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S Sela

Publications and source records attributed to S Sela.

At least 19 recordsLinked to original sources
PubMed2001

Oxidative stress during hemodialysis: effect of heparin.

BACKGROUND: Patients on chronic hemodialysis (HD) are exposed to oxidative stress. An HD session is used in this study as an in vivo model for studying the influence of heparin on oxidative stress caused partially by activated peripheral blood polymorphonuclear leukocytes (PMNLs) during a HD session. METHODS: Each patient underwent HD once with and once without heparin. Oxidative stress was determined by evaluating both the rate of superoxide release from phorbol 12-myristate 13-acetate (PMA)-stimulated PMNLs and plasma levels of oxidized glutathione (GSSG), both measured before and after the dialysis session. RESULTS: In vitro, heparin reduced the rate of superoxide release from separated PMA-stimulated PMNLs. In vivo, the rate of superoxide release from PMNLs was always increased after the dialysis session, regardless of the presence of heparin. However, in the presence of heparin, this increase was significantly smaller. The augmentation in the rate of superoxide release after the dialysis session without heparin was accompanied by a significant elevation of GSSG, reflecting a preceding oxidation of plasma glutathione. CONCLUSIONS: The increase in both parameters, the rate of superoxide release, and the plasma GSSG concentration after HD treatment suggest that heparin in vivo alleviates the oxidative stress induced by the dialysis process. Based on our results, heparin should be the anticoagulant of choice because of its suppressant action on HD-induced oxidative stress.

Adult↗
PubMed2001

Mesna: a novel renoprotective antioxidant in ischaemic acute renal failure.

BACKGROUND: Reactive oxygen species (ROS) play a key role in renal ischaemia-reperfusion injury. After establishing the in vitro anti-oxidative potential of mesna, a sulfhydryl-containing compound, its effect on kidney function and morphology in a rat model of ischaemic acute renal failure (ARF) was examined. METHODS: Mesna (180 mg/kg) was administered at different time points relative to ischaemia and/or reperfusion onset. Kidney function was assessed by glomerular filtration rate (GFR) and fractional sodium excretion (FE(Na)) before a 45-min period of unilateral renal artery clamping and following 90 min of reperfusion. Mesna was administered by bolus, 30 min before the induction of ischaemia, 5 min before ischaemia, 5 min before reperfusion, and 5 min after the onset of reperfusion. RESULTS: Mesna improved function of the ischaemic kidney at each administration. When mesna was administered 5 min before the onset of reperfusion, GFR reached 90-100% of its pre ischaemic value and FE(Na) was improved by 75%. The beneficial effect of mesna was also demonstrated by light and electron microscopy. Kidneys treated with mesna 5 min before reperfusion resembled ischaemic non-reperfused kidneys and showed subtle morphological and ultrastructural changes compared with ischaemic-reperfused kidneys. Mesna had no haemodynamic effect on renal blood flow and did not induce any osmotic diuresis. CONCLUSIONS: We suggest that mesna acts as an antioxidant. Its antioxidant potential together with optimal protection achieved when administered 5 min before reperfusion, supports the conclusion that mesna scavenges ROS generated at the onset of reperfusion, thus diminishing reperfusion injury and organ damage.

Acute Kidney Injury↗
PubMed2001

The polymorphonuclear leukocyte--a new target for erythropoietin.

A previous study from our laboratory has shown that erythropoietin (EPO), beside its traditional role in erythropoiesis, acts as an alleviator of oxidative stress and inflammation in chronic hemodialysis (HD) patients, conferred in part by activated polymorphonuclear leukocytes (PMNLs). To substantiate this phenomenon, the existence of EPO receptors (EPO-Rs) on PMNL membrane was examined at the transcriptional and translational levels. mRNA for EPO-R was detected in PMNLs using specific primers directed towards the extracellular region of human EPO-R cDNA. The predicted 300-bp fragment was amplified by reverse transcriptase-polymerase chain reaction. Subcloning and sequence analysis revealed 100% homology of this fragment with human EPO-R. The receptor protein was detected on the surface of intact PMNLs using (125)I-EPO. The protein was further demonstrated by flow cytometric analysis using a fluorescent monoclonal anti-EPO-R. The percentage of PMNLs expressing EPO-R showed a strong correlation with the level of EPO in the serum, suggesting an upregulation of the receptor by the hormone. Taken together with our recent findings that EPO attenuates the oxidative stress and inflammation contributed by PMNLs in HD patients, the detection of functional EPO-R expression in PMNLs places these cells among the nonerythroid, EPO-responsive target populations.

