Neutralization of gating charges in domain II of the sodium channel alpha subunit enhances voltage-sensor trapping by a beta-scorpion toxin

beta-Scorpion toxins shift the voltage dependence of activation of sodium channels to more negative membrane potentials, but only after a strong depolarizing prepulse to fully activate the channels. Their receptor site includes the S3-S4 loop at the extracellular end of the S4 voltage sensor in domain II of the alpha subunit. Here, we probe the role of gating charges in the IIS4 segment in beta-scorpion toxin action by mutagenesis and functional analysis of the resulting mutant sodium channels. Neutralization of the positively charged amino acid residues in the IIS4 segment by mutation to glutamine shifts the voltage dependence of channel activation to more positive membrane potentials and reduces the steepness of voltage-dependent gating, which is consistent with the presumed role of these residues as gating charges. Surprisingly, neutralization of the gating charges at the outer end of the IIS4 segment by the mutations R850Q, R850C, R853Q, and R853C markedly enhances beta-scorpion toxin action, whereas mutations R856Q, K859Q, and K862Q have no effect. In contrast to wild-type, the beta-scorpion toxin Css IV causes a negative shift of the voltage dependence of activation of mutants R853Q and R853C without a depolarizing prepulse at holding potentials from -80 to -140 mV. Reaction of mutant R853C with 2-aminoethyl methanethiosulfonate causes a positive shift of the voltage dependence of activation and restores the requirement for a depolarizing prepulse for Css IV action. Enhancement of sodium channel activation by Css IV causes large tail currents upon repolarization, indicating slowed deactivation of the IIS4 voltage sensor by the bound toxin. Our results are consistent with a voltage-sensor-trapping model in which the beta-scorpion toxin traps the IIS4 voltage sensor in its activated position as it moves outward in response to depolarization and holds it there, slowing its inward movement on deactivation and enhancing subsequent channel activation. Evidently, neutralization of R850 and R853 removes kinetic barriers to binding of the IIS4 segment by Css IV, and thereby enhances toxin-induced channel activation.

Purification, amino-acid sequence and partial characterization of two toxins with anti-insect activity from the venom of the South American scorpion Tityus bahiensis (Buthidae)

We report here the isolation by a two-step chromatographic procedure of two new toxins from the South American scorpion Tityus bahiensis. Their amino-acid sequences and some of their biological features were established. The two toxins have different biological properties. Toxin TbIT-I had almost no activity or pharmacological effects in vertebrate tissues whereas it was lethal to house flies (LD50 80.0 ng/house fly). In contrast, Tb2-II was active against both mammals (intracerebroventricular injection of 100 ng/mouse was lethal) and insects (LD50 40.0 ng/house fly). The amino-acid sequences of these toxins were established and found to be similar (60-95%) to previously described beta-toxins from the Tityus genus. Based on the available comparative information, this study attempts identify possible structure-function relationships that may be responsible for the differences in bioactivity displayed by these toxins.

In vivo neurotoxicity of Androctonus australis hector scorpion venom: evidence that the supra-thoracic nervous system is not implicated in the clinical manifestations

The severity of scorpion stings is related to the highly active neurotoxins in the venom. In this study, rats whose supra-spinal central nervous system was deprived of its peripheral connections were experimentally poisoned by the venom of Androctonus australis hector scorpion. Clinical signs of severity were not modified when the rats had previously undergone high medullar section. These results suggest that the supra-thoracic nervous system is not implicated in the neurotoxicity manifestations of scorpion envenomation.

