The underlying mechanism for the diversity of disulfide folding pathways

The disulfide folding pathway of bovine pancreatic trypsin inhibitor (BPTI) is characterized by the predominance of folding intermediates with native-like structures. Our laboratory has recently analyzed the folding pathway(s) of four 3-disulfide-containing proteins, including hirudin, potato carboxypeptidase inhibitor, epidermal growth factor, and tick anticoagulant peptide. Their folding mechanism(s) differ from that of BPTI by 1) a higher degree of heterogeneity of 1- and 2-disulfide intermediates and 2) the presence of 3-disulfide scrambled isomers as folding intermediates. To search for the underlying causes of these diversities, we conducted kinetic analyses of the reductive unfolding of these five proteins. The experiment of reductive unfolding was designed to evaluate the relative stability and interdependence of disulfide bonds in the native protein. It is demonstrated here that among these five proteins, there exists a striking correlation between the mechanism(s) of reductive unfolding and that of oxidative folding. Those proteins with their native disulfide bonds reduced in a collective and simultaneous manner exhibit both a high degree of heterogeneity of folding intermediates and the accumulation of scrambled isomers along the folding pathway. A sequential reduction of the native disulfide bonds is associated with the presence of predominant intermediates with native- like structures.

Unique biochemical, cytotoxic, and antitumor activity of camptothecin and 4beta-amino-4'-O-demethylepipodophyllotoxin conjugates

Two compounds having a camptothecin (CPT) analog conjugated to the 4beta-amino-4'-O-demethylepipodophyllotoxin analog were evaluated for their biochemical and biological activities. W1[camptothecin-(para)-4beta-amino-4'-O-demethylepipodophyllotoxin] had no activity against topoisomerase II (TOP II), but inhibited topoisomerase I (TOP I) with an IC(50) value 2-fold higher than CPT. W2 [camptothecin-(ortho)-4beta-amino-4'-O-demethylepipodophyllotoxin] had inhibitory activity against TOP I and TOP II with IC(50) values 1.5-fold higher than either CPT or etoposide (VP-16). Both conjugates had similar cytotoxicity against the KB cell line, although the protein-linked DNA breaks (PLDBs) generated by W2 in KB cells were about 4-fold more than those of W1. No cross-resistance with the two conjugates was seen in a VP-16-resistant KB subline, which showed down-regulation of TOP II and overexpression of the multiple drug resistance-associated protein, or in a vincristine-resistant KB subline with overexpression of gp-170/mdr-1. The CPT-resistant KB variant (KB CPT 100), which has a reduction in TOP I content and another mechanism that occurs post-PLDB formation, was partially resistant to both compounds. W1 was not affected by this post-PLDB resistance mechanism. Cell cycle analysis demonstrated that W1 and W1 had similar cell cycle effects on KB and KB CPT 100 cells, which accumulated in S-phase upon drug treatment. These results suggested that W1 and W2 exerted their cytotoxicity through TOP I. In CPT-resistant cells, however, an unidentified target also may be involved in the cytotoxic action of W1 and TOP II may still be a target for W1. In vivo, W1 was more effective against the growth of human prostate cancer cells in nude mice than VP-16, CPT, or W2. Given its antitumor activity and unique biochemical mechanism of action, W1 warrants exploration as an antitumor compound.

5-(beta-Cyclodextrinylamino)-5-Deoxy-alpha-D-Riboses as Models for Nuclease, Ligase, Phosphatase, and Phosphorylase

beta-Cyclodextrin derivatives crowned with ribose rings (such as 1) catalyzed the hydrolysis, esterification, and phosphorylation of catechol-derived phosphate esters. The vicinal cis-diols on the ribose groups appear to play a major role in the catalytic activity of these enzyme models by the formation of hydrogen bonds which activate the phosphorus atom to nucleophilic attack.

Unfolding of hirudin characterized by the composition of denatured scrambled isomers

The native core structure of hirudin, a thrombin specific inhibitor, contains 24 hydrogen bonds, two stretches of beta-sheet and three disulfide bonds. Hirudin unfolds in the presence of denaturant and thiol catalyst by shuffling its native disulfide bonds and converting to scrambled structures that consist of 11 identified isomers. The composition of scrambled isomers, which characterizes the structure of denatured hirudin, varies as a function of denaturing conditions. The unfolding pathway of hirudin has been constructed by quantitative analysis of scrambled isomers unfolded under increasing concentrations of various denaturants. The results demonstrate a progressive expansion of the polypeptide chain and the existence of a structurally defined stable intermediate along the pathway of unfolding.

