Reactive Amine Functionalized Microelectrode Arrays Provide Short-Term Benefit but Long-Term Detriment to In Vivo Recording Performance

Intracortical microelectrode arrays (MEAs) are used for recording neural signals. However, indwelling devices result in chronic neuroinflammation, which leads to decreased recording performance through degradation of the device and surrounding tissue. Coating the MEAs with bioactive molecules is being explored to mitigate neuroinflammation. Such approaches often require an intermediate functionalization step such as (3-aminopropyl)triethoxysilane (APTES), which serves as a linker. However, the standalone effect of this intermediate step has not been previously characterized. Here, we investigated the effect of coating MEAs with APTES by comparing APTES-coated to uncoated controls in vivo and ex vivo. First, we measured water contact angles between silicon uncoated and APTES-coated substrates to verify the hydrophilic characteristics of the APTES coating. Next, we implanted MEAs in the motor cortex (M1) of Sprague-Dawley rats with uncoated or APTES-coated devices. We assessed changes in the electrochemical impedance and neural recording performance over a chronic implantation period of 16 weeks. Additionally, histology and bulk gene expression were analyzed to understand further the reactive tissue changes arising from the coating. Results showed that APTES increased the hydrophilicity of the devices and decreased electrochemical impedance at 1 kHz. APTES coatings proved detrimental to the recording performance, as shown by a constant decay up to 16 weeks postimplantation. Bulk gene analysis showed differential changes in gene expression between groups that were inconclusive with regard to the long-term effect on neuronal tissue. Together, these results suggest that APTES coatings are ultimately detrimental to chronic neural recordings. Furthermore, interpretations of studies using APTES as a functionalization step should consider the potential consequences if the final functionalization step is incomplete.

[Clinical and endoscopic characteristics of adult celiac disease]

Objective: The study aimed to analyze the clinical and endoscopic characteristics of adult celiac disease (CD) to provide a scientific basis for more effective CD diagnosis and treatment. Methods: In this cross-sectional study, the clinical and endoscopic data of 96 adult CD patients treated in the Department of Gastroenterology of the People's Hospital of Xinjiang Uygur Autonomous Region from March 2016 to December 2021 were retrospectively collected and analyzed. Results: A total of 96 CD patients were diagnosed, including 33 men and 63 women. The average age was 47±14 years (range, 18-81 years). The disease occurred mainly in the age group of 31-60 years. The median course of the disease was 2.0 (0.2-40.0) years. There were 41 (42.7%) classical and 55 (57.3%) non-classical CD patients. All patients with classical CD showed chronic diarrhea, often accompanied by abdominal pain (46.3%, 19/41), abdominal distension (17.1%, 7/41), anemia (65.9%, 27/41), and chronic fatigue (48.8%, 20/41). The main manifestations of non-classical CD were chronic abdominal pain (58.2%, 32/55), abdominal distension (32.7%, 18/55), anemia (40.0%, 22/55), and osteopenia/osteoporosis (38.2%, 21/55). Compared with non-classical CD, anemia developed more frequently in classical CD, and the difference was statistically significant (P = 0.012). The incidence of complications in CD patients was 36.5% (35/96), and the main complications were thyroid disease (19.8%, 19/96), connective tissue disease (6.2%, 6/96), and kidney disease (6.2%, 6/96). There was no significant difference between classical and non-classical CD (P>0.05). The frequency of endoscopic manifestations in CD patients was 84.4% (81/96). Duodenal bulb endoscopy showed nodular changes (72.9%, 70/96), grooved changes (10.4%, 10/96), and focal villous atrophy (9.4%, 9/96). The main manifestations of descending endoscopy were the decrease, flattening, or disappearance of duodenal folds (43.8%, 42/96), scallop-like changes (38.5%, 37/96), and nodular changes (34.4%, 33/96). Conclusions: Adult CD patients are mostly female. CD occurred mainly in the age group of 31-60 years. The clinical manifestations were mainly those of non-classical CD. Some patients often had other autoimmune diseases. Patients with characteristic endoscopic manifestations should be warned about the possibility of developing CD. Clinicians should strengthen the understanding of CD and reduce the related rates of missed diagnosis.

Myoglobin A79G polymorphism association with exercise-induced skeletal muscle damage

We assessed the role of A79G, a polymorphism of the myoglobin gene (MB), in susceptibility to exercise-induced skeletal muscle damage. Between January 2012 and December 2014, a total of 166 cases with exercise-induced skeletal muscle damage and 166 controls were recruited into our study. Genotyping of MB A79G was carried out using polymerase chain reaction coupled with restriction fragment length polymorphism. Using unconditional logistic regression analysis, we found that the GG genotype of MB A79G was associated with higher risk of exercise-induced muscle damage compared with the wild-type genotype, and the OR (95%CI) was 2.91 (1.20-7.59). Compared with the AA genotype, the AG+GG genotype was associated with a significantly increased risk of exercise-induced muscle damage for those with blood lactic acid ≥1.80 mM (OR = 2.05; 95%CI = 1.09-3.88). In conclusion, we found that the A79G polymorphism of the MB gene plays an important role in influencing the development of exercise-induced skeletal muscle damage.

[The effect of nitric oxide donor on the DNA content in Toxoplasma gondii tachyzoite]

OBJECTIVE

To determine the role of sodium nitroprusside (SNP) in regulating DNA synthesis of Toxoplasma gondii tachyzoites.

METHODS

Hypodiploid peak of tachyzoite DNA induced by SNP was assessed according to DNA fragmentation. The effect of SNP on appearance of hypodiploid peak and the effect of Ca2+ on the growth of tachyzoites were evaluated. The intracellular Ca2+ chelator (BAPTA/AM), antagonist of Ca2+ channel (verapamil) and the extracellular Ca2+ chelator (EGTA) were used. The change of DNA content was measured by flow cytometry.

RESULTS

SNP inhibited DNA synthesis of tachyzoites in a dose- and time-dependent pattern. The antiproliferative effect of SNP on tachyzoites was inhibited by verapamil, EGTA and BAPTA/AM. The inhibition of the growth of tachyzoites by SNP was associated with increased subploid peak through a Ca(2+)-dependent mechanism.

CONCLUSION

SNP induced a hypodiploid peak in tachyzoites by altering the Ca2+ concentration in the plasma of tachyzoite, resulting in damages of the parasite.

[Effect of acryl thiourea on liver pathologic changes in mice infected with Schistosoma japonicum]

OBJECTIVE

To observe the effect of acryl thiourea, an inhibitor of phenol oxidase, on pathological changes in the liver of mice infected with Schistosoma japonicum.

METHODS

From day 22 to day 42 postinfection with cercariae, the mice of the acryl thiourea group were each injected i.p. with acryl thiourea at a dose of 300 mg/kg every other day. The mice were killed on the 42nd day postinfection to observe the pathological changes in the liver.

RESULTS

Compared to the infected control group, the liver tissue of the acryl thiourea group showed scattered foci of inflammatory cell infiltration, the mean diameter and area of the foci were significantly reduced (P < 0.01), and there were no eggs in the center of the foci except for some granules.

CONCLUSION

After i.p. injections of acryl thiourea, no typical egg granuloma was found in the liver of infected mice. This was possibly due to the inhibition of schistosome phenol oxidase activity and so the female adult schistosomes could not produce normal eggs.