Lebetin peptides: potent platelet aggregation inhibitors

Lebetins from Macrovipera lebetina snake venom constitute a new class of inhibitors of platelet aggregation. There are two groups of peptides: lebetin 1 (L1; 11- to 13-mer) and lebetin 2 (L2; 37- to 38-mer). The short lebetins are identical to the N-terminal segments of the longer ones. They inhibit platelet aggregation induced by various agonists (e.g. thrombin, PAF-acether or collagen). The shortest lebetin (11-mer) shows potent inhibition of rabbit (IC(50) = 7 nM) and human (IC(50) = 5 nM) platelets. They prevent collagen-induced thrombocytopenia in rats. N- and C-terminal-truncated synthetic L1gamma (sL1gamma; 11-mer) is less active in inhibiting platelet aggregation than the native peptide. Results from Ala scan studies of the sL1gamma peptide indicated that replacement of the residues (P3, G7, P8, P9 or N10) resulted in a remarkable drop in the activity, whereas replacement of residues K2, P4 or K6 by Ala resulted in enhancement of the antiplatelet activity by at least 10-fold. To examine the activity of multimeric L1gamma, several multimeric peptides were synthesized using the multiple-antigen peptide system assembled on a branched lysine core and their antiplatelet activity was evaluated in vitro. The largest multimeric peptides showed a 1,000-fold increase in antiplatelet activity.

Disulfide bridge reorganization induced by proline mutations in maurotoxin

Maurotoxin (MTX) is a 34-residue toxin that has been isolated from the venom of the chactidae scorpion Scorpio maurus palmatus, and characterized. Together with Pi1 and HsTx1, MTX belongs to a family of short-chain four-disulfide-bridged scorpion toxins acting on potassium channels. However, contrary to other members of this family, MTX exhibits an uncommon disulfide bridge organization of the type C1-C5, C2-C6, C3-C4 and C7-C8, versus C1-C5, C2-C6, C3-C7 and C4-C8 for both Pi1 and HsTx1. Here, we report that the substitution of MTX proline residues located at positions 12 and/or 20, adjacent to C3 (Cys(13)) and C4 (Cys(19)), results in conventional Pi1- and HsTx1-like arrangement of the half-cystine pairings. In this case, this novel disulfide bridge arrangement is without obvious incidence on the overall three-dimensional structure of the toxin. Pharmacological assays of this structural analog, [A(12),A(20)]MTX, reveal that the blocking activities on Shaker B and rat Kv1.2 channels remain potent whereas the peptide becomes inactive on rat Kv1.3. These data indicate, for the first time, that discrete point mutations in MTX can result in a marked reorganization of the half-cystine pairings, accompanied with a novel pharmacological profile for the analog.

Construction and functional evaluation of a single-chain antibody fragment that neutralizes toxin AahI from the venom of the scorpion Androctonus australis hector

9C2 is a murine monoclonal IgG that participates in the neutralization of Androctonus australis hector scorpion venom. It recognizes AahI and AahIII, two of the three main neurotoxins responsible for almost all the toxicity of the venom when injected into mammals. Using PCR we cloned the antibody variable region coding genes from 9C2 hybridoma cells and constructed a gene encoding a single-chain antibody variable fragment molecule (scFv). This scFv was produced in the periplasm of Escherichia coli in a soluble and functional form and purified in a single step using protein L-agarose beads yielding 1-2 mg.L(-1) of bacterial culture. scFv9C2 was predominantly monomeric but also tended to form dimeric and oligomeric structures, all capable of binding toxin AahI. The affinity of scFv and the parental mAb for toxin AahI and homologous toxin AahIII was of the same magnitude, in the nanomolar range. Similarly, purified forms of scFv9C2 completely inhibited the binding of toxin AahI to rat brain synaptosomes. Finally, scFv9C2 was efficient in protecting mice against the toxic effects of AahI after injection of the toxin and scFv to mice by the intracerebroventricular route in a molar ratio as low as 0.36 : 1. Thus, we produced a recombinant scFv that reproduces the recognition properties of the parent antibody and neutralizes the scorpion neurotoxin AahI, thereby opening new prospects for the treatment of envenomation.

Adenosine and hemodialysis in humans

BACKGROUND

Infections and hypotension are serious complications that develop during hemodialysis (HD) treatment. Adenosine (ADO), a strong hypotensive and immunosuppressive agent, may participate in these two HD complications, because high concentrations of ADO metabolites are found in dialyzed human plasma. ADO, which is released by endothelial cells, is quickly transformed into inosine (INO) by plasmatic ADO deaminase (ADA) and mononuclear cell ADO deaminase (MCADA). In plasma, the degradation of ADO into INO and its uptake by red blood cells (RBC) are both very rapid, resulting in the short half-life of ADO in blood.

METHODS

Using liquid chromatography, we evaluated ADO and INO plasma concentrations before and after HD session.

