Safety and efficacy of treatment with platelet GPIIb/IIIa receptor blockade in unstable angina patients awaiting PTCA at a referring clinic

BACKGROUND: Although balloon angioplasty has assumed an important role in the management of refractory unstable angina (UA), that is, UA that does not respond to conventional therapy, it is limited by complications related to thrombosis and acute coronary occlusion. The complication rate is higher in patients with UA than in those whose condition is stable. Preprocedural use of abciximab, a monoclonal platelet glycoprotein IIb/IIIa receptor blocker, has been used effectively in patients with UA, but its acceptance may be limited by safety concerns and economic constraints. The current trial investigated a protocol for abciximab pretreatment in patients with UA awaiting transfer from referring hospitals to a site of intervention (the 'drip and ship' protocol). AIMS: This observational study was conducted to evaluate whether a prophylactic, preprocedural regimen of abciximab can be safely and effectively administered to UA patients in referring hospitals while awaiting coronary angioplasty at the interventional clinic. METHODS: From April 1996 to December 1998, 168 consecutive patients with refractory UA (Braunwald class II or III) received abciximab prospectively at the referring clinic before undergoing PTCA or stent implantation at the interventional clinic. The following cost-conscious protocol was used: a 0.25 mg/kg bolus of abciximab followed by 10 micro g/min intravenously for 16 hours, in addition to intravenous nitrates, heparin and aspirin therapy. Patients were then transferred to a facility with PTCA capability via high-speed ambulance transport. No specific alterations of routine-transfer protocol were needed. Platelet aggregation studies were conducted during abciximab infusion. All interventions were performed while abciximab was given. Procedural and clinical success and long-term outcomes also were assessed. RESULTS: The primary angiographic success rate (patients with post-PTCA diameter stenosis < 50%) was 98%, and the in-hospital clinical success rate (angiographic success without major complications) was 98%. No major bleeding complications occurred during the abciximab pretreatment period. Platelet aggregation findings in the study patients showed a stable inhibition of >80% at the time of angioplasty. At 30-day follow-up, all patients were alive and 91% were free of major adverse events. Outcomes of balloon angioplasty and stenting were equally favorable, indicating no device-specific effect. Event-free survival at six months was 89% with a target vessel revascularization rate of 10%. CONCLUSION: Abciximab was administered safely and effectively to angioplasty patients with refractory UA awaiting transfer from a noninterventional setting to the site of angioplasty. These results extend the current knowledge base that has been established in randomized trials performed in interventional centers. The study protocol potentially could make abciximab therapy more feasible economically, and therefore more widely available to patients who are most likely to benefit from prophylactic administration.     

The Saccharomyces cerevisiae LEP1/SAC3 gene is associated with leucine transport

Leucine uptake by Saccharomyces cerevisiae is mediated by three transport systems, the general amino acid transport system (GAP), encoded by GAP1, and two group-specific systems (S1 and S2), which also transport isoleucine and valine. A new mutant defective in both group-specific transport activities was isolated by employing a gap1 leu4 strain and selecting for trifluoroleucine-resistant mutants which also showed greatly reduced ability to utilize l-leucine as sole nitrogen source and very low levels of [¹⁴C]l-leucine uptake. A multicopy plasmid containing a DNA fragment which complemented the leucine transport defect was isolated by selecting for transformants that grew normally on minimal medium containing leucine as nitrogen source and subsequently assaying [¹⁴C]l-leucine uptake. Transformation of one such mutant, lep1, restored sensitivity to trifluoroleucine. The complementing gene, designated LEP1, was subcloned and sequenced. The LEP1 ORF encodes a large protein that lacks characteristics of a transporter or permease (i.e., lacks hydrophobic domains necessary for membrane association). Instead, Lep1p is a very basic protein (pI of 9.2) that contains a putative bipartite signal sequence for targeting to the nucleus, suggesting that it might be a DNA-binding protein. A database search revealed that LEP1 encodes a polypeptide that is identical to Sac3p except for an N-terminal truncation. The original identification of SAC3 was based on the isolation of a mutant allele, sac3-1, that suppresses the temperature-sensitive growth defect of an actin mutant containing the allele act1-1. Sac3p has been previously shown to be localized in the nucleus. When a lep1 mutant was crossed with a sac3 deletion mutant, no complementation was observed, indicating that the two mutations are functionally allelic.     

