular endothelial senescence remains unclear. In this study, we investigated the impact of PM2.5 exposure on vascular endothelial senescence and explored the intervention effects of LBP in human umbilical vein endothelial cells (HUVECs). We found that PM2.5 exposure dose-dependently reduced cell viability and proliferation in HUVECs while increasing the production of reactive oxygen species (ROS), malondialdehyde (MDA), and hydrogen peroxide (H2O2). Additionally, PM2.5 exposure inhibited the activity of superoxide dismutase (SOD). Notably, PM2.5 exposure induced autophagy impairments and cellular senescence. However, LBP mitigated PM2.5-induced cell damage. Further studies demonstrated that correcting autophagy impairment in HUVECs reduced the expression of the senescence markers P16 and P21 induced by PM2.5. This suggests the regulatory role of autophagy in cellular senescence and the potential of LBP in improving HUVECs senescence. These findings provide novel insights into the mechanisms underlying PM2.5-induced cardiovascular toxicity and highlight the potential of LBP as a therapeutic agent for improving vascular endothelial health.

Atomic force microscopy application to study of the biomechanical properties of the aortic intima in the context of early atherosclerosis

Atherosclerosis is characterized by the infiltration of macrophages, accumulation of lipids, activation of endothelial cells and synthesis of extracellular matrix by vascular smooth muscle cells. However, there have been few atomic force microscopy (AFM) studies of the aortic intima in situ in the context of atherosclerosis. By employing a customized liquid cell for AFM, we investigated the aortic intima obtained from male C57BL/6 ApoE-deficient mice (ApoE^-/- ) aged 14 weeks and male C57BL/6 ApoE-sufficient mice (ApoE^+/+ ) aged between 18 and 26 weeks that were fed a high-fat and high-cholesterol diet for 4 weeks and performed force spectroscopy mapping of the biomechanical properties of the intima. In the aortas of ApoE-deficient mice, the intima became stiffer than that of ApoE-sufficient mice. In addition, the cytoskeleton of endothelial cells was enlarged, and extracellular matrix accumulated. The biomechanical properties of the aortic intima are altered in early atherogenesis, which may be induced by the enlargement of the endothelial cell cytoskeleton and the increased synthesis of extracellular matrix by activated smooth muscle cells.

Oxidized Phospholipids in Healthy and Diseased Lung Endothelium

Circulating and cell membrane phospholipids undergo oxidation caused by enzymatic and non-enzymatic mechanisms. As a result, a diverse group of bioactive oxidized phospholipids generated in these conditions have both beneficial and harmful effects on the human body. Increased production of oxidized phospholipid products with deleterious effects is linked to the pathogenesis of various cardiopulmonary disorders such as atherosclerosis, thrombosis, acute lung injury (ALI), and inflammation. It has been determined that the contrasting biological effects of lipid oxidation products are governed by their structural variations. For example, full-length products of 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine oxidation (OxPAPC) have prominent endothelial barrier protective and anti-inflammatory activities while most of the truncated oxidized phospholipids induce vascular leak and exacerbate inflammation. The extensive studies from our group and other groups have demonstrated a strong potential of OxPAPC in mitigating a wide range of agonist-induced lung injuries and inflammation in pulmonary endothelial cell culture and rodent models of ALI. Concurrently, elevated levels of truncated oxidized phospholipids are present in aged mice lungs that potentiate the inflammatory agents-induced lung injury. On the other hand, increased levels of full length OxPAPC products accelerate ALI recovery by facilitating production of anti-inflammatory lipid mediator, lipoxin A4, and other molecules with anti-inflammatory properties. These findings suggest that OxPAPC-assisted lipid program switch may be a promising therapeutic strategy for treatment of acute inflammatory syndromes. In this review, we will summarize the vascular-protective and deleterious aspects of oxidized phospholipids and discuss their therapeutic potential including engineering of stable analogs of oxidized phospholipids with improved anti-inflammatory and barrier-protective properties.

