Activities of cobra venom cytotoxins toward heart and leukemic T-cells depend on localized amino acid differences

Anti-Inflammatory and Immune Regulatory Actions of Naja naja atra Venom

Naja naja atra venom (NNAV) is composed of various proteins, peptides, and enzymes with different biological and pharmacological functions. A number of previous studies have reported that NNAV exerts potent analgesic effects on various animal models of pain. The clinical studies using whole venom or active components have confirmed that NNAV is an effective and safe medicine for treatment of chronic pain. Furthermore, recent studies have demonstrated that NNAV has anti-inflammatory and immune regulatory actions in vitro and in vivo. In this review article, we summarize recent studies of NNAV and its components on inflammation and immunity. The main new findings in NNAV research show that it may enhance innate and humoral immune responses while suppressing T lymphocytes-mediated cellular immunity, thus suggesting that NNAV and its active components may have therapeutic values in the treatment of inflammatory and autoimmune diseases.

DNA Aptamers against Taiwan Banded Krait α-Bungarotoxin Recognize Taiwan Cobra Cardiotoxins

Bungarus multicinctus α-bungarotoxin (α-Bgt) and Naja atra cardiotoxins (CTXs) share a common structural scaffold, and their tertiary structures adopt three-fingered loop motifs. Four DNA aptamers against α-Bgt have been reported previously. Given that the binding of aptamers with targeted proteins depends on structural complementarity, in this study, we investigated whether DNA aptamers against α-Bgt could also recognize CTXs. It was found that N.atra cardiotoxin 3 (CTX3) reduced the electrophoretic mobility of aptamers against α-Bgt. Analysis of the changes in the fluorescence intensity of carboxyfluorescein-labeled aptamers upon binding toxin molecules revealed that CTX3 and α-Bgt could bind the tested aptamers. Moreover, the aptamers inhibited the membrane-damaging activity and cytotoxicity of CTX3. In addition to CTX3, other N. atra CTX isotoxins also bound to the aptamer against α-Bgt. Taken together, our data indicate that aptamers against α-Bgt show cross-reactivity with CTXs. The findings that aptamers against α-Bgt also suppress the biological activities of CTX3 highlight the potential utility of aptamers in regard to the broad inhibition of snake venom three-fingered proteins.

Comparison of the primary structures, cytotoxicities, and affinities to phospholipids of five kinds of cytotoxins from the venom of Indian cobra, Naja naja

The molecular mechanism underlying the hemolytic and cytolytic processes of cobra cytotoxins (CTXs) is not yet fully elucidated. To examine this, we analyzed the amino acid sequences, hemolytic and cytotoxic activities, and affinities to phospholipids of the five major CTXs purified from the venom of Indian cobra, Naja naja. CTX2, CTX7, and CTX8 belonged to S-type, and CTX9 and CTX10 to P-type. Comparisons of CTX7 with CTX8 and CTX9 with CTX10 revealed similar primary structures and hemolytic and cytolytic activities. CTX2, whose primary structure was rather different from the others, showed several times weaker hemolytic and cytolytic biological activities than the others. The comparison of CTX2 with CTX7 suggested the importance of Lys30 in loop II for the strong hemolytic and cytolytic activities of S-type CTXs. Cloning of 12 CTX cDNAs from the Naja naja venom cDNA library revealed that 18 out of 23 substitutions found in CTX cDNAs were nonsynonymous. This clearly indicated the accelerated evolution of CTX genes. Multiple sequence alignment of 51 kinds of CTX cDNAs and calculations of nonsynonymous and synonymous substitutions indicated that the codons coding the three loops' regions, which may interact with the hydrophobic tails of phospholipids, have undergone an accelerated evolution. In contrast, the codons coding for amino acid residues considered to participate in the recognition and binding of the hydrophilic head groups of phospholipids, eight Cys residues, and those likely stabilizing β core structure, were all conserved.

