Hortensins, Type 1 Ribosome-Inactivating Proteins from Seeds of Red Mountain Spinach: Isolation, Characterization, and Their Effect on Glioblastoma Cells

Ribosome inactivating proteins (RIPs) are specific N-β-glycosylases that are well-characterized in plants. Their enzymatic action is to damage ribosomes, thereby blocking protein translation. Recently, several research groups have been working on the screening for these toxins in edible plants to facilitate the use of RIPs as biotechnological tools and biopesticides and to overcome public prejudice. Here, four novel monomeric (type 1) RIPs have been isolated from the seeds of Atriplex hortensis L. var. rubra, which is commonly known as edible red mountain spinach. These enzymes, named hortensins 1, 2, 4, and 5, are able to release the β-fragment and, like many other RIPs, adenines from salmon sperm DNA, thus, acting as polynucleotide:adenosine glycosidases. Structurally, hortensins have a different molecular weight and are purified with different yields (hortensin 1, ~29.5 kDa, 0.28 mg per 100 g; hortensin 2, ~29 kDa, 0.29 mg per 100 g; hortensin 4, ~28.5 kDa, 0.71 mg per 100 g; and hortensin 5, ~30 kDa, 0.65 mg per 100 g); only hortensins 2 and 4 are glycosylated. Furthermore, the major isoforms (hortensins 4 and 5) are cytotoxic toward human continuous glioblastoma U87MG cell line. In addition, the morphological change in U87MG cells in the presence of these toxins is indicative of cell death triggered by the apoptotic pathway, as revealed by nuclear DNA fragmentation (TUNEL assay).

Streptavidin-Saporin: Converting Biotinylated Materials into Targeted Toxins

Streptavidin-Saporin can be considered a type of ‘secondary’ targeted toxin. The scientific community has taken advantage of this conjugate in clever and fruitful ways using many kinds of biotinylated targeting agents to send saporin into a cell selected for elimination. Saporin is a ribosome-inactivating protein that causes inhibition of protein synthesis and cell death when delivered inside a cell. Streptavidin-Saporin, mixed with biotinylated molecules to cell surface markers, results in powerful conjugates that are used both in vitro and in vivo for behavior and disease research. Streptavidin-Saporin harnesses the ‘Molecular Surgery’ capability of saporin, creating a modular arsenal of targeted toxins used in applications ranging from the screening of potential therapeutics to behavioral studies and animal models. The reagent has become a well-published and validated resource in academia and industry. The ease of use and diverse functionality of Streptavidin-Saporin continues to have a significant impact on the life science industry.

Analysis of the Sequence Preference of Saporin by Deep Sequencing

Ribosome-inactivating proteins (RIPs) are RNA:adenosine glycosidases that inactivate eukaryotic ribosomes by depurinating the sarcin-ricin loop (SRL) in 28S rRNA. The GAGA sequence at the top of the SRL or at the top of a hairpin loop is assumed to be their target motif. Saporin is a RIP widely used to develop immunotoxins for research and medical applications, but its sequence specificity has not been investigated. Here, we combine the conventional aniline cleavage assay for depurinated nucleic acids with high-throughput sequencing to study sequence-specific depurination of oligonucleotides caused by saporin. Our data reveal the sequence preference of saporin for different substrates and show that the GAGA motif is not efficiently targeted by this protein, neither in RNA nor in DNA. Instead, a preference of saporin for certain hairpin DNAs was observed. The observed sequence-specific activity of saporin may be relevant to antiviral or apoptosis-inducing effects of RIPs. The developed method could also be useful for studying the sequence specificity of depurination by other RIPs or enzymes.

Isolation, Characterization and Biological Action of Type-1 Ribosome-Inactivating Proteins from Tissues of Salsola soda L

Ribosome-inactivating proteins (RIPs) are known as RNA N-glycosylases. They depurinate the major rRNA, damaging ribosomes and inhibiting protein synthesis. Here, new single-chain (type-1) RIPs named sodins were isolated from the seeds (five proteins), edible leaves (one protein) and roots (one protein) of Salsola soda L. Sodins are able to release Endo's fragment when incubated with rabbit and yeast ribosomes and inhibit protein synthesis in cell-free systems (IC₅₀ = 4.83-79.31 pM). In addition, sodin 5, the major form isolated from seeds, as well as sodin eL and sodin R, isolated from edible leaves and roots, respectively, display polynucleotide:adenosine glycosylase activity and are cytotoxic towards the Hela and COLO 320 cell lines (IC₅₀ = 0.41-1200 nM), inducing apoptosis. The further characterization of sodin 5 reveals that this enzyme shows a secondary structure similar to other type-1 RIPs and a higher melting temperature (Tm = 76.03 ± 0.30 °C) and is non-glycosylated, as other sodins are. Finally, we proved that sodin 5 possesses antifungal activity against Penicillium digitatum.

Effect of Placenta-Derived Mesenchymal Stem Cells in a Dementia Rat Model via Microglial Mediation: a Comparison between Stem Cell Transplant Methods

PURPOSE

Loss of cholinergic neurons in the hippocampus is a hallmark of many dementias. Administration of stem cells as a therapeutic intervention for patients is under active investigation, but the optimal stem cell type and transplantation modality has not yet been established. In this study, we studied the therapeutic effects of human placenta-derived mesenchymal stem cells (pMSCs) in dementia rat model using either intracerebroventricular (ICV) or intravenous (IV) injections and analyzed their mechanisms of therapeutic action.

MATERIALS AND METHODS

Dementia modeling was established by intraventricular injection of 192 IgG-saporin, which causes lesion of cholinergic neurons. Sixty-five male Sprague-Dawley rats were divided into five groups: control, lesion, lesion+ICV injection of pMSCs, lesion+IV injection of pMSCs, and lesion+donepezil. Rats were subjected to the Morris water maze and subsequent immunostaining analyses.

RESULTS

Both ICV and IV pMSC administrations allowed significant cognitive recovery compared to the lesioned rats. Acetylcholinesterase activity was significantly rescued in the hippocampus of rats injected with pMSCs post-lesion. Choline acetyltransferase did not co-localize with pMSCs, showing that pMSCs did not directly differentiate into cholinergic cells. Number of microglial cells increased in lesioned rats and significantly decreased back to normal levels with pMSC injection.

CONCLUSION

Our results suggest that ICV and IV injections of pMSCs facilitate the recovery of cholinergic neuronal populations and cognitive behavior. This recovery likely occurs through paracrine effects that resemble microglia function rather than direct differentiation of injected pMSCs into cholinergic neurons.

Increase in cortical endocannabinoid signaling in a rat model of basal forebrain cholinergic dysfunction

The basal forebrain cholinergic pathways progressively degenerate during the progression of Alzheimer's disease, leading to an irreversible impairment of memory and thinking skills. The stereotaxic lesion with 192IgG-saporin in the rat brain has been used to eliminate basal forebrain cholinergic neurons and is aimed at emulating the cognitive damage described in this disease in order to explore its effects on behavior and on neurotransmission. Learning and memory processes that are controlled by cholinergic neurotransmission are also modulated by the endocannabinoid (eCB) system. The objective of the present study is to evaluate the eCB signaling in relation to the memory impairment induced in adult rats following a specific cholinergic lesion of the basal forebrain. Therefore, CB₁ receptor-mediated signaling was analyzed using receptor and functional autoradiography, and cellular distribution by immunofluorescence. The passive avoidance test and histochemical data revealed a relationship between impaired behavioral responses and a loss of approximately 75% of cholinergic neurons in the nucleus basalis magnocellularis (NBM), accompanied by cortical cholinergic denervation. The decrease in CB₁ receptor density observed in the hippocampus, together with hyperactivity of eCB signaling in the NBM and cortex, suggest an interaction between the eCB and cholinergic systems. Moreover, following basal forebrain cholinergic denervation, the presynaptic GABAergic immunoreactivity was reduced in cortical areas. In conclusion, CB₁ receptors present in presynaptic GABAergic terminals in the hippocampus are down regulated, but not those in cortical glutamatergic synapses.

The Saponin-Mediated Enhanced Uptake of Targeted Saporin-Based Drugs is Strongly Dependent on the Saponin Structure

Saponins are a group of plant glycosides consisting of a steroid or triterpenoid aglycone to which one or more sugar chains are attached. They exhibit cell membrane–permeabilizing properties and, thus, have been investigated for their therapeutic potential. Recently, at a nonpermeabilizing concentration saponinum album from Gypsophila paniculata L. has been described to enhance the cytotoxicity of a chimeric toxin in a cell culture model. To elucidate whether this enhancing effect is also mediated by other saponins, we analyzed the ability of seven different saponins to enhance the cytotoxicity of a targeted chimeric toxin. The chimeric toxin is composed of saporin, a plant ribosome-inactivating toxin, a cleavable adapter, and human epidermal growth factor (EGF). Cytotoxicity on EGF receptor (EGFR)-bearing cells was analyzed both alone and after combined application of saponin and chimeric toxin. Only two of the tested saponins, quillajasaponin and saponinum album, enhanced cytotoxicity by more than 1000-fold, whereas the enhancement factors of the other saponins were only approximately 10-fold. In contrast to saponinum album, quillajasaponin enhanced the cytotoxicity both on control cells lacking EGFR and on target cells, indicating that, in this case, the enhancement is not target cell receptor specific. This is also the case for some of the saponins with low enhancement factors. Saponinum album resulted in a more than 13,600-fold receptor-specific enhancement, decreasing the 50% inhibitory concentration (IC50) from 2.4 nM to 0.18 pM, which renders it the best option to promote saporin-3-based drug uptake while retaining specificity for the EGFR.

