Interaction of rat liver microsomes containing saturated or unsaturated fatty acids with fatty acid binding protein: Peroxidation effect

In the studies described here rat liver microsomes containing labeled palmitic, stearic, oleic or linoleic acids were incubated with fatty acid binding protein (FABP) and the rate of removal of¹⁴C-labeled fatty acids from the membrane by the soluble protein was measured using a model system. More unsaturated than saturated fatty acids were removed from native liver microsomes incubated with similar amounts of FABP. Thein vitro peroxidation of microsomal membranes mediated by ascorbate-Fe⁺⁺, modified its fatty acid composition with a considerable decrease of the peroxidizability index. These changes in the microsomes facilitated the removal of oleic and linoeic acids by FABP, but the removal of palmitic and stearic acids was not modified. This effect is proposed to result from a perturbation of membrane structure following peroxidation with release of free fatty acids from susceptible domains.Abbreviations BSA bovine serum albumin - FABP fatty acid binding protein     

Modulation of the reactivity of the thiol of human serum albumin and its sulfenic derivative by fatty acids

The single cysteine residue of human serum albumin (HSA-SH) is the most abundant plasma thiol. HSA transports fatty acids (FA), a cargo that increases under conditions of diabetes, exercise or adrenergic stimulation. The stearic acid-HSA (5/1) complex reacted sixfold faster than FA-free HSA at pH 7.4 with the disulfide 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB) and twofold faster with hydrogen peroxide and peroxynitrite. The apparent pK(a) of HSA-SH decreased from 7.9±0.1 to 7.4±0.1. Exposure to H(2)O(2) (2mM, 5min, 37°C) yielded 0.29±0.04mol of sulfenic acid (HSA-SOH) per mole of FA-bound HSA. The reactivity of HSA-SOH with low molecular weight thiols increased ～threefold in the presence of FA. The enhanced reactivity of the albumin thiol at neutral pH upon FA binding can be rationalized by considering that the corresponding conformational changes that increase thiol exposure both increase the availability of the thiolate due to a lower apparent pK(a) and also loosen steric constraints for reactions. Since situations that increase circulating FA are associated with oxidative stress, this increased reactivity of HSA-SH could assist in oxidant removal.     

Influence of albumin and non-esterified fatty acids on serum prostacyclin binding in pregnancy

We investigated the etiology of the previously documented decrease in serum prostocyclin binding during pregnancy. Addition of albumin to the serum of pregnant women failed to raise binding to non-pregnant levels. Pregnancy serum bound significantly more prostacyclin following the removal of non-esterified fatty acids and the addition of fatty acid free albumin resulted in a rise in binding to non-pregnant levels. We conclude that serum protein prostacyclin binding is affected by both albumin concentration and non-esterified fatty acids.     

Interaction of prostaglandins and fatty acids with native and acetaldehyde-alkylated proteins

Using intrinsic and probe fluorescence, microcalorimetry and isotopic methods, the interactions of prostaglandins (PG) E2 and F2 alpha and some fatty acids with native and alkylated proteins (human serum albumin (HSA) and rat liver plasma membrane PG receptors), were studied. The fatty acid and PG interactions with human serum albumin (HSA) resulted in effective quenching of fluorescence of the probe, 1.8-anilinonaphthalene sulfonate (ANS), bound to the protein. Fatty acids competed with ANS for the binding sites; the efficiency of this process increased with an increase in the number of double bonds in the fatty acid molecule. PG induced a weaker fluorescence quenching of HSA-bound ANS and stabilized the protein molecule in a lesser degree compared to fatty acids. The sites of PG E2 and F2 alpha binding did not overlap with the sites of fatty acid binding on the HSA molecule. Nonenzymatic alkylation of HSA by acetaldehyde resulted in the abnormalities of binding sites for fatty acids and PG. Modification of the plasma membrane proteins with acetaldehyde sharply diminished the density of PG E2 binding sites without changing the association constants. Alkylation did not interfere with the parameters of PG F2 alpha binding to liver membrane proteins.     

