Comblike poly(a-alkyl g glutamate)s: computer simulation studies of an intermediate thermal phase.

Monte Carlo (MC) simulations have been used to study the structure of an intermediate thermal phase of poly(R-octadecyl ç,D-glutamate). This is a comblike poly(ç-peptide) able to adopt a biphasic structure that has been described as a layered arrangement of backbone helical rods immersed in a paraffinic pool of polymethylene side chains. Simulations were performed at two different temperatures (348 and 363 K), both of them above the melting point of the paraffinic phase, using the configurational bias MC algorithm. Results indicate that layers are constituted by a side-by-side packing of 17/5 helices. The organization of the interlayer paraffinic region is described in atomistic terms by examining the torsional angles and the end-to-end distances for the octadecyl side chains. Comparison with previously reported comblike poly(â-peptide)s revealed significant differences in the organization of the alkyl side chains.

Grape epicatechin conjugates prevent erythrocyte membrane protein oxidation

Epicatechin conjugates obtained from grape have shown antioxidant activity in various systems. However, how these conjugates exert their antioxidant benefits has not been widely studied. We assessed the activity of epicatechin and epicatechin conjugates on the erythrocyte membrane in the presence and absence of a peroxyl radical initiator, to increase our understanding of their mechanisms. Thus, we studied cell membrane fluidity by fluorescence anisotropy measurements, morphology of erythrocytes by scanning electron microscopy, and finally, red cell membrane proteins by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Our data showed that incubation of red cells in the presence of epicatechin derivatives altered membrane fluidity and erythrocyte morphology but not the membrane protein pattern. The presence in the medium of the peroxyl radical initiator 2,2′-azobis(amidinopropane) dihydrochloride (AAPH) resulted in membrane disruptions at all levels analyzed, causing changes in membrane fluidity, cell morphology, and protein degradation. The presence of antioxidants avoided protein oxidation, indicating that the interaction of epicatechin conjugates with the lipid bilayer might reduce the accessibility of AAPH to membranes, which could explain in part the inhibitory ability of these compounds against hemolysis induced by peroxidative insult.

Neonates with Bartter syndrome have enormous fluid and sodium requirements.

AIM: Managing neonatal Bartter syndrome by achieving adequate weight gain is challenging. We assessed the correlation between weight gain in neonatal Bartter syndrome and the introduction of fluid and sodium supplementations and indomethacin during the first 4 weeks of life. METHODS: Daily fluid and electrolytes requirements were analysed using linear regression and Spearman correlation coefficients. The weight gain coefficient was calculated as daily weight gain after physiological neonatal weight loss. RESULTS: We studied seven infants. The highest weight gain coefficients occurred between weeks two and four in the five neonates who either received prompt amounts of fluid (maximum 810 mL/kg/day) and sodium (maximum 70 mmol/kg/day) or were treated with indomethacin. For the two patients with the highest weight gain coefficient, water and sodium supplementations were decreased in weeks two to four leading to a significant negative Spearman correlation between weight gain and fluid supplements (r = -0.55 and -0.68) and weight gain and sodium supplementations (r = -0.96 and -0.72). The two patients with the lowest weight gain coefficient had positive Spearman correlation coefficients between weight gain and fluid and sodium supplementations. CONCLUSION: Infants with neonatal Bartter syndrome required rapid and enormous fluid and sodium supplementations or the early introduction of indomethacin treatment to achieve adequate weight gain during the early postnatal period.

