Treatment of Dementia With Bosutinib: An Open-Label Study of a Tyrosine Kinase Inhibitor

OBJECTIVE

The pursuit of an effective therapeutic intervention for dementia has inspired interest in the class of medications known as tyrosine kinase inhibitors such as bosutinib.

METHODS

Thirty-one patients with probable Alzheimer dementia or Parkinson spectrum disorder with dementia completed 12 months of bosutinib therapy and an additional 12 months of follow-up. The Clinical Dementia Rating scale (as estimated by the Quick Dementia Rating System [QDRS]) was the primary cognitive status outcome measure. Secondary outcome measures included the Repeatable Battery Assessment of Neuropsychological Status (RBANS) and the Montreal Cognitive Assessment. Cox regression methods were used to compare results with population-based estimates of cognitive decline.

RESULTS

The present article reports on cognitive outcomes obtained at 12 months for 31 participants and up to 24 months for a 16-participant subset. Safety and tolerability of bosutinib were confirmed among the study population (Mage = 73.7 years, SDage = 14 years). Bosutinib was associated with less worsening in Clinical Dementia Rating (CDR) scores (hazard ratio = -0.62, p < 0.001, 95% confidence interval [CI]: -1.02 to -0.30) and less decline in RBANS performance (hazard ratio = -3.42, p < 0.001, 95% CI: -3.59 to -3.72) during the year of treatment than population-based estimates of decline. In the 24-month follow-up, wherein 16 patients were observed after 1 year postintervention, 31.2% of participants exhibited worsened CDR levels compared with their 12-month performances.

CONCLUSIONS

Results support an overall positive outcome after 1 year of bosutinib. Future studies should explore the relationship between tyrosine kinases and neurodegenerative pathology as well as related avenues of treatment.

Technical note: Evaluation of fine needle aspiration cytology for the diagnosis of fatty liver in dairy cattle

Fatty liver is a common condition affecting dairy cattle during the periparturient period, characterized by a pathological accumulation of triglycerides (TG) in the hepatocytes. The objective of this study was to evaluate the diagnostic potential of fine needle aspiration cytology in fresh liver specimens using liver TG concentrations as a gold standard. Fifty-seven liver samples from Holstein cows were collected during processing at a slaughterhouse. Tissue and fine needle aspirate samples were obtained from the parietal upper portion of the caudate lobe. Two samples of liver tissue were collected with a 16 gauge × 15 cm biopsy needle for histological and TG concentration assessment. A third sample was collected for cytology using an 18 gauge × 5.08 cm needle. The contents of the needle were transferred to a glass slide, spread, and air-dried. Liver samples were assayed by colorimetry/fluorimetry to determine TG concentrations. Concentrations of TG <2% were considered normal. Histological and cytological evaluations were conducted by 2 different pathologists blind to the visual classification. Sensitivity (Se) and specificity (Sp) were calculated. Cytology had a Se and Sp of 73 and 85%, respectively. Histopathology had a Se and Sp of 45.9 and 100%, respectively. The likelihood of having higher scores for histopathology and cytology increased as a function of liver TG content (mg/g).

Spiers Memorial Lecture. Breeding and building molecular spies

To circumvent the limited spatial resolution of fluorescent protein imaging, we are developing genetically encoded tags for electron microscopy (EM).

Parallel in vivo and in vitro selection using phage display identifies protease-dependent tumor-targeting peptides

We recently developed activatable cell-penetrating peptides (ACPPs) that target contrast agents to in vivo sites of matrix metalloproteinase activity, such as tumors. Here we use parallel in vivo and in vitro selection with phage display to identify novel tumor-homing ACPPs with no bias for primary sequence or target protease. Specifically, phage displaying a library of ACPPs were either injected into tumor-bearing mice, followed by isolation of cleaved phage from dissected tumor, or isolated based on selective cleavage by extracts of tumor versus normal tissue. Selected sequences were synthesized as fluorescently labeled peptides, and tumor-specific cleavage was confirmed by digestion with tissue extracts. The most efficiently cleaved peptide contained the substrate sequence RLQLKL and labeled tumors and metastases from several cancer models with up to 5-fold contrast. This uniquely identified ACPP was not cleaved by matrix metalloproteinases or various coagulation factors but was efficiently cleaved by plasmin and elastases, both of which have been shown to be aberrantly overexpressed in tumors. The identification of an ACPP that targets tumor expressed proteases without rational design highlights the value of unbiased selection schemes for the development of potential therapeutic agents.

