Increased erythrocyte phosphatidylserine exposure in chronic renal failure. (49/2206)

The appearance of phosphatidylserine, an aminophospholipid normally confined to the inner monolayer, at the outer leaflet of red cell membrane may have several pathophysiologic implications. This study examines erythrocyte phosphatidylserine exposure in chronic renal failure (CRF) patients on conservative treatment or on dialysis, to assess possible alterations to phospholipid asymmetry in a condition associated with a state of deranged red cell function. A significant increase in phosphatidylserine-expressing erythrocytes was found in undialyzed patients with CRF (2.32%) and patients on hemodialysis (3.06%) and on peritoneal dialysis (2.14%) compared with control subjects (0.68%). In undialyzed CRF patients, a strong correlation (r = 0.903) was found between the percentage of phosphatidylserine-expressing red cells and the serum creatinine concentration. The increased exposure of phosphatidylserine in uremic erythrocytes may be due to inhibition of phosphatidylserine transport from the outer to the inner leaflet of plasma membrane and may promote an increased erythrophagocytosis. In reconstitution experiments, normal erythrocytes showed an increase in phosphatidylserine-expressing cells when incubated in uremic plasma (3.2% after 2 h versus 1.1% at beginning of incubation), whereas phosphatidylserine-positive uremic erythrocytes decreased when resuspended in normal plasma (2.03% after 2 h and 1.65% after 8 h versus 2.9% at beginning of incubation). Preliminary characterization of the putative uremic compound(s) indicates a molecular weight between 10,000 and 20,000, as well as heat instability. These findings show an impairment of erythrocyte membrane phospholipid asymmetry in CRF patients, regardless of the dialysis treatment. Such abnormality seems related to the uremic state and could contribute to the red cell pathology present in CRF.  (+info)

Restricted receptor segregation into membrane microdomains occurs on human T cells during apoptosis induced by galectin-1. (50/2206)

Galectin-1 induces apoptosis of human thymocytes and activated T cells by an unknown mechanism. Apoptosis is a novel function for a mammalian lectin; moreover, given the ubiquitous distribution of the oligosaccharide ligand recognized by galectin-1, it is not clear how susceptibility to and signaling by galectin-1 is regulated. We have determined that galectin-1 binds to a restricted set of T cell surface glycoproteins, and that only CD45, CD43, and CD7 appear to directly participate in galectin-1-induced apoptosis. To determine whether these specific glycoproteins interact cooperatively or independently to deliver the galectin-1 death signal, we examined the cell surface localization of CD45, CD43, CD7, and CD3 after galectin-1 binding to human T cell lines and human thymocytes. We found that galectin-1 binding resulted in a dramatic redistribution of these glycoproteins into segregated membrane microdomains on the cell surface. CD45 and CD3 colocalized on large islands on apoptotic blebs protruding from the cell surface. These islands also included externalized phosphatidylserine. In addition, the exposure of phosphatidylserine on the surface of galectin-1-treated cells occurred very rapidly. CD7 and CD43 colocalized in small patches away from the membrane blebs, which excluded externalized phosphatidylserine. Receptor segregation was not seen on cells that did not die in response to galectin-1, including mature thymocytes, suggesting that spatial redistribution of receptors into specific microdomains is required for triggering apoptosis.  (+info)

Association between the endoplasmic reticulum and mitochondria of yeast facilitates interorganelle transport of phospholipids through membrane contact. (51/2206)

Membrane association between mitochondria and the endoplasmic reticulum of the yeast Saccharomyces cerevisiae is probably a prerequisite for phospholipid translocation between these two organelles. This association was visualized by fluorescence microscopy and computer-aided three-dimensional reconstruction of electron micrographs from serial ultrathin sections of yeast cells. A mitochondria-associated membrane (MAM), which is a subfraction of the endoplasmic reticulum, was isolated and re-associated with mitochondria in vitro. In the reconstituted system, phosphatidylserine synthesized in MAM was imported into mitochondria independently of cytosolic factors, bivalent cations, ATP, and ongoing synthesis of phosphatidylserine. Proteolysis of mitochondrial surface proteins by treatment with proteinase K reduced the capacity to import phosphatidylserine. Phosphatidylethanolamine formed in mitochondria by decarboxylation of phosphatidylserine is exported to the endoplasmic reticulum where part of it is converted into phosphatidylcholine. In contrast with previous observations with permeabilized yeast cells [Achleitner, G., Zweytick, D., Trotter, P., Voelker, D. & Daum, G. (1995) J. Biol. Chem. 270, 29836-29842], export of phosphatidylethanolamine from mitochondria to the endoplasmic reticulum was shown to be energy-independent in the reconstituted yeast system.  (+info)

