Scielo RSS <![CDATA[Biological Research]]> https://scielo.conicyt.cl/rss.php?pid=0716-976020000002&lang=en vol. 33 num. 2 lang. en <![CDATA[SciELO Logo]]> https://scielo.conicyt.cl/img/en/fbpelogp.gif https://scielo.conicyt.cl https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0716-97602000000200001&lng=en&nrm=iso&tlng=en <![CDATA[UNA CONVERSACION CON EL DR. MARIO LUXORO MARIANI: PREMIO NACIONAL DE CIENCIAS NATURALES, AÑO 2000]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0716-97602000000200002&lng=en&nrm=iso&tlng=en <![CDATA[PROGRAMA BIBLIOTECA CIENTIFICA ELECTRONICA EN LINEA, SCIELO-CHILE: UNA NUEVA FORMA DE ACCEDER A LA LITERATURA CIENTIFICA NACIONAL]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0716-97602000000200003&lng=en&nrm=iso&tlng=en <![CDATA[Plant Polyphenol Antioxidants and Oxidative Stress]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0716-97602000000200004&lng=en&nrm=iso&tlng=en In recent years there has been a remarkable increment in scientific articles dealing with oxidative stress. Several reasons justify this trend: knowledge about reactive oxygen and nitrogen species metabolism; definition of markers for oxidative damage; evidence linking chronic diseases and oxidative stress; identification of flavonoids and other dietary polyphenol antioxidants present in plant foods as bioactive molecules; and data supporting the idea that health benefits associated with fruits, vegetables and red wine in the diet are probably linked to the polyphenol antioxidants they contain.In this review we examine some of the evidence linking chronic diseases and oxidative stress, the distribution and basic structure of plant polyphenol antioxidants, some biological effects of polyphenols, and data related to their bioavailability and the metabolic changes they undergo in the intestinal lumen and after absorption into the organism.Finally, we consider some of the challenges that research in this area currently faces, with particular emphasis on the contributions made at the International Symposium "Biology and Pathology of Free Radicals: Plant and Wine Polyphenol Antioxidants" held July 29-30, 1999, at the Catholic University, Santiago, Chile and collected in this special issue of Biological Research <![CDATA[Free radical chemistry in biological systems]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0716-97602000000200005&lng=en&nrm=iso&tlng=en Mitochondria are an active source of the free radical superoxide (O2-) and nitric oxide (NO), whose production accounts for about 2% and 0.5% respectively, of mitochondrial O2 uptake under physiological conditions. Superoxide is produced by the auto-oxidation of the semiquinones of ubiquinol and the NADH dehydrogenase flavin and NO by the enzymatic action of the nitric oxide synthase of the inner mitochondrial membrane (mtNOS). Nitric oxide reversibly inhibits cytochrome oxidase activity in competition with O2. The balance between NO production and its utilization results in a NO intramitochondrial steady-state concentration of 20-50 nM, which regulates mitochondrial O2 uptake and energy supply. The regulation of cellular respiration and energy production by NO and its ability to switch the pathway of cell death from apoptosis to necrosis in physiological and pathological conditions could take place primarily through the inhibition of mitochondrial ATP production. Nitric oxide reacts with O2- in a termination reaction in the mitochondrial matrix, yielding peroxynitrite (ONOO-), which is a strong oxidizing and nitrating species. This reaction accounts for approximately 85% of the rate of mitochondrial NO utilization in aerobic conditions. Mitochondrial aging by oxyradical- and peroxynitrite-induced damage would occur through selective mtDNA damage and protein inactivation, leading to dysfunctional mitochondria unable to keep membrane potential and ATP synthesis <![CDATA[A comparison of methods employed to evaluate antioxidant capabilities]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0716-97602000000200006&lng=en&nrm=iso&tlng=en Thrce ditferent methodologies frequently employed to evaluate the indexes that report the antioxidant capabilities of pure compounds and/or complex mixtures of antioxidants are applied to a series of mono- and polyphenols, as well as to two wine (red and white) samples. These methodologies are based on the bleaching of a stable radical, the effect of the additive upon luminol chemiluminescence induced by peroxyl radicals, and the effect of the additive upon the bleaching of the fluorescence from a dye molecule. Widely ditferent responses are obtained from the different methodologies. These differences are interpreted in terms of the different factors (stoichiametric factors and/or reactivities) that determines the indexes evaluated by these different methodologies <![CDATA[Antioxidant flavonols from fruits, vegetables and beverages: measurements and bioavailability]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0716-97602000000200007&lng=en&nrm=iso&tlng=en Flavonols are polyphenolic secondary plant metabolites that are present in varying levels in commonly consumed fruits, vegetables and beverages. Flavonols have long held an interest for nutritionists, which has increased following a Dutch study in the early 1990’s showing that dietary intake of flavonols was inversely correlated with the incidence of