Perioperative renal dysfunction and cardiovascular anesthesia: concerns and controversies

In patients with renal disease undergoing cardiovascular surgery, perioperative management continues to be a challenge. Traditional answers have turned into new questions with the introduction of new agents and the redesign of old techniques. For ARF prevention, early recognition of pending deleterious compensatory changes is critical. Theoretically, therapeutic intervention designed to prevent ischemic renal failure should be designed to preserve the balance between RBF and oxygen delivery on one hand and oxygen demand on the other. Maintenance of adequate cardiac output distribution to the kidney is determined by the relative ratio of renal artery vascular resistance to systemic vascular resistance. Indeed, it should not be surprising to learn that norepinephrine (despite its vasoconstricting effect) has been reported to have no deleterious renal effects in patients with low systemic vascular resistance. Until recently, strategies for the treatment of ARF have been directed to supportive care with dialysis (to allow tubular regeneration). Various therapeutic maneuvers have been introduced in an attempt to accelerate the recovery of glomerular filtration, including dialysis, nutritional regimens, and new pharmacologic agents. A recent small prospective trial of low-dose dopamine in the prophylaxis of ARF in patients undergoing abdominal aortic aneurysm repair showed no benefit in those patients receiving dopamine. Conversely, the effects of intravenous atrial natriuretic peptide in the treatment of patients with ARF appear to offer benefit in patients with oliguria. Among 121 patients with oliguric renal failure, 63% of those who received a 24-hour infusion of atrial natriuretic peptide required dialysis within 2 weeks compared with 87% who did not. Whether this effect will be borne out in the future remains to be determined. The administration of epidermal growth factor after induction of ischemic ARF in rats has been shown to enhance tubular regeneration and accelerate recovery of kidney function. Human growth factor administration has been shown to increase GFR 130% greater than baseline in patients with chronic renal failure, but no data for clinical ARF have been reported. In addition, there have been significant improvements in dialysis technology in the treatment of ARF. Modern dialysis uses bicarbonate as a buffer as opposed to acetate, which reduces cardiovascular instability, and has more precise regulation of volume removal. Dialysate profiles and temperatures improve hemodynamics and reduce intradialytic hypotension. Techniques of hemodialysis without anticoagulation have reduced bleeding complications. Finally, dialysis membranes activate neutrophils and complement less with the biocompatible membranes used today that reduce recovery time and dialysis treatment. Evidence indicates that activation of complement and neutrophils by older dialysis membranes caused a greater incidence of hypotension, adding to ischemic renal injury. It remains to be determined whether early and frequent dialysis with biocompatible membranes, as well as other therapeutic interventions, will increase the survival of patients with perioperative ARF.

Small molecule inhibitor of HIV-1 cell fusion blocks chemokine receptor-mediated function

The intersection of the HIV and the chemokine fields began with the observation that HIV entry into cells could be blocked by certain chemokines. Subsequent work showed that HIV entry is dependent on the presence of specific chemokine receptors. These observations led us to evaluate a series of compounds, ureido analogs of distamycin previously reported to block HIV entry into cells in vitro, for chemokine antagonist activity. One of the distamycin analogs, 2,2'[4,4'-[[aminocarbonyl]amino]bis[N,4'-di[pyrrole-2-carboxamide- 1,1'-dimethyl]]-6,8 napthalenedisulfonic acid] hexasodium salt (NSC 651016), is shown here to inhibit syncytia formation and cell fusion. Mechanistic studies showed that this inhibition was not due to conformational changes in gp120-gp41 induced by target cell CD4 and chemokine co-receptor and was therefore not due to interference with binding of HIV-1. Additional mechanistic studies demonstrated that NSC 651016 inhibited chemokine binding to specific chemokine receptors, induced CXCR4 and CCR5 receptor internalization, and inhibited chemokine-induced chemotaxis by macrophage inflammatory protein (MIP)-1alpha, MIP-1beta, RANTES, and stromal-derived factor-1alpha but not monocyte chemotactic protein-1. Thus, we describe a novel compound that inhibits in vivo replication of HIV-1 by down-regulation of co-receptors. These data lead us to propose that NSC 651016 may have in vivo anti-inflammatory activity.

