Angiotensin II modulates ion transport in rat proximal tubules through CYP metabolites

To assess the effect of angiotensin II on ion transport in rat isolated proximal tubules and establish the arachidonic acid cytochrome P450 metabolites' role mediating angiotensin II effect and to analyze whether corticosteroids play a role modulating this effect, we studied the effect of low (10 and 100 pM) and high (0.1-1 microM) angiotensin II concentrations on proximal tubule ion transport, measured as (86)Rb uptake. Low angiotensin II produced a stimulation on the (86)Rb uptake (195.79 +/- 35, 377.9 +/- 81, and 300 +/- 49 pg (86)Rb/microg protein/2 min, for control and 10 and 100 pM angiotensin II, respectively). High angiotensin II concentration inhibited ion transport (0.1 microM, 57.9 +/- 5 and 1 microM, 47.3 +/- 4 pg (86)Rb/microg protein/2 min), this effect was prevented by 17-ODYA and by losartan, while indomethacin had no effect. Dexamethasone treatment increased angiotensin II-induced (86)Rb uptake inhibition and arachidonic acid metabolism (19-, 20-HETE and 12-HETE), while adrenalectomy partly prevented angiotensin II-induced inhibition and decreased cytochrome P450-dependent arachidonic acid metabolism. In conclusion, high doses of angiotensin II produce inhibition of ion transport in rat isolated proximal tubules; this effect is mediated by AT(1) receptors, involves cytochrome P450-dependent arachidonic acid metabolites, and is upregulated by corticosteroids.     

Monomeric midkine induces tumor cell proliferation in the absence of cell-surface proteoglycan binding

Midkine (MK), a retinoic acid-inducible heparin-binding protein, is a mitogen which initiates a cascade of intracellular protein tyrosine phosphorylation mediated by the JAK/STAT pathway after binding to its high affinity p200(+)/MKR cell surface receptor in the G401 cell line [Ratovitski, E. A. (1998) J. Biol. Chem. 273, 3654-3660]. In this study, we determined the biophysical characteristics of purified recombinant murine MK and analyzed the requirements for ligand multimerization and cell surface proteoglycan binding for the G401 cell mitogenic activity of MK. Our studies indicate that the secreted form of MK (M = 13 kDa) exists in solution as an asymmetric monomer with a frictional coefficient of 1. 48 and a Stokes radius of 23.7 A. By constructing bead models of MK using the program AtoB and the program HYDRO to predict the hydrodynamic properties of each model, our data suggest that MK has a dumb-bell shape in solution composed of independent N- and C-terminal domains separated by an extended linker. This asymmetric MK monomer is a biologically active ligand with mitogenic activity on G401 cells in vitro. Neither heparin-induced formation of noncovalent MK multimers nor tissue transglutaminase II covalent multimerization of MK enhanced MK mitogenic activity in this system. Since neither heparin competition nor cell treatment with chondroitinase ABC or heparinase III abolished the mitogenic effects of MK on G401 cells, cell-surface proteoglycan binding by MK does not appear to be a requirement for its observed mitogenic effects. These results provide strong evidence that the MK-specific p200(+)/MKR has distinctive biochemical properties which distinguish it from the receptor tyrosine phosphatase cell-surface proteoglycan PTPzeta/RPTPbeta and support the hypothesis that the diverse biological effects of MK are mediated by multiple cell-specific signal transduction receptors.     

Nitric oxide and inducible nitric oxide synthase expression are downregulated in acute cholestasis in the rat accompanied by liver ischemia

Hepatic blood flow decreases under cholestasis and there is evidence that NO regulates liver microvascular perfusion. Thus, the aim of the present study was to evaluate NO synthesis in cholestasis. Cholestasis was induced by bile-duct ligation (BDL) in male Wistar rats. Bilirubins and enzyme activities were measured in serum. Lipid peroxidation, GSH, GSSG and glycogen were determined in liver. Histopathological analysis was performed. Serum NO2- + NO3- concentration was measured by the Gries reaction. iNOS immunoblot analysis was carried out using an iNOS polyclonal antibody. After 7 days of BDL lipid peroxidation increased while GSH/GSSG ratio decreased. Serum NO2- + NO3- and liver iNOS protein were reduced, accompanied by ischemia as revealed by the histopathological analysis. GSH upregulates NO synthesis by increasing iNOS mRNA levels and iNOS activity, thus the reduction of GSH/GSSG ratio may be responsible for the downregulation of iNOS protein and NO synthesis, which in turn may explain the observed ischemia and the decreased hepatic blood perfusion in cholestasis reported by others.     

Epidemiology of Tropical Neglected Diseases in Ecuador in the Last 20 Years

Background

Tropical and zoonotic diseases are major problems in developing countries like Ecuador. Poorly designed houses, the high proportion of isolated indigenous population and under developed infrastructure represent a fertile environment for vectors to proliferate. Control campaigns in Ecuador over the years have had varying success, depending on the disease and vectors targeted.

Aims

In our study we analyse the current situation of some neglected diseases in Ecuador and the efficiency of the control campaigns (by measuring changes in numbers of cases reported) that the Ecuadorian government has been running to limit the spread of these infectious and parasitic diseases.

Results

Our study reveals that Brucellosis, Chagas Disease, Rabies and Onchocerciasis have been controlled, but small outbreaks are still detected in endemic areas. Leptospirosis and Echinococcosis have been increasing steadily in recent years in Ecuador since the first records. The same increase has been reported world-wide also. Better diagnosis has resulted in a higher number of cases being identified, particularly with regard to the linking of outdoor activities and contact with farm animals as contributing vectors. Improvements in diagnosis are due to regular professional training, implementation of automatized systems, establishing diagnosis protocols and the creation of an epidemiological vigilance network that acts as soon as a case is reported.

