Biomedical subjects

Amandio Vieira

Publications and source records attributed to Amandio Vieira.

10 recordsLinked to original sources

PubMed2006

DNA methylation, riboswitches, and transcription factor activity: fundamental mechanisms of gene-nutrient interactions involving vitamins.

Nutrient-gene interactions occur with a variety of nutrients including some minerals, vitamins, polyunsaturated fatty acids and other lipids. Fundamental molecular mechanisms that underlie many of the effects of nutrients on gene expression are presented herein. Two of the mechanisms described influence gene transcription: DNA methylation and transcription factor activation. Another mechanism, riboswitching, can regulate gene expression at different levels, for example, at the mRNA translation level. The first two mechanisms are widely distributed across animal phyla. Riboswitches are documented primarily in more primitive organisms, but may prove to be of wider relevance. Riboswitches are known for several vitamins; those involving thiamine are presented here. The role of folates and retinoids in DNA methylation and transcriptional factor (nuclear retinoid receptor) activities, respectively, is presented in the context of cell proliferation and differentiation, and related physiological or pathological effects during embryogenesis and cancer.

Animals↗

PubMed2006

Protective activities of Vaccinium antioxidants with potential relevance to mitochondrial dysfunction and neurotoxicity.

Both the neurotransmitter dopamine (DA) and a neurotoxic metabolite, 6-hydroxy DA, can be oxidized to generate hydrogen peroxide and other reactive species (ROS). ROS promote oxidative stress and have been implicated in dopaminergic neurodegeneration, e.g., Parkinson's disease (PD). There is also evidence for a relation between catecholamine-mediated oxidative damage in dopaminergic neurons and the effects of these neurotransmitters on the redox state of cytochrome c (Cytc). In neurons and other cells, oxidative stress may be enhanced by abnormal release of Cytc and other mitochondrial proteins into the cytoplasm. Cytc release can result in apoptosis; but sub-apoptogenic-threshold release can also occur, and may be highly damaging in the presence of DA metabolites. Loss of mitochondrial membrane integrity, a pathological situation of relevance to several aging-related neurodegenerative disorders including PD, contributes to release of Cytc; and the level of such release is known to be indicative of the extent of mitochondrial dysfunction. In this context, we have used a Cytc-enhanced 6-hydroxy DA oxidation reaction to gauge dietary antioxidant activities. Anthocyanin-rich preparations of Vaccinium species (Vaccinium myrtillus, Vaccinium corymbosum, and Vaccinium oxycoccus) as well as a purified glycosylated anthocyanidin were compared. The most potent inhibition of oxidation was observed with V. myrtillus preparation: 50% inhibition with 7 microM of total anthocyanins. This activity was 1.5-4 times higher than that for the other preparations or for the purified anthocyanin. Ascorbate (Vitamin C), at up to 4-fold higher concentrations, did not result in significant inhibition in this assay. Antioxidant activity in the assay correlated strongly (r2>0.91, P<0.01) with reported Vaccinium content of anthocyanins and total cyanidins, but not quercetin or myricetin. The results provide evidence for the high potency of anthocyanins towards a potentially neurotoxic reaction, and provide a basis for in vivo testing of these flavonoids and their physiological metabolites in the context of neuro- and mitochondrio-protective effects.

Animals↗

PubMed2006

Comparative genetic mutation frequencies based on amino acid composition differences.

Genetic variation inferred from large-scale amino acid composition comparisons among genomes and chromosomes of several species, Saccharomyces cerevisiae, Drosophila melanogaster, Ceanorhabditis elegans, H. sapiens, is shown to be correlated (highest, r(2)=0.9855, p<0.01) with reported mutation rates for various genes in these species. This study, based largely on pseudogene data, helps to establish reference mutation frequencies that are likely to be representative of overall genome mutation rates in each of the species examined, and provides further insight into heterogeneity of mutation rates among genomes.

Amino Acid Sequence↗

PubMed2006

Oxidative stress disrupts internalization and endocytic trafficking of transferrin in a human malignant keratinocyte line.