Genome-wide identification and domain organization of lectin domains in cucumber

Lectins are ubiquitous proteins in plants and play important roles in a diverse set of biological processes, such as plant defense and cell signaling. Despite the availability of the Cucumis sativus L. genome sequence since 2009, little is known with respect to the occurrence of lectins in cucumber. In this study, a total of 146 putative lectin genes belonging to 10 different lectin families were identified and localized in the cucumber genome. Domain architecture analysis revealed that most of these lectin gene sequences contain multiple domains, where lectin domains are linked with other domains, as such creating chimeric lectin sequences encoding proteins with dual activities. This study provides an overview of lectin motifs in cucumber and will help to understand their potential biological role(s).

Ablation of μ opioid receptor-expressing GABA neurons in rostromedial tegmental nucleus increases ethanol consumption and regulates ethanol-related behaviors

There has been increasing interest in the rostromedial tegmental nucleus (RMTg), given its potential regulatory role in many aversion-related behaviors. The RMTg contains mostly GABAergic neurons, sends a dense inhibitory projection to dopamine neurons in the midbrain, and is rich with μ-opioid receptors (MOR). Like most addictive drugs, ethanol has both aversive and rewarding properties. However, the cellular mechanisms underlying the effects of ethanol, particularly the aversive effect that limits its intake are not well understood. Recent studies have linked aversion with synaptic inhibition of dopamine neurons in the ventral tegmental area. To determine a potential role that the RMTg plays in the effect of ethanol, in this study, we employed a neurotoxin, dermorphin-saporin (DS), to lesion RMTg neurons prior to assessing ethanol-related behaviors. Rats were infused with DS bilaterally into the RMTg. This manipulation substantially increased the intake and preference for ethanol but not sucrose. It also reduced the number of neurons with MOR and glutamic acid decarboxylase 67 immunoreactivity within the RMTg. These changes did not occur after intra-RMTg infusion of blank saporin or vehicle. Importantly, intra-RMTg DS infusion significantly enhanced expression of conditioned place preference induced by ethanol (2 g/kg, i.p.), and slowed the extinction process. These results suggest that MOR-expressing GABAergic neurons in the RMTg contribute significantly to the regulation of ethanol consumption and related behaviors.

Cholinergic neurons of the basal forebrain mediate biochemical and electrophysiological mechanisms underlying sleep homeostasis

The tight coordination of biochemical and electrophysiological mechanisms underlies the homeostatic sleep pressure (HSP) produced by sleep deprivation (SD). We have reported that during SD the levels of inducible nitric oxide synthase (iNOS), extracellular nitric oxide (NO), adenosine [AD]ex , lactate [Lac]ex and pyruvate [Pyr]ex increase in the basal forebrain (BF). However, it is not clear whether all of them contribute to HSP leading to increased electroencephalogram (EEG) delta activity during non-rapid eye movement (NREM) recovery sleep (RS) following SD. Previously, we showed that NREM delta increase evident during RS depends on the presence of BF cholinergic (ChBF) neurons. Here, we investigated the role of ChBF cells in coordination of biochemical and EEG changes seen during SD and RS in the rat. Increases in low-theta power (5-7 Hz), but not high-theta (7-9 Hz), during SD correlated with the increase in NREM delta power during RS, and with the changes in nitrate/nitrite [NOx ]ex and [AD]ex . Lesions of ChBF cells using IgG 192-saporin prevented increases in [NOx ]ex , [AD]ex and low-theta activity, during SD, but did not prevent increases in [Lac]ex and [Pyr]ex . Infusion of NO donor DETA NONOate into the saporin-treated BF failed to increase NREM RS and delta power, suggesting ChBF cells are important for mediating NO homeostatic effects. Finally, SD-induced iNOS was mostly expressed in ChBF cells, and the intensity of iNOS induction correlated with the increase in low-theta activity. Together, our data indicate ChBF cells are important in regulating the biochemical and EEG mechanisms that contribute to HSP.

Rapid activation of specific phospholipase(s) D by cytokinin in Amaranthus assay system

The suggested link between intracellular cytokinin signaling and phospholipase D (PLD, EC 3.1.4.4.) activity (Romanov et al. 2000, 2002) was investigated. The activity of PLD in the early period of cytokinin action was studied in vivo in derooted Amaranthus caudatus seedlings, using the level of phosphatidylbutanol production as a measure of PLD activity. Rapid activation of phosphatidylbutanol synthesis was demonstrated as early as within 5 min of cytokinin administration. Neomycin, a known phosphatidylinositol-4,5-bisphosphate (PIP(2)) antagonist, strongly repressed both physiological cytokinin effect and cytokinin-dependent PLD activation. N-acylethanolamine (NAE 12), an inhibitor of alpha-class PLD, did not influence significantly cytokinin effect on Amaranthus seedlings. Together, results suggest the involvement of PIP(2)-dependent non-class alpha-PLD in the molecular mechanism of cytokinin action.

T-cell reconstitution without T-cell immunopathology in two models of T-cell-mediated tissue destruction

Antigen-specific T cells play a pivotal role in adaptive immune responses. However, they also contribute to the progression of a variety of diseases including autoimmune disorders, graft rejection and graft-versus-host disease (GVHD). Non-specific immune-ablation treatments compromise the ability of the host to respond to infection, whereas the selective removal of epitope-specific T cells could theoretically ameliorate T-cell-mediated pathology while preserving the rest of the host immune function. In this study we investigated whether it is possible to destroy specific unwanted antigen-specific T cells by incubating polyclonal T-cell populations with major histocompatibility complex (MHC) tetramers that are conjugated to the ribosomal-inactivating toxin, saporin. This strategy resulted in a dramatic reduction in the number of targeted antigen (Ag)-specific CD8 T cells with no observable bystander toxicity in vitro. Moreover, in a model of transferable T-cell-dependent neurological disease induced by intracerebral (i.c.) lymphocytic choriomeningitis virus (LCMV) infection, the targeted killing of LCMV-specific CD8 T cells extended the survival of mice or fully prevented their death, depending on the dose of cells transferred. In addition, the tetramer- saporin conjugate also reduced liver damage in a model of donor T-cell-mediated hepatic destruction. These data provide a proof of principle that MHC tetramers could be exploited for the elimination or clinical manipulation of T-cell responses by linking effector molecules (a toxin in this case) to MHC tetramers. Also, the results suggest that it may be feasible to remodel T-cell responses, especially in immunocompromised hosts who receive adoptive cell transfers with many potential alloreactive cells.

Amyloid beta protein modulates glutamate-mediated neurotransmission in the rat basal forebrain: involvement of presynaptic neuronal nicotinic acetylcholine and metabotropic glutamate receptors

Amyloid beta (Abeta) protein, a 39-43 amino acid peptide deposited in brains of individuals with Alzheimer's disease (AD), has been shown to interact directly with a number of receptor targets including neuronal nicotinic acetylcholine receptors (nAChRs) and glutamate receptors. In this study, we investigated the synaptic effects of Abeta(1-42) on glutamate-mediated neurotransmission in the diagonal band of Broca (DBB), a cholinergic basal forebrain nucleus. Glutamatergic miniature EPSCs (mEPSCs) were recorded using whole-cell patch-clamp recordings from identified cholinergic DBB neurons in rat forebrain slices. In 54% of DBB neurons, bath application of Abeta(1-42) (100 nM), but not Abeta(42-1) (inverse fragment), significantly increased the frequency of mEPSCs without affecting amplitude or kinetic parameters (rise or decay time). In 32% of DBB neurons, bath application of Abeta(1-42) significantly decreased only the frequency but not amplitude of mEPSCs. Application of dihydro-beta-erythroidine (DHbetaE) (an antagonist for the alpha4beta2 subtype of nAChRs) but not alpha-bungarotoxin (an antagonist for the alpha7 subtype of nAChRs) blocked Abeta(1-42)-mediated increases in mEPSC frequency. The Abeta(1-42)-mediated increase in glutamatergic transmission is thus presynaptic and mediated via non-alpha7 AChRs. In contrast, Abeta(1-42)-mediated decreases in mEPSC frequency could not be antagonized by either DHbetaE or alpha-bungarotoxin. However, the Abeta(1-42)-evoked depression in mEPSC frequency was antagonized by (RS)-alpha-methyl-4-carboxyphenyglycine, a nonselective group I/II metabotropic glutamate receptor antagonist. These observations provide further insight into the mechanisms whereby Abeta affects synaptic function in the brain and may be relevant in the context of synaptic failure observed in AD.