coronary heart disease. The main factors that have hindered workers in the field of flavonol research are (i) the accurate measurement of these compounds in foods and biological samples, and (ii) a dearth of information on their absorption and metabolism. This review aims to highlight the work of the authors in attempting to clarify the situation. The sensitive and selective HPLC procedure to identify and quantify common flavonols and their sugar conjugates is described. In addition, the results of an on-going screening program into the flavonol content of common produce and beverages are presented. The bioavailability of dietary flavonols is discussed with reference to an intervention study with onions, as well as pilot studies with tea, red wine and cherry tomatoes. It is concluded that flavonols are absorbable and accumulate in plasma and that consuming high flavonol-containing varieties of fruits and vegetables and particular types of beverages could increase their circulatory levels <![CDATA[Endothelial cell oxidative stress and signal transduction]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0716-97602000000200008&lng=en&nrm=iso&tlng=en Endothelial dysfunction (ED) is an early event in atherosclerotic disease, preceding clinical manifestations and complications. Increased reactive oxygen species (ROS) have been implicated as important mechanisms that contribute to ED, and ROS’s may function as intracellular messengers that modulate signaling pathways. Several intracellular signal events stimulated by ROS have been defined, including the identification of two members of the mitogen activated protein kinase family (ERK1/2 and big MAP kinase, BMK1), tyrosine kinases (Src and Syk) and different isoenzymes of PKC as redox-sensitive kinases. ROS regulation of signal transduction components include the modification in the activity of transcriptional factors such as NFkB and others that result in changes in gene expression and modifications in cellular responses. In order to understand the intracellular mechanisms induced by ROS in endothelial cells (EC), we are studying the response of human umbilical cord vein endothelial cells to increased ROS generation by different pro-atherogenic stimuli. Our results show that Homocysteine (Hcy) and oxidized LDL (oxLDL) enhance the activity and expression of oxidative stress markers, such as NFkB and heme oxygenase 1. These results suggest that these pro-atherogenic stimuli increase oxidative stress in EC, and thus explain the loss of endothelial function associated with the atherogenic process <![CDATA[Scavenger Receptors and Atherosclerosis]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0716-97602000000200009&lng=en&nrm=iso&tlng=en Scavenger receptors were discovered as cell surface proteins capable of binding and internalization of modified lipoproteins. These receptors exhibit a broad ligand binding specificity including potential physiological and pathophysiological ligands other than modified lipoproteins. Different classes of scavenger receptors have been identified, and their relevance in normal and pathological conditions is under investigation. Recent in vitro and in vivo studies strongly support the role of class A and class B scavenger receptors in lipid transport atherogenesis <![CDATA[Lipid peroxidation and antioxidants in hyperlipidemia and hypertension]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0716-97602000000200010&lng=en&nrm=iso&tlng=en Lipid peroxidation and lipid-derived oxidized products have been implicated in the pathogenesis of a variety of human diseases. To clarify the role of oxidative stress in essential hypertension and hypercholesterolemia the in vitro oxidative susceptibility of LDL, the antioxidant status and the lipid peroxide content of blood plasma were examined in hypercholesterolemic (HC), hypertensive (H), hypercholesterolemic/hypertensive (HH) and normolipidemic/normotensive subjects (N). Plasma ascorbate and lipid-soluble antioxidants were lower, while LDL oxidizability, CE-OOH and TL-OOH were higher in H, HC, and HH groups than in the N group. No difference was observed among groups for PL-OOH and isoprostanes. In summary, the results show that: 1) lipid- and water-soluble antioxidants are lower in hypercholesterolemic and hypertensive patients as compared to normal subjects, whereas the lipid peroxide content and the LDL susceptibility to oxidation were higher; 2) total cholesterol, LDL-cholesterol, apoB and CE-OOH were negatively correlated with the content of a-tocopherol; 3) there was a positive correlation between the content of lipid-soluble antioxidants and the resistance of LDL to oxidation; and 4) CE-OOH and TL-OOH were positively correlated with total cholesterol and LDL-cholesterol. <![CDATA[SH Oxidation Stimulates Calcium Release Channels (Ryanodine Receptors) From Excitable Cells]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0716-97602000000200011&lng=en&nrm=iso&tlng=en The effects of redox reagents on the activity of the intracellular calcium release channels (ryanodine receptors) of skeletal and cardiac muscle, or brain cortex neurons, was examined. In lipid bilayer experiments, oxidizing agents (2,2'-dithiodipyridine or thimerosal) modified the calcium dependence of all single channels studied. After controlled oxidation channels became active at sub &micro;M calcium concentrations and