Reduced sensitivity of Niemann-Pick C1-deficient cells to θ-toxin (perfringolysin O): sequestration of toxin to raft-enriched membrane vesicles

-Toxin (perfringolysin O) binds to cell surface cholesterol and forms oligomeric pores that cause membrane damage. Both in cytotoxicity and cell survival assays, a mutant Chinese hamster ovary cell line NPC1(–) that lacked Niemann-Pick C1 showed reduced sensitivity to -toxin, compared with wild-type (wt) cells. BC is a derivative of -toxin that retains cholesterol-binding activity but lacks cytotoxicity. Confocal and electron microscopy revealed the presence of multiple vesicles which bound BC, both on the cell surface and in the extracellular space of these cells. BC binding to raft microdomains was verified by its resistance to 1% Triton X-100 at 4°C and recovery of bound BC in floating low-density fractions on sucrose density gradient fractionation. BC-labeled vesicles were abolished when NPC1(–) cells were depleted of lipoproteins and also when treated with a Rho-associated kinase inhibitor Y-27632. In addition, similar vesicles were observed in wt cells treated with progesterone. In parallel with these results, -toxin sensitivity of NPC1(–) cells was increased when cells were depleted of lipoproteins or treated with Y-27632, whereas that of wt cells was decreased by progesterone. Our findings suggest that sequestration of toxin to raft-enriched cell surface vesicles may underlie reduced sensitivity of NPC1-deficient cells to -toxin.     

Brief inactivation of c-Myc is not sufficient for sustained regression of c-Myc-induced tumours of pancreatic islets and skin epidermis

Background  

Tumour regression observed in many conditional mouse models following oncogene inactivation provides the impetus to develop, and a platform to preclinically evaluate, novel therapeutics to inactivate specific oncogenes. Inactivating single oncogenes, such as c-Myc, can reverse even advanced tumours. Intriguingly, transient c-Myc inactivation proved sufficient for sustained osteosarcoma regression; the resulting osteocyte differentiation potentially explaining loss of c-Myc's oncogenic properties. But would this apply to other tumours?     

Effects of dexamethasone on K(+)-evoked glutamate release from rat hippocampal slices

Dexamethasone (DEX) at physiologically elevated (stress) concentration (1 µM) decreased K⁺-evoked glutamate release from rat hippocampal slices under superfusion in the presence of Ca²⁺. On the contrary 10 µM DEX increased this K⁺-evoked glutamate release while 0.1 µM DEX had no effect. The glucocorticoid antagonist for the classic receptor, RU 486, completely reversed the effect of 1 µM DEX. Actinomycin D had no effect. Dexamethasone at 1 µM had no effect on the Ca²⁺-independent (10 µM Mg²⁺ replacing 1 mM Ca²⁺) K⁺-evoked glutamate release. Dexamethasone at 1 µM or 10 µM had no effect on the phosphate-activated glutaminase—the key enzyme for the biosynthesis of neurotransmitter glutamate. These results suggest that the effect of DEX on K⁺-evoked glutamate release: (i) depends on its concentration; (ii) is exerted on the Ca²⁺-dependent (neurotransmitter release), at least at physiological stress concentrations; and (iii) is exerted via the classical receptor but is nongenomic.     