Role of fatty acids in growth-promoting effect of serum albumin on hamster cells in vitro

Dialyzed serum albumin had considerable growth-promoting effect on cultivated hamster cells. This effect was virtually lost on removal of the fatty acids, and it was completely restored by recombination of the fatty acid-free albumin with the isolated and purified fatty acids. The role of albumin itself appeared to be largely that of a carrier of fatty acids, protecting the cells against toxic effects of fatty acids in free solution. This conclusion was based on two observations: Fatty acids in the absence of albumin were growth-inhibitory except in extremely dilute solutions, and beta-lactoglobulin, a protein possessing, like albumin, the ability to bind and release fatty acids, could replace albumin in the presence of fatty acids with similar growth-promoting effect. Examination of individual molecular types of fatty acids showed that all unsaturated acids tested were growth-promoting, whereas the saturated acids were growth-inhibiting, with the exception of stearic acid in low concentrations. Although the possibility of a mitotic triggering effect was not excluded, the fatty acids presumably stimulated growth by providing substrate for cellular metabolism, since there was a direct relationship between the degree of growth stimulation and the duration of exposure of cells to the fatty acids.     

Increased inhibitory potency of free fatty acid-poor albumin on the released and activity of insulin-degrading enzymes from isolated rat adipocytes and hepatocytes

Isolated rat adipocytes and hepatocytes release protease(s) into the medium which degrade insulin and glucagon. This can be partially inhibited by high concentrations of bovine serum albumin. Free fatty acid-poor albumin prepared by charcoal treatment at pH 3 is a more potent inhibitor than untreated albumin. However, the increase in inhibitory potency depends on the exposure of the albumin to the low pH and not on the removal of the fatty acids. Optimum conditions for this treatment are overnight exposure to pH 3-4 at 37 degrees C. In hepatocytes, but not in adipocytes, the treated albumin also diminishes the release of enzymes into the medium.     

Effect of bovine serum albumin on membrane potential in plant mitochondria

The membrane potential in highly coupled potato ( Solanum tuberosum L.) mitochondria, as measured by changes in safranine absorbance, was significantly increased by addition of bovine serum albumin. Purification of potato mitochondria on Percoll, in removing 50% of free unsaturated fatty acids, decreased the BSA-de-pendent membrane potential. The effect of added linoleic acid and of the natural accumulation of fatty acids during aging was studied. The response of membrane potential to addition of bovine serum albumin appeared to be directly correlated to the amount of free unsaturated fatty acids. Aging in vitro, in releasing free fatty acids, decreased respiratory control and ADP:O ratios and collapsed the membrane potential. During 2–3 h of incubation, addition of BSA completely restored membrane potential and oxidative phosphorylation.
It is concluded that both in fresh and in aged potato mitochondria the effect of bovine serum albumin on oxidative phosphorylation can be ascribed to an effect on membrane permeability to ions. BSA, in binding free unsaturated fatty acids, restored maximal membrane potential. The bovine serum albumin-dependent membrane potential appears to be a sensitive criterion of the functional integrity of the inner mitochondrial membrane.     

Lipid peroxidation contributes to immune reactions associated with alcoholic liver disease.

Increasing evidence indicates the involvement of immune reactions in the pathogenesis of alcoholic liver disease. We have investigated whether ethanol-induced oxidative stress might contribute to immune response in alcoholics. Antibodies against human serum albumin modified by reaction with malondialdehyde (MDA), 4-hydroxynonenal (HNE), 2-hexenal, acrolein, methylglyoxal, and oxidized arachidonic and linoleic acids were measured by ELISA in 78 patients with alcoholic cirrhosis and/or hepatitis, 50 patients with nonalcoholic cirrhosis, 23 heavy drinkers with fatty liver, and 80 controls. Titers of IgG-recognizing epitopes derived from MDA, HNE, and oxidized fatty acids were significantly higher in alcoholic as compared to nonalcoholic cirrhotics or healthy controls. No differences were instead observed in the titers of IgG-recognizing acrolein-, 2-hexenal-, and methylglyoxal-modified albumin. Alcoholics showing high IgG titers to one adduct tended to have high titers to all the others. However, competition experiments showed that the antigens recognized were structurally unrelated. Anti-MDA and anti-HNE antibodies were significantly higher in cirrhotics with more severe disease as well as in heavy drinkers with cirrhosis or extensive fibrosis than in those with fatty liver only. We conclude that antigens derived from lipid peroxidation contribute to the development of immune responses associated with alcoholic liver disease.     