Aspirin induces cell death and caspase-dependent phosphatidylserine externalization in HT-29 human colon adenocarcinoma cells. (52/2206)

The induction of cell death by aspirin was analysed in HT-29 colon carcinoma cells. Aspirin induced two hallmarks of apoptosis: nuclear chromatin condensation and increase in phosphatidylserine externalization. However, aspirin did not induce either oligonucleosomal fragmentation of DNA, decrease in DNA content or nuclear fragmentation. The effect of aspirin on Annexin V binding was inhibited by the caspase inhibitor Z-VAD.fmk, indicating the involvement of caspases in the apoptotic action of aspirin. However, aspirin did not induce proteolysis of PARP, suggesting that aspirin does not increase nuclear caspase 3-like activity in HT-29 cells. This finding may be related with the 'atypical' features of aspirin-induced apoptosis in HT-29 cells.  (+info)

Requirement of intracellular calcium mobilization for peroxynitrite-induced poly(ADP-ribose) synthetase activation and cytotoxicity. (53/2206)

Peroxynitrite is a cytotoxic oxidant produced during shock, ischemia reperfusion, and inflammation. The cellular events mediating the cytotoxic effect of peroxynitrite include activation of poly(ADP-ribose) synthetase, inhibition of mitochondrial respiration, and activation of caspase-3. The aim of the present study was to investigate the role of intracellular calcium mobilization in the necrotic and apoptotic cell death induced by peroxynitrite. Peroxynitrite, in a low, pathophysiologically relevant concentration (20 microM), induces rapid (1 to 3 min) Ca(2+) mobilization in thymocytes. Inhibition of this early calcium signaling by cell-permeable Ca(2+) chelators [EGTA-acetoxymethyl ester (AM), 1, 2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-AM (BAPTA-AM), 8-amino-2-[(2-amino-5-methylphenoxy)methyl]-6-methoxyquinoline-N,N , N',N'-tetraacetic acid-tetra-AM] abolished cytotoxicity as measured by propidium iodide uptake. Intracellular Ca(2+) chelators also inhibited DNA single-strand breakage and activation of poly(ADP-ribose) synthase (PARS), which is a major mediator of cell necrosis in the current model. Intracellular Ca(2+) chelators also protected PARS-deficient thymocytes from peroxynitrite cytotoxicity, providing evidence for a PARS-independent, Ca(2+)-dependent cytotoxic pathway. Chelation of intracellular Ca(2+) blocked the peroxynitrite-induced decrease of mitochondrial membrane potential, secondary superoxide production, and mitochondrial membrane damage. Peroxynitrite-induced internucleosomal DNA cleavage was increased on BAPTA-AM pretreatment in the wild-type cells but decreased in the PARS-deficient cells. Two other apoptotic parameters (phosphatidylserine exposure and caspase 3 activation) were inhibited by BAPTA-AM in both the wild-type and the PARS-deficient thymocytes. Our findings provide evidence for the pivotal role of an early Ca(2+) signaling in peroxynitrite cytotoxicity.  (+info)

Cytotoxicity of sulfonamide reactive metabolites: apoptosis and selective toxicity of CD8(+) cells by the hydroxylamine of sulfamethoxazole. (54/2206)