Adult↗
PubMed2001

Involvement of peripheral polymorphonuclear leukocytes in oxidative stress and inflammation in type 2 diabetic patients.

OBJECTIVE: To determine the extent to which peripheral polymorphonuclear leukocytes (PMNs) contributed to oxidative stress (OS) and inflammation in type 2 diabetic patients. RESEARCH DESIGN AND METHODS: PMNs and plasma were separated from blood withdrawn from 18 type 2 diabetic patients and 16 age- and sex-matched normal control subjects. The rate of superoxide release from phorbol 12-myristate 13-acetate (PMA)-stimulated PMNs and the plasma glutathione (GSH) levels served as measures of OS. Inflammation was assessed by PMN recruitment, expressed by peripheral blood PMN counts, and the in vitro survival of PMNs, which reflects cell necrosis. RESULTS: PMA-stimulated PMNs from diabetes released superoxide significantly faster, and plasma-reduced GSH was lower in diabetic patients than in normal control subjects. The rate of superoxide release from diabetic PMNs showed no correlation with the plasma glucose concentrations, whereas a positive linear correlation with HbA1c was found. The in vitro survival of diabetic PMNs was lower than normal control PMNs when each was incubated in its own serum. The in vitro survival of normal control PMNs was reduced when incubated with diabetic serum, whereas normal control sera promoted the survival of diabetic PMNs. Peripheral PMN counts were higher in diabetic patients than in normal control patients. CONCLUSIONS: Type 2 diabetes is accompanied by a priming of PMNs, resulting in OS and increased self-necrosis. Necrosis starts a chain of inflammatory reactions that result in cell recruitment and in the long run, with OS, may result in endothelial dysfunction. Understanding the contribution of PMNs to OS and inflammation in diabetes may illuminate new mechanisms through which endothelial dysfunction evolves and causes angiopathy and atherosclerosis.

Adult↗
PubMed2000

Effect of lipoteichoic acid on the uptake of Streptococcus pyogenes by HEp-2 cells.

Lipoteichoic acid (LTA) is thought to play a role in the interactions between Streptococcus pyogenes and host cells. We have examined the effect of exogenous LTA on the adherence and entry of S. pyogenes JRS4 strain into HEp-2 epithelial cells. LTA markedly inhibited bacterial entry in a concentration-dependent manner, up to 250 microg ml(-1). In contrast, LTA had only a slight inhibitory effect on adherence. LTA also inhibited the entry but not adherence of Salmonella typhimurium strain into HEp-2 cells. Binding experiments showed a dose-dependent binding of LTA to cells up to 10 microg ml(-1). Confocal laser microscopy imaging and analysis revealed that LTA was internalized by the epithelial cells and colocalized with F-actin. These results might imply that, following binding, exogenous LTA enters HEp-2 cells and exerts a cytotoxic effect that interferes with bacterial internalization. A possible target for LTA activity might be the actin cytoskeleton, which is known to be essential for bacterial uptake.

Bacterial Adhesion↗
PubMed2000

Mutation in csrR global regulator reduces Streptococcus pyogenes internalization.

Transposon (Tn 916) mutagenesis was employed to identify genes in group A streptococcus (GAS) that are involved in bacterial internalization by epithelial cells. One mutant displayed significantly reduced internalization efficiency and was therefore selected for further characterization. The mutant harbored a single Tn 916 insertion in csr, a genetic locus encoding a two-component regulatory system. Mutations in csr were found to derepress hyaluronic acid (HA) capsule synthesis. Since capsule expression has been previously reported to interfere with internalization of GAS, it was possible that the transposon exerted its inhibitory effect either by derepression of capsule synthesis, or by another mechanism. To study the effect of the csr mutation on bacterial internalization, isogenic mutants deficient in either csrR, hasA or both were generated. The hasA mutant adhered to and internalized into HEp-2 cells significantly better than the parent and the csrR mutant strains. The internalization efficiency of the double mutant (csrR(-)/hasA(-)) was reduced by seven-fold compared to that of the hasA mutant. These findings suggest that csrR affects streptococcal entry by modulating capsule expression as well as by another, yet unknown, mechanism.

Bacterial Adhesion↗
PubMed2000

Capsule impedes adhesion to and invasion of epithelial cells by Klebsiella pneumoniae.

