Roles for alpha(2)p24 and COPI in endoplasmic reticulum cargo exit site formation. (33/2483)

A two-step reconstitution system for the generation of ER cargo exit sites from starting ER-derived low density microsomes (LDMs; 1.17 g/cc) is described. The first step is mediated by the hydrolysis of Mg(2+)ATP and Mg(2+)GTP, leading to the formation of a transitional ER (tER) with the soluble cargo albumin, transferrin, and the ER-to-Golgi recycling membrane proteins alpha(2)p24 and p58 (ERGIC-53, ER-Golgi intermediate compartment protein) enriched therein. Upon further incubation (step two) with cytosol and mixed nucleotides, interconnecting smooth ER tubules within tER transforms into vesicular tubular clusters (VTCs). The cytosolic domain of alpha(2)p24 and cytosolic COPI coatomer affect VTC formation. This is deduced from the effect of antibodies to the COOH-terminal tail of alpha(2)p24, but not of antibodies to the COOH-terminal tail of calnexin on this reconstitution, as well as the demonstrated recruitment of COPI coatomer to VTCs, its augmentation by GTPgammaS, inhibition by Brefeldin A (BFA), or depletion of beta-COP from cytosol. Therefore, the p24 family member, alpha(2)p24, and its cytosolic coat ligand, COPI coatomer, play a role in the de novo formation of VTCs and the generation of ER cargo exit sites.  (+info)

Effect of intravenous albumin on renal impairment and mortality in patients with cirrhosis and spontaneous bacterial peritonitis. (34/2483)

BACKGROUND: In patients with cirrhosis and spontaneous bacterial peritonitis, renal function frequently becomes impaired. This impairment is probably related to a reduction in effective arterial blood volume and is associated with a high mortality rate. We conducted a study to determine whether plasma volume expansion with intravenous albumin prevents renal impairment and reduces mortality in these patients. METHODS: We randomly assigned 126 patients with cirrhosis and spontaneous bacterial peritonitis to treatment with intravenous cefotaxime (63 patients) or cefotaxime and intravenous albumin (63 patients). Cefotaxime was given daily in dosages that varied according to the serum creatinine level, and albumin was given at a dose of 1.5 g per kilogram of body weight at the time of diagnosis, followed by 1 g per kilogram on day 3. Renal impairment was defined as nonreversible deterioration of renal function during hospitalization. RESULTS: The infection resolved in 59 patients in the cefotaxime group (94 percent) and 62 in the cefotaxime-plus-albumin group (98 percent) (P=0.36). Renal impairment developed in 21 patients in the cefotaxime group (33 percent) and 6 in the cefotaxime-plus-albumin group (10 percent) (P=0.002). Eighteen patients (29 percent) in the cefotaxime group died in the hospital, as compared with 6 (10 percent) in the cefotaxime-plus-albumin group (P=0.01); at three months, the mortality rates were 41 percent (a total of 26 deaths) and 22 percent (a total of 14 deaths), respectively (P=0.03). Patients treated with cefotaxime had higher levels of plasma renin activity than those treated with cefotaxime and albumin; patients with renal impairment had the highest values. CONCLUSIONS: In patients with cirrhosis and spontaneous bacterial peritonitis, treatment with intravenous albumin in addition to an antibiotic reduces the incidence of renal impairment and death in comparison with treatment with an antibiotic alone.  (+info)

Antioxidant consumption and repletion kinetics in nasal lavage fluid following exposure of healthy human volunteers to ozone. (35/2483)