Treatment with sulfonamide antibiotics in HIV-infected patients is associated with a high incidence (> 40%) of adverse drug events, including severe hypersensitivity reactions. Sulfonamide reactive metabolites have been implicated in the pathogenesis of these adverse reactions. Sulfamethoxazole hydroxylamine (SMX-HA) induces lymphocyte toxicity and suppression of proliferation in vitro; the mechanism(s) of these immunomodulatory effects remain unknown. We investigated the cytotoxicity of SMX-HA via apoptosis on human peripheral blood mononuclear cells and purified cell subpopulations in vitro. CD19(+), CD4(+), and CD8(+) cells were isolated from human peripheral blood by positive selection of cell surface molecules by magnetic bead separation. SMX-HA induced significant CD8(+) cell death (67 +/- 7%) at 100 microM SMX-HA, with only minimal CD4(+) cell death (8 +/- 4%). No significant subpopulation toxicity was shown when incubated with parent drug (SMX). Flow cytometry measuring phosphatidylserine externalization 24 h after treatment with 100 microM and 400 microM SMX-HA revealed 14.1 +/- 0.7% and 25. 6 +/- 4.2% annexin-positive cells, respectively, compared to 3.7 +/- 1.2% in control PBMCs treated with 400 microM SMX. Internucleosomal DNA fragmentation was observed in quiescent and stimulated PBMCs 48 h after incubation with SMX-HA. Our data show that CD8(+) cells are highly susceptible to the toxic effects of SMX-HA through enhanced cell death by apoptosis.  (+info)

Mitochondria connects the antigen receptor to effector caspases during B cell receptor-induced apoptosis in normal human B cells. (55/2206)

We have previously reported that CD40 stimulation sensitizes human memory B cells to undergo apoptosis upon subsequent B cell receptor (BCR) ligation. We have proposed that activation stimuli connect the BCR to an apoptotic pathway in mature B cells and that BCR-induced apoptosis of activated B cells could serve a similar function as activation-induced cell death in the mature T cell compartment. Although it has been reported that caspases are activated during this process, the early molecular events that link the Ag receptor to these apoptosis effectors are largely unknown. In this study, we report that acquisition of susceptibility to BCR-induced apoptosis requires entry of memory B cells into the S phase of the cell cycle. We also show that transduction of the death signal via the BCR sequentially proceeds through a caspase-independent and a caspase-dependent phase, which take place upstream and downstream of the mitochondria, respectively. Furthermore, our data indicate that the BCR-induced alterations of the mitochondrial functions are involved in activation of the caspase cascade. We have found both caspases-3 and -9, but not caspase-8, to be involved in the BCR apoptotic pathway, thus supporting the notion that initiation of the caspase cascade could be under the control of the caspase-9/Apaf-1/cytochrome c multimolecular complex. Altogether, our findings establish the mitochondria as the connection point through which the Ag receptor can trigger the executioners of apoptotic cell death in mature B lymphocytes.  (+info)

Granzyme B-induced loss of mitochondrial inner membrane potential (Delta Psi m) and cytochrome c release are caspase independent. (56/2206)

CTLs kill targets by inducing them to die through apoptosis. A number of morphological and biochemical events are now recognized as characteristic features of the apoptotic program. Among these, the disruption of the inner mitochondrial transmembrane potential (Delta Psi m) and the release of cytochrome c into the cytoplasm appear to be early events in many systems, leading to the activation of caspase-3 and, subsequently, nuclear apoptosis. We show here that, in Jurkat targets treated in vitro with purified granzyme B and perforin or granzyme B and adenovirus, Delta Psi m collapse, reactive oxygen species production, and cytochrome c release from mitochondria were observed. Loss of Delta Psi m was also detected in an in vivo system where green fluorescent protein-expressing targets were attacked by a cytotoxic T cell line that kills predominantly through the granzyme pathway. DNA fragmentation, phosphatidylserine externalization, and reactive oxygen species production were inhibited in the presence of the caspase inhibitors benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone (zVAD-fmk) and benzyloxycarbonyl-Asp-Glu-Val-Asp-fluoromethyl ketone (zDEVD-fmk) in our in vitro system. Importantly, in either the in vitro or in vivo systems, these inhibitors at concentrations up to 100 microM did not prevent Delta Psi m collapse. In addition, cytochrome c release was observed in the in vitro system in the absence or presence of zVAD-fmk. Thus the granzyme B-dependent killing pathway in Jurkat targets involves mitochondrial alterations that occur independently of caspases.  (+info)