The adhesion of K21a, K26, K36, and K50 capsulated Klebsiella strains to ileocecal (HCT-8) and bladder (T24) epithelial cell lines was significantly lower than that of their corresponding spontaneous noncapsulated variants K21a/3, K26/1, K36/3, and K50/3, respectively. Internalization of the bacteria by both epithelial cell lines was also significantly reduced. Similarly, a capsule-switched derivative, K2(K36), that exhibited a morphologically larger K36 capsule and formed more capsular material invaded the ileocecal epithelial cell line poorly compared to the corresponding K2 parent strain. None of the capsulated strains exhibited significant mannose-sensitive type 1 fimbriae, whereas two of the noncapsulated variants K21a/3 and K50/3 exhibited potent mannose-sensitive hemagglutinating activity. Although hemagglutinating activity that could be attributed to mannose-resistant Klebsiella type 3 fimbriae was weak in all strains, in several cases the encapsulated parent strains exhibited lower titers than their corresponding noncapsulated variants. Although the level of adhesion to the ileocecal cells is not different from adhesion to bladder cells, bacterial internalization by bladder cells was significantly lower than internalization by ileocecal cells, suggesting that bladder cells lack components required for the internalization of Klebsiella.

Bacterial Adhesion↗
PubMed1999

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Journal Article↗
PubMed1999

Interaction between erythropoietin and peripheral polymorphonuclear leukocytes in hemodialysis patients.

The effect of erythropoietin (EPO) on the oxidative stress and inflammation caused by polymorphonuclear leukocytes (PMNLs) in chronic hemodialysis (HD) patients was investigated in vivo and in vitro. The studies were performed on isolated PMNLs from peripheral blood of healthy controls and HD patients before and following 6 weeks of EPO treatment. The oxidative stress was expressed by the rate of superoxide release from phorbol 12-myristate 13-acetate stimulated PMNLs, and the inflammatory state was evaluated by in vitro PMNL survival, in addition to white blood cell and PMNL counts of the enrolled subjects. Following 6 weeks of EPO treatment, in HD patients, the rate of superoxide release from PMNLs as well as WBC and PMNL counts fell significantly when compared with the pretreatment values. PMNLs from HD patients and healthy controls incubated in vitro with increasing amounts of EPO displayed a significant reduction in their rates of superoxide release and a significant improvement in survival. We have concluded that EPO interacts with PMNLs, attenuating their primed state in HD patients, thus reducing oxidative stress and the extent of inflammation. To the best of our knowledge, this attenuation of the primed state of PMNLs by EPO is a new finding.

Cell Survival↗
PubMed1999

Closure of the ductus venosus in premature infants: findings on real-time gray-scale, color-flow Doppler, and duplex Doppler sonography.

OBJECTIVE: Our objective was to use gray-scale, color-flow, and duplex Doppler sonography to study the anatomy, flow pattern, and time of closure of the ductus venosus in healthy premature infants. SUBJECTS AND METHODS: We prospectively examined the ductus venosus in 130 premature infants whom we divided into two groups: Group I comprised 27 neonates of gestational age 28-32 weeks, and group II comprised 103 neonates of gestational age 33-36 weeks. Neonates who had undergone umbilical vessel manipulation were excluded from the study. All examinations included gray-scale, color-flow, and duplex Doppler sonography. Patency, length, color flow, and Doppler characteristics of the ductus venosus were recorded. Neonates were examined 1-2 days after birth, 6-7 days after birth, and subsequently every 3-4 days until ductus closure was observed. The time of closure of the ductus for the two groups was compared using the chi-square test. RESULTS: The ductus venosus was patent during the initial examination in 128 of the 130 neonates. Doppler waveform was venous with little variation in velocity. Ductus length slightly exceeded 1 cm in both groups. We found a statistically significant difference in the percentage of infants having a patent ductus venosus after the initial examination: At 1 week after birth, ductus patency was shown in 85% of the infants in group I and in 56% of the infants in group II; at 2 weeks, the respective percentages were 42% and 14%; and at 3 weeks, 27% and 0%. CONCLUSION: The ductus venosus is patent 1-2 days after birth in virtually all premature infants. From 6 days after birth and onward, a significantly greater percentage of smaller premature infants (i.e., 28-32 weeks' gestational age) have a patent ductus venosus than do larger premature infants (i.e., 33-36 weeks' gestational age).

Blood Flow Velocity↗
PubMed1999

Why do we fail with penicillin in the treatment of group A streptococcus infections?

