O. Ziouzenkova - Academia.edu (original) (raw)
Papers by O. Ziouzenkova
Nature Medicine, 2007
The metabolism of vitamin A and the diverse effects of its metabolites are tightly controlled by ... more The metabolism of vitamin A and the diverse effects of its metabolites are tightly controlled by distinct retinoid-generating enzymes, retinoid-binding proteins and retinoid-activated nuclear receptors. Retinoic acid regulates differentiation and metabolism by activating the retinoic acid receptor and retinoid X receptor (RXR), indirectly influencing RXR heterodimeric partners. Retinoic acid is formed solely from retinaldehyde (Rald), which in turn is derived from vitamin A. Rald currently has no defined biologic role outside the eye. Here we show that Rald is present in rodent fat, binds retinol-binding proteins (CRBP1, RBP4), inhibits adipogenesis and suppresses peroxisome proliferator-activated receptor-c and RXR responses. In vivo, mice lacking the Rald-catabolizing enzyme retinaldehyde dehydrogenase 1 (Raldh1) resisted diet-induced obesity and insulin resistance and showed increased energy dissipation. In ob/ob mice, administrating Rald or a Raldh inhibitor reduced fat and increased insulin sensitivity. These results identify Rald as a distinct transcriptional regulator of the metabolic responses to a high-fat diet.
Free Radical Biology and Medicine, 1998
Oxidation of LDL (0.1 microM) in PBS with copper concentrations ranging from 0.03 to 10 microM, e... more Oxidation of LDL (0.1 microM) in PBS with copper concentrations ranging from 0.03 to 10 microM, equal to 0.3-100 Cu2+/LDL, was investigated by monitoring the formation of conjugated dienes at 234 nm. With all 8 LDL samples examined, the kinetics changed strongly at submicromolar Cu2+ concentrations. Based on time-course of the formation of conjugated dienes, cholesteryl linoleate hydroxides and hydroperoxides as well as the antioxidant consumption, two oxidation types were distinguished. Type A oxidations, observed at relatively high Cu2+ concentrations of 10-100 Cu2+/ LDL, represented the conventional kinetics of LDL oxidation with an inhibition period (= lag-time) followed by a propagation phase. In contrast, type C oxidations proceeded after a negligibly short lag time followed by a distinct propagation phase. The rate of this propagation increased rapidly to 0.5 mol diene/mol LDL and then slowed down in the presence of alpha-,gamma-tocopherols and carotenoids, which were consumed faster than tocopherols. The increase in diene absorption was due to the formation of both hydroxides and hydroperoxides suggesting a high initial decomposition of hydroperoxides. At submicromolar concentrations of about 0.1 to 0.5 microM, type C and type A oxidation can be combined resulting in 4 consecutive oxidation phases, i.e. 1st inhibition and 1st propagation (belonging to type C), followed by 2nd inhibition and 2nd propagation (belonging to type A). Increasing copper concentrations lowered the 1st propagation and shortened the 2nd inhibition periods until they melted into one apparent kinetic phase. Decreasing [Cu2+] increased the 1st propagation and 2nd inhibition but lowered the 2nd propagation phase until it completely disappeared. A threshold copper concentration, denoted as Cu(lim), can be calculated as a kinetic constant based on the Cu2+-dependence for the rate of 2nd propagation. Below Cu(lim), LDL oxidation proceeds only via type C kinetics. The Cu2+-dependence of the oxidation kinetics suggests that LDL contains two different Cu2+ biding sites. Cu2+ at the low-affinity binding sites, with half-saturation at 5-50 Cu2+/LDL, initiates and accelerates the 2nd propagation by decomposing lipid hydroperoxides. Cu2+ bound to the high-affinity binding sites, with half-saturation at 0.3-2.0 Cu2+/LDL, is responsible for the 1st propagation. Arguments in favor and against this propagation being due to tocopherol mediated peroxidation (TMP) are discussed. If the lag-time concept is extended to the conjugated diene curves seen for combined oxidation profiles, then a true inhibition phase does not apply to this time interval, but instead represents the time elapsed before the onset of the 2nd propagation phase.
Free Radical Biology and Medicine, 2002
The high cardiovascular mortality in patients receiving hemodialysis (HD) has been attributed, in... more The high cardiovascular mortality in patients receiving hemodialysis (HD) has been attributed, in part, to oxidative stress. Here we examined the effectiveness of antioxidants introduced by means of a novel hemolipodialysis (HLD) procedure in terms of reducing oxidative stress during ex vivo blood circulation. Oxidative stress was studied in a model HD system resembling the extracorporeal circulation of blood during clinical HD. Blood circulation produced an increase of up to 280% in free hemoglobin levels and an increase of 320% in electronegative LDL (LDL Ϫ ) subfraction. A significant correlation between LDL Ϫ and free hemoglobin levels confirmed previous findings that LDL Ϫ formation during ex vivo circulation of blood can be mediated by the oxidative activity of free hemoglobin. These effects were significantly attenuated during HLD using a dialysis circuit containing vitamin E with or without vitamin C. By contrast, HLD with vitamin C alone had a marked pro-oxidant effect. TBARS, lipid hydroperoxides, vitamin E and -carotene content in LDL were not significantly altered by the HD procedure. These findings demonstrate the occurrence of oxidative stress in human plasma where lipoproteins are a target and indicate antioxidant-HLD treatment as a specific new approach to decreasing the adverse oxidative stress frequently associated with cardiovascular complications in high-risk populations of uremic patients.
