Retinal fatty acid binding protein reduce lipid peroxidation stimulated by long-chain fatty acid hydroperoxides on rod outer segments

Effects of diel-cycling hypoxia and salinity on lipid metabolism and fatty acid composition of the oyster Crassostrea hongkongensis

For marine animals living in estuarine, coastal, and intertidal areas, salinity changes and periodic hypoxia are typical stressors; however, how the varying salinity and dissolved oxygen affect the quality and nutrition of marine aquaculture species, such as oysters remains unknown. In this study, we evaluated the diel-cycling hypoxia under different salinities on fatty acid composition and lipid metabolism in oyster Crassostrea hongkongensis digestive glands. After 28 days of exposure, both hypoxia and elevated salinity caused a decrease in the saturated fatty acid (SFA)/polyunsaturated fatty acid (PUFA) ratio of C. hongkongensis, salinity mainly causes changes in C17:0, C17:1, C18:1n9, C20:1n9, C20:4n6, C21:5n3, C22:5n3, with high salinity being more damaging to the fatty acid fractions. Also, Hypoxia accelerates the synthesis of C18:1n9 and C20:4n6. Fatty acid synthase (FAS) synthesis is increased by reduced salinity or hypoxia, but Acetyl CoA carboxylase (ACC) only weakly promotes fatty acid synthesis. Under hypoxic conditions, the activity of both hepatic lipase (HL) and lipoprotein lipase activity (LPL) decreases, which is contrary to the results for dissolved oxygen. The increase in salinity under dissolved oxygen leads to a decrease in LPL activity and an increase in HL activity. Our findings highlighted that exposure to a combination of salinity and hypoxia stressors, can disrupt the protective mechanisms of the oyster and affect the function of its lipid metabolism. Therefore, long-term exposure to periodic hypoxia with salinity changes poses a risk to the nutritional quality of C. hongkongensis, affecting oyster aquaculture and the coastal ecosystem.

Diabetic retinopathy, oxidative stress, and sirtuins: an in depth look in enzymatic patterns and new therapeutic horizons

Diabetic retinopathy (DR) is one of the leading causes of blindness in the world. DR represents the most common microvascular complication of diabetes, and its incidence is constantly rising. The complex interactions between inflammation, oxidative stress, and the production of free oxygen radicals caused by prolonged exposure to hyperglycemia determine the development of DR. Sirtuins (SIRTs) are a recently discovered class of 7 histone deacetylases involved in cellular senescence, regulation of cell cycle, metabolic pathways, and DNA repair. SIRTs participate in the progress of several pathologies such as cancer, neurodegeneration, and metabolic diseases. In DR sirtuins 1,3,5, and 6 play an important role as they regulate the activation of the inflammatory response, insulin sensibility, and both glycolysis and gluconeogenesis. A wide spectrum of direct and indirect activators of SIRTs pathways (e.g., antagomiR, resveratrol, or glycyrrhizin) is currently being developed to treat the inflammatory cascade occurring in DR. We focus on the main metabolic and inflammatory pathways involving SIRTs and DR, as well as recent evidence on SIRTs activators that may be employed as novel therapeutic approaches to DR.

Fatty Acid Signaling Mechanisms in Neural Cells: Fatty Acid Receptors

Fatty acids (FAs) are typically associated with structural and metabolic roles, as they can be stored as triglycerides, degraded by β-oxidation or used in phospholipids’ synthesis, the main components of biological membranes. It has been shown that these lipids exhibit also regulatory functions in different cell types. FAs can serve as secondary messengers, as well as modulators of enzymatic activities and substrates for cytokines synthesis. More recently, it has been documented a direct activity of free FAs as ligands of membrane, cytosolic, and nuclear receptors, and cumulative evidence has emerged, demonstrating its participation in a wide range of physiological and pathological conditions. It has been long known that the central nervous system is enriched with poly-unsaturated FAs, such as arachidonic (C20:4ω-6) or docosohexaenoic (C22:6ω-3) acids. These lipids participate in the regulation of membrane fluidity, axonal growth, development, memory, and inflammatory response. Furthermore, a whole family of low molecular weight compounds derived from FAs has also gained special attention as the natural ligands for cannabinoid receptors or key cytokines involved in inflammation, largely expanding the role of FAs as precursors of signaling molecules. Nutritional deficiencies, and alterations in lipid metabolism and lipid signaling have been associated with developmental and cognitive problems, as well as with neurodegenerative diseases. The molecular mechanism behind these effects still remains elusive. But in the last two decades, different families of proteins have been characterized as receptors mediating FAs signaling. This review focuses on different receptors sensing and transducing free FAs signals in neural cells: (1) membrane receptors of the family of G Protein Coupled Receptors known as Free Fatty Acid Receptors (FFARs); (2) cytosolic transport Fatty Acid-Binding Proteins (FABPs); and (3) transcription factors Peroxisome Proliferator-Activated Receptors (PPARs). We discuss how these proteins modulate and mediate direct regulatory functions of free FAs in neural cells. Finally, we briefly discuss the advantages of evaluating them as potential targets for drug design in order to manipulate lipid signaling. A thorough characterization of lipid receptors of the nervous system could provide a framework for a better understanding of their roles in neurophysiology and, potentially, help for the development of novel drugs against aging and neurodegenerative processes.