Evidence for the importance of electrostatics in the function of two distinct families of ribosome inactivating toxins

Alpha-sarcin and ricin represent two structurally and mechanistically distinct families of site-specific enzymes that block translation by irreversibly modifying the sarcin/ricin loop (SRL) of 23S-28S rRNA. alpha-Sarcin family enzymes are designated as ribotoxins and act as endonucleases. Ricin family enzymes are designated as ribosome inactivating proteins (RIP) and act as N-glycosidases. Recently, we demonstrated that basic surface residues of the ribotoxin restrictocin promote rapid and specific ribosome targeting by this endonuclease. Here, we report that three RIP: ricin A, saporin, and gypsophilin depurinate the ribosome with strong salt sensitivity and achieve unusually fast kcat/Km approximately 10(9)-10(10) M(-1) s(-1), implying that RIP share with ribotoxins a common mechanism of electrostatically facilitated ribosome targeting. Bioinformatics analysis of RIP revealed that surface charge properties correlate with the presence of the transport chain in the RIP molecule, suggesting a second role for the surface charge in RIP transport. These findings put forward surface electrostatics as an important determinant of RIP activity.

Ketanserin-induced baroreflex enhancement in spontaneously hypertensive rats depends on central 5-HT(2A) receptors

1. Ketanserin may influence baroreflex function by blocking 5-HT(2A) receptors and/or alpha(1)-adrenoceptors through central and/or peripheral mechanisms. 2. In the present study, we tested the hypothesis that the baroreflex sensitivity (BRS)-enhancing effects of ketanserin are mediated by central 5-HT(2A) receptors in spontaneously hypertensive rats (SHR). 3. Using a conjugate of a monoclonal antibody to the serotonin reuptake transporter (SERT) and the toxin saporin (anti-SERT-SAP), which specifically eliminates the neurons that express SERT, the effects of ketanserin (0.3 and 3.0 mg/kg, i.g.) on BRS, blood pressure (BP), heart period (HP) and blood pressure variability (BPV) were compared between conscious intact SHR and SHR pretreated with anti-SERT-SAP. 4. Immunochemistry showed that, 2 weeks after intracerebroventricular injection of the toxin, 5-HT expression was strikingly attenuated in the brain, whereas values of BRS, BPV and BP were similar to those in the sham group. In intact SHR, 0.3 mg/kg ketanserin significantly improved BRS (191% control) and reduced BPV without affecting BP; at 3.0 mg/kg, ketanserin significantly increased BRS (197% control) and decreased BPV and BP. In toxin-pretreated SHR, only the high dose of ketanserin improved BRS (132% control), neither of the ketanserin doses reduced BPV, but both significantly decreased BP. 5. We conclude that the BRS-enhancing effects of ketanserin are mediated largely by central 5-HT(2A) receptors, whereas the antihypertensive effect of ketanserin persists even after destruction of serotonergic neurons in the central nervous system.

Behavioral and immunohistological effects of cholinergic damage in immunolesioned rats: Alteration of c-Fos and polysialylated neural cell adhesion molecule expression

The aim of this study was to determine the brain structures as well as the plasticity events associated with the behavioral effects of cholinergic damage. Rats were submitted to injection of 192 IgG-saporin in the medial septum/diagonal band of Broca complex and the nucleus basalis magnocellularis. The immunohistochemical expression of c-Fos protein and PSA-NCAM (polysialylated neural cell adhesion molecule) and the behavioral performances in the nonmatching-to-position task were assessed at various post-lesion times. Thus, 3 days after injection of the immunotoxin, increased c-Fos labeling was observed in the areas of infusion, indicating these cells were undergoing some plastic changes and/or apoptotic processes. A drastic increase was observed in the number of PSA-NCAM positive cells and in their dendritic arborization in the dentate gyrus. At 7 days post-lesion, no behavioral deficit was observed in immunolesioned rats despite the drastic loss of cholinergic neurons. These neurons showed decreased c-Fos protein expression in the piriform and entorhinal cortex and in the dentate gyrus. In the latter, PSA-NCAM induction was high, suggesting that remodeling occurred, which in turn might contribute to sustaining some mnemonic function in immunolesioned rats. At 1 month, cholinergic neurons totally disappeared and behavioral deficits were drastic. c-Fos expression showed no change. In contrast, the increased PSA-NCAM-labeling observed at short post-lesion times was maintained but the plastic changes due to this molecule could not compensate the behavioral deficit caused by the immunotoxin. Thus, as the post-lesion time increases, a gradual degeneration process should occur that may contribute to mnemonic impairments. This neuronal loss leads to molecular and cellular alterations, which in turn may aggravate cognitive deficits.

Neonatal basal forebrain cholinergic hypofunction affects ultrasonic vocalizations and fear conditioning responses in preweaning rats

The present study investigated the effects of intracebroventricular injections of 192 IgG-saporin in 7-day-old rats on (i) ultrasound vocalizations (USVs) on postnatal day (pnd) 13 following isolation and reunion with the mother and (ii) fear conditioning on pnd 18-19 recording both freezing and other behavioural responses as well as USVs. On pnd 13 lesioned and control pups showed comparable USV baseline values; a brief reunion with the mother induced a significant increase in USVs in all rats (maternal potentiation). On pnd 18, during the fear conditioning training, 192 IgG-saporin rats emitted a lower number of USVs. On pnd 19 all rats showed a stronger conditioned response (with full inhibition of locomotion) to auditory than to contextual cues. Surprisingly, lesioned rats showed a stronger fear-conditioned response to contextual cues than controls. These results suggest that early selective removal of the cholinergic basal forebrain paradoxically enhances hippocampally dependent fear-conditioned responses on pnd 19.

Two short sequences from amaranth 11S globulin are sufficient to target green fluorescent protein and beta-glucuronidase to vacuoles in Arabidopsis cells

Vacuolar sorting of seed storage proteins is a very complex process since several sorting pathways and interactions among proteins of different classes have been reported. In addition, although the C-terminus of several 7S proteins is important for vacuolar delivery, other signals seem also to be involved in this process. In this work, the ability of two sequences of the Amaranthus hypochondriacus 11S globulin (amaranthin) to target reporter proteins to vacuoles was studied. We show that the C-terminal pentapeptide (KISIA) and the GNIFRGF internal sequence fused at the C terminal region of genes encoding secretory versions of green fluorescent protein (GFP) and GFP-beta-glucuronidase (GFP-GUS) were sufficient to redirect these reporter proteins to the vacuole of Arabidopsis cells. According to the three-dimensional structure of 7S and 11S storage globulins, this internal vacuolar sorting sequence corresponds to the alpha helical region involved in trimer formation, and is conserved within these families. In addition, these sequences were able to interact in vitro, in a calcium dependent manner, with the sunflower vacuolar sorting receptor homolog to pea BP-80/AtVSR1/pumpkin PV72. This work shows for the first time the role of a short internal sequence conserved among 7S and 11S proteins in vacuolar sorting.

Invariant Ser211 is involved in the catalysis of PD-L4, type I RIP from Phytolacca dioica leaves

Multiple sequence alignment analysis of ribosome inactivating proteins (RIPs) has revealed the occurrence of an invariant seryl residue in proximity of the catalytic tryptophan. The involvement of this seryl residue in the catalytic mechanism of RIPs was investigated by site-directed mutagenesis in PD-L4, type 1 RIP isolated from Phytolacca dioica leaves. We show that the replacement of Ser211 with Ala apparently does not influence the N-beta-glycosidase activity on ribosomes (determined as IC(50) in a cell-free system), but it reduces the adenine polynucleotide glycosylase activity (APG), assayed spectrophotometrically on other substrates such as DNA, rRNA, and poly(A). The ability of PD-L4 to deadenylate polynucleotides appears more sensitive to the Ser211Ala replacement when poly(A) is used as substrate, as only 33% activity is retained by the mutant, while with more complex and heterogeneous substrates such as DNA and rRNA, its APG activity is 73% and 66%, respectively. While the mutated protein shows a conserved secondary structure by CD, it also exhibits a remarkably enhanced tryptophan fluorescence. This indicates that, although the overall protein tridimensional structure is maintained, removal of the hydroxyl group locally affects the environment of a Trp residue. Modelling and docking analyses confirm the interaction between Ser211 and Trp207, which is located within the active site, thus affecting RIP adenine polynucleotide glycosylase activity. Data accumulated so far confirm the potential involvement of Ser211 in the catalytic mechanism of type 1 RIP PD-L4 and a possible role in stabilizing the conformation of Trp207 side chain, which participates actively in the protein enzymatic activity.

