Biomedical subjects

A Bdolah

Publications and source records attributed to A Bdolah.

At least 19 recordsLinked to original sources

PubMed2000

Recovery from sarafotoxin-b induced cardiopathological effects in mice following low energy laser irradiation.

OBJECTIVE: Low energy laser irradiation has been shown to accelerate various biological processes, including regeneration of injured tissues. In the present work we studied the effect of low energy laser irradiation on ischemic mice hearts, following administration of sarafotoxin-b, a powerful vasoconstrictor peptide of the endothelin/sarafotoxin family. METHODS: Immediately after injection of the toxin and two days later, hearts were exposed to low energy laser irradiation. Eight days after the injection the mice were sacrificed and their hearts were processed for light and electron microscopy. RESULTS: Sarafotoxin-b induced an approximate 2-fold increase in the relative cavity volume of the left ventricle. Low energy laser irradiation of the sarafotoxin-injected mice caused a significant decrease (62%) in the left ventricular dilatation. Electron microscopy of the sarafotoxin-injected mice hearts revealed that the extent of formation of large vacuoles in the cytoplasm of the cardiomyocytes as well as disorganization of the myofibrils were much higher than in the laser irradiated mice. CONCLUSIONS: Our study indicates that low energy laser irradiation enhanced recovery of the damaged cardiomyocytes from the ischemia induced by sarafotoxin-b.

Animals↗

PubMed1998

Positive Darwinian selection in Vipera palaestinae phospholipase A2 genes is unexpectedly limited to the third exon.

The venom of Vipera palaestinae contains a two-component toxin, consisting of an acidic phospholipase A2 (PLA2) and a basic protein. Here we report the cloning and sequence analysis of the complete V. palaestinae PLA2 genes. Since in all Viperidae PLA2 multigene families the 5' and 3' flanking regions are highly conserved, we designed oligonucleotide primers that allow amplification of the whole PLA2 multigene family in a single step. The structural organization of both genes is the same as in the Vipera ammodytes PLA2 multigene family, there being five exons separated by four introns. Comparison of V. palaestinae PLA2 genes with other Viperidae PLA2 genes has shown that the structural organization of the genes and the nucleotide sequence of all introns and flanking regions are highly conserved, whereas the third exon clearly shows a higher number of amino acid replacements, an indication of positive Darwinian selection. The positive Darwinian selection is surprisingly limited to the third exon, in contrast to other Viperidae PLA2 genes, where it is present in all mature protein coding exons.

Amino Acid Sequence↗

PubMed1997

Resistance of the Egyptian mongoose to sarafotoxins.

The Egyptian mongoose (Herpestes ichneumon) is known for its resistance to viperid and elapid venoms. The current work demonstrates that it is also resistant to the venom of Atractaspis and its most toxic component, sarafotoxin-b. Intravenous administration of this toxin, at a dose of about 13 times LD100 for mice, resulted in disturbance in electrocardiograms in the mongoose, which returned to normal after several hours. Sarafotoxin-b failed to induce contraction of mongoose aortal preparations. Endothelin-1, which was demonstrated in tissue extracts of the mongoose by immunological methods, induced contraction of the isolated mongoose aorta. This contraction, however, was greatly reduced when endothelin-1 was applied on top of sarafotoxin-b. Binding studies revealed endothelin/sarafotoxin-specific binding sites in brain and cardiovascular preparations of the mongoose. It is suggested that some structural features of endothelin/sarafotoxin receptors in the mongoose enable them to differentiate between the two peptides.

Animals↗

PubMed1996

Protein and cDNA structures of an acidic phospholipase A2, the enzymatic part of an unusual, two-component toxin from Vipera palaestinae.

In the venom of Vipera palaestinae an unusual, two-component toxin was found. The two components of the toxin are an acidic phospholipase A2 (VpaPLA2) and a basic protein, both with an apparent molecular mass of about 15 kDa. Each component alone is not toxic; however, their mixture is lethal. We have determined the amino acid and cDNA sequences of VpaPLA2. The protein primary structure was solved by sequencing the peptides generated by chemical cleavage of the molecule using CNBr, formic acid and hydroxylamine-hydrochloride and by enzymatic fragmentation with trypsin and chymotrypsin. VpaPLA2 consists of 122 amino acid residues and has all the structural characteristics of subgroup IIA PLA2s. It shows the highest amino acid similarity to a non-toxic phospholipase A2 from Eristocophis macmahoni (82%), whereas the most similar toxic phospholipases A2 share about 70% of residues with VpaPLA2. The substitution of His20 for a hydrophobic residue (Leu) in VpaPLA2 might be one of the reasons that its complex with the basic protein could not be observed.

