Edgar Zenteno

Chemical characterization of root exudates from rice (Oryza sativa) and their effects on the chemotactic response of endophytic bacteria

Root exudates represent an important source of nutrients for microorganisms in the rhizosphere and seem to participate in early colonization inducing chemotactic responses of rhizospheric bacteria. We characterized the root exudates collected from rice plantlets cultured under hydroponic conditions and assessed their effects on the chemotaxis of two strains of endophytic bacteria, Corynebacterium flavescens and Bacillus pumilus, collected from the rice rhizosphere. We compared these chemotactic effects on endophytic bacteria with those on two strains of plant-growth-promoting bacteria, Azospirillum brasilense (isolated from the corn rhizosphere) and Bacillus sp. (from the rice rhizosphere). The root exudates were collected at different time intervals. The highest concentration and diversity of amino acids and carbohydrates were found during the first 2 weeks after seeding. Histidine, proline, valine, alanine, and glycine were the main amino acid residues identified during the 4 weeks of culture. The main carbohydrates identified were glucose, arabinose, mannose, galactose, and glucuronic acid. The chemotactic responses of the analyzed endophytic bacteria to root exudates were 3.9 to 5.1 times higher than those of A. brasilense and 2.2 to 2.8 times higher than Bacillus sp. Our results indicate that rice exudates may induce a higher chemotactic response for endophytic bacteria than for other bacterial strains present in the rice rhizosphere.

Review: Immunity mechanisms in crustaceans

Crustacean aquaculture represents a major industry in tropical developing countries. As a result of high culture densities and increasing extension of aquaculture farms, the presence of diseases has also increased, inducing economic losses. Invertebrates, which lack adaptive immune systems, have developed defense systems that respond against antigens on the surface of potential pathogens. The defense mechanisms of crustaceans depend completely on the innate immune system that is activated when pathogen-associated molecular patterns are recognized by soluble or by cell surface host proteins, such as lectins, antimicrobial, clotting, and pattern recognition proteins, which, in turn, activate cellular or humoral effector mechanisms to destroy invading pathogens. This work is aimed at presenting the main characteristics of the crustacean proteins that participate in immune defense by specific recognition of carbohydrate containing molecules, i.e. glycans, glycolipids, glycoproteins, peptidoglycans, or lipopolysaccharides from Gram-negative and Gram-positive bacteria, viruses, or fungi. We review some basic aspects of crustacean effector defense processes, like agglutination, encapsulation, phagocytosis, clottable proteins, and bactericidal activity, induced by these carbohydrate-driven recognition patterns.

Neuroprotective effect of alpha-asarone on spatial memory and nitric oxide levels in rats injected with amyloid-β(25-35).

The chemical alpha-asarone is an important active substance of the Acori graminei rhizome (AGR). It has pharmacological effects that include antihyperlipidemic, antiinflammatory, and antioxidant activity. Our aim was to study the effects alpha-asarone on nitric oxide (NO) levels in the hippocampus and temporal cortex of the rat after injection of the fraction 25-35 from amyloid-beta (Abeta((25-35))). In addition we examined the working spatial memory in an eight-arm radial maze. Our results showed a significant increase of nitrites in the hippocampus and temporal cortex of Abeta((25-35))-treated rats. Other evidence of neuronal damage was the expression of a glial-fibrillar-acid protein and a silver staining. There were impairments in the spatial memory evaluated in the eight-arm radial maze. We wanted to determine whether alpha-asarone improves the memory correlated with NO overproduction and neuronal damage caused by the injection of Abeta((25-35)) into rats. Then animals received a 16-day treatment of alpha-asarone before the Abeta((25-35)) injection. Our results show a significant decrease of nitrite levels in the hippocampus and temporal cortex, without astrocytosis and silver-staining cells, which correlates with memory improvement in the alpha-asarone-treated group. Our results suggest that alpha-asarone may protect neurons against Abeta((25-35))-caused neurotoxicity by inhibiting the effects of NO overproduction in the hippocampus and temporal cortex.