Vinyldeoxyadenosine in a sarcin-ricin RNA loop and its binding to ricin toxin a-chain

8-Vinyl-2'-deoxyadenosine (8vdA) is a fluorophore with a quantum yield comparable to that of 2-aminopurine nucleoside. 8vdA was incorporated into a 10-mer stem-tetraloop RNA (8vdA-10) structure for characterization of the properties of the base, 8-vinyladenine (8-vA), with respect to adenine as a substrate or inhibitor for ribosome-inactivating proteins. Ricin toxin A-chain (RTA) and pokeweed antiviral protein (PAP) catalyze the release of adenine from a specific adenosine on a stem-tetraloop (GAGA) sequence at the elongation factor (eEF2) binding site of the 28S subunit of eukaryotic ribosomes, thereby arresting translation. RTA does not catalyze the release of 8-vinyladenine from 8vdA-10. Molecular dynamics simulations implicate a role for Arg180 in oxacarbenium ion destabilization and the lack of catalysis. However, 8vdA-10 is an active site analogue and inhibits RTA with a Ki value of 2.4 microM. Adenine is also released from the second adenosine in the modified tetraloop, demonstrating an alternative mode for the binding of this motif in the RTA active site. The 8vdA analogue defines the specificities of RTA for the two adenylate depurination sites in a RNA substrate with a GAGA tetraloop. The rate of nonenzymatic acid-catalyzed solvolysis of 8-vinyladenine from the stem-loop RNA is described. Unlike RTA, PAP catalyzes the slow release of 8-vinyladenine from 8vdA-10. The isolation of 8-vA and its physicochemical characterization is described.

Superficial NK1 expressing spinal dorsal horn neurones modulate inhibitory neurotransmission mediated by spinal GABA(A) receptors

Lamina 1 projection neurones which express the NK1 receptor (NK1R+) drive a descending serotonergic pathway from the brainstem that enhances spinal dorsal horn neuronal activity via the facilitatory spinal 5-HT3 receptor. Selective destruction of these cells via lumbar injection of substance P-saporin (SP-SAP) attenuates pain behaviours, including mechanical and thermal hypersensitivity, which are mirrored by deficits in the evoked responses of lamina V-VI wide dynamic range (WDR) neurones to noxious stimuli. To assess whether removing the origin of this facilitatory spino-bulbo-spinal loop results in alterations in GABAergic spinal inhibitory systems, the effects of spinal bicuculline, a selective GABA(A) receptor antagonist, on the evoked neuronal responses to electrical (Abeta-, Adelta-, C-fibre, post-discharge and Input) and mechanical (brush, prod and von Frey (vF) 8 and 26 g) stimuli were measured in SAP and SP-SAP groups. In the SAP control group, bicuculline produced a significant dose related facilitation of the electrically evoked Adelta-, C-fibre, post-discharge and input neuronal responses. The evoked mechanical (prod, vF8 g and 26 g) responses were also significantly increased. Brush evoked neuronal responses in these animals were enhanced but did not reach significance. This facilitatory effect of bicuculline, however, was lost in the SP-SAP treated group. The generation of intrinsic GABAergic transmission in the spinal cord appears dependent on NK1 bearing neurons, yet despite the loss of GABAergic inhibitory controls after SP-SAP treatment, the net effect is a decrease in spinal cord excitability. Thus activation of these cells predominantly drives facilitation.

Selective deletion of antigen-specific CD8+ T cells by MHC class I tetramers coupled to the type I ribosome-inactivating protein saporin

CD8+ cytotoxic T lymphocytes (CTLs) are important effector cells responsible for tissue destruction in several autoimmune and allograft-related diseases. To discover if pathogenic T cells could be selectively deleted, we investigated the ability of a toxin coupled to major histocompatibility complex (MHC) class I tetramers to kill antigen-specific CD8+ T cells. H2-D(b) tetramers were assembled using streptavidin conjugated to the ribosome-inactivating protein (RIP) saporin (SAP). These tetramers inhibited ribosome activity in vitro, retained the T-cell receptor (TCR)-binding specificity of their nontoxic counterparts, and were internalized by 100% of target cells, leading to cell death in 72 hours. Cytotoxicity was dependent on the tetramer dose and avidity for the T cell. A single injection of the SAP-coupled tetramer eliminated more than 75% of cognate, but not control, T cells. This work demonstrates the therapeutic potential of cytotoxic tetramers to selectively eradicate pathogenic clonotypes while leaving overall T-cell immunity intact.

Anti-nociceptive effects of selectively destroying substance P receptor-expressing dorsal horn neurons using [Sar9,Met(O2)11]-substance P-saporin: behavioral and anatomical analyses

Lumbar intrathecal injections of substance P-saporin (SP-sap) destroy dorsal horn neurons that express the neurokinin-1 receptor (NK-1R) resulting in decreased responses to a range of noxious stimuli and decreased hyperalgesia and allodynia. Forebrain injections of SP-sap produce considerable non-specific damage raising some concern about use of this toxin in vivo. The more stable and selective substance P congener, [Sar9,Met(O2)11]substance P coupled to saporin (SSP-sap) produces much more selective forebrain lesions at significantly lower doses. The present study sought to determine the anatomic and nocifensive behavioral effects of lumbar intrathecal injections of the more precisely targeted SSP-sap. On the basis of loss of lamina I NK-1R staining, lumbar intrathecal SSP-sap was seven times more potent than SP-sap and produced no loss of NK-1R expressing neurons in deeper laminae (III-VI or X). Transient decreases in hotplate responding occurred at 44 degrees C and 47 degrees C but not 52 degrees C during the first 3 weeks after SSP-sap injection with return to baseline by 4 weeks. Operant escape responses were reduced at 0.3 degrees C, 44 degrees C and 47 degrees C for at least 4 months. In the formalin test, SSP-sap also was about seven times more potent than SP-sap in reducing phase two behavior in both female Long Evans and male Sprague-Dawley rats. Both SSP-sap and SP-sap reduced formalin-induced FOS expression in deep and superficial laminae of the L4 dorsal horn in parallel with the reduction in phase 2 behavior. In summary, SSP-sap is highly effective in destroying lamina I NK-1R expressing neurons, without loss of deep NK-1R neurons. The behavioral effects of SSP-sap are similar to SP-sap suggesting that the antinociceptive effects of both toxins are indeed due to selective loss of NK-1R neurons in lamina I. SSP-sap is an attractive agent for possible treatment of chronic pain.

Combined damage to entorhinal cortex and cholinergic basal forebrain neurons, two early neurodegenerative features accompanying Alzheimer's disease: effects on locomotor activity and memory functions in rats

In Alzheimer's disease (AD), cognitive decline is linked to cholinergic dysfunctions in the basal forebrain (BF), although the earliest neuronal damage is described in the entorhinal cortex (EC). In rats, selective cholinergic BF lesions or fiber-sparing EC lesions may induce memory deficits, but most often of weak magnitude. This study investigated, in adult rats, the effects on activity and memory of both lesions, alone or in combination, using 192 IgG-saporin (OX7-saporin as a control) and L-N-methyl-D-aspartate to destroy BF and EC neurons, respectively. Rats were tested for locomotor activity in their home cage and for working- and/or reference-memory in various tasks (water maze, Hebb-Williams maze, radial maze). Only rats with combined lesions showed diurnal and nocturnal hyperactivity. EC lesions impaired working memory and induced anterograde memory deficits in almost all tasks. Lesions of BF cholinergic neurons induced more limited deficits: reference memory was impaired in the probe trial of the water-maze task and in the radial maze. When both lesions were combined, performance never improved in the water maze and the number of errors in the Hebb-Williams and the radial mazes was always larger than in any other group. These results (i) indicate synergistic implications of BF and EC in memory function, (ii) suggest that combined BF cholinergic and fiber-sparing EC lesions may model aspects of anterograde memory deficits and restlessness as seen in AD, (iii) challenge the cholinergic hypothesis of cognitive dysfunctions in AD, and (iv) contribute to open theoretical views on AD-related memory dysfunctions going beyond the latter hypothesis.

Crystallization and Preliminary X-Ray Diffraction Analysis of PD-L1, a Highly Glycosylated Ribosome Inactivating Protein with DNase Activity

PD-L1 is a highly glycosylated type 1 ribosome inactivating protein, from Phytolacca dioica leaves, with the peculiarity to act also as a DNase. PD-L1 has been successfully crystallized using vapour diffusion and seeding techniques. Crystals belong to the monoclinic C2 space group, with unit cell dimensions a=161.01, b=34.73, c=120.63 A, beta=127.99 degrees . Two molecules are present in the asymmetric unit. Phase determination has been achieved using molecular replacement.

