Identification of vaccine candidates against serogroup B meningococcus by whole-genome sequencing

Neisseria meningitidis is a major cause of bacterial septicemia and meningitis. Sequence variation of surface-exposed proteins and cross-reactivity of the serogroup B capsular polysaccharide with human tissues have hampered efforts to develop a successful vaccine. To overcome these obstacles, the entire genome sequence of a virulent serogroup B strain (MC58) was used to identify vaccine candidates. A total of 350 candidate antigens were expressed in Escherichia coli, purified, and used to immunize mice. The sera allowed the identification of proteins that are surface exposed, that are conserved in sequence across a range of strains, and that induce a bactericidal antibody response, a property known to correlate with vaccine efficacy in humans.

Protein-protein interactions and 5'-splice-site recognition in mammalian mRNA precursors

Exactly how specific splice sites are recognized during the processing of complex precursor messenger RNAs is not clear. Small nuclear ribonucleoprotein particles (snRNPs) are involved, but are not sufficient by themselves to define splice sites. Now a human protein essential for splicing in vitro, called alternative splicing factor/splicing factor 2, is shown to cooperate with the U1 snRNP particle in binding pre-mRNA. This cooperation is probably achieved by specific interactions between the arginine/serine-rich domain of the splicing factor and a similar region in a U1 snRNP-specific protein.

Primary structure of the human splicing factor ASF reveals similarities with Drosophila regulators

We described previously the purification of a human protein, called alternative splicing factor (ASF), that can switch utilization of alternative 5' splice sites in an SV40 early pre-mRNA. We now report the isolation of a cDNA, designated ASF-1, that encodes this protein. ASF-1 consists of 248 amino acid residues, including an 80 residue RNA-binding domain at its N-terminus and a 50 residue C-terminal region that is 80% serine plus arginine. ASF-1 produced in E. coli can activate splicing in vitro and switch 5' splice-site utilization, establishing that the recombinant protein is sufficient to supply these activities. Analysis of additional cDNAs revealed that ASF pre-mRNA can itself be alternatively spliced, surprisingly, by utilization of a shared 5' splice site and two closely spaced 3' splice sites. Use of the upstream site results in a second mRNA (ASF-2) in which translation of the downstream exon occurs extensively in an alternative reading frame distinct from ASF-1.

The splicing factor U2AF35 mediates critical protein-protein interactions in constitutive and enhancer-dependent splicing

The splicing factor U2AF (U2 snRNP auxiliary factor) is a heterodimer with subunits of 65 and 35 kD (U2AF65 and U2AF35). U2AF65 binds specifically to 3' splice sites, but previous studies failed to demonstrate a function for U2AF35. Here, we report that U2AF35 is required for constitutive splicing and also functions as a mediator of enhancer-dependent splicing. Nuclear extracts deficient in U2AF35 were inactive; however, both constitutive and enhancer-dependent splicing could be restored by the addition of purified recombinant U2AF35. In vitro protein-RNA interaction studies with pre-mRNAs containing either a constitutive or regulated splicing enhancer revealed that U2AF35 directly mediates interactions between U2AF65 and proteins bound to the enhancers. Thus, U2AF35 functions as a bridge between U2AF65 and the enhancer complex to recruit U2AF65 to the adjacent intron.

Functional domains of the human splicing factor ASF/SF2

The human splicing factor ASF/SF2 displays two predominant activities in in vitro splicing assays: (i) it is an essential factor apparently required for all splices and (ii) it is able to switch utilization of alternative 5' splice sites in a concentration-dependent manner. ASF/SF2 is the prototype of a family of proteins typified by the presence of one or two RNP-type RNA binding domains (RBDs) and a region highly enriched in repeating arginine-serine dipeptides (RS regions). Here we describe a functional analysis of ASF/SF2, which defines several regions essential for one, or both, of its two principal activities, and provides insights into how this type of protein functions in splicing. Two isoforms of the protein, which arise from alternative splicing, are by themselves inactive, but each can block the activity of ASF/SF2, thereby functioning as splicing repressors. Some, but not all, mutations in the RS region prevent ASF/SF2 from functioning as an essential splicing factor. However, the entire RS region can be deleted without reducing splice site switching activity, indicating that it is not absolutely required for interaction with other splicing factors. Experiments with deletion and substitution mutants reveal that the protein contains two related, but highly diverged, RBDs, and that both are essential for activity. Each RBD by itself retains the ability to bind RNA, although optimal binding requires both domains.