To obtain information on the real-time events occurring within human respiratory tract lining fluids (RTLFs) during ozone exposure, sequential nasal lavage was performed on 13 human volunteers exposed on separate occasions to 0.2 parts per million O3 and filtered air (2-h exposures, with intermittent exercise). Nasal lavage was performed and blood samples obtained at four time points throughout each exposure: pre-exposure (Pre-E), 1 h into exposure (1h-E), immediately post-exposure (0h-PE) and 1 h post-exposure (1h-PE). Endobronchial mucosal biopsies were obtained at 1.5 h-post exposure (1.5h-PE). Nasal RTLF neutrophilia was not apparent during, or 1.5 h after, 03 exposure. Furthermore, activation of the pre-existing neutrophil population did not occur. Airway permeability was not altered by this 03 exposure regimen. Sequential lavage resulted in significant washout of RTLF ascorbic acid, reduced glutathione, extracellular superoxide dismutase and myeloperoxidase at 1h-E, 0h-PE and 1.5h-PE relative to baseline Pre-E values. In contrast, RTLF uric acid (UA), total protein and albumin concentrations did not display washout kinetics. Of the antioxidants examined, only UA was clearly depleted by 03, concentrations, falling by 6.22 micromol x L(-1) at 1h-E, compared with 1.61 micromol x L(-1) (p<0.01) during control air exposure. The establishment of a new pseudo-steady-state concentration of RTLF UA (70% of Pre-E values) during the second hour of O3 exposure was coincident with a small but significant increase in plasma UA concentration (19.27 (O3) versus 1.95 micromol x L(-1) (air), p<0.05). These data demonstrate that inhalation of 0.2 parts per million 03 results in the depletion of nasal respiratory tract lining fluid uric acid and that this regional loss of uric acid leads to a small increase in plasma uric acid concentration. Whilst the reaction of uric acid with inspired 03 may confer protection locally, the role of upper airway uric acid as a sink for inhaled O3 is not supported by these findings.  (+info)

Co-introduction of an antisense gene for an endogenous seed storage protein can increase expression of a transgene in Arabidopsis thaliana seeds. (36/2483)

We have investigated whether the expression in Arabidopsis thaliana seeds of a transgene (the Phaseolus vulgaris arcelin (arc)5-I gene) could be enhanced by the simultaneous introduction of an antisense gene for an endogenous seed storage protein (2S albumin). Seeds of plants transformed with both the arc5-I gene and a 2S albumin antisense gene contained reduced amounts of 2S albumins and increased arcelin-5 (Arc5) accumulation levels compared to lines harboring the arc5-I gene only. Arc5 production could be enhanced to more than 24% of the total seed protein content, suggesting that antisense technology could be of great utility to favor high expression of transgenes.  (+info)

The human and rat recombinant receptors for advanced glycation end products have a high degree of homology but different pharmacokinetic properties in rats. (37/2483)

The accelerated formation of advanced glycation end products (AGEs) is implicated in diabetic microvascular and macrovascular complications. The binding of AGEs to their cellular surface receptor (RAGE) induces vascular dysfunction and in particular an increase in vascular permeability. We previously demonstrated that rat recombinant RAGE (rR-RAGE) produced in insect cells corrected the hyperpermeability due to RAGE-AGE interaction and that pharmacokinetic properties of rR-RAGE after i.v. administration in rats were compatible with a potential therapeutic use. In the present study, we showed that recombinant human RAGE (rH-RAGE) had a similar efficacy in inhibiting AGE-induced endothelial alteration and in reducing the hyperpermeability observed in streptozotocin-induced diabetic rats. (125)I-rH-RAGE elimination half-life after i.v. administration was similar in diabetic and normal rats (53.7 +/- 7.6 and 45.3 +/- 4.0 h, respectively). The presence of AGEs is responsible for a higher distribution volume in diabetic rats compared with normal rats (15.3 +/- 2.7 and 7.7 +/- 0. 7 l/kg, respectively). Immunoreactive (125)I-rH-RAGE decreased more rapidly than did immunoreactive (125)I-rR-RAGE. The differences between (125)I-rH-RAGE and (125)I-rR-RAGE pharmacokinetics in rat may be related to differences in potential O-glycosylation and protease cleavage sites between the two RAGE molecules.  (+info)

Hepatoma-specific antitumor activity of an albumin enhancer/promoter regulated herpes simplex virus in vivo. (38/2483)