Astrocytic reaction to a lesion, under hormonal deprivation

Gonadal hormones can influence the morphology and function of glial cells, particularly astrocytes. Here we explore the hypothesis that 17beta-estradiol (E2) exerts a positive effect on astrocytes within the region of the cholinergic neurons of the basal forebrain, an area heavily implicated in memory and attentional processes. Female rats were ovariectomized at 3 months of age and lesioned with the immunotoxin 192 IgG-saporin before receiving a subcutaneous pellet containing 0.25mg of estrogen or placebo, released over 60 days. The control, non-ovariectomized group was treated identically. At the end of the treatment, we used image analysis procedures to evaluate changes in the levels of glial fibrillary acidic protein (GFAP) expression in the area of the lesion. Infusion of the immunotoxin induced a slight increase in GFAP expression in some subjects, compared to the contralateral side. However, when differences within animals where factored in, GFAP expression in ovariectomized animals treated with E2 was undistinguishable from intact controls. By contrast, in ovariectomized animals treated with placebo, GFAP expression was significantly higher. These results suggest that E2 deprivation may exacerbate the effects of an immunotoxic lesion, and, more importantly, that E2 administration may contribute to structural recovery of lesioned cholinergic neurons by blocking GFAP expression in the area. These results are particularly relevant in the context of female aging and postmenopausal dementia, and further highlight other potential levels at which to design interventions to preserve an intact cholinergic system, which may be crucial to prevent Alzheimer's disease.

Truncations of gelonin lead to a reduction in its cytotoxicity

Gelonin is a single chain ribosome-inactivating protein (RIP) with potential applications as a bullet of immunoconjugate for the treatment of cancer and AIDS. Using truncated forms of gelonin, we now report the relationship between its conformation and function. Circular dichroism (CD) and fluorescence spectra show that the N-terminus forms beta-sheets whereas the C-terminus contains alpha-helices of secondary structures. Biological experiments indicate that all gelonin truncation mutants lose partial toxicity compared to intact gelonin, an effect most strongly seen with C-terminally truncated gelonin. Similar evidence is also provided using a DNase-like activity assay. In addition, the intact gelonin exhibits the highest cytotoxicity to cancer cells. These results suggest that truncations of the terminal region of gelonin negatively regulate its function dominantly and that, due to its toxicity, intact gelonin is an important potential immunoconjugate.

The C-terminus of pokeweed antiviral protein has distinct roles in transport to the cytosol, ribosome depurination and cytotoxicity

Pokeweed antiviral protein (PAP) produced by pokeweed plants is a single-chain (type I) ribosome-inactivating protein (RIP) that depurinates ribosomes at the alpha-sarcin/ricin loop of the large rRNA, resulting in inhibition of translation. Unlike the type II RIPs, which have an active and a binding moiety, PAP has only the active moiety. The mechanism by which toxins without a binding moiety gain access to cytosolic ribosomes is not known. We set up yeast as a simple and genetically tractable system to investigate how PAP accesses ribosomes and showed that the mature form of PAP is targeted to the cytosol from the endomembrane system in yeast. In the present study, we performed a systematic deletion analysis to identify the signal required for transport of PAP to the cytosol. We demonstrate here that processing of the C-terminal extension and sequences at the C-terminus of the mature protein are critical for its accumulation in the cytosol. Using a series of PAP mutants, we identified the C-terminal signal and demonstrated that it is distinct from the sequences required for ribosome depurination and cytotoxicity. The C-terminal motif showed sequence similarity to type II RIPs that retrotranslocate from the endoplasmic reticulum to the cytosol. These results demonstrate that a conserved sequence at the C-terminus of a type I RIP mediates its transport to the cytosol and suggest that type I and II RIPs may use a common signal to enter the cytosol.

Multimodality molecular imaging of glioblastoma growth inhibition with vasculature-targeting fusion toxin VEGF121/rGel

Vascular endothelial growth factor A (VEGF-A) and its receptors, Flt-1/FLT-1 (VEGFR-1) and Flk-1/KDR (VEGFR-2), are key regulators of tumor angiogenesis and tumor growth. The purpose of this study was to determine the antiangiogenic and antitumor efficacies of a vasculature-targeting fusion toxin (VEGF(121)/rGel) composed of the VEGF-A isoform VEGF(121) linked with a G(4)S tether to recombinant plant toxin gelonin (rGel) in an orthotopic glioblastoma mouse model by use of noninvasive in vivo bioluminescence imaging (BLI), MRI, and PET.

METHODS

Tumor-bearing mice were randomized into 2 groups and balanced according to BLI and MRI signals. PET with (64)Cu-1,4,7,10-tetraazacyclododedane-N,N',N'',N'''-tetraacetic acid (DOTA)-VEGF(121)/rGel was performed before VEGF(121)/rGel treatment. (18)F-Fluorothymidine ((18)F-FLT) scans were obtained before and after treatment to evaluate VEGF(121)/rGel therapeutic efficacy. In vivo results were confirmed with ex vivo histologic and immunohistochemical analyses.

RESULTS

Logarithmic transformation of peak BLI tumor signal intensity revealed a strong correlation with MRI tumor volume (r = 0.89, n = 14). PET with (64)Cu-DOTA-VEGF(121)/rGel before treatment revealed a tumor accumulation (mean +/- SD) of 11.8 +/- 2.3 percentage injected dose per gram at 18 h after injection, and the receptor specificity of the tumor accumulation was confirmed by successful blocking of the uptake in the presence of an excess amount of VEGF(121). PET with (18)F-FLT revealed significant a decrease in tumor proliferation in VEGF(121)/rGel-treated mice compared with control mice. Histologic analysis revealed specific tumor neovasculature damage after treatment with 4 doses of VEGF(121)/rGel; this damage was accompanied by a significant decrease in peak BLI tumor signal intensity.

CONCLUSION

The results of this study suggest that future clinical multimodality imaging and therapy with VEGF(121)/rGel may provide an effective means to prospectively identify patients who will benefit from VEGF(121)/rGel therapy and then stratify, personalize, and monitor treatment to obtain optimal survival outcomes.

Decreased vesicular acetylcholine transporter and α4β2 nicotinic receptor density in the rat brain following 192 IgG-saporin immunolesioning

Degeneration of cholinergic neurons is a well known characteristic of Alzheimer's disease (AD). Two radioligands were studied in a rat model of cholinergic degeneration to evaluate their potential efficacy for molecular imaging of AD. Following specific cholinergic-cell immunolesioning with 192 IgG-saporin (SAP), ex vivo autoradiography was performed with (123)IBVM, a radioligand which targets the vesicular acetylcholine transporter (VAChT). Following the decay of (123)I, the same animals had in vitro autoradiography performed with (125)I-A-85380, a marker for nicotinic acetylcholine receptors (nAChRs). As expected significant, widespread decreases in (123)IBVM uptake were observed in SAP treated animals. Moderate but significant reductions in (125)I-A-85380 binding in the hippocampus (Hip) and cerebellum (Cbm) were also observed following SAP immunolesioning. The results with (123)IBVM confirm and extend previous work investigating the uptake of radioiodinated IBVM in this animal model. The results with (125)I-A-85380 are unique and are in contrast with work performed in this animal model with other nAChR radioligands, indicating the favourable properties of this radioligand for molecular imaging.

From anxiety to autism: spectrum of abnormal social behaviors modeled by progressive disruption of inhibitory neuronal function in the basolateral amygdala in Wistar rats

RATIONALE

Social behaviors are disrupted in several psychiatric disorders. The amygdala is a key brain region involved in social behaviors, and amygdala pathology has been implicated in disease states ranging from social anxiety disorder to autism.

OBJECTIVE

To test the effects of progressive disruption of the inhibitory function within the basolateral nucleus of the amygdala (BLA) on conspecific social interaction in rats and investigate functional networks from the ventral medial prefrontal cortex (mPFCv) to the BLA.

MATERIALS AND METHODS

BLA inhibitory tone was disrupted by priming it with the stress-peptide corticotrophin releasing factor (CRF) receptor agonist urocortin 1 (Ucn 1, 6 fmol), or by selective lesioning of a subset of BLA-GABAergic interneurons containing neurokinin 1 receptors using the targeted toxin SSP-Saporin. The effects of the disruption of GABAergic tone in the BLA were examined using a repeated exposure and habituation paradigm of social interaction (SI/h). Lesions and selectivity of lesions were confirmed postmortem. Additionally, effects of stimulating mPFCv on cFos activity in interneurons of the BLA were examined.

RESULTS

Rats primed with Ucn 1 showed persistent social inhibition, which could be overcome with habituation, putatively modeling social anxiety. Rats with a selective lesioning of a subset of GABAergic interneurons in the BLA exhibited persistent social inhibition that was not reversed by SI/h paradigm. We also demonstrate selective functional inputs to this subset of interneurons when mPFCv was activated.

CONCLUSIONS

These models with different gradations of disrupted BLA inhibition could help to study social dysfunction in disorders ranging from social anxiety to autism spectrum disorders.

Lesions to the nucleus basalis magnocellularis lower performance but do not block the retention of a previously acquired learning set

Rats were first trained to acquire an olfactory discrimination learning set (ODLS) on 40 olfactory-unique discrimination problems. Following acquisition of ODLS, animals were lesioned bilaterally in the nucleus basalis magnocellularis (nBM) using either quisqualic acid (QUIS) or 192 IgG-saporin (SAP). QUIS animals performed significantly worse than control animals following surgery and SAP animals performed transiently worse than control animals. Despite lowered performances, both QUIS and SAP animals performed significantly better than expected by chance on trial 2 indicating retention of the ODLS previously acquired. Implications for the role of the nBM in aspects of cognitive flexibility and its role in acquisition versus retention are discussed.