Binding of lysophosphatidylcholine to the rat liver fatty acid binding protein

In this study, lysophosphatidylcholine (lysoPC) was shown to bind to a fatty acid binding protein isolated from rat liver. To demonstrate the binding, lysoPC was incorporated into multilamellar liposomes and incubated with protein. For comparison, binding of both lysoPC and fatty acid to liver fatty acid binding protein, albumin, and heart fatty acid binding protein were measured. At conditions where palmitic acid bound to liver fatty acid binding protein and albumin at ligand to protein molar ratios of 2:1 and 5:1, respectively, lysoPC binding occurred at molar ratios of 0.4:1 and 1:1. LysoPC did not bind to heart fatty acid binding protein under conditions where fatty acid bound at a molar ratio of 2:1. Competition experiments between lysoPC and fatty acid to liver fatty acid binding protein indicated separate binding sites for each ligand. An equilibrium dialysis cell was used to demonstrate that liver fatty acid binding protein was capable of transporting lysoPC from liposomes to rat liver microsomes, thereby facilitating its metabolism. These studies suggest that liver fatty acid binding protein may be involved in the intracellular metabolism of lysoPC as well as fatty acids, and that functional differences may exist between rat liver and heart fatty acid binding protein.     

Displacement of sulphobromophthalein from albumin and fatty-acid-binding protein by oleic acid

The absorption of sulphobromophthalein changes upon addition of bovine serum albumin or fatty-acid-binding protein at pH 8.4. The sulphobromophthalein spectrum is changed most drastically after the addition of albumin than in the presence of fatty-acid-binding protein isolated from rat liver, suggesting as a first approximation that binding capacity of albumin is much higher than that of fatty-acid-binding protein. When both soluble proteins are saturated with oleic acid it is observed a decrease in the binding of sulphobromophthalein which suggests that the presence of fatty acids in those soluble proteins may affect the binding of other ligands.     

Heme binding to albuminoid proteins is the result of recent evolution

We hypothesize that the structure of the heme binding site of paralogous albuminoids alpha-fetoprotein and serum albumin has evolved from the ancestor vitamin D binding protein through the 'phylogenetic intermediate' afamin, the most recently discovered albuminoid. Heme binding to plasma proteins should serve not only as a buffer for heme homeostasis, avoiding heme binding to lipoproteins with the consequent oxidative stress, but also for heme transfer to the liver, complementing the function of hemopexin.     

Crystallographic analysis reveals common modes of binding of medium and long-chain fatty acids to human serum albumin

Human serum albumin (HSA) is an abundant plasma protein that is responsible for the transport of fatty acids. HSA also binds and perturbs the pharmacokinetics of a wide range of drug compounds. Binding studies have revealed significant interactions between fatty acid and drug-binding sites on albumin but high-resolution structural information on ligand binding to the protein has been lacking. We report here a crystallographic study of five HSA-fatty acid complexes formed using saturated medium-chain and long-chain fatty acids (C10:0, C12:0, C14:0, C16:0 and C18:0). A total of seven binding sites that are occupied by all medium-chain and long-chain fatty acids have been identified, although medium-chain fatty acids are found to bind at additional sites on the protein, yielding a total of 11 distinct binding locations. Comparison of the different complexes reveals key similarities and significant differences in the modes of binding, and serves to rationalise much of the biochemical data on fatty acid interactions with albumin. The two principal drug-binding sites, in sub-domains IIA and IIIA, are observed to be occupied by fatty acids and one of them (in IIIA) appears to coincide with a high-affinity long-chain fatty acid binding site.     