The activation of CD14, TLR4, and TLR2 by mmLDL induces IL-1β, IL-6, and IL-10 secretion in human monocytes and macrophages

Atherosclerosis is considered a chronic inflammatory disease in which monocytes and macrophages are critical. These cells express CD14, toll-like receptor (TLR) 2, and TLR4 on their surfaces, are activated by minimally modified low-density lipoprotein (mmLDL) and are capable of secreting pro-inflammatory cytokines. The aim of this research was thus to demonstrate that the activation of CD14, TLR2, and TLR4 by mmLDL induces the secretion of cytokines.MethodsHuman monocytes and macrophages were incubated with monoclonal antibodies specific for CD14, TLR4, and TLR2 prior to stimulation with mmLDL. Cytokine secretion was then compared to that observed upon mmLDL stimulation in untreated cells.ResultsStimulation with mmLDL induced the secretion of pro-inflammatory cytokines. Blocking CD14 in monocytes inhibited secretion of interleukin (IL)-1β (72%), IL-6 (58%) and IL-10 (63%), and blocking TLR4 inhibited secretion of IL-1β by 67%, IL-6 by 63% and IL-10 by 60%. Blocking both receptors inhibited secretion of IL-1β by 73%, IL-6 by 69% and IL-10 by 63%. Furthermore, blocking TLR2 inhibited secretion of IL-1β by 65%, IL-6 by 62% and IL-10 by 75%. In macrophages, we found similar results: blocking CD14 inhibited secretion of IL-1β by 59%, IL-6 by 52% and IL-10 by 65%; blocking TLR4 inhibited secretion of IL-1β by 53%, IL-6 by 63% and IL-10 by 61%; and blocking both receptors inhibited secretion of IL-1β by 69%, IL-6 by 67% and IL-10 by 65%. Blocking TLR2 in macrophages inhibited secretion of IL-1β by 57%, IL-6 by 40% and IL-10 by 72%.ConclusionOur study demonstrates that CD14, TLR4, and TLR2 participate in the immune response against mmLDL by inducing the production of pro-inflammatory cytokines in both monocytes and macrophages. These findings suggest that the activation of these receptors by mmLDL contributes to the inflammatory process of atherosclerosis.

Effect of glycine in streptozotocin-induced diabetic rats

Inadequate utilization of glucose in diabetes mellitus favors diverse metabolic alterations that play a relevant role in the physio-pathology of chronic complications of this disease. Streptozotocin-induced diabetic rats were treated daily with glycine (130 mM as optimal concentration) or taurine (40 mM) for six months. Groups of diabetic rats without treatment were used as controls. Glucose, total cholesterol, triacylglycerol, and glycated hemoglobin were determined periodically after inducing diabetes. Rats were killed after 6 months of treatment and histological analyses were performed. Diabetic groups that received glycine or taurine showed significant lower concentrations of glucose, total cholesterol, triacylglycerol, and glycated hemoglobin than diabetic control rats (P<0.05) after 6 months treatment. Histological analyses of diabetic rats showed pancreatic atrophy and necrosis, vacuolization, decrease of beta cells, and diffuse glomerulosclerosis. Diabetic rats treated with glycine or taurine showed less enlargement of the glomerular basal membrane than control diabetic rats. Our results suggest that glycine and taurine reduced the alterations induced by hyperglycemia in streptozotocin-induced diabetic rats probably due to inhibition of oxidative processes.

Amyloid-β25–35 impairs memory and increases NO in the temporal cortex of rats

beta-Amyloid plays an important role in the neurodegeneration process of Alzheimers disease (AD), but its neurotoxic mechanisms are not clear. It has been associated with the increase of oxidative stress and cognitive impairment because the beta-amyloid peptide 25-35 (Abeta((25-35))) has the critical neurotoxic properties of the full-length Abeta(1-42). Our present study shows the role of Abeta((25-35)) when injected into the temporal cortex on the nitric oxide pathways, 3-nitrotyrosine, neuronal death, and the spatial memory of rats 1 month after the injection. Our data showed that Abeta((25-35)) increases oxidative stress, causes neuronal damage, and decreases spatial memory in rats. Notably, the injection of the fraction Abeta((25-35)) caused an increase of nNOS and iNOS immunoreactivity in the temporal cortex and hippocampus. We demonstrated a significant increase of reactive astrocytosis, which was accompanied by neuronal damage in the temporal cortex and hippocampus of rats injected with Abeta((25-35)). These data suggest that the fraction Abeta((25-35)) injected into the temporal cortex might contribute to understanding the role of nitric oxide on the biological changes related to the neuropathological progression and the memory impairment in AD.