Guanidinylated neomycin delivers large, bioactive cargo into cells through a heparan sulfate-dependent pathway

Facilitating the uptake of molecules into living cells is of substantial interest for basic research and drug delivery applications. Arginine-rich peptides have been shown to facilitate uptake of high molecular mass cargos into cells, but the mechanism of uptake is complex and may involve multiple receptors. In this report, we show that a derivative of the aminoglycoside antibiotic neomycin, in which all of the ammonium groups have been converted into guanidinium groups, can carry large (>300 kDa) bioactive molecules across cell membranes. Delivery occurs at nanomolar transporter concentrations and under these conditions depends entirely on cell surface heparan sulfate proteoglycans. Conjugation of guanidinoneomycin to the plant toxin saporin, a ribosome-inactivating agent, results in proteoglycan-dependent cell toxicity. In contrast, an arginine-rich peptide shows both heparan sulfate-dependent and -independent cellular uptake. The high selectivity of guanidinoneomycin for heparan sulfate suggests the possibility of exploiting differences in proteoglycan compositions to target delivery to different cell types.

The rGel/BLyS fusion toxin specifically targets malignant B cells expressing the BLyS receptors BAFF-R, TACI, and BCMA

B lymphocyte stimulator (BLyS) is crucial for B-cell survival, and the biological effects of BLyS are mediated by three cell surface receptors designated B cell-activating factor receptor (BAFF-R), transmembrane activator and calcium modulator and cyclophilin ligand interactor (TACI), and B-cell maturation antibody (BCMA). Increased expression of BLyS and its receptors has been identified in numerous B-cell malignancies. We generated a fusion toxin designated rGel/BLyS for receptor-mediated delivery of the recombinant gelonin (rGel) toxin to neoplastic B cells, and we characterized its activity against various B-cell tumor lines. Three mantle cell lymphoma (MCL) cell lines (JeKo-1, Mino, and SP53) and two diffuse large B-cell lymphoma (DLBCL) cell lines (SUDHL-6 and OCI-Ly3) expressing all three distinct BLyS receptors were found to be the most sensitive to the fusion toxin (IC(50) = 2-5 pmol/L and 0.001-5 nmol/L for MCL and DLBCL, respectively). The rGel/BLyS fusion toxin showed specific binding to cells expressing BLyS receptors and rapid internalization of the rGel component into target cells. The cytotoxic effects of rGel/BLyS were inhibited by pretreatment with free BLyS or with soluble BAFF-R, TACI, and BCMA decoy receptors. This suggests that the cytotoxic effects of the fusion toxin are mediated through BLyS receptors. The rGel/BLyS fusion toxin inhibited MCL cell growth through induction of apoptosis associated with caspase-3 activation and poly (ADP-ribose) polymerase cleavage. Our results suggest that BLyS has the potential to serve as an excellent targeting ligand for the specific delivery of cytotoxic molecules to neoplastic B cells expressing the BLyS receptors, and that the rGel/BLyS fusion toxin may be an excellent candidate for the treatment of B-cell malignancies especially MCL and DLBCL.

Solution behavior of a novel biopharmaceutical drug candidate: a gonadotropin-toxin conjugate

There is little known about the solution structure and stability of peptide-protein conjugates, which comprise a new class of potential biopharmaceutical agents. This study describes the solution behavior of gonadotropins-releasing hormone (GnRH) chemically conjugated to pokeweed antiviral protein (PAP). The conjugate adopts a well-defined conformation across a pH range of 4 to 8. Even after heating to 80 degrees C, the conjugate retains a significant amount of secondary and tertiary structure. Heating for 1 h at 60 degrees C does lead to chemical damage, as determined by cation exchange chromatography. Using an experimental design approach, the optimal pH and salt concentration for limiting chemical damage was determined.

Long-term effects of neonatal basal forebrain cholinergic lesions on radial maze learning and impulsivity in rats

We examined long-term behavioural effects of neonatal lesions of the cholinergic basal forebrain obtained by intracerebroventricular injections of 192 IgG saporin (192 IgG-Sap). Five-month-old Wistar male rats (injected with 192 IgG-Sap or phosphate-buffered saline on postnatal day 7) were tested using operant chambers with two nose-poking holes, delivering one food pellet immediately or five pellets after a delay. The length of delay progressively increased over days (from 0 to 100 s). When compared with controls, 192 IgG-Sap rats showed a slight preference for smaller immediate over larger delayed rewards, thus indicating elevated intolerance to delay (i.e. more impulsivity). Sibling animals were tested in a computerized radial maze (baited vs. nonbaited arm procedure). 192 IgG-Sap rats appeared slower than controls in accomplishing the task. The neonatal 192 IgG-Sap lesion did not alter cortical levels of serotonin and/or its metabolites, but induced a marked cortical cholinergic loss. Our data suggest that a prolonged basal forebrain cholinergic hypofunction produces (i) an impairment in cognitive performances that is detectable only when highly complex tasks are used; (ii) a slight enhancement of the impulsive behavioural profile. This animal model may thus be useful to investigate some cognitive deficits and other secondary symptoms seen in Alzheimer's disease.

Distinct mechanisms mediating methamphetamine-induced neuronal apoptosis and dopamine terminal damage share the neuropeptide substance p in the striatum of mice

Methamphetamine (METH) is an addictive psychostimulant that induces damage to the dopamine terminals and the apoptosis of some neurons of the striatum. Our laboratory demonstrated using either a single bolus dose (30 mg/kg) or a binge (10 mg/kg 4x at 2-h intervals) of METH that pharmacological blockade of the substance P receptor (neurokinin-1) attenuates METH-induced damage to both the presynaptic dopamine terminals and the apoptosis of some neurons of the striatum. To determine the phenotype of striatal neuron ablated by METH, we combined TUNEL (Terminal Deoxyncleotidyl Transferase-Mediated dUTP Nick End Labeling) with immunofluorescence for selective markers of projection and interneurons. METH induces the loss of approximately 20% of the projection neurons. The cholinergic and gamma-aminobutyric acid (GABA)-parvalbumin interneurons sustain losses of 30% and 50%, respectively. The somatostatin/neuropeptide Y (NPY)/nitric oxide synthase (NOS) interneurons are not impacted by METH. To investigate the mechanism by which substance P mediates METH-induced damage in this part of the brain, we ablated the striatal interneurons that express the neurokinin-1 receptor (NK-1R) with the selective neurotoxin substance P-SAP. Ablation of the NK-1R-expressing interneurons prevented METH-induced apoptosis in the striatum but was without effect on depletion of dopamine terminal markers. We propose that substance P mediates the apoptosis of some striatal neurons via the intrastriatal activation of nitric oxide synthesis. In contrast, substance P may mediate damage of the dopamine terminals via an extrastriatal mechanism involving the substantia nigra and cortical glutamate release.

Selective depletion of cortical noradrenaline by anti-dopamine beta-hydroxylase-saporin impairs attentional function and enhances the effects of guanfacine in the rat

RATIONALE

Previous data indicate that depletion of cortical noradrenaline (NA) impairs performance of an attentional five-choice serial reaction time task (5CSRT) under certain conditions. This study employed a novel immunotoxin, anti-dopamine-beta hydroylase (DbetaH)-saporin, to make relatively selective lesions of the noradrenergic projections to the prefrontal cortex (PFC) in rats trained to perform the 5CSRT.

OBJECTIVES

The aim of this work is to examine (1) the effect of cortical noradrenaline depletion on sustained attentional performance in the 5CSRT under a variety of test conditions and (2) the effects of guanfacine, a selective alpha-2 adrenoceptor agonist on attentional performance in sham and NA-depleted rats.

MATERIALS AND METHODS

Animals received either intramedial prefrontal anti-DbetaH-saporin or vehicle and were tested on the baseline task with a variety of additional manipulations including (1) decreasing target duration, (2) increasing rate and (3) temporal unpredictability of target presentation and (4) systemic guanfacine.

RESULTS

Anti-DbetaH-saporin infused into the PFC produced a substantial loss of DbetaH-positive fibers in that region and in other adjacent cortical areas. There was no significant depletion of DA or 5-HT. NA-depleted animals were not impaired on the baseline task, but were slower to respond correctly under high event rate conditions, and their discriminative accuracy was reduced when stimulus predictability decreased. Guanfacine significantly reduced discriminative accuracy in NA-depleted animals only.

CONCLUSION

Selective cortical NA depletion produced deficits on the 5CSRT test of sustained attention, especially when the attentional load was increased and in response to systemic guanfacine. These results are consistent with a role of coeruleo-cortical NA in the regulation of effortful attentional processes.