Biochemical and molecular responses in oysters Crassostrea brasiliana collected from estuarine aquaculture areas in Southern Brazil

Biochemical and molecular responses were evaluated in oysters Crassostrea brasiliana collected from three oyster farms, at Guaratuba Bay, southern Brazil, forming a pollutant gradient: Farm 1 (reference site - farther from the urban area), Farm 2 (intermediate site) and Farm 3 (nearest to the urban area). Oxidative stress markers, DNA damage and transcript levels of CYP2AU1, CYP2-like1, CYP2-like2, SULT-like, GPx-like, SOD-like, CAT-like, GSTmicrosomal-like, GSTomega-like, FABP-like and ALAd-like genes were analyzed in the gills. The levels of polycyclic aromatic hydrocarbons, linear alkylbenzenes and polychlorinated biphenyls were also evaluated in the soft tissues of the oysters and in the sediment of the Farms. Higher GSTomega-like, CYP2AU1 and FABP-like transcript levels, GR and G6PDH activities and lipid peroxidation levels were observed in oysters from Farms 2 and 3, suggesting pollutant effects on oysters. Alterations in oxidative stress markers also suggest a response against a prooxidant condition in C. brasiliana due to pollutant effects.

Five decades with polyunsaturated Fatty acids: chemical synthesis, enzymatic formation, lipid peroxidation and its biological effects

I have been involved in research on polyunsaturated fatty acids since 1964 and this review is intended to cover some of the most important aspects of this work. Polyunsaturated fatty acids have followed me during my whole scientific career and I have published a number of studies concerned with different aspects of them such as chemical synthesis, enzymatic formation, metabolism, transport, physical, chemical, and catalytic properties of a reconstructed desaturase system in liposomes, lipid peroxidation, and their effects. The first project I became involved in was the organic synthesis of [1-¹⁴C] eicosa-11,14-dienoic acid, with the aim of demonstrating the participation of that compound as a possible intermediary in the biosynthesis of arachidonic acid “in vivo.” From 1966 to 1982, I was involved in several projects that study the metabolism of polyunsaturated fatty acids. In the eighties, we studied fatty acid binding protein. From 1990 up to now, our laboratory has been interested in the lipid peroxidation of biological membranes from various tissues and different species as well as liposomes prepared with phospholipids rich in PUFAs. We tested the effect of many antioxidants such as alpha tocopherol, vitamin A, melatonin and its structural analogues, and conjugated linoleic acid, among others.

Activation and reversal of lipotoxicity in PC12 and rat cortical cells following exposure to palmitic acid

Lipotoxicity involves a series of pathological cellular responses after exposure to elevated levels of fatty acids. This process may be detrimental to normal cellular homeostasis and cell viability. The present study shows that nerve growth factor-differentiated PC12 cells (NGFDPC12) and rat cortical cells (RCC) exposed to high levels of palmitic acid (PA) exhibit significant lipotoxicity and death linked to an "augmented state of cellular oxidative stress" (ASCOS). The ASCOS response includes generation of reactive oxygen species (ROS), alterations in the mitochondrial transmembrane potential, and increase in the mRNA levels of key cell death/survival regulatory genes. The observed cell death was apoptotic based on nuclear morphology, caspase-3 activation, and cleavage of lamin B and PARP. Quantitative real-time PCR measurements showed that cells undergoing lipotoxicity exhibited an increase in the expression of the mRNAs encoding the cell death-associated proteins BNIP3 and FAS receptor. Cotreatment of NGFDPC12 and RCC cells undergoing lipotoxicity with docosahexaenoic acid (DHA) and bovine serum albumin (BSA) significantly reduced cell death within the first 2 hr following the initial exposure to PA. The data suggest that lipotoxicity in NGFDPC12 and cortical neurons triggers a strong cell death apoptotic response. Results with NGFDPC12 cells suggest a linkage between induction of ASCOS and the apoptotic process and exhibit a temporal window that is sensitive to DHA and BSA interventions.