International journal of clinical pharmacology and therapeutics, 1999
The possible oxidative complications induced by free hemoglobin (Hb) released during the blood st... more The possible oxidative complications induced by free hemoglobin (Hb) released during the blood storage are discussed together with therapeutic strategies using vitamin E and specific inhibitor haptoglobin. Prooxidative properties of Hb in blood have been examined using LDL as a marker for oxidative stress, which contribute to toxicity observed in a number of pathologies aggravated by hemolysis or hemorrhagic lesions as well as after the transfusion of stored blood. Experiments were performed using fresh blood or stored blood that was obtained from a blood bank on the day corresponding to the identified expiration date. Oxidation of LDL was determined by means of the formation of mildly oxidized LDL (LDL-) using anion exchange chromatography. Concentrations of Hb were determined spectrophotometrically. Hb-mediated oxidative processes in cellular membranes have been well documented over the past decade. We showed that catalytic activity of Hb released during blood storage was sufficie...
Journal of lipid research, 1996
In 59 healthy human subjects (37 male and 22 female) the concentrations of the lipid-soluble anti... more In 59 healthy human subjects (37 male and 22 female) the concentrations of the lipid-soluble antioxidants alpha- and gamma-tocopherol, alpha- and beta-carotene, lycopene, cryptoxanthin, canthaxanthin, and lutein + zeaxanthin were determined in plasma (mumol/L) and in isolated low density lipoproteins (LDL) (mumol/mmol cholesterol). Plasma alpha-tocopherol concentrations were significantly correlated with plasma total cholesterol concentrations (r2 = 0.51, P < 0.0001) yet not with the LDL alpha-tocopherol content (r2 = 0.05, ns). Plasma gamma-tocopherol concentrations were weakly correlated with plasma total cholesterol (r2 = 0.12, P < 0.003) and both absolute and cholesterol standardized plasma gamma-tocopherol concentrations correlated strongly with the LDL gamma-tocopherol content (r2 = 0.58 and r2 = 0.72, respectively). In contrast, carotenoid concentrations did not correlate with cholesterol concentrations, but their LDL content correlated significantly with the respective...
Journal of Nutrition, 2013
Zinc (Zn) deficiency and obesity are global public health problems. Zn deficiency is associated w... more Zinc (Zn) deficiency and obesity are global public health problems. Zn deficiency is associated with obesity and comorbid conditions that include insulin resistance and type 2 diabetes. However, the function of Zn in obesity remains unclear.
Proceedings of the National Academy of Sciences, 2003
Increased levels of triglyceride-rich lipoproteins provoke lipid accumulation in the artery wall,... more Increased levels of triglyceride-rich lipoproteins provoke lipid accumulation in the artery wall, triggering early inflammatory responses central to atherosclerosis like endothelial adhesion molecule expression. The endogenous mechanisms limiting such reactions remain poorly defined. Lipoprotein lipase (LPL) plays a central role in lipid metabolism by hydrolyzing triglyceride rich lipoproteins and releasing fatty acids. We found that LPL treatment reversed tumor necrosis factor ␣ and very low-density lipoprotein (VLDL)-stimulated endothelial vascular cell adhesion molecule 1 (VCAM1) induction and VCAM1 promoter responses, thus recapitulating effects reported with synthetic peroxisome proliferator-activated receptor (PPAR) agonists. In fact, these LPL effects on VCAM1 were absent in endothelial cells isolated from PPAR␣-deficient mice. This finding suggests a novel antiinflammatory role for LPL. Further studies reveal specificity for PPAR activation through lipolysis in regards to lipoprotein substrate (VLDL Ͼ Ͼ Ͼ Ͼ LDL > HDL), PPAR isoform (PPAR␣ Ͼ Ͼ Ͼ Ͼ PPAR␦ > PPAR␥), and among fatty acid-releasing lipases. These PPAR responses required intact LPL catalytic activity. In vivo, transgenic mice overexpressing LPL had increased peroxisome proliferation, but not in the genetic absence of PPAR␣. Although human plasma possesses minimal PPAR␣ activation despite containing abundant free fatty acids, marked PPAR␣ activation is seen with human plasma after LPL is added in vitro or systemically released in vivo. These data suggest a previously uncharacterized pathway in which the key lipolytic enzyme LPL can act on circulating lipoproteins to generate PPAR␣ ligands, providing a potentially important link between lipoprotein metabolism and distal PPAR␣ transcriptional effects.
Lipids, 1996
Oxidation resistance (OR) of low density lipoproteins (LDL) is frequently determined by the conju... more Oxidation resistance (OR) of low density lipoproteins (LDL) is frequently determined by the conjugated diene (CD) assay, in which isolated LDL is exposed to Cu 2 § as prooxidant in the range of 1-10 ~tM. A brief review on major findings obtained with this assay will be given. A consistent observation is that vitamin E supplements or oleic acid-rich diets increase OR. Oxidation indices measured by the CD assay and effects of antioxidants very significantly depend on the Cu 2 § concentration used for LDL oxidation. For medium and high Cu 2 § concentrations, the relationship between lag time and propagation rate can be described by a simple hyperbolic saturation function, which has the same mathematical form as the Michaelis-Menten equation. At medium and high Cu 2 § concentrations (0.5 to 5 ~tM), vitamin E increases lag time in a dose-dependent manner. The increase is higher for 0.5 ~tM Cu 2 § as compared to 5 I-tM. At low Cu 2 § concentrations (0.5 ~tM or less), the mechanism of LDL oxidation changes. Significant oxidation occurs in a preoxidation phase, which commences shortly after addition of Cu 2+. Preoxidation is not inhibited by vitamin E. It is concluded that much additional work is needed to validate the importance of oxidation indices derived from CD and similar assays.