[Dynamic changes in amino acid and glucose in culture medium with adult Schistosoma japonicum]

OBJECTIVE

To observe the dynamic changes in the contents of amino acid(AA), glucose(Gluc) and triglyceride(TG) in the culture medium containing adult Schistosoma japonicum.

METHODS

The contents of AA, Gluc and TG in the culture medium during the incubation period for d0 to 6 d were detected by amino acid automatic analyzer and automatic biochemical analyzer.

RESULTS

The contents of Arg, Thr, Met, and Lys and Gluc were reduced, Asp and Ala increased apparently. CONCLUASION: Increasing the levels of Arg, Thr, Met Lys and Gluc, reducing the levels of Asp and Ala, and changing the culture medium in time might be in favor of the in vitro cultivation of S. japonicum.

Exogenous nitric oxide induces apoptosis in Toxoplasma gondii tachyzoites via a calcium signal transduction pathway

The mechanism by which nitric oxide (NO)-dependent cytotoxicity acts against Toxoplasma gondii tachyzoites is poorly understood. An NO donor, sodium nitroprusside (SNP), was used to induce death in T. gondii tachyzoites in vitro as a model for investigating (i) whether NO is capable of inducing apoptosis-like death in tachyzoites and (ii) whether a calcium signal transduction pathway is involved. Exposure to 2 mM SNP resulted in a pattern of tachyzoite death that shares many features with metazoan apoptosis and it may involve a calcium signal transduction pathway. Motility and cell survival in these parasites showed a gradual decline with increasing levels of SNP. Features common to metazoan apoptosis are observed after exposure to 2 mM SNP. Ethylene glycol bis-(beta-aminoethyl ether)-N,N,N',N'-tetra-acetic acid (EGTA), Verapamil and bis-(o-aminophenoxy) ethane-N,N,N',N'-tetra-acetic acid/acetoxymethyl ester (BAPTA/AM) partially increased the cell survival concomitant with decreased [Ca2+]i in cells exposed to SNP. An NO scavenger (N-acetylcysteine), the analogue of SNP (devoid of NO), inhibited the rate of apoptosis after SNP treatment compared with SNP treatment without scavenger, but alone did not induce apoptosis. Taken together, the results indicate that SNP is capable of inducing apoptosis in T. gondii tachyzoites via a calcium signal transduction pathway.

Sequential repression and activation of the CCAAT enhancer-binding protein-alpha (C/EBPalpha ) gene during adipogenesis

CCAAT enhancer-binding protein-alpha (C/EBPalpha) functions as a pleiotropic transcriptional activator of adipocyte genes during adipogenesis. Nuclear factor C/EBP undifferentiated protein (CUP), an isoform of activator protein-2alpha (AP-2alpha), binds to repressive elements in the C/EBPalpha gene promoter, silencing the gene until late in the differentiation program. The CUP regulatory element overlaps a Sp (GT-box) element in the promoter to which Sp3 (or Sp1) can bind. Binding by Sp3 or Sp1 and CUP/AP2-alpha is mutually exclusive. Sp3 is a strong transcriptional activator of the C/EBPalpha gene promoter in 3T3-L1 preadipocytes and Schneider cells, this activation being repressed by CUP/AP-2alpha. Sp3 is expressed throughout differentiation, whereas CUP/AP-2alpha, which is expressed only by preadipocytes, is down-regulated during differentiation coincident with transcription of the C/EBPalpha gene. Thus, CUP/AP-2alpha delays access of Sp3 to the Sp regulatory element, preventing premature expression of C/EBPalpha and thereby interference by C/EBPalpha (which is antimitotic) with mitotic clonal expansion, an essential early event in the differentiation program.

Role of the CCAAT enhancer binding proteins (C/EBPs) in adipocyte differentiation

Members of the C/EBP family of transcription factors play essential roles in the adipocyte differentiation program. Treatment of growth-arrested 3T3-L1 preadipocytes with appropriate hormonal agents causes the cells to synchronously reenter the cell cycle and to undergo mitotic clonal expansion. Expression of C/EBPbeta and delta occur early in clonal expansion, later followed by C/EBPalpha (which is anti-mitotic) as the cells exit the cell cycle begin to express adipocyte genes. C/EBPalpha serves as transcriptional activator of many adipocyte genes whose expression produce the adipocyte phenotype. Recent work in this laboratory has focussed on the roles of C/EBPbeta and delta in the differentiation program, in particular the mechanisms by which they activate transcription of the C/EBPalpha gene. Several regulatory elements, both repressive and activating, in proximal promoter of the gene have been identified. The cognate transacting factors that interact with these elements have been characterized and their functions elucidated. These factors have been incorporated into a model for a cascade that leads to transcriptional activation of the C/EBPalpha gene and the terminal steps in the differentiation program.

An ergonomic design and performance evaluation of pipettes

This paper describes the results of an investigation of the differences in performance, postures, strains on hand-arm-shoulder musculature, and subjective ratings of three pipettes (models A, B, and C). Both models A and B were pipettes available on the market. Model C was developed for this study of an ergonomically designed pipette. The gripping posture of the three models was distinct both in the anatomical and in the functional sense. Working with models A and B required a four-finger grasp with a thumb operated plunger. Model C required a finger-palmar power grip and the plunger was operated by the fingers. Performance evaluation of the different pipettes in different tasks indicated that using the proposed model C resulted in a 2-3% lower fault rate, a 10% shorter completion time, and the highest subjective ratings among the three. Postural analysis results indicated that when using model C, the shoulder was the least abducted, the wrist was the least extended, and the wrist was the least radially extended. Model C appeared to provide the greatest opportunity for delicate adjustments of posture in response to the activity of the skin receptors and reduced the strains on the upper body musculature, justifying the ergonomic input into the design.

Pyridinylimidazole compound SB 203580 inhibits the activity but not the activation of p38 mitogen-activated protein kinase

p38 MAPK is a Ser/Thr protein kinase activated by various inflammatory cytokines and a variety of stress stimuli. It is involved in many physiological processes, including the production of inflammatory cytokines. We have previously reported the design and synthesis of a series of pyridinylimidazole compounds that are selective inhibitors of p38 MAPK. These compounds, exemplified by SB 203580, are exceptionally effective in cell-based assays, including the inhibition of inflammatory cytokine production. SB 203580 is widely used as a tool to dissect the role of p38 MAPK in various physiological processes. It has previously been established that SB 203580 acts primarily to block the catalytic activity of p38 MAPK. However, it has been suggested that in cells, the compounds could also inhibit p38 MAPK activation by virtue of their ability to bind to the inactive enzyme. We undertook careful studies to definitively demonstrate that treatment with SB 203580 had no effect on Thr(180) and Tyr(182) phosphorylation, and hence activation of p38 in vivo. SB 203580, however, potently inhibited the activity of p38 MAPK as demonstrated by the inhibition of the activation of MAPKAP K2, a specific physiological substrate of p38 MAPK. This was observed regardless of stimuli or cell type. Identical results were obtained when the p38 MAPK cascade was partially reconstituted in vitro. Thus, our data clearly indicate that SB 203580 specifically inhibits the activity of p38 MAPK but not its activation by upstream MAPKK.