Amino Acid Sequence↗

PubMed1995

Amino acid sequences of a heterodimeric neurotoxin from the venom of the false horned viper (Pseudocerastes fieldi).

The main toxic component of the venom of the false horned viper, Pseudocerastes fieldi, is a heterodimeric neurotoxin composed of a basic subunit, Cb II, and one of two acidic subunits, either Cb I alpha or Cb I beta. The nontoxic acidic subunit increases the toxicity of the basic subunit. Both subunits have phospholipase A2 (PLA2) amino acid sequences. Cb I alpha and Cb I beta themselves are inactive towards phosphatidylcholine and when complexed with Cb II promote a delay in the onset of phospholipase activity of Cb II. Cb I alpha and Cb I beta do hydrolyze the synthetic substrate, 3-octanoyloxy-4-nitrobenzoic acid, but at < 1% the rate of Cb II. Comparisons of the amino acid sequences of Cb II and Cb I alpha with the corresponding acidic and basic subunits of other heterodimeric neurotoxins show high amino acid sequence identity. Some of the amino acids which are different between the acidic and basic subunits are in highly conserved sequences in their respective types of PLA2. This suggests that these amino acid changes in the conserved regions are important for the structure and function of the heterodimeric proteins.

Amino Acid Sequence↗

PubMed1994

Biological activities of [Thr2]sarafotoxin-b, a synthetic analogue of sarafotoxin-b.

The 21 amino acid sarafotoxins (SRTX) c and d/e as well as endothelin-3 (ET-3) are known to be less toxic and weaker pharmacologically than the other isopeptides SRTX-a, SRTX-b and ET-1. Since SRTX-c, SRTX-d/e and ET-3 possess a Thr instead of a Ser at position 2, we investigated the possibility that this mutation could be responsible for the observed biological differences. Here we show that the synthetic [Thr2]SRTX-b has indeed a lower vasoconstriction efficacy (approximately 35%) in the rabbit aorta, but it is nearly as potent as SRTX-b in toxicity tests and in influencing contraction of the rat uterus. Using monoclonal antibodies directed against the structurally related endothelin-1, we also show that the antigenicity of the analogue is comparable to that of SRTX-b, suggesting that the overall structure of the two peptides is similar, despite the substitution at position 2. We suggest that the Thr2 substitution contributes to the lower activity of the 'weak' peptides in some systems; however, additional substitutions found in the 'weak' peptides of the ET/SRTX family most probably contribute to their low pharmacological activity.

Amino Acid Sequence↗

PubMed1993

Cloning and sequence analysis of cDNAs encoding precursors of sarafotoxins. Evidence for an unusual "rosary-type" organization.

Sarafotoxins (SRTXs) are 21-amino acid peptides structurally and functionally similar to endothelins (ETs). To understand how SRTXs are overproduced in venom glands of the snakes Atractaspis engaddensis and hence used as toxins, we cloned cDNAs encoding SRTXs and elucidated their nucleotide sequences. We predict that SRTX precursors are large prepropolypeptide chains with an unusual "rosary-type" structure made of 12 successive similar stretches of 40 residues (39 in the first stretch). Each stretch begins with a "spacer" of 19 invariant residues (18 in the first stretch) immediately followed by the sequence of one SRTX isoform. Six different isoforms are identified within a single precursor molecule. Maturation of the precursor may require endopeptidases that cleave the Leu-Cys bond and the Trp-Arg/Lys bond invariably found at the SRTX N and C termini, respectively.

Amino Acid Sequence↗

PubMed1993

Sarafotoxins and endothelins: evolution, structure and function.

The venom of the burrowing asp Atractaspis engaddensis contains several 21 amino acid residue peptides known as sarafotoxins. The sarafotoxins are homologous to the mammalian endothelin family, and they have similar biological activities. This review covers recent advances in the study of the chemical and biological properties of the sarafotoxins and endothelins.

Amino Acid Sequence↗

PubMed1992

Involvement of tyrosyl residue(s) in binding of endothelin and sarafotoxin to their receptors in rat brain and heart.

The possible involvement of tyrosyl residue(s) in the binding of endothelins and sarafotoxins to their receptors was examined by the use of tetranitromethane. Incubation of rat cerebellar, hypothalamic, caudate putamen and atrial membranes with the reagent (100 microM, pH 8.1, 20 min) was accompanied by a decrease in their capacity to bind endothelins and sarafotoxin. Experiments employing nitration at different pH values (6.0 vs. 8.1) and studies on the effect of dithiothreitol on the nitrated preparations indicated that the modified residue(s) is most probably a tyrosyl and not a cysteinyl residue, and that there is no oligomerization of the receptors. These data are discussed in relation to the structural data recently obtained by cloning and expression of the endothelin/sarafotoxin receptors.