Integration of G-protein coupled receptor signaling pathways for activation of a transcription factor (EGR-3)

We recently reported the use of a gene-trapping approach to isolate cell clones in which a reporter gene had integrated into genes modulated by T-cell activation. We have now tested a panel of clones from that report and identified the one that responds to a variety of G-protein coupled receptors (GPCR). The β-lactamase tagged EGR-3 Jurkat cell was used to dissect specific GPCR signaling in vivo. Three GPCRs were studied, including the chemokine receptor CXCR4 (Gi-coupled) that was endogenously expressed, the platelet activation factor (PAF) receptor (Gq-coupled), and β2 adrenergic receptor (Gs-coupled) that was both stably transfected. Agonists for each receptor activated transcription of the β-lactamase tagged EGR-3 gene. Induction of EGR-3 through CXCR4 was blocked by pertussis toxin and PD58059, a specific inhibitor of MEK (MAPK/ERK kinase). Neither of these inhibitors blocked isoproterenol or PAF-mediated activation of EGR-3. Conversely, β2- and PAF-mediated EGR-3 activation was blocked by the p38, specific inhibitor SB580. In addition, both β2- and PAF-mediated EGR-3 activation could be synergistically activated by CXCR4 activation. This combined result indicates that EGR-3 can be activated through distinct signal transduction pathways by different GPCRs and that signals can be integrated and amplified to efficiently tune the level of activation.

A One-Arm Homologous Recombination Approach for Developing Nuclear Receptor Assays in Somatic Cells

Drug discovery is in need of technologies that enable investigators to develop cell-based assays that accurately reflect the functional consequence of small molecule intervention on biological processes. Here, we describe a strategy that uses both one-arm homologous recombination and the beta-lactamase (BLA) reporter system, a sensitive and robust transcriptional reporter for gene activation. We demonstrate that this powerful approach can be utilized for developing cell-based assays for the glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) in HEK293 somatic cells. Specifically, one-arm homologous recombination was used to introduce the GAL4 DNA-binding domain (GAL4DBD) in the GR and MR genomic loci such that a chimeric GAL4DBD-GR (ligand-binding domain) [GAL4DBD-GR(LBD)] and GAL4DBD-MR(LBD) transcript is produced from the strong CMV promoter in HEK293 cells previously stably transfected with the UAS(GAL4)-BLA reporter construct. Dexamethasone- and aldosterone-responding BLA-positive cells were isolated by fluorescence-activated cell sorting, and then further expanded into separate cell lines. The sensitivity and robustness of the resulting GR and MR assays are demonstrated by the fact that the addition of dexamethasone and aldosterone to the two transgenic clonal cell lines for 16 h results in high Z' values (>0.8) and EC(50) values of 1 and 0.3 nM, respectively. These assays illustrate the flexibility of this technology to generate high-performance cellular assays for nuclear receptor targets without the need for target-specific cDNA.

A collaborative screening program for the discovery of inhibitors of HCV NS2/3 cis-cleaving protease activity

This report describes the development of a cell-based assay for high-throughput screening and detection of small-molecule inhibitors for hepatitis C virus (HCV) NS2/3 protease. The HCV NS2/3 protease is essential for the normal infectious cycle of HCV. Generation of a cell-based assay for this cis-acting viral protease involved reporter constructs in which the NS2/3 protease sequence was inserted between the ,B-lactamase (BLA) reporter and a ubiquitin-based destabilization domain. In stable cell lines, NS2/3 cis cleavage of the NS2/3-BLA fusion protein resulted in differential stability of the cleaved versus uncleaved BLA reporter, providing a robust readout for protease activity. BLA reporter activity was shown to be a function of NS2/3-specific protease activity, by using genetic mutants of the NS2/3 sequence. In addition, the cell-based assay was validated and screened in a 384-well format on a fully automated robotic platform where small-molecule inhibitors of NS2/3 protease activity were identified.