RESULTS

Before the HD session, ADO and INO plasma concentrations were higher in hemodialyzed patients than in controls and in peritoneally dialyzed patients. At the end of the HD session, ADO plasma concentration was increased. ADO plasma concentration for the undialyzed patients was in the same range as that of the controls. Before HD, ADA activity was higher in hemodialyzed patients (559 +/- 349 IU) than in controls (219 +/- 48 IU), and the activity rose during the session (665 +/- 135 IU). ADA activity in the undialyzed patients (222 +/- 80 IU) was in the same range as that of the controls (219 +/- 48 IU). Before the HD session, the MCADA activity (247 +/- 144 IU) was lower than in controls (624 +/- 99 IU). HD did not modify ADO RBC uptake. ADO inhibited mononuclear cell proliferation and interferon-gamma production in humans. Finally, as much as 50 microM INO does not inhibit ADO uptake by RBC and does not modify ADA and MCADA activities.

CONCLUSIONS

These data indicate that chronic HD inhibited MCADA activity and increased ADO plasma concentration. Both high ADO plasma concentration and low MCADA activity may be involved in dialysis-induced immune system failure and thereby favor infectious diseases.

Maurotoxin versus Pi1/HsTx1 scorpion toxins. Toward new insights in the understanding of their distinct disulfide bridge patterns

Maurotoxin (MTX) is a scorpion toxin acting on several K(+) channel subtypes. It is a 34-residue peptide cross-linked by four disulfide bridges that are in an "uncommon" arrangement of the type C1-C5, C2-C6, C3-C4, and C7-C8 (versus C1-C5, C2-C6, C3-C7, and C4-C8 for Pi1 or HsTx1, two MTX-related scorpion toxins). We report here that a single mutation in MTX, in either position 15 or 33, resulted in a shift from the MTX toward the Pi1/HsTx1 disulfide bridge pattern. This shift is accompanied by structural and pharmacological changes of the peptide without altering the general alpha/beta scaffold of scorpion toxins.

Ion channel activation by SPC3, a peptide derived from the HIV-1 gp120 V3 loop

SPC3 is a multibranched peptide containing eight identical GPGRAF motifs which are derived from the human immunodeficiency virus (HIV)-1 gp120 V3 loop consensus sequence. This molecule was reported to prevent the infection of CD4+ cells by various HIV-1 and HIV-2 strains. However, the molecular mode of action of SPC3 remains unclear. Here, we investigated the possibility that SPC3 could interact with alpha/beta-chemokine receptors following observations that, first, the V3 loop is likely to be involved in alpha/beta-chemokine receptor-dependent HIV entry and, second, natural ligands of these receptors are potent inhibitors of cell infection. To address this point, we examined the effects of SPC3 on Xenopus oocytes either uninjected or expressing exogenous human CXCR4 alpha-chemokine receptors. Extracellular applications of micromolar concentrations of SPC3 onto Xenopus oocytes trigger potent inward chloride currents which can be inhibited by increasing extracellular Ca2+ concentration. This effect can be blocked by chloride channel antagonists and is highly specific to SPC3 as it is not triggered by structural analogs of SPC3. The SPC3-induced chloride conductance in oocytes is alpha/beta-chemokine receptor dependent because: (i) SPC3 alters the sensitivity of this channel to external applications of human recombinant MIP-1alpha, a natural ligand of human CCR5 receptor, and (ii) the amplitude of the inward current could be increased by the expression of exogenous human CXCR4 chemokine receptor. The effect of SPC3 appears to rely on the activation of a phospholipase A2 signaling pathway, but is not affected by changes in cytosolic Ca2+ concentration, or by alterations in Gi/Go protein, adenylate cyclase, phospholipase C or protein kinase C activity. Altogether, the data indicate that SPC3 is capable of activating a surface alpha/beta-chemokine-like receptor-mediated signaling pathway in competent cells, thereby triggering, either directly or indirectly, a Ca2+-inactivated chloride conductance.

