Carmen V. Ferreira

Violacein: properties and biological activities.

The violet pigment violacein is an indole derivative, isolated mainly from bacteria of the genus Chromobacterium, which exhibits important antitumoural, antimicrobial and antiparasitary properties. Furthermore, the formulation of violacein in different polymeric carriers developed so far offers alternative approaches to overcoming physiological barriers and undesirable physicochemical properties in vivo, thus improving its efficacy.

Cytotoxicity of apigenin on leukemia cell lines: implications for prevention and therapy

Natural-food-based compounds show substantial promise for prevention and biotherapy of cancers including leukemia. In general, their mechanism of action remains unclear, hampering rational use of these compounds. Herein we show that the common dietary flavonoid apigenin has anticancer activity, but also may decrease chemotherapy sensitivity, depending on the cell type. We analyzed the molecular consequences of apigenin treatment in two types of leukemia, the myeloid and erythroid subtypes. Apigenin blocked proliferation in both lineages through cell-cycle arrest in G2/M phase for myeloid HL60 and G0/G1 phase for erythroid TF1 cells. In both cell lines the JAK/STAT pathway was one of major targets of apigenin. Apigenin inhibited PI3K/PKB pathway in HL60 and induced caspase-dependent apoptosis. In contrast, no apoptosis was detected in TF1 cells, but initiation of autophagy was observed. The block in cell cycle and induction of autophagy observed in this erythroleukemia cell line resulted in a reduced susceptibility toward the commonly used therapeutic agent vincristine. Thus, this study shows that although apigenin is a potential chemopreventive agent due to the induction of leukemia cell-cycle arrest, caution in dietary intake of apigenin should be taken during disease as it potentially interferes with cancer treatment.

Phosphoprotein levels, MAPK activities and NFκB expression are affected by fisetin

Flavonoids, polyphenolic phytochemicals, are ubiquitous in plants and are commonly present in the human diet. They may exert diverse beneficial effects, including antioxidant and anticarcinogenic activities. The present study was designed to evaluate three biomolecules that play important roles in the apoptotic process: mitogen-activated protein kinases, protein phosphatases and NFκB, using HL60 cells treated with fisetin as an experimental model. Our results demonstrated that cells treated with fisetin presented high expression of NFκB, activation of MAPK p38 and an increase of phosphoprotein levels; inhibition of enzymes involved in redox status maintenance were also observed. Our findings reinforce the hypothesis that fisetin is likely to exert beneficial and/or toxic actions on cells not through its potential as antioxidant but rather through its modulation of protein kinase and phosphatase signaling cascades. Additionally, our results also indicate that the cellular effects of fisetin will ultimately depend on the cell type and on the extent to which they associate with the cells, either by interactions at the membrane or by uptake into the cytosol.

Inhibition of reverse transcriptase activity of HIV by polysaccharides of brown algae

Brown algae have two kinds of acid polysaccharides present in the extracellular matrix: sulfated fucan and alginic acid. We have previously isolated and characterized fucans from several species of brown seaweed. The characterized fucans from Dictyotaceae are heterofucans containing mainly fucose, galactose, glucose, xylose, and/or uronic acid. The fucan from Fucus vesiculosus is a homofucan containing only sulfated fucose. We assessed the activity of these fucans as inhibitors of HIV from reverse transcriptase (RT). Using activated DNA and template primers poly(rA)-oligo(dT), we found that fucans at a concentration of 0.5-1.0 microg/mL had a pronounced inhibitory effect in vitro on the avian reverse transcriptase, with the exception of xylogalactofucan isolated from Spatoglossum schröederi, which had no inhibitory activity. The alginic acid (1.0 microg/mL) inhibited the reverse transcriptase activity by 51.1% using activated DNA. The inhibitory effect of fucans was eliminated by their desulfation. Furthermore, only xylofucoglucuronan from S. schröederi lost its activity after carboxyreduction. We suggest that fucan activity is not only dependent on the ionic changes but also on the sugar rings that act to spatially orientate the charges in a configuration that recognizes the enzyme, thus determining the specificity of the binding.

Hydroxyapatite surface solubility and effect on cell adhesion.

In living organisms the biological hydroxyapatite is in constant contact with body fluids, such as blood serum and saliva. Thus, dissolution, solubility and precipitation take place as part of the interaction of this material with biological fluids in tissues. In this work we have obtained the solubility constant for the system formed from aqueous solutions in equilibrium with hydroxyapatite and thus indirectly obtained the composition of the modified hydroxyapatite surface. In order to check the effects of this equilibrium and of the modification that the surface of hydroxyapatite suffers in aqueous solutions, we cultured pre-osteoblasts onto hydroxyapatite discs before and after equilibrium. The results revealed key steps of the mechanism for the bioactivity of hydroxyapatite, which are the solubilization of hydroxyapatite and the equilibrium that is formed on the surface. These processes modify the hydroxyapatite surface, whose composition is changed to a new calcium phosphate compound with the chemical formula of CaHPO4. A clear description of the transformations that occur on the surface of hydroxyapatite and of the interplay between these transformations and cell activity are two fundamental aspects of processes in which hydroxyapatite takes part, such as bone substitution, bone remodeling, osteoporosis and caries.

