Lead neurotoxicity: effects on brain nitric oxide synthase

Lead (Pb), a ubiquitous and potent neurotoxicant, induces several neurophysiological and behavioural changes, while Pb alters the function of multiple organs and systems, it primarily affects the central nervous system. In human adults, encephalopathy resulting from Pb intoxication is often characterized by sleeplessness, poor attention span, vomiting, convulsions and coma; in children, Pb-induced encephalopathy is associated with mental dullness, vomiting, irritability and anorexia; diminished cognitive function resulting in a mental deficit has been also observed during Prolonged exposure to Pb. Pb can produce oxidative stress, disrupt the blood–brain barrier and alter several Ca²⁺-dependent processes, including physiological processes that involve nitric oxide synthesis on central nervous system in development and adult animals. This review summarizes recent evidence showing that Pb can interfere with the production of nitric oxide and can disrupt the function of nitric oxide synthase. Lead interferes with nitric oxide-related physiological mechanisms, and Pb neurotoxicity may affect processes involved in learning and memory.     

Functional and structural analysis of the internal ribosome entry site present in the mRNA of natural variants of the HIV-1

The 5'untranslated regions (UTR) of the full length mRNA of the HIV-1 proviral clones pNL4.3 and pLAI, harbor an internal ribosomal entry site (IRES). In this study we extend this finding by demonstrating that the mRNA 5'UTRs of natural variants of HIV-1 also exhibit IRES-activity. Cap-independent translational activity was demonstrated using bicistronic mRNAs in HeLa cells and in Xenopus laevis oocytes. The possibility that expression of the downstream cistron in these constructs was due to alternative splicing or to cryptic promoter activity was ruled out. The HIV-1 variants exhibited significant 5'UTR nucleotide diversity with respect to the control sequence recovered from pNL4.3. Interestingly, translational activity from the 5'UTR of some of the HIV-1 variants was enhanced relative to that observed for the 5'UTR of pNL4.3. In an attempt to explain these findings we probed the secondary structure of the variant HIV-1 5'UTRs using enzymatic and chemical approaches. Yet subsequent structural analyses did not reveal significant variations when compared to the pNL4.3-5'UTR. Thus, the increased IRES-activity observed for some of the HIV-1 variants cannot be ascribed to a specific structural modification. A model to explain these findings is proposed.     

Lateral orbitofrontal cortex involvement in initial negative aesthetic impression formation

It is well established that aesthetic appreciation is related with activity in several different brain regions. The identification of the neural correlates of beauty or liking ratings has been the focus of most prior studies. Not much attention has been directed towards the fact that humans are surrounded by objects that lead them to experience aesthetic indifference or leave them with a negative aesthetic impression. Here we explore the neural substrate of such experiences. Given the neuroimaging techniques that have been used, little is known about the temporal features of such brain activity. By means of magnetoencephalography we registered the moment at which brain activity differed while participants viewed images they considered to be beautiful or not. Results show that the first differential activity appears between 300 and 400 ms after stimulus onset. During this period activity in right lateral orbitofrontal cortex (lOFC) was greater while participants rated visual stimuli as not beautiful than when they rated them as beautiful. We argue that this activity is associated with an initial negative aesthetic impression formation, driven by the relative hedonic value of stimuli regarded as not beautiful. Additionally, our results contribute to the understanding of the nature of the functional roles of the lOFC.     

Manganese and ammonia interactions in the brain of cirrhotic rats: effects on brain ammonia metabolism

Hepatic encephalopathy is a major complication of cirrhosis. Ammonia and manganese have been associated with hepatic encephalopathy underlying mechanisms. Motor impairment and brain edema are common signs of hepatic encephalopathy. In the present study a model of liver damage in rats was combined with ammonia and manganese exposure to evaluate the role of these substances separately and their interactions on brain glutamine, water content and motor coordination. Additionally, we explored brain levels of each substance -Mn and ammonia- in the presence or absence of the other. Liver damage was induced by bile duct ligation. Rats were exposed to MnCl₂ in drinking water (1 mg Mn/ml) and to ammonia in chow pellets containing 20% ammonium acetate (w/w). As expected, manganese and ammonia levels increased in the brain of cirrhotic rats exposed to these substances; in these animals, glutamine brain levels also increased and positively correlated with tissue water content in cortex. A three way-ANOVA showed that manganese favored ammonia and glutamine accumulation in brain, and possibly their subsequent deleterious effects, as evidenced by the fact that manganese and ammonia accumulation in the brain of cirrhotic rats severely affected motor function. These results suggest that even when controlling ammonia levels in cirrhotic patients, reduction of manganese intake is also a potential strategy to be considered in clinical practice.     