Conclusion

Control campaigns performed in Ecuador have been successful in recent years, although natural phenomena limit their efficiency. Leptospirosis and Echinococcosis infections remain a growing problem in Ecuador as it is worldwide.     

Origin and Evolution of Sulfadoxine Resistant Plasmodium falciparum

The Thailand-Cambodia border is the epicenter for drug-resistant falciparum malaria. Previous studies have shown that chloroquine (CQ) and pyrimethamine resistance originated in this region and eventually spread to other Asian countries and Africa. However, there is a dearth in understanding the origin and evolution of dhps alleles associated with sulfadoxine resistance. The present study was designed to reveal the origin(s) of sulfadoxine resistance in Cambodia and its evolutionary relationship to African and South American dhps alleles. We sequenced 234 Cambodian Plasmodium falciparum isolates for the dhps codons S436A/F, A437G, K540E, A581G and A613S/T implicated in sulfadoxine resistance. We also genotyped 10 microsatellite loci around dhps to determine the genetic backgrounds of various alleles and compared them with the backgrounds of alleles prevalent in Africa and South America. In addition to previously known highly-resistant triple mutant dhps alleles SGEGA and AGEAA (codons 436, 437, 540, 581, 613 are sequentially indicated), a large proportion of the isolates (19.3%) contained a 540N mutation in association with 437G/581G yielding a previously unreported triple mutant allele, SGNGA. Microsatellite data strongly suggest the strength of selection was greater on triple mutant dhps alleles followed by the double and single mutants. We provide evidence for at least three independent origins for the double mutants, one each for the SGKGA, AGKAA and SGEAA alleles. Our data suggest that the triple mutant allele SGEGA and the novel allele SGNGA have common origin on the SGKGA background, whereas the AGEAA triple mutant was derived from AGKAA on multiple, albeit limited, genetic backgrounds. The SGEAA did not share haplotypes with any of the triple mutants. Comparative analysis of the microsatellite haplotypes flanking dhps alleles from Cambodia, Kenya, Cameroon and Venezuela revealed an independent origin of sulfadoxine resistant alleles in each of these regions.     

Growth recovery on glucose under aerobic conditions of an Escherichia coli strain carrying a phosphoenolpyruvate:carbohydrate phosphotransferase system deletion by inactivating arcA and overexpressing the genes coding for glucokinase and galactose permease

In Escherichia coli the phosphotransferase system (PTS) consumes one molecule of phosphoenolpyruvate (PEP) to phosphorylate each molecule of internalized glucose. PEP bioavailability into the aromatic pathway can be increased by inactivating the PTS. However, the lack of the PTS results in decreased glucose transport and growth rates. To overcome such drawbacks in a PTS(-) strain and reconstitute rapid growth on glucose phenotype (Glc(+)), the glk and galP genes were cloned into a plasmid and the arcA gene was inactivated. Simultaneous overexpression of glk and galP increased the growth rate and regenerated a Glc(+) phenotype. However, the highest growth rate was obtained when glk and galP were overexpressed in the arcA(-) background. These results indicated that the arcA mutation enhanced glycolytic and respiratory capacities of the engineered strain.     

The structure of S. lividans acetoacetyl‐CoA synthetase shows a novel interaction between the C‐terminal extension and the N‐terminal domain

The adenosine monoposphate‐forming acyl‐CoA synthetase enzymes catalyze a two‐step reaction that involves the initial formation of an acyl adenylate that reacts in a second partial reaction to form a thioester between the acyl substrate and CoA. These enzymes utilize a Domain Alternation catalytic mechanism, whereby a ～110 residue C‐terminal domain rotates by 140° to form distinct catalytic conformations for the two partial reactions. The structure of an acetoacetyl‐CoA synthetase (AacS) is presented that illustrates a novel aspect of this C‐terminal domain. Specifically, several acetyl‐ and acetoacetyl‐CoA synthetases contain a 30‐residue extension on the C‐terminus compared to other members of this family. Whereas residues from this extension are disordered in prior structures, the AacS structure shows that residues from this extension may interact with key catalytic residues from the N‐terminal domain. Proteins 2015; 83:575–581. © 2014 Wiley Periodicals, Inc.     

Eicosanoids and tumor necrosis factor-alpha in the kidney

The thick ascending limb of Henle's loop (TAL) is capable of metabolizing arachidonic acid (AA) by cytochrome P450 (CYP450) and cyclooxygenase (COX) pathways and has been identified as a nephron segment that contributes to salt-sensitive hypertension. Previous studies demonstrated a prominent role for CYP450-dependent metabolism of AA to products that inhibited ion transport pathways in the TAL. However, COX-2 is constitutively expressed along all segments of the TAL and is increased in response to diverse stimuli. The ability of Tamm-Horsfall glycoprotein, a selective marker of cortical TAL (cTAL) and medullary (mTAL), to bind TNF and localize it to this nephron segment prompted studies to determine the capacity of mTAL cells to produce TNF and determine its effects on mTAL function. The colocalization of calcium-sensing receptor (CaR) and COX-2 in the TAL supports the notion that activation of CaR induces TNF-dependent COX-2 expression and PGE? synthesis in mTAL cells. Additional studies showed that TNF produced by mTAL cells inhibits ??Rb uptake, an in vitro correlate of natriuresis, in an autocrine- and COX-2-dependent manner. The molecular mechanism for these effects likely includes inhibition of Na?-K?-2Cl? cotransporter (NKCC2) expression and trafficking.