Selective cholinergic depletion of the hippocampus spares both behaviorally induced Arc transcription and spatial learning and memory

We demonstrated previously that when hippocampal-dependent learning and plasticity are compromised by fornix lesions, behaviorally induced expression of the immediate early gene, Arc, is correspondingly low. The medial septum and the vertical diagonal band are major sources of subcortical afferents that innervate the hippocampus via the fornix. Here we assessed the specific contribution of cholinergic afferents from these regions to the impairments in spatial learning and behavioral induction of Arc transcription produced by fornix lesions. The immunotoxin, 192 IgG-saporin, was used to produce selective lesions of cholinergic cell bodies in the medial septum and vertical diagonal band. Rats were then trained on both cued and spatial delayed match-to-place tasks in a radial arm water maze. Animals with 192 IgG-saporin lesions learned both cue and place discrimination tasks in the water maze normally, and showed only a mild and transient impairment when switching from the cued to the spatial version of the task. Following behavioral testing, rats explored two novel environments sequentially in a setting known to induce Arc expression in hippocampal pyramidal neurons. In marked contrast to the effects of complete fornix transection, quantitative in situ autoradiography revealed no differences in Arc mRNA expression between sham and lesion animals in CA1, CA3 or stratum radiatum. The conclusion from these data is that cholinergic deafferentation alone cannot account for the spatial learning deficits or impaired behavioral induction of Arc transcription produced by fornix lesions.

Cholinergic modulation of sensory interference in rat primary somatosensory cortical neurons

Sensory interaction was studied using extracellular recordings from 275 neurons in the primary somatosensory (SI) cortex of pentobarbital-anesthetized rats. Tactile stimulation was applied to the receptive field using a 1 mm diameter probe that indented the skin for 20 ms, at 0.5 Hz, (test stimulus). Tactile test responses of SI neurons decreased during simultaneous application of a gentle tickling (distracter stimuli) continuously for 60 s on a separate receptive field located in the same or the contralateral hindlimb (ipsi- or contralateral distraction). This decrease in neural response produced by distracter stimuli was interpreted as "sensory interference". Sensory interference was observed in 66% and 61% of recorded SI neurons when ipsi- or contralateral distracters were applied, respectively and was blocked by a novel stimulus obtained by increasing the stimulation frequency of the test tactile stimuli from 0.5 to 2 Hz. The number of neurons showing sensory interference in response to a contralateral distracter was not modified after corpus callosum transection, suggesting that interhemispheric connections are not crucial for sensory interference. In contrast, the number of neurons showing sensory interference decreased in animals with 192 IgG-saporin basal forebrain lesions that decreased the number of cortical cholinergic fibers. This finding indicates that cholinergic afferents from the basal forebrain are fundamental to sensory interference and suggests that the associative cortices - basal forebrain - sensory cortices network may be implicated in sensory interference.

Effect of selective cholinergic denervation on the serotonergic system: implications for learning and memory

The cholinergic system has been widely implicated in cognitive processes and cholinergic loss is a classical hallmark in Alzheimer disease. Increasing evidence supports a role of the serotonergic system in cognition, possibly through a modulation of cholinergic activity. We compared selective cholinergic denervation by administration of the immunotoxin 192 IgG-saporin in the nucleus basalis of Meynert (NBM) with intracerebroventricular (ICV) lesions of the basal forebrain in male rats 7 days after lesioning. NBM lesions induced significant changes in cholinergic markers in the frontal cortex, whereas ICV lesions produced significant decreases in cholinergic markers both in the frontal cortex and hippocampus. Only ICV lesions lead to memory impairments in passive avoidance and Morris water maze tasks. Both models lead to reductions of serotonin levels in the frontal cortex. Similar changes in 5-hydroxytriptophan levels were observed, suggesting a downregulation of the rate-limiting enzyme for the synthesis of serotonin along with the cholinergic deficit. Neither 5-HT1A nor 5-HT1B receptors seem to mediate this process. These data imply that the serotonergic system in the frontal cortex can compensate for diminished cholinergic function and support the investigation of the serotonergic system as a therapeutic target to treat Alzheimer disease.

Effects of hypocretin-1 in 192-IgG-saporin-lesioned rats

Hypocretin, also known as orexin, is a neuropeptide located in the perifornical region of the lateral hypothalamus; this region projects to all the major arousal centres including the basal forebrain. The basal forebrain contains a mixed population of neurons, some of which are cholinergic. To identify the relative contribution of the noncholinergic neurons to arousal, here we utilized 192-IgG-saporin to lesion the basal forebrain cholinergic neurons and determine whether microinjection of hypocretin-1 to the basal forebrain is still effective in inducing arousal. In Sprague-Dawley rats given 192-IgG-saporin (intraventricular, 6 microg; n=7) 92% of the basal forebrain cholinergic neurons were destroyed compared to nonlesioned rats (n=5). In the lesioned rats microinjection of hypocretin-1 (0.0625, 0.125 or 0.25 nmol in 250 nL) to the basal forebrain increased waking and suppressed sleep (both non-REM and REM) in a concentration-dependent manner and to the same extent as in nonlesioned rats. These results suggest that, in the absence of the basal forebrain cholinergic neurons, the basal forebrain noncholinergic neurons are able to convey hypocretin's arousal signal unabated.

Substance P-saporin down-regulates substance P receptor immunoreactive sensory dorsal root ganglion neurons innervating the lumbar intervertebral discs in rats

STUDY DESIGN

To examine changes in substance P receptors on dorsal root ganglion cells innervating the rat lumbar intervertebral discs using immunohistochemistry and a retrograde neurotracing method.

OBJECTIVE

We evaluated the effects of intradiscal administration of substance P-saporin, a toxin selective for cells expressing substance P receptors.

SUMMARY OF BACKGROUND DATA

The rat L5/6 intervertebral disc is multi-segmentally innervated from the L1-L6 dorsal root ganglions. Substance P and the neurokinin-1 receptor contribute to inflammatory pain transmission. Substance P immunoreactive-sensory nerve fibers in human intervertebral discs and immunoreactive-dorsal root ganglion neurons innervating rat intervertebral discs have been reported to be important in the transmission of discogenic low back pain. In the current study, we evaluated the effects of intradiscal administration of substance P-saporin, a toxin selective for cells expressing substance P receptor.

METHODS

Sixteen rats were used (control group, n = 8; substance P-saporin group, n = 8). To detect dorsal root ganglion neurons innervating the L5/6 intervertebral disc, neurotracer (fluoro-gold crystals) was placed into the intervertebral disc. Seven days after fluoro-gold application, the L5/6 intervertebral disc was exposed and injected with 175 ng of sterile substance P-saporin (substance P-saporin group, n = 8). Fourteen days after the first operation, each dorsal root ganglion was harvested, sectioned, and processed for neurokinin-1 immunohistochemistry using rabbit antibody to neurokinin-1. The numbers of fluoro-gold labeled neurons, and fluoro-gold labeled and neurokinin-1 immunoreactive neurons were counted in both groups.

RESULTS

Neurons innervating the L5/6 intervertebral discs, retrogradely labeled with fluoro-gold, were distributed throughout dorsal root ganglions from L1 to L6 in both groups. Of fluoro-gold labeled neurons, the proportion of neurokinin-1 immunoreactive neurons was 35% in the control group. However, the proportion of neurokinin-1 immunoreactive neurons was 8% after administration of substance P-saporin into the intervertebral discs (substance P-saporin group). Substance P-saporin significantly decreased the ratio of neurokinin-1 immunoreactive neurons.

CONCLUSION

Substance P-saporin decreased the ratio of neurokinin-1 immunoreactive neurons innervating the disc related to discogenic low back pain. Substance P-saporin may be a useful tool to investigate the mechanism of discogenic low back pain.

Overexpression of biologically active VEGF121 fusion proteins in Escherichia coli

Vascular endothelial growth factor-A (VEGF) exists as five different isoforms, which exert their growth stimulatory effects through interaction with the FLK and KDR receptors. The VEGF(121) isoform has been employed as a highly selective carrier of therapeutic agents to target tumor endothelial cells resulting in inhibition of tumor growth and metastasis. VEGF(121) and VEGF(121)/rGel fusion toxin containing hexa-histidine tags were expressed in Escherichia coli AD494 (DE3) pLysS. Media containing glycerol as a primary carbon source increased the specific expression levels of soluble VEGF(121) and VEGF(121)/rGel (mg/L/OD10) by more than two-fold over LB media when grown in a batchtype cultivation in a bioreactor. High cell densities over OD 40 were achieved using a fed-batch method and employing feeding medium containing glycerol and yeast extract. The overall production of the target proteins was improved 18-fold for VEGF(121) (59.2mg/L) and 27-fold for VEGF(121)/rGel (42.5mg/L), respectively, compared to the conventional flask cultivation method (3.3 and 1.6mg/L for VEGF(121) and VEGF(121)/rGel, respectively). The purified VEGF(121) and VEGF(121)/rGel fusion proteins were biologically active as assessed by phosphorylation of KDR receptors and cytotoxicity against KDR expressing cells.