Participation of a sialic acid-specific lectin from freshwater prawn Macrobrachium rosenbergii hemocytes in the recognition of non-self cells

Phagocytic activity of circulating hemocytes from freshwater prawns is mediated by a small group of granulocytes. Recognition of nonself cells by these cells seems to be mediated by two independent mechanisms: specific, via O-acetylsialic acid, as well as N-acetylated sugars on recognized cells and a nonspecific one. Both mechanisms show differences in their optimal temperature and time differences for activity. Hemocytes with phagocytic activity interact positively with rabbit IgG raised against the serum lectin. Attempts to elucidate the nature of the membrane-lectin on hemocytes performed by electroimmunotransfer blot assays on cell lysates indicates the presence of two major proteins with a molecular weight of 68-72 kDa. Electron microscopy revealed a regular distribution of lectin on hemocyte plasma membranes. Our results suggest the active participation of a membrane lectin in the recognition of nonself.

Altered glycosylation pattern of proteins in Alzheimer disease

Abstract. Post-translational modifications due to glycosylation of proteins in human brains from patients with Alzheimer disease (AD) were analyzed using lectin histochemistry. Results indicate a significant increase in the production of Oglycosylated (containing Galβ1,3GalNAcα1,0 Ser/Thr or GalNAcα1,0 Ser/Thr) proteins in neuritic plaques and neurofibrillary tangles which are the major histopathological hallmarks of AD brains. These alterations were determined by positive labelling with lectins obtained from Amaranthus leucocarpus(ALL) and Macrobrachium rosenbergii (MRL) respectively. Immunohistochemistry indicated that the lectin-staining labelled specifically both neurofibrillary tangles and neuritic plaques. In contrast, lectins labelling was restricted to microvessels in normal control brains. These results provide evidence that modifications of the specific glycosylation patterns are closely related with the presence of the hallmark lesions of this disease, suggesting that an abnormal enzymatic processing of proteins may be an early event in the neuronal degeneration which characterises AD

Antioxidant effects of Epicatechin on the hippocampal toxicity caused by Amyloid-beta 25-35 in rats

Amyloid-beta is involved in neurodegeneration in Alzheimers disease. The Amyloid-beta fraction 25-35 (Amyloid-beta 25-35) is believed to cause neurotoxicity through oxidative stress. We evaluated the antioxidant effects of Epicatechin on the Abeta25-35-caused hippocampal toxicity in vivo. Biochemical and histological evaluations, and learning and memory tasks, were assessed. Amyloid-beta 25-35 (100 microM/microL) or vehicle was injected into the CA1 hippocampal region of the rat 5 h after a single oral dose of Epicatechin (30 mg/kg). Lipid peroxidation and reactive oxygen species formation were measured in Amyloid-beta- and Amyloid-beta-Epicatechin-treated groups at 2 h and 24 h after dosing and formation of the lesion. There was an increase in lipid peroxidation and reactive oxygen species formation at 2-h and 24-h postlesion. Learning and memory tests were made 27-30 days after surgery in independent groups under the same experimental conditions. Immunohistochemical detection of glial-fibrilar acidic protein (GFAP) was evaluated in hippocampal tissues from the animals 30-days postsurgery. Amyloid-beta 25-35 caused a significant increase in lipid peroxidation and reactive oxygen species and a decrease in memory skills. In addition, hippocampal tissues from Amyloid-beta 25-35-treated animals showed an increased immunoreactivity against GFAP. In contrast, animals pretreated with Epicatechin had a significant decrease in lipid peroxidation and reactive oxygen species and an improvement in memory skills. GFAP immunoreactivity was also decreased. Our results showed that Amyloid-beta 25-35-caused oxidative damage of the hippocampus was blocked by the administration of Epicatechin.

Bacterial agglutination by the sialic acid specific serum lectin from Macrobrachium rosenbergii

We have isolated a serum lectin from the freshwater prawn, Macrobrachium rosenbergii that agglutinates Bacillus cereus and Aeromona sp. This lectin also agglutinates other bacteria such as Pasteurella haemolytica biotype A (capsular serotype 12), several serotypes from P. multocida and Staphylococcus aureus and to a lesser extent Escherichia coli and Salmonella arizona.Lectin recognition of well known polysaccharide components seems to involve several bacterial O-keto and O-methyl containing sugars, the N-acetyl-sugar residues and teichcoic from the polysaccharide cell wall.