Synthesis of 11-thialinoleic acid and 14-thialinoleic acid, inhibitors of soybean and human lipoxygenases

Lipoxygenases catalyse the oxidation of polyunsaturated fatty acids and have been invoked in many diseases including cancer, atherosclerosis and Alzheimer's disease. Currently, no X-ray structures are available with substrate or substrate analogues bound in a productive conformation. Such structures would be very useful for examining interactions between substrate and active site residues. Reported here are the syntheses of linoleic acid analogues containing a sulfur atom at the 11 or 14 positions. The key steps in the syntheses were the incorporation of sulfur using nucleophilic attack of metallated alkynes on electrophilic sulfur compounds and the subsequent stereospecific tantalum-mediated reduction of the alkynylsulfide to the cis-alkenylsulfide. Kinetic assays performed with soybean lipoxygenase-1 showed that both 11-thialinoleic acid and 14-thialinoleic acid were competitive inhibitors with respect to linoleic acid with K(i) values of 22 and 35 microM, respectively. On the other hand, 11-thialinoleic acid was a noncompetitive inhibitor with respect to arachidonic acid with K(is) and K(ii) values of 48 and 36 microM, respectively. 11-Thialinoleic acid was also a noncompetitive inhibitor of human 15-lipoxygenase-1 with arachidonic acid (K(is) = 11.4 microM, K(ii) = 18.1 microM) or linoleic acid as substrate (K(is) = 20.1 microM, K(ii) = 20.0 microM), and a competitive inhibitor of human 12-lipoxygenase with arachidonic acid as substrate (K(i) = 2.5 microM). The presence of inhibitor did not change the regioselectivity of soybean lipoxygenase-1, human 12- or 15-lipoxygenase-1.

Alpha-tocopherol protects against oxidative damage to lipids of the rod outer segments of the equine retina

Oxidative stress is a possible risk factor for eye diseases. Lipid peroxidation is one of the major events induced by oxidative stress and is particularly active in polyunsaturated fatty acid (PUFA)-rich biomembranes. This work evaluated endogenous lipid antioxidants, in vitro non-enzymatic lipid peroxidation of rod outer segment membranes (ROS), the fatty acid composition during oxidative damage of total lipids from equine retina and ROS, and the protective action of alpha-tocopherol (alpha-Toc). The major lipid soluble antioxidant was alpha-Toc followed by retinoids and carotenoids. The retina contained a high percentage of PUFAs, mainly docosahexaenoic acid (22:6n-3) and arachidonic acid (20:4n-6). Lipid peroxidation of the equine ROS, induced by Fe(2+)-ascorbate, was monitored using chemiluminescence (CL) with or without pre-treatment with alpha-Toc. With alpha-Toc pre-treatment, CL values were significantly decreased. The most abundant fatty acid was 22:6n-3. After 3h incubation, 95% of total PUFAs were destroyed by peroxidation, whereas in alpha-Toc pre-treated ROS the percentage was significantly decreased. The results show that the retina has an endogenous lipid soluble antioxidant system. ROS were highly sensitive to oxidative damage, since their fatty acid composition was markedly modified during the lipid peroxidation process. The protective role of alpha-Toc as an antioxidant was evident and it could be used in the treatment of equine ocular diseases in which free radicals are involved.

Different mechanisms of saturated versus polyunsaturated FFA-induced apoptosis in human endothelial cells