Hedgehog signaling maintains chemoresistance in myeloid leukemic cells

The development of resistance against chemotherapy remains one of the major challenges in the clinical management of leukemia. There is still limited insight into the molecular mechanisms that maintain the chemotherapy-resistant phenotype, despite the obvious clinical relevance that such knowledge would have. In this study, we show that the chemotherapy-resistant phenotype of myeloid leukemia cells correlates with activation of the Hedgehog (Hh) pathway, whereas in chemosensitive cells, such activation is less pronounced. Importantly, the overexpression of Hh pathway components induces chemoprotection and inhibition of the pathway reverts chemoresistance of Lucena-1 cells, apparently by interfering with P-glycoprotein-dependent drug resistance. Our data thus identify the Hh pathway as an essential component of multidrug resistance (MDR) myeloid leukemia and suggest that targeting the Hh pathway might be an interesting therapeutic avenue for overcoming MDR resistance in myeloid leukemia.

Structural and proactive safety aspects of oxidation debris from multiwalled carbon nanotubes

The removal of oxidation debris from the oxidized carbon nanotube surface with a NaOH treatment is a key step for an effective functionalization and quality improvement of the carbon nanotube samples. In this work, we show via infrared spectroscopy and ultrahigh resolution and accuracy mass spectrometry that oxidation debris obtained from HNO(3)-treated multiwalled carbon nanotubes is a complex mixture of highly condensed aromatic oxygenated carbonaceous fragments. We have also evaluated their cytotoxicity by using BALB/c 3T3 mouse fibroblasts and HaCaT human keratinocytes as models. By knowing the negative aspects of dissolved organic carbon (DOC) to the water quality, we have demonstrated the removal of these carbon nanotube residues from the NaOH solution (wastewater) by using aluminium sulphate, which is a standard coagulant agent used in conventional drinking water purification and wastewater treatment plants. Our results contribute to elucidate the structural and proactive safety aspects of oxidation debris from oxidized carbon nanotubes towards a greener nanotechnology.

From immune response to cancer: a spot on the low molecular weight protein tyrosine phosphatase

Abstract.Reversible tyrosine phosphorylation is a key posttranslational regulatory modification of proteins in all eukaryotic cells in normal and pathological processes. Recently a pivotal janus-faced biological role of the low molecular weight protein tyrosine phosphatase (LMWPTP) has become clear. On the one hand this enzyme is important in facilitating appropriate immune responses towards infectious agents, on the other hand it mediates exaggerated inflammatory responses toward innocuous stimuli. The evidence that LMWPTP plays a role in oncological processes has added a promising novel angle. In this review we shall focus on the regulation of LMWPTP enzymatic activity of signaling pathways of different immunological cells, the relation between genetic polymorphism of LMWPTP and predisposition to some type of inflammatory disorders and the contribution of this enzyme to cancer cell onset, growth and migration. Therefore, the LMWPTP is an interesting target for pharmacological intervention, thus modifying both inappropriate cellular immune responses and cancer cell aggressiveness.

Modulation of Src Activity by Low Molecular Weight Protein Tyrosine Phosphatase During Osteoblast Differentiation

Background: Src kinase plays a critical role in bone metabolism, particularly in osteoclasts. However, the ability of Src kinase to modulate the activity of other bone cells is less well understood. In this work, we examined the expression and activity of Src and low molecular weight protein tyrosine phosphatase (LMWPTP) during osteoblast differentiation and assessed the modulation of Src kinase by LMWPTP. Methods: Differentiation of MC3T3-E1 pre-osteoblasts was induced by incubation with ascorbic acid and β-glycerophosphate for up to 28 days. Src phosphorylation and LMWPTP expression were analyzed by immunoblotting. Src dephosphorylation in vitro was assessed by incubating immunoprecipitated Src with LMWPTP followed by assay of the residual Src activity using Sam68 as substrate. The importance of LMWPTP in Src dephosphorylation was confirmed by silencing pre-osteoblasts with siRNA-LMWPTP and then assessing Src phosphorylation. Results: Pre-osteoblast differentiation was accompanied by a decrease in phosphorylation of the activator site of Src and an increase in phosphorylation of the inhibitory site. The expression of total Src was unaltered, indicating that post-translational modifications play a pivotal role in Src function. LMWPTP expression was higher in periods when the activator site of Src was dephosphorylated. LMWPTP dephosphorylated pY527-Src and pY416-Src in vitro, with greater specificity for pY527Src. Activation of LMWPTP produced strong activation of Src mediated by fast dephosphorylation of pY527-Src, followed by slower deactivation of this kinase via dephosphorylation of pY416Src. Conclusion: These results provide new insight into the mechanisms governing the dynamics of Src activity during osteoblast differentiation. A fuller understanding of these mechanisms will improve our knowledge of bone metabolism and of the regulation of Src in other types of cells.

Anti-inflammatory properties of a heparin-like glycosaminoglycan with reduced anti-coagulant activity isolated from a marine shrimp.

The anti-inflammatory properties of a heparin-like compound from the shrimp Litopenaeus vannamei are related. Besides reducing significantly (p<0.001) the influx of inflammatory cells to injury site in a model of acute inflammation, shrimp heparin-like compound was able to reduce the matrix metalloproteinase (MMPs) activity in the peritoneal lavage of inflamed animals. Moreover, this compound also reduced almost 90% the activity of MMP-9 secreted by human activated leukocytes. Negligible anti-coagulant activities in aPPT assay and a poor bleeding potential make this compound a better alternative than mammalian heparin as a possible anti-inflammatory drug.