Comparison of the Heart and Estrogen/Progestin Replacement Study (HERS) cohort with women with coronary disease from the National Health and Nutrition Examination Survey III (NHANES III)

BACKGROUND

The Heart and Estrogen/Progestin Replacement Study (HERS) is the first large clinical trial designed to test the efficacy of postmenopausal estrogen/progestin therapy for secondary prevention of coronary heart disease (CHD). To examine the representativeness of the HERS cohort to the general population of postmenopausal women with CHD, we compared the baseline cardiovascular risk factor data from HERS with similar data from women presumed to have CHD from the National Health and Nutrition Examination Survey (NHANES) III.

METHODS

Age, race, and cardiovascular disease risk factors were compared in the 2763 postmenopausal women younger than 80 years old, with a uterus, and with documented CHD in HERS versus 145 similarly aged women with clinical or electrocardiographic evidence of CHD from phase I of NHANES III.

RESULTS

There were fewer current smokers in HERS (13%) than in the NHANES cohort (21.7%, p = 0.05). Similarly, a history of hypertension was less prevalent in HERS (58.6%) than in the NHANES cohort (69.3%, p = 0.03). Women with fasting triglyceride levels >3.39 mmol/L or fasting glucose levels >16.6 mmol/L were excluded from HERS, resulting in fewer diabetics (22.9% vs 29.5%, p = 0.26) and lower serum triglyceride levels (1.88 mmol/L vs 2.25 mmol/L, p = 0.19) in HERS versus the NHANES cohort. Systolic and diastolic blood pressure, body mass index, physical activity, and total LDL and HDL cholesterol were not significantly different between the two groups.

CONCLUSIONS

The HERS cohort had fewer CHD risk factors than women with myocardial infarction or angina in NHANES III, although comparison is hindered by differences in selection criteria. The many women with diabetes and hypertriglyceridemia in the NHANES cohort emphasizes the importance of testing strategies for secondary prevention of CHD in this high-risk subgroup.

A synthetic all D-amino acid peptide corresponding to the N-terminal sequence of HIV-1 gp41 recognizes the wild-type fusion peptide in the membrane and inhibits HIV-1 envelope glycoprotein-mediated cell fusion

Recent studies demonstrated that a synthetic fusion peptide of HIV-1 self-associates in phospholipid membranes and inhibits HIV-1 envelope glycoprotein-mediated cell fusion, presumably by interacting with the N-terminal domain of gp41 and forming inactive heteroaggregates [Kliger, Y., Aharoni, A., Rapaport, D., Jones, P., Blumenthal, R. & Shai, Y. (1997) J. Biol. Chem. 272, 13496-13505]. Here, we show that a synthetic all D-amino acid peptide corresponding to the N-terminal sequence of HIV-1 gp41 (D-WT) of HIV-1 associates with its enantiomeric wild-type fusion (WT) peptide in the membrane and inhibits cell fusion mediated by the HIV-1 envelope glycoprotein. D-WT does not inhibit cell fusion mediated by the HIV-2 envelope glycoprotein. WT and D-WT are equally potent in inducing membrane fusion. D-WT peptide but not WT peptide is resistant to proteolytic digestion. Structural analysis showed that the CD spectra of D-WT in trifluoroethanol/water is a mirror image of that of WT, and attenuated total reflectance-fourier transform infrared spectroscopy revealed similar structures and orientation for the two enantiomers in the membrane. The results reveal that the chirality of the synthetic peptide corresponding to the HIV-1 gp41 N-terminal sequence does not play a role in liposome fusion and that the peptides' chirality is not necessarily required for peptide-peptide interaction within the membrane environment. Furthermore, studies along these lines may provide criteria to design protease-resistant therapeutic agents against HIV and other viruses.

Fatal chronic relapsing thrombotic thrombocytopenic purpura following autologous bone marrow transplantation for chronic myeloid leukemia

Thrombotic thrombocytopenic purpura (TTP) is a severe and potentially fatal syndrome increasingly reported shortly after allogeneic bone marrow transplantation. We report a 49-year-old patient who developed a recurrent and ultimately fatal form of TTP late after autotransplant for chronic myeloid leukemia.