N-acetyl cysteine protects osteoblastic function from oxidative stress

We tested the protective potential of an antioxidant amino acid derivative, N-acetyl cysteine (NAC), in controlling oxidative stress against osteoblasts. Osteoblastic cells extracted from rat bone marrow were cultured. Oxidative stress was induced by adding 100 μM H₂O₂ into the culture media. Then, some H₂O₂-treated cultures were cotreated with 2.5 or 5 mM NAC. Addition of H₂O₂ decreased the number of cells to 50% of untreated cultures at days 2. Addition of 5 mM NAC into H₂O₂ cultures resulted in a dose-dependent increase in the number of cells, with the cell number being 50% greater than that in the 100 μM H₂O₂ culture. The gene expression levels of type I collagen, osteopontin, and osteocalcin were downregulated threefold by H₂O₂ on day 7. The H₂O₂-suppressed gene expression was fully recovered by NAC cotreatment. The mineralizing capability, assessed by Von Kossa staining on day 15, were approximately 1.8 times greater in the NAC + H₂O₂ cotreated group than in the culture with H₂O₂ alone. These NAC-mediated restorations were associated with an NAC dose-dependent increase of intracellular glutathione and a NAC dose-dependent decrease of intracellular reactive oxygen species. In conclusion, oxidative stress induced by H₂O₂ substantially impairs the proliferation, differentiation, and mineralization of osteoblasts. More importantly, the addition of NAC into the culture was found to restore these damages to a near normal level due to the improved redox balance, warranting further in vivo studies to test its therapeutic potential as a local antioxidative stress drug.

N-acetyl cysteine protects TMJ chondrocytes from oxidative stress

Temporomandibular joint (TMJ) inflammation is closely associated with oxidative stress. This study tested the potential of N-acetyl cysteine (NAC), an anti-oxidant amino-acid derivative, in alleviating oxidative stress-related damage in TMJ chondrocytes. The inflammatory condition was simulated by the addition of hydrogen peroxide (H₂O₂) to TMJ-derived chondrocyte cultures. Exposure to H₂O₂ decreased the cell population by half within 2 days as a result of induced apoptosis and reduced proliferation. Gene expression of aggrecan and collagen II, as well as glycosaminoglycan production, were reduced by more than 70%. These compromised chondrocyte viability and function were fully restored by the addition of NAC to the cultures. NAC reduced the H₂O₂-elevated intracellular reactive oxygen species to the normal level and increased cellular glutathione reserves. These results indicate that NAC restores oxidative stress-induced cell death and severe functional impairment in TMJ chondrocytes, and warrant in vivo testing to explore its therapeutic potential as an anti-inflammatory agent.

Individual variation and intraclass correlation in arachidonic acid and eicosapentaenoic acid in chicken muscle

Chicken meat with reduced concentration of arachidonic acid (AA) and reduced ratio between omega-6 and omega-3 fatty acids has potential health benefits because a reduction in AA intake dampens prostanoid signaling, and the proportion between omega-6 and omega-3 fatty acids is too high in our diet. Analyses for fatty acid determination are expensive, and finding the optimal number of analyses to give reliable results is a challenge. The objective of the present study was i) to analyse the intraclass correlation of different fatty acids in five meat samples, of one gram each, within the same chicken thigh, and ii) to study individual variations in the concentrations of a range of fatty acids and the ratio between omega-6 and omega-3 fatty acid concentrations among fifteen chickens. Fifteen newly hatched broilers were fed a wheat-based diet containing 4% rapeseed oil and 1% linseed oil for three weeks. Five muscle samples from the mid location of the thigh of each chicken were analysed for fatty acid composition. The intraclass correlation (sample correlation within the same animal) was 0.85-0.98 for the ratios of total omega-6 to total omega-3 fatty acids and of AA to eicosapentaenoic acid (EPA). This indicates that when studying these fatty acid ratios, one sample of one gram per animal is sufficient. However, due to the high individual variation between chicken for these ratios, a relatively high number of animals (minimum 15) are required to obtain a sufficiently high power to reveal significant effects of experimental factors (e.g. feeding regimes). The present experiment resulted in meat with a favorable concentration ratio between omega-6 and omega-3 fatty acids. The AA concentration varied from 1.5 to 2.8 g/100 g total fatty acids in thigh muscle in the fifteen broilers, and the ratio between AA and EPA concentrations ranged from 2.3 to 3.9. These differences among the birds may be due to genetic variance that can be exploited by breeding for lower AA concentration and/or a more favorable AA/EPA ratio to produce meat with health benefits.