Isolation and structural characterization of a cytotoxic L-amino acid oxidase from Agkistrodon contortrix laticinctus snake venom: preliminary crystallographic data

We have purified a cytotoxic L-amino acid oxidase (LAO) from Agkistrodon contortrix laticinctus snake venom by means of Superdex-200 gel filtration, followed by phenyl-Sepharose CL-4B chromatography. The purified enzyme (ACL LAO) is a dimer on gel filtration, with a M(r) of 60,000 for the monomer as estimated by SDS-PAGE. LAO activity was tested against 15 amino acids, but only 9 were oxidized by the enzyme, suggesting that it presents some degree of specificity. ACL LAO has apoptosis-inducing activity in an HL-60 cell culture assay. After 24 h treatment with 25 micrograms/ml of ACL LAO, the typical DNA fragmentation pattern of apoptotic cells was observed on agarose gel electrophoresis. NMR analysis showed the presence of a flavin mononucleotide prosthetic group. To solve its 3-D structure, crystals of the purified protein were grown in 0.1 M Tris-HCl, pH 8.5, and 2 M (NH(4))(2)SO(4). Diffraction data collected to 3.5 A showed that the protein crystallized in the tetragonal system, with unit cell a = b = 103.22 A, c = 183.45 A. This is the first report of preliminary crystallization data for a snake venom L-amino acid oxidase.

Repressive effect of Sp1 on the C/EBPalpha gene promoter: role in adipocyte differentiation

Expression of C/EBPalpha is required for differentiation of 3T3-L1 preadipocytes into adipocytes. Previous investigations indicated that transcription of the C/EBPalpha gene is sequentially activated during differentiation, initially by C/EBPbeta and C/EBPdelta and later by C/EBPalpha (autoactivation). These events are mediated by a C/EBP regulatory element in the promoter of the C/EBPalpha gene. This article presents evidence that members of the Sp family, notably Sp1, act repressively on the C/EBPalpha promoter prior to the induction of differentiation. Sp1 was shown to bind to a GC box at the 5' end of the C/EBP regulatory element in the C/EBPalpha promoter and, in so doing, to competitively prevent binding to and transactivation of the promoter by the C/EBPs. One of the differentiation inducers methylisobutylxanthine (a cAMP phosphodiesterase inhibitor) or Forskolin, both of which increase the cellular cAMP level, causes down-regulation of Sp1. This decrease in Sp1 level early in the differentiation program appears to facilitate access of C/EBPbeta and/or C/EBPdelta to the C/EBP regulatory element and, thereby, derepression of the C/EBPalpha gene.

LYS49 phospholipase A2 myotoxins lyse cell cultures by two distinct mechanisms

Three Lys49 phospholipase A2 (PLA2) myotoxins from Agkistrodon contortrix laticinctus (ACLMT), Bothrops jararacussu (bothropstoxin-I) and Bothrops asper (myotoxin II) snake venoms are enzymatically inactive on artificial substrates, yet addition of these toxins to cell cultures causes the release of fatty acids derived from the hydrolysis of membrane phospholipids. Bothropstoxin-I treated with p-bromophenacyl bromide is no longer enzymatically active on cell cultures, suggesting the toxin, not tissue PLA2, may hydrolyze the phospholipids. The NB41A3 cell line is sensitive to lysis by ACLMT by two separate mechanisms. The first mechanism is predominant at lower concentrations of ACLMT (0.1-0.5 microM) and over long incubation periods (24 h) with toxin. This mechanism is antagonized by methylprednisolone (MePDN). The second is predominant at higher concentrations of toxin (1-5 microM) incubated over a short period (1 h) and is not antagonized by MePDN. There is no correlation between enzymatic activity and toxicity at the higher concentrations (5 microM; 1 h) when the enzymatic activity of ACLMT is compared with a noncytolytic PLA2 from Naja naja atra venom (1 microM). However, over a 24 h period, triglyceride formation relative to fatty acids remaining free is about 10-fold greater for ACLMT (ratio about 40:1) than for the PLA2 from Naja naja atra venom (ratio about 4:1), suggesting the two enzymes act on substrates associated with different cellular compartments under this condition. Therefore, two mechanisms of Lys49 PLA2-induced myonecrosis exist and these are dependent on toxin concentration. The MePDN-sensitive mechanism associated with triglyceride accumulation correlates with myotoxicity.

Derepression of the C/EBPalpha gene during adipogenesis: identification of AP-2alpha as a repressor

During adipogenesis, CCAAT/enhancer binding protein alpha (C/EBPalpha) serves as a pleiotropic transcriptional activator of adipocyte genes. Previously, we identified dual repressive elements in the C/EBPalpha gene and a putative transacting factor (C/EBPalpha undifferentiated protein, or CUP) expressed by preadipocytes, but not adipocytes, that bind to these elements. In the present investigation, CUP was purified 17,000-fold from nuclear extracts of 3T3-L1 preadipocytes. Amino acid sequence and mass spectral analysis of tryptic peptides derived from purifed CUP (molecular mass approximately 50 kDa) revealed that the repressor is (or contains) an isoform of the transcription factor, AP-2alpha. Electrophoretic mobility shift and Western blot analysis on purified CUP and preadipocyte nuclear extracts confirmed the identity of CUP as AP-2alpha. Both AP-2alpha protein and CUP binding activity are expressed by preadipocytes and then decrease concomitantly during differentiation of 3T3-L1 preadipocytes into adipocytes. Consistent with a repressive role of AP-2alpha/CUP, an AP-2alpha1 expression vector, cotransfected with a C/EBPalpha promoter-reporter construct into 3T3-L1 adipocytes, inhibited reporter gene transcription. Taken together with previous results, these findings suggest that in preadipocytes the C/EBPalpha gene is repressed by AP-2alpha/CUP, which, upon induction of differentiation, is down-regulated, allowing expression of the gene.

Repression of transcription mediated by dual elements in the CCAAT/enhancer binding protein alpha gene

During adipocyte differentiation, the expression of C/EBPalpha is activated, which in turn serves to transcriptionally activate numerous adipocyte genes. A previous search for cis elements that regulate transcription of the C/EBPalpha gene led to the identification of a potential repressive element within the proximal 5' flanking region of the gene. Nuclear extracts from 3T3-L1 preadipocytes, but not adipocytes, were found to contain a factor, CUP (C/EBPalpha undifferentiated protein), that binds to this site (the CUP-1 site). In the present investigation, we show that C/EBPalpha promoter-luciferase constructs containing both the proximal 5' flanking and the entire 5' untranslated regions of the gene exhibit an expression pattern during adipocyte differentiation comparable to that of the endogenous C/EBPalpha gene. Mutation of the CUP-1 site in these constructs had little effect on reporter gene expression; however, when this mutation was combined with deletion of the 5' untranslated region, reporter gene expression by preadipocytes was dramatically up-regulated. Consistent with this finding, a second CUP binding site (the CUP-2 site) was identified in the 5' untranslated region. Although mutation of either CUP element in constructs containing both the 5' flanking and 5' untranslated region had little effect on reporter gene transcription, mutation of both CUP elements markedly activated transcription. Thus, it appears that dual CUP regulatory elements repress transcription of the C/EBPalpha gene prior to induction of the adipocyte differentiation program.