Targeting viral vectors to appropriate cell types so that normal cells are not adversely affected is an important goal for gene therapy. Previously, we described a novel approach to viral gene therapy using a conditional, replication-competent herpes simplex virus (HSV), where replication and associated cytotoxicity are limited to a specific cell-type by the regulated expression of an essential immediate-early viral gene product. In this report we analyze the hepatoma-specific replication, cytotoxicity and anti-tumor effect of recombinant HSV G92A, regulated by the albumin enhancer/promoter. G92A efficiently replicated in vitro in two human hepatoma cell lines expressing albumin, but not in four human non-hepatoma, albumin-non-expressing tumor cell lines, while all cell lines were equally susceptible to a tissue nonspecific HSV recombinant, hrR3. In vivo, G92A replicated well in subcutaneous xenografts of human hepatoma cells (Hep3B) in athymic mice, but not in non-hepatoma subcutaneous tumors (PC3 and HeLa), whereas, hrR3 replicated well in both tumor types. Intratumoral inoculation of G92A inhibited the growth of established subcutaneous hepatoma tumors in nude mice, but not prostate tumors. Replication-competent viral vectors controlled by cell-specific transcriptional regulatory sequences provide a new therapeutic strategy for tumor therapy.  (+info)

Factors affecting blood clearance and in vivo distribution of polyelectrolyte complexes for gene delivery. (39/2483)

Self-assembling polycation/DNA complexes represent a promising synthetic vector for gene delivery. However, despite considerable versatility and transfectional activity in vitro, such materials are quickly eliminated from the bloodstream following intravenous injection (plasma alpha half-life typically less than 5 min). For targeted systemic delivery a more prolonged plasma circulation of the vector is essential. Here we have examined factors contributing to rapid elimination of poly(L-lysine) (pLL)/DNA complexes from the bloodstream, and implicate the binding of proteins to the polyelectrolyte complexes as a likely cause for their blood clearance. pLL/DNA complexes reisolated from serum associate with several proteins, depending on their net charge, although the major band on SDS-PAGE co-migrates with albumin. Serum albumin binds to pLL/DNA complexes in vitro, forming a ternary pLL/DNA/albumin complex which regains some ethidium bromide fluorescence and fails to move during agarose electrophoresis. Albumin also causes increased turbidity of complexes, and reduces their zeta potential to the same level (-16 mV) as is measured in serum. We propose that rapid plasma elimination of polycation/DNA complexes results from their binding serum albumin and other proteins, perhaps due to aggregation and phagocytic capture or accumulation of the ternary complexes in fine capillary beds.  (+info)

Targeting of transferrin receptors in nude mice bearing A431 and LS174T xenografts with [18F]holo-transferrin: permeability and receptor dependence. (40/2483)

The goal of this study was to investigate whether 18F-labeled transferrin (Tf), which has a molecular weight (Mr) of approximately 79,000, binds to Tf receptor sites in tumors in a specific manner within the time frame commensurate with the half-life of 18F (109.7 min). We have previously shown that [18F]holo-Tf ([18F]Tf) maintains all properties of native Tf in vitro and that it can specifically target liver Tf receptor sites in vivo. METHODS: The distribution of [18F]Tf, using [18F]albumin (Alb) or [14C]Alb as a control, was studied over a 6-h period in nude mice bearing LS174T and A431 xenografts of a high- and low-permeability tumor, respectively. RESULTS: Measurements of Tf receptor concentration in the tumor extracts suggest similar binding capacities. In vivo, liver uptake values were higher for [18F]Tf than for both [18F]Alb and [14C]Alb throughout the study, indicating specific binding. In contrast, tumor Tf uptake values remained below those of the Alb tracers, and tumor-to-blood ratios of [18F]Tf in each xenograft increased in parallel with those of the Alb tracers. The permeabilities of [14C]Alb and [18F]Tf in LS174T were calculated to be 1.29+/-0.49 and 1.03+/-0.38 microL/min/g (mean +/- SD), respectively, whereas the permeabilities of the two tracers in A431 were 0.79+/-0.24 and 0.44+/-0.04 microL/min/g. Pharmacokinetic modeling of the data using these permeabilities and the high plasma and extracellular concentrations of endogenous Tf showed that the observed uptake values in the two xenografts are consistent with a non-receptor-mediated distribution. In the liver, the absence of permeability barriers yields specific [18F]Tf binding to receptors compared with the [14C]Alb control, within 5 min after injection. CONCLUSION: Receptor-mediated accumulation of [18F]Tf in tumor xenografts is impaired by rate-determining permeability and competition from endogenous Tf and is not achieved in a time frame of 6 h.  (+info)