Analysis of the extent of unfolding of denatured insulin-like growth factor

Insulin-like growth factor (IGF-1) contains three disulfide bonds. In the presence of denaturant and thiol catalyst, IGF-1 shuffles its native disulfide bonds and denatures to form a mixture of scrambled isomers. The composition of scrambled IGF varies under different denaturing conditions. Among the 14 possible scrambled IGF isomers, the yield of the beads-form isomer is shown to be directly proportional to the strength of the denaturing condition. This paper demonstrates a new approach to quantify the extent of unfolding of the denatured protein.

Mesolimbic neuronal activity across behavioral states

A goal of neurophysiology of the mesolimbic system is to determine the activity patterns within the regions in the prefrontal cortex, ventral neostriatum, and amygdala that regulate behavioral patterns to seek rewards. A new technology has been introduced in which arrays of microwires are implanted in different brain regions while activity patterns of ensembles of neurons are recorded for long periods of time during freely moving behaviors. Multichannel instrumentation and software is used for data acquisition and analysis. An initial hypothesis was that neural signals would be encountered in the nucleus accumbens and associated regions specifically related to reward. However, an initial study of neural activity and behavioral patterns during a simple lever press for intravenous cocaine (1 mg/kg) revealed that phasic excitatory or inhibitory neural activity patterns often appear prior to the reward phase. Individual neurons throughout the mesolimbic system appear to code information specific to sensory and motor events, tones, or lever presses in the chain of tasks leading to all rewards so far studied. Different spatial temporal patterns also appear within the same neural populations, as reward is changed from injected cocaine to heroin, from ingested pure water to ethanol in water or sucrose. Overall, patterns of activity for each neuron are found to shift dynamically during the operant task as changes are made in the target reward. Significant shifts in activity of mesolimbic neurons that are unrelated to specific sensory-motor events also appear during complex sessions, such as during a bout of ethanol consumption to reach satiation or during progressive ratio tasks with increasing difficulty. An emerging hypothesis is that some candidate neural elements in the mesolimbic system code the anticipated reward, whereas others serve internal logic functions of motivation that mediate extinction or resumption of specific goal-directed behaviors.

Optical symmetry filtering by use of anisotropic self-diffraction in BaTiO3 crystals

We propose what we believe to be a novel and simple method for optical symmetry filtering, using anisotropic self-diffraction in BaTiO(3) crystals. This method allows us to distinguish a centrosymmetric pattern from a noncentrosymmetric pattern easily with scale invariance. It is self-referential; no extra reference element is required. Both the theory and the experiment are demonstrated.

Manganese potentiates nitric oxide production by microglia

Manganese toxicity has been associated with clinical symptoms of neurotoxicity which are similar to the symptoms observed in Parkinson's disease. Earlier reports indicated that reactive microglia was present in the substantia nigra of patients with Parkinson's disease. Using N9 microglial cells, the current study was designed to determine whether high levels of manganese were associated with microglial activation. Results indicated that manganese significantly increased the bacterial lipopolysaccharide-induced nitric oxide production. This potent activity of manganese was not shared by other transition metals tested, including iron, cobalt, nickel, copper and zinc. Immunohistochemical staining and Western blot analysis indicated that manganese increased the cellular production of inducible nitric oxide synthase. Northern blot analysis indicated that manganese likely increased iNOS gene transcription since this agent increased the mRNA level of the inducible nitric oxide synthase. In contrast to other transition metals tested, manganese did not appear to be cytotoxic to microglial cells. These results suggested that manganese could induce sustained production of neurotoxic nitric oxide by activated microglial cells, which might cause detrimental consequences to surrounding neurons.

Quantitative analysis of the composition of the native and scrambled ribonuclease A

Reversible conversion between the native and scrambled proteins can be applied to analyze the denaturation curve of a disulfide-containing protein. In the case of RNase A, scrambled species could not be well separated from the native species by HPLC to permit precise quantitative analysis of the extent of denaturation. Methods are developed here to overcome this problem. The methods exploit the difference of conformational stability between the native and scrambled RNase A. When a sample of partially denatured RNase A was placed under mild reducing conditions (0.2-1 mM dithiothreitol for 10 min), the disulfide bonds of the native RNase A remain intact, whereas those of scrambled isomers become fully reduced. The native and fully reduced species of RNase A can be completely separated by HPLC. Alternatively, a mixture of partially denatured RNase A can be treated with mild concentration of proteolytic enzymes (trypsin or thermolysin). In this approach, scrambled isomers of RNase A were totally fragmented and readily separated from the native RNase A. These methods allow analysis and construction of the denaturation curves of RNase A in the presence of urea, GdmCl and GdmSCN.