Apoptosis and underlying mechanisms were evaluated in human umbilical vein endothelial cells (HUVECs), in target tissues of late diabetic vascular complications [human aortic endothelial cells (HAECs) and human retinal endothelial cells (HRECs)], and in endothelial progenitor cells (EPCs) exposed to FFAs, which are elevated in obesity and diabetes. Saturated stearic acid concentration dependently induced apoptosis that could be mediated via reduced membrane fluidity, because both apoptosis and membrane rigidity are counteracted by eicosapentaenoic acid. PUFAs triggered apoptosis at a concentration of 300 micromol/l in HUVECs, HAECs, and EPCs, but not HRECs, and, in contrast to stearic acid, involved caspase-8 activation. PUFA-induced apoptosis, but not stearic acid-induced apoptosis, strictly correlated (P < 0.01) with protein expression of E2F-1 (r = 0.878) and c-myc (r = 0.966). Lack of c-myc expression and activity owing to quiescence or transfection with dominant negative In373-Myc, respectively, renders HUVECs resistant to PUFA-induced apoptosis. Because c-myc is abundant in growing cells only, apoptosis triggered by PUFAs, but not by saturated stearic acid, obviously depends on the growth/proliferation status of the cells. Finally, this study shows that FFA-induced apoptosis depends on the vascular origin and growth/proliferation status of endothelial cells, and that saturated stearic acid-induced apoptosis and PUFA-induced apoptosis are mediated via different mechanisms.

Isotope sensitive branching and kinetic isotope effects in the reaction of deuterated arachidonic acids with human 12- and 15-lipoxygenases

Lipoxygenases (LOs) catalyze lipid peroxidation and have been implicated in a number of human diseases connected to oxidative stress and inflammation. These enzymes have also attracted considerable attention due to large kinetic isotope effects (30-80) for the rate-limiting hydrogen abstraction step with linoleic acid (LA) as substrate. Herein, we report kinetic isotope effects (KIEs) in the reactions of three human LOs (platelet 12-hLO, reticulocyte 15-hLO-1, and epithelial 15-hLO-2) with arachidonic acid (AA). Surprisingly, the observed KIEs with AA were much smaller than the previously reported values with LA. Investigation into the origins for the smaller KIEs led to the discovery of isotope sensitive branching of the reaction pathways. Product distribution analysis demonstrated an inversion in the regioselectivity of 15-hLO-1, with hydrogen abstraction from C13 being the major pathway with unlabeled AA but abstraction from C10 predominating when the methylene group at position 13 was deuterated. Smaller but clear changes in regioselectivity were also observed for 12-hLO and 15-hLO-2.

Toxicity of fatty acid hydroperoxides towards Yarrowia lipolytica: Implication of their membrane fluidizing action

Linoleic acid hydroperoxide (HPOD), substrate of hydroperoxide lyase, an enzyme of the lipoxygenase pathway, can be transformed into many aromatic compounds, the so-called "green notes". The presence of linoleic acid hydroperoxide in the culture medium of Yarrowia lipolytica, the yeast expressing the cloned hydroperoxide lyase of green bell pepper, undoubtedly exerted an inhibition on the growth and a toxic effect with 90% of yeast cells died after 120 min of exposition in 100 mM HPOD solution. The increase in cell membrane fluidity evaluated by measuring fluorescence generalized polarization with the increasing concentration of HPOD in the medium confirmed the fluidizing action of HPOD on yeast membrane. In addition, we determined by infrared spectroscopy measurement that this compound rapidly diffused into model phospholipids [1, 2-Dimyristoyl-D54-sn-Glycero-3-Phosphocholine (DMPC-D54)] bilayer, modifying their general physical state and their phase transition. In the presence of various concentrations of HPOD, the phase transition of DMPC-D54 occurred with an increase of both the corresponding wave number shift and the temperature range but the phase transition temperature was not modified. These results show that the toxic effects of HPOD on the yeast Yarrowia lipolytica may be initially linked to a strong interaction of this compound with the cell membrane phospholipids and components.

Lipid-protein modifications during ascorbate-Fe2+ peroxidation of photoreceptor membranes: protective effect of melatonin