Disruption of thiol homeostasis and nitrosative stress in the cerebrospinal fluid of patients with active multiple sclerosis: evidence for a protective role of acetylcarnitine

Recent studies suggest that NO and its reactive derivative peroxynitrite are implicated in the pathogenesis of multiple sclerosis (MS). Patients dying with MS demonstrate increased astrocytic inducible nitric oxide synthase activity, as well as increased levels of iNOS mRNA. Peroxynitrite is a strong oxidant capable of damaging target tissues, particularly the brain, which is known to be endowed with poor antioxidant buffering capacity. Inducible nitric oxide synthase is upregulated in the central nervous system (CNS) of animals with experimental allergic encephalomyelitis (EAE) and in patients with MS. We have recently demonstrated in patients with active MS a significant increase of NOS activity associated with increased nitration of proteins in the cerebrospinal fluid (CSF). Acetylcarnitine is proposed as a therapeutic agent for several neurodegenerative disorders. Accordingly, in the present study, MS patients were treated for 6 months with acetylcarnitine and compared with untreated MS subjects or with patients noninflammatory neurological conditions, taken as controls. Western blot analysis showed in MS patients increased nitrosative stress associated with a significant decrease of reduced glutathione (GSH). Increased levels of oxidized glutathione (GSSG) and nitrosothiols were also observed. Interestingly, treatment of MS patients with acetylcarnitine resulted in decreased CSF levels of NO reactive metabolites and protein nitration, as well as increased content of GSH and GSH/GSSG ratio. Our data sustain the hypothesis that nitrosative stress is a major consequence of NO produced in MS-affected CNS and implicate a possible important role for acetylcarnitine in protecting brain against nitrosative stress, which may underlie the pathogenesis of MS.     

Candida albicans phospholipomannan promotes survival of phagocytosed yeasts through modulation of bad phosphorylation and macrophage apoptosis

The surface of the pathogenic yeast Candida albicans is coated with phospholipomannan (PLM), a phylogenetically unique glycolipid composed of beta-1,2-oligomannosides and phytoceramide. This study compared the specific contribution of PLM to the modulation of signaling pathways linked to the survival of C. albicans in macrophages in contrast to Saccharomyces cerevisiae. C. albicans endocytosis by J774 and disregulation of the ERK1/2 signal transduction pathway was associated downstream with a reduction in Bad Ser-112 phosphorylation and disappearance of free Bcl-2. This suggested an apoptotic effect, which was confirmed by staining of phosphatidylserine in the macrophage outer membrane. The addition of PLM to macrophages incubated with S. cerevisiae mimicked each of the disregulation steps observed with C. albicans and promoted the survival of S. cerevisiae. Externalization of membranous phosphatidylserine, loss of mitochondrial integrity, and DNA fragmentation induced by PLM showed that this molecule promoted yeast survival by inducing host cell death. These findings suggest strongly that PLM is a virulence attribute of C. albicans and that elucidation of the relationship between structure and apoptotic activity is an innovative field of research.     

Effects of season-dependent irradiance levels and nitrogen-deficiency on photosynthesis and photoinhibition in field-grown rice (Oryza sativa)

Photoinhibition and acclimation of photosynthesis in rice plants grown under N-sufficient (NS) and N-deficient (ND) field conditions were investigated during the tropical wet (WS) and dry (DS) seasons in the Philippines. Diurnal patterns of CO₂ assimilation were examined. There was a transient peak in CO₂ assimilation in the leaves of the NS plants in the early morning during the DS and the WS, which was not seen in the ND plants in either season. ND leaves had lower Ribulose bisphosphate carboxylase/oxygenase (Rubisco) contents and lower chlorophyll contents. A lowered quantum yield of photosystem II (φPSII) was observed in the ND plants at an intermediate irradiance though no differences between N treatments were seen at high irradiance. Analysis of carotenoids indicated a small increase in the de-epoxidation state of the xanthophyll cycle (DES) at mid-day in the ND leaves compared to NS. Photoinhibition was greater in ND leaves when incident mid-day irradiance was increased by altering the leaf angle. Although Rubisco contents were lower in ND plants, photosynthesis in situ did not decline proportionally. For NS plants, Chlorophyll content, but not Rubisco content, was season-dependent and results are discussed in terms of the interaction between irradiance use and N content of rice leaves.