Legume nodule senescence: roles for redox and hormone signalling in the orchestration of the natural aging process

Research on legume nodule development has contributed greatly to our current understanding of plant-microbe interactions. However, the factors that orchestrate root nodule senescence have received relatively little attention. Accumulating evidence suggests that redox signals contribute to the establishment of symbiosis and senescence. Although degenerative in nature, nodule senescence is an active process programmed in development in which reactive oxygen species (ROS), antioxidants, hormones and proteinases have key roles. Nodules have high levels of the redox buffers, ascorbate and glutathione, which are important in the nodulation process and in senescence. These metabolites decline with N-fixation as the nodule ages but the resultant decrease in redox buffering capacity does not necessarily lead to enhanced ROS or oxidative stress. We propose models by which ROS and antioxidants interact with hormones such as abscisic acid in the orchestration of nodule senescence.     

Aspirin inhibits serine phosphorylation of insulin receptor substrate 1 in growth hormone treated animals

In this study, we demonstrate that pretreatment with aspirin inhibits GH-induced insulin resistance. GH was observed to lead to serine phosphorylation of IRS-1, a phenomenon which was reversed by aspirin in liver, muscle and WAT in parallel with a reduction in JNK activity. In addition, our data show an impairment of insulin activation in the IR/IRS/PI(3)kinase pathway and a reduction in IRS-1 protein levels in rats treated with GH, which was also reversed in the animals pretreated with aspirin. Overall, these results provide new insights into the mechanism of GH-induced insulin resistance.     

Protective effect of the inhibition of the renin-angiotensin system on aging

Experimental studies indicate that chronic long-term inhibition of the renin-angiotensin system (RAS) can prevent most of the deleterious effects due to aging in the cardiovascular system and in the kidney of the normal mouse and rat. In this review, all the information available on this subject provided by several studies performed by our research group during the last years is been described. Treatment was initiated either after weaning or at 12 months of age that is about half the normal life span of the rat. A converting enzyme inhibitor: enalapril or an angiotensin II type 1 (AT1) receptor blocker: losartan were used to inhibit the RAS. Cognitive behaviour, emotionality, and locomotor activity were also determined at 10 and 18 months of age in treated since weaning and untreated control rats to elucidate the participation of angiotensin II in memory disfunction. A similar observation was obtained in animals treated from 12 to 18 months of age. Results have demonstrated a significant protective effect on the function and the structure of the cardiovascular system, the kidney and the brain in all the treated animals. Damage observed at 12 months of age was not very significant, but treatment stop further deterioration that was evident in untreated animals. The similarity of the results detected with either enalapril or losartan treatment, clearly indicates that most of the effects are exerted through AT1 receptors. Analysis of the nitric oxide and antioxidant enzymes systems suggest that the protective effect is related to an antioxidant action of the RAS inhibitors and a reduced formation of reactive oxygen species. AngII inhibition might produce changes in the mechanisms of oxidative stress specially at the mitochondrial level. Prevention of mitochondrial decrease and/or damage would be related with the delay of the normal aging process.     

Secretions of interleukin-1beta and tumor necrosis factor alpha by whole fetal membranes depend on initial interactions of amnion or choriodecidua with lipopolysaccharides or group B streptococci

The present study evaluated the secretions of interleukin (IL)-1beta and tumor necrosis factor (TNF) alpha by fetal membranes stimulated with group B streptococci (GBS) and lipopolysaccharide (LPS). The aim was to evaluate the initial response of full-thickness membranes to the microbial insult using an in vitro experimental model that allowed testing of the individual contributions of amnion and choriodecidua to stimulation. Full-thickness membranes were obtained after delivery by elective cesarean section from women at 37-40 wk of gestation without evidence of active labor. The membranes were mounted in Transwell devices, physically separating the upper and lower chambers. The LPS (500 ng/ml) or GBS (1 x 10(6) colony-forming units/ml) was added to either the amniotic or choriodecidual surface, and accumulation of IL-1beta and TNFalpha were measured in both compartments using a specific ELISA. Fetal membranes followed different patterns of secretion of proinflammatory cytokines that depended on the side to which the stimulus was added or the nature of the stimulus itself. The TNFalpha was secreted by amnion and choriodecidua in the presence of LPS or GBS, and stimulation with GBS induced a greater synthesis of IL-1beta than did stimulation with LPS. Choriodecidual tissue was more responsive than amniotic tissue, and this response tended to be higher even when the stimulation was only on the amniotic side. However, the amnion plays an active role in recognizing LPS or GBS, contributing a significant amount of TNFalpha. Thus, cooperative and bidirectional communications occur between amnion and choriodecidua in response to bacterial products, which include intermembranous cytokine traffic and signaling between tissues.     

A monomer form of the glutathione S-transferase Y7F mutant from Schistosoma japonicum at acidic pH

Dissociation and unfolding of homodimeric glutathione S-transferase Y7F mutant from Schistosoma japonicum (SjGST-Y7F) were investigated at equilibrium using urea as denaturant. The conserved residue Tyr7 plays a central role in the catalytic mechanism and the mutation Tyr-Phe yields an inactive enzyme that is able to bind the substrate GSH with a higher binding constant than the wild type enzyme. Mutant SjGST-Y7F is a dimer at pH 6 or higher and a stable monomer at pH 5 that binds GSH (K value of 1.2x10(5)+/-6.4x10(3)M(-1) at pH 6.5 and 6.3x10(4)+/-1.25x10(3)M(-1) at pH 5). The stability of the SjGST-Y7F mutant was studied by urea induced unfolding techniques (DeltaG(W)=13.86+/-0.63kcalmol(-1) at pH 6.5 and DeltaG(W)=11.22+/-0.25kcalmol(-1) at pH 5) and the monomeric form characterized by means of size exclusion chromatography, fluorescence, and electrophoretic techniques.     