The rod outer segment (ROSg) membranes are essentially lipoprotein complexes. Rhodopsin, the major integral protein of ROSg, is surrounded by phospholipids highly enriched in docosahexaenoic acid (22:6 n3). This fluid environment plays an important role for conformational changes after photo-activation. Thus, ROSg membranes are highly susceptible to oxidative damage. Melatonin synthesized in the pineal gland, retina and other tissues is a free radical scavenger. The principal aim of this work was to study the changes in the ROSg membranes isolated from bovine retina submitted to nonenzymatic lipid peroxidation (ascorbate-Fe2+ induced), during different time intervals (0-180 min). Oxidative stress was monitored by increase in the chemiluminescence and fatty acid alterations. In addition we studied the in vitro protective effect of 5 mm melatonin. The total cpm originated from light emission (chemiluminescence) was found to be lower in those membranes incubated in the presence of melatonin. The docosahexaenoic acid content decreased considerably when the membranes were exposed to oxidative damage. This reduction was from 35.5 +/- 2.9% in the native membranes to 12.65 +/- 1.86% in those peroxidized during 180 min. In the presence of 5 mm melatonin we observed a content preservation of 22:6 n3 (23.85 +/- 2.77%) at the same time of peroxidation. Simultaneously the alterations of membrane proteins under oxidative stress were studied using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Loss of protein sulfhydryl groups and increased incorporation of carbonyl groups were utilized as biomarkers of protein oxidation. In membranes exposed to Fe2+ -ascorbate, we observed a decrease of protein thiols from 50.9 +/- 3.38 in native membranes to 1.72 +/- 2.81 nmol/mg of protein after 180 min of lipid peroxidation associated with increased incorporation of carbonyl groups into proteins from 7.20 +/- 2.50 to 12.50 +/- 1.12 nmol/mg of protein. In the SDS-PAGE we observed a decrease in the content of all the proteins, mainly rhodopsin, as a consequence of peroxidation. Melatonin, prevent both lipid peroxidation and protein oxidation.

An overview of lipid peroxidation with emphasis in outer segments of photoreceptors and the chemiluminescence assay

The onset of lipid peroxidation within cellular membranes is associated with changes in their physicochemical properties and with the impairment of protein functions located in the membrane environment. This article provides current information on the origin and function of polyunsaturated fatty acids in nature, lipid peroxidation of cellular membranes: enzymatic (lipoxygenases) and non-enzymatic. The latest knowledge on in vivo biomarkers of lipid peroxidation including isoprostanes, isofurans and neuroprostanes are discussed. A further focus is placed on analytical methods for studying lipid peroxidation in membranes with emphasis in chemiluminescence and its origin, rod outer segments of photoreceptors, the effect of antioxidants, fatty acid hydroperoxides and lipid protein modifications. Since rhodopsin, the major integral protein of rod outer segments is surrounded by phospholipids highly enriched in docosahexaenoic acid, the author proposes the outer segments of photoreceptors as an excellent model to study lipid peroxidation using the chemiluminescence assay since these membranes contain the highest concentration of polyunsaturated fatty acids of any vertebrate tissue and are highly susceptible to oxidative damage.

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

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

Pulmonary surfactant protein A inhibits the lipid peroxidation stimulated by linoleic acid hydroperoxide of rat lung mitochondria and microsomes

Reactive oxygen species play an important role in several acute lung injuries. The lung tissue contains polyunsaturated fatty acids (PUFAs) that are substrates of lipid peroxidation that may lead to loss of the functional integrity of the cell membranes. In this study, we compare the in vitro protective effect of pulmonary surfactant protein A (SP-A), purified from porcine surfactant, against ascorbate-Fe(2+) lipid peroxidation stimulated by linoleic acid hydroperoxide (LHP) of the mitochondria and microsomes isolated from rat lung; deprived organelles of ascorbate and LHP were utilized as control. The process was measured simultaneously by chemiluminescence as well as by PUFA degradation of the total lipids isolated from these organelles. The addition of LHP to rat lung mitochondria or microsomes produces a marked increase in light emission; the highest value of activation was produced in microsomes (total chemiluminescence: 20.015+/-1.735 x 10(5) cpm). The inhibition of lipid peroxidation (decrease of chemiluminescence) was observed with the addition of increasing amounts (2.5 to 5.0 microg) of SP-A in rat lung mitochondria and 2.5 to 7.5 microg of SP-A in rat lung microsomes. The inhibitory effect reaches the highest values in the mitochondria, thus, 5.0 microg of SP-A produces a 100% inhibition in this membranes whereas 7.5 microg of SP-A produces a 51.25+/-3.48% inhibition in microsomes. The major difference in the fatty acid composition of total lipids isolated from native and peroxidized membranes was found in the arachidonic acid content; this decreased from 9.68+/-1.60% in the native group to 5.72+/-1.64% in peroxidized mitochondria and from 7.39+/-1.14% to 3.21+/-0.77% in microsomes. These changes were less pronounced in SP-A treated membranes; as an example, in the presence of 5.0 microg of SP-A, we observed a total protection of 20:4 n-6 (9.41+/-3.29%) in mitochondria, whereas 7.5 microg of SP-A produced a 65% protection in microsomes (5.95+/-0.73%). Under these experimental conditions, SP-A produces a smaller inhibitory effect in microsomes than in mitochondria. Additional studies of lipid peroxidation of rat lung mitochondria or microsomes using equal amounts of albumin and even higher compared to SPA were carried out. Our results indicate that under our experimental conditions, BSA was unable to inhibit lipid peroxidation stimulated by linoleic acid hydroperoxide of rat lung mitochondria or microsomes, thus indicating that this effect is specific to SP-A.