Purification, characterization and molecular modelling of two toxin-like proteins from the Androctonus australis Hector venom

Two toxin-like proteins (AahTL1 and AahTL3) were purified from the venom of the scorpion Androctonus australis Hector (Aah). AahTL1 and AahTL3 are the first non toxic proteins cross-reacting with AahI toxins group which indicates that these proteins can be used as a model of vaccins. In order to study structure-function relationships, their complete amino-acid sequences (66 residues) were determined, by automated Edman degradation. They show more than 50% of similarity with both AahI and AahIII antimammal toxins. Three-dimensional structural models of AahTL1 and AahTL3 constructed by homology suggest that the two proteins are structurally similar to antimammal scorpion alpha-toxins specific to voltage dependent Na+ channels. The models showed also that amino-acid changes between potent Aah toxins and both AahTL1 and AahTL3 disrupt the electrostatic potential gradient at their surface preventing their interaction with the receptor, which may explain their non toxicity.

Chemical synthesis and characterization of Pi1, a scorpion toxin from Pandinus imperator active on K+ channels

Pi1 is a 35-residue toxin cross-linked by four disulfide bridges that has been isolated from the venom of the chactidae scorpion Pandinus imperator. Due to its very low abundance in the venom, we have chemically synthesized this toxin in order to study its biological activity. Enzyme-based proteolytic cleavage of the synthetic Pi1 (sPi1) demonstrates half-cystine pairings between Cys4-Cys25, Cys10-Cys30, Cys14-Cys32 and Cys20-Cys35, which is in agreement with the disulfide bridge organization initially reported on the natural toxin. In vivo, intracerebroventricular injection of sPi1 in mice produces lethal effects with an LD50 of 0.2 microgram per mouse. In vitro, the application of sPi1 induces drastic inhibition of Shaker B (IC50 of 23 nM) and rat Kv1.2 channels (IC50 of 0.44 nM) heterologously expressed in Xenopus laevis oocytes. No effect was observed on rat Kv1.1 and Kv1.3 currents upon synthetic peptide application. Also, sPi1 is able to compete with 125I-labeled apamin for binding onto rat brain synaptosomes with an IC50 of 55 pM. Overall, these results demonstrate that sPi1 displays a large spectrum of activities by blocking both SK- and Kv1-types of K+ channels; a selectivity reminiscent of that of maurotoxin, another structurally related four disulfide-bridged scorpion toxin that exhibits a different half-cystine pairing pattern.

Modulation of adenosine concentration by opioid receptor agonists in rat striatum

There is evidence that adenosine and morphine interact in the striatum. However, little is known about the precise role of the opioid receptor subtypes implicated in the modulation of adenosine tissue concentration and in adenosine receptor expression and function. We sought to evaluate, in the absence of withdrawal symptoms, the effects of the short-term administration of selective mu-, delta- or kappa-opioid receptor agonists on adenosine concentration and on adenosine A(2A) receptor function in rat striatum. Adenosine A(2A) receptor was chosen because the neuronal sub-population expressing this receptor coexpresses enkephalin, suggesting that adenosine A(2A) receptor may be regulated by opioid receptor agonists. Oxymorphone hydrochloride mu-opioid receptor agonist, 6 mg/kg/day), +[-(5 alpha,7 alpha, 8 beta)-(-)-N-methyl-N(7-(1-pyrrolidinyl)1-oxaspiro (4.5)dec-8-yl) benzenacetamide] (U69593) (kappa-opioid receptor agonist, 0.75 mg/kg/day), and (+)-4[(alpha R)-alpha-((2S,5R)-4-allyl-2, 5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide) (SNC80) (delta-opioid receptor agonist, 9 mm/kg/day), or vehicle, were administered i.p 3 x daily during 5 days to groups of rats (n=6). We also investigated the effects of opioid receptor agonists on adenosine uptake by striatal cell extracts. We found that administration of mu- or delta-opioid receptor agonists significantly decreased adenosine uptake in striatal cell extracts and increased adenosine concentration (mean+24% and +45% for mu- and delta-opioid receptor agonist, respectively, relative to controls). None of the receptor agonists tested induced obvious modifications of adenosine A(2A) receptor function. However, the delta-opioid receptor agonist induced an increase in adenosine A(2A) mRNA expression (mean 44%). We conclude that mu and delta receptor agonists inhibit adenosine uptake by striatal cell extracts and increase adenosine concentrations in rat striatum.