The reliability of environmental measures of the college alcohol environment

Much of what we know about students' drinking patterns and problems related to alcohol use is based on survey research. Although local and national survey data are important to alcohol-prevention projects, they do not sufficiently capture the complexity of the alcohol environment. Environmental prevention approaches to alcohol-related problems have been shown to be effective in community settings and researchers have begun to study and adapt such approaches for use on college campuses. Many environmental approaches require systematic scanning of the campus alcohol environment. This study assessed the inter-rater reliability of two environmental scanning tools (a newspaper content analysis form and a bulletin analysis form) designed to identify alcohol-related advertisements targeting college students. Inter-rater reliability for these forms varied across different rating categories and ranged from poor to excellent. Suggestions for future research are addressed.

Host cell factor requirement for hepatitis C virus enzyme maturation

The cellular chaperone, HSP90, is identified here as an essential factor for the activity of NS2/3 protease of hepatitis C virus. The cleavage activity of NS2/3 protease synthesized in reticulocyte lysate is ATP-dependent, as evidenced by ATP depletion experiments and inhibition with nonhydrolyzable ATP analogs. Geldanamycin and radicicol, ATP-competitive inhibitors of the chaperone HSP90, also inhibit the cleavage of in vitro-synthesized NS2/3. Furthermore, these HSP90 inhibitors prevent NS2/3 cleavage when the protease is expressed in mammalian cells. The physical association of NS2/3 with HSP90 is demonstrated by immunoprecipitation. Thus, by way of a chaperone/folding activity, an HSP90-containing complex is required for maturation of the polyprotein that encodes the enzymes essential for hepatitis C virus replication.

Aclarubicin treatment restores SMN levels to cells derived from type I spinal muscular atrophy patients

Proximal spinal muscular atrophy (SMA) is a common motor neuron disorder caused by mutation of the telomeric survival of motor neuron gene SMN1. The centromeric survival of motor neuron SMN2 gene is retained in all SMA patients but does not produce sufficient SMN protein to prevent the development of clinical symptoms. The SMN1 and SMN2 genes differ functionally by a single nucleotide change. This change affects the efficiency with which exon 7 is incorporated into the mRNA transcript. Thus, SMN2 produces less full-length mRNA and protein than SMN1. We have screened a library of compounds in order to identify ones that can alter the splicing pattern of the SMN2 gene. Here, we report that the compound aclarubicin increases the retention of exon 7 into the SMN2 transcript. We show that aclarubicin effectively induces incorporation of exon 7 into SMN2 transcripts from the endogenous gene in type I SMA fibroblasts as well as into transcripts from a SMN2 minigene in the motor neuron cell line NSC34. In type I fibroblasts, treatment resulted in an increase in SMN protein and gems to normal levels. Our results suggest that alteration of splicing pattern represents a new approach to modification of gene expression in disease treatment and demonstrate the feasibility of high throughput screens to detect compounds that affect the splicing pattern of a gene.

A ubiquitin-based tagging system for controlled modulation of protein stability

Many biotechnology applications depend on the expression of exogenous proteins in a predictable and controllable manner. A key determinant of the intracellular concentration of a given protein is its stability or "half-life." We have developed a versatile and reliable system for producing short half-life forms of proteins expressed in mammalian cells. The system consists of a series of destabilization domains composed of varying numbers of a mutant form of ubiquitin (UbG76V) that cannot be cleaved by ubiquitin hydrolases. We show that increasing the number of UbG76V moieties within the destabilization domain results in a graded decrease in protein half-life and steady-state levels when fused to heterologous reporter proteins as well as cellular proteins. Cells expressing a destabilized beta-lactamase reporter act as a robust, high-throughput screening (HTS)-compatible assay for proteasome activity within cells.