Interferon-beta is required for interferon-alpha production in mouse fibroblasts

The type I interferons--interferon-alpha (IFN-alpha) and interferon-beta (IFN-beta)--are critical for protection against viruses during the acute stage of viral infection [1,2]. Furthermore, type I interferons have been implicated as important mediators in the regulation of lymphocyte development [3], immune responses [4,5] and the maintenance of immunological memory of cytotoxic T cells [6,7]. The different IFN-alpha subtypes are encoded by 12 genes in the mouse [8] whereas IFN-beta is encoded by only one gene [9]. IFN-alpha and IFN-beta have a high degree of sequence homology and are thought to interact with the same surface receptor on target cells [10,11]. As an approach to analysing the different biological functions of IFN-alpha and IFN-beta, we have generated a mouse strain with an inactivated IFN-beta gene. We report here that embryonic fibroblasts from such mice produce neither IFN-beta nor IFN-alpha upon Sendal virus infection, whereas the production of IFN-alpha by leukocytes from the same strain of mice is intact. IFN-alpha production in embryonic fibroblasts from IFN-beta-/- mice could be rescued by 'priming' the cells using exogenous IFN-beta. These results imply a unique role for IFN-beta in the induction of type I interferons in peripheral tissues.

Dilation of the human immunodeficiency virus-1 envelope glycoprotein fusion pore revealed by the inhibitory action of a synthetic peptide from gp41

We have monitored fusion between cell pairs consisting of a single human immunodeficiency virus-1 (HIV-1) envelope glycoprotein-expressing cell and a CD4+ target cell, which had been labeled with both a fluorescent lipid in the membrane and a fluorescent solute in the cytosol. We developed a new three-color assay to keep track of the cell into which fluorescent lipids and/or solutes are redistributed. Lipid and solute redistribution occur as a result of opening a lipid-permissive fusion pore and a solute-permissive fusion pore (FPS), respectively. A synthetic peptide (DP178) corresponding to residues 643-678 of the HIV-1LAI gp120-gp41 sequence (Wild, C.T., D.C. Shugars, T.K. Greenwell, C.B. McDanal, and T.J. Matthews. 1994. Proc. Natl. Acad. Sci. USA. 91:12676-12680) completely inhibited FPS at 50 ng/ml, whereas at that concentration there was 20-30% fusion activity measured by the lipid redistribution. The differences detected in lipid mixing versus contents mixing are maintained up to 6 h of coculture of gp120-41-expressing cells with target cells, indicating that DP178 can "clamp" the fusion complex in the lipid mixing intermediate for very long time periods. A peptide from the NH2-terminal of gp41, DP107, inhibited HIV-1LAI gp120-gp41-mediated cell fusion at higher concentrations, but with no differences between lipid and aqueous dye redistribution at the different inhibitor concentrations. The inhibition of solute redistribution by DP178 was complete when the peptide was added to the fusion reaction mixture during the first 15 min of coculture. We have analyzed the inhibition data in terms of a fusion pore dilation model that incorporates the recently determined high resolution structure of the gp41 core.

Human erythrocyte glycolipids promote HIV-1 envelope glycoprotein-mediated fusion of CD4+ cells

We examined the role of target membrane glycolipids in CD4-mediated HIV-1 fusion by altering the glycolipid levels in CD4+ cells. CD4+ human cells exhibited 50% reduction in extent of fusion with gp120-gp41 expressing cells (TF228) when grown in the presence of a glycolipid synthesis inhibitor PPMP. We added erythrocyte glycolipids (GL) to fusion-incompetent CD4+ non-human cells by influenza-hemagglutinin-mediated fusion between GL-containing liposomes and target cells. Human erythrocyte GL (HuGL)-modified CD4+ non-human cells became susceptible to fusion with TF228 cells. Transfer of bovine erythrocyte glycolipids (BoGL) to CD4+ non-human cells under similar conditions did not complement HIV-1 fusion. Furthermore, addition of HuGL, but not BoGL, to PPMP-inhibited cells rescued fusion to the original levels. Our observations demonstrate that human erythrocyte glycolipids promote CD4-mediated HIV-1 fusion and certain glycolipid(s) from human erythrocytes may serve as alternative and/or additional cofactors in HIV-1 entry.