A subpopulation of estrogen receptors are modified by O-linked N-acetylglucosamine

Estrogen receptors (ER) are ligand-inducible transcription factors regulated by Ser(Thr)-O-phosphorylation. Many transcription factors and eukaryotic RNA polymerase II itself are also dynamically modified by Ser(Thr)-O-linked N-acetylglucosamine moieties (O-GlcNAc). Here we report that subpopulations of murine, bovine, and human estrogen receptors are modified by O-GlcNAc. O-GlcNAc moieties were detected on insect cell-expressed, mouse ER (mER) by probing with bovine milk galactosyltransferase, followed by structural analysis. Wheat germ agglutinin-Sepharose affinity chromatography also readily detected terminal GlcNAc residues on subpopulations of ER purified from calf uterus, from human breast cancer cells (MCF-7), or from mER produced by in vitro translation. These data suggest that greater than 10% of these populations of estrogen receptors bear O-GlcNAc. Site mapping of insect cell expressed mER localized one major site of O-GlcNAc addition to Thr-575, within a PEST region of the carboxyl-terminal F domain. Based upon their relative resistance to both hexosaminidase and to in vitro galactosylation, O-GlcNAc moieties appear to be largely buried on native mER. This dynamic saccharide modification, like phosphorylation, may play a role in modulating the dimerization, stability, or transactivation functions of estrogen receptors.

Melittin and phospholipase A2 from bee (Apis mellifera) venom cause necrosis of murine skeletal muscle in vivo

Melittin and phospholipase A2 (PLA2) from bee (Apis mellifera) venom were rested for their ability to induce necrosis of skeletal muscle cells after intramuscular injection into mice. Light and electron microscopic examination of tissue indicated that both melittin (4 micrograms/g) and bee venom PLA2 (4 micrograms/g) caused necrosis of skeletal muscle cells within 30 min after i.m. injection. Early changes in the cells consisted of delta lesions, indicating a ruptured plasma membrane, and hypercontraction of myofibrils. By 24 hr the affected cells appeared as an amorphous mass of disorganized and disrupted myofibrils contained in an intact basal lamina. To ensure that the myotoxic activity of the melittin preparation was not due to contaminating. PLA2 activity, the preparation was treated with p-bromophenacyl bromide (p-BPB), a known inhibitor of PLA2 activity. The p-BPB-treated melittin was determined to have no detectable PLA2 activity using a sensitive muscle cell culture assay, and it still induced myonecrosis, although to a lesser extent and of a slower onset. Additionally, p-BPB treatment of purified bee venom PLA2 completely inhibited its myotoxic activity. These results indicate that both melittin and bee venom PLA2 are capable of inducing necrosis of skeletal muscle cells upon i.m. injection, and that the catalytic and myotoxic activities of bee venom PLA2 are inihibited by p-BPB. Also, melittin and contaminating PLA2 in the melittin fraction may be acting synergistically to induce a stronger and more rapid myotoxic effect than occurs with either alone.

Similarities and differences in mechanisms of cardiotoxins, melittin and other myotoxins

Myonecrosis induced in vivo by cardiotoxin, melittin, and Asp49 and Lys49 phospholipase A2 (PLA2) myotoxins involves rapid lysis of the sarcolemma, myofibril clumping, and hypercontraction of sarcomeres. In contrast, skeletal muscle necrosis induced by crotamine and myotoxin a is much slower, consisting of mitochondrial and sarcoplasmic reticulum swelling, myofibril degeneration, and lack of sarcolemma or transverse tubule damage. The mechanisms contributing to the myonecrosis induced by these peptides were evaluated. Two cardiotoxins and two Lys49 PLA2 myotoxins lysed primary cultures of human skeletal muscle within 24 hr at a concentration of 0.25 microM, while melittin, crotamine, and myotoxin a, and an Asp49 PLA2 myotoxin were non-cytolytic at concentrations up to 5.0 microM, suggesting that cytolysis is not a good measure of myotoxicity. Crotamine and the Lys49 PLA2 myotoxin altered Ca2+ ion flux in human heavy sarcoplasmic reticulum by opening the ryanocine receptor. Whole-cell patch-clamp studies demonstrated that administrating crotamine intracellularly increased Na+ currents. Free fatty acids, liberated by activation of tissue phospholipase C or by the PLA2 activity of the myotoxins, were monitored for crotamine, myotoxin a and a Lys49 PLA2 myotoxin in cell cultures in which the lipids had been radiolabeled. Only the Lys49 myotoxin produced significant amounts of fatty acid in cell cultures, supporting a potential role for fatty acid production only in the mechanism of sarcolemma-destroying myotoxins. These findings, coupled with those in the literature, support a hypothesis in which the myotoxins and/or products of lipase activity (e.g. fatty acids) are acting at a site existing on both the Na+ channel and a protein involved in Ca2+ release and probably serving a modulatory function for ion regulation. Based on the similarities in mechanisms between the toxins and fatty acids, the most likely site would be a fatty acid binding site on the protein (either similar to that on fatty acid binding proteins, or an acylated cysteine residue) or in the membrane.

Presynaptically acting snake venom phospholipase A2 enzymes attack unique substrates

Synaptosomes were incubated with bovine serum albumin (BSA) to examine whether the presynaptic action of snake venom phospholipase A2 (PLA2) toxins is due either to the release of fatty acids resistant to extraction by BSA or to the liberation of a specific fatty acid type. In the presence of BSA (0.5% or 1.0%) two PLA2 enzymes from Naja naja atra and Naja naja kaouthia snake venoms that do not have a predominant presynaptic action at the neuromuscular junction (PS-) did not stimulate acetylcholine (ACh) release from synaptosomes. In contrast, two PLA2 enzymes (beta-bungarotoxin, scutoxin) that do have a predominant presynaptic action at the neuromuscular junction (PS+) did stimulate ACh release. BSA did not antagonize PS- enzymes by more efficiently extracting the fatty acids produced by these enzymes relative to PS+ enzymes. While absolute amounts of total and unsaturated fatty acid produced overlapped for the PS- and PS+ enzymes, the two PS+ enzymes produced a significantly greater absolute amount and relative percentage of palmitic acid (16:0) than did either of the PS- enzymes. However, the levels of free palmitic acid remaining in the synaptosomes where they would exert effects on ACh release were similar for the N. n. kaouthia PLA2 (PS-) and beta-bungarotoxin (PS+). Therefore, the total (supernatant plus synaptosomal) amount of palmitic acid produced per se did not account for stimulation of ACh release, since the greater amounts produced by the PS+ enzymes were removed from the synaptosomes by BSA. The production of higher levels of palmitic acid suggests either that PS+ enzymes gain access to sites containing phospholipid substrates unavailable to the PS- enzymes, or that they have a different substrate preference. These findings suggest new possibilities for the mechanism of PS+PLA2 action, including site-directed enzymatic activity and protein acylation.

No role for enzymatic activity or dantrolene-sensitive Ca2+ stores in the muscular effects of bothropstoxin, a Lys49 phospholipase A2 myotoxin

The role of low levels of phospholipase A2 (PLA2) activity and intracellular Ca2+ stores in the pharmacological action of bothropstoxin (BthTX), a myotoxic Lys49 PLA2 homologue isolated from the venom of Bothrops jararacussu, was investigated. We examined the muscular effects of BthTX in the mouse diaphragm and its PLA2 activity in radiolabeled human and rat primary cultures of skeletal muscle. Although it is a Lys49 PLA2 homologue, BthTX had a low, but easily detectable, level of enzymatic activity relative to two Asp49 PLA2 enzymes from Naja naja kaouthia and Naja naja atra venoms, and this activity was reduced by about 85% in the presence of Sr2+ (4.0 mM). However, the replacement of 1.8 mM Ca2+ by 4 mM Sr2+ did not alter the BthTX-induced contracture and blockade of the muscle twitch tension. In addition, Sr2+ decreased by 50% the time required to cause 50% paralysis, and evoked approximately a four-fold increase in the number of spontaneous spikes. In isolated sarcoplasmic reticulum preparations, BthTX opened the intracellular Ca2+ release channel (ryanodine receptor) and lowered the threshold of Ca(2+)-induced Ca2+ release by a second, as yet unidentified, mechanism. However, in intact muscle, dantrolene, an antagonist of some forms of intracellular Ca2+ release, had no effect on the actions of BthTX. These findings do not support any role for the low levels of PLA2 activity, or dantrolene-sensitive intracellular Ca2+ stores, in the action of BthTX. The mechanism whereby Sr2+ stimulates the pharmacological activity of BthTX remains to be clarified.