Oxidative stress is involved in epidermal cell pathology. One potential mechanism for this toxicity that has previously not been explored in epidermal cells involves modulation of endocytic trafficking and the implications that such modulation can have for altered cell function. The effects of oxidative stress on endocytic trafficking are not well understood, particularly relating to how general or cell-type specific such effects may be. With induction of oxidative stress by hydrogen peroxide, for example, both impaired and enhanced cell-surface binding and endocytic trafficking have been reported for transferrin (Tf), a circulatory iron-carrier protein. The objective of the current study was to characterize the effect of oxidative stress on internalization and endocytic trafficking of Tf in an epidermoid cell line (A431). Evidence is presented for a significant dose-dependent impairment of cellular Tf internalization after treatment with hydrogen peroxide over a wide range of concentrations from 0.06 to 5.8 mM. Scatchard analysis of binding revealed that peroxide treatments resulted in a large decrease, more than fourfold, in the number of cell-surface Tf-binding sites (Bmax) but little change in the dissociation constant (Kd). With respect to endocytic trafficking of Tf, evidence is presented that transport of internalized transferrin back out of the cell (i.e., Tf recycling) is significantly impaired as a result of oxidative stress at all the peroxide concentrations tested. The oxidative stress-dependent changes in endocytic trafficking in these malignant human keratinocytes are compared with those reported for other cell types.

Binding Sites↗

PubMed2006

Evidence for a specific cell membrane retinol-binding protein transport mechanism in a human keratinocyte line.

The epidermis is highly sensitive to retinoids, and vitamin A (retinol) is a critical factor in the regulation of skin cell differentiation and proliferation. Despite extensive knowledge of retinoid-mediated gene transcription effects on epidermal cells and evidence for retinoid-mediated suppression of carcinogenesis in skin, basic transport events, especially cellular uptake, of this vitamin remain poorly understood and controversial. Herein, evidence is presented for receptor-mediated uptake of retinol-binding protein, RBP, the specific circulatory vitamin A carrier, in the A431 human epidermal cell line. Cellular RBP uptake was significantly inhibited by anti-RBP IgG. Addition of transthyretin (TTR), a circulatory protein that can interact with RBP, to the internalization assay also significantly reduced RBP uptake to 49.4+/-4.6% (+/- SEM) of control values (p<0.01). RBP uptake was impaired by sucrose, a known inhibitor of early endocytosis, but not significantly affected by a disruptor of later trafficking events, chlorpromazine. Binding analysis indicated saturable RBP binding to the cell surface and a total of about 94,000 binding sites/cell. Based on dissociation constants, two RBP binding sites were detected with a 50-fold affinity difference: 0.7 and 35.0 nM, with 12,000 and 82,000 receptors/cell, respectively. These results indicate that high affinity RBP receptors capable of internalizing RBP independently of TTR exist in these malignant keratinocytes, and that TTR influences binding of RBP to its putative receptor(s). Overall, the data establish membrane transport parameters for RBP, and provide a basis for examining modulation of vitamin A endocytosis that may accompany changes in proliferation or differentiation state of epidermal cells.

Antibodies, Monoclonal↗

PubMed2005

Modeling robust oscillatory behavior of the hypothalamic-pituitary-adrenal axis.

A mathematical model of the hypothalamic-pituitary-adrenal (HPA) axis of the human endocrine system is proposed. This new model provides an improvement over previous models by introducing two nonlinear factors with physiological relevance: 1) a limit to gland size; 2) rejection of negative hormone concentrations. The result is that the new model is by far the most robust; e.g., it can tolerate at least -50% and +100% perturbations to any of its parameters. This high degree of robustness allows one, for the first time, to model features of the system such as circadian rhythm and response to hormone injections. In addition, relative to its closest predecessor, the model is simpler; it contains only about half of the parameters, and yet achieves more functions. The new model provides opportunities for teaching endocrinology within a biological or medical school context; it may also have applications in modeling and studying HPA axis disorders, for example, related to gland size dynamics, abnormal hormone levels, or stress influences.

Adrenal Cortex↗

PubMed2004

A cytochrome c-enhanced peroxidation reaction with potential use in screening dietary antioxidants.

Reactive oxygen species (ROS) that result from events such as cellular respiration can cause damage to biological molecules and tissues. A variety of endogenous and dietary antioxidants function in moderating the extent of oxidative damage in the body. In this report, a pro-oxidant system is presented as an assay for screening possible antioxidant activities of dietary factors. The assay reaction involves peroxidatic oxidation of the redox indicator N,N,N',N'-tetramethyl-1,4-phenylenediamine (TMPD). It is shown that the reaction rate is enhanced by up to 10-fold in the presence of cytochrome c (cyt c), a mitochondrial electron transport protein. The extent to which selected dietary antioxidant factors inhibit the cytochrome c-enhanced peroxidatic oxidation of TMPD is also reported. Considering the known pathological consequences of mitochondrial membrane disruption and cytochrome c release in the cell, this reaction and assay may be of pathological and therapeutic relevance.