Conformational changes in cell surface HIV-1 envelope glycoproteins are triggered by cooperation between cell surface CD4 and co-receptors

We have continuously measured CD4-induced conformational changes of cell surface-expressed human immunodeficiency virus type-1 envelope glycoprotein gp120-gp41 in situ using 4,4'-dianilino-1, 1'-binaphthyl-5,5'-disulfonic acid, a fluorescent probe that binds to hydrophobic groups. CD4-expressing human T cell lines induced significant and rapid conformational changes (<1 min delay) in gp120-gp41 from T cell-tropic strains, and little conformational changes in gp120-gp41 from macrophage-tropic strains, with equivalent levels of envelope expression. Conversely, CD4-expressing human macrophages induced significant and rapid conformational changes in gp120-gp41 from macrophage-tropic strains, and little conformational changes in gp120-gp41 from T cell-tropic strains. Thus, the conformational changes undergone by gp120-gp41, which lead to membrane fusion, are highly cooperative and require both receptor and co-receptor. We used a dye transfer assay to show that neither membrane lipid fusion or fusion pore formation can occur with host cells having different tropism from the envelope.

Conformational changes and fusion activity of vesicular stomatitis virus glycoprotein: [125I]iodonaphthyl azide photolabeling studies in biological membranes

The interaction of VSV glycoprotein (VSV G) with biological membranes was studied by photosensitized labeling. The method is based on photosensitized activation by the fluorescent lipid analog 3,3'-dioctadecyloxacarbocyanine (DiO) of a hydrophobic probe, [125I]iodonaphthyl azide (125INA), that rapidly partitions into the membrane bilayer of virus and cells. 125INA labeling of proteins and lipids can be confined to the site of chromophore localization by photosensitized labeling. Photoactivation using visible light of target membrane labeled with DiO and 125INA, to which unlabeled virions are bound, results in exclusive labeling of envelope glycoproteins inserted into the target membrane [Pak et al. (1994) J. Biol. Chem. 269, 14614]. In this study, we labeled lipid symmetric erythrocyte ghosts with 125INA and DiO. Photosensitized activation of VSV prebound to labeled ghosts with visible light resulted in VSV G labeling under fusogenic conditions. Photoactivation of 125INA by UV light, which is nonspecific, produced labeled VSV G at both acidic and neutral pH. Photosensitized labeling of VSV G by DiO-125INA-ghosts was also observed at pH 5.5, 4 degrees C, in the absence of mixing between viral and cellular lipids, suggesting insertion of the ectodomain of VSV G. Soluble VSV G lacking the transmembrane domain inserted into DiO-125INA-ghosts under the same conditions as intact VSV G. DiO inserted into intact VSV appeared to be a suitable fluorophore for continuous kinetic measurements of membrane fusion by fluorescence dequenching. Our photosensitized labeling results establish biochemical correlates for the three states of VSV G, which we had proposed based on kinetic data [Clague et al., Biochemistry 29, 1303]. In addition, we found that VSV G insertion into the target membrane is reversible, suggesting a "velcro"-like attachment of the fusogenic domain with the target membrane.

What studies of fusion peptides tell us about viral envelope glycoprotein-mediated membrane fusion (review)