Red cells, hemoglobin, heme, iron, and atherogenesis

OBJECTIVE

We investigated whether red cell infiltration of atheromatous lesions promotes the later stages of atherosclerosis.

METHODS AND RESULTS

We find that oxidation of ferro (FeII) hemoglobin in ruptured advanced lesions occurs generating ferri (FeIII) hemoglobin and via more extensive oxidation ferrylhemoglobin (FeIII/FeIV=O). The protein oxidation marker dityrosine accumulates in complicated lesions, accompanied by the formation of cross-linked hemoglobin, a hallmark of ferrylhemoglobin. Exposure of normal red cells to lipids derived from atheromatous lesions causes hemolysis and oxidation of liberated hemoglobin. In the interactions between hemoglobin and atheroma lipids, hemoglobin and heme promote further lipid oxidation and subsequently endothelial reactions such as upregulation of heme oxygenase-1 and cytotoxicity to endothelium. Oxidative scission of heme leads to release of iron and a feed-forward process of iron-driven plaque lipid oxidation. The inhibition of heme release from globin by haptoglobin and sequestration of heme by hemopexin suppress hemoglobin-mediated oxidation of lipids of atheromatous lesions and attenuate endothelial cytotoxicity.

CONCLUSIONS

The interior of advanced atheromatous lesions is a prooxidant environment in which erythrocytes lyse, hemoglobin is oxidized to ferri- and ferrylhemoglobin, and released heme and iron promote further oxidation of lipids. These events amplify the endothelial cell cytotoxicity of plaque components.

Oxidized phospholipids in control of inflammation and endothelial barrier

The levels of circulating oxidized phospholipids (OxPLs) become increased in chronic and acute pathologic conditions such as hyperlipidemia, atherosclerosis, increased intimamedia thickness in the patients with systemic Lupus erythematosus, vascular balloon injury, acute lung injury (ALI), and acute respiratory distress syndrome (ARDS). These pathologies are associated with inflammation and activation of endothelial cells. Depending on the biological context and the specific group of phospholipid oxidation products, OxPL may exhibit both proinflammatory and anti-inflammatory effects. This review will summarize the data showing a dual role of OxPL in modulation of chronic and acute inflammation as well as OxPL effects on pulmonary endothelial permeability. Recent reports show protective effects of OxPL in the models of endotoxin and ventilator-induced ALI and suggest a potential for using OxPL-derived cyclopenthenone-containing compounds with barrier-protective properties for drug design. These compounds may represent a new group of therapeutic agents for the treatment of lung syndromes associated with acute inflammation and lung vascular leak.

Endothelial cell regulation by phospholipid oxidation products

Oxidized phospholipids accumulate in atherosclerotic lesions, on lipoproteins, in other states of chronic inflammation, on apoptotic cells, necrotic cells and cells exposed to oxidative stress. These lipids regulate the transcription of over 1000 gene, regulating many endothelial functions, by activating several different cell surface receptors and multiple signaling pathways. These lipids also have important effects not involving transcription that regulate cell junctions and leukocyte binding. Thus these lipids are potent regulators of endothelial cell function with broad effects comparable in extent but differing from those of cytokines.

Death-signaling pathways in human myeloid cells by oxLDL and its cytotoxic components 7beta-hydroxycholesterol and cholesterol-5beta,6beta-epoxide