Effect of maurotoxin, a four disulfide-bridged toxin from the chactoid scorpion Scorpio maurus, on Shaker K+ channels

Maurotoxin is a 34-residue toxin isolated from the venom of the Tunisian chactoid scorpion Scorpio maurus palmatus and contains four disulfide bridges that are normally found in long-chain toxins of 60-70 amino acid residues, which affect voltage-gated sodium channels. However, despite the unconventional disulfide-bridge pattern of maurotoxin, the conformation of this toxin remains similar to that of other toxins acting on potassium channels. Here, we analyzed the effects of synthetic maurotoxin on voltage-gated Shaker potassium channels (ShB) expressed in Xenopus oocytes. Maurotoxin produces a strong, but reversible, inhibition of the ShB K+ current with an IC50 of 2 nM. Increasing concentrations of the toxin induce a progressively higher block at saturating concentrations. At nonsaturating concentrations of the toxin (5-20 nM), the channel block appears slightly more pronounced at threshold potentials suggesting that the toxin may have a higher affinity for the closed state of the channel. At the single channel level, the toxin does not modify the unitary current amplitude, but decreases ensemble currents by increasing the number of depolarizing epochs that failed to elicit any opening. A point mutation of Lys23 to alanine in maurotoxin produces a 1000-fold reduction in the IC50 of block by the toxin suggesting the importance of this charged residue for the interaction with the channel. Maurotoxin does not affect K+ currents carried by Kir2.3 channels in oocytes or Na+ currents carried by the alphaIIa channel expressed in CHO cells.

Synthesis, 1H NMR structure, and activity of a three-disulfide-bridged maurotoxin analog designed to restore the consensus motif of scorpion toxins

Maurotoxin (MTX) is a 34-residue toxin that has been isolated from the venom of the chactidae scorpion Scorpio maurus palmatus. The toxin displays an exceptionally wide range of pharmacological activity since it binds onto small conductance Ca(2+)-activated K(+) channels and also blocks Kv channels (Shaker, Kv1.2 and Kv1.3). MTX possesses 53-68% sequence identity with HsTx1 and Pi1, two other K(+) channel short chain scorpion toxins cross-linked by four disulfide bridges. These three toxins differ from other K(+)/Cl(-)/Na(+) channel scorpion toxins cross-linked by either three or four disulfide bridges by the presence of an extra half-cystine residue in the middle of a consensus sequence generally associated with the formation of an alpha/beta scaffold (an alpha-helix connected to an antiparallel beta-sheet by two disulfide bridges). Because MTX exhibits an uncommon disulfide bridge organization among known scorpion toxins (C1-C5, C2-C6, C3-C4, and C7-C8 instead of C1-C4, C2-C5, and C3-C6 for three-disulfide-bridged toxins or C1-C5, C2-C6, C3-C7, and C4-C8 for four-disulfide-bridged toxins), we designed and chemically synthesized an MTX analog with three instead of four disulfide bridges ([Abu(19),Abu(34)]MTX) and in which the entire consensus motif of scorpion toxins was restored by the substitution of the two half-cystines in positions 19 and 34 (corresponding to C4 and C8) by two isosteric alpha-aminobutyrate (Abu) derivatives. The three-dimensional structure of [Abu(19), Abu(34)]MTX in solution was solved by (1)H NMR. This analog adopts the alpha/beta scaffold with now conventional half-cystine pairings connecting C1-C5, C2-C6, and C3-C7 (with C4 and C8 replaced by Abu derivatives). This novel arrangement in half-cystine pairings that concerns the last disulfide bridge results mainly in a reorientation of the alpha-helix regarding the beta-sheet structure. In vivo, [Abu(19),Abu(34)]MTX remains lethal in mice as assessed by intracerebroventricular injection of the peptide (LD(50) value of 0. 25 microg/mouse). The structural variations are also accompanied by changes in the pharmacological selectivity of the peptide, suggesting that the organization pattern of disulfide bridges should affect the three-dimensional presentation of certain key residues critical to the blockage of K(+) channel subtypes.