Aspirin inhibits serine phosphorylation of IRS-1 in muscle and adipose tissue of septic rats

Whole body insulin resistance has been demonstrated in septic patients and in infected animals. In this study, we demonstrate that sepsis induces insulin resistance and that pretreatment with aspirin inhibits sepsis-induced insulin resistance. Sepsis was observed to lead to serine phosphorylation of IRS-1, a phenomenon which was reversed by aspirin in muscle and WAT, in parallel with a reduction in JNK activity. In addition, our data show an impairment of insulin activation of IR and IRS-1 tyrosine phosphorylation in septic rats and, consistent with the reduction of IRS-1 serine phosphorylation observed in septic animals pretreated with aspirin, there was an increase in IRS-1 protein levels and tyrosine phosphorylation in muscle and WAT. Overall, these results provide important new insights into the mechanism of sepsis-induced insulin resistance.     

Structural and immunochemical relationship between the O-antigenic polysaccharides from the enteroaggregative Escherichia coli strain 396/C-1 and Escherichia coli O126

The structure of the O-antigen polysaccharide (PS) from the enteroaggregative Escherichia coli strain 396/C-1 has been determined. Sugar and methylation analyses together with 1H and 13C NMR spectroscopy were the main methods used. Inter-residue correlations were determined by 1H,1H-NOESY, 1H,13C-heteronuclear multiple-bond correlation and dipole-dipole cross-correlated relaxation experiments. The PS is composed of pentasaccharide repeating units with the following structure: [structure: see text]. Analysis of NMR data reveals that on average the PS consists of approximately 13 repeating units and indicates that the biological repeating unit contains an N-acetylglucosamine residue at its reducing end. This structure is different to that reported for the O-antigen polysaccharide from E. coli O126. Monospecific anti-E. coli O126 rabbit serum from The International Escherichia and Klebsiella Centre did not distinguish between the E. coli strain 396/C-1 and the E. coli O126 reference strain, neither in slide agglutination nor in an indirect enzyme immunoassay. Subsequent successful serotyping of the E. coli strain 396/C-1 showed it to be E. coli O126:K+:H27.     

Amlodipine decreases fibrosis and cardiac hypertrophy in spontaneously hypertensive rats: persistent effects after withdrawal

Our objective was to examine the effect of chronic treatment with amlodipine on blood pressure, left ventricular hypertrophy, and fibrosis in spontaneously hypertensive rats and the persistence of such an effect after drug withdrawal. We investigated the effects of treatment with 2, 8 and 20 mg/kg/day of amlodipine given orally for six months and at three months after drug withdrawal. Systolic blood pressure was measured using the tail-cuff method. At the end of the study period, the heart was excised, the left ventricle was isolated, and the left ventricle weight/body weight ratio was calculated as a left ventricular hypertrophy index. Fibrosis, expressed as collagen volume fraction, was evaluated using an automated image-analysis system on sections stained with Sirius red. Age-matched untreated Wistar-Kyoto and SHR were used as normotensive and hypertensive controls, respectively. Systolic blood pressure was reduced in the treated SHR in a dose-dependent way and after amlodipine withdrawal it increased progressively, without reaching the values of the hypertensive controls. Cardiac hypertrophy was reduced by 8 and 20 mg/kg/day amlodipine, but when treatment was withdrawn only the group treated with 8 mg/kg/day maintained significant differences versus the hypertensive controls. All three doses of amlodipine reduced cardiac fibrosis and this regression persisted with the two highest doses after three months without treatment. We concluded that antihypertensive treatment with amlodipine is accompanied by a reduction in left ventricular hypertrophy and regression in collagen deposition. Treatment was more effective in preventing fibrosis than in preventing ventricular hypertrophy after drug withdrawal.     

Size and age structure of the striped marlin Tetrapturus audax (Pisces: Xiphidae), at Cabo San Lucas, Baja California sur, México

The striped marlin (Tetrapturus audax) is found in temperate and tropical waters of the Pacific and Indian Ocean. It is particularly abundant in the southern tip of the Baja California peninsula. Specimens brought to Cabo San Lucas port (22 degrees 53' N y 109 degrees 54' W) by the sport fishery fleet that operates withing a radius of 54 km from 1988 to 1993 were sexes, measured and weighed. A total 1030 individuals were sampled. Dorsal fin spines (389) were collected for age estimation. The spines were sectioned and hyaline-opaque bands counted. The relation of length to spine radius was similar for males and females. The fourth dorsal spine reflected the growth of the fish. The rhythm of growth mark formation is yearly and related to the sea surface temperature. Ten age groups were found and the seventh group was the most abundant, followed by groups "6" and "8". The age structure of the striped marlin was stable in the study period. The observed sizes were 160-280 cm jaw length with 90% of the organisms measuring between 190 and 225 cm. The small individuals recruit to the fishery from June to December.