Neuronal spike activity in the nucleus accumbens of behaving rats during ethanol self-administration

Many lines of evidence support the importance of the nucleus accumbens (NAC) for ethanol-reinforced behavior. The nature of the neuronal activity that occurs in this region during ethanol self-administration is not known. We recorded from ensembles of single-units primarily located within the shell of the NAC during operant responding for oral ethanol solutions by well-trained rats. Of 90 units recorded from seven sessions from seven rats, 41 (46%) did not exhibit significant changes in relation to the experimental events. Of the 49 units (54%) that did exhibit significant phasic changes, alterations in firing rate occurred in relation to the following experimental events: operant response (63%), tone stimulus (20%), and ethanol delivery (63%). In addition, changes in spike activity during the intervals between the three experimental events were noted in 33% of the units. Most units (55% of responsive units) responded to multiple experimental events. Thus different but overlapping populations of neurons in the NAC represent each event that occurs along the temporal dimension of a single trial performed to obtain ethanol reward. The data suggest that the NAC plays a crucial role in linking together conditioned and unconditioned internal and external stimuli with motor plans to allow for ethanol-seeking behavior to occur.

Factor VIIa's first epidermal growth factor-like domain's role in catalytic activity

Factor VIIa-tissue factor complex formation initiates the extrinsic blood coagulation pathway. We investigated factor VIIa's first epidermal growth factor-like (egf1) domain's role in the catalytic activity increase caused when factor VIIa binds tissue factor. Starting with a factor VIIa with factor IX's egf1 domain (factor VII(IXegf1)a), we made 4 proteins with egf1 residues changed to those in factor VIIa, including E51A, D64Q, FG74-75PA, and K79R. We measured each enzyme's affinity for tissue factor and determined the enzymes' kinetic constants with and without tissue factor. The Kd for factor VII(IXegf1)a binding to tissue factor was 60-200-fold higher than that of factor VIIa depending on the assay employed. Only factor VII(IXegf1)a with the K79R (K79Ra) mutation, among all the mutants, had an effect on binding with a Kd 3-8-fold lower than that of factor VII(IXegf1)a. In kinetic analyses with a small peptide substrate, in the absence of tissue factor, factor VIIa, factor VII(IXegf1)a, and K79Ra had similar kcat's and Km's. With tissue factor, due to a kcat decrease, factor VII(IXegf1)a's catalytic efficiency (kcat/Km) was 2-fold lower than factor VIIa's. K79Ra's catalytic efficiency was intermediate between those of factor VIIa and factor VII(IXegf1)a. With factor X as substrate, in the absence of tissue factor, K79Ra and factor VII(IXegf1)a had catalytic efficiencies 1.5-fold and 2-fold lower than that of factor VIIa. In contrast, with tissue factor and with factor X as substrate, due to higher Km's, factor VII(IXegf1)a and K79Ra had only 9% and 33% of factor VIIa's catalytic efficiency. Our results suggest the egf1 domain's role in tissue factor binding involves critical alignment of tissue factor with factor VIIa's catalytic domain. Proper alignment in turn promotes optimal catalytic activities.

Denatured states of tick anticoagulant peptide. Compositional analysis of unfolded scrambled isomers

In the presence of denaturant and thiol catalyst, a disulfide-containing protein denatures and converts to a mixture of scrambled isomers, which can be purified and structurally characterized. Scrambled isomers adopt a different conformation and a varied extent of unfolding. Their relative concentration (composition) signals the state of unfolding of the denatured protein and is determined by the denaturing condition. In this report, tick anticoagulant peptide (TAP) (60 amino acids and 3 disulfides) has been denatured in the presence of urea, guanidine hydrochloride, guanidine thiocyanate, organic solvents, and at elevated temperature. The recoveries of scrambled TAP were analyzed. The results demonstrate that each denaturing condition generates a unique structure (composition of scrambled species) of denatured TAP. Among various species of scrambled TAP, the beads-form species contains the smallest disulfide loop and appears to represent the most extensively unfolded state. The yield of the beads-form species as a fraction of the total denatured TAP is invariably determined by the strength of the denaturing condition.

