Kovalentno vezivanje glikoinozitolfosfolipida (GPI) za hemoglobin pod dejstvom insulina praćeno je aktiviranjem proteaze iz membrane eritrocita

Recently, it was demonstrated that prolonged hyperinsulinism associated with hypoglycemia, both in vivo and in vitro, caused covalent glycoinositolphospholipid (GPI) binding to the C termini of both hemoglobin beta-chains, which resulted in the formation of a novel, hitherto unrecognized, minor hemoglobin fraction (GPI-Hb) (Niketic et al. Biochem. Biophys. Res. Commun. 239 (1997)435). In this study, it was demonstrated that exposure of erythrocyte membranes to insulin causes the activation of membrane protease as well as that the formation of GPI-Hb parallels its activity. It is suggested that the insulin-activated protease is able to catalyze. albeit slowly, the transpeptidation, i.e., the replacement of the carboxy-terminal amino acid(s) residues of the Hb beta-chains with GPI as an exogenous nucleophile. To our knowledge the present results show for the first time that insulin stimulates protease activity in erythrocyte membranes, as well as that insulin-activated protease may be involved in post-translational GPI binding to proteins.U našim ranijim radovima pokazano je da u uslovima hiperinsulinizma i hipoglikemije, in vivo i in vitro, dolazi do kovalentnog vezivanja glikoinozitolfosfolipida (GPI) za karboksilne krajeve oba β-niza molekula hemoglobina (Hb), što se manifestuje nastajanjem nove, do tada nepoznate, manje frakcije hemoglobina (GPI-Hb) (Niketić et al., Biochem. Biophys. Res. Commun. 239 (1997) 435). U ovom radu je pokazano da vezivanje insulina za membrane eritrocita izaziva aktiviranje membranske proteaze, te da je nastajanje GPI-Hb u korelaciji sa proteaznom aktivnošću. Pretpostavljeno je da proteaza aktivirana insulinom može, mada sporo, da katalizuje reakciju transpeptidacije, tj. zamenu aminokiselinskih ostataka sa karboksilnog kraja β-nizova molekula Hb sa GPI-lipidom kao egzogenim nukleofilom. Prema našem saznanju opisani rezultati prvi puta pokazuju da insulin stimuliše proteaznu aktivnost u eritrocitima, te da je ova aktivnost povezana sa post-translacionim vezivanjem GPI-lipida za proteine

Concord grape Juice, cognitive function and driving performance: a 12 week, placebo controlled, randomised, crossover trial in mothers of pre-teen children

Background: Daily consumption of Concord grape juice (CGJ) over three to four months has been shown to improve memory function in adults with mild cognitive impairment, and reduce blood pressure in hypertensive adults. These benefits are likely due to the high concentration of polyphenols in CGJ. Increased stress can impair cognitive function and elevate blood pressure. Thus we examined the potential beneficial effect of CGJ in individuals experiencing somewhat stressful demanding lifestyles. Objective: To examine the effects of twelve weeks’ daily consumption of CGJ on cognitive function, driving performance, and blood pressure in healthy, middle-aged working mothers. Design: Twenty five healthy mothers of pre-teen children, aged 40-50 years, who were employed for > 30 hours/week consumed 12oz (355ml) CGJ (containing 777mg total polyphenols) or an energy, taste and appearance matched placebo daily for twelve weeks according to a randomised, crossover design with a four week washout. Verbal and spatial memory, executive function, attention, blood pressure and mood were assessed at baseline, six weeks and twelve weeks. Immediately following the cognitive battery, a subsample of seventeen females completed a driving performance assessment in the University of Leeds Driving Simulator. The twenty five minute driving task required participants to match the speed and direction of a lead vehicle. Results: Significant improvements in immediate spatial memory and driving performance were observed following CGJ relative to placebo. There was evidence of an enduring effect of CGJ such that participants who received CGJ in arm 1 maintained better performance in the placebo arm. Conclusions: Cognitive benefits associated with chronic consumption of flavonoid-rich grape juice are not exclusive to adults with mild cognitive impairment. Moreover, these cognitive benefits are apparent in complex everyday tasks such as driving. Effects may persist beyond cessation of flavonoid consumption and future studies should carefully consider the length of washout within crossover designs