The Journal of Lipid Research, 2012
Although statin therapy is a cornerstone of current low density lipoprotein (LDL)-lowering strate... more Although statin therapy is a cornerstone of current low density lipoprotein (LDL)-lowering strategies, there is a need for additional therapies to incrementally lower plasma LDL cholesterol. In this study, we investigated the effect of several methylenedioxyphenol derivatives in regulating LDL cholesterol through induction of LDL receptor (LDLR). INV-403, a modifi ed methylenedioxyphenol derivative, increased LDLR mRNA and protein expression in HepG2 cells in a dose-and time-dependent fashion. These effects were apparent even under conditions of HMG-CoA reductase inhibition. Electrophoresis migration shift assays demonstrated that INV-403 activates SREBP2 but not SREBP1c, with immunoblot analysis showing an increased expression of the mature form of SREBP2. Knockdown of SREBP2 reduced the effect of INV-403 on LDLR expression. The activation of SREBP2 by INV-403 is partly mediated by Akt/GSK3  pathways through inhibition of phosphorylation-dependent degradation by ubiquitin-proteosome pathway. Treatment of C57Bl/6j mice with INV-403 for two weeks increased hepatic SREBP2 levels (mature form) and upregulated LDLR with concomitant lowering of plasma LDL levels. Transient expression of a LDLR promoterreporter construct, a SRE-mutant LDLR promoter construct, and a SRE-only construct in HepG2 cells revealed an effect predominantly through a SRE-dependent mechanism. INV-403 lowered plasma LDL cholesterol levels through LDLR upregulation. These results indicate a role for small molecule approaches other than statins for lowering LDL cholesterol. -Ying, Z., R. Desikan, X. Xu, A. Maiseyeu, C. Liu, Q. Sun, O. Ziouzenkova, S. Parthasarathy, and S. Rajagopalan. Modifi ed methylenedioxyphenol analogs lower LDL cholesterol through induction of LDL receptor expression. J. Lipid Res. 2012. 53: 879-887.
Journal of Internal Medicine, 2007
PPARs and their metabolic modulation: new mechanisms for transcriptional regulation? (Review) J I... more PPARs and their metabolic modulation: new mechanisms for transcriptional regulation? (Review) J Intern Med 2007; 262: 184-198.
Journal of Biological Chemistry, 1999
Human blood contains a form of minimally modified low density lipoprotein (LDL), termed LDL-, who... more Human blood contains a form of minimally modified low density lipoprotein (LDL), termed LDL-, whose origin remains unknown. Exploring the mechanism of formation, we found that LDL- can be produced in plasma in the absence of oxygen following LDL incubation with oxidized hemoglobin species. A high degree of apolipoprotein B100 modification results from covalent association of hemoglobin with LDL involving dityrosine formation but not due to the malonaldehyde epitope formation. This was evidenced by the cross-reactivity of oxidized LDL with antibodies against hemoglobin that was accompanied by a 60-fold increase in dityrosine levels. In this study we found significantly higher LDL- levels in the blood of hemodialysis patients, perhaps contributing to their greatly increased risk of atherosclerosis. The mechanism of LDL- formation was studied during ex vivo blood circulation using a model system resembling clinical hemodialysis in terms of the induction of inflammatory responses. This circulation increased free hemoglobin and LDL- levels compared with non-circulated blood without appreciable lipid peroxidation. Pronounced increases in LDL- were found also during circulation of plasma supplemented with nanomolar hemoglobin levels. The increase in dityrosine content and presence of heme in LDL after blood circulation suggest that LDL is modified, in part, by hemoglobin-LDL conjugates containing heme. Thus, hemoglobin-mediated reactions leading to LDL oxidation in plasma can account for high LDL- levels in hemodialysis patients.
Journal of Biological Chemistry, 2003
Low density lipoprotein (LDL) exists in various forms that possess unique characteristics, includ... more Low density lipoprotein (LDL) exists in various forms that possess unique characteristics, including particle content and metabolism. One circulating subfraction, electronegative LDL (LDL(-)), which is increased in familial hypercholesterolemia and diabetes, is implicated in accelerated atherosclerosis. Cellular responses to LDL(-) remain poorly described. Here we demonstrate that LDL(-) increases tumor necrosis factor alpha (TNFalpha)-induced inflammatory responses through NF kappa B and AP-1 activation with corresponding increases in vascular cell adhesion molecule-1 (VCAM1) expression. LDL receptor overexpression increased these effects. In contrast, exposing LDL(-) to the key lipolytic enzyme lipoprotein lipase (LPL) reversed these responses, inhibiting VCAM1 below levels seen with TNFalpha alone. LPL is known to act on lipoproteins to generate endogenous peroxisomal proliferator-activated receptor alpha (PPAR alpha) ligand, thus limiting inflammation. These responses varied according to the lipoprotein substrate triglyceride content (very low density lipoprotein &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt; LDL &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt; high density lipoprotein). The PPAR alpha activation seen with LDL, however, was disproportionately high. We show here that MUT LDL activates PPAR alpha to an extent proportional to its LDL(-) content. As compared with LDL(-) alone, LPL-treated LDL(-) increased PPAR alpha activation 20-fold in either cell-based transfection or radioligand displacement assays. LPL-treated LDL(-) suppressed NF kappa B and AP-1 activation, increasing expression of the PPAR alpha target gene I kappa B alpha, although only in the genetic presence of PPAR alpha and with intact LPL hydrolysis. Mass spectrometry reveals that LPL-treatment of either LDL or LDL(-) releases hydroxy-octadecadienoic acids (HODEs), potent PPAR alpha activators. These findings suggest LPL-mediated PPAR alpha activation as an alternative catabolic pathway that may limit inflammatory responses to LDL(-).
Free Radical Biology and Medicine, 1995
Antioxidants such as vitamin E protect unsaturated fatty acids of LDL against oxidation. In the e... more Antioxidants such as vitamin E protect unsaturated fatty acids of LDL against oxidation. In the ex vivo model used, LDL was exposed to Cu'+ ions, a potent prooxidant capable of initiating the oxidation of LDL. The lag time, indicating the delay of conjugated diene formation in LDL due to antioxidant protection, was measured in 54 cystic fibrosis (CF) patients with plasma a-tocopherol levels below (Group A, n = 30) or above (Group B, n = 24) 15.9 pmol/L (mean -2 SD of Swiss population).