Pharmacological treatments for alcoholism: revisiting lithium and considering buspirone

OBJECTIVE

Previous research has suggested that both lithium and buspirone could lessen alcoholics' desire to drink as well as reduce the actual amounts of alcohol consumed. The purpose of this study was to compare lithium and buspirone monotherapy with placebo on outcomes of abstinence, alcohol quantity consumed, treatment retention and compliance, and medication side effects.

METHODS

We conducted a randomized, double-blind, placebo-controlled, three-arm parallel group, clinical trial that compared lithium and buspirone with placebo in 156 alcohol-dependent men.

RESULTS

Study retention rates for the three treatment groups at 3 and 6 months, respectively, were 61% and 46% for lithium, 44% and 27% for buspirone, and 52% and 38% for placebo (p = NS, for 3 and 6 months). Overall abstinence rates were 28% and 19% at 3 and 6 months, respectively. However, mean daily quantities of alcohol consumed and percentage of drinking days decreased significantly (p < 0.0001) over time in all treatment groups. Differential improvement was seen only for the decrement in quantity consumed in the buspirone group, compared with the placebo group, but only at a trend level (p = 0.07). According to pill counts, compliance did not differ significantly among the treatment groups.

CONCLUSIONS

These results do not support the hypothesis that either lithium or buspirone, compared with placebo, produces differential reductions in alcohol consumption. The results suggest the need to enhance treatment retention to maximize outcomes.

Treatment attrition among alcohol-dependent men: is it related to novelty seeking personality traits?

"Dropouts" are a major concern when monitoring treatment efficacy in clinical trials. Alcohol-dependent patients are especially prone to discontinuing treatment, perhaps because of impulsive behavior. The Tridimensional Personality Questionnaire (TPQ) measures a trait-like quality, novelty seeking, which may reflect impulsiveness. We tested the hypotheses that higher TPQ Novelty Seeking subscale scores would be associated with increased rates of treatment dropout and increased risk for dropping out earlier. A total of 170 alcohol-dependent men who participated in a double-blind, placebo-controlled pharmacotherapeutic trial for decreasing relapse drinking completed the TPQ and were monitored until treatment dropout. Logistic regression and Cox proportional hazards models were used to (1) describe the relationship between the TPQ Novelty Seeking score and the dichotomous outcome variable, treatment dropout; and (2) assess the effects of a number of potential confounding covariates on the relationship between the risk factor, novelty seeking, and the time to the outcome event. The mean Novelty Seeking score was significantly higher among study dropouts compared with nondropouts (p = 0.003). Higher Novelty Seeking scores were associated with a higher adjusted odds ratio for dropping out (adjusted odds ratio = 1.07, 95% confidence interval [CI] = 1.00-1.15) and a higher adjusted hazard rate for dropping out earlier (adjusted hazard rate = 1.05, 95% CI = 1.00-1.09). The TPQ Novelty Seeking subscale score may identify a subgroup of alcohol-dependent men who are at risk for dropping out of treatment. This information may be useful for developing treatment plans to encourage these high-risk patients to remain in treatment.

A genome-wide functional assay of signal transduction in living mammalian cells

We describe a genome-wide functional assay for rapid isolation of cell clones and genetic elements responsive to specific stimuli. A promoterless beta-lactamase reporter gene was transfected into a human T-cell line to generate a living library of reporter-tagged clones. When loaded with a cell-permeable fluorogenic substrate, the cell library simultaneously reports the expression of a large number of endogenous genes. Flow cytometry was used to recover individual clones whose reporter-tagged genes were either induced or repressed following T-cell activation. Responsive clones were expanded and analyzed pharmacologically to identify patterns of regulation associated with specific genes. Although demonstrated using T cells, the genomic assay could be applied to map downstream transcriptional consequences for any propagating cell line in response to any stimulus of interest.