Chemical synthesis and characterization of maurocalcine, a scorpion toxin that activates Ca(2+) release channel/ryanodine receptors

Maurocalcine is a novel toxin isolated from the venom of the chactid scorpion Scorpio maurus palmatus. It is a 33-mer basic peptide cross-linked by three disulfide bridges, which shares 82% sequence identity with imperatoxin A, a scorpion toxin from the venom of Pandinus imperator. Maurocalcine is peculiar in terms of structural properties since it does not possess any consensus motif reported so far in other scorpion toxins. Due to its low concentration in venom (0.5% of the proteins), maurocalcine was chemically synthesized by means of an optimized solid-phase method, and purified after folding/oxidation by using both C18 reversed-phase and ion exchange high-pressure liquid chromatographies. The synthetic product (sMCa) was characterized. The half-cystine pairing pattern of sMCa was identified by enzyme-based cleavage and Edman sequencing. The pairings were Cys3-Cys17, Cys10-Cys21, and Cys16-Cys32. In vivo, the sMCa was lethal to mice following intracerebroventricular inoculation (LD(50), 20 microg/mouse). In vitro, electrophysiological experiments based on recordings of single channels incorporated into planar lipid bilayers showed that sMCa potently and reversibly modifies channel gating behavior of the type 1 ryanodine receptor by inducing prominent subconductance behavior.

Maurotoxin and the Kv1.1 channel: voltage-dependent binding upon enantiomerization of the scorpion toxin disulfide bridge Cys31-Cys34

Maurotoxin (MTX) is a 34-amino acid polypeptide cross-linked by four disulfide bridges that has been isolated from the venom of the scorpion Scorpio maurus palmatus and characterized. Maurotoxin competed with radiolabeled apamin and kaliotoxin for binding to rat brain synaptosomes and blocked K+ currents from Kv1 channel subtypes expressed in Xenopus oocytes. Structural characterization of the synthetic toxin identified half-cystine pairings at Cys3-Cys24, Cys9-Cys29, Cys13-Cys19 and Cys31-Cys34 This disulfide bridge pattern is unique among known scorpion toxins, particularly the existence of a C-terminal '14-membered disulfide ring' (i.e. cyclic domain 31-34), We therefore studied structure-activity relationships by investigating the structure and pharmacological properties of synthetic MTX peptides either modified at the C-terminus ¿i.e. MTX(1-29), [Abu31,34]-MTX and [Cys31,34, Tyr32]D-MTX) or mimicking the cyclic C-terminal domain [i.e. MTX(31-34)]. Unexpectedly, the absence of a disulfide bridge Cys31-Cys34 in [Abu 31,34]-MTX and MTX(1-29) resulted in MTX-unrelated half-cystine pairings of the three remaining disulfide bridges for the two analogs, which is likely to be responsible for their inactivity against Kv1 channel subtypes. Cyclic MTX(31-34) was also biologically inactive. [Cys31,34, Tyr32]D-MTX, which had a 'native', MTX-related, disulfide bridge organization, but a D-residue-induced reorientation of the C-terminal disulfide bridge, was potent at blocking the Kv1.1 channel. This peptide-induced Kv1.1 blockage was voltage-dependent (a property not observed for MTX), maximal in the low depolarization range and associated with on-rate changes in ligand binding. Thus, the cyclic C-terminal domain of MTX seems to be crucial for recognition of Kv1.3, and to a lesser extent, Kv1.2 channels and it may contribute to the stabilization and strength of the interaction between the toxin and the Kv1.1 channel.

Toxicity during early development of the mouse nervous system of a scorpion neurotoxin active on sodium channels

The lethal effects of scorpion envenomation is due to neurotoxins active on voltage-sensitive sodium channels. Dysfunctions of the peripheral and central nervous systems with neurological manifestations are commonly observed after scorpion stings, specially in young children. Since the neurotoxicity of venom fraction is greatly higher by intracerebroventricular than by subcutaneous injections, a direct effect of venom on CNS cannot be excluded specially in infants where the blood-brain barrier is not fully functional. We investigated the activity of a neurotoxin from the scorpion Androctonus australis hector (AahII) in newborn mice at 3, 7 and 14 days after birth and in adults. Young mice (P3, P7) were more sensitive to AahII injected subcutaneously than were adults, but were less sensitive to intracerebroventricular injection. The affinity of AahII for its receptor site on brain synaptosomes from P3 and P7 mice was slightly higher and the density of the binding sites was half that of adult mice. After subcutaneous injection of [125I]-AahII it was also observed that a small amount of radioactivity was found in brains of neonate mice but not in that of adults. This amount is however extremely lower than the value of the LD50 determined by intracerebroventricular injection. Results are consistent with a peripheral action of AahII and show that its toxic activity changes during the mouse nervous system development.