were not inhibited by increasing the calcium concentration to 0.5 mM. Subsequent reduction reversed these effects. Channels purified from amphibian skeletal muscle exhibited the same behavior, indicating that the SH groups responsible for modifying the calcium dependence belong to the channel protein. Parallel experiments that measured calcium release through these channels in sarcoplasmic reticulum vesicles showed that following oxidation, the channels were no longer inhibited by sub mM concentrations of Mg2+. It is proposed that channel redox state controls the high affinity sites responsible for calcium activation as well as the low affinity sites involved in Mg2+ inhibition of channel activity. The possible physiological and pathological implications of these results are discussed <![CDATA[Amyloid-ß-peptide reduces copper(II) to copper(I) independent of its aggregation state]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0716-97602000000200012&lng=en&nrm=iso&tlng=en Alzheimer’s disease (AD) is characterized by the deposition of amyloid b-peptide (Aß) and neuronal degeneration in brain regions involved in learning and memory. One of the leading etiologic hypotheses regarding AD is the involvement of free radical-mediated oxidative stress in neuronal degeneration. Recent evidence suggests that metals concentrated in amyloid deposits may contribute to the oxidative insults observed in AD-affected brains. We hypothesized that Aß peptide in the presence of copper enhances its neurotoxicity generating free radicals via copper reduction. In the present study, we have examined the effect of the aggregation state of amyloid-ß-peptide on copper reduction. In independent experiments we measured the copper-reducing ability of soluble and fibrillar Aß1-40 forms by bathocuproine assays. As it was previously observed for the amyloid precursor protein (APP), the Aß peptide showed copper-reducing ability. The capacity of Aß to reduce copper was independent of the aggregation state. Finally, the Aß peptide derived from the human sequence has a greater effect than the Aß peptide derived from the rat sequence, suggesting that histidine 13 may play a role in copper reduction. In agreement with this possibility, the Aß peptide reduces less copper in the presence of exogenous histidine <![CDATA[The cellular mechanisms of body iron homeostasis]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0716-97602000000200013&lng=en&nrm=iso&tlng=en Cells tightly regulate iron levels through the activity of iron regulatory proteins (IRPs) that bind to RNA motifs called iron responsive elements (IREs). When cells become iron-depleted, IRPs bind to IREs present in the mRNAs of ferritin and the transferrin receptor, resulting in diminished translation of the ferritin mRNA and increased translation of the transferrin receptor mRNA. Similarly, body iron homeostasis is maintained through the control of intestinal iron absorption. Intestinal epithelia cells sense body iron through the basolateral endocytosis of plasma transferrin. Transterrin endocytosis results in enterocytes whose iron content will depend on the iron saturation of plasma transferrin. Cell iron levels, in turn, inversely correlate with intestinal iron absorption. In this study, we examined the relationship between the regulation of intestinal iron absorption and the regulation of intracellular iron levels by Caco-2 cells. We asserted that IRP activity closely correlates with apical iron uptake and transepithelial iron transport. Moreover, overexpression of IRE resulted in a very low labile or reactive iron pool and increased apical to basolateral iron flux. These results show that iron absorption is primarily regulated by the size of the labile iron pool, which in turn is regulated by the IRE/IRP system. <![CDATA[Zinc in the prevention of Fe2initiated lipid and protein oxidation]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0716-97602000000200014&lng=en&nrm=iso&tlng=en In the present study we characterized the capacity of zinc to protect lipids and proteins from Fe2+-initiated oxidative damage. The effects of zinc on lipid oxidation were investigated in liposomes composed of brain phosphatidylcholine (PC) and phosphatidylserine (PS) at a molar relationship of 60:40 (PC:PS, 60:40). Lipid oxidation was evaluated as the oxidation of cis-parinaric acid or as the formation of 2-thiobarbituric acid-reactive substances (TBARS). Zinc protected liposomes from Fe2+ (2.5-50 muM)-supported lipid oxidation. However, zinc (50 muM) did not prevent the oxidative inactivation of glutamine synthelase and glucose 6-phosphate dehydrogenase when rat brain superntants were oxidized in the presence of 5 muM Fe2+ and 0.5 mM H2O2 .We also studied the interactions of zinc with epicatechin in the prevention of liid oxidation in liposomes. The simulaneous addition of 0.5 muM epicatechin (EC) and 50 muM zinc or EC separately. Zinc (50 muM) also protecte liposomes from the stimulatory effect of aluminum on Fe2+-initiated lipid oxidation. Zinc could play an important role as an antioxidant in biological systems, replacing iron and other metals with pro-oxidant activity from binding sites and interacting with other components of the oxidant defense system. <![CDATA[Ascorbate protects (+)-catechin from oxidation both in a pure chemical system and human