Oxidized low-density lipoprotein contains many potentially proatherogenic molecules, including oxysterols, which have been shown to induce apoptosis in various cell lines. The aim of this study was to investigate the pathway of apoptosis induced by oxidized low-density lipoprotein and the oxysterols, 7beta-hydroxycholesterol and cholesterol-5beta,6beta-epoxide, in two human monocytic cell lines. The HL-60 cells appeared to be more sensitive to oxidized low-density lipoprotein than U937 cells, whereas the isolated oxysterols were more potent inducers of apoptosis in the U937 cells. Caspase-2 inhibition decreased the number of viable cells in oxidized low-density lipoprotein-treated samples; however, it protected against cholesterol-5beta,6beta-epoxide-induced cell death. Western blot analysis was utilized to examine the effect of caspase-2 inhibition on the expression of the antiapoptotic protein Bcl-2. Pretreatment with the inhibitor protected against the decrease in Bcl-2 expression in oxidized low-density lipoprotein- and 7beta-hydroxycholesterol-treated U937 cells. In HL-60 cells, Bcl-2 was overexpressed in oxidized low-density lipoprotein-treated cells, but in the presence of the inhibitor Bcl-2 expression was returned to control levels. Depleted ATP concentrations in the cells suggest that both apoptosis and necrosis may have occurred simultaneously. Our results highlight differences in the signaling pathways induced by oxidized low-density lipoprotein, 7beta-hydroxycholesterol, and cholesterol-5beta,6beta-epoxide in U937 and HL-60 cells.

Qualitative and quantitative comparison of the cytotoxic and apoptotic potential of phytosterol oxidation products with their corresponding cholesterol oxidation products

Phytosterols contain an unsaturated ring structure and therefore are susceptible to oxidation under certain conditions. Whilst the cytotoxicity of the analogous cholesterol oxidation products (COP) has been well documented, the biological effects of phytosterol oxidation products (POP)have not yet been fully ascertained. The objective of the present study was to examine the cytotoxicity of β-sitosterol oxides and their corresponding COP in a human monocytic cell line (U937), a colonic adenocarcinoma cell line (CaCo-2) and a hepatoma liver cell line (HepG2). 7β-Hydroxysitosterol, 7-ketositosterol, sitosterol-3β,5α,6β-triol and a sitosterol-5α,6α-epoxide–sitosterol-5β,6β-epoxide (6:1) mixture were found to be cytotoxic to all three cell lines employed; the mode of cell death was by apoptosis in the U937 cell line and necrosis in the CaCo-2 and HepG2 cells. 7β-Hydroxysitosterol was the only β-sitosterol oxide to cause depletion in glutathione, indicating that POP-induced apoptosis may not be dependent on the generation of an oxidative stress. A further objective of this study was to assess the ability of the antioxidants α-tocopherol, γ-tocopherol and β-carotene to modulate POP-induced cytotoxicity in U937 cells. Whilst α/γ-tocopherol protected against 7β-hydroxycholesterol-induced apoptosis, they did not confer protection against 7β-hydroxysitosterol-or 7-ketositosterol-induced toxicity, indicating that perhaps COP provoke different apoptotic pathways than POP. β-Carotene did not protect against COP- or POP-induced toxicity. In general, results indicate that POP have qualitatively similar toxic effects to COP. However, higher concentrations of POP are required to elicit comparable levels of toxicity.

Induction of lipoprotein lipase gene expression in Chlamydia pneumoniae-infected macrophages is dependent on Ca2+ signaling events

Unregulated uptake of low density lipoprotein (LDL) in macrophages is the hallmark of early atherogenic lesions, and Chlamydia pneumoniae infection of macrophages induces this process by an unknown mechanism. It was therefore aimed in this study to investigate (i) the role of C. pneumoniae in macrophage expression of the lipoprotein lipase (LpL) gene, (ii) the probable role of Ca2+ influx signals and (iii) the effect of the process on LDL uptake. Lipoprotein lipase mRNA expression and LpL activity in infected RAW-264.7 cells were significantly upregulated. A biphasic Ca2+ influx signal was observed in infected cells with a moderate influx (303 nM Ca2+) favoring optimal LpL gene expression. Also, the antagonists of L-type Ca2+ channel in macrophages significantly down-regulated LpL gene expression and the biomolecular content of C. pneumoniae responsible for the observed events was in part found to be Chlamydia lipopolysaccharide (cLPS). Investigations aimed at determining the specific relevance of Ca(2+)-dependent lipoprotein lipase gene expression in C. pneumoniae-infected macrophages showed that the condition caused enhanced uptake of LDL which was abrogated by Calphostin-C-mediated down-regulation of LpL. This discovery of a specialized Ca2+ influx signal-mediated LpL upregulation in C. pneumoniae-infected macrophages provides a mechanistic insight into early events involving C. pneumoniae in macrophage foam cell formation resulting from LDL uptake.