Cell-permeant caged InsP3 ester shows that Ca2+ spike frequency can optimize gene expression

Inositol 1,4,5-trisphosphate (InsP3) releases calcium from intracellular stores and triggers complex waves and oscillations in levels of cytosolic free calcium. To determine which longer-term responses are controlled by oscillations in InsP3 and cytosolic free calcium, it would be useful to deliver exogenous InsP3, under spatial and temporal control, into populations of unpermeabilized cells. Here we report the 15-step synthesis of a membrane-permeant, caged InsP3 derivative from myo-inositol This derivative diffused into intact cells and was hydrolysed to produce a caged, metabolically stable InsP3 derivative. This latter derivative accumulated in the cytosol at concentrations of hundreds of micromolar, without activating the InsP3 receptor. Ultraviolet illumination uncaged an InsP3 analogue nearly as potent as real InsP3, and generated spikes of cytosolic free calcium, and stimulated gene expression via the nuclear factor of activated T cells. The same total amount of InsP3 analogue elicited much more gene expression when released by repetitive flashes at 1-minute intervals than when released at 0.5- or > or = 2-minute intervals, as a single pulse, or as a slow sustained plateau. Thus, oscillations in cytosolic free calcium levels at roughly physiological rates maximize gene expression for a given amount of InsP3.

Quantitation of transcription and clonal selection of single living cells with beta-lactamase as reporter

Gene expression was visualized in single living mammalian cells with beta-lactamase as a reporter that hydrolyzes a substrate loaded intracellularly as a membrane-permeant ester. Each enzyme molecule changed the fluorescence of many substrate molecules from green to blue by disrupting resonance energy transfer. This wavelength shift was detectable by eye or color film in individual cells containing less than 100 beta-lactamase molecules. The robust change in emission ratio reveals quantitative heterogeneity in real-time gene expression, enables clonal selection by flow cytometry, and forms a basis for high-throughput screening of pharmaceutical candidate drugs in living mammalian cells.

Tyrosine phosphorylation at the membrane-microfilament interface: a p185neu-associated signal transduction particle containing Src, Abl and phosphorylated p58, a membrane- and microfilament-associated retroviral gag-like protein

Microfilaments are associated with the microvillar membrane in the 13762 ascites rat mammary carcinoma cells by stable interaction with a large, multimeric signal transduction particle (STP) containing the (proto)oncogene receptor p185(neu). In vitro kinase assays on isolated microvilli and microvillar fractions enriched in the putative signal transduction particle showed a high specific activity of tyrosine kinase activity compared to that of membranes from EGF receptor-overexpressing A431 cells maximally activated by EGF. Assays of velocity sedimentation fractions from microvillar lysates in the presence and absence of the exogenous tyrosine kinase substrate poly-glu-tyr polypeptide (poly-E(4)Y) suggested association of the tyrosine kinase activity with STP-enriched microvillar fractions. The particulate fractions also contained discrete endogenous tyrosine-phosphorylated proteins, including prominent bands of approximately 42 and 58 kDa. Addition of ATP to these fractions resulted in a rapid increase in tyrosine phosphorylation of these and several other proteins, as detected by anti-phosphotyrosine blots. Immunoprecipitation and immunoblotting with anti-phosphotyrosine antibody of SDS-solubilized ascites cells and microfilament core fractions showed nine major bands; the electrophoretic mobilities of most of these in the cell immunoprecipitate and microfilament core were the same. In vivo and in situ phosphorylation, phosphoamino acid analysis, immunoprecipitation, 2-dimensional isoelectric focusing/SDS PAGE and immunoblot analysis showed that one of the prominent substrates is p58(gag), a retroviral Gag-like cytoplasmic STP component implicated in stabilizing microfilament-membrane interactions. Immunoblotting identified two peripheral membrane tyrosine kinases, p6O(src) and p120(abl), stably associated with the p185(neu)-containing signal transduction particle. These results provide further evidence for the constitutive activation of this aggressive mammary tumor and suggest a rote for phosphorylation of p58(gag) in organization of the STP at the membrane-microfilament interface in these cells.