This review describes the numerous and innovative methods used to study the structure and function of viral fusion peptides. The systems studied include both intact fusion proteins and synthetic peptides interacting with model membranes. The strategies and methods include dissecting the fusion process into intermediate stages, comparing the effects of sequence mutations, electrophysiological patch clamp methods, hydrophobic photolabelling, video microscopy of the redistribution of both aqueous and lipophilic fluorescent probes between cells, standard optical spectroscopy of peptides in solution (circular dichroism and fluorescence) and attenuated total reflection-Fourier transform infrared spectroscopy of peptides bound to planar bilayers. Although the goal of a detailed picture of the fusion pore has not been achieved for any of the intermediate stages, important properties useful for constraining the development of models are emerging. For example, the presence of alpha-helical structure in at least part of the fusion peptide is strongly correlated with activity; whereas, beta-structure tends to be less prevalent, associated with non-native experimental conditions, and more related to vesicle aggregation than fusion. The specific angle of insertion of the peptides into the membrane plane is also found to be an important characteristic for the fusion process. A shallow penetration, extending only to the central aliphatic core region, is likely responsible for the destabilization of the lipids required for coalescence of the apposing membranes and fusion. The functional role of the fusion peptides (which tend to be either nonpolar or aliphatic) is then to bind to and dehydrate the outer bilayers at a localized site; and thus reduce the energy barrier for the formation of highly curved, lipidic 'stalk' intermediates. In addition, the importance of the formation of specific, 'higher-order' fusion peptide complexes has also been shown. Recent crystallographic structures of core domains of two more fusion proteins (in addition to influenza haemagglutinin) has greatly facilitated the development of prototypic models of the fusion site. This latter effort will undoubtedly benefit from the insights and constraints gained from the studies of fusion peptides.

Fusion peptides derived from the HIV type 1 glycoprotein 41 associate within phospholipid membranes and inhibit cell-cell Fusion. Structure-function study

The fusion domain of human immunodeficiency virus (HIV-1) envelope glycoprotein (gp120-gp41) is a conserved hydrophobic region located at the N terminus of the transmembrane glycoprotein (gp41). A V2E mutant has been shown to dominantly interfere with wild-type envelope-mediated syncytium formation and virus infectivity. To understand this phenomenon, a 33-residue peptide (wild type, WT) identical to the N-terminal segment of gp41 and its V2E mutant were synthesized, fluorescently labeled, and characterized. Both peptides inhibited HIV-1 envelope-mediated cell-cell fusion and had similar alpha-helical content in membrane mimetic environments. Studies with fluorescently labeled peptide analogues revealed that both peptides have high affinity for phospholipid membranes, are susceptible to digestion by proteinase-K in their membrane-bound state, and tend to self- and coassemble in the membranes. In SDS-polyacrylamide gel electrophoresis the WT peptide formed dimers as well as higher order oligomers, whereas the V2E mutant only formed dimers. The WT, but not the V2E mutant, induced liposome aggregation, destabilization, and fusion. Moreover, the V2E mutant inhibited vesicle fusion induced by the WT peptide, probably by forming inactive heteroaggregates. These data form the basis for an explanation of the mechanism by which the gp41 V2E mutant inhibits HIV-1 infectivity in cells when co-expressed with WT gp41.

Radioimmunotherapy of experimental pancreatic cancer with 131I-labeled monoclonal antibody PAM4

We examined the therapeutic efficacy of 131I-labeled murine monoclonal antibody (MAb) PAM4 against human pancreatic cancers carried as xenografts in athymic nude mice. Animals bearing the CaPan1 tumor (0.2 cm3) were either untreated or were given, 131I-labeled nonspecific Ag8 antibody. By week 7 mean tumor size had grown 16.5 +/- 8.4-fold and 4.2 +/- 2.5-fold for the untreated and 131I-Ag8-treated animals, respectively. In contrast, animals administered 131I-PAM4 exhibited marked regression of tumors to an average of 15% of initial tumor volume. Since most pancreatic cancer patients present with large tumor burdens, the limitation of 131I-PAM4 treatment with respect to initial tumor size was investigated in animals bearing tumors of approximately 0.5 cm3, 1.0 cm3 and 2.0 cm3. Significant extension of survival time (>3-fold increase) was noted for both the 0.5 cm3 and 1.0 cm3 131I-PAM4-treated groups, compared to their respective untreated controls. Even in the group bearing large 2.0-cm3 tumors, survival was increased 2-fold over the control group. To further improve anti-tumor effects in large tumors, 2 injections of 131I-PAM4 were administered at a 4-week interval to animals bearing tumors of approximately 1.0 cm3. Significant extended survival was noted for the group receiving 2 doses when compared to the group receiving only 1 dose.