Bovine serum albumin does not completely block synaptosomal cholinergic activities of presynaptically acting snake venom phospholipase A2 enzymes

Bovine serum albumin (BSA), which binds fatty acids, was used to test the contribution of free fatty acid to the presynaptic toxicity of phospholipase A2 (PLA2) enzymes. The effects of BSA on inhibition of [14C]choline uptake and stimulation of [14C]acetylcholine (ACh) release in synaptosomes by PLA2 enzymes that do not have a predominant presynaptic action at the neuromuscular junction (PS-) were compared with those on the cholinergic actions of PLA2 enzymes that do have a predominant presynaptic action at the neuromuscular junction (PS+). The inhibition of choline uptake by the Naja naja atra PLA2, a PS- PLA2, was completely antagonized by BSA (0.5%); whereas that by beta-bungarotoxin, a PS+ PLA2, was unaffected by BSA. The inhibition of choline uptake by two other PS+ PLA2 toxins (scutoxin and pseudexin) was partially antagonized by BSA. The effects of the PLA2 enzymes were antagonized in the same manner by BSA whether on Na(+)-dependent or on Na(+)-independent choline uptake. Likewise, the stimulation of ACh release by two PS- PLA2 enzymes (from Naja naja atra and Naja naja kaouthia snake venoms) was completely blocked by BSA; whereas that by beta-bungarotoxin was unaffected and that by scutoxin and pseudexin was only partially antagonized by BSA. The results suggest that the PS- PLA2 enzymes are completely dependent on fatty acid production for their cholinergic toxicity and that BSA can be used to investigate further the neurotoxic mechanisms of PS+ PLA2 enzymes in synaptosomes.

Antibodies having markedly different effects on enzymatic activity and induction of acetylcholine release by two presynaptically-acting phospholipase A2 neurotoxins

The enzymatic and acetylcholine-releasing activities of two presynaptically-acting phospholipase A2 neurotoxins (pseudexin B and scutoxin) were studied in a synaptosomal fraction. Scutoxin (100 nM) induced greater [14C]acetylcholine release than did pseudexin B (100 nM). Both toxins caused fatty acid production in the synaptosomal fraction, although pseudexin B was more active than scutoxin. One monoclonal antibody raised against pseudexin B (#4) had no effect on the enzymatic activity of either pseudexin B or scutoxin. Two other monoclonal antibodies (#3 and #7), also raised against pseudexin B, antagonized the enzymatic activity of pseudexin B and scutoxin. Monoclonal antibody #3 was more effective than #7 in reducing the amount of acetylcholine released by the toxins, whereas #7 was more effective than #3 in reducing fatty acid production. Although antibody #3 caused complete inhibition of phospholipase A2 activity of pseudexin B on purified substrates, it only reduced phospholipase A2 activity by 35% in synaptosomes. These findings support the hypothesis that gross phospholipase A2 activity does not play a role in stimulation of acetylcholine release by the presynaptically-acting phospholipase A2 neurotoxins.

Possible mechanisms of action of cobra snake venom cardiotoxins and bee venom melittin

Cobra snake venom cardiotoxins and bee venom melittin share a number of pharmacological properties in intact tissues including hemolysis, cytolysis, contractures of muscle, membrane depolarization and activation of tissue phospholipase C and, to a far lesser extent, an arachidonic acid-associated phospholipase A2. The toxins have also been demonstrated to open the Ca2+ release channel (ryanodine receptor) and alter the activity of the Ca(2+)+Mg(2+)-ATPase in isolated sarcoplasmic reticulum preparations derived from cardiac or skeletal muscle. However, a relationship of these actions in isolated organelles to contracture induction has not yet been established. The toxins also bind to and, in some cases, alter the function of a number of other proteins in disrupted tissues. The most difficult tasks in understanding the mechanism of action of these toxins have been dissociating the primary from secondary effects and distinguishing between effects that only occur in disrupted tissues and those that occur in intact tissue. The use of cardiotoxin and melittin fractions contaminated with trace ('undetectable') amounts of venom-derived phospholipases A2 has continued to be common practice, despite the problems associated with the synergism between the toxins and enzymes and the availability of methods to overcome this problem. With adequate precautions taken with regard to methodology and interpretation of results, the cobra venom cardiotoxins and bee venom melittin may prove to be useful probes of a number of cell processes, including lipid metabolism and Ca2+ regulation in skeletal and cardiac muscle.

Characterization of a novel trans-sialidase of Trypanosoma brucei procyclic trypomastigotes and identification of procyclin as the main sialic acid acceptor

Here we report the presence of a trans-sialidase on the surface of Trypanosoma brucei culture-derived procyclic trypomastigotes. The enzyme is not detected in lysates of bloodstream trypomastigotes enriched for either stumpy or slender forms. The trans-sialidase catalyzes the transfer of alpha(2-3)-linked sialic acid residues to lactose. beta-galactopyranosyl residues are at least 100 times better acceptors for sialic acid than alpha-galactopyranosyl residues. In the absence of efficient acceptors, the purified enzyme transfers sialic acid to water, i.e., it acts as a sialidase. Although the T. cruzi and T. brucei trans-sialidases have very similar donor and acceptor specificities, they are antigenically distinct. Sodium dodecyl sulfate-polyacramide gel electrophoresis under nonreducing conditions and silver staining of the purified trans-sialidase reveals a single band of 63 kD. When the surface membrane of live procyclic trypomastigotes is trans-sialylated, using radioactive sialyllactose as the donor substrate, it appears that the only sialylated surface molecule is procyclin. Pronase treatment of live parasites removes only part of the surface sialic acid, in agreement with recent data showing that the glycosylphosphatidylinositol anchor of procyclin is sialylated (Ferguson, M. A. J., M. Murray, H. Rutherford, and M. J. McConville. 1993. Biochem. J. In press).