Cyclosporine A and purinergic receptors in rat kidney

Previous reports have demonstrated that Cyclosporine A (CyA) chronically administered induces an increase in adenosine plasma concentration by inhibiting adenosine uptake by red blood cells (RBC). We hypothesized that this effect may modulate, by a down regulation, the mRNA expression of adenosine receptors in rat kidney. Since high blood pressure (HBP) is a classical side effect of CyA treatment, nicardipine, a dihydropyridine calcium channel blocker, is often associated with CyA in treatment. To distinguish between the effects of CyA-induced HBP and the effects of CyA by itself, we have evaluated the effects of CyA and/or nicardipine on the mRNA expression of A1 and A2a adenosine receptors. The study was performed on five groups of rats (n= 8) receiving during 21 days either serum saline (0.5 ml i.p), CyA (12 mg/kg/day, i.p), nicardipine (1.2 mg/kg i.p) or nicardipine + CyA. The last (or fifth) group was injected with vehicle (0.5 ml i.p). Blood samples for adenosine assay were collected in the renal artery at day 21, just before the rat kidneys were removed for quantitation of adenosine A1 and A2a mRNA concentration by RT-PCR. We make two conclusions :i) Nicardipine induces a decrease in mRNA expression of A1 but not of A2a adenosine receptors. However, because nicardipine lowered both blood pressure and A1 mRNA expression, it is not possible to conclude if A1 mRNA decrease is implicated in the nicardipine effects on blood pressure.ii) CyA induces an increase in renal artery adenosine concentration and a decrease in mRNA expression of A1 and A2a adenosine receptors.

KTX3, the kaliotoxin from Buthus occitanus tunetanus scorpion venom: one of an extensive family of peptidyl ligands of potassium channels

A new ligand of the K+ channels sensitive to KTX was purified from the venom of Buthus occitanus tunetanus, using two steps of high-performance-liquid-chromatography and by following its ability to compete with [125I]-KTX for binding to the KTX receptor on rat brain synaptosomes. Amino-acid analysis, amino acid sequencing and mass spectroscopy defined this new ligand. KTX3, as a 37-amino acid peptide, with three disulfide bridges. Its sequence shares 76% identity with KTX. The main differences between the two peptides are in the N-terminal region and the residue position 34 located in the region involved in channel recognition. These differences may explain the 5-fold lower binding affinity of KTX3, IC50=50 pM, than KTX to rat brain synaptosomes. Specific antibodies raised against KTX (1-37) were not able to recognize KTX3.

Chemical synthesis and structure-activity relationships of Ts kappa, a novel scorpion toxin acting on apamin-sensitive SK channel

Tityus kappa (Ts kappa), a novel toxin from the venom of the scorpion Tityus serrulatus, is a 35-residue polypeptide cross-linked by three disulphide bridges and acts on small-conductance calcium-activated potassium channels (SK channels). Ts K was chemically synthesized using the solid-phase method and characterized. The synthetic product, sTs kappa, was indistinguishable from the natural toxin when tested in vitro in competition assay with radiolabelled apamin for binding to rat brain synaptosomes (IC50 = 3 nM). The sTs kappa was further tested in vivo for lethal activity to mice following intracerebroventricular inoculation (LD50 = 70 ng per mouse). The half-cystine pairings were formerly established by enzyme-based cleavage of sTs kappa; they were between Cys7-Cys28, Cys13-CyS33 and Cys17-Cys35, which is a disulphide bridge pattern similar to that of other short scorpion toxins. According to previous studies on SK channel-acting toxins, the putative influence of certain basic residues of Ts kappa (i.e. Arg6, Arg9, Lys18, Lys19) in its pharmacological activity was investigated using synthetic point-mutated analogues of the toxin with an Ala substitution at these positions. Data from binding assay, together with conformational analysis of the synthetic analogues by 1H-NMR, suggest that Arg6, and to a lesser extent Arg9, are important residues for an high-affinity interaction of this toxin with SK channels; interestingly these residues are located outside the alpha-helical structure, whereas the pharmacologically important basic residues from other SK channel-specific toxins had been located inside the alpha-helix.