Solubilization and reconstitution of vesicular stomatitis virus envelope using octylglucoside

Reconstituted vesicular stomatitis virus envelopes or virosomes are formed by detergent removal from solubilized intact virus. We have monitored the solubilization process of the intact vesicular stomatitis virus by the nonionic surfactant octylglucoside at various initial virus concentrations by employing turbidity measurements. This allowed us to determine the phase boundaries between the membrane and the mixed micelles domains. We have also characterized the lipid and protein content of the solubilized material and of the reconstituted envelope. Both G and M proteins and all of the lipids of the envelope were extracted by octylglucoside and recovered in the reconstituted envelope. Fusion activity of the virosomes tested either on Vero cells or on liposomes showed kinetics and pH dependence similar to those of the intact virus.

Dilation of the influenza hemagglutinin fusion pore revealed by the kinetics of individual cell-cell fusion events

We have monitored kinetics of fusion between cell pairs consisting of a single influenza hemaglutinin (HA)-expressing cell and a single erythrocyte (RBC) that had been labeled with both a fluorescent lipid (Dil) in the membrane and a fluorescent solute (calcein) in the aqueous space. Initial fusion pore opening between the RBC and HA-expressing cell produced a change in RBC membrane potential (delta psi) that was monitored by a decrease in Dil fluorescence. This event was followed by two distinct stages of fusion pore dilation: the flux of fluorescent lipid (phi L) and the flux of a large aqueous fluorescent dye (phi s). We have analyzed the kinetics of events that occur as a result of transitions between a fusion pore (FP) and a solute permissive fusion pore (FPs). Our data are consistent with a fusion pore comprising six HA trimers.

Heat-resistant factors in human erythrocyte membranes mediate CD4-dependent fusion with cells expressing HIV-1 envelope glycoproteins

It has been shown that human CD4 expressed in nonhuman cells does not support HIV-1 entry into those cells and that components from human cells in addition to CD4 are required to overcome the block. We have used human red blood cells (huRBC) as a source for the accessory components since their membrane composition is less complex than that of nucleated cells and they are well characterized. Components were transferred by fusion of huRBC to nonhuman CD4(+) cells mediated by influenza hemagglutinin or polyethylene glycol. The RBC-modified nonhuman CD4(+) cells were labeled with fluorescent markers and incubated with gp 120-gp41-expressing cells labeled with a different fluorescent probe. Fusion between RBC- modified nonhuman CD4(+) cells and gp 120--gp41-expressing cells was quantified by fluorescence video microscopy. Human erythrocyte components transferred to nonhuman CD4+ cells conferred HIV-1 envelope glycoprotein-mediated fusion susceptibility to those cells. The fusion was enhanced by pretreatment of the erythrocytes for 10 min at 56 degrees. No gp 120--gp41-mediated fusion was observed when components from nonhuman RBC were transferred to nonhuman CD4+ cells. Human cell lines with pre-RBC characteristics (K562-CD4) also supported HIV-1 envelope glycoprotein-mediated fusion.

Effect of X31 influenza virus fusion on phosphatidylserine asymmetry in erythrocytes

Influenza virus fusion is mediated by its fusion protein, hemagglutinin (HA). HA undergoes a low pH dependent conformational change that results in insertion into the cell membrane bilayer, formation of a fusion pore, and merging of membrane lipids and establishment of cytoplasmic continuity. Erythrocytes, which can serve as targets of influenza virus fusion, display an asymmetric transbilayer arrangement of their phospholipids. The effect of influenza virus fusion on erythrocyte phosphatidylserine asymmetry was determined. Influenza virus were bound to erythrocytes containing the fluorescent membrane probe NBD-PS in the inner leaflet. Induction of fusion by exposure to a low pH environment resulted in movement of PS to the outer leaflet of the cell as well as hemolysis. Insertion of the fusion protein into erythrocytes and subsequent fusion can be distinguished from hemolysis by examining the interaction of a soluble form of HA (BHA) with cells and by monitoring viral fusion at low temperatures. No hemolysis was observed under either condition. BHA binding and insertion into cells did not affect the asymmetry of PS. Incubation of influenza virus fusion at pH 5, 0 degrees C resulted in complete fusion but no outward movement of PS was observed. These findings suggest the viral fusion pore does not involve a rearrangement of the transbilayer phospholipid organization of the target membrane.