Activation and repression of transcription by the gap proteins hunchback and Krüppel in cultured Drosophila cells

We have studied the ability of the Drosophila gap proteins Krüppel and hunchback to function as transcriptional regulators in cultured cells. Both proteins bind to specific sites in a 100-bp DNA fragment located upstream of the segment polarity gene engrailed, which also contains functional binding sites for a number of homeo box proteins. The hunchback protein is a strikingly concentration-dependent activator of transcription, capable of functioning both by itself and also synergistically with the pair-rule proteins fushi tarazu and paired. In contrast, Krüppel is a transcriptional repressor that can block transcription induced either by hunchback or by several different homeo box proteins. While repression of the homeo box protein activators requires a Krüppel-binding site on the DNA, repression of hunchback can occur efficiently in the absence of a Krüppel-binding site. We discuss the possible molecular mechanisms underlying these activities, as well as the potential significance of these results with respect to segmentation in Drosophila.

The human splicing factor ASF/SF2 can specifically recognize pre-mRNA 5' splice sites

ASF/SF2 is a human protein previously shown to function in in vitro pre-mRNA splicing as an essential factor necessary for all splices and also as an alternative splicing factor, capable of switching selection of 5' splice sites. To begin to study the protein's mechanism of action, we have investigated the RNA binding properties of purified recombinant ASF/SF2. Using UV crosslinking and gel shift assays, we demonstrate that the RNA binding region of ASF/SF2 can interact with RNA in a sequence-specific manner, recognizing the 5' splice site in each of two different pre-mRNAs. Point mutations in the 5' splice site consensus can reduce binding by as much as a factor of 100, with the largest effects observed in competition assays. These findings support a model in which ASF/SF2 aids in the recognition of pre-mRNA 5' splice sites.

Identification of an snRNP-associated kinase activity that phosphorylates arginine/serine rich domains typical of splicing factors

The U1 snRNP-specific 70K protein is one of the few snRNP proteins from higher eukaryotic cells that is phosphorylated in vivo (1,2). Immunoaffinity purified spliceosomal snRNPs (U1, U2, U5, and U4/U6) were tested for their ability to phosphorylate in vitro the U1-specific 70K protein. An snRNP-associated kinase activity which phosphorylates all U1-70K isoelectric variants was identified. Like its in vivo counterpart, this snRNP-associated enzyme phosphorylates solely serine residues of the 70K protein, preferentially utilizing ATP as a phosphodonor. Tryptic phosphopeptide analysis revealed an overlapping set of at least four radiolabeled peptides in the in vivo and in vitro phosphorylated protein, suggesting that the snRNP-associated serine kinase is responsible, at least in part, for the 70K protein phosphorylation observed in vivo. Chymotryptic digestion of in vitro, 32P-labeled 70K protein and in vitro phosphorylation studies with a synthetic peptide, indicated that the multiple 70K phosphorylation sites are limited to a highly charged, C-terminal domain of the protein. In vitro phosphorylation studies with the splicing factor ASF/SF2 and several deletion mutants demonstrated that, similar to the U1-70K protein, the snRNP-associated serine kinase phosphorylates the carboxy terminal RS-rich domain of ASF/SF2. A potential general role for this enzyme in the phosphorylation of splicing factors and its consequences for pre-mRNA splicing regulation are discussed.