Adrenal carcinoma tumor progression and penultimate cell surface oligosaccharides

Many previous studies have implicated cell surface saccharides, and sialylglycoconjugates in particular, as important mediators of tumor cell metastasis. In this report, we have used three different specific sialidases and a highly sensitive high-performance liquid chromatographic sialic acid assay to probe the cell surfaces of several murine adrenal carcinoma variants. In contrast to several earlier studies on other metastatic variants, we find no significant differences in the overall levels of cell surface or total cellular sialic acid among three Y1 murine adrenal carcinoma variants with widely different metastatic phenotypes. However, using highly purified, linkage-specific sialyltransferases, in conjunction with V. cholerae sialidase, to probe the cell surface saccharide topography of specific penultimate oligosaccharides, we do find striking differences in oligosaccharide structures underlying the sialic acid moieties. Two tumorigenic and metastatic variants (F2 and F4) contain about 6-fold more penultimate Gal beta 1----4GlcNAc sialylation sites than a related tumorigenic but nonmetastatic variant (HSR) when CMP-[3H]-N-acetylneuraminic acid and the Gal beta 1----4GlcNAc alpha 2,6 sialyltransferase are used to probe the adrenal carcinoma cell surfaces. The metastatic variants also are found to contain 4- to 4.5-fold more Gal beta 1----3GalNAc sialylation sites than the nonmetastatic variant when the Gal beta 1----3GalNAc alpha 2,3 sialyltransferase is used as a cell surface probe. Earlier work, which used the same sialyltransferase probes on sialidase-treated murine melanoma variants (A. Passaniti and G. W. Hart, J. Biol. Chem., 263: 7591-7603, 1988), also showed similar quantitative differences in penultimate structures between metastatic variants. However, in contrast to the adrenal carcinoma cells, the highly metastatic melanoma cells have severalfold lower levels of sialylatable penultimate Gal beta 1----4GlcNAc and Gal beta 1----3GalNAc saccharides compared to their nonmetastatic counterparts. Thus, while the precise structural alterations or surface accessibilities of penultimate saccharides appear to be cell type dependent, these results suggest that pronounced changes in penultimate cell surface sialo-oligosaccharide moieties occur during progression to a malignant phenotype in two widely different tumor systems. These types of alterations in the underlying penultimate oligosaccharide structures of cell surface sialoglycoconjugates may be a common feature of highly metastatic cells arising from very different tumor cell types.

Preliminary evidence for a postsynaptic action of beta-bungarotoxin in mammalian skeletal muscle

Two hours after treatment with beta-bungarotoxin (0.34-0.4 microM), when there was complete neuromuscular block, the peak contracture response to 50 microM succinylcholine was significantly reduced by about 35% in the mouse phrenic nerve-diaphragm preparation. Additionally, significant phospholipase A2 activity was detected on primary cell cultures from skeletal muscle which were incubated for 2 hr with concentrations of beta-bungarotoxin greater than or equal to 0.1 microM. Thus, beta-bungarotoxin appears to have pharmacologically and biochemically detectable postsynaptic actions in mammalian muscle systems.

A novel cell surface trans-sialidase of Trypanosoma cruzi generates a stage-specific epitope required for invasion of mammalian cells

When trypomastigotes of T. cruzi emerge from cells of the mammalian host, they contain little or no sialic acids on their surfaces. However, rapidly upon entering the circulation, they express a unique cell surface trans-sialidase activity. This enzyme specifically transfers alpha (2-3)-linked sialic acid from extrinsic host-derived macromolecules to parasite surface molecules, leading to the assembly of Ssp-3, a trypomastigote-specific epitope. The T. cruzi trans-sialidase does not utilize cytidine 5' monophospho-N-acetylneuraminic acid as a donor substrate, but readily transfers sialic acid from exogenously supplied alpha (2-3)-sialyllactose. Monoclonal antibodies that recognize sialic acid residues of Ssp-3 inhibit attachment of trypomastigotes to host cells, suggesting that the unusual trans-sialidase provides Ssp-3 with structural features required for target cell recognition.

Snake venom cardiotoxins and bee venom melittin activate phospholipase C activity in primary cultures of skeletal muscle

The effects of cardiotoxin fractions from Naja naja kaouthia and Naja naja atra snake venoms and synthetic melittin peptide were examined on lipolytic activity in red blood cells and primary skeletal muscle cultures. Both native cardiotoxin fractions caused considerable production of free fatty acids in red blood cells. This production was abolished when the fractions were first treated with p-bromophenacyl bromide to reduce the venom phospholipase A2 activity contamination. In equine and human primary cultures of skeletal muscle, the N. n. kaouthia cardiotoxin (10 microM) and melittin (2 microM) caused a breakdown of phospholipids and production of free fatty acids and diacylglycerol in the absence of lysophospholipid formation. Additionally, melittin at higher concentrations (10 microM) caused triglyceride breakdown. These studies do not support the suggestion that snake venom cardiotoxins and melittin selectively activate endogenous phospholipase A2 activity. Instead, the toxins primarily activate endogenous phospholipase C activity and, in the case of melittin at high concentrations, triglyceride lipase activity.

Effects of a cardiotoxin from Naja naja kaouthia venom on skeletal muscle: involvement of calcium-induced calcium release, sodium ion currents and phospholipases A2 and C

Snake venom cardiotoxin (CTX) fractions induce contractures of skeletal muscle and hemolysis of red blood cells. The fractions also contain trace amounts of venom-derived phospholipase A2 (PLA2) contamination and activate tissue phospholipase C (PLC) activity. The present study examines the mechanisms of action of a CTX fraction from Naja naja kaouthia venom in skeletal muscle. Sphingosine competitively antagonized CTX-induced red blood cell hemolysis, but not skeletal muscle contractures. CTX rapidly lowered the threshold for Ca(2+)-induced Ca2+ release in heavy sarcoplasmic reticulum fractions, as monitored with arsenazo III. There was also a slower time-dependent reduction of Na+ currents, as assessed by whole cell patch-clamp techniques. The CTX fractions elevated levels of free fatty acids and diacylglycerol for 2 hr in primary cultures of human skeletal muscle by a combined action of venom-derived PLA2 contamination in the fraction and activation of endogenous PLC activity. The activation of tissue PLC activity could be readily distinguished from the contribution of the venom PLA2 by p-bromophenacyl bromide treatment of CTX fractions. The mechanism of action involved in contractures of skeletal muscle appears to be related to the immediate and specific effect of CTX (Ca2+ release by the sarcoplasmic reticulum), while the mechanisms involved in hemolysis of red blood cells and decreased Na+ currents in skeletal muscle most likely relate to long-term effects on lipid metabolism.

Immunochemical cross-reactivity of two phospholipase A2 neurotoxins, agkistrodotoxin and crotoxin

Polyclonal rabbit antisera were raised against the phospholipase A2 neurotoxin agkistrodotoxin (AGTX) from Agkistrodon blomhoffii brevicaudus venom and against the phospholipase A2 subunit (component-B, CB) of crotoxin from Crotalus durissus terrificus venom. Anti-AGTX antibodies cross-reacted strongly with crotoxin and crotoxin-like molecules and more weakly with other phospholipases A2 from the venoms of Viperidae and Crotalidae. On the other hand, anti-CB antibodies cross-reacted with AGTX, and also recognized ammodytoxin A and the phospholipase A2 from Vipera berus venom, but not other phospholipases A2 from Crotalidae and Viperidae. Anti-AGTX and anti-CB antibodies were able to inhibit the phospholipase A2 activity and to neutralize the lethal potency of the homologous and heterologous toxins (AGTX or crotoxin). Immunoaffinity chromatography columns were used to isolate anti-AGTX antibodies which recognized CB (91% of the total anti-AGTX antibodies), and anti-CB antibodies which recognized AGTX (52% of the total anti-CB antibodies). Immunochemical investigations performed with each type of antibody indicated that the majority of AGTX antigenic determinants are present on crotoxin component-B and on phospholipases A2 from Viperidae venoms, and that some of these determinants are involved in the neutralization of lethal potency and in the inhibition of enzymatic activity of AGTX and crotoxin.