TFPIbeta, a second product from the mouse tissue factor pathway inhibitor (TFPI) gene

Tissue factor pathway inhibitor (TFPI) contains three Kunitz domains separated by two connecting regions. We have cloned another naturally occurring TFPI gene product from a mouse lung cDNA library which we have called TFPIbeta. TFPIbeta is derived from alternative splicing of the TFPI gene. Analysis of the cDNA shows that mouse TFPIbeta protein is identical to TFPI from the N'-terminus through the second connecting region. However, mouse TFPIbeta possesses neither a third Kunitz domain nor an Arg, Lys-rich C'-terminus but instead has a completely different C'-terminal (beta-domain) sequence which is not homologous to any known protein. Northern blot analyses show that the tissues for mouse TFPIbeta synthesis are heart and lung; in contrast, TFPI appears in Northern blots of heart and spleen. Both TFPIbeta and TFPI messages first appear in 7-day-old mouse embryos, but only the TFPI mRNA persists until 17 days. Purified recombinant TFPIbeta shows an apparent molecular weight of 38 kDa. Kinetic studies indicate that mouse TFPIbeta is a slow-binding enzyme inhibitor for human factor Xa. In addition, heparin does not enhance the inhibition of factor Xa by mouse TFPIbeta although it does accelerate factor Xa inhibition by TFPI.

Photorefractive Incoherent-to-Coherent Optical Converter Based on Anisotropic Self-Diffraction in BaTiO(3)

A photorefractive incoherent-to-coherent optical converter (PICOC) is demonstrated; conversion is accomplished by anisotropic self-diffraction in BaTiO(3). The setup of the PICOC is easy, and only two writing beams are required. The diffraction efficiency reaches 50%, and the resolution is 22 line pairs (lp)/mm in a typical-size crystal. Further, the resolution reaches 40 lp/mm when a BaTiO(3):Rh crystal of thickness 1.2 mm is used, and the diffraction efficiency is as high as 51%. The resolution of the PICOC can be increased effectively by reduction of the crystal thickness with no penalty for low diffraction efficiency.

Safety study and characterization of E1A-liposome complex gene-delivery protocol in an ovarian cancer model

A phase I clinical trial of E1A-liposome complex is currently ongoing in patients with HER-2/neu-overexpressing breast or ovarian cancers. To optimize the E1A-liposome complex for a further stage of clinical trial, several aspects of the current protocol have been examined in an animal model. In the orthotopic ovarian cancer model, different doses of lipid in the the E1A-liposome complex, which is currently used in clinical trials, were tested for the in vivo gene-transfer efficacy and tumor-suppression function. A lowered lipid dose--1/13 of the previous amount--produced gene expression level and E1A tumor-suppression efficacy similar to that of the original protocol. Mini-E1A, an E1A construct without its immortalization domain and yet capable of repressing HER-2/neu, was proved to be as potent as E1A in suppressing tumor development in vivo. These changes in the E1A-liposome complex will significantly reduce any potential adverse effects caused by lipid vector and E1A DNA. To examine further whether residual E1A DNA may still exist in normal organs after the E1A-liposome treatment, PCR was used to detect E1A DNA in mice that survived for 1 1/2 years after the last treatment. E1A DNA was detected only in the lungs and kidneys, but not in livers, hearts, spleens, brains, uterus or the ovaries. Furthermore, resistance of the E1A DNA extracted from tissues to the digestion of Dpnl restriction enzyme, which can cleave the methylated E1A plasmid DNA generated by methylation-competent bacteria, suggested integration of E1A DNA into the chromosome of the lungs and kidneys. Experimental results presented here provide important information for safety concerns and for the design of future phase II and phase III trials.