Barriers to seeking treatment for major depression

The purpose of this study was to examine the reasons people with an episode of Major Depression do or do not seek treatment for the episode. We interviewed 101 persons who met criteria for an RDC Major Depressive episode that lasted at least 4 weeks within 3 years of the interview date, exploring in detail the reasons they gave for seeking or not seeking treatment. GAS ratings indicated that all subjects were moderately impaired at the time of the episode. We found that 55% of the subjects did not seek treatment for this episode, while 45% did. Significant predictors of treatment seeking included a history of prior treatment, higher education, and greater episode length. Non-seekers felt they could handle the episode themselves, did not consider it serious or did not recognize it as an illness. Seekers on the other hand felt the episode was too painful and lasted too long and caused significant disruption in their interpersonal relationships and role functioning. We discuss the implications of these findings in terms of the importance of continued educational efforts to encourage treatment seeking as well as the need for further research to explore the manner in which people decide that affective signs and symptoms have reached a threshold that leads to treatment seeking.

A controlled trial of tranexamic acid therapy for the reduction of bleeding during treatment of acute myeloid leukemia

In order to determine the efficacy of the antifibrinolytic agent tranexamic acid (TA) in reducing bleeding and platelet transfusions during the treatment of acute myeloid leukemia (AML), we conducted a randomized placebo-controlled double-blind study. Patients with AML undergoing induction or postremission consolidation chemotherapy were randomized into TA or placebo groups. Patients were not given platelet transfusions prophylactically but only when bleeding occurred. The severity of any bleeding event was scored. Thirty eight patients were randomized during induction. There were no significant differences between the two groups in the number of bleeding events and their severity or in the number of platelet transfusions given. Eighteen patients were studied during consolidation. In contrast, to the induction period, during consolidation there was a significantly less severe bleeding tendency in the TA group resulting in a lower platelet transfusion requirement [3.7 +/- 4.1 vs. 9.3 +/- 3.3 platelet units (p < .05)]. TA was well tolerated and no side effects were seen and no specific thromboembolic events were noticed. We conclude that giving TA during the thrombocytopenic period of AML patients undergoing consolidation chemotherapy is beneficial and safely reduces platelet transfusions.

Synergistic inhibition of human immunodeficiency virus type 1 envelope glycoprotein-mediated cell fusion and infection by an antibody to CD4 domain 2 in combination with anti-gp120 antibodies

Antibodies to several epitopes of the human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein (gp120-gp41) can synergize in inhibiting HIV-1 infection. In the present study we tested the ability of a monoclonal antibody (MAb), 5A8, which interacts with CD4 domain 2, and other CD4-specific MAbs to synergize with antibodies against gp120. We have previously found that 5A8 inhibits HIV-1 entry without interfering with gp120 binding to CD4, presumably by affecting a postbinding membrane fusion event. Because antibodies to the gp120 V3 loop also affect post-CD4-gp120-binding events, 5A8 was first tested in combination with anti-V3 loop antibodies for possible synergy. The anti-V3 loop antibodies 0.5 beta, NEA-9205, and 110.5 acted synergistically with 5A8 in inhibiting syncytium formation between gp120-gp41- and CD4-expressing cells. A human MAb to an epitope of gp120 involved in CD4 binding, IAM 120-1B1, and another anti-CD4 binding site antibody, PC39.13, also exerted synergistic effects in combination with 5A8. Similarly, an antibody against the gp120 binding site on CD4, 6H10, acted synergistically with an anti-V3 loop antibody, NEA-9205. However, a control anti-CD4 antibody, OKT4, which does not significantly inhibit syncytium formation alone, produced only an additive effect when combined with NEA-9205. Serum from HIV-1-infected individuals, which presumably contains antibodies to the V3 loop and the CD4 binding site, exhibited a strong synergistic effect with 5A8 in inhibiting infection by a patient HIV-1 isolate (0104B) and in blocking syncytium formation. These results indicate that therapeutics based on antibodies affecting both non-gp120 binding and gp120 binding epitopes of the target receptor molecule, CD4, could be efficient in patients who already contain anti-gp120 antibodies and could also be used to enhance passive immunization against HIV-1 in combination with anti-gp120 antibodies.