Amino Acid Sequence↗

PubMed1992

Endothelin and sarafotoxin: influence on steroid-regulated motility of rat uterus.

The sarafotoxins (SRTX) and endothelins (ET) were shown to influence the motility of the isolated rat uterus by inducing an increase in the rate and in the maximum tension of the spontaneous rhythmic contractions and a suppression of the relaxation phase of these contractions. Ovariectomized rats, 24 weeks post-operation, show no spontaneous motility of their uteri and the SRTX/ET peptides induce only a slight tonic increase in the uterine tension. Treatment with 17 beta estradiol restores spontaneous motility and sensitivity to the SRTX/ET peptides in all three contraction modes. It is concluded that the influence of the SRTXs and ETs on uterine motility depends on the hormonal status of the animal.

Animals↗

PubMed1992

The secretion of Duvernoy's gland of Malpolon monspessulanus induces haemorrhage in the lungs of mice.

A toxic protein that induces death of mice with profuse bleeding from the nostrils was isolated from the secretion of Duvernoy's gland of Malpolon monspessulanus (Colubridae). The toxic protein, referred to as CM-b, showed mainly one band on SDS-PAGE corresponding to a mol. wt of 24,000. Its intravenous LD50 in mice was 1 microgram/g and i.v. injections of lethal or sublethal doses induced haemorrhage in the lungs. When injected into the skin of mice, however, the toxin was not haemorrhagic. CM-b showed no proteolytic or procoagulant activity. The nature of this and other components from Duvernoy's secretion of colubrids that cause similar effects remains to be established.

Animals↗

PubMed1992

Activity of sarafotoxin/endothelin peptides in the heart and brain of lower vertebrates.

The effects of sarafotoxin-b (SRTX-b) and endothelin-1 (ET-1) were tested in the fish tilapia (Ore niloticus x O. aureus hybrids) and torpedo (Torpedo ocellata), the toad (Bufo viridis), the agama lizard (Agama stellio) and water snake (Natrix tessellata). In isolated heart preparations of the fish and agama, peptide doses of 0.05-0.5 micrograms/ml induced positive inotropic effects, reduction of the contraction rate and arrhythmia, leading to cardiac arrest. In the toad, a negative inotropic effect and a reduction of the contraction rate were observed, whereas the water snake was hardly affected by either SRTX-b or ET-1. In the agama, an i.v. injection of 15 micrograms of SRTX-b caused changes in the ECG, culminating in A-V block that led to cardiac arrest, while in the toad an injection of 45 micrograms induced only transient disturbances in the ECG. Binding studies with 125I-SRTX-b revealed specific binding sites for SRTX-b and ET-1 in the heart and brain preparations of fish (tilapia and torpedo) and agama, whereas no specific binding could be demonstrated in the toad or in the snake. These results suggest that most vertebrates tested are sensitive to SRTX/ET, while the snake may possess receptors that are of a different structure.

Animals↗

PubMed1992

Paradoxical signal transduction mechanism of endothelins and sarafotoxins in cultured pituitary cells: stimulation of phosphoinositide turnover and inhibition of prolactin release.

Endothelins (ET-1, ET-2, ET-3 and vasoactive intestinal contractor, VIC) and sarafotoxins (SRTX-b and SRTX-c) appear to bind with high affinity to a homogeneous class of binding sites in cultured rat pituitary cells. All of these ligands seem to interact with the same receptor (ETA-R), except for SRTX-c which apparently binds to a separate receptor. Binding was followed by phosphodiesteric cleavage of phosphoinositides, resulting in the formation of inositol phosphates. No consistent effect on basal or gonadotropin-releasing hormone (GnRH)-induced release of luteinizing hormone (LH) was exerted by ET or SRTX during 2 h of static incubation. On the other hand, both groups of vasoactive peptides inhibited basal and thyrotropin-releasing hormone (TRH)-induced prolactin secretion. Surprisingly, activation of phosphoinositide turnover by TRH in pituitary mammotrophs led to stimulation of prolactin secretion, whereas activation of the same pathway by ET or SRTX resulted in inhibition of prolactin secretion. ET and SRTX stimulated inositol phosphate formation in GH3 cell line and in the gonadotroph-like cell line alpha T-3 (which is capable of producing the alpha subunit of the gonadotrophins), indicating that the peptides interact with both pituitary mammotrophs and gonadotrophs. The very low concentrations (nM range) needed to stimulate phosphoinositide turnover and to inhibit prolactin secretion, as well as the recent finding that ETs are present in the hypothalamo-pituitary axis suggest that ET might participate in the neuroendocrine modulation of pituitary functions. One such possibility is that ETs might be members of the prolactin inhibiting factors (PIFs) family.