Contribution of bee venom phospholipase A2 contamination in melittin fractions to presumed activation of tissue phospholipase A2

Melittin from bee venom has been suggested to activate tissue phospholipase A2 (PLA2) activity, and subsequently has been used as a specific PLA2 probe. The melittin in most cases was obtained commercially and used without further purification or treatment. To test the hypothesis that commercially obtained melittin specifically activates tissue PLA2, we radiolabeled the lipids of immortalized epithelial cells by incubating the cells for 22 hr with 14C-linoleic acid. The cells were then incubated with 2 microM melittin, 2nM bee venom PLA2, 2 microM melittin treated with p-bromophenacyl bromide (p-BPB) or PLA2 plus p-BPB-treated melittin. Lipids were extracted and separated by thin-layer chromatography. The radioactivity in each lipid fraction was then quantitated. The melittin-stimulated PLA2 activity observed in cells was primarily associated with phosphatidylcholine. Fatty acid release was decreased by 75% when the melittin fraction was pretreated with p-BPB to reduce contaminating venom PLA2 activity. Adding PLA2 to the p-BPB-treated melittin at an amount about equal to the original contamination (0.1%) resulted in the same PLA2 activity in cell as observed with the untreated melittin fraction. These findings suggest that bee venom PLA2 contamination, even at very low levels, can account for approximately 75% of the PLA2 activity in cells treated with commercial melittin fractions.

Interactions in red blood cells between fatty acids and either snake venom cardiotoxin or halothane

Phospholipase A2 (PLA2) activity enhances snake venom cardiotoxin (CTX)-induced and general anesthetic (halothane)-induced hemolysis of red blood cells. In the case of halothane-induced hemolysis, this effect appears to be related primarily to free fatty acids. In the present study, the interaction between CTXs and halothane and the effects of different free fatty acids on cardiotoxin and halothane-induced hemolysis were examined. The hemolytic actions of halothane and a CTX from Naja naja kaouthia venom were examined in erythrocytes with different phospholipid and free fatty acid composition from five species. The extent of hemolysis by CTX or halothane was dependent upon the species examined and appeared to be inversely related to the amount of saturated free fatty acid in the membrane. The order of susceptibility of red blood cells from five species to hemolysis was similar for halothane- and N. n. kaouthia CTX-induced hemolysis, but very different for osmotic fragility. The slope of the hemolysis dose-response curve was considerably steeper for halothane than for CTX. Hemolysis due to N. n. kaouthia CTX was greatly increased by halothane in erythrocytes from humans and horses and to a lesser extent in erythrocytes from sheep, goats and cows. Hemolysis induced by halothane and the N. n. kaouthia or Naja naja atra CTXs was enhanced by unsaturated fatty acids. In contrast, hemolysis induced by halothane was decreased and that caused by the two CTXs was relatively unaffected by saturated fatty acids. Halothane and CTXs differ in their exact mechanisms, but appear to act upon similar fatty acid-sensitive processes.

Neutralization of lethal potency and inhibition of enzymatic activity of a phospholipase A2 neurotoxin, crotoxin, by non-precipitating antibodies (Fab)

Rabbit antibodies were prepared against both purified catalytic (component-B) and purified non-catalytic (component-A) subunits of crotoxin, the major phospholipase A2 neurotoxin from the South American rattlesnake. They cross-react with crotoxin-like toxins from the venom of several Crotalus species as well as with single-chain phospholipase A2 neurotoxins from Crotalid and Viperid venoms (agkistrodontoxin and ammodytoxin A) but not from Elapid venoms (notexin). Immunological cross-reactions of anti-component-A and anti-component-B sera with crotoxin and with its isolated components A and B showed that component-A exposes determinants of low immunogenicity which are present on component-B, whereas the major antigenic determinants of component-B are not present on component-A. Anti-component-B antibodies, but not anti-component-A antibodies, neutralize the lethal potency of crotoxin and inhibit its enzymatic activity. Furthermore, non-precipitating anti-component-B Fab fragments were as potent as antibodies, indicating that crotoxin neutralization results from the binding of the antibodies to the catalytic subunit, rather than the formation of an immunoprecipitate.

Effect of a phospholipase A2 with cardiotoxin-like properties, from Bungarus fasciatus snake venom, on calcium-modulated potassium currents

The action of a 16,300 mol. wt phospholipase A2 with cardiotoxin-like properties from Bungarus fasciatus venom on membrane electrical properties of two human cell types was examined in vitro by using tight-seal whole-cell recording methods. Epithelial cells exhibited a voltage- and Ca2(+)-activated K+ current; the sensitivity for voltage activation of the K+ current was enhanced by increasing free Ca2+ in the recording pipette from 10(-8) M to 2 x 10(-6) M. In contrast, peripheral blood lymphocytes possessed voltage-activated K+ currents that were inhibited by increasing intracellular Ca2+. Exposure of either preparation to B. fasciatus toxin (0.2-5 x 10(-6) M) for up to 30 min in the bath did not alter membrane leakage current, as judged by the maintenance of low pre-treatment values over the range of -140 mV to -40 mV. However, the sensitivity for voltage activation of the K+ current was enhanced in the epithelial cells even at the lowest concentrations tested. In contrast to the results with epithelial cells, toxin exposure inhibited the activation of voltage-activated K- currents in human lymphocytes, suggesting a specific increase in intracellular Ca2- levels in both cell types. The fluorescent probe indo-1/AM was used to monitor cytoplasmic Ca2+ levels. Exposure of either lymphocytes or epithelial cells to toxin (10(-6) M) resulted in a transient increase in Ca2+. However, while the Ca2+ response to toxin was transient, K-channel modulation by the toxin appeared to be irreversible over the experimental time course. The longer-lasting modulation of Ca2(+)-regulated K+ channels may reflect an irreversible action of the B. fasciatus phospholipase A2 on a Ca2+-dependent regulatory process.

Effects of divalent cations on snake venom cardiotoxin-induced hemolysis and 3H-deoxyglucose-6-phosphate release from human red blood cells

At a low concentration of Naja naja kaouthia cardiotoxin (3 microM) Ca2+, Sr2+ and Ba2+ (2 mM), had little to no effect on 3H-deoxyglucose-6-phosphate (3H-dGlu-6-p) or hemoglobin release. At higher concentrations of N. n. kaouthia cardiotoxin (greater than or equal to 10 microM), Ca2+ (2 mM), but not Sr2+ or Ba2+, significantly enhanced 3H-dGlu-6-p and hemoglobin release. Mn2+ (2 mM) almost completely inhibited 3H-dGlu-6-p release and hemolysis at both the 3 microM and 10 microM concentrations of cardiotoxin. At a fixed concentration of N. n. kaouthia cardiotoxin (3 microM). Ca2+ at low concentrations (0.5 mM) enhanced 3H-dGlu-6-p and hemoglobin release, but at higher concentrations caused a dose-dependent inhibition of cardiotoxin action. The cardiotoxin from N. n. kaouthia venom (3 microM) induced 3H-dGlu-6-p release and hemolysis release with similar time courses and to similar extents. 3H-dGlu-6-p release induced by cardiotoxin was greatly enhanced as the pH of the medium was increased from 7.0 to 8.5. Similarities between 3H-dGlu-6-p and hemoglobin release do not support opening of pores in the plasmalemma of all red blood cells as the mode of action of cardiotoxins, but suggests that complete lysis of a subpopulation of cells occurs. Cardiotoxins have two components of lysis, only one of which is Ca2+-dependent. The Ca2+-dependent lysis is only evident at higher cardiotoxin concentrations and is likely due to trace phospholipase A2 contamination in the toxin fraction. Mn2+ is an effective antagonist of cardiotoxin action.