Suppression of Inflammation and Arthritis by Orally Administrated Cardiotoxin from Naja naja atra

Cardiotoxin (CTX) from Naja naja atra venom (NNAV) reportedly had analgesic effect in animal models but its role in inflammation and arthritis was unknown. In this study, we investigated the analgesic, anti-inflammatory, and antiarthritic actions of orally administered CTX-IV isolated from NNAV on rodent models of inflammation and adjuvant arthritis. CTX had significant anti-inflammatory effects in models of egg white induced nonspecific inflammation, filter paper induced rat granuloma formation, and capillary osmosis tests. CTX significantly reduced the swelling of paw induced by egg white, the inflammatory exudation, and the formation of granulomas. CTX reduced the swelling of paw, the AA clinical scores, and pathological alterations of joint. CTX significantly decreased the number of the CD4 T cells and inhibited the expression of relevant proinflammatory cytokines IL-17 and IL-6. CTX significantly inhibited the secretion of proinflammatory cytokine IL-6 and reduced the level of p-STAT3 in FLS. These results suggest that CTX inhibits inflammation and inflammatory pain and adjuvant-induced arthritis. CTX may be a novel therapeutic drug for treatment of arthritis.

Roles of lysine residues and N-terminal alpha-amino group in membrane-damaging activity of Taiwan cobra cardiotoxin 3 toward anionic and zwitterionic phospholipid vesicles

In contrast to a slight increase in activity toward phosphatidylcholine (EYPC)/dimyristoyl phosphatidic acid (DMPA) vesicles, guanidination of Naja naja atra cardiotoxin 3 (CTX3) and selective trinitrophenylation of N-terminal alpha-amino group enhanced notably membrane-damaging activity on EYPC/egg yolk sphingomyelin (EYSM) vesicles. Chemically modified CTX3 showed a reduction in its hemolytic activity and cytotoxicity. These reflected that membrane-damaging activity of CTX3 was affected by phospholipid compositions. Phospholipid-binding capability and oligomeric assembly upon binding with lipid vesicles did not closely correlate with membrane-damaging potency of native and modified CTX3. Moreover, different topographical contacts and distinctive modes for the binding of CTX3 and its modified derivatives with anionic phospholipid vesicles (EYPC/DMPA) and zwitterionic phospholipid vesicles (EYPC/EYSM) were observed. Compared with in the case of EYPC/DMPA, the interaction between CTX molecules and EYPC/EYSM was drastically reduced by increasing salt concentration and heparin. Taken together, our data indicate that guanidination of Lys residues and trinitrophenylation of alpha-amino group alter differently the interacted modes upon absorption on anionic phospholipid vesicles and zwitterionic phospholipid vesicles. The findings also suggest that positively charged residues of CTX3 play a distinctive role in damaging anionic and zwitterionic phospholipid vesicles.

Membrane-bound conformation of Naja nigricollis toxin gamma affects its membrane-damaging activity

To address whether the conformational events associated with the absorption of Naja nigricollis toxin gamma on water-lipid interface plays a vital role in its membrane-damaging activity, the present study is carried out. Membrane-damaging activity of toxin gamma on 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC)/1, 2-dimyristoyl-phosphatidic acid (DMPA) vesicles was approximately 13-fold of that on 1, 2-dipalmitoyl-phosphatidylcholine (DPPC)/DMPA vesicles, while the binding affinity of toxin gamma for POPC/DMPA was twofold of that for DPPC/DMPA. Time-resolved fluorescence, acrylamide quenching and Fourier transform infrared spectra showed that POPC/DMPA-bound toxin gamma and DPPC/DMPA-bound toxin gamma did not adopt the same conformation. Moreover, geometrical arrangement of toxin gamma in contact with POPC/DMPA vesicles was different from that with DPPC/DMPA vesicles as evidenced by N-(fluorescein-5-thiocarbamoyl)-1,2-dihexadecanoyl-phosphatidylcholine fluorescence enhancement and cross-linking of membrane-bound toxin gamma. Taken together, our data show that different membrane packing densities arising from phospholipid acyl chain affect membrane-bound conformation of toxin gamma, thus changing its membrane-damaging activity.