The Drosophila RNA-binding protein RBP1 is localized to transcriptionally active sites of chromosomes and shows a functional similarity to human splicing factor ASF/SF2

An RNA-binding protein gene (rbp1) from Drosophila melanogaster, encoding an RNA recognition motif and an Arg-Ser rich (RS) domain, has been characterized. The predicted amino acid sequence of rbp1 is similar to those of the human splicing factor ASF/SF2, the Drosophila nuclear phosphoprotein SRp55, and the Drosophila puff-associated protein B52. Northern and immunohistochemical analyses showed that rbp1 is expressed at all stages in all tissues and that the RBP1 protein is localized to the nucleus. Consistent with a role in mRNA metabolism, indirect immunofluorescence reveals that the RBP1 protein colocalizes with RNA polymerase II on larval salivary gland polytene chromosomes. RBP1 protein made in Escherichia coli was tested for splicing activity using human cell extracts in which ASF has been shown previously both to activate splicing and to affect the choice of splice sites in alternatively spliced pre-mRNAs. In these assays, RBP1 protein, like ASF, is capable of both activating splicing and switching splice site selection. However, in each case, clear differences in the behavior of the two proteins were detected, suggesting that they have related but not identical functions. The general nuclear expression pattern, colocalization on chromosomes with RNA polymerase II, the similarity to ASF/SF2, SRp55, and B52, along with the effect on alternative splicing shown in vitro, suggest that rbp1 is involved in the processing of precursor mRNAs.

A population-based study of salivary lysozyme concentrations and candidal counts

The relationship between salivary lysozyme concentration and oral candida load was examined in 595 adults. Unstimulated whole saliva, and citrate-stimulated parotid and submandibular/sublingual saliva were collected from each participant. Candida colony-forming units (c.f.u.) in unstimulated whole saliva were determined. An enzyme-linked immunosorbent assay for lysozyme using commercially available antibodies was developed. This assay showed a linear relation of salivary lysozyme concentrations from 0.5 to 4.0 ng/ml. Significant negative relations were observed between lysozyme concentration and flow rate: r = -0.16 (p < 0.001) for stimulated parotid and r = -0.22 (p < 0.0001) for stimulated submandibular/sublingual saliva. The lysozyme concentration in stimulated submandibular/sublingual saliva was higher in males than in female, but no sex difference was observed for stimulated parotid saliva. The lysozyme concentration of stimulated parotid saliva was positively correlated with candida counts (r = 0.18: p < 0.005). Further study of groups according to their levels of candida in whole saliva revealed that lysozyme concentrations were higher in the high candida (> or = 1000 c.f.u./ml) group than in the zero and moderate candida categories in stimulated parotid saliva (p < 0.001): there were no concentration differences in stimulated submandibular/sublingual saliva. These results suggest that parotid lysozyme concentration increases as candida load increases.

Effect of exenatide on splanchnic and peripheral glucose metabolism in type 2 diabetic subjects

OBJECTIVE

Our objective was to examine the mechanisms via which exenatide attenuates postprandial hyperglycemia in type 2 diabetes mellitus (T2DM).

STUDY DESIGN

Seventeen T2DM patients (44 yr; seven females, 10 males; body mass index = 33.6 kg/m(2); glycosylated hemoglobin = 7.9%) received a mixed meal followed for 6 h with double-tracer technique ([1-(14)C]glucose orally; [3-(3)H]glucose i.v.) before and after 2 wk of exenatide. In protocol II (n = 5), but not in protocol I (n = 12), exenatide was given in the morning of the repeat meal. Total and oral glucose appearance rates (RaT and RaO, respectively), endogenous glucose production (EGP), splanchnic glucose uptake (75 g - RaO), and hepatic insulin resistance (basal EGP × fasting plasma insulin) were determined.

RESULTS

After 2 wk of exenatide (protocol I), fasting plasma glucose decreased (from 10.2 to 7.6 mm) and mean postmeal plasma glucose decreased (from 13.2 to 11.3 mm) (P < 0.05); fasting and meal-stimulated plasma insulin and glucagon did not change significantly. After exenatide, basal EGP decreased (from 13.9 to 10.8 μmol/kg · min, P < 0.05), and hepatic insulin resistance declined (both P < 0.05). RaO, gastric emptying (acetaminophen area under the curve), and splanchnic glucose uptake did not change. In protocol II (exenatide given before repeat meal), fasting plasma glucose decreased (from 11.1 to 8.9 mm) and mean postmeal plasma glucose decreased (from 14.2 to 10.1 mm) (P < 0.05); fasting and meal-stimulated plasma insulin and glucagon did not change significantly. After exenatide, basal EGP decreased (from 13.4 to 10.7 μmol/kg · min, P = 0.05). RaT and RaO decreased markedly from 0-180 min after meal ingestion, consistent with exenatide's action to delay gastric emptying.

