Tuning the aspect ratio of silver nanospheroids embedded in silica: erratum.

We present a corrigendum to our Letter [Opt. Lett.35, 703 (2010)10.1364/OL.35.000703]. In the original Letter we inadvertently included in Fig. 2(a) a TEM micrograph corresponding to a different, but very similar, sample. This corrigendum replaces Fig. 2(a) with a correct version. Since the main results are rather based in optical absorption measurements, and their modeling by using the T-matrix method, this correction does not affect the results and conclusions of the original Letter.

Superlinear Photoluminescence by Ultrafast Laser Pulses in Dielectric Matrices with Metal Nanoclusters.

An intense photoluminescence emission was observed from noble metal nanoclusters (Pt, Ag or Au) embedded in sapphire plates, nucleated by MeV ion-implantation and assisted by an annealing process. In particular, the spectral photoluminescence characteristics, such as range and peak emission, were compared to the behavior observed from Pt nanoclusters embedded in a silica matrix and excited by UV irradiation. Correlation between emission energy, nanoclusters size and metal composition were analyzed by using the scaling energy relation EFermi/N1/3 from the spherical Jellium model. The metal nanocluster luminescent spectra were numerically simulated and correctly fitted using the bulk Fermi energy for each metal and a Gaussian nanoclusters size distribution for the samples. Our results suggest protoplasmonics photoluminescence from metal nanoclusters free of surface state or strain effects at the nanoclusters-matrix interface that can influence over their optical properties. These metal nanoclusters present very promising optical features such as bright visible photoluminescence and photostability under strong picosecond laser excitations. Besides superlinear photoluminescence from metal nanoclusters were also observed under UV high power excitation showing a quadratic dependence on the pump power fluence.

Ultrafast optical phase modulation with metallic nanoparticles in ion-implanted bilayer silica.

The nonlinear optical response of metallic-nanoparticle-containing composites was studied with picosecond and femtosecond pulses. Two different types of nanocomposites were prepared by an ion-implantation process, one containing Au nanoparticles (NPs) and the other Ag NPs. In order to measure the optical nonlinearities, we used a picosecond self-diffraction experiment and the femtosecond time-resolved optical Kerr gate technique. In both cases, electronic polarization and saturated absorption were identified as the physical mechanisms responsible for the picosecond third-order nonlinear response for a near-resonant 532 nm excitation. In contrast, a purely electronic nonlinearity was detected at 830 nm with non-resonant 80 fs pulses. Regarding the nonlinear optical refractive behavior, the Au nanocomposite presented a self-defocusing effect, while the Ag one presented the opposite, that is, a self-focusing response. But, when evaluating the simultaneous contributions when the samples are tested as a multilayer sample (silica-Au NPs-silica-Ag NPs-silica), we were able to obtain optical phase modulation of ultra-short laser pulses, as a result of a significant optical Kerr effect present in these nanocomposites. This allowed us to implement an ultrafast all-optical phase modulator device by using a combination of two different metallic ion-implanted silica samples. This control of the optical phase is a consequence of the separate excitation of the nonlinear refracting phenomena exhibited by the separate Au and Ag nanocomposites.

Tuning the aspect ratio of silver nanospheroids embedded in silica.

A method is proposed to control the aspect ratio (epsilon) of elongated nanoparticles obtained by ion implantation in a transparent matrix. The procedure was tested for Ag spheroids in silica and we could accurately change epsilon in the range from the maximum value obtained by the ion implantation (around 3.0 in this case) to 1.0 (spherical shape). The values of epsilon were determined in several steps from optical extinction spectroscopy measurements, by fitting the modification and splitting of the surface plasmon resonance peak, using the T-matrix method. In the initial (maximum deformation) and final (undeformed) states, transmission electron microscopy images were obtained, showing a good agreement with the T-matrix results in both cases.

Hipokalemia, acidosis tubular distal y tiroiditis de Hashimoto / No disponible

No disponible

Plasminogen activator inhibitor-1 activity and 4G/5G polymorphism in hemodialysis.