The mechanism of cytotoxicity by Naja naja atra cardiotoxin 3 is physically distant from its membrane-damaging effect

In order to dissect out whether multiple activities of cardiotoxins (CTXs) are connected, to some extent, with each other, studies on reduced and S-carboxyamidomethylated (Rcam) Naja naja atra CTX3 were carried out in the present study. Although both CTX3 and Rcam-CTX3 induced apoptotic death of PC-3 cells as evidenced by propodium iodide/annexin V double staining, degradation of procaspases and DNA fragmentation, the cytotoxicity of Rcam-CTX3 was mostly 100-fold lower than that noted with native toxin. However, Rcam-CTX3 retained approximately 38% of the membrane-damaging activity of native toxin as revealed by the decrease in calcein self-quenching from phospholipid vesicles. These results are likely to reflect that the mechanism of cytotoxicity by CTX3 is not heavily dependent on its membrane-perturbing effect, and suggest that the structural elements within CTX3 responsible for the two activities are probably separated.

Evidence that L1AD3, an apoptosis-inducing cyclic peptide, binds a leukemic T-cell membrane protein receptor

Human leukemic T-lymphocytes undergo extensive and rapid apoptosis in the presence of L1AD3, a small cyclic peptide derivative of cobra cardiotoxin. The first step in this process involves its binding to membranes of susceptible cells. By the use of a biotin "handle" synthetically incorporated at the N-terminus of L1AD3, we show that binding is saturable and selective: normal human peripheral blood lymphocytes do not bind this peptide. Fluorescence resonance energy transfer experiments indicate that the binding sites are separated by at least 55 A. Loss of binding occurs if membrane proteins are enzymatically degraded, suggesting that L1AD3's target is a cell-membrane surface protein receptor. Finally, crosslinking of cyclic BTNL1AD3 peptide to a leukemic T-cell membrane surface receptor, as examined using a biotin-avidin blot, indicated a molecular weight of approximately 34,400.

A cyclic peptide, L1AD3, induces early signs of apoptosis in human leukemic T-cell lines

L1AD3 is a small cyclic synthetic peptide designed to resemble the first loop of a cobra venom cytotoxin. Instead of inducing membrane disruption similar to that caused by the parent toxin, L1AD3 promotes extensive and unusually rapid apoptosis in leukemic T-cells without making the plasma membrane permeable to small fluorescent dyes. Within 4 h, micromolar concentrations of L1AD3 almost totally inhibit thymidine incorporation, and ATP levels decrease significantly. By contrast, normal human white blood cells are not affected by L1AD3, nor is heart cell function affected by it. If L1AD3 kills by interacting with targets that are different from those of currently applied agents, this peptide, or a derivative of it, could become a useful adjunct for cancer chemotherapy.

Cardiotoxin-III selectively enhances activation-induced apoptosis of human CD8+ T lymphocytes

Cardiotoxin-III (CTX-III), a major cardiotoxin isolated from the venom of the Taiwan cobra (Naja naja atra), is a highly basic, hydrophobic, toxic protein, which can induce lysis of mononuclear cells by an unknown mechanism. This study was undertaken to investigate the effects of CTX-III on untreated and PHA-activated peripheral blood mononuclear cells (PBMCs) in vitro. The results show that treatment of PHA-activated lymphocytes with CTX-III (10 microg/ml) induced apoptosis and depletion of the CD8(+) population. In both untreated and PHA-treated lymphocytes, interferon-gamma production was dramatically reduced and interleukin-2 (IL-2) production was moderately reduced by CTX-III treatment. In PHA-activated lymphocytes, CD4 expression was increased, whereas CD8 and IL-2R beta chain (CD25) expression were decreased. In contrast, CTX-III had no effect on the viability of PHA-activated monocytes but significantly enhanced their tumor necrosis factor-alpha production. These results show that CTX-III selectively enhanced activation-induced apoptosis in CD8(+) T cells. CTX-III was found to bind to the cell membrane of PHA-stimulated PBMCs, and three CTX-III-binding proteins, with molecular weights of 92, 77, and 68 kDa, were identified. We therefore propose that CTX-III interacts with one or more cell surface proteins and initiates a signal pathway causing functional changes. These findings provide an insight into the immunomodulatory properties of CTX-III and suggest a novel method for the selective induction of apoptosis in CD8(+) T lymphocytes.