Protective effect of indoleamines on in vitro ascorbate-Fe2+ dependent lipid peroxidation of rod outer segment membranes of bovine retina

Rod outer segment membranes (ROS) are highly vulnerable to autooxidation because of their high content of long chain polyunsaturated fatty acids (PUFAs). Melatonin and N-acetylserotonin are indoleamines synthesized in the pineal gland, retina and other tissues. These compounds are free radical scavengers and indirect antioxidants because of their stimulatory effect on antioxidative enzymes. We compared the in vitro protective effect of melatonin and N-acetylserotonin on the ascorbate-Fe2+ induced lipid peroxidation of PUFAs located in ROS membranes. This process was measured by chemiluminescence and fatty acid composition of total lipids of ROS. We assayed increasing concentrations of melatonin (0-10 mm) and N-acetylserotonin (0-2 mm). In both cases the total cpm originated from light emission (chemiluminescence) was found to be lower in those membranes incubated in the presence of either melatonin or N-acetylserotonin; this decreased proportional to the concentration of the indole. Thus, 10 mm melatonin and 2 mm N-acetylserotonin produced a reduction of 51 +/- 6 and 100% in the total chemiluminescene (lipid peroxidation), respectively. We also noticed a PUFAs protection: the docosahexaenoic acid content decreased considerably when the membranes were submitted to oxidative damage. This reduction was from 37.6 +/- 2.1% in the native membranes to 6.2 +/- 0.8% in those which were peroxidized. These changes were less pronounced in treated ROS membranes; as an example in the presence of 10 mm melatonin or 2 mm N-acetylserotonin we observed a content preservation of 22:6 n-3 (23.6 +/- 1.2 and 39.1 +/- 1.2% respectively). The concentration of each compound required to inhibit 50% of the lipid peroxidation (IC50) was 9.82 mm for melatonin and 0.43 mm for N-acetylserotonin, respectively. N-acetylserotonin shows a protective effect about 20 times higher than that of melatonin.

Binding of low molecular mass compounds to proteins studied by liquid chromatographic techniques

The newest achievements in the application of miscellaneous liquid chromatographic techniques such as size-exclusion, ion-exchange and reversed-phase high-performance liquid chromatography, and thin-layer chromatography for the elucidation of the various aspects of the binding of ligands to proteins are compiled and briefly discussed. Examples of employment in pharmaceutical and clinical chemistry, drug design, enzyme kinetic studies and environmental protection are presented.

Peroxidation stimulated by lipid hydroperoxides on bovine retinal pigment epithelium mitochondria: effect of cellular retinol-binding protein

This study analyzes the effect of cellular retinol-binding protein (CRBP), partially purified from retinal pigment epithelium (RPE) cytosol, on the non-enzymatic lipid peroxidation induced by fatty acid hydroperoxides of mitochondrial membranes isolated from bovine RPE. The effect of different amounts (50, 75 and 100 nmol) of linoleic acid hydroperoxide (LHP), arachidonic acid hydroperoxide (AHP) and docosahexaenoic acid hydroperoxide (DHP) on the lipid peroxidation of RPE mitochondria was studied; RPE mitochondria deprived of exogenously added hydroperoxide was utilized as control. The process was measured simultaneously by determining chemiluminescence as well as polyunsaturated fatty acid (PUFA) degradation of total lipids isolated from RPE mitochondria. The addition of hydroperoxides to RPE mitochondria produces a marked increase in light emission that was hydroperoxide concentration dependent. The highest value of activation was produced by LHP. The major difference in the fatty acid composition of total lipids isolated from native and peroxidized RPE mitochondria incubated with and without hydroperoxides was found in the docosahexaenoic acid content, this decreased 40.90+/-3.01% in the peroxidized group compared to native RPE mitochondria. The decrease was significantly high: 86.32+/-2.57% when the lipid peroxidation was stimulated by 100 nmol of LHP. Inhibition of lipid peroxidation (decrease of chemiluminescence) was observed with the addition of increasing amounts (100-600 microg) of CRBP to RPE mitochondria. The inhibitory effect reaches the highest values in the presence of LHP.