Microcell mediated chromosome transfer maps the Fanconi anaemia group D gene to chromosome 3p

Fanconi anaemia (FA) is an autosomal recessive disorder characterized by progressive pancytopenia, short stature, radial ray defects, skin hyperpigmentation and a predisposition to cancer. Cells from FA patients are hypersensitive to cell killing and chromosome breakage induced by DNA cross-linking agents such as mitomycin C (MMC) and diepoxybutane (DEB). Consequently, the defect in FA is thought to be in DNA crosslink repair. Additional cellular phenotypes of FA include oxygen sensitivity, poor cell growth and a G2 cell cycle delay. At least 5 complementation groups for Fanconi anaemia exist, termed A through E. One of the five FA genes, FA(C), has been identified by cDNA complementation, but no other FA genes have been mapped or cloned until now. The strategy of cDNA complementation, which was successful for identifying the FA(C) gene has not yet been successful for cloning additional FA genes. The alternative approach of linkage analysis, followed by positional cloning, is hindered in FA by genetic heterogeneity and the lack of a simple assay for determining complementation groups. In contrast to genetic linkage studies, microcell mediated chromosome transfer utilizes functional complementation to identify the disease bearing chromosome. Here we report the successful use of this technique to map the gene for the rare FA complementation group D (FA(D)).

Mechanism of arrestin 2 function in rhabdomeric photoreceptors

Arrestins have emerged as one family of proteins that mediate the inactivation of G-protein-coupled receptors. We have isolated cDNA clones encoding two arrestin isoforms of the dipteran visual system, Calliphora arrestin 1 (Arr1) and arrestin 2 (Arr2). Microsequencing established that the arr2 gene encodes the Calliphora 49-kDa protein characterized previously as a photoreceptor-specific protein that undergoes reversible binding to light-activated rhodopsin and thereby activates the phosphorylation of metarhodopsin. Ultrastructural localization of Arr2 to the rhabdomeral part of the photoreceptor cell and quantitation of the amount of Arr2 bound suggest that Arr2 directly interacts with light-activated rhodopsin. In a reconstituted system containing affinity purified Arr2 and isolated rhabdomeric membranes, Arr2 binds to non-phosphorylated and phosphorylated metarhodopsin with comparable affinity. Reaction time courses reveal that Arr2 binding precedes phosphorylation of metarhodopsin, contrary to what has been reported so far for vertebrate photoreceptors. The phosphorylation-independent binding of Arr2 to metarhodopsin provides a mechanism for the rapid inactivation of the long-lived activated rhodopsin state which is characteristic for invertebrate photoreceptors. The dephosphorylation of rhodopsin is catalyzed by a Ca(2+)-dependent protein phosphatase which is shown here for the first time to exist in a membrane-associated form. Only metarhodopsin molecules with bound Arr2 are resistant to dephosphorylation. Thus, in fly photoreceptors, Arr2 acts as a regulatory protein that controls the phosphorylation as well as the dephosphorylation of the light-activated visual pigment.

Isolation of Drosophila genes encoding G protein-coupled receptor kinases

G protein-coupled receptors are regulated via phosphorylation by a variety of protein kinases. Recently, termination of the active state of two such receptors, the beta-adrenergic receptor and rhodopsin, has been shown to be mediated by agonist- or light-dependent phosphorylation of the receptor by members of a family of protein-serine/threonine kinases (here referred to as G protein-coupled receptor kinases). We now report the isolation of a family of genes encoding a set of Drosophila protein kinases that appear to code for G protein-coupled receptor kinases. These proteins share a high degree of sequence homology with the bovine beta-adrenergic receptor kinase. The presence of a conserved family of G protein-coupled receptor kinases in vertebrates and invertebrates points to the central role of these kinases in signal transduction cascades.