Vezivanje lipida za hemoglobin pod dejstvom insulina

Under hypoglycemic conditions, concomitant hyperinsulinism causes an apparent modification of hemoglobin (Hb) which is manifested by its a aggregation (Niketic et al.. Clin. Chim. Acia 197 (1991) 47). In the present work the causes and mechanisms underlying this Hb modification were Studied. Hemoglobin isolated from normal erythrocytes incubated with insulin was analyzed by applying P-31-spectrometry and lipid extraction and analysis. To study the dynamics of the plasma membrane during hperinsulinisra a fluorescent lipid-analog was applied. In the presence of insulin phosphatidylserine (PS). phosphatidylethanolamine (PE) and cholesterol were found to bind to Hb. Lipid binding resulted in Hb aggregation, a condition that can be reproduced when phospholipids arc incubated with Hb in vitro. Using a fluorescent lipid-analog, it was also shown that exposing crythrocytes to supraphysiological concentrations of insulin in vitro resulted in the internalization of lipids. The results presented in this work, may have relevance to cases of diabetes mellitus and hypoglycemia.Uranijim radovima je pokazano da hiperinsulinizam u uslovima hipoglikemije izaziva modifikaciju molekula hemoglobina koja se manifestuje njegovim agregiranjem (Niketić et al., Clin. Chim. Acta 197 (1991) 47). U ovom radu ispitivana je ova modifikacija molekula hemoglobina, kao i mehanizam njenog nastajanja. Primenom 31P-spektrometrije i analizom lipidnog ekstrakta utvrđeno je da u normalnim eritrocitima inkubiranim sa insulinom dolazi do vezivanja fosfatidil-serina, fosfatidil-etanolmina i holesterola za molekul hemoglobina. Vezivanje fosfolipida za hemoglobin dovodi do njegovog agregiranja što je potvrđeno eksperimentima u kojima je hemoglobin inkubiran sa fosfolipidima in vitro. Primenom fluorescentnog lipidnog analoga pokazano je da pri izlaganju eritrocita suprafiziološkim koncentracijama insulina dolazi do internalizacije membranskih lipida. Dobijeni rezultati mogu biti od značaja za pacijente obolele od šećerne bolesti i hipoglikemije

Mangan-superoksid-dismutaza (MnSOD) katalizuje NO-zavisno nitrovanje ostatka tirozina

The peroxynitrite-induced nitration of manganese superoxide dismutase (MnSOD) tyrosine residue, which causes enzyme inactivation, is well established, This led to suggestions that MnSOD nitration and inactivation in vivo, detected in various diseases associated with oxidative stress and overproduction of nitric monoxide (NO), conditions which favor peroxynitrite formation, is also caused by peroxynitrite. However, our previous ill vitro study demonstrated that exposure of MnSOD to NO led to NO conversion into nitrosonium (NO+) and nitroxyl (NO-) species, which caused enzyme modifications and inactivation. Here it is reported that MnSOD is tyrosine nitrated upon exposure to NO, as well as that MnSOD nitration contributes to inactivation of the enzyme. Collectively, these observations provide a compelling argument supporting the generation of nitrating species in MnSOD exposed to NO and shed a new light on MnSOD tyrosine nitration and inactivation ill vivo. This may represent a novel mechanism by which MnSOD protects cell from deleterious effects associated with overproduction of NO. However, extensive MnSOD modification and inactivation associated with prolonged exposure to NO will amplify the toxic effects caused by increased cell superoxide and NO levels.Dobro je poznato da peroksinitrit izaziva nitrovanje ostataka tirozina u mangan-superoksid- dismutazi (MnSOD) što dovodi do inaktivacije enzima. Pokazano je da nitrovanje i inaktivacija MnSOD-a nastaje u raznim bolestima za koje je karakteristič an oksidativni stres i povećana produkcija azot-monoksida (NO). Pošto se pri ovim uslovima očekuje nastajanje peroksinitrita predloženo je da peroksinitrit izaziva nitrovanje i inaktivaciju MnSOD in vivo. U našem prethodnom radu pokazali smo da MnSOD katalizuje transformaciju NO u nitrozonijum (NO+) i nitroksil (NO–) reaktivne vrste, te identifikovali neke od modifikacija molekula enzima koje pri tome nastaju izazivajući njegovu inaktivaciju. U ovom radu je pokazano da pri izlaganju MnSOD azot-monoksidu dolazi i do nitrovanja ostatka tirozina u molekulu enzima, što doprinosi njegovoj inaktivaciji. Ovi rezultati ukazuju da pri interakciji MnSOD sa NO dolazi do nastajanja nitrujućih vrsta, što baca novo svetlo na proces nitrovanja ostataka tirozina i inaktivaciju MnSOD in vivo. Ovo može da predstavlja novi mehanizam kojim MnSOD štiti ćeliju odštetnih efekata izazvanih hiperprodukcijom azot-monoksida. Međutim ekstenzivne modifikacije i inaktivacija MnSOD do kojih dolazi pri produženom izlaganju enzima NO, uvećaće toksične efekte izazvane povećanim koncentracijama superoksida i NO u ćeliji