Acute pharyngotonsillitis caused by beta-haemolytic group A streptococcus (GAS) is a common childhood disease. Phenoxymethyl penicillin remains the drug of choice, as no resistance has been reported so far. Nevertheless, the failure of penicillin to eradicate streptococci from the throat occurs in up to 35% of patients with pharyngotonsillitis, and might present clinical concern. Various explanations have been proposed over the years to account for this perplexing phenomenon. Among these are coexistence of oropharyngeal beta-lactamase-producing bacteria that degrade penicillin, growth interference by aerobic and anaerobic commensals, penicillin tolerance, reinfection, and poor antibiotic compliance. Although GAS has been considered an extracellular pathogen, recent studies have demonstrated that strains of this bacterium can internalize epithelial cells both in vitro and in vivo. The intracellular niche may protect the bacterium from penicillin that does not gain high intracellular concentration. In support of this hypothesis, GAS strains were shown to survive 4-7 days inside cultured epithelial cells. In addition, it was found that GAS strains isolated from patients with eradication failure harbour the internalization-associated gene, prtF1/sfbI, in higher prevalence than do strains recovered from patients with successful eradication. Thus, internalization and intracellular survival represent a novel explanation for penicillin eradication failure.

Humans↗
PubMed1998

Participation of peripheral polymorphonuclear leukocytes in the oxidative stress and inflammation in patients with essential hypertension.

Oxidative stress and inflammation have recently been linked to endothelial damage in essential hypertension (EH). Activated peripheral polymorphonuclear leukocytes (PMN) damage surrounding tissue by releasing reactive oxygen species (ROS) and proteolytic enzymes before self-necrosis. PMN necrosis further exacerbates inflammation and promotes chemotaxis and PMN recruitment. The number and properties of PMN from untreated EH patients is the focus of the present study. Oxidative stress was assessed by measuring the rate of superoxide anion release from separated, phorbol ester-stimulated PMN and the redox state of plasma glutathione. Inflammation was estimated indirectly by determining PMN number and their in vitro survival. PMN from EH patients (n = 37) released superoxide anion faster (P < .0001) than those of normotensives (NC, n = 37), 17.7 +/- 1.14 v 9.54 +/- 0.51 nmol/10 min/10(6) cells. The redox state of glutathione was twofold higher in EH plasma (P < .02) indicating systemic oxidative stress. PMN survival in vitro correlates linearly with the rate of superoxide release (r2 = 0.60, P < .02) and PMN count of EH patients, although in the normal range, were significantly higher (P < .0001), indicating necrosis and recruitment. Hypertensive plasma significantly reduced NC PMN viability, whereas normal plasma significantly increased EH PMN viability. What our studies show is that EH is accompanied by a primed state PMN that does not correlate with the levels of blood pressure. PMN priming in EH patients reflects an in vivo exposure to a constant stimulus ending in oxidative stress, increased self-necrosis, and cell recruitment. Oxidative stress and inflammation will result in endothelial damage and atherosclerosis in the long run.

Adult↗
PubMed1998

Protein F1 is required for efficient entry of Streptococcus pyogenes into epithelial cells.

It was recently reported that strains of Streptococcus pyogenes are capable of inducing entry of the bacterium into epithelial cells; however, nothing is known regarding the gene(s) and the underlying mechanism(s) involved. Using isogenic mutants of S. pyogenes JRS4 strain that are defective in the expression of each of the surface proteins F1 and M6, it was demonstrated that both are required for efficient internalization. Expression of F1 on the surface of a poorly invading S. pyogenes strain significantly enhances its internalization efficiency. Protein F1-mediated internalization is inhibited by UR, the nonrepetitive fibronectin-binding domain of this protein, and to a lesser extent, by the repetitive fibronectin-binding domain, RD2. Polyclonal anti-human fibronectin antibodies completely abolish F1-mediated internalization; increasing fibronectin concentrations result in a significant enhancement of bacterial uptake. The findings shown here suggest that protein F1 mediates streptococcal internalization and that the M6 protein is required for more efficient entry of the bacterium.

Adhesins, Bacterial↗
PubMed1998

Renal ischemia-reperfusion injury: contribution of nitric oxide and renal blood flow.