Acquired hemophilia A: report of two cases

Two patients who presented with active bleeding and were diagnosed with acquired hemophilia A (AHA) are reported herein. One was a 27-year-old woman who experienced spontaneous oozing from an episiotomy wound six days after her second normal delivery. Bleeding became progressively worse, despite treatment with primary sutures and curettage of the uterus at a local hospital. She underwent emergency exploratory laparotomy because of intra-abdominal bleeding, during which perforations of the uterus were discovered. Unremitting bleeding from the surgical wound occurred after surgery. The patient was finally diagnosed with AHA when Factor VIII (FVIII) inhibitor (titer, 19 Bethesda units (BU)/ml) was detected in her plasma. She died of refractory hemorrhaging, despite intensive treatment with Factor IX concentrate infusion and cyclophosphamide therapy. The second patient was a 22-year-old man who sustained spontaneous and recurrent intramuscular hemorrhage in the right thigh for one month. Laboratory studies including complete blood count, biochemical evaluation, coagulation screening and immunologic assays were all within normal limits, except for a prolonged activated partial thromboplastin time. Idiopathic AHA was diagnosed after the detection of plasma FVIII inhibitor with a concentration of 5.9 BU/ml. The patient's coagulopathy was successfully managed with plasma exchange and subsequent treatment with oral prednisolone and cyclophosphamide.

Cholesterol oxides induce programmed cell death in microglial cells

N9 microglial cells were used as a model to examine the effect of cholesterol oxides on central nervous system microglia. Results indicated that 25-OH-cholesterol was the most cytotoxic agent among the cholesterol oxides tested. During the process of cell death, this agent caused prominent nuclei condensation and significant DNA fragmentation, a phenomenon association with programmed cell death. Cholesterol oxides were able to potentiate the bacterial lipopolysaccharide (LPS)-induced nitric oxide production to various degrees. Consistent with this finding, Northern blot analysis indicated that 25-OH-cholesterol potentiated the LPS-induced nitric oxide synthase RNA levels. The cytotoxicity of 25-OH-cholesterol could be prevented by methyl-beta-cyclodextrin, a glucose polymer known to cause cholesterol oxide efflux from cells. While much attention has been focused on the cytotoxicity of cholesterol oxides on immune cells within the blood, including lymphocytes and macrophages, the results from this study indicated for the first time that these agents are toxic to microglial cells derived from the central nervous system.

Newer concepts of blood coagulation

In this report we describe an in vitro model of blood coagulation reactions that mimics as closely as possible the in vivo condition. Our model indicates that the tissue factor-factor VIIa complex initiates coagulation by activating small amounts of both factor IX and factor X in the environment of the tissue factor bearing cell. Factor Xa and factor IXa formed in the initial reaction then play very distinct roles in the subsequent interactions of the clotting mechanism leading to a burst of thrombin generation on the platelet surface. Our results also indicate that factor XI can be activated by thrombin in the absence of factor XII and that the function of factor XI is simply to enhance conversion of factor IX to factor IXa resulting in enhanced thrombin generation on the platelet surface.

Addition of aprotinin to organ preservation solutions decreases lung reperfusion injury

BACKGROUND

Organ preservation injury is associated with endothelial cell damage, destabilization of mitochondrial and cell membranes, and the release of proteolytic enzymes. In addition to its well-known clinical effect of reducing perioperative blood loss, aprotinin has antiproteolytic and membrane-stabilizing properties. We hypothesized that adding aprotinin to Euro-Collins (EC) and University of Wisconsin (UW) solutions would decrease preservation injury in cultured endothelial cells and a whole organ rat lung model.

METHODS

Bovine aortic endothelial cells were cultured and stored in the respective solution at 4 degrees C for 12 or 48 hours. Endothelial cell viability after storage was assessed by dimethylthiazole tetrazolium cytotoxicity assay. In the whole organ model, rat lungs were isolated, flushed with the respective solution, and stored at 4 degrees C for 6 or 12 hours. The lungs were ventilated with 100% O2 and reperfused with fresh blood. Alveolar-arterial O2 difference, O2 tension, capillary filtration coefficient, and compliance were determined.

RESULTS

Endothelial cell viability was optimized with the addition of aprotinin to EC and UW at a dose of 150 KIU/mL (0.02 mg/mL). In the isolated perfused lung model, after 6 hours of ischemic storage, aprotinin-enhanced (100 KIU/mL [0.014 mg/mL]) EC and UW decreased alveolar-arterial O2 difference, increased O2 tension, and decreased capillary filtration coefficient compared with EC and UW alone. After 12 hours of ischemic storage, aprotinin-enhanced EC and UW decreased alveolar-arterial O2 difference, increased O2 tension, decreased capillary filtration coefficient, and increased compliance compared with EC and UW alone.