Ncb5or deficiency increases fatty acid catabolism and oxidative stress

The endoplasmic reticulum-associated NADH cytochrome b(5) oxidoreductase (Ncb5or) is widely distributed in animal tissues. Ncb5or(-/-) mice develop diabetes at age 7 weeks and have increased susceptibility to the diabetogenic oxidant streptozotocin. Ncb5or deficiency also results in lipoatrophy and increased hepatocyte sensitivity to cytotoxic effects of saturated fatty acids. Here we investigate the mechanisms of these phenomena in prediabetic Ncb5or(-/-) mice and find that, despite increased rates of fatty acid uptake and synthesis and higher stearoyl-CoA desaturase (SCD) expression, Ncb5or(-/-) liver accumulates less triacylglycerol (TAG) than wild type (WT). Increased fatty acid catabolism and oxidative stress are evident in Ncb5or(-/-) hepatocytes and reflect increased mitochondrial content, peroxisome proliferator-activated receptor-γ coactivator 1α (PGC-1α) expression, fatty acid oxidation rates, oxidative stress response gene expression, and oxidized glutathione content. Ncb5or(-/-) hepatocytes readily incorporate exogenous fatty acids into TAG but accumulate more free fatty acids (FFA) and have greater palmitate-induced oxidative stress responses and cell death than WT, all of which are alleviated by co-incubation with oleate via TAG channeling. A high fat diet rich in palmitate and oleate stimulates both lipogenesis and fatty acid catabolism in Ncb5or(-/-) liver, resulting in TAG levels similar to WT but increased intracellular FFA accumulation. Hepatic SCD-specific activity is lower in Ncb5or(-/-) than in WT mice, although Ncb5or(-/-) liver has a greater increase in Scd1 mRNA and protein levels. Together, these findings suggest that increased FFA accumulation and catabolism and oxidative stress are major consequences of Ncb5or deficiency in liver.     

Surface-enhanced Raman spectroscopy study of the interaction of the antitumoral drug emodin with human serum albumin

Surface-enhanced Raman spectroscopy was employed in this work to study the interaction between the antitumoral drug emodin and human serum albumin (HSA), as well as the influence of fatty acids in this interaction. We demonstrated that the drug/protein interaction can take place through two different binding sites which are probably localized in the IIA and IIIA hydrophobic pockets of HSA and which correspond to Sudlow's I and II binding sites, respectively. The primary interaction site of this drug seems to be site II in the defatted albumin. Fatty acids seem to displace the drug from site II to site I in nondefatted HSA, due to the high affinity of fatty acids for site II. The drug interacts with the protein through its dianionic form in defatted HSA (when placed in the site II) and through its neutral form in the site I of nondefatted albumins.     

Metabolic Changes Induced by Cold Stress in Rat Liver Mitochondria

The mechanisms involved in the metabolic changes induced by cold stress in isolated rat liver mitochondria were studied. Respiration, ATP synthesis, and membrane potential as well as the contents of several metabolites were determined in liver mitochondria from cold-exposed rats. At different times of cold exposure, the force-flux relationships showed net variation in flux (enhanced respiration, diminished ATP synthesis) with no associated variation in force (H+ gradient); this suggested that decoupling rather than classical uncoupling was involved in the effects of cold stress. The flux control coefficient of the H+ leak on basal respiration was slightly increased by 380 h of cold exposure. Cold stress also induced a diminution in total membrane fatty acids, Zn2+, Fe3+, ATP, and ADP/O ratios; the content of cytochromes c + c1 and b oscillated. The contents of Ca2+, Na+, Pi, and cytochromes a + a3 were not affected, whereas matrix ADP, AMP, K+, and Mg2+ were markedly increased. Basal and oleic acid-stimulated respiration of mitochondria from cold-stressed rats was inhibited by GDP, carboxyatractyloside, or albumin. These agents did not affect basal respiration in control mitochondria. Western blot analysis showed enhanced expression of a protein of about 35 kDa, presumably the uncoupling protein 2, induced by long-term cold exposure. The overall data suggest that cold stress promoted decoupling of oxidative phosphorylation, and hence, changes in several matrix metabolites, by increasing free fatty acids and the UCP2 content.     

A radiochemical procedure for the assay of fatty acid binding by proteins

Protein-bound and unbound fatty acids can be efficiently separated at 0 degree C using a hydrophobic column-packing material (Lipidex 1000) similar to the separation of protein-bound and unbound steroids (E. Dahlberg, M. Snochowski, and J.-A. Gustafsson (1980) Anal Biochem. 106, 380-388). Protein-bound fatty acids are also removed by Lipidex 1000 when treatment is performed at 37 degrees C. Lipidex 1000 does not exhibit binding properties for soluble proteins at 0 and 37 degrees C, in contrast to dextran-coated charcoal. Lipidex 1000 appeared to be useful for the delipidation of protein samples at 37 degrees C and for a radiochemical assay of fatty acid-binding by microgram amounts of protein at 0 degree C. With this assay we obtained results on palmitate binding to serum albumin similar to those reported on the basis of equilibrium dialysis. Delipidated proteins from dealbuminized rat liver cytosol maximally bind about 4 nmol palmitate/mg protein.     