Free Radical Biology and Medicine, 2002
The high cardiovascular mortality in patients receiving hemodialysis (HD) has been attributed, in... more The high cardiovascular mortality in patients receiving hemodialysis (HD) has been attributed, in part, to oxidative stress. Here we examined the effectiveness of antioxidants introduced by means of a novel hemolipodialysis (HLD) procedure in terms of reducing oxidative stress during ex vivo blood circulation. Oxidative stress was studied in a model HD system resembling the extracorporeal circulation of blood during clinical HD. Blood circulation produced an increase of up to 280% in free hemoglobin levels and an increase of 320% in electronegative LDL (LDL Ϫ ) subfraction. A significant correlation between LDL Ϫ and free hemoglobin levels confirmed previous findings that LDL Ϫ formation during ex vivo circulation of blood can be mediated by the oxidative activity of free hemoglobin. These effects were significantly attenuated during HLD using a dialysis circuit containing vitamin E with or without vitamin C. By contrast, HLD with vitamin C alone had a marked pro-oxidant effect. TBARS, lipid hydroperoxides, vitamin E and -carotene content in LDL were not significantly altered by the HD procedure. These findings demonstrate the occurrence of oxidative stress in human plasma where lipoproteins are a target and indicate antioxidant-HLD treatment as a specific new approach to decreasing the adverse oxidative stress frequently associated with cardiovascular complications in high-risk populations of uremic patients.
European Journal of Clinical Nutrition, 1997
Objective: To study the in¯uence of supplementation with antioxidants on factors, which might inc... more Objective: To study the in¯uence of supplementation with antioxidants on factors, which might increase the risk of coronary heart disease (CHD) in Iranians. Design: Twenty-one male volunteers enter the prospective, single-blind, randomized study. Setting: The supplementation was conducted at the Cardiovascular Center, University of Tehran, the biochemical analysis were carried out in the University of Graz. Subjects: Twenty-one male medical students were recruited by advertisement. Five subjects were dropped out due to lack of the compliance. Methods: One group of Iranians received 30 mg/d b-carotene and placebo for a-tocopherol; the other received b-carotene plus 400 IU a-tocopherol for ten weeks. Concentrations of antioxidants in plasma and low density lipoproteins (LDL), plasma lipid pro®le, autoantibody against oxidized LDL (oLAb) and malondialdehyde (MDA) concentrations in plasma were measured. Oxidative resistance of LDL was estimated using conjugated diene assay. Results: Iranians had a signi®cantly lower plasma levels of total cholesterol (P`0.002), LDL-cholesterol (P`0.01) and high density lipoprotein-cholesterol (P`0.002), compared to healthy Austrian subjects (n 13). Although the baseline concentrations of a-tocopherol and b-carotene were comparable with Austrians, lycopene, canthaxanthin and lutein were signi®cantly higher in Iranians (P`0.03±0.001). In vitro oxidative resistance of LDL, measured as lag-time, was slightly higher (P`0.01) in Iranians comparing with Austrians. Plasma MDA and oLAb concentrations were signi®cantly higher in Iranians (P`0.001). Both dietary supplementations reduced plasma MDA concentrations (P`0.001±0.001). A key ®nding was that a supplement combined with atocopherol caused also a signi®cant increase of oLAb concentration (P b 0.01) as well as the signi®cant increase of lag-time (P b 0.005).
Diabetes, 2013
Mechanisms for sex- and depot-specific fat formation are unclear. We investigated the role of ret... more Mechanisms for sex- and depot-specific fat formation are unclear. We investigated the role of retinoic acid (RA) production by aldehyde dehydrogenase 1 (Aldh1a1, -a2, and -a3), the major RA-producing enzymes, on sex-specific fat depot formation. Female Aldh1a1(-/-) mice, but not males, were resistant to high-fat (HF) diet-induced visceral adipose formation, whereas subcutaneous fat was reduced similarly in both groups. Sexual dimorphism in visceral fat (VF) was attributable to elevated adipose triglyceride lipase (Atgl) protein expression localized in clusters of multilocular uncoupling protein 1 (Ucp1)-positive cells in female Aldh1a1(-/-) mice compared with males. Estrogen decreased Aldh1a3 expression, limiting conversion of retinaldehyde (Rald) to RA. Rald effectively induced Atgl levels via nongenomic mechanisms, demonstrating indirect regulation by estrogen. Experiments in transgenic mice expressing an RA receptor response element (RARE-lacZ) revealed HF diet-induced RARE activation in VF of females but not males. In humans, stromal cells isolated from VF of obese subjects also expressed higher levels of Aldh1 enzymes compared with lean subjects. Our data suggest that an HF diet mediates VF formation through a sex-specific autocrine Aldh1 switch, in which Rald-mediated lipolysis in Ucp1-positive visceral adipocytes is replaced by RA-mediated lipid accumulation. Our data suggest that Aldh1 is a potential target for sex-specific antiobesity therapy.
Blood Purification, 1999
A large number of clinical studies support the hypothesis that the risk for atherosclerosis is as... more A large number of clinical studies support the hypothesis that the risk for atherosclerosis is associated with the proportion of different LDL subfractions in blood. Electronegatively modified forms of LDL (LDL(-)) isolated using different chromatographic techniques are characterised by significant differences in the protein and lipid content as compared to the native LDL subfraction. LDL(-) composition appears to influence its atherogenic properties as well as its high susceptibility to oxidation and impaired metabolism. Increased LDL(-) levels are found in subjects with coronary artery disease, particularly in diabetics and patients undergoing haemodialysis (HD). Whether elevated LDL(-) levels are due to the LDL oxidation in blood remains disputed despite the oxidative character of LDL(-) modification. Plausible means for LDL(-) formation in blood include glycation and protein-radical interactions with ApoB 100. The latter can prevail during HD as observed in in vitro studies using a model HD system. The rapid and progressive formation of LDL(-) during standard HD can be significantly reduced employing haemolipodialysis (HLD), which provides local delivery of specific antioxidants (vitamin E and C) to blood at concentrations above normal physiologic levels. This procedure appears to be more effective than oral supplementation with antioxidants and may be a promising approach to reducing the rapid progression of atherosclerosis in HD patients.