CONCLUSIONS

Exenatide improves 1) fasting hyperglycemia by reducing basal EGP and 2) postmeal hyperglycemia by reducing the appearance of oral glucose in the systemic circulation.

Memory-related changes of nitric oxide synthase activity and nitrite level in rat brain

The changes of nitric oxide synthase (NOS) activity and nitrite level in rat brain regions after spatial learning were investigated. NOS activity was assayed by conversion of [3H]L-arginine to [3H]L-citrulline, and a sensitive fluorometric assay for quantification of nitrite was used. Compared with sham-trained rats, NOS activity and nitrite level in hippocampus and cortex, and also the nitrite level in cerebellum, was elevated significantly one day after rats had learnt a water-rewarded spatial alteration task. These results suggest a spatial memory-related changes of endogenous NO in rat brain, and support the idea that NO participates in learning and memory processes.

Lactoferrin-derived peptides and Lactoferricin chimera inhibit virulence factor production and biofilm formation in Pseudomonas aeruginosa

AIMS

To investigate the bactericidal activity of lactoferrin-derived peptides and a new LF-derived peptides chimera (LFchimera) against P. aeruginosa and the influence on virulence factors of P. aeruginosa.

METHODS AND RESULTS

Lactoferricin (LFcin) and lactoferrampin (LFampin) are highly bioactive peptides isolated from the N-terminal region of lactoferrin (LF) by pepsin digestion. In this study, we designed LFchimera containing LFcin amino acids 17-30 and LFampin amino acids 268-284. Pseudomonas aeruginosa cells were incubated in medium with peptides at different concentrations, and then the assays of viability, pyocyanin, elastase activity and biofilm formation of P. aeruginosa were performed. We found that the concentration-dependent antibactericidal activity and down-regulating pyocyanin, elastase and biofilm formation of LFchimera were significantly stronger than those of LF, LFcin, LFampin or LFcin plus LFampin.

CONCLUSIONS

Our results indicated that LF, LFcin, LFampin and LFchimera were potential candidates to combat P. aeruginosa, and LFchimera was the most effective in them.

SIGNIFICANCE AND IMPACT OF THE STUDY

The new LFchimera has better activity against P. aeruginosa than LF, LFcin and LFampin and may be a promising new compound for treatment of P. aeruginosa infection.

Glucose and lipid effects of the ileal apical sodium-dependent bile acid transporter inhibitor GSK2330672: double-blind randomized trials with type 2 diabetes subjects taking metformin

AIMS

To investigate the pharmacodynamics, pharmacokinetics and safety/tolerability of blocking reuptake of bile acids using the inhibitor GSK2330672 (GSK672) in patients with type 2 diabetes (T2D).

METHODS

Subjects with T2D taking metformin were enrolled in two studies in which they took metformin 850 mg twice daily for 2 weeks prior to and during the randomized treatment periods. In the first crossover study (n = 15), subjects received GSK672 45 mg, escalating to 90 mg, twice daily, or placebo for 7 days. The second parallel-group study (n = 75) investigated GSK672 10-90 mg twice daily, placebo or sitagliptin for 14 days.

RESULTS

In both studies, GSK672 reduced circulating bile acids and increased serum 7-α-hydroxy-4-cholesten-3-one (C4), an intermediate in the hepatic synthesis of bile acids. Compared with placebo, in the parallel-group study 90 mg GSK672 twice daily reduced fasting plasma glucose [FPG; -1.21 mmol/l; 95% confidence interval (CI) -2.14, -0.28] and weighted-mean glucose area under the curve (AUC)0-24 h (-1.33 mmol/l; 95% CI -2.30, -0.36), as well as fasting and weighted-mean insulin AUC0 -24 h . GSK672 also reduced cholesterol (LDL, non-HDL and total cholesterol) and apolipoprotein B concentrations; the maximum LDL cholesterol reduction was ∼40%. There was no change in HDL cholesterol but there was a trend towards increased fasting triglyceride levels in the GSK672 groups compared with placebo. In both studies, the most common adverse events associated with GSK672 were gastrointestinal, mostly diarrhoea (22-100%), which appeared to be independent of dose.