Antioxidants↗

PubMed2003

A novel method for monitoring surface membrane trafficking on hippocampal acute slice preparation.

Protein trafficking has attracted considerable attention as a potential regulator of neuronal plasticity. Therefore, it is of interest to study the mechanism involved in protein trafficking in experimental paradigms commonly used in this context. Here, we present a method for cell surface protein biotinylation in the acute hippocampal slice, the most commonly used preparation for electrophysiological recordings. We validated this procedure with two previously characterized cell surface receptors, glutamate receptor subunit A (GluR A) and the transferrin receptor (TfR). We observed a glutamate-dependent increase in the degradation of surface GluR A, whereas the TfR did not show significant degradation in the time window used. In addition, the presented method offers the opportunity to study processes such as internalisation and recycling, and can also be applied to examine the effect of normal and pathological patterns of activity on membrane protein trafficking in commonly used preparations for electrophysiological recordings.

Animals↗

PubMed2002

Comparative 17beta-estradiol response and lipoprotein interactions of an avian apolipoprotein.

Apolipoprotein D (apo D), a member of the lipocalin protein family, has been identified and cloned in several mammalian species; its physiological functions, however, remain poorly understood. As with other lipocalins, apo D can bind small hydrophobic ligands. Lipids and hormones, such as cholesterol, arachidonic acid, and progesterone can bind to apo D; but the physiological significance of these interactions is not clear. We previously reported the existence of an avian (Gallus domesticus) apo D-like protein, and indicated a possible role for it in reproduction. This report provides a further comparative characterization of this avian protein. Evidence is presented that the putative avian apo D, like some (e.g., human) but not other (e.g., rat) mammalian apo Ds, preferentially associates with high density lipoproteins (HDL) in the circulation. These results confirm the apolipoprotein nature of the avian apo D-like protein, and indicate that it has conserved the HDL-interaction property of some mammalian apo Ds. The response of circulatory levels of the avian protein to 17beta-estradiol treatment is also examined. Large estrogen-dependent increases are known to occur in the circulatory levels of some avian apolipoproteins, such as apo B and vitellogenins, that represent major yolk precursors and nutrient sources for the embryo. Although the avian apo D-like protein is also a known yolk precursor, the minor estrogen-dependent increase observed for this apolipoprotein (less than 7% that of apo B) distinguishes it from the major yolk-precursor apolipoproteins. The response of the avian apo D-like protein to 17beta-estradiol is more like that of other yolk precursor proteins that transport regulatory molecules such as vitamin A and thyroid hormones.

Animals↗

PubMed2002

The small GTPase Rab22 interacts with EEA1 and controls endosomal membrane trafficking.

Rab22a is a small GTPase that is expressed ubiquitously in mammalian tissues and displays the highest sequence homology to Rab5. In BHK-21 cells, overexpression of the wild-type Rab22a caused formation of abnormally large vacuole-like structures containing the early-endosomal antigen EEA1 but not Rab11, a marker of recycling endosomes or the late-endosomal/lysosomal markers LAMP-1 and lyso-bis-phosphatidic acid. In HeLa cells, overexpressed Rab22a was found on smaller EEA1-positive endosomes, but a portion of the protein was also found in the Golgi complex. Using the yeast two-hybrid system and a biochemical pull-down assay, the GTP-bound form of Rab22a was found to interact with the N-terminus of EEA1. In HeLa cells overexpressing Rab22a or its mutants affected in the GTPase cycle, no significant changes were observed in the uptake of Alexa-transferrin. However, the GTPase-deficient Rab22a Q64L mutant caused a redistribution of transferrin-positive endosomes to the leading edges of cells and a fragmentation of the Golgi complex. In BHK cells, the Q64L mutant caused the accumulation of a fluid phase marker, TRITC-dextran, and a lysosomal hydrolase, aspartylglucosaminidase, in abnormal vacuole-like structures that contained both early and late endosome markers. Both the wild-type Rab22a and the Q64L mutant were found to interfere with the degradation of EGF. These results suggest that Rab22a may regulate the dynamic interactions of endosomal compartments and it may be involved in the communication between the biosynthetic and early endocytic pathways.

Animals↗