Comparison of the cytotoxic effects of beta-sitosterol oxides and a cholesterol oxide, 7beta-hydroxycholesterol, in cultured mammalian cells

Phytosterols are plant sterols found in foods such as oils, nuts and vegetables. Phytosterols, in the same way as cholesterol, contain a double bond and are susceptible to oxidation. The objective of the present study was to assess the potential toxic effects of beta-sitosterol oxides on U937 cells. The effects of increasing concentrations (0-120 microm) of beta-sitosterol oxides on cellular cytotoxicity, apoptosis, antioxidant status and genotoxicity was assessed over 12, 24 and 48 h exposure periods. Following 12 h, the viability of cells treated with 120 microm-beta-sitosterol oxides was reduced to 51.7 % relative to control. At 24 and 48 h, both 60 and 120 microm-beta-sitosterol oxides caused a significant decrease in cell viability. For comparison, a decrease in viability of cells treated with a cholesterol oxide, 7beta-hydroxycholesterol (7beta-OH, 30 microm), was evident at 24 h. An increase in apoptotic cells, assessed using Hoechst 33342, indicates that the mode of cell death in U937 cells following exposure to 7beta-OH (30 microm) and beta-sitosterol oxides (60 and 120 microm) was by apoptosis. The increase in apoptotic cells after 12 h following treatment with 120 microm-beta-sitosterol oxides was accompanied by a decrease in cellular glutathione. Similarly, 7beta-OH (30 microm) treatment resulted in decreased glutathione at 12 h. Catalase activity was not affected by any of the treatments. beta-Sitosterol oxides had no genotoxic effects on U937 and V79 cells as assessed by the comet and sister chromatid exchange assays respectively. In general, the results indicate that thermally oxidised derivatives of beta-sitosterol demonstrate similar biological effects as 7beta-OH in U937 cells, but at higher concentrations.

Human invasive trophoblasts transformed with simian virus 40 provide a new tool to study the role of PPARgamma in cell invasion process

Invasive cytotrophoblasts play a key role in the development of human placenta and is therefore essential for subsequent development of the embryo. Human implantation is characterized by a major trophoblastic invasion that offers a unique model of a controlled and oriented tumor-like process. The ligand-activated nuclear receptor peroxisome proliferator-activated receptor gamma (PPARgamma) modulates cell growth and differentiation and might be therefore considered as a tumor suppressor. We have recently reported that PPARgamma, in synergy with its dimerization partner retinoid X receptor (RXR)alpha, controls the invasion of human primary cytotrophoblasts. Because these cells are unable to replicate in culture, we have, in the present study, transformed these primary cells with the simian virus 40 large T antigen for studying the role of PPARgamma in cell invasion process. Our results show that the cell line human invasive proliferative extravillous cytotrophoblast (HIPEC) 65 expressed markers of human invasive primary cytotrophoblast as determined by immunocytochemistry, immunobloting and real-time RT-PCR, and were highly invasive in vitro. We have next studied the role of PPARgamma/RXRalpha heterodimers in cell proliferation and invasion. Our results show that PPARgamma and RXRalpha are co-expressed by HIPEC 65 and that, as commonly observed, activation of PPARgamma/RXRalpha heterodimers with the specific PPARgamma agonist rosiglitazone induced lipid droplet accumulation as revealed by oil red O staining. Treatment with rosiglitazone or with the natural PPARgamma agonist 15-deoxy-delta-(12,14) PGJ2 did not modify cell growth, but interestingly, activation of PPARgamma by this synthetic (rosiglitazone) or natural (15d-PGJ2) ligand markedly inhibited cell invasion in a concentration-dependent manner. Finally, we showed that other potential natural PPARgamma ligand such as oxidized-but not native-low-density lipoprotein inhibited cell invasion. This proliferative and invasive human cytotrophoblast cell line from extravillous origin provides a new tool for studying specifically the role of PPARgamma in the control of cell invasion.