The effect of snake venoms and their components on adrenomedullary cells: catecholamine efflux and cell damage

The effects of snake venom on the cholinergic system have been well-studied; however, no similar studies have been performed on the adrenergic system. Adrenomedullary cells secrete catecholamine (CA) on stimulation; thus they are an ideal system to study the effect of snake venoms on CA secretion or inhibition. Snake venoms from different Families and Genera were investigated. All snake venoms investigated, caused CA efflux. CA can be released when cytolysis takes place; so in order to assert CA efflux was not due to cytolysis, venoms were added after the cells were treated with KCl. Most venom, with the exception of sea snake (Hydrophiidae) venom, was found to induce CA release due to cytolysis. The effects of purified components such as phospholipase A2, neurotoxin I, and cardiotoxin were also investigated. Neurotoxin I caused neither cytolysis nor CA efflux. Cardiotoxin caused marked cytolysis, but with slightly less damaging effects than that of cobra venom. Some ion channel blockers prevented cytolysis induced by cardiotoxin. The CA efflux induced by cardiotoxin may be mediated through Ca2+ channels because the efflux could be completely depressed by a Ca2+ channel blocker (1 mM CdCl2).

Cytotoxic potency of cardiotoxin from Naja sputatrix: development of a new cytolytic assay

The possible involvement of specific regions/loops of cardiotoxin from Naja sputatrix venom in mediating its cytolytic activity is evaluated using a new cytolytic assay. In this assay, the amount of chloramphenicol acetyltransferase (CAT) that is released upon lysis of the cellular membranes by the cytotoxin has been measured as an index of cytolysis. This newly developed CAT system is more sensitive than the traditional haemolysis method utilizing red blood cells or the lactate dehydrogenase assay for cytolysis. Series of chimaeric toxin molecules have been constructed by swapping the loops between highly hydrophilic neurotoxin and highly hydrophobic cardiotoxin molecules from Naja sputatrix, which are known to exhibit structural similarity (three-finger conformation) but to have different functional properties. Comparison of the cytolytic activities of the recombinant chimaeric toxins demonstrated the possible involvement of all three loops of cardiotoxin in its cytolytic potency. However, the first two loops of the protein appear to make the major contribution to its lytic activity. cDNAs encoding cardiotoxin and the chimaeric toxins, when expressed in transfected cultured Chinese hamster ovary cells, resulted in cell lysis, indicating that these cDNAs can be developed as useful cytolytic agents.

Separation and structure-function studies of Taiwan cobra cardiotoxins

Six cardiotoxins (CTXs) and one cardiotoxin-like basic protein (CLBP) from Naja naja atra (Taiwan cobra) venom were separated by a SP-Sephadex C-25 column. CTXn and CTXI were well separated by eluting with ammonium acetate buffer, and the separation of CLBP from CTXIV and CTXV mixtures was achieved using sodium phosphate buffer. These findings suggest a differential interaction of CTXs with the chromatographic matrix using different buffer systems. Chemical modification studies on cationic residues of CTXI suggested that there was no single lysine or arginine residue exclusively responsible for its biological activity. Moreover, it was found that the cytotoxicity and hemolytic sites of CTXI could be dissociated by chemical modifications. It suggests the potentiality for preparing toxin derivatives in which a specific activity is retained.

A membrane-lytic immunoconjugate selective for human tumor T-lymphocytes

An immunoconjugate was constructed from a monoclonal antibody recognizing human T-lymphoblastoid cells and a membrane-lytic cytotoxin purified from the venom of the Thailand cobra. Activities of this novel immunoconjugate were compared using human and murine T-lymphocyte cell lines. The ability of the conjugate to inhibit human T-cell proliferation, as measured by incorporation of [3H]thymidine, was three to four times higher than its ability to inhibit proliferation of mouse L1210 cells. The immunoconjugate EC50 for human CEM cells was equivalent to 0.1 nmoles per 2 x 10(5) target cells. Immunoconjugate selectivity paralleled the monoclonal antibody's binding characteristics. Preincubation with free antibody blocked the effect of the conjugate, but only upon the human target cells. This study supports the feasibility of directing a toxic moiety to the surface of a cancer cell to accomplish cell destruction without requiring prior toxin internalization and uncoupling from its antibody carrier.