Factors influencing the hemolysis of human erythrocytes by cardiotoxins from Naja naja kaouthia and Naja naja atra venoms and a phospholipase A2 with cardiotoxin-like activities from Bungarus fasciatus venom

The effects of red blood cell age and incubation conditions (temperature, divalent cation type and concentration, pH and glucose) on hemolysis induced by cardiotoxin fractions from Naja naja atra and Naja naja kaouthia venoms, a phospholipase A2 with cardiotoxin-like activities from Bungarus fasciatus venom and bee venom phospholipase A2 were examined. Hemolysis by the snake venom toxins was dependent on red blood cell age (aged more susceptible than fresh) and the temperature of incubation (37 degrees C greater than 20 degrees C). Divalent cations at 0.5-2.0 mM enhanced (Ca2+) or slightly decreased (Sr2+, Ba2+) hemolysis due to N. n. kaouthia and N. n. atra toxins, and greatly decreased (Ca2+, Sr2+, Ba2+) hemolysis by these toxins at higher concentrations (5-40 mM). For the B. fasciatus phospholipase A2, Ba2+ and Sr2+ could not fully support hemolysis in any concentration while both low (less than 0.5 mM) and high (greater than 40 mM) Ca2+ enhanced hemolysis. Bee venom phospholipase A2 only induced hemolysis (greater than 10% at greater than 40 mM) at high concentrations of Ca2+. Increasing the pH from 7.5 to 8.5 greatly increased the levels of hemolysis by the snake venom toxins and enzyme. Glucose (5.3 mM) increased hemolysis by the snake venom components at low concentrations of divalent cations (2 mM) and slightly decreased hemolysis at high concentrations (40 mM). Treatment with p-bromophenacyl bromide abolished phospholipase A2 activity of bee venom and B. fasciatus phospholipases, but did not affect hemolytic potency of N. n. kaouthia or B. fasciatus toxins. A similar mechanism, which is independent of phospholipase A2 activity, may be involved in hemolysis by the N. n. kaouthia and N. n. atra cardiotoxins. The B. fasciatus cardiotoxin-like phospholipase A2 appears to have two mechanisms of hemolysis; the first is similar to that of the two typical cardiotoxins and the second appears dependent on phospholipase A2 activity and is only evident at high Ca2+ concentrations.

Effects of a toxic phospholipase A2 (AgTx) from the venom of the Pit viper (Agkistrodon halys (Pallas)) on the crayfish stretch receptor neuron

Neurotoxicity of an isolated fraction (V) of the venom from the snake Agkistrodon halys (Pallas) was studied on the crayfish stretch receptor using a two-electrode voltage-clamp technique. The toxin was previously shown to have less phospholipase A2 activity but to be more toxic in mice compared with bee venom phospholipase A2. At 5 micrograms ml-1 (0.35 microM) the AgTx had very little effects on the electrophysiological properties of the receptor neuron whereas at 50 micrograms ml-1 (3.5 microM) the leak conductance was increased about three times and the net outward (K) current was reduced to 70% of control. The net inward (Na) current was not affected except for a small (+ 10 mV) shift in the I-V relationship. The resting membrane potential and the membrane capacitance were not changed by AgTx. These effects of AgTx were similar to those seen after exposure to bee venom phospholipase A2 at concentrations 10-20 times lower. At concentrations of AgTx which presynaptically affect the frog neuromuscular transmission (5-10 micrograms ml-1) the effects on ion channels in the stretch receptor neuron are very small and probably reflect the low phospholipase A2 activity compared with that of bee venom phospholipase A2.

Interaction with chick myotube cholinergic receptors of an alpha-neurotoxin isolated from venom of the banded krait (Bungarus fasciatus)

A postsynaptic acting short chain alpha-toxin, B.f. III, was isolated from venom of the banded krait (Bungarus fasciatus) using ion-exchange chromatography. The toxin, a basic protein (pI = 10) has an apparent molecular weight of 6,500 as determined by SDS-polyacrylamide gel electrophoresis. It shares immunological determinants with alpha-bungarotoxin, as it cross-reacted with antibodies raised in rabbits against alpha-bungarotoxin. B.f. III inhibits binding of 125I-alpha-bungarotoxin to cultured chick myotubes with an IC50 of 3 X 10(-10) M. The rate of association with chick myotube nAChR was 3 times faster than that of alpha-bungarotoxin, and binding was slowly reversible. The toxin is a less potent antagonist than alpha-bungarotoxin; in ion flux experiments, measuring influx of 86Rb in chick myotubes, B.f. III inhibited carbachol-induced influx of 86Rb (IC50 = 5 X 10(-9) M) at concentrations higher than those needed for alpha-bungarotoxin (IC50 = 6 X 10(-10) M).

Membrane endopeptidases of human neutrophil

Recent studies using inhibitors or synthetic substrates of serine protease suggest that membrane protease activity may be essential for neutrophil chemotaxis, phagocytosis, degranulation, and superoxide production. However, little is known about the nature and localization of the proteases. In this study, we demonstrated that intact human neutrophils hydrolyzed [125I]glucagon. The degradation of glucagon was temperature dependent and was not dependent on the release of lysosomal enzymes. Two endopeptidases were demonstrated: a metalloendopeptidase which accounted for two thirds of the intact cell activity, and a serine endopeptidase, accounting for the rest of the activity. Both enzymes had a neutral to alkaline pH optimum (pH 7-9). The metalloendopeptidase had a Km of 15.3 microM and Vmax of 5.9 nmol/5 X 10(6) cells/45 min. The corresponding values for the serine endopeptidase were 33.3 microM and 5.0 nmol/5 X 10(6) cells/45 min, respectively. Inhibition of the membrane metalloendopeptidase or serine endopeptidase by 1,10-phenanthroline or diisopropylfluorophosphate, respectively, did not inhibit the production of superoxide by phorbol myristate acetate-stimulated neutrophils.

Localization of abscess with an iodinated synthetic chemotactic peptide

N-formyl Nle-Leu-Phe-Nle-Tyr-Lys is a potent synthetic chemotactic peptide (CP), which binds to chemotactic receptors of neutrophils with high affinity. Because the peptide contains a tyrosine moiety, it can be readily labeled with a radioactive iodine. In this study, we investigated the possibility of abscess localization by i.v. administration of this radioiodinated CP. The peptide was iodinated with 125I using chloramine-T and purified using Bio-Gel P-2 chromatography. The final preparation had a purity of 88.5 +/- 3.8% (n = 6) and a specific radioactivity of 600-800 ci/mM. The iodinated CP bound to rabbit neutrophils specifically; its binding could be prevented by non-labeled CP. When 4-6 ng of 125-I-CP per kg body weight was injected into abscess-bearing rabbits, there was an immediate, but transient neutropenia, followed by a rebound neutrophilia. The abscess to muscle (A/M) ratio was 11.6 +/- 1.1 at 6 hrs and 11.0 +/- 4.7 at 24 hrs after injection; while the abscess to blood (A/B) ratio was 0.9 +/- 0.2 and 3.7 +/- 0.6 at 6 and 24 hrs post injection, respectively. Control animals injected with Na125I revealed an A/M ratio of 2.9 +/- 0.2 and an A/B ratio of 0.9 +/- 0.3 at 6 hrs after injection. Analysis of the radioactivity in the blood after 125I-CP administration, revealed that the majority (less than 87%) of the radioactivity was present as 125I-CP in the plasma fraction. Our results suggest that radioiodinated synthetic CP shows promise for abscess localization. However, further refinement of the method is required.