Nature Medicine, 2007
The metabolism of vitamin A and the diverse effects of its metabolites are tightly controlled by ... more The metabolism of vitamin A and the diverse effects of its metabolites are tightly controlled by distinct retinoid-generating enzymes, retinoid-binding proteins and retinoid-activated nuclear receptors. Retinoic acid regulates differentiation and metabolism by activating the retinoic acid receptor and retinoid X receptor (RXR), indirectly influencing RXR heterodimeric partners. Retinoic acid is formed solely from retinaldehyde (Rald), which in turn is derived from vitamin A. Rald currently has no defined biologic role outside the eye. Here we show that Rald is present in rodent fat, binds retinol-binding proteins (CRBP1, RBP4), inhibits adipogenesis and suppresses peroxisome proliferator-activated receptor-c and RXR responses. In vivo, mice lacking the Rald-catabolizing enzyme retinaldehyde dehydrogenase 1 (Raldh1) resisted diet-induced obesity and insulin resistance and showed increased energy dissipation. In ob/ob mice, administrating Rald or a Raldh inhibitor reduced fat and increased insulin sensitivity. These results identify Rald as a distinct transcriptional regulator of the metabolic responses to a high-fat diet.
Free Radical Biology and Medicine, 1998
Oxidation of LDL (0.1 microM) in PBS with copper concentrations ranging from 0.03 to 10 microM, e... more Oxidation of LDL (0.1 microM) in PBS with copper concentrations ranging from 0.03 to 10 microM, equal to 0.3-100 Cu2+/LDL, was investigated by monitoring the formation of conjugated dienes at 234 nm. With all 8 LDL samples examined, the kinetics changed strongly at submicromolar Cu2+ concentrations. Based on time-course of the formation of conjugated dienes, cholesteryl linoleate hydroxides and hydroperoxides as well as the antioxidant consumption, two oxidation types were distinguished. Type A oxidations, observed at relatively high Cu2+ concentrations of 10-100 Cu2+/ LDL, represented the conventional kinetics of LDL oxidation with an inhibition period (= lag-time) followed by a propagation phase. In contrast, type C oxidations proceeded after a negligibly short lag time followed by a distinct propagation phase. The rate of this propagation increased rapidly to 0.5 mol diene/mol LDL and then slowed down in the presence of alpha-,gamma-tocopherols and carotenoids, which were consumed faster than tocopherols. The increase in diene absorption was due to the formation of both hydroxides and hydroperoxides suggesting a high initial decomposition of hydroperoxides. At submicromolar concentrations of about 0.1 to 0.5 microM, type C and type A oxidation can be combined resulting in 4 consecutive oxidation phases, i.e. 1st inhibition and 1st propagation (belonging to type C), followed by 2nd inhibition and 2nd propagation (belonging to type A). Increasing copper concentrations lowered the 1st propagation and shortened the 2nd inhibition periods until they melted into one apparent kinetic phase. Decreasing [Cu2+] increased the 1st propagation and 2nd inhibition but lowered the 2nd propagation phase until it completely disappeared. A threshold copper concentration, denoted as Cu(lim), can be calculated as a kinetic constant based on the Cu2+-dependence for the rate of 2nd propagation. Below Cu(lim), LDL oxidation proceeds only via type C kinetics. The Cu2+-dependence of the oxidation kinetics suggests that LDL contains two different Cu2+ biding sites. Cu2+ at the low-affinity binding sites, with half-saturation at 5-50 Cu2+/LDL, initiates and accelerates the 2nd propagation by decomposing lipid hydroperoxides. Cu2+ bound to the high-affinity binding sites, with half-saturation at 0.3-2.0 Cu2+/LDL, is responsible for the 1st propagation. Arguments in favor and against this propagation being due to tocopherol mediated peroxidation (TMP) are discussed. If the lag-time concept is extended to the conjugated diene curves seen for combined oxidation profiles, then a true inhibition phase does not apply to this time interval, but instead represents the time elapsed before the onset of the 2nd propagation phase.
Free Radical Biology and Medicine, 2002
The high cardiovascular mortality in patients receiving hemodialysis (HD) has been attributed, in... more The high cardiovascular mortality in patients receiving hemodialysis (HD) has been attributed, in part, to oxidative stress. Here we examined the effectiveness of antioxidants introduced by means of a novel hemolipodialysis (HLD) procedure in terms of reducing oxidative stress during ex vivo blood circulation. Oxidative stress was studied in a model HD system resembling the extracorporeal circulation of blood during clinical HD. Blood circulation produced an increase of up to 280% in free hemoglobin levels and an increase of 320% in electronegative LDL (LDL Ϫ ) subfraction. A significant correlation between LDL Ϫ and free hemoglobin levels confirmed previous findings that LDL Ϫ formation during ex vivo circulation of blood can be mediated by the oxidative activity of free hemoglobin. These effects were significantly attenuated during HLD using a dialysis circuit containing vitamin E with or without vitamin C. By contrast, HLD with vitamin C alone had a marked pro-oxidant effect. TBARS, lipid hydroperoxides, vitamin E and -carotene content in LDL were not significantly altered by the HD procedure. These findings demonstrate the occurrence of oxidative stress in human plasma where lipoproteins are a target and indicate antioxidant-HLD treatment as a specific new approach to decreasing the adverse oxidative stress frequently associated with cardiovascular complications in high-risk populations of uremic patients.
International journal of clinical pharmacology and therapeutics, 1999
The possible oxidative complications induced by free hemoglobin (Hb) released during the blood st... more The possible oxidative complications induced by free hemoglobin (Hb) released during the blood storage are discussed together with therapeutic strategies using vitamin E and specific inhibitor haptoglobin. Prooxidative properties of Hb in blood have been examined using LDL as a marker for oxidative stress, which contribute to toxicity observed in a number of pathologies aggravated by hemolysis or hemorrhagic lesions as well as after the transfusion of stored blood. Experiments were performed using fresh blood or stored blood that was obtained from a blood bank on the day corresponding to the identified expiration date. Oxidation of LDL was determined by means of the formation of mildly oxidized LDL (LDL-) using anion exchange chromatography. Concentrations of Hb were determined spectrophotometrically. Hb-mediated oxidative processes in cellular membranes have been well documented over the past decade. We showed that catalytic activity of Hb released during blood storage was sufficie...