Monoclonal antibodies against the Androctonus australis hector scorpion neurotoxin I: characterisation and use for venom neutralisation

A series of monoclonal antibodies (mAbs) specific for the alpha-neurotoxin I (Aah I) from the venom of the dangerous Androctonus australis hector scorpion were obtained using carrier protein-coupled toxin. Competitive RIA, receptor assays and mouse toxicity tests were performed to characterise mAbs in terms of affinity and neutralisation. Cross-reactivity studies and two-site ELISA results allowed some classification of mAbs into three groups. One mAb, 9C2, was particularly interesting since it recognised the parent toxin I with a K(D) of 0.15 nM and was also reactive with toxins of the same immunological group. Its ability to neutralise the toxic effect of the parent toxin and the venom fraction has been investigated. This anti-Aah I mAb 9C2, associated with anti-Aah II mAb 4C1, provides a valuable tool to neutralise the toxicity of the venom.

An ultrarapid prognostic index in microprolactinoma surgery

OBJECT

Prolactinomas account for approximately 40% of pituitary tumors. If the tumor does not exceed 10 mm at its largest diameter (microprolactinoma), the chances of definitive cure as a result of surgery alone vary from 62 to 89% depending on the series. Until now, however, there was no mechanism to predict whether total excision of a tumor had been accomplished. To improve the chances of total excision, we compared the peri- and postoperative kinetics of circulating prolactin (PRL) in patients judged to be cured and those not cured.

METHODS

The pre-, peri-, and postoperative variations in blood PRL concentrations were determined using assays conducted at 10-minute intervals. Of the 36 patients included in the study, 27 were considered cured (resumption of a normal menstrual cycle within 6 months, PRL concentration at 9 days [mean +/- standard deviation 2.5+/-2.1 ng/ml] and 12 months [4.5+/-2.2 ng/ml] after the operation < 10 ng/ml and normally stimulated by metoclopramide and thyrotropin-releasing hormone [TRH]). Nine patients were not cured (PRL 20+/-15.7 ng/ml at 9 days after surgery, with no response to metoclopramide and TRH). The kinetics of PRL decrease in definitively cured patients were characterized by the following: 1) the initial slope of the curve decreased by at least 11% within the first 10 minutes after resection, and 2) immediate postoperative PRL concentrations were 20 ng/ml or less.

CONCLUSIONS

The measurement of the kinetics of PRL decrease during surgery allows the chance of gross-total resection to be successfully predicted less than 25 minutes after excision of the adenoma. Provided an ultrarapid assay is available (the test used in the present study took < 15 minutes), this prognostic index would be useful to make a decision to continue the surgical procedure when the initial PRL slope is judged to be insufficient. Its use may also be extended to other pituitary tumors such as somatotropic adenoma and basophilic adenoma (Cushing's disease).

V3 loop-derived peptide SPC3 inhibits infection of CD4- and galactosylceramide- cells by LAV-2/B

SPC3, a synthetic multibranched peptide including the GPGRAF consensus motif of the human immunodeficiency virus type 1 (HIV-1) gp120 V3-loop is a potent inhibitor of HIV infection of human CD4+ lymphocytes, macrophages and CD4-/galactosylceramide+ human colon epithelial cells and is currently tested in phase II clinical trials (FDA protocol 257 A). The antiviral property of SPC3 was further investigated for its ability to inhibit LAV-2/B, an HIV-2 clone with a CD4-independent tropism. SPC3 inhibited the LAV-2/B-mediated infection of B-cell line which does not express the CD4 and the galactosylceramide molecules on their cell surface, suggesting an SPC3-sensitive CD4/galactosylceramide-independent pathway of viral infection in HIV susceptible cells. The molecular mechanism of the peptide inhibition was also investigated. The data suggested that the SPC3-mediated inhibition does not result from a direct competition between SPC3 and gp120 binding to the cell surface of the target cell.