The contributions of nitric oxide (NO) and renal blood flow (RBF) were examined in ischemia-reperfusion injury in the rat kidney. The function of both kidneys was assessed by glomerular filtration rate (GFR), and fractional excretion of sodium (FENa), calculated before, during unilateral renal artery clamping (45 min), and following reperfusion (90 min). RBF was measured in the same model by ultrasonic flowmetry. Intrarenal NO levels were modulated by administration of S-nitroso-N-acetylpenicillamine (SNAP), L-arginine, acetylcholine, and the NO synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME). SNAP increased GFR from 0.20 +/- 0.04 ml/min in control ischemic kidney to 0.38 +/- 0.06 ml/min and reduced FENa from 19.3 +/- 3.4 to 9.5 +/- 1.8%. Similar results were observed when L-arginine was administered. Acetylcholine had no effect on GFR or FENa. RBF was fully restored within 60 min following reperfusion, with no change in the rate of recovery by L-arginine. L-NAME aggravated the ischemia-reperfusion injury, preventing full restoration of RBF, further reducing GFR and worsening FENa. In conclusion, ischemia-reperfusion injury ends in low intrarenal levels of NO. We propose that this low NO level results from damage to the endothelial receptor signal transduction process and is not due to impaired NO synthase activity or to changes in RBF.

Acetylcholine↗
PubMed1997

Insertional inactivation of streptolysin S expression is associated with altered riboflavin metabolism in Streptococcus pyogenes.

Transposon Tn916 mutagenesis was used to create a mutant of Streptococcus pyogenes M type 3, designated ISS417, in which the ability to produce streptolysin S (SLS) and several other exoproteins was impaired. Concomitantly, the mutant became dependent upon riboflavin for growth and was able to grow in Todd Hewitt broth (THB) when supplemented with riboflavin or riboflavinrich yeast extract. The parent strain was apparently able to utilize THB-derived components as a substitute for riboflavin, while the mutant was not. Although the parent strain grew well in synthetic medium, it was unable to produce SLS, except when it was supplemented with a small amount of THB. Thus, a component of THB was able to "trigger" SLS formation in the parent strain. The mutant grew well in this medium, but was unable to produce SLS even when it was supplemented with THB. Southern hybridization analysis revealed that the ISS417 mutant harbours a single transposon insertion in its chromosome. Phage transduction experiments showed that the riboflavin dependency and the inability to make SLS phenotypes are co-transducible. The pleotrophic properties of the ISS417 mutant differ from those reported for insertional inactivation of the mga locus which regulates production of a number of surface proteins in S. pyogenes and the sar locus which regulates production of a number of exoproteins in Staphylococcus aureus. In view of the possibility that there exist a genetic linkage between the riboflavin biosynthetic pathway and expression of the oxygen-stable SLS, we hypothesize that SLS has a role in the growth economy of S. pyogenes.

Bacterial Proteins↗
PubMed1997

Proteins M6 and F1 are required for efficient invasion of group A streptococci into cultured epithelial cells.

Group A streptococci were recently shown to be capable of invading human epithelial cell monolayers. Cell invasion might be an important virulence trait of streptococci that enable the pathogen to gain entry into deeper tissues after initial binding to host cells. Nothing is known concerning the nature of streptococcal components that mediate invasion. Using isogenic mutants of strain JRS4 that are defective in the expression of either M6 protein or protein F1, or both proteins, it was demonstrated that both adhesins are required for efficient invasion. Further more, expression of protein F1 on the surface of a non-invasive strain rendered the latter invasive, suggesting that protein F1 is directly involved in the invasion process.

Adhesins, Bacterial↗
PubMed1997

Molecular and structural differences between rat brain D-1 and renal DA-1 dopamine receptors.

Renal DA-1 dopamine receptors in proximal tubules (PTs) of the Wistar-Kyoto (WKY) rat display pharmacological binding properties which are different from central nervous system (CNS) striatal D-1 dopamine receptors. In general, the renal DA-1 receptors display affinity binding values of dopaminergic drugs which are 6-36-fold less than those seen for brain D-1 receptors. The renal and brain DA receptors also displayed differential sensitivity toward the alkylating agent, N-ethylmaleimide (NEM). Inactivation of 50% of DA-1 renal receptors was achieved at lower concentrations of NEM (5.2 microM), relative to brain D-1 receptors (140 microM). Western blot analyses of rat pituitary GH4C1 cells, transfected with human CNS D-1 receptor cDNA, with human anti-D-1 dopamine receptor antiserum, detected a single polypeptide with M(r) of 66 kDa. In PTs, a specific polypeptide of higher molecular weight (M(r) = 72 kDa) was seen. Surprisingly, in rat striatal membranes, the D-1 antiserum failed to detect any proteins within this molecular weight range. Photoaffinity labeling studies with a DA-1 selective photoligand, identified the identical protein by autoradiography and Western blots in kidney, but not in striate. Together, these data indicate that renal DA-1 dopamine receptors have distinct molecular properties relative to brain D-1 dopamine receptors.

Animals↗