Journal of lipid research, 1996
In 59 healthy human subjects (37 male and 22 female) the concentrations of the lipid-soluble anti... more In 59 healthy human subjects (37 male and 22 female) the concentrations of the lipid-soluble antioxidants alpha- and gamma-tocopherol, alpha- and beta-carotene, lycopene, cryptoxanthin, canthaxanthin, and lutein + zeaxanthin were determined in plasma (mumol/L) and in isolated low density lipoproteins (LDL) (mumol/mmol cholesterol). Plasma alpha-tocopherol concentrations were significantly correlated with plasma total cholesterol concentrations (r2 = 0.51, P < 0.0001) yet not with the LDL alpha-tocopherol content (r2 = 0.05, ns). Plasma gamma-tocopherol concentrations were weakly correlated with plasma total cholesterol (r2 = 0.12, P < 0.003) and both absolute and cholesterol standardized plasma gamma-tocopherol concentrations correlated strongly with the LDL gamma-tocopherol content (r2 = 0.58 and r2 = 0.72, respectively). In contrast, carotenoid concentrations did not correlate with cholesterol concentrations, but their LDL content correlated significantly with the respective...
Journal of Nutrition, 2013
Zinc (Zn) deficiency and obesity are global public health problems. Zn deficiency is associated w... more Zinc (Zn) deficiency and obesity are global public health problems. Zn deficiency is associated with obesity and comorbid conditions that include insulin resistance and type 2 diabetes. However, the function of Zn in obesity remains unclear.
Proceedings of the National Academy of Sciences, 2003
Increased levels of triglyceride-rich lipoproteins provoke lipid accumulation in the artery wall,... more Increased levels of triglyceride-rich lipoproteins provoke lipid accumulation in the artery wall, triggering early inflammatory responses central to atherosclerosis like endothelial adhesion molecule expression. The endogenous mechanisms limiting such reactions remain poorly defined. Lipoprotein lipase (LPL) plays a central role in lipid metabolism by hydrolyzing triglyceride rich lipoproteins and releasing fatty acids. We found that LPL treatment reversed tumor necrosis factor ␣ and very low-density lipoprotein (VLDL)-stimulated endothelial vascular cell adhesion molecule 1 (VCAM1) induction and VCAM1 promoter responses, thus recapitulating effects reported with synthetic peroxisome proliferator-activated receptor (PPAR) agonists. In fact, these LPL effects on VCAM1 were absent in endothelial cells isolated from PPAR␣-deficient mice. This finding suggests a novel antiinflammatory role for LPL. Further studies reveal specificity for PPAR activation through lipolysis in regards to lipoprotein substrate (VLDL Ͼ Ͼ Ͼ Ͼ LDL > HDL), PPAR isoform (PPAR␣ Ͼ Ͼ Ͼ Ͼ PPAR␦ > PPAR␥), and among fatty acid-releasing lipases. These PPAR responses required intact LPL catalytic activity. In vivo, transgenic mice overexpressing LPL had increased peroxisome proliferation, but not in the genetic absence of PPAR␣. Although human plasma possesses minimal PPAR␣ activation despite containing abundant free fatty acids, marked PPAR␣ activation is seen with human plasma after LPL is added in vitro or systemically released in vivo. These data suggest a previously uncharacterized pathway in which the key lipolytic enzyme LPL can act on circulating lipoproteins to generate PPAR␣ ligands, providing a potentially important link between lipoprotein metabolism and distal PPAR␣ transcriptional effects.
Lipids, 1996
Oxidation resistance (OR) of low density lipoproteins (LDL) is frequently determined by the conju... more Oxidation resistance (OR) of low density lipoproteins (LDL) is frequently determined by the conjugated diene (CD) assay, in which isolated LDL is exposed to Cu 2 § as prooxidant in the range of 1-10 ~tM. A brief review on major findings obtained with this assay will be given. A consistent observation is that vitamin E supplements or oleic acid-rich diets increase OR. Oxidation indices measured by the CD assay and effects of antioxidants very significantly depend on the Cu 2 § concentration used for LDL oxidation. For medium and high Cu 2 § concentrations, the relationship between lag time and propagation rate can be described by a simple hyperbolic saturation function, which has the same mathematical form as the Michaelis-Menten equation. At medium and high Cu 2 § concentrations (0.5 to 5 ~tM), vitamin E increases lag time in a dose-dependent manner. The increase is higher for 0.5 ~tM Cu 2 § as compared to 5 I-tM. At low Cu 2 § concentrations (0.5 ~tM or less), the mechanism of LDL oxidation changes. Significant oxidation occurs in a preoxidation phase, which commences shortly after addition of Cu 2+. Preoxidation is not inhibited by vitamin E. It is concluded that much additional work is needed to validate the importance of oxidation indices derived from CD and similar assays.