CONCLUSIONS

The addition of aprotinin to EC and UW solutions increases endothelial cell viability in hypoxic cold storage conditions. In terms of whole organ function, aprotinin improves lung preservation as demonstrated by increased oxygenation and compliance, and decreased capillary permeability. This study is clinically applicable as there is already extensive experience with the use of aprotinin in heart and lung transplant recipients, in addition to its routine use in conventional cardiac operations.

Unique chemical reactivity of His-21 of CRM-197, a mutated diphtheria toxin

CRM-197 is a mutated diphtheria toxin (63000 Da) widely used as a carrier protein of conjugated vaccines. Among the 14 histidines of CRM-197, His-21 was found to be modified selectively with iodoacetamide based reagents. This finding suggests a simplified method for the preparation of conjugate vaccines crosslinked to CRM-197. A bifunctional iodoacetamide, N,N'-(2-hydroxy-1,3-propanediyl)-bis-12-iodoacetamidel (I-CH2-CONH-CH2-CH(OH)-CH2-NHCO-CH2-I) (HPBIA), was synthesized and allowed to react with CRM-197. In the alkaline buffer of pH 8.0-8.4, HPBIA was shown to react and intra-bridge His-21 and Lys-24 of CRM-197 sequentially. At lower pH (7.1-7.5) in the phosphate buffer, the reactivity of Lys-24 toward HPBIA was suppressed drastically. Under these conditions, His-21 could be specifically labeled with HPBIA. Initial experiments have demonstrated that HPBIA modified CRM-197 is able to crosslink to a cysteine-containing peptide. These results offer a potential route for improving the homogeneity of CRM-197 based protein-peptide as well as protein-polysaccharide conjugates.

Unfolding and refolding of cardiotoxin III elucidated by reversible conversion of the native and scrambled species

Cardiotoxin analogue III (CTX III) isolated from the venom of the Taiwan Cobra (Naja naja atra) is a small molecular weight, all beta-sheet protein, cross-linked by four disulfide bridges. The unfolding and refolding mechanisms of CTX III have been examined by monitoring the reversible conversion of the native and scrambled species. It is found that, in the presence of a denaturant (urea/guanidinium hydrochloride) and a thiol catalyst, CTX III forms a mixture of scrambled species by shuffling its four native disulfide bonds. Complete unfolding of CTX III can be achieved using either 3.0-4.0 M guanidinium hydrochloride (GdmCl) or 5.0-6.0 M urea. It is observed that GdmCl is thermodynamically more potent but kinetically less efficient than urea in unfolding CTX III. The rate constants of unfolding of CTX III in 8 M urea are significantly greater than that obtained in 5.0 M GdmCl and 8.0 M GdmCl. Interestingly, upon removal of the denaturant, scrambled species of CTX III is found to refold spontaneously through dynamic reshuffling of the non-native disulfides to attain the native disulfide linkages. In addition, CTX III contains highly reactive lysines which are modified by trace amounts of cyanate contaminant which exists invariably even in high-grade urea solutions. The reactive lysines of CTX III are modified by cyanate both in the native and unfolded states of the protein. The modification is nonselective, and the modified product is found to consist of highly heterogeneous species. Surprisingly, these heterogeneous species of modified CTX III are observed to display stability and folding/unfolding properties indistinguishable from those of the native CTX III. The knowledge obtained from the present study, on the conditions to convert the scrambled species, could provide useful clues for a rational design for snake venom cardiotoxins with potential therapeutic applications.

Comparison of mesocorticolimbic neuronal responses during cocaine and heroin self-administration in freely moving rats

To compare neuronal activity within the mesocorticolimbic circuit during the self-administration of cocaine and heroin, multiple-channel single-unit recordings of spike activity within the rat medial prefrontal cortex (mPFC) and nucleus accumbens (NAc) were obtained during the consecutive self-administration of cocaine and heroin within the same session. The variety of neuronal responses observed before the lever press are termed anticipatory responses, and those observed after the lever press are called post-drug infusion responses. For the total of the 110 mPFC and 111 NAc neurons recorded, 30-50% of neurons, depending on the individual sessions, had no alteration in spike activity in relation to either cocaine or heroin self-administration. Among the neurons exhibiting significant neuronal responses during a self-administration session, only a small portion (16-25%) of neurons responded similarly under both reinforcement conditions; the majority of neurons (75-84%) responded differently to cocaine and heroin self-administration as revealed by variations in both anticipatory and/or post-drug infusion responses. A detailed video analysis of specific movements to obtain the self-administration of both drugs provided evidence against the possibility that locomotive differences contributed to the observed differences in anticipatory responses. The overall mean activity of neurons recorded in mPFC and NAc measured across the duration of the session segment for either cocaine or heroin self-administration also was different for some neurons under the two reinforcement conditions. This study provides direct evidence that, in mPFC and NAc, heterogeneous neuronal circuits mediate cocaine and heroin self-administration and that distinct, but overlapping, subpopulations of neurons in these areas become active during operant responding for different reinforcers.