The differential catalytic activity of ribosome-inactivating proteins saporin 5 and 6 is due to a single substitution at position 162

Saporin, a type I ribosome-inactivating protein produced by the soapwort plant Saponaria officinalis belongs to a multigene family that encodes its several isoforms. The saporin seed isoform 6 has significantly higher N-glycosidase and cytotoxic activities compared with the seed isoform 5, although the two have identical active sites. In the present study, we have investigated the contribution of non-conservative amino acid changes outside the active sites of these isoforms towards their differential catalytic activity. The saporin 6 residues Lys134, Leu147, Phe149, Asn162, Thr188 and Asp196 were replaced by the corresponding saporin 5 residues, Gln134, Ser147, Ser149, Asp162, Ile188 and Asn196, to generate six variants of saporin 6, K134Q, L147S, F149S, N162D, T188I and D196N. By functional characterization, we show that the change in amino acid Asn162 in saporin 6 to aspartic acid residue of saporin 5 contributes mainly to the lower catalytic activity of saporin 5 compared with saporin 6. The non-involvement of other non-conservative amino acids in the differential catalytic activity of these isoforms was confirmed with the help of the double mutations N162D/K134Q, N162D/L147S, N162D/F149S, N162D/T188I and N162D/D196N.

Up-regulation of cation-independent mannose 6-phosphate receptor and endosomal-lysosomal markers in surviving neurons after 192-IgG-saporin administrations into the adult rat brain

The cation-independent mannose 6-phosphate receptor (CI-MPR) is a single transmembrane domain glycoprotein that plays a major role in the trafficking of lysosomal enzymes from the trans-Golgi network to the endosomal-lysosomal (EL) system. Because dysfunction of EL system is associated with a variety of neurodegenerative disorders, it is possible that the CI-MPR may have a role in regulating neuronal viability after toxicity/injury. In the present study, we report that 192-IgG-saporin-induced loss of basal forebrain cholinergic neurons causes a transient up-regulation of CI-MPR protein levels in surviving neurons of the basal forebrain and frontal cortex but not in the brainstem region, which was relatively spared by the immunotoxin. This was accompanied by a parallel time-dependent increase in other EL markers, ie, cathepsin D, Rab5, and LAMP2 in the basal forebrain region, whereas in the frontal cortex the levels of cathepsin D, and to some extent Rab5, were increased. Given the critical role of the EL system in the clearance of abnormal proteins in response to changing conditions, it is likely that the observed increase in the CI-MPR and components of the EL system in surviving neurons after 192-IgG-saporin treatment represents an adaptive mechanism to restore the metabolic/structural abnormalities induced by the loss of cholin-ergic neurons.

Spinal NK-1 receptor expressing neurons mediate opioid-induced hyperalgesia and antinociceptive tolerance via activation of descending pathways

Opioids can induce hyperalgesia in humans and in animals. Mechanisms of opiate-induced hyperalgesia and possibly of spinal antinociceptive tolerance may be linked to pronociceptive adaptations occurring at multiple levels of the nervous system including activation of descending facilitatory influences from the brainstem, spinal neuroplasticity, and changes in primary afferent fibers. Here, the role of NK-1 receptor expressing cells in the spinal dorsal horn in morphine-induced hyperalgesia and spinal antinociceptive tolerance was assessed by ablating these cells with intrathecal injection of SP-saporin (SP-SAP). Ablation of NK-1 receptor expressing cells prevented (a) morphine-induced thermal and mechanical hypersensitivity, (b) increased touch-evoked spinal FOS expression, (c) upregulation of spinal dynorphin content and (d) the rightward displacement of the spinal morphine antinociceptive dose-response curve (i.e., tolerance). Morphine-induced hyperalgesia and antinociceptive tolerance were also blocked by spinal administration of ondansetron, a serotonergic receptor antagonist. Thus, NK-1 receptor expressing neurons play a critical role in sustained morphine-induced neuroplastic changes which underlie spinal excitability reflected as thermal and tactile hypersensitivity to peripheral stimuli, and to reduced antinociceptive actions of spinal morphine (i.e., antinociceptive tolerance). Ablation of these cells likely eliminates the ascending limb of a spinal-bulbospinal loop that engages descending facilitation and elicits subsequent spinal neuroplasticity. The data may provide a basis for understanding mechanisms of prolonged pain which can occur in the absence of tissue injury.

The growth factor fusion construct containing B-lymphocyte stimulator (BLyS) and the toxin rGel induces apoptosis specifically in BAFF-R-positive CLL cells

The cytokine B lymphocyte stimulator (BLyS) mediates its effect through cell-surface receptors BAFF-R, TACI, and BCMA. BLyS receptors are expressed only on B cells and not present in other normal cells including normal T lymphocytes. Chronic lymphocytic leukemia (CLL) is a B-cell disease and CLL lymphocytes express BLyS receptors. Gelonin, a type 1 ribosome-inactivating toxin, lacks cell membrane binding domain and hence is nontoxic to intact cells. We generated a construct of recombinant gelonin (rGel) fused to BLyS to specifically target quiescent B-CLL lymphocytes. The construct rGel/BLyS specifically binds and internalizes through BAFF-R into CD19(+) B-CLL lymphocytes and induces apoptosis at nanomolar concentrations. In contrast, rGel alone was not able to internalize into these leukemic lymphocytes. Mechanistically, the rGel/BLyS construct inhibits protein synthesis with an IC(50) of less than 3 nM compared with more than 5000 nM for rGel toxin alone. This rGel/BLyS-mediated decrease in protein synthesis was associated with a decline in short-lived proteins such as MCL-1 and XIAP, the 2 survival proteins in B-CLL. There was a strong relationship between a decrease in these proteins and the cleavage of PARP, a hallmark feature of apoptosis. Taken together, these data suggest that the rGel/BLyS fusion toxin may have potential therapeutic efficacy for B-CLL patients.

Inhibition of Prostate Tumor Growth and Bone Remodeling by the Vascular Targeting Agent VEGF121/rGel

The pathophysiology of tumor growth following skeletal metastases and the poor response of this type of lesion to therapeutic intervention remains incompletely understood. Vascular endothelial growth factor (VEGF)-A and its receptors play a role in both osteoclastogenesis and tumor growth. Systemic (i.v.) treatment of nude mice bearing intrafemoral prostate (PC-3) tumors with the vascular ablative agent VEGF(121)/recombinant gelonin (rGel) strongly inhibited tumor growth. Fifty percent of treated animals had complete regression of bone tumors with no development of lytic bone lesions. Immunohistochemical analysis showed that VEGF(121)/rGel treatment suppressed tumor-mediated osteoclastogenesis in vivo. In vitro treatment of murine osteoclast precursors, both cell line (RAW264.7) and bone marrow-derived monocytes (BMM), revealed that VEGF(121)/rGel was selectively cytotoxic to osteoclast precursor cells rather than mature osteoclasts. VEGF(121)/rGel cytotoxicity was mediated by Flt-1, which was down-regulated during osteoclast differentiation. Analysis by flow cytometry and reverse transcription-PCR showed that both BMM and RAW264.7 cells display high levels of Flt-1 but low levels of Flk-1. Internalization of VEGF(121)/rGel into osteoclast precursor cells was suppressed by pretreatment with an Flt-1 neutralizing antibody or by placenta growth factor but not with an Flk-1 neutralizing antibody. Thus, VEGF(121)/rGel inhibits osteoclast maturation in vivo and it seems that this process is important in the resulting suppression of skeletal osteolytic lesions. This is a novel and unique mechanism of action for this class of agents and suggests a potentially new approach for treatment or prevention of tumor growth in bone.

Lack of localization of 5-HT6 receptors on cholinergic neurons: implication of multiple neurotransmitter systems in 5-HT6 receptor-mediated acetylcholine release

The involvement of the cholinergic system in learning and memory together with the cognitive enhancing properties of 5-HT6 receptor antagonists led us to study the relationship between 5-HT6 receptors and cholinergic neurotransmission. A selective cholinergic lesion, induced by injection of the immunotoxin 192-IgG-Saporin into the nucleus basalis magnocellularis, failed to alter the density of 5-HT6 receptor mRNA or protein expression in the deafferentated frontal cortex, suggesting that 5-HT6 receptors are not located on cholinergic neurons. The 5-HT6 receptor antagonist SB-357134 (0.001-1 microM) induced a concentration-dependant K+-evoked [3H]acetylcholine (ACh) release in vitro in rat cortical and striatal slices, which was blocked by tetrodotoxin. SB-357134, up to 1 microM, stimulated glutamate release in cortical and striatal slices. In the cortex, riluzole (1 microM) blocked the SB-357134-induced K+-stimulated [3H]ACh release, and simultaneous administration of MK-801 (1 microM) and SB-357134 (0.05 microM) elicited an increase in K+-evoked ACh release. In the striatum, SB-357134, 1 microM, decreased dopamine release, and the increase in K+-evoked [3H]ACh release induced by 5-HT6 receptor blockade was reversed by the D1 receptor antagonist, SCH23390 (1 microM). In both the frontal cortex and striatum, bicuculline, 1 microM, showed no effect on SB-357134-evoked [3H]ACh. These results are discussed in terms of neurochemical mechanisms involved in 5-HT6 receptor functions.