The Journal of Lipid Research, 2012
Although statin therapy is a cornerstone of current low density lipoprotein (LDL)-lowering strate... more Although statin therapy is a cornerstone of current low density lipoprotein (LDL)-lowering strategies, there is a need for additional therapies to incrementally lower plasma LDL cholesterol. In this study, we investigated the effect of several methylenedioxyphenol derivatives in regulating LDL cholesterol through induction of LDL receptor (LDLR). INV-403, a modifi ed methylenedioxyphenol derivative, increased LDLR mRNA and protein expression in HepG2 cells in a dose-and time-dependent fashion. These effects were apparent even under conditions of HMG-CoA reductase inhibition. Electrophoresis migration shift assays demonstrated that INV-403 activates SREBP2 but not SREBP1c, with immunoblot analysis showing an increased expression of the mature form of SREBP2. Knockdown of SREBP2 reduced the effect of INV-403 on LDLR expression. The activation of SREBP2 by INV-403 is partly mediated by Akt/GSK3  pathways through inhibition of phosphorylation-dependent degradation by ubiquitin-proteosome pathway. Treatment of C57Bl/6j mice with INV-403 for two weeks increased hepatic SREBP2 levels (mature form) and upregulated LDLR with concomitant lowering of plasma LDL levels. Transient expression of a LDLR promoterreporter construct, a SRE-mutant LDLR promoter construct, and a SRE-only construct in HepG2 cells revealed an effect predominantly through a SRE-dependent mechanism. INV-403 lowered plasma LDL cholesterol levels through LDLR upregulation. These results indicate a role for small molecule approaches other than statins for lowering LDL cholesterol. -Ying, Z., R. Desikan, X. Xu, A. Maiseyeu, C. Liu, Q. Sun, O. Ziouzenkova, S. Parthasarathy, and S. Rajagopalan. Modifi ed methylenedioxyphenol analogs lower LDL cholesterol through induction of LDL receptor expression. J. Lipid Res. 2012. 53: 879-887.
Journal of Internal Medicine, 2007
PPARs and their metabolic modulation: new mechanisms for transcriptional regulation? (Review) J I... more PPARs and their metabolic modulation: new mechanisms for transcriptional regulation? (Review) J Intern Med 2007; 262: 184-198.
Journal of Biological Chemistry, 1999
Human blood contains a form of minimally modified low density lipoprotein (LDL), termed LDL-, who... more Human blood contains a form of minimally modified low density lipoprotein (LDL), termed LDL-, whose origin remains unknown. Exploring the mechanism of formation, we found that LDL- can be produced in plasma in the absence of oxygen following LDL incubation with oxidized hemoglobin species. A high degree of apolipoprotein B100 modification results from covalent association of hemoglobin with LDL involving dityrosine formation but not due to the malonaldehyde epitope formation. This was evidenced by the cross-reactivity of oxidized LDL with antibodies against hemoglobin that was accompanied by a 60-fold increase in dityrosine levels. In this study we found significantly higher LDL- levels in the blood of hemodialysis patients, perhaps contributing to their greatly increased risk of atherosclerosis. The mechanism of LDL- formation was studied during ex vivo blood circulation using a model system resembling clinical hemodialysis in terms of the induction of inflammatory responses. This circulation increased free hemoglobin and LDL- levels compared with non-circulated blood without appreciable lipid peroxidation. Pronounced increases in LDL- were found also during circulation of plasma supplemented with nanomolar hemoglobin levels. The increase in dityrosine content and presence of heme in LDL after blood circulation suggest that LDL is modified, in part, by hemoglobin-LDL conjugates containing heme. Thus, hemoglobin-mediated reactions leading to LDL oxidation in plasma can account for high LDL- levels in hemodialysis patients.
Journal of Biological Chemistry, 2003
Low density lipoprotein (LDL) exists in various forms that possess unique characteristics, includ... more Low density lipoprotein (LDL) exists in various forms that possess unique characteristics, including particle content and metabolism. One circulating subfraction, electronegative LDL (LDL(-)), which is increased in familial hypercholesterolemia and diabetes, is implicated in accelerated atherosclerosis. Cellular responses to LDL(-) remain poorly described. Here we demonstrate that LDL(-) increases tumor necrosis factor alpha (TNFalpha)-induced inflammatory responses through NF kappa B and AP-1 activation with corresponding increases in vascular cell adhesion molecule-1 (VCAM1) expression. LDL receptor overexpression increased these effects. In contrast, exposing LDL(-) to the key lipolytic enzyme lipoprotein lipase (LPL) reversed these responses, inhibiting VCAM1 below levels seen with TNFalpha alone. LPL is known to act on lipoproteins to generate endogenous peroxisomal proliferator-activated receptor alpha (PPAR alpha) ligand, thus limiting inflammation. These responses varied according to the lipoprotein substrate triglyceride content (very low density lipoprotein &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt; LDL &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt; high density lipoprotein). The PPAR alpha activation seen with LDL, however, was disproportionately high. We show here that MUT LDL activates PPAR alpha to an extent proportional to its LDL(-) content. As compared with LDL(-) alone, LPL-treated LDL(-) increased PPAR alpha activation 20-fold in either cell-based transfection or radioligand displacement assays. LPL-treated LDL(-) suppressed NF kappa B and AP-1 activation, increasing expression of the PPAR alpha target gene I kappa B alpha, although only in the genetic presence of PPAR alpha and with intact LPL hydrolysis. Mass spectrometry reveals that LPL-treatment of either LDL or LDL(-) releases hydroxy-octadecadienoic acids (HODEs), potent PPAR alpha activators. These findings suggest LPL-mediated PPAR alpha activation as an alternative catabolic pathway that may limit inflammatory responses to LDL(-).
Free Radical Biology and Medicine, 1995
Antioxidants such as vitamin E protect unsaturated fatty acids of LDL against oxidation. In the e... more Antioxidants such as vitamin E protect unsaturated fatty acids of LDL against oxidation. In the ex vivo model used, LDL was exposed to Cu'+ ions, a potent prooxidant capable of initiating the oxidation of LDL. The lag time, indicating the delay of conjugated diene formation in LDL due to antioxidant protection, was measured in 54 cystic fibrosis (CF) patients with plasma a-tocopherol levels below (Group A, n = 30) or above (Group B, n = 24) 15.9 pmol/L (mean -2 SD of Swiss population).