Isolation of a novel visual-system-specific arrestin: an in vivo substrate for light-dependent phosphorylation

Absorption of a photon of light by rhodopsin triggers mechanisms responsible for excitation as well as regulation of the phototransduction cascade. Arrestins are a family of proteins that appear to be responsible for terminating the active state of G-protein-coupled receptors. One of the major substrates of light-dependent phosphorylation in the visual cascade of Drosophila was purified and partially sequenced. The complete primary structure of the protein was determined by isolating the corresponding gene, which revealed it to be a new isoform of arrestin, Arr2. Arr2 is 401 residues in length, and shares 47% sequence identity with the Drosophila Arr1 protein and 42% with human arrestin. We show that the two Drosophila arrestin genes are differentially regulated, and that Arr2 is a specific substrate for a calcium-dependent protein kinase. This is the first demonstration of in vivo regulation of arrestins in a transduction cascade, and provides a new level of modulation in the function of G-protein-coupled receptors.

Surface exposure of phosphatidylserine is associated with the swelling and osmotically-induced fusion of human erythrocytes in the presence of Ca2+

An assay for procoagulant activity has been used to investigate the Ca2(+)-dependent exposure of phosphatidylserine at the surface of human erythrocytes that were induced to swell and to fuse osmotically. Since the phosphatidylserine of human erythrocytes is located in the inner leaflet of the plasma membrane, it is inaccessible in intact cells which therefore had no procoagulant activity in an isotonic solution of sucrose. The procoagulant activity of erythrocytes incubated in increasingly hypotonic, sucrose solutions containing Mg2+ paralleled the percentage haemolysis, reflecting the accessibility of phosphatidylserine in an increasing number of lysed cells. However, cells in mildly hypotonic sucrose solutions containing Ca2+ had an abnormally high procoagulant activity indicating that phosphatidylserine was exposed in intact cells under these conditions. Erythrocytes that were subjected to continuous swelling at 37 degrees C, which was induced by entry of the permeant molecule poly(ethylene glycol) 400 (PEG 400) developed procoagulant activity in the presence of Ca2+ prior to extensive lysis. Cells treated in this way also fused. With Mg2+, PEG 400-treated erythrocytes lysed without fusing, and the development of procoagulant activity paralleled the rate of lysis. Erythrocytes incubated with ionophore A23187, subtilisin, and Ca2+ developed procoagulant activity (with less than 20% lysis), and they fused on subsequent exposure to a hypotonic medium. The procoagulant activity reached its maximum before fusion could be induced in the hypotonic medium. It is concluded that the entry of Ca2+ facilitates a translocation of phosphatidylserine to the outer leaflet of the erythrocyte plasma membrane that plays an important role in fusion protocols that involve cell swelling. It is also suggested that transbilayer movements of phosphatidylserine could be an important control factor in the cell biology of membrane fusion phenomena.

The effect of space radiation of the nervous system

The long-term effects of irradiation by accelerated heavy ions on the structure and function of the nervous system have not been studied extensively. Although the adult brain is relatively resistant to low LET radiation, cellular studies indicate that individual heavy ions can produce serious membrane lesions and multiple chromatin breaks. Capillary hemorrhages may follow high LET particle irradiation of the developing brain as high RBE effects. Evidence has been accumulating that the glial system and blood-brain barrier (BBB) are relatively sensitive to injury by ionizing radiation. While DNA repair is active in neural systems, it may be assumed that a significant portion of this molecular process is misrepair. Since the expression of cell lethality usually requires cell division, and nerve cells have an extremely low rate of division, it is possible that some of the characteristic changes of premature aging may represent a delayed effect of chromatin misrepair in brain. Altered microcirculation, decreased local metabolism, entanglement and reduction in synaptic density, premature loss of neurons, myelin degeneration, and glial proliferation are late signs of such injuries. HZE particles are very efficient in producing carcinogenic cell transformation, reaching a peak for iron particles. The promotion of viral transformation is also efficient up to an energy transfer of approximately 300 keV/micron. The RBE for carcinogenesis in nerve tissues remains unknown. On the basis of available information concerning HZE particle flux in interplanetary space, only general estimates of the magnitude of the effects of long-term spaceflight on some nervous system parameters may be constructed.