INTRODUCTION: Chronic insufficiency alters homeostasis, in part due to endothelial inflammation. Plasminogen activator inhibitor-1 (PAI-1) is increased in renal disease, contributing to vascular damage. We assessed PAI-1 activity and PAI-1 4G/5G polymorphism in hemodialysis (HD) subjects and any association between thrombotic vascular access (VA) events and PAI-1 polymorphism. METHODS: Prospective, observational study in 36 HD patients: mean age: 66.6 +/- 12.5 yr, males n=26 (72%), time on HD: 28.71 +/- 22.45 months. Vascular accesses: 10 polytetrafluoroethylene grafts (PTFEG), 22 arteriovenous fistulae (AVF), four dual lumen catheters (CAT). Control group (CG): 40 subjects; mean age: 60.0 +/- 15 yrs, males n=30 (75%). Group A (GA): thrombotic events (n=12), and group B (GB): No events (n=24). Groups were no different according to age (69.2 +/- 9.12 vs. 65.3 +/- 14.5 yrs), gender (males: 7; 58.3% vs. 18; 81.8%), time on HD (26.1 +/- 14.7 vs. 30.1 +/- 38.7 months), causes of renal failure. Time to follow-up for access thrombosis: 12 months. RESULTS: PAI-1 levels in HD: 7.21 +/- 2.13 vs. CG: 0.42 +/- 0.27 U/ml (p<0.0001). PAI-1 4G/5G polymorphic variant distribution in HD: 5G/5G: 6 (17%), 4G/5G: 23 (64%); 4G/4G: 7 (19%) and in CG: 5G/5G: 14 (35%); 4G/5G: 18 (45%); 4G/4G: 8 (20%). C-reactive protein (CRP) in HD: 24.5 +/- 15.2 mg/L vs. in CG 2.3 +/- 0.2 mg/L (p<0.0001). PAI-1 4G/5G variants: GA: 5G/5G: 3; 4G/5G: 8; 4G/4G: 1; GB: 5G/5G: 3; 4G/5G: 15; 4G/4G: 6. Thrombosis occurred in 8/10 patients (80%) with PTFEG, 3/22 (9%) in AVF, and 1/4 (25%) in CAT. Among the eight PTFEG patients with thrombosis, seven were PAI 4G/5G. CONCLUSIONS: PAI-1 levels were elevated in HD patients, independent of their polymorphic variants, 4G/5G being the most prevalent variant. Our data suggest that in patients with PTFEG the 4G/5G variant might be associated with an increased thrombosis risk.

Clopidogrel diminishes hemodialysis access graft thrombosis.

BACKGROUND: The most common complication of hemodialysis access graft is thrombosis. Clopidogrel, an inhibitor of platelet aggregation, was assessed to prevent this serious complication. METHODS: Nineteen patients on chronic hemodialysis whose vascular accesses were grafts were divided into two groups: Group A (n=11, 58%) consisted of patients who did not receive anti-thrombotic therapy after graft placement; Group B (n=8, 42%) received clopidogrel 75 mg/day from two days after surgery onwards. Both groups were well matched with respect to age, gender, cause of renal failure, hematocrit, platelet count and Kt/V. All patients' thrombotic episodes were followed up from the day of graft surgery until thrombosis was diagnosed. Finally, the survival difference between both groups was determined. RESULTS: Ten thrombotic episodes were diagnosed in Group A while no events were reported in Group B (p<0.001). Graft access days of patency were significantly more in Group B than in Group A (350.8+/-166 vs 86.8+/-69, p<0.001). The time elapsed from dialysis initiation to graft placement was not different (Group A: 18+/-12 days; Group B: 20+/-10 days). Days in hemodialysis were different between both groups (Group A: 195.9+/-96; Group B: 545.5+/-291, p<0.001) and all patients of Group A (n=11, 57.9%) and two patients of Group B (25%) died (p=0.001). No major bleeding events were reported. CONCLUSIONS: Clopidogrel significantly decreased thrombotic graft episodes. Patients on clopidogrel had a prolonged vascular access patency, longer time on hemodialysis and longer survival.

Low initial vitamin B12 levels in Helicobacter pylori--positive patients on chronic hemodialysis.