Redox-changes associated with the glutathione-dependent ability of the Cu(II)-GSSG complex to generate superoxide

The intracellularly-occurring Cu(I)-glutathione complex (Cu(I)-[GSH](2)) has the ability to reduce molecular oxygen into superoxide. Removal of such radicals leads to the irreversible conversion of Cu(I)-[GSH](2) into the redox-inactive Cu(II)-GSSG complex. The present study addressed the potential of reduced glutathione, ascorbate and superoxide to reductively regenerate Cu(I)-[GSH](2) from Cu(II)-GSSG, and investigated the redox changes involved in such process. Results show that: (i) among the three tested reductants, only GSH is able to reduce the Cu(II) bound to GSSG; (ii) during the reduction of Cu(II)-GSSG, a Cu(I)-GSSG intermediate would be formed (supported here by Cu(I) and GSSG recovery data and by NMR studies); (iii) when GSH is present in a molar excess equal or greater than 1:3, the reduction of Cu(II)-GSSG into Cu(I)-[GSH](2) is quantitative and complete. Under such conditions, the Cu(II)-GSSG complex acquires a superoxide-generating capacity which is identical to that seen with the Cu(I)-[GSH](2) complex. Within cells, the concentrations of GSH are at least 2- to 3-fold order of magnitude higher than those expected for the Cu(II)-GSSG complex. Thus, we postulate that the interaction between GSH and Cu(II)-GSSG could be seen as a potential mechanism to regenerate continuously the Cu(I)-[GSH](2) complex and thereby affect the ability of the latter to generate superoxide.     

Generation of superoxide radicals by copper–glutathione complexes: Redox-consequences associated with their interaction with reduced glutathione

The interaction between Cu²⁺ ions and GSH molecules leads to the swift formation of the physiologically occurring Cu(I)–[GSH]₂ complex. Recently, we reported that this complex is able to reduce molecular oxygen into superoxide in a reversible reaction. In the present study, by means of fluorescence, luminescence, EPR and NMR techniques, we investigated the superoxide-generating capacity of the Cu(I)–[GSH]₂ complex, demonstrated the occurrence and characterized the chemical nature of the oxidized complex which is formed upon removing of superoxide radicals from the former reaction, and addressed some of the redox consequences associated with the interaction between the Cu(I)–[GSH]₂ complex, its oxidized complex form, and an in-excess of GSH molecules. The interaction between Cu(I)–[GSH]₂ and added GSH molecules led to an substantial exacerbation of the ability of the former to generate superoxide anions. Removal of superoxide from a solution containing the Cu(I)–[GSH]₂ complex, by addition of Tempol, led to the formation and accumulation of Cu(II)–GSSG. Interaction between the latter complex and GSH molecules permitted the re-generation of the Cu(I)–[GSH]₂ complex and led to a concomitant recovery of its superoxide-generating capacity. Some of the potential redox and biological implications arising from these interactions are discussed.     

Cytogenotoxicity biomarkers in fat snook Centropomus parallelus from Cananéia and São Vicente estuaries, SP, Brazil

The aquatic environment receives many contaminants that can induce damages at the molecular, biochemical, cellular and physiological levels. Centropomus parallelus, an important food resource for local populations, is a predator fish that feeds on small fishes and benthic invertebrates, thus being vulnerable to the bioconcentration and biomagnification processes. This study aimed to evaluate cytogenotoxic responses in erythrocytes from C. parallelus juveniles collected in the Cananéia and São Vicente estuaries, both in winter and in summer. After anesthesia, blood samples were collected by caudal puncture. Blood smears were prepared on glass slides and stained with May-Grünwald-Giemsa dye. Two thousand cells were analyzed per slide (1000x), and nuclear abnormalities (NA) and micronuclei (MN) were scored. The São Vicente sample showed MN and NA frequencies (%/1000 cells) of 0.325 and 3.575, in winter, and of 0.125 and 2.935 in summer respectively; the Cananéia sample showed frequencies of 0.0325 and 0.03, in winter, and of 0.065 and 0.355 in summer, respectively. The rates found in São Vicente were significantly higher than those found in Cananéia, evidencing that the levels of pollution in that estuary were high enough to induce genetic damages.     

BioGPS: an extensible and customizable portal for querying and organizing gene annotation resources

Online gene annotation resources are indispensable for analysis of genomics data. However, the landscape of these online resources is highly fragmented, and scientists often visit dozens of these sites for each gene in a candidate gene list. Here, we introduce BioGPS http://biogps.gnf.org, a centralized gene portal for aggregating distributed gene annotation resources. Moreover, BioGPS embraces the principle of community intelligence, enabling any user to easily and directly contribute to the BioGPS platform.     

Crystal Structure of a Yeast Aquaporin at 1.15 Å Reveals a Novel Gating Mechanism

Aquaporins are transmembrane proteins that facilitate the flow of water through cellular membranes. An unusual characteristic of yeast aquaporins is that they frequently contain an extended N terminus of unknown function. Here we present the X-ray structure of the yeast aquaporin Aqy1 from Pichia pastoris at 1.15 Å resolution. Our crystal structure reveals that the water channel is closed by the N terminus, which arranges as a tightly wound helical bundle, with Tyr31 forming H-bond interactions to a water molecule within the pore and thereby occluding the channel entrance. Nevertheless, functional assays show that Aqy1 has appreciable water transport activity that aids survival during rapid freezing of P. pastoris. These findings establish that Aqy1 is a gated water channel. Mutational studies in combination with molecular dynamics simulations imply that gating may be regulated by a combination of phosphorylation and mechanosensitivity.