Neurotoxicity of 25-OH-cholesterol on sympathetic neurons

Cultured rat sympathetic neurons derived from postnatal rat superior cervical ganglia (SCG) were used to compare the neurotoxicity of several cholesterol oxides. The cholesterol oxides tested included: 7-beta-OH-, 7-keto-, 19-OH-, 22(R)-OH-, 22(S)-OH-, and 25-OH-cholesterol. These agents caused an acute as well as a delayed toxicity in sympathetic neurons with 25-OH-cholesterol appearing to be the most toxic. A time-dependent experiment indicated that 25-OH-cholesterol at 4 microg/ml (10 microM) was able to kill 50% of the cells in 36 h. Morphological studies indicate that most of the cells do not exhibit a structural change similar to that observed in neuronal programmed cell death. Whole-cell patch clamp recording of untreated controls and 25-OH-cholesterol (2 microg/ml)-treated cells indicated that this toxicity was not accompanied by significant changes in voltage-dependent calcium channel activity. A number of pharmacological agents including ethylene glycolbis (beta-aminoethyl ether) N,N,N',N'-tetraacetic acid (EGTA), cycloheximide, KCl, vitamin E, and methyl-beta-cyclodextrin were able to prevent the 25-OH-cholesterol-induced cell death to various degrees. These results suggest that, in addition to causing pathological changes in cells directly involved in atherosclerosis, cholesterol oxides may induce neurotoxicity in sympathetic neurons.

Neurotoxicity of cholesterol oxides on cultured cerebellar granule cells

Cultured rat cerebellar granule cells were used to determine the potential neurotoxicity of cholesterol oxides. The cholesterol oxides tested included: 7-beta-OH-, 7-keto-, 19-OH-, 22(R)-OH-, 22(S)-OH- and 25-OH- cholesterol. Among them, 7-beta-OH- and 7-keto-cholesterol were the most efficacious in causing neuronal death such that 20 microg/ml (50 microM) of these agents killed more than 80% of cells in 2 days. 7-beta-OH-cholesterol at this concentration killed 50% of cells in approximately 7 h. A number of pharmacological agents were tested for their abilities to prevent neuronal death induced by cholesterol oxides. Among them, aurintricarboxylic acid, vitamin E and methyl-beta-cyclodextrin were able to prevent cholesterol oxide-induced neurotoxicity in a dose-dependent manner. These results suggest that, in addition to causing pathological changes in cells directly involved in atherosclerosis, cholesterol oxides may induce toxicity in neurons of the central nervous system.

Cloning, expression, and characterization of mouse tissue factor pathway inhibitor (TFPI)

Tissue factor pathway inhibitor (TFPI) acts to regulate the initiation of coagulation by first inhibiting factor Xa. The complex of factor Xa/TFPI then inhibits the factor VIIa/tissue factor complex. The cDNA sequences of TFPI from several different species have been previously reported. A high level of similarity is present among TFPIs at the molecular level (DNA and protein sequences) as well as in biochemical function (inhibition of factor Xa, VIIa/tissue factor). In this report, we used a PCR-based screening method to clone cDNA for full length TFPI from a mouse macrophage cDNA library. Both cDNA and predicted protein sequences show significant homology to the other reported TFPI sequences, especially to that of rat. Mouse TFPI has a signal peptide of 28 amino acid residues followed by the mature protein (in which the signal peptide is removed) which has 278 amino acid residues. Mouse TFPI, like that of other species, consists of three tandem Kunitz type domains. Recombinant mouse TFPI was expressed in the human kidney cell line 293 and purified for functional assays. When using human clotting factors to investigate the inhibition spectrum of mouse TFPI, it was shown that, in addition to human factor Xa, mouse TFPI inhibits human factors VIIa, IXa, as well as factor XIa. Cloning and expression of the mouse TFPI gene will offer useful information and material for coagulation studies performed in a mouse model system.