Animals↗

PubMed1991

Contractile effects and binding properties of endothelins/sarafotoxins in the guinea pig ileum.

Seven of the eight known isopeptides of the endothelin/sarafotoxin (ET/SRTX) family were tested on the isolated guinea pig ileum and found to cause a concentration-dependent increase in basal tone. The rate or the amplitude of the spontaneous rhythmic contractions of the ileal smooth muscle were essentially not affected by any of the peptides. The maximum contraction elicited by vasoactive intestinal contractor (VIC) was slightly stronger than that induced by endothelin-1 (ET-1) or sarafotoxin-b (SRTX-b), and significantly stronger than the maximal contractions elicited by sarafotoxin-a (SRTX-a), sarafotoxin-c (SRTX-c), or endothelin-3 (ET-3). Sarafotoxin-d (SRTX-d) caused, essentially, no contraction but a rather marked relaxation. The potencies of the various peptides to induce the increase in tension, in terms of EC50 values (cumulative effective concentrations that induce half-maximum response), ranged between 6 and 95 nM depending on the peptide. VIC, ET-1, SRTX-b and SRTX-a had similar potencies and were significantly more potent than SRTX-c and ET-3. A high concentration of SRTX-b elicited no additional response when applied to the organ bath after one of the other peptides had shown a maximal effect. Binding experiments with ileal membranes revealed similar binding properties for the various peptides. Competition with iodinated SRTX-b showed no meaningful differences between the various peptides. It is concluded that all the ET/SRTX peptides compete for the same receptor subtype in the ileum. In terms of efficacy, VIC can be considered as a full agonist of this receptor, SRTX-d is probably an antagonist, while all the other peptides behave as partial agonists.

Animals↗

PubMed1991

Kinetic and cross-linking studies indicate different receptors for endothelins and sarafotoxins in the ileum and cerebellum.

Kinetics of ligand/receptor interactions using ET-1, ET-3 and SRTX-b were studied and cross-linking experiments carried out in guinea pig ileum and rat cerebellar preparations. Dissociation studies indicate that the two regions are characterized by different receptor subtypes and different modes of ligand binding. Autoradiographic patterns obtained following cross-linking of ET-1 and ET-3 to the different tissues support these conclusions.

Animals↗

PubMed1991

Evolution of the sarafotoxin/endothelin superfamily of proteins.

Sixteen protein and nucleic acid sequences from the vasoconstrictor sarafotoxin/endothelin/endothelin-like superfamily of peptides were studied, and the evolutionary relationships between the sarafotoxin and endothelin gene families as well as the phylogenetic topology within each gene family and the three endothelin subfamilies was reconstructed. The endothelin gene family has diverged from an ancestral gene that has experienced an exon duplication event followed by two gene duplication events. The sarafotoxins' lineage diverged from the ancestral gene prior to the first endothelin gene duplication event. Analysis of the resulting phylogenetic trees revealed that in several lineages, the peptides have independently accumulated identical replacements in position 2, therefore supporting the hypothesis that residue 2 is crucial to their activity.

Amino Acid Sequence↗

PubMed1991

The evolutionary history of the sarafotoxin/endothelin/endothelin-like superfamily.

The evolutionary relationships among 17 protein and nucleic acid sequences from the sarafotoxin/endothelin/endothelin-like superfamily of peptides were studied. The endothelin/endothelin-like gene family has diverged from an ancestral gene that has experienced an exon duplication event followed by two complete gene duplications. The sarafotoxin lineage diverged from the ancestral gene prior to the first gene duplication event. In several lineages, the peptides have independently accumulated identical amino acid replacements in position 2. This finding supports the hypothesis that residue 2 is crucial to biological activity.

Amino Acid Sequence↗

PubMed1990

Endothelin/sarafotoxin receptor induced phosphoinositide turnover: effects of pertussis and cholera toxins and of phorbol ester.

The induction of phosphoinositide hydrolysis (PI) by endothelin/sarafotoxin (ET/SRTX) receptors in rat heart myocytes was investigated by the use of bacterial toxins as well as a phorbol ester. Both pertussis- and choleratoxin enhanced the stimulation of PI hydrolysis. Phorbol ester treatment of the myocytes for short periods distinguished between two types of PI-hydrolysis, the one induced by endothelins and the other by sarafotoxins. The possible mediation of G-protein (s) in the induction by ET/SRTX receptors of PI-hydrolysis is discussed.

Animals↗