Free Radical Biology and Medicine, 2002
The high cardiovascular mortality in patients receiving hemodialysis (HD) has been attributed, in... more The high cardiovascular mortality in patients receiving hemodialysis (HD) has been attributed, in part, to oxidative stress. Here we examined the effectiveness of antioxidants introduced by means of a novel hemolipodialysis (HLD) procedure in terms of reducing oxidative stress during ex vivo blood circulation. Oxidative stress was studied in a model HD system resembling the extracorporeal circulation of blood during clinical HD. Blood circulation produced an increase of up to 280% in free hemoglobin levels and an increase of 320% in electronegative LDL (LDL Ϫ ) subfraction. A significant correlation between LDL Ϫ and free hemoglobin levels confirmed previous findings that LDL Ϫ formation during ex vivo circulation of blood can be mediated by the oxidative activity of free hemoglobin. These effects were significantly attenuated during HLD using a dialysis circuit containing vitamin E with or without vitamin C. By contrast, HLD with vitamin C alone had a marked pro-oxidant effect. TBARS, lipid hydroperoxides, vitamin E and -carotene content in LDL were not significantly altered by the HD procedure. These findings demonstrate the occurrence of oxidative stress in human plasma where lipoproteins are a target and indicate antioxidant-HLD treatment as a specific new approach to decreasing the adverse oxidative stress frequently associated with cardiovascular complications in high-risk populations of uremic patients.
European Journal of Clinical Nutrition, 1997
Objective: To study the in¯uence of supplementation with antioxidants on factors, which might inc... more Objective: To study the in¯uence of supplementation with antioxidants on factors, which might increase the risk of coronary heart disease (CHD) in Iranians. Design: Twenty-one male volunteers enter the prospective, single-blind, randomized study. Setting: The supplementation was conducted at the Cardiovascular Center, University of Tehran, the biochemical analysis were carried out in the University of Graz. Subjects: Twenty-one male medical students were recruited by advertisement. Five subjects were dropped out due to lack of the compliance. Methods: One group of Iranians received 30 mg/d b-carotene and placebo for a-tocopherol; the other received b-carotene plus 400 IU a-tocopherol for ten weeks. Concentrations of antioxidants in plasma and low density lipoproteins (LDL), plasma lipid pro®le, autoantibody against oxidized LDL (oLAb) and malondialdehyde (MDA) concentrations in plasma were measured. Oxidative resistance of LDL was estimated using conjugated diene assay. Results: Iranians had a signi®cantly lower plasma levels of total cholesterol (P`0.002), LDL-cholesterol (P`0.01) and high density lipoprotein-cholesterol (P`0.002), compared to healthy Austrian subjects (n 13). Although the baseline concentrations of a-tocopherol and b-carotene were comparable with Austrians, lycopene, canthaxanthin and lutein were signi®cantly higher in Iranians (P`0.03±0.001). In vitro oxidative resistance of LDL, measured as lag-time, was slightly higher (P`0.01) in Iranians comparing with Austrians. Plasma MDA and oLAb concentrations were signi®cantly higher in Iranians (P`0.001). Both dietary supplementations reduced plasma MDA concentrations (P`0.001±0.001). A key ®nding was that a supplement combined with atocopherol caused also a signi®cant increase of oLAb concentration (P b 0.01) as well as the signi®cant increase of lag-time (P b 0.005).
Diabetes, 2013
Mechanisms for sex- and depot-specific fat formation are unclear. We investigated the role of ret... more Mechanisms for sex- and depot-specific fat formation are unclear. We investigated the role of retinoic acid (RA) production by aldehyde dehydrogenase 1 (Aldh1a1, -a2, and -a3), the major RA-producing enzymes, on sex-specific fat depot formation. Female Aldh1a1(-/-) mice, but not males, were resistant to high-fat (HF) diet-induced visceral adipose formation, whereas subcutaneous fat was reduced similarly in both groups. Sexual dimorphism in visceral fat (VF) was attributable to elevated adipose triglyceride lipase (Atgl) protein expression localized in clusters of multilocular uncoupling protein 1 (Ucp1)-positive cells in female Aldh1a1(-/-) mice compared with males. Estrogen decreased Aldh1a3 expression, limiting conversion of retinaldehyde (Rald) to RA. Rald effectively induced Atgl levels via nongenomic mechanisms, demonstrating indirect regulation by estrogen. Experiments in transgenic mice expressing an RA receptor response element (RARE-lacZ) revealed HF diet-induced RARE activation in VF of females but not males. In humans, stromal cells isolated from VF of obese subjects also expressed higher levels of Aldh1 enzymes compared with lean subjects. Our data suggest that an HF diet mediates VF formation through a sex-specific autocrine Aldh1 switch, in which Rald-mediated lipolysis in Ucp1-positive visceral adipocytes is replaced by RA-mediated lipid accumulation. Our data suggest that Aldh1 is a potential target for sex-specific antiobesity therapy.
Blood Purification, 1999
A large number of clinical studies support the hypothesis that the risk for atherosclerosis is as... more A large number of clinical studies support the hypothesis that the risk for atherosclerosis is associated with the proportion of different LDL subfractions in blood. Electronegatively modified forms of LDL (LDL(-)) isolated using different chromatographic techniques are characterised by significant differences in the protein and lipid content as compared to the native LDL subfraction. LDL(-) composition appears to influence its atherogenic properties as well as its high susceptibility to oxidation and impaired metabolism. Increased LDL(-) levels are found in subjects with coronary artery disease, particularly in diabetics and patients undergoing haemodialysis (HD). Whether elevated LDL(-) levels are due to the LDL oxidation in blood remains disputed despite the oxidative character of LDL(-) modification. Plausible means for LDL(-) formation in blood include glycation and protein-radical interactions with ApoB 100. The latter can prevail during HD as observed in in vitro studies using a model HD system. The rapid and progressive formation of LDL(-) during standard HD can be significantly reduced employing haemolipodialysis (HLD), which provides local delivery of specific antioxidants (vitamin E and C) to blood at concentrations above normal physiologic levels. This procedure appears to be more effective than oral supplementation with antioxidants and may be a promising approach to reducing the rapid progression of atherosclerosis in HD patients.