CONCLUSIONS

In subjects with T2D on metformin, GSK672 improved glucose and lipids, but there was a high incidence of gastrointestinal adverse events.

Potential role of alpha-synuclein and metallothionein in lead-induced inclusion body formation

Lead (Pb) produces aggresome-like inclusion bodies (IBs) in target cells as a toxic response. Our prior work shows metallothionein (MT) is required for this process. We used MT-I/II double knockout (MT-null) and parental wild-type (WT) cell lines to further explore the formation process of Pb-induced IBs. Unlike WT cells, MT-null cells did not form IBs after Pb exposure. Western blot of cytosol showed soluble MT protein in WT cells was lost during Pb exposure as IBs formed. Transfection of MT-I into MT-null cells allowed IBs formation after Pb exposure. Considering Pb-induced IBs may be like disease-related aggresomes, which often contain alpha-synuclein (Scna), we investigated Scna expression in cells capable (WT) and incapable (MT-null) of producing IBs after Pb exposure. Scna protein showed poor basal expression in MT-null cells. Pb exposure increased Scna expression only in WT cells. MT transfection increased Scna transcript to WT levels. In WT or MT-transfected MT-null cells, Pb-induced Scna expression rapidly increased and then decreased over 48 h as Pb-induced IBs were formed. A direct interaction between Scna and MT was confirmed ex vivo by antibody pulldown assay where the proteins coprecipitated with an antibody to MT. Pb exposure caused increased colocalization of MT and Scna proteins with time only in WT cells. In WT mice after chronic Pb exposure Scna was localized in renal cells containing forming IBs, whereas MT-null mice did not form IBs. Thus, Scna could be component of Pb-induced IBs and, with MT, may play a role in IBs formation.

The mechanism of memory impairment induced by Aβ chronic administration involves imbalance between cytokines and neurotrophins in the rat hippocampus

It has been demonstrated that the onset and progression of Alzheimer's disease (AD) are associated with inflammatory disorders in the brain. Although the interactions of inflammatory cytokines with neurotrophins have been reported in vitro, the balance change between inflammatory cytokines and neurotrophic factors (NTFs), such as nerve growth factor (NGF), brain derived neurotrophic factor (BDNF), and glial cell line-derived neurotrophic factor (GDNF), due to amyloid β (Aβ) chronic administration in vivo is still unclear. The hypothesis of the present study was that the accumulation of Aβ activated glial cells to produce inflammatory mediators and NTFs to maintain the neurons survival, however the failure of crosstalk between NTFs and inflammatory cytokines might occur in the brain and the NTFs expressions would decrease after Aβ chronic treatment, which, therefore, would contribute to the neuronal death and memory impairments. Thus, the present study measured the learning and memory behavior, glial cells activities, cytokines (IL-1α, IL-1β and TNF-α) concentrations and NTFs (NGF, BDNF and GDNF) gene and protein levels in rats after i.c.v injection of Aβ(25-35) for 14 days. The results showed that Aβ (25-35)-treated animals exhibited failure of balance between inflammatory cytokines and NTFs system (increased cytokines levels, decreased NGF protein expression and reduced NTFs gene transcriptions), which might contribute to the cognitive impairments. The findings from this study provide valuable evidence that correct regulation of the crosstalk between inflammatory cytokines and NTFs could be a direction for AD therapy in the future.