Selenium supplementation acting through the induction of thioredoxin reductase and glutathione peroxidase protects the human endothelial cell line EAhy926 from damage by lipid hydroperoxides

The human endothelial cell line EAhy926 was used to determine the importance of selenium in preventing oxidative damage induced by tert-butyl hydroperoxide (tert-BuOOH) or oxidised low density lipoprotein (LDLox). In cells grown in a low selenium medium, tert-BuOOH and LDLox killed cells in a dose-dependent manner. At 555 mg/l LDLox or 300 microM tert-BuOOH, >80% of cells were killed after 20 h. No significant cell kill was achieved by these agents if cells were pre-incubated for 48 h with 40 nM sodium selenite, a concentration that maximally induced the activities of cytoplasmic glutathione peroxidase (cyGPX; 5.1-fold), phospholipid hydroperoxide glutathione peroxidase (PHGPX;1.9-fold) and thioredoxin reductase (TR; 3.1-fold). Selenium-deficient cells pre-treated with 1 microM gold thioglucose (GTG) (a concentration that inhibited 25% of TR activity but had no inhibitory effect on cyGPX or PHGPX activity) were significantly (P<0.05) more susceptible to tert-BuOOH toxicity (LC(50) 110 microM) than selenium-deficient cells (LC(50) 175 microM). This was also the case for LDLox. In contrast, cells pre-treated with 40 nM selenite prior to exposure to GTG were significantly more resistant to damage from tert-BuOOH and LDLox than Se-deficient cells. Treatment with GTG or selenite had no significant effect on intracellular total glutathione concentrations. These results suggest that selenium supplementation, acting through induction of TR and GPX, has the potential to protect the human endothelium from oxidative damage.

Induction of glutathione synthesis by oxidized low-density lipoprotein and 1-palmitoyl-2-arachidonyl phosphatidylcholine: protection against quinone-mediated oxidative stress

Exposure of endothelial cells to oxidized low-density lipoprotein (oxLDL) leads to diverse cellular effects, including induction of the intracellular antioxidant GSH. It is not known whether lipid-or protein-derived oxidation products cause GSH induction and whether this involves increased activity of the key enzyme in its synthesis, glutamate-cysteine ligase (GCL). Furthermore, the effect of oxLDL exposure on the cell's ability to combat oxidative stress has not been previously examined. In the present study we found that, in bovine aortic endothelial cells, LDL or 1-palmitoyl-2-arachidonyl phosphatidylcholine oxidized by different reactive oxygen and nitrogen species induced GSH synthesis. However, prevention of GSH synthesis during exposure to oxLDL caused extensive cell death. The mediator causing GSH induction was shown to be a polar lipid and resulted in the increased activity of GCL as well as increased protein levels of the regulatory subunit of GCL. Pretreatment with both oxLDL and the polar lipid subfraction of the oxLDL protected cells against the toxicity of 2,3-dimethoxynaphthoquinone (DMNQ), a superoxide- and H(2)O(2)-forming compound. The potential of a low level of lipid peroxidation products to initiate cytoprotective pathways are discussed.

alpha-Tocopherol, but not gamma-tocopherol inhibits 7 beta-hydroxycholesterol-induced apoptosis in human U937 cells

Oxysterols, particularly those oxidised at position 7, are toxic to cells in culture and have been shown to induce apoptosis in cell types such as vascular endothelial cells, smooth muscle cells and monocytes. The precise mechanism by which oxysterols induce apoptosis is unknown but may involve the generation of oxidative stress. In the present study we examined the ability of alpha-TOC, alpha-TOC acetate (alpha-TOCA) and gamma-TOC to protect against 7 beta-hydroxycholesterol (7 beta-OHC)-induced apoptosis of human monocytic U937 cells. 7 beta-OHC is one of the most commonly detected oxysterols in foods and its level in plasma has been positively associated with an increased risk of atherosclerosis. The present study demonstrates a significant decrease in cell membrane integrity and cellular glutathione levels when U937 cells were treated with 30 microM 7 beta-OHC. DNA fragmentation also occurred, as measured by agarose gel electrophoresis, and the number of apoptotic cells increased as assessed by nuclear morphology. Analysis by HPLC showed that there was a greater incorporation of gamma-TOC into U937 cells after a 48 h incubation, than either alpha-TOC or alpha-TOCA. However, despite the increased uptake of gamma-TOC, only alpha-TOC, and not gamma-TOC or alpha-TOCA was effective at inhibiting 7 beta-OHC-induced apoptosis in U937 cells.