BACKGROUND: Helicobacter pylori has been identified as a possible cause of vitamin B12 deficiency in the general population. We assessed any potential relationship between low cyanocobalamin serum levels and Helicobacter pylori status in hemodialysis patients and subsequently correlated these results with the existence of anemia (a common complication in hemodialysis patients), and macrocytosis. METHODS: In 29 chronic hemodialysis patients, active H. pylori infection was diagnosed using two different methods regardless of digestive symptoms: by searching for bacterial antigens in stools and by the detection of urea breakdown through breath testing. If these results were non-coincident, gastroscopy was performed and antral biopsies obtained. Patients were subsequently divided into group A (H. pylori-positive, n = 8, 28%) and group B (H. pylori-negative, n = 21, 72%). The corresponding initial values of erythrocytic folic acid, vitamin B12 and homocysteine prior to the first hemodialysis session of each patient were retrospectively collected. RESULTS: Vitamin B12 levels (normal 200- 900 pg/ml) were significantly lower in group A compared to group B (225.4 +/- 111.9 vs. 707.9 +/- 258.3 pg/ml, p < 0.011). In group A, 5 patients (63%) had vitamin B12 deficiency (154 +/- 24.6 pg/ml). Baseline hematocrits, erythrocyte folic acid and serum homocysteine levels were not different between the groups, but mean corpuscular volumes were significantly higher in group A compared to group B (109.7 +/-14.1 vs. 91.8 +/- 8.8 fl, p = 0.002). CONCLUSIONS: H. pylori-positive chronic hemodialysis patients may present with lower vitamin B12 blood levels and macrocytosis. H. pylori infection should be suspected in this population when low or low-normal vitamin B12 levels or macrocytosis exist.

Thrombotic events of arteriovenous fistulae in hemodialysis patients related to the C677T thermolabile variant of methylenetetrahydrofolate reductase.

BACKGROUND: Hyperhomocysteinemia is a risk factor for thrombosis, a frequent complication of vascular access (VA) in hemodialysis (HD). The enzyme methylenetetrahydrofolate reductase (MTHFR) is necessary for the remethylation of homocysteine (Hcy) to methionine. It has been postulated that patients homozygous and, to a lesser extent, heterozygous for the C677T thermolabile variant of this enzyme present a reduced catalytic activity, with secondary increases in plasmatic Hcy levels (normal: 10 +/- 5 micromol/L) and an elevated risk of vascular thromboses. METHODS: Sixty-two patients on chronic HD were divided into two groups: group A (n = 23, 37.1%) was normal for the enzyme (CC); group B (n = 39, 62.9%) was heterozygous (CT). Both groups were not different according to age, sex, time on HD, hematocrits (Hct), baseline levels of Hcy, folic acid and vitamin B12. After the 1st HD session patients were started on folic acid 10 mg/day and 500 microg/week of intravenous (i.v.) methylcobalamin. RESULTS: Two years later, thrombotic events were not different between the two groups. Group A = 5 (21.7%) vs. group B = 12 (30.7%), Hcy levels were significantly different between final and baseline measurements (group A 21.5 +/- 5.2 vs. 16.6 +/- 3.9 micromol/L, p = 0.02; group B 22.1 +/- 8.9 vs. 16.1 +/- 3.9 micromol/L, p = 0.008), folic acid (group A 22.1 vs. 346.9 ng/ml, range (r) =166-527, p < 0.001; group B 19.2 vs. 218.5 ng/ml, r = 138-298, p < 0.001) and vitamin B12 (group A 1489 vs. 3192.3 pg/ml, r = 1494-4890, p = 0.01; group B 1086 vs. 1513.8 pg/ml, r = 1092-1934, p = 0.02). CONCLUSIONS: HD patients heterozygous for the C677T variant of the enzyme MTHFR can present a similar risk of thrombotic events in arteriovenous fistulae (AVF) compared to patients normal for the enzyme at a 1-yr follow-up. These results could be explained by an adequate control of Hcy levels after folic acid and methylcobalamin replacement therapy.

N-acetylcysteine reduces malondialdehyde levels in chronic hemodialysis patients--a pilot study.