plasma]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0716-97602000000200015&lng=en&nrm=iso&tlng=en We evaluated the interaction between ascorbic acid (AA) and (+)-catechin (CTCH) in potassium phosphate solution, pH 7.4 (PPS) and in human plasma. In both systems, the oxidation was started by adding 2,2’-azobis-(2-amidinopropane) clorhidrate (AAPH). The concentrations of AA and CTCH were determined by HPLC using electrochemical detection. In PPS, CTCH was oxidized by AAPH (50 muM), in either the absence or presence of different initial concentrations of AA (25-200 muM). In the presence of AA, CTCH depletion was delayed, an effect that was dependent upon the initial concentration of AA. When 100 muM AA was added after the oxidation had begun, CTCH depletion was arrested for 30 min. The kinetics of AA oxidation by AAPH was also characterized in PPS. AA (100 muM) was completely consumed after 60 min of reaction at 37 muC, in both the absence and presence of 100 mM CTCH. When human plasma was incubated with 50 mM AAPH in the absence of added CTCH, AA was completely consumed after 45-60 min. CTCH did not prevent AA depletion in human plasma at the concentrations tested (10, 50 100 muM). The results point out that AA is able to protect other aqueous soluble antioxidants, e.g.: CTCH <![CDATA[Effect of nitric oxide and plant antioxidants on microsomal content of lipid radicals]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0716-97602000000200016&lng=en&nrm=iso&tlng=en The antioxidant ability of nitric oxide (NO) generated by a chemical donor and of commercially available antioxidant preparations was assayed. SNAP (S-Nitroso-N-acetylpenicilamine) was used as the NO donor, and Ginkgo biloba, wheat and alfalfa preparations were tested. Lipid peroxidation was assayed by EPR employing a reaction system consisting of rat liver microsomes, ADP, FeCl3, NADPH and POBN in phosphate buffer, pH=7.4. In vitro NO exposure decreased microsomal lipid peroxidation in a dose-dependent manner. The dose responsible for inhibiting the microsomal content of lipid radical adducts by 50% (LD50) for SNAP was 550 mu M (NO generation rate 0.1 mu M/min). The addition of 50 mM hemoglobin to the incubation media prevented NO effect on lipid peroxidation. The addition of an amount of the antioxidant preparations equivalent to the LD50 doses inhibited lipid peroxidation by 21, 15, and 33% for wheat, alfalfa, Ginkgo biloba preparations respectively in the presence of 550 mu M SNAP. We detected a decrease in the content of lipid radical adducts after simultaneous supplementation, although it was less than 50%, even when LD50 doses of the products were added. This suggests that NO and the natural antioxidants inhibit lipid peroxidation by a mechanism that has both common and non-shared features <![CDATA[Nitric Oxide: Oxygen Radical Interactions in Atherosclerosis]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0716-97602000000200017&lng=en&nrm=iso&tlng=en Atherosclerosis is one of the most common diseases and the principal cause of death in western civilization. The pathogenesis of this disease can be explained on the basis of the ‘oxidative-modification hypothesis,’ which proposes that low-density lipoprotein (LDL) oxidation represents a key early event. Nitric oxide (.NO) regulates critical lipid membrane and lipoprotein oxidation events by a) contributing to the formation of more potent secondary oxidants from superoxide (i.e.: peroxynitrite), and b) its antioxidant properties through termination reactions with lipid radicals to possibly less reactive secondary nitrogen-containing products (LONO, LOONO). Relative rates of production and steady state concentrations of superoxide and .NO and cellular sites of production will profoundly influence the expression of differential oxidant injury-enhancing and protective effects of .NO. Full understanding of the physiological roles of .NO, coupled with detailed insight into .NO regulation of oxygen radical-dependent reactions, will yield a more rational basis for intervention strategies directed toward oxidant-dependent atherogenic processes <![CDATA[Mitochondrial Function and Nitric Oxide Utilization]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0716-97602000000200018&lng=en&nrm=iso&tlng=en Atherosclerosis is one of the most common diseases and the principal cause of death in western civilization. The pathogenesis of this disease can be explained on the basis of the ‘oxidative-modification hypothesis,’ which proposes that low-density lipoprotein (LDL) oxidation represents a key early event. Nitric oxide (.NO) regulates critical lipid membrane and lipoprotein oxidation events by a) contributing to the formation of more potent secondary oxidants from superoxide (i.e.: peroxynitrite), and b) its antioxidant properties through termination reactions with lipid radicals to possibly less reactive secondary nitrogen-containing products (LONO, LOONO). Relative rates of production and steady state concentrations of superoxide and .NO and cellular sites of production will profoundly influence the expression of differential oxidant injury-enhancing and protective effects of .NO. Full understanding of the physiological roles of .NO, coupled with detailed insight into .NO regulation of oxygen radical-dependent reactions, will yield a more rational basis for intervention strategies directed toward oxidant-dependent atherogenic processes