The mechanism for the effect of selenium supplementation on immunity

Lipid peroxide (LPO) in lymphocytes from mice was evaluated by measuring substances reactive to thiobarbituric acid (TBA). The product resulting from the reaction of TBA with lymphocytes was extracted with n-butyl and fluorescence intensity was determined. The degree of lipid peroxidation, expressed as fluorescence intensity f547, was assessed for stimulation of lymphocytes with concanavalin A (Con A), and was related to lymphocyte proliferation in response to Con A if Se was administered. The lymphocyte proliferation was determined by [3H]thymidine incorporation, expressed as cpm. The effect of superoxide dismutase (SOD), added to cell culture on lymphocyte proliferation was also evaluated. It was found that LPO in lymphocytes before Con A stimulation was significantly less than that after stimulation (p < 0.001), and that SOD promoted lymphocyte proliferation dose dependently. The addition of Na2Seo3 to lymphocyte culture or supplementation in drinking water to mice decreased the produced LPO in lymphocyte in response to Con A. In the presence of Se, there is an inverse correlation between the levels of LPO in lymphocyte and the stimulated proliferation (r = -0.8902, r = -0.9439). In conclusion, active oxygen species scavenging was proposed as one of the mechanisms for Se to promote immunity.

Analyses of the genomic methylation status of the human cyclin A1 promoter by a novel real-time PCR-based methodology

The role of CpG methylation in the regulation of tissue-specific gene expression is highly controversial. Cyclin A1 is a tissue-specifically expressed gene that is strongly methylated in non-expressing tumor cell lines. We have established a novel real-time PCR method to quantitate genomic CpG methylation of the cyclin A1 promoter. Genomic DNA samples from different human organs were treated with bisulfite and amplified with methylation-specific primers and with primers amplifying methylated as well as non-methylated DNA. PCR product quantitation was obtained by using a fluorogenic probe labeled with FAM and TAMRA. These analyses demonstrated that the human cyclin A1 promoter was methylated in kidney, colon, spleen, testis, and small intestine, but not in brain, liver, pancreas, or heart. Expression of cyclin A1 was predominantly found in testis. Low level expression of cyclin A1 was present in spleen, prostate, leukocytes, colon, and thymus. Taken together, our data provide evidence that CpG methylation patterns of the human cyclin A1 promoter in human organs do not generally correlate with cyclin A1 gene expression in vivo.

Comparative studies on binding of 3 different ligands to the N-methyl-D-aspartate recognition domain in brain synaptic membranes treated with Triton X-100

Treatment with a low concentration of Triton X-100 almost tripled the binding of [3H]D,L-(E)-2-amino-4-propyl-5-phosphono-3-pentenoic acid (CGP 39653), a novel competitive antagonist at an N-methyl-D-aspartate (NMDA)-sensitive subclass of brain excitatory amino acid receptors, in synaptic membranes of the rat brain. The binding linearly increased with increasing protein concentrations of up to 0.4 mg/ml and also increased in proportion to incubation time with a plateau within 60 min after the initiation of incubation at 2 degrees C in Triton-treated membranes. Elevation of incubation temperature from 2 degrees C to 30 degrees C resulted in a marked decrease in the binding at equilibrium by 80%, and a maximal level was obtained within 1 min after the initiation of incubation at 30 degrees C with a gradual decline of up to 10 min. Bound [3H]CGP 39653 was rapidly dissociated by the addition of excess unlabeled L-glutamic acid (Glu), and the time required to attain complete dissociation was 60 min at 2 degrees C and 1 min at 30 degrees C, respectively. Among several agonists and antagonists tested, Glu was the most potent displacer of [3H]CGP 39653 binding with progressively less potent displacement by D-2-amino-5-phosphonovaleric, (+-)-3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic (CPP), D-2-amino-7-phosphonoheptanoic, N-methyl-D-aspartic and N-methyl-L-aspartic acids.(ABSTRACT TRUNCATED AT 250 WORDS)

The mortality trends of falls among the elderly adults in the mainland of China, 2013-2020: A population-based study through the National Disease Surveillance Points system

BACKGROUND

Fall in elderly is a major public health problem. Characterizing trends in fall mortality in different subpopulations could help identifying the needs and developing preventive program for target groups. Here we evaluated the trends of fall-related deaths in Chinese mainland among adults aged ≥60 years specific in sex, age, and provinces, to measure the change in this mortality rate between 2013 and 2020, and to explore the underlying factors influencing this change.