BACKGROUND: Oxidative stress has been implicated in the development of endothelial damage in hemodialysis (HD). We have assessed the effects of N-acetylcysteine (NAC), a compound with antioxidant effects, on malondialdehyde (MDA), a marker of oxidative stress on lipid peroxidation. METHODS: A clinical trial was conducted in which 24 chronic HD patients were divided into 2 groups according to gender, age, time on HD and cause of renal failure. The NAC group (n = 12) received 600 mg of NAC twice a day for 30 days. The remaining patients constituted the control group (n = 12). MDA levels were measured pre- and post-dialysis at the beginning of the study (baseline) and on day 30 (30 days). RESULTS: Baseline pre- and post-dialysis MDA levels were not different between both groups and were above normal values. A significant decrease was found in the NAC group when either pre- or post-dialysis MDA levels were compared to the corresponding control group levels on day 30 (pre-dialysis NAC vs control group 3.01 +/- 0.6 vs 4.5 +/- 0.73 micromol/l, p < 0.0001, post-dialysis NAC vs control group 2.76 +/- 0.5 vs 4.39 +/- 0.7 micromol/l, p < 0.0001). Only in the NAC group were pre-dialysis MDA 30-day levels different from pre-dialysis baseline levels (3.01 +/- 0.6 vs 5.07 +/- 1.6 micromol/l, p < 0.002). Post-dialysis MDA 30-day concentrations were significantly lower than post-dialysis MDA baseline levels (2.76 +/- 0.5 vs 4.32 +/- 0.7 micromol/l, p < 0.002) and pre-dialysis MDA 30-day measurements (2.76 +/- 0.5 vs 3.01 +/- 0.6 micromol/l, p < 0.011). CONCLUSIONS: MDA levels are elevated in chronic HD patients and are not significantly reduced by HD. NAC significantly reduces malondialdehyde levels in chronic HD patients.

Late-onset cytomegalovirus-associated interstitial nephritis in a kidney transplant.

Cytomegalovirus is the most important viral infection in kidney transplants, but rarely affects the allograft after the sixth month posttransplantation. We present a patient who developed renal failure eighteen months posttransplant; a kidney biopsy showed cytomegalovirus inclusions, acute tubular necrosis and mild interstitial nephritis. After intravenous ganciclovir, renal function transiently improved. Cytomegalovirus pp65 antigen was weekly reported as negative. One month later another biopsy was performed due to renal failure. The findings were consistent with tubular atrophy and severe interstitial nephritis. No cytomegalovirus cellular inclusions were found on histology, including immunohistochemical and polymerase chain reaction studies; pp65 antigen studies were persistently negative. Despite an attempt to recover renal function with steroid therapy, the patient restarted hemodialysis 20 months posttransplantation. This report suggests that cytomegalovirus should be considered as a late cause of kidney failure even in the absence of infection-related symptoms. The irreversible allograft damage can be caused despite the successful eradication of the virus with intravenous ganciclovir.

Ultrasonographic diagnosis of ovine cystic echinococcosis.

The sanitary and economic impact of cystic echinococcosis is serious in those countries where it becomes endemic. Ultrasonography is one technique that may be used to diagnose this disease in endemic areas. In parasitized sheep, hydatid cysts appear sonographically as a round hypoechoic structure. Twenty two sheep destined for slaughter were studied sonographically and imaging findings compared to post-mortem findings. Three sheep with hydatid cysts were identified. Eighty additional sheep not destined for slaughter were also studied. Echinococcus granulosus cysts were detected in three animals. Forty sheep from a non-endemic area had no hepatic cysts. The in vivo sonographic study of sheep provides a useful screening tool for echinococcosis.

Cyclosporine-associated thrombotic microangiopathy during daclizumab induction: a suggested therapeutic approach.

A woman on daclizumab developed thrombotic microangiopathy secondary to cyclosporine after a living-unrelated kidney transplant. Despite cyclosporine discontinuation, hemolysis persisted. The second dose of daclizumab was postponed 24 h, and after a maximum of two sessions of plasmapheresis (to avoid further modifications in daclizumab schedule) with plasma exchange, daclizumab was administered. Plasma infusions were prescribed until D-dimer and fibrinogen-degradation products normalized; thereafter, FK-506 was started without recurrence of the hemolytic picture and renal function restored. This observation suggests that in patients on daclizumab who develop thrombotic microangiopathy secondary to immunosuppressants, if discontinuation of the offending drug is unsuccessful, plasmapheresis with plasma exchange can be performed when the lowest levels of daclizumab exist, followed by daclizumab infusion. Plasma prescription must be continued thereafter until D-dimer and figrinogen-degradation products normalize. However, if hemolysis persists when daclizumab levels are high, plasma infusions are useful and plasmapheresis avoided. FK-506 administration did not result in recurrence of hemolysis during daclizumab induction.