Protein and lipid nitration: role in redox signaling and injury

Protein and lipid nitration represent novel footprints of oxidative and nitrative stress processes. In this review, we first discuss the mechanisms of formation of protein 3-nitrotyrosine and nitrated fatty acids as well as their key biological and signaling actions. Elevation of protein 3-nitrotyrosine levels is associated to tissue injury, and some specific nitrated proteins play a causative role in disease progression; on the other hand, the substantiation on the role of tyrosine nitration on redox signaling is rather scarce. Herein, we also provide evidence to support that the nitration of lipids (i.e. to nitrofatty acids) results in the formation of novel endogenous modulators of redox processes, partially counteracting pro-inflammatory effects of oxidant exposure.     

The effect of soluble rat liver proteins on the activity of microsomal stearoyl-CoA and linoleoyl-CoA desaturase.

1. The influence of bovine serum albumin and soluble rat liver proteins on the activity of rat liver microsomal delta9 and delta6 desaturases has been studied. 2. In the absence of bovine serum albumin, the delta9 desaturase which converts stearoyl-CoA into oleoyl-CoA, shows a non-linear correlation between enzyme activity and protein concentration. 3. Optimum concentrations of bovine serum albumin have three main effects on the enzyme activity: (i) establishes a linear relationship between enzyme activity and protein concentration, (ii) stimulates the enzyme activity 2--3-fold and (iii) raises the optimum substrate concentration from 10 to 100 muM. 4. A highly purified soluble liver protein of molecular weight 24 000 also stimulated the enzyme activity and brought about a linear relationship between enzyme activity and protein concentration. 5. It was concluded that the non-linear kinetics were due to limiting amounts of substrate binding protein in the microsomal preparations. 6. The delta6 desaturase which converts linoleoyl-CoA into gamma-linolenoyl-CoA was also stimulated by bovine serum albumin and soluble liver proteins. 7. The significance of the fatty acid-binding proteins is discussed.     

Oxidative damage of albumin in advanced liver disease

Albumin has a number of biological functions and the serum albumin level is related to prognosis in advanced liver disease. Oxidative stress is believed to play an important role in the pathogenesis of liver failure. The aim of the present study was to characterize oxidative modification of albumin in patients with various degrees of liver failure and to investigate implications for its binding function. Patients with liver cirrhosis (n=10), acute-on-chronic liver failure (n=8) and healthy controls (n=15) were included in the study. Three fractions of albumin were separated by HPLC according to the redox state of cysteine-34 and detected by fluorescence as well as UV absorption. Carbonyl groups were measured as a marker of oxidative modification in plasma proteins and, by western blotting, on albumin. Progressive oxidative modification of albumin was found with increasing severity of liver failure indicated by an increased content of carbonyl groups and oxidation of cysteine-34. Fluorescence properties of albumin were altered by oxidation and, in patients with acute-on-chronic liver failure, by high plasma levels of bilirubin. This alteration of albumin fluorescence by bilirubin provides evidence for a preferred binding of bilirubin to the fully reduced form of albumin.     

Oxidative stress and ischemia-modified albumin in chronic ischemic heart failure

Abstract

Objectives

Knowledge about the role of oxidative stress in human diseases, including cardiovascular system disorders, emphasizes the need for reliable markers of oxidative stress. Here, we evaluated the levels of the novel marker ischemia-modified albumin (IMA), albumin-adjusted IMA (adj-IMA), and the IMA/serum albumin ratio (IMAR) in patients with chronic ischemic heart failure (CIHF).

Methods

A total of 55 patients with CIHF and 40 age- and sex-matched healthy individuals were included in the study. Serum levels of IMA, total antioxidant status, and total oxidant status were analyzed, and the adj-IMA level, IMAR, and oxidative stress index were calculated.

Results

Serum IMA, IMAR, total oxidant status levels, and oxidative stress index were significantly higher in patients with CIHF than in the controls (all P < 0.0001), whereas albumin and total antioxidant status levels were significantly lower in the CIHF patients (P < 0.0001 and P = 0.0004, respectively). However, there was no significant difference in serum adj-IMA levels between the groups (P = 0.8).

Discussion

We observed impaired oxidant/antioxidant status in favor of oxidative stress in CIHF patients. Oxidative stress may be a key factor in the development of hypoalbuminemia in CIHF. Further studies are needed to establish the relationships among IMA, albumin, and redox balance in CIHF.