METHODS

Mortality data were retrieved from the National Disease Surveillance Points system(DSPs) of China, a national-level and provincial-level representative data source, to estimate the impact of elderly falls on mortality in the mainland of China and the specific provinces from 2013 to 2020. The joinpoint regression model was used to estimate the temporal trend of mortality in elderly fallen by calculating the annual percentage change (APC).

FINDINGS

The age-standardized falls mortality was 10·438 per 100 000 in 2020. The age-standardized mortality of elderly falls in total and female showed a steady increasing trend (APC=1·96%, p = 0·023 total; APC=3·42%, p = 0·003 female), with it was stable in males (APC=1.26%, p>0·05). Fall mortality among the elderly was more common in people over 70 years of age and increased sharply. The death rates and APCs were highest among the oldest age groups(aged≥85 years). The higher fall mortality was mainly focused in the southeast and central regions, and lower rates were in the northeast provinces and Tibet.

INTERPRETATION

Since 2013, the overall fall-related mortality trend among individuals aged ≥60 years has been consistently increasing in China, making it most critical public health challenge. Adherence interventions and increased social support for those at most risk should be considered.

FUNDING

None.

Further evidence for multiple forms of an N-methyl-D-aspartate recognition domain in rat brain using membrane binding techniques

Pretreatment with sulfhydryl-reactive agents, such as N-ethylmaleimide and p-chloromercuriphenylsulfonic acid, invariably resulted in marked inhibition of the binding of DL-(E)-2-amino-4-[3H]propyl-5-phosphono-3-pentenoic acid ([3H]CGP 39653), a competitive antagonist at an N-methyl-D-aspartate (NMDA)-sensitive subclass of central excitatory amino acid receptors, in brain synaptic membranes extensively washed and treated with Triton X-100, but did not significantly affect the binding of L-[3H]-glutamic acid ([3H]Glu), an endogenous agonist. The pretreatment was effective in reducing the binding of [3H]-CGP 39653 at equilibrium, without altering the initial association rate, and decreased the affinity for the ligand. Pretreatment with sulfhydryl-reactive agents also enhanced the potencies of NMDA agonists to displace [3H]-CGP 39653 binding and attenuated those of NMDA antagonists, but had little effect on the potencies of the agonists and antagonists to displace [3H]Glu binding. The binding of both [3H]CGP 39653 and [3H]Glu was similarly sensitive to pretreatment with four different proteases in Triton-treated membranes, whereas pretreatment with phospholipase A2 or C markedly inhibited [3H]CGP 39653 binding without altering [3H]Glu binding. Moreover, both phospholipases not only induced enhancement of the abilities of NMDA agonists to displace the binding of [3H]CGP 39653 and [3H]Glu, but also caused diminution of those of NMDA antagonists. These results suggest that both sulfhydryl-reactive agents and phospholipases may predominantly interfere with radiolabeling of the NMDA recognition domain in a state favorable to an antagonist by [3H]CGP 39653, with concomitant facilitation of that in an antagonist-preferring form by [3H]Glu. The possible presence of multiple forms of the NMDA recognition domain is further supported by these data.

Preparation of new nitrogen-bridged heterocycles. 49. A new access to thieno[3,4-b]indolizine derivatives

The title compounds, together with 3-vinylindolizine-1-carbonitriles (4-56%), were prepared in 1-18% yields from the S-alkylation of pyridinium 1-[3-ethoxycarbonyl-1-[cyanomethylthio(thiocarbonyl)]]all ylides with alkyl halides, followed by treatment of the resulting pyridinium salts with a base and then a dehydrogenating agent. In several reactions of pyridinium salts obtained from reaction of the allylides with benzylic halides, trace amounts of bis[1-cyano-9-(ethoxycarbonyl)thieno[3,4-b]indolizin-3-yl] disulfides with an interesting superimposed structure were also isolated. The structures of these compounds were confirmed by X-ray analyses.