Design versus Assessment of Concrete Structures Using Stress Fields and Strut-and-Tie Models

Stress fields and strut-and-tie models are widely used for design and assessment of structural concrete members. Although they are often used in the same manner for both purposes, developing suitable stress fields and strut-and-tie models for the design of a new structure or for assessment of the strength of an existing one should not necessarily be performed following the same approach. For design, simple load-carrying models in equilibrium with the external actions can be considered. From the various possibilities, those leading to better behavior at serviceability limit state and to simple reinforcement layouts should be selected (or a combination of them). For the assessment of existing structures, however, avoiding unnecessary strengthening (or minimizing it) should be the objective. Thus, simple stress fields or strut-and-tie models are to be iteratively refined whenever the calculated strength of the member is insufficient with respect to the design actions. This can be done by accounting for kinematic considerations to calculate the higher possible strength of the member accounting for its actual geometry and available reinforcement (allowing to calculate the exact solution according to limit analysis). In this paper, the differences between the two approaches for design and assessment are clarified and explained on the basis of some examples. A number of strategies are comprehensibly presented to obtain suitable stress fields and strut-and-tie models in both cases. The results of exact solutions according to limit analysis (developed using elastic-plastic stress fields) are finally compared to 150 tests of the literature showing the consistency and generality of the presented approaches

Da li holesterol vezan za hemoglobin utiče na anti-oksidativni enzimski sistem u humanim eritrocitima?

In a previous study, it was shown that the lipid fraction, which is occasionally observed in red blood cell hemolysates, represents cholesterol (Ch) associated with phospholipid firmly bound to haemoglobin (termed Hb-Ch). The current study was conducted to investigate whether Hb-Ch could affect the primary anti-oxidant enzyme defence system in human erythrocytes. Sixty healthy volunteers were used for the current study. Group 1 consisted of 28 subjects without or with a low level of Hb-Ch. Group 2 comprised 32 subjects with a considerably higher level of Hb-Ch. The activities of erythrocyte superoxide dismutase, catalase, glutathione peroxidase and glutathione reductase, as well as the content of methaemoglobin (metHb) were measured in both groups. The results indicated that the amount of Hb-Ch neither influenced the activities of the erythrocyte anti-oxidant enzymes nor altered the level of metHb. However, a higher amount of Hb-Ch changed the correlations in the part of the anti-oxidant defence system relating to glutathione, suggesting increased peroxidative pressure from plasma lipids. Group 2 also had significantly increased concentrations of total plasma Ch and triglycerides. Together, these facts are strong indications that the anti-oxidant defence system in human erythrocytes finely retunes its composition according to plasma oxidative demands.U prethodnom radu pokazano je da lipidna frakcija koja se javlja u hemolizatu zdravih ljudi predstavlja holesterol (asosovan sa fosfolipidima) čvrsto vezan za hemoglobin (Hb-Ch). U ovom radu ispitivan je uticaj Hb-Ch na anti-oksidativni enzimski sistem u humanim eritrocitima. Određena je aktivnost superoksid-dizmutaze, katalaze, glutation-peroksidaze i glutation-reduktaze, kao i sadržaj met-hemoglobina (metHb) u eritrocitima 60 ljudi, podeljenih u dve grupe na osnovu količine Hb-Ch. Rezultati pokazuju da količina prisutnog Hb-Ch ne menja aktivnost merenih enzima, niti nivo metHb. Međutim, u grupi ispitanika sa povećanim sadržajem Hb-Ch zapažene su korelativne promene u delu anti-oksidativnog enzimskog sistema povezanog sa glutationom. U istoj grupi detektovane su i veće koncentracije ukupnog holesterola i triglicerida u plazmi, što zajedno ukazuje na povećani peroksidativni pritisak iz plazme. Ovi rezultati ukazuju da odbrambeni anti-oksidativni enzimski sistem u humanim eritrocitima prilagođava svoju organizaciju prema zahtevima iz svog okruženja.