Uuttoprosessin suunnittelu

Teknologian kehitys ja prosessien tiukempi valvonta ovat alentaneet selluteollisuuden häviöitä tehden prosesseista suljetumpia. Valitettavasti nämä edistysaskeleet teknologiassa ovat lisänneet prosessiin kuulumattomien yhdisteiden määrää kemikaalien talteenottokierrossa. Näistä kemikaaleista haitallisimpia ovat kloridi- ja kaliumyhdisteet, jotka tulevat prosessiin raaka-aineiden ja prosessikemikaalien mukana. Kloridi ja kalium muodostavat emäksisissä liuoksissa epäorgaanisia liukoisia yhdisteitä, jotka rikastuvat lipeäkiertoon. Soodakattilassa kloridien läsnäolo alentaa tuhkan sulamislämpötilaa sekä tarttumispistettä, lisää korroosiota ja saostumien muodostumista kattilan pinnalle. Nämä seuraukset voivat vähentää vuosituotantoa ja nostaa korjauskustannuksia. Kaliumin ja kloridin rikastumista talteenottokiertoon voidaan estää poistamalla ne prosessista. Prosessiin kuulumattomat yhdisteet tulisi poistaa talteenottoprosessista ja säilyttää samalla korkea kemikaalien talteenottoprosentti. Koska kaliumin ja kloridin rikastumiskertoimet soodakattilan tuhkassa ovat korkeita, on tuhkan käsittely tehokasta. Kloridin ja kaliumin poistoon on kehitetty menetelmiä, joilla voidaan vähentää hyödyllisten kemikaalien häviöitä. Näitä menetelmiä ovat uutto, ioninvaihto, elektrodialyysi, jäähdytyskiteytys ja haihdutuskiteytys. Menetelmissä tuhka jaetaan kloridi- ja kaliumpitoiseen osaan ja natriumsulfaattipitoiseen osaan. Kloridi ja kalium poistetaan prosessista ja loput palautetaan lipeäkiertoon. Kloridin ja kaliumin poistoa tuhkasta tutkittiin uuttamalla tuhkaa vedellä. Parhaissa käyttöolosuhteissa natriumsulfaatin liukoisuus veteen on huomattavasti alhaisempi kuin kaliumkloridin liukoisuus veteen. Optimaalinen uuttolämpötila ja tuhka-vesisuhde määritettiin siten, että kloridi- ja kaliumpitoisuudet suodoksessa olivat mahdollisimman korkeat sekä natriumin ja muiden anioneiden pitoisuudet suodoksessa mahdollisimman alhaiset. Saatuja tuloksia käytettiin jatkuvatoimisen uuttoprosessin suunnittelussa.

Epithelial Sodium Channel-Mediated Sodium Transport Is Not Dependent on the Membrane-Bound Serine Protease CAP2/Tmprss4.

The membrane-bound serine protease CAP2/Tmprss4 has been previously identified in vitro as a positive regulator of the epithelial sodium channel (ENaC). To study its in vivo implication in ENaC-mediated sodium absorption, we generated a knockout mouse model for CAP2/Tmprss4. Mice deficient in CAP2/Tmprss4 were viable, fertile, and did not show any obvious histological abnormalities. Unexpectedly, when challenged with sodium-deficient diet, these mice did not develop any impairment in renal sodium handling as evidenced by normal plasma and urinary sodium and potassium electrolytes, as well as normal aldosterone levels. Despite minor alterations in ENaC mRNA expression, we found no evidence for altered proteolytic cleavage of ENaC subunits. In consequence, ENaC activity, as monitored by the amiloride-sensitive rectal potential difference (ΔPD), was not altered even under dietary sodium restriction. In summary, ENaC-mediated sodium balance is not affected by lack of CAP2/Tmprss4 expression and thus, does not seem to directly control ENaC expression and activity in vivo.

Ligand binding to heparan sulfate proteoglycans induces their aggregation and distribution along actin cytoskeleton

Cell surface heparan sulfate proteoglycans (HSPGs) participate in molecular events that regulate cell adhesion, migration, and proliferation. The present study demonstrates that soluble heparin-binding proteins or cross-linking antibodies induce the aggregation of cell surface HSPGs and their distribution along underlying actin filaments. Immunofluorescence and confocal microscopy and immunogold and electron microscopy indicate that, in the absence of ligands, HSPGs are irregularly distributed on the fibroblast cell surface, without any apparent codistribution with the actin cytoskeleton. In the presence of ligand (lipoprotein lipase) or antibodies against heparan sulfate, HSPGs aggregate and colocalize with the actin cytoskeleton. Triton X-100 extraction and immunoelectron microscopy have demonstrated that in this condition HSPGs were clustered and associated with the actin filaments. Crosslinking experiments that use biotinylated lipoprotein lipase have revealed three major proteoglycans as binding sites at the fibroblast cell surface. These cross-linked proteoglycans appeared in the Triton X-100 insoluble fraction. Platinum/carbon replicas of the fibroblast surface incubated either with lipoprotein lipase or antiheparan sulfate showed large aggregates of HSPGs regularly distributed along cytoplasmic fibers. Quantification of the spacing between HSPGs by confocal microscopy confirmed that the nonrandom distribution of HSPG aggregates along the actin cytoskeleton was induced by ligand binding. When cells were incubated either with lipoprotein lipase or antibodies against heparan sulfate, the distance between immunofluorescence spots was uniform. In contrast, the spacing between HSPGs on fixed cells not incubated with ligand was more variable. This highly organized spatial relationship between actin and proteoglycans suggests that cortical actin filaments could organize the molecular machinery involved in signal transduction and molecular movements on the cell surface that are triggered by heparin-binding proteins.