Influence of the spectrin network on fusion of influenza virus with red blood cells

We examined the influence of the physical state of the membrane skeleton on low pH fusion of influenza virus A/PR 8/34 with intact human red blood cells. Spectrin, the major component of the skeleton, is known to become denaturated at 50 degrees C. After heat treatment of erythrocytes at 50 degrees C we observed an enhanced kinetics of fusion monitored spectrofluorometrically by the octadecylrhodamine fluorescence dequenching assay, while the extent of fusion was not affected. The accelerated fusion of influenza virus after preincubation of red blood cells at 50 degrees C is not mediated by alterations of the lipid phase of the target. From ESR measurements using spin-labelled phospholipids we conclude that heat-induced alterations of the spectrin network did not affect either the phospholipid asymmetry or the fluidity of the exoplasmic and the cytoplasmic leaflets of the erythrocyte membrane. Moreover, as deduced from our previous investigations, the swelling behaviour of red blood cells could not be responsible for the observed effect. Possible mechanisms for the spectrin effect include a change in the ability of the target membrane to bend locally, and a change in the rate of formation and development of the fusion pore.

Differences in dispersion of influenza virus lipids and proteins during fusion

Digitally enhanced low-light-level fluorescence video microscopy and immunochemical staining were used to examine influenza virus envelope lipid and protein redistribution during pH-induced fusion. Video microscopy was performed using viruses labeled with either the lipid analogue octadecylrhodamine B (R18) or fluorescein isothiocyanate (FITC) covalently linked to envelope proteins. Viruses were bound to human red blood cells, and the pattern and intensity of fluorescence were monitored for 30 min while cell-virus complexes were perfused with pH 7.4 or 4.8 media at temperatures either above or below 20 degrees C. R18 showed complete redistribution and dequenching by 30 min at all incubation temperatures, confirming reports that viral fusion occurs at subphysiological temperatures. FITC-labeled protein showed spatial redistribution at 28 degrees C but no change at low temperature. Electron microscopy observations of immunochemical staining of viral proteins confirmed both that protein redistribution at 37 degrees C was slower than R18 and the failure of movement within 30 min at 16 degrees C. Video microscopy monitoring of RNA staining by acridine orange of virus-cell complexes showed redistribution to the RBCs at all temperatures but only after low pH-induced fusion. The results are consistent with differential dispersion of viral components into the RBC and the existence of relatively long-lived barriers to diffusion subsequent to fusion pore formation.

Transient domains induced by influenza haemagglutinin during membrane fusion

During low pH-induced fusion of influenza virus with erythrocytes we have observed differential dispersion of viral lipid and haemagglutinin (HA) into the erythrocyte membrane, and viral RNA into the erythrocyte using fluorescence video microscopy. The movement of both viral lipid and HA from virus to cell was restricted during the initial stages of fusion relative to free diffusion. This indicates the existence of relatively long-lived barriers to diffusion subsequent to fusion pore formation. Fluorescence anisotropy of phospholipid analogues incorporated into the viral membrane decreased when the pH was lowered to levels required for optimum fusion. This indicates that the restricted motion of viral membrane components was not due to rigidification of membrane lipids. The movement of HA from the fusion site was also assessed by photosensitized labelling by means of a fluorescent substrate (NBD-taurine) passing through the band 3 sialoglycoprotein (the erythrocyte anion transporter). We also examined the flow of lipid and aqueous markers during fusion of HA-expressing cells with labelled erythrocytes. During this cell-cell fusion, movement of lipid between fusing membranes begins before the fusion pore is wide enough to allow diffusion of aqueous molecules (M(r) > 500). The data indicate that HA is capable of creating domains in the membrane and controlling continuity of aqueous compartments which are bounded by such domains.